Keywords: Input-Output and Input-to-State Stability, Algebraic Control Methods, Output Regulation and Disturbance Rejection
Abstract: A temperature and humidity controller is designed for a direct expansion air conditioning (DX A/C) system making use of a state feedback decoupling approach of nonlinear control systems. It is shown that the nonlinear dynamics of a DX A/C system can be input-output decoupled by dynamic state feedback. The resulting decoupled system is of minimum phase. Thereafter, the decoupled model is used to design a pole placement controller with guaranteed stability. Unlike controllers based on approximate local linearization of the DX A/C model, the controller proposed is global in the sense that it can track temperature and humidity setpoints in the complete operating range of the DX A/C system. Effectiveness of the controller designed is demonstrated by simulation results.

Keywords: Geometric Control Methods, Algebraic Control Methods
Abstract: Bilinear systems form models of wide-ranging applications in diverse areas of engineering and natural sciences. Investigating fundamental properties of such systems has been a prosperous subject of interest and remains essential toward the advancement of systems science and engineering. In this paper, we introduce an algebraic framework utilizing the theory of symmetric group to characterize controllability of bilinear systems evolving on special orthogonal and Euclidean groups. Our development is based on the most notable Lie algebra rank condition and offers an alternative to controllability analysis. The main idea of the developed approach lies in identifying the mapping of Lie brackets of vector fields governing the system dynamics to permutation multiplications on a symmetric group. Then, by leveraging the actions of the resulting permutations on a finite set, controllability and controllable submanifolds for bilinear systems evolving on the special Euclidean group can be explicitly characterized.

Keywords: Geometric Control Methods
Abstract: Recently a class of Hamiltonian control systems was defined for open irreversible thermodynamic systems. These systems are Hamiltonian control systems defined on a symplectic manifold, however departing from standard Hamiltonian control systems, due to the property that the Hamiltonian function is homogeneous in the generalized momentum variables. In this paper we study the class of state feedbacks preserving the geometric structure of such Homogeneous Hamiltonian control systems and rendering the closed-loop system again a Homogeneous Hamiltonian control system. It is shown that only a constant control preserves the canonical Liouville form. Hence a non-trivial state feedback necessarily changes the geometric structure in closed-loop defined by a modified Pfaffian form. Finally we derive a matching equation on the nonlinear feedback and the closed-loop Pfaffian form.

Keywords: Robotics, Geometric Control Methods, Input-Output and Input-to-State Stability
Abstract: This paper presents a path following control (PFC) approach to generate guidance virtual fixtures with dynamic constraints (time-varying constraints) for physical human-robot interaction tasks. Using input-output feedback linearization and a parallel transport frame, the system dynamics are linearized and decomposed into tangential and orthogonal direction with respect to a time-varying path, which is parametrized as a regular threefold continuously differentiable curve. The presented PFC approach is combined with compliance control, which enables the systematic generation of virtual fixtures. An experiment on a six-axis industrial robot reveals the potential of this approach to generate virtual fixtures with dynamic constraints.

Keywords: Modelling of Distributed Parameter Systems, Geometric Control Methods, Dissipativity and Passivity
Abstract: This paper proposes a particular type of Stokes-Dirac structure for describing a Laplacian used in Poisson's equations on topologically non-trivial manifolds, i.e., not Euclidian. The operator matrix representation of the structure includes not only exterior differential operators, but also codifferential operators in the sense of the dual of the pairing between differential forms. Since the successive operation of the matrix is equivalent to the Laplace-Beltrami operator, we call it a Stokes-Dirac operator. Furthermore, the Stokes-Dirac operator is augmented by harmonic differential forms that reflect the topological geometry of manifolds. The extension enable us to describe a power balance of particular boundary energy flows on manifolds with a non-trivial shape.

Keywords: Observer and Filter Design, Mechatronic Systems and Devices
Abstract: In this paper we consider the problem of velocity estimation and stabilization for balancing an inverted pendulum equipped with a reaction wheel. A homogeneous differentiator is proposed for velocity estimation, and it is shown that a bias in sensor readings yields steady-state estimation error. The proposed observer is augmented with a reduced-order bias estimator and local asymptotic stability of the coupled observers is shown. The proposed solution is tested and compared with another approach on an experimental setup.

Keywords: Process Industry, Observer and Filter Design, Lyapunov-Based Control Design
Abstract: Subsea wet gas compression is an enabling boosting technology for cost-efficient production of small and remote gas condensate fields. These wet gas compressors are capable of compressing gases containing up to 5% liquid, removing the need for pre-separation and thereby reducing the investment and maintenance costs. However, the presence of liquid in the gas significantly changes the compression performance from that of dry gas, resulting in a reduced process gain and an increased normal operating region for increasing liquid content. A novel backstepping process controller was previously proposed to track and stabilize a desired pressure reference inside the normal operating region, requiring feedback from several variables, including the mass flow. Mass flow is an inaccurate and expensive measurement. Therefore, a full-order high-gain observer is derived for the wet gas compression process with proven local exponential convergence. The performance of the derived observer is studied and compared in simulations.

Keywords: Mechatronic Systems and Devices, Observer and Filter Design, Robust and Adaptive Estimation
Abstract: This paper presents a nonlinear electric circuit model of the circular DEAP membrane actuator model coupled with a viscoelastic mechanical phenomena. A parameters of the model are found by parameter identification process and then an adaptive observer to estimate the real load force is applied. The authors developed an adaptive observer for state affine system for the case without knowledge of the load mass of DEAP membrane. The results are compared with experiments obtaining a good agreement.

Keywords: Estimation and Filtering, Diagnosis, Condition Monitoring, and Performance Assessment, Energy and Power Systems
Abstract: Iterative learning approaches are well developed for the design of feedback controllers of dynamic systems which perform identical control tasks during multiple successive executions. Such tasks are characterized by identical reference trajectories in each of the iterations to be run. Exploiting this information, it becomes possible to reduce tracking errors by adapting the control signal not only on the basis of information of the state variables from the current iteration but also by accounting for the history of the tracking errors from previous trials. Although such control strategies are part of an active field of research, the corresponding dual task, namely, the design of state and disturbance observers for systems with successively repeated state trajectories has not yet received the same amount of attention. Therefore, a discrete-time iterative learning observer design, aiming at the combined state and disturbance estimation, is presented in this paper. The resulting approach is validated in numerical simulations for the simplified model of the charging/discharging dynamics of Lithium-Ion battery systems.

Keywords: Observer and Filter Design, Control of Discrete Event Systems, Control of Sampled-Data Systems
Abstract: We propose a technique to modify a given discrete-time (nonlinear) observer so that the state estimate remains in a given convex set, without altering the observer performances in terms of convergence and robustness to external disturbances. The proposed approach can be used to remove the peaking phenomenon or to attenuate the effect of impulsive outliers in the measures. It assumes that it is possible to execute a certain number of computations between any two sampling times in order to refine the current estimate and bring it back into the prescribed set. The proposed technique can be applied to any class of nonlinear observers for which a quadratic Lyapunov function is used to prove stability.

Keywords: Estimation and Filtering, Micro-/Nanosystems
Abstract: Effective demodulation of amplitude and phase is a requirement in a wide array of applications. Recent efforts have increased the demodulation performance, in particular, the Lyapunov demodulator allows bandwidths up to the carrier frequency of the signal. However, being inherently restricted to a single order filtering of the input signal, signal components outside its passband are not sufficiently attenuated for all applications, such as in multifrequency atomic force microscopy. In this article, the structure of the Lyapunov demodulator is transformed to an equivalent form, taking advantage of the internal model representation of the sinusoid to be tracked. A generalization of this formulation allows the application of standard filtering techniques in order to shape the characteristics of the demodulator, while retaining the perfect tracking condition provided by the internal model. Guidelines for the filter design are provided in order to achieve the desired characteristics, such as filtering order, tracking bandwidth, and transient performance. The resulting generalized Lyapunov demodulator structure is highly flexible, allows for direct employment of any standard filter type, is computationally simple, and easy to implement requiring only a bandpass filter, a single integrator, and two nonlinear transformations. Numerical results demonstrate the effectiveness of the approach, and provide a comparison of the various filters considered.

Keywords: Mathematical Modelling and Simulation, Motion and Vibration Control, Production, Manufacturing and Process Industry
Abstract: Liquid sloshing is a free surface flow phenomenon with particular impact in applications such as dynamics of vehicles, ships or aircrafts (e.g. sloshing in tanks), solutions for vibration damping (e.g. tuned liquid mass dampers), as well as in industrial automation and robotic systems (e.g. handling of liquid-filled vessels). Whether sloshing effects are utilized to reduce vibrations or, on the contrary, introduce disturbing forces to the system, the understanding of the liquid sloshing dynamics is crucial to obtain the respective desired system behavior. To this end, due to the complex dynamic effects, numerical methods are vital means for analysis and optimization. In the present work, we focus on the transport and handling of liquid-filled containers in the context of robotics and automation, analyzed using the method Smoothed Particle Hydrodynamics (SPH). The properties and potential of the chosen numerical approach are investigated and evaluated by examples from literature, and several extensions over conventional SPH implementations are proposed in order to enhance accuracy and robustness.

Keywords: System Design and Integration, Software Tools, Smart Structures
Abstract: The concept of automating the computation steps in a design process along different simulation tools leads to a more efficient use of knowledge and computational resources. In this paper the software tool SyMSpace, which realizes this automatization, and the available components concerning the simulation of piezoelectrically actuated systems is presented.

The finite element model of a circular piezoelectric patch on a rectangular aluminium substrate using novel mixed finite elements is used as an example to show how to create a well-documented and easy-to-use component. Tangential displacements and normal normal stresses (TDNNS) are used as mechanical degrees of freedom and the finite elements are readily available in open source software package Netgen/NGSolve.

In order to simplify the installation and usage of specialized (open source) software tools and help to reproduce results in scientific publications, the concept of (docker) containers is integrated in SyMSpace.

Keywords: System Design and Integration, Software Tools, Production, Manufacturing and Process Industry
Abstract: A model based design process for mechatronic industrial automation systems is shown. Here, FMI (Functional Mock-Up Interface) techniques allow the implementation of advanced mechatronic system models directly on the programmable logic control (PLC) by means of an automated workflow that realizes a direct transfer of the model from the modeling and simulation environment to the automation environment. Up to now, this approach works fine for lumped parameter systems, e.g. robotic handling systems. For fluid transport applications suitable reduced models have to be considered in order to use this approach as well. This contribution gives insight into actual developments at B&R with the objective to provide a simple model based design process based on reduced models for the automation of industrial fluid transport systems.

Keywords: Mathematical Modelling and Simulation, Production, Manufacturing and Process Industry, System Design and Integration
Abstract: The Digital Twin is considered as one of the key technology trends and attracts high attention in aca-demic and application-specific publications. Besides the general understanding of the Digital Twin as a digital replica of a physical asset, many different perspectives and conceptions exist. In this paper, we will give an overview of different viewpoints of the Digital Twin and its related aspects. Furthermore, we describe a technological vision of a next generation Digital Twin and its application in the field of mech-atronics systems. Motivated from a technical- and simulation-influenced perspective, we look at the economic aspects of the Digital Twin and give an answer to the question if the next generation Digital Twin will form an ecosystem. Based on an exemplary lemonade production, a system of mechatronic systems, we show the main principles of our technical vision: a network of digital artefacts empowered by semantic technologies, the transfer of models between partners in the value chain and along the lifecycle as well as the use of models to generate new services - especially in the operation and service phase - like a Digital Plant Companion.

Keywords: Mathematical Modelling and Simulation, Motion and Vibration Control, System Design and Integration
Abstract: In the field of vibration technology mechatronic systems are frequently used for noise and vibration control, condition monitoring or energy harvesting. Numerical simulations and optimizations support the virtual design and development process. Yet, most systems are usually designed as auxiliary systems based on existing host structures and are optimized for only one main purpose (e.g. maximum vibration reduction). Time costly parameter optimizations with complex models in late phases of the development process are still common.

