JPH0776701B2 - Optical displacement detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement detecting device, and more particularly to improvement of a three-grating type optical displacement detecting device.

[0002]

2. Description of the Related Art In various measuring machines, machine tools, and more recently, various information machines, various displacement detecting devices are used to detect the amount of displacement of two members that move relative to each other. Optical displacement detectors are commonly used where quantity detection is required. This optical displacement detection device is provided with a main scale and an index scale on each member that moves relatively, for example, irradiates the main scale with light through a grating provided on the index scale, and further through a main scale grating. Light is received by a light receiver, and the relative movement amount of the member is detected from the phase change and the like. As such an optical displacement detector, in addition to a detector that utilizes a change in the overlap of two normal types of gratings,
A three-lattice type displacement detector using three types of lattices is well known (Journal of the optical society of America, 196
5, vol.55, No.4, p373-381).

The three-lattice type displacement detector 10 shown in FIG.
The second grating 12 and the third grating 14 arranged in parallel, the first grating 16 arranged in parallel so as to be relatively movable between the two gratings 12 and 14, and the second grating 16 arranged on the left side in the drawing. It includes a light emitting element 18 and a light receiving element 20 arranged on the right side of the third grating 14 in the drawing. Then, the light emitted from the light emitting element 18 reaches the light receiving element 20 through the second grating 12, the first grating 16, and the third grating 14, and the light receiving element 20 is restricted by the respective gratings 12, 16, 14. The illumination light is photoelectrically converted and further amplified by the preamplifier 22 to obtain a detection signal s.

Here, when the first grating 16 moves relative to the second grating 12 and the third grating 14 in the x direction, for example, the gratings 12, 1 of the illumination light from the light emitting element 18 are moved.
The amount of light blocked by 6, 14 gradually changes, and the detection signal s is output as a substantially sine wave. The pitch P ₁ of the first grating 26 and the wavelength P ₁ of the detection signal s correspond to each other, and the reference grating 16 is obtained from the wavelength of the detection signal s and its division value.
The amount of relative movement of is measured. Therefore, one moving member that relatively moves the first grating 16 and the second grating 1
By disposing the second and third gratings 14 on the other moving member, the relative movement amount of both moving members can be detected.

[0005]

By differentiating the moving displacement amount of the relative moving member, the relative speed of both moving members can be obtained. Therefore, the displacement detecting device as described above is used as the speed detecting device. Can also be considered. However, if the detection signal obtained by photoelectric conversion has a sine wave shape as in the conventional case, the differential signal thereof also becomes a trigonometric function (cosine wave), which causes a problem that the speed calculation is complicated. On the other hand, if the movement displacement amount can be output in a triangular wave shape, the signal can be processed at high speed with a simple differentiating circuit. Therefore, a triangular wave shape can be used for speed control of a high-speed moving object represented by a linear motor or the like. There is a strong demand for a detection device that can obtain an output signal.

[0006] However, although it has been found that the conventionally proposed optical displacement detection device makes it possible to obtain a substantially triangular wave output signal, a curve is drawn around the maximum value and the minimum value of the output signal. The "blurring" has occurred, and the development of an optical displacement detection device capable of obtaining a more accurate triangular wave output signal has been awaited. The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide an optical displacement detection device capable of obtaining a detection signal having a triangular wave shape with extremely few "blurring" with a simple configuration. .

[0007]

In order to achieve the above object, the present invention provides the main scale and the index scale of the main scale and the index scale based on the periodic intensity change of light limited by the second grating, the first grating and the third grating. In the optical displacement detection device for detecting relative movement, the first grating has a correction dark line in the center of the bright line portion and has a correction bright line in the center of the dark line portion. Further, in the optical displacement detection device according to a second aspect of the present invention, the correction dark line and the correction bright line have a width of 1/10 to 1/5 of the bright line portion and the dark line portion, respectively.

