Adaptive motion control of a robotic arm with movable counterweights

This paper proposes a new robotic arm which has active movable counterweights as an actuator in addition to motor drives. The active counterweights reduce gravity effect of cantilever structure adaptively by movement of counterweights. Additionally, the counterweight has offset angle between links and movement axis of the counterweight. This structure makes it possible to regulate joint angles not using joint motors but only using gravity of the counterweights. Using the two features, gear reduction ratio of motors decreases and base unit becomes light and small. Consequently, the robotic arm has flexibility and is suitable for narrow and high altitude environment such as on vehicles. It is however difficult to control the robot precisely due to the effects of physical parameter errors and friction. Therefore, an adaptive control method of this new robotic arm is proposed. The usefulness of the method is demonstrated by experiments using a prototype.