METHOD AND MACHINE FOR GRADING TIMBER ELEMENTS

Abstract: A method for testing stiffness and strength or stress grading timber elements (TE) comprises the steps of conveying timber elements (TE) sequentially to a test position on a grading machine, supporting each timber element (TE) in the test position on one edge at or near its ends, testing each timber element (TE) on edge, and grading the element based on the applied force or load and long span deflection. Embodiments of in-line and rotary grading machines for carrying out the test are disclosed.

Description: METHOD AND MACHINE FOR GRADLNG TIMBER ELEMENTS FIELD OF INVENTION The invention comprises a method and machine for stiffness, strength or stress grading structural timber BACKGROUND Stress grading techniques are important in measuring the strength and/or stiffness of structural and other timber Timber for structural applications, and other timber, is graded to strength/stiffness grades To ensure structural timber and glue-laminated beams meet minimum performance standards, the timber/beams must be non-destructively tested for strength and/or stiffness Modulus of elasticity (MoE) is used as a measure of the stiffness of structural timber, and also re-manufactured timber such as glue-lammated beams The timber elements are stiffness graded on the basis of their measured MoE In general the timber elements are graded conservatively However the more representative the grading MoE is, the greater is the accuracy in predicting the actual strength and stiffness of the element This increased accuracy may result in more timber being graded into higher structural grades, so that the return to the manufacturer is increased Another important measurement is Modulus of Rupture (MoR) The modulus of rupture is measure of strength and is determined by a test where a load is applied to an element and the load is increased until the element ruptures Performing a MoR test on an element can provide an approximate strength guide for other elements from the same batch Current mechanical grading approaches involve taking a number of measurements of stiffness over the length of the timber element on its side, and averaging these to produce an average MoE (MoEp aVerage ), or determining the lowest stiffness section of the element to produce an minimum MoE (MoEp mm ), based on which the element is graded Structural grading systems have also used visual tests with grain gradient and knots contributing to a lower grading of the board. SUMMARY OF LNVENTION It is the object of the present invention to provide an improved or at least alternative method and apparatus for stiffness, strength or stress grading structural timber. In broad terms in one aspect the invention comprises a method for testing and stiffness, strength or stress grading timber elements comprising the steps of: conveying timber elements sequentially to test position on a grading machine, supporting each timber element in said test position on one edge at or near its ends, testing each timber element while in said test position by applying to an opposite edge of the element intermediate of the length of the element a predetermined force or load and assessing the resulting long span deflection of the element, or by applying to an opposite edge of the element intermediate of the length of the element a the force or load required to deflect the element a predetermined amount and assessing the required force or load, and grading the element based on the applied force or load and long span deflection. In one form the method may comprise applying a predetermined force or load and measuring the resulting long span deflection of the element and also applying at least one further force or load to the element of a different such as a higher magnitude and assessing the resulting deflection, and grading the element based on both or all of the resulting deflections. In another form the method may comprise applying a force or load sufficient to deflect the element a predetermined amount and assessing the required force or load, and also applying at least one further force or load sufficient to deflect the element by a second and different predetermined amount and assessing the required force or load, and grading the element based on both or all required forces or loads. In broad terms in another aspect the invention comprises an automatic machine for testing and stiffness, strength or stress grading timber elements comprising: conveying means for conveying timber elements sequentially to and from a test position of said machine, element support means for supporting each element under test in said test position at or near either end of the element and on its edge, force applying means for applying force or load to an opposite edge of an element in said test position intermediate of the length of the element, means for assessing either the resulting deflection of an element under test from a predetermined force or load, or for assessing the force or load required to deflect the element by a predetermined amount, and grade calculation means arranged to grade the timber element based on the applied force or load and deflection of the element. In one form the machine is arranged to apply a predetermined force or load and assess the resulting deflection of an element under test, and to also apply at least one further force or load to the element of a different magnitude while the element remains in said test position and assess the resulting deflection, and to grade the timber element based on both or all of the resulting deflections. In another form the machine is arranged to apply a force or load sufficient to deflect an element under test a predetermined amount and assess the required force or load, and to also apply