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Technical Briefs

Simultaneous Large Scale Sheet Metal Geometry and Strain Measurement

[+] Author and Article Information
A. D. Spence2

Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, L86 4L7, Canadaadspence@mcmaster.ca

D. W. Capson

Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, L86 4L7, Canada

M. P. Sklad

Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, L86 4L7, Canada

H.-L. Chan3

 McMaster University, 1280 Main Street West, Hamilton, ON, L86 4L7, Canada

J. P. Mitchell4

 McMaster University, 1280 Main Street West, Hamilton, ON, L86 4L7, Canada

2

Corresponding author.

3

Present address: Princess Margaret Hospital, Toronto, ON, M5G 2M9, Canada.

4

Present address: Northern Digital Inc., Waterloo, ON, N2V 1C5, Canada.

J. Manuf. Sci. Eng 130(5), 054502 (Sep 11, 2008) (7 pages) doi:10.1115/1.2976121 History: Received March 16, 2007; Revised May 05, 2008; Published September 11, 2008

The need to simultaneously measure sheet metal geometry and strain arises during research, die tryout, statistical process control production part approval, or in response to manufacturing exceptions. Several optical systems have been developed for strain and geometry measurement of small specimens. Large scale geometric measurement is possible using coordinate measuring machines equipped with touch probes. This Technical Brief summarizes the extension of these methods using three dimensional gray level point clouds obtained from either laser digitizers or an in-house developed stereo vision system.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

Square grid strain calculation (5)

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Figure 4

Existing strain grid measurement methods: (a) handheld CCD measuring camera (6) and (b) tabletop strain grid measuring system (7)

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Figure 5

CMM mounted measurement sensors: (a) laser digitizer system and (b) stereo vision system

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Figure 6

Laser digitizer results for Fig. 2 part: (a) grouped ellipses, (b) forming limit diagram, and (c) thickness strain plot

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Figure 7

Square grid data processing steps: (a) stereo vision image after removal of noisy areas, (b) circular disk dilation, (c) circular disk erosion, (d) black/white complementing and removal of too small/too large regions, (e) corner detection, (f) centerline calculation, (g) parabolic construction and intersection, and (h) extracted intersection point

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Figure 9

Laser digitizer and stereo computer vision mounted on manually operated portable arm CMMs: (a) ShapeGrabber (29) laser digitizer and (b) stereo computer vision

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Figure 8

Stereo computer vision results for part in Fig. 2

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Figure 2

Circle and square grid examples: (a) circle grid etched tailor welded steel part used for laser digitizing. Left side thickness 0.64 mm and right side thickness 1.14 mm. Underformed cicles have a 2.54 mm diameter on 3.175 mm pitch centers; (b) 2.54 square grid printed aluminum part used for stereo vision.

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Figure 1

Forming limit diagram (redrawn from Ref. 3)

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