Performance enhancement of an integrated electro-hydraulic actuator using dynamic modeling and optimization

For robotic applications, hydraulic actuation is still an open research issue. A hydraulic actuation solution based on integrated hydraulics is presented in the form of an integrated electro-hydraulic Actuator (IEHA). This actuator tackles some issues related to compactness and self-contained autonomous robotic systems. One of its primary uses is the actuation of the hydraulic humanoid robot HYDROïD. Primary experimental validation of the IEHA actuator has suffered from several low-performance issues. The main reason for such performance is due to that inner friction forces and leakage losses were not addressed or modeled yet. In this paper, a detailed dynamic model of the IEHA actuator is needed to identify the mechanical components that affect the volumetric and mechanical efficiencies of the actuator. The dynamic model focuses on the dynamics of essential parameters and components like the micro-pump pistons, their internal leakage, and friction during actuation. The design parameters of these mechanical parts are optimally calculated to produce a new enhanced dynamic model. The new IEHA model is verified through simulation to actuate the ankle pitch rotation of the robot. A genetic algorithm is used to optimize the geometrical and design parameters while enhancing the overall mechanical and volumetric efficiencies of the IEHA. The IEHA model was able to generate a locomotion gait cycle successfully for a walking speed of 1.17 m/s. Simulation results have shown that the design enhancements led to 95% and 97% volumetric and mechanical efficiencies respectively. Finally, the new enhanced IEHA prototype is tested experimentally. The output flow of the new prototype has improved by approximately 58%.