In this paper a holistic approach for the design and optimization of mechatronic systems is presented. Efficient and parametric models of the mechanical host structure are integrated within a multi-objective optimization environment for mechatronic systems. This will help to accelerate product development cycles and enables fast parameter studies in combination with detailed and accurate numerical models. The performance of the proposed approach is demonstrated by an exemplary application, where the structural dynamics, vibration control and energy flows are considered within a holistic optimization.

Keywords: System Design and Integration, Energy and Power Systems, Software Tools
Abstract: In the last decades, the increasing globalization as well as an increasing competitive situation lead to individualized products. This change is accompanied by an increasing variant variety, which leads to a high level of complexity in supply chain networks (SCNs). In particular, suppliers of mechatronic systems have to face the challenge of the increasing complexity of variants and the complexity of its corresponding SCNs. Since the mechatronic systems consist of different components from different industries, suppliers are usually widespread. Although variant variety is a major driver for complexity of SCNs especially regarding mechatronic products, both topics are currently viewed independently within the field of complexity research. This paper is motivated by the case study of the SCNs of the production of gas-insulated switchgears (GIS). The GIS are produced in a modular and customized way worldwide. In order to minimize increasing production costs resulting from the modularization, the company is developing a globally distributed SCN. In this SCN, standard modules are prefabricated in low-wage countries. The subsequent variant creation takes place in European plants. The final customization can be completed by adjustments during commissioning. Customer requirements lead accordingly to a dynamic SCN, in which both the participating value-adding partners and the relationships within the network change. The dynamics, the diverse relationships and the numerous actors create a high degree of complexity with a reduced added-value transparency. This paper contributes a detailed literature analysis and illustrates the research needs of a holistic approach of complexity assessment for the development of product variants and their SCNs. As a result, a holistic approach for the assessment of both, product variants and SCNs, is developed.

Keywords: Dissipativity and Passivity, Control of Hybrid and Switched Systems
Abstract: This article addresses output feedback stabilization of continuous-time nonlinear systems by choosing control actions from a finite set. Working under the assumption that the system under consideration is passive and large-time norm observable, we propose a static feedback mapping, from the output space to the finite set of control actions, which is shown to be practically stabilizing if the convex hull of certain control actions (in the chosen finite set) contains the origin in its interior. Consequently, to construct this stabilizing feedback, it suffices to have, in addition to a zero symbol, another m + 1 elements in the control set which form an m-simplex in R^m (the input, and output space).

Keywords: Lyapunov-Based Control Design, Dissipativity and Passivity, Lyapunov Stability Methods
Abstract: In this paper we introduce a new notion of passivity which we call Krasovskii's passivity and provide a sufficient condition for a system to be Krasovskii's passive. Based on this condition, we investigate classes of port-Hamiltonian and gradient systems which are Krasovskii's passive. Moreover, we provide a new interconnection based control technique based on Krasovskii's passivity. Our proposed control technique can be used even in the case when it is not clear how to construct the standard passivity-based controller, which is demonstrated by examples of a Boost converter and a parallel RLC circuit.

Keywords: Dissipativity and Passivity, Control of Sampled-Data Systems, Numerical Modelling Methods and Computational Aspects
Abstract: In this paper gradient and Hamiltonian dynamics are investigated in both discrete- time and sampled-data contexts. At first, the discrete gradient function is profitably employed to define discrete gradient and Hamiltonian dynamics. On these bases, it is shown that representations of these forms can be recovered when computing the sampled-data equivalent models to gradient and Hamiltonian continuous-time dynamics.

Keywords: Mechatronic Systems and Devices, Dissipativity and Passivity, Lyapunov-Based Control Design
Abstract: In this paper an adaptive control scheme is developed for enhancing the Interconnection and Damping Assignment Passivity-Based Control (IDA-PBC) technique. The primary objective of the adaptive component is to stabilize a class of Underactuated Mechanical Systems (UMSs) in the presence of uncertainties that are not necessarily matched. This class of UMSs is characterized by the solvability of the IDA-PBC matching condition and an additional adaptive condition. We analyze the asymptotic stability behavior of the Inertia Wheeled Inverted Pendulum (IWIP) under three types of uncertainties: input disturbance, physical damping (friction) and parameter uncertainties in the total energy of the system. Simulations illustrate the effectiveness of the approach.

Keywords: Dissipativity and Passivity, Numerical Modelling Methods and Computational Aspects
Abstract: In this paper we propose a convex Sum-of-Squares optimization problem for finding outer approximations of forward reachable sets for nonlinear uncertain Ordinary Differential Equations (ODE’s) with either (or both) L2 or point-wise bounded input disturbances. To make our approximations tight we seek to minimize the volume of our approximation set. Our approach to volume minimization is based on the use of a convex determinant-like objective function. We provide several numerical examples including the Lorenz system and the Van der Pol oscillator.

Keywords: Model-Predictive Control, Robotics, Mechatronic Systems and Devices
Abstract: The paper proposes first steps towards the formalization and characterization of time-varying turnpikes in optimal control of mechanical systems. We propose the concepts of velocity steady states, which can be considered as partial steady states, and hyperbolic velocity turnpike properties for analysis and control. We show for a specific example that, for all finite horizons, both the (essential part of the) optimal solution and the orbit of the time-varying turnpike correspond to (optimal) trim solutions. Hereby, the present paper appears to be the first to combine the concepts of trim primitives and time-varying turnpike properties.

Keywords: Control of Distributed Parameter Systems, Model-Predictive and Optimal Control, Dissipativity and Passivity
Abstract: We investigate the turnpike problem in optimal control, in the context of time- evolving shapes. We focus here on the heat equation model where the shape acts as a source term, and we search the optimal time-varying shape, minimizing a quadratic criterion. We first establish existence of optimal solutions under some appropriate sufficient conditions. We provide necessary conditions for optimality in terms of usual adjoint equations and then, thanks to strict dissipativity properties, we prove that state and adjoint satisfy a measure-turnpike property, meaning that the extremal time-varying solution remains essentially close to an optimal solution of an associated static problem. We illustrate the turnpike phenomenon in shape design with several numerical simulations.

Keywords: Model-Predictive and Optimal Control, Dissipativity and Passivity, Control of Networked Systems
Abstract: In this paper, we analyze an economic model predictive control scheme with terminal region and cost, where the system is optimally operated in a certain subset of the state space. The predictive controller operates with a cyclic horizon, which means that starting from an initial length, the horizon is reduced by one at each time step before it is restored to its maximum length again after one cycle. We give performance guarantees for the closed loop, and under a suitable dissipativity condition, establish convergence to the optimal subset. Moreover, we present conditions under which asymptotic stability of the optimal subset can be guaranteed. The results are illustrated in a practical example from the context of Networked Control Systems, which initially motivated the development of the theory presented in this paper.

Keywords: Dissipativity and Passivity
Abstract: In this paper we present a method for automated verification of dissipativity by numerical means for discrete time systems with polynomial dynamics and stage cost. It relies on sum-of-squares techniques in order to compute storage functions that satisfy a dissipation inequality. The method can also be used to treat systems subject to constraints. Moreover, an Taylor approximation based extension to more general nonlinear stage costs is presented which enables the computation of approximate local storage functions.

Keywords: System Design and Integration, Motion and Vibration Control, Precision Systems
Abstract: This paper proposes a method to design a wide-bandwidth cascade structure feedback (FB) controller for a mechatronic system with resonant modes. The notable feature of the proposed method is to optimally design both the structure and parameters of a FB controller that performs wide-bandwidth FB control while meeting the specified control stability requirements. The proposed method searches for an optimum controller structure, in terms of the sequence of element compensators, as well as including a hybrid optimization-based controller parameter design method. The effectiveness of the proposed method was verified through numerical simulations using a laboratory galvano scanner.

Keywords: System Design and Integration, Optomechatronic Systems, Motion and Vibration Control
Abstract: This paper presents the system and control design of a novel high performance piezo-actuated fast steering mirror (FSM) for high speed optical scanning which is centered around an easy-to-manufacture membrane-like mechanical flexure and uses an optical sensor system for position measurement. With the membrane flexure the first fundamental resonance mode of the actuator is placed as high as 6.7 kHz, while still enabling an optical angular range of +/- 4.8 mrad. Using a PI controller together with three notch filters designed in a loop shaping approach for maximizing the system bandwidth and tracking of high resolution raster trajectories, a closed-loop bandwidth as high as 2.7 kHz and a positioning uncertainty of 3.8 urad rms is obtained. The obtained tracking error when tracking a 250 Hz raster scanning trajectory with a scan amplitude of 2.2 mrad is as small as 73.8 urad rms (3.6% of scan amplitude).

Keywords: Micro-/Nanosystems, Micro- and Nano-sensors, Adaptive and Robust Control
Abstract: Atomic force microscope (AFM) provides a unique possibility in nanoscience research and development for interrogation and manipulation of matter at nanoscale. Miniaturization of AFM significantly reduces the manufacturing cost and breaks the barrier to widespread adoption of this scientific instrument. This paper presents the characterization and control of a novel microelectromechanical system (MEMS)-based AFM. For in-plane motion, the device is equipped with a micro stage with integrated electrostatic actuators and electrothermal sensors. For use in taping-mode AFM imaging, a microcantilever is embedded within the device, featuring a piezoelectric layer for actuation. Positive position feedback (PPF) controller is used to attenuate the highly resonant dynamics of the stage. Scanning performance of device is evaluated by tracking a raster pattern where a 50 Hz triangular signal is applied to the actuators along the X axis. To reduce the tracking error, turnaround points of triangular signal are smoothed by using an optimization method. Moreover, the closed-loop bandwidth is increased with inversion-based feedforward technique. A 50 Hz optimal reference signal combined with an inversion-based feedforward technique results in a fivefold decrease in root mean square of tracking error compared with triangular reference signal.

Keywords: Sensors and Measurement Systems, Optomechatronic Systems, System Design and Integration
Abstract: This work deals with the system design, control and the experimental results of a scanning laser sensor in which the optical path is scanned by a novel high performance compact fast steering mirror (FSM). The system design satisfies the Scheimpflug condition even though only the illumination path is scanned, such that an FSM with a small aperture size and high bandwidth can be used. To scan the area of interest with the FSM, raster trajectories are employed, which provide an uniform spatial resolution over the scan area. To track the trajectory a feedback controller is designed using the H∞-approach, such that a closed loop bandwidth of 1.4 kHz is achieved. The FSM can follow triangular signals up to 200 Hz with the maximum actuation range of 3°. This enables a framerate of up to two frames per second for an image with 100x100 pixels. With the scanning system a maximum spatial resolution of 60 µm and a scan range of 25 mm can be achieved.

Keywords: Micro-/Nanosystems, Micro- and Nano-sensors, Sensors and Measurement Systems
Abstract: This paper investigates the benefit of active mechanical Q-control for electrical surface potential measurements in atomic force microscopy. The effective quality-factor of the electrically stimulated cantilever oscillation is additionally increased mechanically at the same frequency with an active analog Q-controller, while in lift-mode. It is shown experimentally that the cantilever oscillation amplitude and therefore the measurement sensitivity is improved by a factor of 15. By spectral noise analysis around the resonance frequency of the cantilever, an increase of the signal-to-noise ratio from 2.5dB to 23dB is achieved.

Keywords: System Design and Integration, Precision Systems, Sensors and Measurement Systems
Abstract: The integrated planar 6-DOF drive system evolves from the combination of a 3D planar motor to actuate x, y, and φz and three individual vertical actuators which allow actuation in z, φx and φy. In all axes aerostatic guiding is applied while the vertical actuators additionally implement a pneumatic weight compensation to carry the static weight of the slider which is why these elements are also referred to as lifting and actuation units (LAU). For 6D closed loop control the displacements and tilting angles are measured with a high precision multichannel plane mirror interferometer system.

