JPH11258190A - Measuring method for moisture content of wood - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring method in which the distribution of the moisture content in an arbitrary place on the section of wood can be measured mondestructively by a simple device. SOLUTION: The electric resistance and the temperature in several places between mutually opposite side faces in arbitrary sections 1, 2, 3, 4 of wood are measured. Their values are substituted into a multiple regression expression which is found in advance by a multiple regression analysis, and the moisture content in respective parts between the side faces on the respective sections 1, 2, 3, 4 of the wood is found. The electric resistance and the temperature of the wood in several places on a side face which is the section 3 in a position adjacent to the section 1 and which is a direction at right angles to the side face of the section 1 are measured. The moisture content of the wood is found in the same manner as above. On the basis of data on the moistutre content based on the temperature and the electric resistance of the wood between the respective side faces at right angles to each other, the moisture content in a small region in a prescribed divided area at the inside of the wood is computed by a reverse projection method in which the moisture content is projected reversely on a prescribed section. Thereby, the distribution of the moisture content at the inside of the wood is found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for measuring the electrical resistance and the like at several points on an arbitrary section of wood.
The present invention relates to a method for measuring the moisture content of wood for estimating the moisture content distribution inside the wood.

[0002]

2. Description of the Related Art In general, drying of wood is performed by artificially controlling the temperature, humidity, and the like so as not to cause cracks or other damage due to a decrease in water content. Therefore, in order to carry out these operations automatically and continuously, it is first necessary to grasp the water content inside the wood and its temporal change.

[0003] On the other hand, in recent years, house makers have tended to have a stronger need for supplying a drying agent in order to stabilize the dimensional accuracy of the members used for producing high-quality houses or to improve the accuracy of precut processing. Therefore, in a wood drying process in a building wood production factory, more accurate drying management is required.

Conventionally, the measurement of the moisture content of wood has been carried out using a gravimetric method or an electric moisture content meter. This gravimetric method means that a small specimen is collected from wood and the water content of the small specimen is determined by JI.
It was measured by a total drying method according to S standard. Also,
For example, as disclosed in JP-A-3-140853, an electric water content meter inserts a pair of electrodes into the surface of wood, detects electric resistance or electric capacity between the electrodes, and reads the value. This was compared with a calibration curve created by resistance or capacity for a known moisture content to determine the moisture content.

[0005]

Here, in order to control the drying of wood with high accuracy, it is necessary to obtain the water content distribution inside the wood. However, in the case of the above-mentioned prior art gravimetric method, in order to collect small specimens from wood, first cut a cross section of the wood to a thickness of several cm, and then divide the wood into appropriate numbers vertically and horizontally to obtain small specimens. It is necessary to make it, and since it is performed manually, the workability is poor and there is a problem in practical use. Moreover, the wood to be inspected as a sample is divided into pieces and cannot be made into a product, so that the actual moisture content of the wood cannot be tested.

On the other hand, an electric water content meter only measures the water content near the surface of wood, and it is difficult to know the internal water content distribution which is the most important factor in quality control of large cross-section materials such as columns. Met. Further, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 3-140853, there has been proposed a device capable of estimating the water content of the entire cross section even when there is a water gradient inside the wood. It was not possible to calculate chipping and even partial moisture content inside.

Moreover, in the above-mentioned conventional measuring methods, the drying operation during operation at high temperature and high humidity has to be interrupted every time the measurement is carried out, so that the water content information from the wood can be continuously monitored. There were problems such as inability to do so.

As described above, in the conventional method for measuring the moisture content of wood, the drying efficiency may be reduced, and the quality of the produced dried material may become unstable. When such wood is used as a building material, Troubles, such as breaks and cracks, may occur after construction.

The present invention has been made in view of the above-mentioned conventional technology, and it is possible to nondestructively measure a water content distribution at an arbitrary portion of a wood cross section with a simple device, and it is also possible to perform continuous monitoring. An object of the present invention is to provide a method for measuring wood moisture content.

[0010]

SUMMARY OF THE INVENTION The present invention measures the electrical resistance and temperature at a plurality of locations between mutually facing side faces in an arbitrary cross section of wood, and calculates the water content estimating equation obtained in advance by multiple regression analysis. Substituting into the multiple regression equation to determine the moisture content of each part between the side surfaces of the cross section, furthermore, at a plurality of positions between the side surfaces in a direction orthogonal to the side surface and a cross section at a position close to the cross section. The electric resistance and the temperature are measured, and the water content is determined in the same manner as described above. Then, based on the moisture content data based on the temperature and the electric resistance between the mutually orthogonal side surfaces, the back projection method of back-projecting the moisture content onto a predetermined cross section is used to reduce the size of a predetermined divided area inside the wood. This is a wood moisture content measurement method in which the moisture content of a region is calculated and the moisture content distribution inside the wood is determined.

