JP2002236033A - Optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a smaller and compact optical encoder having a high resolu tion. SOLUTION: In the optical encoder 1, light from an LED passes through a light transmission type mobile grating 31, formed on a semiconductor moving plate 3 and is reflected on a reflection grating 41 of a reflection grating plate 4. The resulting image of the reflection grating is detected by a grating-like photodiode 32 formed on the semiconductor moving plate 3. The mobile grating 31 and the photodiode 32 are incorporated into a common semiconductor board and the grating-like photodiode allows the obtaining of lens effects, to eliminate the need for any lens optical system thereby realizing a smaller and compact encoder. An A-phase signal obtained from the group of photodiodes arranged on the semiconductor board, and the differential signal of an inversion signal thereof are generated as the A-phase signal and a B-phase signal and a differential signal of an inversion signal thereof is generated as the B-phase signal, thereby obtaining an encoding signal with limited errors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder which can be configured to be small and compact and can accurately detect the position of a moving object.

[0002]

2. Description of the Related Art A detector for detecting the amount of rotation or movement of a moving object is called a rotary encoder or a linear encoder. Generally, a moving grating plate and a fixed grating plate are arranged between a light source and a light receiving element. Based on a change in the amount of transmitted light that passes from a light source to a light receiving element through a moving grating and a fixed grating formed on a plate, the amount of movement of a moving object that moves integrally with the moving grating plate is detected. It is configured.

[0003] Since the resolution of an optical encoder having this configuration is determined by the grating pitch, a high-resolution encoder can be realized by reducing the grating pitch. However, if the gap between the moving grating plate and the fixed grating plate is not reduced accordingly in order to reduce the grating pitch, the S / N ratio decreases due to light leakage. In addition, the S / N ratio decreases unless the gap variation between the gratings due to the movement of the moving grating is reduced.

[0004] Since there is a limit in reducing the gap between the gratings and in suppressing the gap variation, a method using parallel rays is used to avoid a decrease in the S / N ratio due to light leakage and gap variation. Is valid. In order to convert the divergent light from the light source into parallel light, a lens optical system such as a collimator lens may be used, and an optical encoder including such a lens optical system is also known. However, the light source generally used in the optical encoder is an LED, and L
Since the ED is not a point light source, it is difficult to obtain high-quality parallel rays. In addition, the addition of a lens optical system increases the size of the apparatus.

On the other hand, there is known a method for realizing a high-resolution optical encoder by utilizing the light diffraction phenomenon. In the encoder according to this method, light emitted from a point light source such as a semiconductor laser and collimated by a lens is transmitted through a fine pitch grating, and light received due to diffraction and interference generated when the parallel light passes through the grating. The amount of movement of the moving object is detected based on the change in the amount of light received by the element. When this method is adopted, the grid pitch can be made smaller than that of the encoder having the above configuration, and the distribution of light due to interference is close to a sine wave, so that accurate electric division can be performed. However, since high precision is required for the grating itself and the mechanism of the device, there are drawbacks in that the price of the device is high and the reliability of the semiconductor laser used as the light source is low.

Next, as an optical encoder, a spatial filter encoder that forms an image of a moving grating on a light receiving element arranged in a lattice shape through a lens has been proposed in Japanese Patent Application Laid-Open No. H6-118088 by the present applicant. . In this method, the harmonic effect of the signal caused by the grating movement can be canceled by the filter effect, so that a signal close to a sine wave can be obtained, and therefore, the resolution can be increased by using the divider. . But,
If the grating pitch is reduced, it is difficult to increase the contrast of the received light image, and the size of the device is increased due to the use of a lens optical system.

[0007]

Here, "Application of ITS to image formation analysis and displacement measurement of grating" (SP
IE, Vol. 136, No. 1 on application of optics to metrology
European Conference (1977), pp. 325-332) ("ANA
LYSIS OF GRATING IMAGING AND ITS APPLICATION
TO DISPLACEMENT METROLOGY ", SPIE Vol.136 1st
European Congress on Optics Applied to Metr
ology (1977), pp. 325-332), reports on the theory of triple lattices and its application to displacement measurement. As described in this report, the index grating plate and the reflection grating plate face each other, the light emitting source and the light receiving element are arranged behind the index grating plate, and the light emitted from the light source passes through the index grating of the index grating plate. Then, the light reflected by the reflection grating of the reflection grating plate and transmitted through the index grating again is detected by the light receiving element, whereby the amount of movement of the reflection grating can be detected.

According to this configuration, even if the distance between the index grating and the reflection grating is increased, the contrast is not affected, and the contrast due to the fluctuation of the gap between these gratings is hardly affected.

Therefore, based on the theory of a three-grating using a reflection grating, it is possible to realize a high-resolution optical encoder which is not affected by the width of the fixed grating and the moving grating and the fluctuation of the spacing. is there.

However, there are the following problems to be solved when applied to an optical encoder.

First, in the encoder having this structure, since the light emitting source and the light receiving element need to be arranged behind the index grating, there is a problem that the structure is complicated and the light amount detecting efficiency is low. When used as an encoder, it is necessary to use at least two light receiving elements to generate signals whose phases are shifted from each other by 1/4 phase in order to detect the moving direction of a moving object to be detected. . However, behind the index grating, a light emitting source and at least two light receiving elements are arranged, and 1 /
It is difficult to realize a configuration for extracting a signal whose phase is shifted by four phases.

