Decoupling identification with closed-loop-controlled elements for two-link arm with elastic joints

The purpose of our study is to build a precise model by applying the technique of system identification for the model-based control of a nonlinear robot arm, taking jointelasticity into consideration. We previously proposed a systematic identification method, called "decoupling identification", for a "SCARA-type" planar two-link robot arm with elastic joints caused by the Harmonic-drive reduction gears. The proposed method serves as an extension of the conventional rigid-joint-model-based identification. The robot arm is treated as a serial two-link two-inertia system with nonlinearity. The decoupling identification method using linkaccelerometer signals enables the serial two-link two-inertia system to be divided into two linear one-link two-inertia systems. The MATLAB's commands for state-space model estimation are utilized in the proposed method. Physical parameters such as motor inertias, link inertias, jointfriction coefficients and joint-spring coefficients are estimated through the identified one-link two-inertia systems. This paper describes an accuracy evaluation of the identification method through experimental results using the two-link arm with "closed-loop-controlled elements". The results show the method is applicable to a "PUMA-type" vertical robot arm under gravity.