Publikation
Design and Analysis of a Nonlinear Parallel-Mechanism Coupling for Dynamic Humanoid Legs
Rohit Kumar; Heiner Peters; Felix Wiebe; Franek Stark; Janne Janzen; Dennis Mronga; Shubham Vyas; Frank Kirchner
In: IEEE-RAS Humanoids 2026. IEEE-RAS International Conference on Humanoid Robots (Humanoids-2026), 2026 IEEE-RAS 25th International Conference on Humanoid Robots, December 6-9, Silicon Valley, California, USA, IEEE, 2027.
Zusammenfassung
Humanoids have become increasingly popular for both research and commercial applications, pushing the demand for lightweight leg mechanisms that support agile, dynamic, and energy efficient locomotion. Reducing distal leg inertia through proximal actuation has therefore become a com- mon design objective. However, designing compact transmission architecture that preserves torque capability, and maintain efficient force transmission remains a significant challenge. In this paper, we present a coupled series-parallel transmission architecture for a humanoid leg, combining knee parallel mechanism, an ankle parallel mechanism, and a nonlinear knee-ankle coupling with all actuators placed closer to the hip. The proposed design lets knee and ankle pitch motion coordinate with each other. As the knee flexes, the coupling passively assists ankle dorsiflexion for foot clearance, and as the knee extends, it adds to ankle plantar flexion during push-off. The coupling also redistributes ankle pitch loads through the knee transmission that lowers the effort on ankle actuators. We derive the nonlinear transmission models for this coupling and analyze their effects on joint motions, actuator velocities, torque distribution. The resulting leg achieves an effective reflected mass of 0.37 kg at the foot for a 6 kg leg overall, demonstrating effectiveness of the proposed transmission architecture for minimizing distal leg inertia in dynamic humanoid robots. A hardware prototype is developed to validate the proposed design and demonstrate its feasibility.