JPH0914916A - Grating interference type displacement detector - Google Patents

Abstract

PURPOSE: To provide a grating interference type displacement detector with higher resolutions which can reduce width dimensions of a scale and moreover, simplify an optical system for guiding coherent light to the scale. CONSTITUTION: A plurality of grating patterns PT1 , PT2 and PT3 are formed on a scale S in a multiplex fashion with different grating angles α1 , α2 and α3 and a slight difference of pitches P1 , P2 and P3 to form a diffraction grating G, which is irradiated with a luminous flux. A first light mixing means is provided to mix diffraction light of different orders generated by one grating pattern for making an interference fringe and a second light mixing means to mix diffraction light of the same order generated by the different grating patterns for making an interference fringe to obtain a plurality of detection signals different in cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grating interference type displacement detecting device. More specifically, the grating interference type displacement detection device which detects the absolute displacement amount between the scale and the detector by utilizing the interference of light can be used for downsizing of the scale.

[0002]

BACKGROUND ART As one of the ones aiming at higher resolution of a photoelectric encoder, a scale having a fine pitch (usually about 1 μm) is formed on a scale by using holography technology,
A grating interference type displacement detection device has been proposed in which the scale is used as a diffraction grating to positively generate diffraction to obtain a detection signal (Japanese Patent Laid-Open No. 47-10034).

On the other hand, a first scale having a plurality of grating tracks having different grating pitches, a second scale having a grating window corresponding to each grating track, a light source and a photoelectric conversion element arranged to face each grating window. An optical absolute position encoder constituted by and is known (Japanese Patent Laid-Open No. 4-7).
6419 prior art).

[0004]

However, since the former grating interference type displacement detecting device has a small grating pitch, if the moving speed of the scale becomes fast, the processing of the detecting circuit cannot follow and a miscount occurs. However, there is a problem that the moving speed is restricted or the processing speed of the detection circuit must be sufficiently increased. Therefore, if the fine pitch diffraction grating of the grating interference type displacement detection device is used for one of the grating tracks of the latter absolute position encoder,
A high-resolution absolute position encoder can be realized, and restrictions on the moving speed can be eliminated.

However, since it is difficult to form a long pitch grating by a holographic technique, the scale grating is forced to be manufactured in separate steps, and the scale manufacturing process becomes complicated. Further, the detection of a long pitch requires a second scale, and the detection of a fine pitch requires a coherent light source. For example, a detector with a different detection principle is mixed and the detector becomes large and complicated. Problems also arise.

Therefore, the applicant of the present invention has solved the above-mentioned problems of the conventional grating interference type displacement detection device, can be scaled by one manufacturing technique, and the detector can be large and complicated. At the same time as the present invention, a high-resolution grating interference type displacement detection device that does not exist and has no restriction on the moving speed was proposed. This will be described with reference to FIGS.

FIG. 4 shows a detection optical system of the displacement detecting device.
5 is a plan view of the scale as seen from above.
You. As shown in these figures, the grid is on the scale S.
Multiple (here three) diffractions with slightly different pitches
Lattice track T_1,T_2,T_ThreeAre formed respectively.
That is, the grid pitch P₁First diffraction grating track T of
₁And the grid pitch P_Two(P_Two> P₁) 2nd diffraction grating
Rack T_TwoAnd the grid pitch P _Three(P_Two> P_Three> P₁)of
Third diffraction grating track T_ThreeAnd are formed respectively
You.

A laser diode LD ₁ is provided as a light source for irradiating the diffraction grating tracks T _1, T _2, T ₃ with a laser beam. Laser diode LD
_The laser beam emitted from ₁ is split by the half mirror HM ₁ , and one of the laser beams is bent in a plane passing through the center of the first diffraction grating track T ₁ to serve as a light source for irradiating the first diffraction grating track. The other laser beam is directed to the half mirror HM ₂ where it is further split. One of the laser beams divided by the half mirror HM ₂ is bent in a plane passing through the center of the second diffraction grating track T ₂ and serves as a light source for irradiating the second diffraction grating track. The other laser beam directed to the mirror M _1, where the third bent direction in a plane passing through the center of the third diffraction grating track T ₃
It becomes a light source for irradiation of the diffraction grating track.

