The Improved DLR Wrist: Design and Analysis of 2-Degrees-of-Freedom Rotational Mechanism Using Spatial Antiparallelogram Linkages

Abstract

This article presents a kinematic analysis and modification of a wrist mechanism of the DLR robot arm, which is based on antiparallelogram linkages. This mechanism is modified to improve the range of motion (ROM), to reduce the parasitic motion, and to approximately perform the decoupled output motion. For these purposes, the elliptical rolling motion of an overconstrained antiparallelogram is first investigated in consideration of its structural modification. Also, a specific joint that has a relatively small movement is developed as a flexible hinge by further minimizing its angular displacement for design simplification. The axode analysis of the instantaneous screw axis for wrist movements is conducted to compare the rotational performance between the original and modified mechanisms. Moreover, their workspace qualities are evaluated through analyses of the workspace and the kinematic isotropy index. Finally, the improved DLR wrist of the final modification is prototyped, and its wide circumduction is demonstrated.