JPH0783704A - Optical encoder - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement to be realized by minimizing variation in the center level of an encoder signal. CONSTITUTION:Two sets of four types of detection windows A, detection window A bars, detection windows B and detection window B bars are arranged in the direction of movement on an index scale 3. The detection windows A, the detection window A bars, the detection windows B and the detection window B bars in the left row set are arranged in the specified order in the direction vertical to the direction of movement and the detection windows A, the detection window A bars, the detection windows B and the detection window B bars in the right row set are arranged in the vertical direction in the order opposite to that of the detection windows in the left row. This prevents influence of variation in the quantity of light in direction of movement and variations in the quantity of light in the direction opposite to the direction of movement respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder, for example, an optical encoder such as an optical transmissive rotary encoder or an optical transmissive linear encoder.

[0002]

2. Description of the Related Art In an optical transmission type rotary encoder,
The light from the light source passes through the main scale and index scale to reach the light receiving element, the light passing through is detected by the light receiving element, and a two-phase sine wave output with a 90 ° phase difference indicating the relative movement amount between the main scale and the index scale ( Encoder signal) is obtained.

However, when the main scale and the index scale are not arranged in parallel with each other, when the index scale and the main scale do not move relative to each other in parallel, and when the grid scale of the main scale has uneven brightness, When the optical axis of the light source is deviated and the light is not evenly applied to the main scale, the received light amount of each detection window is not constant, so the center level of the encoder signal obtained by the light receiving element fluctuates. As a result, the detection accuracy decreases.

Therefore, conventionally, as shown in FIGS. 6 and 7, four types of detection windows A (0
°), A bar (180 °), B (90 °), B bar (2
70 °). As shown in FIG. 6A, the positional relationship among the detection windows A, A bar, B, and B bar is such that the detection window A and the detection window B and the detection window B bar and the detection window A bar are along the moving direction, respectively. , Detection window A and detection window B bar, detection window B and detection window A
Each bar runs along a direction perpendicular to the direction of travel.

Further, as shown in FIG. 6 (b), there is also one in which the detection windows A, B, A bar, and B bar are arranged along the moving direction.

As shown in FIG. 9, a photodiode 14a as a light receiving element arranged opposite to the detection window A and a photodiode 14b as a light receiving element arranged opposite to the detection window A bar are connected in parallel with opposite polarities. Then, the sum of the outputs of the photodiodes 14a and 14b is amplified by the operational amplifier 15. Although not shown, the detection windows B and B also have detection windows A and
It is amplified in the same way as A bar.

[0007]

In the prior art as described above, even if the four kinds of detection windows A, A bar, B and B bar are arranged on the index scale, the fluctuation of the center level of the encoder signal can be completely eliminated. I can't get rid of it.

The reason will be described in detail below with reference to FIG.

In FIG. 8A, the light amount distribution is 30% to 60%.
FIG. 9B is a diagram in which the index scale moves to a position changing to%, FIG. 8B shows fluctuations in the light amount of the received light signal from the detection window A bar at that time, and FIG.
FIG. 8D shows a light amount variation of the received light signal from the detection window A at the same time as in (b), and FIG. 8D is a diagram in which the received light signals from the detection window A and the detection window A bar are differentially amplified.

As shown in FIG. 8 (a), the detection window A and the detection window A bar arranged on the index scale have X in the moving direction between the main scale and the index scale.
They are arranged with a gap.

Therefore, the light amount over the range S is 30% to 6%.
When it changes to 0%, even if the light amount of the light receiving signal A bar signal and A signal from the detection window A and the detection window A bar changes, X
The light amount changes over the range S due to the gap.

That is, between the A bar signal and the A signal, the light amount changes from a constant light amount (30%) (variation from 30% to 60%), and until the light amount reaches the constant light amount (60%) again, X
The change in the amount of received light deviates by the distance.

As shown in FIGS. 8B and 8C, A
For the bar signal and the A signal, the change in the amount of light received by the index scale fluctuates from dark to bright.
The amplitudes of the A-bar signal and the A-signal also fluctuate as the light amount changes.

