A New Passive Controller for a Hydraulic Human Power Amplifier

A new, intrinsically passive controller for hydraulic human power amplifier is presented. The hydraulic human power amplifier is a tool that amplifies (or attenuates) the force that the human exerts on it. The control objective is to cause the system to behave like a passive mechanical tool when interacting with the human and with the work environment with a specified power scaling factor. Although a previous Proportional-integral with velocity feedforward force controller [1] works well in the constrained space, it lacks robustness or performance during freemotion because of the sensitivity to the implementation of velocity feedforward term. The difficulty in implementing the velocity feedforward term also prevents the controller from being intrinsically passive. The new controller recasts the human power amplifier problem into one of velocity coordination by generating a fictitious reference mechanical system. Force amplification become a natural consequence of velocity coordination. This enables the controller to be intrinsically passive and to achieve good performance both in free motion and constrained motion. These properties have been experimentally validated.