A pneumatic actuator with solenoid valves is a discontinuous-input system because each valve can be either in on or off state. For such an actuator, this paper proposes a sliding-mode control scheme based on an averaged continuous-input equivalent model for the open-loop system. The averaged model is obtained from the nonlinear dynamics of the open-loop discontinuous-input system undergoing pulse-width-modulation (PWM) at the input (i.e., valve open/close action). The PWM duty cycle will be regarded as a continuous input to the proposed averaged model, and thus generated by the proposed sliding-mode controller. By adjusting the PWM duty cycle, the controller switches between seven modes of operation of the open-loop system in order to select the ones with necessary and sufficient amounts of drive energy to achieve position tracking. We will show that this results in reduced position error and valve switching activity for the actuator. The proposed control scheme is experimentally used in the position control of a pneumatic actuator and the results are presented.

For a pneumatic teleoperation system, sliding-mode control laws ensuring both transparency and low switching (open/close) activity of the valves are developed. Each pneumatic actuator has four on/off valves, thus sixteen possible combinations (“operating modes”) for the valves exist but only seven of them are both functional and unique. While previous works have focused on three-mode sliding-based position control of one pneumatic actuator, this paper develops seven-mode sliding-based bilateral control of a teleoperation system comprising a pair of pneumatic actuators. The proposed bilateral sliding control scheme is experimentally validated on a pair of actuators arranged in a force-position teleoperation architecture. The results demonstrate that leveraging the additional modes of operation leads to more efficient and smooth control of the system.

This paper proposes a sliding mode law for precise position control with minimal switching activity for a robotic system that uses on/off (solenoid) pneumatic actuators, For a two-chamber pneumatic actuator with four binary solenoid valves, there is a total of sixteen possible input combinations defined directly from the state of the four on/off solenoid valves present in the system. However, only seven of these discrete operating modes are considered both functional and unique. Accordingly, we use a seven-mode sliding controller that minimizes the position error using modes that have both the necessary and sufficient amounts of drive energy and, thus, involve reduced switching activity. An analysis of the closed-loop system stability is carried out. The performance of the proposed control design is experimentally verified on a single pneumatic actuator comprising of two chambers driven by four on/off solenoid valves.