In view of the above, an object of the present invention is to provide:
It is an object of the present invention to realize an optical encoder that can be configured to be small and compact and that can detect a moving speed and a moving direction (moving position) based on the theory of a three-grating using a reflection grating.

[0013]

The present inventor detects the moving direction of a moving object by forming a grating and a light receiving element on a common semiconductor substrate based on the theory of a three-grating using a reflection grating. A phase and B phase signals that are shifted in phase by the necessary 1/4 phase can be generated, so that the distance between the reflecting grating and the moving grating can be widened and the moving object can be controlled without being affected by the fluctuation of the distance. They have come up with a small and compact optical encoder for detecting the amount of movement.

That is, the present invention provides a light source, a reflection grating plate on which a plurality of reflection gratings are formed at a constant pitch or angle, a moving grating plate on which a plurality of light transmission gratings are formed at a constant pitch or angle, An optical encoder having a light receiving element that receives a reflected light image emitted from a light source, transmitted through the light transmission grating, and reflected by the reflection grating,
The light transmission grating and the light receiving element are formed on a common semiconductor substrate. The light receiving element is a grating formed at a constant pitch or angle, and the moving grating is formed based on a detection signal obtained from each light receiving element. The relative movement direction and speed (movement position) of the plate and the reflection grating plate are detected, and the light transmission grating is formed in a light passing slit formed in the semiconductor substrate or formed in the semiconductor substrate. It is a thin film portion for light transmission.

In the present invention, the light receiving elements and the light transmission gratings can be alternately arranged on the semiconductor substrate. Alternatively, a region where only the light receiving elements are arranged at predetermined intervals and a region where only the light transmission grating is arranged at predetermined intervals may be formed on the semiconductor substrate.

Here, when the light receiving elements and the light transmission gratings are alternately arranged as in the former case, detection signals (A-phase signal and B-phase signal) shifted by 90 degrees are obtained as follows. be able to.

In the first embodiment, a first area in which the light receiving elements and the light transmitting gratings are alternately arranged and a second area in which the light receiving elements and the light transmitting gratings are alternately formed are formed. I do. In addition, the light reception of the first area may be shifted by 90 degrees from the detection signal obtained from the light reception element of the first area with respect to the detection signal obtained from the light reception element of the second area. The positional relationship between the element and the light receiving element in the second area is determined. As a result, for example, an A-phase signal is obtained from the first area, and a B-phase signal is obtained from the second area.

In this case, a third region in which the light receiving elements and the light transmitting gratings are alternately arranged, and a fourth region in which the light receiving elements and the light transmitting gratings are alternately formed are formed. A third detection signal obtained from the light receiving element in the third area is shifted by 180 degrees from a detection signal obtained from the light receiving element in the first area.
Determining the position of the light receiving element in the area of the second area; and detecting the detection signal obtained from the light receiving element in the fourth area of the second area.
It is desirable to determine the position of the light receiving element in the fourth area so that the phase is shifted by 180 degrees with respect to the detection signal obtained from the light receiving element in the area.

With this configuration, for example, an inverted signal of the A-phase signal is obtained from the third area, and a B-phase determination signal is obtained from the other fourth area.

Next, in a second embodiment, each light receiving element is a two-part type light receiving element arranged at a predetermined interval.
Of the two-split type light receiving elements, so that the phase of the first detection signal is shifted by 90 degrees with respect to the second detection signal obtained from the other second split light-receiving element. The interval between the light receiving elements is determined. According to this configuration, for example, an A-phase signal is obtained from the first two-piece light receiving element, and a B-phase signal is obtained from the other second two-piece light receiving element.

In this case, the first region in which the light receiving elements and the light transmission gratings are alternately arranged at a constant interval, and the light receiving elements and the light transmission gratings are also alternately arranged at the same interval as the first region. A second region arranged in the second region; the first and second detection signals obtained from the first and second two-split type light receiving elements in the first region are provided in the second region. The phases of the third and fourth detection signals obtained from the first and second two-piece light receiving elements are 180
It is desirable to determine the mutual positional relationship so as to shift by degrees.

In this way, since the A-phase signal and its inverted signal and the B-phase signal and its inverted signal are obtained, it is possible to obtain an encoded output with a small error component based on these signals.

On the other hand, when the region where the light receiving elements are arranged and the region where the light transmission gratings are arranged are formed as separate regions on the semiconductor substrate, the following is performed.
It is possible to obtain detection signals (A-phase signal and B-phase signal) shifted by 90 degrees in phase.

That is, the phase of the detection signal obtained from the even-numbered second light-receiving element group is different from the detection signal obtained from the odd-numbered first light-receiving element group in the first area. The distance between the light receiving elements is determined so as to be shifted by 180 degrees. As a result, for example, an A-phase signal is obtained from the first light receiving element group, and an inverted signal thereof is obtained from the second light receiving element group.

In addition, a third region in which the light receiving elements are arranged at regular intervals is formed; a detection signal obtained from an odd-numbered third light receiving element group in the third region is The intervals between the light receiving elements are determined such that the phases of the detection signals obtained from the even numbered fourth light receiving element groups are shifted by 180 degrees; and the detection obtained from the first and third light receiving element groups is further performed. The positional relationship between these light receiving element groups is determined so that the phases of the signals are shifted by 90 degrees. As a result, a B-phase signal is obtained from the third light receiving element group, and an inverted signal thereof is obtained from the fourth light receiving element group.

