Showing papers by "M Maarten Steinbuch published in 2008"

Adaptive Iterative Learning Control for High Precision Motion Systems

Abstract: Iterative learning control (ILC) is a very effective technique to reduce systematic errors that occur in systems that repetitively perform the same motion or operation. However, several characteristics have prevented standard ILC from being widely used for high precision motion systems. Most importantly, the learned feedforward signal depends on the motion profile (setpoint trajectory) and if this is altered, the learning process has to be repeated. Secondly, ILC amplifies non-repetitive disturbances and noise. Finally, its performance may be limited due to position-dependent dynamics. This paper presents the design and implementation of a time-frequency adaptive ILC that is applicable for motion systems which executes the same motion or operation. It employs the same control system block diagram as standard ILC, but instead of a fixed robustness filter it uses a time-varying filter. By using the results of the time-frequency adaptive ILC, i.e., the shape of the learned feedforward signal, a ldquopiecewise ILCrdquo is proposed that leads to the design of a single learned feedforward signal suitable for different setpoints. The results are experimentally shown to work for a high precision motion system.

Explicit MPC design and performance evaluation of an ACC Stop-&-Go

Abstract: This paper presents the synthesis, the implementation and the performance evaluation of an Adaptive Cruise Control (ACC) Stop-&-Go (S&G) design. A Model Predictive Control (MPC) framework is adopted, enabling hybrid control synthesis. Performance of the controller is evaluated, distinguishing between comfort of the resulting longitudinal vehicle behavior and the behavior due to traffic requirements. Comfort is related to vestibularly detectable variables, whereas required behaviour is related to visually and auditorily detectable variables. Metrics are determined to enable objective performance evaluation of an ACC (S&G) system in a qualitative manner.

Norm optimal Cross-Coupled Iterative Learning Control

Abstract: In this paper, we focus on improving contour tracking in precision motion control (PMC) applications through the use of Cross-Coupled Iterative Learning Control (CCILC). Initially, the relationship between individual axis errors and contour error is discussed, including insights into the different reasons for implementing CCILC versus individual axis ILC. A Norm Optimal (N.O.) framework is used to design optimal learning filters based on design objectives. The general N.O. framework is reformatted to include the contour error, as well as individual axis errors. General guidelines for tuning the different weighting matrices are presented. The weighting approach of this framework enables one to focus on individual axis or contour tracking independently. The performance benefits of N.O. CCILC versus ILC are illustrated through simulation and experimental testing on a multi-axis robotic testbed.

Explicit MPC design and performance-based tuning of an Adaptive Cruise Control Stop-&-Go

Abstract: This paper presents the synthesis, the implementation and the performance-based tuning of an adaptive cruise control (ACC) stop-&-go (S&G) design. A model predictive control (MPC) framework is adopted to design the controller. Performance of the controller is evaluated, distinguishing between comfort of the resulting longitudinal vehicle behavior and the behavior due to traffic requirements. Corresponding metrics are incorporated in the controller design. Performance functions, relating the metrics explicitly to comfort and traffic requirements enable tuning of the resulting controller. As a result, the performance of the controller can be changed by a single performance-based weight. Simulation results for varying controller performance in various traffic situations are shown.

Validation of a new adaptive deformable mirror concept

Abstract: A new prototype adaptive deformable mirror for future AO-systems is presented that consists of a thin continuous membrane on which push-pull actuators impose out-of-plane displacements. Each actuator has ±10?m stroke, nanometer resolution and only mW’s heat dissipation. The mirror’s modular design makes the mechanics, electronics and control system extendable towards large numbers of actuators. Models of the mirror are derived that are validated using influence and transfer function measurements. First results of a prototype with 427 actuators are also presented.

Hybrid component specification optimisation for a medium-duty hybrid electric truck

Abstract: This paper presents a modelling and simulation approach for determining the optimal degree-of-hybridisation for the drive train (engine, electric machine size) and the energy storage system (battery, ultra capacitor) for a medium-duty truck. The results show that the degree-of-hybridisation of known medium-duty hybrid electric trucks is close to the optimal degree-of-hybridisation using the methods as described in this paper. Furthermore, it is found that the Li-ion battery is from an energy and power density as well as cost point of view the most preferable energy storage system.

