WO2005078435A1

WO2005078435A1 - Method and system for determining the modulus of elasticity of green lumber

Info

Publication number: WO2005078435A1
Application number: PCT/NZ2005/000017
Authority: WO
Inventors: Gavin Wallace
Original assignee: Institute Of Geological & Nuclear Sciences Limited
Priority date: 2004-02-13
Filing date: 2005-02-14
Publication date: 2005-08-25

Abstract

The present invention comprises a method of determining the modulus of elasticity of green lumber comprising the steps of assessing the attenuation of gamma rays passing through at least two areas of the green lumber, assessing the thickness of the lumber, providing an impact on one end of the lumber, detecting vibrations in the lumber caused by the impact, assessing the length of the lumber, assessing the acoustic velocity of the lumber from the detected vibrations and the length of the lumber, determining the density of the lumber from the attenuation of the gamma rays and the thickness assessment of the lumber, and determining the modulus of elasticity of the lumber from the determined acoustic velocity and the density of the lumber.

Description

METHOD AND SYSTEM FOR DETERMINING THE MODULUS OF ELASTICITY OF GREEN LUMBER

FIELD OF INVENTION

The invention relates to a method and system for determining the modulus of elasticity in green lumber and in particular the determining the modulus of elasticity in green lumber using acoustics and gamma rays.

BACKGROUND

The strength of a piece of lumber defines the use to which it can be put within the building industry. It is of considerable benefit when processing lumber to define the potential end use at the earliest opportunity. In this way, unnecessary processing of inferior lumber can be avoided. The strength of lumber is proportional to its stiffness and the stiffness of lumber can be measured by its modulus of elasticity.

The dynamic modulus of elasticity of a piece of sawn lumber is defined as the product of the density of the lumber and the square of the velocity of an acoustic wave transmitted longitudinally within the lumber.

Many devices have been proposed that determine a modulus of elasticity or stiffness measurement or prediction for lumber in various stages. For example, one device uses an impact at one end of a cut log and a detector at the other to measure a longitudinal wave through the log. The acoustic velocity of the log is then determined from the detected wave and the modulus of elasticity estimated. Other devices use impacts and detectors such as accelerometers to detect acoustic velocities in wood at different stages in the drying process. These devices all use an estimate of the density of the lumber in the modulus of elasticity calculation. SUMMARY OF INVENTION

It is the object of the present invention to provide an improved or alternative device for measuring the modulus of elasticity of lumber.

In broad terms in one aspect the invention comprises a method of determining the modulus of elasticity of green lumber comprising the steps of assessing the attenuation of gamma rays passing through at least two areas of the green lumber, assessing the thickness of the lumber, providing an impact on one end of the lumber, detecting vibrations in the lumber caused by the impact, assessing the length of the lumber, assessing the acoustic velocity of the lumber from the detected vibrations and the length of the lumber, determining the density of the lumber from the attenuation of the gamma rays and the thickness assessment of the lumber, and determining the modulus of elasticity of the lumber from the determined acoustic velocity and the density of the lumber.

Preferably the thickness of the lumber is measured using laser beams.

Preferably the impact on the lumber is provided by a striking instrument such as a hammer.

Preferably the impact on the lumber is triggered by a device to detect the presence of lumber.

Preferably the presence of lumber is detected by the lumber breaking a light beam.

Preferably the vibrations in the lumber are detected with a microphone.

Preferably the vibrations in the lumber are detected at one end of the lumber.

Preferably the vibrations are digitally recorded and Fourier transformed to determine the resonant frequency of the vibrations in the lumber. Preferably the digitally recorded vibrations are filtered before being Fourier transformed.

Preferably the length of the lumber is measured using light. Alternatively the length of the lumber may be measured using mechanical means.

Preferably the method further includes the step of assessing the stress grading of the lumber from the modulus of elasticity and density.

Preferably the method further includes the step of assessing a drying regime for the lumber from the modulus of elasticity and density.

