JP2010156603A - Device and method for measuring thickness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thickness measuring device and a thickness measuring method capable of measuring the thickness of an optically transparent object, even when it is difficult to discriminate between a receiving position of light returning from its front face and a receiving position of light returning from the rear face. <P>SOLUTION: The thickness measuring device 1 includes: a light projecting part 2; a light receiving part 13 capable of respectively receiving light L23 reflected by an arrangement surface when no optically transparent objects 9 are present on the arrangement surface 11A, and light L22 reflected by the rear face when the optically transparent object is present on the arrangement surface; and a measuring part 8 for measuring the thickness of the optically transparent object on the basis of the correlation between the distance &Delta;X2 between a receiving position X3 of light reflected at the light receiving part and a receiving position X2 of light reflected by the rear face, and the thickness d1 of the optically transparent object. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a thickness measuring apparatus and a thickness measuring method for measuring the thickness of a light transmissive object.

Conventionally, a thickness measuring device for measuring the thickness of a transparent body such as glass has been provided (see Patent Document 1). This thickness measuring apparatus uses a CCD as a light receiving element, and is configured such that reflected light from the front surface of the transparent body and reflected light from the back surface are received by the CCD. Then, the light receiving position of the reflected light on the CCD is determined corresponding to the reflection position of the front surface and the back surface, and the peak position where the light reception level reaches the peak in each of the reflected light irradiation regions on the front surface and the back surface. A method is used in which each is detected and the thickness of the transparent body is measured based on the peak positions.
JP 2004-93206 A

  As described above, the conventional thickness measuring device detects the light receiving positions of the reflected light from the front surface and the reflected light from the back surface of the transparent body, and measures the thickness of the transparent body based on the both light receiving positions. However, for example, when the light transmittance of the transparent body is relatively high or when the transparent body is relatively thin, the light receiving position of the reflected light from the front surface and the light receiving position of the reflected light from the back surface are discriminated. This makes it difficult to measure the thickness.

  The present invention has been completed based on the above circumstances, and its purpose is when it is difficult to discriminate the light receiving position of the reflected light from the front surface and the light receiving position of the reflected light from the back surface. The present invention provides a thickness measuring device and a thickness measuring method capable of measuring the thickness of a light transmissive object.

  (1) As a means for achieving the above object, a thickness measuring apparatus according to the first invention is a thickness measuring apparatus for measuring the thickness of a light transmitting object existing on a predetermined arrangement surface. A light projecting portion that emits light obliquely toward the arrangement surface, and first reflected light that is specularly reflected light from the arrangement surface when the light-transmissive object is not present on the arrangement surface; A light receiving unit capable of receiving second reflected light that is specularly reflected light from the arrangement surface when the light transmissive object is present on the arrangement surface, and the first reflected light of the light receiving unit. A measuring unit that measures the thickness of the light transmissive object based on a correlation between a light receiving position and a distance between the light receiving position of the second reflected light and the thickness of the light transmissive object.

For example, if the incident angle of light from the light projecting unit toward the arrangement surface, the refractive index of the light-transmitting object, and the refractive index around the light-transmitting object are fixed, the inventor of the present application performs the first reflection in the light-receiving unit. The distance between the light receiving position and the second reflected light receiving position varies depending on the thickness of the light transmissive object, that is, between the distance between the light receiving positions and the thickness of the light transmissive object. We found that the correlation was established.
Therefore, in the present invention, the thickness of the light transmissive object is measured based on the above correlation. Thereby, even if it is difficult to discriminate between the light receiving position of the reflected light from the front surface and the light receiving position of the reflected light from the back surface, the thickness of the light transmissive object can be measured.

但し、ｄ１：光透過性物体の厚さ
ΔＸ２：第１反射光の受光位置と第２反射光の受光位置との距離
θ１：投光部から光透過性物体への光の入射角度
ｎ１：光透過性物体の周囲の屈折率
ｎ２：光透過性物体の屈折率
ｋ：受光部の受光面の角度に応じた係数 (2) The second invention is the thickness measuring apparatus according to the first invention, wherein the measuring unit measures the thickness d1 of the light transmissive object based on the following arithmetic expression.

