Structural design and motion analysis of parallel ankle joints for humanoid robots

In the development of humanoid robots, ankle joint design is critical for achieving both stability and flexibility. This study introduces a novel parallel ankle joint, designed to address the limitations of existing designs, including restricted range of motion and high leg inertia. First, we developed the structure of the parallel ankle joint and conducted a degree-of-freedom analysis. Next, we examined the kinematic relationship and derived the Jacobian matrix to relate the ankle joint's orientation to the actuator's output rotation. Finally, experimental results confirmed both the feasibility of the design and the accuracy of the kinematic analysis, demonstrating that humanoid robots equipped with this new parallel ankle joint can successfully perform dynamic movements such as squatting, stepping, and omnidirectional walking.