Showing papers by "M Maarten Steinbuch published in 2006"

Plasma needle for in vivo medical treatment: recent developments and perspectives

Abstract: In this paper we describe the hitherto unravelled facts on the interactions of a cold atmospheric plasma with living cells and tissues. A specially designed source, plasma needle, is a low-power discharge, which operates under the threshold of tissue damage. When applied properly, the needle does not cause fatal cell injury which would result in cell death (necrosis). Instead, it allows precise and localized cell removal by means of the so-called cell detachment. In addition, plasma can be used for bacterial disinfection. Because of mild treatment conditions, plasma disinfection can be performed in vivo, e.g. on wounds and dental cavities. Presently, one strives to obtain a better control of the operating device. Therefore, plasma has been characterized using a variety of diagnostics, and a smart system has been designed for the positioning of the device with respect to the treated surface.

Development of a smart positioning sensor for the plasma needle

Abstract: In the study of plasma–surface interactions, a well-defined distance from the surface is desired. In this paper, an innovative method is proposed for using the intrinsic properties of a low-power atmospheric plasma to control this distance. It is proposed that the vicinity of a (even poorly) conducting surface imposes a change in the plasma impedance. This effects the reflection of electrical power, which can easily be measured, and provides a non-contact sensor for the distance between the plasma source and the substrate. For this sensor to work, a low-loss and efficient matching network is designed, such that changes in the reflected power are relatively high. With this high-quality matching network at hand, a characterization of the plasma needle is performed in terms of impedance and related parameters. Although characterization is not essential for the development of the sensor, it contributes to fundamental knowledge about the plasma source. Finally, coherence measurements are performed to determine the performance of the above described sensor in different experimental settings.

Control of a hydraulically actuated continuously variable transmission

Abstract: Vehicular drivelines with hierarchical powertrain control require good component controller tracking, enabling the main controller to reach the desired goals. This paper focuses on the development of a transmission ratio controller for a hydraulically actuated metal push-belt continuously variable transmission (CVT), using models for the mechanical and the hydraulic part of the CVT. The controller consists of an anti-windup PID feedback part with linearizing weighting and a setpoint feedforward. Physical constraints on the system, especially with respect to the hydraulic pressures, are accounted for using a feedforward part to eliminate their undesired effects on the ratio. The total ratio controller guarantees that one clamping pressure setpoint is minimal, avoiding belt slip, while the other is raised above the minimum level to enable shifting. This approach has potential for improving the efficiency of the CVT, compared to non-model based ratio controllers. Vehicle experiments show that adequate tracking is obtained together with good robustness against actuator saturation. The largest deviations from the ratio setpoint are caused by actuator pressure saturation. It is further revealed that all feedforward and compensator terms in the controller have a beneficial effect on minimizing the tracking error.

Modelling and LPV control of an electro-hydraulic servo system

Abstract: This paper aims to show the modelling and control of an hydraulic servo system, targeting at frequency domain based controller design and the implementation of a LPV controller. The actual set-up consists of a mass, moved by a hydraulic cylinder and an electro-hydraulic servo valve. A nonlinear parametric model of the system, a number of fitted linear black box models as well as a LPV model combining these fits have been determined. In discretization of the control strategies for implementation on a digital control system, a new discretization algorithm is derived for LPV structures. Simulations and experimental results indicate the potential benefits of a position dependent controller over a classical controller, but show the limitations as well.

Feedback control of occupant motion during a crash

Abstract: Passive in-vehicle safety systems such as the air bag and the belt restrain the occupant during a crash. However, often their behavior is not optimal in terms of occupant injuries. This paper discusses an approach to design an ideal restraint system. The problem is formulated as a feedback tracking problem with the objective to force the controlled variables, i.e., the acceleration of the head and the chest of the occupant, to follow a priori defined reference signals by simultaneous manipulation of the belt and the air bag. The reference signals have to reflect minimal injuries to the head, the chest, and the neck. More or less realistic numerical models of a crash test are far too complex to be used in control design processes. Therefore, a strategy is presented to derive simple, linear MIMO models. These models approximate the local dynamic behavior of the complex model and are suitable for control design. Analysis of the interactions in these simple models makes it plausible that the control ...