The paper introduces the concept of the integrated planar 6-DOF drive system and explains the design of the realized system for a travel range of Ø100 mm in x, y and 10 mm in z. The three key components: the lifting and actuation units, the planar direct drive system and the multichannel interferometer system are explained in more detail including preliminary investigations of these individual systems which were carried out to evaluate and improve the performance prior to the integration into the overall system.

Keywords: Estimation and Filtering, Mathematical Modelling and Simulation, Sensors and Measurement Systems
Abstract: The presented work illustrates an investigation on the observer synthesis for a highly nonlinear railway running gear system. The specific focus is on the longitudinal dynamics and the associated adhesion effects, i.e. the friction conditions between wheel and rail. This interface strongly influences the brake and the traction performance of trains and, thus, its detailed consideration is of crucial importance in terms of safety and comfort. The observer design is accomplished for the experimental running gear developed at the German Aerospace Center (DLR). The article focuses on the first steps of the observer synthesis: (i) the set-up of the observer model, (ii) the selection of an appropriate observer method, (iii) and the validation of the observer in a simulation environment. The determining aspect of the model implementation is the consideration of the nonlinear wheel-rail contact. To cover this nonlinear behavior an Extended Kalman Filter (EKF) is used in combination with a parameter estimator for the friction characteristics in the wheel-rail interfaces. In the end, the received results prove that the observer accurately estimates the system behavior and provides reliable information on the adhesion characteristics and related longitudinal dynamics. Based on this findings one of the upcoming steps at the DLR is to validate the observer in the real-time environment of the test rig. Regarding the use of the presented approach in a train some significant improvements of traction control systems are enabled. A first application could be an enhanced brake control to narrow down the variance of brake distances in daily operation. Furthermore, an advanced usability of the condition based monitoring of traction and brake systems is facilitated with the additional information on the friction conditions.

Keywords: Estimation and Filtering, Sensors and Measurement Systems, System Design and Integration
Abstract: The German Aerospace Center (DLR) bundles its railway research in the long-term Project ''Next Generation Train`` (NGT). The NGT is a high speed train concept in light-weight design and double-deck configuration. To reduce wheel and rail wear and to enhance the passenger capacity, a mechatronic running gear with independently rotating wheels (IRW) is designed. This configuration requires an advanced control of the lateral dynamics in order to fully exploit the potential in minimizing wear and noise. In terms of a model-based control design, the controller performance highly depends on the estimated lateral position of the running gear relative to the track. In a practical environment it is difficult to directly measure this displacement of the wheel-pair. Therefore this article deals with the question which sensor configuration enables an appropriate estimation of the lateral displacement and is suitable for observer design. Hence, an observability analysis and an observer synthesis to estimate the lateral position for the nonlinear system of the 1:5 scaled hardware running gear is carried out. For validation purposes three estimators are implemented at the real-time environment of the testbed and the estimation errors of the observer configurations are compared.

Keywords: System Design and Integration, Test and Validation
Abstract: REPOINT-Light is a novel railway track switch concept which is designed to enhance the reliability of the railway network by implementing a closed loop control concept and introducing actuator redundancy in the railway switch design. After successful experiments and tests in a laboratory environment, the full-scale demonstrator of the switch is deployed in a railway testing site. This paper presents the performance of a designed controller by showing the experimental data of brushless AC motors assembly within three active bearers of the track switch. The controller is implemented in real time operation mode using NI-LabVIEW software NI hardware (CompactRIO 9035) and. The principle challenge of the controller is to synchronize the movement of six motors in three active bearers of the REPOINT-Light switch.

Keywords: Mathematical Modelling and Simulation, Test and Validation, Automotive Systems
Abstract: This paper presents an application of formal methods based on model checking techniques for safety verification of a railway interlocking system. The proposed model checking techniques are implemented on a timed automaton model of the considered interlocking systems and with respect to safety operational specification that are expressed as computation tree logic formulas. The freely available UPPAAL model checker is used to perform the model checking task and simulation results of the performed verification are presented.

Keywords: Mathematical Modelling and Simulation, Motion and Vibration Control, Automotive Systems
Abstract: This paper discusses a formation control approach for managing the safe movement of train platoons in moving block signaling scheme. The considered control objective is that of maintaining a bounded safe distance between adjacent trains which move simultaneously on the same track segment. This paper shows that the convoy can achieve the formation input-to-state stability property by simple feedback control gain on each train in the convoy.

Keywords: Sensors and Measurement Systems, Robotic Manipulators, Test and Validation
Abstract: A study on the synergy-based control of an anthropomorphic hand is proposed in this paper. The robotic hand is equipped with three-axis optical force sensors placed on thumb, index, and middle fingertips in order to obtain a better grasping quality in terms of adaptability and contact forces with respect to the physical object properties. A fully-actuated hand is used in the experiments since this allows to select different postural synergies and explore how the hand behaves in case of decoupled finger motion. Therefore, the proposed method can be extended to two different application cases: purely synergy-based contact force control and synergy-based contact force control with decoupled fingers. While the first control strategy allows to simplify the grasping by selecting only the synergy weights in order to obtain the desired value of the mean contact forces among the fingers, the second allows both to control the contact force individually on each finger in order to better adapt the hand to the object and to preserve the simplicity in the grasp design provided by the synergy-based approach. Experimental tests have been performed in both the cases to show the performance of the proposed methods and to highlight the capability of the proposed control strategies to regulate the contact forces properly.

Keywords: Optimal Control, System Design and Integration, Mechatronics Education
Abstract: This work demonstrates the swing-up of a custom-built spherical pendulum, which is mounted on the 7-axis industrial robot KUKA LWR IV+. The swing-up trajectory for this system with nine degrees of freedom is calculated offline in a three-step process: First, an optimal control problem for the pendulum model with fewer states and inputs is solved. Then, using the inverse kinematics of the robot model and the forward dynamics of the complete system, this trajectory is converted to a feasible starting solution for the third step, which is solving the optimal control problem for the complete system. Finally, the swing-up is shown experimentally using a two-degrees-of-freedom control structure comprising the calculated trajectory for the feedforward control and a time-variant linear quadratic regulator (LQR) as a feedback controller.

Keywords: Estimation and Filtering, Robotic Manipulators, Data-Based Methods and Machine Learning
Abstract: Human robot collaboration requires specific properties of modern lightweight robots that differ from conventional robots. One of these is the property of reacting to external forces acting on the robot structure, which typically requires joint torque measurements. In contrast to that, this paper presents an approach for estimating the external joint torques based on two different information sources, the motor current and the torsional deformation. To obtain an accurate estimation based on the torsional deformation, disturbing effects and inaccuracies of the angular measurements have to be taken into account. An approach for modeling, identification and cancellation of these effects is presented. Furthermore, the fusion of both estimations is discussed and the validation of the approach on a lightweight robot is presented.

Keywords: Robotic Manipulators, Motion and Vibration Control
Abstract: To improve the tracking performance of industrial robot manipulators, a nested-loop iterative learning control (ILC) structure is presented. It consists of an inner loop that deals with drive dynamics, and an outer loop which addresses impreciseness of kinematic parameters as well as joint static bias. A data-based frequency inversion technique with motion constraints is utilized for fast inner loop convergence. The outer loop measures the end eector deviation with a laser tracker and uses inverse Jacobian matrix for joint reference modication. Analysis of the algorithm is given, and is experimentally demonstrated on a six degree-of-freedom robot manipulator. It is shown that the proposed method mitigates the maximum dynamic tracking error by an order of magnitude, and is applicable to dierent payloads due to small system variation from torque shielding of gear reduction.

Keywords: Robotic Manipulators, Test and Validation, Mathematical Modelling and Simulation
Abstract: This paper deals with the modelling, validation and control of the ESA space manipulator DELIAN. A numerical model accounting for joints and links flexibility is developed, and structural parameters are identified through experiments on the real robot. Then, the model is validated comparing the behavior of the simulated system with the real one. Moreover, an analysis aiming to understand the contribution of each elastic element to the overall flexibility is carried out. Finally, wave-based control technique is combined to the well-known P/PI scheme in order to reduce system vibrations. Especially, a velocity-based implementation of the WBC is introduced which provides superior performance with respect to the position-based one.

Keywords: Robotics, Observer and Filter Design
Abstract: For a robot operating in unknown environment, fast detection of occurring collisions is mandatory in order to react accordingly. This is especially the case when robots are interacting with humans. For this application area often lightweight robots are used to decrease the damage potential. Resulting link vibrations can be met with vibration damping control by the use of acceleration sensors. When already equipped for control applications, the accelerometers can also be used for detecting link collisions. A method for collision detection with acceleration sensors based on joint torque estimation is presented and compared to a generalized momentum observer which is frequently used for this purpose, as can be found in literature. The methods are compared in an experiment on a three-degrees-of-freedom (3-DOF) robot with flexible links where the contact force is measured additionally.

Keywords: Stochastic Control
Abstract: Quantum Error Correction (QEC) relies on feedback schemes stabilizing quantum superposition and coherence. This lecture investigates QEC with a control perspective. Firstly, we present the structure of the stochastic non-linear state equations governing the classical input/output relationships for open quantum systems. Then, we describe two feedback schemes: measurement based-feedback where the controller is a classical system; coherent feedback where the controller is another open quantum system (autonomous feedback or reservoir/dissipation engineering). We explain how these feedback schemes underlay recent experimental results in super-conducting quantum circuits to protect quantum states stored in an harmonic oscillator (cat-qubit). We conclude by proposing a time-scale combination of these feedback schemes in order to stabilize and protect quantum information, the objective of QEC.

Keywords: Mathematical Modelling and Simulation, Test and Validation
Abstract: The increasing complexity of systems requires the consideration of simulations in the product development process. At Bosch, simulations are widely used in many different areas, from Powertools to Electronic Control Units for powertrain, steering and braking systems, to highly complex systems, like autonomous driving functions. Still, results of simulation models are limited used in release decisions due to missing trust in their reliability. In this contribution, the approach for simulation-based release developed at Bosch in the project Virtualized Release will be presented. First, the main challenges are briefly discussed, i.e., model based system design and automated driving. Then, meaningful elements necessary for increasing trust in simulations, e.g. methods, tools, processes and qualification concepts, are presented. In the focus on technologies, I will show approaches for determination of simulation and model quality that are applicable for a wide range of problems. To implement these approaches successfully, harmonized quality criteria between supplier and OEM are essential and will be discussed.

Keywords: Output Regulation and Disturbance Rejection, Stochastic Control
Abstract: The problem of output regulation for linear stochastic systems is addressed. We first define and solve the ideal problem of output regulation via error feedback. We note that its solution is not implementable in practice because the Brownian motion is not available for measure. Therefore, we define an approximate problem for which we provide a practical solution. The implemented controller is hybrid, in that a continuous-time, deterministic control law is supplemented by a discrete-time, stochastic correction. This correction is performed using an a-posteriori approximation of the variations of the Brownian motion provided by a nonlinear estimator. The resulting hybrid closed-loop system is nonlinear, as the scalars approximating the increments of the Brownian motion depend nonlinearly on the states and the inputs. The error between the solution of the approximate problem and the solution of the ideal problem is characterised. We show that the ideal solution is retrieved as the sampling time tends to zero. We illustrate the results by means of a numerical example.

