Tracking control of a pneumatic muscle actuator using one servovalve

In this article, a model-based tracking control of a pneumatic muscle actuator using only one 5/3 proportional directional valve is investigated. Pneumatic muscles are difficult to control due to their highly nonlinear system dynamics and hysteresis effects, but they offer advantages such as high power/weight ratio, low costs, easy maintenance and flexibility. The actuator consists of two muscles moving a mass horizontally fixed on a linear guide rail. The challenge is to control those two muscles with only one 5/3 proportional directional control valve. Based on the idea of a cascaded control structure a nonlinear model-based control algorithm is computed. The inner loop control is implemented as a force controller added by a force disturbance observer to estimate unmodeled muscles forces. A position control in the outer loop is added and implemented as a linear tracking controller. The implemented control structure shows good follow-up error and stationary precision in measurements. The shown control approach contributes to an improved path control performance of pneumatic muscle actuators.