Showing papers by "M Maarten Steinbuch published in 2004"

Modeling and identification for high-performance robot control: an RRR-robotic arm case study

Abstract: This paper explains a procedure for getting models of robot kinematics and dynamics that are appropriate for robot control design. The procedure consists of the following steps: 1) derivation of robot kinematic and dynamic models and establishing correctness of their structures; 2) experimental estimation of the model parameters; 3) model validation; and 4) identification of the remaining robot dynamics, not covered with the derived model. We give particular attention to the design of identification experiments and to online reconstruction of state coordinates, as these strongly influence the quality of the estimation process. The importance of correct friction modeling and the estimation of friction parameters are illuminated. The models of robot kinematics and dynamics can be used in model-based nonlinear control. The remaining dynamics cannot be ignored if high-performance robot operation with adequate robustness is required. The complete procedure is demonstrated for a direct-drive robotic arm with three rotational joints.

Simulation and control of an automotive dry clutch

Abstract: In this work the dynamic behavior and control of an automotive dry clutch is analyzed. Thereto, a straight-forward model of the clutch is embedded within a dynamic model of an automotive powertrain comprising an internal combustion engine, drivetrain and wheels moving a vehicle through tire-road adhesion. The engagement of the clutch is illustrated using the model best suited for simulation, based on work of Karnopp. These simulation results are used for conceiving a decoupling controller for the engine and clutch torque. Simulation results with the controller showing significant improvement over the un-controlled case in terms of vehicle launch comfort. A modified controller is proposed that results in even more appreciated drive comfort while not deteriorating other system behavior.

Jerk derivative feedforward control for motion systems

Abstract: This work discusses reference trajectory relevant model based feedforward design. For motion systems which contain at least one rigid body mode and which are subject to reference trajectories with mostly low frequency energy, the proposed feedforward controller improves tracking performance significantly. The feedforward controller may be of much lower order than the plant. The proposed feedforward controller is introduced using a model of an industrial XY-table as an application example.

Benefits of over-actuation in motion systems

Abstract: This paper studies the benefits of using additional actuators in the design of motion systems. The motion part and disturbance attenuation part require different placement of the actuators to work optimally, which is not possible in traditional designs. Allowing extra actuators in the design makes it possible to overcome this limitation. In this way the controllability of the internal dynamics of the structure can be both maximized for feedback and minimized for feedforward. By tuning a static relation between the actuators it is possible to minimize the excitation of resonances in the feedforward path. Feedback controller design is based on an existing vibration control strategy, which enables placement of the bandwidth beyond the lowest resonance frequencies. The idea is demonstrated by the example of a levitated beam.

Trajectory planning and feedforward design for high performance motion systems

Abstract: This paper gives an algorithm for fourth order trajectory planning with constrained dynamics for single axis motion control. A model-based feedforward controller is derived that makes full use of these trajectories. Application to industrial high-precision electromechanical motion systems is motivated. Issues like time-optimality, implementation and digitization are considered. Simulation results show superior effectiveness in comparison with rigid-body feedforward.

Method of adaptive interactive learning control and a lithographic manufacturing process and apparatus employing such a method

Abstract: By applying time-frequency analysis to a given standard iterative learning control or ILC an adaptive filter for the learned feed-forward loop is designed. This time varying filter varies according to the momentary frequency content of the error signal and allows to discriminate between areas of deterministic and stochastic error. Its application results in selective application of ILC to those intervals where error signals of high level are concentrated and allows application of a single ILC acquisition to different setpoint trajectories. The adaptive filter finds particular use in lithographic scanning systems where it is used for varying scan length.

Mathematical model of the 5-DOF sled dynamics of an electrodynamic maglev system with a passive sled

Abstract: A model that describes the five-degrees-of-freedom (5-DOF) dynamics of a passively levitated electrodynamic maglev system is presented. The model is based on the flux-current-force interactions and the geometric relationships between the levitation coils and the permanent magnets on the sled. The model is presented in a parametric state-space formulation, suitable to extract model parameters from input-output measurements in a minimum mean-square error sense. The proposed structure is very well suited for parameter estimation and to later develop robust feedback control of the sled dynamics.

