JP2715623B2 - Encoder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an encoder, and more particularly to an encoder using diffraction and interference.

[Conventional technology]

Conventionally, as this type of encoder, for example,
No. 309816 is known, and specifically,
It has a configuration as shown in the figure.

The coherent light emitted from the laser diode 60 generates a condensed light beam by a condensing lens 61 and is split into two P and S polarized light beams by a polarizing beam splitter 62. Then, each polarized light is reflected by the reflecting mirrors 63a and 63b, respectively, and reaches the transmission type diffraction grating 64 with a predetermined equal incident angle.

The diffraction grating 64 has a predetermined pitch along the measurement direction, and is provided movably along the measurement direction.

Here, the condenser lens 61 is a polarizing beam splitter 6
2. Each light beam passing through the reflecting mirrors 63a and 63b is condensed on the diffraction grating 64.

Now, each light beam that has crossed the diffraction grating 64 with a predetermined equal incident angle is
The light is diffracted in a direction perpendicular to the pitch direction of the light 64 and becomes a parallel light beam by a lens 65 for correcting a change in the diffraction angle.

Here, the lens 65 for correcting the change in the diffraction angle is
Even if the diffraction angle changes due to the wavelength change of the output light due to the temperature change of the laser diode 60, it functions to cancel the influence of the change in the diffraction angle.
That is, even when the diffraction angle changes, the lens 65 is configured so that the diffraction grating 64 is turned into a parallel light beam while directing two light beams illuminating two predetermined directions in the same direction, and the two parallel lights always overlap. ing.

After that, the parallel light beam passing through the lens 65 is
, And becomes a circularly polarized light, and is split into two by the beam splitter 67. Then, each of the split light beams is photoelectrically detected by the light receiving elements 69a and 69b via the polarizing plates 68a and 68b, and based on output signals of the light receiving elements 69a and 69b according to the movement of the diffraction grating 64 in the measurement direction. The amount of movement of the diffraction grating 44 can be detected based on the phase difference between the two output signals.

Therefore, in the encoder described above, the arrangement of the lens 65 for correcting the change in the diffraction angle allows the detector to always detect the interference light even when the diffraction angle changes, so that highly accurate measurement can be performed. Things.

[Problems to be solved by the invention]

In the prior art as described above, a laser diode
The change in the diffraction angle of the moving diffraction grating 64 due to the wavelength change due to the temperature change of 60 is corrected by the arrangement of the lens 65 for correction.

However, this correction lens 65 and moving diffraction grating
Adjustment such as focusing and optical axis alignment with 64 is troublesome and difficult.

Further, as described above, this apparatus is advantageous in changing the diffraction angle with respect to the wavelength fluctuation of the light source, but the transmission type movable diffraction grating 64 has insufficient correction for the fluctuation in the vertical direction in FIG. is there.

That is, due to this change, the emission directions of the two diffracted lights reaching the detectors 69a and 69b change and the state of condensing the detection light via the correction lens 65 changes, so that the detectors 69a and 69b The interference state on the detection surface changes greatly.

As a result, the output signal detected by the detector may become unstable.

As described above, the present invention has been made in view of these problems, and an object of the present invention is to provide a high-precision encoder with a simple configuration and extremely easy adjustment, and at a low cost.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a scale (6) on which a measuring diffraction grating (6A) having a predetermined periodic pitch is formed, and a parallel light beam supplying means (1, 1) for supplying a coherent parallel light beam. and 2) a flat Yukimitsu flux dividing the first light flux L ₁ and the second light flux L _2, first and second in the scale (6)
An illumination system having illumination optical means for irradiating the light beam in two predetermined directions; and a detection system (7, 8, 9a, 9b, 9) for receiving the diffracted light generated by the scale (6) and photoelectrically detecting it. 10a, 10b, 11), wherein the detection system detects the relative movement amount of the scale (6) in the pitch direction with respect to the illumination system and the detection system. To correct the diffraction angle fluctuation due to the wavelength change of the supply means (1, 2) and the mechanical fluctuation of the scale (6), a periodic pitch equal to and parallel to the measuring diffraction grating (6A) is used. Correction grating (5A, 5a, 5
b, 50a, 50b) are disposed so as to face the irradiation side of the scale (6), and the illumination optical means (3, 4a, 4b, 30, 31a, 31b) is provided with the correction diffraction grating (5A, 5a). , 5b, 50a, 50b) said first and second light beams L _1, L ₂ and configured to vertically incident on the correction diffraction grating (5A, through 5a, 5b, 50a, and 50b) the diffracted light LD _1, the LD ₂ the measuring diffraction grating of the first and second light flux (6A) with respect to those for illuminating a predetermined two directions.

