Showing papers in "Journal of Dynamic Systems Measurement and Control-transactions of The Asme in 2001"

Stochastic System Identification for Operational Modal Analysis: A Review

Abstract: This paper reviews stochastic system identification methods that have been used to estimate the modal parameters of vibrating structures in operational conditions. It is found that many classical input-output methods havean output-only counterpart. For instance, the Complex Mode Indication Function (CMIF) can be applied both to Frequency Response Functions and output power and cross spectra. The Polyreference Time Domain (PTD) method applied to impulse responses is similar to the Instrumental Variable (IV) method applied to output covariances. The Eigensystem Realization Algorithm (ERA) is equivalent to stochastic subspace identification.

Creep, Hysteresis, and Vibration Compensation for Piezoactuators: Atomic Force Microscopy Application

Abstract: Structural vibrations and hysteresis nonlinearities in piezoactuators have been fundamental limitations when using these actuators for high-speed precision-positioning applications. Positioning speed (bandwidth) is limited by structural vibrations, typically, to about one-tenth the fundamental vibrational frequency of the piezoprobe. Further, precision in positioning is limited by hysteresis nonlinearities, which can result in signie cant errors for large-range positioning applications. This paper shows that signie cant improvements in precision and bandwidth can be achieved by using an inversion-based approach to compensate for hysteresis and vibrations in the piezodynamics. Theapproach decouplestheinversion into 1 )inversion of thehysteresisnonlinearity and 2 )inversion ofthe structuraldynamics,toe ndaninputvoltageproe lethatachievesprecisiontracking ofa desiredpositiontrajectory. Theapproachisappliedtoapiezoactuator,andexperimentalresultsshowthatanorderofmagnitudeimprovement in positioning speed is achieved, while maintaining precision tracking of the desired position trajectory. I. Introduction P IEZOACTUATORS can achieve nanometer resolution positioning and are hence increasingly being used for ultraprecision positioning in aerospace applications, 1;2 vibration control, scanning probe microscopy for surface characterization, and nanofabrication. 3i5 Two major limitations of present positioning techniquesusing piezoactuatorsare 1 )lowoperating bandwidthdue to positioning errors caused by structural vibrations at high speeds and 2) low precision for relatively large-range displacements (due to errors caused by hysteresis nonlinearities ), resulting in restricted positioning range. This paper presents a method to improve both the accuracy and the speed of piezoactuators by using an inversionbased approach to e nd the voltage input to the piezoactuators that compensates for the hysteresis nonlinearities and the structural vibrations. This approach e rst decouples the system dynamics into two separate subsystems that model 1 ) the hysteresis nonlinearity

Structural Health Monitoring Using Statistical Pattern Recognition Techniques

Abstract: All members of the Los Alamos Structural Health Monitoring Team contributed to this study reported herein. The team members include George Papcum and Michael L. Fugate from the CIC3 Group, and Scott Doebling from the Engineering Analysis Group. Funding for this investigation came primarily through Los Alamos National Laboratory Director’s Funded Postdoctoral Fellows Program. The authors also thank Gregg Johnson and Mike Todd of NRL for providing the experimental data and allowing the publication of the test results.

Application of a Fast-Stabilizing Frequency Domain Parameter Estimation Method

Abstract: A new noniterative frequency domain parameter estimation technique is proposed. It is based on a weighted total least squares approach, starting from multiple input multiple output frequency response functions. One of thespecific advantages of the technique lies in the very stable identification of the system poles as a function of the specified system order leading to easy-to-interpret stabilization diagrams. This implies a potential for automating the method and to apply it to "difficult" estimation cases. Several real-life case studies are discussed, one related to holographic modal analysis in the medium frequency range, one to the modal testing of a fully trimmed vehicle.