In broad terms in one aspect the invention comprises a method of determining the modulus of elasticity of green lumber conveyed on a conveyor system comprising the steps of assessing the attenuation of gamma rays passing through at least two areas of the green lumber passing between the gamma ray sources and detectors, assessing the thickness of the lumber as the lumber passes thickness assessment means, providing an impact on one end of the lumber, detecting vibrations in the lumber caused by the impact as the lumber passes a vibration detection means, assessing the length of the lumber as the lumber passes length detection means, assessing the acoustic velocity of the lumber from the detected vibrations and the length of the lumber, determining the density of the lumber from the attenuation of the gamma rays and the thickness assessment of the lumber, and determining the modulus of elasticity of the lumber from the determined acoustic velocity and the density of the lumber.

In broad terms in another aspect the invention comprises a system for determining the modulus of elasticity of green lumber comprising a gamma ray device arranged to pass gamma rays through at least two areas of the lumber and record the attenuation of the gamma rays passed through the lumber, means for assessing the thickness of the lumber, a striking device arranged to provide an impact on one end of the lumber, microphone means arranged to detect vibrations in the lumber caused by the impact on the lumber by the striking device, means for measuring the length of the lumber, computation means arranged to determine the acoustic velocity of the lumber from the vibrations detected by the microphone means and the means for measuring the length of the lumber, the computation means further arranged to determine the density of the lumber from the attenuation of the gamma rays and the thickness of the lumber, and the computation means further arranged to determine the modulus of elasticity form the acoustic velocity and the density of the lumber.

Preferably the means for assessing thickness of the lumber includes at least laser beam.

Preferably the striking device is a hammer.

Preferably the impact on the lumber by the striking device is triggered by a device to detect the presence of lumber.

Preferably the vibrations in the lumber are detected at one end of the lumber.

Preferably the vibrations are digitally recorded and Fourier transformed in the computation device to determine the resonant frequency of the vibrations in the lumber.

Preferably the digitally recorded vibrations are filtered in the computation device before being Fourier transformed.

Preferably the means for measuring the length of the lumber uses light. Alternatively the means for measuring the length of the lumber is by mechanical means.

Preferably the computation device also provides a stress grading of the lumber using the modulus of elasticity. Preferably the computation device further provides a drying regime for the lumber using the modulus of elasticity and the density.

In broad terms in another aspect the invention comprises a system for determining the modulus of elasticity of green lumber conveyed on a conveyor system comprising a gamma ray device arranged to pass gamma rays through at least two areas of the lumber and record the attenuation of the gamma rays passed through the lumber as the lumber passes between the gamma ray sources and detectors, thickness assessment means for assessing the thickness of the lumber as the lumber passes the thickness assessment means, a striking device arranged to provide an impact on one end of the lumber as the lumber passes the striking device, microphone means arranged to detect vibrations in the lumber caused by the impact on the lumber by the striking device as the lumber passes the microphone means, means for measuring the length of the lumber as the lumber passes the length measuring means, computation means arranged to determine the acoustic velocity of the lumber from the vibrations detected by the microphone means and the means for measuring the length of the lumber, the computation means further arranged to determine the density of the lumber from the attenuation of the gamma rays and the thickness of the lumber, and the computation means further arranged to determine the modulus of elasticity form the acoustic velocity and the density of the lumber.

BRIEF DESCIPTION OF DRAWINGS

The invention will be further described by way of example only and without intending to be limiting with reference to the following drawings, wherein: Figure 1 A shows the components used in the invention; Figure IB shows an embodiment of the invention on a production line; Figure 2 shows the densities of a number of samples repeated three times; Figure 3 A is a sound recording of vibrations in a sample of 100 x 50 mm lumber; Figure 3B is a sound recording of vibrations in a sample of 100 x 50 mm lumber; Figure 4A is a frequency spectrum of the sound recording of Figure 3 A; Figure 4B is a frequency spectrum of the sound recording of Figure 3B; Figure 5 A is a sound recording of vibrations in a sample; Figure 5B is a frequency spectrum of the sound recording of Figure 5 A; Figure 6 A is a sound recording of vibrations in a sample; and Figure 6B is a frequency spectrum of the sound recording of Figure 6A.

DETAILED DESCRIPTION

Figure 1 is a block diagram showing the components used to determine the modulus of elasticity in accordance with the invention. The components include a gamma ray device 2, thickness measuring device 3, microphone 4, computation device 5, length measuring device 5, striking device 6, lumber detector 7, and look up tables 8.

