JP2003172638A - Optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical encoder based on three-grating theory which can accurately detect the origin position. <P>SOLUTION: An optical linear encoder 1 comprises a movable grid plate 5 made of a semiconductor substrate, where a light transmitting grid group 3 for detecting A-phase signal and B-phase signal, photodiode groups 4A and 4B and a photodiode group 4C for detecting the origin position are formed. Also on a reflection grid plate 7, a reflection grid group 6C for detecting the origin position together with reflection grid groups 6A and 6B for detecting A-phase signal and B-phase signal. As the reflection grid group 6C comprises a reflection grid 63 consisting of a light transmitting slit pattern and a reflection grid 64 consisting of a light reflection slit pattern, a reverse signal can be obtained from the photodiode group 4C for receiving these reflection light image and the origin position of the moving grid plate 5 can be differentially detected based on them. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder based on the theory of three gratings using a semiconductor substrate provided with a light transmission grating and a light receiving element, and particularly, it accurately generates an origin position signal for position detection. The present invention relates to an optical encoder that is small and compact in size.

[0002]

2. Description of the Related Art The applicant of the present invention first disclosed in Japanese Unexamined Patent Publication No. 2000-32
Japanese Patent No. 1097 proposes an optical encoder based on the theory of three gratings. In this optical encoder, an LED as a light source, a movable plate made of a semiconductor substrate in which a light transmission grating and a light receiving element (photodiode) are formed with a constant pitch, and a reflection grating with a constant pitch are formed. A reflection grating plate is provided, and a moving plate is arranged between the LED and the reflection grating plate.

In the optical encoder having this structure, the movable plate is integrated with the object to be measured, and is moved in the arrangement direction of the light transmission grating and the photodiode along the direction orthogonal to the optical axis of the light emitted from the LED. . The light emitted from the LED first illuminates the back surface of the movable plate, passes through the light transmission grating formed on the movable plate, and irradiates the surface of the reflection grating plate in a grid pattern. Since the reflection grating is also formed on the reflection grating plate at a constant pitch, only the component of the light emitted to the reflection grating plate that is applied to each reflection grating is reflected.
The reflection grating image illuminates the moving plate again and is received by the vertical stripe photodiodes formed at a constant pitch and a constant width.

The vertically-striped light transmission grating and the photodiode formed on the moving grating plate function as two grating plates.
Therefore, the amount of light received by the photodiode changes sinusoidally in accordance with the relative movement of the reflecting grating plate and the moving grating plate based on the theory of three gratings using the reflecting grating. Therefore, a pulse signal corresponding to the relative moving speed can be obtained based on the photocurrent of the photodiode, and the relative moving speed can be calculated based on the pulse rate of the pulse signal.

Further, by arranging the photodiodes so that the A-phase signal and the B-phase signal having different phases by 90 degrees can be obtained, the moving direction of the moving grating plate can be determined based on these two-phase signals.

As described above, in the optical encoder disclosed in the above publication, since the light transmission grating and the light receiving element are manufactured by the semiconductor manufacturing technique, it is possible to manufacture a grating with a fine pitch. A high resolution encoder can be realized. Further, since the light receiving elements formed in a vertical stripe pattern 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 width of the gap between the reflection grating and the light transmission grating and the variation of the gap do not adversely affect the resolution, so that the mounting accuracy of the members in which these are formed is secured. Adjustment work can be simplified, and the restrictions on the installation location are reduced. In addition to this, since the distance between the reflection grating and the light transmission grating can be widened, there is an advantage that the environment resistance can be improved by housing the reflection grating side in a protective case or the like.

[0007]

Here, in order to detect the relative position between the movable plate made of a semiconductor substrate and the fixed side reflection grating plate, it is necessary to detect the origin position which is the reference of the position and the rotation angle. There is. In order to detect the origin position, it is conceivable to form a light receiving element for origin position detection on the semiconductor substrate and to form a reflection grating for origin position detection on the reflection grating plate. In this case, the pulse width of the origin position detection signal generated based on the received light amount of the light receiving element changes due to the change in the received light amount. Therefore, the origin position may not be detected accurately.

