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A Wall-Mounted Robot Arm Equipped With a 4-DOF Yaw-Pitch-Yaw-Pitch Counterbalance Mechanism

Because industrial robots are relatively heavy, most of motor torque are used to support the weight of a robot. Consequently, high-capacity motors and speed reducers are needed, resulting in a low energy efficiency and an increase in the manufacturing cost. To deal with this problem, a variety of spring-based counterbalance mechanisms (CBM) have been developed to mechanically compensate for the gravitational torque caused by the robot weight and payload. However, conventional CBMs are limited to pitch joints whose axis of rotation is horizontal to the ground and it is difficult to apply them to robot arms with different joint configurations, such as humanoid robot arms. In this study, we propose a CBM with a passive yaw-pitch structure consisting of a spring and wire. Through geometrical analysis and experiments, we demonstrate that the proposed CBM can effectively compensate for the gravitational torque due to robot weight and payload.