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Research Papers

Linear Sensor Arrangement for Softwood Grain Angle Measurements by Directional Reflection

[+] Author and Article Information
Q. Pan, G. S. Schajer

Department of Mechanical Engineering,
University of British Columbia,
Vancouver, BC V6T 1Z4, Canada

Manuscript received July 24, 2018; final manuscript received September 22, 2018; published online October 19, 2018. Assoc. Editor: Shiro Biwa.

ASME J Nondestructive Evaluation 2(1), 011003 (Oct 19, 2018) (6 pages) Paper No: NDE-18-1028; doi: 10.1115/1.4041567 History: Received July 24, 2018; Revised September 22, 2018

A linear sensor arrangement is presented as a means of measuring the three-dimensional grain angle of wood. The measurement principle is based on an optical characteristic of a wood surface where the microscopic cell structure causes preferential reflection of light perpendicular to the wood grain. This response is notable among the several other techniques for measuring wood grain angle in that it enables identification of diving (out-of-plane) angle in addition to the surface (within-plane) angle. The basic measurement principle has been previously investigated using a circular array of light sensors to measure the spatial distribution of the light reflected from a wood surface. That procedure works reasonably well for surface points near the center of the circle and for modest dive angles. The linear sensor arrangement investigated here is designed to extend measurement functionality so as to be able to measure grain angle at any point along a central line and over a greater range of dive angle. A prototype scanner system is presented together with example experimental results for clear wood samples and for a face knot sample.

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References

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Figures

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Fig. 1

Light reflection from wood with cells parallel to the surface. (a) Side view and (b) reflected light intensity within a parallel plane above the wood surface. x = longitudinal wood direction, y = transverse wood direction, θ = wood grain rotation angle.

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Fig. 2

Light reflection from wood cells with dive angle δ. (a) Side view and (b) reflected light intensity within a parallel plane above the wood surface. v = central displacement of reflection line, h = height of parallel plane above the measured surface.

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Fig. 3

Arrangements of light sensors to identify location of specular reflection: (a) circle method and (b) linear method

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Fig. 4

Apparatus for measuring wood grain angle by the linear method

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Fig. 5

Measured surface and dive angle profiles for specimens with apparent surface angle θ = 10 deg and dive angles δ = 0 deg, 3 deg, 6 deg, and 10 deg

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Fig. 6

Typical light intensity profiles measured at various dive angles δ with surface angle θ = 0 deg. The curves are corrected measurement distance and incidence angle variations using Eqs. (6)(8).

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Fig. 7

Scan lines (30 mm long, 2 mm spacing) used to measure the grain angles around a 8 mm diameter knot in a sample of lodgepole pine, pinus contorta. (a) Side (end grain) view with knot position superimposed and (b) face view.

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Fig. 8

Measured surface and dive angles along the scan lines indicated in Fig. 7. The knot lies within scan distance 9 to 17 mm.

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