FI127964B - Method for quick sampling to determine crack formation in wood on a production line using contactless ultrasound - Google Patents

Abstract

The invention relates to a method for determining cracking in wood. The procedure is that a cross-section of the wood is measured with ultrasound on the opposite sides relative to the normal to the surface at an angle of 0.2-25 degrees, with air-coupled ultrasonic sensors (1-4) placed on the same side of the intersection plane, with which it is transmitted and received an acoustic signal propagating in the board (5) in at least two different directions, preferably on two different frequencies. Based on the measurements, parameters that determine the crack formation in the wood are calculated independently of the direction of the fracture / cracks, and the results are used for monitoring and / or controlling the board.

Description

METHOD FOR QUICK SAMPLING OF WOOD

DETERMINATION OF CRACKING FROM A PRODUCTION LINE

IN URGENT ULTRASOUND

20150297 prh 07-01-2019

The present invention relates to a method for determining wood cracking according to the preamble of claim 1.

The process can be utilized in industrial processes. In particular, the internal cracking of massive planks made from the most valuable part of the wood, especially in the drying and heat treatment of wood, remains one of the major quality-reducing factors. In processes, it would be important to be able to diagnose internal cracking quickly and without material degradation, whereby low-grade plank or part of the plank could be detected and removed from production or used for less demanding applications without destroying good quality material. The presented method 15 is capable of estimating the number and location of cracks of critical size for use.

Drying of wood is considered to be the most significant cause of cracking of massive wood planks. Each wood and plank has different properties, so the formulas used for drying wood 20 are always compromises and the cracking of drying is still a major problem today. The drying crack in the wood dries mainly due to the moisture gradient in the wood, which causes stress in the wood because the wood shrinks unevenly as it dries. The dried top layer of wood shrinks more than the still wetter inner part of the wood, which tends to form cracks in the top layer.

Towards the end of the drying process, the stresses are reversed when the stress on the wood surface and the tensile stress on the inner part are possible, and internal cracks are thus possible. In addition to the stresses caused by the differences in humidity, the drying wood is under stress due to the anisotropic shrinkage of the wood. In addition to macro cracks

20150297 prh 07-01-2019 There are always micro cracks in the drying process, which can cause macro cracks to grow uncontrollably. When processing wood further, other processes may also crack, especially if the wood is subjected to significant mechanical stress. On the other hand, storage also causes cracking, especially if the humidity and temperature of the air change significantly. This is a problem especially in planks and wood structures that come in contact with the outside air.

Recently, especially, the glulam beam industry has grown 10 strongly due to e.g. large-scale production of wooden block houses. Today, all lumber that goes into glulam beams is subjected to strength testing, but there are still occasional reports of collapse of glulam beams and, at worst, loss of life. According to 15 Sanabria doctoral dissertation studies (published in 2011), for example, in Germany, between 1912 and 2006, 528 adhesive beams were broken in 428 sites, 70% of which were caused by longitudinal cracks, 62% of which were glued. Thus, 38% were due to wood cracking. Possibly 20, especially in these cases, the wood has already had a critical inside crack, which as a result of exertion has begun to grow and eventually the beam has given up.

The method described herein is suitable for detecting such critical cracks already at the manufacturing stage.

Air gaps in the top layer of wood can be detected, for example, by thermal camera technology. The external and internal properties and defects of wood can be analyzed by combining machine vision and X-ray technology, but the cost of the method and its insensitivity to small cracks are a problem.

Microwave-based internal crack detection methods have been developed but have the problem of being extremely sensitive to moisture and insensitive to small cracks.

Several studies have shown that internal damage to wood planks can be measured by ultrasound. Characteristics of wood panels, such as cracking, strength and density, have been determined by ultrasound on-line measurement. Acoustic measuring devices that operate at ultrasonic lower frequencies have also been developed to diagnose internal tree defects. Due to the low frequency, the methods are not suitable for detecting small cracks. Ultrasonic measuring instruments have been developed and patented in the industry. The methods are typically based on contact measurement, where e.g.

roller type sensor solutions. Methods have been developed specifically for the hardwood industry and have been able to detect internal cracking under industrial conditions. However, according to current understanding, contact-based ultrasound measurement has been found to be unreliable in line measurement applications e.g. due to varying contact and contamination.