When the A-bar signal and the A-signal, which has a difference in the amount of received light at the X intervals from the A-bar signal, are differentially amplified, FIG.
As shown in (d), the center level of the first encoder signal fluctuates over the range (S + X). That is, with respect to the reference voltage, the center level fluctuates by L intervals when the light amount is 30%, and the center level fluctuates by M intervals when the light amount is 60%.

Although not described, the same applies to the B-bar signal and the B-signal, and the center level of the second encoder signal obtained from the differential amplification of the B-bar signal and the B-signal also varies. Will end up.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical encoder capable of performing highly accurate measurement by minimizing the fluctuation of the center level of the encoder signal. Is.

[0017]

In order to solve the above-mentioned problems, an optical encoder according to a first aspect of the present invention comprises a light source,
A main scale having a constant pitch grid scale, a first detection window having a first reference scale corresponding to the grid scale, and 90 relative to the first reference scale.
A second detection window having a second reference graduation that is out of phase with a third detection window; a third detection window having a third reference graduation that is 90 degrees out of phase with the second reference graduation; Third
A fourth detection window having a fourth reference scale that is 90 ° out of phase with the reference scale, and an index scale that moves relative to the main scale, and a detection window for each of the index scales. Placed facing each other,
A light receiving unit that receives light from the light source that has passed through the main scale and the index scale, and a 90 ° position indicating a relative movement amount between the main scale and the index scale based on a light receiving signal from the light receiving unit. In the optical encoder provided with a signal output means for processing the signal into a two-phase sinusoidal signal having a phase difference and outputting the signal, the index scale includes the first to fourth detection windows arranged in the longitudinal direction of the lattice pattern. And a second window group consisting of the first to fourth detection windows having a phase difference of 90 ° with respect to the first window group, and 90 ° with respect to the second window group. A third window group consisting of the first to fourth detection windows having a phase difference of 4 and a fourth window consisting of the first to fourth detection windows having a phase difference of 90 ° with respect to the third window group. A group of windows, Signal output means, a light reception signal that has passed through the same detection window and the second window group and the first window group after adding each signal processing to the two-phase sine wave signal.

Further, in the optical encoder of the second aspect of the present invention, the index scale has a first detection window which is arranged in one direction with respect to a longitudinal direction of the grating pattern. A second window consisting of the window group and the first to fourth detection windows having a phase difference of 90 ° with respect to the first window group and arranged from the other direction with respect to the longitudinal direction of the grating pattern. Equipped with a flock.

Further, in the optical encoder of the third aspect of the invention, the index scale is arranged in one direction with respect to the array direction of the grating pattern.
To a first window group including a fourth detection window, and a first window group having a phase difference of 90 ° with respect to the first window group and arranged from another direction with respect to the array direction of the lattice pattern. And a second window group including a fourth detection window.

[0020]

As described above, on the index scale, the first window group consisting of the first to fourth detection windows arranged in the longitudinal direction of the lattice pattern, and 90 with respect to the first window group.
A second window group consisting of the first to fourth detection windows having a phase difference of ° and a first window consisting of the first to fourth detection windows having a phase difference of 90 ° to the second window group. Since the third window group and the fourth window group including the first to fourth detection windows having a phase difference of 90 ° with respect to the third window group are provided,
It is less affected by the movement direction and the fluctuation of the light amount in the direction perpendicular to the movement direction, and the center level of the encoder signal hardly changes.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is an overall configuration diagram showing an optical linear encoder according to an embodiment of the present invention.

This optical linear encoder includes a light source 1
And a transmissive main scale 2 (see FIG. 4) in which a pattern of light and dark 50:50 is vapor-deposited at a constant pitch, and an index scale 3 that is disposed opposite to the main scale 2 and moves relative to the main scale 2. And eight photodiodes (detection units) 4a to 4h for detecting light passing through the main scale 2 and the index scale 3.

