A PARALLEL ROBOT-ARM REGIONAL STRUCTURE WITH ACTUATIONAL REDUNDANCY

The kinematics of spatial two-closed-loop linkages with 3 DOF suitable for application as fully parallel regional structures of robot arms is studied. Possible configurations of such linkages are enumerated; two of them are reduced to 6-bar linkages with multi-DOF rotational joints. One of these cases has potential for redundant parallel actuation without significant increase in linkage inertia. The kinematic model is derived for this particular case and the inverse kinematic solution is presented in closed form. It is shown that the direct kinematic problem has no meaning in the case of actuational redundancy by considering the constraints imposed by loop closure. The study of differential motions culminates in the derivation of the jacobian of the inverse kinematic transformation. Singularities are identified on the basis of the jacobian and are classified as stationary or uncertainty singularities. Finally considerations are given for finding the actuator torques to counteract a given load.