JP2637696B2 - Measurement method of cell number of foam sheet by laser beam attenuation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to foaming by laser beam attenuation, in which a laser beam is transmitted through a foam sheet to be measured, and the number of cells or cell density per unit thickness is estimated based on the attenuation rate of the transmitted light. The present invention relates to a method for measuring the number of cells in a body sheet.

[0002]

2. Description of the Related Art In general, foam sheets such as polystyrene and polyethylene are used as a material for tableware trays and simple tableware.

[0003] The thickness of the foam sheet ranges from a relatively thin one of about several mm to a thick one exceeding 10 mm depending on the application. However, in order to sufficiently fulfill the function as a product, the foam sheet is required. Is desired to be uniform in thickness. Therefore, various thickness measuring methods for continuously measuring the thickness of the foam sheet in the manufacturing process have been proposed.

The thickness measuring method is roughly classified into a contact type and a non-contact type, and an infrared type is widely used as the non-contact type. In the infrared method, a method of irradiating an infrared ray to a foam sheet and measuring how much the infrared ray is absorbed when passing through the foam sheet (infrared absorptivity), and estimating the thickness is adopted.

[0005]

However, in order to strictly control the quality more strictly, not only the thickness of the foam sheet but also the number of cells or the cell density existing in a unit thickness of the foam sheet is required. It is preferable to make it uniform. If the cell structure is rough due to the non-uniform cell density, there is a problem that, in addition to the variation in the strength of the foam container, the possibility that the fluid or the like filled in the container infiltrates or flows out increases. is there. Further, since infrared rays do not pass through a thick foam sheet exceeding 10 mm, there are restrictions on the measurement target.

Therefore, the thickness is as constant as possible, and
The goal is to manufacture trays and dishes that have a uniform cell density in the future. To achieve this goal, it is necessary to accurately measure not only the thickness of the foam sheet but also the cell density per unit volume. Is essential.

However, at present, various methods for measuring the thickness have been proposed, but no method for measuring the number of cells per se has been proposed.

The present invention has found that the number of cells through which the laser beam has passed is proportional to the attenuation factor of the laser beam, and by determining this attenuation factor, the number of cells at the point where the laser beam passes through the foam sheet is determined. An object of the present invention is to provide a method for measuring the number of cells of a foam sheet by laser light attenuation for estimating cell density.

[0009] Since the laser beam passes through a thick foam sheet exceeding 10 mm, the range of the object to be measured can be expected to be widened.

[0010]

In order to solve the above-mentioned problems and to achieve the object, a method of measuring the number of cells of a foam sheet by laser light attenuation according to the present invention is described. The transmitted light intensity of the transmitted laser light is the first
The detector detects and compares the intensity of the transmitted light detected by the first detector with the output value of the laser light from the light emitting source by the calculation unit, thereby obtaining the cells of the foam sheet at the above-described laser light transmitting portions. It is characterized by measuring the number.

In the method for measuring the number of cells of a foam sheet by laser light attenuation according to the present invention, the half mirror disposed between the light emitting source and the foam sheet described above allows the laser beam emitted from the light emitting source to be irradiated. A second detector for detecting a part of the first detector is used.
The transmitted light intensity detected by the detector may be corrected.

Further, according to the method of the present invention for measuring the number of cells of a foam sheet by attenuating a laser beam, the above-mentioned modulator connected to a light emitting source modulates a laser beam applied to the foam sheet and modulates the laser beam. The transmitted light intensity of the laser light may be detected by the first detector via a filter that transmits only light.

[0013]

According to the present invention, the laser beam emitted from the light emitting source is attenuated at a constant rate each time it passes through each cell of the foam sheet to be measured. The degree of the attenuation depends only on the state of the cell surface of the foam sheet, that is, the physical properties of the foam sheet. That is, regardless of the thickness of the foam sheet, the degree of attenuation is large when the number of cells at the location where laser light is transmitted is large, and is small when the number of cells at the location where laser light is transmitted is small.

