Development of model-based remote maintenance robot system. IV. A practical stiffness control method for redundant robot arm

For part III, see ibid., pp. 1237-1244. A simple stiffness control method for a seven-degree-of-freedom redundant robot arm is presented. The method is very practical method for application to a real robot system. The robot arm is able to move compliantly by this method without heavy computation. The method uses the transpose of the Jacobian matrix to transform the end-point forces into the joint torques for force feedback, but does not require either inverse of the Jacobian matrix or solution of the kinematic equation. Also, the method uses the "joints potential" but does not require pseudo-inverse of the Jacobian matrix to keep the configuration of an arm even if the arm is redundant. The authors have applied this control method to their dual experimental robot arms. Both arms are anthropomorphic and have seven degrees of freedom except for the one degree of freedom of the gripper and are part of the model-based remote maintenance robot system TAROS (Toshiba Advanced Robot System). The arms were able to carry out compliantly such tasks as turning a crank or fastening a bolt and to grope on the surface of the work object and locate the positions of holes.