Lightweight leg design shares actuators to boost humanoid robot agility
Design and Analysis of a Nonlinear Parallel Mechanism Coupling for Dynamic Humanoid Legs
Robotics
Summary
Humanoid robots need leg mechanisms that are both light and strong to move quickly and efficiently. The authors designed a new leg that uses a clever way to connect the knee and ankle so that motors near the hip can help both joints work better. As the robot bends its knee, the system helps lift the foot, and when the knee straightens, it helps push off the ground. This approach lowers the weight at the foot and reduces the peak forces and speeds the motors must handle, making walking and running easier for robots.
What this means in practice
- •For robotics engineers: Use the nonlinear coupled leg mechanism to design humanoid robots with lower foot inertia for faster, more energy-efficient walking and running.
- •For prosthetics designers: Incorporate coupled knee-ankle transmissions to improve energy efficiency and reduce motor demands in robotic leg prostheses.
Authors
Rohit Kumar, Heiner Peters, Felix Wiebe, Franek Stark, Janne Janzen, Dennis Mronga, Shubham Vyas, Frank Kirchner
Abstract
Humanoids increasingly demand lightweight leg mechanisms for agile, dynamic, and energy-efficient locomotion. Reducing distal inertia through proximal actuation has thus become a common design goal. Yet, compact transmissions that preserve torque capability and efficient force transmission remain hard to achieve. This paper presents a novel series-parallel leg design combining a knee parallel mechanism, an ankle parallel mechanism, and a nonlinear knee-ankle coupling where all actuators placed closer to the hip. As the knee flexes, the coupling passively assists ankle dorsiflexion for foot clearance and, as it extends it assists plantarflexion for push-off, redistributing ankle load through the knee transmission. We derive the coupling's nonlinear transmission models and validate them in simulation and on hardware. The design shows that the shared transmission lets both joints draw on each other's actuator capacity by easing the knee's peak torque demand under load and the ankle's peak speed demand during fast motion. %Together With the leg's proximal actuator placement, the leg achieves an effective reflected mass of 0.37kg at the foot for a 6kg leg, demonstrating very low distal leg inertia for dynamic humanoid robots.