JP5288873B2 - Method for measuring moisture in wood - Google Patents

Description

  The present invention relates to a non-destructive method for measuring moisture in wood.

Generally, wood is made into a product by sawing a raw wood (log) into a square cross section, drying it, and performing finishing processing such as molding and pre-cutting. Since the density of wood differs depending on the moisture content, and therefore the strength also differs, the degree of moisture content is a very important factor.
In the lumbering process, depending on the moisture content, it is selected whether to use for pillars and beams or plate materials, and after the drying process, it is sorted again by the moisture content, and it is determined whether finishing processing or re-drying is performed. Moreover, after curing is performed after the drying step, it is transferred to final processing according to the moisture content, or re-dried as a rejected product.

The moisture content of wood is a mass percentage and is generally expressed on a dry basis.

Here, U: moisture content, M: mass of wood containing moisture, Mo: mass of wood containing no moisture The method of obtaining this moisture content is usually based on the “total dry method”. "Determines Mo of the formula (Equation 1) by drying. JISz2101 stipulates that the value of Mo when the target wood reaches a constant weight in a well-ventilated oven at 100 to 105 ° C., and the JAS wood moisture content standard is 15%, 20%, etc. Is determined with this value.

Further, there is a chemical analysis method as a chemical measurement method for obtaining the moisture content. This method heats wood together with a solvent and quantifies the extracted water. Generally, the “K. Fischer method” using the following reaction is used. SO ₂ + I ₂ + 2H ₂ O → 2HI + H ₂ SO ₄
However, it is necessary to take a sample and measure and analyze both the dry method and the chemical analysis method, so it takes too much time and time, and it is difficult to adopt it in the actual wood industry factory line because of its immediate effect and cost. It is.

Conventionally, as an indirect method (non-destructive method) for measuring the moisture content of wood, the following moisture meter using a change in electricity with respect to the moisture content in wood has been put into practical use.
1) The direct current and alternating current resistance principle applies the fact that the logarithm of the specific resistance of wood with respect to direct current and low frequency current has a linear relationship with the internal moisture, and the sensor part has a needle shape or a stamp shape. .
2) The dielectric constant and microwave principle are based on the fact that the dielectric constant or dielectric loss of wood in a high frequency and microwave range has a linear relationship with internal moisture. For the large in-line type, there are a dielectric type and a method of sandwiching between electrodes, and a microwave is a method of transmitting microwaves by specific contact.

However, in the direct current and alternating current resistance method, the specific resistance is affected by the material temperature, and the resistance value when the current flows between the electrode sensors (wood part) is replaced with the amount of moisture, so the measurement depth is 15 mm at most. There are problems such as a point that is shallow and local, and a moisture content of 30% or more has a large measurement error.
The dielectric constant is less affected by temperature, but it is affected by the density of the real wood. The portable type has a measurable depth of about 20 mm, and the in-line pinching method and transmission type method detect relatively internal moisture. Yes, but there is a problem that it is expressed by the average value of the cross section.

As described above, the disadvantage of the moisture meter is that it is very inadequate for the measurement depth currently required for quality control of building wood. Although it also senses moisture, the problem is that it only represents the average amount of moisture.
For example, depending on the method of artificial drying, a desiccant having a moisture content extremely high in the cross section of the column material and a low moisture content in the surface portion is produced. This certainly clears the average of 20% or 15% or less of the JAS standard, but after assembling as a house, the internal moisture is in the raw material state, which can cause serious wrinkles.

  The present invention has been made to solve the above-described problems, and its purpose is non-destructive, simple, and reliable, such as residential beams, girders, and pillars. An object of the present invention is to provide a method capable of detecting the moisture state of wood having a large cross section up to the inclination of internal moisture and external moisture and grasping the density.

In order to achieve the above object, the present invention applies momentary rotational force to timber, measures the acceleration at that time, obtains the moment of inertia from the measured acceleration value, and compares it with the moment of inertia when the specimen is homogeneous. It is characterized by determining the water distribution in the material.