Good contact in ultrasonic measurements can be achieved by water contact, thus determining internal defects in the wood, but this method is mainly suitable for static measurement if the materials do not significantly absorb moisture.

Measurement of the density of wood panels and of the cracking and density of veneer sheets has also been demonstrated using

20150297 prh 07-01-2019 air-connected wood applications e.g.

ultrasonic sensors and diameters. Other uses of air-connected ultrasonic sensors include detection of extended plank adhesive defects and inspection of plywood veneer bonding. Airborne Ultrasonic Plywood Internal Adhesive Fault Measuring Devices have been developed and are used in the plywood industry. Currently, manufacturers of devices include

GreCon International (USA) and Electronic Wood Systems (Germany).

Solutions for the application of air-coupled ultrasound measurement to the detection of internal defects in wood have been proposed e.g. using wideband ultrasonic transducers and measuring, for example, the change of the characteristic frequency due to the adhesive.

Typically, piezoelectric ultrasonic sensors are used to detect ultrasonic signals, which convert mechanical vibration into an electrical signal. The preamplifier amplifies the weak pulse from the sensor, and then amplifies the signal into a measuring system typically consisting of filters, amplifiers, and an analyzer. Typical signal parameters to be analyzed are travel time and amplitude. The frequency content of the signals has also been used in the analyzes. The development of air-coupled capacitive ultrasonic transducers has also progressed recently and capacitive transducers for industrial applications have also been developed.

The ultrasonic method has been used especially in quality control applications in the process industry. food, plastic, metal industry. In the woodworking industry, ultrasound has been used e.g. to determine the strength properties of wood and to detect glue defects.

It is an object of the invention to provide a method for determining wood cracking which eliminates uncertainties associated with current production methods.

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In particular, an object of the invention to provide a process and / or control of wood products is to monitor the production process quickly, easily, efficiently and reliably. The processes involved in the production of wood products include:

drying, planing, gluing and various wood modifications such as heat treatment.

The object of the invention is achieved by a process characterized by what is claimed.

20150297 prh 07-01-2019

In the method of the invention, ultrasound is used to measure a cross-section of wood using air-coupled ultrasonic transducers on opposite sides of a normal angle to the surface of the object to be measured at 0.2 to 25 degrees that are on the same side of the 5 cross-sectional planes. Two sensors transmit ultrasonic bursts to the plank surface and the cracking of the plank affects the ultrasonic signal propagated on the plank, which is measured by the receiving sensors. In the method, the direction, quality, and amount of plank cracking are determined by measuring the amplitude, velocity, phase, and shape of the ultrasound signal 10 in at least two directions at different ultrasonic frequencies. It is essential for the operation of the method that the size, frequency and angle of the sensors are such that, due to the measuring angle, the wave interference does not significantly affect the measurement, thus the wavelength of the propagating wave 15 is significantly larger than the phase difference caused by the sensor.

The effect of other characteristics of the plank, such as density and humidity, which influence the passage of the ultrasound signal can be effectively eliminated by determining reflections from the ultrasonic signal which are insensitive to internal cracking.

On the other hand, measurements of non-fractured sites can be used to determine the basic properties. This presupposes that the wood is not cracked, which in turn is easily detected by ultrasonic measurements. The effect of the branches on the propagation of the ultrasound signal in the plank is very different with respect to the effect of the cracks, and the effect of the branches can be eliminated by using multivariate signal analysis.

The invention can be applied especially in industrial processes for quality control, both as stand-alone on-site testing and on-line measurement.

Air-connected measurement also enables non-contact measurement, whereby, for example, potential substances on the surface of the wood, such as pitch, do not soil the sensors and affect the measurement as strongly as in contact measurement. In air-connected measurement, the sensors do not interfere with the propagation of the plank on the production line and do not require accurate timber control.

