Abstract: In order to improve the load capacity of spherical parallel mechanism, a novel 4-RRS redundant spherical parallel mechanism is proposed. The structural configuration of such 4-RRS parallel mechanism is introduced and sketched out. The statics model is built. When the actuated joints are locked, the reciprocal screw system applied on the moving platform is obtained by using the reciprocal product. The force of each joint and the deformation of limbs are solved based on the built statics model. Take the redundant and non-redundant mechanisms as the examples, the maximum force and torque applied on the limb joint are obtained. The maximum force and torque of redundant mechanism are less than the ones of non-redundant mechanism. The stiffness analysis of performed. The compliance matrix and the generalized displacement of the center of the moving platform are derived. Compared the stiffness and force performance of the redundant mechanism with the non-redundant mechanism, the generalized displacement of the center of the moving platform of the redundant mechanism is less than the ones of the non-redundant mechanism.

Key words: generalized displacement, parallel mechanism, redundant sphere, statics, stiffness