A digital servo tuning system for industrial robots.

Abstract

Servo parameter tuning for industrial robots before delivery is very important, because the trajectory-tracking accuracy depends mainly on the tuning results. However, conventional trial and error tuning work is time-consuming.This paper describes a new servo parameter tuning system for industrial robots. This system is composed of a robot identification function and a servo design function. The identification function is based on an accurate frequency response analysis, called Multi-Decimation (MD) method. The servo design function is based on a stable method in the cut-off frequency region for calculating a two degrees of freedom (2 D. O. F.) PID digital servo parameters.In a SCARA robot used for tuning experiments, vibrational characteristics, caused by speed reduction mechanisms, extend over a wide frequency range. The proposed tuning system could be used to successfully identify the wide range of frequency response, using input-output data within only two seconds. Also, optimal servo parameters were obtained by the servo design method.Consequently, tuning time for a new SCARA robot has been shortened to one-tenth the previously required time. The system has been implemented in a portable laptop-computer. Therefore, it is easy to retune servo parameters for changing payloads, and to maintain robots in a customer's factories, without an instrument such as an FFT servo analyzer.