Active Self-weight Compensation for Direct-drive Robot Arm

In recent years, multi degree-of-freedom(DOF) robot arms for delicate movements are required in various fields such as industry, medical care, and service industry. For the delicate movements, high-precision force control is required. To achieve this, it is necessary to use direct-drive without gears that reduce back driverbility. However, conventional robot arms use gears to gain the large torque that supports the weight of the arm and hinder the realization of direct-drive. Therefore, in this study, we proposed a direct-drive robot arm with active self-weight compensation by motors. Then, the effect of the proposed method is shown by simulating the torque required to support the arm when the self-weight compensation is performed by the self-weight compensation motor in a 7-DOF manipulator. Furthermore, we actually manufactured a three DOF direct-drive robot arm using the proposed method. All the motors were placed at the base of the arm to prevent the increase in inertia of the robot arm, and the power was transmitted by wires and tubes.