NZ519475A - Measuring wood properties by optical investigation of tracheid orientations - Google Patents

Abstract

A method of determining one or more fibre properties of a wood specimen by shining a light beam on the surface of the specimen to create a light scatter pattern on a portion of the surface and measuring the intensity of the light scatter pattern around at least one substantially constant radius in order to determine the one or more fibrous properties from the intensity measured around at least one constant radius

Description

I. >t / 51 75 NEW ZEALAND PATENTS ACT 1953 No: 519475 Date: 11 June 2002 COMPLETE SPECIFICATION METHOD AND APPARATUS FOR DETERMINING WOOD PARAMETERS, INCLUDING GRAIN ANGLE We, INDUSTRIAL RESEARCH LIMITED, a New Zealand company of Brooke House, 24 Balfour Road, Parnell, Auckland, New Zealand, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 1 - INTELLECTUAL PROPERTY OFFICE OF N.Z 06 JUN 2003 RECEIVED 58210 l.DOC to -f 2 METHOD AND APPARATUS FOR DETERMINING WOOD PARAMETERS, INCLUDING GRAIN ANGLE.

FIELD OF THE INVENTION The present invention relates to apparatus and methods for determining characteristics of wood specimens using optical techniques.

BACKGROUND TO THE INVENTION Higher standards for the quality of dried wood, and the need for overall process efficiency, are driving the search for methods of screening wood products as early as possible in the production chain.

Measuring timber quality, preferably in the green as-sawn state, and assessing basic wood properties that will cause problems, such as warp and twist, are of interest. Increasingly, juvenile wood is becoming a significant proportion of the world's wood supply, and it is well known in the industry that such wood is particularly prone to these 20 distortions.

The reasons for this are in the nature of the fibres that make up wood. Figure 1 shows, in schematic form, two wood fibres or tracheids, one long 10 and one short 11. The terms "grain", "tracheid" and "fibre" can be used interchangeably. Tracheids are tubular 25 in nature with a wall thickness of about 5 microns. The hollow centre may be dry or sap filled and is usually about 25 microns in diameter. Fibre length in softwoods is 2000-3000 microns. Fibres are locally parallel, and their direction is the grain direction visible on the surface of wood, for example a plank. Over an entire surface of a wood sample, however, the fibre direction may vary, for example due to knots or other defects 30 in the wood.

The mechanically significant component of a fibre wall consists of layers of molecular strands of cellulose, wound in a helical structure. These strands are termed "microfibrils 12". The microfibril angle (MFA) is the angle 13 that the microfibrils make with the longitudinal axis of the hollow fibre. It is known that long fibres are associated with a low MFA, while short fibres have a higher MFA. The stability of wood as it dries is the aggregate of the forces generated by the microscopic shape changes of its cellular structure. It is known that the fibres shrink most perpendicularly to the cellulose winding, as indicated by arrows 14 and 15. Thus, a short fibre with a high MFA, will suffer a high component of along-fibre (grain) shrinkage. In contrast, a long fibre has a low MFA and will be associated with low along-fibre shrinkage. If a sawn board contains a mixture of fibre types in different locations, the possibility of differential shrinkage and stress relief via warping is a distinct possibility.

Extensions to this concept of the fibre controlling the shape of a board as it dries, are the effects of systematic changes in fibre angle with respect to the board's surface. For example, the grain swirl in the vicinity of a knot, or the systematic shift in angle across a board caused by spiral grain, i.e. grain which spirals about the pith. The latter is particularly prevalent in plantation wood in NZ, and is commonly seen as twisting in dried timber which contains the pith, the condition that captures the maximum influence of this particular defect.

Long softwood fibres are associated with high strength, and such fibres are found nearest the bark on trees. Mechanical bending tests show that this outerwood has higher stiffiiess than typical core wood. Thus, there is a loose correlation between low MFA, long fibres, and high wood stiffiiess, and vice versa, namely, high MFA, short fibres and low wood stiffiiess. A further, undesirable, feature of wood is the presence of compression wood, in which the fibres are characterised by large MFA, and high density, but low stiffiiess.

Techniques using the phenomenon of tracheid scatter have been used previously for determining properties of fibres in wood. Referring to Figure 2a, when an intense spot of light 26 falls upon a wood surface 25, a portion is reflected at the surface, some is scattered, and some enters the wood. Wet or dry, some light is scattered longitudinally along tracheids, either within their tubular interior, or within the walls. An incident light spot of the order of 0.5 mm in diameter covers many tracheids in the cross-fibre direction. As the incident light travels through the tracheid tubes or their walls, the spot transforms into an ellipse that is visible as an oval shape 20 on the wood surface 25. The oval 20 is termed "scatter ellipse", "scatter pattern" or "tracheid scatter".

The scatter ellipse 20, created by shining a laser or other light source onto a wood surface, contains information on the tracheids under investigation. For example, the orientation (0) 21 of the major axis 22 indicates the orientation (in the plane of the wood surface) of the tracheid with respect to the wood edge 23, the length of the major axis 22 indicates (although is not necessary an exact measure of) the length of the tracheid, and the eccentricity (the ratio of major axis 22 length to minor axis 24 length) of the ellipse gives an indication of the uncertainty in the measured orientation of the major axis 22. These tracheid parameters, once extracted from the scatter pattern 20, can be used to infer information as to the nature of the wood under investigation. It should be appreciated that as a scatter pattern 20 is produced by a number of tracheids in the vicinity of the laser spot 26, the scatter parameters relate generally to all those tracheids. The scatter parameter will provide a reasonable indicative measure of any particular tracheid in the vicinity, as they will all have similar properties (such as length and orientation). The properties of the tracheids only vary considerably on a global scale.

The method conventionally employed for collecting scatter data involves imaging the laser spot and its surroundings using a solid state camera, and then subjecting a frame of the image to analysis. Using an algorithm, a best fit ellipse is generated for the scatter pattern, based on light intensities of the scatter pattern that exceed a particular threshold value. Such analysis shows that the scatter shape is not truly an ellipse, and is only approximately symmetric in shape. Repeated images of the same scatter region, analysed for the best ellipse orientation at a constant illumination level, give standard deviations to below a degree, but there is usually a systematic variation in the apparent grain angle derived at different threshold levels. This is illustrated in Fig 2b, which shows the orientation derived for approximately the same location on a piece of dry wood, for two lasers; a gas laser whose spot was focussed down into a small and very regular spot, and a diode laser, the beam of which, though focussed, is rather elliptical.

The light levels on the axis are quasi logarithmic, and the scale therefore covers around three decades.

In the conventional method, defining an orientation is a compromise between choosing a low light level, where the scatter extends furthest and the ellipse defined by a given light level has its greatest eccentricity, (which aids the measurement of its orientation, but at the cost of increased noise), and the use of higher light levels where the wood scatter path is shorter, but the ellipse becomes more circular and its orientation more difficult to establish. The very uniform spot from the gas laser probably is a small advantage, but even that seems to show a systematic shift of almost a degree between light levels of 50 and those of 150 units. The conclusion is that excessive effort on algorithms capable of repeatably extracting an angle at a particular location and intensity may lead to unwarranted confidence that the grain orientation has been precisely measured, largely because the real intensity contours are irregular to some degree and are not simply noisy ellipses.

SUMMARY OF INVENTION It is an object of the invention to provide improved methods and apparatus for investigating characteristics of wood specimens. In general terms, the invention relates to various methods and associated apparatus for obtaining characteristics of scatter ellipses generated on a wood specimen, and then inferring characteristics of the tracheids or fibres in the wood specimen from the scatter ellipse characteristics. A map of tracheid characteristics can be obtained for the specimen. The invention further relates to various methods and associated apparatus that utilise the map of characteristics of fibres in a wood specimen, to infer properties of the wood itself.