[0008]

In the optical displacement detection device according to the present invention, the correction bright line is provided in the dark line portion of the second grating and the correction dark line is provided in the bright line portion as described above, and therefore, the detection signal that normally causes "blurring" The correction bright line and the correction dark line act on the maximum portion and the minimum portion, and a triangular wave shape detection signal with less rounding can be obtained. That is, the "blurring" occurs because the contrast of the light passing through the third grating draws a gentle curve in the bright portion and the dark portion due to the diffraction effect of the light. On the other hand, according to the present invention, the light amount is slightly decreased at the maximum contrast portion, and the light amount is slightly increased at the minimum contrast portion. Therefore, the portion that becomes a gentle curve due to the diffracting action of light is cut by the correction bright line and the correction dark line, and the contrast becomes a rectangular wave shape or a trapezoidal wave shape formed by almost straight lines. As a result, when the main scale and the index scale are moved relative to each other, the detection signal obtained by photoelectric conversion by the light receiver has very little "blurring".

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. It should be noted that the reference numeral 100 is added to the portion corresponding to the above-mentioned conventional technique and the description thereof is omitted. FIG. 1 is a vertical sectional view showing the basic structure of an optical displacement detecting device according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line II-II of FIG. . In the figure, in the optical displacement detection device 110, the main scale 130 thereof is provided on the moving member 132, and the index scale 134 is provided on the moving member 136. And the moving member 1
The amount of relative movement of 32 and 136 is detected.

On the upper surface of the index scale 134 in FIG. 1, one light emitting element 118 and four light receiving elements 120 are provided.
a, 120b, ... 120d are arranged. The lead wires of the light emitting element 118 and each light receiving element 120 are fixed to the printed board 138. As shown in FIG. 3, the main scale 130 made of the glass substrate is provided with a long first grating 116 extending in the X direction in the figure. The first grating 116 extends in a direction orthogonal to the extending direction. It is composed of a reflection line portion (bright line portion) and a transmission line portion (dark line portion). On the other hand, the index scale 134, as is clear from FIG. 4, has the second lattice 112 and the third lattices 114a, 114.
b, ... 114d. Then, the second lattice 112
Corresponds to the light emitting device 118 and is formed of a transmission grating formed so as to be orthogonal to the X direction. Also, the third lattice 114
114d are light receiving elements 120, respectively.
a, 120b, ... 120d.

Since the present embodiment is a reflection type displacement detecting device, there is no choice but to have a wide gap between the gratings.
Therefore, it is greatly affected by diffraction. Therefore, in order to increase the linear portion in the photoelectric conversion output, the bright line portion width of the second grating 112 is set to be approximately the same as the bright line portion width of the first grating 116. The bright line portion width of the third grating 114 is defined as the ratio of the interstitial gap u between the second grating 112 and the first grating 116 and the interstitial gap (u + v) between the second grating 112 and the third grating 114 (in the reflection type, it is always According to 2), the width of the bright line portion of the first grating 116 is 2
Double the amount. I have decided. The second lattice 112
It is desirable that the width of the bright line portion of is thin in order to prevent the influence of the diffraction effect. However, if the width of the bright line portion is too thin, the light energy becomes small. . Further, in the case of the reflection type, it is desirable that the interstitial gap u = v is 1 mm or more because experiments show that if the interstitial gap is too small, the interstitial gap becomes sinusoidal.

In consideration of the above points, in the present embodiment, the pitch P ₁ of the first grating 116 is 100 μm (the bright line portion 50 μm).
m, dark line portion 50 μm, corrected dark line w = 4 μm, corrected bright line w =
4 μm), the pitch P ₂ of the second grating 112 is 400 μm (bright line portion 40 μm, dark line portion 360 μm), and the pitch P ₃ of the third grating 114 is 200 μm (bright line portion 100 μm, dark line portion 100).
μm).

