Development of Knee Joint with Linear Actuator and Parallel Springs for Load Jumping

Recently, the jumping ability of humanoid robots has made significant progress. However, in practical scenarios, robots always need to complete jumping movement carrying additional payloads. This puts more serious challenges on system: it demands higher torque output yet faces the performance limitations of the motor. To solve these challenges, this paper proposes a novel knee joint design that integrates a linear actuator and parallel springs. The linear actuator constructs a triangular mechanism with variable side length through ball screw. This realizes the variable reduction ratio characteristics of the joint. Compared with fixed reduction ratio, it provides higher torque output when taking off and better cushioning performance when landing. The introduced parallel spring mechanism works synergistically with the linear actuator, which effectively reduces the torque demand of motor, thereby enhancing the overall reliability of the system. Finally, we conducted jumping tests based on a single knee joint platform with a 10 kg load and verified the effectiveness of the design.