CA2062447C - Reflective grain defect scanning - Google Patents

Abstract

Grain defect scanning is accomplished by a pair of light detectors directed toward an inspection point illuminated by a collimated light beam incident upon the inspection surface at a given angle of incidence. one detector, the specular detector, is positioned along the specular angle of reflection as defined by the angle of incidence and the other detector, the diffuse detector, lies substantially along the angle of incidence. When specular reflection dominates, as when the inspection point corresponds to clearwood, the specular detector indicates a higher reflective light intensity than the diffuse detector. When diffuse reflection dominates, however, as when the inspection point corresponds to a grain defect, both detectors indicate similar reflective light intensity. Grain defect discrimination is accomplished by calculating a ratio of specular detector output to diffuse detector output. Further analysis of the relative magnitudes of the detector outputs provides a basis for identifying grading marks, such as ink and wax marks, at the inspection point.

Description

2/27/91 ~ ~ 2 ~ 7 REFLECTIVE GRAIN DEFECT SCANNING

Field of the Invention The present invention relates to wood product proce~sing and particularly to a method and apparatus for detection of grain de~ects by re~lective s~nn;ng.

Background of the Invention Automatic detection of grain defects improves wood processing operations. Overall production efficiency and product quality can be increased by automatic grain defect detection and corresponding product grading, processingl or remedial action. Unfort~mately, existing defect sc~nn;ng techniques have been complex and, therefoxe, not always availa~le where ~he benefit o~ automatîc grain defect detection does not outweigh the expense of such sc~nning techniques. For example, grain de~ect scanning of plywood panels or solid lumber would improve production, but cannot be accomplished by through-grain scanning techniques and must be accomplished by relatively more complicated and expensive 2Q reflective scanning methnds. Grain defect scanning of panels and solid wood material has not been regarded as feasible because of the complexity and expense o~ heretofore available reflective scanning technologies.

2 ~ & ~ 7 A simple and relatively low cost reflective grain defe~t scanning method and apparatus would make available the benefits of automated grain defect detection in the production of, for example, plywood panels and hardwood stock.

summarY of the Invention In accordance with the present invention, the surface of a woodgrain article is characterized by computing a ratio of specular reflection to diffuse reflection as measured from separate view angles of a point of incidence o~ a scanning energy beam. A grain defect is indicated by similar ensrgy reflection magnitudes while clearwood is in~icated by a substantially greater specular re~lection relative to the dif~u e reflection.

Grain defe~t scanning in accordance with a preferred embod; ent of the present invention is accomplished by scanning of an inspection point illuminated by a collimated light beam directed toward an inspection surface at a given angle of incidence. A pair of light detectors provide simultaneous views of the point of incidence as represented by reflected light intensity. One detector, the specular dete~tor, is positioned along the specular angle of reflection as defined by the angle of incidence with respect to the inspection sur~ace. The other detector, the diffuse detector, lies substantially along the angle of incidence.
Specular reflection from th~ inspection point dominates when the inspection point corresponds to clearwood. In such case, the ' 2Q~2~
ecular detector indicates a higher reflective li~ht intensity than the diffuse detector. Diffuse reflection dominates when the inspection poi~t corresponds to a grain defect. Both detectors indicate similar reflective light intensity for diffuse liyht reflection. Grain defect dis~rimination is accomplished by calculating a ratio o~ specular dete~tor output to diffuse detector output whereby a ratio substantially greater than unity indicates clearwood and a ratio close t.o unity i~dica-tes a grain defect at the inspection point.

Brief Descri~tion of the Drawinqs FIG. 1 is a perspective view of a reflective grain defect apparatus according to a f irst embodiment of the present invention and a woodgrain article subject to grain defect inspection.

FIG. 2 is a side view of the apparatus and woodgrain article taken along lines 2-2 of FIG. 1.

FIG~ 3 is a reference syste~ used to illustrate two light re~lection models believed to account ~or light re~lection from a woodgrain ~urface.

FI~. 4 illustrates in perspective a diffuse light reflection model.

FIG. 5 plots re~lected light intensity according to the 7:
ffuse light reflect.ion model.

FIG. 6 illustrates in perspective a specular di~fuse li~ht re~lection model.

FIG. 7 plots reflect~d light intensity according to the specular di~fuse light re~1ection model.