According to the optical displacement detection device constructed as described above, the light L emitted from the light emitting element 118 passes through the second gratings 114a, 114b, ...
16 and the reflected light is reflected by the third gratings 114a, 114.
b, ... 114d through the light receiving elements 120a, 120b,
The light is received by 120d, and the relative movement in the X direction can be detected by the three-grating system. A feature of the present invention is that the correction dark line is provided in the center of the bright line portion of the first grating and the correction bright line is provided in the center of the dark line portion. It is configured as shown in FIG.

As is clear from the figure, the first grating 116
Are light line portions 150a, 150b, ... And dark line portions 152a,
It has 152b, .... The correction dark lines (w = 4 μm) 154a, 154b, ...
Are provided, and correction bright lines (w = 4 μm) 156a, 156b, ... Are provided in the center of the dark line portions 152a, 152b ,. Therefore, the structure corresponding to FIG. 10 can be expressed as shown in FIG. 6 in the present embodiment. It should be noted that FIG. 9A shows a lattice configuration, and FIG.
4 shows the contrast of the light having passed through 4, and FIG. 7C shows the contrast of the light obtained by this example.

In the figure, the irradiation light L from the light emitting element 118 is the second grating 112, the first grating 116, and the third grating 11.
The light passes through 4 to reach the light receiving element. Here, it is assumed that the optical transmission portions of the second grating 112, the first grating 116, and the third grating 114 are aligned in a straight line as shown in FIG. Then, as shown by a two-dot chain line frame D in the same figure, in an ideal state in which the bright line portion width of the second grating 112 can be regarded as a line light source, the light emitted to the light receiving element is The contrast has a rectangular wave shape as shown by the alternate long and short dash line in FIG. 7B, and the photoelectric conversion signal waveform obtained when the first grating 116 is relatively moved has a perfect triangular wave shape. However, considering the practical bright line width and light diffraction of the second grating, a pseudo trapezoidal signal waveform having a gentle curve at the maximum and minimum portions as shown by the solid line in FIG. Will end up.

On the other hand, in this embodiment, as shown in FIG.
As shown in (E), the correction dark line 15 is formed in the center of the bright line portion 150.
4. A correction bright line 156 is provided at the center of the dark line portion 152. As a result, at the maximum contrast, the correction dark line 1
54 acts on the direction in which the light amount decreases, and in the minimum portion of the detection signal, the corrected bright line 156 acts on the direction in which the light amount increases. Therefore, as shown by the dotted line in FIG. Is drawn.

As a result, by superimposing the solid line portion and the dotted line portion in FIG. 6B, it is possible to obtain almost perfect trapezoidal wave-shaped contrast as shown in FIG. 6C.
Substantially curved portions can be eliminated. Therefore, by relatively moving the main scale 132 and the index scale 134, it is possible to obtain a triangular wave detection signal from the photodetector 120 with very little “blurring”. Then, in the present embodiment, the light receiver 12
The outputs of 0a, 120b, 120c and 120d are voltage outputs differentially amplified by the amplifier circuit shown in FIG. That is, each of the light receivers 120a, 120b ... 120d is composed of a phototransistor.
The current output I _{a of} 20 _a is output as a voltage change by a current / voltage conversion amplifier 174 including an operation amplifier 170 and a resistor 172 connected in parallel. Also,
The current output I _b of the phototransistor 120b is output as a voltage change by the current / voltage conversion amplifier 176 having the same configuration. Each phototransistor 120a,
Since the current outputs I _a and I _b of 120 _b have opposite phases,
A resistor 178 and an operational amplifier 1 connected in parallel
By performing differential amplification by the differential amplification amplifier 182 composed of 80, it is possible to obtain the voltage output A-phase output as shown by the solid line in FIG. Similarly, the light receiver 120
From the outputs of c and 120d, it is possible to obtain the B-phase output (shown by the dotted line in FIG. 8A) which is 90 degrees out of phase with the A-phase output and which has been differentially amplified.

