A Method of Estimating Resistive and Viscous Parameters in a System Operating with a DC Servomotor

Abstract

A study has been made to estimate the resistive and viscous friction components of a system operating with a DC servomotor in a PWM mode. This is carried out by digital computation based on an equivalent circuit representing a motor and its load; no analog means are used. This technique will be useful for optimum control of a servomotor, because it can be implemented only with a feed-forward technique requiring the details of system parameters for determining current command. Motor winding resistance, device resistance and grease viscosity are essential factors which are very sensitive to temperature. Here, mechanical viscous friction is represented by an equivalent resistance, and the armature resistance and MOSFETs' on-resistance are treated as yet another parameter. They are determined from the time differences between real zero-crossings for current/speed and the ones computed from four reference quantities. The theory and test data obtained in a system using an i80960 MPU are presented.