However, d1: Thickness of the light transmitting object ΔX2: Distance between the light receiving position of the first reflected light and the light receiving position of the second reflected light θ1: Incident angle of light from the light projecting unit to the light transmitting object n1: Light Refractive index around transparent object n2: Refractive index of light transmissive object k: Coefficient according to angle of light receiving surface of light receiving unit

(3) The third invention is the thickness measuring apparatus according to the first or second invention, wherein the incident angle of the emitted light from the light projecting unit with respect to the arrangement surface can be regularly reflected on the arrangement surface. The maximum angle is set.
According to the present invention, for example, even if the difference between the refractive index of the light transmitting object and the refractive index of the surrounding medium of the light transmitting object is small, the light receiving position of the first reflected light and the light receiving position of the second reflected light. Therefore, it is possible to suppress a decrease in accuracy of thickness measurement.

  (4) A thickness measuring method according to a fourth aspect of the present invention is a thickness measuring method for measuring the thickness of a light-transmitting object existing on a predetermined arrangement surface, wherein the light-transmitting property is measured on the arrangement surface. When there is no object, the first step of emitting light toward the arrangement surface and receiving the first reflected light specularly reflected by the arrangement surface by a predetermined light-receiving surface; and the light transmittance on the arrangement surface When there is an object, a second step of emitting light and regularly reflecting the second reflected light on the arrangement surface by the light receiving surface, a light receiving position of the first reflected light on the light receiving surface, and the And a third step of measuring the thickness of the light transmissive object based on the correlation between the distance between the light receiving positions of the second reflected light and the thickness of the light transmissive object.

  According to the present invention, it is possible to measure the thickness of a light-transmitting object even when it is difficult to discriminate between the light receiving position of reflected light from the front surface and the light receiving position of reflected light from the back surface. is there.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram of a thickness measuring apparatus 1 according to this embodiment. As shown in the figure, the thickness measuring device 1 is a device for measuring the thickness of a transparent body 9 having optical transparency (eg, glass, flux, etc., an example of the “light transmitting object” of the present invention). is there. In the figure, the transparent body 9 has a high reflectivity material 11 (for example, a plate material made of a metal material such as aluminum) having, for example, a high reflectivity surface 11A (an example of the “arrangement surface” of the present invention). The state arrange | positioned on the top is illustrated.

1. Configuration of Thickness Measuring Device As shown in FIG. 1, the thickness measuring device 1 includes a light projecting unit 2, a light receiving unit 13, and a CPU 8.

  The light projecting unit 2 emits light L1 from an oblique direction toward the high reflectivity material 11 or the transparent body 9. Specifically, the light projecting unit 2 includes, for example, a light projecting element 3 that irradiates laser light or the like, and a light projecting drive circuit 12 that drives the light projecting element 3. On the other hand, it is configured to emit light L1 from an oblique direction.

  The light receiving unit 13 receives the reflected light L2 emitted from the light projecting unit 2 and reflected by the high reflectivity material 11 or the transparent body 9. Specifically, the light receiving unit 13 includes a CCD 5 that receives the reflected light L2, a CCD drive circuit 4, and an amplifier circuit 6. As the CCD 5, a one-dimensional CCD line sensor or a two-dimensional CCD having a two-dimensional light receiving area can be applied.

  A signal generated for each pixel in the CCD 5 is read out by the CCD drive circuit 4. The CCD drive circuit 4 functions as a signal output unit that outputs a light reception signal SG1 indicating a light reception level for each position (specifically, for each cell) on the light receiving surface 5A of the CCD 5, and the output light reception signal SG1 is Amplified by the amplifier circuit 6 and taken into the CPU 8.

The CCD 5 is arranged so as to be able to receive the next reflected light L2 (L21 to L23).
“Surface reflected light L21”: When the transparent body 9 is on the high reflectivity material 11, the reflected light L2 emitted from the light projecting unit 2 and regularly reflected by the surface 9A of the transparent body 9
“Back surface reflected light L22”: When the transparent body 9 is present on the high reflectivity material 11, the reflected light L2 emitted from the light projecting unit 2 and regularly reflected by the back surface 9B of the transparent body 9 (“ Example of “2 reflected light”)
“Arrangement surface reflected light L23”: When there is no transparent body 9 on the high reflectivity material 11, the reflected light L2 emitted from the light projecting portion 2 and reflected by the surface 11A of the high reflectivity material 11 (“ Example of “first reflected light”)

  The CPU 8 controls the light projecting drive circuit 12, the CCD drive circuit 4 and the like, and executes a thickness measurement process described below. Further, a memory 14 and an operation unit 15 are connected to the CPU 8.