Optimization aided loop shaping for motion systems

Abstract: An approach is proposed which improves the quality and speed of manual loop shaping. Loop shaping is an iterative and creative controller design procedure where the control engineer uses frequency response function (FRF) data of the plant to shape the open loop response such that it satisfies stability, performance and robustness specifications. The advantage compared to automated controller design methods is that the control engineer can exploit all available a priori knowledge and expertise about the plant during the design process. As an assisting tool in manual loop shaping, we add a global optimization method, i.e. a genetic algorithm, where the objective function resembles as good as possible what the control engineer wants. As a result, the tuning process is substantially accelerated. The approach has been implemented in a Matlab-based control tuning tool showing good results.

Real-time control of the 3-DOF sled dynamics of a null-flux Maglev system with a passive sled

Abstract: The real-time control of the three degrees of freedom (DOF) dynamics of an electrodynamic (EDS) Maglev vehicle is presented. The design is based on a 5-DOF state-space model of the sled dynamics that uses a simple algebraic model to describe the interaction between the null-flux coils on the track and the permanent magnets on the sled. A first-order sliding mode controller with integral error term is used to control heave, pitch, and roll in real time from position-attitude information measured with sensors located on the sled. Experimental results show that control of the 3-DOF dynamics of the levitated vehicle in real time can be successfully achieved by the proposed method.

Removing non-repetitive disturbances in iterative learning control by 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 practice, the tracking error consists of both a repetitive part which is equal every iteration and a non-repetitive part which varies every iteration. ILC can only compensate for the repetitive part, the non-repetitive part limits the achievable performance of ILC. In this paper, a wavelet based filtering method is presented which identifies and removes the non-repetitive part of the tracking error by a comparison of two error realizations for each iteration of ILC. The filtered error signal is used as input for the learning scheme of ILC. Simulations and experiments show that the wavelet filtering method improves the performance of ILC, resulting in a smaller tracking error and in a learned feedforward signal that contains significantly less non-repetitive disturbances.

A piecewise linear approach towards sheet control in a printer paper path

Abstract: In this paper an approach towards sheet control in a printer paper path is presented. To make the control problem feasible, the complex overall control question is formulated in a hierarchical control set-up with a low level motor control part and a high level sheet control part. To understand the essence of the sheet control problem we consider a basic paper path in which industrial constraints and requirements are relaxed. Furthermore, the motor control part is assumed to be ideal and the sheet dynamics are captured in the piecewise linear modeling formalism. Based on the model of the sheet dynamics, the controller synthesis is carried out. Both state and output feedback control designs are presented and stability and tracking performance are analyzed. The effectiveness of the control design approaches is demonstrated via simulations.

Distributed control in adaptive optics: Deformable mirror and turbulence modeling

Abstract: Future large optical telescopes require adaptive optics (AO) systems whose deformable mirrors (DM) have ever more degrees of freedom. This paper describes advances that are made in a project aimed to design a new AO system that is extendible to meet tomorrow's specifications. Advances on the mechanical design are reported in a companion paper [6272-75], whereas this paper discusses the controller design aspects. The numerical complexity of controller designs often used for AO scales with the fourth power in the diameter of the telescope's primary mirror. For future large telescopes this will undoubtedly become a critical aspect. This paper demonstrates the feasibility of solving this issue with a distributed controller design. A distributed framework will be introduced in which each actuator has a separate processor that can communicate with a few direct neighbors. First, the DM will be modeled and shown to be compatible with the framework. Then, adaptive turbulence models that fit the framework will be shown to adequately capture the spatio-temporal behavior of the atmospheric disturbance, constituting a first step towards a distributed optimal control. Finally, the wavefront reconstruction step is fitted into the distributed framework such that the computational complexity for each processor increases only linearly with the telescope diameter.