The detection system for the first diffraction grating track T ₁ is basically the same as that of Japanese Patent Publication No. 6-38050. However,
For simplification of description, the optical system for obtaining the 90-degree phase difference signal is omitted here. The laser beam for irradiating the first diffraction grating track is divided into two by the half mirror HM ₃ .
After that, both beams are reflected by the mirrors M _{2 and} M ₃ , and are symmetrically incident on the same point of the first diffraction grating track T _{1 at} the same incident angle. The first-order diffracted light L ₁ passing from the mirror M ₂ through the first diffraction grating track T ₁ is directed to the half mirror HM ₄ . The −1st-order diffracted light L _1c passing through the first diffraction grating track T ₁ from the mirror M ₃ is directed to the half mirror HM ₅ .
Beam reflected respectively by the half mirror HM _4, HM ₅ are mixed by the half mirror HM _6, make a photoelectric conversion element interference fringe on (light receiving element) PD _1, where it is converted into an electric signal.

The laser beam for irradiating the second diffraction grating track is reflected by the mirror M ₄ , and the second diffraction grating track T ₂
Is incident on. Then, the diffracted first-order diffracted light L ₂ goes to the half mirror HM ₇ . On the other hand, the beam of the first-order diffracted light L ₁ diffracted by the first diffraction grating track T ₁ and transmitted through the half mirror HM ₄ is reflected by the mirror M ₅ and travels to the half mirror HM ₇ . Half mirror HM
_{At 7} , the two beams L _{2 and} L ₁ are mixed and form an interference fringe on the photoelectric conversion element (light receiving element) PD ₂ , where they are converted into electric signals.

[0011] The third diffraction grating tracks irradiated laser beam is reflected by the mirror M _6, M _7, is incident on the third diffraction grating track T _3. Therefore, the diffracted −1st order diffracted light L
_3c heads to the half mirror HM ₈ . On the other hand, the beam of the −1st-order diffracted light L _1c diffracted by the first diffraction grating track T ₁ and transmitted through the half mirror HM ₅ is the mirror M.
₈ is reflected by, toward the half mirror HM _8. The two beams L _{3c and} L _1c are mixed by the half mirror HM ₈ to form interference fringes on the photoelectric conversion element (light receiving element) PD ₃ and converted into an electric signal there.

Here, when the electric field of each diffracted light is represented by the complex amplitude of the displacement x of the scale,

(Equation 1) However, all the amplitudes were set to the same 1.

[0013] Therefore, the electric field E ₁ of the interference fringes appearing on the light-receiving element PD ₁ is

(Equation 2)

Since the intensity of light is proportional to the square of the absolute value of the complex amplitude of the electric field, the intensity I ₁ of this interference light is

(Equation 3)

Therefore, the signal detected by the light receiving element PD ₁ periodically changes at a pitch twice the grating pitch P ₁ with respect to the movement x of the scale S. The pitch P _m1 is expressed by _{P m1 = P 1/2 ..................................................................} (7). For example, the lattice pitch P ₁ of the first diffraction grating track T ₁ is 0.5 [μm], the light receiving element PD ₁
The pitch P _m1 of the signal detected at is P _m1 = 0.5 / 2 = 0.25 [μm].

[0016] Similarly, the electric field E ₂ of the interference fringes appearing on the light-receiving element PD ₂ is

(Equation 4)

The intensity I _{2 of the} interference light is

(Equation 5)

[0018] Therefore, the signal detected by the light receiving element PD ₂ from the grating pitch P ₂ of the grating pitch P ₁ of the first diffraction grating track T ₁ to the movement x of the scale S and the second diffraction grating track T ₂ , The cycle changes at the pitch P _m2 calculated as follows. P _m2 = 1 / {(1 / P ₁ )-(1 / P ₂ )} = (P ₁ · P ₂ ) / (P ₂ −P ₁ ) ……………………………… (10)

Here, in order to set P _m2 to be k ₁ times P _m1 , from formulas (7) and (10), P _m2 = k ₁ · P _m1 (P ₁ · P ₂ ) / ( _{P 2 -P 1) = k 1} · P 1/2 P 2 = (k 1 · P 1) / (k 1 -2) becomes .......................................... (11).