2. Thickness Measurement Processing The thickness measurement device 1 has two modes for measuring the thickness of the transparent body 9. The first is a “first mode” using the front surface reflected light L21 and the back surface reflected light L22, and the second is a “second mode” using the back surface reflected light L22 and the arrangement surface reflected light L23. . The user can select either the first mode or the second mode with the operation unit 15.

2-1. First Mode FIG. 2 is a schematic diagram showing optical paths of the front surface reflected light L21 and the back surface reflected light L22, and FIG. 3 is a flowchart showing the first mode processing. In addition, the meaning of each code | symbol in FIG. 2 is as follows.
θ1: Incident angle of the outgoing light L1 of the light projecting unit 2 with respect to the surface 9A of the transparent body 9 θ2: Refraction angle of the outgoing light L1 of the light projecting unit 2 on the surface 9A of the transparent body 9 n1: Medium in contact with the transparent body 9 Refractive index of (for example, air) n2: Refractive index of the transparent body 9 itself d1: Thickness of the transparent body 9

  When the user wants to use the first mode, the transparent body 9 is placed on the high reflectance material 11 and the first mode is selected and executed by the operation unit 15. Then, the CPU 8 executes the first mode process shown in FIG. First, in S10, the light projecting unit 2 is caused to execute a light projecting operation. Thereby, the emitted light L1 from the light projecting unit 2 is irradiated onto the transparent body 9, and the front surface reflected light L21 and the back surface reflected light L22 are received by the CCD 5, respectively. In step S12, the CCD driving circuit 4 is driven to receive the light reception signal SG1 from the CCD 5.

  FIG. 4 is a waveform diagram showing the light reception level on the CCD 5. The symbol X1 in the figure is the light receiving position of the front surface reflected light L21 (hereinafter referred to as “front surface light receiving position X1”), and the symbol X2 is the light receiving position of the back surface reflected light L22 (hereinafter referred to as “back surface reflected position X2”). is there. In S14, the CPU 8 detects the front surface light receiving position X1 and the back surface light receiving position X2 based on the light receiving signal SG1. For example, two pixel positions where the light reception level has a peak (maximum value) are specified and set as these light reception positions X1 and X2.

  In S16, the thickness of the transparent body 9 is measured based on the light receiving positions X1 and X2. For example, if the incident angle θ1 and the refractive indexes n1 and n2 are constant, there is a correlation between the distance ΔX1 between the front surface light receiving position X1 and the rear surface light receiving position X2 and the thickness d1 of the transparent body 9. The distance ΔX1 indicates a value corresponding to the thickness d1 of the transparent body 9. Therefore, in the present embodiment, a plurality of thicknesses d1 and distances ΔX1 are sampled in advance for the transparent body 9 having various thicknesses, and a relational expression (d1 = c · ΔX1 c) based on the correspondence between the thickness d1 and the distance ΔX1. Is a proportionality coefficient), and its relational expression information is stored in the memory 14. Then, the CPU 8 measures the thickness d1 of the transparent body 9 that is the current measurement object based on the distance ΔX1 based on the light reception signal SG1 captured in S12 and the relational expression information, and ends the first mode process. . Note that a correspondence table between the thickness d1 and the distance ΔX1 is created from the plurality of samplings, stored in the memory 14, and the thickness d1 is measured based on the distance ΔX1 and the correspondence table. Good.

2-2. Second Mode FIG. 5 is a schematic diagram showing the optical path of the arrangement surface reflected light L23 when there is no transparent body 9, and FIG. 6 shows the optical paths of the back surface reflected light L22 and the arrangement surface reflected light L23 when there is the transparent body 9. FIG. 7 is a flowchart showing the second mode process. In addition, the code | symbol d2 in FIG. 6 is mentioned later, The meaning of the code | symbol other than this is the same as that of FIG.