According to the present invention, since the acceleration of the rolling of the wood is measured, the moisture distribution in the wood of the wood having a large cross section used as a beam, girder, or pillar material for a house is relatively easily and reliably grasped. be able to.
The moisture distribution of wood is not uniform even when the type of wood is the same, but the difference in solids is large, but the difference in relative values of acceleration measurements or the moment of inertia and the moment of inertia when the specimen is homogeneous It is possible to easily detect the inclination of the internal moisture and the external moisture, and it is possible to accurately determine whether or not the moisture content is dry by checking the moisture content of the lumber product on the lumber line, and by applying it to log sorting As a result, it is possible to accurately select the material for the column and the column, increase the efficiency of the drying process, and obtain excellent effects such as accurate sorting of the drying material by checking the degree of drying.

  The acceleration measuring means is an acceleration sensor or an angular acceleration sensor.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 and FIG. 2 show an outline of a method for measuring moisture in wood according to the present invention, and 1 is a measuring table having a slope 100. In addition, the support 2 is disposed at a position facing the slope 100, and a passage is formed between the slope 100 and the support 2.
Reference numeral 3 denotes a specimen for measuring moisture in the material, which is normally “log”. The test body 3 is positioned at the uppermost part of the measuring table 1, is fastened with a stopper (not shown), and is rolled between the passages by removing the stopper.
Reference numeral 4 denotes an acceleration sensor which is disposed on the support 2 and the inclined surface 100 and measures moisture in the material by measuring an instantaneous moving speed of the test body.

The acceleration sensor 4 has one set (light transmitting side and receiving side) sandwiching the test body 3 from above and below, and four sets 41-41 ′, 42-42 ′, 43-43 ′, and 44- 44 'is used, and in the left-right direction, the sensors 41 and 42 and the sensors 43 and 44 are adjacent to each other with a short distance.
When an object is rolled, the distance between the sensors 41-41 ′ and 42-42 ′ is determined, so the speed is calculated by the passing time, and the speed is also calculated in the section of the rolling sensors 43-43 ′ and 44-44 ′. Is done.

That is, light is emitted from the sensor, and when the test body 3 passes between the sensors, the light is blocked, the sensor reacts, and a test body is formed using a set of speed sensors and a set of adjacent speed sensors. Is measured for the time required to pass between two points, and the passing speed is calculated from the distance between adjacent sensors set in advance.
In this way, two specimen speeds are obtained. The speed obtained from the sensors 41-41 ′ and 42-42 ′ is v ₀ , and the speed obtained from the sensors 43-43 ′ and 44-44 ′ is v. If the distance between the sensors 41-41 ′ and 43-43 ′ (or the distance between the sensors 42-42 ′ and 44-44 ′) is s, the acceleration is obtained from the following equation (Equation 2).

The acceleration data thus obtained is processed by a processing process of a computer PC electrically connected to the acceleration sensor.
That is, the acceleration according to the equation (Equation 2) is expressed by the following equation (Equation 3).

The moment of inertia I is calculated by substituting into.
Here, M is the mass of the specimen, g is the acceleration of gravity, α is the inclination angle of the slope, and R is the diameter of the specimen.
Also, the moment of inertia I ′ when the specimen is homogeneous is calculated from the following equation (Equation 4).

  Then, the ratio of the moments of inertia I and I ′ is obtained. When I / I ′ is greater than 1, it indicates that the outside is heavier than the inside in the cross section of the test body 3, and I / I ′ is greater than 1. When it is small, it indicates that the inside is heavier than the outside in the cross section of the specimen 3, and when the ratio is exactly 1, it indicates homogeneity.

In order to confirm the above points, the present inventors conducted a preliminary experiment using a resin test specimen as a test specimen. The internal structure of the resin specimen is heavy, the specific gravity is 1.8 from the center to 2r / 3 (r: radius), the specific gravity is 0.9 from 2r / 3 to r, and the specific gravity (density) Comparison with 1.3 homogeneous specimens.
The internal structure of the resin test specimen with a heavy outside has a specific gravity of 0.9 from the center to 2r / 3 and a specific gravity of 1.8 from 2r / 3 to r, which is a specific gravity (density) of 1.4. Comparison with a homogeneous specimen.