Alternatively, the semiconductor substrate includes a first region in which the light receiving elements are arranged at predetermined intervals, a second region in which the light transmission gratings are arranged at predetermined intervals, and Forming third regions arranged at predetermined intervals,
The first region and the third region include first to fourth light receiving elements as the light receiving elements, and these light receiving elements are arranged in the order of the first, fourth, third, and second light receiving elements. , And the interval between the adjacent light receiving elements is set to 270.
What is necessary is just to set it so that it may shift.

According to this configuration, an A-phase signal and its inverted signal are obtained from the first and third light receiving elements, and a B-phase signal and its inverted signal are obtained from the second and fourth light receiving elements.

In addition, when the first and third regions are arranged with the second region in which the light transmission grating is formed interposed therebetween, the positioning error of the semiconductor substrate with respect to the reflection grating plate causes Even if the light receiving element of the semiconductor substrate is inclined with respect to the reflection grating of the reflection grating plate, a phase change of a detection signal obtained from the light receiving element can be suppressed, and highly accurate detection can be performed.

As described above, when the inverted signals of the A-phase signal and the B-phase signal are obtained, the first differential signal is generated from the A-phase signal and the inverted signal thereof, and the B-phase signal and the inverted signal are generated. By using the signal processing circuit that generates the second differential signal from the signal and its inverted signal, it is possible to generate the A phase and the B signal with small error components.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an optical linear encoder to which the present invention is applied will be described below with reference to the drawings.

FIGS. 1A to 1C are views showing a schematic configuration of the optical linear encoder of this embodiment. The optical linear encoder 1 of the present embodiment will be described with reference to these drawings.
Is basically composed of an LED 2 as a light source, a semiconductor moving plate 3 in which a moving grating and a light receiving element are built, a reflective fixed grating plate 4, and a control circuit unit 5.
As will be described later, the semiconductor moving plate 3 is provided with a light-transmitting grating 31 in the form of a vertical stripe at a constant pitch and a constant width, and a photodiode 32 (a hatched portion in FIG. 1C) as a light receiving element in a plane direction. Are formed alternately. On the fixed grating plate 4, on the light-receiving side surface 4a, vertical stripe-shaped reflection gratings 41 having a fixed width and a fixed width are arranged in a plane direction.

The control circuit section 5 includes a signal processing section 51 for forming an A-phase signal and a B-phase signal which are shifted in phase by 1/4 phase based on the detection signal of the photodiode 32;
Moving speed of the semiconductor moving plate 3 based on the phase and B phase signals,
A calculation unit 52 for calculating movement information such as a movement direction;
A display unit 53 for displaying the calculation result and a lamp driving unit 54 for feedback-controlling the driving of the LED 2 are provided.

The arithmetic unit 52, the display unit 53, and the lamp drive unit 54 may of course be connected as external circuits without being built in the control circuit unit 5.

FIG. 2 shows a cross-sectional structure of a portion of the semiconductor moving plate 3 where a light transmitting slit is formed and a photodiode is formed. The semiconductor moving plate 3 includes a semiconductor substrate 33 such as a silicon substrate.
As can be seen from (b), the light-transmissive moving grating 31 of a vertical stripe pattern having a constant pitch and a constant width is formed by etching removal.

As can be seen from FIG. 2A, the portion of the semiconductor substrate remaining between the moving gratings 31 in the semiconductor substrate 33 is formed by doping the semiconductor substrate portion 34 with boron from the surface. A pn junction photodiode 32 composed of the formed boron doped layer 35 is formed. Of course, the photodiode 32 may be formed in the semiconductor substrate 33 by other methods.

The boron doped layer 3 of each photodiode 32
5 is connected to an electrode layer 36 made of aluminum.
The common electrode layer 37 also made of aluminum is connected to the semiconductor substrate 33 side. Of course, a conductive material other than aluminum can be used as the electrode material.

The electrode layer 36 and the semiconductor substrate 33 are insulated by an insulating layer 38 made of a silicon oxide film. The exposed surface of the semiconductor substrate 33 is covered with a silicon oxide film in order to ensure durability. Similarly, the surface of the boron doped layer 35 is also covered by the silicon oxide film.

In the linear encoder 1 of the present embodiment configured as described above, the semiconductor moving plate 3 is integrated with the object to be measured (not shown) so as to be in the direction orthogonal to the optical axis L, and furthermore, the slit and the photodiode. When moved in the arrangement direction, the light emitted from the LED 2 first irradiates the back surface of the semiconductor moving plate 3, passes through the light transmission grating 31 formed on the semiconductor moving plate 3, and reflects the fixed fixed grating plate. 4 is illuminated in a checkered pattern.

