JP4595697B2 - Reflective optical gap sensor - Google Patents

Description

  The present invention relates to a gap sensor that detects a gap between two opposing objects, and relates to a reflective optical gap sensor that uses a diffraction image of light.

Conventionally, a reflective optical gap sensor that irradiates a surface to be measured with light from a light emitting diode, receives the reflected light with a photodiode, and detects a change in light intensity with respect to a gap variation between the detection unit and the surface to be measured has been disclosed. (For example, refer to Patent Document 1).
FIG. 10 is a block diagram of the main part of a conventional reflective gap sensor.
In FIG. 10, 72 is a surface to be measured, 73 is a detection unit, 74 is a lighting unit, and 75 is a calculation unit.
The detection unit 73 includes an LED 81 and a photodiode 82 that receives the reflected light emitted from the LED 81 and reflected by the measurement surface 72.
The lighting unit 74 is a drive power source for causing the LED 81 to blink at a predetermined frequency.
The calculation unit 75 calculates the gap length between the upper end of the detection unit 73 and the measured surface 72 from the short-circuit current of the photodiode 82, and includes a current amplifier 91, a bandpass filter 92, a rectifier circuit 93, A smoothing circuit 94, an arithmetic circuit 95, and a linear gain compensation circuit 96 are included.

Next, the operation will be described.
When the gap between the detection unit 73 and the measured surface 72 changes, the short-circuit current of the photodiode 82 changes. The change of the short-circuit current is calculated by the calculation unit 75 so as to be a voltage signal proportional to the gap length, and the gap change is detected.
In addition, a capacitor 85 is connected between the electrodes of the photodiode 82, and a part of the short-circuit current is passed through the capacitor, and a change in the short-circuit current due to a change in the ambient temperature is caused by using a change in the dielectric constant of the capacitor with respect to the temperature. Corrections are made so as not to affect the detection characteristics.
As described above, the conventional reflective optical gap sensor detects the gap between the detection unit and the measured surface by detecting the change in the light intensity with respect to the gap variation of the measured surface, and uses the change in the dielectric constant of the capacitor. Thus, the temperature fluctuation component of the light intensity was compensated.

Further, conventionally, an analysis of an image formed when incoherent light passes through two diffraction gratings arranged with a gap is performed, and the analysis result is disclosed. (For example, refer nonpatent literature 1).
FIG. 11 is a configuration diagram of slits used for image analysis.
In FIG. 11, the relationship between the distance between the lattices of the two lattices G ₁ and G ₂ and the slit pitch of the lattice is
p ₁ = (1 + Z ₁ / Z ₂ ) p ₂ / N
When satisfying the relationship
p _i = p ₁ Z ₂ / Z ₁
In the image of the period p _i which is shown, it has been shown to be formed on an image plane.
here,
Z ₁ = distance between the gratings G ₁ and G ₂ Z ₂ = distance between the grating G ₂ and the image plane p ₁ = slit pitch of the grating G ₁ p ₂ = slit pitch of the grating G ₂ .
N is an integer and corresponds to the period of the grating G _1. For example, in the case of N = 1, imaging with respect to the (1 + Z ₁ / Z ₂ ) p ₂ period component of G ₁ is shown.
Japanese Patent No. 3103156 Journal of Japan Society for Precision Engineering Vol.62, No.7,1996

The conventional reflective optical gap sensor detects the change in light intensity with respect to the gap fluctuation, so that it has the problem of being affected by the ambient temperature. In the above-described conventional technology, the change in the dielectric constant with respect to the temperature of the capacitor is used. However, due to variations in characteristics of photodiodes and capacitors, it is difficult to accurately correct over a wide temperature range, and it is difficult to obtain a reflective optical gap sensor with good temperature characteristics.
The present invention has been made in view of such problems, and an object thereof is to obtain a reflective optical gap sensor having good temperature characteristics in a wide temperature range.