In the present embodiment, the A-phase output and the B-phase output each have a triangular wave shape as shown in FIG. 8A, and each output is differentiated by differentiating circuits 182 and 184 to obtain The differential signal indicated by the solid line 8 (B) and the differential signal indicated by the dotted line in the figure are obtained from the B-phase output, and the larger one of the differential signals is selected and output by the maximum value selection circuit 186. , A signal proportional to speed can be obtained. That is, for the A-phase signal and the B-phase signal that are triangular wave detection signals, if the voltage in the moving direction x of the main scale 132 and the index scale 136 is Ex, the absolute value thereof is proportional to the displacement x as shown in the following equation. There is. | E _x | = | k · x | where k is a proportional constant representing the slope. Therefore, the derivative is as shown in the following equation. | DE _x / dt | = | k · dx / dt | = | k · v _x | Here, v _x is the speed, and the maximum value of the differential signal shown in FIG. It is a proportional function of the velocity v _x .

As described above, the three-grating type optical displacement detector according to the present embodiment can obtain an appropriate triangular wave shape output, and is particularly suitable for speed detection.
In FIG. 6, the first grating is replaced with the transmission type for the sake of convenience of description, but it goes without saying that if the reflection type optical displacement detector shown in FIG. Can be obtained. Further, in the present embodiment, the pitch P ₂ of the second grating is 400 μm, but the pitch P ₂ is 200
It is also preferable to use a large amount of light energy as μm (bright line portion 40 μm, dark line portion 160 μm). Also,
When the present invention is applied to the transmission type displacement detector, it is possible to reduce the influence of the diffraction effect by making the inter-grating gaps u and v very small. It is possible to obtain a substantially triangular wave-shaped signal without prescribing or defining the bright line width of the third grating,
By directly applying the present invention, it is possible to obtain a triangular wave-shaped output signal without "blurring".

[0020]

As described above, according to the optical displacement detection device of the present invention, the correction dark line is provided at the center of the bright line portion of the first grating and the correction bright line is provided at the center of the dark line portion. It is possible to obtain an appropriate triangular wave shape output with very little "blurring".

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a schematic configuration of an optical displacement detection device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an arrangement of a light emitting element and a light receiving element of the optical displacement detection device according to the embodiment.

FIG. 3 is an explanatory diagram of a main scale (first grating) of the optical displacement detection device according to the embodiment.

FIG. 4 is an explanatory diagram of index scales (second grating and third grating) of the optical displacement detection device according to the embodiment.

FIG. 5 is an explanatory diagram of a detailed configuration of a first grating according to the embodiment.

FIG. 6 is an explanatory diagram of an operation of the optical displacement detection device according to the embodiment.

FIG. 7 is an explanatory diagram of a differential amplifier circuit used in this embodiment.

FIG. 8 is an explanatory diagram of an output state of a speed proportional signal.

9 is a view of the reflection type displacement detection device corresponding to FIG.

FIG. 10 is an explanatory diagram of a general three-lattice type displacement detection device.

[Explanation of symbols]

 10,110 Optical displacement detection device 118 Light emitting element 120 Light receiving element 12,112 Second grating 14,114 Third grating 16,116 First grating 130 Main scale 134 Index scale 150 Bright line part 152 Dark line part 154 Correction dark line 156 Correction Clear line

Front Page Continuation (72) Inventor Shingo Kuroki 165 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Mitutoyo R & D Laboratory, Inc. (56) References

Claims (2)

[Claims] 1. A first grating formed on a main scale, and a second grating formed on an index scale that moves relative to the main scale, the second grating being arranged so as to optically sandwich the first grating. And a third grating, a light source arranged on the first grating non-facing surface side of the second grating, and a light receiver arranged on the first grating non-facing surface side of the third grating, In the optical displacement detection device for detecting relative movement of the main scale and the index scale from the periodic intensity change of light limited by the two gratings, the first grating, and the third grating, the first grating is a bright line portion. An optical displacement detection device having a correction dark line in the center and a correction bright line in the center of the dark line portion. 2. The optical displacement detection device according to claim 1, wherein the corrected dark line and the corrected bright line have widths of 1/10 to 1/5 of the bright line portion and the dark line portion, respectively. Displacement detection device.