In a preferred embodiment of the invention, the method measures, at two different frequencies, the cracking of wood through and across the sheet, with transducers on opposite sides of the wood at an angle of 0.2 to 25 degrees with respect to the surface, on the same side of the cross section. The direction of the crack affects the response. If the crack direction is the same as the ultrasound propagation direction, the effect is negligible or the crack may even amplify the signal. Typically, the crack has the greatest effect on the propagation of the ultrasound signal when the crack is perpendicular to the propagation direction.

By comparing ultrasound signals measured in different directions at the same point, the angle of the crack can be estimated.

By appropriately selecting the frequencies, the interference of the waves can be minimized, on the other hand, measurements can be made at different points on the production line, and by synchronizing the measurements, the same result can be obtained as if they were made from the same cross-section.

20150297 prh 07-01-2019

In the method of the present invention, the air-coupled echo sound method is used to determine wood cracks. By monitoring the target cross-section on opposite sides of the wood at a normal angle of 0.2 to 25 degrees, with air-coupled ultrasonic transducers on the same side of the cross-section plane at two frequencies 30, it is possible to more accurately and rapidly detect cracks in the wood. accelerate and optimize wood processing formulas for wood products of different sizes and qualities to produce a high quality, non-cracked wood product.

The invention will now be explained in more detail with reference to the accompanying drawing, in which Fig. 1 shows a diagram of an embodiment of the method according to the invention. The diagram of Fig. 1 shows a cross-section of 5 5 wood planks extending along the production line. Air-connected ultrasonic transducers 1-4 are placed above and below the plank and on the sides. Sensors 1-2 act as transmitters and sensors 3-4 act as receivers. The number of ultrasonic sensors may vary from application to application and may be positioned in a desired and convenient manner relative to the timber being measured.

Figure 2 is a schematic view of another embodiment of the method of the invention. Fig. 2 is a plan view showing a top view of timber (6) advancing along a production line. Above, below and to the side of the plank are located air-coupled ultrasonic sensors, the figure showing a transducer (1) and a receiver (3), which measure in one direction.

The number of ultrasonic sensors may vary from application to application and may be positioned in a desired and convenient manner relative to the timber being measured.

20150297 prh 07-01-2019

In the following, the method according to the invention and its applications will be described by way of example.

Example 1. Determination of cracking in longitudinally moving plank

Referring now to Figure 1, a first embodiment of the method of the invention, wherein the cracking of a longitudinally moving plank (5) on a production line is determined.

In this example, GMP (Gas Matrix Piezoelectric) is used as transverse ultrasonic transducers

116 kHz sensors and 210 kHz GMP sensors (1-4) as transducer transducers. The sensors (1-4) are fixed to the frame structure of the production line and are arranged such that the transmitter and receiver sensors (1-4) are on opposite sides of the 5 sawn timber (5), preferably 50 mm from the edges of the measured plank. The sensors (1-4) are preferably in opposite directions at an angle of 10 degrees with respect to the normal surface of the target (5). The sensors (1-4) are acoustically protected so that the attachment is made by 10 rubber insulated mounting bolts. Before starting the measurement, the ultrasonic measurement is calibrated with a blank measurement, which can also utilize the ultrasonic signal reflected from the receiver sensor. The sensors (1-4) are connected to an ultrasonic measuring unit consisting of e.g. a preamplifier 15 and an amplifier, as well as low and high pass filters.

The signal from the measurement unit is directed to the signal analyzer and the measurement control unit for controlling the measurement and

The analyzer outputs perform a measurement analysis of the existing ones.

Measurements are taken to determine the cracking of the plank.

In this case, the measurement control and analysis unit is a computer equipped with an analog / digital converter that converts the measured signals into control and

20150297 prh 07-01-2019 analytical software suitable for the application. The computer runs a program that continuously measures the ultrasound measurement channels, analyzes the results, and sends the measurement data wired or wirelessly to the monitoring computer.

