The Effect of Adding Zeroes to Feedforward Controllers

[+] Author and Article Information
B. Haack, M. Tomizuka

Department of Mechanical Engineering, University of California, Berkeley, CA 94720

J. Dyn. Sys., Meas., Control 113(1), 6-10 (Mar 01, 1991) (5 pages) doi:10.1115/1.2896362 History: Received February 02, 1989; Revised August 27, 1989; Online March 17, 2008


The effect of adding zeroes to two types of feedforward controllers, stable pole zero cancelling (SPZC) controllers and zero phase error tracking (ZPET) contollers, is discussed. When there are uncancellable zeroes in the feedback system, additional zeroes in the feedforward controller can reduce the tracking and/or the contour error. For multi-axis contouring with mismatched axis dynamics, a ZPET controller cancels the phase error and provides good contouring accuracy. With a SPZC controller which does not cancel the phase lag, the axes can be “matched” for equal phase lag by adding zeroes to the feedforward controller.

Copyright © 1991 by The American Society of Mechanical Engineers
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