The increased interest in wearable robots for rehabi-litation and human assistance has also increased demands for lightweight and elastic actuators with inhe-rent compliance for safe human-robot interactions. Although braided type McKibben actuators are frequently used as artificial muscles for robotic applications, they have two drawbacks. First, the weight and size of the necessary compressor and control valves limit the applications of these actuators as autonomous robots. Second, the control accuracy of these actuators is decreased by long tube connections that often cause pressure oscillations. This paper describes a pressure tracking controlled servo drive, using a McKibben actuator and miniaturized unconstrained on off valves, which are smaller in size and easier to implement. The properties of unconstrained on-off valves are discussed, and different pressure control algorithms are compared. The pressure tracking control was also tested experimentally for its ability to track irregular waveforms at various pressure levels.

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