Three-dimensional Motion Mechanism with Tendon-Driven Gravity Compensation

The greater the number of degrees of freedom a manipulator possesses, the higher the gravitational torque required, which can result in excessive energy consumption. One of the solutions to this problem is gravity compensation, which mechanically suppresses the gravitational force and torque without external energy supply. Although numerous studies on gravity compensation have been conducted over the past decades, certain challenges persist, such as increased manipulator weight and restricted range of motion due to additional components required for gravity compensation. Therefore, this study proposed a tendon-driven mechanism of gravity compensation. In this method, springs are employed for gravity compensation, and these elements can be mounted away from manipulators. Moreover, this mechanism has a spherical joint actuated by parallel tendon mechanism, which enables manipulators to realize three-dimensional motion. The novelty of the proposed approach lies in the absence of additional components within the manipulator body. By utilizing a tendon-driven and parallel-tendon mechanism, the proposed design overcomes the limitations of conventional gravity compensation methods. In this study, we created a two-link manipulator according to this proposed mechanism and confirmed the effectiveness of the proposed gravity compensation mechanism.