FIG. 8 ~lots reflacted light intensity ~or clearwood and for grain defects and illustrates the ~ethod o~ distinguishing therebetween in accordance with the present invention~

FIGS. 9 and 10 illustrate side and top views, respectively, of a second embod.iment o~ the present invention implemented as an across ~rain line scanning device ~or longitudinal matexial feeding applications.

FIG. 11 is a flow chart illustrating steps associated with operation of the d~vice of FIGS. 1 and 2.

FIG. 12 illustrates a modi~ication for more accurate detection o~ knotwood dimensions applicable to the embodiments o~ the present invention illustrated herein.

Detailed Description of the Invention FIGS. 1 and 2 illustrate a ~irsk embodiment of th~ presen~

2 ~ 7 vention, a grain defect detection apparatus 20 using reflective scanning~ In FIGS. 1 and ~, an elongate woodgrain artisle 12, having a longitudinal axis 1~ and inspection surface 1~, is ~ubject to grain defect scanning at an inspection point 18 of surface 16~
As used herein, the term "inspection point" ~hall refer to a point of incidence of s~anning light directed Upon an inspection sur~ace, not necessarily a static point on the inspection sur~ace. ~rticle 12 has wood fiber lying substantially along it~ longitu~;nal axi5 14, but may have grain defects or gross deviations from ths normal direction o~ the wood ~iber, e.g., kn~twood. Grain defect detection d~vice 20 identifies grain de~ects at the inspection point 18 of article 12. As discussed more fully below, translation of article 12 relative to apparatus 20 and along longitudinal axis 14, i.e. as in lonyitudinal material feeding applications, provides grain defect scAnn;ng along a line 18' corresponding to a plurality of inspection points 18 as defined by such longitudinal movement.

The embodiment of FIGS. 1 and 2 i5 essentially a single point or pixel based device adapted for relatively narrow scanning width applications, but illustrates the basic opera~ional principles of the present invention. A second embodiment o~ the present inventiQn, described below, uses an across grain linescA~ning techniquQ and arrays o~ light detectors to implement a more 2~ practical, i.e., broader width, grain de~ect scannlng application in accordance with the present invention.

~2~
Grain defect detection apparatus ~0 includes a pair of light detection devices, detectors 22 and 2~, each bearing upon inspection point 18 and lying along the line of material feed, i.e., in the plane of incidence 25 orthogonal to the surfaca 16 and containing the line 18'. Detectors 22 and 24 lia symmetrically within plane of incidence 25. The lines o~ sight to inspection point 18 ~or each detection device are symmetric about a vertical ref~rence axis 30 which is within plane of incidence 25, normal to surface 16, and coincident with the point 18. A light source 26 directs a collimated light beam 27, e.g. a low power laser beam, toward point 1a and substantially, as close as possible, along the line of cight betwesn detector 24 and inspaction point 18. Each detector 22 and 24 produces an output signal representative of a level of re~lected light nergy detected. A discrimination circuit 23 rPceives the output from de ectors 22 and 24 to identify.grain defects a~ a given inspection point 18. Discrimination circuit 28 may be a general purpose computer or dedicated circuitry adapted in conventional manner to practice the present invention as described herein.