A unified approach to driver assistance systems based on artificial potential fields

Abstract: This paper presents an approach to vehicle control based upon the paradigm of artificial potential fields. Using this method, the dynamics of the vehicle are coupled with the environment in a manner that ensures that the system exhibits safe motion in the absence of driver inputs. The driver remains in control of the vehicle, however, with the control systems presenting a predictable and safe set of dynamics. With the control approach presented here, integration of various assistance systems can be easily achieved through simple superposition of individual potential and damping functions. A simple example of a combined lanekeeping and stability system demonstrates how this can be accomplished. Preliminary simulation results suggest that both safety and driveability are achievable with such a system, prompting further investigation.

Output-Only Subspace-Based Structural Identification: From Theory to Industrial Testing Practice

Abstract: We address the problem of structural model identification during normal operating conditions and thus with uncontrolled, unmeasured, and nonstationary excitation. We advocate the use of output-only and covariance-driven subspace-based stochastic identification methods. We explain how to handle nonsimultaneously measured data from multiple sensor setups, and how robustness with respect to nonstationary excitation can be achieved. Experimental results obtained for three real application examples are shown.

Transparency and Stability Robustness in Two-Channel Bilateral Telemanipulation

Abstract: This paper presents a two-channel architecture and design approach that enables a simultaneous increase in the transparency and stability robustness of a bilateral teleoperation system, and additionally provides a high degree of transparency robustness to uncertainty in the operator and environment dynamics. The former is provided by the use of a loop-shaping filter incorporated on the master-to-slave motion command, and the latter by local feedback loops around both the master and slave manipulators. The proposed architecture and design approach are illustrated on a single-degree-of-freedom example with and without a communication channel time delay. Finally, the implications of scaling on the stability of the teleoperator loop are discussed. @DOI: 10.1115/1.1387018#

Identification of a driver steering model, and model uncertainty, from driving simulator data

Abstract: Vehicle active safety systems are designed to improve driving safety while the driver is still in control of the vehicle. For the design of such systems, driver-controller interaction can be significant and should not be neglected. Pilutti @1# shows that a lane departure warning system can be improved by considering variations in driver state. An active controller that uses direct intervention of vehicle motion will lend to driver-controller interaction issued, and generally requires a thorough investigation of driver behavior before active safety controllers can be implemented @2‐4 # For vehicle lateral control, the steering wheel angle is the primary means for control actuation. Many driver models try to approximate the real driver’s road tracking performance, assuming certain driver inputs and outputs. Several driver models have been developed in the literature ~e.g., @5‐9#!. A well-known result from human factors research is the ‘‘crossover’’ model @5,6#. The crossover model states that the open loop frequency response of the driver-vehicle combination approximates that of transfer function v c /s around the crossover frequency, where v c is the crossover frequency. Many driver models can be regarded as different realizations of the crossover model ~e.g., @7,8#!. These models have similar characteristics around the crossover frequency and differ more at higher and lower frequency ranges. Models of the driver steering control, based on system identification, which can be used for on-line implementation have also been reported in @10,11#. Although these models approximate the driver behavior well, no driver model is expected to represent the real driver completely. Furthermore, for the purpose of controller design, it is common practice to use a low-order driver model. Therefore, it is reasonable to expect that significant driver model uncertainty exists. This driver model uncertainty can have a significant effect on the performance of the designed control system. To successfully design an active safety controller, including warning and direct intervention, it is necessary to obtain a reasonable representation of this driver model uncertainty. The uncertainty can be used to represent the difference between one real driver and the driver model at any instant in time, or to represent the change in driving behavior with time. On a larger scale, the uncertainty can also be used to represent the variation across several different drivers if the designed system is to be used by different drivers. However, studies of driver model uncertainty have not been reported in the literature. This article aims to develop a model for the driver model uncertainty using the measured data from real drivers driving a fixed-base driving simulator. In general, model uncertainty can be divided into structured uncertainty ~e.g., parametric uncertainty! and unstructured uncertainty ~e.g., additive uncertainty due to unmodeled dynamics!. Driver model uncertainty includes contributions from: model order, parameter uncertainty, and nonlinearity @12#. In this study, the parametric uncertainty is used to represent the variation of driver behavior during a period of time. The unstructured uncertainty is used to account for unmodeled dynamics and nonlinearity of the real driver. Intuitively, higher order models can capture additional dynamic characteristics of the real driver, and can be considered more ‘‘complete.’’ If a linear low order model is used for the driver, the difference in model order will contribute to the model uncertainty. From the controller design viewpoint, the parametric uncertainty may be dealt with using adaptive control techniques and the unstructured uncertainty may be addressed using robust control techniques. The contribution of this research work is a new approach to compute the driver model with parametric and unstructured uncertainty from driving simulator data. 2 Identification of Driver Model From Simulator Data In this study it is proposed to use system identification techniques and driving simulator data to obtain a driver model and the model uncertainty. We consider a black-box driver model where the lateral deviation from the centerline of the road ~y! is treated as the input of the driver. The driver’s output is the steering wheel angle ~d!. The idea of this model is shown schematically in Fig. 1. The objective of this research is to obtain a nominal driver model (Gd) with parametric uncertainty and unstructured model uncertainty ~D! from the driving simulator data. This idea is shown in Fig. 2, where an additive model uncertainty is used. It is noted that the measured d is not completely related to the input signal y. Therefore, a disturbance term e8 is used to represent the portion of the data that cannot be included in D. In order to understand the identification results more clearly, it is helpful to examine the data in more detail.

