Design and Model Analysis of a Robotic Joint with Circular Electro-hydraulic Actuator

In the past few decades, many robotic exoskeletons with various actuators have been successful developed. However, there remains challenge of designing a robotic joint with advantages of Iightweight, compact structure, and excellent kinematics performance. For a robotic joint, how to achieve the desired function and optimize the structure is worth exploring. In this paper, we present a novel joint with circular electro-hydraulic actuator for hip flexion and extension which combines the motion characteristic of a rotary motor and a simple structure with adequate torque source quality. First, through using motion data of the human hip joint, the reciprocating motion of the piston and output torque of the joint was determined in the structure design. Then, according to the mathematical model of the electro-hydraulic servo valve and the flow equation of the hydraulic cylinder, a mathematical model of the valve control cylinder was proposed. Finally, transfer function of the hydraulic servo system was obtained for convenience of observation and analysis. This research provides a theoretical basis for the study of the control and application of the servo drive system.