A Decoupling Servo Pressure Controller for Pneumatic Muscle Actuators

A pressure servo controller for pneumatic muscle actuators (PMAs) is presented and tested in three test scenarios. Unlike most previous non-linear control approaches, the current contribution demonstrated that a linear controller design becomes feasible after a slight reformulation of the non-linear plant dynamics. The controller is designed by pole placement in the discrete-time domain. It is demonstrated experimentally that the controller solves the control task and compensates pneumatic cross-coupling effects between different PMAs connected to a shared kinematic structure with an additional disturbance cancellation. When the initial PMA volume is kept constant, a closed-loop cutoff frequency of about 6 Hz is achieved. Beyond that, a sine pressure trajectory with 1 Hz is tracked successfully at time-varying volume, and the pressure changes triggered by volume changes are significantly reduced. The controller is easy to implement and therefore suitable to run on low-cost embedded hardware.