Multirate feedforward control of robot manipulators

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. Furthermore, A. Shimada, et. al. have described 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 are attempted, it is difficult to evaluate control performance since generally manipulators have joint angle sensors mounted on the output side of reduction gears, especially since the product of the angle of rotors and the reduction gear ratio does not always correspond with the joint angles. In order to solve this problem, this paper illustrates the design process for a state reference for manipulators, and introduces a prototype robot manipulator that has precision rotary encoders installed on the output side of the joints. This means that the manipulator as a platform not only has rotary encoders attached to servo motors but special rotary encoders. We describe experimental control results obtained by applying this control technique.