Optimal Sensor Placement Methodology for Identification with Unmeasured Excitation

Abstract: A methodology is presented for designing cost-effective optimal sensor configurations for structural model updating and health monitoring purposes. The optimal sensor configuration is selected such that the resulting measured data are most informative about the condition of the structure. This selection is based on an information entropy measure of the uncertainty in the model parameter estimates obtained using a statistical system identification method. The methodology is developed for the uncertain excitation case encountered in practical applications for which data are to be taken either from ambient vibration tests or from other uncertain excitations such as earthquake and wind. Important issues related to robustness of the optimal sensor configuration to uncertainties in the structural model are addressed. The theoretical developments are illustrated by designing the optimal configuration for a simple 8-DOF chain-like model of a structure subjected to an unmeasured base excitation and a 40-DOF truss model subjected to wind/earthquake excitation. @DOI: 10.1115/1.1410929#

A Recursive Multibody Dynamics and Sensitivity Algorithm for Branched Kinematic Chains

Abstract: In this work an efficient dynamics algorithm is developed, which is applicable to a wide range of multibody systems, including underactuated systems, branched or tree-topology systems, robots, and walking machines. The dynamics algorithm is differentiated with respect to the input parameters in order to form sensitivity equations. The algorithm makes use of techniques and notation from the theory of Lie groups and Lie algebras, which is reviewed briefly. One of the strengths of our formulation is the ability to easily differentiate the dynamics algorithm with respect to parameters of interest. We demonstrate one important use of our dynamics and sensitivity algorithms by using them to solve difficult optimal control problems for underactuated systems. The algorithms in this paper have been implemented in a software package named Cstorm (Computer simulation tool for the optimization of robot manipulators), which runs from within Matlab and Simulink. It can be downloaded from the website http://www.eng.uci.edu/ bobrow/ @DOI: 10.1115/1.1376121#

On the Number and Placement of Accelerometers for Angular Velocity and Acceleration Determination

Abstract: This paper identifies the minimum number of accelerometers nec-essary to measure rigid body acceleration. Notwithstanding thatonly 9 scalar unknowns must be identified, 12 devices compose aminimum set of transducers. This redundancy is necessary toavoid singularities in the equations. Conditions for the sensorplacement are given. It is also shown that when the determinationof the angular velocity is not required, a reduced set of 9 sensorscan be adopted. @DOI: 10.1115/1.1386649#

