JPH05209723A - Method for measuring thickness of transparent sheet - Google Patents

Abstract

PURPOSE:To measure the thickness of a transparent sheet highly accurately by setting the path of laser light at a light path when the distance between preset two points is measured by triangulation, and using the difference between the distance values between two points, when the transparent sheet is not arranged yet and when the sheet is arranged, and a refractive index. CONSTITUTION:The path of laser light of a laser displacement gage 1 is set so that a distance D between a point A and a spot light source P is measured based on an angle 9 of the laser light, which is received by a light receiving part 3 at a point B, with the distance C between the point A and the point B that is a constant as a reference. In this light path, a transparent sheet 4 to be measured is arranged in parallel with a diffusing and reflecting surface so that the laser light is refracted one time and made to pass without reflection. When the light is refracted and made to pass through the sheet 4, the angle theta of the laser light, which is received by the light receiving part 3 at the point B, is changed to the same angle when the position of the spot light source P is located at a point Q. The distance D as the constant is measured as a distance (d) between the point A and the point Q, and deviation Z is generated. A refractive index (n) of the transparent sheet 4 to be measured is applied on the deviation Z. Thus, a thickness (t) is computed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent sheet thickness measuring method, and more particularly to a non-contact type measuring method using a laser beam of a laser displacement meter.

[0002]

BACKGROUND OF THE INVENTION Conventionally, in order to measure the thickness of a transparent sheet, a measurement method by mechanical contact, that is, a mere measurement in which a transparent sheet which is an object to be measured is sandwiched by a measuring device such as a micrometer is used. It is widely used because the method is simple and inexpensive, and highly accurate measurement is possible. However, with such a measuring method, when the transparent sheet is made of a delicate material, the surface of the transparent sheet may be scratched or soiled when the transparent sheet is clamped by the measuring instrument, and therefore the measurement cannot be performed.

Therefore, in the case of a transparent sheet made of a material that cannot be measured by the contact type measuring method as described above, the thickness is measured by utilizing the difference in infrared absorption which increases or decreases depending on the thickness of the transparent sheet. A non-contact infrared absorption type thickness measuring method is used.

[0004]

However, in the above infrared absorption type thickness measuring method, since the infrared absorption of the transparent sheet which is the object to be measured is utilized, the transparency changes depending on the color tone or the haze of the transparent sheet. In that case, the infrared absorption also changes, so an error is likely to occur. Further, it has a drawback that the device is expensive because the measuring mechanism is complicated.

Incidentally, in the measuring method by the mechanical contact,
When measuring the thickness uniformity of a long or wide transparent sheet, there is a drawback that it is troublesome and complicated.

Therefore, an object of the present invention is to provide a non-contact type measuring method capable of easily and highly accurately measuring the thickness of a transparent sheet.

[0007]

The present inventors have achieved the present invention as a result of extensive studies to achieve the above object.

That is, in the method for measuring the thickness of a transparent sheet according to the present invention, the optical path of the laser beam of the laser displacement meter is set to the optical path for measuring the preset distance between two points by triangulation, A transparent sheet to be measured is arranged in the optical path of the laser beam so that the laser beam can be refracted and passed at least once without being totally reflected, and the distance between two points obtained by changing the refraction of the transparent sheet. It is characterized in that the thickness of the transparent sheet is calculated from the difference between the two-point distance value when the original transparent sheet is not arranged and the refractive index of the transparent sheet.

A preferred embodiment of the transparent sheet thickness measuring method according to the present invention calculates the thickness of the transparent sheet by adding a temperature correction value when the refractive index of the transparent sheet to be measured changes with temperature. That is.

In the present specification, the transparent sheet means
The term “transparent sheet” refers to a sheet that transmits laser light, and the transparency, haze, and color tone are not particularly limited as long as the sheet transmits laser light, and includes a semitransparent sheet.

[0011]

According to the present invention, the optical path of the laser beam of the known laser displacement meter is set to the optical path for measuring the preset distance between two points by triangulation, and the optical path of the laser beam is set. By arranging the transparent sheet to be measured therein so that the laser light can be refracted and passed at least once without being totally reflected, the laser light is refracted when passing through the transparent sheet, and the optical path is changed. By changing this optical path,
The light receiving angle of the diffused light of the light receiving portion changes, and the distance between the two fixed points apparently changes. The degree of this change corresponds to the thickness of the transparent sheet under a constant refractive index. Therefore, the thickness of the transparent sheet can be calculated by adding the refractive index of the transparent sheet to the degree of the change with respect to the determined distance value between the two points when the original transparent sheet is not arranged.

A laser displacement meter is used to measure the thickness of a non-transparent sheet, and the measuring method is to measure the distance to one side of the sheet and the distance to the other side of the sheet, respectively. The thickness is obtained by subtracting the distance between the two laser displacement meters from the sum obtained by measuring using the laser displacement meter. In such a measuring method, since it is an absolute condition that the laser light is reflected on both surfaces of the sheet, it is impossible to measure the thickness of the transparent sheet through which the laser light is transmitted without being reflected.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic explanatory view showing an example of the measuring method of the present invention, and FIGS. 2 to 5 are schematic explanatory views showing other examples.