Haptic feedback designs in teleoperation systems for minimal invasive surgery

Abstract: One of the major shortcomings of state-of-the-art robotic systems for minimal invasive surgery is the lack of haptic feedback for the surgeon. In order to provide haptic information, sensors and actuators have to be added to the master and slave device. A control system should process the data and make a coupling between slave and master. Despite the significant amount of research on haptic devices, this control design problem is, largely, an open problem. This paper reports the results on three model-based control designs. Using the formalism of passivity, a robust controller has been designed, and is compared to a gain scheduled controller (LPV) which is adaptable for changes in the tissue characteristics.

Stability parameter identification for a centrifugal compression system

Abstract: This paper presents the application of a lumped parameter model to describe the dynamic behavior of a centrifugal compression system including surge. The response of the model is compared with experimental surge measurements from an industrial single stage compressor test rig. A parametric analysis of the model reveals the large influence of the stability parameter on the transient response. However, a good value for this parameter is not easily obtained from surge data. Therefore, an identification method is proposed to uniquely determine the stability parameter that is based on an approximate realization algorithm, making use of the fact that the step response of the system has the characteristics of a first order system. Simulation results show that this method can provide an estimate for the stability parameter of a centrifugal compression system.

Nonlinear stabilization of slip in a continuously variable transmission

Abstract: One way to predict and control the output torque of a geared neutral CVT is to use the relationship between slip in the variator and transmitted belt torque. This relationship is often referred to as the traction curve. For small slip values, the output torque increases almost linearly with slip. However, at approximately 2% slip, the maximum output torque is reached. For larger slip values, the output torque shows even a decline. Hence, measuring the traction curve in open loop is not possible. Stability analysis shows that by modifying the plant with a nonlinear feedback control torque depending on the slip, a stable closed loop plant with two new defined inputs is obtained. An open loop input torque at this plant now uniquely defines the slip in the system. The primary shaft angular velocity is controlled using a robust stabilizing controller. This controller is tuned using measured frequency response functions at different slip values.

On noise- and period-time sensitivity in high order repetitive control

Abstract: Repetitive control is useful if periodic disturbances act on a control system. Perfect (asymptotic) disturbance rejection is achieved if the period-time is exactly known. The improved disturbance rejection at the periodic frequency and its harmonics is achieved at the expense of a degraded system sensitivity at intermediate frequencies. A convex optimization problem is defined for the design of high-order repetitive controllers, where a trade-off can be made between robustness for changes in the period-time and for reduction of the error spectrum in-between the harmonic frequencies. The high order repetitive control algorithms are successfully applied in experiments with the tracking control of a CD-player system.

Large adaptive deformable membrane mirror with high actuator density

Abstract: With the future growing size of telescopes, new, high-resolution, affordable wavefront corrector technology with low power dissipation is needed. A new adaptive deformable mirror concept is presented, to meet such requirements. The adaptive mirror consists of a thin (30-50 μm), highly reflective, deformable membrane. An actuator grid with thousands of actuators is designed which push and pull at the membrane’s surface, free from pinning and piston effects. The membrane and the actuator grid are supported by an optimized light and stiff honeycomb sandwich structure. This mechanically stable and thermally insensitive support structure provides a stiff reference plane for the actuators. The design is extendable up to several hundreds of mm's. Low-voltage electro-magnetic actuators have been designed. These highly linear actuators can provide a stroke of 15 micrometers. The design allows for a stroke difference between adjacent actuators larger than 1 micron. The actuator grid has a layer-based design; these layers extend over a large numbers of actuators. The current actuator design allows for actuator pitches of 3 mm or more. Actuation is free from play, friction and mechanical hysteresis and therefore has a high positioning resolution and is highly repeatable. The lowest mechanical resonance frequency is in the range of kHz so a high control bandwidth can be achieved. The power dissipation in the actuator grid is in the order of milliwatts per actuator. Because of this low power dissipation active cooling is not required. A first prototype is currently being developed. Prototypes will be developed with increasing number of actuators.

