GB2043265A - Apparatus for determining the stiffness of timber and method of grading timber - Google Patents

Abstract

In order to measure its stiffness, an item of timber L has a known deflection imparted to it by means of an adjustably positionable roller 9 disposed between two pairs of rollers 1,2 and 3,4 and the load necessary to produce this deflection is detected by means of a load cell 12. The rollers 1, 3 have their axes fixed and act as datum rollers while the other rollers 2, 4 are mounted at the outer ends of two pivotally mounted arms 5 and 7 whose inner ends are engaged by common adjustable stop 11 and whose outer ends are urged towards rollers 1 and 3 by air actuators 17 and 18. The movable rollers 2, 4 are driven rollers so that even if the timber L is too stiff to be given the full deflection by the roller 9, it will still be passed through the machine. A device 22 is provided for marking the timber in dependence upon the detected load. <IMAGE>

Description

SPECIFICATION Apparatus for determining the stiffness of timber and method of grading timber The present invention relates to apparatus for determining the stiffness of timber, particularly but not exclusively, timber for structural use.

According to the present invention there is provided apparatus for determining the stiffness of timber comprising a first pair of rollers and a second pair of rollers, the rollers of each pair forming a respective nip and the nips lying in a common plane, the rollers all being rotatable about parallel axes, one roller of each pair, being that roller disposed to the same side of the common plane, being a datum roller and fixed in position, but rotatable about its axis, the other roller of each pair being movable against an adjustable resilient force away from the associated one roller of the pair, means for rotating at least one roller of each pair about its axis to feed a piece of timber through the nips, a deflecting roller mounted for rotation about an axis parallel to the axis of the first and second pairs of rollers, and disposed to the same side of the plane as the datum rollers and between the first pair of rollers and the second pair of rollers and positioned to deflect said piece of timber by a predetermined deflection towards the other side of the plane, and means for detecting the load necessary to produce such a deflection.

Preferably the datum roller of each pair is undriven while the other roller of each pair is driven via a flexible coupling. In this way, if the timber is too stiff to be urged into contact with the datum rollers, it will still be driven through the apparatus.

We also provide a method of grading timber comprising deflecting a span of the timber using the above apparatus and measuring the load required to be applied to the span of timber to produce the deflection of the timber. The timber may then be marked or otherwise processed, e.g. directed to different destinations, in dependence upon the measured load.

The invention will be further described with reference to the accompanying drawings in which the sole figure is a very schematic longitudinal plan view upon one embodiment of apparatus according to the present invention.

The apparatus shown in the Figure is intended to grade timber according to the load required to bend a span of timber by a predetermined, adjustable amount with the span of the timber being simply supported at its longitudinal centre.

The apparatus is in the form of a single bay comprising two pairs of rollers, 1,2 and 3,4 defining respective nips through which an item of timber is fed; the rollers 1-4 are all rotatable about parallel axes, the rollers 2 and 4 being driven via respective double-hookes couplings and the rollers 1 and 3 being undriven. The rollers 1,3 are of the same diameter, are undriven and are fixedly mounted to the machine frame 10 for rotation about axes which lie in a common vertical plane. The points on the peripheries of the rollers 1 and 3 closest the rollers 2, 4 thus define a parallel vertical plane. Halfway between the rollers 1 and 3 is also fixedly mounted a timber deflection roller 9 rotatable about an axis which is parallel to the axes of rollers 1 and 3 but located in front of the abovementioned common plane.Roller 9 is mounted on an arm 13 pivoted to the machine frame at 14 about an axis parallel to that of the rollers. The rotational position of the arm 13 is set by a handle wheel 15 which acts on the arm 13 via a load cell 12. The position of the roller 9 is thus adjustable to suit the timberto be graded. The point on the periphery of the roller 9 closest the timber feed path is located beyond the corresponding points on the rollers 1 and 3 so that the timber L passing through the machine in contact with the rollers 1,9 and 3 is deflected outwardly by roller 9 midway between the rollers 1 and 3.

The timber is urged into contact with the rollers 1 and 3 by the associated rollers 2 and 4which, in operation, are movable outwards (i.e. away from the associated rollers 1,3) against the action of an adjustable resilient force. The roller 2 is mounted at one end of an arm 5 which is pivoted.at 6 to the machine frame about an axis parallel to the axes of the rollers. The roller 4 is similarly supported on an arm 7 pivoted at 8 to the machine frame 10. The gap at each of the nips, in the absence of an item of timber, is adjustable. To this end, the arms 5 and 7 may rotate about the pivots 6 and 8 and be engaged by a horizontally adjustable stop 11 so that increasing the distance of this stop will increase the gaps at the nips between the rollers 1,2 and 3, 4.Resilient biases are applied to the rollers 2 and 4 e.g. by means of pneumatic actuators behind them, to hold the gaps at the nips to that defined by the position of the stop.

The machine is initially set to suit the cross section of timber to be graded as follows: 1. The openings between pinch rolls 1,2 and 3,4 are set to suit timber thickness by adjustment of hand wheel 6 which controls the position of stop 11.

2. The pinch pressure of rolls 2 and 4 is set by adjustment of an air pressure regulator supplying air to air actuators 17 and 18 which act on the arms 5 and 7 respectively.

