JPH03115911A - Thickness measuring instrument for transparent body - Google Patents

Abstract

PURPOSE:To accurately measure the thickness of even a plate to be measured which has a transparent material by interposing 1/2-wavelength plates and polarization beam splitters which are arranged in respective detectors while having mutually different polarizing directions in the optical path of laser light. CONSTITUTION:The polarizing direction of laser light 22a with which one surface of a plate 1 to be measured is irradiated from a 1st detector 21 is set to a constant direction by the angle of rotation of a 1st 1/2-wavelength plate 23a and the polarizing direction of the 2nd 1/2-wavelength plate 23b of a 2nd detector 21a is set differently from the polarizing direction of the 1st 1/2-wavelength plate 23a. The polarizing direction of laser light 22b outputted from the 2nd detector 21b is different from the polarizing direction of the laser light outputted by the 1st detector 21a. Further, the polarization beam splitters 25a and 25b which pass only polarizing-directional laser light beams of their detectors are arranged, so the laser light beams of the opposite sides which differ in polarizing direction are never made incident on photodetectors. Consequently, the thickness of the plate 1 to be measured is accurately calculated according to photodetection position signals outputted by the photodetectors 12a and 12b of the detectors 21a and 21b.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thickness measuring device for measuring the thickness of a plate to be measured using a laser beam, and particularly to a thickness measuring device for measuring the thickness of a plate to be measured using a laser beam. The present invention relates to a thickness measuring device for a transparent body that measures the thickness.

[Prior Art] A thickness measuring device using a laser beam has been put into practical use as one of the thickness measuring devices for accurately measuring the thickness of a thin plate or the like in a non-contact manner. For example, as shown in FIG. 6, a thickness measuring device using such a laser beam has a pair of detectors 2 and 3 arranged facing each other on both sides of the plate 1 to be measured, and a laser beam is emitted from each detector 2 and 3, respectively. The light beam 4.5 is applied to each surface 1a, l of the plate 1 to be measured.
b is irradiated at a predetermined angle θ, and the reflected laser light is received.

In each of the detectors 2 and 3, as shown in FIG. 7, a recess 7 is formed on one side of a box-shaped case 6, and a recess 7 is formed at opposite positions within the recess 7. A projection lens 8 and an imaging lens 9 through which laser light enters and exits six windows.
The assistant is fixed. Laser light 4 is on the surface of case 6.
The shutter knob 10 that forcibly shuts off is exposed.

FIG. 8 is a diagram showing the principle of measuring the position of the surface 1a of the plate 1 to be measured using one detector 2. Laser light 4 outputted from laser light source 11 is irradiated by projection lens 8 onto surface 1a of plate 1 to be measured at an incident angle θ. The laser beam 4 reflected by the surface 1a is incident on a light receiver 12 consisting of a position sensor via an imaging lens 9. In this case, if the surface 1a of the plate 1 to be measured exists at the position P, the laser beam 4 is configured such that the light focused by the imaging lens enters the center position of the light receiver 12. Then, when the surface 1a of the plate 1 to be measured moves upward by a distance from the focal position P, the light receiver 11
The light receiving position of moves downward by dl. Conversely, when the surface 1a of the plate 1 to be measured moves downward by a distance D2 from the focal point P, the light receiving position of the light receiver 11 moves in three directions by a distance d2.

Therefore, the light receiving position d of the laser beam 4 on the light receiver 11
,,d2 is detected, the distance of the plate 1 to be measured, ,D2
The surface position shown by can be calculated.

Returning to FIG. 6, the distance fiD^ of each surface 1a, lb of the plate 1 to be measured from the position P of each detector 2, 3 at each detector 2.3.
, DB are calculated, the thickness t of the plate 1 to be measured can be calculated by confirming the distance between each detector 2.3 using a reference material whose thickness is known in advance.

[Problems to be Solved by the Invention] However, even with the thickness measuring device configured as described above, there are still the following problems to be solved.

That is, the thickness measuring device shown in FIG. 6 cannot measure the thickness of a plate to be measured that has a light-transmitting property such as glass or transparent plastic.

