Kinematic design of a 3-DOF force-controlled end-effector module

Industrial robots with a force-controlled end-effector module can perform continuous contact operations, such as chamfering, deburring, and polishing. However, the commercially available force-controlled end-effector modules only have one degree-of-freedom (DOF) with limited dexterity. In this work, a 3-legged Prismatic-Prismatic-Spherical (3PPS) parallel manipulator is proposed for the development of a dexterous 3-DOF (θx — θy — Z) force-controlled end-effector module. As the 3PPS parallel manipulator has a unique kinematic characteristics, i.e., zero-torsion rotations, its orientation can be always represented by a rotation about an axis fall on the x-y plane of the reference coordinate frame. Utilizing such a kinematic equivalence, the kinematic design issues, such as displacement, singularity, and workspace analyses, are significantly simplified. In addition, to generalize the kinematic analysis algorithms for design optimization, the passive prismatic joint in each leg is placed with a tilting angle with respect to the horizontal plane. Simulation results are provided to demonstrate the effectiveness of the proposed analysis algorithms.