In particular, when measuring the number of cells of the foam sheet and thus the cell density according to the present invention, a characteristic feature is that even if the same foam sheet remains in a predetermined thickness, The point is that the number of cells is the same even when is thinned by pressing.

Therefore, if the light attenuation per unit transmission length in the natural state of the foam sheet, that is, the light attenuation rate is measured in advance, the thickness of the foam sheet can be calculated from the actually measured total light attenuation. Can also. The number of cells in the portion where the laser light has passed can be estimated from the amount of attenuation of the laser light. That is, if the thickness is known, the cell density is almost specified.

In addition, by using a half mirror to guide a part of the laser beam to the second detector and using the transmitted output light amount with reference to the output, an error due to laser output fluctuation can be completely removed. Accuracy can be measured.

Further, when a modulator and a filter are used, a wavelength region other than the specific frequency same as the laser beam is absorbed by the filter, and the modulation of the laser detected by the second detector and the first and second modulations are performed.
By comparing the modulation with the laser detected by the detector, a wavelength region not synchronized with the modulation signal can be removed, and a more accurate measurement can be performed by eliminating a disturbance factor.

[0018]

Next, a first embodiment in which the present invention is applied to an apparatus for measuring the number of cells of a polystyrene foam sheet will be described with reference to FIGS.

As shown in FIG. 1, the apparatus 10 includes a light emitting source 12 for irradiating a laser beam L having a predetermined output, and a condensing section 14 for condensing a laser beam L ′ transmitted through a polystyrene foam sheet P. A first detector 16 (for example, a light receiving element is a photodiode) for measuring the transmitted light intensity of the laser light, and the transmitted light intensity detected by the first detector 16 and the output value of the laser light L from the light emitting source 12. It is provided with a calculation unit 18 for taking in and measures the number N of cells of the polystyrene foam sheet P by a method described below.

First, a laser beam L having a specific frequency is irradiated onto a polystyrene foam sheet P to be measured. The polystyrene foam sheet P having a predetermined thickness d is translucent and has a random cell structure as shown in FIG. 2, and the inside of each cell _SN is an air chamber.

Therefore, a part of the laser light L is attenuated by scattered reflection on the surface of each cell _{SN as} shown by an arrow in FIG. The transmitted light intensity of the attenuated laser light L '
The detection rate is detected by the detector 16, and the arithmetic section 18 compares the output value of the laser light L from the light emitting source 12 to determine the attenuation rate of the laser light. According to the attenuation rate, the number of reflection surfaces (= the number of cells N) at the laser beam transmission portion can be estimated,
Further, the thickness d of the foam sheet P can be almost specified.

The analysis principle and measurement method will be described in more detail.
explain. Generally, the attenuation of the laser light L is_1-N
Reflection on the surface of the cell and cell S_1-NBoth absorption inside
Cell S of the foam sheet P_1-NIs empty inside
Because it is a room of mind, you can think of only scattering reflection
(See FIG. 2). Therefore, the incident light intensity of the laser light L is
I _iAnd the transmitted light intensity is I_O, Each cell surface S_i(I = 1, 2,
.., N)_iThen I_OIs the next
It is expressed by equation (1). I_O= (T_NT_N-1... T_i... T_ThreeT_TwoT₁) I_i (1) On the other hand, the light attenuation in the foam sheet P is a spatial average.
Then, it can be expressed by Lambert's law of the following equation (2)
I can do it. In the equation (2), α is an absorption coefficient of the foam sheet P,
d is the thickness of the foam sheet P. I_O= I_iExp (−αd) (2) Considering both equations (1) and (2), Log (T_NT_N-1... T_i... T_ThreeT_TwoT₁) = (− ΑLoge) d (3) That is, each cell S_NSurface transmittance T_iDirectly
It is impossible to determine the total volume in the optical path in the direction of thickness d.
Minute value (= T_NT_N-1... T_i... T_ThreeT_TwoT₁) Is the attenuation of transmitted light
Can be measured from Force each T_iOne to get information about
As shown in FIG. 1, the method of
Compressed by sandwiching between extremely transparent glass plates 20, 20
By changing the thickness d and measuring the transmitted light intensity.
is there. If this transmitted light intensity does not depend on the thickness d, each cell
S_NSurface transmittance T_iIs almost equal overall from the experimental results
Can be estimated.

