Modeling and control of McKibben artificial muscle robot actuators

The McKibben artificial muscle is a pneumatic device characterized by its high level of functional analogy with human skeletal muscle. While maintaining a globally cylindrical shape, the McKibben muscle produces a contraction force decreasing with its contraction ratio, as does skeletal muscle. The maximum force-to-weight ratio can be surprisingly high for a limited radial dimension and for a conventional pressure range. A 50 g McKibben muscle can easily develop more than 1000 N under 5 bar pressure for an external radius varying from about 1.5 to 3 cm. Thus, robotics specialists are interested in this well-adapted artificial muscle for motorizing powerful yet compact robot arms. The basic McKibben muscle static modeling developed in the paper, which is based on the three main parameters (i.e., initial braid angle, initial muscle length, and initial muscle radius) and includes a three-parameter friction model of the thread against itself, has shown its efficiency in both isometric and isotonic contraction.