The dynamic modulus of elasticity of a piece of lumber is defined as the product of the density of the lumber and the square of the velocity of an acoustic wave within the lumber. The modulus of elasticity can be used to predict the strength of the green lumber after drying. By determining the modulus of elasticity of the green lumber before drying the lumber can be graded and processed as necessary for its final purpose. The green lumber is cut to its final size and then the modulus of elasticity is determined before the lumber is dried.

To determine the modulus of elasticity both the density of the lumber and the velocity of an acoustic wave within the lumber need to be determined.

The density of the lumber is determined using gamma ray device 2 and thickness measuring device 3. The lumber passes between a source of gamma rays and a gamma ray detector in the gamma ray device. As the lumber passes through the gamma ray device the gamma rays at the detector are measured. These gamma rays are attenuated by the lumber and the amount of attenuation is related to the amount of lumber being scanned. The thickness of the lumber is measured with thickness measuring device 3. In one embodiment laser beams are used to measure the thickness of the lumber. In other embodiments the thickness may be measured by other means, for example the thickness of the lumber may be measured mechanically.

The green density of the lumber can be calculated from: p_g = -[B + ]n(j-)/x]/A 1 where p_g is the green lumber density, A and B are constants, x is the thickness of the lumber, / is the intensity of the gamma rays after passing through the lumber and Io is the intensity of the gamma rays when no lumber is present. The constants are determined from calibrating the gamma ray device for the particular application. These constants vary with different gamma ray devices and for different applications.

Figure IB shows an embodiment of the invention on a production line. In this embodiment lumber moves along a conveyor belt system 11 in the direction of arrow 19. An example of lumber is shown by board 12. The lumber passing along the conveyor belt system may comprise lumber of differing lengths and cross sections.

As the lumber moves along the conveyor system 11 it passes a plurality of detectors 13 and 14 that provide a nominal length indication. In Figure IB the detectors are photocells. In the embodiment shown in Figure IB five photocells and associated detectors are used to provide an indication of the nominal length of the lumber. However, any suitable number of photocells may be used; for example, in some applications seven photocells may be used.

Thickness detector 16 detects the thickness of lumber on the conveyor system. A lumber detector detects the presence of lumber on the conveyor system. Any suitable device may be used to detect the presence of lumber on the conveyor system. For example, a microswitch may be used to detect the presence of lumber on the conveyor system. A shaft encoder 15 may be used to record the relative movement of the board to determine width of the board and relation to density measurement. The shaft encoder is used to correlate density and sound measurements.

Once the lumber is detected the lumber detector provides a signal to the striking device 17. Typically the signal will be an electrical signal. Upon receipt of the signal the striking device 17 strikes one end of the lumber. In one embodiment the striking device is a hammer. In other embodiment any blunt instrument may be used. The action of striking the lumber sets up an acoustic wave within the lumber. In preferred embodiments the signal to the striking device 17 is provided so that the striking device strikes each piece of lumber in the same relative place. For example, the signal from the lumber detector may be timed so that the striking device 17 always strikes the lumber at one edge of the lumber.

In preferred embodiments information from the length detectors and thickness detector may be processed to provide a force parameter to the striking device. This allows the force of the striking device to be varied and different force impacts to be provided to lumber of different weights. This overcomes the problem of the striking device providing a force to the lumber that shifts the lumber on the conveyor system 11.

Microphone 18 is used to detect the acoustic wave within the lumber. In preferred embodiments microphone 18 is positioned at one end of the lumber. This end may be either the end with the striker or the end opposite the striker. As the lumber moves past the microphone on the conveyor system the microphone detects any acoustic waves in the lumber. In preferred embodiments the microphone records acoustic waves from the lumber for a plurality of vibrations within the lumber. For example, microphone 18 may be adapted to record for 50 ms for each piece of lumber. The acoustic wave detected by the microphone 18 is then converted to a digital signal. The conversion into a digital signal may take place at either the microphone 18 or the computation device 20.

It should be noted that the arrangement of the apparatus shown in Figure IB is one embodiment only and is not intended to be limiting. This embodiment illustrates the use of the invention in an on-the-line application where measurements are preformed as the lumber moves along a conveyor system. In this embodiment the lumber is not stopped at any stage of the process. For example in an on-the-line system the lumber may pass the striker etc at a rate of one hundred and twenty boards per minute or even faster. The invention is arranged to work at the speed of the conveyor where the speed of the conveyor is set by other requirements in the lumber processing plant.