Since the fixed grating plate 4 is also formed with the reflection gratings 41 having a constant pitch and the same width, the fixed grating plate 4
Is reflected, only the component irradiated on each reflection grating 41 is reflected. The reflection grating image irradiates the semiconductor moving plate 3 again,
Light is received by the vertical stripe-shaped photodiode 32 formed with a constant pitch and a constant width. As described above, in the present example, the vertically-striped light transmission grating 31 and the photodiode 32 formed on the semiconductor moving plate 3 function as two grating plates. Therefore, based on the theory of three gratings using a reflection grating, in the photodiode 32, the amount of received light changes in a sinusoidal manner in accordance with the relative movement between the reflection grating 41 and the moving gratings (31, 32). Therefore, a pulse signal corresponding to the relative moving speed can be obtained based on the photocurrent of the photodiode 32, and the relative moving speed can be calculated based on the pulse rate of the pulse signal.

Further, as shown in FIG. 1A, for example, an A-phase signal is generated based on the sum of the outputs of the odd-numbered photodiodes, and only 1 / 4λ is obtained based on the sum of the outputs of the even-numbered photodiodes. It is also possible to generate a phase-shifted B-phase signal. The moving direction of the moving grid can be determined based on these two-phase signals.

As described above, in the optical linear encoder 1 of the present embodiment, since the moving grating and the light receiving element are manufactured by the semiconductor manufacturing technology, a grating with a minute pitch can be manufactured. Therefore, a high-resolution encoder can be realized.

Further, since the light receiving elements formed in the form of vertical stripes at a constant pitch function as a grating, and the grating itself has a lens effect, it is not necessary to use a lens optical system, and the device can be downsized. .

Further, according to the theory of three gratings, the gap between the reflection grating and the moving grating is not widened and the fluctuation of the gap does not adversely affect the resolution. The adjustment work for securing the space can be simplified, and the restriction on the mounting place can be reduced.

In addition to this, since the distance between the reflection grating and the moving grating can be increased, there is an advantage that, for example, the side of the reflection grating can be housed in a protective case or the like to improve environmental resistance.

(Arrangement of light receiving element and light transmission grating) FIG.
Shows another arrangement example of the light-transmitting grating 31 and the photodiode 32 in the form of vertical stripes formed on the semiconductor moving plate 3.
This is an example in which 2 are alternately arranged.

In the example shown in FIG. 4A, the semiconductor substrate 3A
Are formed with four regions 301 to 304 in which vertical stripe light transmission gratings and vertical stripe photodiodes are alternately formed. Here, the A-phase signal is obtained from the photodiode group in the area 301, and the position of the photodiode group in the area 302 is determined so that the phase is shifted by 90 degrees with respect to the detection signal obtained from the photodiode group in the area 301. A B-phase signal is obtained from the photodiode group.

The photodiode group in the region 303 located below the region 301 has a phase difference of 180 degrees with respect to the detection signal obtained from the photodiode group in the region 301 so that a detection signal can be obtained. The position of the photodiode group is determined. Accordingly, an inverted signal of the A-phase is obtained from the photodiode group in the region 303. Similarly, the arrangement is defined so that a B-phase inversion signal can be obtained from the photodiode group in the region 304 located on the side of the region 303.

In the example shown in FIG. 4B, the semiconductor substrate 3B
And four rows of regions 4 in a direction orthogonal to the direction of movement of the substrate.
01 to 404 are formed. In the uppermost region 401, vertical stripe-shaped light transmission gratings and vertical stripe-shaped photodiodes are alternately formed at a constant pitch in the substrate movement direction. The region 402 is arranged so that the phase of the detection signal of the photodiode is shifted by 90 degrees from the region 401. The region 403 below the region 402 is arranged so that the phase of the detection signal of the photodiode is shifted by 180 degrees with respect to the region 401 at the top. Further, the region 404 is arranged so that the phase of the detection signal of the photodiode is shifted by 180 degrees with respect to the region 402.

As a result, for example, an A-phase signal is obtained from the photodiode group in the area 401, a B-phase signal is obtained from the photodiode group in the area 402, and an inverted A-phase signal is obtained from the photodiode group in the area 403. Region 40
The photodiode group of No. 4 obtains a B-phase inverted signal.

In the example shown in FIGS. 4C and 4D, a plurality of regions, ie, three regions 501 to 50 in the figure, are provided on the semiconductor substrate 3C at regular intervals along the moving direction (lateral direction).
3 are formed. In each region, vertical stripe-shaped light transmitting portions 31C (portions indicated by oblique lines) and vertical stripe-shaped photodiodes 32C formed therebetween are alternately formed at a constant pitch.

The area 5 is located between the adjacent areas 501 and 502.
If one pitch is between 02 and 503, each area is １ ／.
As shown in FIG. 4D, four photodiodes 32C are formed within the width of the pitch. The width of each photodiode 32C is 1/16 pitch, and the interval between the photodiodes is 1/8 pitch. Although a 1/32 pitch gap is provided between the photodiodes on both the left and right sides and the area boundary, the gap is not limited to 1/32 pitch. The ratio of the width of the light transmitting grating or light transmitting portion to the photodiode is also 1: 1.
However, the present invention is not limited to this.

When this arrangement is adopted, for example, an A-phase signal can be obtained from the leftmost photodiode in each region, a B-phase signal can be obtained from the right-hand photodiode, and an A-phase inverted signal can be obtained from the right-hand photodiode. Is obtained, and a B-phase inverted signal is obtained from the rightmost photodiode.