That is, the laser beam 4 of the upper detector 2 on the plate 1 to be measured
The irradiation position and the irradiation position of the laser beam 5 of the lower detector 3 must match the thickness measurement position of the plate 1 to be measured, so if the plate 1 to be measured has a translucent property, Even if the orientation of each detector 2.3 is set so that the light emitting direction and the light receiving direction do not directly oppose each other as shown in FIG. side laser light source 11
A portion of the empty laser beam is incident. Therefore, the light receiving position signal from the other party's laser beam is mixed into the light receiving position signal from the own side's laser beam, making it impossible to accurately detect the light receiving position.

Therefore, the conventional thickness measuring device cannot measure the thickness of a plate to be measured which has a translucent property.

The present invention was made in view of these circumstances, and
By interposing a 1/2 wavelength plate and a polarizing beam splitter in each detector in the optical path of the laser beam, which are set to have different polarization directions, the laser beams output from the opposite detector are received. It is an object of the present invention to provide a thickness measuring device for a light-transmitting body, which prevents light from entering a device and can accurately measure the thickness of a plate to be measured even if it has a light-transmitting property.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the thickness measuring device for a transparent body of the present invention converts the laser light output from the laser light source into a first 1/1
Irradiating one surface of a plate to be measured having a translucent property through a two-wavelength plate and a polarizing beam splitter that passes only light in the polarization direction set by the first 112-wavelength plate,
The laser beam reflected from this one surface is transferred to the first 1/2
The light is received by a light receiver through a polarizing beam splitter that passes only the light in the polarization direction set by the wave plate, and the image position of the irradiation point formed on the light receiver is detected,
a first detector that outputs a first position signal indicating the position of one surface of the plate to be measured; 1/1 of the laser beam
Via a second 1/2 wavelength plate set in a polarization direction different from the polarization direction set in the two-wavelength plate and a polarizing beam splitter that passes only the light in the polarization direction of this second 1/2 wavelength plate. irradiate the other surface of the plate to be measured at a predetermined angle,
The laser beam reflected on the other surface is received by a light receiver via a polarizing beam splitter that passes only the light in the polarization direction of the second 1/2 wavelength plate. a second detector that detects the position of the irradiation point and outputs a second position signal indicating the position of the other surface of the plate to be measured; The first output from the second detector. and a data processing section that calculates the thickness of the plate to be measured from the second position signal.

[Operation] In general, the polarization direction of laser light output from a laser light source is largely biased in a certain specific direction.

By changing the rotation angle of the 1/2 wavelength plate, the polarization direction of the laser light output from the laser light source can be set to any direction. Therefore, the polarization direction of the laser beam irradiated from the first detector onto one surface of the plate to be measured is the first 1/2.
It is set in a fixed direction depending on the rotation angle of the wave plate.

Therefore, the polarization direction of the laser light inputted to the light receiver of the first detector also faces in a fixed direction.

On the other hand, since the polarization direction of the second 1/2 wavelength plate of the second detector is set to be different from the polarization direction of the first 1/2 wavelength plate, the output from the second detector is The polarization direction of the laser beam is different from the polarization direction of the laser beam output from the first detector.

A polarizing beam splitter is installed in the incident path of the laser beam to the receiver of each detector, which allows only the light in the polarization direction of the laser beam of the own detector to pass through. No light enters its own receiver.

Therefore, the thickness of the plate to be measured can be accurately calculated based on each light receiving position signal output from the light receiver of each detector.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the main parts of a thickness measuring device for a transparent body according to an embodiment. The first . Second detector 21a.

21 and b are arranged facing each other on the same plane. Inside the case 6a of the first detector 21, the laser light source 11a
The laser beam 22a outputted from the first 172 wavelength plate 2
For example, the polarization direction in 3a is as shown in FIG.
After the direction is changed to be parallel to the plane of the paper, the light is input to the polarizing beam splitter 24a. This polarizing beam splitter 24a has a function of passing only light having a preset polarization direction, and in this embodiment, the polarization direction of the passing light is set to be the same as that of the first 1/2 wavelength plate 23a. has been done. Therefore, the laser beam 22a that has passed through the polarizing beam splitter 24a and vibrates in a direction parallel to the plane of the drawing is incident on the surface 1a of the plate 1 to be measured at a predetermined angle θ via the projection lens 8a. Note that the light projection lens 8a emits the laser beam 22a.
This is to narrow down the image into a thin line, and its focal position F
The vertical position of the first detector 21a is set by a moving mechanism (not shown) so that the upper surface 1a of the plate 1 to be measured is approximately located at point a.