For example, if k ₁ = 64 times, P ₁ = 0.5 [μm] as described above, and P ₂ = (64 × 0.5) / (64-2) = 0.516129 [μm] ], A periodic signal having a pitch of P _m2 = 64 × 0.25 = 16 [μm] can be obtained.

[0021] Similarly, the electric field E ₃ of the interference fringes appearing on the light-receiving element PD ₃ is

(Equation 6)

The intensity I _{3 of the} interference light is

(Equation 7)

[0023] Therefore, the signal detected by the light receiving element PD ₃ from the grating pitch P ₁ and the grating pitch P ₃ of the third diffraction grating track T ₃ of the first diffraction grating track T ₁ to the movement x of the scale S , With a pitch P _m3 calculated as follows. P _m3 = 1 / {(1 / P ₁ )-(1 / P ₃ )} = (P ₁ · P ₃ ) / (P ₃ −P ₁ ) ……………………………… (14)

Here, in order to set P _m3 to be k ₂ times P _m1 , P _m3 = k ₂ · P _m1 (P ₁ · P ₃ ) / (from equations (7) and (14). _{P 3 -P 1) = k 1} · P 1/2 P 3 = (k 2 · P 1) / become _{(k 1 -2) ................................. (15} ).

For example, when k ₂ = 64 × 64 = 4096 times, P ₁ = 0.5 [μm] as described above, and P ₃ = (4096 × 0.5) / (4096-2) = 0 If set to 0.500244 [μm], a periodic signal having a pitch of P _m3 = 4096 × 0.25 = 1024 [μm] can be obtained.

As described above, since a plurality of diffraction grating tracks having slightly different pitches may be formed to extract a signal having a very long pitch, one scale manufacturing technique,
For example, it can be made with holographic technology. Further, since the detection systems for obtaining the detection signals of the respective pitches are basically the same, it is possible to minimize the size increase and complexity of the detector.

As described above, the three pitches P _m1, P
A periodic signal of _m2, P _m3 can be obtained, but in reality it is 9
It is necessary to insert an optical system for detecting a 0-degree phase difference (shifted by ¼ cycle of pitch) signal to obtain a total of six detection signals. Incidentally, as an optical system for detecting a 90-degree phase difference signal, each half mirror HM6 _, HM, like the grating interference type displacement detection device described in Japanese Patent Publication No. 6-38050.
_7, a beam splitter is provided in the rear of the HM _8, the mixed wave mixed with the half mirror HM _6, HM _7, HM ₈ and 2 minutes,
By inserting a quarter wave plate in one optical path,
It is possible to obtain a detection signal having a phase difference of 90 degrees from the detection signal of the other mixed wave.

Therefore, the pitch P thus obtained is
The signal of _m1 is I _1cos and I _1sin , and the signal of pitch P _m2 is I _2cos
6 and I _2sin and a signal having a pitch P _m3 are expressed as I _3cos and I _3sin , and the absolute position data X _abs in the range of the pitch P _m3 is obtained by calculating these with an electric circuit.
This will be described with reference to the circuit block diagram shown in FIG.

In FIG. 6, two signals I _1cos and I _1sin having a 90-degree phase difference are passed through the phase conversion circuit 1, and the position (phase θ ₁ ) in one cycle of the pitch P _m1 is calculated.
The phase conversion circuit 1 is generally called an interpolation circuit,
There are several methods, but here, the A / D converter 11
A method using A and 11B and the memory (phase data conversion ROM) 12 will be described. Input signals I _1cos and I _1sin are A /
A / D conversion is performed by the D converters 11A and 11B, and the output data specifies the address of the phase data conversion ROM 12.
The phase data conversion ROM 12 stores phase information determined by a combination of input data. The phase in this case is 0
When set to have discrete values up to 249, P _m1 =
In the case of 0.25 [μm], the resolution is 1 nm.

_With respect to I _2cos and I _2sin , the same phase conversion circuit 2 is used to calculate the phase θ ₂ . The phase in this case is a discrete value from 0 to 255. For I _3cos and I _3sin , the same phase conversion circuit 3 is used to calculate the phase θ ₃ . The phase in this case is a discrete value from 0 to 255.