Next, FIGS. 5 and 6 show different examples of the alternate arrangement of the light transmission grating and the photodiodes. As shown in these figures, a semiconductor substrate 310 has a first region 340 in which light transmission gratings 320 and photodiodes 330 are alternately arranged at predetermined intervals, and a light transmission grating 350 and photodiodes 360 which are also alternately arranged at predetermined intervals. And a second region 370 arranged in the first region.

The photodiode 330 in the first area 340 is a two-part photodiode, one of which is a photodiode 331 for obtaining an A-phase detection signal, and the other of which is a photodiode for obtaining a B-phase detection signal. 332. Similarly, the second area 370
The photodiode 360 in FIG. 1 also includes a two-part photodiode 361 and a photodiode 362.

Here, each of the two-divided photodiodes 331 and 332 in the first region 330 and each of the two-divided photodiodes 361 and 362 on the side of the second region 370 are 1 /
There is a positional relationship shifted by two pitches. Therefore, the second area 3
70, each two-part photodiode 361, 362
Respectively, an inverted signal of the A phase and an inverted signal of the B phase are obtained. FIG. 6 shows an example of the arrangement of each two-division type photodiode.

Note that, as shown in FIG.
0, each photodiode 3 from which an A-phase signal can be obtained.
The electrode wiring layer 381 connected to the photodiode 31 and the electrode wiring layer 38 connected to each photodiode 332 from which a B-phase signal can be obtained.
2. Each photodiode 361 that can obtain an inverted signal of A phase
Wiring layer 383 connected to each other, the electrode wiring layer 3 connected to each photodiode 362 from which a B-phase inversion signal is obtained.
84 are formed.

As shown in FIG. 5B, a semiconductor substrate 390 having a concave portion 391 formed on the front surface is attached to the back surface of the semiconductor substrate 310, and the concave portion 391 of this semiconductor substrate is formed.
If a configuration in which a light emitting source 392 such as a surface emitting laser or an LED is disposed on the bottom surface of the light emitting device is adopted, a compact detection mechanism with an integrated light emitting source can be configured.

FIGS. 7 and 8 show an arrangement in which a region where photodiodes are arranged at regular intervals and a region where light transmission gratings are arranged at regular intervals are separately formed on the surface of the semiconductor substrate. An example is shown.

As shown in this figure, on the surface of a semiconductor substrate 410, a region 4 in which light transmitting gratings 420 are arranged at regular intervals in the semiconductor substrate moving direction at regular intervals.
30 are formed, and regions 440 and 450 in which photodiodes are arranged at regular intervals are formed in a vertically symmetric state with the region 430 interposed therebetween.

In the region 440, the odd-numbered photodiodes 441 and the even-numbered photodiodes 442 are arranged at intervals such that the phases of the detection signals are shifted by 180 degrees. Similarly, in the region 450, since the odd-numbered photodiodes 451 and the even-numbered photodiodes 452 are arranged at the same interval as in the region 440, the phases of their detection signals are shifted by 180 degrees. It has become. Furthermore, the photodiode group 441 in the region 440 and the region 45
The photodiode group 451 of 0 has a relationship shifted by １ ／ pitch. Therefore, if an A-phase signal is obtained from the photodiode group 441 in the area 440, an inverted A-phase signal is obtained from the photodiode group 442 in the same area 440. Also, the photodiode group 45 in the region 450
A B-phase signal is obtained from 1 and a B-phase inverted signal is obtained from the photodiode group 452. FIG. 8 shows an example of the arrangement of each photodiode.

Note that, also in this example, the semiconductor substrate 410
On the surface of each photodiode 4 from which an A-phase signal can be obtained.
41, an electrode wiring layer 46 connected to each photodiode 451 from which a B-phase signal is obtained.
2. Each photodiode 442 from which an inverted signal of A phase can be obtained
And the electrode wiring layer 4 connected to each photodiode 452 from which a B-phase inverted signal is obtained.
64 are formed.

As shown in FIG. 7C, a semiconductor substrate 490 having a concave portion 491 formed on the front surface is attached to the back surface of the semiconductor substrate 410, and the concave portion 491 of the semiconductor substrate is formed.
If a configuration in which a light emitting source 492 such as a surface emitting laser or an LED is disposed on the bottom surface of the device is adopted, a compact detection mechanism in which the light emitting source is integrated can be configured.

Here, the semiconductor substrate 41 having the structure shown in FIG.
When 0 is used, it is necessary to accurately position the semiconductor substrate 410 with respect to the fixed grating plate on which the reflection grating is formed. That is, as shown in FIG. 9A, when the semiconductor substrate 410 is positioned with respect to the fixed grid plate 4A in a state of being inclined in the direction indicated by the arrow A or B, the reflection grating 4b of the fixed grid plate 4A and , Semiconductor substrate 41
0 light transmission grating 420, light receiving elements 441, 442, 45
1, 452 are mutually inclined. FIG. 9B shows a state of being inclined in the direction of arrow A.

In this case, according to experiments performed by the present inventors,
It has been confirmed that even at a small inclination angle of about 0.15 degrees, the phase shift of the detection signal obtained from each light receiving element becomes about 45 degrees. Further, for example, when the sensor is tilted in the direction of arrow B and the angle change is about 0.5 degrees, the output difference between the A-phase and B-phase detection signals is about 0.2 V (1 V which is the reference value output).
About 20%). Therefore, after the semiconductor substrate 410 is positioned and attached to the fixed grid plate 4A, an actual detection signal is measured, and
It is necessary to adjust the signal level.