The same computer controls a wood grading system that can mark / remove too much cracked planks or parts of planks. For each plank, cracking information is obtained about the size of the crack and where cracking has been observed. Each type of wood product has certain critical cracking limits that must not be exceeded. Limit values have been determined based on theoretical calculations, which have also been experimentally verified e.g. by testing planks for substance.

Example 2. Application of Multivariate Methods

In the exemplary embodiment, the method works similarly to Example 1 or 3-32 and refers to the figures

1-2, but the method uses a multivariate method for analyzing measurements.

The main method used for analyzing measurements is a multivariate method, which may be, for example, multivariate regression, principal component regression (PCR) or partial least squares (PLS) method. By measuring the calibration samples, a multivariate matrix is formed that contains, for each calibration sample, column by column the manually determined internal cracking and the measured and calculated values of the parameters of the ultrasound method.

Inner cracking is determined by a violating standard method.

Any of the above

20150297 prh 07-01-2019 Using the multivariate method, the error between the crack function matching and the actual cracking is minimized. This produces a multivariate matrix containing coefficients for the ultrasonic parameters as well as constant factors. The internal cracking is determined by measuring the parameters of the ultrasound method from the sample and using model functions based on the matrix coefficients determined during calibration.

In multivariate classification analysis, linear and nonlinear classification methods such as Bayes classifier, neural networks, genetic algorithms or 30 nearest neighbor classifiers can be used. In this example, the classification was made with the Bayes classifier. Initially, the model is taught to predict the classes of cracking generated by the specified ultrasound parameters, which requires a series of specimens that have been determined to have a material-deleterious interior cracking, as in the above-mentioned regression models. The resulting 5 models predict the probability that the ultrasound track falls within a given crack class.

Example 3. Determination of cracking from transversely moving plank

In the exemplary embodiment, the method works similarly to 10 in Examples 1-2 or 4-32, and with reference to Figures 1-2. In a further preferred embodiment of the invention, the cracking of the wood is determined by the transverse movement of the planks (5).

Here, a sufficiently comprehensive measurement can be made using, for example, matrix sensors (1-4), a plurality of sensors (1-4) and / or such that the sensor (s) pair (1-4) moves and / or scans such that the plank (5) sufficiently comprehensive.

Example 4. Inclined measurement

In the exemplary embodiment, the method works similarly to Examples 1-3 or 5-32 and refers to Figures 1-2. In the example, the ultrasonic sensors are not connected

20150297 prh 07-01-209 perpendicular to the receiver, the angles between the transmitter and the transmitter can be adjusted so as to pass between the transmitting and receiving transducers, above or below and / or from the side.

Example 5. Measurement deviating from a straight line

In the exemplary embodiment, the method works similarly to Examples 1-4 or 6-32 and refers to Figures 1-2. Example

20150297 prh 07-01-209 The ultrasonic transducers (1-4) placed on opposite sides are not aligned with each other.

Example 6. Determination of cracking as a reference measurement

In the exemplary embodiment, the method operates in a manner similar to Example 5 in Examples 1-5 or 7-32 and refers to Figures 1-2. In a further preferred embodiment of the invention, the planks are measured before and after the process (e.g., drying or heat treatment) to obtain a very accurate determination of process changes in the plank and to improve the accuracy of the crack determination determination.

Example 7. Determination of cracking as differential measurement

In the exemplary embodiment, the method works similarly to Examples 1-6 or 8-32 and refers to Figures 1-2. In a further preferred embodiment of the invention, planks are scanned, multiple sensors or a matrix sensor solution are used, and differences between adjacent measurements are determined spatially. In this case, considerably smaller differences in the measurement parameters can be detected than when using straightforward measurement values alone. By utilizing the speed and magnitude of changes in ultrasound parameters and the spatial dimension, the crack analysis can be further refined.

Example 8. Utilization of Cracking Assay in Strength Sorting

In the exemplary embodiment, the method works similarly to Examples 1-7 or 9-32 and refers to Figures 1-2.