Iterative learning control with wavelet filtering

Abstract: The tracking performance of systems that perform repetitive tasks can be significantly improved using iterative learning control (ILC). During successive iterations, ILC learns a high performance feedforward signal from the measured tracking error. In practical applications, the tracking errors of successive experiments contain a repetitive part and a non-repetitive part. ILC only compensates for the repetitive part, while the non-repetitive part also enters the learning scheme and deteriorates the performance of ILC. In this paper, analysis of the tracking error of ILC shows the influence of non-repetitive disturbances. The disturbances of the last two iterations appear to have the largest influence on the tracking error. In order to remove the non-repetitive disturbances from the tracking error, a wavelet filtering method is proposed, which identifies and removes the non-repetitive disturbances by a comparison of the time–frequency content of two error realizations for each iteration of ILC. The wavelet filtered error signal contains only the repetitive disturbances and is used as input for ILC. Both simulations and experiments show that with wavelet filtering, a better tracking performance is obtained together with a feedforward signal that contains significantly less disturbances. Copyright © 2007 John Wiley & Sons, Ltd.

An LMI-based L 2 gain performance analysis for reset control systems

Abstract: In this paper we present a general LMI-based analysis method to determine an upperbound on the L2 gain performance of a reset control system These computable sufficient conditions for L2 stability, based on piecewise quadratic Lyapunov functions, are suitable for all LTI plants and linear-based reset controllers, thereby generalizing the results available in literature Our results furthermore extend the existing literature by including tracking and measurement noise problems by using strictly proper input filters We illustrate the approach by a numerical example

Data-Driven Controller Unfalsification With Analytic Update Applied to a Motion System

Abstract: Ellipsoidal unfalsified control is a plant-model-free, data-driven control design method. It recursively checks, using available data, whether the ability of a controller to meet a predefined performance requirement is (un)falsified. The set of unfalsified controllers is described by an ellipsoid in the control parameter space. The update of the ellipsoid employing new measurements can be computed analytically, hence, it is computationally cheap. This adaptive scheme is applied to an experimental motion system, namely to an industrial inkjet printer at a sample rate of 1 kHz. The results clearly show that the algorithm updates the control parameter set when the performance requirement is not met with the currently implemented one. The resulting closed-loop behavior resembles the predefined reference model in the dominant frequency range.

Reference governors for controlled belt restraint systems

Abstract: This paper presents a novel control strategy for real-time controlled restraint systems. Todaypsilas restraint systems typically include a number of airbags, and a three-point seat belt with load limiter and pretensioner. In the class of realtime controlled restraint systems, the restraint actuator settings are continuously manipulated during the crash. The control strategy developed here is based on reference management, in which a nonlinear device - a reference governor - is added to a primal closed loop controlled system. This governor determines an optimal setpoint in terms of injury reduction and constraint satisfaction by solving a constrained optimization problem. Prediction of the vehicle motion, required to predict future constraint violation, is included in the design and is based on linear regression of past crash data. Simulation results with a MADYMO model show that a significant injury reduction is possible, without prior knowledge of the crash. Furthermore, it is shown that the algorithms are sufficiently fast to be implemented on-line.

Continuous impulsive force controller for Forbidden-Region Virtual Fixtures

Abstract: Forbidden-region virtual fixtures (FRVFs) are traditionally imposed on users via proportional-derivative (PD) control. To reduce user penetration into the forbidden region, this paper proposes a new controller, hereafter called continuous impulsive force (CIF) controller. The CIF controller generates passive impulsive forces throughout users' motion into the forbidden region. These impulsive forces annihilate users' velocity into the forbidden region. Superimposed on typical PD control forces, the CIF control forces reduce users' incursion into the forbidden region, and render the feel of fully plastic collisions.

