JPH05223563A - Laser displacement meter - Google Patents

Abstract

PURPOSE:To measure an object to be measured properly without any measurement error even if the object is transparent by a laser displacement meter. CONSTITUTION:A laser displacement meter 1 is provided with a laser light source 2 and a light-reception part 3, a laser beam 5a which is cast from the laser light source 2 is reflected on the surface of an object 4 to be measured, a reflection beam 5b enters a light-detection element of the light-reception part 3 as a normal measurement light, and then the amount of displacement is measured according to a laser beam distribution at that time. Also, light- screening plates 7 where a small hole 6 is formed are laid out in parallel slightly away from the surface of the object 4 to be measured. The light-screening plate 7 travels while maintaining a parallel posture for the surface of the objet 4 to be measured in a direction which is parallel to a light-projection axis by a drive device 10 in axial direction. A normal reflection beam 5b passes through the small hole 6 and then enters the light-reception part 3 but nearly all of a pseudo measurement beam 5c toward the light-reception part 3 are screened by the light-screening plate 7 and do not enter the light-reception part 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser displacement meter used for shape measurement, and more particularly to a laser displacement meter suitable for measuring the shape of transparent optical parts.

[0002]

2. Description of the Related Art A laser displacement meter is known as one of the devices for measuring the shape of an article. This laser displacement meter is composed of a laser light source that irradiates a laser beam at an angle with respect to the surface of the object to be measured, and a light receiving section on which reflected light from the surface of the object to be measured enters. When the height of the surface of the object to be measured changes, the optical axis of the reflected light moves in parallel, so the amount of displacement of the surface can be found by detecting the position of the incident point in the light receiver.

[0003]

However, when a laser displacement meter is used to measure the shape of a transparent optical component, there arises a problem. That is, when the object to be measured is a transparent material, the laser light from the laser light source not only reflects on the surface of the object to be measured, but also enters the inside of the object to be measured and is reflected on the inner surface of the object to be measured. Further, there is a case where the light is emitted from the vicinity of the incident point on the measured object to the outside of the measured object and is incident on the light receiver as pseudo measurement light. In this case, the laser light is incident on a plurality of points on the light receiver, the amount of displacement cannot be correctly detected, and a measurement error occurs.

The present invention is intended to solve the above problems, and an object of the present invention is to correctly measure an object to be measured without a measurement error even if the object is transparent.

[0005]

According to the present invention, a laser beam from a laser light source is irradiated obliquely to the surface of an object to be measured,
A laser displacement meter that detects the displacement of the surface of the object to be measured by detecting the position of the laser light that is incident on the light receiving section by entering the reflected laser light from the surface of the object to be measured into the object to be measured. In the vicinity of the surface of, a light-shielding plate having a small hole is formed for passing the laser light incident on the surface of the object to be measured from the laser light source and the laser light reflected from the surface of the object to be measured in common. To do.

It is possible to provide an axial driving device for moving the light shielding plate in parallel with the optical axis of the laser light from the laser light source.

The axial driving device can also be driven according to the displacement of the surface of the object to be measured detected by the light receiving section.

[0008]

When the laser light source irradiates the surface of the object to be measured with laser light, the light other than the laser light actually reflected on the surface of the object to be measured is blocked by the light shielding plate or does not enter the light receiving portion. It passes through a small hole in the light shield at an angle.
Therefore, only the regular reflected light is incident on the light receiving portion, and the reflected light from the inside of the transparent body, which causes the measurement error, is not incident on the light detection element of the light receiving portion.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a structural example of a laser displacement meter of the present invention. The laser displacement meter 1 includes a laser light source 2 and a light receiving unit 3. The laser light source 2 and the light receiving unit 3 are
The light projecting axis and the light receiving axis are arranged so as to be symmetrical with respect to the surface of the DUT 4. The laser light 5a emitted from the laser light source 2 is reflected on the surface of the DUT 4, and the reflected light 5b enters the photodetector of the light receiving unit 3 as the regular measurement light, and the displacement amount is determined by the laser light distribution at that time. taking measurement. Further, a light shielding plate 7 having a small hole 6 formed so that the incident light 5a and the reflected light 5b can pass through in the vicinity of the surface of the DUT 4 at the same time.
Are arranged parallel to each other with a slight distance from the surface of the DUT 4. This shading plate 7 is a guide rail 8 schematically shown by a broken line.
As a result, it is possible to move in a direction parallel to the projection axis while maintaining a parallel posture with respect to the surface of the DUT 4. Further, one end of a supporting rod 9 having an inclination parallel to the light projecting axis is fixed to the light shielding plate 7, and the other end of the supporting rod 9 is connected to an axial driving device 10.