Most of the laser beam 22a incident on the surface 1a of the plate 1 to be measured, which has a translucent property, is transmitted downward through the plate 1 to be measured;
A polarizing beam splitter 25a in which a portion of the light is reflected and the polarization direction of the passing light is set in the same direction as the polarization direction set in the first I72 wavelength plate 23a via the imaging lens 9a.
1.2 H
is incident on the

The light receiver 12a is exposed to the surface 1a by the incident laser beam 22a.
The image position of the irradiation point is detected and a first position signal da indicating the surface position is sent to the data processing section 26. Note that the image position da is indicated by the distance from the reference position near the 0 center position of the light receiver 12a, for example.

On the other hand, a second detector 21 disposed below the plate 1 to be measured
．． In the case 6b of b, the first detector 2 ], a
A laser light source 1.1b is disposed on the extension direction side of the laser light 22a outputted from the laser light source 1.1b. Laser light 22b outputted from laser light source 11b and vibrating in a certain direction has its polarization direction changed by second I/2 wavelength plate 23b to a direction perpendicular to the plane of the paper, and then is input to polarizing beam splitter 24b. . The polarization direction of the light passing through the polarization beam splitter 24b is set to match the polarization direction of the second 172-wavelength plate 23b. The laser beam 22b that has passed through the polarizing beam splitter 24b and vibrates in a direction perpendicular to the plane of the drawing is incident on the lower surface 1b of the plate 1 to be measured at a predetermined angle θ via the projection lens 8b.

Then, the second detector 2 is positioned so that the lower surface 1b of the plate 1 to be measured is approximately located at the focal point Fb of the light projecting lens 8b.
1. The vertical position of b is set by a moving mechanism (not shown).

Most of the laser beam 122b incident on the surface of the fixed plate 1 to be measured 122b passes through the plate 1 to be measured upward, but a portion is reflected and passes through the imaging lens 9b. The light passes through a polarizing beam splitter 25b whose polarization direction is set in the same direction as the polarization direction set on the second I/2 wavelength plate 23b, and enters the light receiver 12b. The light receiver 12b detects the position of the irradiation point on the surface 1b by the incident laser beam 22b, and sends a second position signal db indicating the surface position to the data processing section 26.

The data processing unit 26 processes the input first . second position signal d
a, db and the first set by a moving mechanism (not shown).
．． Distance between second detectors 21a and 21b. The thickness t of the plate 1 to be measured is calculated from .

According to such a device for measuring the thickness of a transparent material, the laser beam 22a output from the first detector 21a has only a component in the polarization direction parallel to the paper surface, so even if it has a transparent property, The second detector 21.
Even if the transmitted light is incident within the space a, the transmitted light does not pass through each of the polarizing beam splitters 24b and 25b whose polarization direction is set perpendicular to the plane of the paper. Therefore, the laser light 22a output from the first light receiver 21a is not incident on the laser light source 1.1b and the light receiver 1.2b.
Another laser beam 22 is added to the light receiving position signal db output from b.
Noise caused by a is not mixed in. In addition, generally, the output level of the laser light source 1b is maintained at a constant level by detecting its intensity with a light receiver placed near the laser emission port, so that other laser light 22a does not enter. You can precisely control the output level.

Light receiver 12a of first detector 21a and laser light source 1
1a as well, the laser beam 22 from the second detector 21b
The influence of b can be eliminated.

Therefore, even if the object 1 to be measured has a translucent property, its thickness t can be accurately measured.

Furthermore, in the embodiment device, since the first detector 21a and the second detector 21b are arranged on the same plane,
As shown in FIG. 3, even if the plate 1 to be measured moves upward from the center position as shown by the dotted line, the measurement position will only move to the right by ΔS, and each laser beam 22a, 22b will Since the irradiation positions are opposite to each other, even if the surface of the plate 1 to be measured is in a state of fine pruning, the correct thickness t can always be calculated.

Note that if the directions of the first detector 21a and the second detector are set at right angles, for example, when the plate 1 to be measured moves up and down, the irradiation positions of each laser beam no longer face each other, so that accurate It is not possible to obtain a thickness t.

Note that, as shown in FIG. 4, when the object to be measured 1 is tilted by, for example, a small angle α, the measurement error becomes a function of tan.

