Based on the study of the mechanics features of pneumatic artificial muscle including the nonlinearities in material, geometry, and with the method of nonlinear finite element analysis, the three-dimensional finite element model of a pneumatic artificial muscle was established. The analytical results were confirmed by the experiment with the use of a pneumatic artificial muscle test bench.

The human wrist has three rotational DOFs. Elbow muscle group work together to drive the wrist joint. According to the above characteristics of human wrist, parallel mechanism with three rotational DOFs of the imitation of human wrist is built. Traditional method for calculating DOF based on arithmetic is not that accurate. The method for analysis of DOF based on theory of constraint screw is explained. According to theory of constraint screw, the parallel mechanism built was analyzed. All the kinematic pairs in the mechanism will be expressed with screws so that the common constraints and the over constraints will be obtained. Through analysis above, the DOFs of the mechanism can be calculated and which a few degrees of freedom of the mechanism will be known. The new method avoids the disadvantages of the traditional method.