Design of variable counterbalance mechanism based on spring to minimize required torque of robot arm with variable payload

Recently, with the increasing requirement of human-robot cooperation, robot safety has become an important issue in the robotics field. Counterbalance mechanisms were proposed as a solution to address this problem as it can ensure intrinsic safety and minimize the required torque of the actuators. However, previous counterbalance mechanisms were designed to compensate for the gravitational torque generated due to the weight of robots. Therefore, actuators should be selected to provide sufficient torque to support the payload. In this study, we propose a variable counterbalance mechanism for counterbalance mechanism improvement. The proposed mechanism can adjust the counterbalancing torque according to the weight of the payload attached at the end effector of the robot arm, such as a tool, gripper, or grasped object. Therefore, the torque required to support not only the self-weight of the robot arm but also any additional external load can be compensated effectively using the proposed variable counterbalance mechanism. Moreover, a 1 degree-of-freedom variable counterbalance arm was constructed to verify the effectiveness of the proposed mechanism. Various simulations and experimental results showed that the proposed variable counterbalance mechanism can effectively decrease the torque required to support the robot mass and payload. Hence, low-capacity actuators can be used for designing robots with desired specifications (e.g., maximum payload and repeatability) and safety.