Kinematic Design of a 3-DOF Force-controlled End-effector with Flexure Joints for Robotic Finishing Applications

This work focuses on kinematic design of a three degree-of-freedom (DOF) θ
x
-θ
y
-Z force-controlled end-effector for robotic finishing applications. Among various possible parallel mechanism configurations that can achieve θ
x
-θ
y
-Z motions, 3-legged Prismatic-Prismatic-Spherical (3PPS) configuration is selected for the end-effector design due to its desired kinematic characteristics and dynamic behavior. As the orientation of the end-effector’s moving platform can be represented by a rotation about an axis in the horizontal plane, close-form solutions for both forward and inverse displacement analysis can be readily derived. Other critical design issues, such as velocity analysis, singularity analysis, and workspace analysis, are addressed. Based on kinematic analysis, the required displacements of the passive prismatic joints are within a few millimeters. Therefore, light-weight flexure-based prismatic joints are employed to replace the conventional heavy linear guides, which can significantly improve the dynamic performance of the force-controlled end-effector. Finally, the structure design of this force-controlled end-effector is provided.