Modal framework for closed-loop analysis of over-actuated motion systems

Abstract: A large class of motion systems used in precision applications is required to meet increasing levels of tracking performance whereas costs should not rise drastically. Allowing for more actuators and sensors than rigid-body modes, which is called over-actuation, higher levels of performance can be obtained without increasing mechanical stiffness. However, the design of MIMO controllers for motion systems is not straightforward and a better understanding of the modal behavior in closedloop would be valuable. In this paper we introduce a new framework to analyze multivariable controllers for over-actuated motion systems in modal form. This approach enables us to analyze various closed-loop properties, such as modal tracking behavior and modal disturbance attenuation. Both feedback and feedforward performance is evaluated at the same time, using a global performance measure. The new approach is illustrated by an example.

Modelling the electromechanical interactions in a null flux EDS Maglev system

Abstract: The fundamental electromechanical interactions in a passive null-flux electrodynamic Maglev system (EDS) are mediated by the voltages induced in the levitation coils by the sled magnets, and by the forces exerted on the sled as a result of the induced currents. This paper presents a reliable and compact method to calculate these interactions by using analytical expressions of the magnetic field of a permanent magnet. The proposed approach provides a highly efficient and numerically stable approach to the computation of the flux induced in the levitation coils as well as the induced voltages and currents and lift, drag and guidance forces acting on the sled's magnets. The analytical model is compared to a simplified algebraic model suitable for realtime control of EDS Maglev suspension dynamics. Both models are compared with measurements and show good predictive quality.

Reference trajectory relevant jerk derivative feedforward control for motion systems

Abstract: This work discusses reference trajectory relevant model based feedforward design. For motion systems which contain at least one rigid body mode and which are subject to reference trajectories with mostly low frequency energy, the proposed feedforward controller improves tracking performance significantly. The feedforward controller may be of much lower order than the plant. The proposed feedforward controller is introduced using a model of an industrial XY-table as an application example.

Standard and lifted approaches of iterative and learning control applied on a motion system

Abstract: Iterative Learning Control (ILC) is a technique for improving the performance of systems or processes that operate repetitively over a x ed time interval. The basic idea of ILC is that it exploits every possibility to incorporate past repetitive control information, such as tracking errors and control input signals into the construction of the present control action. Past control information is stored and then used in the control action in order to ensure that the system meets the control specications such as convergence. The goal of the research presented in this paper is to liken two different ILC techniques applied to the wafer stage of a wafer scanner motion system. Namely, we consider briey the concepts of standard and lifted ILC and we evaluate the ILC performance in terms of tracking errors.

Integrated design of a lightweight positioning system

Abstract: In this paper a new approach to the design of positioning systems is introduced. The approach aims at the design of fast and accurate systems that are lightweight compared to classical designs. The new design reduces peak power requirements and thermal effects that deteriorate performance of the whole system.

Modelling slip- and creepmode shift speed characteristics of a pushbelt type continuously variable transmission

Abstract: A new model for transient behavior of a pushbelt type CVT is proposed in order to be able to simulate variator behavior under slip conditions. This model is compared to existing models. Compared to those models better agreement with measurements was found.

Modeling and identification for robot motion control

Abstract: This chapter deals with the problems of robot modelling and identification for high-performance model-based motion control A derivation of robot kinematic and dynamic models was explained Modelling of friction effects was also discussed Use of a writing task to establish correctness of the models was suggested Guidelines for design of an exciting identification trajectory were given A Kalman filtering technique for on-line reconstruction of joint motions, speeds, and accelerations was explained A straightforward but efficient estimation of parameters of the rigid-body dynamic model with friction effects was described The effectiveness of the procedure was experimentally demonstrated on a direct-drive robot with three revolute joints For this robot, models of kinematics and rigid-body dynamics were derived in closed-form, and presented in full detail The correctness of the models was established in simulation Results of experimental estimation of the dynamic model parameters were presented The appropriateness of the dynamic model for model-based control purposes was verified However, it was also indicated that this model is still not sufficient for a perfect match to the real robot dynamics, as these dynamics may contain more effects than covered by the rigid-body model A procedure to identify the dynamics not covered by the rigid-body model was proposed With these additional dynamics available, more advanced feedback control designs become possible

Classifying disc defects in optical disc drives by using time-series clustering

Abstract: Optical disc drives are subject to various disturbances and faults. A special type of fault is the so-called disc defect. In this paper we present an approach for disc defect classification. It is based on hierarchical clustering of measured signals that are affected by disc defects. The time-series are mapped into a feature space after which the feature vectors are clustered in a hierarchical fashion. Finally, signals are fitted onto the clusters to obtain single representations for each fault class. The resulting class descriptions can then be used for (on-line) classification of new disc defects. The approach is evaluated by applying it to a set of test data.

