Clearance-Induced Position Uncertainty of Linkages and Parallel Manipulators

[+] Author and Article Information
Kwun-Lon Ting

Center for Manufacturing Research, Tennessee Technological University

Kuan-Lun Hsu

Graduate Assistant, Mechanical Engineering Department, Tennessee Technological University, Cookeville, TN 38505

Jun Wang

Professor, School of Mechanical Engineering, Hubei University of Technology, Wuhan, Hubei, China

1Corresponding author.

ASME doi:10.1115/1.4037619 History: Received August 09, 2016; Revised July 31, 2017


The paper presents a simple and effective kinematic model and methodology to assess the extent of the position uncertainty caused by joint clearances for any linkage and manipulator connected with revolute or prismatic pairs. The model is derived and explained with geometric rigor based on Ting's rotatability laws. It offers a simple prismatic joint clearance link model that catches the translation and oscillation characteristics of the slider within the clearance and separates the geometric effect of clearances from the input error. It is a general method, which is effective for multiloop linkages and parallel manipulators. It settles the dispute on the position uncertainty effect to parallel and serial robots due to joint clearance. The discussion is illustrated and carried out through symmetric planar eight-bar parallel robots. It finds that at a target position, the uncertainty region of a three degree-of-freedom three-leg parallel robot is enclosed by a hexagon with curve edges, while that of its serial counterpart is enclosed by a circle within the hexagon. A numerical example is presented. The finding and proof, though only based on three-leg planar 8-bar parallel robots, have a wider implication suggesting that based on the kinematic effect of joint clearance, parallel robots tends to inherit more position uncertainty than their serial counterparts. The use of more loops in linkages as well as parallel robots cannot fully offset the adverse effect on position uncertainty caused by the use of more joints.

Copyright (c) 2017 by ASME
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