The index scale 2 has a two-phase sine wave signal (encoder signal) having a 90 ° phase difference indicating the relative movement amount between the main scale 2 and the index scale 3.
Two sets of four types of detection windows A, A bar, B, and B bar for detection are arranged in the moving direction. The detection window B is 90 ° out of phase with the detection window A, the detection window A bar is 90 ° out of phase with the detection window B, and the detection window B bar is 90 ° out of phase with the detection window A bar. ing. As shown in FIG. 1A, the detection window A, the detection window A bar, the detection window B, and the detection window B bar of each set are arranged in the direction perpendicular to the moving direction. The order of arrangement is reversed. That is, FIG.
In the left column of (a) (hereinafter referred to as the left column), the detection window A,
While the detection window B bar, the detection window A bar, and the detection window B are arranged in this order, the detection window B, the detection window A bar, and the detection window from the top in the right column of FIG. 1A (hereinafter referred to as the right column). The bar B and the detection window A are arranged in this order.

The eight photodiodes 4a to 4h
Are arranged facing the eight detection windows A, A bar, B, B bar of the index scale 3, respectively. That is, the photodiode 4a is the detection window A in the left column, the photodiode 4b is the detection window B in the left column, the photodiode 4c is the detection window A in the left column, and the photodiode 4d is the detection window B in the left column. 4e is a detection window B in the right row, photodiode 4f is a detection window A bar in the right row, photodiode 4g is a detection window B bar in the right row, and photodiode 4h is a detection window A in the right row. There is. Therefore, the light of the light source 1 is detected by the detection windows A, A bar, B of the main scale 2 to the index scale 3,
It passes through the B bar and reaches the photodiodes 4a to 4h.

As shown in FIG. 3, the photodiode 4a corresponding to the detection window A in the left column, the photodiode 4h corresponding to the detection window A in the right column, and the photodiode 4c corresponding to the detection window A bar in the left column. And the photodiode 4f corresponding to the detection window A bar in the right column are connected in parallel with each other with opposite polarities, and the photodiodes 4a, 4h, 4c, 4 are connected.
The sum of the outputs of f is amplified by the operational amplifier (signal output means) 5.

As shown in FIG. 1A, the index scale 3 has four types of detection windows A (0 °), detection windows A bar (180 °), detection windows B (90 °), and detection windows B bar. (2
70 °) are arranged in two sets in the movement direction, and the detection window A, the detection window A bar, the detection window B, and the detection window B bar in the left column are arranged in a predetermined order in the movement direction and the right direction. The detection window A, the detection window A bar, the detection window B, and the detection window B bar of the column set are arranged in the vertical direction in the order opposite to the order of the detection windows in the left column. 3 is small on the lower side and is large on the upper side (when there is a linear light amount variation in the direction perpendicular to the moving direction), the light receiving amount of the detection window A in the left column is 80, and the light receiving amount in the right column is the detection window A. Is 20, the sum of the received light amounts of the detection windows A of both sets is 100, the received light amount of the detection window B bar of the left column set is 60, and the received light amount of the detection window B bar of the right column set is 40, the sum of the amount of light received by the detection windows B of both groups is 10
It becomes 0, and the sum of the amount of received light is 1 for the detection windows A and B.
It becomes 00. Therefore, it is hardly affected by the change in the light amount in the direction perpendicular to the moving direction, and the center level of the encoder signal hardly changes, so that highly accurate measurement can be performed.

Further, for example, when the amount of received light is large on the detection window side of the set in the right column and small on the detection window side of the set in the left column (when there is a linear change in the light amount in the moving direction), the detection window A of the set in the left column is shown. Is 40 and the light receiving amount of the detection window A in the right column is 60,
The sum of the amount of light received by the detection windows A of both sets is 100, the amount of light received by the detection window B bar of the left column is 40, and the amount of light received by the detection window B bar of the right column is 60. The sum of the received light amounts of the window B bar is 100, and the sum of the received light amounts of the detection windows A and B is 100. Therefore, it is unlikely to be affected by the change in the light amount in the moving direction, and the center level of the encoder signal hardly changes, so that highly accurate measurement can be performed.