3. The deflection to suit timber thickness set by adjustment of hand wheel 15.

4. Grade limits to suit species and cross section are entered into an associated computer (not shown) by thumb wheel switches via a hexadecimal chart and cross checked via binary lights and chart.

The machine is set to run continuously, its speed (preferably adjustable between 30-180 m/min) is set to suit the overall system conditions.

A positional encoder 19 directly coupled to the drive roll 2, is arranged to produce impulses corresponding to 1 Omm spacings along the timber. These impulses are fed to the computer which takes its load readings via load cell 12 every 10th impulse (i.e.

at 100mm intervals).

lust pass operation Timber L is fed to the machine from the right hand side between pinch rolls 1 and 2 which, with a relatively low pressure setting of air actuator 17, grip the timber and drive it into the machine. After a short time delay, to ensure that the timber is fully within the grip of rolls 1 and 2 air actuator 17 is switched to its high pressure setting.

The leading end of the timber is registered by photo-electric cell 21, which together with the 1 Omm impulses from the encoder 19 provides the datum point to ensure that the timber is fully within the high pressure grip of rolls 1, 2 and 3,4 when the computer registers its initial 1st pass load value.

1st pass load measurements are recorded every 100 mm along the length of timber until the trailing end passes photo-electric cell 20 when the computer will register its final load measurement and record the number of 10mm impulses to the end.

A 1st pass identification mark is sprayed onto the front end of the timber by sprays 22, this allowing correct orientation for the second pass.

2nd pass operation The timber L is turned over and returned to the infeed end of the machine. The same procedure takes place as for the 1 st pass. The leading end is registered by photo-electric cell 21, impulses are counted to the initial load measurement point. 1st and 2nd pass loads are averaged by the computer, this average load is compared to the grade limit loads and a colour code is sprayed onto the corresponding point on the timber. Thus the timber is grade colour coded every 100mm along its length. A final long spray mark is added to the end of the timber showing the grade for that piece.

Use of a two pass system obviates the need for a double bay arrangement for grading the timber for bending in both directions; a double bay arrangement poses the problem of avoiding interaction between the bays as regards the measurements.

The illustrated construction has an important advantage in that the movable rollers 2, 4 are the driven ones and are movable away from the associated rollers 1,3 against the action of a resilient force.

Pieces of timber with a high stiffness and a low breaking strength can break when bending to the full deflection set on the apparatus and indeed this is the case in prior art apparatuses where a fixed load or deflection is applied to the timber by the apparatus.

The present apparatus avoids this problem by virtue of the fact that the rollers 2 and 4 are movable outwards against the action of a resilient force. Thus when a piece of timber is stiffer than a predetermined value, the force with which the rollers 2,4 are urged inwardly is insufficient to cause the timber to be deflected into contact with the rollers 1 and 3. The deflection of the timber is thus reduced and so damage to it is avoided; the magnitude of the resilient force however is set beyond the level that results from deflecting timber of the highest grade the full amount. The timber still passes as the highest grade. That the rollers 2 and 4 are driven ensures that the timber is fed through the machine despite its not being in contact with the rollers 1 and 3.

The fact that the rollers 1 and 3 act on the same surface of the timber as the deflection roller 9 (by means of which the applied force is measured) means that a known deflection is applied to the timber, thus avoiding inaccurate measurements arising from variations in thickness ofthe timber.

Claims (10)

1. Apparatus for determining the stiffness of timber comprising a first pair of rollers and a second pair of rollers, the rollers of each pair forming a respective nip and the nips lying in a common plane, the rollers all being rotatable about parallel axes, one roller of each pair, being that roller disposed to the same side of the common plane, being a datum roller and fixed in position, but rotatable about its axis, the other roller of each pair being movable against an adjustable resilient force away from the associated one roller of the pair, means for rotating at least one roller of each pair about its axis to feed a piece of timber through the nips, a deflecting roller mounted for rotation about an axis parallel to the axis of the first and second pairs of rollers, and disposed to the same side of the plane as the datum rollers and between the first pair of rollers and the second pair of rollers and positioned to deflect said piece of timber by a predetermined deflection towards the other side of the plane, and means for detecting the load necessarvto produce such a deflection.

2. Apparatus according to Claim 1 wherein the datum rollers are undriven while the other roller of each pair is arranged to be driven via a flexible coupling.

3. Apparatus according to Claim 1 or 2 wherein the position of the deflecting roller is adjustable to vary the deflection imparted to the timber.

4. Apparatus according to any one of the preceding claims wherein the load detecting means is a load cell operatively associated with the deflecting roller.

5. Apparatus according to any one of the preceding claims wherein the other roller of each pair is mounted on a respective arm mounted for pivoting about an axis substantially parallel to those of the pairs of rollers, the respective arms extending towards one another and being engaged by a common, adjustable stop.

6. Apparatus according to any one of the preceding claims wherein means are provided for placing markings on the timber passing through the machine in dependence upon the detected load necessary to produce said deflection.

7. Apparatus for determining the stiffness of timber, such apparatus being constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. A method of grading timber comprising deflecting a span of the timber using apparatus according to any one of the preceding claims and measuring the load required to be applied to the span of timber to produce the deflection of the timber.

9. A method according to Claim 8 and including the step of marking, or otherwise processing, the timber in accordance with the measured load.

10. A method of grading timber substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.