JP2003004488A - Optical encoder - Google Patents

Abstract

(57) [PROBLEMS] To realize an optical encoder based on the theory of a three-grid capable of detecting an origin position. An optical linear encoder 1 includes a moving grating plate 5 made of a semiconductor substrate, and includes a light transmission grating 3 for detecting A-phase and B-phase signals and grating-like photodiodes 4A and 4B. One origin point detection photodiode 4 </ b> C is formed between the transmission gratings 3.
The reflection grating plate 6 is also used for detecting the A and B phase signals.
A reflection grating 6C for detecting the origin position is formed together with A and 6B. The origin position of the moving grid plate 5 can be detected based on the detection signal of the photodiode 4C, and the moving position of the moving grid plate can be detected based on this.

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 a three-plate grating theory using a semiconductor substrate having a light transmission grating and a light receiving element, and particularly to a compact encoder capable of generating an origin position signal for position detection. The present invention relates to a compact optical encoder.

[0002]

2. Description of the Related Art The applicant of the present invention first disclosed in Japanese Patent Laid-Open No. 2000-3210
In Japanese Patent Publication No. 97, an optical encoder based on the three-plate lattice theory is proposed. 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 moved in the direction orthogonal to the optical axis of the light emitted from the LED and in the arrangement direction of the light transmission grating and the photodiode. . 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 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 detecting the origin position.

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

A further object of the present invention is to propose an optical encoder based on the theory of a three-plate grating capable of detecting the origin position with high accuracy.

[0011]

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 light of a predetermined shape arranged at a constant pitch. A transmission grating, and a light receiving element which is emitted from the light source, passes through the light transmission grating, and receives a reflected light image reflected by the reflection grating, based on a detection signal obtained from each light receiving element, at least, An optical encoder for detecting relative movement positions of the reflection grating and the light transmission grating: a reflection grating plate having the reflection grating formed thereon, and a semiconductor having the light transmission grating and the light receiving element formed therein. A substrate; and the light-receiving element for at least one origin position detection for detecting an origin position serving as a reference for detecting the relative position of the reflection grating plate and the semiconductor substrate. It is characterized in that it contains an optical element.

Here, in order to arrange the light receiving element for detecting the origin position without impeding the reduction in size and size, it is necessary to form the light receiving element for detecting the origin position in the region between the light transmission gratings. desirable.

Further, in order to guide the reflected light to the origin position detecting light receiving element, at least one origin position detecting reflection grating for detecting the origin position may be formed in the reflection grating.

On the semiconductor substrate, the light transmission regions in which the light transmission gratings are arranged at a constant pitch, and the first light receiving element in which the light receiving elements are arranged at a constant pitch on one side of the light transmission region. A region, a second light receiving region in which the light receiving elements are arranged at a constant pitch on the other side of the light transmitting region, and a pair of the light transmitting gratings arranged adjacent to each other in the light transmitting region. When the arranged light receiving element for origin position detection is formed, the reflection grating for origin position detection may be formed at a position on the reflection grating plate that can face the light receiving element for origin position detection.

Next, in order to solve the shortage of the amount of light received by the light-receiving element for origin position detection so that the origin position can be detected reliably, a plurality of origin position detection elements arranged at a fixed pitch are used. Adopting a configuration equipped with a light receiving element and the same number of the above-mentioned origin position detecting reflection gratings arranged at the same pitch, the origin position is determined based on the output of the origin position detecting light receiving element at the position where the most light is received. It is desirable to detect.

Further, in order to increase the S / N ratio of the detection signal of the origin position detecting light receiving element and detect the origin position with high accuracy, a plurality of the origin position detecting light receiving elements arranged at different pitches, An origin position detecting light receiving element at the position with the largest amount of received light is adopted by adopting a configuration including the same number of the origin position detecting reflection gratings arranged at a pitch corresponding to each of these origin position detecting light receiving elements. It is desirable to detect the origin position based on the output of.