As for the detection windows A and A bar, the total amount of light received by the detection windows A of both sets is equal to the total amount of light received by the detection windows A of both sets, so that the photodiodes 4a and 4h shown in FIG.
Is equal to the outputs of the photodiodes 4c and 4f, and the sum of the outputs is amplified by the operational amplifier 5. The center level of the encoder signal output from the operational amplifier 5 hardly changes. The details will be described later.

FIG. 1B is a diagram showing the arrangement of the detection windows of the index scale according to the second embodiment of the present invention.

In this embodiment, two detection windows Z for detecting the reference points and two detection windows R for monitoring the light amount are added to the index scale of FIG. 1, and FIG.
As shown in FIG. 7, the detection windows Z and R are arranged in a row in the order of the detection window Z, the detection window R, the detection window R, and the detection window Z from the top along the direction perpendicular to the moving direction. According to this embodiment, it is possible to accurately detect the reference point and the light amount without being affected by the light amount variation in the direction perpendicular to the moving direction.

FIG. 1C is a diagram showing the arrangement of the detection windows of the index scale according to the third embodiment of the present invention.

In the embodiment of FIG. 1, four types of detection windows A (0
), Detection window A bar (180 degrees), detection window B (90
2), and the detection window B bar (270 °) is provided in two sets in the direction perpendicular to the moving direction, and the detection window A, the detection window A bar, the detection window B, and the detection window B bar in the upper set are arranged in the moving direction. Are arranged in a predetermined order along the lower row of the detection window A, the detection window A bar,
The detection window B and the detection window B bar are arranged along the moving direction in the order opposite to the order of the upper detection windows. Therefore,
For example, when the amount of received light is small on the left side of the index scale 3 and large on the right side (when there is a linear light amount variation in the moving direction), the detection windows A and B of the upper group and the detection windows B and A of the lower group are The amount of received light is 60, the upper detection window A bar,
The light receiving amount of the detection windows B bar and A in the lower group of B and 30 is 30, the sum of the light receiving amounts of the detection windows A of both upper and lower groups is 90, and the light receiving amounts of the other detection windows A bar, B and B bar are Is 90. Therefore, it is hardly affected by the change in the light amount in the moving direction, and the center level of the encoder signal hardly changes, so that highly accurate measurement is possible.

Further, for example, when the amount of received light is large on the detection window side of the upper set and small on the detection window side of the lower set (when there is a linear change in the light amount in the direction perpendicular to the moving direction), the detection window A of the upper set is detected. , B bar, A bar, B has a light receiving amount of 70, and the detection windows B, A bar, B bar, A of the lower set have a light receiving amount of 30,
The sum of the received light amounts of the upper and lower detection windows A is 100, and the sum of the received light amounts of the other detection windows B bar, A bar, and B is 10 as well.
It becomes 0. Therefore, it is unlikely to be affected by fluctuations in the amount of light in the direction perpendicular to the moving direction, and the center level of the encoder signal hardly changes, so that highly accurate measurement is possible.

FIG. 1D is a view showing the arrangement of the detection windows of the index scale according to the third embodiment of the present invention. In the embodiment of FIG. 1, a case where two sets of four types of detection window A (0 °), detection window A bar (180 °), detection window B (90 °), and detection window B bar (270 °) are used. However, instead of this, as shown in FIG.
(0 °), detection window A bar (180 °), detection window B (90
4) and four detection windows B bar (270 °) may be used. As a result, it is less likely to be affected by fluctuations in the light amount, and it is possible to perform measurement with higher accuracy. The number of windows is determined by the relationship between the light receiving area and the size of the windows, and the larger the number of windows, the higher the accuracy. The photodiode is arranged so as to face each of the detection windows.

The comparison between FIGS. 1A, 1C and 1D and the conventional index scale is as follows.

That is, as shown in FIG. 5A, the detection window A,
In the case of an index scale in which A bar, B, and B bar are formed (hereinafter referred to as a 2 × 2 index scale), the center level fluctuates by L intervals at a light amount of 30% with respect to the reference voltage, and the light amount is 60%. In%, the center level fluctuates by M intervals.

