Tsu-Chin Tsao

Robust Adaptive and Repetitive Digital Tracking Control and Application to a Hydraulic Servo for Noncircular Machining

This paper presents the development of robust digital tracking control algorithms and their real-time implementation on an electrohydraulic servo-actuator for tool positioning in norcircular machining. Robust adaptive feedforward controller for tracking arbitrary signals and robust repetitive controller for tracking periodic signals against disturbances and unmodeled dynamics have been developed. Experimental results are presented to illustrate the control system synthesis procedures and tracking performance

A description of the dynamic behavior of fuzzy systems

An approach is presented for analyzing the global behavior of a fuzzy dynamical system that applies the concept and method of cell-to-cell mapping to obtain the evolving trend of the states of a fuzzy dynamical system. The behavior of the fuzzy system is characterized by equilibria, periodic motions, and their domain of attractions. Min-max operation accumulates the fuzziness of a fuzzy system in every step of iterations and makes the state evolution obscure. The proposed method transforms a given fuzzy mapping to at Z-to-Z mapping and does not accumulate fuzziness. Both the real and fuzzy initial state response analyses are discussed. An inverted pendulum controlled by a fuzzy controller is analyzed to illustrate the validity of the method. >

Optimal Feed-Forward Digital Tracking Controller Design

This paper presents an approach for optimal digital feed-forward tracking controller design. The tracking problem is formulated as a model matching problem, in which the distance between a specified tracking reference model and the achievable tracking performance by feedforward compensation is minimized. Desired input/output characteristics, finite length preview action, tracking of specific classes of constrained signals, time domain reference signal velocity or acceleration bound, and frequency domain weighting are conveniently incorporated in the proposed controller design and their roles in tracking performance are discussed. The tracking error bound is also explicitly expressed in terms of the controller design parameters. An l 1 norm optimal tracking controller is proposed as a solution to the mechanical tolerance control problem. A motion control example illustrates the design approach and several aspects of the resulting optimal feedforward controller, including the optimality of the zero phase error tracking controller

Two-parameter robust repetitive control with application to a novel dual-stage actuator for noncircular Machining

This work presents a robust repetitive controller design for a novel dual-stage actuator system. The dual-stage actuator, which consists of an electrohydraulic actuator for 25-mm-gross motion and a piezoelectric actuator for 40-/spl mu/m fine motion, is designed for noncircular machining application. The controller is designed through a sequence of two single-input-single-output (SISO) designs by exploiting the triangular structure of the two by two actuator system dynamics. The tracking error from the first stage electrohydraulic actuator is used as reference for the second stage piezoelectric actuator. In this master-slave control arrangement, the overall sensitivity function is the product of two sensitivity functions from each actuators servo loop. Thus, performance is improved at the frequencies where the sensitivity values are already well less than one. In the real-time control implementation, the effects of finite word length are analyzed and addressed via controller order reduction and realization. In an experiment of tracking an automotive cam profile at the rate of 10 cycles per second (600 rpm), the proposed dual-stage servo system generated tracking error of 4-/spl mu/m peak-to-valley and 0.80-/spl mu/m root-mean-square (RMS) value, showing a substantial improvement over the 16 micron peak-to-valley and 2.64-/spl mu/m RMS errors generated by the electrohydraulic servo system alone.

Repetitive Control for Asymptotic Tracking of Periodic Signals With an Unknown Period

Repetitive control schemes for asymptotic tracking and disturbance rejection of periodic signals with an unknown period are presented. A sampled data recursive scheme for identifying the period of a periodic signal with a resolution finer than the sampling interval is presented. Discrete-time self-tuning repetitive controllers, which adapt both the periodic signal period and sampling interval, are proposed based on the period identification scheme. The fine adaptation of the controller sampling interval makes the identified signal period an exact integer multiples of the controller sampling interval and renders a superior tracking performance than that of the conventional fixed sampling interval repetitive controllers. Experimental results on a linear motion system are presented to demonstrate the effectiveness of the proposed control schemes.

