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Research Papers

Variation Analysis and Robust Fixture Design of a Flexible Fixturing System for Sheet Metal Assembly

[+] Author and Article Information
Bing Li, Hongjian Yu

Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, P. R. China

Xiaojun Yang1

Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, P. R. Chinalibing.sgs@hit.edu.cn

Ying Hu

Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China; The Chinese University of Hong Kong, Hong Kong, P. R. China

1

Corresponding author.

J. Manuf. Sci. Eng 132(4), 041014 (Aug 03, 2010) (13 pages) doi:10.1115/1.4002033 History: Received October 27, 2008; Revised August 04, 2009; Published August 03, 2010; Online August 03, 2010

Flexibility of assembly systems is crucial to maintaining the competitiveness in the rapidly changing market. In this paper, a novel flexible fixturing system for sheet metal part assembly is presented, which utilizes parallel robots as reconfigurable fixture elements. The method of influence coefficients, combined with finite element analysis and screw theory, is used to analyze the variations in sheet metal assembly. In the analysis of assembly variations, a total of six variations involved in prewelding, underwelding, and afterwelding process are intensively considered. Screw theory is employed to model the kinematic and constraint features corresponding to the fixturing schemes. A robust fixture layout design model is developed based on the Lagrangian conditional extremum method. A case study illustrates that the robust optimal methodology and an optimal fixture layout scheme with less sensitivity can be obtained.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Diagram of serial assembly and parallel assembly: (a) assembly in-serial and (b) assembly in-parallel

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Figure 2

Diagram of reconfigurable fixture based on parallel robot

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Figure 3

Flexible fixturing system with 4-2-1 fixturing scheme composed of parallel robots: (a) 3D model and (b) schematic diagram

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Figure 4

Illustrative diagram of parallel mechanisms used for flexible fixtures: (a) 3-UPU/UPU (3-DoF), (b) 3-UPU/UPS (4-DoF), and (c) 3-RUPR/UPS (4-DoF)

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Figure 5

Illustrative diagram of inverse kinematics solution

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Figure 6

Simulation of positional workspace of the three parallel mechanisms: (a) 3-UPU/UPU (3-DoF), (b) 3-UPU/UPS (4-DoF), and (c) 3-RUPR/UPS (4-DoF)

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Figure 7

Flowchart of the variations in the assembly process

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Figure 8

Illustrative diagram of welding variation

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Figure 9

Diagram of the 2-1 locating scheme: (a) optimum setting of 2-1 scheme and (b) variation in 2-1 scheme

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Figure 10

Diagram of different slot orientation arrangements

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Figure 11

Diagram of the 4 locating scheme: (a) diagram of 4 locating scheme and (b) variations in four locating scheme

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Figure 12

Diagram of square finite element model

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Figure 13

Distribution map of assembly variation

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Figure 14

Robust assembly fixture design of two sheet metal parts: (a) illustrative diagram of underbody assembly and (b) schematic plan of underbody assembly

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Figure 15

Finite element model of sheet metal assembly

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