In order to solve the above problems, the present invention is configured as follows.
According to the first aspect of the present invention, a detection unit including a light source, a light receiving element, and a grating is attached to one of two members arranged to face each other, and the emitted light from the light source is transmitted to the other member having a reflection surface. In the reflection-type optical gap sensor that detects the gap between the two members by detecting the reflected light with the light receiving element, the grating includes a first grating having an equal pitch for limiting the emitted light, Irradiating the reflecting surface with light transmitted through the first grating, the second grating having an equal pitch for limiting the reflected light, and the first grating generated by the light transmitted through the first grating and the second grating. A third grating that detects an image of the transmitted light of the light source, detects a change in the period of the image corresponding to a change in the gap between the members, and detects a gap between the members.
According to the second aspect of the present invention, a detection unit including a light source, a light receiving element, and a grating is attached to one of two members arranged opposite to each other, and the light emitted from the light source is reflected on the other side. In the reflection type optical gap sensor that detects the gap between the two members by irradiating the member with the reflected light and detecting the reflected light with the light receiving element, the grating includes a first grating of equal pitch that restricts the emitted light. Irradiating the reflecting surface with light transmitted through the first grating and the second grating, the second grating having an equal pitch that further restricts light transmitted through the first grating, and generated by the reflected light. A third grating for detecting an image of transmitted light of the first grating is provided, a change in the period of the image generated in response to a gap change between the members is detected, and a gap between the members is detected. .
According to a third aspect of the present invention, the first to third gratings are arranged so that a principal ray of the emitted light is incident perpendicularly to a grating surface of the first to third gratings. Is.
According to a fourth aspect of the present invention, the detection unit includes a prism so that the principal ray of the emitted light is incident perpendicularly to the lattice plane.

According to the first or second aspect of the invention, since the change in the phase of the image with respect to the change in the gap is detected, the change in the light intensity due to the temperature does not affect the detection characteristic, so that a gap sensor with good temperature characteristics can be obtained. I can do it.
According to the third aspect of the present invention, if each grating plane is arranged so that the principal ray of the emitted light is perpendicularly incident on the grating planes of the first to third gratings, the detection signal becomes large and noise is generated. Strong detection is possible.
According to the fourth aspect of the present invention, if the prism is provided so that the emitted light is incident perpendicularly to the grating, the optical path can be shortened, so that the relative inclination between the detection unit and the reflecting surface is affected. Small and stable detection characteristics can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a reflective optical gap sensor showing a first embodiment of the present invention.
In the figure, 1 is a light emitting diode that emits incoherent emitted light, 11 is a first grating that generates linear light beams of equal pitch from the emitted light, and 12 is a reflecting surface 5 irradiated by linear light beams of equal pitch. The second grating 13 for limiting the reflected light from the first grating 13 is for detecting an image formed on the third grating 13 by the third grating. Reference numeral 2 denotes a photodiode for converting an optical signal transmitted through the third grating into an electric signal. Reference numeral 3 denotes a glass substrate for patterning the first lattice 11, the second lattice 12, and the third lattice 13, respectively. Reference numeral 5 denotes a reflection surface of the surface to be measured. In the present embodiment, the first grating 11 and the second grating 12 can be formed on the same glass substrate.

FIG. 2 is a side view of the reflective optical gap sensor of this embodiment.
In FIG. 2, reference numeral 4 denotes a detector, which is composed of the light emitting diode 1, the first grating 11, the second grating 12, the third grating 13, the photodiode 2, and a sensor case 7 for housing and fixing them, and is not shown. It is fixed to the member.
In FIG. 2, Z ₁₁ is the distance from the first grating 11 to the reflection surface 5 of the other member, and Z ₁₂ is the distance from the reflection surface 5 to the second grating 12. The sum of Z ₁₁ and Z ₁₂ corresponds to Z ₁ in FIG. Z ₂ is the distance between the second lattice 12 and the third lattice 13 and corresponds to Z ₂ in FIG.

Next, the lattice pattern of each lattice will be described.
In FIG. 1, assuming that the directions indicated by the arrows are the x-axis direction, the y-axis direction, and the z-axis direction, respectively, each lattice has a lattice pattern of equal pitch in the y-axis direction having slits in the x-axis direction.
The slit pitch of the grating is determined in consideration of the gap to be detected and the size of the detection unit. However, as shown in Non-Patent Document 1, the slit pitch p ₁ of the first grating 11 and the A relationship of p ₂ = p ₁ N / (1 + Z ₁ / Z ₂ ) is necessary between the slit pitches p ₂ of the two lattices 12 and is formed so as to satisfy this relationship. Incidentally, Z1 is a function of the gap length and by applying the Z ₁ Set p ₂ at the center and becomes the gap length of the measurement.
Slit pitch p ₃ of the third grid 13 is formed such that the pitch is equal to the image period p _i generated on the third grating. The image period p _i is given by p _i = p ₁ Z ₂ / Z ₁ , and Z ₁ varies with the gap length, but p ₃ is set by applying Z ₁ at the gap length which is the center of measurement.