The present invention is b~tter understood with refe:rence to two light reflection models helieved to represent components of light reflected from a woodgrain surface. FIG. 3 provides a re~erence system, similar in arrangement to that of apparatus 20, useful in illustrating the light reflection modals. Beam 27 is , CA 02062447 l998-0~-l3 represented by its angle of incidence 32 relative to axis 30, and, unless otherwise stated, remains fixed. Reflective light intensity is represented as would be detected by a movable light detector 36 maintained within plane of incidence 25 at a given distance from inspection point 18 and expressed as a function of angular position 34 relative to axis 30. Plotting the output of detector 36, for a fixed angle of incidence 32, against a range of angular positions 34 illustrates the character of each light reflection model.
The first light reflection model, illustrated in FIG. 4, represents diffuse reflection where light reflects in all directions from the point of incidence. FIG. 5 plots reflective light intensity according to the diffuse reflection model for detector 36 having angular positions -90 degrees through 90 degrees. The plot function, I=Iocos~ is an evenly contoured response, symmetric about reference axis 30, and having maxima normal to surface 16, and coincident with axis 30. It is noted that purely diffuse reflection is independent of the angle of incidence 32 for beam 27. Returning briefly to FIGS. 1 and 2, according to the diffuse reflection model detectors 22 and 24, being symmetric about axis 30, will register substantially equal light intensity with respect to diffuse reflection.
The second light reflection model, illustrated in FIG. 6, iS termed "specular diffuse", meaning that some of the reflecting light acts as though it undergoes specular or mirror-like ~0~2~17 ,flection while the other components act as though it reflects from a diffuse surface. In FIG. 6, diffuse reflection component emanates from inspection point 18 according to the above described diffuse reElection model. Specular reflection component 5 42, however, emanates from inspection point 18 along the sur~ace of a cone 44 having a central axis collinear with line 18' and a half angla (9~-i) relative to surface 16 where i e~uals the angle of incidence 32. Accordingly, the specular component 42 de~ines a semi-circular arc 45 within a plane 47 orthogonal to sur~ace 16 and to plane of incidence 25. The cone-like shape of the specular component 42 is believed to result from surface 16 having substantially regular sur~ace contour along a first climension parallel to longitudinal axis 14, i.eO, along the length of ~iber cells, and an irregular surface contour in a second orthogonal dimension transverse to axis 14, i.e, transverse to the fiber cells. The sp~cular diffuse component 40 of reflected light is believed to be caused primarily by the cellulose fibers in the cell walls, while the dif~use component i5 caused primarily by the remaining cell structure, cavities, resin, etc.

FIG. 7 plots light intensity according to the specular'diffuse model for a fixed angle of incidence 32 and a range of detector 36 positions from -90 degrees through 90 degrees. In FIG. 7, the dif~use component 40 appears, in accordance with the diffuse re~lection model, as an evenly contoured response symm~tric about axis 30. The specular component 42 appears as a more narrow 2 O 5 ,5~ q ~
sponse cen~ered about a specular reflection angle 46 lying along the surface of cone 4~. Note that the specular reflection angle 46 is equal in magnitude to the incident angle 36. The composite reflection response ~8, according to the specular diffuse reflection model~ generally follows the diffuse component 40, but has a characteristic maximum centered about the specular re~lection angle 46.

Experimentation indicates that light reflecting off a woodgrain article behavss according to a combination of the diffuse reflection model and the specular diffuse reflection model. More importantly, experimentation has shown that specular di~~use reflection dominates for clearwood reflections and dif~u~e re~lection dominates for grain defect reflectionsO Grain defect detection according to the present invention discriminates between specular diffuse reflection and dif~use reflection in order to distinguish clearwood and grain defects. Accordingly, grain de~ect detection is accomplished by discriminating between the substantially symmetric response o~ FIG. 5 and the asymmetric response of FIG. 7.

FIG. 8 plots a typical clearwood function 50 and a typical grain def~ct ~unction 52. More particularly, function 50 illustrates d~tector 36 output~ Por an inspection point 18 corresponding to a clearwood portion oP surface l.6 while function 5~ illustrates detector 36 output ~or an inspection point 18 2 i.~
rresponding to a grain de~ect por~ion, e.g., kno~wood, of surface 16. The difference between functions 50 and 52 provides a basis for discrimination by apparatus 20 clearwood v~r~us grain defect wood.

With reference to FIGS. 1, 2 and 8, detectors 22 and 24 of apparatus 20 are placed symmetrically relative to axis 30 and light beam 27 is directed along an incidence angle 54 substantially collinear with the line of sight from detector 22 to inspection point 18. The detector 22 lies on the specular re~lection angle 46, i.e., along the surface o~ cone 44 o~ the specular diffuse re~lection model. This arrangement provides two separate angular views of the inspection point 18~ Detector 22, the specular detector, is positioned to detect the ~;mll~ associated with the specular reflection component 42 of the specular dif~use re~lection as well as di~use reflection. The diffuse detector 24 is positioned to monitor diffuse reflection only.

