Method of controlling a high-friction electro-mechanical servo-mechanism to minimize the power needed to hold a loaded output member

Abstract

The invention provides a method for controlling an electromechanical servomechanism () for moving an output member relative to a variable load (). The servomechanism includes: a motor () having at least one coil (A,B orC) adapted to be supplied with current and having a rotor () with an output shaft (); a mechanical transmission () arranged between the output shaft and the load, the transmission having a mechanical friction related to the load; a servoamplifier () arranged to supply current to the motor coil in response to an input signal (in line); a command signal (in line) for commanding the position of the load; a load position feedback signal (in line) compared (in summing point) to the command signal and arranged to produce an error signal (in line); and means () for generating an offset signal (in line) that is summed (in summing point) with the error signal to modify the servoamplifier input signal (in line). The improved method comprises the steps of: generating the offset signal as a function of the command and feedback signals and the currents supplied to the motor coil after the position of the output member as remained substantially constant for a predetermined time; and adjusting the offset signal so that the motor current is reduced until the position of the output member changes so as to minimize the steady-state power dissipation in the motor.