In order to improve the detection accuracy, a reflection member (40) is arranged at a position parallel to the scale (6), and the correction optical grating (30, 31a, 31b) is used by the illumination optical means (30, 31a, 31b). The diffracted light beams LD ₁ (m) and LD ₂ (−m) of the first and second light beams generated in the direction normal to the surface on which 6A) is formed are re-incident on the diffraction grating for measurement (6A). It is desirable to adopt a configuration that causes re-diffraction.

Further, in order to improve the illumination efficiency, the correction diffraction grating, the first light flux L ₁ and blazed grating having a diffraction characteristics of mutually opposite to each passage region between the second light flux L ₂ (50a, 50
It is preferable to configure the correction diffraction grating in b).

(Operation)

According to the present invention, the correction diffraction grating 5A having the same pitch as the measurement diffraction grating 6A on the scale 6 is arranged so as to face the illumination side of the diffraction grating on the scale, so that diffraction from the measurement diffraction grating 6A is performed. It is noted that the problem that the diffraction angle of light fluctuates due to a change in the wavelength of the light source and the problem that the scale 6 mechanically fluctuates in the direction perpendicular to the surface of the scale 6 (normal direction) can be solved.

Specifically, as shown in FIG. 1A, when the collimated light L is illuminated perpendicularly to the correction diffraction grating 5, ± m-order diffracted light is generated. Considering, for example, the m-th order diffracted light L (m) generated in the θ _m direction, the m-order diffracted light L (m) is re-diffracted in the direction deflected by θ _m by the measuring diffraction grating 6A on the scale. The -m-order diffracted light LD is generated in a direction orthogonal to the measurement diffraction grating 6A.

However, the m-th order diffracted light on the right side of the 0th order diffracted light is + m
And the left-hand diffracted light is the -mth-order diffracted light.

Here, the wavelength of the illumination light beam lambda, the diffraction grating 5A, the pitch of 6A P, the order of the diffracted light m (integer), when the diffraction angle is theta _m, Is established. At this time, the diffraction angle of the m-th order diffracted light is θ
The diffraction angles of the _m and −m-order diffracted lights are θ _−m , and both have θ _m =
- [theta] _-m relationship is established but, for simplicity of explanation in the following, the diffraction angle of the ± m order diffracted light will be described as both theta _m.

Now, when the light source wavelength λ fluctuates with a temperature change, it can be seen from the above equation (1) that the diffraction angle θ _m changes. As shown in FIG. 1A, when the light source wavelength λ is shifted to a shorter wavelength side,
Diffraction angle theta _m of -m order diffracted light LD generated from correction diffraction grating 5 is smaller becomes theta _mL. Similarly, the diffraction angle θ _m of the m-th order diffracted light LD (m) generated by diffracting the −m order diffracted light LD by the measurement diffraction grating 6A also becomes θ _mL and becomes smaller.

Therefore, the m-th order diffracted light LD (m) re-diffracted by the measurement diffraction grating 6A always exits in a direction orthogonal to the measurement diffraction grating 6A.

Further, also in the case where the light source wavelength λ shifts to the longer wavelength side and the diffraction angle θ _m of the −m-order diffracted light LD by the correction diffraction grating 5A becomes θ _mH and becomes large, the measurement diffraction grating 6A diffraction angle theta _m of diffracted light LD (m) is, theta _mH has become, the m order diffracted light LD (m) is always injected to the perpendicular to the measurement grating 6A direction.

As described above, in the present invention, although the diffracted light for detection can always be emitted in a direction orthogonal to the diffraction grating 6A for measurement, the diffracted light for detection LD (emitted from the scale according to the wavelength variation of the light source) m) is shifted laterally by X _1.

However, since the illumination and measuring the diffraction grating 6A and correction diffraction grating 5A with collimated light of a certain size, the lateral shift amount X ₁ of the diffracted light to be detected to the diameter of the collimated light is negligibly small Become.

