A cascaded tracking control concept for pneumatic muscle actuators

Pneumatic muscles are interesting in their use as actuators in robotics, because they have a high power/weight ratio, a high tension force and a long durability. However, their physical model is highly nonlinear. In this paper a nonlinear control strategy is presented. The main objective is to control a trolley, which is driven by an artificial muscle to follow a reference path. The cascaded control, which is presented here is based on a physical model of an experimental setup. The inner loop is responsible for the force control, which cancels the nonlinearities of the system and ensures therefore a linear input/output behavior. The outer control loop consists of a feedforward and an observer based feedback controller. In addition the observer is extended with a disturbance observer in order to compensate model errors. Measurement results show the efficiency of the presented control strategy.