Stability and causality constraints on frequency response coefficients applied for non-parametric H 2 and H ∞ control synthesis

Abstract: The value of norm-based control synthesis methodologies heavily depends on the quality of the model at hand. The acquisition of low-order control oriented models however is often a non-trivial task. This paper pursuits the non-parametric synthesis of optimal controllers while omitting parametrization of the plant. As a result, the actual parametrization is performed on the controller such that no data-reduction is performed without knowledge of closed-loop relevant behavior. The synthesis of frequency response coefficients of an optimal controller for a sampled version of the mixed-sensitivity problem is considered. To convexify the problem, the actual optimization is performed over the frequency response coefficients of the Youla parameter Qi. Using the Youla parameter, the set of stabilizing controllers is mapped onto the set of stable transfer functions. The main contribution of this paper is the derivation of algebraic constraints over Qi that guarantee the existence of a rational stable interpolant over the points Qi. Simulations shows that the frequency response coefficients found via the proposed approach show similar behavior as model based methods.

Non-parametric identification of higher order sinusoidal output describing functions

Abstract: In this paper the concept of the Higher Order Sinusoidal Output Describing Functions (HOSODF) is presented. HOSODF can be defined for the class of causal, stable, time invariant non-linear systems which give a sinusoidal response to a specific harmonic excitation. The HOSODF relate the magnitude and phase of the individual harmonics, which together compose that specific input signal, to the sinusoidal output signal of such a system. HOSODF are the dual of the Higher Order Sinusoidal Input Describing Functions (HOSIDF). Like the HOSIDF, the HOSODF are the results of an extension of linear techniques towards non-linear systems analysis. Using the HOSODF, the non-linear systems under investigation can be modeled as a cascade of the HOSODF and a Virtual Harmonics Compressor (VHC). The VHC is defined as a non-linear component which transforms a harmonic input signal y(t) into a sinusoidal output signal y(t) with frequency ω, amplitude â and phase φ. This input signal y(t) consists of an infinite amount of harmonics of the output signal y(t) with frequency nω, amplitude â and phase nω with n = 0, 1, ...∞. Special attention is paid to the non-parametric identification of the HOSODF. The identification requires control of the frequency and amplitude of the sinusoidal output of the system within its domain of possible sinusoidal output signals. This specific state of these non-linear systems can be reached by incorporating the system under test in a feedback loop. In this loop the desired sinusoidal output is defined as the control objective of a dedicated repetitive controller consisting of a memory loop with positive feedback. The design of the learning filter required for stability is also addressed. As a spinoff of the identification technique, the authors see opportunities for advanced non-linear control of shaker systems aimed at sinusoidal excitation of non-linear systems.

Circle criterion in linear control design

Abstract: This paper presents a method for higher-order controller design with improved low-frequent disturbance rejection properties. Given a default PID-based controller, the circle criterion is used to construct an extra controller part that deals with resonances resulting from closing the loop. The advantage is twofold. First, a closed-loop shaping method is obtained that is straightforward, graphically-supported, and intuitively clear. Second, it applies to existing control designs and therefore exploits (or even further extends) the design freedom and low-frequency performances therein. The effectiveness of the method is demonstrated using examples from the wafer scanning industry.

The Empact CVT: modelling, simulation and experiments

Abstract: This paper shows the implementation of a simulation model for new electromechanically actuated metal V-belt type Continuously Variable Transmission (CVT), referred to as the Empact CVT. An analysis of the dynamics of the actuation system and of the driveline shows that the eigenfrequencies of the system depend on both the CVT ratio and the slip in the variator. An accurate variator model is required to incorporate all characteristic dynamics. The implemented variator model is an explicit formulation of a model which gives an estimation of the tension forces and compression forces in the pushbelt. The simulation model also includes slip, shifting losses based on transient variator models and friction. Simulations are compared to measurements, showing good results.

Design of a slave robot for laparoscopic, thoracoscopic surgery

Abstract: Conventional Minimally Invasive Surgery (MIS) generally provides the surgeon with an uncomfortable body posture, limited force feedback and unnatural eye-handcoordination when manipulating camera and instruments through small incisions. A masterslave system with force-feedback is being developed, since such a system can overcome the inconveniences of MIS. This paper is about the design of the slave robot for MIS in the abdomen and chest. By applying design principles on kinematically and statically determined design: hysteresis of position is minimized; and stresses, deformations and dynamical behaviour are highly predictable. This improves the reliability of the robot.