  When the user wants to use the second mode, first, the second mode is selected and executed by the operation unit 15 without arranging the transparent body 9 on the high reflectivity material 11 as shown in FIG. Then, the CPU 8 executes the second mode process shown in FIG. First, in S20, the light projecting unit 2 is caused to perform a light projecting operation. Thereby, the emitted light L1 from the light projecting unit 2 is irradiated on the surface 11A of the high reflectivity material 11, and the arrangement surface reflected light L23 is received by the CCD 5. Next, in S22, the CCD drive circuit 4 is driven to receive the light reception signal SG1 from the CCD 5 (an example of the “first step” in the present invention).

  FIG. 8 is a waveform diagram showing the light reception level on the CCD 5. The symbol X3 in the figure is the light receiving position of the arrangement surface reflected light L23 (hereinafter referred to as “arrangement surface light receiving position X3”), the solid line waveform U1 is the light reception waveform when there is no transparent body 9, and the dotted line waveform U2 is This is a light reception waveform when the transparent body 9 is present, and the meanings of the other symbols are the same as those in FIG. In S24, the CPU 8 detects the arrangement surface light reception position X3 based on the light reception signal SG1 by the same method as in S14 of FIG.

  Next, when the user places the transparent body 9 on the high reflectivity material 11 and performs a predetermined operation on the operation unit 15, the CPU 8 causes the light projecting unit 2 to execute the light projecting operation again in S26. Thereby, the emitted light L1 from the light projecting unit 2 is irradiated onto the transparent body 9, and the front surface reflected light L21 and the back surface reflected light L22 are received by the CCD 5, respectively. Next, in S28, the CCD drive circuit 4 is driven to receive the light reception signal SG1 from the CCD 5 (an example of the “second step” in the present invention).

  Here, for example, when the transparent body 9 is relatively thin, the peak waveform corresponding to the back surface light receiving position X2 and the peak waveform corresponding to the front surface light receiving position X1 are close as shown by the dotted waveform U2 in FIG. For this reason, it is difficult to distinguish the back surface light receiving position X2 and the front surface light receiving position X1 from the light receiving signal SG1. For example, when the light transmittance of the transparent body 9 is relatively high and the reflectance at the surface 9A is relatively smaller than the reflectance of the high reflectance material 11, it corresponds to the back surface light receiving position X2. Since the peak waveform corresponding to the surface light receiving position X1 is relatively small with respect to the peak waveform, it is difficult to determine the back surface light receiving position X2 and the surface light receiving position X1 from the light receiving signal SG1. Therefore, there is a possibility that the thickness of the transparent body 9 cannot be measured by the first mode process.

  On the other hand, in the second mode process, it is not always necessary to determine the back surface light receiving position X2 and the front surface light receiving position X1. Specifically, in S30, the CPU 8 detects at least the back surface reflection position X2 based on the light reception signal SG1 by the same method as in S14 of FIG. If the back surface light receiving position X2 and the front surface light receiving position X1 can be discriminated, the back surface reflection position X2 is detected. If the back surface light receiving position X2 cannot be discriminated, the pixel position at which the light reception level has the maximum value is regarded as the back surface reflection position X2. May be. In short, the light receiving position of the back surface reflected light L22 in which the front surface reflected light L21 is mixed may be set as the back surface reflected position X2.

  Subsequently, in S32, the CPU 8 measures the thickness d1 of the transparent body 9 based on the arrangement surface light receiving position X3 and the back surface light receiving position X2 (an example of “third step” in the present invention). At this time, the CPU 8 functions as a “measurement unit” of the present invention. For example, if the incident angle θ1 and the refractive indexes n1 and n2 are constant, there is a correlation between the distance ΔX2 between the arrangement surface light receiving position X3 and the back surface light receiving position X2 and the thickness d1 of the transparent body 9. (Proportional coefficient α) is established, and the distance ΔX2 indicates a value corresponding to the thickness d1 of the transparent body 9. This can be proved as follows with reference to FIG.

  In addition, the code | symbol d2 (= (DELTA) X2 * cos (theta) 1 = (DELTA) X2 * k) of FIG. 6 shows the value according to distance (DELTA) X2. The symbol a is a distance (hereinafter referred to as “incident distance a”) between the incident position of the outgoing light L1 on the front surface 9A and the incident position of the refracted light L1 ′ on the rear surface 9B along the front surface 9A. . In the present embodiment, k = cos θ1 is set on the assumption that the arrangement surface reflected light L23 is incident on the light receiving surface 5A of the CCD 5 at a right angle. However, k varies depending on the angle of the light receiving surface 5A.