Figure IB does not show an arrangement of gamma ray sources and detectors. The gamma ray sources and detectors could be positioned at any suitable location along the conveyor system. The gamma ray sources and detectors could be positioned either before or after the impact and microphone means.

In a more general embodiment, referring back to Figure 1 A, the acoustic velocity in the lumber is measured using the microphone 4, striking device 6 and length measuring device 5. Striking device 6 is used to provide an impact on one end of the lumber. The presence of the lumber within the range of the striking device is detected by lumber detection means 7. The lumber detection means may be any detector that can detect the presence of the lumber. In one embodiment the lumber detector is a light source and light detector where lumber between the source and detector is detected by the lack of light at the light detector. In other embodiments different lumber detectors can be used. For example, the presence of lumber could be detected by a microswitch.

Figure 2 shows the consistency of the density measurement over one hundred pieces of lumber. Each piece of lumber was scanned three times and the density of each run was plotted against the mean density. As can be seen from Figure 2 the density measurements are consistent over a number of runs.

In use several beams of gamma rays may be used to measure the gamma ray attenuation of the lumber. An average density is then calculated for the lumber and used to represent the piece of lumber. In preferred embodiment a plurality of gamma ray sources and detectors are positioned so that lumber passes between at least two pairs of sources and detectors. For example, in a preferred embodiment four pairs of gamma ray sources and detectors are spaced about a conveyor system so that each piece of lumber passes between at least two pairs of gamma ray sources and detectors and the longer pieces of lumber pass between all the pairs of gamma ray sources and detectors. Either the sources are above the conveyor system and the detectors are below or the sources are below the conveyor system and the detectors are above.

In alternative embodiments the attenuation of gamma rays through the lumber may be combined with a continuous thickness measurement of the lumber to produce an average density. Alternatively again the attenuation of gamma rays through the lumber may be measured in a single place on the lumber and combined with either a single or continuous thickness measurement to produce an average density.

Figures 3A and 3B show examples of wavelengths recorded with a microphone after lumber has been struck with a striking device on two pieces of green 100 x 50 mm lumber. The left hand side of these Figures shows the background noise before the acoustic wave impacted on the microphone. The acoustic wave then echoed through the lumber and produced the decaying image of the Figures.

After measurement with the microphone the measured signals are digitised in an A/D converter. The signals may also be filtered to remove unwanted noise from the same. Following digitisation and filtering the signals are transformed from time based signals to frequency based signals using a Fourier transform. The Fourier transformed images of Figures 3A and 3B are shown in Figures 4A and 4B respectively. Both of these Figures clearly show a resonant peak and harmonics of the acoustic velocity wave in the lumber.

The wavelength of the resonance modes of a piece of lumber of length L are Λ_n = n = 1,2,3,... 2 where both ends of the lumber are free. The corresponding resonant frequencies are f = τ ³ where v is the acoustic longitudinal velocity. Because of secondary effects, the base frequency/_/ can be perturbed and it is preferably to use an average of the harmonics of the base frequency to calculate the base frequency//. As can be seen in Figures 4 A and 4B the harmonics above the fundamental frequency are clearly distinguishable and easy to measure.

Length measuring device 5 measures the length of the lumber. The length may be measured nominally using either light or mechanical sensors or may be measured more precisely using laser or transducer sonic range finders. The length measurement is provided to computation device 1 and used in determining the acoustic velocity of the lumber.

The computation device 1 determines the acoustic longitudinal velocity from the length measurement of the lumber, the wavelengths of at least one resonant mode and at least one resonant frequency.

The computation device is then used to determine the modulus of elasticity from the density and the acoustic longitudinal velocity. The modulus of elasticity is MOE = pv² where p is the density measurement. The modulus of elasticity measured here is a dynamic modulus of elasticity that is not tied to any particular moisture content within the lumber.

The two pieces of lumber were 6 metres long and had acoustic velocities of 3288 and 2856 m/s. These acoustic velocities combined with the density readings for each piece of lumber provided a modulus of elasticity of 11200 MPa for the first piece of lumber and 8450 MPa for the second piece of lumber.

Figure 5A shows a sound recording from a piece of lumber on a moving conveyor system. The nominal length of the piece of lumber is 5.12 m. As can be seen in Figure 5 A the vibrations are recorded for nearly 50 ms. The period before the first peak in this recording contains background noise as is to be expected in a production environment.

