GB1591462A

GB1591462A - Grain slope measuring apparatus

Info

Publication number: GB1591462A
Application number: GB24723/77A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-06-24
Also published as: SE7806829L

Description

(54) IMPROVEMENTS IN OR RELATING TO GRAIN SLOPE MEASURING APPARATUS (71) We, THE PLESSEY COMPANY LIMITED, a British Company of Vicarage Lane, Ilford, Essex, 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: This invention relates to timber grain slope or timber grain slope angle indicating apparatus.

There is a requirement to determine the grain slope angle of sawn or planed timber with respect to a reference such as the edge of a board.

According to the present invention timber grain slope indicating apparatus comprises means for projecting a light spot on to a timber surface, scanning means for causing a path, described across the grain and spaced apart from the spot, to be scanned by detector means effective to detect light originating from the spot which passes through the tracheids of the timber to emerge on the said path, and for determining the position of a location along the path whereat the light emerging is of maximum intensity whereby the timber grain slope is indicated.

The light spot and an image reflected from the timber adjacent the spot and received by the detector means may be scanned synchronously by the scanning means.

The grain slope indicated may be expressed as an angle between a line which passes through the said point and the centre of the spot and a reference line such as the timber edge.

It will be appreciated that light travels most readily along and in line with the timber grain or tracheids and it will therefore be apparent that the line as just before mentioned which passes through the said point and the centre of the spot is parallel with the grain.

The means for detecting the location of the point on the path may comprise a pair of optical detectors arranged to receive light from two adjacent areas which are scanned along the path with the junction therebetween substantially oblique to the path, the grain direction being indicated in dependence upon the signals from the optical detectors. The location of the point may be identified and scan movement inhibited when the said point lies between the said areas such that both detectors receive substantially the same intensity of light.

Scan movement may be controlled in dependence upon signals from the detectors thereby to define a servo system in which the said point is maintained between the said areas whereby the detector outputs are constrained to be maintained both at the same level.

The detectors may be light detector diodes.

The means for projecting the light spot may comprise a laser and the means for scanning the path may comprise a glass block light deflector or the like via which the beam from the laser is passed to the surface of the timber, an image of the two areas on the timber surface adjacent the spot being focussed via a lens on to the pair of detectors whereby a curved path on the timber surface is scanned by the detectors consequent upon rotation of the glass block deflector.

The laser spot may be arranged to pass through the aperture in an apertured mirror to a further mirror and from the further mirror to the timber surface, light reflected from the timber surface being reflected from the further mirror to the apertured mirror and from the apertured mirror to a lens to be focussed by the lens on to the detectors of the.

pair.

The angle setting of the further mirror may be arranged to be adjustable whereby the grain on various parts of the timber may be examined.

Means may be provided for moving the timber with respect to the laser and for scanning the timber with the further mirror in a direction transverse to timber movement.

A reference cycle may be provided whereby the laser beam may be directed by means of the further mirror on to a reference sample for setting up purposes.

Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a generally schematic plan view of a timber board illuminated with a laser spot; Figure 2 is a graph showing light levels on the board in a circular path described around the spot of radius r; Figure 3 is a generally schematic diagram showing a light spot on the surface of a timber board and areas associated with the spot from which light is reflected to a pair of diode light detectors; Figure 4a is a generally schematic diagram of an optical arrangement including a laser for scanning a light spot in timber for grain slope angle determination purposes;; Figure 4b is a generally schematic diagram showing the manner in which the spot produced by the laser and the associated areas shown in Figure 3 are deflected across the timber surface; Figure 5 is a generally schematic diagram showing apparatus for scanning a spot across a surface of timber for grain direction determination purposes; and Figure 6 is a generally schematic block diagram showing a system for determining grain direction in sawn or planed timber.

In soft wood timber the grain direction is the direction in which the wood fibres or tracheids are oriented. There is a requirement for a device or apparatus which can measure the angle of inclination between the grain direction with respect to the cut edge of a board. This angle is designated herein as H and is described as the timber grain slope angle. In order to be compatible with timber handling machinery which is in use at present, it is necessary that the measuring apparatus should be capable of measurement on moving timber and that it should be a non-contact device.

Referring now to the drawings, Figure 1 shows the optical effect obtained when a laser beam strikes a timber surface of a board 1 normally to produce a spot 2 of about 1 millimetre in diameter on the board 1. Light from the spot passes along the tracheids of the timber and re-emerges from the timber surface. Light passing at right angles to the grain direction indicated by arrows 3 is attenuated rapidly as it passes through the tracheid cell walls. Light travelling along the direction of the grain however is attenuated very much less through a given distance from the centre of the laser beam spot 1. An area 4 extending longitudinally of the grain is therefore produced within which emerging light exceeds a predetermined intensity.