First, a first section and a second section are set at arbitrary positions substantially perpendicular to the longitudinal direction of the wood, and the same number, for example, 5 pairs of electric resistance measurements are made on two opposite sides of the first section. First electrodes are provided at substantially equal intervals to each other, and then on the two opposite sides of the second section other than the two sides on which the first electrodes are provided in the first section. Similarly, the same number, for example, five pairs of second electrodes for measuring electric resistance are provided, and the second electrodes are also set at substantially equal intervals.

[0012] In the vicinity of the first section, one of the two side surfaces to which the first electrode is attached is inserted toward the center of the wood, and the number equal to the number of the first electrode pairs, for example, 5 Temperature sensors, such as a first thermocouple, are also provided in the vicinity of the second section, and similarly, one of the two side surfaces to which the second electrode is attached is inserted from one side surface toward the center of wood, and A number of temperature sensors, such as five second thermocouples, are provided, equal in number to the two electrode pairs.

[0013] Then, the electrical resistance value and the in-material temperature are measured at a plurality of locations, in this case, at five locations in each of the first section and the second section. After this measurement, the first section is equally divided into five small specimens, which are divisions between the set positions of the pair of first electrodes, parallel to each other, and the second section is similarly divided into the pair of second electrodes. Are equally divided into five small test pieces, which are divisions between the set positions. Here, the directions of the paired electrodes of the first section and the second section are perpendicular to each other, and the first section and the second section are divided at right angles to each other to form a small specimen. Next, the water content of each of the small test pieces divided into 5 was measured by the dry method, and the water content by the dry method was used as an objective variable, and the electric resistance value and the temperature in each material were used as multiple explanatory variables. Analysis is performed to obtain a multiple regression equation for estimating the water content of each small specimen.

The wood to be measured for which the moisture content is to be determined has a first section and a second section similar to the above-mentioned reference wood, and the first electrode, the second electrode, the first temperature sensor, and the second temperature sensor are attached. Then, the electrical resistance value and the in-material temperature of each part corresponding to the small specimen are measured. Then, the electric resistance value and the in-material temperature are substituted into the multiple regression equation to calculate the water content for each part.

Next, based on the water content of each of the small and vertical small sample portions, the cross section of the inside of the wood to be measured is subjected to a backprojection method in which the water content is back-projected to a predetermined cross section. The multiplied number, that is, the water content of each divided 5 × 5 divided into 25 regions is calculated, and the water content of the measured wood is measured nondestructively and continuously.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 5 show an embodiment of the present invention. First, a wood 12 as a test tree for obtaining an equation for estimating a water content is provided with four arbitrary cross sections 1 along the longitudinal direction of the wood 12. 2, 3, and 4 are set. The arbitrary cross sections 1, 2, 3, 4 are set relatively close.

As shown in FIG. 2, five arbitrary needle-like electrodes 5a, 5b, 5c, 5d, 5e, and 5A for measuring electric resistance are provided on two opposing side surfaces of the arbitrary cross section 1 as shown in FIG. , 5
B, 5C, 5D, 5E are provided at substantially equal intervals,
2 It is inserted shallowly inside. In the optional cross section 2, FIG.
As shown in the figure, the electrodes 5A, 5B, 5C, 5
The thermocouples 7A, 7B, 7C, 7D, and 7E, which are five temperature sensors, are provided on the electrodes 5a to 5E from the side on which D and 5E are provided.
In the direction between e and 5A to 5E, the wood 12 is inserted into the vicinity of the center of the wood 12 at substantially equal intervals. The arbitrary cross section 3 includes electrodes 5a to 5e, 5 provided on the arbitrary cross section 1 as shown in FIG.
On the side surface orthogonal to the two side surfaces into which A to 5E are inserted,
Five needle-like electrodes 6a, 6b, 6 for measuring electric resistance
c, 6d, 6e, 6A, 6B, 6C, 6D, and 6E are provided at substantially equal intervals, and are inserted shallowly into the wood 12. As shown in FIG. 5, the arbitrary cross section 4 has five thermocouples 8 from the side where the electrodes 6A to 6E are provided.
A, 8B, 8C, 8D, 8E are electrodes 6a to 6e, 6A
The wood 12 is inserted into the vicinity of the center of the wood 12 at substantially equal intervals in the direction from to 6E.