Keywords: Output Regulation and Disturbance Rejection, Analysis of Networked Systems
Abstract: We investigate output regulation for linear networked control systems using the emulation approach. We consider a regulator solving the problem for linear systems in the absence of the network, by following the Francis-Wonham framework. Next, the network is taken into consideration, in particular the induced time-varying inter-transmission intervals and scheduling constraints, and we model the overall system dynamics as a hybrid system. We show that only practical regulation can be achieved in general since the steady-state control input steering the output to zero cannot be generated in the networked context (in general). Explicit upper bounds on the output asymptotic gain and on the maximum allowable transmission interval guaranteeing boundedness of the closed-loop trajectories are provided, which are shown to be related.

Keywords: Output Regulation and Disturbance Rejection
Abstract: The paper deals with the problem of output regulation for nonlinear systems under the assumption of periodic exosystem. We build on the results presented in Astol et al. (2015) showing that asymptotic regulation can be achieved with an innite dimensional regulator embedding a linear internal model copying all the harmonics that are multiple of the one associated to the exosystem. The regulator follows a post-processing structure in which the (innite dimensional) internal model is driven by the error and a static stabiliser is considered for the cascade extended system. The post-processing structure traces the one proposed by Francis and Wonham into a linear framework. The presented analysis is limited to nonlinear systems that have unitary relative degree and that are minimum-phase.

Keywords: Input-Output and Input-to-State Stability, Analysis of Networked Systems, Control of Distributed Parameter Systems
Abstract: We prove a small-gain theorem for interconnections of n nonlinear heterogeneous input-to-state stable control systems of a general nature, covering partial, delay and ordinary differential equations. We use in this paper the summation formulation of the ISS property, but the method can be adapted to other formulations of the ISS concept as well. The proof is based on the recent characterizations of the input-to-state stability for infinite-dimensional systems in terms of weaker stability properties.

Keywords: Input-Output and Input-to-State Stability, Lyapunov Stability Methods, Analysis of Networked Systems
Abstract: For networks consisting of input-to-state stable systems, it is well-known that the popular Lyapunov function called the max-separable function can be constructed by solely relying on component-wise inverse maps of one single path characterizing the monotonicity of dissipation inequalities of component systems. Numerical algorithms have been developed to compute such a path. This paper proposes a useful closed-form expression for the inverse maps of a path and its extension to generate a sufficient variety of paths. The solution not only gives nonlinear scalings of the max-separable Lyapunov function explicitly, but also substantiates the rounding-off technique to remove the non-differentiable nature from the max-separable function.

Keywords: Input-Output and Input-to-State Stability, Lyapunov Stability Methods, Analysis of Networked Systems
Abstract: In this paper we consider countable couplings of finite-dimensional input-to-state stable systems. We consider the whole interconnection as an infinite-dimensional system on the ell_infty state space. We develop stability conditions of the small-gain type to guarantee that the whole system remains ISS and highlight the differences between finite and infinite couplings by means of examples. We show that using our methodology it is possible to study uniform global asymptotic stability of nonlinear spatially invariant systems by solving a finite number of nonlinear algebraic inequalities.

Keywords: Test and Validation, Diagnosis, Condition Monitoring, and Performance Assessment
Abstract: A key aspect of control development for mechatronic systems is the simulative verification. Extensive simulation studies allow early-stage adaptations and quality and safety assessments prior to validation on the real system. The verification of modern systems generates a huge amount of data that requires automated verification methods. A crucial part of the verification is the detection of oscillations, which can deteriorate the closed-loop performance and in the worst case even lead to destabilisation. In this paper, we present an oscillation detection method that derives from the continuous process plant monitoring and is suitable for many control problems in the domain of mechatronic systems. A core element is the Empirical Mode Decomposition (EMD) combined with the assessment of the decomposed modes. For high robustness and computational efficiency, the method is extended by a tailored signal pre-processing. A normalised oscillation index provides a measure for the oscillation strength and enables the systematic analysis of crucial control signals to reveal possible optimisation potentials. A multi-component control loop for a complex nonlinear mechatronic system in the development stage is examined to demonstrate the applicability of the proposed method. The results show the reliable detection and analysis of crucial oscillations. The method is used for quality improvement and assurance already in the development phase of a product or system.

Keywords: Mathematical Modelling and Simulation, Sensors and Measurement Systems, Interfaces (Visual, Haptic, …)
Abstract: The concept of Digital Twin has become very popular. By collecting relevant information on the state and usage of physical entities and linking them to the simulation models contained in the Digital Twin, many opportunities for operation support arise. By enriching and deploying models that were developed for example during the design phase, different applications are presented with relevance for the operation phase. The examples cover the fields of data aquisition, data analytics, predictive and prescriptive analytics and show the benefit of having an integrated Digital Twin concept along the whole lifecycle.

Keywords: Data-Based Methods and Machine Learning, Test and Validation, Diagnosis, Condition Monitoring, and Performance Assessment
Abstract: A key barrier in the industrial adoption of condition monitoring is the lack of large and reliable data sets about the full lifetime of bearings in machines. This data is useful for model training as well as for validation purposes. This paper demonstrates how a living lab, consisting of 7 identical drive train sub-systems, can enable smart machine maintenance and support the adoption of condition monitoring technologies in the industry. The living lab allows to perform accelerated lifetime tests of bearings and to speed up the process of collecting large amounts of data about degrading bearings. It is shown that the data can be used to benchmark diagnostic algorithms. Three methods are compared: a data driven approach developed by the Linz Center of Mechatronics (LCM), a diagnostic method of Flanders Make (FM) and an approach developed by the Center for Intelligent Maintenance Systems (IMS). It is concluded that the method of IMS and FM, employing bearing specific features, tend to be slightly more sensitive to early detect bearing faults than the data driven approach employed by LCM. On the contrary, the method of LCM does not require specific system knowledge and is not limited to bearing monitoring only. The method is more widely applicable to fault monitoring problems. Besides a benchmark study, the living lab can also be used to develop, test and validate new diagnostic and prognostic methods. In this way, the living lab provides opportunities to enable a wider adoption of condition monitoring technologies in industry.

Keywords: Biomedical Systems, Mathematical Modelling and Simulation, Test and Validation
Abstract: To reduce manufacturing costs, a new simple radio frequency (RF) surgical generator based on a push-pull oscillator is developed for cutting tissue. In order to systematically design and test feedback controllers keeping the generator's output voltage constant, we will present two different models of the considered RF generator. The first one is a nonlinear state space model derived using the generator's equivalent circuit diagram and Kirchhoff's laws and the second one is a Hammerstein model. The models are based on physical principles and are successfully validated on a generator prototype, ensuring a good match with the static and dynamic behavior of the considered RF generator. The obtained state space model is well suited to simulate the RF generator, while the Hammerstein model is appropriate to design controllers for the generator's output voltage.

Keywords: Fault Detection and Isolation, Estimation and Filtering, Elektromagnetic Actuators and Electric Machines
Abstract: This paper presents a new method of disturbance observer based control (DOBC) for multi-input-multi-output (MIMO) highly-coupled unstable systems based on the game theory and the H-infinity synthesis. First motivated by the Youla parameterization of full order state observer feedback control, a full order state observer (FOSO) based DOBC is proposed for single-input-single-output (SISO) systems. Then inspired by the FOSO based DOBC design, a disturbance decoupling method is proposed for MIMO systems using game theoretic observer design. By using error dynamics from the proposed observers, single-input-multi-output (SIMO) virtual plants are constructed. Inverses of those virtual plants for a certain bandwidth are found by solving the model matching problem using H-infinity solver. The proposed DOBC is applied to an open loop unstable MIMO Active Magnetic Bearing Spindle (AMBS). Simulation and experimental results show that the disturbances are effectively estimated and compensated.

Keywords: Robust and Adaptive Estimation, Optimization-Based Observers, Parameter Estimation, and Moving Horizon Estimation, Power Electronics and Drives
Abstract: Classical tracking algorithms often employed for HF injection techniques used to estimate position of ac machine depend on machine inductances. To overcome this dependency, a new approach to extract the sign of the rotor position estimation error is developed and then, a new adaptive step-by step sliding mode observer is proposed as an alternative solution to estimate the rotor position, speed and acceleration of the machine. The gains of this observer are made variable in order to reduce the chattering effects. Moreover, Low-pass-filters usually used in the pulsating-wave signal injection technique are removed leading to reduce the cost and complexity of implementation and improve the estimation in term of delays. The performance of the proposed algorithm is compared with respect to the existing tracking algorithms and the step by step sliding without gains variation in simulations and experiments.

Keywords: Robust and Adaptive Control, Observer and Filter Design, Mechatronic Systems and Devices
Abstract: In this paper the observer for full nonlinear model without signal injection for 1-DOF MagLev system is presented. Instrumental for the development of the theory is the use of parameter estimation-based observers, which combined with the dynamic regressor extension and mixing parameter estimation technique, allow the reconstruction of the magnetic flux. With the knowledge of the latter it is shown that the mechanical coordinates can be estimated with suitably tailored nonlinear observers. The observed state can be used in the globally asymptotically stabilizing controller.

Keywords: Lyapunov-Based Control Design
Abstract: Dynamic programming is an established approach to solving optimal control problems. Application of dynamic programming in continuous time is however difficult due to the necessity of solving the (generalized) Hamilton-Jacobi-Bellman equation. In this paper, direct strategy evaluation in combination with policy iteration through simulations is used to bypass this obstacle.

Keywords: System Design and Integration, Motion and Vibration Control, Mathematical Modelling and Simulation
Abstract: The authors have investigated the fundamental properties of crawling-like locomotion robots that generate forward motion utilizing the effects of wobbling and sliding. This paper discusses an application of the robot to a paper-feeding system. First, we introduce our new robot model that can generate high-speed crawling-like gait on level ground and the typical forward motion. Second, we outline the paper-feeding system, and numerically show that it can achieve the target manipulation by generating a reciprocating motion of the body frame.

Keywords: Biomedical Systems, Robotic Manipulators, System Design and Integration
Abstract: This paper deals with functional electrical stimulation (FES)-assisted control for a standing-up motion from a squatting position. The motivation of this study is that standing-up from squatting position is important especially for elderly and disabled people who used to sit on the floor. Our proposed method considers a reaction force direction by using the characteristic of the stimulated muscle. The developed FES standing-up system has the pantograph mechanism which allows us to carry out a standing-up motion from a squatting position in the limited space. Experimental results with healthy participants are shown to confirm the validity of the propose method.

Keywords: Motion and Vibration Control, Robot Navigation, Programming, and Vision
Abstract: This paper reports the maneuvering experiments of a wall climbing robot on a vertical wall. We have developed a wall climbing robot to inspect walls of buildings or tunnels. The robot has a pair of driving wheels and a coaxial propeller thruster, and maintains the position and orientation by the pushing force of the thruster. Although we already have verified the maneuvering control of the robot on a sloped surface, the experiments on a vertical wall were not conducted since the propeller thruster was not powerful enough to lift the whole weight of the robot. Hence we redesigned the robot mechanism and structure, and also improved the thruster force control according to the redesigning. First, we summarize the mechanical system of the wall climbing robot, and especially take up the improvement of the gimbal mechanism equipped with the propeller thruster. Next, we show the onboard control system composed of sensors and actuators, and represent how to appropriately determine two gimbal angles corresponding to the robot orientation in a gravity field. The driving control of two wheels is also switchable to both velocity control and position control, in accordance with the manual operation. Finally, we demonstrate the maneuvering experiments on a vertical wall, and discuss the reproducibility of linear and turning motions of the robot.