Further, as shown in FIG. 1B, even when the distance g between the correction diffraction grating 5A and the measurement diffraction grating 6A of the scale 6, that is, the so-called gap g, changes by Δg due to the vertical movement of the scale 6, as shown in FIG. 1B. The m-th order diffracted light LD (m) that is re-diffracted by the measuring diffraction grating 6A is always the measuring diffraction grating.
Inject in the direction perpendicular to 6A. At this time, as in the case where the wavelength fluctuates, the detection diffracted light LD (m) emitted from the scale is shifted in the horizontal direction according to the mechanical fluctuation of the scale, but the collimated light having a certain size is emitted. in order illuminates, lateral shift amount X ₂ of the diffracted light to be detected to the diameter of the collimated light is negligibly small.

Therefore, the present invention provides a measuring diffraction grating on a scale.
Just by arranging the correction diffraction grating 5A having the same pitch as 6A on the light source side facing the measurement diffraction grating 6A, not only can the effects of the diffraction angle change and the gap change due to the wavelength change be eliminated, It can be understood that the adjustment is extremely simple and the configuration is very advantageous in manufacturing.

〔Example〕

FIG. 2 is a schematic block diagram of the first embodiment of the present invention, and this embodiment will be described in detail with reference to FIG.

A diffraction grating 6A for measuring an amplitude grating in which transmission regions and light shielding regions are alternately formed at a predetermined pitch is provided on the scale 6 of the parallel plane plate, and the scale 6 is provided so as to be movable in the horizontal direction. ing.

An illumination system is provided above the scale 6, and a detection system is provided below the scale 6.

First, an illumination system will be described. Coherence (coherent) emitted from a laser diode 1 as a light source
Are collimated (parallel light flux) by the collimating lens 2. Then, the polarized beam splitter 3 causes, for example, P-polarized light in the transmission direction (polarized light in the paper direction) and S-polarized light in the reflection direction (polarized light in a direction perpendicular to the paper surface).
And divided into These two polarized light beams (L ₁ , L ₂ )
Is illuminated perpendicularly to the diffraction grating 5A formed on the plane-parallel plate 5 by the reflection members 4a and 4b.

Here, the diffraction grating 5A is formed of the same amplitude grating as that of the main scale, and is used to correct a change in diffraction angle due to a wavelength change of the laser diode 1 and a mechanical change in the vertical direction of the main scale. Function as a diffraction grating.

The illumination lights L ₁ and L ₂ are diffracted by the correction diffraction grating 5A, and each order of diffraction light is generated. Then, ± m order diffracted light LD _1, LD ₂ from the correction diffraction grating 5A illuminates the diffraction grating 6A on the scale 6 from two directions of the incident angle theta _m.
These two ± m-order diffracted lights LD ₁ and LD ₂ are re-diffracted by the diffraction grating 6A of the scale 6, and ± m-order re-diffracted light LD ₁ (m), LD generated in the vertical direction of the measurement diffraction grating 6A. ₂ (-m)
Travels on the same optical path toward the detection system.

Now, when the wavelength of the light beam output from the laser diode 1 changes, and when the gap between the correction diffraction grating 5A and the measurement diffraction grating 6A of the scale 6 changes,
As shown in FIGS. 1A and 1B, two diffracted lights LD ₁ (m) and LD ₂ (−m) emitted in a direction perpendicular to the measuring diffraction grating 6A of the scale 6 and directed to the detection system are: Although it does not change at all in the injection direction, it shifts in the opposite direction in the measurement direction by X ₁ and X ₂ .

However, the two diffracted lights guided to the detection system are LD ₁
(M), LD ₂ (−m), when it is collimated by the above-described collimating lens 2, it has a light beam diameter of a predetermined size. beam diameter is sufficiently large relative to _1, X _2.

Therefore, since both diffracted lights substantially overlap and travel on the same optical path, the S / N ratio is always high and stable without substantially changing the interference state of the interference light detected by the detector described later. An output signal can be detected.

Here, an example in which the wavelength of the light beam output from the laser diode 1 fluctuates will be considered.