[0017]

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 this figure, an 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 light transmitting grating 3 and photodiode groups 4A, 4B and one photodiode 4C are formed. , A reflection grating group (fixed grating plate) 7 having reflection grating groups 6A and 6B and one reflection grating 6B formed on the surface thereof, and a control circuit section 8.
As will be described later, the moving grid plate 5 of this example is a light source integrated moving plate unit in which the LEDs 2 are integrated. L
The light emitted from the ED 2 is transmitted through the light transmission grating 3 formed on the moving grating plate 5, and is reflected by the reflection grating group 6 of the reflection grating plate 7.
Irradiate A, 6B, and the reflection grating 6C. The reflected light image reflected by this reflection grating group is the photodiode group 4A, 4
The light is received by B and the photodiode 4C, and the detection signals of the photodiode groups 4A, 4B and the photodiode 4C are supplied to the control circuit unit 8.

The control circuit section 8 includes a photodiode group 4A,
Based on the detection signals of 4B and photodiode 4C,
An A-phase signal and a B-phase signal whose phases are shifted by 1 / 4λ,
A signal processing unit 9 that forms a Z signal indicating the origin position of the moving grid plate 5, and movement information such as the moving speed, moving direction, and moving position of the moving grid plate 5 based on these A-phase, B-phase signal and Z signal. A calculation unit 10 for calculation, a display unit 11 for displaying the calculation result, and a lamp drive unit 12 for feedback-controlling the driving of the LED 2 are 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 section taken along a line cc. It is a schematic sectional drawing.

Explaining with reference to these figures, the movable plate unit 20 of the light source integrated type of the present 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 a light transmitting region 24 in which light transmitting gratings 3 having a constant pitch and a constant width are arranged at a constant interval is formed in the central portion of the surface 23 thereof. ing. A photodiode 4C for detecting the origin position is formed between the pair of light 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 above the light transmitting region 24, and a second light receiving region 26 in which the photodiodes 4B are arranged is also formed below the light transmitting region 24. Are 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), the reflection grating groups 6A are arranged on the upper side and the reflection grating groups 6B on the lower side at regular intervals. Are arranged. Further, in the center of the moving grating plate 5 in the moving direction, one reflecting grating 6C for detecting the origin position is formed 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 is a structure in which a thin film portion 41 formed by performing wet etching from the back surface side of the movable plate 5 is provided with slits as the light transmission grating 3 having a constant pitch and a constant width by dry etching such as ICP. ing. In addition, a photodiode 4C for detecting the origin position is provided in a region between the pair of adjacent light transmission gratings 3 located at the substantially center.
Is built in.

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. The same applies to the case of the second light receiving region 26. The same applies to the photodiode 4C for detecting the origin position. As can be seen from this figure, a pn junction photodiode 31A having a boron-doped layer 51 formed by doping boron from the surface of a moving lattice plate 5 made of a silicon substrate,
31B 'is built in. Each photodiode 31
Electrode wiring layers 35 and 36 made of aluminum are connected to the boron-doped layer 51 of A and 31B ′, 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 also has a silicon oxide film 5.
Covered by 6.

Next, FIG. 5 shows the arrangement relationship of the photodiodes and the arrangement relationship of the reflection gratings in the first and second light receiving regions 25 and 26. As shown in this figure, assuming that the pitch of the light transmission grating 3 is P, in the first light receiving region 25, the photodiode 31 for detecting the A phase signal is detected.
A photodiode 31B 'for outputting the inverted signals of the A and B phases,
The A-phase inverted signal output photodiode 31A 'and the B-phase signal output photodiode 31B are periodically arranged in this order with a pitch of (3/4) p and a width of (1/2) p. There is. These photodiodes have a light transmission grating 3
Are arranged with a p / 2 offset.
Also in the second light receiving area 26, photodiodes 31A, 31B ', 31A' and 31B for detecting each phase are arranged in the same position as the first light receiving area 25 in the same order.

Here, the origin position detecting photodiode 4C is formed in the remaining region between the pair of adjacent light transmission gratings 3, and the width thereof is set to be slightly smaller than p / 2. There is.

On the other hand, in the reflection grating plate 7,
Upper reflection grating group 6A corresponding to photodiode group 4A
Like the light transmission grating 3, the reflection grating 61 configuring 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.

