High-Precision Control of AC Servo Motor Positioning Systems by Friction Compensation

Abstract

In the AC servo motor positioning system, friction and elastic deformation significantly degrade the positioning accuracy. We propose a method of compensating for those effects based on the estimated load torque by a disturbance observer. The proposed observer is driven by a motor current command and an encoder signal without adding any external sensors. Experimental investigation was carried out using a newly developed system for driving an AC servo motor. Torque ripple of the AC servo motor was estimated in detail and modeled as a Fourier expansion for compensation in real time on DSP. This torque ripple model drastically improves the accuracy of torque estimation up to 2% against the added torque under load torque, that is, 4% to 40% of the nominal motor torque. Moreover, the coupled behavior of friction and elastic deformation was estimated by the above method, and it was confirmed that the stiffness and friction can be precisely and simultaneously estimated.