In one aspect the present invention may be said to consist in a method of determining one or more fibre properties of a wood specimen including the steps of: a) shining a light beam on the surface of the specimen to create a light scatter pattern on a portion of the surface, b) measuring the intensity of the light scatter pattern around at least one substantially constant radius, and c) determining the one or more fibre properties from the intensity measured around the at least one constant radius.

In another aspect the present invention may be said to consist in a method of determining grain orientation of wood specimen including the steps of a) shining a light beam on the surface of the specimen to create a light scatter pattern on a portion of the surface, b) measuring the intensity of the light scatter pattern around at least one substantially constant radius, c) determining the points of highest light intensity around the constant radius using a Fourier analysis, and d) determining grain orientation from the points of highest light intensity.

In another aspect the present invention may be said to consist in an apparatus for determining one or more fibre properties of a wood specimen including: a light source to produce a light scatter pattern on the specimen surface, an intensity detector array arranged to measure the intensity of the light scatter pattern around at least one substantially constant radius, and a processor connected to the detector array to receive the light intensity measurements and determine the one or more fibre properties from the light intensity measurements.

In another aspect the present invention may be said to broadly consist in an apparatus for determining grain orientation of a wood specimen including: a light source to produce a light scatter pattern on the specimen surface, an intensity detector array arranged to measure the intensity of the light scatter pattern around at least one substantially constant radius, and a processor connected to the detector array to receive the light intensity measurements and adapted to determine the points of highest light intensity around the constant radius using a Fourier analysis, and determine grain orientation from the points of highest light intensity. 7 BRIEF LIST OF FIGURES Preferred embodiments of the invention will be described with reference to the following figures, of which: Figure 1 is a schematic diagram of a long and short tracheid in a wood specimen, Figure 2a is a schematic diagram of a tracheid scatter pattern, Figure 2b is a plot of apparent grain angle as a function of brightness level obtained using apparatus with a diode and a gas laser respectively, Figure 3a is a plot of scatter ellipses calculated at four intensity levels on a wet sawn sample, Figure 3b is a plot of brightness as a function of azimuth at four different radii.

Figures 4a and 4b are a schematic diagram of one embodiment of the invention for creating and analysing tracheid scatter, Figure 5 is a schematic diagram of another embodiment of the invention for creating and analysing tracheid scatter, Figure 6 is a schematic diagram of another embodiment of the invention for creating and analysing tracheid scatter, Figure 7a is a plot of logarithmic intensity attenuation of the scatter from a laser along 20 and perpendicular to the grain, Figure 7b is a plot of approximately log-linear intensity attenuation along major and minor axes of a scatter ellipse, over modest intensity changes, Figure 8 is a plot of scattering intensity along the major axis and minor axis, and intensity along the major axis scaled by approximately 0.32 to bring the parallel and 25 perpendicular scatter into alignment, Figure 9 is a map of grain direction for three sides of a wet 100x50mm sample, 600mm long, indicating an area of grain swirl with an associated knot at the lower edge, Figure 10 is a schematic diagram of a plank prone to twist, Figures 1 la and 1 lb show a sample of knotted wood and grain direction respectively, 30 Figures 11c and lid show a grayscale image of a cut log showing systematic brightness eccentricity changes between pith and bark, Figure 12 is a plot showing the correlation between major axis scatter length, brightness eccentricity and MoE of dry wood, 8 Figure 13 is a plot showing the comparison of scatter ellipses at two intensities on three wood samples before and after drying, Figure 14 is a plot showing the increase in major axis scatter length from pith to bark across a rough-sawn wet cant, and Figure 15 is a schematic diagram of a plank prone to the type of warp called crook.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the invention will now be described. It will be appreciated that the methods and associated apparatus described could be used in various combinations to obtain the required characteristic information of a wood specimen.

Microscope pictures have been taken by the applicant of laser light injected into the surface of p. radiata wood and then transmitted up to several millimeters in the along-grain direction. These indicate that in both late and early wood, most light near the point where the light is incident is travelling in the lumens of the tracheids, while with increasing distance most light is propagated in the tracheid walls with the latter acting as waveguides. Whether there is a continuous loss of energy from a tracheid along its length, or whether there is scattering at the end of a tracheid where light must scatter into the next tracheid, the result is that the original spot of light is transformed into grain-oriented pattern which is quasi-elliptical in shape.

OBTAINING TRACHEID PARAMETERS FROM A SCATTER ELLIPSE Methods and associated apparatus according to the invention will be described that enable a variety of tracheid parameters to be obtained by analysing the intensity of a scatter ellipse around one or more constant radii.

In a preferred embodiment of the invention, a method and/or apparatus are provided for obtaining grain angle of a wood specimen. The preferred method and/or apparatus may be utilised in various end user applications, as required, to obtain characteristic information about wood that can be inferred or otherwise obtained from grain angle information.

A preferred method for obtaining grain angle of a wood specimen by analysing a scatter ellipse will be described with reference to Figures 3a and 3b. Figure 3a shows the scatter ellipse contours 30-33 at several different intensities generated from a laser spot incident on a sample of rough-sawn wet wood. The data were recorded from one frame of a CMOS camera. When analysed by shape, the best-fit ellipses to the actual intensity contours 30-33 do not share a common origin, because of the basic irregularity of the ellipses. Such plots emphasise also that the eccentricities of the ellipses 30-33 are intensity-dependent; i.e. the mathematical ellipticity cannot describe the entire scatter pattern.

To establish grain orientation, a preferred embodiment of the invention can be employed that uses simpler processing than the existing ellipse fitting technique, but which still yields acceptable accuracy. The method involves producing a scatter pattern on the wood specimen surface using incident light, such as a laser beam. However, rather than derive a best-fit ellipse to the scatter pattern, the preferred embodiment identifies the azimuth of maximum scatter intensity at a fixed radius around the point of incident light. The azimuth of maximum scatter intensity indicates the orientation of the major axis of the scatter ellipse, which is correlated to grain angle. To do this, the intensity of scatter is measured around a circle, at a fixed radius from the point at which the light source forming the scatter ellipse is incident on the wood specimen. This intensity pattern is analysed to determine the one, or preferably two (approximately diametrically opposed), points around the circle at which maximum intensity occurs. It will be appreciated that the term point can more generally mean a small area, the size being commensurate with the resolution of the apparatus measuring the point. The line through these two points indicates the major axis, and from this, the orientation of the major axis of the ellipse, and hence localized grain angle can be found.

The analysis step involves determining the phase angle of the maximum intensity points using any suitable technique. Due to the irregularity of the scatter ellipse, the points of maximum brightness may not be exactly diametrically opposite. Therefore, preferably the analysis step involves using an azimuthal Fourier analysis, which addresses this, and at the same time provides a stable method of interpolating between sensors.

The azimuthal Fourier analysis will be described with reference to Figure 3b, in which the data of Fig 3a are shown as intensity data as a function of azimuth around circles of 10, 20, 30 and 50 pixels radius (approximately 1, 2, 3 and 5mm). Two peaks are seen at azimuths of about 10 and 190 degrees, which indicate the points of maximum intensity of the scatter pattern, and hence major axis orientation. As can be seen from the data, successful identification of the direction of the intensity maximum is not particularly sensitive to the radius chosen, though the choice of a very small radius is undesirable because the intensity becomes dominated by the unscattered light of the illuminating spot, and too large a radius will result in undesirably low light levels and consequent poor signal to noise ratios. Greater accuracy can be obtained by expressing each of the curves of Fig 3b as a sum of azimuthal harmonics by Fourier analyzing the data at each radius. The even harmonics (i.e. those with brightness maxima in pairs 180 degrees apart) describe the stretching of the scatter into a symmetric ellipse. The odd harmonics describe an asymmetry around the scatter ellipse, for example the condition described earlier in which the brightness maxima were not 180 degrees apart. By concentrating on the even harmonics, the stretch of the scatter into a symmetric ellipse is described.

