Energetically Passive Multi-Degree-of-Freedom Hydraulic Human Power Amplifier With Assistive Dynamics

This paper develops a control approach for a multi-degree-of-freedom (DoF) hydraulic human power amplifier (HHPA) which is a tool with which a human interacts physically. The control objective is to use the hydraulic actuators to amplify the human force while ensuring that the closed-loop system is energetically passive with respect to a scaled human and environment input power, so as to enhance the safety and coupling stability. A multi-DoF virtual velocity coordination approach is used to recast the force control problem as one of coordination between the velocities of fictitious inertia and of the HHPA. To aid the human to perform specific tasks, additional passive assistance dynamics are incorporated to include a passive velocity field controller (PVFC) for path guidance, and an artificial potential field for obstacle avoidance (OA). Control of the hydraulic actuators is defined by a passivity-based controller that considers the natural energy storage of the hydraulic actuators to fully account for the nonlinear pressure dynamics. The controllers specify the required flows which are then satisfied by either a servo-valve or an energy efficient hydraulic transformer. Experimental results demonstrate good control performance and effective task assistance.