Pressure Estimation-Based Robust Force Control of Pneumatic Actuators

Pneumatic actuators enjoy a number of unique advantages, such as high power density and low cost, in comparison with the widely used electromagnetic actuators. In this paper, a new force control approach is presented for pneumatic actuation systems, with the objective of providing robust control performance while eliminating the need for pressure sensors to reduce the cost and complexity of the system. To achieve this goal, a unique pressure estimation algorithm is developed to provide the required chamber pressure information. This pressure estimation algorithm is formulated according to two simultaneous conditions, established based on the measured actuation force and the average air pressure in the actuator. Utilizing these conditions, the chamber pressures can be calculated through simple algebraic equations instead of complex pressure observers. For the force controller design, the dynamic model of the entire system is developed, and the standard sliding mode control approach is applied to obtain a robust control law. In the experiments, the hypothesis of constant average pressure was verified. Also, the pressure estimation algorithm and the corresponding robust control approach were implemented, and the effectiveness demonstrated by the sinusoidal and square-wave force tracking.