The second azimuthal harmonics derived from the data in Fig 3b dominate the spectra, and the grain orientation data derived from its phase and the phase of the next two even harmonics (where they contained significant power) is given in Table I. 11 TABLE I - Fig 3b azimuthal intensity and radius.

Detector radius, pixels Grain angle from 2nd harmonic phase From 4th From 6th 11.2 - - 12.9 14.3 - 14.0 13.2 13.6 50 12.7 11.8 12.9 These values are obtained using the preferred method of the invention as described, and compare quite well with the orientation obtained from a full ellipse shape analysis of an existing method, which is computationally more time consuming. For a high intensity threshold, corresponding to a small radius, the orientation ellipse was 12.7deg, rising to 10 13.3deg for a low threshold. The latter would correspond approximately to the 30 pixel radius in the Table. In situations where speed of processing is an issue, acceptable accuracy may be obtainable from such azimuthal phase analysis.

Choice of the (even) Fourier component used to define direction provides an automatic 15 level of smoothing. The data of Fig 3b from the CMOS camera can be used to compute ^ harmonics far above the lowest three shown in Table I. The higher harmonics in fact describe the small scale irregularities within the scatter which occur because of small-scale differences in tracheid or surface roughness. Experience has shown that adequate directional accuracy, and stability against the "pulling' by local bright zones, comes 20 from the use of the second harmonic alone. A second harmonic in principle requires only light input from four detectors to define it. However if the light is extremely directional, (smaller in extent than a single detector) the system will receive identical information as the light rotates across a single sensor. In such a case the direction computed would be constant over this rotation. In practice the scatter patterns are 25 sufficiently wide in angular extent that such quantisation not serious. With 16 detectors around a circle, the effect was not seen. 12 Therefore, in summary, the preferred method of finding localized grain angle on the face of a wood specimen includes creating a scatter pattern using an incident light source, capturing light intensity information around a fixed radius centred on the light 5 spot, and conducting an azimuthal Fourier analysis of the light intensity data to determine the points of maximum intensity around the circle, the phase angle of which can be used to infer grain orientation. The angle can be found using just the second azimuthal harmonic of intensity, although more harmonics (such as higher order even harmonics and/or the first and/or higher order odd harmonics) and/or the constant term, 10 can be utilised to increase accuracy. The number of harmonics utilised can be decided upon depending upon the accuracy and speed processing requirements for the end application of the invention.

A preferred embodiment of an apparatus 40 for determining grain angle according to the 15 preferred method is shown in Figures 4a and 4b in schematic form. The apparatus 40 includes a laser source 41 for shining a laser beam 42 through a hole in a circular array of photodetectors 47, and through a lens 42A onto a spot 45 on the wood specimen 44 under investigation. This laser spot 45 creates a scatter pattern 46 on the surface of the wood specimen. The scatter pattern, which typically may be 5-10mm in extent, is 20 enlarged by lens 42A so that its image 48 falls onto the circular array of photodetectors 47 disposed on the apparatus to measure the intensity of scattered light 46 from the specimen at a constant radius 49 around the laser spot 45. The output of the array of photodetectors 47 is passed to a processor 43, which carries out the Fourier analysis as described above to determine the grain angle. Alternatively, other suitable processing 25 methods could be used. For example, if there are enough photodetectors 47, the processor could simply identify the detectors which detect the highest intensity, and use this information to determine grain angle. This grain angle information can then be output in a suitable form, for subsequent use in a desired application. For example, it may be used to find a map of grain angles of the surface of the specimen, for subsequent 30 analysis and determination of specimen properties. The number of photodectors 47 required is dependent on the highest azimuthal harmonic required by the end user. At least four photodetectors 47 are required to detect the second harmonic.

Even though only a few detectors are needed to define a direction, their radial dimension is preferably chosen such that the light does not change greatly over them. In the scale of the wood surface, this dimension is of the order of a millimetre. To ensure that information is not lost in the azimuthal direction, it is good practice, although not essential, to physically fill the circle with detectors as much as possible to ensure that no light is missed. Since discrete detectors will be square or round, it will be inevitably found that adequate definition in the radial direction means that rather more than the minimum of four detectors are required to "fill" the circle. The eight detectors shown in Fig 4b can define the grain angle to 2-3 degrees in radiata pine, and the directional quantisation effects referred to earlier are just evident. Conventionally, processing is envisaged in blocks of 2n detectors because of the efficiency of fast Fourier transform routines. For so few detectors, the FFT has no advantage over a discrete Fourier transform, the use of which allows arbitrary numbers of detectors. Theoretically, reducing the array in Fig 4b to seven increases the definition of the angle to that of sixteen regularly spaced detectors, because for a perfectly symmetric scatter pattern half the diodes give repeated information. Using commercially available bare silicon photodiodes of 1.3mm in the azimuthal direction in Fig 4b, 15 diodes mounted on a circuit board define a circle on the board of effective radius 20mm. Grain angles are measured to an accuracy of the order of a degree, limited mainly by the natural irregularities if the scatter pattern, and quantization of azimuth is not detectable on wood samples.

While the he photodetectors 47 illustrated in Figure 4a, 4b are discrete detectors, with suitable adjustment of the optical magnification, they could be pixels of fixed coordinates in a solid-state camera or photodiodes within a custom chip, though in the latter cases the laser 41 could never be concentrically mounted, and its beam would need to be injected to the viewing axis via a mirror (for example, as described later with reference to Figure 5).

Since collecting data in an industrial situation will usually require the fastest possible methods, the preferred embodiment provides a way of finding the grain angle to an acceptable level of accuracy without the need to perform intensive image processing on the scatter ellipse 46, as is required by existing methods which for example best-fit an ellipse to the image formed in a camera. The use of a number of discrete photodetectors also allows analysis to be performed in at wavelengths in the infrared, beyond 1 lOOnm, the wavelength limit of the silicon detectors in CMOS and CCD arrays.

The apparatus and method described can be utilised in suitable end applications where obtaining grain angle of wood is required. The grain angle information may simply be displayed in some form, for example visually, to an end user. Alternatively, the captured information could be passed to another system for subsequent use. In a possible application, the apparatus 40, or a conventional camera scanner, can be adapted to scan over the entire surface of the wood under test. For example, it may be supported in a x-y axis scanning apparatus. Alternatively, the wood under test could be placed on a conveyancing bed that can be moved relative to the fixed apparatus 40 or camera. At each point on the surface, a scatter ellipse 46 is created using the incident laser beam 42, and the resulting scatter ellipse 46 analysed to provide grain angle information on the tracheid(s) in the vicinity of the spot 45. By scanning the surface, a map of tracheid parameters, over the surface is obtained, which can be later utilised to determine bulk characteristics of the wood specimen. For example, this map could be used to determine the wood specimen's propensity to twist during drying, as described later on.

In addition to determining grain angle in accordance with the preferred method and/or apparatus 40 according to the invention, optional adaptations can be employed to further obtain information relating to grain length and/or a measure of error in parameters determined using the apparatus. These adaptations of the preferred embodiment may be utilised in various end user applications, as required, to obtain characteristic information about wood that can be inferred or otherwise obtained from grain angle, grain length and/or error information.

For example, one further embodiment involves determining radial fall off of the intensity of a scatter ellipse, which is a parameter that can be used to infer these properties. In this embodiment, the apparatus 40 is adapted as shown in Figure 5 to include a second concentric ring of detectors at a greater radius than the first. To measure the intensity fall-off accurately requires the precise measurements of low intensities, and it has been found that unwanted reflections of the bright laser, particularly at the lens surfaces in Fig 4b limit what can be achieved. As shown in Figure 5, the laser beam is introduced into the optic axis of the lens 52 by a small angled mirror 53 attached to the lens 52 at its centre, so that the reduction in aperture is minimal. The narrow band filter 54 centred at the laser wavelength allows operation in ambient light. A light absorber 55 at the centre of the rings 51a, 51b suppresses reflection from the bright image of the spot centre, which could otherwise re-reflect from the interference filter or other surface back onto the photodiodes, washing out the desired information. The processor 43 is adapted to carry out the method of analysis of the intensity patterns detected by the concentric photodiode arrays 51a, 51b, to determine grain length and/or error information. For example, the processor can use the readings of the two concentric rings of photodiodes 51a, 51b to determine the fall off of intensity in a radial direction from the inner ring 51ato the outer ring 51b. A third or subsequent set of concentric rings could optionally added, to provide more information.