When the wavelength of the light source at 25 ° is λ of 780 mm, the variation Δλ of the light source at ± 25 ° from 25 ° is ± 6n.
m, the gap g between the correction diffraction grating 5A and the scale measurement diffraction grating 6A is 5 mm, and the pitch P between the diffraction gratings 5A and 6A is 4 mm.
μm, the diameter φ of the collimated light beam is 2 mm, and the diffraction grating 5A generated by the correction diffraction grating 5A and the scale measurement diffraction grating 6A.
1 when attempting to detect the diffracted light, the horizontal shift amount X ₁ of the detection light due to the wavelength variation 12nm of the light source with respect to the temperature change of 50 DEG from 0 DEG, was obtained from the relationship of the above equation (1) and Figure 1A , Becomes

Therefore, since the lateral shift amount X ₁ relative to beam diameter φ is approximately 1%, without adversely affecting the substantial detection accuracy, always detects an output signal high and stable S / N ratio.

Also, consider an example in which the gap between the correction diffraction grating 5A and the measurement diffraction grating 6A of the scale 6 fluctuates.

The light source wavelength λ is 780 nm, the gap g between the correction diffraction grating 5A and the scale measurement diffraction grating 6A is 5 mm, the gap variation Δg is 100 μm, and the pitch P of the diffraction gratings 5A and 6A is 4
μm, the diameter of the collimated light beam is 2 mm. Further, ± 1 generated by the correction diffraction grating 5A and the measurement diffraction grating 6A.
When trying to detect the diffracted light, the horizontal shift amount X ₂ of the detection light due to the gap variation is determined from the relationship of the above equation (1) and Figure 1B, Becomes

Therefore, since it is the lateral shift amount X ₂ also approximately 1% of the beam diameter phi, also in this case, always possible to detect the output signal high and stable S / N ratio.

The luminous flux diameter φ of the collimated illumination light is optimized according to the gap g between the correction diffraction grating 5A and the measurement diffraction grating 6A, the wavelength variation range of the light source, the gap variation range, the pitch of each diffraction grating, and the like. It can be arbitrarily selected.

Now, the scale 6 is emitted and travels on the same optical path 2
The two diffracted lights LD ₁ (m) and LD ₂ (−m) are polarized in directions orthogonal to each other, and when they pass through the quarter-wave plate 7, they become circularly polarized lights in opposite directions. Then, the light is split into two optical paths by the beam splitter 8, and is photoelectrically detected by the detectors 10a and 10b through the respective polarizing plates 9a and 9b.

At this time, for example, the polarizing plates 9a and 9b are adjusted and arranged so that a phase difference of 90 ° is provided between two photoelectrically detected sine wave output signals so that the direction can be discriminated.

The two sine-wave output signals whose phases are relatively shifted by 90 ° are subjected to signal processing by a method applied in a conventional photoelectric encoder as shown in FIG. 4, for example.

As shown in the figure, a preamplifier 20 for amplifying each output signal obtained from each detector, a waveform shaping circuit 21 for shaping each amplified signal into a pulse, and a direction for converting each pulse signal into a binary pulse signal A measurement value can be obtained by providing a discrimination circuit 22, a counting circuit 23 that counts the pulse signals through the direction discrimination circuit, and a display unit 24 that displays a measurement result by counting the pulse signals in a desired format. .

With the above configuration, stable detection of an output signal having a high S / N ratio can be realized.

In the present embodiment, the correction diffraction grating 5A and the measurement diffraction grating 6A are formed of an amplitude grating, but may be formed of a periodic uneven phase grating having a predetermined pitch. .

 Next, a second embodiment will be described.

In this embodiment, instead of the correction diffraction grating 5A shown in FIG. 2, blaze gratings 50a and 50b having a saw-tooth shape as shown in FIG. 3 are applied to increase the diffraction efficiency and increase the illumination efficiency of the entire apparatus. Is significantly improved.

In addition, on the scale 6 of the present embodiment, there is provided a measuring diffraction grating 6A formed of an uneven phase grating having a predetermined periodic pitch P.

The blazed gratings 50a and 50b have first and second sawtooth-shaped teeth opposite to each other in order to generate the strongest diffracted light in two predetermined directions with respect to the measuring diffraction grating 6A. It has two regions.

At this time, the angle of the sawtooth-shaped grating slope is δ, the diffraction angle θ _{B of} the diffracted light having the strongest intensity, and the blaze gratings 50a and 50b.
Assuming that the refractive index of b is n, the relationship of n sin δ = sin (θ _B + δ) (2) is established.