In a further embodiment, the planks are measured before and after the strength sorting, where the planks are subjected to low mechanical stress. This gives a very accurate analysis of the changes in the 30 planks and the

20150297 prh 07-01-2019 Accuracy can be improved by directly comparing results with previous measurements of the same plank, and especially detecting cracks born and / or growing / exertion.

Example 9. Monitoring Method

In the exemplary embodiment, the method functions similarly to Examples 1-8 or 11-32 and also refers to Figures 1-2, but in this embodiment, the control connection to the classification system is missing. Thus, in this Example 10, the method works solely to monitor cracking and to output measured values to the monitoring device. This embodiment can be used, for example, to study and optimize a process, or, for example, to investigate the optimal drying or behavior of non-previously calibrated wood materials in the process being studied. Likewise, crack propagation or size changes under storage or under various conditions, which can also be cyclically modified, can be tested and monitored. The method can also be applied in research applications, e.g., cyclic fatigue tests or creep tests.

Example 10. Control Method

In the exemplary embodiment, the method functions similarly to Examples 1-8 or 11-32 and also refers to Figures 1-2, but the monitoring system is absent in this embodiment. Thus, in this example, method 25 serves only as a classifier.

This embodiment can be used, for example, in routine processes.

Example 11. Compression Drying Application

In the exemplary embodiment, the method functions similarly to that of Examples 1-10 or 13-32 and refers to Figures 1-2. Here

In the example 20150297 prh 07-01-20199, the method is coupled to determine cracks in wood during the compression drying process, which are affected not only by drying / drying but also by the compression force exerted on the wood. The method can be used to determine cracking in a process by measuring modified planks before and after the process.

Example 12. Heat treatment application

In the exemplary embodiment, the method works similarly to Examples 1-10 or 14-32 and also refers to Figures 1-2. In this 10 examples, the method is coupled to determine cracks in the wood during the heat treatment process, which are affected e.g. intensity of heat treatment. The method can be used to determine cracking in a process by measuring modified planks before and after the process.

Example 13. Other wood modification applications

In the exemplary embodiment, the method works similarly to Examples 1-10 or 14-32 and also refers to Figures 1-2. Herein, the wood drying and / or modification method includes, for example, molecular capillary drying, chemical and / or biological modification, impregnation treatment, oil treatment and / or surface treatment. The method can be used to determine cracking in a process by measuring modified planks before and after the process.

Example 14. Various wood product applications

In the exemplary embodiment, the method works similarly to Examples 1-13 or 15-32 and also refers to Figures 1-2. In this example, the object to be measured is not plank, but the method can also be applied to other types of wood or wood-based products such as glued wood, logs,

20150297 prh 07-01-2019 round wood, cut to various shapes, wood plastic composites and sandwich structures.

Example 15. Glued wood products

In the exemplary embodiment, the method works in a manner similar to that of Examples 1-14 or 16-32 and also refers to Figures 1-2. In this example, the object to be measured is not plank, but the object contains an adhesive seam. In this case, the method can be used to separate the internal cracks of the wood from the glue stacks, whereby both the glue defects and the internal crack can be more accurately determined than if a known method for detecting glue defects is used.

Example 16. Wood component line measurement

In the exemplary embodiment, the method works similarly to Examples 1-15 or 17-32 and also refers to Figures 1-2. In this 15 examples, the method is coupled to determine cracking on a component line that produces components for different products. The product may be, for example, glued sawn lumber, whereby the production line may automatically discard the internally split pieces and parts of parts as the branches are removed.

Example 17. Static measurement

In the exemplary embodiment, the method works similarly to Examples 1-15 or 18-32 and also refers to Figures 1-2. In this example, the method is coupled to determine cracking from a stationary tree (5), whereby the method can determine cracking from measurement points. By moving the sensors (14), it is possible, for example, to estimate the size of the crack in the longitudinal and width directions and to determine the total cracking of the object to be measured manually by scanning and / or using, for example, robotics.

