Compliance Control For A Hydraulic Quadruped Robot

In recent years, quadruped robot has draw wide attention for its significant advantages such as running speed, kinematic flexibility, environment adaption and load capacity.Therefore they are expected to be employed for a variety of tasks like material transportation, geographic expedition and disaster rescue etc. However, in these scenarios the environment terrains are unstructured or unknown, which means robots will confront with impacts and crashes when negotiating the ground. If left unattended, these impacts may damage the mechanical components, destroy the stability of actuator control, or even make the robots crash down. In this thesis, the research is focused on dealing with the impact during the robot’s locomotion, and experiments are carried out on our quadruped robot platform. All the research result in this paper has significant importance on improving the locomotion stability and environment adaption of the quadruped robot.Firstly, the kinematic of the quadruped robot is analyzed by using geometric method,and a constraint condition is proposed to copy with the redundancy problem during the inverse kinematic analysis process. This work lays a solid foundation for the locomotion control of quadruped robot.Secondly, an embedded controller based on TMS320F28335 DSP is designed for the joint actuator servo control of the quadruped robot, and the controller is also programed to communicate with the onboard computer in intermediate layer. Based on this work, the control algorithm ADRC is implemented to improve the tracking performance of the hydraulic actuator when considering its nonlinearity and asymmetric.Thirdly, a compliance control strategy based on force feedback is proposed to deal with the impact, the controller is a combination of active compliance and passive compliance.The passive component is used to help cushioning the impacts and the active part is to dissipate the impact energy by using the damping characteristics of the hydraulic actuator.Falling down experiments were carried out on a one dimension actuator system, and the results show that this method is effective to realize stable contacting when considering the impacts. Then the design principle of the proposed compliance controller is discussed based on the simulation and experiment results.Finally, an inverse kinematic algorithm is proposed to make the robot’s leg work like a one dimension actuator system, and then the compliance control is implemented incartesian space for the quadruped robot. Experiment results show that the proposed compliance control method is effective to decrease the impact and improve the stability of the locomotion.