Research Papers

Assessing Position Error Due to Clearances and Deformations of Links in Parallel Manipulators

[+] Author and Article Information
Jokin Aginaga

Assistant Professor
Public University of Navarra,
Pamplona, 31006 Spain
e-mail: jokin.aginaga@unavarra.es

Oscar Altuzarra

e-mail: oscar.altuzarra@ehu.es

Erik Macho

Associate Professor
e-mail: erik.macho@ehu.es
University of the Basque Country,
Bilbao, 48013 Spain

Xabier Iriarte

Assistant Professor
Public University of Navarra,
Pamplona, 31006 Spain
e-mail: xabier.iriarte@unavarra.es

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received April 4, 2012; final manuscript received February 4, 2013; published online March 26, 2013. Assoc. Editor: James Schmiedeler.

J. Mech. Des 135(4), 041006 (Mar 26, 2013) (8 pages) Paper No: MD-12-1187; doi: 10.1115/1.4023633 History: Received April 04, 2012; Revised February 04, 2013

Two of the main sources of position error in parallel manipulators are clearances at joints and elastic deformations of the links. The former are usually necessary in order to produce a smooth movement between the pin and the hub of a joint. The latter are unavoidable and they tend to be greater in manipulators designed for pick-and-place tasks due to the need of light links. It can be stated that the end-effector pose error depends on the mechanism configuration, the applied external wrenches, the nature and magnitude of clearances, and the rigidity of the mechanical components. This paper proposes a procedure to calculate position error in parallel manipulators due to both clearances and elastic deformations. Although the procedure is applicable to any planar or spatial parallel manipulator, a planar 5R mechanism is used as an illustrative example in order to make it easier to understand.

Copyright © 2013 by ASME
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Fig. 1

Scheme of the error calculation procedure

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Fig. 2

CAD model of the Par2. Courtesy of Laboratoire d'Informatique, de Robotique et de Microélectronique de Montpellier—University of Montpellier and Foundation Tecnalia.

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Fig. 3

Pick-and-place trajectory, velocity, and acceleration for 5R mechanism

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Fig. 4

Pose parameters of a 2 DOF 5R planar parallel manipulator

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Fig. 5

Joint clearances of the 5R planar mechanism

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Fig. 6

Local frames in bars L1 to L4

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Fig. 7

Nominal and actual trajectories. Errors are amplified by a factor of 50.

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Fig. 8

Error due only to clearance

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Fig. 9

Error due only to elasticity

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Fig. 10

Error due to clearances and elasticity of links

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Fig. 11

Error due to clearances and elasticity of links with T = 1 s

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Fig. 12

Error due to clearances and elasticity of links with T = 2 s




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