Then, the electric resistance between the electrodes is measured by a four-terminal method, and the temperature inside the wood 12 is measured. next,
3 cm thick specimens 9 and 10 are sampled from arbitrary cross sections 1 and 3 and the specimen 9 is paired with a pair of electrodes 5A, 5a to 5E, respectively.
The sample is divided into small test pieces 9A, 9B, 9C, 9D and 9E containing 5e. The small test pieces 9A to 9E are formed to be parallel to each other and to have the same width. Similarly, the Kiguchi test piece 10 also has a pair of electrodes 6.
A, small specimens 10A, 10B, 1 including 6a to 6E, 6e
Divided into 0C, 10D and 10E, small specimens 10A to 10E
Are formed in the same width in parallel with each other, and small specimens 9A to 9E
Are located at right angles to. And each small sample 9
For each of A to 10E, the moisture content is determined by a completely dry method. Then, multiple regression analysis was performed using the moisture content as a target variable and the electrical resistance and temperature as explanatory variables by the completely dry method, and each small specimen 9A to
A multiple regression equation, which is an equation for estimating the water content at 10E, is obtained.

Next, four arbitrary cross sections are set along the longitudinal direction of the wood 12 from which the moisture content is to be determined.
As in the case of the wood 12 whose moisture content was previously determined, five pairs of electrodes are attached to two arbitrary cross sections, and five thermocouples are set to the other two arbitrary cross sections. The temperature is measured. The values of the electric resistance and the temperature are substituted into the above multiple regression equation to calculate the water content. At this time, the water content is calculated for each part corresponding to the small test pieces 9A to 10E obtained by dividing each arbitrary cross section of the wood 12 into five equal parts. Further, the water content of each small area obtained by dividing the cross-section of the inside of the wood 12 into 5 × 5 divided into 25 sections by a back-projection is calculated by the back projection method, and this is displayed as a water content distribution map in the material.

In the back projection method, a resistance value in a predetermined section in a predetermined direction is set as projection data corresponding to a moisture content between side surfaces in the direction, and a distribution of the resistance value is obtained for the section. A certain resistance value is obtained for a range of 0 to 180 degrees or a range of 0 to 360 degrees in the projection direction of the cross section, and this is subjected to Fourier transform and inverse Fourier transform,
This is to calculate the intensity distribution of the cross-sectional data from the projection data. This problem was mathematically solved by Radon in 1917, and nowadays CT
Widely applied to medical instruments such as MR and MR. here,
Scan in orthogonal directions to obtain projection data,
The distribution of the moisture content of the cross section is obtained by back-projecting based on this.

According to the wood moisture content measuring method of the present invention,
It is possible to non-destructively and continuously estimate the water content of the test tree and display it as a water content distribution diagram of the cross section of the wood. Then, by providing electrodes and thermocouples at predetermined positions on the wood to be measured and setting them in a dryer, the moisture content information inside the wood is obtained without interrupting drying during operation at high temperature and high humidity. It does not need to make small specimens as in the measurement of water content by the dry method, and is simple and has good work efficiency. Further, the estimated moisture content is accurate, and quality control of the desiccant can be reliably performed. It is possible to easily follow the change in the water content due to a difference in the drying schedule or the like, or to visually easily know the change or the like. Thereby, drying damage and the like can be prevented beforehand, and the cost of drying can be reduced and the operation can be completely automated. In other words, since the water content unevenness in the drying process can be reduced and a water content management system for supplying wood with a uniform water content to the processing process can be constructed, lumber mills, glued lumber mills, and wooden house manufacturers It is expected to be widely used in wood-related industries such as. The moisture content distribution measuring device to which the present invention is applied can be relatively easily introduced into a factory drying system.

[0022]

The present invention will be described in detail below with reference to specific examples. First, wood 12 as a test material for obtaining a multiple regression equation for estimating the water content in this embodiment is a cedar core material (12 cm square, 50 cm in length, water content 40 to 140).
%, No spine split, 18 pieces), and drying conditions are a temperature from normal temperature to 100 ° C. (18 conditions), a period of about 3 to 30 days, and a finished water content of about 19 to 55%.

The electrodes 5a to 5e and 6A to 6e are made of, for example, stainless steel nails having a diameter of 2 mm and a length of 43 mm.
The electrodes 5A to 5e, 6 are located at positions of 36, 84, 108 mm.
A to 6e were inserted, and the electric resistance was measured by a four-terminal method.
Then, a prepared hole having a diameter of 2 mm and a depth of 60 mm is formed on one side surface of the arbitrary cross section 2 or 4 at a position of 12, 36, 84, or 108 mm from one end similarly to the electrode. Pairs 7A to 7E and 8A to 8E were inserted, and the internal temperature of the wood 12 was measured.