In order to avoid such a change in the light receiving element detection signal due to the positioning error of the semiconductor substrate 410 with respect to the fixed grating plate, it is desirable to adopt the following configuration.

That is, as in the case of FIG. 7, on the surface of the semiconductor substrate 410, a region 430 in which the light transmission gratings 420 are arranged at regular intervals in the semiconductor substrate moving direction at regular intervals is formed. With the region 430 sandwiched therebetween, regions 440 and 450 in which photodiodes are arranged at regular intervals are formed in a vertically symmetric state. However, each area 4
In 40 and 450, photodiodes that output detection signals of each phase are arranged as follows.

As shown in FIG. 10, in the region 440, the phase of the detection signal between adjacent photodiodes is 27
Each photodiode 4 at a 3/4 pitch so as to shift by 0 degree
71, 482, 472, 481 are arranged. As a result,
Since the photodiodes 471 and 472 are arranged at a (1 + ／) pitch, the detection signal obtained from one of them is A
If it is a phase signal, an inverted signal of the A phase is obtained from the other. In addition, the photodiode 481 is
B shifted by 90 degrees from the A-phase signal obtained from
A phase signal is obtained. Therefore, an inverted signal of the B phase is obtained from the other photodiode 482. In the other region 450, the same light receiving element arrangement is employed.

In the upper and lower regions 440 and 450 sandwiching the region 430 where the light transmission grating 420 is formed, A
When the light receiving elements are arranged at an equal pitch so as to obtain the phase signal, the inverted signal of the B phase, the inverted signal of the A phase, and the B signal, It was confirmed that voltage fluctuation can be suppressed. Therefore, if such a configuration is adopted, accurate detection can be performed. Further, in this light receiving element arrangement, since the pitch between the light receiving elements is widened, a secondary advantage that insulation between the elements can be easily obtained is also obtained.

(Method of Improving S / N Ratio) Here, in the examples shown in FIGS. 4 to 8 and FIG. 10, an error is obtained by obtaining a differential signal of the obtained A-phase signal and its inverted signal. A-phase signal with a small number of signals can be generated. Similarly, by obtaining a differential signal between the obtained B-phase signal and its inverted signal, it is possible to generate a B-phase signal with less error.
By using such a differential signal, the S / N ratio of the optical encoder can be improved.

Next, another method for improving the S / N ratio will be described below. The photodiode formed on the above-mentioned semiconductor moving plate is irradiated with light from the back side, so that the dark current may increase and the S / N ratio may decrease. If this adverse effect is avoided, the S / N ratio can be improved. This can be done as follows.

Referring to FIG. 11, the semiconductor substrate 3 shown in FIGS. 1 and 2 will be described as an example. On the back side of the semiconductor moving plate 3, that is, on the light source side, a reflection made of a material such as aluminum or gold is used. Film (light shielding film) by a method such as evaporation
What is necessary is just to laminate. In this case, if a reflective film is formed also on the side surface of the photodiode 32, the effect is further improved. In the drawing, the area where the reflection film can be formed is indicated by a dotted line.

(Method of Forming Light Transmitting Portion) Next, in order to form a light transmitting grating on a semiconductor substrate, the surface of the semiconductor substrate may be dry-etched. When dry etching is employed, the substrate surface can be engraved vertically. Alternatively, wet etching, which is an inexpensive manufacturing method, can be employed. In this case, since the anisotropic etching is caused by the crystal orientation, slits on the side surfaces inclined with respect to the semiconductor substrate surface are formed as shown in FIG.

Also in this case, if a reflective film is formed on the back surface (light source side) of the portion remaining as the photodiode by a method such as vapor deposition on the portion indicated by the dotted line, the dark current of the photodiode can be reduced, and the S / S The N ratio can be improved.

(Other Embodiments) In each of the above examples, the light transmission type moving grating of the semiconductor moving plate is a light passing slit formed in the semiconductor substrate. It is also possible to form a thin film through which a quantity of light can be transmitted by etching the semiconductor substrate, and make each thin film portion a moving grating.

Further, as shown in FIG. 3, by etching a portion on the back surface side of the semiconductor substrate 33A on which the photodiode 32A is formed, a thin film portion through which sufficient light can be transmitted is formed. It can be used as the moving grating 31A. Such a transparent semiconductor light receiving element is disclosed in Japanese Patent Application No. Hei 10-1998 filed on April 30, 1998.
No. 120848, proposed in the drawings.

On the other hand, in the above example, the side on which the reflection grating 41 is formed is the fixed side.
May be set as a moving side, and the side of the semiconductor moving plate 3 may be set as a fixed side.

In the above example, an LED is used as a light source, but other light sources such as a laser light source may be used.

Further, the above example relates to a linear encoder, but the present invention is similarly applicable to a rotary encoder. In this case, the light transmitting portion and the photodiode portion may be formed at a constant angle in the circumferential direction.

[0079]

As described above, in the optical encoder of the present invention, a reflection grating image capable of detecting information relating to the relative movement between the reflection grating and the moving grating based on the triple grating theory is used as the light receiving element. And a configuration in which the moving grating and the light receiving element are formed on a common semiconductor substrate.