FIG. 3 is a plan view showing the configuration of the third grating.
The first grating 11 and the second grating 12 are each composed of only one slit group, while the third grating 13 is composed of four slit groups a ₁₁ , a ₁₂ , b ₁₁ , b ₁₂ , a ₂₁ , a _22. , B ₂₁ , b ₂₂ , and arranged on the left and right of the x-axis center line passing through the intersection x ₀ with the principal ray on the third lattice plane.
Slit gun _{a 11} and _{a 12, b 11} and _{b 12, a 21} and _{a 22, b 21} and _{b 22} are configured to respectively have a phase difference of electrically 180 degrees to each other, slit-gun _{a 11} and b ₁₁ , a ₁₂ and b ₁₂ , a ₂₁ and b ₂₁ , a ₂₂ and b ₂₂ are each configured to have a phase difference of 90 degrees electrically.

Next, the gap detection operation of the present embodiment will be described.
FIG. 4 is a schematic diagram showing changes in the image period when the gap changes. It is shown for _{a 11} image of the slit Gujo on the third grating 13. The same applies to the slit groups on the other third lattices 13.
4, the range indicated by squares represent the detection range by a ₁₁ slit county. The sinusoidal waveform indicates the image intensity distribution. The solid line shows the image intensity distribution in a certain gap, and the dotted line shows the image intensity distribution when the gap changes. Image pitch is changed to p _{i 'from} p _i by a gap change, a ₁₁ phase change of the average θ within a slit-gun occurs.

FIG. 5 is a circuit diagram of the detection circuit.
Only the detection from the slit groups a ₁₁ , a ₁₂ , b ₁₁ , and b ₁₂ is shown, and the detection from the slit groups a ₂₁ , a ₂₂ , b ₂₁ , and b ₂₂ is the same and will be omitted.
In FIG. 5, reference numerals 21, 22, 23, and 24 denote photodiodes disposed behind the slit groups a ₁₁ , a ₁₂ , b ₁₁ , and b ₁₂ , respectively. 61 respectively output voltage signals va ₁₁ of the photodiode 21, 22, 23, 24 at the _{amplifier, va} 12, vb 11, converted to _{vb 12.} 62 is a differential amplifier, to obtain a vb ₁ is a differential signal va ₁ and _{vb 11} and _{vb 12} is a differential signal va ₁₁ and _{va 12.} Reference numeral 63 denotes a phase calculation unit which calculates tan ⁻¹ (va ₁ / vb ₁ ) to obtain a phase signal θ ₁ .
Similarly, θ ₂ is obtained from the signal of the photodiode detected through the slit groups a ₂₁ , a ₂₂ , b ₂₁ and b ₂₂ . Reference numeral 64 denotes a phase difference calculation unit that calculates a difference (θ ₁ −θ ₂ ) between the phase signal θ ₁ and the phase signal θ ₂ . Since (θ ₁ −θ ₂ ) and the gap have a certain relationship, the gap can be detected.

FIG. 6 is a perspective view of a reflective optical gap sensor showing a second embodiment of the present invention.
FIG. 7 is a side view of the reflective optical gap sensor of this embodiment.
The difference between this embodiment and the first embodiment is that, in the first embodiment, the reflecting surface 5 is irradiated with the light transmitted through the first grating 11, but in this embodiment, the first grating 11 and the second grating 12 are irradiated. This is a point that the reflecting surface 5 is irradiated with the light transmitted through.
In FIG. 7, Z ₁ is a distance between the first grating 11 and the second grating 12, and corresponds to Z ₁ in the slit configuration diagram shown in FIG. Z ₂₁ is the distance from the second grating 12 to the reflecting surface 5, Z ₂₂ is the distance from the reflecting surface 5 to the third grating 13, and the sum of both is Z _{2 in the} slit configuration diagram shown in FIG. Corresponding to
In the first embodiment, the phase change of the image on the third grating 13 due to the change of Z ₁ is detected. However, in this embodiment, the phase change of the image on the third grating 13 according to the change of Z ₂ is detected. To detect.
Since the phase detection operation is the same as that of the first embodiment, the description thereof is omitted.
In the present embodiment, the second grating 12 and the third grating 13 can be formed on the same glass substrate.