Data-based design of high-performance motion controllers

Abstract: This paper presents a data-based design of a linear feedback controller, which realizes desired closed-loop sensitivity and complementary sensitivity transfer functions. These transfer functions are specified via a single model-based performance cost. The data-based equivalent of this cost is derived, and its utility for the feedback design is demonstrated. A designer can prescribe the controller structure and complexity. Experimental results obtained in a direct-drive robot motion control problem show the quality of the design.

Design specifications for hybrid vehicles

Abstract: The NWO research programme called "Impulse Drive" focusses on design methodologies for hybrid vehicles with significant reduction of fuel consumption (50% - 75%) and CO2 emissions on a representative drive cycle. Powertrain hybridization implies adding a secondary power source or Energy Exchange System (EES) to a primary power source in order to increase the driving functions of a vehicle. The EES can enhancethe fuel consumption, emissions, comfort, driving performance and safety. In this paper a "bottom-up design process" is discussed, which focusses on determining the generic design specifications of the EES independent of the applied component technology and topology. In this paper the influence of an EES onenergy exchange with vehicle load and engine will be investigated separately. The simulation results show that the vehicle energy recovery efficiency is strongly determined by the motor/generator efficiencies, sizes and vehicle mass. The fuel economy is improved due to avoiding lower efficiency operation of the engine by increase of generator and motor size of the EES.

Data-based LQG control

Abstract: In spite of the current state of control theory, a fundamental issue in control remains open: which model is appropriate for control design? Mathematical models of complex systems are not always reliable, while adaptive and robust control methods have not completely overcome the danger of modelling errors. Furthermore, the design of an accurate model from first principles or from system identification, is often a time consuming and not a straightforward task. In this work [1], another approach to design controllers for a system is discussed. The control action that realizes system regulation or tracking control is derived without the use of any model or preliminary information about the system, but is merely based on input-output data observed from the system. This way, the step of modelling or system identification is not required anymore. Such a control strategy is known as data-based control. Standard model-based discrete-time finite horizon optimal control is obtained using a state-space description of the system. A linear quadratic cost function is optimized resulting in two difference Riccati equations, with which the optimal state feedback and state observer gains can be computed. Since a linear quadratic cost function is used together with Gaussian process and measurement noises, the combination of the optimal control and the state observation is known as Linear Quadratic Gaussian (LQG) control. Reference [2] presents an algorithm that omits the need for a state-space model of the system, when computing the solution to the discrete-time finite horizon LQG problem. The computation makes use of closed-form solutions to the difference Riccati equations instead of the normally used recursive solutions. This way, the solution no longer requires an explicit system model, but is based on a finite number of Markov parameters of the system that equal the values of the impulse response at discrete sample times. These parameters can be estimated on-line from almost any set of input/output data of the system using ARMarkov representations [3]. The combination of on-line Markov parameter estimation and data-based LQG control can be used to construct a moving horizon controller. A system can then be regulated using only the input and output data, without requiring any model of the system or any parametric representation of the controller. Based on the measured input/output data, the controller can adapt its action to the actual dynamics. Consequently, the data-based controller can also be used to control systems with changing dynamics. Apart from state regulation, the data-based controller can be used for tracking control tasks. The effectiveness of data-based LQG control is evaluated in simulations and in experiments. Simulations show that, in case of time-invariant plants, a model-based and data-based LQG controller give identical results while in case of time-varying plants, the data-based controller is able to adapt itself to the changing dynamics. Although not yet delivering a high tracking performance, experimental results obtained on a direct-drive robot of spatial kinematics look promising. At this moment, a high computational burden is the most important factor which limits the performance. Reduction of the computational costs, so performance improvement can be obtained with a longer horizon length is under investigation.