As soon as the wood 12 seems to have reached the desired moisture content, an arbitrary section 1, 3 to 3 cm thick
Samples 9 and 10 are collected and used as a pair of electrodes 5A,
Small specimens 9A to 9E including 5a to 6E and 6e, 10A to 1
0E was prepared, and the water content of each small test piece was determined by a completely dry method.

The estimated moisture content range is set to 100% or less, and the objective variable is the moisture content (MC;%) by the completely dry method, and the explanatory variables are electric resistance (R; kΩ) and temperature in the material (t; ° C). The relationship between electric resistance and temperature with respect to water content was determined by multiple regression analysis.

As a result, the multiple regression equation for estimating the water content is
It was as follows. MC = −0.144 × R−0.532 × t + 70.7
25

Next, the wood for which the moisture content is to be determined is a pillar material having a cedar core (12 cm square, 50 cm in length, an average moisture content of 73%, no split) as in the case of the wood 12, and the drying temperature is normal temperature.
Four arbitrary sections are set along the longitudinal direction, and timber 12
Similarly to the above, electrodes are attached to two arbitrary cross sections, and thermocouples are set to the other two arbitrary cross sections, and electric resistance and temperature are measured. The values of the electric resistance and the temperature are substituted into the above-described multiple regression equation, and the water content of the two arbitrary cross sections to which the wood electrode is attached is calculated. Then, the water content of each of the small regions obtained by dividing the cross section of the inside of the wood into 5 grids of 5 × 5 by a back projection method in a grid pattern was calculated, and the results are shown in FIG.

In order to confirm the above calculation results, immediately after measuring the electric resistance and the temperature, one piece of a 3 cm thick wood tip specimen was sampled from the vicinity of any two arbitrary cross sections where the electrodes were attached. Then, the small test piece was divided into 25 parts of 5 × 5 to make a small test piece, and the water content of the small test piece was obtained by a completely dry method. The average value of the two wood test pieces is shown in FIG. Was.

As a result, the difference between FIG. 6 and FIG. 7 is small, and the method for measuring the water content of wood of the present invention has no problem in practical accuracy, and it is possible to non-destructively measure the water content of the center of wood. found. As in the case of the wood 12, the drying temperature is normal temperature, and the moisture content can be measured in a relatively high moisture content region.

Next, the other wood for which the moisture content is to be determined is the same as the wood 12 for which the moisture content was previously determined.
(Square, length 50cm, average moisture content 73%, no split)
Then, the drying temperature is set to 50 ° C., the electrodes and the thermocouple are set as in the case of the wood 12, and the electric resistance and the temperature are measured. The values of the electric resistance and the temperature are substituted into the above-described multiple regression equation, and the water content of the two arbitrary cross sections to which the wood electrode is attached is calculated. Then, the back panel projection method was used to calculate the water content of each of the small regions obtained by dividing the cross section of the wood inside the wood into 5 × 5 divided into 25 sections in a grid pattern, and the results are shown in FIG.

After measuring the electric resistance and the temperature, in order to confirm the above calculation results, one sample of a 3 cm-thick wood-mouth specimen was immediately sampled from the vicinity of two arbitrary cross-sections where electrodes were attached. Then, the small test piece was divided into 25 pieces of 5 × 5 to make a small test piece, and the moisture content of the small test piece was determined by a completely dry method. The average value of the two wood test pieces is shown in FIG. Was.

From this result, there is no problem in practical accuracy.
It was found that the water content of the center and the like could be measured nondestructively. The moisture content can be measured even in the low moisture content and high temperature regions as in the case of this wood, and the moisture content during continuous drying can be estimated.

[0033]

According to the method for measuring the moisture content of wood of the present invention, an arbitrary cross section of wood during the drying process is measured nondestructively and continuously, and a change in moisture content due to a difference in a drying schedule and the transition thereof are visually observed. Can easily be known. Also,
Drying damage can be prevented beforehand, and low-cost drying, automation of the drying operation, and the like can be easily performed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a test tree of one embodiment of a method for measuring wood moisture content according to the present invention.

FIG. 2 shows an arbitrary cross section 1 and electrodes 5a, 5b, 5 in FIG.
It is a longitudinal section showing c, 5d, 5e, 5A, 5B, 5C, 5D, and 5E.