In view of this point, an object of the present invention is to propose an optical encoder based on the theory of a three-plate grating capable of accurately detecting the origin position.

Another object of the present invention is to propose an optical encoder based on the theory of three-gratings, which has a small and compact origin position detection mechanism.

[0010]

In order to solve the above problems, the present invention provides a light source, a reflection grating of a predetermined shape arranged at a constant pitch, and a transmission of a predetermined shape arranged at a constant pitch. A light receiving element that receives a reflected light image emitted from the light source, transmitted through the transmission grating, and reflected by the reflection grating, and based on a detection signal obtained from each light receiving element, at least the reflection In an optical encoder for detecting the relative movement position of the grating and the transmission grating,
It has a reflection grating plate on which the reflection grating is formed, and a semiconductor substrate on which the transmission grating and the light receiving element are formed, and the light receiving element includes the reflection grating plate and the semiconductor substrate. At least a pair of first and second origin position detecting light receiving elements for detecting an origin position serving as a reference for detecting a relative position are included, and the reflection grating detects the origin position. At least one pair of first and second origin position detecting reflection gratings are included, and the first origin position detecting light receiving element and the first origin position detecting reflection grating can face each other. The second origin position detecting light receiving element and the second origin position detecting reflection grating are formed at positions where they can face each other, and the first and second origin position detecting Reflection One of the child, a light reflection pattern of a predetermined shape formed on the light transmitting surface, the other is characterized in that a light transmission pattern of a predetermined shape formed on the light reflecting surface.

In the optical encoder of this structure, since inverted signals are obtained from the first and second origin position detecting light receiving elements, by generating these differential signals,
The origin position can be accurately detected without being affected by the fluctuation of the light amount.

Here, a plurality of pairs of the first and second origin position detecting light receiving elements and a plurality of pairs of the first and second pairs.
It is desirable to have a reflection grating for detecting the origin position.

Further, in order to dispose the origin position detecting light receiving element without obstructing the reduction in size and size, it is desirable to form the origin position detecting light receiving element in the region between the transmission gratings.

Next, in the present invention, on the semiconductor substrate, the transmission regions in which the transmission gratings are arranged at a constant pitch, and the light receiving elements are arranged at a constant pitch on one side of the transmission region. It is possible to employ a configuration in which a first light receiving region that is present and a second light receiving region in which the light receiving elements are arranged at a constant pitch on the other side of the transmissive region are formed. In this case, on the reflection grating plate, a first reflection grating area in which the reflection gratings are arranged at a constant pitch at a position facing the first light receiving area,
A second reflection grating region in which the reflection gratings are arranged at a constant pitch at a position facing the second light receiving region, and the first reflection grating region arranged between the first and second reflection grating regions. A configuration in which the second origin position detecting reflection grating is formed may be adopted.

In this case, the reflection grating plate is
A light reflection surface including the first and second reflection grating regions and the formation region of the first origin position detection reflection grating, and a light transmission including the second formation position of the origin position detection reflection grating. A light transmission pattern that functions as the reflection grating and a light transmission pattern that functions as the first origin position detection reflection grating, and the light transmission surface is formed on the light reflection surface. Can form a light reflection pattern that functions as the second origin position detecting reflection grating.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an optical linear encoder based on the theory of a three-plate grating to which the present invention is applied will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an optical linear encoder of this example. As shown in the figure, the optical linear encoder 1 includes an LED 2 as a light source, a moving grating plate 5 made of a semiconductor substrate in which a transmission grating group 3 and photodiode groups 4A, 4B, 4C are formed, and a reflection grating. The groups 6A, 6B and 6C are basically composed of a reflection grating plate (fixed grating plate) 7 having a surface formed thereon and a control circuit section 8. The moving grid plate 5 of this example has an L
It is a moving plate unit integrated with a light source in which the ED 2 is integrated. Light emitted from the LED 2 passes through the light transmission grating 3 formed on the moving grating plate 5 and illuminates the reflection grating groups 6A, 6B, 6C of the reflection grating plate 7. The reflected light image reflected by this reflection grating group is the photodiode group 4A, 4
Light is received by B and 4C, and each photodiode group 4A, 4B,
The 4C detection signal is supplied to the control circuit unit 8.