at least one further force or load sufficient to deflect the element by a second and different predetermined amount and assess the required force, and to grade the timber element based on both or all required forces or loads. In a rotary form of the machine said means to support each element under test on its edge may comprise pairs of indexed element holding means spaced about a common axis of rotation extending longitudinally of the machine, one of each pair of indexed holding means being positioned on either side of said force applying means along a longitudinal axis of the machine. The pairs of indexed element holding means may comprise pairs of openings shaped to receive the timber elements, one in each of two wheels mounted to a central shaft or shafts extending longitudinally of the machine. The machine comprises a drive system arranged to rotate the pairs of indexed holding means together in steps during operation of the machine. Each timber element presented to the machine is received into a pair of indexed holding means, is rotated to said test position by a rotational step or steps of the machine, and is carried from said test position after testing of a further rotation step or steps of the machine. In an in-line form of the machine the machine may comprise a table extending longitudinally of the machine and including end support means provided one at or near either end of said table and arranged to raise each timber element received by the machine on the table to said test position by elevating each timber element above the table. The table may include or be composed of a number of driven rollers. In either form of the machine the force applying means typically comprises a ram carrying a load head for contacting a timber element under test. Means to assess force or load may comprise one or more load cells. BRIEF DESCRIPTION OF THE DRAWINGS Preferred forms of machine and the method of the invention are further described with reference to the accompanying drawings, by way of example and without intending to be limiting, wherein: Figure 1 is a diagram schematically illustrating the grading method of the invention in principle, Figure 2 is a side view of one form of in-line single point loading grading machine of the invention, Figure 3 is an end view of the machine of Figure 2 in the direction of arrow A in Figure 2. Figure 4 is a side view of a grading machine which is generally similar to that of Figures 2 and 3 but which is an in-line two point loading grading machine, Figure 5 is a perspective view of a rotary two point loading grading machine of the invention, Figure 6 is a side view of the machine of Figure 5, Figure 7 is a view of one of the element support wheels of the grading machine of Figures 5 and 6, Figure 8 is a schematic view end-on of a conveyor arrangement for conveying timber elements to and from a grading machine of the type of Figures 5 to 1 , Figure 9 is a schematic view from above of the input conveying means to another of grading machine of the invention, Figure 10 is a side view of the grading machine of Figure 9, Figure 11 schematically illustrates the principle of operation of a further grading machine of the invention from one side relative to the directional material flow, Figure 12 is a schematic view of the grading machine of Figure 11 from above, Figure 13 is a flow chart of the operation of a grading machine and method of the invention. Figures 14A and 14B are graphs of bending stiffness in GPa for a batch of timber elements graded according to the long span MoEj grading method of the invention and for timber graded by a conventional MoEpmin grading method, and Figures 14C and 14D are graphs of bending strength in MPa for a batch of timber elements graded using the long span MoEj method of the invention and for timber graded by a conventional MoEpmin method. DETAILED DESCRIPTION OF PREFERRED FORMS As referred to previously, commonly timber elements are machine graded by taking a number of measurements of stiffness over the length of the timber element on its side (as a plank), averaging these, and grading the timber element based on the average of the measurements, (the MoE paver age basis), or by determining the lowest stiffness section of the element then grading the element based on the stiffness assessment of this lowest stiffness section (the MoEpmin basis). Typically the timber elements pass lengthwise through the grading machine as it is tested at a number of points over its length. In the grading method of the invention each timber element is graded by taking a single measurement of the stiffness of the element, taken when the element is supported in long span (as a joist) at or near either end of the element, and by applying a test force or forces to the element intermediate of the length of the element without moving the element lengthwise, and the element is graded based on this single point measurement(s), taken while the element is supported on its edge, rather than by taking a number of measurements of stiffness over the length of the timber element, and typically on its side. The method of the invention grades the element based on long span deflection and load, and we refer to the method of the invention as the LMoEj method. Each timber element is moved into a test position, is tested without being moved significantly longitudinally during testing, or without the point or points at which load is applied moving along the length of the element. Load is applied to the element in the test position at a single point or multiple points simultaneously, intermediate of the length of the element which is supported at or near its ends. The LMoEj grading may be based on force or load and deflection at a single a deflection point, or the element