Example 18. Measurement of wooden structures

In the exemplary embodiment, the method works similarly to Examples 1-17 or 19-32 and also refers to Figures 1-2. In this example, the method is coupled to determine cracking 5 from a stationary wood structure (5), wherein the method can determine cracking from measurement points. By moving the sensors (1-4), it is possible, for example, to estimate the crack size in the longitudinal and width directions, and to determine the total cracking of the object to be measured manually by scanning and / or using, for example, robotics.

Example 19. Measurement of Adhesive Beams

In the exemplary embodiment, the method works similarly to Examples 1-18 or 20-32 and also refers to Figures 1-2. In this example, the method is coupled to determine cracking from the glued beam structure (5), whereby the method can determine cracking from the measurement points and move sensors (1-4) to estimate, for example, the size of the crack in longitudinal and width robot technology.

Example 20. Multi-sensor application

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In the exemplary embodiment, the method works similarly to Examples 1-19 or 21-32 and also refers to Figures 1-2. In this example, for example, the method is associated with an electromagnetic method using radio, microwave, such as optical, electric

IR, NIR, impedance, X-ray or gamma measurement to determine other properties of the plank such as moisture, density, oxicity, skewness, heart / surface and / or juvenile. In this way, the method can be further refined, since the parallel method used is not sensitive to cracking and thus it is very efficient to eliminate error measurements caused by a failure other than cracking.

Example 21. Dimensional measurement

In the exemplary embodiment, the method works similarly to 5 in Examples 1-20 or 22-32 and also refers to Figures 1-2.

While performing a crack measurement, the dimensions of the object to be measured can be determined as reflection measurements. The reflected pulse can be determined by both the transmitting and the transmitting receiving transducers, whereby a distance determination can be made on all four sides.

In the case of the transmitting transducer, this is a normal reflection measurement, the transducing transducer being used to determine a second burst of the measurement signal, which is the second reflection of the transmitted signal from the surface of the plank.

Separate measurement of air temperature and humidity is required for accurate dimensional measurements if the conditions at the measuring site vary greatly.

20150297 prh 07-01-2019

Example 22. Determination of plank shape defects

In the exemplary embodiment, the method operates similarly to Example 1-21 or 23-32 and also refers to Figures 1-2.

At the same time as the crack measurement and similarly to the dimensional measurement, the shape defects of the object to be measured, such as imperfection, twist, blade and discontinuity, and curvature as reflection measurements can be determined. If the shape defect 25 is significant, the shape defect measurement can be performed as in Example 21.

Example 23. Determination of cracking of deformed plank

In the exemplary embodiment, the method works similarly to Examples 1-22 or 24-32 and also refers to Figures 1-2.

Determining the cracking of a severely deformed plank is challenging because, due to deformations, the target surfaces may not be correctly positioned relative to the transmitting and receiving sensors. In this case, the plank can be guided, for example, by four rollers (two above and below 5 before and after the measuring point) such that a sufficient angular position of the target surfaces relative to the sensors is achieved at the measuring point.

Example 24. Calibration Method

In the exemplary embodiment, the method works similarly to Examples 1-23 or 25-32 and also refers to Figures 1-2.

The method can be calibrated continuously by measuring only air when there is no object to be measured. In this way, reference values can be determined for each ultrasound parameter used, while taking into account changes in conditions during long-term measurement.

Example 25. Automatic measurement for different dimensions

In the exemplary embodiment, the method works similarly to Examples 1-24 or 26-32 and also refers to Figures 1-2.

The method can be used to determine the position and dimension of the plank continuously, as in Example 21 (Dimension Measurement).

20150297 prh 07-01-2019

Thus, a suitable analysis algorithm previously defined for each dimension can be continuously used in the crack detection method.

Example 26. Single sensor reflection and diameter

In the exemplary embodiment, the method works similarly to Examples 1-25 or 27-32 and also refers to Figures 1-2. The method may also be adapted to include a reflector in place of the receiving sensor, which reflects the signal passed through the target in the desired direction, from which the signal can be reflected back to the transmitting sensor by means of the reflector (s).