Each output is boosted by amplifiers with a time constant of 20microseconds,sufficient to resolve a distance of 0.2mm on a board moving at a high mill processing speed of lOm/s, and comfortably below the anticipated scatter ellipse size on the board of several millimeters. A multiplexer followed by an ADC sequentially samples the 30 detector channels, and the intensities from the two rings are processed by a discrete Fourier transform in a 20microseconds, and the amplitudes and phases needed are passed to a controlling PC or other processor. Though not optimised for speed, the total time of 40ms means that 25000 analysed images per second are available from relatively simple processing.

In the method of this embodiment, the constant term of the azimuthal Fourier series (corresponding to the average brightness around the detector arrays 51a, 51b) and the second harmonic are used to create a smoothed representation of the scatter ellipse. The light magnitude in the brightest direction is given by the sum of the constant term plus the amplitude of the second harmonic, and the direction of this maximum is given by 16 the phase of the second harmonic with respect to the reference direction of the diode rings. The brightness in the cross-grain direction is given by the constant term minus the second harmonic. The inner and outer detector rings give measurements that are independent of each other, and so provide a measure of confidence in the estimate of grain angle. It should be noted, however, that the above method could alternatively be performed with the apparatus 40 with just the single ring of photodetectors 47.

In addition to determining the direction of the tracheids in accordance with the above method, it has been found that a useful indication of the "eccentricity" of the brightness pattern comes from the ratio of maximum to minimum brightness. A smoothed value of this is given by the ratio: (Average +second harmonic amplitude)/( average -second harmonic amplitude) where average is the constant term of the Fourier series.

To distinguish this from the more conceptually simple eccentricities of ellipses of constant brightness such as those in Fig 3 a, a brightness eccentricity is defined as the above quantity minus one, i.e.

(Average + second harmonic)/(average-second harmonic) -1 This quantity is zero if the scatter pattern is circular, and increases progressively as the scatter becomes more elliptical or extended along the tracheids. The eccentricity of ellipse of constant brightness (based on the major-to-minor axis ratio) obtained using prior art methods is a poor indicator of the scatter shape. As the illumination intensity (or wood colour) changes, the position of this contour moves on the wood surface, and because of different attenuations along and across the grain, the eccentricity so defined will alter. The brightness eccentricity of the scatter according to this embodiment as defined earlier for the ring of photodetectors at a fixed radius is an improved descriptor (compared to prior art ellipse eccentricity) because it is illumination independent.

The ellipticity determined according to this embodiment gives an indication of the accuracy of grain angle measured using the apparatus 50. The grain angle measured from a more circular ellipse is likely to be less accurate than that measured from a more eccentric ellipse. The eccentricity also gives a relative indicator of fibre length, wherein the more eccentric an ellipse is, the long the grain in that region is. To some extent, the ellipticity is also a descriptor of the fibres, since it is independent of the laser, and similarly compensates for reflectivity changes on the wood surface. The brightness eccentricity is radius dependent, because the intensity is falling off differently in the along-grain and perpendicular directions. It should be noted that the ellipticity measures found as described above, could also be found using the apparatus 40 with just the single circular array of detectors 47.

While the he photodetectors 51a, 51b illustrated in Figure 5 are discrete detectors, with suitable adjustment of the optical magnification, they could be pixels of fixed coordinates in a solid-state camera or photodiodes within a custom chip, though in the latter cases the laser 41 could never be concentrically mounted, and its beam would need to be injected to the viewing axis via a mirror.

Information independent of the intensity, to provide an absolute measures of fibre length, may be obtained from the fall-off in intensity in accordance with another embodiment of the invention. Fibre length information can be subsequently used to indicate the pulp type a wood chip will produce, estimate the MoE to be expected from sawn timber, or provide some other measure that may indicate a propensity for the wood specimen to distort, for example warp.

An apparatus 60 for obtaining intensity fall off data that demonstrates the method is shown Figure 6. The detector array 61 here comprises photodiodes pre-aligned along the major and minor axes of the scatter ellipse. It measures the intensity along the major and minor axes, and determines the attenuation in intensity along each axis as the distance from the light source increase. By the use of collimators 63, each detector views an area of about 100 microns diameter on the wood surface 64 to enable the processor 62 to record the scatter intensities 65 in orthogonal directions.

Over a small range, this intensity fall-off is approximately exponential along major 22 and minor axes 24, and this defines two characteristic lengths, Xmajor and A,mjnor. This is the distance over which the intensity falls by e. The fibres can be classified by these lengths which are independent of illumination intensity. After calibration, the major axis 22 characteristic length will provide an approximate measure of fibre length. The ratio of attenuation distance along the major 22 and minor 24 axes is approximately constant for a particular location and describes the effect of the wood on the light, i.e. it defines the scatter in orthogonal directions, and may also be calibrated to indicate fibre length. The same principles apply to wet or dry wood, but calibration values will be different for each state.

Over a wide range of intensity, the simple exponential fall-off is seen to be an approximation. The characteristic length increases with distance from the illumination point because, superimposed on the attenuation law is the geometric effect of the energy spreading from a point. Despite this, the logarithmic intensity along the minor axis 24 remains a constant fraction of that along the major axis. Hence, if the characteristic lengths of the major 22 and minor 24 axes for the simple exponential fall off over a limited intensity range have a ratio R, then the nonlinear decay over a wide range of intensity along the minor axis can be still be obtained by multiplying the major axis distance scale by R.

Figure 7a illustrates the extent of the scatter created from the apparatus 60 when sensitive detectors 61 are used. The intensity of the scatter 65 from a laser spot on dry wood 64 is tracked along the major 22 and minor axes 24 of the scattering ellipse by the processor 62 using the output of the array 61. The wood sample has an MOE of 13GPa and is therefore of long fibre type. Figure 7a shows that the light fell in a systematic way by more than four orders of magnitude (the values shown are natural logarithms of intensity) over a length of 15mm from the spot centre in the grain direction. In the transverse directions, the fall is much faster. Over any decade of intensity, the light falls approximately exponentially. The non-linearity is revisited later in connection with multiwavelength analysis. It will be apparent that with calibration of the sensitivity of a solid state camera of wide dynamic range, data such as that of Figure 7a, collected by apparatus 60, could be collected from the pixels along major and minor axes, and the camera apparatus adapted to scan a board, as described previously.

The data shown in Figure 7a obtained by the apparatus in Figure 6 illustrate the nature of radial intensity fall attenuation. While a solid state camera, or the apparatus of Figure 60 could be used to obtain intensity fall off in accordance with the invention, these are not preferable approaches due to the intensive processing required. Using the relationship identified, the applicants have developed an apparatus that requires less intensive processing to obtain a measure of grain length from intensity fall off. The apparatus 50 of Figure 5 is preferably used to carry out the above method of obtaining and processing radial attenuation information to produce a measure of localised absolute fibre length. The radial attenuation of intensity can be determined from the intensity measured by each set of concentric photodiodes 51a, 51b. With two or more concentric rings of detectors, the spatial fall-off in intensity can be estimated by combining their information. As described, each ring provides values of maximum and minimum intensity at a known radii, the two maxima being in the along-grain direction, and the two minima in the cross-grain direction. If the fall-off between the rings is assumed to be exponential, values of the characteristic lengths, Xmajor and Xminor. Can be readily calculated for the two directions using the known intensity drop off and the distance between the rings.