Modeling, identification and control of a metrological Atomic Force Microscope with a 3DOF stage

Abstract: Atomic Force Microscopes (AFMs) are widely used for the investigation of samples at nanometer scale. In this paper, we present the modeling, the identification and the control of a metrological AFM. The metrological AFM is used for the calibration of transfer standards for commercial AFMs. Therefore, the focus of the presented work is on scanning accuracy rather than on scanning speed. The contribution of this paper is the combination of 3 degree-of-freedom (DOF) control, including position feedforward, with an AFM with fixed cantilever and a piezo-stack driven stage. The amount of coupling between all DOFs is assessed by a non-parametric MIMO identification of the AFM. Since the dynamics appear to be decoupled in the frequency range of interest, feedback controllers are designed using loopshaping techniques for each DOF separately. Position feedforward is added to the stage in x and y direction, which improves the tracking performance by a factor two. The controlled stage is able to track scanning profiles within the sensor bound of 5 nm. With the proposed control method, the metrological AFM can produce images of the transfer standards with a sensor bound of 2 nm. Furthermore, real-time imaging of the sample is possible without the need for a-posteriori image correction. Finally, it is shown that the proposed control method almost completely compensates the hysteresis in the system.

Frequency domain approach for the design of heavy-duty vehicle speed controllers

Abstract: The large parameter variations in heavy-duty trucks make it difficult to find appropriate settings for fixed structure speed controllers. Satisfying the design specifications with experience based trial-and error control design methods is very time-consuming. This paper discusses the modelling and model verification of a vehicular driveline and the model based, systematic design and tuning of speed controllers, using frequency domain techniques. Experiments with a real truck show that the performance and robustness of the closed loop system is within the specifications. The focus is on the cruise control, but the approach is also applicable to other speed controllers.

Modeling of disturbance forces of a x-y manipulator on a floating platform

Abstract: This paper describes a multi-body dynamics model for predicting disturbance forces and torques caused by a multistage manipulator (2 DOF) on a magnetically suspended platform (6 DOF). The manipulator consists of a beam attached to two parallel linear ironless actuators and a rotary arm underneath the beam. The model prediction can be used as a feed-forward in the control of the magnetic suspension of the platform. The model is verified with an experimental setup, that consists of a manipulator on an aluminium platform which is connected to the fixed world via a 6 DOF F/T sensor. The sensor is used to measure the forces and torques, that an ideal magnetic suspension will have to provide to compensate the for the disturbances given a certain movement of the manipulator. The measurements are compared with the predictions of the multi-body dynamics model.

The Empact CVT: modeling, simulation and experiments

Abstract: This paper shows the implementation of a simulation model for new electromechanically actuated metal V-belt type Continuously Variable Transmission (CVT), referred to as the Empact CVT. An analysis of the dynamics of the actuation system and of the driveline shows that the eigenfrequencies of the system depend on both the CVT ratio and the slip in the variator. An accurate variator model is required to incorporate all characteristic dynamics. The implemented variator model is an explicit formulation of a model which gives an estimation of the tension forces and compression forces in the pushbelt. The simulation model also includes slip, shifting losses based on transient variator models and friction. Simulations are compared to measurements, showing good results.

Needle for mechanically assisted insertion

Abstract: The invention concerns a needle for mechanically assisted insertion of the needle into an object and, in particular, for automated insertion, comprising a cylindrical body (32), enclosing a channel (33), and a cutting (34) part at the exit of the channel (33), the cutting part (34) comprising at least one surface defining at least one bevel (35) and at least one transition edge (37) of the bevel, the cutting part (34) comprising at least one irregularity (39) on said surface, the irregularity (39) generating a change in the shape of a measured insertion resistance force profile of the needle into the object, in order to permit the detection of the position of the needle in the object during its insertion.