Example 27. Application of Capacitive Ultrasonic Sensors

In the exemplary embodiment, the method works similarly to Examples 1-26 or 28-32 and also refers to Figures 1-2. The method may also be adapted so that a transmitting and / or receiving transducer (1-4) is provided with a capacitive or other type of ultrasonic transducer.

Example 28. Matrix Sensor Application

In the exemplary embodiment, the method works similarly to Examples 1-27 or

29-32 and also refer to the figures

1-2.

The method can also be applied so that a transmitting / transmitting and / or receiving / receiving transducer (s) is provided with a matrix transducer which can make multiple measurements at different locations of the subject being studied.

The matrix sensor can be implemented, for example, based on capacitive sensor technology.

Example 29. Replacement Sensor Application

In the exemplary embodiment, the method works similarly to Examples 1-28 or

30-32 and also refer to the figures

1-2.

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The method can also be applied in that the transmitters of the transmitting transducer (s) (1-4) become more focused and / or the function of the transmitting transducer (s) is reversed, i.e. the transmitters and transmitters are measured at the same location and / or directions are analyzed. This allows for further measurement.

Example 30. Multi-receiver application

In the exemplary embodiment, the method works similarly to Examples 1-29 or 31-32 and also refers to Figures 1-2. The method may also be applied such that two or more sensors are located in place of the transmitting and / or receiving sensor (1-4) instead of one sensor. By positioning the sensors (1-4) at an appropriate angle and relative to each other, the measurement can be further refined and accelerated, since it is possible to simultaneously measure two points of timber. This is especially useful for fast line mapping.

Example 31. Strength Measurement

In the exemplary embodiment, the method works similarly to Examples 1-30 or 32 and also refers to Figures 1-2.

The method can also be applied to strength measurement by analyzing the elastic properties of the wood material at the 15 locations free from cracking or other internal defects.

By combining this information with measurements from cracks and other defects, the strength of the wood can be further assessed.

Example 32. Multisensor application for high strength new measurement

In the embodiment, the method works similarly to the examples

1-31 and also refer to the figures

1-2.

In this example, the method is

20150297 prh 07-01-20199 attached for example electromagnetic method of radio wave, microwave, such as optical, electric

IR, NIR, impedance, X-ray or gamma measurement to determine other properties of the plank, such as moisture, density, oxicity, skewness, heart / surface area, and the rigid measurement method, because this determines very precisely.

and / or the proportion of young trees.

(Example 31) can be, for example, wood

I still see moisture

The invention is not limited to the above exemplifying embodiments, but may vary within the scope of the claims.

Claims (6)

Claim: Method for determining cracking in timber, characterized in that an intersection of the timber is measured by ultrasound with air-coupled ultrasonic sensors (14) positioned on opposite sides of the timber at an angle of 0.2-25 degrees relative to the normal to the surface and on the same side of the intersection plane, by which an ultrasonic signal propagating in the timber (5) is transmitted and received in at least two different directions at at least two different frequencies, and parameters determining the crack formation in the timber regardless of the direction of the crack are calculated from the measurements, and that the results are used for monitoring the quality of the timber and / or controlling a production process. Method according to claim 1, characterized in that the ultrasonic sensors can be placed so that the wood (5) to be measured can be passed between, above or below and / or alongside the sensors (1-4), which enables the function as a line measurement. Method according to claims 1-2, characterized in that the cracks can be determined at industrial line speeds throughout the wood (5) by passing it in the transverse or longitudinal direction and / or by moving the sensors (1-4) and / or by using a sensor matrix and / or multiple sensors. Method according to claims 1-3, characterized in that a dimensional measurement and / or edge measurement determined by reflection measurement can be used in automatic determination of the crack formation in wood products of different dimensions. Method according to claims 1-4, characterized in that other methods which are not sensitive to cracking can be used in the measurement and this measurement information which is independent of the ultrasonic measurement can be used. Method according to claims 1-5, characterized in that the measurement can be continuously calibrated by measuring the ultrasonic signals propagated through a standard object and / or the air.