In the figure, 1 is a laser displacement meter, 2 is a laser beam projecting section, 3 is a laser beam receiving section, 4 is a transparent sheet to be measured, and 5 is a projecting section 2 and a receiving section 3 of the laser displacement meter 1. It is a diffuse reflection surface that is parallel to. Further, the point A is the position of the laser light projecting unit 2 (hereinafter, simply referred to as the point A),
Point B is the position of the laser light receiving portion 3 (hereinafter simply referred to as point B), C is the distance from point A to point B and is a preset constant (hereinafter simply referred to as distance C), and D is from point A. The distance to the diffuse reflection surface 5 and a preset constant (hereinafter,
The distance is simply referred to as D), P is the position of the point light source on the diffuse reflection surface 5 of the laser light emitted from the light projecting portion 2 (hereinafter referred to as point light source P), n is the refractive index of the transparent sheet 4, and t is the transparent sheet 4. , Θ is the angle of the laser beam received by the light receiving portion 3 at the point B, and the thickness t of the transparent sheet 4 which is the object to be measured.
And a variable that changes depending on the refractive index n (hereinafter, simply referred to as an angle θ). Further, in the following description, reference numerals not mentioned above will be explained each time.

The optical path of the laser beam of the laser displacement meter 1 is
The optical path when the preset distance between two points is measured by triangulation, that is, the laser light emitted from the point A is received by the light receiving unit 3 at the point B using the point P of the diffuse reflection surface 5 as the point light source. To set. That is, the distance D between the point A and the point light source P is measured from the angle θ of the laser light received by the light receiving unit 3 at the point B with reference to the distance C which is the distance between the point A and the point B and is a constant. To set. In the present invention, the distance D measured by triangulation is set as a preset constant.

The laser displacement meter 1 set as described above
The transparent sheet 4 to be measured is arranged parallel to the diffuse reflection surface 5 in the optical path of the laser light, and the laser light is refracted at least once without being totally reflected. In the case of FIG. 1, it is point light source P that refracts and passes through the transparent sheet 4.
The laser light is diffusely reflected at and is received by the light receiving unit 3.

By refracting and passing through the transparent sheet 4,
The angle θ of the laser light received by the light receiving unit 3 at the point B changes to the same angle as when the position of the point light source P is at the point Q as shown by the dotted line. Therefore, the distance D which is originally a constant
Will be measured as the distance d that is the distance between the points A and Q, and the deviation Z that is the distance between the points P and Q will occur.
The deviation Z corresponds to the thickness t under a constant refractive index n of the transparent sheet 4. Therefore, the thickness t can be calculated by adding the refractive index n of the transparent sheet 4, which is the object to be measured, to this deviation Z. A calculation formula [1] for obtaining the thickness t from the deviation Z and the refractive index n is shown below.

[0019]

[Formula 1]

In the present invention, when the refractive index n of the transparent sheet 4 to be measured changes with temperature, temperature correction is performed. Further, when it is difficult to precisely manage the distance C and the distance D, such as when the distance C and the distance D, which are constants, change due to conditions such as a measurement environment, the thickness t is set to the constant t. And the angle θ are calculated and a calibration curve is created to perform zero / span correction.

Further, in the present invention, it is preferable to control the automatic calculation / calculation by using a personal computer or the like to make the above calculation formula [1] into software and further inputting various correction values.

The method for measuring the thickness of the transparent sheet according to the present invention has been described above. However, in the present invention, it is possible to measure even when the arrangement position of the transparent sheet to be measured changes as shown in FIGS. You can

The embodiment shown in FIG. 2 is a case where the transparent sheet 4 is obliquely arranged with respect to the diffuse reflection surface 5, that is, the laser light is refracted and passes through the transparent sheet 4 twice.

In this case, the position of the point light source on the diffuse reflection surface 5 is not P but P ', and the optical path to the light receiving portion 3 at the point B is P'-X-Y-B. BY // XP 'here. The angle θ at this time is equal to the angle ∠YP ″ O formed by the BY extension point and the diffuse reflection surface 4. Therefore, the apparent distance is measured as the distance d which is the distance between the points A and Q. ,
A deviation Z, which is the distance between the points P and Q, occurs. From the deviation Z and the refractive index n, the thickness t is calculated by the above calculation formula [1]. The case of this embodiment is shown below as a calculation formula [2].

[0025]

[Formula 2]

In the above calculation formula [2], P'is a diffuse reflection surface 5 of the laser light refracted and passed by the transparent sheet 4.
Position of the point light source, P ″ is the position of the point light source when viewed from the point B through the transparent sheet 4, α is the angle that the transparent sheet 4 forms with the diffuse reflection surface 5, and β is (90 ° -α). The other symbols are as described above, that is, when the laser light refracts and passes through the transparent sheet 4 twice, if the angle α formed by the transparent sheet 4 and the diffuse reflection surface 5 is determined, the conditions are as described above. The thickness t can be obtained by applying the calculation formula [2].