Two sets of concentric photodiodes 51a, 51b can provide a sufficient measure of intensity attenuation, although the apparatus can be adapted to include further sets of concentric rings to provide a better measure of intensity fall off. Alternatively, as previously noted, a CMOS camera or similar could capture the radial intensity attenuation, and the information processed in accordance with the preferred method to obtain a measure of absolute fibre length. Either the entire CMOS array could capture intensity information, or more preferably, concentric rings of pixels in a CMOS camera can be used to obtain constant radius intensity profiles. Using concentric rings to capture information is more preferable, due to the lesser amount of data processing required. This improves overall speed in industrial applications.

Therefore the method of the invention for characterising the material is carried out by determining an intensity attenuation distance of the scatter ellipse 65, along the major 22 and minor 24 axes. This is correlated with tracheid length to provide an absolute measure. This measure is independent of the intensity factors noted above. When intensity data are available from, for example, a linear response CMOS camera of limited dynamic range, the description of the scatter along the major and minor axes is by an intensity-independent wood parameter, the logarithmic decay constant. This is shown in Figure 7b. The scatter intensities along and perpendicular to the major axis of the ellipse are given by: I = Ioexp(-x/81) and I = Ioexp(-x/41) The lengths 81 and 41 pixels define characteristic lengths A, over which the intensity falls by e. From a knowledge of the camera magnification, these dimensions can be converted to absolute fibre length in millimeters. Similar relationships can be determined for other measures of intensity drop off in other specimens, as required.

The longer the tracheids, the greater the characteristic attenuation length will be along the major axis 22. Since the intensity falls approximately exponentially along both major 22 and minor 24 axes, the two decay curves can be overlayed by scaling one axis by the ratio of the scale lengths. This ratio (e.g. A,maj0Aminor) describes the shape of the scatter pattern 46, independent of illumination intensity. This contrasts with the use of ellipse eccentricity in existing techniques which use a camera to define an ellipse of constant intensity. In the case of the data in Figure 7b, the ratio of major to minor axes of the scatter ellipse changes from 1.5 to 1.7 as the illumination threshold defining the ellipse is lowered. The scatter characteristics therefore are not uniquely defined by a function of the axes ratio, such as the mathematical ellipticity. The method of using intensity decay lengths, and their ratio, according to the present invention, provides an improved description of tracheid length. The description of the scatter in terms of the decay length ratio will enable a fibre length predictor to be measured, since this ratio will be related to fibre length for a particular species. In this embodiment of the invention, when using conventional camera array detectors, the required intensity measurements of the scatter ellipse along the major 22 and minor 24 axes are obtained. If the apparatus 60 is used to measure intensity about circles of two or more fixed radii, decay lengths can be calculated as previously outlined. The processor 52 in the apparatus 50 utilises this information to determine the absolute tracheid length according to the method of the invention. The apparatus 50 can scan the entire wood specimen, as previously described, to build a map of tracheid length.

In summary, the preferred description of the scatter is in terms of characteristic attenuation distances □ along and perpendicular to the grain, which are illumination dependent and characteristic of the wood. Such lengths are obtainable from convention camera-type equipment, or more preferably equipment using multiple rings of detectors A knowledge of the system magnification allows these lengths to be expressed in millimetres. For a given timber species, the characteristic length along the grain, or the ratio of the length, can be calibrated against actual fibre length. A simpler descriptor of the scatter, which is also illumination dependent, comes from the brightness eccentricity defined around a detector ring of fixed radius. This value increases with fibre length, so giving relative fibre length information when a board is scanned. The major axis of a contour of constant brightness, or an eccentricity defined by brightness contours gives relative fibre length, but is the least attractive because it is illumination-dependent.

The apparatus and method described can be utilised in suitable end applications where obtaining grain angle, fibre length (relative or absolute) and/or scatter eccentricity of wood is required. The grain angle, grain length and/or scatter eccentricity information may simply be displayed in some form, for example visually, for an end user. The length of the scatter, that is the length of the major axis 22 of the scatter ellipse 46, will be of the order of a tracheid. Tracheid length is related to the length of the major axis 22 of the scatter ellipse 46. Alternatively, the captured information could be passed to another system for subsequent use. In a possible application, the apparatus 50, 60 or a camera, can be adapted to scan over the entire surface of the wood under test. For example, it may be supported in a x-y axis scanning apparatus. Alternatively, the wood under test could be placed on a conveyancing bed that can be moved relative to the fixed apparatus 50 or camera. At each point on the surface, a scatter ellipse is created using the incident laser beam, and the resulting scatter ellipse analysed to provide grain angle, grain length and/or eccentricity information on the tracheid(s) in the vicinity of the spot. By scanning the surface, a map of tracheid parameters, over the surface is obtained, which can be later utilised to determine bulk characteristics of the wood specimen. For example, this map could be used to determine the wood specimen's MoE and/or propensity to warp during drying, as described later on.

In a further embodiment, a method and apparatus are utilised to assist in distinguishing compression wood from normal wood. In this embodiment measurements are obtained from multiple scatter ellipses, each created using incident light of a different wavelength. In non-compression wood, the ratio R will vary with fibre length, but it is reasonably independent of wavelength. In compression wood, the ratio R becomes wavelength dependent. Multiwavelength measurements can be used to extract not only a fibre length, for example whether it is short or long, but whether it is merely a short fibre, or it is a short fibre of compression wood.

For this embodiment of the invention, the multiple ring apparatus 50 shown in Figure 5, or alternatively a camera scatter apparatus, is adapted to provide incident laser beams of different wavelengths. For example, multiple laser sources can be used. For each point on the surface of the specimen, a scatter ellipse is generated using a particular incident wavelength and then the scatter parameters determined. This process is repeated several times in the same spot using different incident wavelengths. The apparatus is scanned in the usual way over the entire specimen to build a map of the tracheids characteristics, each tracheid characteristic being determined using multiple measurements in one spot. The multiple measurements in one spot provide information that can be used to distinguish good wood from compression wood.

More particularly, the tracheids of compression wood do not transmit light well due to the smooth inner wall of the tracheid being creviced to varying degrees with helical 23 cracks between bundles of microfibrils at a pitch of about a micron. Such crevices are visible with optical microscopes. If the tracheids are acting as light guides, their transmission must be impaired for light of wavelength comparable to this pitch, but the walls will still seem smooth to much longer waves. Since visible and NIR radiation spans the range of approximately 0.5 to 2 microns, wavelength-dependent effects should be expected in this range which might assist classification of the fibre type.

In one implementation of the invention, scatter intensity measurements were made at wavelengths of 670, 830 and 1300nm of long-fibre wood and severe compression wood, using the point scanning apparatus 50. Measurements were made across both semi-minor axes of the ellipse, and along one semi-major axis. Figure 8 shows the logarithmic light decay from the illumination point on long-fibre wood at 670nm. The minor axes data are virtually identical. By scaling the major axis co-ordinates by a factor R equal to 0.35, the data for both axes have been made to overlay. Alternatively, since a measure of "goodness" is a long fibre, the inverse of R would give a parameter which related to the eccentricity of the scatter.

This is the counterpart of the approximately exponential attenuation on each axis noted earlier (see Figure 7b). In that case also, an adjustment of the scale length of one axis would bring the two scatter directions into registration. It is convenient that the same effect holds over the wide intensity range covered here even though the true fall-off is not exponential. The scale factor adjustments R were found to be relatively insensitive to wavelength for normal wood. On compression wood, the same type of axis scaling was possible, but now the scale factor was wavelength dependent (Table III): Table III Wavelength, nm Axis scale factor R, normal wood Axis scale factor R, comp wood A 670 0.32 l\ 0.88 I* 830 0.35 ' .0j 0.65 1300 0.4 ■/ W 0.6 \I 24 The scale factor R in the Table III above loosely describes the eccentricity of the scatter. It varies little with wavelength for good wood. The scatter ellipse at 670nm for example is slightly more elongated than that at 1300nm, because its long axis scale must be reduced more to register with the cross-axis intensities. Compression wood produces 5 marked changes. All scale factors are closer to one (the scattering is less elliptical than before), but now the effect is much more marked at the short wavelength. This is the dependence which was anticipated due to the micron-scale irregularities in the walls of the compression wood tracheids.