Therefore, the angle δ of the slopes of the blaze gratings 50a and 50b is given by the above equation (2). Becomes

Here, in order to achieve the compensation for the wavelength variation and the gap variation which is the object of the present invention, the brake gratings 50a, 50b
Angle θ of the strongest diffracted light generated by
_B is the angle θ at which the measurement diffraction grating 6A diffracts the illumination light beam.
equal to _m, moreover blaze grating 50a, 50b pitch P _B equally needs to be configured with the pitch P of the diffraction grating 6A of the scale 6.

Therefore, from the above equations (1), equation (3) is It is desirable to form the blaze gratings 50a and 50b so as to substantially satisfy the expression (4).

In this embodiment, as shown in FIG. 3, the blazed gratings 50a and 50b are integrally formed on the same parallel plane plate 50. However, the blazed gratings 50a and 50b are separated on the same plane. It may be arranged.

Next, a third embodiment of the present invention will be described. FIG. 5 shows a schematic configuration of the third embodiment, and members having the same functions as those in FIG. 2 are denoted by the same reference numerals.

In this embodiment, the transmission type diffraction grating 6A of the first embodiment is used.
Is a reflection type, and detection light reflected and diffracted by the measurement diffraction grating 6A is guided to a detection system via a reflection mirror 11.

The configuration of the present embodiment is basically the same as that of FIG. 1, and a detailed description thereof will be omitted.

In FIG. 5, correction diffraction gratings 5a and 5b are provided separately on the same plane.For example, a transmission area for transmitting detection light reflected and diffracted from the measurement diffraction grating 6A on a parallel plane plate, Correcting diffraction gratings 5a and 5b
May be formed.

It goes without saying that a blaze grating as described in detail in the first embodiment may be provided in place of the correction diffraction gratings 5a and 5b to improve the illumination efficiency.

Next, a fourth embodiment of the present invention will be described. FIG. 6 shows a schematic configuration of the fourth embodiment. Members having the same functions as those in FIGS. 2 and 5 are denoted by the same reference numerals.

In the present embodiment, compared to the third embodiment, the optical members 30 and
Quarter-wavelength plates 31a and 31b are provided to change the optical path of the illumination light and the detection light, and the state of the illumination light flux is changed.
The diffraction light generated in the direction (normal direction) orthogonal to the pitch direction of the measurement diffraction grating 6A is reflected and re-enters the measurement diffraction grating 6A.

 The fourth embodiment will be described in detail with reference to FIG.

The light beam from the laser diode 1 is collimated by the collimating lens and enters the optical member 30.

The optical member 30 has a substantially trapezoidal first block whose upper bottom is notched so that illumination light and emission light pass therethrough.
30a and a second block 30b, and the bottom surfaces of the blocks are joined to each other. This bonding surface is formed of a polarization beam splitter, and the optical member 30 functions as a polarization beam splitter.

The collimated light from the collimating lens 2 is converted into P-polarized light (polarized in the direction of the paper) in the transmission direction and S-polarized light (polarized in the direction perpendicular to the direction of the paper) in the reflecting direction by the polarizing beam splitting surface 31A of the optical member 30. The light is separated and reflected by each inclined surface of the optical member 30, and each light beam exits the optical member 30 so as to be parallel to each other.

Then, the luminous fluxes of the P-polarized light and the S-polarized light are divided into quarter-wave plates 31a, 31
After passing through 1b, the light becomes circularly polarized light in opposite directions to each other, then diffracted by the correction diffraction gratings 5a and 5b, and ± m-order diffracted lights LD ₁ and LD ₂ are incident on the scale 6 from two directions at an incident angle θ _m The measurement diffraction grating 6A is illuminated. This measurement diffraction grating 6A
Reflects and diffracts the diffracted light beams LD ₁ and LD ₂ , and the ± m-order reflected diffracted light beams LD ₁ (m) and LD in the vertical direction of the measuring diffraction grating 6A.
₂ Generates (-m). Then, the reflected diffracted light beams are regularly reflected by the reflecting member 40, and re-enter the measuring diffraction grating 6A. Then, these two re-incident lights are converted into a diffraction grating for measurement.
Diffracted by 6A, ± m order reflected diffracted light LD ₁ (m, m),
LD ₂ (−m, −m) goes back to the original optical path again and passes through the correction diffraction gratings 5a and 5b and the quarter-wave plates 31a and 31b.