FIG. 7 shows changes in the respective phases θ _1, θ _2, θ ₃ with respect to the movement x of the scale S. Pitch P
_{Since m2} is 1/64 of the pitch P _m3 and the phase resolution of θ ₃ is set to 1/256 of P _m3 , it has a smaller (higher) resolution than P _m2 . Similarly, the pitch P _m1 is 1/64 of the pitch P _m2 , and the phase resolution of θ ₂ is P _m2.
Since it is set to 1/256, the resolution is smaller (higher) than P _m1 . In this way, by making the phase resolution of the one-step-long pitch smaller (higher) than the one-step-shorter pitch, it is possible to specify the number of cycles of the long pitch in the short-pitch phase. it can.

In FIG. 7, when the scale S stops at a certain position, the phase θ ₁ is θ ₁ ′, θ ₂ is θ ₂ ′, and θ ₃ is θ ₃ ′.
Is shown. θ ₂ ′ is the M th period in pitch P _m3 from θ ₃ ′, and θ ₁ ′ is the N th period in pitch P _m2 from θ ₂ ′. It can be specified by performing a logical operation. For example, in FIG.
The four steps of ₃ correspond to the pitch P _m2 . Then θ ₂ '
In order to specify that is the M-th of P _m3 , the quotient obtained by dividing θ ₃ 'by 4 is obtained.

However, since the time when θ ₂ switches from 255 to 0 and the step of θ ₃ do not always coincide with each other, the following calculation is performed to provide redundancy. θ
_If 3'is divided by 4, the quotient is m, and the remainder is s ₁ , then s
_{If 1} = 0 and 128 ≦ θ ₂ ′, then M = m−1. If s ₁ = 3 and θ ₂ ′ <128, then M = m +.
1. Under other conditions, M = m. Also, θ ₁ 'is P
It is also the same as specifying the Nth position in _m2 .
If θ ₂ 'is divided by 4, the quotient is n, and the remainder is s ₂ , then
If s ₂ = 0 and 125 ≦ θ ₁ ′, N = n−1. If s ₂ = 3 and θ ₁ ′ <125, N = n +.
1. Under other conditions, N = n.

After specifying M and N from θ ₃ ′ and θ ₂ ′ in this way, X _abs = M · P _m2 + N · P _m1 + (θ ₁ ′ / 250) P _m1 …………………… (16) The absolute position data X _abs can be calculated. However, it is assumed that the numbers M and N start from 0. By the above, a high resolution grating interference type displacement detection device capable of reading the absolute position between the pitches P _m3 of 1024 [μm] with a resolution of 1 nm can be realized.

However, since the scale S used in the above-mentioned grating interference type displacement detecting device has a plurality of diffraction grating tracks T _1, T _{2 and} T ₃ which are parallel to each other in the moving direction, the scale dimension of the scale S is large. There was a problem of becoming. In addition, there is a problem that the optical system for guiding the laser beam from the light source (laser diode LD ₁ ) to each diffraction grating track T _1, T _2, T ₃ is complicated.

It is an object of the present invention to provide a grating interference type displacement detecting device which eliminates the drawbacks while maintaining the advantages of the grating interference type displacement detecting device proposed by the present applicant. In other words, it is a high-resolution displacement detection device that can be scaled by one manufacturing technology, and the detector does not become large and complicated, and has no restriction on the moving speed. It is an object of the present invention to provide a grating interference type displacement detection device which can be performed and can simplify an optical system for guiding coherent light to a scale.

[0037]

DISCLOSURE OF THE INVENTION A grating interference type displacement detecting apparatus of the present invention comprises a scale having a diffraction grating in which a plurality of grating patterns having different grating angles and slightly different grating pitches are multiply formed. An interference fringe is formed by mixing a light source that irradiates a diffraction grating of this scale with a light beam and diffracted light of different orders generated by one grating pattern of diffracted light of different directions generated by each grating pattern of the diffraction grating. Detection including a first light mixing means for producing, second light mixing means for mixing the diffracted lights of the same order generated by the different grating patterns to form interference fringes, and a light receiving element for photoelectrically converting these interference fringes And a plurality of detection signals having different periods are simultaneously generated according to the relative displacement between the scale and the detector.