This Table suggests a multiwavelength classification scheme. If the wood is normal, R will be wavelength independent, and its value will indicate fibre length. Values around 0.35 will indicate long fibres (since the test piece here is known to have long fibres), shorter fibres will have greater values corresponding to a smaller ellipticity of the scatter. However, if R is wavelength dependent, and greatest for the short wavelength, the wood must be suspected of being compression wood, not just short fibre wood.

UTILISING TRACHEID PARAMETERS In further embodiments of the invention, a map of one or more localized tracheid parameters over a wood specimen are obtained. The map can be used determine characteristics of the wood specimen. Scatter parameters may be derived from wet and very rough sawn timber.

For example, in another embodiment, the values of the parameters of the ellipse 46 are used, for example, the major axis 22 length, eccentricity or the brightness eccentricity, and their spatial changes, in algorithms to indicate defects such as knots or compression wood.

A map obtained in accordance with this further embodiment can be used to determine 30 large grain defects using measured grain orientation that may indicate other types of distortion occurring. A valuable use of grain orientation would be to scan sawn wood to eliminate pieces with large grain defects such as swirl, cross, or spiral grain before the drying process. These types of grain structure in a specimen of wood could lead to distortions occurring. For this, it is useful to have the dimensions of the scatter ellipse as well as its orientation, since the combined data enable a confidence to be attached to a measurement. For example, a sudden, apparently large grain angle change will have a big uncertainty if the ellipse eccentricity has suddenly fallen. But clues to the reasons 5 for the fall in eccentricity may be in the size of the ellipse. Severe compression wood for example may collapse the scatter ellipse to a small circle. To obtain a map of scatter ellipse dimensions and orientation, and apparatus as shown in Figure 5 could be used.

Figure 9 shows grain angle orientation measured in accordance with this embodiment of the invention over a matrix of points, 2cm apart on a piece of 100x50mm wet timber. This information can be used to determine defects in accordance with the method of the invention. The size of the lines represents the eccentricity of an ellipse of constant intensity measured with a CMOS camera, and since the minor axis scatter is fairly constant, this eccentricity broadly represents relative fibre length. Two sides 91, 93 and the face 92 of the sample 94 are shown.

This board 90 has been inspected for grain swirls, defined by a consistent change in grain angle over more than two spots, with the angle change between lower and upper limits; knots, defined a region of large grain angle changes and low eccentricity; and resin or pith areas, defined by patches of unusually big scatter. Abnormal scatter areas, where there is a sudden localised change, not supported by neighbouring measurements, are also detected. Other classification schemes, for example to detect extended regions where the average grain direction differs significantly from the board axis, are clearly possible.

On the face of the board, an area of swirling grain 135 (marked by thickened vectors) is detected; close by, on a side face, the grain angles change rapidly, and the scatter length falls. This is obviously the knot associated with the grain swirls on the face. The large 30 face swirl may be a reason to reject the piece because it could cause an abrupt bend in the piece after drying.

In one further embodiment, a grain angle scanning apparatus is used to obtain a map of localized grain angles, over one or more faces of a wood specimen. Preferably, a grain angle apparatus such as that shown in Figures 4a, 4b or 5 is used. Alternatively, the map could be obtained using an existing technique, which utilises a CMOS camera and additional componentry that find a best -fit ellipse to the scatter pattern, and determine the grain angle from the orientation of the ellipse. A map of grain angle obtained on two faces of a specimen can be used to obtain the average grain angle difference between the faces, and its persistence along the length of the board. This information can be used as an indicator of the likelihood of the board twisting when it is dried. To approach twist prediction using tracheid scatter, the wood sample is measured from a pair of faces using an apparatus such as that shown Figures 4a, 4b and 4c, to produce a tracheid orientation map. The map can be represented as shown in Figure 10. The data would most advantageously be collected by an apparatus which scanned the grain angle along opposite faces simultaneously, immediately the wood exits a saw, with samples acquired at perhaps 20mm intervals. Since twist is a bulk property, the existence of a difference in orientation in the average grain direction between opposite faces is physically a good test of twist likelihood. Tests conducted show that this difference in angle on the 50mm faces of 100x50 timber correlated with twist.

The results are listed in Table II, which shows that the two samples with grain angle differences which exceed 10 degrees twisted badly when dried, whereas the samples with differences below 5 degrees scarcely twisted. Twist is generally most apparent when the pith is boxed as shown in Figure 10 and the grain directions on opposite faces are clearly spiral. However, the important observation in Table II is that a difference in average grain angle across the piece is a warning of a possible twist. The greater the persistence of the difference along a board, the greater the danger of twist occurring. A suitable indicator could be the total accumulated grain difference along a sample, or equivalently, the average difference over a unit length. 27 TABLE II sample Average grain difference, deg Twist per 600mm, deg CI 2.5 <0.5 C2 11.7 4.5 C4 2.4 <0.5 C6 13.4 3.2 C7 4.5 <0.5 Although the dive angle can be found close to the edges of a board using the scatter orientation on adjacent faces (since the true orientation of the tracheids is the vector sum of those orientations) the average grain direction difference of the entire opposite faces is a better parameter for twist prediction.

Separate detectors could be used to view opposite edges of a board, or angled mirrors 10 may be used in a multi-spot system which projects spots onto the face a board and reflects at least one spot onto each of the adjacent side faces.

It should be appreciated that obtaining a map of grain angles could be carried out using an existing apparatus, and the information used in accordance with this embodiment of the invention to determine twist propensity.

Maps of major axis 22 length of a scatter intensity contour or the brightness eccentricity derived from a detector circle show relative changes in MoE, MFA and/or other tracheid characteristics that can be used in wood stability prediction, such as determining the propensity to warp. Either, these predictions can relate to warp occurring upon drying of wet wood, or warp of dry wood. The maps could be used anywhere a saw cut is opened, for example across the face of a cant, or in timber sawn from a log or cant.

Dry Wood 25 In another embodiment of the invention a method is provided in which relative or absolute fibre lengths are utilised to determine various characteristics of a wood specimen. Whether or not an absolute fibre length is extracted from optical scatter, knowledge of relative or absolute changes in fibre length (relative or absolute) over the surface of a specimen provides usable information. For example, using this method provides a map of relative fibre length changes over the specimen, that in turn enables relative changes in MoE to be predicted, or changes in MFA to be identified, both of which might indicate the possibility of distortion occurring during drying.

Figures 11a to lid show a section of a log cut from pith to bark and intersecting the centre of a branch stub or knot. More particularly, Figure 11a shows a sample of wood with a knot, Figure 1 lb shows the grain angle around the knot, and Figures 11c and lid show the sample scanned on a grid of 5mm using the apparatus of Figure 5. The brightness eccentricity at each grid point has been plotted as a gray scale, with black represent low eccentricity, i.e. no preferred scatter direction, or short fibre. The pith was intersected at the lower right, and appears as a black line. Away from the knot, the brightness eccentricity increases outwards to the bark. An contour of broadly constant brightness eccentricity is shown, with lighter shades (longer fibres) above, and darker shades (shorter fibres) below it. This contour closely follows an annual ring (not shown) The brightness eccentricity is mirroring the well-known increase in fibre length with age. Boards cut from this log would contain mixed fibre lengths, and hence mixed MFA, and be expected to show differential shrinkage and hence distortion upon drying. The amount of distortion to be expected could be calibrated by correlating brightness eccentricity gradients with subsequent distortion in test pieces.