FIG. 8 is a side view of a reflective optical gap sensor showing a third embodiment of the present invention.
This embodiment is different from the second embodiment in that the principal ray a of the light emitted from the light emitting diode 1 is incident on the respective grating planes of the first grating 11, the second grating 12, and the third grating 13 perpendicularly. This is the point where each grid is arranged.
In the present embodiment, since the chief ray is incident on each grating plane perpendicularly, the detection signal becomes large and a noise-resistant gap sensor can be obtained.

FIG. 9 is a side view of a reflective optical gap sensor showing a fourth embodiment of the present invention.
In FIG. 9, reference numeral 14 denotes a prism. The prism 14 is installed so that the principal ray “a” of the light emitted from the light emitting diode 1 is perpendicularly incident on each grating surface and the reflecting surface 5. In the present embodiment, the first grating 11 also serves as the second grating 12.
In this embodiment, the chief ray a is perpendicularly incident on each grating surface and reflecting surface, so that the optical path can be shortened, and the irradiation position on each grating varies with the relative inclination between the detection unit and the reflecting surface. Can be reduced, so that stable detection can be performed.

  As described above, in the present invention, the change in the phase of the image is obtained from the change in the pitch of the image to be formed due to the change in the gap between the detection unit and the reflecting surface, and the gap is detected. Thus, a gap sensor with good temperature characteristics can be obtained.

The perspective view of the reflection type optical gap sensor which shows 1st Example of this invention. The side view of the reflection type optical gap sensor which shows 1st Example of this invention The top view which shows the structure of the 3rd grating | lattice of this invention Schematic diagram showing changes in image period of the present invention Circuit diagram of detection circuit of the present invention The perspective view of the reflection type optical gap sensor which shows 2nd Example of this invention. Side view of a reflective optical gap sensor showing a second embodiment of the present invention. Side view of a reflective optical gap sensor showing a third embodiment of the present invention. Side view of a reflective optical gap sensor showing a fourth embodiment of the present invention. Block diagram of the main parts of a conventional reflective gap sensor Slit configuration diagram showing diffraction image analysis

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting diode 11 1st grating | lattice 12 2nd grating | lattice
13 Third lattice
14 Prism 2, 21, 22, 23, 24 Photodiode 3 Glass substrate 4 Detector 5 Reflecting surface 61 Amplifier 62 Differential amplifier 63 Phase calculator 64 Phase difference calculator 7 Case

Claims (4)

A detection unit including a light source, a light receiving element, and a grating is attached to one of the two members disposed to face each other, and the other member having a reflecting surface is irradiated with the light emitted from the light source, and the reflected light is irradiated to the other member. In a reflective optical gap sensor that detects a gap between both members by detecting with a light receiving element,
The lattice is
A first grid of equal pitches to limit the emitted light;
Irradiating the reflecting surface with light transmitted through the first grating, and a second grating having an equal pitch for limiting the reflected light;
A third grating for detecting an image of the transmitted light of the first grating generated by the light transmitted through the first grating and the second grating;
A reflection-type optical gap sensor, wherein a change in the period of the image generated in response to a gap change between the members is detected to detect a gap between the members. A detection unit including a light source, a light receiving element, and a grating is attached to one of the two members disposed to face each other, and the other member having a reflecting surface is irradiated with the light emitted from the light source, and the reflected light is irradiated to the other member. In a reflective optical gap sensor that detects a gap between both members by detecting with a light receiving element,
The lattice is
A first grid of equal pitches to limit the emitted light;
A second grating of equal pitch that further restricts light transmitted through the first grating;
Irradiating the reflecting surface with light transmitted through the first grating and the second grating, and comprising a third grating for detecting an image of transmitted light of the first grating generated by the reflected light,
A reflection-type optical gap sensor, wherein a change in the period of the image generated in response to a gap change between the members is detected to detect a gap between the members.   3. The first to third gratings are arranged so that a principal ray of the emitted light is incident perpendicularly to a grating plane of the first to third gratings. Reflective optical gap sensor.   The reflective optical gap sensor according to claim 1, wherein the detection unit includes a prism so that a principal ray of the emitted light is incident perpendicularly to a lattice plane.

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