may be deflected with a first predetermined force or load and the amount of deflection assessed and then deflected with a second predetermined force or load and the second deflection amount assessed for example. Referring to Figure 1, force or load F is applied to a timber element intermediate of its length, with the timber element supported at or near its either end at points S. During testing the timber element is supported on its edge, as a joist. As referred to previously, a predetermined force or load may be applied and the resulting amount of deflection d of the timber element assessed, or a force or load required to deflect the element by a predetermined deflection amount d applied and the required force or load measured. The timber element is graded based on the measured long span deflection and force or load. Figures 2 and 3 show an in-line single point loading grading machine of the invention. The machine comprises a base 1 which supports a number of rollers 2 extending across the longitudinal axis of the machine as shown. The rollers form a table. A suitable conveyor delivers timber elements to be graded to the machine one by one in-line end first and on their edge, to one end of the machine in the direction of arrow B in Figure 2, and on to the roller table. In Figure 2 a timber element TE is shown in broken lines on the machine in the test position. At either end of the roller table the machine comprises hydraulic rams 3. Each ram carries means which will contact the bottom edge of timber element TE under test, and in the preferred form each ram carries a transversely extending roller 4. The rams 3 are arranged to raise the timber element TE to an elevated test position above the roller table. In Figure 2 the rollers 4 carried by rams 3 are shown elevated in broken lines and the timber element TE is shown in the test position. The position of the rams 3 is adjustable longitudinally of as indicated by arrows C in Figure 2. Typically timber elements will be graded in batches of similar length elements, and at set up of the machine before beginning grading of a batch the position of the support rams 3 is adjusted so that the end support rams will be positioned appropriately for the batch length. The rams 3 are suitably mounted for adjustable sliding movement along the length of frame members 5 forming part of the base of the machine. A force or load applying ram 6 is mounted above the roller table as shown, on frame 7. The force applying ram 6 carries a single point load head 8 which will contact the upper edge of the timber element TE under test, which is supported as a joist on the machine. Ram 6 moves load head 8 in the direction of arrow D in Figure 2 In use timber elements are conveyed to the machine The elements approach the machine end first in line (one element after another) Each element received by the machine is carried by the driven rollers 2 onto the machine until it is generally centred on the machine. The rams 3 then operate to elevate the timber element standing on its edge, to the test position shown The ram 6 moves the load head 8 towards the timber element to contact the upper edge of the timber element and deflect the timber element Either a predetermined force or load may be applied by the ram 6 and the resulting deflection of the timber element measured, or the force or load required to deflect the timber element by a predetermined amount applied and the required force or load measured A single measurement may be taken by for example applying a force and measuring the resulting deflection of the timber element, and the element graded based on the single measurement, or alternatively two or more measurements may be taken by applying a first predetermined force and measuring the resulting deflection and then applying for example a second higher force and measuring the resulting deflection, and the timber element graded based on both measurements Alternatively the higher force may be applied first and the lower force second for example Grading may be based on the three or more deflections caused by three or more predetermined forces or loads applied Instead of applying a predetermined force or forces and measuring deflection, the timber element may be caused to deflect to one or more different positions and the required force(s) measured A control system controls the drive to the roller table 2, and actuation of the element support rams 3 and load applying ram 6 The amount of deflection of the timber element under test may be measured by means associated with the ram to measure the stroke of the ram, or alternatively by an electronic beam or machine vision system for example, and force may be measured by one or more load cells associated with the load head 8 for example, or any other suitable form of load transducer(s) Figure 4 shows an in-line grading machine which is similar to that of Figures 2 and 3 except that the load head of the machine of Figure 4 is a two point load head Ram 6 carries beam 9 which m turn carries rollers 10 by which load is applied to the upper edge of the element under test at two points between the ends of the element, simultaneously Figures 5, 6 and 7 show a rotary two point loading grading machine of the invention In this machine main cross member 1 1 which extends longitudinally of the machine mounts force or load applying ram 6 which carries beam 9 by which force is applied to a timber element TE under test at two points via rollers or other suitable contact points 10 at either end of beam 9 (see Figure 6) The position of the rollers 10 along the length of beam 9 may be adjustable A shaft or shafts 12 is/are mounted on a base 13 of the machine and extends longitudinally of the machine The shaft 12 is journalled and bearings in bearing