The control circuit section 8 includes a photodiode group 4A,
A signal processing unit 9 that forms an A-phase signal and a B-phase signal that are out of phase by 1 / 4λ based on the detection signals of 4B and 4C, and a Z signal that indicates the origin position of the moving grating plate 5, and these A-phase signals. A calculation unit 10 for calculating movement information such as a moving speed, a moving direction, and a moving position of the moving grid plate 5 based on the B-phase signal and the Z signal, and a display unit 11 for displaying a calculation result.
The lamp drive unit 12 that feedback-controls the drive of the LED 2 is provided.

2A to 2C are a schematic plan view showing a moving plate unit integrated with a light source, a schematic cross-sectional view taken along a line bb, and a portion cut along a line cc. It is a schematic sectional drawing.

Explaining with reference to these figures, the moving plate unit 20 with a built-in light source of this example has an LED holding plate 21 made of a silicon substrate and a silicon substrate similarly laminated and adhered to the surface of the LED holding plate 21. And a moving grid plate 5 composed of A recess 22 having a constant depth is formed on the surface of the LED holding plate 21, and the LED 2 is mounted therein. The LED 2 of this example is a surface-emitting diode, and has a structure in which a light emitting layer of GaAlAs is formed on an AuZn substrate, for example.

The moving grating plate 5 is also made of a silicon substrate, and on the surface 23 thereof, a light transmitting region in which elongated transmission gratings 3 for transmitting light with a constant pitch and a constant width are arranged in a central portion at a constant interval. 24 are formed. A photodiode 4C for detecting the origin position is formed between the transmission gratings 3 in the light transmission region 24. A first light receiving region 25 in which the photodiode groups 4A are arranged is formed on the upper side of the light transmitting region 24, and a second light receiving region 2 in which the photodiodes 4B are arranged is also formed below the light transmitting region 24.
6 is formed.

On the other hand, on the surface of the reflection grating plate 7 which is a fixed grating plate, as shown in FIG. 1 (b), reflection grating groups 6A are arranged on the upper side at regular intervals and the reflection grating group 6B is on the lower side. Are arranged. Further, in the center of the moving grating plate 5 in the moving direction, a reflecting grating 6C for detecting the origin position is arranged at a position between the upper and lower reflecting grating groups 6A and 6B.

Next, FIG. 3 is an enlarged partial sectional view of the light transmission region 24 formed in the central portion of the surface 23 of the moving grating plate. As can be seen from this figure, the light transmission region 2 of this example
Reference numeral 4 denotes a thin film portion 4a formed by performing wet etching from the back surface side of the moving plate 5, and a transmission grating 3 having a constant width and a constant pitch by dry etching such as ICP.
The slit 1 is formed. In addition, a photodiode 4C for detecting the origin position is formed in the area between the transmission gratings 31.

FIG. 4 is an enlarged partial sectional view showing the photodiodes 31A and 31B included in the photodiode group 4A formed in the first light receiving region 25. Second
The same applies to the case of the light receiving area 26. The same applies to the photodiode 4C for detecting the origin position. As can be seen from this figure, the pn junction photodiodes 41A, 4A, 4A and 4B provided with the boron-doped layer 51 formed by doping the surface of the moving lattice plate 5 made of a silicon substrate with boron.
1B is built in. Each photodiode 41A, 4
Electrode wiring layers 35 and 36 made of aluminum are connected to the boron-doped layer 51 of 1B, and a common electrode layer 53 made of aluminum is connected to the n-layer side of the moving lattice plate 5. The electrode wiring layers 35 and 36 and the moving grid plate 5 are insulated from each other by an insulating layer 54 made of a silicon oxide film.
The exposed surface of the moving lattice plate 5 is covered with a silicon oxide film 55 to ensure durability. Similarly,
The surface of the boron-doped layer 51 is also covered with the silicon oxide film 56.