Figure 12 shows data taken from a dried piece of timber, which over a distance of 90mm, progressed from pith to 14 year-old wood. The MoE 120 of small sticks 9mm by 11mm, and 343mm long was measured acoustically and compared with tracheid scatter measurements, measured in pixels out to an arbitrary intensity level, 30mm from one end of the sticks. The MoE increases from 6 to 16GPa moving outwards from the pith, while the major axis scatter 121 length (defined here by the distance taken to fall to 29 a particular level) increased from 20 to 28 pixels (approximately 2 to 3 mm actual length since 1 pixel here equaled 1 OOmicrometres.).

The correlation between scatter length in pixels and MOE is given by: Scatter Length = 0.795MOE + 15.8 R2 =0.93 Since the minor axis length was a near constant 16 pixels, the MOE here is approximately proportional to the difference in scatter along major and minor axes. 10 Slightly better correlation was obtained between scatter length and MOE/density, which is a surrogate indicator for MFA. Fig 12 also shows the brightness eccentricity measurements for the same sample, recorded with the apparatus of Figure 5. They also correlate well with MoE, which in turn is known to correlate with fibre length. Either scatter length or brightness eccentricity is therefore shown to correlate with MOE, and 15 by inference with fibre length.

Optical surface-scanning a timber sample can therefore yield spatial maps of a parameter which correlates with sonic speed (since sonic speed and MoE are closely related), but which is a more direct indicator of fibre length, and thus the MFA which is 20 ultimately implicated in the shrinking process during timber drying. The knowledge of shrinkage potential can be used to determine distortion propensity. The sonic maps described in US Patents 6,305,224, and 6,308,571 could be replaced by relative optical scatter length plots produced in accordance this embodiment.

Wet Wood The relative tracheid length method according to the invention works on rough sawn wet wood as well as for dry or planed dry wood. The scatter is usually slightly greater both along and across the grain in wet wood, and although rough surfaces introduce 30 random elements, an ellipse orientation is apparent. The larger penetration in the almost translucent fresh-sawn wood tends to compensate for the roughness of the sawing. Figure 13 shows examples of scatter data (in the form of contours at two intensity levels) from the same piece of wood in a freshly sawn, wet state, and after drying.

Spots 1 and 9, are for sapwood (saturated in its wet state), while spot 8, is from very rough sawn core wood (near fibre saturation point in its wet state). The shape of the ellipse is altered, but a scatter ellipse can be defined as for dry wood. Any calibrations relating attenuation distances to fibre lengths will require calibration for the wet 5 condition.

The tracheid scatter lengths across a wet, freshly sawn cant are shown in Figure 14. The scatter major axis length 140 increases with distance from pith as it did for the dry sample in Figure 12, as would be expected since fibre length, MOE and sound speed all 10 should increase from pith to bark. Though the scatter data pass from drier corewood characteristic of radiata pine to saturated sapwood, no sudden change is seen in the scatter length which might indicate the passage through the quite abrupt moisture transition which occurs in this timber.

Early and latewood Though the colour of latewood is darker than early season wood, due to the thickened tracheid wall, measurement on radiata pine show that the ellipse scatter length is reduced by only about 10% in the direction of the major axis for latewood, and is almost 20 unchanged in the cross-grain direction.

Given the lack of extreme contrast between early and latewood scatter length, and the similar lack of contrast between the scatter from core and sapwood, there is no reason that relative scatter lengths could not be used to predict warp propensity on wood before 25 it is dried and planed. Useful data have been obtained on surfaces of extreme roughness.

Warp is one type of distortion that can occur during drying. In a particular embodiment of the invention, the propensity for wood to warp can be determined using a map of 30 fibre lengths. Warping occurs where the length of fibres in one area of the specimen is different to that in another. The long fibres have a low MFA and therefore shrink less than short fibres with a high MFA. This leads to different shrinkage rates over the 31 specimen, and a consequent warping. For example, as shown in Figure 15 a plank of wood 150 with long fibres 151 along the edge of one side, and shorter fibres 152 on the other edge, will cause the wood to bend laterally 153 during drying. This particular type of warp is called crook. The potential to warp in other planes can also be investigated in a similar manner.

The foregoing describes the invention and preferred embodiments thereof. Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated in the scope thereof. 32

Claims (60)

Claims

1. A method of determining one or more fibre properties of a wood specimen including the steps of: 5 a) shining a light beam on the surface of the specimen to create a light scatter pattern on a portion of the surface, b) measuring the intensity of the light scatter pattern around at least one substantially constant radius, and c) determining the one or more fibre properties from the intensity measured 10 around the at least one constant radius.

2. A method according to claim 1 wherein the step c) determining the one or more fibre properties from the intensity measured includes the step of determining the orientation of the major axis of the scatter pattern. 15

3. A method according to claim 2 wherein determining the orientation of the major axis includes the step of determining least one point of highest light intensity around the at least one constant radius. 20

4. A method according to claim 3 further including determining at least two points of highest light intensity around the at least one constant radius.

5. A method according to claim 4 wherein the points of highest light intensity around the constant radius are determined from one or more azimuthal Fourier 25 components of the intensity measured around the constant radius.

6. A method according to claim 5 wherein the points of highest intensity around the constant radius are determined from the phase of at least the second azimuthal harmonic. 30 33

7. A method according to claim 6 wherein the points of highest intensity around the constant radius are determined from one or more further harmonics and/or constant term. 5

8. A method according to claim 7 wherein the points of highest intensity are determined from the sum of the constant Fourier term and the second harmonic.

9. A method according to claim 4 wherein the light intensity is measured using light intensity detectors arranged in a circular array and the points of highest light 10 intensity are determined from the detectors.

10. A method according to claim 8 or 9 wherein a fibre property is grain angle, which is determined from the orientation of the major axis, which in turn is determined from the orientation of the highest intensity points. 15

11. A method according to claim 10 wherein the intensity of the light scatter pattern is measured around two or more substantially constant radii to provide an error measure.

12. A method according to claim 8 wherein the step d) determining the one or more 20 fibre properties from the measured intensity further includes the step of determining the orientation of the minor axis of the scatter pattern.

13. A method according to claim 12 wherein the step of determining the orientation of the minor axis includes determining the difference between the constant term and the 25 second harmonic.

14. A method according to claim 13 further including determining a measure of eccentricity of the scatter pattern from: 30 (Constant term + Second Harmonic)/(Constant Term - Second Harmonic) 34

15. A method according to claim 14 further including determining a measure of eccentricity of the scatter pattern from: (Constant term + Second Harmonic)/(Constant Term - Second Harmonic) -1

16. A method according to claim 14 or 15 wherein a fibre property is grain angle, which is determined from the orientation of the major axis, which in turn is determined from the orientation of the highest intensity points, and the measure of eccentricity provides a measure of accuracy in the determined grain angle.

17. A method according to claim 14 or 15 wherein a fibre property is grain length, which is determined from the measure of eccentricity.

18. A method according to claim 17 wherein the intensity of the light scatter pattern is measured around two or more substantially constant radii.

19. A method according to claim 10 wherein the intensity of the light scatter pattern is measured around two or more substantially constant radii, and determining the one or more fibre properties from the intensity around the two or more constant radii further includes determining a measure of radial attenuation of light intensity.

20. A method according to claim 19 wherein another fibre property is grain length, the measure of radial attenuation of light intensity along the major and minor axes of the scatter pattern is determined, and fibre length is determined from the ratio of the rate of exponential attenuation of light intensity with respect to distance along the major and minor axes respectively.

