Simultaneous control of the motion and stiffness of redundant closed-loop link mechanisms with elastic elements

This paper describes the position and stiffness control of planar redundant link mechanisms with elastic elements in order to utilize the flexibility of robots. Assigning both of the two-dimensional position and stiffness of an output link as an output vector, the procedure of the forward kineto-static analysis for the planar redundant link mechanisms with elastic elements is formulated. The mechanisms have elastic linearactuators composed of a coil spring and linearactuator and rotary actuators and multi jointed links. An inverse kineto-static analysis to obtain the optimum input motions which can generate the desired position and stiffness of the output link while taking into account the motion range of the linearactuator is also conducted and applied to the optimum motion control of the mechanism. Several simulations and experiments with a prototype of a planar closed-loop manipulator with 5 DOF and 4 output show the effectiveness of the proposed method.