First, the following equation is established between the incident angle θ1, the refraction angle θ2, the incident distance a, and the thicknesses d1 and d2.
[Formula 1]

従って、上記比例係数α（ｄ１＝α・ｄ２）は次の数式３で表すことができる。
［数式３］

Next, when the incident distance a is eliminated from the above equation 1, the following equation 2 is established.
[Formula 2]

Therefore, the proportionality coefficient α (d1 = α · d2) can be expressed by the following Equation 3.
[Formula 3]

［数式５］

Further, an expression (Expression 5) representing the refraction angle θ2 can be derived from Snell's expression (Expression 4).
[Formula 4]

[Formula 5]

Then, when the refraction angle θ2 is eliminated from Equation 3 and Equation 5, the following Equation 6 can be obtained.
[Formula 6]

  As is apparent from Equation 6, the proportional coefficient α can be obtained from the incident angle θ1 and the refractive indexes n1 and n2, and if these are fixed values, the proportional coefficient α is also constant. This means that a correlation (d1 = α · d2) is established between the distance ΔX2 between the light receiving position X3 and the back surface light receiving position X2 and the thickness d1 of the transparent body 9. Therefore, in this embodiment, a plurality of thicknesses d1 and distances ΔX2 are sampled in advance for the transparent body 9 having various thicknesses, and a relational expression (d1 = kα · ΔX1) based on the correspondence between the thickness d1 and the distance ΔX2. The relational expression information is stored in the memory 14. Then, the CPU 8 measures the thickness d1 of the transparent body 9 that is the current measurement object based on the distance ΔX2 based on the light reception signal SG1 captured in S22 and S28 and the above relational expression information, and performs the second mode process. finish. Note that a correspondence table between the thickness d1 and the distance ΔX2 is created from the plurality of samplings, stored in the memory 14, and the thickness d1 is measured based on the distance ΔX2 and the correspondence table. Good.

3. Effects of the Present Embodiment According to the present embodiment, in the second mode, the distance ΔX2 between the arrangement surface light receiving position X3 and the rear surface light receiving position X2 using the back surface reflected light L22 and the arrangement surface reflected light L23, Based on the correlation with the thickness d1 of the transparent body 9, the thickness d1 of the transparent body 9 is measured. Therefore, even when it is difficult to discriminate between the front surface light receiving position X1 and the back surface light receiving position X2, the thickness d1 of the transparent body 9 can be measured.

  In the present embodiment, not only the second mode but also the first mode can be used. As described above, the first mode can be used only when the front surface light receiving position X1 and the back surface light receiving position X2 can be discriminated, but the thickness d1 is set while the transparent body 9 is placed on the high reflectivity material 11. There is an advantage that it can be measured. Therefore, it is preferable to have both the first mode and the second mode.

  Furthermore, the incident angle θ1 of the emitted light L1 from the light projecting unit 2 is set to a maximum angle (an angle slightly smaller than the critical angle) that can be regularly reflected by the surface 11A of the high reflectivity material 11. Therefore, for example, even if the difference between the refractive index n2 of the transparent body 9 and the refractive index n1 of the surrounding medium (for example, air) of the transparent body 9 is small, the light receiving position X2 of the back surface reflected light L22 and the arrangement surface reflected light L23 Since the distance ΔX2 with respect to the light receiving position X3 can be increased, it is possible to suppress a decrease in thickness measurement accuracy.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and the drawings, and for example, the following various aspects are also included in the technical scope of the present invention. In particular, among the constituent elements of each embodiment, constituent elements other than the constituent elements of the top-level invention can be omitted as appropriate because they are additional elements.
(1) In the second mode processing of the above embodiment, the order of the processing of S20 to S24 and the processing of S26 to S30 may be reversed. Moreover, it is not necessary to perform the processing of S20 to S24 every time the second mode processing is executed. For example, the arrangement surface light reception position X3 may be detected once and stored in the memory 14, and thereafter, the arrangement surface light reception position X3 stored in the memory 14 may be used. Then, for example, when there is a change in the arrangement of the thickness measuring device 1 or a change in the surrounding environment, the processes of S20 to S24 may be performed again.

  (2) In the above embodiment, the correspondence table between the thickness d1 and the distance ΔX2 is used in the second mode processing, but the present invention is not limited to this. For example, the thickness of the transparent body 9 may be measured based on the arithmetic processing according to Equation 6.

