Variable reduction ratio knee joint inspired by cruciate ligament for legged robot

Recent years, with the development of the legged robots, higher torque output and lower backdrivability are required. However, existing legged robots often use larger torque motor or reduction ratio gearbox to reach the power requirement, which will increase the size and weight also lower the backdrivability. To make the robot more dynamic and agile, the variable ratio crossed four-bar mechanism(VRC) based on the human cruciate ligament has been proposed. The knee joints with VRC have a wide range of motion which can make the robot jump more like a human. Also the feature that the reduction ratio raises when flexing and reduce when extending can provide rational torque curve. In this paper, we designed a robot leg whose knee joint used the VRC and optimized the link parameters to maximize the jumping height of the robot. The main contribution of this paper are a design of the legged robot with the VRC; the dynamics model of the robot and the kinematic analysis of the VRC; the optimization of the mechanism's design parameters that can maximum the robot's jumping height; a simulation of the high jumping process.