Showing papers by "Chia-Hsiang Menq published in 1993"

Compensation for form error of end-milled sculptured surfaces using discrete measurement data

Abstract: In this research, improvement of the form accuracy of parts having end-milled sculptured surfaces is studied. The proposed scheme uses the discrete measurement data from coordinate measuring machines and consists of three steps: optimal match, decomposition, and compensation. The optimal macth is used to best fit the measurement data with the design form so as to determine sampled form errors. The decomposition is developed to characterize the sampled form errors into the deterministic and the random components, which are associated with the waviness and the roughness of the form errors, respectively. Then, in the compensation step, compensation for the waviness is applied to improve the form accuracy of an end-milled sculptured surface. An experiment is conducted to demonstrate the effectiveness of the proposed scheme.

Precision Tracking Control of Discrete Time Nonminimum-Phase Systems

Abstract: In this paper, a precision tracking control scheme for linear discrete time nonminimum-phase systems is proposed. This control scheme consists of a preview filter, a tracking-performance filter, a command feedforward controller, and a feedback controller. A command feedforward controller, whose design is based on the minimal order inverse model of the plant being controlled, will result in a completely decoupled system. The preview filter is introduced to compensate the phase and gain errors induced by the nonminimum phase zeros or lightly damped zeros of the system. Using the command feedforward controller along with the proposed preview filter, the tracking performance of the proposed control scheme can be characterized by the frequency response of the tracking-performance filter. For the design of the preview filter, a generalized Nth order preview filter and its associated penalty function that quantifies the tracking error of a design are defined. It is shown that, given the desired bandwidth and the order of the preview filter, the optimal solution for the design of the preview filter can be obtained explicitly. The proposed control scheme together with the optimal preview filter is shown to be very effective in achieving precision tracking control of discrete time MIMO nonminimum phase systems. It is also shown that the tracking performance is improved as the order N of the preview filter is increased.

Concurrent process planning for finish milling and dimensional inspection of sculptured surfaces in die and mould manufacturing

Abstract: With the introduction of computer-aided tools, traditional manufacturing tasks such as design, machining and inspection are now highly automated. However, due to the complexity and enormous knowledge involved in each process, most of these activities are still dealt with separately. Recent development of concurrent engineering emphasizes the importance of bringing manufacturing knowledge into the early design stage for optimum product and process design. In this paper, a knowledge-based CAD/CAM system which integrates process planning for finish milling and dimensional inspection of sculptured surfaces in die and mould manufacturing is presented. Optimum production plans are determined by minimizing the integral cost of machining and inspection. NC path generation and inspection planning are then verified by dynamic geometric simulations which provide the designer with the evaluations of machinability and inspectability. The implied significance is that strong inter-dependency may exist among var...

Characterization and compensation of discrete-time non-minimum-phase systems for precision tracking control

Abstract: The objective of this study is to characterize the unstable zeros of discrete-time non-minimum-phase systems and to compensate the gain and phase errors induced by unstable zeros for tracking control. These two objectives are attempted via examining the frequency response of unstable zeros. The gain error and phase shift induced by unstable zeros are first presented. It is well known that they are undesirable and cannot be cancelled directly via the method of pole-zero cancellation. Through investigating the characteristics of unstable zeros, a systematic approach is then given to compensate the gain and phase errors induced by unstable zeros. Using this approach, both a simple tracking control method and a precision tracking control method are proposed. The design procedure is presented and the design formulae are given. Simulation results are presented to illustrate the effectiveness of the proposed methods.

Real Time Estimation of Elastic Deformation for End-Point Tracking Control of Flexible Two-Link Manipulators

Abstract: In this paper, an elastic-deformation estimator is proposed for real time end-point tracking control of a flexible two-link manipulator. Due to the noncolocated characteristics of the system, the inverse model (from end-point motion to control torques) is divided into two subsystems, namely, the stable subsystem and the unstable one, corresponding to the causal part and noncausal part of the system's elastic motion, respectively. A digital filter is formulated to replace the unstable subsystem so as to estimate the noncausal part of the elastic motion associated with a specified end-point motion

Experiments on the Tracking Control of a Flexible One-Link Manipulator

Abstract: Experimental study on the tracking control of a flexible one-link manipulator is reported in this paper. A tracking control scheme is developed based on the system transfer function. In the proposed control scheme, the desired control input for a given end-point trajectory is obtained by using a command feedforward controller instead of solving the inverse dynamic equations of the system. The proposed control scheme regqures small amount of computations and can be easily implemented for real time control. The experimental results are presented, which shows very good tracking performance