Next, FIG. 5 shows the positional relationship between the photodiodes and the reflective grating in the first and second light receiving regions 25 and 26. As shown in this figure, the transmission grating group 3 includes a plurality of transmission gratings 31, which are arranged at a pitch P. In the photodiode group 4A arranged in the first light receiving region 25,
A photodiode 41A for detecting an A-phase signal, a photodiode 41B for detecting a B-phase signal, a photodiode 41A 'for detecting an A-phase inverted signal, and a photodiode 41B for detecting an B-phase inverted signal are included. They are arranged periodically in order. The light-receiving surface of each photodiode is a vertically long rectangle with a width of P / 2, and each has a width of 3P.
They are arranged at intervals of / 4. These photodiodes are arranged in a state of being offset by P / 2 with respect to the transmission grating 31.

Similarly, the photodiode group 4B arranged in the second light receiving region 26 also includes photodiodes 41A, 41B, 41A 'and 41B' for detecting signals of respective phases, and these first light receiving regions are also included. They are arranged in the same order at the same position as in the case of No. 25.

Here, the photodiode group 4C for detecting the origin position includes a plurality of pairs of photodiodes,
Each pair of photodiodes includes a Z-phase signal detection photodiode 41Z and a Z-phase inverted signal detection photodiode 41Z '. Photodiodes 41Z, 41
Z'is a region between the transmission gratings 31 and is offset by 90 degrees from the photodiode 41A for detecting the A-phase signal, and the photodiode 41 for detecting the A'-phase signal.
It is arranged at a position corresponding to A '. The width of each of the photodiodes 41Z and 41Z 'is set to be slightly smaller than P / 2.

On the other hand, in the reflection grating plate 7,
Upper reflection grating group 6A corresponding to photodiode group 4A
Similar to the transmission grating 31, the reflection grating 61 constituting the above has a width of P / 2 and is arranged at a pitch P. Similarly, the reflection gratings 62 constituting the lower reflection grating group 6B corresponding to the photodiode groups 4B are arranged at the same pitch and the same width as the upper reflection grating 61.

The origin position detecting reflection grating group 6C includes a plurality of pairs of reflection gratings, and each pair of reflection gratings is formed at a position corresponding to the Z-phase signal detecting photodiode 41Z. The phase reflection grating 63 and the Z ′ phase reflection grating 64 formed at a position corresponding to the Z ′ signal detecting photodiode 41Z ′ are included. The width of these reflection gratings 63 and 64 is also P / 2.

Here, in this example, the reflection grating plate 7 is made of a transparent glass substrate, and the surface thereof is shown in FIG.
A light reflection surface 71 having a reflection film is formed in the shaded area, and the other portion remains as a light transmission surface 72. The light reflecting surface 71 has the above-described reflection grating 61,
A light transmission slit pattern that functions as 62 and the reflection grating 63 is formed. On the other hand, the reflection grating 6
4 is defined by the light reflection pattern patterned on the light transmitting surface 72.

In the optical linear encoder 1 of the present embodiment thus constructed, the moving grating plate 5 is integrated with the object to be measured (not shown) in the direction orthogonal to the optical axis L,
It is moved in the array direction of the slit and the photodiode. The light emitted from the LED 2 first illuminates the back surface of the moving grating plate 5, passes through the light transmitting grating group 3 formed on the moving grating plate 5, and is placed at a fixed position on the reflecting grating plate 7. Are radiated in a checkered pattern. Since the reflection grating plate 7 is also formed with the reflection grating groups 6A and 6B (light transmission grating pattern in this example) having a constant pitch and the same width, each reflection grating 6A among the lights irradiating the reflection grating plate 7, Only the component other than the component irradiated on 6B is reflected. The reflection grating image illuminates the moving grating plate 5 again and is received by the photodiode groups 4A and 4B.

