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.

Copyright © 2019 by ASME
Your Session has timed out. Please sign back in to continue.


Forest Products Laboratory, 2010, “ Wood Handbook: Wood as an Engineering Material,” USDA Forest Products Laboratory, Madison, WI, Technical Report No. 190.
Bechtel, F. K. , Byers, R. K. , Logan, J. D. , Allen, J. R. , Strevy, M. G. , and Uskoski, D. A. , 1996, “ Apparatus for Testing Lumber Stiffness,” U.S. Patent No. 5503024.
Schajer, G. S. , 2001, “ Lumber Strength Grading Using X-Ray Scanning,” For. Prod. J., 51(1), pp. 43–50.
McDonald, K. A. , 1978, “ Lumber Defect Detection by Ultrasonics,” USDA Forest Products Laboratory, Madison, WI, Research Paper No. FPL 311.
McLauchlan, T. A. , Norton, J. A. , and Kusec, D. J. , 1973, “ Slope of Grain Indicator,” For. Prod. J., 23(5), pp. 50–55.
Steele, P. H. , Neal, S. C. , and McDonald, S. M. , 1991, “ The Slope-of-Grain Indicator for Defect Detection in Unplanned Hardwood Lumber,” For. Prod. J., 41(1), pp. 15–20.
Daval, V. , Pot, G. , Belkacemi, M. , Meriaudeau, F. , and Collet, R. , 2015, “ Automatic Measurement of Wood Fiber Orientation and Knot Detection Using an Optical System Based on Heating Conduction,” Opt. Soc. Am., 23(26), pp. 33529–33539.
Schajer, G. S. , and Orhan, F. B. , 2006, “ Measurement of Wood Grain Angle, Moisture Content and Density Using Microwaves,” Holz Roh-Werkst., 64(6), pp. 483–490. [CrossRef]
Zhou, J. , and Shen, J. , 2003, “ Ellipse Detection and Phase Demodulation for Wood Grain Orientation Measurement Based on the Tracheid Effect,” Opt. Lasers Eng., 39(1), pp. 73–89. [CrossRef]
Hu, C. , Tanaka, C. , and Ohtani, T. , 2004, “ On-Line Determination of the Grain Angle Using Ellipse Analysis of the Laser Light Scattering Pattern Image,” J. Wood Sci., 50(4), pp. 321–326.
Matthews, P. C. , and Soest, J. F. , 1986, “ Method for Determining Localized Fiber Angle in a Three Dimensional Fibrous Material,” U.S. Patent No. 4606645.
Soest, J. , Matthews, P. , and Wilson, B. , 1993, “ A Simple Optical Scanner for Grain Defects,” Fifth International Conference on Scanning Technology and Process Control for the Wood Products Industry, Atlanta, GA, Oct. 25–27, pp. 192–200.
McGunnigle, G. , 2009, “ Estimating Fibre Orientation in Spruce Using Lighting Direction,” IET Comput. Vision, 3(3), pp. 143–158. [CrossRef]
Schajer, G. S. , and Sutton, D. B. , 2016, “ Identification of 3D Wood Grain Angle by Directional Reflection Measurement,” Wood Mater. Sci. Eng., 11(3), pp. 170–175. [CrossRef]
Nicodemus, F. , 1965, “ Directional Reflectance and Emissivity of an Opaque Surface,” Appl. Opt., 4(7), pp. 767–775. [CrossRef]
Glaeser, G. , 1999, “ Reflections on Spheres and Cylinders of Revolution,” J. Geometry Graph., 3(2), pp. 121–139.
Pan, Q. , and Schajer, G. S. , 2018, “ Two-Line Spatial Reflection Method for Measuring Wood Grain Direction,” For. Prod. J. (in press). http://www.forestprodjournals.org/doi/abs/10.13073/FPJ-D-18-00004?code=frps-site


Grahic Jump Location
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.

Grahic Jump Location
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.

Grahic Jump Location
Fig. 3

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

Grahic Jump Location
Fig. 4

Apparatus for measuring wood grain angle by the linear method

Grahic Jump Location
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

Grahic Jump Location
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).

Grahic Jump Location
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.

Grahic Jump Location
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.



Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In