Since the transmittance T _i at each cell _SN surface is considered to be approximately equal from the experimental results (ΔT), from the above equation (3), -αd = (N / Log) LogT or , Α = − (LogT / Log) · (N / d) (4) Thus, the attenuation coefficient α of the laser light is N /
d, ie, proportional to the cell density M (= N / d),
If the attenuation coefficient α is known, the cell density M (= N / d) can be almost estimated. However, as is clear from the equations (2) and (4), the attenuation rate of the laser light L is α which is directly proportional to the cell density M.
And the product of the thickness d of the foam sheet P, and the two cannot be measured individually. That is, if the value of the thickness d of the foam sheet P is known in advance, the absorption coefficient α can be estimated.

In the apparatus shown in FIG. 1, the foam sheet P is inclined at an angle θ with respect to the normal line for the following reason. In the actual measurement, the foam sheet P is not always perpendicular to the laser optical axis x at the time of measurement due to flapping or waving of the foam sheet P on the production line. If it can be confirmed that the attenuation rate of the laser beam does not change as long as the laser beam passes through the same cell arranged in the direction, it is useful to eliminate a measurement error due to the displacement of the foam sheet.

In this embodiment, the influence of the angle θ and each cell
S_N(S cell is compressed Pressed and crushed
To determine the effect of
P is sandwiched between optical glasses 20 and 20 having extremely high transmittance.
From the uncompressed state and gradually compress
Transmitted light intensity (that is, laser light measured by the first detector 16)
L ′ output) and the transmitted light intensity measurement at an arbitrary angle θ.
The average was determined. This measurement process will be described.

When the laser beam L is incident with an inclination of θ with respect to the normal to the incident surface, the optical path length d is simply set to d / cos θ under the condition that the transmittances at the respective cell _SN surfaces are equal. Just replace it. Therefore, from the above equation (2), θ
The output light intensity I _O (θ) / I _O normalized by the output when θ = 0 when tilted only by θ can be expressed by the following equations (5) and (6). I _O (θ) / I _O = exp {−αd (1 / cos θ−1)} (5) That is, if this is expressed in logarithm, Log (I _O (θ) / I _O ) = − ( αd / Loge10) · (1 / cos θ−1) (6)

Normally, it is considered that θ << 1, so that 1 / co
sθ-1 ≒ θ ^2/2 becomes, [Delta] I the increment of I _O by theta _O
If put and can be obtained ^{_{ΔI O / I O ≒ -αdθ 2}} /2 ··· (7). Here, the minus sign is attached to the angle θ.
Means that the output decreases as increases. As described above, since the output decrease is proportional to θ ² , it can be seen that the output decrease sharply increases when the angle θ becomes a certain magnitude, but can be almost ignored when the angle θ is small.

Next, the effects obtained as a result of the measurement according to the present embodiment will be described with reference to FIGS.

FIG. 3 shows that a relatively thick polystyrene foam sheet P is gradually compressed from an uncompressed state (thickness d = 4.0 mm) (d = 4.0 mm → d ′ = 3.2 m).
m), only the reflection state of each cell _SN surface is changed (transmittance T _i → T _i ′ on each cell _SN surface), and the transmitted light intensity (detected by the first detector 16 at the time of no compression and at the time of compression) The transmission intensities of the laser beams thus obtained are referred to as I _O and I _O ′).

