Realization of Bi-articular Driven Robotic Arm with Planetary Gear Based on Disturbance Observer

In this paper, we attempt to equip the bi-articular driving system with a robot arm. Bi-articular driving system is a unique actuator of animals and contribute to animals’ flexible motion control. The arm has an actuator that can drive two joints simultaneously, so there is difference between conventional robot arms and the robot arm. Conventional robots have actuators in each joint, so they can not move smoothly like animals. In order to mimic bi-articular driving system, we use a planetary gear system that has three inputs and two outputs. This three inputs and two outputs characteristic is similar with the animals’ limbs, however, it does not match completely and it needs some compensation 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. In addition, we verify the simplification of the force control on end effector which is one of the characteristics of the bi-articular driving system.