Figure 2 illustrates how 'the light level emerging from a point P on a circle of radius r varies with the angle + which is measured with respect to a line 5 which passes through the centre of the spot 2 orthogonally to the grain direction indicated by the arrows 3.

The maximum light level is found when P lies on a path 6 which passes through the centre of the spot parallel to the grain direction as indicated by the arrows 3. This maximum level drops if the scanning radius r is increased. The minimum light level is found when P lies on the line 5 which is perpendicular to the grain direction and which passes through the centre of the laser beam.

In order to determine the grain slope angle 8 the spot of light 2 is injected into the timber surface and as the point P moves around the circle of radius r centred on the light spot, the position of one of two points PM on the path 6 is detected where the light emerging is of maximum intensity. The positions whereat this maximum occurs depend upon three things, (1) the slope of grain, (2) condition of the timber surface i.e. surface roughness, and (3) local variations in the light transmission properties of the timber e.g. variations due to spring and summer-wood lines.

The absolute value of the emitted light intensity is dependent on timber defects such as rot, blue stain and compression wood which will alter the level of emitted light intensity but will not alter the position of the maximum. Defects such as knots and crossgrain will alter the position of the maximum since they are in themselves grain disturbances. The light at the point P can be used to produce an electrical signal which is a maximum at the points PM whereby the slope of grain angle is indicated.

The effects as just before mentioned, constitute a noise component which is added to the signal. If a measurement is taken at a single location, then the noise component may be of comparable size to the signal, and the noise component will of course vary in accordance with the character and quality of the timber. In order therefore to achieve a sufficiently accurate measurement a number of measurements are taken at different locations and an average result is obtained over the set of measurements which yields the true grain slope angle. The accuracy required determines the number of measurements which must be taken.

Figure 3 shows a means by which the points PM on the path 6 of maximum light level may be detected the aura in area 4 represents the distribution of light emitted from the timber above a predetermined intensity, and D1 and D2 are two detectors receiving light from shaded areas 7 and 8 respectively. Since the area 3 is symmetrical about the X axis, it follows that the light levels received by the detectors D1 and D2 are equal. Suppose now that the aura in the area 4 is rotated about the centre of the spot 2 the light received by the diodes D1 and D2 becomes progressively more unequal as the angle is increased.

Consider a board which has grain slope angle 0. Then the aura will be inclined at an angle 8 to the axis which is orthogonal to the board edge. If the detectors D1 and D2 are rotated about the centre of spot 2, their outputs will become equal only when their angle of rotation with respect to the board edge equals 0. It follows that the line forming the border between the diodes D1 and D2 then lies on the path 6 of maximum light level.

Furthermore the angle of rotation can be used as a direct indication of the grain slope angle and it will be appreciated that a servo system may be utilised wherein optical apparatus operatively associated with the diodes D1 and D2 may be constrained automatically to rotate to maintain equal signal outputs from the diodes.

Figure 4A shows a practical arrangement suitable for small angle measurements. The light source is a laser 9. An imaging lens 10 forms an image of the surface of timber 11 on detectors D1 and D2. A mirror 12 with a hole 1 2a in its surface through which laser beam 13 passes is used so that the laser beam falls in the centre of the light returning from the timber surface to the imaging lens 10.

This may be achieved in other ways as for example by deflecting the laser beam 13 with a small mirror positioned on the axis of the imaging lens 10 or by passing the laser beam through the imaging lens. A deflector mirror 14 synchronously deflects the laser beam 13 and light 15 returning from the timber. The purpose of this deflector mirror 14 is to allow the arrangement to take many measurements at different points on the timber surface as the mirror 14 is rotated. This mirror 14 effects a scan nominally at right angles to the grain of the timber the motion of the timber itself is in a longitudinal direction roughly parallel to the grain and this guarantees that each discrete measurement of the grain slope is made at a different location on the timber surface and thus the condition required so that averaging can reduce the effect of surface noise to an acceptable level is obtained.

A rotatable glass block deflector 16 is provided which operates by refraction at the air/glass, glass/air boundaries. As it is rotated the laser beam is deflected laterally.

For small deflections this has to a first order the same effect as rotating D1 and D2 around the laser beam in the direction of arrows A; the arrows B indicating the direction of movement produced by the deflector mirror 14 (see Figure 4b). A glass block deflector rotation mechanism (not shown) may form part of a servo loop which balances when the outputs from D1 and D2 are equal the drive which must be applied to- the glass block deflection mechanism for balance is then a measure of the grain slope angle 8. In practice the deflection mechanism operatively associated with the glass block may comprise a simple galvonometer movement which deflects in proportion to the signal applied to it.Alternatively, the angle through which the glass block deflector has rotated may be measured by some other means and used to compute the grain slope angle.

