Development of a model-based remote maintenance robot system (IV) - a practical stiffness control method for redundant robot arm

A simple stiffness control method for a seven degrees of freedom redundant robot arm is presented. This stiffness control method is a very practical method to apply to a real robot system. The robot arm is able to move compliantly by this method without heavy computation. This method uses 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 `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. Those are the reasons why this method does not require heavy computation for calculation of the control algorithm. We have applied this control method to our dual experimental robot arms. Both arms are anthropomorphic and have seven degrees of freedom except for the one degree of freedom of a gripper. These arms are parts of our 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 also the arms were able to grope on the surface of the work-object and locate the positions of holes.