[0038]

According to the grating interference type displacement detector of the present invention, diffracted lights of different orders generated in one grating pattern among diffracted lights of different directions generated in each grating pattern of the diffraction grating are mixed and interfered. The first light mixing means for forming a fringe can obtain a detection signal which changes in a short period, and the second light mixing means for mixing the diffracted light of the same order generated by different grating patterns to form an interference fringe. It is possible to obtain a detection signal that changes with a long period. Further, in order to obtain these detection signals, it is sufficient to form a plurality of grating patterns having different grating angles and slightly different grating pitches on the scale, so that one scale manufacturing technique can be used. Moreover, since the plurality of grating patterns are multiply formed on the scale, the width dimension of the scale can be reduced and the optical system for guiding the coherent light to the scale can be simplified. Also, since the detection system that obtains the detection signal of each pitch is basically the same,
It is possible to suppress the size and complexity of the detector. Of course, there is no restriction on the moving speed.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will now be described with reference to the drawings.
This will be described in detail. FIG. 1 shows the displacement detection device according to the present embodiment.
Indicates a scale. As shown in (A), scale S
Has a diffraction grating G formed therein. The diffraction grating G is a grating
The angles are different from each other and the grid pitch is slightly different.
Multiple (three) grid patterns PT _1,PT_2,PT_ThreeMany
It is formed in layers (overlapping in order).

First grid pattern PT₁Is shown in Fig. 1 (B)
As shown, the lattice angle with respect to the moving direction of the scale S is
Right angle (α₁= 90 degrees) and the grid pitch (shift
Pitch in the moving direction is P₁Is formed. Second grid
Pattern PT_TwoScales as shown in FIG.
An angle (α_Two= 45
Angle, and the grid pitch (pitch in the moving direction).
H) is P_Two(P_Two> P₁) Is formed. Third lattice
Pattern PT_ThreeScales as shown in FIG.
The lattice angle is the second lattice pattern PT with respect to the moving direction of S.
_TwoAn angle (α_Three= 45 degrees)
The grid pitch (pitch in the moving direction) is P_Three(P_Two>
P_Three> P ₁) Is formed. By the way, like this
When the scale S is made by holography technology,
It can be made by sequentially interfering light from three directions. Ah
Even if you use an EB (electronic drawing) device,
There are problems in terms, but it is possible to manufacture.

FIG. 2 is a perspective view showing a detection optical system using the scale S of FIG. 1, and FIG. 3 is a view of the detection optical system seen from above. The optical system for obtaining the interference signal of the first grating pattern PT ₁ is basically the same as the Japanese Patent Publication No. 6-38050. However, for simplification of description, the optical system for obtaining the 90-degree phase difference signal is omitted here. The laser beam emitted from the laser diode LD ₁ which is the light source is divided into two by the half mirror HM ₁ , and then both beams are reflected by the mirrors M _{1 and} M ₂ and symmetrically diffracted by the diffraction grating G at the same incident angle. Is incident on the same point. The incident point is P
Then, the surface formed by P, M _{1 and} HM ₁ is assumed to be installed parallel to the moving direction of the scale S.

The diffracted light that has passed through the diffraction grating G from the mirror M ₁ is one straight 0th-order light and three first-order diffracted lights L
Divided into _1, L _{2 and} L ₃ . The first-order diffracted light L ₁ diffracted by the first grating pattern PT ₁ proceeds to the half mirror HM ₂ on the moving direction of the scale S. The first-order diffracted light L ₂ diffracted by the second grating pattern PT ₂ proceeds to the mirror M ₄ which is out of the moving direction of the scale S. The first-order diffracted light L ₃ diffracted by the third grating pattern PT ₃ travels on the opposite side of the first-order diffracted light L ₂ with the _first-order diffracted light L ₁ interposed therebetween.

The diffracted light passing through the diffraction grating G from the mirror M _{2 is} also divided into one straight 0th-order light and three −1st-order diffracted lights L _1c, L _{2c and} L _3c . The −1st order diffracted light L _1c diffracted by the first grating pattern PT ₁ proceeds to the half mirror HM ₃ on the moving direction of the scale S. Second lattice pattern PT
_The −1st-order diffracted light L _2c diffracted by ₂ travels in a direction deviating from the moving direction of the scale S. The −1st order diffracted light L _3c diffracted by the third grating pattern PT ₃ travels to the mirror M ₆ on the opposite side of the −1st order diffracted light L _2c with the −1st order diffracted light L _1c interposed therebetween.

