Tendon routing resolving inverse kinematics for variable stiffness joint

Recently, the tendon-driven mechanism with variable joint stiffness has received attention for use in the development of a humanoid robot operated in an uncertain environment with physical contact. In this paper, we propose a mechanism to control the position and joint stiffness of a tendon-driven manipulator independently, using dedicated actuators. This mechanism consists of two parts: a component that transforms the movements of the tendons to activate the actuators, and a component that applies tensile forces to adjust the joint stiffness. We named this mechanism “tendon routing resolving inverse kinematics” (TRIK). The methodology for designing this mechanism for various tendon-driven manipulators is presented with several examples. We designed TRIK for a manipulator with one degree of freedom and nonconstant-moment arms. Finally, experiments of variable joint stiffness with nonlinearly elastic components were conducted to validate the proposed mechanism.