Figure 5B shows a frequency spectrum for the sound recording of Figure 5 A. A fast Fourier transform is taken of the sound recording of Figure 5 A to produce the spectrum of Figure 5B. Resonance peaks are present in this frequency spectrum. As shown in Figure 5B the first peak occurs at 296.73 Hz, the second at 593.89 Hz, and the third at 908.33 Hz. The fundamental is then calculated from the second and third harmonics as 299.46 Hz and this value is used to determine the acoustic velocity in the lumber. This value is then combined with an average density determined from gamma ray measurements of the lumber to provide a dynamic modulus of elasticity for this piece of lumber. From the dynamic modulus of elasticity and the density of the lumber a drying regime can be determined for the lumber and/or a final use can be determined for the lumber.

Figure 6A shows a sound recording from a piece of lumber on a moving conveyor system. The nominal length of the piece of lumber is 4.82 m. As can be seen in Figure 6A the vibrations are recorded for nearly 50 ms. The period before the first peak in this recording contains background noise as is to be expected in a production environment.

Figure 6B shows a frequency spectrum for the sound recording of Figure 6A. A fast Fourier transform is taken of the sound recording of Figure 6A to produce the spectrum of Figure 6B. Resonance peaks are present in this frequency spectrum. As shown in Figure 6B the first peak occurs at 241.80 Hz, the second at 491.67 Hz, and the third at 726.25 Hz. The fundamental is then calculated from the second and third harmonics as 244.39 Hz and this value is used to determine the acoustic velocity in the lumber. This value is then combined with an average density determined from gamma ray measurements of the lumber to provide a dynamic modulus of elasticity for this piece of lumber. From the dynamic modulus of elasticity and the density of the lumber a drying regime can be determined for the lumber and/or a final use can be determined for the lumber. The computation device may be further arranged to grade the lumber based on the modulus of elasticity of the lumber and to determine a drying regime that should be applied to the lumber.

It should be noted that the order of measuring the length and thickness of the lumber, the gamma ray attenuation of the lumber and the acoustic velocity of the lumber need not be the order described above. These measurements all form part of the modulus of elasticity measurement and may be performed in any order.

It should also be noted that gamma rays are considered to be the same as x-rays and either a gamma ray or an x-ray source may be provided in the gamma ray device.

The term 'comprising' as used in this specification and claims means 'consisting at least in part of, that is to say when interpreting statements in this specification and claims which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present.

The foregoing describes the invention including preferred forms thereof. Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated in the scope hereof as defined by the accompanying claims.

Claims

1. A method of determining the modulus of elasticity of green lumber comprising the steps of assessing the attenuation of gamma rays passing through at least two areas of the green lumber, assessing the thickness of the lumber, providing an impact on one end of the lumber, detecting vibrations in the lumber caused by the impact, assessing the length of the lumber, assessing the acoustic velocity of the lumber from the detected vibrations and the length of the lumber, determining the density of the lumber from the attenuation of the gamma rays and the thickness assessment of the lumber, and determining the modulus of elasticity of the lumber from the determined acoustic velocity and the density of the lumber.

2. A method of determining the modulus of elasticity of green lumber as claimed in claim 1 wherein the thickness of the lumber is measured using laser beams.

3. A method of determining the modulus of elasticity of green lumber as claimed in claim 1 or claim 2 wherein the impact on the lumber is provided by a striking instrument such as a hammer.

4. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 3 wherein the impact on the lumber is triggered by a device to detect the presence of lumber.

5. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 4 wherein the presence of lumber is detected by the lumber breaking a light beam.

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6. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 5 wherein vibrations in the lumber are detected with a microphone.

7. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 6 wherein vibrations in the lumber are detected at one end of the lumber.

8. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 7 wherein vibrations are digitally recorded and Fourier transformed to determine the resonant frequency of the vibrations in the lumber.

9. A method of determining the modulus of elasticity of green lumber as claimed in claim 1 wherein the digitally recorded vibrations are filtered before being Fourier transformed.

10. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 9 wherein the length of the lumber is measured using light.

11. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 10 further comprising the step of assessing the stress grading of the lumber from the modulus of elasticity and density.

