Implementation of Multirate Feedforward Control on Robot Manipulators with Elastic Joints

This paper introduces a novel multirate feedforward control method for robot manipulators with elastic joints. Perfect tracking control methodology using multirate feedforward control was proposed by H. Fujimoto, et al. Then, A. Shimada, et al. have prsented its application to robot manipulators; however, they only described the controller design process and gave a few simulation results. In addition, they did not provide details on how the state reference should be designed. Even if experiments were attempted, it would be difficult to evaluate control performance since generally manipulators have joint angle sensors mounted on the output side of reduction gears In order to solve this, this paper illustrates the design process for the state reference, and introduces a prototype robot manipulator that has precision rotary encoders installed on the output side of the joints. This means that the manipulator has not only the rotary encoders attached to servo motors but special precision rotary encoders. We describe experimental results obtained by applying this control technique.