Keywords: Human Operator Assistant System, Robotic Manipulators
Abstract: This paper proposes a telescopic mechanism for narrow space photographing. In recent years, many tall buildings have been constructed around the world. Most of the buildings have narrow ceiling spaces for housing the duct pipes and electrical cables on every floor. Inspecting the ceiling space is legally required, and many specialists periodically have inspected the ceiling space by using omnidirectional cameras. However, photographing by specialists has the problem that the inspection area is extremely small. Only the head and shoulder of every inspector are able to enter into the ceiling space because of the smallness of the inspection hole attached to the ceiling. For this reason, the photographable area has been limited to the neighbourhood of the inspection hole. In addition to the small inspection hole, most ceilings are suspended by some long screw-nuts, and heavy objects such as humans or mobile robots are not able to be put on the ceiling. Although applying the propeller-typed drone equipped with a camera may be remembered, the application involves the risk of both winding up the dust and cutting the electrical cables in the ceiling space. Thus we newly propose a wearable system to take the photograph of the whole area in the narrow ceiling space. The wearable system is mainly composed of a body attachment and an expansion/contraction mechanism, and each user operates the expansion/contraction of the device by using a hoisting tool. In this paper, the concept of the wearable system for narrow space photographing is proposed, and the telescopic mechanism is shown in details, which is the key element of the expansion/contraction mechanism.

Keywords: Robot Navigation, Programming, and Vision, Interfaces (Visual, Haptic, …), Software Tools
Abstract: Most existing localization methods in mobile robotics are based on a single kind of representation and present limitations in operational environments that have different areas with different characteristics. Using hybrid maps combining feature based representations and occupancy grids provides robustness and flexibility in many applications. If several sensors are considered, better results may be achieved in a larger variety of cases. Furthermore, when a precise model of the environment can be built in advance, it can improve subsequent accuracy and robustness, and also significantly simplify the development and setup processes. This short paper discusses the motivation of this kind of localization and presents ideas and tools for creating, editing and using hybrid maps in an intuitive and convenient way. Integration with popular robotics software such as Gazebo and ROS is addressed.

Keywords: Motion and Vibration Control, Adaptive and Robust Control, Mathematical Modelling and Simulation
Abstract: The suspension design in rail vehicles have to balance sufficient stiffness for guidance with enough compliance for steering, creating a well-known design conflict. Active suspensions have been proposed as an alternative to optimise the suspension forces for different scenarios. This means that the vehicle is not reliant on a sub-optimal combination of passive components and can therefore reduce the energy dissipated in the wheel-rail contact patch and subsequent wear. Previous research on mechatronic rail vehicles has shown the performance improvement on various track profiles compared to conventional vehicles. Using individually driven independently rotating wheels has shown the biggest improvement in performance. In this paper, the results of a multi-body physics simulation of such a vehicle on a conventional track switch are presented. The simulation study shows that mechatronic vehicles promise a significant reduction in wear on track switches. More ambitiously, they could be developed in the future to produce a steering action to achieve switching from the vehicle and remove the dependency on moveable track switches.

Keywords: Robot Navigation, Programming, and Vision, Sensors and Measurement Systems, Estimation and Filtering
Abstract: The aim of this paper is to accomplish the unmanned ground vehicle (UGV) full self-governance by developing tools that are able to give an accurate automatic localization in an accurate environment map. Many techniques have been developed to make the most type of sensors solving the Simultaneous Localization and Mapping (SLAM) problem. A solution to SLAM in dynamic environments would expand robotic applications and would open up a vast range of potential applications. In this context, we propose the adaptive smooth variable structure filter (SVSF) based approach to solve the cooperative SLAM problem and reconstruct a reliable 2D environment representation. In our work, we introduce a covariance matrix to assess the uncertainty of the adaptive SVSF. The proposed algorithm is validated in real-world and the obtained results confirm the efficiency and robustness of our approach in a dynamic environment.

Keywords: Robotic Manipulators, Precision Systems, System Design and Integration
Abstract: The mechatronic design of a flexure based robot is presented. The six degree-of-freedom robot is designed to combine a sub-micrometer repeatability with cubic workspace of 1 l and acceleration of 5G.

The repeatability is enabled by the use of flexure joints, particularly a butterfly joint and a recently developed spherical joint. The flexure geometry and the robot kinematics are optimised on high end-effector stiffness while realising the required workspace.

A high-resolution optical encoder is selected in line with the accuracy requirement. An iron core torque motor is selected to enable the required accelerations. Both are contactless to avoid friction.

Experimental results for one of the actuated joints are presented. The required stroke and acceleration can be realised. Highly predictable position-torque behaviour is found, which allows good tracking using feedforward. The main disturbance is found to be the amplifier's current noise. This effect is minimised by H2 control.

The position stability due to current noise is 1.6 urad, limiting repeatability. Adding inertia is proposed for further reduction.

Keywords: Precision Systems, Motion and Vibration Control
Abstract: To accomplish high-speed and high-precision positioning for systems with a pulse-width modulation (PWM)-type input, an iterative calculation method to solve a frequency-shaped final-state control (FSC) problem. The frequency-shaped FSC method calculates a feedforward input that drives a system from the initial state to a target state, where the input is chosen such that it will be smooth and the gains of its Fourier transformation at given frequencies will be minimal. Because the conventional frequency-shaped FSC supposes that the control input is generated through the zero-order hold, we have extended the frequency-shaped FSC so that it can be applied to the PWM-type systems.

Keywords: Mechatronics Education, Smart Structures, Production, Manufacturing and Process Industry
Abstract: Modern manufacturing industry is currently facing significant challenges with regard to the concept of Industry 4.0. The promise of increased productivity and flexibility in manufacturing processes cannot be achieved without implementation of systems and advance methods based on smart technologies. Implementation of Industrial Internet of Things (IIoT), Condition Monitoring, Big Data, Cloud computing, virtual and augmented reality in maintenance processes will significantly increase the effectivity and quality of manufacturing processes as well as eliminate the human factor. Under this perspective, cyber–physical systems can be accessible from remote location; process parameters can be visualized at real time and prediction of unexpected production stop due to machine breakdown will be significantly reduced. The paper deals with the development of effective approach to smart maintenance education with training on the job for maintenance worker using augmented reality smart glasses. Digital model of a production component is visualized with assembly instruction in the field of view of the maintainer. Critical work instructions are highlighted and enable to the worker to train maintenance process without machine breakdown. On real example will be demonstrated the signification and effectivity for maintenance of electric device and potential for application in different types of modern industrial processes.

Keywords: Modelling of Distributed Parameter Systems, Control of Distributed Parameter Systems, Model-Order Reduction
Abstract: Heat transfer in a conductive solid structure actuated by a Peltier element arranged in the middle is studied. The nonlinear initial-boundary value problem corresponding to a designed experimental setup is formulated with taking into account Peltier and Seebeck thermoelectric effects related to the conventional theory of heat transfer. The method of separation of variables is applied to the three-dimensional system linearized with respect to the temperature. By applying a Fourier analysis, the eigenvalues and eigenforms are found for the resulting one-dimensional system subject to a constant external voltage. As a result, the original system with a piecewise control law is reduced to a sequence of spatially one-dimensional systems which are still nonlinear with respect of the input voltage. The space-time distributions of the temperature and heat flux in the considered structure are obtained for given control signals. Finally, promising numerical results are presented.

Keywords: Model-Order Reduction, Numerical Modelling Methods and Computational Aspects, Output Regulation and Disturbance Rejection
Abstract: The transfer of the reduction concept of moment matching from linear to nonlinear systems has been coined over the last years by cite{astolfi2010model}. In this and further publications, the focus lies on the extension of emph{input Krylov subspace}-based moment matching to the nonlinear case. The generalization is based on the steady-state interpretation of moment matching and involves the difficult solution of a nonlinear partial differential equation (PDE). Moreover, the time domain interpretation of emph{output Krylov subspace}-based moment matching has been also investigated for linear systems (cite{astolfi2010steady, ionescu2016two}) using the dual Sylvester equation, and transferred to the nonlinear case in cite{ionescu2013families, ionescu2016nonlinear}.

The aim of this short contribution is (i) to comprehensively explain the steady-state perception of emph{output Krylov moment matching} given by Ionescu [2016]. Another goal is (ii) to state our progress concerning a practicable output Krylov subspace-based nonlinear moment matching method, so that it and further topics can be discussed at the conference.

Keywords: Data-Based Methods and Machine Learning, Mathematical Modelling and Simulation, Energy and Power Systems
Abstract: Thermal comfort is influenced by many factors and can vary significantly between different individuals. Therefore, modeling personal thermal comfort is a complex challenge and requires a detailed knowledge about environmental as well as physical or even mental conditions of an occupant. However, only limited data are available which is usually restricted to environmental measurements. Furthermore in the context of commercial buildings, the calculation effort must be kept as low as possible that scaling issues related to the large number of occupants are reduced. To cope with this problem, the presented paper analyzes thermal sensation voting data collected in an open-plan office in Singapore and uses LASSO regression techniques for the identification of the most important comfort features. Well known relations between thermal comfort and the corresponding vote are considered via suitable constraints. To define a common set of optimal features, the individual regression problem is extended to an arbitrary number of occupants. This leads to multiple LASSO optimization problems that are coupled by nonlinear if-statements. A reformulation method is presented which results in a mixed integer quadratic program by introducing binary activation variables. Eventually, the method is applied to comfort modeling and the resulting model structures are compared regarding their complexity, number of selected features and prediction accuracy.

Keywords: Motion and Vibration Control, Estimation and Filtering, Data-Based Methods and Machine Learning
Abstract: Data-driven feedforward control can significantly improve the positioning performance of motion systems. The aim of this paper is to exploit the concept of batch-to-batch learning control with basis function, applied in an online fashion. This enables learning within a task while maintaining task flexibility. A recursive least squares optimization is proposed on the basis of input/output data to compute the optimal feedforward parameters. The proposed method is successfully validated in simulation, and applied to a benchmark motion system leading to a major performance improvement compared to only feedback control.

Keywords: Optimal Control, Aerospace Systems, Robot Navigation, Programming, and Vision
Abstract: Thermal soaring gliders exploit naturally occurring rising air (called thermals) as sources of energy. These sources generally appear in uncertain and random way as their position and strength are hardly predictable. Several atmospheric factors affect the behavior of thermals (season, time of the day and nature of vegetation on the ground, etc). However, a statistical model of thermals to be encountered can be build. Soaring in a optimal manner while taking advantage of thermals represents thus a stochastic optimization problem that can be solved and implemented in an autonomous glider. The present paper details how to find an optimal trajectory for going through given checkpoints, with the objective of doing as much rounds as possible within a predetermined time. The optimal control of the glider is determined by determining i) whether the glider should climb a thermal with a specific strength when it encounters one, or to cruise, ii) the optimal speed to fly during the cruising phases. The problem is solved using dynamic programming and the proposed optimal path planning strategy is validated by simulation.

Keywords: System Design and Integration, Aerospace Systems, Optimal Control
Abstract: In this paper, we propose a method to improve the networked UAV control system using event-triggered control and model predictive control (MPC). Although the UAV control over the network has many advantages, it involves a long-time delay and packet loss, which adversely affect real-time control performance. Delay compensation algorithms in the networked control system (NCS) have been proposed to address such issues, however, they do not consider the resource limit of the network so that the network congestion may occur. In that case, the packet loss and network delay issues can even be worsened. In this study, we propose a method to reduce the generation of less important control signals and to use the network more efficiently by using event-triggered control. Since the event-triggered control method is also influenced by the network delay, an event trigger function suitable for NCS is designed. We validated the effectiveness of networked UAV control system and event-triggered control by simulation.

Keywords: Optimal Control, Nonlinear Control, Aerospace Systems
Abstract: The problem of area coverage using unmanned aerial vehicles is becoming increas- ingly important, e.g. for search-and-rescue missions, exploration, and environmental monitoring. The area coverage control problem spans multiple levels, from path planning to tracking and flight control, which are normally time scale separated. Area coverage in highly dynamic environments requires tight integration of these levels to achieve maximum performance and to avoid collision. We propose to fuse the path following level and the mobile platform control level to achieve better performance. By doing so, dynamic constraints, static and dynamic obstacle avoidance and energy efficiency are taken into account. Specifically, we shift the assignment of the reference path velocity from the planner to the controller which leads to improved performance while satisfying all system constraints and therefore increases safety and reliability. Simulation results for a quadcopter illustrate the performance of the proposed algorithm.