In this way, even if the vertical position of the object to be measured 1 changes slightly, the correct thickness t can always be measured. Therefore, this measuring device can be used to continuously measure the thickness of glass on a production line in a glass manufacturing factory, for example. Maximum effectiveness can be achieved by incorporating it into a quality control system that monitors thickness variations.

FIG. 5 is a schematic diagram showing an apparatus for measuring the thickness of a transparent body to which the present invention is applied. The same parts as in FIG. 1 are given the same reference numerals.

In this measuring device, the 1/2 wavelength plate 23. ? .

23b, each laser light source 1.1a11b
A rotation mechanism 3]a, 3]b that enables the laser light sources 11a, 11b to rotate themselves is attached. Also,
Each polarizing beam splitter 24a, 24b, 25a, 25
Adjustment mechanism 32a that adjusts the polarization direction of the light that also passes through b.
, 32b33a, 33b are attached. and,
By adjusting each rotation mechanism 31a, 31b, each laser light source 1
．． Laser light 22a output from la, 11b.

The polarization directions of the light beams 22b may be set to be orthogonal to each other. Adjustment mechanisms 32a, 32b for each polarizing beam splitter,
33a and 33b may also be adjusted so that only the laser beam on their own side passes through them. Therefore, substantially the same effect as the embodiment shown in FIG. 1 can be obtained.

[Effects of the Invention] As explained above, if the thickness of the light-transmitting body of the present invention is fixed5, then the half-wave plate and the polarized light are set in each detector so that the polarization directions are different from each other. A beam splitter is interposed in the optical path of the laser beam.

Therefore, the laser light output from the detectors on the opposite side is prevented from entering the light receiver, and even if the plate to be measured has a translucent property, the thickness can be accurately measured.

[Brief explanation of drawings]

1 to 4 show a thickness measuring device for a transparent body according to an embodiment of the present invention. FIG. 1 is a schematic diagram showing the main parts, and FIG. FIGS. 3 and 4 are diagrams for explaining the direction, and FIGS. 3 and 4 are diagrams for explaining the effect. FIG. Figures 6 to 8 show a general thickness measuring device. Figure 6 is a schematic diagram showing the whole, Figure 7 is an external view of the detector, and Figure 8 is a diagram showing the principle of dimension measurement. be. 1... Board to be measured, la, ], b... Surface, 11a. 11b... Laser light source, 12a, 12b... Light receiver, 6 2 ], a... First detector, 21b... Second detector, 22a, 22b-... Laser light, 23 a-・
- First 1/2 wavelength plate, 23 b - Second 172 wavelength plate, 24 a. 24b, 25a, 25b---polarizing beam splitter, 26...data processing section.

Claims (1)

[Claims] Laser light (22a) output from a laser light source (11a)
) to the first 1/2 wavelength plate (23a) and this first 1/2 wavelength plate (23a).
The light is irradiated onto one surface of the plate to be measured (1) having a translucent property through a polarizing beam splitter (24a) that allows only light in the polarization direction set by the /2 wavelength plate to pass through, and the light is reflected from this one surface. The laser beam is received by a light receiver (12a) via a polarizing beam splitter (25a) that allows only light in the polarization direction set by the first 1/2 wavelength plate to pass through, and a light beam is formed on this light receiver. a first detector (21a) that detects the position of the irradiation point on the one surface of the plate to be measured and outputs a first position signal indicating the position of the one surface of the plate to be measured; The laser beam (22b) output from the laser light source (11b) is set in a polarization direction different from the polarization direction set by the first half-wave plate. a second 1/2 wavelength plate (23b) and a polarizing beam splitter (24b) that passes only light in the polarization direction of the second 1/2 wavelength plate.
irradiate the other surface of the plate to be measured at a predetermined angle through the
The laser beam reflected on the other surface is transferred to the second 1/2
The light is received by a light receiver (12b) via a polarizing beam splitter (25b) that allows only light in the polarization direction of the wave plate to pass through,
a second detector (21b) that detects the position of the irradiation point on the other surface formed on the light receiver and outputs a second position signal indicating the position of the other surface of the plate to be measured; 1,
A thickness measuring device for a transparent body, comprising a data processing unit (26) that calculates the thickness of the plate to be measured from first and second position signals output from a second detector.