Here, the reflection grating 6C for detecting the origin position
Are formed with the same width at positions between the corresponding reflection gratings 61 and 62 in the upper and lower reflection grating groups 6A and 6B. In this example, these three reflection gratings 61, 62,
6C is formed in a continuous state.

In the optical linear encoder 1 of the present embodiment constructed as described above, the moving grating plate 5 is integrated with the object to be measured (not shown), and the slit is formed in the direction orthogonal to the optical axis L and in the slit. And move in the array direction of the photodiodes. The light emitted from the LED 2 first illuminates the back surface of the moving grating plate 5 and passes through the light transmitting grating 3 formed on the moving grating plate 5 to pass through the reflection grating plate 7 arranged at a fixed position. Irradiate in a checkered pattern. Since the reflection gratings 7 having the same width are also formed on the reflection grating plate 7 at a constant pitch, only the component of the light emitted from the reflection grating plate 7 that is applied to each reflection grating 6 is reflected. The reflection grating image illuminates the moving grating plate 5 again and is received by the photodiode groups 4A and 4B.

In this way, the vertically-striped light transmission grating 3 formed on the moving grating plate 5 and the photodiode groups 4A and 4B function as two grating plates. Therefore, based on the theory of the three-plate grating using the reflection grating 6, the photodiode group 4A,
In 4B, the amount of received light changes sinusoidally in response to the relative movement of the fixed side reflection grating 6 and the moving side light transmission grating 3. Therefore, a pulse signal corresponding to the relative movement speed can be obtained based on the photocurrents of the photodiode groups 4A and 4B, and the relative movement 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 31A and 31A ', and the B-phase signal can be accurately obtained based on the outputs of the photodiodes 31B and 31B'. Based on these two-phase signals, the moving direction of the moving grid plate 5 can also be determined.

Here, the optical linear encoder 1 of the present 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, as shown in FIG.
Is formed with a p / 2 width light receiving element 4C for origin position detection, and the fixed grating plate 7 is also formed with a p / 2 width reflection grating 6C for origin position detection. The moving lattice plate 5 moves,
When they pass through the coincident position, as shown in FIG. 6B, the detection signal of the photodiode 4C is a triangular wave having a bottom width p and a predetermined height V (peak voltage obtained from the photodiode). One appears. Signal processing unit 9 of this example
Then, the waveform is shaped by setting the trigger level at the position of V / 2 of this signal, and the rectangular wave signal z having the width of p / 2 shown in FIG. 6C is generated.

In the signal processing unit 9, based on the detection signals from the photodiode groups in the first and second light receiving regions,
(D), A-phase signal of period p as shown in (e) and B
Generating a phase signal. Then, these rectangular wave signals z
And the logical product of the A and B phase signals
An origin signal Z representing the origin position with a pulse width of p / 4 as shown in (f) is generated. Based on this origin signal Z,
Since the absolute position of the moving grid plate 5 can be detected, the moving position of the moving grid plate 5 can be detected based on this.

(Another Example of Origin Position Detection Mechanism) In the above example, the main signal (A phase signal, B phase signal) is detected using a plurality of light transmission gratings, reflection gratings and photodiodes. On the other hand, the origin signal Z is detected by using a single reflection grating and a photodiode. As a result, the amount of light received by the photodiode 4C for detecting the origin position may be insufficient, and the origin position may not be reliably detected. In order to avoid this adverse effect, as shown in FIG. 7 (a), if three sets of reflection gratings and photodiodes for origin position detection are arranged, as shown in FIG. 7 (b), the central photodiode 4 is arranged.
The amount of light received by C1 can be tripled as compared with the case of one set.

In this case, the photodiodes 4C2 on both sides are
Since the peak value of the received light amount of 4C3 is also high, S / N
The ratio cannot be increased. In order to increase the S / N ratio and improve the detection accuracy of the origin position, as shown in FIG. 8 (a), the left and right reflection gratings 6C2, 6C3 and the photodiodes are different from the reflection gratings 6C1 and photodiode 4C1 at the center. The pitches of 4C2 and 4C3 may be different.
By doing so, as shown in FIG. 8B, the light receiving amount of the photodiode 4C1 located in the center can be increased and the peak value of the light receiving amount of the left and right photodiodes can be lowered. Therefore, the S / N ratio can be increased and the origin position can be detected with high accuracy.