The case where the angle is 45 ° as described above and the angle is 45 ° is shown as a calculation formula [3] below based on FIG.

[0028]

[Formula 3]

In addition to the above-mentioned FIGS. 2 and 3, as shown in FIGS. 4 and 5, the transparent sheet 4 may be arranged and the edge portion of the transparent sheet 4 may be used for the measurement. That is, in FIG. 4, the transparent sheet 4 is arranged in parallel with the diffuse reflection surface 5 so that the laser light from the light projecting unit 2 does not pass therethrough, and only the laser light diffusely reflected by the point light source P is refracted and passed once. Further, FIG. 5 shows that the transparent sheet 4 is obliquely arranged with respect to the diffuse reflection surface 5, the laser light is refracted and passed once and then diffused and reflected by the diffuse reflection surface 5, and the laser light diffusely reflected is a transparent sheet. This is a mode in which the light is received by the light receiving unit 3 without passing through 4.

Experimental examples of the present invention will be described below. Experimental Example 1 A transparent sheet made of polycarbonate (PC) having a refractive index n = 1.59 is arranged in parallel with the diffuse reflection surface by a laser displacement meter having the distance C set to 20 mm and the distance D set to 40 mm to adjust the thickness. It was measured. The transparent sheet has a nominal thickness of 1
mm, 2 mm, 3 mm, 5 mm, and 8 mm,
Measurements by a micrometer and infrared absorption method were also performed at the same time. The results are shown in Table 1 below. A commercially available LB series manufactured by Keyence Corporation was used as the laser displacement meter, and the diffuse reflection surface was a blank sheet. As the infrared absorption type thickness measuring device, an infrared thickness measuring device manufactured by Kurabo Industries, Ltd. was used.

[0031]

[Table 1]

From the results shown in Table 1, it can be seen that the measuring method of the present invention enables measurement with the same accuracy as a micrometer. In the case of the infrared absorption type, the price of the device is 10 in order to obtain the same accuracy as the measuring method of the present invention.
This is about double the cost and extremely high cost. In addition, it takes time and effort to perform the measurement because the measurement conditions such as the measurement position are strict.

Experimental Example 2 An experiment was conducted in the same manner as in Experimental Example 1 except that a semi-transparent sheet was used. The measurement method of the present invention gave substantially the same results, while the infrared absorption measurement method , There was a considerable error. This is probably because the infrared absorption of the transparent sheet changed according to the change in transparency.

As can be seen from Experimental Examples 1 and 2, according to the measuring method of the present invention, the thickness of the transparent sheet is refracted by using the laser light of a known laser displacement meter which is relatively simple as an instrument. Based on the principle, the measurement can be performed very easily and easily at low cost. Further, it is preferable that the measuring device is connected to a computer, and the calculation formulas described above are made into software so that measurement, calculation and display can be easily and automatically performed.

If a laser displacement meter capable of simultaneously measuring the amount of received laser light is used, the amount of laser light attenuated (or the degree of absorption) of the laser light attenuated by absorption after passing through the transparent sheet. ) Is calculated, and the light transmittance per unit thickness is found from the attenuation amount and the calculated thickness of the transparent sheet, so that the transparency of the transparent sheet can be measured.

[0036]

According to the present invention, as long as a laser beam can be transmitted, it is not affected by changes in transparency such as color tone and haze of a transparent sheet, so that it has an effect of reducing errors.

Further, in comparison with the infrared absorption type thickness measuring method, not only the measuring range is wide, but also the apparatus used uses a laser beam of a known laser displacement meter which is relatively simple and inexpensive as an instrument. However, if the accuracy is about the same, the cost is 1/10, and if the apparatus is about the same, the accuracy is 10 times, so that the cost is low.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an example of a measuring method of the present invention.

FIG. 2 is a schematic explanatory view showing another example.

FIG. 3 is a schematic explanatory view showing another example.

FIG. 4 is a schematic explanatory view showing another example.

FIG. 5 is a schematic explanatory view showing another example.

[Explanation of symbols]

 1 Laser displacement meter 2 Laser light projector 3 Laser light receiver 4 Transparent sheet 5 Diffuse reflection surface

Claims (2)

[Claims] 1. An optical path of a laser beam of a laser displacement meter is set to an optical path for measuring a preset distance between two points by triangulation, and a transparent sheet to be measured is provided in the optical path of the laser beam. The distance between two points, which is arranged so that the laser light passes through refraction at least once without being totally reflected, and the distance between two points obtained by changing the transparent sheet through refraction and the distance between two points when the original transparent sheet is not arranged. A method for measuring the thickness of a transparent sheet, comprising calculating the thickness of the transparent sheet from the difference between the value and the refractive index of the transparent sheet. 2. The thickness measurement of the transparent sheet according to claim 1, wherein when the refractive index of the transparent sheet to be measured changes with temperature, a temperature correction value is added to calculate the thickness of the transparent sheet. Method.