However, in the case of an index scale (hereinafter 4 × 2 index scale) in which two sets of detection windows A, A bar, B and B bar are formed as shown in FIGS. 1 (a) and 1 (c). As shown in FIG. 5A, when the light amount changes from 30% to 60% with respect to the reference voltage, it slightly changes, and there is almost no change from the reference voltage.

Further, in the case of an index scale in which four sets of detection windows A, A bar, B, and B bar are formed as shown in FIG. 1D (hereinafter, 4 × 4 index scale), FIG. As shown in d), it can be seen that the fluctuation of the center level is smaller than that of the 4 × 2 index scale.

In this embodiment, the case where the present invention is applied to the optical transmission type linear encoder has been described, but it may be applied to the optical rotary encoder or the reflection type encoder.

[0041]

As described above, according to the optical encoder of the present invention, it is difficult to be affected by the fluctuation of the light quantity in the moving direction and the fluctuation of the light quantity in the direction perpendicular to the moving direction, and the center level of the encoder signal is reduced. Can be measured with high accuracy, since is almost unchanged.

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement of detection windows of an index scale of an optical encoder according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram showing an optical linear encoder according to an embodiment of the present invention.

FIG. 3 is a detection circuit diagram of the optical encoder of the embodiment of FIG.

FIG. 4 is a front view of a main scale.

FIG. 5 is a comparison diagram of fluctuations in center level.

FIG. 6 is a diagram showing an arrangement of detection windows of an index scale of a conventional optical encoder.

7 is a diagram showing the relationship between the detection windows of FIG.

FIG. 8 is a curve diagram for explaining a change in the center level due to a change in the amount of received light in the moving direction.

FIG. 9 is a detection circuit diagram of a conventional optical encoder.

[Explanation of symbols]

 1 Light source 2 Main scale 3 Index scale 4a-4h Photodiode 5 Operational amplifier A, A bar, B, B bar Detection window

Claims (3)

[Claims] 1. A light source, a main scale on which a grid pitch of a constant pitch is formed, a first detection window on which a first reference graduation corresponding to the grid graduation is formed, and with respect to the first reference graduation. A second detection window having a second reference scale that is 90 degrees out of phase, and a third detection window that has a third reference scale that is 90 degrees out of phase with the second reference scale; An index scale having a fourth detection window formed with a fourth reference scale that is 90 ° out of phase with the third reference scale, the index scale moving relative to the main scale, and each of the index scales. A light receiving unit that is arranged to face the detection window, receives a light from the light source that has passed through the main scale and the index scale, and the main scale based on a light receiving signal from the light receiving unit. 9 representing the amount of relative movement between the index scale
An optical encoder comprising: a signal output unit for processing a signal into a two-phase sine wave signal having a 0 ° phase difference and outputting the signal; wherein the index scale includes the first to the first units arranged in a longitudinal direction of the lattice pattern. A first window group including four detection windows, a second window group including the first to fourth detection windows having a phase difference of 90 ° with respect to the first window group, and the second window group. A third window group consisting of the first to fourth detection windows having a phase difference of 90 °, and the first to fourth detection windows having a phase difference of 90 ° with respect to the third window group. A fourth window group consisting of the two-phase sine wave after adding the received light signals that have passed through the same detection windows of the first window group and the second window group, respectively. An optical encoder characterized by performing signal processing on a signal. 2. The index scale includes a first window group including the first to fourth detection windows arranged in one direction with respect to a longitudinal direction of the lattice pattern, and the first window group. A second window group having the phase difference of 90 ° and arranged from the other direction with respect to the longitudinal direction of the grating pattern, the second window group including the first to fourth detection windows. Item 1. The optical encoder according to Item 1. 3. The index scale is provided with respect to the first window group, the first window group including the first to fourth detection windows arranged in one direction with respect to the array direction of the lattice pattern. A second window group having the phase difference of 90 ° and arranged from the other direction with respect to the array direction of the grating pattern, the second window group including the first to fourth detection windows. The optical encoder according to claim 1.