Multi-channel inverse control using adaptive finite impulse response

Abstract

A method and apparatus for multi-channel control of a multiple input, multiple output, servo-driven plant utilizes finite impulse response (FIR) filters to model the inverse of the plant. Each channel includes a servo FIR filter that generates a servo command to drive the plant's servo controller, a valve current FIR filter that bypasses the PID stage of the servo controller to avoid undesirable effects of the PID loop, and a cross FIR filter for each of the remaining channels that compensates for physical coupling in the plant between the channels. The servo FIR filter is calculated by an adaption routine that involves applying an identification signal to the plant, applying the plant's response to the filter and then updating the filter's coefficients using the error that exists between the identification signal and the filter output. To reduce the convergence time, the identification signal is separated into parts in accordance with the amplitude spectral response of the plant and the parts are applied sequentially. The valve current and cross FIR filters are calculated using a forward drive adaption routine in which the identification signal is applied to the filter and the filter output to the plant. The forward drive adaption routine utilizes the phase response of the plant which is provided by way of another FIR filter that includes the inverse a plitude frequency response of the plant. Non-linear error correction is provided via an error store that provides an error correction that is added to the desired command.