Abstract: A 3-DOF parallel wire driven stiffness-variable manipulator is presented by making use of the elasticity of wires and the redundant actuation. Based on static and stiffness analysis, the study on stiffness control is made. Firstly, by projecting the tension of wires into the joint space, the relation between joint forces and tension of wires and that between joint forces and resultant forces are studied, and a 3 dimension force vector closure theory is presented. Then, the joint stiffness matrix and the manipulating stiffness matrix are deduced according to differential transform theory, and a numerical example is given subsequently. The result shows that the stiffness relates not only to stiffness of wires but also to tension of wires. So it can be changed by regulating the tension of wires. Finally, stiffness control to this stiffness-variable manipulator is studied by separating position control and tension control, and a numerical example is done for verifying it.

Key words: Force vector closure Differential transformation Stiffness-variable, Parallel wire driven, Stiffness control