housings 14 mounted on uprights 15 and lateral frame parts 16 as shown Two "wheels" 17 are carried by shaft(s) 12, one on either side of the machine as shown Each of the wheels 17 comprises a number of openings 18 or slots shaped to receive the timber elements, around the periphery of the wheels as particularly shown in Figure 7 The wheels are indexed together on the shaft 12 so that the slots 18 about the peripheries of the wheels form pairs of indexed element holding means spaced about a common axis of rotation extending longitudinally of the machine A suitable drive system is arranged to drive rotation of the shaft 12 and wheels 17 so that they rotate in steps Timber elements TE may be delivered to the machine and conveyed from the machine after grading as schematically shown in Figure 8 Conveyor 19 delivers timber elements one at a time into empty slots or openings in the wheels 17 In each step a timber element is received by the machine and entered into a pair of slots and a graded element is dropped onto conveyor 20 which conveys the graded timber elements away from the grading machine Each rotational steps brings a timber element into the test position beneath the ram 6 and beam 9, which while the element is stationary descends and deflects the element to test and grade the element Again a predetermined force or forces may be applied and the resulting deflection or deflections of the element measured, or the element may be caused to deflect by a predetermined amount or amounts and the force or forces required measured, and a grading given to the element under test. Each pair of openings or slots, one in each of the wheels 17, forms a pair of indexed element holding means. It is not necessary that the exact arrangement shown in the drawings be used and alternatively for example the "wheels" could be formed by spokes radiating from a centre hub with each spoke comprising an opening or other means arranged to hold a timber element. The position of the wheels 17 is adjustable longitudinally along the shaft 12 in the direction of arrows E for different batch lengths. The drive system arranged to rotate the shaft 12 and wheels 17 may comprise an hydraulic or electric stepper motor for example. The machine shown in the drawings is a two point loading machine but alternatively a rotary machine of the type described may apply force or load to elements under test at a single point. Figures 9 and 10 schematically show the configuration of a further form of grading machine of the invention, capable of grading elements of a variety of lengths which are fed to the machine. Figure 9 shows four timber elements TE1, TE2, TE3, and TE4 each of a different length on an input conveyor to the machine, comprised of a number of parallel conveyor chains as shown. The elements may be supported on their edge by for example lugs on the conveyor chains which push the timber elements. The timber elements are justified to one side (the left hand side of Figures 9 and 10) and span different lengths. The conveyor chains 94, 95, 96 and 97 are provided at slightly different heights. Shorter elements such as TE1 and TE2 are supported by chains 95 and 96 at one end (all elements are supported by chain 94 at the justified end), while longer elements such as TE3 and TE4 are supported by chain 97. Chains 95 and 96 are lower than chains 94 and 97, to prevent them from interfering with deflection of the longer elements TE3 and TE4 when a load is applied. The spacing of chains 95, 96 and 97 may be adjustable relative to the reference chain 94. Load rams 97, 98 and 99 provide a force at a distance substantially halfway between each chain 95, 96 and 97 and the reference chain 94. The position of the load rams may be adjusted when the chain spacing is adjusted. Load cells and sensors are associated with each ram to deflect the deflection of the timber elements on the test. In use elements of a variety of lengths can be fed on edge to the grading machine. The elements are justified on one side and each element is supported by the chain appropriate to its length at its other end. The machine senses which of chains 95, 96 and 97 supports any particular element and operates the appropriate load ram to test that element. When the element is beneath the load ram the chain conveyor stops and the load ram applies a force to the element and measures the resulting deflection (or vice versa). Figures 1 1 and 12 schematically show the configuration of another form of grading machine of the invention. Timber elements TE are conveyed in the direction of arrow G in the figures, beneath load applying rails 100 which cause the elements to deflect as the elements pass underneath the rails, as shown. As the timber elements pass beneath load rails 100 they are deflected by a predetermined amount and pass below load cells 101, and as the elements continue they are deflected by a further amount and pass below load cells 102. The load applied by each timber element to the load cells is measured and the timber elements are graded based on the known deflection and measured load. Figure 13 is a flow chart showing the basic operational steps of a grading machine of the invention which grades timber elements by applying two different loads while testing each element and assessing the resulting deflections, in a LMoEj test. At setup for a particular batch of sawn timber the timber dimensions are input into the machine, and any physical adjustments to the machine are made to set the machine up for the batch dimensions. The input timber dimensions include the cross-sectional dimensions of the timber pieces eg 100 mm x 50 mm or 200 mm x 50 mm, as well as the approximate length of the timber elements. The machine calculates the loads to be applied and the appropriate