W~th detector 22 lying on the angle 46, detector 22 output indicates a light intensity I1 for cleaxwood and a light intensity I~ ~or grain defects. Similarly, with detector ~4 lying on axis 54, detector 24 indicates a light intensity I3 for clearwood and a light intensity I4 for grain de~ects. $he light intensity values Iz, I3 and I4 are substantially equal while the inten~ity value I1 is relatively greater. Measuring the relative output magnitudes of detectors 22 and 24 provides a basis for discriminating between 2~2l~7 ~ earwood and yrairl defect wood. In particular, the discrimination ~unction is expressPd as the ratio of detector 22 output to detector 24 output where a result substantially greater than unity, e.g., I1 divided by I3, indicates clearwood, and a result substantially near unity, e.g. I2 divided by I4, indicates grain defect wood. Discrimination circuit 28 divides detector 22 output magnitude by detector 24 output magnitude~ For a result substantially greater than unity, discri.mination circuit 28 identifies the inspection point 1~ as corresponding to clearwood, and for a result substantially near unity discrimination circuit 28 identifies the inspection point 18 as corresponding to a grain defect. Typical clearwood yields a ratio of approximately 1.8 to 2 while knotwood yields a ratio near unity. It may be appreciated that discrimination is based on the relative output magni.tucles of detectors 22 and 24, not absolute output magnitudes. ~ccordingly, variations between woodgrain patterns of individual wood articles in~p~cted, resulting in different absolute levels of reflected light for individual articles, are substantially masked.

As will be apparent to those skilled in the art, by suitably indexing the position of article 12 relative to apparatus 20 and collecting detec~or 22 and 24 data ~or each in~exed position it is possible to gather suf~icient data to characterize surface 16 as to grain dafects along the line 18'. In FIGS. 1 and 2, indexing rollers 70 contact the upper sur~ace 16 and lower sur~ace oP
article 12 and roller control 72 moves article 12, by way of 2~2l~7 llers 70, in indexed fashion while providing article 12 position data to discrimination circuit 28. Discrimination circui 28 may then associate a physical location on surface 16 with the inspection point 18 for each indexed position of article 12. By such association, the location of detected grain defects may be specified using apparatus 20. Multiple scanning passes across dif~erent portions of surface 16 would prsvide scanning of the entire surface 16. Discrimina~ion circuit 28 then constructs a data representation 74 o~ surface 16 as output useful in subsequent wood processing operatiQns to ~;r; ze use o~ article 12. For example, article 12 may be cut into smaller dimension products using knowledge o~ grain de~ect positions so as to maximize stress capabilities of the resulting product as by avoiding grain defects near product edges.

While the embodiment of FIGS. 1 and 2 provides an accurate method of grain defect detection, this embodiment may not be practical in most wood processing operations.

FIGS. 9 and 10 illustrate side and top views, respectively, of a second more practical embudiment of the present invention imp}emented as an acro~s grain linescanning device for longitudinal material ~eeding applications. In FIGS. 9 and 10, an across grain linascanning apparatus 100 includes detector arrays 122 and 124, each including corresponding individual detec~ors 122a-122c and 124a-124c, respectively. In the illustrated embodiment, each of 20~2;~7 .ays 122 and 1~4 contains three detectors, but it should be apparent how the present invention may be practiced using arrays 122 and 12~ with more or less than three detectors. As described more fully below, apparatus 100 defines an across grain inspection line 118 comprising contiguous transverse inspection sections 118a-118c. Apparatus 100 detects grain defects at surface 116 of a woodgrain article 112 by movement of article 112 along i-ts longitudinal axis ~14 relative to apparatus 100 as by indexing rollers 170 and roller con~rol 172. Roller control 172 provides to discrimination circuit 128 the article 112 position data whereby circuit 128 may associate a physical location on surface 116 for line 118 to each indexed position of article 112.

Corresponding detectors of arrays 122 and 124, e.g., detectors 122a and 124a, lie within sepaxate and parallel planes o~ incidence (not shown) each orthogonal to the surface 116. In other words, each set of corresponding detector pairs is similar in arrangement and operational relation to that of detectors 22 and 24 ~FIGS. 1 and 2). The output signals from corxesponding detectors of arrays 122 and 124 are compared as described above for detectors 22 and 24 to detect grain defects where each set of corresponding detectors inspects a corresponding one of transverse inspection sections 118a-118c of surface 116. For example, the transverse inspection section 118a is subject to grain defect inspec:tion by comparing the output of detectors 122a and 124a. Movement of article 112 along its longitudinal axis 114 while performing grain ~ 2 ~
fect inspection at inspection sections ll~a-118c a~complishes inspection along corresponding longi~udinal areas 118a'-118c' whereby the surface 116 is inspected for grain de~ects.