The test results for the resin test piece with a heavy, homogeneous, and heavy inside showed an error of 3 to 5% from the calculated value. FIG. 3 shows the test results. When the value of the vertical axis is 1, the moment of inertia ratio is the same when the calculated diameter and length are the same and the density (homogeneous) is the same. Therefore, theoretically, the value of the homogeneous test specimens with specific gravity (density) 1.3 and 1.4 should be 1, but an error due to the manual rolling method occurs.
However, when the specific gravity (density) is 1.3 and the inner specific gravity (density) is heavy, that is, when it is difficult to rotate, the value is smaller than 1 as indicated by the blue circle in the figure. When the specific gravity (density) is 1.4 and the outside specific gravity (density) is heavy, that is, when it is easy to rotate, the value is larger than 1 as indicated by the green circle in the figure.
From these results, it was found that by measuring the acceleration and the inertial moment accompanying it, it was possible to estimate whether the outside of a certain material was heavy or the inside was heavy.

  Based on the above results, measurements were made using small cedar logs processed to an actual length of 20 cm and a diameter of 20 cm. Since the actual log is not uniform in internal specific gravity (density), the average value was obtained by measuring five times from each position obtained by dividing the circle into six equal parts. The result is shown in FIG. 4, and in the raw material state, the outer side is usually heavier in the red heart material, while the inner side is heavier in the black heart material. In the initial state, the ratio of moments of inertia was greater than 1 for the red heartwood and less than 1 for the black heartwood. This indicates that the assumption made from the results of testing with the resin was valid.

Then, the test body was left to dry in a 20 degreeC thermostat. In the initial state, when the inertia moment ratio is larger than 1 (red circles, red white circles), the wood loses moisture from the outside, so the inside becomes relatively heavy. The value gradually decreased and approached 1. In the middle, the value of the moment of inertia ratio was sometimes less than 1. This is probably because the inside became relatively heavy due to the influence of residual moisture in the center, and the degree was large. Eventually, the moisture was lost and the specific gravity (density) of the wood was affected, and the inertia moment ratio again exceeded 1.
On the other hand, the test piece (black circle) with a heavy inside from the beginning had a low moisture content due to its high moisture content, and the inertia moment ratio remained at a value of 1 or less throughout.
Assuming that the density distribution becomes homogeneous as it dries, the ratio of inertia moment is close to 1, and the variation is considered to be small. The “red heart (light) red-white circle” fits this well. .

Based on the above, the specific gravity (density) including moisture in the material is estimated from the acceleration and angular acceleration values when an acceleration sensor or angular acceleration sensor is attached to the log or lumber product and given a constant rotational force for a moment. It is possible. It can also be seen that by measuring the acceleration accompanying the rotation of the wood and the inertial moment associated therewith, it is possible to estimate the weight distribution inside the log or square bar. By measuring the mass at the same time, for example, in the case of a log, for example, the difference in specific gravity (density) inside and outside can be estimated regardless of the weight of the log, and the state of moisture can also be estimated.
In addition, a square lumber product such as a pillar material or a beam material can be regarded as a rotating body of an object, and particularly the internal residual moisture after drying can be detected.

The application of the present invention will be described. By applying an instantaneous torque to the target timber and measuring the acceleration accompanying the rotation of the timber and the inertial moment accompanying the rotation, the operation is performed every predetermined time. It is possible to know the temporal change of the cross-section moisture content distribution (inclination of internal moisture and external moisture) accompanying drying in wood.
Also, by applying an instantaneous torque to each different piece of wood and measuring the acceleration accompanying the rotation of the wood and the inertial moment accompanying it, the cross-section moisture content distribution (internal moisture and external moisture) of each piece of wood is measured. It is possible to grasp the inclination of moisture.

For example, there are cedar materials that have a large amount of moisture in the material and those that have a small amount of material. Now, when the moisture distribution of cedar logs is divided into cases, it is as shown in FIGS. Assuming that the patterns are A to D, A is external water: low, internal water: low, B is external water: high, internal water: low, C is external water: low, internal water: high, D is external water: Many, internal moisture: many, these four types can not be determined by just measuring the overall weight, there is no electrical principle moisture meter for such a large cross-section.
In the present invention, the difference between A and D is detected by an acceleration sensor, and the moisture content distribution of the cross section is selected before the lumbering process. In the above example, A and B are mainly used as columns and beams, and C and If D is mainly a plate material, the efficiency of the next drying step can be increased.