A new approach to stability analysis of variable speed machining systems

Abstract This paper presents a new method for the stability analysis of variable speed machining systems. By using spindle angular position as the independent variable, the system dynamics are modeled as a linear periodic time-varying system with fixed delay. This representation is proven much easier to analyze and to numerically simulate than the time-varying delay representation, which traditionally uses the real-time as the independent variable. With a finite difference scheme, the infinite dimensional periodic time-varying system is approximated by a finite dimensional periodic time-varying discrete system, which in turn is converted to a time-invariant system by multiplying the time-varying state transition matrix over one period of speed variation. System-relative stability becomes tractable by spectral radius analysis. This approach makes possible the quantitative characterization of system stability as a function of variable speed profiles as well as other system parameters such as stiffness and damping of the cutting process and the tool/workpiece structure. Verifications for the face milling process by numerical simulation and experiment for both constant and variable speed are given.

Saturation-Induced Instability and Its Avoidance in Adaptive Control of Hard Disk Drives

This paper presents an investigation of the design and implementation of minimum-variance adaptive controllers for computer hard disk drive (HDD) read-write track following. A common characteristic of minimum-variance controllers, adaptive or not, is that they rely on prediction filters with large high- frequency gains to predict broadband disturbances, and this often produces control-signal saturation and eventual loss of stability. Two methods are introduced here to address this issue. The first method, suitable for online adaptive control, uses frequency weighting to constrain the high-frequency gain of the prediction filter. The second method, suitable for tuning fixed-gain controllers, employs an adaptive scheme iteratively over a finite duration. Both methods were implemented on a commercial hard disk drive, and experimental results demonstrate their effectiveness.

Using Camless Valvetrain for Air Hybrid Optimization

The air-hybrid engine absorbs the vehicle kinetic energy during braking, puts it into storage in the form of compressed air, and reuses it to assist in subsequent vehicle acceleration. In contrast to electric hybrid, the air hybrid does not require a second propulsion system. This approach provides a significant improvement in fuel economy without the electric hybrid complexity. The paper explores the fuel economy potential of an air hybrid engine by presenting the modeling results of a 2.5L V6 spark-ignition engine equipped with an electrohydraulic camless valvetrain and used in a 4531 kg passenger car. It describes the engine modifications, thermodynamics of various operating modes and vehicle driving cycle simulation. The air hybrid modeling projected a 64% and 12% of fuel economy improvement over the baseline vehicle in city and highway driving respectively. This is possible without reducing the vehicle weight to compensate for additional hardware and without reducing engine displacement.

A Linearized Electrohydraulic Servovalve Model for Valve Dynamics Sensitivity Analysis and Control System Design

This paper presents the derivation of a linearized model for flapper-nozzle type two-stage electrohydraulic servovalves from the nonlinear state equations. The coefficients of the linearized model are derived in terms of the valve physical parameters and fluid properties explicitly, and are useful for valve design and sensitivity analysis. When using this model structure to fit experimental frequency response data, the results render closer agreement than when using existing low order linear models. This model also suggests important servovalve dynamic properties such as the nonminimum phase zero and the transfer function relative degree, and how they relate to the valve component arrangement. Because of the small modeling errors over a wide frequency range, a high bandwidth control system can be designed. A robust performance controller is designed and implemented to demonstrate the utility of the model.

Robust performance control of electrohydraulic actuators for electronic cam motion generation

This paper addresses digital control design and implementation for an electrohydraulic servo actuator used in electronic cam motion generation. The actuator dynamics, due to a broad range of motion trajectories, have different degrees of nonlinearity and are represented by a number of linear models with associated bounds of unmodeled dynamics. For each specified range of motion trajectories, a robust performance controller corresponding to the particular linear model is designed to ensure consistent performance under the effect of nonlinear dynamics in the range. A repetitive controller and a feedforward controller are added as plug-ins to the robust performance feedback controller. Experimental results are given to demonstrate the effectiveness of the digital motion control synthesis.