Mathematical Modeling of an electro-hydraulic actuator for humanoid robots

The work presented in this paper is based on a novel integrated and compact hydraulic robotic actuator [1] (BIA patentUS20110085922), intended for the hydraulic humanoid robot HYDROïD. This actuator solves the problem of autonomy for hydraulic humanoid robots as it can be integrated to operate each joint separately. Thus, eliminating the need for a central hydraulic power pack. Also, due to its small size, it can be placed as near as possible to the robot joints to minimize the possible drawbacks of hydraulic actuation units. The main problem for this prototype came from its compactness, causing the inability to study the dynamic properties of this hydraulic actuator such as leakage, friction and compressibility. Therefore, any enhancement or modification for its tiny mechanical components for performance improvement is not possible. As it lacks a mathematical model that represent the dynamics of the system at hand. Here comes the contribution of this paper, where a detailed mathematical model for the actuator is presented and simulated using MATLAB/Simulink. To validate this model, a sim-mechanics model based on its actual CAD design was presented and the two models were compared to verify the deduced dynamic model for the system. The results showed the accuracy of proposed mathematical model as a vital tool to represent the actuator and enhance it in future prototypes. Key-Words: Hydraulic Actuation, Integration Technology, Humanoid robot, HYDROïD Robot, Dynamic model, System verification.