Analysis of reset control systems consisting of a FORE and second-order loop

Abstract: Reset controllers consist of two parts a linear compensator and a reset element. The linear compensator is designed, in the usual ways, to meet all closed-loop performance speci cations while relaxing the overshoot constraint. Then, the reset element is chosen to meet this remaining step-response speci cation. In this paper, we consider the case when such linear compensation results in a second-order (loop) transfer function and where a rst-order reset element (FORE) is employed. We analyze the closed-loop reset control system addressing performance issues such as stability, steadystate response and transient performance. This material is based upon work supported by the National Science Foundation under Grant No.CMS9800612. MIE Department, University of Massachusetts, Amherst, MA 01003; chen@ecs.umass.edu. Now with Motorola, Inc. MIE Department, University of Massachusetts, Amherst, MA 01003; chait@ecs.umass.edu. ECE Department, University of Massachusetts, Amherst, MA 01003; hollot@ecs.umass.edu.

Dynamic Optimization of Lean Burn Engine Aftertreatment

Abstract: The competition to deliver fuel e cient and environmentally friendly vehicles is driving the 1 2 Submitted to Journal of Dynamics Systems, Measurement, & Control automotive industry to consider ever more complex powertrain systems. Adequate performance of these new highly interactive systems can no longer be obtained through traditional approaches, which are intensive in hardware use and nal control software calibration. This paper explores the use of Dynamic Programming to make model-based design decisions for a lean burn, direct injection spark ignition engine, in combination with a three way catalyst and an additional threeway catalyst, often referred to as a lean NOx trap. The primary contribution is the development of a very rapid method to evaluate the tradeo s in fuel economy and emissions for this novel powertrain system, as a function of design parameters and controller structure, over a standard emission test cycle.

Experimental Nonlinear Dynamics of a Shape Memory Alloy Wire Bundle Actuator

Abstract: In this paper, the nonlinear dynamics of a new Shape Memory Alloy (SMA) actuator possesses impressive payload lifting capabilities are presented. This actuator cons 48 SMA wires mechanically bundled in parallel forming one powerful muscle. It designed to lift up to 45.4 kg (100 lbs), which is approximately 300 times its weight. SMA actuator was tested in open-loop experiments with different loads and diff inputs, such as step, ramp, sinusoid, and half sinusoid, and its dynamic character were evaluated. An important observation made during the dynamic analysis wa unpredictability of the actuator’s response when low to moderate voltages were app This characteristic suggests possible chaotic behavior of the actuator, which could a the system design and cause control difficulties in fine and high accuracy task investigation into chaos was conducted using time histories, phase plots, Poincare ́ maps, and power spectrum density plots. As shown in the diagrams presented in this p system response to sinusoidal inputs with a larger mean voltage is periodic, wh lower mean voltages produce unpredictable responses that indicate chaotic behav @DOI: 10.1115/1.1344243 #

Learning Input Shaping Technique for Non-LTI Systems

Abstract: It is well known that a conventional input shaping technique is not very effective in suppressing residual vibrations for non-LTI systems, such as substantially nonlinear or time-varying systems. In an effort to increase the effectiveness for such systems, this paper presents a learning input shaping technique (LIST), which iteratively updates the parameters of the IST from the previous trials. Simulations are presented for 4 different cases: 1) when the natural frequency or damping of a system does not estimated well; 2) when a system has time varying vibration; 3) when a system has nonlinear flexibility; and 4) when a closed loop system includes the saturation limit in the loop. The experiments are made by using a 6-DOF industrial robot to evaluate the method. Results of both the simulations and experiments show that the residual vibrations become considerably smaller as iteration goes on, thereby demonstrating the effectiveness of the LIST.

H∞-Based Robust Torque Control of Harmonic Drive Systems

Abstract: In this paper, the torque control of a harmonic drive system for constrained-motion andfree-motion applications is examined in detail. A nominal model for the system is obtainedin each case from experimental frequency responses of the system, and the deviation ofthe system from the model is encapsulated by a multiplicative uncertainty. Robust torquecontrollers are designed using this information in an