Light source 126 of apparatus 100 includes a laser source 126a directed at a deflecting mirror 125b which in turn projects light beam 127 through a telecentric lens/mirror assembly 126c. This arrangement may be known to those skilled in the art as a telecentric flying spot linescanning system whereby light beam 127 remains substantially parallel to a plane orthogonal to surface 116 and containing axis 114 and maintains a given angle of incidence 154. This longitudinal orientation ~or light beam 127 is important as it maintains a longitudinal orientation for the cone 4~ (FIG.
6) according to the specular diffuse light re~lection model. With light beam 127 tracing across the grain of article 112 as ~escribed, difi~use reflection measured by corresponding detectors is similar due to the symmetry of such diffuse reflection and symmetric positioning o~ corresponding detectors within axrays 122 and 124. Accordingly, each detector of a pair of corresponding detectors measures similar light intensity for diffuse reflection from sur~ace 116.

Specular di~use reflection, however, is not symmetric. This as~mmetry relates the maximum spacing to the view angle, i.e., relates ths maximum spacing between detectors within each array 122 and 124 to the detector view angle. According to the specular 1~

2 ~
Pfuse reflection model, as the light beam 12~ moves transversely across the article 11~ at a given angle of incidence, the cone ~54 (FIG. 6) similarly moves transversely across article 112. The detectors within array 122 must be spaced so as to maintain a view angle including the surface of cone ~4 such that the specular component 42 of reflected light, when presentl may be detecte~
More particularly, ~he view angle of each detector of array 122 includes the arc 45 (FIG. 6) so long as the light beam 127 is incident at the corresponding transverse portion of line 118. In a practical application, view angles on the order of +/- twelve degr~es should be adequate. Thus, by maintaining proper spacing between detectors 122, i.e., not too far apart, specular reflection from beam 127 as it moves through each of transverse sections 118a-118c is detected by a corresponding one of detectors 122a-122c, respectiv~ly.

In operation, article 12 is moved along its longitudinal axis 114 relative to apparatus 100 as light beam 127 traces across its grain to define the line 118. Light source 126 providas to discrimination circuit 128 the light beam 127 position dat:a, i.e., its transverse position along line 118. As previously noted, index rollex control 172 provides the article 112 position data to discrimination circuit 128. The light beam 127 position data from light source 126 together with the article 112 position clata fro~
roller control 172 provides to discrimination circuit 128 sufficient information to associate a physical location on surface 2 ~ 7 ; corresponding to a current point of incidence for light beam 127. By suitably sampling data from arrays 122 and 124 in coordination with knowledge of the actual point of incidence of light beam 127, discrimination circuit 128 constructs data 174 as 5output representing surface 116. For example, as light beam 127 moves through inspection section 118b, discrimination circuit 128 collects data from detectors 122b and 124b at given rate corresponding to a given number of points along section .118b, and calculates a corresponding set of ratio values thereof, so as to 10identify grain defects along the corresponding portion of surface 116. Surface 116 representation data 174 i5 then made available to subsequent wood processing steps to ~;r;ze use of article 112, The pxesent invention has shown an inherent ability to 15discriminate not only between normal grain patterns and grain defects~ but also between wood and certain grading marks thereon, particularly felt tip ink marks and wax crayon marks. Ink is taken up more readily by the diffuse rela~ed wood structures, i.e., cell cavities, resin, etc., than by the specular diffuse related ZOcomponents, i.e., the cellulose fibers in the cell walls,. This suppresses the diffuse detector 24 output much more than' the specular diffuse detector 22 output such that the ratio of detector 22 to detector 24 output rises to a very high level, higher than that associated with clearwood. This high ratio in connection with 25an unusually low detector 2~ output yields a clear "lnk signature.l' In knotwoods the specular diffuse components are virtually 2~2~7 nexistent and the ratio for knotwoods remains unchanged when marked by ink. Accordingly, lnk marks upon knotwood may not be detectableO As for wax crayon marks, the wax provide~ a specular surface on the wood while the wax pigment suppresses the diffuse reflection. Again this yields a very high detector output ratio, but with a characteristic low specular diffuse detector 22 output.
Wax marks are generally detectable whether on Xnotwood or clearwood.