As shown in FIG. 2, the axial drive unit 10 includes a stepping motor 11 and a rotary sleeve 14 which is connected to a rotary shaft 12 of the motor 11 and has a female screw 13 cut therein. Further, a male screw 15 is cut at the other end of the support rod 9, and the female screw 13 of the rotary sleeve 14 is
Is screwed onto. When the motor 11 rotates, the support rod 9 moves back and forth in the axial direction according to the rotation direction of the motor 11, and along with this, the light shielding plate 7 also moves parallel to the light projecting axis. Here, it is assumed that the support rod 9 is pushed out when the motor 11 rotates forward.

In the light receiving section 3, as schematically shown in FIG. 3, a plurality of detection elements 3a are linearly arranged in a plane including both the light projecting axis and the light receiving axis at right angles to the light receiving axis. There is. The number of detection elements 3a is appropriately selected according to the required resolution. The output of each detection element 3a is supplied to the position detection circuit 16 as shown in FIG.
The incident position, that is, the amount of displacement is detected from the laser light distribution (shown by the broken line). From the position detection circuit 16, for example, as shown in FIG.
It is assumed that the output when b is incident is 0, a positive output corresponding to the deviation is generated when the deviation is in the direction A, and a negative output is generated when the deviation is in the direction B. To do. The displacement signal S obtained by the position detection circuit 16 is supplied to the display device 17, and the displacement from the reference position is displayed by positive and negative numerical values. Further, the displacement signal S is supplied to the motor 11 via the servo circuit 18, and the motor 11 rotates in a predetermined direction at a predetermined speed according to the magnitude and positive / negative of the displacement signal S. In the present embodiment, the servo circuit 18 is configured to drive the motor 11 in the direction in which the support rod 9 is pushed out, that is, in the positive rotation direction, when the positive displacement signal S is supplied. The signal processing may be digital or analog.

Next, the operation of measuring the shape of a transparent optical component as an object to be measured using the above laser displacement meter will be described.

Now, it is assumed that the relationship between the laser displacement meter 1, the DUT 4, and the light shielding plate 7 is as shown in FIG. At this time, the laser light 5a emitted from the laser light source 2 passes through the small hole 6 of the light shielding plate 7 and is applied to the surface of the DUT 4, and is reflected by the surface and again passes through the small hole 6 to detect the light of the light receiving portion 3. It is incident on the element 3a. On the other hand, depending on the shape of the DUT 4, the laser light 5c that has entered the inside from the surface is internally reflected as shown in the figure, and this reflected laser light 5c serves as pseudo measurement light and is the photodetection element 3a of the light receiving unit 3. May be incident on. However, in this embodiment, since the light shield 7 is arranged near the surface of the DUT 4, and the small hole 6 is located only near the reflection position of the surface of the DUT 4, it is possible to perform the normal operation. Although the reflected light 5b is incident on the light receiving unit 3, almost all of the pseudo measurement light 5c traveling toward the light receiving unit 3 is blocked by the light shielding plate 7 and does not enter the light receiving unit 3. Therefore, correct measurement can be performed without error. Further, even if there is incidental pseudo measurement light passing through the small hole 6, it is considered that most of the pseudo measurement light is incident only in a direction different from the direction toward the light detection element 3a of the light receiving section 3, and therefore the measurement error is I won't.

In the present embodiment, the irregular shape of the surface of the object 4 is continuously measured by sending the object 4 at a constant speed in a certain direction. Therefore, the height of the surface changes according to the movement of the DUT 4. Assuming that the height of the surface of the DUT 4 is lowered from the height indicated by the solid line to the height indicated by the broken line by L1 as shown in FIG. 3, the irradiation position of the laser beam 5b on the light receiving section 3 is the A side. Move to
A positive displacement signal S corresponding to the displacement is obtained from the position detection circuit 16. Thereby, the amount of displacement of the surface of the DUT 4 is detected. Further, the displacement signal S is supplied to the servo circuit 18. Since the servo circuit 18 is configured to drive the motor 11 in the forward rotation direction when the positive displacement signal S is supplied, the motor 11 rotates forward and the support rod 9 is pushed out. The light shield 7 moves to the position shown by the broken line in FIG. As a result, the shading plate 7 approaches the surface of the DUT 4 and the distance between the shading plate 7 and the surface of the DUT 4 is maintained constant. Further, the small hole 6 of the light shielding plate 7 moves in the horizontal direction by the distance L2 and coincides with a new irradiation position of the laser beam 5a.

On the contrary, if the height of the surface of the object to be measured 4 becomes high, the light shielding plate 7 moves in a direction away from the surface of the object to be measured 4 and the distance between the light shielding plate 7 and the surface of the object to be measured 4 is increased. Is maintained constant, and the small hole 6 of the light shielding plate 7 moves to a new irradiation position of the laser beam 5a.