Keywords: Data-Based Modelling, Input-Output and Input-to-State Stability, Pneumatic and Hydraulic Systems
Abstract: This paper presents nonlinear control approaches based on extended linearisation techniques for a high-speed linear axis driven by pneumatic muscles. Its guided carriage is actuated by a nonlinear drive system consisting of two pulley tackles with pneumatic muscle actuators mounted at both sides. This innovative drive concept allows for an increased workspace as well as higher carriage velocities as compared to a direct actuation. The proposed control scheme has a cascaded structure, where two alternative design methods in the framework of extended linearisation are discussed and investigated: eigenvalue placement (EVP) and an optimal design based on the state-dependent Riccati equation (SDRE). Unmodelled hysteresis in the force characteristic of the pneumatic muscles is counteracted by an additional control loop with proportional-integral (PI) behaviour. Implementations of both control approaches on a test rig are compared to each other and show excellent closed-loop performance.

Keywords: Model-Predictive Control, Robotics
Abstract: We investigate real-time motion generation for a humanoid robot climbing a wall. We apply nonlinear model predictive control (NMPC) to optimize the climbing path and motion of the limbs simultaneously. To climb a wall, the robot must determine which hold it will grasp in each step. Kinematic constraints vary depending on the holds grasped by the robot, and these constraints will change as the robot climbs. To determine which hold to grasp while considering kinematics constraints, our proposed method introduces a potential function on the wall and state-dependent weights. We also propose online configuration of the performance index for NMPC to reduce the computational cost. This enables optimization under a complicated wall model. Only information in the vicinity of the humanoid robot is utilized for optimization because the control input over a finite future horizon is optimized at each sampling time of NMPC. We simulate the behavior of a climbing robot to show that the computation time is nearly the same as a sampling period.

Keywords: System Design and Integration, Mathematical Modelling and Simulation, Robot Navigation, Programming, and Vision
Abstract: This paper presents some of the developments made in the construction of a modular climbing robot for infrastructure inspection. The development and optimization of independent vacuum generator systems for each leg is presented, with the flow-rate taking priority over the relative pressure. It also describes the general robot structure, as well as the initial mathematical models required for the development of a control system based on a biomimetic organic model. Finally, it is highlighted the use of simulators to help the iterative design process of a strongly mechatronic system. Some of the obtained results have been experimentally validated

Keywords: Output Regulation and Disturbance Rejection, Robust and Adaptive Control, Optimization-Based Observers, Parameter Estimation, and Moving Horizon Estimation
Abstract: In Marconi et al. 2007, it was shown that a solution to the output regulation problem for minimum-phase normal forms always exists. That approach, however, yields only an existence result, and no general analytic procedure is known to actually choose the regulator's degrees of freedom, even for simple problems. In this paper we propose an adaptive regulator that, leveraging the aforementioned existence result, self-tunes online according to an optimization policy. To this aim, the regulator may employ every system identification scheme that fulfills some given strong stability properties, and the asymptotic regulation error is proved to be directly related to the prediction capabilities of the identifier.

Keywords: Robust and Adaptive Control, Output Regulation and Disturbance Rejection, Input-Output and Input-to-State Stability
Abstract: This paper investigates the output-feedback adaptive control problem, exploiting the so-called congelation of variables method, to achieve output regulation for systems with time-varying parameters. To overcome the coupling between the input and the time-varying parameters, a strong minimum-phase property, i.e. input-to-state stability (ISS) of the inverse dynamics, is assumed. This property allows replacing the original coupling with a new coupling between the output and the varying parameters, which can be dominated via backstepping. A set of high-gain Kreisselmeier filters is then designed to guarantee that the state estimation error dynamics are also ISS. Finally, implementing the backstepping controller with a strengthened nonlinear damping term guarantees that all trajectories of the closed-loop system are bounded and that the output converges to zero asymptotically.

Keywords: Output Regulation and Disturbance Rejection, Robust and Adaptive Control, Lyapunov-Based Control Design
Abstract: This paper studies the adaptive output regulation problem for a class of nonlinear systems. Under a mild immersion condition, a novel adaptive internal model is proposed by using immersion and invariance (I&I) adaptive control and incorporating a high-gain observer. This, together with a high-gain feedback, is shown to be able to solve the desired regulation problem in a semiglobal sense.

Keywords: Output Regulation and Disturbance Rejection
Abstract: In this paper, the output tracking problem for linear and nonlinear systems in normal form is revisited in the case of non-minimum phase dynamics and in the absence of any model for the exosystem generating the periodic reference signal. The asymptotic output tracking is obtained by replacing the classical stability condition for the zero dynamics driven by the reference signal with the existence of a solution to a two-point boundary value problem. The latter solution allows to generate the ideal steady-state evolution of the zero dynamics. This strategy allows to retain two interesting features of standard tracking and regulation approaches, namely, i) the use of a simple linear feedback structure and without the need of solving any partial differential equation (as in tracking) and ii) avoiding minimum phase requirements (as in output regulation). Since the same kind of two-point boundary value problem usually arises in the application of the Pontryagin Minimum Principle in optimal control, a natural question to ask is whether there is an underlying connection; hence, in the linear case, further insights are achieved by comparison with an alternative solution based on optimal control problem formulated for an auxiliary affine system.

Keywords: Output Regulation and Disturbance Rejection, Control of Hybrid and Switched Systems, Lyapunov-Based Control Design
Abstract: The problem of rejection of a sinusoidal disturbance with unknown frequency acting on an unknown single-input single-output stable linear system is addressed in this paper. We present a new hybrid approach that does not require knowledge of the frequency response of the transfer function over the range of frequencies of interest. The proposed controller reposes upon a switching strategy within a family of linear controllers based on the adaptive feedforward / internal model control methodology. A dead-beat frequency estimation method is integrated in the controller. The method also accounts for the presence of bounded sensor noise as well as imprecise frequency estimation. It is shown that, within a finite number of switchings, the regulation error is ultimately bounded by a function of the norm of the noise that depends on the choice of the controller and the estimator gains.

Keywords: Control of Networked Systems, Analysis of Networked Systems, Observer and Filter Design
Abstract: In the study of network synchronization it is common to consider that the nodes in the network interact through static and diffusive couplings. However, this type of couplings has a limitation: for certain systems and certain network topologies, the maximum number of nodes that can be synchronized is relatively small. This paper presents a potential solution for relaxing the aforementioned limitation. In particular, it is demonstrated that if the static couplings in the network are replaced by dynamic interconnections then the number of nodes that can be synchronized is increased. As a particular example, a star network of Hindmarsh-Rose neurons is considered. The stability of the synchronous solution in the network is investigated by using the Master Stability Function approach in combination with the largest transverse Lyapunov exponents. Ultimately, the obtained results are experimentally validated in a network of electronic Hindmarsh-Rose neurons.

Keywords: Lyapunov-Based Control Design, Control of Networked Systems, Lyapunov Stability Methods
Abstract: This paper deals with a systematic way to check if a certain class of nonlinear systems can define a contraction. The proposed approach combines the use of sector bound condition or monotonic condition satisfied by the nonlinearities with the use of an adequate control function matrix. The contraction analysis results are provided under the form of linear matrix inequalities (LMIs). The design of a nonlinear control law (that is a control law depending on nonlinearities) is proposed in order for the closed loop to be a contraction. The adaptation of the contraction results to the synchronization identical nonlinear systems is also investigated by considering two kind of communication graphs (full and general undirected ones).

Keywords: Control of Networked Systems, Analysis of Networked Systems
Abstract: In this paper we explore the use of dynamic saturations on the interconnections of linear systems over a network, to reduce the effect of impulsive perturbations corrupting the exchanged information. First, we show that the proposed redesign preserves the synchronization property of the network. Second, simulation results show that dynamic saturations are a promising tool to reduce the impact of impulsive perturbations affecting the communication among the agents.

Keywords: Analysis of Networked Systems, Control of Networked Systems
Abstract: The paper develops new sufficient conditions for synchronization of a network of N nonlinearly coupled Chua oscillators interconnected via the first state coordinate only. The nonlinear coupling strength is governed by a function residing within a sector, i.e. it is bounded from above and below by linear functions. The derived sufficient conditions provide a trade-off between the characteristics of the sector and the interconnection topology of the network to guarantee the synchronization of the oscillators.

Keywords: Control of Sampled-Data Systems, Control of Networked Systems, Dissipativity and Passivity
Abstract: This paper considers the synchronization problem of nonlinear systems with sampled-data couplings. In particular, we focus on full synchronization of two strictly semi-passive systems interconnected with sampled-data couplings. First, we show that the solution of the coupled sampled-data systems is ultimately bounded from the property of strict semi-passive systems. Then, we show the existence of the synchronization manifold and derive a sufficient condition for full synchronization of the systems. Finally, we show numerical simulation results with the Hindmarsh-Rose neuron systems to illustrate the validity of these theoretical results.

Keywords: Control of Networked Systems, Biological and Biomedical Systems
Abstract: This paper studies the influence of the coupling type on the network desynchronization and proposes the algorithms to control it. We consider the FitzHugh-Nagumo network with random topology and different coupling values for different nodes. The simple mean field control which is similar for all nodes can be applicable for desynchronization of FitzHugh-Nagumo network with direct coupling. However, the network with diffusive coupling is much harder to desynchronize. In this case for large enough coupling values one should use different control algorithms for different nodes to desynchronize the network.

Keywords: Motion and Vibration Control, Adaptive and Robust Control, Production, Manufacturing and Process Industry
Abstract: Many industrial processes are affected by periodic disturbances. For instance, vibration of steel strips in hot-dip galvanizing lines entail an inhomogeneous zinc coating of the final product. Excitation by periodic disturbances is also frequently encountered in other control systems. Thus, a number of customized methods for rejection control of unwanted oscillations have been developed in the literature. In this paper, a method for eliminating a multi-harmonic periodic disturbance at an arbitrary user-defined position of a steel strip is proposed. The control task is particularly complicated because the disturbance input, a (single) displacement sensor, a (single) electromagnetic actuator, and the system output to be controlled are located at different positions along the strip. In addition, the electromagnetic actuator used as control input features neither a force sensor nor a distance sensor for measuring the air gap between the strip and the magnetic core. Hence, the actuator operates in a pure feedforward mode. The developed control method is validated by means of an experimental test rig that mimics a scenario from an industrial hot-dip galvanizing line.

Keywords: Motion and Vibration Control, Test and Validation, Elektromagnetic Actuators and Electric Machines
Abstract: The paper is devoted to experimental study of possibilities for consensus control of the unbalanced rotors for the machine used in the vibration technology. This problem is treated as an ensuring the prescribed phase shift between the vibrating rotor actuators and has a significant value for the various kinds of the vibration technology, such as vibrating transportation, drilling, and so on. It can not been considered without taking into account the natural tendency of in-phase or anti-phase synchronization of the mechanically coupled oscillating units (cf. Huygens clock synchronization). This phenomenon prevents the controller efforts in maintaining the desired value of the phase shift.

In the paper, the control laws for frequency stabilization simultaneously with cooperative control for assuring the desired phase shift between the rotors angular positions are derived and experimentally studied by means of the mechatronic vibration testbed. It is obtained that for the low and medium frequencies the self-synchronization of unbalanced rotors does not prevent achieving the desired phase shift between the rotors. For a high frequency band, the Huygens self-synchronization of rotors manifests itself, narrowing the range of the achievable phase shift.