Therefore, according to the encoder of the present invention, it is not necessary to arrange a light receiving element as a separate component behind the moving grating, and it is sufficient to simply arrange a light source. Further, since the lattice-shaped light receiving element itself formed on the semiconductor substrate has a lens effect, a spatial filter encoder can be realized without using a lens optical system. Therefore, the device can be made small and compact.

Further, since the moving grating is formed on the semiconductor substrate, there is an advantage that a grating with a minute pitch can be formed with high accuracy by a semiconductor manufacturing technique.

Further, according to the theory of the three-lattice grid, the distance between the reflection grating and the moving grating is not narrowed and the fluctuation of the distance does not lower the contrast of the detection signal. There is an advantage that the mounting operation of the formed components is simplified, and the restrictions on the mounting positions of these components are relaxed.

[Brief description of the drawings]

FIGS. 1A to 1C are explanatory diagrams showing a configuration of an optical linear encoder to which the present invention is applied.

2 (a) and 2 (b) are schematic cross-sectional configuration diagrams of a photodiode and a light transmission type moving grating formed on the semiconductor moving plate of FIG. 1. FIG.

FIG. 3 is a sectional view showing another example of the semiconductor moving plate.

FIGS. 4A to 4D are explanatory diagrams showing three examples of an arrangement form of a region including a light transmission grating and a photodiode.

5A and 5B are diagrams showing an example of the arrangement of light transmission gratings and photodiodes formed on the surface of a semiconductor substrate, wherein FIG. 5A is a plan view, FIG. 5B is a cross-sectional view, and FIG. It is an enlarged partial plan view shown as.

FIG. 6 is an explanatory diagram showing an example of the arrangement of the split photodiodes in FIG. 5;

FIGS. 7A and 7B are diagrams showing an example of the arrangement of light transmission gratings and photodiodes formed on the surface of a semiconductor substrate, wherein FIG. 7A is a plan view thereof, FIG. 7B is a cross-sectional view of a portion cut along the line bb, (C) is a sectional view of a portion cut along the line cc.

FIG. 8 is an explanatory diagram showing an example of the arrangement of the photodiodes in FIG. 7;

FIG. 9 is an explanatory diagram showing a problem in the example of arrangement of the photodiodes in FIG. 8;

FIG. 10 is an explanatory diagram showing an example of the arrangement of the photodiodes in which the problem caused by the arrangement of the photodiodes in FIG. 8 has been solved.

FIG. 11 is an explanatory diagram showing a method for improving the S / N ratio of a light receiving element.

FIG. 12 is an explanatory diagram showing a case where a light transmitting portion of a light receiving element is formed by wet etching.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 optical linear encoder 2 LED 3 semiconductor moving plate 31 light-transmitting moving grating 32 photodiode 33 semiconductor substrate 34 semiconductor substrate portion 35 boron doped layer 36 electrode layer 37 common electrode layer 38 silicon oxide film (insulating layer) 4 reflection grating plate 41 Reflection grating 5 Control circuit unit 51 Signal processing unit 52 Operation unit 53 Display unit 54 Lamp drive control unit 310, 410 Semiconductor substrate 320, 350, 420 Light transmission grating 330, 350 Bipartite photodiode 441, 442, 451, 452, 471 , 472, 4
81,482 Photodiodes 340,370 Regions in which light transmitting gratings and photodiodes are alternately arranged 440,450 Regions in which photodiodes are arranged at regular intervals 430 Regions in which light transmitting gratings are alternately arranged at regular intervals

Continued on the front page F term (reference) 2F065 AA00 AA02 AA07 AA22 BB02 DD03 FF07 FF16 FF18 GG07 HH13 JJ09 JJ18 JJ26 LL28 LL41 MM03 QQ29 2F103 BA31 BA37 CA03 DA01 DA12 EA17 EA19 EA12 EB12 EB12 EB12 EB12 EB12

Claims (9)

