Novel robot arm with bi-articular driving system using a planetary gear system and disturbance observer

In this paper, we develop a robot arm with a bi-articular driving system which can incorporate the principle of the bi-articular muscle characteristics of animals. The arm is different from the conventional robot arms that are driven by actuators inserted in each joint, since it has an additional actuator that can generate the torques in two joints at the same time so that the actuator works as a bi-articular muscle. In order to mimic bi-articular driving system, we adopt a planetary gear system that has three inputs and two outputs. This three inputs and two outputs characteristic is similar with the muscle system, however, it does not match one by one and it needs some strategy to make the planetary gear system work as a muscle system. To this end we suggest novel control algorithms: the first is a feedforward control and the second is a feedback control based on the disturbance observer. Details on the design of a robot arm with a planetary gear and control algorithms are given in this paper.