Piecewise Kinematically Redundant Planar Parallel Manipulator for a Hybrid Machine Tool

It is well-known that, one of the main disadvantages of parallel manipulators is their abundant singularities that diminish the usable workspace and limit their applications for machine tools. To overcome this problem, a 3-PPR planar parallel one in a non-conventional architecture is developed in this paper for a hybrid machine tool. The proposed architecture is shown to have some kinematic advantages in terms of partially decoupled motion, large workspace, unlimited orientation capability, base-mounted actuators and no singularities. Moreover, it is designed to be possibly kinematically redundant in a piecewise manner whenever needed. Two identical active revolute joints are added to two limbs yielding 1-PPR+2-PRPR kinematically redundant architecture. To tackle the redundancy, two real-time redundancy resolution approaches are presented and compared. The proposed redundant manipulator is shown to effectively pass through singularities with feasible joint velocities and no abrupt changes in the profile.