[Claims] 1. A light source, a reflection grating plate formed with a plurality of reflection gratings having a predetermined pitch or angle and a predetermined shape, and a moving grating plate formed with a plurality of light transmission gratings having a predetermined pitch or angle and a predetermined shape. A light receiving element that receives a reflected light image emitted from the light source, transmitted through the light transmission grating, and reflected by the reflection grating, wherein the light transmission grating and the light receiving element are common. The light receiving element is formed in a semiconductor substrate, and the light receiving element is a lattice of a predetermined shape formed at a constant pitch or angle. The moving direction and the speed are detected, and the light transmitting grating is formed by a light transmitting slit formed in the semiconductor substrate or a light transmitting slit formed in the semiconductor substrate. A first region in which the light receiving elements and the light transmission gratings are alternately arranged on the semiconductor substrate, and a second region in which the light receiving elements and the light transmission gratings are alternately arranged on the semiconductor substrate. And a first detection signal obtained from the light receiving element in the first area is 90 degrees in phase with a second detection signal obtained from the light receiving element in the second area. An optical encoder characterized in that a positional relationship between a light receiving element in the first area and a light receiving element in the second area is set so that the light is shifted. 2. The device according to claim 1, wherein the light receiving elements and the light transmission gratings are alternately arranged.
And a fourth area in which the light receiving elements and the light transmission gratings are alternately arranged. A third detection signal obtained from the light receiving elements in the third area is the first detection signal. The position of the light receiving element in the third area is set so that the phase is shifted by 180 degrees with respect to the first detection signal obtained from the light receiving element in the area. The position of the light receiving element in the fourth area is set such that the obtained fourth detection signal is 180 degrees out of phase with the third detection signal obtained from the light receiving element in the second area. An optical encoder, comprising: 3. A light source, a reflection grating plate formed with a plurality of reflection gratings of a predetermined shape at a constant pitch or angle, and a moving grating plate formed of a plurality of light transmission gratings of a predetermined shape at a constant pitch or angle. A light receiving element that receives the reflected light image emitted from the light source, transmitted through the light transmission grating, and reflected by the reflection grating, wherein the light transmission grating and the light receiving element are common. The light receiving element is formed in a semiconductor substrate, and the light receiving element is a grating of a predetermined shape formed at a constant pitch or angle. Based on a detection signal obtained from each light receiving element, the relative position of the moving grating plate and the reflection grating plate is determined. The moving direction and the speed are detected, and the light transmitting grating is formed by a light transmitting slit formed in the semiconductor substrate or a light transmitting slit formed in the semiconductor substrate. A thin film portion for use in the semiconductor substrate, wherein the semiconductor substrate is formed with a region in which the light receiving elements and the light transmission gratings are alternately arranged. A first detection signal obtained from one of the first two-split type light receiving elements, and a phase of 90 degrees with respect to a second detection signal obtained from the other second two-split type light receiving element. An optical encoder characterized in that the distance between these two-divided light receiving elements is determined so as to shift. 4. The light-receiving element and the light-transmitting grating according to claim 3, wherein the first area in which the light-receiving elements and the light-transmitting gratings are alternately arranged at regular intervals is the same as the first area. A second region alternately arranged at intervals; and a first and a second detection signal obtained from the first and second two-split type light receiving elements in the first region,
The positional relationship is determined such that the phases of the third and fourth detection signals obtained from the first and second two-split type light receiving elements in the second region are shifted by 180 degrees, respectively. Optical encoder. 5. A light source, a reflection grating plate formed with a plurality of reflection gratings of a predetermined shape at a constant pitch or angle, and a moving grating plate formed of a plurality of light transmission gratings of a predetermined shape at a constant pitch or angle. A light receiving element that receives the reflected light image emitted from the light source, transmitted through the light transmission grating, and reflected by the reflection grating, wherein the light transmission grating and the light receiving element are common. The light receiving element is formed in a semiconductor substrate, and the light receiving element is a lattice of a predetermined shape formed at a constant pitch or angle. The moving direction and the speed are detected, and the light transmitting grating is formed by a light transmitting slit formed in the semiconductor substrate or a light transmitting slit formed in the semiconductor substrate. A first region in which the light receiving elements are arranged at predetermined intervals and a second region in which the light transmission gratings are arranged at predetermined intervals. An optical encoder, characterized in that: 6. The second light-receiving element group located at an even-numbered position with respect to a first detection signal obtained from an odd-numbered first light-receiving element group at the first region. An optical encoder characterized in that the intervals between the light receiving elements are set such that the phase of a third detection signal obtained from the light receiving element is shifted by 180 degrees. 7. The light receiving element according to claim 6, wherein the light receiving element includes third regions arranged at regular intervals, and is obtained from an odd-numbered third light receiving element group in the third region. The distance between the light receiving elements is set such that the phase of the fourth detection signal obtained from the even-numbered fourth light receiving element group is shifted by 180 degrees with respect to the second detection signal. An optical encoder characterized in that the positional relationship between the light receiving element groups is set such that the phases of the first and second detection signals obtained from the first and third light receiving elements are shifted by 90 degrees. 8. A light source, a reflection grating plate formed with a plurality of reflection gratings of a predetermined shape at a constant pitch or angle, and a moving grating plate formed of a plurality of light transmission gratings of a predetermined shape at a constant pitch or angle. A light receiving element that receives the reflected light image emitted from the light source, transmitted through the light transmission grating, and reflected by the reflection grating, wherein the light transmission grating and the light receiving element are common. The light receiving element is formed in a semiconductor substrate, and the light receiving element is a grating of a predetermined shape formed at a constant pitch or angle. Based on a detection signal obtained from each light receiving element, the relative position of the moving grating plate and the reflection grating plate is determined. The moving direction and the speed are detected, and the light transmitting grating is formed by a light transmitting slit formed in the semiconductor substrate or a light transmitting slit formed in the semiconductor substrate. A first region in which the light receiving elements are arranged at predetermined intervals; a second region in which the light transmission gratings are arranged at predetermined intervals; Third regions arranged at predetermined intervals are formed, and the first region and the third region include first to fourth light receiving elements as the light receiving elements. , The first, the fourth, the third, and the second light receiving elements are repeatedly arranged in this order, and the interval between the adjacent light receiving elements is such that the phases of the detection signals obtained from those light receiving elements are shifted by 270 degrees from each other. An optical encoder characterized by being set to: 9. The method according to claim 2, wherein a first differential signal is generated based on the first and third detection signals, and based on the second and fourth detection signals. And a signal processing circuit for generating a second differential signal.