FIG. 3 shows an arbitrary cross section 2 and thermocouples 7A and 7B in FIG.
It is a longitudinal cross-sectional view which shows 7C, 7D, and 7E.

FIG. 4 shows an arbitrary cross section 3 and electrodes 6a, 6b, 6 in FIG.
It is a longitudinal section showing c, 6d, 6e, 6A, 6B, 6C, 6D, and 6E.

FIG. 5 shows an arbitrary cross section 4 and thermocouples 8A and 8B in FIG.
It is a longitudinal cross-sectional view which shows 8C, 8D, and 8E.

FIG. 6 is a front view showing the water content of wood at room temperature drying according to the wood water content measurement method of the present invention.

FIG. 7 is a front view showing the moisture content of the wood of FIG. 6 by a completely dry method.

FIG. 8 is a front view showing the moisture content of wood at the time of high-temperature drying by the wood moisture content measuring method of the present invention.

FIG. 9 is a front view showing the moisture content of the wood of FIG. 8 according to a completely dry method.

[Explanation of symbols]

1, 2, 3, 4 Arbitrary cross section 5A to 5E, 5a to 5e, 6A to 6E, 6a to 6e
Electrode 7A-7E, 8A-8E Thermocouple 9,10 Kiguchi 9A-9E, 10A-10E Small specimen 12 Wood

Claims (2)

[Claims] 1. An electric resistance and a temperature at a plurality of locations between side faces facing each other in an arbitrary cross section of wood are measured, and these values are substituted into a multiple regression equation which is a water content estimation equation previously obtained by a multiple regression analysis. Determine the moisture content of each part between the side surfaces of the cross section, respectively, and further measure the electrical resistance and temperature at a plurality of locations between the side surfaces in a direction orthogonal to the side surface in a cross section at a position close to the cross section, The water content is determined in the same manner as described above, and based on the water content data based on the temperature and the electric resistance between the mutually orthogonal sides, the back projection method of back-projecting the water content onto a predetermined cross section is used to estimate the inside of the wood. A method for calculating the water content of a small area in a predetermined divided area to obtain a water content distribution inside the wood. 2. A measurement target wood to be measured and a reference wood which is placed in a similar state with the same dimensions as the measurement target wood and is used as a basis for moisture content measurement, are prepared with respect to the longitudinal direction of the reference wood. A first cross section and a second cross section set at an arbitrary position at a substantially right angle, and a plurality of pairs for opposing each other are provided on two opposing side surfaces of the first cross section and located at substantially equal intervals. And a plurality of pairs of second electrodes for measuring electrical resistance, which are provided in a plurality of pairs facing each other on two side surfaces orthogonal to the two side surfaces on which the electrodes are provided in the first cross section of the second cross section, and located at substantially equal intervals. An electrode and the same number of first temperature sensors as the number of pairs of the first electrodes inserted from one of the two side surfaces provided near the first cross section and having the first electrode attached thereto toward the center of the wood. , The second electrode is provided near the second section, The same number of second temperature sensors as the pair of the second electrodes are provided to be inserted from one of the two side surfaces toward the center of the wood, and a plurality of the second temperature sensors are provided for each of the first section and the second section. The electrical resistance value and the in-material temperature are measured, and after this measurement, the wood sample including the first cross section is divided into small specimens including the set positions of the pair of first electrodes evenly and parallel to each other, and The wood sample including the two cross sections is equally divided into small specimens including the set positions of the pair of second electrodes in parallel with each other, and the water content of these small specimens is measured by the dry method, and the water content by the dry method is measured. Rate as a target variable, the above-mentioned electrical resistance values and the above-mentioned respective temperatures in the material are used as explanatory variables, and multiple regression analysis is performed to obtain a multiple regression equation for estimating the water content for each of the above-mentioned electrodes. Set the first cross section and the second cross section in the same way as the above standard wood Attach one electrode, second electrode, first temperature sensor, second temperature sensor, measure the electrical resistance value and material temperature for each part corresponding to between the above electrodes, and measure the electrical resistance value and material temperature By substituting into the multiple regression equation, the water content of each part between the electrodes is calculated, and the backprojection method of back-projecting the water content on a predetermined cross section based on the water content between two mutually perpendicular sides is performed. Calculate the water content of each small area divided into a number obtained by multiplying the number of small test pieces between the electrodes by measuring the inside of the measured wood, and non-destructively and continuously hydrate the wood to be measured. A method for measuring wood moisture content, characterized by obtaining a water content distribution.