FIG. 11 is a flow chart illustrating operation of the device o~ FIGS. 1 and 2 for each indexed inspection point .including di~crimination of grain defects as w811 as ink and wax ma:rkings on wood article 12. It should be apparent to those sXilled in the art how the ~teps illustrated in FIG. 11 may be applied to the device of FIGS. g and 10. More particularly, the steps illustrated in FIG. 11 correspond to each sampling of data taken from corresponding detector points of arrays 122 and 124.

In FIG. 11, pxocessîng by discrimination circuit 28 of each sampling of data collected from detectors 22 and 24 begins in block 200 where the output o~ the specular detector 22 is stored in the variable D1 and diffuse detector 24 output is stored in the variable D2. In block 20Z discrimination circuit 2a computes the ratio D1/D2 for storage in the variable RATI0, The value of RATIO
~5 will determine branching through the flow chart and actual RATI0 values for branching decisions will vary depending on the ~ ~4~ 7 ~plication. In decision block 204 the value of RATIo ls compar~d to unity. If substantially equal ~o unity, e.g. below the value 1.3, processing branches to block 206 where cliscrimination circuit 28 identifies the portion of surface 16 corresponding to inspection point 18 as a grain defect. A negative result in block 204 passes processing control to decision block 207. If decision bloc~ 207 determines that the value of RATI0 is approximately equal to the value two, e.g. in the range o~ 1~3 ~o 2.~, processing branches to blocX 208 where discrimination circuit 28 identiPies the portion of surface 116 corresponding to inspection point 18 as a normal grain pattern. Processing from either of blocks 206 or 208 continues to block 210 where discrimination circuit 28 stores the values D1 and D2 and maintains statistical data representing typical D1 and D2 values useful in discriminating between ink and wax marks. Continuing to block ~12, discrimination circuit 28 incorporates the identification of the inspection point 18, e.g.
grain dePect or normal grain pattern, by updating a surface 16 database structure.

If decision block 207 determines khat RATI0 is not substan~ially equal to the value two, e.g. greatar than the value three, processing branches to block ~14 where the portion of surface 16 corresponding to inspection point 18 is identified as being m~rked either by ink or wax. Should discrimination between ink and wax markings be desired, block 216 references statistical ~ata previously stored as typical D1 and D2 values. Decision block 2 OI62L1~7 9 tests for an unusually high D1 value, inferring a wax mark in block 220, and decision block 222 tests ~or an unusually low D~
value, inferring in ~lock 224 an ink mark. If decision block 222 determines that D2 is not unusually low, the type of marking is identified as unknown in block ~26. In any case, processing eventually reaches block 212 where discriminatio.n circuit 2~ wo-lld suitahly update the surfacP 16 database structure relative to the corresponding portion of surface 16 as being marked, either by wax, by ink, or unknown. ~fter sc~nni ng the entixe sur~ac 16, the surface 16 data structure may be referenced to identify the location oE grain defects as well as interpret detected ink and wax markings thereon.

FIG. 12 illustrates a modification applicable to both of the illustrated embodiments of the present invention for more accurately determining the dimension of knotwoodO The modification will be described with reference to the embodiment of FIGS. 1 and 2. There exists an extensive region below knots, toward the butt o~ the log from which the sample has been cut, where the grain carrie~ a diving component, i.e. the direction of the wood fiber has a component oriented into the surface 16. The ratio of detector 22 output to detector 24 output, being greater than unity, for this region will correctly indicate clearwood, but the actual ~pecular reElection peak angle deviates from the specular angle de~ined by the sur~ace 16 o~ article 12. This reduces the ratio o~ detector 2.2 output to detector 24 output and th.is can extend the lg 2~2~l~7 parent dimension of knots. FIG. 8 i~ strat2s this deviation.
In FIG. 8, detector 22 output for clearwood response 50 does not actually peak at the specular angle 46, rather at an adj acent angle 49. Angl~ 49 may be on either side of angle 46 depending on the direction of material fe~ding, i.e. whether the butt end leads~
It may be d~sirable to detect the peak value for the specular component of reflected light so as to ~ e the calculated detestor 22 to detector 2~ output ratio. Should it be desirable to minimi~e the effect due to such diving grain, it is suggested that a pair o~ detectors, 322a and 322b in FIG. 12, replace detector 22. Detectors 322a and 322b are positioned above and below, respectively, the specular reflection a~gle 46 and their outputs are appropriately combined to captur~ the peak specular value and produce what would otherwise be detector ~2 output~

