Shyr-Long Jeng

Modeling of piezoelectric actuator for compensation and controller design

This work proposes a novel method for describing the hysteretic non-linearity of a piezoelectric actuator. The hysteresis behavior of piezoelectric actuators, including the minor loop trajectory and the residual displacement near zero input, are modeled by a set of hysteresis operators, including a gain and an input-dependent lag, as well as the parameter scheduling method. A hysteresis model, using the identified parameters, and containing only the dominant hysteresis operator, is presented herein. Based upon a simplified hysteresis model, tracking is controlled to reduce the non-linear effects in the characteristics of the piezoelectric actuator. A proportional-integral (PI) controller, with inverse model feed-forward, suppresses the tracking error to within ±1% full span range (FSR) of the actuator, noticeably improving the tracking performance of the piezoelectric actuator.

ANALYSIS OF MINIMUM CLAMPING FORCE

Abstract Our objective is to determine the minimum clamping force that keep the workpiece stable during the metal cutting process. In analyzing the stability of the workpiece, one usually proves that no instant center of motion can occur on the clamping plane. However, previous search algorithms for the instant center of motion either lack theoretical sufficiency or computational efficiency. This paper presents a new method derived from the correlation between cutting force and clamping moment. This method increases the search efficiency by pruning inadequate search directions. In addition, examples are provided to illustrate minimum clamping force analysis under different fixturing conditions.

Electronic cam motion generation with special reference to constrained velocity, acceleration, and jerk.

Electronic cam motion involves velocity tracking control of the master motor and trajectory generation of the slave motor. Special concerns such as the limits of the velocity, acceleration, and jerk are beyond the considerations in the conventional electronic cam motion control. This study proposes the curve-fitting of a Lagrange polynomial to the cam profile, based on trajectory optimization by cubic B-spline interpolation. The proposed algorithms may yield a higher tracking precision than the conventional master-slaves control method does, providing an optimization problem is concerned. The optimization problem contains three dynamic constraints including velocity, acceleration, and jerk of the motor system.

Least squares approach to odometry based on multiple optical mouse sensors

This work describes an optical measuring device that comprises multiple laser mouse sensors to estimate 3-DOF planar motion. The linear least squares (LLS) method and nonlinear least squares (NLS) method are adopted to estimate the positions in this over-determined system. Two circular trajectories - non-orientated and self-orientated - are employed to evaluate the feasibility of the proposed device. The results are presented and validated by simulations and experimentally. For a circular trajectory with self-orientation, the estimated positions of device determined using the NLS method are associated with apparently smaller positional errors than those calculated using the LLS method. The noise at the sensor outputs has a large impact on the estimate of position. The analysis is essential to examining the error sources and increasing the accuracy of odometric measurement.

Outrigger Force Measure for Mobile Crane Safety Based on Linear Programming Optimization

This work presents a linear programming simplex method for evaluating allowable reaction forces of multiple outriggers with stability constraints. Minimum/maximum pruning approach is adopted to increase the computational efficiency of assessing the outrigger forces when a mobile crane is kept level by the supports of four outriggers. Determining the outrigger forces is an effective means of preventing a mobile crane from tipping over or outrigger failures. Two indices, i.e., moment-index and force-index, which quantify the tendency of tip-over behavior of mobile cranes and examine the bearing capacity of outrigger, are introduced to improve the safety measures. The safety hoist criteria of two mobile crane types equipped with different outriggers are analyzed to demonstrate the feasibility of the proposed scheme. An intelligent anti-upset device that utilizes the outrigger-based stability measures and selectively suppresses critical steering commands in real time is implemented to ensure safe crane operations.

Multi-Level Balanced Isolated Floating Difference Amplifier

An innovative amplifier is proposed for applications involving high capacitive load and large voltage output swing, such as piezoelectric (PZT) actuator drivers. This amplifier is configured in a multi-level arrangement with floating amplifiers, yielding a high voltage gain as a sum of all individual gains from its operational amplifiers. The merits of such an amplifier also include a wide bandwidth and high potential power. Experiments using a six-level arrangement demonstrate a 100 kHz bandwidth with plusmn200 V output swing for different capacitive loadings.

Modeling and Diagnosis of Motion Error of Multi-Axis Machines Using a Ball Bar Test

The contouring accuracy of a multi-axis machine has a critical effect on the quality of many advanced technology products. One of the best approaches to assessing the contouring performance of machine tools is through double ball bar measurement. During circular interpolation motion, the machine traverses, with two axes at a time, a circular trajectory, with each axis subject to sinusoidal changes in acceleration, velocity, and position. The motion error is measured by detecting the relative distance between a point on the spindle nose and another point on the machine table and plotting this distance in polar coordinates. The present paper derives mathematical models and diagnosis procedures for first and second-order motion error resulting from the active degrees of freedom of a multi-axis machine. The theoretical results are verified by both computer simulation and double ball bar testing experiments.