operational speed of the load applying ram. During testing of each element the load ram moves down continuously past three load set points LI, L2, and L3. At each of load points LI and L2 the measured deflection valve is supplied to a microprocessor or programmed logic controller which controls operation of the machine. The long span modulus of elasticity is calculated based on the measured deflections, and each timber element is assigned a grading, which may be marked on to the element using an automated system such as a spray paint or dye applicator for example. Figures 14A and 14B are graphs of bending stiffness in GPa for timber graded according to the long span LMoEj grading method of the invention and a conventional MoEpmin grading method. Figures 14C and 14D are graphs of bending strength in MPa for timber graded using the LMoEj method of the invention and a conventional MoEpmin method. It can be seen that the LMoEj grading method of the invention produces higher quality results than the conventional MoE pmm grading method. The results in Figure 14A show a considerably better fit (and correspondingly higher regression value) than those of Figure 14B. The same is also true of the bending strength gradings of Figures 14C and 14D where the bending strength grading of the invention performs better than conventional bending strength grading. The foregoing describes the grading method, and forms of grading machine, of the invention Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated within the scope hereof as defined in the accompanying claims.

Claims: 1. A method for testing and stiffness, strength or stress grading timber elements comprising the steps of: conveying timber elements sequentially to test position on a grading machine, supporting each timber element in said test position on one edge at or near its ends, testing each timber element while in said test position by applying to an opposite edge of the element intermediate of the length of the element a predetermined force or load and assessing the resulting long span deflection of the element, or by applying to an opposite edge of the element intermediate of the length of the element a the force or load required to deflect the element a predetermined amount and assessing the required force or load, and grading the element based on the applied force or load and long span deflection. 2. A method according to claim 1 comprising applying a predetermined force or load and measuring the resulting long span deflection of the element and also including applying at least one further force or load to the element of a different magnitude and assessing the resulting deflection, and grading the element based on both or all of the resulting deflections. 3. A method according to claim 2 wherein said further force or load or at least one said further force or load has a higher magnitude. 4. A method according to claim 1 comprising applying a force or load sufficient to deflect the element a predetermined amount and assessing the required force or load, and also including applying at least one further force or load sufficient to deflect the element by a second and different predetermined amount and assessing the required force or load, and grading the element based on both or all required forces or loads. 5. An automatic machine for testing and stiffness, strength or stress grading timber elements comprising * conveying means for conveying timber elements sequentially to and from a test position of said machine, element support means for supporting each element under test in said test position at or near either end of the element and on its edge, force applying means for applying force or load to an opposite edge of an element in said test position intermediate of the length of the element, means for assessing either the resulting deflection of an element under test from a predetermined force or load, or for assessing the force or load required to deflect the element by a predetermined amount, and grade calculation means arranged to grade the timber element based on the applied force or load and deflection of the element. 6. A machine according to claim 5 arranged to apply a predetermined force or load and assess the resulting deflection of an element under test, and to also apply at least one further force or load to the element of a different magnitude while the element remains in said test position and assess the resulting deflection, and to grade the timber element based on both or all of the resulting deflections. 7. A machine according to claim 5 arranged to apply a force or load sufficient to deflect an element under test a predetermined amount and assess the required force or load, and to also apply at least one further force or load sufficient to deflect the element by a second and different predetermined amount and assess the required force, and to grade the timber element based on both or all required forces or loads 8. A machine according to any one of claims 5 to 7 wherein said means to support each element under test on its edge comprises pairs of indexed element holding means spaced about a common axis of rotation extending longitudinally of the machine, one of each pair of indexed holding means being positioned on either side of said force applying means along a longitudinal axis of the machine, and wherein the machine comprises a drive system arranged to rotate the pairs of indexed holding means together about said common axis in steps during operation of the machine, whereby each timber element presented to the machine is received into a pair of indexed holding means, is rotated to said test position by a rotational step or steps of the machine, and is carried from said test position after testing of a further rotation step or steps of the machine. 