12. A method of determining the modulus of elasticity of green lumber as claimed in any one of claims 1 to 11 further comprising the step of assessing a drying regime for the lumber from the modulus of elasticity and density.

13. A method of determining the modulus of elasticity of green lumber conveyed on a conveyor system comprising the steps of assessing the attenuation of gamma rays passing through at least two areas of the green lumber passing between the gamma ray sources and detectors,

133901 1 assessing the thickness of the lumber as the lumber passes thickness assessment means, providing an impact on one end of the lumber, detecting vibrations in the lumber caused by the impact as the lumber passes a vibration detection means, assessing the length of the lumber as the lumber passes length detection means, assessing the acoustic velocity of the lumber from the detected vibrations and the length of the lumber, determining the density of the lumber from the attenuation of the gamma rays and the thickness assessment of the lumber, and determining the modulus of elasticity of the lumber from the determined acoustic velocity and the density of the lumber.

14. A system for determining the modulus of elasticity of green lumber comprising a gamma ray device arranged to pass gamma rays through lumber and record the attenuation of the gamma rays passed through the lumber, means for assessing the thickness of the lumber, a striking device arranged to provide an impact on one end of the lumber, microphone means arranged to detect vibrations in the lumber caused by the impact on the lumber by the striking device, means for measuring the length of the lumber, computation means arranged to determine the acoustic velocity of the lumber from the vibrations detected by the microphone means and the means for measuring the length of the lumber, the computation means further arranged to determine the density of the lumber from the attenuation of the gamma rays and the thickness of the lumber, and the computation means further arranged to determine the modulus of elasticity from the acoustic velocity and the density of the lumber.

15. A system for determining the modulus of elasticity of green lumber as claimed in claim 14 wherein the means for assessing thickness of the lumber includes at least laser beam.

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16. A system for determining the modulus of elasticity of green lumber as claimed in claim 14 or claim 15 wherein the striking device is a hammer.

17. A system for determining the modulus of elasticity of green lumber as claimed in any one of claims 14 to claim 16 wherein the impact on the lumber by the striking device is triggered by a device to detect the presence of lumber.

18. A system for determining the modulus of elasticity of green lumber as claimed in any one of claims 14 to 17 wherein the presence of lumber is detected by the lumber breaking a light beam.

19. A system for determining the modulus of elasticity of green lumber as claimed in any one of claims 14 to 18 wherein the vibrations in the lumber are detected at one end of the lumber.

20. A system for determining the modulus of elasticity of green lumber as claimed in any one of claims 14 to 19 wherein the vibrations are digitally recorded and Fourier transformed in the computation device to determine the resonant frequency of the vibrations in the lumber.

21. A system for determining the modulus of elasticity of green lumber as claimed in claim 20 wherein the digitally recorded vibrations are filtered in the computation device before being Fourier transformed.

22. A system for determining the modulus of elasticity of green lumber as claimed in any one of claims 14 to 21 wherein the means for measuring the length of the lumber uses light.

23. A system for determining the modulus of elasticity of green lumber as claimed in any one of claims 14 to 22 wherein the computation device also provides a stress grading of the lumber using the modulus of elasticity and density.

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24. A system for determining the modulus of elasticity of green lumber as claimed in any one of claims 14 to 23 wherein the computation device further provides a drying regime for the lumber using the modulus of elasticity.

25. A system for determining the modulus of elasticity of green lumber conveyed on a conveyor system comprising a gamma ray device arranged to pass gamma rays through at least two areas of the lumber and record the attenuation of the gamma rays passed through the lumber as the lumber passes between the gamma ray sources and detectors, thickness assessment means for assessing the thickness of the lumber as the lumber passes the thickness assessment means, a striking device arranged to provide an impact on one end of the lumber as the lumber passes the striking device, microphone means arranged to detect vibrations in the lumber caused by the impact on the lumber by the striking device as the lumber passes the microphone means, means for measuring the length of the lumber as the lumber passes the length measuring means, computation means arranged to determine the acoustic velocity of the lumber from the vibrations detected by the microphone means and the means for measuring the length of the lumber, the computation means further arranged to determine the density of the lumber from the attenuation of the gamma rays and the thickness of the lumber, and the computation means further arranged to determine the modulus of elasticity form the acoustic velocity and the density of the lumber.

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