(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

Although an LED is used as the light source in the above example, it is also possible to use another light source such as a laser light source.

Furthermore, although the above example relates to a linear encoder, the present invention is also applicable 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.

[0040]

As described above, according to the present invention, based on the three-plate lattice theory, the reflection grating and the light transmission grating are used to cause the light receiving element to receive the reflection grating image capable of detecting the information on the relative movement between them. In such an optical encoder, the light transmitting grating and the light receiving element are formed on a common semiconductor substrate, and the light receiving element for detecting the origin position is arranged between the light transmitting gratings formed on the semiconductor substrate. Has been adopted.

Therefore, according to the present invention, it is possible to realize an optical encoder which is small and compact and which can detect the origin position by the theory of a three-plate grating.

Further, in the present invention, a plurality of sets of the light receiving element for origin position detection and the reflection grating for origin position detection are arranged, and the output for origin position detection is obtained from the light receiving element located at the center. . According to this configuration, it is possible to solve the shortage of the amount of light received by the light receiving element for detecting the origin position, and to reliably perform the origin position detection operation.

Further, when the sets of the light receiving elements for detecting the origin position and the reflection grating are arranged at different pitches, the light receiving amounts of the light receiving elements on both sides are significantly reduced with respect to the light receiving amount of the central light receiving element. Since it is possible, S of the origin position detection signal
Since a large / N ratio can be obtained, the origin position can be detected accurately.

[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.

FIG. 6 is an explanatory diagram for explaining an origin position detection operation in the linear encoder in FIG.

FIG. 7 is an explanatory diagram showing another example of the origin position detection mechanism.

FIG. 8 is an explanatory diagram showing still another example of the origin position detection mechanism.

[Explanation of symbols]

1 Optical linear encoder 2 LED 3 Light transmission grating 4A, 4B Photodiode group (light receiving element) 4C photodiode 31A, 31A ', 31B, 31B' photodiodes 5 Moving lattice plate 6A, 6B Reflective grating group 61, 62 reflective grating 6C reflective grating 7 Reflective grating plate 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 CA01 CA03 DA01 DA12                       DA13 EA15 EB02 EB12 EB16                       EB32

Claims (6)

[Claims] 1. A light source, a reflection grating of a predetermined shape arranged at a constant pitch, a light transmission grating of a predetermined shape arranged at a constant pitch, and a light emitted from the light source and transmitted through the light transmission grating. An optical system that has a light receiving element that receives a reflected light image reflected by the reflection grating, and detects at least a relative movement position of the reflection grating and the light transmission grating based on a detection signal obtained from each light receiving element. An encoder, comprising: a reflection grating plate on which the reflection grating is formed; and a semiconductor substrate on which the light transmission grating and the light receiving element are formed, wherein the light receiving element includes the reflection grating An optical encoder including at least one light receiving element for origin position detection for detecting an origin position serving as a reference for detecting a relative position between the plate and the semiconductor substrate. . 2. The optical encoder according to claim 1, wherein the light receiving element for detecting the origin position is formed in a region between the light transmission gratings. 3. The optical encoder according to claim 1, wherein the reflection grating includes at least one origin position detecting reflection grating for detecting the origin position. 4. The semiconductor substrate according to claim 3, wherein the light 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 light transmission area. A first light receiving area that is arranged, a second light receiving area in which the light receiving elements are arranged at a constant pitch on the other side of the light transmitting area, and a pair that are adjacently arranged in the light transmitting area. Is formed between the light transmission grating of the origin position detection light-receiving element, the origin of the origin position detection at the position of the reflection grating plate facing the light-receiving element for origin position detection, An optical encoder having a reflection grating formed therein. 5. The plurality of origin position detecting light-receiving elements arranged at a constant pitch, and the same number of the origin position detecting reflection gratings arranged at the same pitch. An optical encoder characterized in that 6. The plurality of origin position detecting light-receiving elements arranged at different pitches, and the same number of the origins arranged at a pitch corresponding to each of the origin position detecting light-receiving elements. An optical encoder having a reflection grating for position detection.