A Unified Force Controller for a Proportional-Injector Direct-Injection Monopropellant-Powered Actuator

This paper describes the modeling and control of a proportional-injector direct-injection monopropellant powered actuator for use in power-autonomous human-scale mobile robots. The development and use of proportional (as opposed to solenoid) injection valves enables a continuous and unified input/output description of the device, and therefore enables the development and implementation of a sliding-mode-type controller for the force control of the proposed actuator that provides the stability guarantees characteristic of a sliding mode control approach. Specifically, a three-input, singleoutput model of the actuation system behavior is developed, which takes a nonlinear noncontrol-canonical form. In order to implement a nonlinear controller, a constraint structure is developed that effectively renders the system single-input, single-output and control canonical, and thus of appropriate form for the implementation of a sliding mode controller. A sliding mode controller is then developed and experimentally implemented on the proposed actuator. Experimental results demonstrate closed loop force tracking with a saturation-limited bandwidth of approximately 6 Hz.