In typical applications, the angle of incidence 54 is on the order of 45 degrees and the diametex of light beam 27 is on the order of one to two millimeters. Light polari~ation orientation may be optimized in some applications, but has generally been found satisfactory at a variety of polarization orientatians.

In certain hardwood species, the "ring porous" types, there are wide bands of large cells t"vessels"~ that appear on the face of a sur~aced board. These vessels can be on the order of 1 mm by 7.5 4 mm in size, and form relatively large pits when the wood i5 ~urfaced. Typical species are the red and white oaks, where these : ~0~2/-l~7 ~ nds of vessels give the wood surface an appearance that is usually desirable for i~s use in furniture or trim moldings.
Unfortunately, these ~ells can also strongly scatter and absorb light beam 2~ since the cell size is large enough to encompass the typical collimated laser beam used in this application. Further/
in certain species a structure called ~'tyloses'l form~ in the vessels and absorbs the optical radiation even more strongly.

To address this problem with ring porous type hardwoods, the apparatus 20 may be adapted in three ways. The adaptation will be described with reference to the embodiment of FIGS. 1 and 2, but is equally applicable to the embodiment of FIGS. 9 and 10~ First, increase the angle of incidence 54 to about fifty-five degrees.
Second, increase the laser spot si~e, i.e. the area of point 18, in the cross scan direction, i.e. along the normal grain direction to 4 or 5 mm to pro~ride an elongate area o~ incidence. This is achieved with a cylindrical lens in the laser path, usually pre-scan. This will not increase the spot size in the orthogonal direction (across the grain). Such elongation in the scan direction would decrease the ability o~ the apparatus 20 to resolve the edge of the defect areas. Third, orient the laser polarization parallel to the plane of incidence 25. These adaptations are not required for other hardwoods (the "diffuse-porous" ~pecies), or for so~twood species, which do not have vessels. Tha increases i~ angle of incidence 54 and area of point 1~ axe not generally desirable, bu~ represent a trade-off in order ~1 2~2l~7 ~ better detect defects in the ring porous species. It should be apparent to those skilled in ~he art how these adaptations may be applied to the apparatus 100 of FIGS. 9 and 10.

Thus, a method and apparatus for detection oP yrain defects by reflective scanning has been shown and described. Th~ method and apparatus accordiny to the present in~ention is an inherently simple and low cost technology when applied to across grain scanning in longitudinal material feed applications. The method and apparatus ha~ provided excellent discrimination for }cnotwood, both live and dead, in a wide range of solid wood products such as softwood veneers, hardwood and softwood boardst and shingles. The method and apparatus is useful in a wide range of surface conditions such as characterization of dirty, stained, rough cut, knife planed, or abrasive planed surfaces.

While a preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that modifications relative to the illustrated embodiment are 2~ possible without departure fro~ the scope of the invention. For example, the present invention may be practiced by a variety of techniques beyond light energy scanning such as acoustics or any othar ~orm of energy that undergoes "specular-diffuse reflection'l.

Xt will be appreciated, therefore, that the SCOp~! O~ the present invention is not restricted to the particular embodiment 2~2~7 'hat has been described and illustrated, but rather includes any modifications as fall wi~.hin the appended claims and equivalents thereof.

Claims (15)

1. A method of characterizing an energy reflective surface, said method comprising:
directing an energy source along a line of incidence to an inspection point of said surface;
monitoring first reflective energy emanating from said inspection point along a line of reflection corresponding to a specular angle of reflection relative to said line of incidence and said inspection point;
monitoring diffuse second reflective energy emanating from said inspection point along a line other than said line of reflection; and calculating a ratio of said first and second reflective energy to characterize said surface at said inspection point.

2. The method according to claim 1 wherein said ratio characterizes said inspection point as one of predominately specular reflective or predominately diffuse reflective.