As described above, even if the foam sheet P having a predetermined thickness d is compressed to change the thickness and change the surface condition, the transmitted light intensity of the laser beam hardly changes (I _O ≒ I _O ′). ),
The relationship of αd = α′d ′ is obtained from the equation (2). Similarly,
Even when the thickness d of the foam sheet P having a thickness of 2.0 mm, 6.0 mm or 8.0 mm is compressed within an appropriate range, the total number N of cells in the transmission light path is substantially constant. since maintained, the transmittance T _i of each cell S _N surface from the above equation (4) it can be concluded that is approximately the same (= T) in the whole area of the foam sheet (see FIG. 4).

[0031] Then the angle theta variously changed, the transmitted light intensity normalized by the transmitted light intensity I _O of the time of _{θ = 0 I O (θ)} /
FIG. 5 shows an example of measuring I _O.

According to FIG. 5, Log (I _O (θ) / I _O ) and (l / cos θ-1) are in a proportional relationship, that is, the relationship of the above-mentioned equation (6) holds. It turns out that there is. Since this relational expression is obtained assuming T _i ≡T (i = 1,..., N), it can be inferred from FIG. 5 that the transmittances of the surfaces of the cells _SN are equal.

From the above two measurement results, it can be seen that the transmittance of each cell _SN surface of the polystyrene foam sheet P is substantially equal on all surfaces. Therefore, when the thickness d of the foam sheet P in the non-compressed free state is known in advance by another method, the cell density M can be measured from the above-described equation (4). When the above information is obtained, the thickness d can be measured on the contrary.

From the above, the measuring method of the present embodiment is based on, for example, inspecting the foam sheet P as a product material, so that the liquid is infiltrated at a stage before manufacturing a container (not shown) as a final product. The risk of spillage can be determined. Such a risk is inversely proportional to the total number of cells in the thickness direction of the foam sheet P. Therefore, if the cell number N is equal to or more than a predetermined value, there is no danger of infiltration or the like.

Next, referring to FIG. 6, the present invention relates to an apparatus 2 for measuring the number N of cells of a polyethylene foam sheet P '.
A second embodiment applied to 0 will be described.

In the method of measuring the number of cells of a foam sheet by laser light attenuation according to the present embodiment, the half mirror 21 is disposed between the light emitting source 12 and the foam sheet P ′ described above. The output fluctuation of the laser light L emitted from the light emitting source 12 due to the power supply voltage fluctuation or the like is detected by the second detector 22, and detected by the first detector 16 based on the fluctuation signal from the second detector 22. The transmitted light intensity is standardized. Although the measurement object of the present embodiment is a polyethylene foam sheet P ′, the other configuration of the device used for the measurement and the method of measuring the number of cells using this device are almost the same as those of the first embodiment.
The same reference numerals as in FIG. 1 are used in FIG. 6 to simplify the description.

However, according to the present embodiment, the sample light L "is taken out by the half mirror 21 and the change signal of the sample light L" is input to the arithmetic unit 18 while being checked by the second detector 22. Correct the minute. Therefore, an error due to a change in the intensity of the laser beam due to a change in the voltage or deterioration of the light emitting source can be accurately corrected, and measurement with higher accuracy than in the first embodiment can be performed.

Next, referring to FIG. 7, the present invention relates to an apparatus 3 for measuring the number of cells N of a polyethylene foam sheet P '.
A third embodiment applied to 0 will be described.

In the method of measuring the number of cells of the foam sheet by the laser beam attenuation, the modulator 31 connected to the light emitting source 12 modulates the laser beam L applied to the foam sheet P ′, and modulates the transmitted light. The intensity is detected by the first detector 16, and the calculation unit 18 compares the intensity with the output value of the laser light L from the laser source 12 in the light emitting source 12. Therefore, the filter 32 that transmits only the modulated laser light L ′ is the first filter.
It is arranged immediately before the detector 16. Other configurations of the device used in the present embodiment and the method for measuring the number of cells using this device are almost the same as those in the first and second embodiments, and therefore, the same reference numerals as in FIG. The description is omitted here.

