Development of a parallel-elastic robot leg for loaded jumping

Legged robot in middle-large size has limited capacity in jumping especially when loaded in practical situation. Parallel elasticity in motor-driven joint has a primary advantage that the spring force will help to increase resultant torque exceeding the motor's performance limitation, which serial elasticity does not. To achieve good performance for jumping motion, we design a novel parallel elastic robot leg, which could realize loaded high jump. Structure of the robot leg uses parallel four-bar mechanism equipped with a tension spring across two hinge points, which is a pattern of Parallel Elastic Actuation (PEA). In this paper, a simplified principle model is constructed to analyze robot dynamics, and simulate the motion trajectory for a maximum-height jump. Then, several hardware principles are followed in robot design conforming to spring-mass model. Moreover, a prototype of the parallel leg is developed, on which the loaded vertical jump experiments are achieved. The results of experiment validate the ability in loaded jumping of the robot leg, which could implement a vertical loaded jump in maximum jumping height of 30cm (total mass 6. 5kg, spring stiffness 225N/m) and 33cm (10kg, 450N/m).