More specifically, if the density (high, low) of the cross sections A to D is adjusted and rolling is attempted, the result is as shown in FIGS. That is, A starts to rotate with a relatively small force, but the rotational acceleration is the smallest. B begins to rotate with a greater force than A and rotational acceleration is relatively easy to attach. C turns with greater power than A. However, the internal acceleration is difficult to counter the rotation acceleration. D starts to rotate with the greatest force, and the rotational acceleration is the largest.

  Therefore, if rolling is performed from the same position as shown in FIG. 7, the rolling is performed in the order of D> B> C> A. That is, the acceleration differs when a constant rotational force is applied. Based on this knowledge, the present invention reads the difference in acceleration due to the moisture content distribution with a sensor. An accelerometer 4 is arranged as shown in FIG. 8 and a constant rotational force (N / m) is applied to the log 3. If given, the value of acceleration changes depending on the internal weight distribution (moisture distribution), and in this example, acceleration D> acceleration A. From this, the density (moisture) distribution in the log can be estimated by the numerical value of the accelerometer.

As means for measuring the rotational acceleration of the timber of the present invention, the acceleration sensor 4 and the angular acceleration sensor 4 'can be used.
FIG. 10 shows an example using the acceleration sensor 4. The acceleration sensor measures acceleration when moving along two points on a straight line, and the physical quantity detected by the acceleration sensor is an instantaneous acceleration value of a tangent to the traveling direction of the timber. The acceleration in the right-angle direction is almost zero, and the perpendicular direction perpendicular to the traveling direction is also almost zero. When a constant rotational force is applied, the log is likely to rotate or difficult to rotate in relation to the weight and moisture distribution of the log, that is, the moment of tangent when a constant rotational force is applied. It detects a change in acceleration.

Since the acceleration sensor 4 measures the tangential acceleration, as shown in FIG. 10 (c), the longitudinal ends of the timber 3 are gripped by the chucks 8 and 8, and the acceleration sensor 4 is mechanically attached to the surface of the timber 3 and fixed. The actuators provided in the chucks 8 and 8 also give a certain rotation to the timber 3 and read the acceleration value.
FIG. 11 shows a method of attaching the acceleration sensor 4, where (a) is a square member, (b) is a square member such as a beam or a girder, and in either case, the acceleration sensor 4 has a material cross section. It is important to attach to the tangent on the circle with the center.
As shown in FIGS. 12 (a) and 12 (b), the acceleration sensor 4 is attached at least one place in the center of the material, preferably one place every 50 cm according to the length of the material. If the measured value deviates greatly from the reference value, it is determined that the measurement is rejected.

13 and 14 show an example using an angular acceleration sensor 4 '. The angular acceleration sensor 4 ′ measures a physical quantity with respect to the rotational motion of the object, and detects how much the turn is faster or slower per second when a constant rotational force is applied.
In the present invention, the angular acceleration sensor 4 'measures the change in the angular velocity per unit time, that is, the instantaneous change in the rotation speed of the timber when it is rolled, and relates to the weight of the timber and the state of moisture distribution. Applying the fact that the inertia moment (the amount representing the difficulty of rotating a rotating object) increases as the angular acceleration of the lever decreases, the state of moisture distribution is grasped.

When the angular acceleration sensor 4 'is attached, it is attached to the center of the log shaft, the sensor is incorporated in the lifting chucks 8 and 8, and the angular acceleration value is read by giving a constant rotation.
FIG. 14 shows a method of attaching the angular acceleration sensor 4 '. (A) is a case of a square member, (b) is a case of a square member such as a beam or a girder. In any case, the acceleration sensor 4' It is important to attach it to the center of the section of the material when rotating.