As described above, the vertically-striped transmission grating group 3 and the photodiode groups 4A and 4B formed on the moving plate 5 function as two grating plates. Therefore, the reflection grating groups 6A, 6
In the photodiode groups 4A and 4B based on the theory of the three-plate grating using B, the fixed side reflection grating groups 6A and 6B are used.
And the amount of received light changes in a sine wave shape corresponding to the relative movement of the transmission grating group 3 on the moving side. Therefore, the photodiode group 4A,
A pulse signal corresponding to the relative moving speed can be obtained based on the photocurrent of 4B, and the relative moving speed can be calculated based on the pulse rate of the pulse signal.

Further, the A-phase signal can be accurately obtained based on the outputs of the photodiodes 41A and 41A ', and the B-phase signal can be accurately obtained based on the outputs of the photodiodes 41B and 41B'. The moving direction of the moving plate 5 can also be determined based on these two-phase signals.

Further, the optical linear encoder 1 of this example
In this case, the Z signal for detecting the origin position of the moving grating plate 5 can be obtained together with the A phase signal and the B phase signal. That is, when the moving grating plate 5 moves, the Z-phase detection signal as shown in FIG. 6 is obtained from the photodiodes 41Z and 41Z '. Each pair of photodiodes 41Z, 41Z '
When the pair of reflection gratings 63 and 64 on the moving plate side coincide with each other, triangular waves w and w ′ having peak voltage values appear in the output signals of the photodiodes 63 and 64. The signal processing unit 9 of this example generates a differential signal of these inverted signals, and based on this, generates a rectangular wave signal representing the origin position of the moving plate. As described above, in this example, the origin position of the moving plate is detected by differentially detecting the Z-phase signal, so that the origin position can be accurately detected without being affected by the change in the light amount.

(Other Embodiments) In the above example, the reflection grating plate on which the reflection grating is formed is the fixed side, but the side of the reflection grating plate is the moving side and the side of the moving plate is the fixed side. May be

Further, although the LED is used as the light source in the above example, it is also possible to use other light sources such as a laser light source.

Further, although the above example relates to a linear encoder, the present invention can be similarly applied to a rotary encoder. In this case, the light transmission grating and the photodiode may be formed at regular angular intervals in the circumferential direction.

[0038]

As described above, according to the present invention, based on the theory of three-gratings, a reflection grating and a light transmission grating are used to receive a reflection grating image capable of detecting information on their relative movements by a light receiving element. In the optical encoder thus configured, the light transmission grating and the light receiving element are formed on a common semiconductor substrate, and a pair of light receiving elements for origin position detection are arranged between the light transmission gratings formed on the semiconductor substrate. An inverted signal is obtained from the light receiving element.

Therefore, according to the present invention, the differential detection of the origin position can be performed by generating the differential signal from the inverted signal obtained from the light receiving element for origin position detection, so that the origin position can be detected. It is possible to perform the processing accurately without being affected by the fluctuation of the light amount. Further, the optical encoder with the origin position detection function can be made compact and compact.

[Brief description of drawings]

1A and 1B are schematic configuration diagrams showing an optical linear encoder based on the theory of a three-plate grating to which the present invention is applied.

2 (a), (b) and (c) are schematic plan views showing the moving plate unit integrated with a light source of FIG. 1, schematic cross-sectional views taken along the line bb, and cc. It is a schematic sectional drawing of the part cut | disconnected by the line.

FIG. 3 is an enlarged partial cross-sectional view showing a portion of a light transmission grating formed on the moving plate of FIG.

FIG. 4 is an enlarged partial sectional view showing a portion of a photodiode formed on the moving plate of FIG.

