Compact Gravity-Balanced Design of Serial Robots Under Payload Variation

This paper presents a gravity-balanced design of serial robots under payload variation. The proposed design is realized by installing a compact gear-spring mechanism (CGSM) onto each joint so that the gravitational torque at the joint is canceled by the supplemental spring force. The significance of this design is that it can perfectly balance variable payloads through an energy-free adjustment of the spring position. In this work, the design concept, modeling, performance analysis, and practical demonstration of the gravity-balanced design of the robot are described. It was found that a theoretical model of a robot can completely cancel the gravitational torques at the joints with the proposed design. Moreover, the motor torques of the robot were practically reduced significantly, with a torque reduction rate of 74.1% for a 1 kg payload.