9. A machine according to claim 8 wherein said pairs of indexed element holding means comprise pairs of openings shaped to receive the timber elements, one in each of two wheels mounted to a central shaft or shafts extending longitudinally of the machine. 10. A machine according to any one of claims 5 to 7 wherein said conveying means is arranged to deliver the timber elements one by one in line end first to said test position. 11. A machine as claimed in claim 10 wherein said conveying means is arranged to deliver the timber elements one by one in line end first from said test position. 12. A machine according to claims 10 and 11 also comprising a table extending longitudinally of the machine and including end support means provided one at or near either end of said table and arranged to raise each timber element received by the machine on the table to said test position by elevating each timber element above the table. 13. A machine according to claim 12 wherein said table includes or is composed of a number of rollers extending transversely of a longitudinal axis of the machine. 14. A machine according to either one of claims 12 and 13 wherein the machine comprises a base which carries said table and to which are mounted said end support means for elevating the timber elements to said test position. 15. A machine as claimed in any one of claims 5 to 14 wherein said force applying means comprises a ram carrying a load head for contacting a timber element under test. 16. A machine according to claim 15 wherein said load head is arranged to contact a timber element under test at a single contact point. 17. A machine according to claim 15 wherein said load head is arranged to contact a timber element under test at two contact points 18. A machine according to any one of claims 14 to 17 including means associated with said ram to assess the deflection of an element under test by measuring the stroke of said ram during testing 19. A machine according to any one of claims 5 to 18 including means to assess force comprising one or more load cells 20. A machine according to any one of claims 15 to 19 wherein said ram is mounted above said test position 21. An automatic machine for testing and stress grading timber elements comprising: element support means for supporting each element under test in said test position at or near either end of the element and on its edge, comprising indexed element holding means spaced about a common axis of rotation extending longitudinally of the machine and on either side of said force applying means, a drive system arranged to rotate the indexed holding means together about said common axis in steps during operation of the machine, whereby each timber element presented to the machine is rotated to said test position by a rotational step or steps of the machine, and is carried from said test position after testing of a further rotation step or steps of the machine, force applying means for applying force or load to an opposite edge of an element in said test position intermediate of the length of the element, means for assessing either the resulting deflection of an element under test from a predetermined force or load, or for assessing the force or load required to deflect the element by a predetermined amount, and grade calculation means arranged to grade the timber element based on the applied force or load and deflection of the element. 22. An automatic machine for testing and stress grading timber elements comprising: a table extending longitudinally of the machine including a number of rollers extending transversely of a longitudinal axis of the machine, end support means provided one at or near either end of said table and arranged to raise each timber element received by the machine on its edge to a test position by elevating each timber element above the table, force applying means for applying force or load to an opposite edge of an element in said test position intermediate of the length of the element, means for assessing either the resulting deflection of an element under test from a predetermined force or load, or for assessing the force or load required to deflect the element by a predetermined amount, and grade calculation means arranged to grade the timber element based on the applied force or load and deflection of the element. 23. A method for stiffness, strength or stress grading timber elements comprising the steps of conveying elements to be graded sequentially to a grading machine, supporting each timber element on one edge at or near its ends and applying a force intermediate of the length of the element to the opposite edge and measuring the deflection of the element or measuring the load used to deflect the element a particular distance, determining a long span modulus of elasticity (LMoEj) from the deflection or load, and grading the element based on the LMoEj measurement. 24. An automated apparatus for stiffness, strength or stress grading structural timber elements comprising means for conveying the elements sequentially to and from a test bed arranged to receive each element, means to support the element on its edge at or near either end, means to apply force to the element intermediate of the length of the element, means to measure deflection of the element or means to measure the force used to deflect an element by a particular distance, and means to calculate a long span modulus of elasticity (LMoEj) from the deflection or load and grade the element.

Inventors: GAUNT DOUGLAS JOHN, GAUNT, DOUGLAS, JOHN
Applicants: GAUNT DOUGLAS JOHN, NEW ZEALAND FOREST RES INST LT, GAUNT, DOUGLAS, JOHN, NEW ZEALAND FOREST RESEARCH INSTITUTE LTD
Application year: 2000
Main classification: G01N3
IPC codes: B27M3, G01N3, G01N33