In the present invention, the rotational acceleration of timber by the acceleration sensor may be measured by collecting a specimen having a predetermined length, but can also be performed by a log lumber line. FIG. 9 shows this state. In a normal case, the peeled log 3 climbs on the conveyor 6 or the like before reaching the sawing line, and the log is a means 7 such as an arm just before sawing. And is scanned by video for optimum lumbering.
When hanging on this lumber deck, an acceleration sensor or angular acceleration sensor 4 is attached, a constant rotational force is given to the log 3, and it is measured that the acceleration value varies depending on the weight of the log and the moisture state inside the material. is there. The time required for the measurement is a few seconds, so that it is one of the patterns as shown in FIGS. 5A to 5D or the inclination of moisture in the cross section is detected. Therefore, it is possible to improve the drying efficiency.

In addition, although this invention is suitable for the measurement of the moisture content distribution in the state of a log, it can also be used for the measurement of the moisture state of a lumber product with a comparatively large cross section like a beam, a girder, and a pillar material.
That is, the highest quality display D15 and SD15 of the Japanese Agricultural Standards as column materials indicate that the average value of the cross section is 15% or less, but the internal distribution is ignored. This is because the distribution of internal moisture is not known by weight, and the moisture meter senses only about 20 mm from the surface, but in practice, the moisture distribution in the inside is different even at the same average moisture content.

If the present invention is applied and a certain torque is applied to the lumber product, the acceleration value changes depending on the moisture distribution inside, so that it is possible to sense the inclination of the internal moisture and the external moisture by measurement with an acceleration sensor.
If the moisture content check by acceleration measurement is performed at the curing stage after the drying process, it is possible to instantly determine those with a small moisture content gradient and those with a high internal moisture content, so the former is selected as a pass product for final processing. The latter can be transferred to re-drying or curing with the latter as a rejected product, and a reliable lumber product with excellent quality can be supplied to the market.

Further, the present invention is advantageously applied to the detection of the internal residual moisture of the dried lumber product. At present, before the final sizing process of dry lumber products, the dry lumber products are measured on the line by moisture measurement using a moisture meter and strength measurement by pressurization. Next, the internal residual moisture is detected by acceleration measurement, and if it does not meet the set standard, it will be rejected, the re-drying process will be performed, and those that have entered the set standard will pass after strength measurement. It is commercialized as a product. As a result, a lumber product with excellent quality can be obtained.

It is a perspective view which shows the outline | summary of the moisture measuring method in the timber of this invention. It is a side view of the method of the present invention. It is a diagram which shows the relationship between the specific gravity of a sample when experimenting using resin, and a moment of inertia ratio. It is a diagram which shows the relationship between the drying time of a cedar log measured by applying this invention, and a moment of inertia ratio. (A)-(d) is sectional drawing which shows the moisture distribution pattern of a cedar log. (A)-(d) is explanatory drawing which shows the cross-sectional density of each pattern of FIG. It is explanatory drawing which shows typically the acceleration of each pattern of FIG. (A) (b) is explanatory drawing which shows the relationship of the acceleration of the patterns A and D in FIG. It is explanatory drawing which shows the example which applied this invention to the sawmill line. (A) is a perspective view of the attachment state of an acceleration sensor, (b) is a perspective view of an acceleration generation state, (c) is a side view of an actual measuring apparatus. (A) is sectional drawing which shows the attachment position of the sensor to a square member, (b) is sectional drawing which similarly shows the attachment position of the sensor to square members, such as a beam and a girder. (A) (b) is a side view which shows the example of suitable arrangement | positioning of an acceleration sensor. (A) is a perspective view of the attachment state of an angular acceleration sensor, (b) is a perspective view of an angular acceleration generation state, (c) is a side view of an actual measurement apparatus. (A) is sectional drawing which shows the attachment position of the angular acceleration sensor to a regular square material, (b) is sectional drawing which similarly shows the attachment position of the angular acceleration sensor to square materials, such as a beam and a girder.

Explanation of symbols

3 Wood (log)
4 Acceleration sensor
4 'angular acceleration sensor

Claims (2)

  Apply momentary rotational force to the timber, measure the acceleration at that time, determine the moment of inertia from this measured acceleration, and determine the water distribution in the timber by the ratio to the moment of inertia when the specimen is homogeneous A method for measuring moisture in wood, characterized by The method for measuring moisture in a wood according to claim 1 , wherein the acceleration measuring means is either an acceleration sensor or an angular acceleration sensor.

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