Figure 5 shows an arrangement which may be used for more accurate measurements of large grain slope angles. The optical path is similar to that of Figure 4 except that the glass block deflector 16 of Figure 4 is removed and replaced by a beam rotator which is positioned as shown. The beam rotator consists of a plane mirror 17 mounted obliquely on a drive shaft 1 7a which is operated by drive mechanism 17b. Since both the laser beam 13 and the detected light are reflected from this mirror, their spacing on the timber surface remain the same as the drive shaft is rotated. The result achieved is therefore that a relative circular movement between the laser beam and the image detector is produced from the timber surface and the effect is to rotate both the laser beam and the detectors D1 and D2 about a common centre point.The result is then substantially the same as rotating D1 and D2 about the laser beam and scanning the whole along the X axis longitudinally of the timber in line with the grain. There is also a coich has the same light transmission properties as a piece of straight grain timber. It is possible by means of applying a suitable drive to the reflector mirror 14 to cause the laser beam to fall on this reference. The reference piece 18 is arranged so that its grain is parallel to the board edge. Its purpose is to act as a check on the zero reading of the grain slope measuring device. By repetitively deflecting the laser beam on to the reference piece 18 any error in the zero measurement may be detected and eliminated.

Referring now to Figure 6 a block diagram is shown of a system for determining the grain direction on a piece of timber 19. The apparatus comprises a laser 20, a beam vibrator and deflector 21 and a beam rotator 22 via which light from the laser is passed to the surface of the timber 19. The beam rotator corresponds with the glass block deflector 16 shown in Figure 4a or the mirror 17 shown in Figure 5 and serves for scanning the laser spot under the control of a feedback signal as will hereinafter be explained. The beam vib rator and deflector 21 is utilised for scanning the spot across the timber surface and for deflecting the spot on to a reference sample 23 for setting-up purposes.During setting-up conditions light rom the laser 20 is suitably deflected by the beam vibrator and deflector 21 so that it passes through the beam rotator 22 and follows the path indicated by the broken line 24 to the reference sample 23.

During measurement conditions light reflected from the timber passes to a detector unit 25 including detector diodes D1 and D2.

Signals from the diodes D1 and D2 are passed via lines 26 and 27 to a gating circuit 28 through which they normally pass to a comparator 29. If however one or other of the signals on the lines 26, 27 falls below a predetermined threshold level a gating signal is applied on line 30 to operate the gate 28 so that signals are not fed to the comparator 29.

Signals are normally fed to the comparator 29 and the magnitude and sign of the output signal resulting on line 31 is determined in accordance with the magnitude of the signals on line 32 and 33. When the signals on lines 32 and 33 are of the same magnitude, then the output signal from the comparator on line 31 is zero whereas if the signal from diode D1 exceeds diode D2 then the output is positive say whereas if the signal from diode D2 exceeds diode D1 then the signal will be negative. The signal on line 31 is fed via a data memory 34 to the beam rotator 22.

The signal fed to the beam rotator 22 adjusts the angle of the beam and the beam rotator 22 is calibrated to afford a direct measurement of grain slope angle. This signal which is fed to the beam rotator 22 is fed also to an A to D converter 35 to provide an output signal on line 36 which is indicative of grain slope angle. When a gating signal is present on the line 30 this gating signal as well as being applied to the gate 28 is applied also to the data memory 34 and the signal level in the memory when the gating signal is applied is frozen and continuously thereafter applied to the beam rotator 22 until the gating signal is removed. The output signal on the line 31 is fed to the data memory 34 via a switch 37 which is operated by apparatus 38 which senses the presence of timber and assumes position A when timber is present.In the absence of timber, the switch is returned to a position B and under these conditions the signal for the beam rotator 22 is supplied by an offset memory device 39. The value of the signal in the offset memory device is determined by a setting-up procedure utilising the reference sample 23 and the value of the signal in the offset memory is determined in accordance with the result of the reference signal setting-up procedure whereby the signal provided from the offset memory ensures that the nominal zero position or normal position of the beam rotator 22 corresponds with a zero grain slope angle as provided on the reference piece 23.

WHAT WE CLAIM IS: 1. Timber grain slope indicating apparatus, comprising means for projecting a light spot on to a timber surface, scanning means for causing a path, described across the grain and spaced apart from the spot, to be scanned by detector means effective to detect light originating from the spot which passes through the tracheids of the timber to emerge on the said path, and for determining the position of a location along the path whereat the light emerging is of maximum intensity whereby the timber grain slope is indicated.

2. Timber grain slope indicating apparatus as claimed in claim 1, wherein the light spot and an image reflected from the timber adjacent the said spot and received by the detector means are scanned synchronously by the scanning means.

3. Apparatus as claimed in claim 1 or claim 2, wherein the grain slope is expressed as an angle between a line which passes through the said location and the centre of the spot and a reference line substantially parallel with the grain.