Keywords: Motion and Vibration Control, Nonlinear Control
Abstract: This study addresses the control problem for a pneumatic isolation table system that includes a discrete valued input actuator. Control performance occasionally deteriorates if it is impossible to use an adequate high sampling frequency for the system. A combined method of multirate control and model predictive control is proposed to improve control performance if the sampling frequency to measure state variables is insufficiently low. The effectiveness of the proposed method is verified via numerical simulations for a pneumatic isolation table system model.

Keywords: Motion and Vibration Control, Precision Systems
Abstract: In this paper, we propose a quadruple-stage actuator system for a magnetic-head positioning system in hard disk drives (HDDs). The quadruple-stage actuator system consists of a voice coil motor, a milli actuator with two piezoelectric (PZT) elements, a micro actuator with two PZT elements, and a thermal actuator. The milli actuator is the first generation of a secondary actuator for a dual-stage actuator in the HDDs and moves a sway mode of a suspension. The micro actuator is the second generation of the secondary actuator for the dual-stage actuator in the HDDs and moves a yaw mode of the suspension. The thermal actuator is a new actuator for future HDDs and moves position of read/write elements in a horizontal direction with thermal expansion. The simulation results of sensitivity functions show that the proposed quadruple-stage actuator system can improve a performance of disturbance compensation by about 6 dB from that of a triple-stage actuator system.

Keywords: Motion and Vibration Control, Estimation and Filtering, Adaptive and Robust Control
Abstract: This paper addresses the filtered-error recursive least squares (FeRLS) algorithm for disturbance feedforward control in active vibration isolation systems. The controller structure consists of a generalized finite-impulse response (FIR) filter to include a set of pre-determined poles and self-tuning zeros. In addition, residual noise shaping is included to add frequency weighting and improve robustness. Compared to existing filtered-error least mean squares (FeLMS) algorithms, two major improvements are distinguished. First, faster convergence is obtained without the necessity of pre-whitening and an orthonormal basis. Second, the parameters are estimated without steady-state variance. These improvements are demonstrated using simulation studies, which show the potential of the algorithm in active vibration isolators.

Keywords: Motion and Vibration Control, Nonlinear Control, Precision Systems
Abstract: In this paper a linear bandpass filter is compared to a hybrid integrator-gain based bandpass filter regarding its usefulness in active vibration isolation. Vibration isolation refers to a form of skyhook damping in which a velocity output signal from a system having structural dynamics is fed back to a controller, the latter having bandpass characteristics. At those frequencies where the controller passes the input signal (after gain multiplication) a force proportional to velocity is obtained that can be used to provide active damping to the system, ie damping of one (or more) of its structural modes. Outside this frequency band the controller input signal is attenuated, which is often desirable in view of incorrect sensor information at low frequencies and/or to avoid amplification of high-frequency noise. In this context, the use of a hybrid integrator-gain system will be studied regarding its possible phase advantages compared to linear integrators. These advantages stem from the control design itself, in the sense that by design the control output force signal and the input velocity error signal have equal sign. In the context of vibration control, an enhanced transient (closed-loop) response is obtained, ie less overshoot and reduced settling times, but at the cost of increased rise times.

Keywords: Motion and Vibration Control, Production, Manufacturing and Process Industry, Automotive Systems
Abstract: This paper presents an effective performance shaping methodology of discrete-time sliding mode control (DSMC) with disturbance observer (DOB) based on the analysis of error dynamics. DSMC with DOB exhibits excellent tracking performance and robustness subject to external disturbances and unknowns including uncertain parameters and unmodelled dynamics. In addition, DSMC with DOB can be easily implemented in various control applications attributed to its simple structure and discrete-domain representation. However, the performance cannot be easily predicted by the controller parameters of DSMC with DOB, and much tuning effort is required to achieve the desired performance. This paper derives a relationship between the performance and the controller parameters of DSMC with DOB using a disturbance-to-error transfer function. In addition, a tuning methodology for shaping the performance of DSMC with DOB is also suggested. Finally, the developed analysis is demonstrated experimentally in a commercial linear motor system.

Keywords: Mathematical Modelling and Simulation, Adaptive and Robust Control, Estimation and Filtering
Abstract: Occurring uncertainties in dynamical systems can be difficult to handle. A solution can be found in exploiting cooperativity, which avoids the so-called wrapping effect and, hence, simplifies tasks such as the computation of guaranteed state enclosures, the design of interval observers, forecasting worst-case bounds and the identification of unknown parameters. Since not all dynamical systems are originally cooperative, a transformation of the state-space representation has been shown to be effective for ordinary differential equations. However, general approaches are not suitable for fractional order differential equations as they come with different stability regions. This paper shows a control approach for fractional order differential equations and then provides two different methods to transform the derived controlled system models into a cooperative form. The first method is applicable to systems with purely real eigenvalues while the other works for partially conjugate complex ones. Both methods are then validated on a battery system to compare the results and discuss their respective applicability.

Keywords: Robust and Adaptive Control
Abstract: Given a parametrized stabilizing controller, the approach presented in this work seeks to find optimal parameters with respect to an infinite-horizon cost. Since the latter is in general not computable, it is suggested to apply an adaptive actor-critic structure to approximate the respective value function. The actor is realized explicitly using the projected subgradient method. A particular challenge arises from the fact that the approximated value function is time-varying depending on the evolution of the dynamical system and critic's approximation of the value function. Provided that a certain stability constraint is convex and under persistence of excitation conditions, it is shown that the actor and critic parameters converge to prescribed vicinities of the optimal values. The whole setup is done in continuous time. A computational study is presented.

Keywords: Adaptive and Robust Control
Abstract: This paper presents a novel least mean squares approach for active control of structural mechanic systems. Order tracking is used to estimate the gradient for a steepest descent approach more precisely than the standard narrow-band filtered-x least mean squares (FxLMS). The derivation for the new order tracking based least mean square (OLMS) algorithm is presented for a single-input single-output system. The update equations of the OLMS are then compared with an FxLMS algorithm, leading to an interpretation that the FxLMS incorporates order tracking properties. Both algorithms are compared in simulations to show their different convergence performances at multiple frequencies. If only one frequency is present, the OLMS shows similar performance. However, in the case of multiple frequencies being present, the OLMS shows a significant performance increase. The presence of multiply frequencies lowers the performance of the FxLMS. This is analogous to the performance of the OLMS with an improper order tracking filter.

Keywords: Robust and Adaptive Control
Abstract: The paper introduces notions of robustness margins geared towards the analysis and design of systems that switch and oscillate. While such phenomena are ubiquitous in nature and in engineering, a theory of robustness for behaviors away from equilibria is lacking. The proposed framework addresses this need in the framework of p-dominance theory, which aims at generalizing stability theory for the analysis of systems with low-dimensional attractors. Dominance margins are introduced as natural generalisations of stability margins in the context of p-dominance analysis. In analogy with stability margins, dominance margins are shown to admit simple interpretations in terms of familiar frequency domain tools and to provide quantitative measures of robustness for multistable and oscillatory behaviors in Lure systems. The theory is illustrated by means of an elementary mechanical example.

Keywords: Adaptive and Robust Control
Abstract: In this paper, we propose a design method of state feedback controllers for discrete-time linear systems whose state space matrices contain stochastic parameters. For such systems, if the parameters fluctuate according to the normal distribution, it is impossible to strictly guarantee the “conventional deterministic control performance” due to the unlimited parameter variations. Then, in our problem setup, we consider incorporating the “stochastic stability” into the conventional deterministic H2 performance. We derive a design condition on state feedback controllers which achieve deterministic H2 performance and stochastic stability simultaneously in terms of linear matrix inequalities (LMIs) via extended LMI. The effectiveness of the proposed method is illustrated through a numerical example.

Keywords: Robust and Adaptive Control, Iterative and Repetitive Learning Control, Lyapunov-Based Control Design
Abstract: The increasing availability of information-rich data sets offers an invaluable opportunity to complement and improve the performance of existing model-based feedback algorithms. Following this principle, in this paper we present a novel class of Data-Enabled Extremum Seeking (DEES) algorithms for static maps, which make use of current and recorded data in order to solve a convex optimization problem characterized by a variational inequality. The optimization dynamics synergistically combine ideas from concurrent learning and classic neuroadaptive extremum seeking in order to dispense with the assumption of requiring a persistence of excitation condition in the closed-loop system. Using analytical tools for nonlinear systems we show that for a general class of optimization dynamics it is possible to tune the parameters of the controller to guarantee convergence in nite time to an arbitrarily small neighborhood of the set of optimizers. The results are illustrated in a scalar constrained minimization problem.

Keywords: Geometric Control Methods, Lyapunov Stability Methods
Abstract: We study the problem of source seeking with an acceleration controlled unicycle without position measurements. It is assumed that only real-time measurements of the source signal are available. The proposed control law is based on an approximation of the symmetric product of suitably chosen vector fields. The approximation of the symmetric product can be traced back to known averaging results for mechanical systems under vibrational control. Compared to known extremum seeking control laws by means of Lie bracket approximations, the proposed approach has the advantage that the velocity remains bounded in the high-frequency limit. We prove semi-global practical asymptotic stability for the acceleration-driven unicycle system under the proposed control law.

Keywords: Lyapunov Stability Methods, Lyapunov-Based Control Design, Robust and Adaptive Control
Abstract: The paper deals with the extremum seeking problem for a class of cost functions depending only on a part of state variables of a control system. This problem is related to the concept of partial asymptotic stability and analyzed by Lyapunov's direct method and averaging schemes. Sufficient conditions for the practical partial stability of a system with oscillating inputs are derived with the use of Lie bracket approximation techniques. These conditions are exploited to describe a broad class of extremum-seeking controllers ensuring the partial stability of the set of minima of a cost function. The obtained theoretical results are illustrated by the Brockett integrator and rotating rigid body.

Keywords: Geometric Control Methods, Robust and Adaptive Control
Abstract: In this work, discrete-time extremum seeking algorithms for unconstrained optimization problems are developed. A general class of non-commutative maps and one- and two point function evaluation polices are presented to approximate a gradient-descent algorithm, suitable for extremum seeking problems. Moreover, adaptive step size rules are discussed to achieve faster convergence and vanishing steady state oscillations.

Keywords: Robust and Adaptive Control
Abstract: In this paper, we address the problem of steering the input of a convex function to a value that minimizes the function under a convex constraint. We consider the case where the constraint cannot be violated of more than a user-defined value during the whole transient phase. The mathematical expression of both the cost function and the constraint are assumed to be unknown. The only information available are the on-line values of the cost and the constraint. To tackle this problem, an optimization law, based on a modified-barrier function, and involving the gradient of both the cost function and the constraint, is firstly designed. The Lie bracket formalism is then exploited to approximate this law, by combining time-periodic signals with the on-line measurements of both the cost and the constraint. The stability property of the resulting constrained extremum seeking system is proved, and its effectiveness is shown in simulation.

Keywords: Optomechatronic Systems, Elektromagnetic Actuators and Electric Machines, Sensors and Measurement Systems
Abstract: High throughput qualification of semiconductor devices is needed to improve cost efficiency. This paper describes a nano-precision capable, multi-agent, flexible positioning platform, which can be used to increase (metrology) throughput in semiconductor industry by parallelization of measurements. It is based on magnetic levitation and control in 6-DoF, combining large x- and y-motions with sub-nanometer scanning resolution in a single stage. The system architecture of this flexible positioning platform has the ability to operate many devices in parallel. Each device can function as a lab-on-instrument to perform various tasks at the nanoscale, e.g. metrology, inspection, deposition, transport, cleaning, etc. A demonstrator setup was successfully designed, built and tested. With coarse positioning sensors a position resolution at sub-micrometer level is achieved, while the maximum acceleration and speed are above 10 m/s^2 and 1 m/s respectively. Future testing includes integration of sub-nanometer-precision sensors and local control optimization to demonstrate sub-nanometer scanning performance.