  (3) In the above embodiment, the case where the incident angle θ1 and the refractive indexes n1 and n2 are constant has been described as an example, but the present invention is not limited to this. At least one of the incident angle θ1 and the refractive indexes n1 and n2 can be set and changed, and the proportionality coefficient α may be changed according to the changed value. For example, when a plurality of light-transmitting objects of different materials (refractive indexes) are to be measured, the user inputs the refractive index n2 of each light-transmitting object with the operation unit 15 and responds to this input value. The proportional coefficient α may be changed. With such a configuration, even if the incident angle of light from the light projecting unit to the light-transmitting object, the refractive index of the surrounding (medium) of the light-transmitting object, and the refractive index of the light-transmitting object are different, By changing the above parameters, the thickness of various light transmissive objects can be measured.

  (4) Furthermore, there is a method in which the proportionality coefficient α can be grasped without inputting the refractive index n2 of the light transmissive object. That is, the second mode is executed for the transparent body 9 whose thickness d1 is known in advance, the distance ΔX2 (d2) is obtained, and the refractive index of the light-transmitting object that is currently measured is obtained from the equation d1 = α · d2. Can be calculated in accordance with. For example, when the user inputs a thickness d1 known in advance to the operation unit 15 and executes the second mode, the CPU 8 causes the input thickness d1 and the distance ΔX2 obtained by executing the second mode. From this, the proportionality coefficient α is obtained.

The block diagram of the thickness measuring apparatus which concerns on one Embodiment of this invention. Schematic diagram showing the optical path of the front surface reflected light and the back surface reflected light Flow chart showing first mode processing Waveform diagram showing light reception level on CCD Schematic diagram showing the optical path of reflected light (with transparent body) Schematic diagram showing back side reflected light and optical path of reflected light (no transparent body) Flow chart showing second mode processing Waveform diagram showing light reception level on CCD

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Thickness measuring device 2 ... Projection part 8 ... CPU (measurement part)
9 ... Transparent body (light transmissive object)
9B ... Back side 11A ... Front side (placement side)
13 ... light receiving portion L22 ... back surface reflected light (second reflected light)
L23 ... Arrangement surface reflected light (first reflected light)
SG1 ... light reception signal X2 ... back surface reflection position X3 ... position surface light reception position

Claims (4)

A thickness measuring device for measuring the thickness of a light transmissive object existing on a predetermined arrangement surface,
A light projecting unit that emits light obliquely toward the arrangement surface side;
First reflected light that is specularly reflected light from the placement surface when the light-transmissive object is not present on the placement surface, and from the placement surface when the light-transmissive object is present on the placement surface. A light receiving unit capable of receiving the second reflected light, which is specularly reflected light, and
The thickness of the light transmissive object is measured based on the correlation between the distance between the light receiving position of the first reflected light and the light receiving position of the second reflected light in the light receiving unit and the thickness of the light transmissive object. And a thickness measuring device. The thickness measuring device according to claim 1,
The measurement unit is configured to measure the thickness d1 of the light transmissive object based on the following arithmetic expression.

However, d1: Thickness of the light transmitting object ΔX2: Distance between the light receiving position of the first reflected light and the light receiving position of the second reflected light θ1: Incident angle of light from the light projecting unit to the light transmitting object n1: Light Refractive index around transparent object n2: Refractive index of light transmissive object k: Coefficient according to angle of light receiving surface of light receiving unit The thickness measuring device according to claim 1 or 2,
An incident angle of the light emitted from the light projecting unit with respect to the arrangement surface is set to a maximum angle that allows regular reflection on the arrangement surface. A thickness measurement method for measuring the thickness of a light transmissive object existing on a predetermined arrangement surface,
A first step of emitting light toward the arrangement surface when the light-transmissive object is not present on the arrangement surface and receiving the first reflected light regularly reflected on the arrangement surface by a predetermined light-receiving surface;
A second step of emitting light when the light-transmitting object is present on the arrangement surface and receiving the second reflected light specularly reflected by the arrangement surface by the light-receiving surface;
The thickness of the light transmissive object is measured based on the correlation between the light receiving position of the first reflected light and the light receiving position of the second reflected light on the light receiving surface and the thickness of the light transmissive object. And a third step of measuring the thickness.

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