Then, the detection light LD ₁ (m, m) is in the S polarization state, while the detection light LD ₂ (−m, −m) is in the P polarization state. Therefore, the two light beams reflected on the inclined surface of the optical member 30 are guided on the same optical path toward the detection system by the polarization beam splitting surface of the optical member 30. Thereafter, the two light beams that have passed through the quarter-wave plate 7 become circularly polarized lights in opposite directions to each other, are split into two light beams by the beam splitter 8, and are passed through the respective polarizing plates 9a and 9b to the respective detectors 10a and 10b. Thus, for example, two output signals whose phases are relatively shifted by 90 ° are photoelectrically detected.

As described above, in the present embodiment, since the ± 1st-order diffracted light is re-diffracted on the diffraction grating 6A of the scale movable by the arrangement of the reflection member 40, photoelectric detection is performed every time the scale moves by one pitch. The output signal thus shifted is 8π out of phase.

Therefore, as compared with the devices described in the first and second embodiments, a sine wave output signal that is twice as high can be obtained, and the detection accuracy can be doubled.

In the signal processing system, the movement amount and direction of the scale can be detected by, for example, the configuration shown in FIG.

As described above, the correction diffraction gratings 5a and 5b of the present embodiment are arranged separately, but a reflection surface is formed on a parallel plane plate, and the diffraction gratings 5a and 5b May be formed and integrated.

Also in the present embodiment, as shown in FIG. 7, instead of the correction diffraction gratings 5a and 5b, the directions of the teeth of the saw-toothed grating are set on the left and right of the reflection surface 41 in order to generate diffracted light in directions opposite to each other. By providing the opposite blaze gratings 50a and 50b, the diffraction efficiency can be improved.

As shown in FIG. 8, the scale 6 falls from the state shown by the dotted line to the state shown by the solid line by θ in the groove direction orthogonal to the pitch direction of the correction diffraction gratings 50a and 50b formed on the plane-parallel plate 50. 7, the reflecting surface 41 as shown in FIG. 7 is more desirably configured such that the directions of the incident light and the reflected light in the groove direction of the diffraction grating 6A of the scale 6 become equal. .

This can be achieved, for example, by configuring the groove directions of the diffraction gratings 50a and 50b with right-angle mirrors as shown in FIGS. 9A and 9B.

9A and 9B are cross-sectional views of the correction diffraction gratings 50a and 50b in the measurement direction (grating pitch direction), and FIG. 9B is a sectional view of the correction diffraction gratings 50a and 50b. It is an arrow view of -A section.

As shown in FIG. 9A (b), a block-shaped member 50c having a V-shaped groove has reflecting surfaces 41a and 41b formed in the V-shaped groove. And, the block-shaped transmission member 50c is the ninth A
As shown in FIG. 7A, the diffraction gratings 50a and 50b are bonded between the respective gratings 50a and 50b of the parallel plane plate 50 on which the diffraction gratings 50a and 50b are formed.

Further, as shown in FIG. 9B (a), reflection surfaces 41a and 41b are formed on the inclined surface of the right-angle prism 50c. And 9B
As shown in FIG. 2B, the right-angle prism 50c having the reflection surfaces 41a and 41b is bonded above the transmission area of the parallel flat plate 50 on which the diffraction gratings 50a and 50b are formed with the transmission area interposed therebetween.

As described above, the right-angle mirror shown in FIGS. 9A and 9B can be manufactured very easily, which is advantageous in cost.

In each embodiment of the present invention, as the correction diffraction grating,
It has been shown that an amplitude grating, a blazed grating or a phase grating having an uneven shape can be used, and an amplitude grating or a phase grating having an uneven shape can be used as a diffraction grating on a scale.

For this reason, these may be used arbitrarily in combination, and it goes without saying that other components that function as a diffraction grating can also be applied.

Further, in each embodiment of the present invention, an example in which the scale 6 moves is shown, but the scale 6 may be fixed and the illumination system and the detection system may move integrally.

〔The invention's effect〕

As described above, according to the present invention, the correction diffraction grating is disposed so as to face the scale diffraction grating, and the correction diffraction grating 5A is provided.
By simply adding a simple configuration that illuminates two light beams vertically, the S / N ratio of each detector is always high and stable even when the diffraction angle change and gap change due to wavelength change occur. A high-performance encoder capable of obtaining a highly reliable detection signal can be achieved.