4. Apparatus as claimed in any one of the preceding claims wherein the detector means comprises a pair of optical detectors arranged to receive light from two adjacent areas which are scanned along the path, the grain direction being indicated in dependence upon the signals from the optical detectors.

5. Apparatus as claimed in claim 4 wherein the position of the location is identified and scan movement inhibited when the said location lies between the said areas such that both detectors receive substantially the same intensity of light from the spot.

6. Apparatus as claimed in claim 4 or claim 5 wherein scan movement is controlled in dependence upon signals from the detectors thereby to define a servo system in which the said location is maintained between the said areas whereby the detector outputs are constrained to be maintained both at the same level.

7. Apparatus as claimed in claim 4 claim 5 or claim 6 wherein the means for projecting the light spot comprises a laser, and the means for scanning the path comprises a glass block light deflector via which a beam from the laser is passed to the surface of the timber, an image of the two areas on the timber surface adjacent the spot being focussed via a lens on to the said pair of detectors whereby a curved path on the timber surface is scanned by the detectors consequent upon rotation of the glass block deflector.

8. Apparatus as claimed in claim 4 claim 5 claim 6 or claim 7 wherein the laser spot is arranged to pass through an aperture in an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. rator and deflector 21 is utilised for scanning the spot across the timber surface and for deflecting the spot on to a reference sample 23 for setting-up purposes. During setting-up conditions light rom the laser 20 is suitably deflected by the beam vibrator and deflector 21 so that it passes through the beam rotator 22 and follows the path indicated by the broken line 24 to the reference sample 23. During measurement conditions light reflected from the timber passes to a detector unit 25 including detector diodes D1 and D2. Signals from the diodes D1 and D2 are passed via lines 26 and 27 to a gating circuit 28 through which they normally pass to a comparator 29. If however one or other of the signals on the lines 26, 27 falls below a predetermined threshold level a gating signal is applied on line 30 to operate the gate 28 so that signals are not fed to the comparator 29. Signals are normally fed to the comparator 29 and the magnitude and sign of the output signal resulting on line 31 is determined in accordance with the magnitude of the signals on line 32 and 33. When the signals on lines 32 and 33 are of the same magnitude, then the output signal from the comparator on line 31 is zero whereas if the signal from diode D1 exceeds diode D2 then the output is positive say whereas if the signal from diode D2 exceeds diode D1 then the signal will be negative. The signal on line 31 is fed via a data memory 34 to the beam rotator 22. The signal fed to the beam rotator 22 adjusts the angle of the beam and the beam rotator 22 is calibrated to afford a direct measurement of grain slope angle. This signal which is fed to the beam rotator 22 is fed also to an A to D converter 35 to provide an output signal on line 36 which is indicative of grain slope angle. When a gating signal is present on the line 30 this gating signal as well as being applied to the gate 28 is applied also to the data memory 34 and the signal level in the memory when the gating signal is applied is frozen and continuously thereafter applied to the beam rotator 22 until the gating signal is removed. The output signal on the line 31 is fed to the data memory 34 via a switch 37 which is operated by apparatus 38 which senses the presence of timber and assumes position A when timber is present.In the absence of timber, the switch is returned to a position B and under these conditions the signal for the beam rotator 22 is supplied by an offset memory device 39. The value of the signal in the offset memory device is determined by a setting-up procedure utilising the reference sample 23 and the value of the signal in the offset memory is determined in accordance with the result of the reference signal setting-up procedure whereby the signal provided from the offset memory ensures that the nominal zero position or normal position of the beam rotator 22 corresponds with a zero grain slope angle as provided on the reference piece 23. WHAT WE CLAIM IS:

1. Timber grain slope indicating apparatus, comprising means for projecting a light spot on to a timber surface, scanning means for causing a path, described across the grain and spaced apart from the spot, to be scanned by detector means effective to detect light originating from the spot which passes through the tracheids of the timber to emerge on the said path, and for determining the position of a location along the path whereat the light emerging is of maximum intensity whereby the timber grain slope is indicated.

apertured mirror to a deflector mirror and from the deflector mirror to the timber surface, light reflected from the timber surface being reflected from the deflector mirror to the apertured mirror and from the apertured mirror to a lens to be focussed by the lens on to the detectors of the pair.

9. Apparatus as claimed in claim 8 wherein means are provided for moving the timber with respect to the laser and for scanning the timber with the said deflector mirror in a direction substantially transverse to timber movement.

10. Apparatus as claimed in claim 8 or claim 9 where a reference cycle is provided so that the laser beam can be directed by means of the deflector mirror on to a reference sample for setting purposes.

11. Apparatus as claimed in claim 1 and substantially as herein described with reference to figures 1, 2, 3 and 4 of the accompanying drawings.

12. Apparatus as claimed in claim 1 and substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

13. Apparatus as claimed in claim 1 and substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.