Explosive Output to Enhance Jumping Ability: A Variable Reduction Ratio Design Paradigm for Humanoid Robots Knee Joint

2025-06-14

AI Summary

Fixed gear ratios in humanoid robot knee joints mismatch dynamic requirements during jumping, while motor performance degrades at high speeds—leading to insufficient burst torque, limited jump height, and reduced obstacle-clearing capability. Method: This paper proposes a dynamic variable-ratio design paradigm wherein the gear ratio decreases in real time with knee extension. By coupling transmission ratio with joint kinematics, the design delivers high torque during initial takeoff and suppresses motor overspeed in late extension, thereby extending the high-power output window. A compact linear-actuated slider-crank mechanism is innovatively developed to realize the variable ratio, and a co-model integrating motor characteristics and joint kinematics is established. Parameters are optimized using an explosive jumping control strategy. Results: Experiments demonstrate a 63 cm vertical jump on a single-knee platform—28.1% higher than the best fixed-ratio baseline—and full-body achievements of 1.1 m horizontal jump, 0.5 m vertical jump, and 0.5 m box jump.

Technology Category

• Intelligent Robots: Motion and Path Planning
• Search and Optimization: Sampling/Simulation-based Search
• Humans and AI: Planning and Decision Support for Human-Machine Teams

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• Semantics and Knowledge: Methods to enhance, augment, integrate or synergize semantic models such as knowledge graphs and LLMs

Abstract

Enhancing the explosive power output of the knee joints is critical for improving the agility and obstacle-crossing capabilities of humanoid robots. However, a mismatch between the knee-to-center-of-mass (CoM) transmission ratio and jumping demands, coupled with motor performance degradation at high speeds, restricts the duration of high-power output and limits jump performance. To address these problems, this paper introduces a novel knee joint design paradigm employing a dynamically decreasing reduction ratio for explosive output during jump. Analysis of motor output characteristics and knee kinematics during jumping inspired a coupling strategy in which the reduction ratio gradually decreases as the joint extends. A high initial ratio rapidly increases torque at jump initiation, while its gradual reduction minimizes motor speed increments and power losses, thereby maintaining sustained high-power output. A compact and efficient linear actuator-driven guide-rod mechanism realizes this coupling strategy, supported by parameter optimization guided by explosive jump control strategies. Experimental validation demonstrated a 63 cm vertical jump on a single-joint platform (a theoretical improvement of 28.1% over the optimal fixed-ratio joints). Integrated into a humanoid robot, the proposed design enabled a 1.1 m long jump, a 0.5 m vertical jump, and a 0.5 m box jump.

Problem

• Enhancing knee joint explosive power for humanoid robot agility
• Addressing mismatch between knee transmission ratio and jumping demands
• Overcoming motor performance degradation during high-speed jumps

Innovation

• Variable reduction ratio for explosive jumps
• Linear actuator-driven guide-rod mechanism
• Dynamic coupling strategy minimizes power loss