5 is an explanatory diagram showing an arrangement relationship between a light transmission grating and photodiodes formed on the moving grating plate of FIG. 1 and a reflection grating formed on a reflection grating plate.

6 is a signal waveform diagram for explaining an origin position detection operation in the linear encoder of FIG.

[Explanation of symbols]

1 Optical linear encoder 2 LED 3 Light transmission grating 4A, 4B, 4C Photodiode group 41A, 41A ', 41B, 41B' photodiodes 5 Moving lattice plate 6A, 6B, 6C Reflective grating group 61, 62, 63, 64 Reflective grating 7 Reflective grating plate 71 Light reflection surface 72 Light transmitting surface 8 Control circuit section 20 Moving plate unit with integrated light source 21 LED holding plate 22 recess 23 substrate surface 24 Light transmission area 25 First light receiving area 26 Second light receiving area

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F103 BA32 BA37 BA43 CA02 CA03                       DA01 DA12 EA15 EA17 EA19                       EA20 EB06 EB12 EB16 EB27                       EB33 EB37 ED02 ED07 ED29                       FA02 FA11

Claims (5)

[Claims] 1. A light source, a reflection grating of a predetermined shape arranged at a constant pitch, a transmission grating of a predetermined shape arranged at a constant pitch, and a reflection light emitted from the light source and transmitted through the transmission grating. An optical encoder that has a light receiving element that receives a reflected light image reflected by a grating, and that detects at least a relative movement position of the reflection grating and the transmission grating based on a detection signal obtained from each light receiving element. A reflection grating plate on which the reflection grating is formed, and a semiconductor substrate on which the transmission grating and the light receiving element are formed, and the light receiving element includes the reflection grating plate and the semiconductor. At least a pair of first and second origin position detecting light receiving elements for detecting an origin position serving as a reference for detecting the relative position of the substrate are included. At least a pair of first and second origin position detecting reflection gratings for detecting the origin position are included, the first origin position detecting light receiving element and the first origin position detecting reflection grating. Are formed at positions where they can face each other, and the second origin position detecting light receiving element and the second
The origin position detecting reflection grating is formed at a position where they can face each other, and one of the first and second origin position detecting reflection gratings has a predetermined shape of light reflecting surface formed on the light transmitting surface. The optical encoder is characterized in that it is a pattern and the other is a light transmission pattern of a predetermined shape formed on the light reflecting surface. 2. The method according to claim 1, further comprising a plurality of pairs of the first and second origin position detecting light receiving elements and a plurality of pairs of the first and second origin position detecting reflection gratings. An optical encoder characterized by. 3. The optical encoder according to claim 1, wherein the first and second origin position detecting light receiving elements are formed in a region between the transmission gratings. 4. The semiconductor substrate according to claim 3, wherein the transmission gratings are arranged at a constant pitch on the semiconductor substrate, and the light receiving elements are arranged at a constant pitch on one side of the transmission area. A first light receiving region and a second light receiving region in which the light receiving elements are arranged at a constant pitch on the other side of the transmissive region, and the reflection grating plate is provided with the first light receiving region. A first reflection grating area in which the reflection gratings are arranged at a constant pitch at a position facing the light receiving area, and the reflection gratings are arranged at a constant pitch in a position facing the second light receiving area. And a second reflection grating region, and the first and second origin position detecting reflection gratings arranged between the first and second reflection grating regions. Expression encoder. 5. The light reflection surface according to claim 4, wherein the reflection grating plate includes a light reflection surface including the first and second reflection grating regions and a formation region of the first origin position detecting reflection grating, And a light transmitting surface including a formation region of the origin position detecting reflection grating, wherein the light reflecting surface and the first origin position detecting reflection grating function as the reflection grating. The optical encoder, wherein a light transmission pattern that functions as a light reflection pattern that functions as the second origin position detection reflection grating is formed on the light transmission surface.