Although various methods can be applied to the modulation method, amplitude modulation is the most preferable. By applying amplitude modulation to the laser beam L by the modulator 31, only the upper and lower widths of the amplitude can be extracted by the filter 32. it can. Therefore, the disturbance factor (the same external frequency component as the laser light emitted from the light emitting source) is removed by the arithmetic unit 18 and only the laser light L ′ synchronized with the modulation can be detected. Therefore, by using the half mirror 21 and the second detector 22 together, more accurate measurement becomes possible.

The photodiodes used in the first and second detectors 16 and 22 are photodiodes in each embodiment. However, the present invention is not limited to this, and phototransistors may be used. Further, in each of the embodiments, the measurement target was the polystyrene foam sheet P or the polyethylene foam sheet P ′. However, the present invention is not limited to this. Can be measured.

【The invention's effect】

As described above, according to the present invention, the attenuation rate can be determined from the transmitted light intensity of the laser light transmitted through the foam sheet as the object to be measured and the output value of the laser light from the light emitting source. Therefore, without contacting the foam sheet at all, the value of this attenuation factor allows the number of cells of the laser beam transmitting portion to be estimated with high speed and high accuracy, and the number of cells per unit thickness, that is, the cell density can be almost specified. .

Therefore, the present invention is most suitable for measurement of a soft foam sheet manufactured at a high speed, and a material such as a tray or tableware having a uniform thickness and a uniform cell density by thorough quality control. Advantages such as being suitable for equipment for stably manufacturing sheets are provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment applied to an apparatus for measuring the number of cells of a polystyrene foam sheet.

FIG. 2 is a schematic sectional view showing a cell structure of a polystyrene foam sheet.

FIG. 3 is a graph (graph) showing a measurement result of laser light transmitted light intensity when a 4.0 mm polystyrene foam sheet is gradually compressed.

FIG. 4 is a table (table) showing measurement results of transmitted light intensity of laser light when polystyrene foam sheets having different thicknesses are compressed.

FIG. 5 is a diagram (graph) showing a measurement example of transmitted light intensity of laser light when the angle θ is changed.

FIG. 6 is a schematic configuration diagram of a second embodiment applied to an apparatus for measuring the number of cells of a polyethylene foam sheet.

FIG. 7 is a schematic configuration diagram of a third embodiment applied to an apparatus for measuring the number of cells of a polyethylene foam sheet.

[Explanation of symbols]

10, 20, 30 Apparatus for measuring the number of cells of a foam sheet 12 Light source 16 First detector 18 Operation unit 21 Half mirror 22 Second detector 31 Modulator P, P 'Foam sheet L, L', L ”Laser light S cell N cell number

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-98237 (JP, A) JP-A-6-50873 (JP, A) JP-A-2-124446 (JP, A)

Claims (3)

(57) [Claims] 1. A first detector detects a transmitted light intensity of a laser beam emitted from a light emitting source onto a foam sheet and transmitted through a cell, and detects the transmitted light intensity detected by the first detector and the transmitted light intensity in the light emitting source. A method for measuring the number of cells of a foam sheet by attenuating a laser beam, wherein the number of cells of the foam sheet at a transmitting portion of the laser beam is measured by comparing an output value of the laser beam with an arithmetic unit. 2. A half mirror disposed between the light emitting source and the foam sheet leads to a second detector for detecting a part of laser light emitted from the light emitting source. 2. The method for measuring the number of cells of a foam sheet by laser light attenuation according to claim 1, wherein the transmitted light intensity detected by the first detector is corrected by the signal. 3. A modulator connected to the light-emitting source modulates a laser beam applied to the foam sheet and controls a transmitted light intensity of the laser beam through a filter that transmits only the modulated laser beam. The method according to claim 1 or 2, wherein the number of cells in the foam sheet is determined by laser light attenuation.