As described above, in this embodiment, the position of the light shielding plate 7 is fed back in accordance with the displacement of the surface of the object to be measured 4, and the light shielding plate 7 moves parallel to the projection axis. The center of the small hole 6 of the shading plate 7 can be made to coincide with the laser spot on the surface of the DUT 4, and the position of the shading plate 7 is always moved to an optimum position to eliminate unnecessary reflected light, that is, pseudo measurement. It is possible to reliably block light.

Next, a specific example of dimensions of the laser displacement meter will be described with reference to FIG. Here, the case where the DUT 4 is a transparent thin plate and the pseudo measurement light 5c is generated from the back surface will be described.

The thickness of the transparent thin plate of the DUT 4 shown in FIG. 6 is h ₂ , the refractive index is n ₂ , the incident angle of the laser beam 5a emitted from the laser displacement meter is θ ₁ , and the refractive index of air is n. _Set to ₁ .
In order to block the pseudo measurement light 5c reflected on the back surface of the DUT 4 and obtain an accurate measurement value, a small hole 6 having a diameter d _{1 is formed} at a point separated from the surface of the DUT 4 by a distance h _1. Place the open light shield 7. When the maximum spot diameter of the laser beam used for measurement is r _max , the minimum value d _1min of the diameter of the small hole 6 is expressed as follows.

D _1min = 2h ₁ tan θ ₁ + r _{max Further} , the distance d ₂ from the original reflection point when the pseudo measurement light 5c reflected from the back surface of the DUT 4 reaches the front surface of the DUT 4 is as follows: It is expressed as.

D ₂ = 2h ₂ tan [arcsin {(n ₁ / n ₂ ) sin θ ₁ }] Therefore, the maximum value d _1max of the small hole 6 for blocking the pseudo measurement light 5c is expressed as follows.

From d _1max = 2 (d ₂ + h ₁ tan θ ₁ ) −r _max or more, an appropriate d ₁ may be determined so that d _1min <d ₁ <d _1max .

For example, θ ₁ = 30 degrees, r _max = 60 μ
m laser displacement meter, h ₂ = 1 mm, n ₂ = 1.3
When trying to measure the transparent thin plate of (n ₁ = 1.0),
If h ₁ = 0.1 mm is adopted, d _1min = 0.18 m
Since m and d _1max = 0.77 mm, d ₁ = 0.4 m
m. As a result, a sufficient time margin for feedback can be obtained, so that the shading plate 7 can be driven by the stepping motor 11 to follow the displacement of the surface of the DUT 4.

[0024]

As described above, in the laser displacement meter of the present invention, except for the laser light actually reflected on the surface of the object to be measured, a small hole is formed at an angle which is blocked by the light shielding plate or does not enter the light receiving portion. Since it does not enter the light receiving portion, accurate measurement is possible even if the object to be measured is a transparent body.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of a laser displacement meter of the present invention.

FIG. 2 is a partial cross-sectional view showing a configuration example of an axial drive device.

FIG. 3 is an explanatory diagram schematically showing a state of laser light incident on a light receiving section.

FIG. 4 is a block diagram showing an electric circuit system of the laser displacement meter.

FIG. 5 is a graph showing a relationship between a detected position and a displacement signal in the position detection circuit.

FIG. 6 is an explanatory diagram for examining the size of small holes in the light shielding plate.

[Explanation of symbols]

1: Laser displacement meter, 2: Laser light source, 3: Light receiving part, 3
a: detection element, 4: object to be measured, 5a: incident laser light, 5
b: regular measurement light, 5c: pseudo measurement light, 6: small hole, 7: light-shielding plate, 8: guide rail, 9: support rod, 10: axial drive device, 11: stepping motor, 12: rotating shaft, 1
3: Female thread, 14: Rotating sleeve, 15: Male thread, 1
6: Position detection circuit, 17: Display device, 18: Servo circuit

Claims (3)

[Claims] 1. A laser beam from a laser light source is obliquely applied to the surface of an object to be measured, a reflected laser beam from the surface of the object to be measured is incident on a light receiving section, and the laser light is incident on the light receiving section. In the laser displacement meter for detecting the displacement of the surface of the measured object by detecting the position of, the laser beam incident on the surface of the measured object from the laser light source and the surface of the measured object in the vicinity of the surface of the measured object. A laser displacement meter having a light-shielding plate formed with a small hole through which a laser beam reflected from the laser beam passes in common. 2. The laser displacement meter according to claim 1, further comprising an axial drive device for moving the light shielding plate in parallel with the optical axis of the laser light from the laser light source. 3. The laser displacement meter according to claim 2, wherein the axial driving device is driven according to the displacement of the surface of the object to be measured detected by the light receiving section.