Keywords: Elektromagnetic Actuators and Electric Machines
Abstract: In hybrid reluctance actuators for high precision motion control, the magnetic hysteresis in the ferromagnetic stator and mover usually affects the precision. Therefore, this paper proposes magnetic flux estimation and control to compensate for the hysteresis. To measure the magnetic flux at various frequencies, the output signal of a search coil is combined with that of the current monitor of the employed current amplifier in a magnetic flux estimator. Finally, a magnetic flux controller is designed and implemented. For evaluation of the hysteresis compensation, the performance of the hybrid reluctance actuator is compared with both flux and current control. Experimental results show that flux control successfully compensates for some of the nonlinearities of the hybrid reluctance actuator, as the hysteresis is reduced by up to a factor 8.2 and the phase lag of the mover position is reduced by up to 6° in comparison with the case of current control.

Keywords: Smart Actuators
Abstract: In this paper we document a novel laboratory experimental platform for non-contact planar manipulation (positioning) of millimeter-scale objects using acoustic pressure. The manipulated objects are either floating on a water surface or rolling on a solid surface. The pressure field is shaped in real time through an 8-by-8 array (matrix) of ultrasonic transducers. The transducers are driven with square voltages whose phase-shifts are updated periodically every 20 milliseconds based on the difference between the desired and true (estimated from video) position. Numerical optimization is used within every period of a discrete-time feedback loop to determine the phase shifts for the voltages. The platform can be used as an affordable testbed for algorithms for non-contact manipulation through arrays of actuators as all the design and implementation details for the presented platform are shared with the public through a dedicated git repository. The platform can certainly be extended towards higher numbers of simultaneously yet independently manipulated objects and larger manipulation areas by expanding the transducer array.

Keywords: System Design and Integration, Smart Structures, Mathematical Modelling and Simulation
Abstract: Adaptive structures in civil engineering are based on active structural elements. In this paper, an active beam element is considered with potentially multiple fluidic inputs spatially distributed over the beam’s length. It is modeled by a one-dimensional beam equation. The inputs are realized as torque inputs, where the torque is proportional to the pressure of the fluid. A method to calculate the optimal input values analytically depending on a given static load case is presented in the first part of the paper. In the second part, by generalizing the static load using a sufficient number of discrete loads evenly distributed along the beam, optimal actuator positions can be calculated for a given number of actuators. The cost function is based on extending the idea of the Gramian compensability matrix to systems governed by spatially distributed ordinary differential equations. Since the number of actuators can be a design variable, this yields a Pareto front supporting the user in selecting an appropriate number. A fluidic actuator serves as example to illustrate the potential of the proposed placement algorithm.

Keywords: Mathematical Modelling and Simulation, Smart Actuators
Abstract: In this paper, a constrained distributed parameter port-Hamiltonian model of the ionic polymer metal composite (IPMC) is proposed. This model describes the multiscale structure of the system. Submodels are coupled by boundary multi-scale (BMS) elements. In order to preserve the causality of the system, Lagrangian multipliers are introduced to deal with the coupling between the electro-mechanical diffusion in the polymer and the flexible beam structure of the actuator. Finally, a structure-preserving discretization scheme and some appropriate projections are used to derive an explicit model suitable for simulation. The accuracy of the model is verified using experimental data.

Keywords: Smart Actuators, Sensors and Measurement Systems, System Design and Integration
Abstract: This paper introduces a new Self-Sensing Actuation approach for simultaneous estimation of external loads and Piezoelectric Actuator (PEA) displacement at a frequency where the PEA’s impedance change presents good sensitivity to both electrical and mechanical excitations. Experiments are conducted for static operations to support these claims and to help demonstrate the dependence of the PEA’s mechanical and electrical properties on external excitations: mechanical stresses with a low preload (less than the recommended 15 MPa for dynamic operations) and electric fields

Keywords: Geometric Control Methods
Abstract: In this paper, we consider a problem of transforming nonlinear control systems into linear controllable systems. For affine control systems, we introduce the notion of A-orbital feedback equivalence which generalizes the concept of orbital feedback equivalence. We study the A-orbital feedback equivalence of a single-input affine control system with n state variables to a control system which can be considered as a linear controllable system with n-1 state variables. For this case, we prove a necessary and sufficient condition for A-orbital feedback equivalence, develop an algorithm for transforming an affine system into a linear controllable system, and establish a relationship between A-orbital feedback equivalence and orbital feedback equivalence.

Keywords: Output Regulation and Disturbance Rejection, Numerical Modelling Methods and Computational Aspects
Abstract: The problem of aircraft take-off under windshear conditions is considered as a differential game. A simplified five-dimensional nonlinear model of aircraft dynamics, assuming the flight in a vertical plane, is used. The overloads, differences between the projections of the thrust and drag, respectively lift, forces are considered as control variables. The corresponding technically relevant control, the aerodynamic angle of attack, can always be retrieved. Stable numerical algorithms for solving Hamilton-Jacobi-Bellman-Isaacs equations arising from differential games with state constraints are used to compute the value function and design an appropriate feedback control.

Keywords: Lyapunov-Based Control Design, Output Regulation and Disturbance Rejection, Robust and Adaptive Control
Abstract: In this paper, we deal with the problem of aircraft take-off control in the presence of a windshear. A simplified point mass nonlinear model of aircraft dynamics assuming the flight in a vertical plane is used. A reference trajectory is constructed to satisfy the altitude, relative path inclination and relative velocity state constraints. An integrator backstepping based control design procedure using barrier Lyapunov functions is suggested to track the constructed reference trajectory under state constraints and windshear disturbances.

Keywords: Robust and Adaptive Control, Control of Hybrid and Switched Systems, Lyapunov-Based Control Design
Abstract: This paper presents a framework for design and analysis of an L1 adaptive controller with switching reference systems. Use of switching reference systems allows the desired behavior to be scheduled across the operating envelope, which is often required in aerospace applications. The analysis uses a switched reference system that assumes perfect knowledge of uncertainties and uses corresponding non-adaptive controller. Provided that this switched reference system is stable, it is shown that the closed-loop system with unknown parameters and disturbances and the L1 adaptive controller can behave arbitrarily close to this reference system. Simulations of the short period dynamics of a transport class aircraft during the approach phase illustrate the theoretical results.

Keywords: Lyapunov-Based Control Design, Output Regulation and Disturbance Rejection
Abstract: This paper deals with missile longitudinal dynamics control. The angle of attack tracking problem is considered for an unpowered flight phase of a short range tail-controlled missile with the zero engine thrust. For the control synthesis, a simplified missile dynamics model that includes the actuator dynamics is used. The tracking control law is designed using the integrator backstepping approach. The aerodynamic polynomials dependence on absolute values of the angle of attack is considered from the perspective of applying the integrator backstepping technique.

Keywords: Numerical Modelling Methods and Computational Aspects, Model-Predictive and Optimal Control, Output Regulation and Disturbance Rejection
Abstract: In this paper we present an approach for testing flight control laws with optimal disturbances using differential game theory. The approach is based on a state constrained differential game formulation in which the criterion under investigation is introduced in the cost function. In this differential game the first player representing disturbances acting on the closed loop system is trying to maximize the value of the criterion at a fixed terminal time point. For our application this player may not only model typical disturbances for flight control systems, such as wind gusts, but also pilot commands or other external influences which can drive the closed loop system to an unsafe state. The second, minimizing, player represents a control law parametrization and is subject to state constraints such as limits for actuator positions and rates. The value of this game provides a lower bound of the criterion under investigation for the given control structure and the bounded disturbances as well as the bounded parametrization of the control law. The numerical solution for this problem type is obtained by employing a highly parallelized solver implemented on a grid computer. The current implementation of this solver allows for the solution of nonlinear state constrained differential games in up to seven dimensions. An example problem formulation is presented for testing the longitudinal controller of a generic aircraft model using a worst case pilot command as disturbance input.

Keywords: Robust and Adaptive Control, Geometric Control Methods, Robotics
Abstract: Human assist control for a control system driven by a human operator attracts much attention, and we have proposed a human assist control strategy by using a control barrier function (CBF). However, the method is valid only for time-invariant environments; we cannot apply the method to a moving obstacle avoidance problem of a vehicle. In fact, the time-varying state constraint problem is a difficult problem. In this paper, we consider a time-invariant graph space for a time-varying state space. Then, we propose a time-varying CBF and human assist control based on the time-varying CBF for given time-varying environments. Moreover, we propose environment-adaptive human assist control for unknown environments. Finally, we confirm the effectiveness of the proposed method by computer simulation.

Keywords: Robotic Manipulators, Human Operator Assistant System, Production, Manufacturing and Process Industry
Abstract: This work focuses on synchronizing a 7-axis industrial robot with an object that is moved in the workspace by a human operator. In an experimental setup, the robot draws several curves on the moving object, where all 7 axes of the robot are in use. Based on feedback linearization, an active compliance control strategy is developed to synchronize the end-effector with the moving object. The path progress on the curve is dynamically monitored in order to stop it, if the object is moving too fast. Experiments show that a precise tracking accuracy is achieved besides a good human-robot usability.

Keywords: Control of Hybrid and Switched Systems, Robotics, Lyapunov Stability Methods
Abstract: In a modern aging society, electric wheelchairs are an essential means of transportation for the elderly. The methods for passing over a step safely with an electric wheelchair have attracted much attention. When an electric wheelchair contacts a step with speed 0, the vehicle does not receive a great shock. In this study, we propose a contact assist CBF based on a relaxed CBF. Moreover, we propose a method of human assist control using the contact assist CBF. We aim to design a control system such that the speed of a vehicle converges to 0 at the moment when the vehicle contacts the step. The effectiveness of the method is confirmed by two computer simulations.

Keywords: Robotics, Dissipativity and Passivity, Control of Time-Delay Systems
Abstract: This paper proposes a new control method for bilateral teleoperation systems with communication delay. Under the proposed control law, the passivity from external forces to velocities and the position synchronization in the working spaces are attained. The master and slave arms can have different mechanical structures and have redundant degree-of-freedom. The proposed control can work even on singular postures, because it uses no inverses of Jacobian matrices. The bad effect of the transmission delay on stability is canceled by local damping terms, since there exists a dissipativity for a supply rate on the actions of the position-signal's delay and the local damping term. We show the property of the storage functional for the supply rate, which makes it possible to show the synchronization via Barbalat's lemma. When both the arms are stopped, the force from the environment in the working space is properly transmitted to the other arm as the force on the operation space balancing with the human's manipulation force.

Keywords: Robotic Manipulators, Interfaces (Visual, Haptic, …), Hydraulic and Pneumatic Actuators
Abstract: Soft robots can sense deformations caused by small external forces such that the robot itself is a suitable interface for teaching motions. We present an operational concept for collaborative continuum robots, consisting of an adapted force-free control as haptic interface for recording points and a replay algorithm to execute point-to-point motions with an extension to multi-point trajectories. The proposed method is general with the exception of an estimate of transition times between arbitrary static configurations which depends on the dynamic constraints of the considered robot. In-spite of it's simplicity the provided setup illustrates the potential of interactive continuum robots for individualized assistance.

Keywords: Human Operator Assistant System, Interfaces (Visual, Haptic, …)
Abstract: In a human-robot collaboration framework, the authority over the execution of tasks can be shared between the human user and the automatic controller. In case of disagreement, the human user may exert a significant amount of effort opposing the robotic counterpart. Therefore, a prompt assessment of user intent is of the utmost importance in shared systems. In this paper a novel strategy, inspired by anti-windup techniques, is proposed to adjust the component of automatic control according to the sensed human effort. A haptic human-robot interface is developed and the method is validated in a shared control application in which both the human user and the automatic controller can steer a simulated ground vehicle. Evidence is shown that the proposed method can reduce the required human effort, with performance comparable to the state-of-the-art.