3. The method according to claim 1 wherein said energy source is a light energy source.

4. A method of characterizing a surface, the method comprising:
directing a light beam upon said surface at a given angle of incidence;
detecting diffuse reflected light from said surface and resulting from said light beam;
detecting specular reflected light from said surface as defined by said given angle of incidence and resulting from said light beam;
computing a ratio of said specular reflected light to said diffuse reflected light; and characterizing said surface in response to said computed ratio.

5. The method according to claim 4 wherein said surface is the surface of a wood grain article and said characterizing step includes characterizing said surface at a point of incidence of said light beam as being normal wood grain structure in response to said computed ratio being substantially greater than unity and as being a grain defect in response to said ratio being substantially equal to unity.

6. A method of characterizing surface features of an elongate wood grain article having a grain structure lying along its longitudinal axis, the method comprising:
directing a collimated light beam at the surface of said wood grain article and along an angle of incidence relative to said Irface~, said light beam being within an incidence plane orthogonal to said surface, said light beam being incident upon said surface at an incidence point at said surface, said incidence plane being substantially parallel to said longitudinal axis;
detecting first and second reflected light energy of said light beam at first and second locations, respectively, within said incidence plane, the first location being along a surface specular angle as defined by said angle of incidence; and characterizing surface features at said incidence point by computing a ratio of said first and second reflected light energy.

7. A method according to claim 6 wherein said incidence point is characterized as a grain defect in response to said ratio being computed as near unity and characterized as clearwood in response to said ratio being computed as being substantially greater than unity.

8. A method according to claim 6 wherein said step of characterizing surface features comprises identifying at said incidence point the presence of at least one of a normal grain structure, a grain defect, an ink mark, and a wax crayon mark.

9. A method of distinguishing a grain defect and a normal grain structure at an inspection point at the surface of a woodgrain article, the method comprising directing a light beam at said inspection point whereby light reflected from said inspection point, said light beam having an angle of incidence relative to said surface;
measuring at a first detection point a first reflected light intensity substantially along a specular angle of reflection relative to said angle of incidence;
measuring at a second detection point a second reflected light intensity at an angle of reflection other than said specular angle of reflection;
computing a ratio of said first reflected light intensity to said second reflected light intensity; and identifying said inspection point as corresponding to normal grain when said ratio is substantially greater than unity and identifying said inspection point as corresponding to a grain defect when said ratio is substantially equal to unity.

10. A method according to claim 9 wherein said inspection point, said first detection point, and said second inspection point are coplanar within an incidence plane orthogonal to said surface and aligned with the normal grain direction of said article.

11. A method according to claim 10 wherein said first and second inspection points are substantially equidistant from said inspection point and substantially symmetric with respect to an axis normal to said surface and within said incidence plane.

12. A method according to claim 9 wherein said first and second detection points are substantially equidistant from said inspection point.

13. A method according to claim 9 wherein said article is a ring porous type hardwood species, said angle of incidence is substantially 55 degrees relative to a vector normal to said surface and coincident with said inspection point, and said inspection point is an elongate area of said light beam as incident upon said surface.

14. A device for identifying grain defects at an inspection point at the surface of a woodgrain article, the device comprising:
a light source directing a beam of light to said inspection point, said beam of light being within an incidence plane orthogonal to said surface and having an angle of incidence relative to said surface;
a first light detector positioned at a given distance from said inspection point within said incidence plane and adapted to provide a first output signal representative of reflected light intensity emanating from said inspection point and substantially along a specular angle of reflection with respect to said angle of incidence;
a second light detector positioned at said given distance from said inspection point within said incidence plane and adapted to provide a second output signal representative of reflected light intensity emanating from said inspection point and substantially along said angle of incidence; and discrimination means for identifying grain defects at said inspection point, said discrimination means including means for receiving said first and second output signals and for computing a ratio of said first output signal magnitude to said second output signal magnitude whereby in response to a computed ratio substantially equal to unity said discrimination means identifies a grain defect at said inspection point and in response to a computed ratio substantially greater than unity said discrimination means identifies clearwood at said inspection point.

15. A device according to claim 14 wherein said light beam is a collimated light beam.

15. A device according to claim 14 wherein the lines of sight from each of said first and second light detectors to said inspection point are substantially symmetric about an axis normal to said surface and coincident with said inspection point.