In addition, since the correction diffraction grating can be manufactured relatively easily, and adjustment when the correction diffraction grating is incorporated in the encoder is extremely easy, the cost can be reduced and the cost can be reduced.

In addition, since the correction diffraction grating is simply arranged in the illumination optical path, there is an advantage that the device can be configured to be extremely compact without increasing the size of the device.

[Brief description of the drawings]

1A and 1B are diagrams illustrating the principle of the present invention. Second
FIG. 1 is a diagram showing a schematic configuration of the first embodiment of the present invention. FIG. 3 is a view showing a main part of a second embodiment of the present invention. FIG. 4 is a block diagram of a signal processing system according to the first embodiment of the present invention. FIG. 5 is a diagram showing a schematic configuration of a third embodiment of the present invention. FIG. 6 is a diagram showing a schematic configuration of a fourth embodiment of the present invention. FIG. 7 is a view showing a state of a correction diffraction grating having a reflecting surface. FIG. 8 is a view showing a state where the scale is tilted in the groove direction of the correction diffraction grating. 9A and 9B are diagrams showing the structure of a correction grating for correcting the tilt of the scale. FIG. 10 is a diagram showing a schematic configuration of a conventional encoder. [Explanation of Signs of Main Parts] 1. Laser Diode (Parallel Beam Supply Unit) 2. Collimator Lens (Parallel Beam Supply Unit) 3. Polarized Beam Splitter (Illumination Optical Unit) 4a, 4b ... Reflecting Member (Illumination) Optical means) 31a, 31b: quarter-wave plate (illumination optical means) 30: Optical member (illumination optical means) 5A, 5a, 5b, 50a, 50b: Correction diffraction grating 6: Scale 6A Diffraction grating for measurement 40,41a, 41b …… Reflective member

Claims (3)

(57) [Claims] 1. A scale on which a diffraction grating for measurement having a predetermined periodic pitch is formed, a parallel light beam supplying means for supplying a coherent parallel light beam, and the parallel light beam is supplied to a first light beam and a second light beam.
An illumination system for irradiating the scale with the first and second light beams in two predetermined directions, and an illumination system for receiving the diffracted light generated by the scale and photoelectrically detecting the light. An encoder that detects a relative movement amount of the scale in the pitch direction with respect to the illumination system and the detection system by the detection system. A diffraction grating for correction having a periodic pitch equal to and parallel to the measurement diffraction grating of the scale and in the same direction in order to correct the accompanying diffraction angle fluctuation and mechanical fluctuation of the scale is opposed to the irradiation side of the scale. The illumination optical unit is arranged so that the first and second luminous fluxes are perpendicularly incident on the correction diffraction grating, and the correction diffraction grating is configured to pass through the correction diffraction grating. The diffraction grating is arranged so as to illuminate the diffraction gratings of the first and second luminous fluxes in two predetermined directions with respect to the measurement diffraction grating. An encoder characterized in that diffracted light of the first and second light beams generated in a direction normal to a surface on which the scale grating is formed by means is re-entered on the measurement diffraction grating to be diffracted again. 2. The correction diffraction grating according to claim 1, wherein said correction diffraction grating is formed of a blazed grating having diffraction characteristics opposite to each other in respective passing regions of said first light beam and said second light beam. An encoder according to. 3. A scale on which a diffraction grating for measurement having a predetermined periodic pitch is formed, a parallel light beam supplying means for supplying a coherent parallel light beam, and the parallel light beam is supplied to a first light beam and a second light beam.
An illumination system for irradiating the scale with the first and second light beams in two predetermined directions, and an illumination system for receiving the diffracted light generated by the scale and photoelectrically detecting the light. An encoder that detects a relative movement amount of the scale in the pitch direction with respect to the illumination system and the detection system by the detection system. A diffraction grating for correction having a periodic pitch equal to and parallel to the measurement diffraction grating of the scale and in the same direction in order to correct the accompanying diffraction angle fluctuation and mechanical fluctuation of the scale is opposed to the irradiation side of the scale. The illumination optical unit is arranged so that the first and second luminous fluxes are perpendicularly incident on the correction diffraction grating, and the correction diffraction grating includes a first light flux and a second light flux. Each Formed by blazed grating of opposite diffraction characteristics from each other in the passage area, the first through the correction diffraction grating
An encoder for illuminating the measurement diffraction grating of the diffracted light of the second light flux in two predetermined directions.