Real-time Control of the 3-DOF Sled Dynamics of a Null-Flux Maglev System with a Passive Sled

Abstract: The real-time control of the 3-DOF dynamics of an electrodynamic (EDS) maglev vehicle is presented. The design is based on a 5-DOF state-space model of the sled dynamics that uses a simple algebraic model to describe the interaction between the null-flux coils on the track and the permanent magnets on the sled. A first order sliding mode controller with integral error term is used to control heave, pitch and roll in real time from position-attitude information measured with sensors located on the sled. Experimental results show that control of the 3-DOF dynamics of the levitated vehicle in real-time can be successfully achieved by the proposed method.

Modeling for simulation of hybrid drivetrain components

Abstract: Designing a hybrid drivetrain is a complex task, due to the unknown sensitivity of vehicle performance to system components specifications, the interaction between systems components, and the ability to operate the system components at different set points at any time. Therefore, many researchers [1-6] have made efforts formulating, and developing holistic hybrid drivetrain analysis, design, and optimization models including the top-level vehicle system control. However, an integral design approach [6] is usually characterized by large computation times, complex design problem formulations, multiple subsystem simulations, analyses, and non-smooth, or non-continuous models. In this paper, the influence of the component efficiencies, whereby the engine operation strategy (engine-, or system optimal operation) on the fuel economy, and the Energy Management Strategy (EMS) is investigated. Thereby, a relative simple Rule-Based (RB) EMS [11] is used, and is compared with the strategy based on Dynamic Programming (DP). The series-parallel transmission of the Toyota Prius has been used as a case study. The component modeling, and simulation results from the RB EMS, and DP are compared with results from the simulation platform ADVISOR. Finally, it is shown, that modeling the component efficiencies by only a few characteristic parameters, and using the RB EMS, the fuel consumption can be calculated very quickly, and with sufficient accuracy. In future work, the influence of topology choice on the fuel economy, and the EMS will also be investigated.

Performance of variable-gain controlled optical storage drives

Abstract: A method for performance assessment of a variable-gain control design for optical storage drives is proposed based on a quantitative performance measure. The variable-gain strategy is used to overcome well-known control design tradeoffs (for linear systems) between low-frequency tracking properties and high-frequency noise sensitivity. A performance analysis is conducted to support the design of the variable-gain controller which subsequently is shown to outperform linear controllers.

Identification and control of a vehicle restraint system

Abstract: To minimize occupant injuries, passive in-vehicle safety systems like the safety belt and the airbag restrain the occupant during a crash. This paper presents a design approach for a feedback controller for the belt force to reduce the maximum chest acceleration as a measure for the risk of occupant injuries. Only frontal crashes are considered. The available, experimentally validated numerical crash model is too complex to be used as a controller design model. Therefore, approximate linear models for the transfer from belt force to chest acceleration are derived by analysing the effect of stepwise perturbations of the belt force on the chest acceleration. Using these linear models, loop shaping is applied to arrive at a controller that satisfies a set of a priori defined criteria. The controller is implemented in and evaluated with the complex crash model, showing that a reduction of approximately 60 per cent in the adopted injury measure can be achieved. Furthermore, it is shown that this approach can be applied in different situations.

Actuator tests for a large deformable membrane mirror

Abstract: In the design of a large adaptive deformable membrane mirror, variable reluctance actuators are used. These consist of a closed magnetic circuit in which a strong permanent magnet provides a static magnetic force on a ferromagnetic core which is suspended in a membrane. By applying a current through the coil which is situated around the magnet, this force is influenced, providing movement of the ferromagnetic core. This movement is transferred via a rod imposing the out-ofplane displacements in the reflective deformable membrane. In the actuator design a match is made between the negative stiffness of the magnet and the positive stiffness of the membrane suspension. If the locality of the influence functions, mirror modes as well as force and power dissipation are taken into account, a resonance frequency of 1500 Hz and an overall stiffness of 1000 N/m for the actuators is needed. The actuators are fabricated and the dynamic response tested in a dedicated setup. The Bode diagram shows a first eigenfrequency of 950 Hz. This is due to a lower magnetic force than expected. A Helmholtz coil setup was designed to measure the differences in a large set of permanent magnets. With the same setup the 2nd quadrant of the B-H curve is reconstructed by stacking of the magnets and using the demagnetization factor. It is shown that the values for Hc and Br of the magnets are indeed lower than the values used for the initial design. New actuators, with increased magnet thickness, are designed and currently fabricated.