21. A method according to claim 1 wherein a fibre property is grain angle, and further including obtaining a map of grain angles over two or more surfaces of the wood specimen, determining the change in grain angle over the surfaces, and determining the propensity for the wood to twist from the change in grain angle. 35

22. A method according to claim 21 wherein a fibre property is grain length, and further including obtaining a map of grain lengths over one or more surfaces of the wood specimen, determining the change in grain length over the surfaces, and determining the propensity for the wood specimen to warp from the change in grain length.

23. A method according to claim 21 wherein a fibre property is grain length, and further including obtaining a map of grain lengths over one or more surfaces of the wood specimen, determining the grain length over the surfaces, and determining the MoE of the wood specimen.

24. A method according to claim 19 wherein the intensity of the light scatter pattern is measured around two or more substantially constant radii a plurality of times, each time using a different wavelength of light, and further including the step of determining whether the wood specimen is compression wood from the measure of attenuation at different wavelengths.

25. An apparatus for determining one or more fibre properties of a wood specimen including: a light source to produce a light scatter pattern on the specimen surface, an intensity detector array arranged to measure the intensity of the light scatter pattern around at least one substantially constant radius, and a processor connected to the detector array to receive the light intensity measurements and determine the one or more fibre properties from the light intensity measurements.

26. An apparatus according to claim 25 wherein the intensity detector is one or more circular arrays of photodetectors.

27. An apparatus according to claim 25 wherein the intensity detector is a camera with one or more circular arrays of pixels utilized to measure the intensity of light scatter around one or more constant radii. 36

28. An apparatus according to claim 26 or 27 wherein the processor is adapted to determine the orientation of the major axis of the scatter pattern from the intensity measurements to determine the fibre property. 5

29. An apparatus according to claim 28 wherein to determine the orientation of the major axis, the processor is adapted to determine at least one point of highest light intensity around the at least one constant radius. 10

30. An apparatus according to claim 29 wherein the processor is adapted to determine at least two points of highest light intensity around the at least one constant radius.

31. An apparatus according to claim 30 wherein to determine the two points of 15 highest light intensity, the processor is adapted to determine one or more azimuthal Fourier components of the intensity measured around the constant radius.

32. An apparatus according to claim 31 wherein the processor is adapted to determine the phase of at least the second azimuthal harmonic to determine the two 20 points of highest light intensity.

33. An apparatus according claim 32 wherein the processor is further adapted to determine the points of highest intensity around the constant radius from one or more further harmonics and/or constant term. 25

34. An apparatus according to claim 33 wherein the processor is adapted to determine the sum of the constant Fourier term and the second harmonic to determine the two points of highest light intensity. 30

35. An apparatus according to claim 29 or 30 wherein the processor determines the major axis from the position of one or more detectors that measure the one or more points of highest light intensity. 37

36. An apparatus according to claim 34 or 35 wherein a fibre property is grain angle, and the processor is adapted to determine this from the orientation of the major axis, which in turn is determined from the orientation of the highest intensity points.

37. An apparatus according to claim 34 wherein the processor is further adapted to determine the orientation of the minor axis of the scatter pattern.

38. An apparatus according to claim 37 wherein the processor is adapted to determine the difference between the constant term and the second harmonic to determine the minor axis orientation.

39. An apparatus according to claim 38 wherein the processor is adapted is further adapted to determine a measure of eccentricity of the scatter pattern from: 15 (Constant term + Second Harmonic)/(Constant Term - Second Harmonic)

40. An apparatus according to claim 38 wherein the processor is further adapted to determine a measure of eccentricity of the scatter pattern from: (Constant term + Second Harmonic)/(Constant Term — Second Harmonic) -1

41. An apparatus according to claim 39 or 40 wherein a fibre property is grain angle, and the processor is adapted to determine this from the orientation of the major axis, which in turn is determined from the orientation of the highest intensity points, and the measure of eccentricity provides a measure of accuracy in the determined grain angle. 30

42. An apparatus according to claim 39 or 40 wherein a fibre property is grain length, and the processor is adapted to determine this from the measure of eccentricity. 38

43. An apparatus according to claim 36 wherein the intensity detector measures the light scatter pattern around two or more substantially constant radii, and the processor is adapted to determine the radial attenuation of light intensity. 5

44. An apparatus according to claim 43 wherein a fibre property is grain length, and the processor is adapted to determine the radial attenuation of light intensity along the major and minor axes of the scatter pattern and is further adapted to determine grain length from the ratio of the rate of exponential attenuation of light intensity with respect to distance along the major and minor axes respectively. 10

45. An apparatus according to claim 25 further including a conveyancing apparatus for a wood specimen to enable a map of fibre properties to be obtained of one or more surfaces of the wood specimen. 15

46. An apparatus according to claim 25 wherein the light source and intensity detector are connected to an xy scanner to enable a map of fibre properties of a wood specimen to be obtained of one or more surfaces of the wood specimen.

47 An apparatus according to claim 45 or 46 wherein a fibre property is grain angle 20 and a map of grain angles is obtained, and wherein the processor is adapted to determine the change in grain angle over the surfaces, and determine the propensity for the wood to twist from the change in grain angle.

48. An apparatus according to claim 47 wherein a fibre property is grain length and 25 a map of grain length is obtained, and wherein the processor is further adapted to determine the change in grain length over the surfaces, and determine the propensity for the wood specimen to warp from the change in grain length.

49. An apparatus according to claim 47 wherein a fibre property is grain length and 30 a map of grain length is obtained, and wherein the processor is further adapted to determine the grain length over the surfaces, and determine the MoE of the wood specimen from the grain length. 39

50. An apparatus according to claim 43 wherein the intensity detector measures the light scatter pattern around two or more substantially constant radii at a plurality of wavelengths, and the processor is adapted to determine whether the wood specimen is compression wood from the radial attenuation of light intensity at a plurality of wavelengths.

51. A method of determining grain orientation of a wood specimen including the steps of: a) shining a light beam on the surface of the specimen to create a light scatter pattern on a portion of the surface, b) measuring the intensity of the light scatter pattern around at least one substantially constant radius, c) determining the points of highest light intensity around the constant radius using a Fourier analysis, and d) determining grain orientation from the points of highest light intensity.

52. An apparatus for determining grain orientation of a wood specimen including: a light source to produce a light scatter pattern on the specimen surface, an intensity detector array arranged to measure the intensity of the light scatter pattern around at least one substantially constant radius, and a processor connected to the detector array to receive the light intensity measurements and adapted to determine the points of highest light intensity around the constant radius using a Fourier analysis, and determine grain orientation from the points of highest light intensity.

53. A method of determining one or more fibre properties of a wood specimen according to claim 1 and substantially as herein described with reference to any embodiment disclosed.

54. A method of determining one or more fibre properties of a wood specimen according to claim 1 and substantially as herein described with reference to any embodiment shown in the accompanying Figures 3a-l 5. - INTELLECTUAL PROPERTY OFHCE OF N.Z 2 5 MAY » RECEIVED 40

55. An apparatus for determining one or more fibre properties of a wood specimen according to claim 25 and substantially as herein described with reference to any embodiment disclosed. 5

56. An apparatus for determining one or more fibre properties of a wood specimen according to claim 25 and substantially as herein described with reference to any embodiment shown in the accompanying Figures 3a-15.

57. A method of determining grain orientation of a wood specimen according to 10 claim 51 and substantially as herein described with reference to any embodiment disclosed.

58. A method of determining grain orientation of a wood specimen according to claim 51 and substantially as herein described with reference to any embodiment shown 15 in the accompanying Figures 3 a-15.

59. An apparatus for determining grain orientation of a wood specimen according to claim 52 and substantially as herein described with reference to any embodiment disclosed.

60. An apparatus for determining grain orientation of a wood specimen according to claim 52 and substantially as herein described with reference to any embodiment shown in the accompanying Figures 3a-15. INTELLECTUAL PROPERTY OFRCE OF N.2 2 5 MAY 2004 RECEIVED