Dynamic Analysis and Verification of the Robot Leg Employing the Water-Based Electro-Hydraulic Actuator (EHA)

The aim of this paper is to apply the water-based Electro-Hydraulic Actuator (EHA) to a robotic leg device. To assess its applicability, kinematic and dynamic analyses have been performed. The EHA is a linear actuator where the power cylinder is driven by hydraulic pressure from a pump. In this study, one robotic leg was considered, and its motion was simulated by exoskeletal parallel actuation, mimicking a human configuration. Water was used as the working fluid for the EHA in this study, as conventional oil hydraulics have drawbacks such as contamination, cost, and fire risk. Therefore, a new type of actuator was tested and verified for a robotic leg. The Euler-Lagrange equation was employed to derive the dynamic equation, using an inverted pendulum as a simplified model for the robotic leg. An experimental set-up was constructed, and pressure measurements of the EHA were compared with calculations from the dynamics, incorporating measured angle and angular acceleration values. The experimental results indicated that the pressure percentage difference averaged ∼22%. The graph of the calculated pressure appeared smoother than the measured curve, as the dynamics calculation utilized measurements from the mechanical system. In the future, more rigorous dynamics will be considered, and a feedback controller will be designed for improved robot operation.