Ellipsoidal unfalsified control: stability

Abstract: Unfalsified control is a direct data-driven, plant-model-free controller design method, which recursively falsifies controllers that fail to meet the required performance specification, making them ineligible to actually control the plant. In this paper it is shown that sufficient conditions for stability can be derived for unfalsified control with an ellipsoidal unfalsified set, ellipsoidal unfalsified control (EUC), under the mild assumption that there exists at least some region in the original candidate controller pool, which contains controllers that meet the performance specifications. One of these conditions is a finite number of controller switches, which is guaranteed by imposing a maximum volume ratio between two consecutive ellipsoidal unfalsified sets.

Sufficient Conditions for Data-driven Stability of Ellipsoidal Unfalsified Control

Abstract: Unfalsified Control is a direct data-driven, plant-model-free controller design method, which recursively falsifies controllers that fail to meet the required performance specification, making them ineligible to actually control the plant. In this paper it is shown that sufficient conditions for stability can be derived for Unfalsified Control with an ellipsoidal Unfalsified set, Ellipsoidal Unfalsified Control (EUC). These conditions are: feasibility of the adaptive control problem, discarding of demonstrable destabilizing controllers and a finite number of controller switches. The latter is guaranteed by imposing a maximum volume ratio between two consecutive ellipsoidal Unfalsified sets and a minimum stepsize on the controller adjustments.

Design of a printhead alignment sensor for a temperature varying environment

Abstract: First findings are presented of an absolute position sensor for active alignment of printheads with respect to the printer frame over a distance of one meter. A string is stretched along the guidance serving as an absolute reference. The developed sensor measures the position of the printhead relative to this string. It is cheap and it is robust for temperature variations in the order of tens of degrees. The target accuracy is 1 /spl mu/m over a range of about 2 mm. Although only one measurement direction is of interest for the application, it can actually be used as a 2D sensor. If an extra sensor is added to the same string, a 4D sensor can be created.

Practical issues in model-based surge control for centrifugal compressors

Abstract: The performance and operating range of centrifugal compressors is limited by the occurrence of an aerodynamic instability called surge. This paper deals with the technological barriers for feedback stabilization of full-scale centrifugal compression systems. A dynamic model for a single stage compressor test rig is presented and a surge control strategy is discussed. Then the critical problems of model accuracy and sensor and actuator limitations are discussed. These problems are illustrated with simulation results and experimental data. We conclude by suggesting directions for further work in order to successfully implement active surge control in full-scale applications.

An exploration of nonlinear control of linear motion systems

Abstract: The idea is to use a linear parameter varying (LPV) controller for an LTI plant to facilitate different performance properties in different parameter ranges. Consider for example the intentionally LPV closed-loop system CP 1+CP = 2 s2+( √ 8−2e)s+2 with error-dependent damping. The step response is depicted in black together with the responses of the base linear system with various damping ratios. i i

Cascaded Sheet Feedback Control in a Printer Paper Path

Abstract: Our research focusses on longitudinal sheet control in a cut sheet printer paper path. The control problem is split up into a low level that encompasses motor control design for tackling local disturbances and uncertainties, and a high level that performs sheet feedback control, resulting in robustness at the sheet level. Consequently, a cascade control structure is chosen. The design of sheet controllers is considered here under the assumption of perfect low-level motor control.

Robust Sheet Control in an Uncertain Printer Paper Path

Abstract: The research described in this abstract focusses on sheet feedback control in an uncertain printer paper path. Given a prescribed sheet reference trajectory, xs,r, the control goal is to make sheets track the reference trajectory in the presence of uncertain system parameters and to attenuate disturbances acting on the system. As a case-study we consider the three pinch paper path depicted in Fig. 1, in which each pinch is driven by a separate motor. The sheet position xs, defined as the position of the leading edge, is assumed to be measured.