Of the first-order diffracted light L ₁ and the -1st-order diffracted light L _1c diffracted by the first grating pattern PT ₁ , the light reflected by the half mirrors HM _{2 and} HM ₃ is the half mirror HM _4.
Are mixed together to form interference fringes on the photoelectric conversion element (light receiving element) PD _{1 and} are converted into electric signals there. Here, by the half mirrors HM _2, HM _{3, and} HM ₄ , each lattice pattern P
_First light that forms interference fringes by mixing diffracted lights L _{1 and} L _1c of different orders generated by _one grating pattern PT ₁ among diffracted lights of different directions generated by T _1, PT _{2 and} PT ₃ A mixing means is configured.

The first-order diffracted light L ₁ transmitted through the half mirror HM ₂ is deflected in direction by the mirror M ₃ and proceeds to the half mirror HM ₅ . On the other hand, the first-order diffracted light L ₂ diffracted by the second grating pattern PT ₂ is bent in direction by the mirror M ₄ and proceeds to the half mirror HM ₅ . The two lights L _{1 and} L ₂ are mixed by the half mirror HM ₅ , and the photoelectric conversion element (light receiving element) PD
Interference fringes are created on ₂ and converted there into electrical signals. Here, the second light mixing for mixing the diffracted lights L _{1 and} L ₂ of the same order generated by different grating patterns PT _{1 and} PT ₂ by the half mirror HM ₅ and the mirrors M _{3 and} M ₄ to form an interference fringe Means are configured.

The −1st-order diffracted light L _1c transmitted through the half mirror HM ₃ is bent by the mirror M ₅ and proceeds to the half mirror HM ₆ . On the other hand, the -1st-order diffracted light L _3c diffracted by the third grating pattern PT _3, the process proceeds to the half mirror HM ₆ bent direction by the mirror M _6. 2 with half mirror HM ₆
The two lights L _{1c and} L _3c are mixed and form interference fringes on the photoelectric conversion element (light receiving element) PD ₃ , where they are converted into electric signals. Here, half mirror HM ₆ and mirrors M _5, M
₆ constitutes a second light mixing unit that mixes diffracted lights L _{1c and} L _3c of the same order generated by different grating patterns PT _{1 and} PT ₃ to form interference fringes.

In this way, with respect to the moving direction of the scale S, the diffraction grating G in which a plurality of grating patterns PT _1, PT _{2 and} PT ₃ having different grating angles (α _1, α _2, α ₃ ) are formed in multiple layers By using, the respective lattice patterns PT _1, PT
The direction of the diffracted light diffracted by _2, PT ₃ can be changed. Therefore, since the respective grating pattern information can be taken out independently, the displacement can be detected in the same manner as the one using the plurality of diffraction grating tracks shown in FIGS.

That is, similarly to the grating interference type displacement detection device shown in FIGS. 4 to 7, P ₁ = 0.5 [μm] P ₂ = 0.516219 [μm] P ₃ = 0.500244 [μm] Then, the interference signal at the light receiving element PD ₁ is 0.25 [μ
m], the interference signal at the light receiving element PD ₂ is 16 [μm], and the interference signal at the light receiving element PD ₃ is a periodic signal having a pitch of 1024 [μm].

Therefore, if an optical system for detecting a 90-degree phase difference signal is inserted to obtain a total of 6 detection signals and these are input to the detection circuit shown in FIG. 6, a detection signal in the range of 1024 [μm] is obtained. A high-resolution grating interference type displacement detection device capable of reading the absolute position with 1 nm resolution can be realized. Moreover, according to this embodiment, the plurality of grating patterns PT _1, PT _{2 and} PT ₃ are multiply formed on the scale S, so that the advantages of the grating interference type displacement detecting device shown in FIGS. 4 to 7 are maintained. However, the drawback can be solved. That is, the width dimension of the scale S can be reduced, and the optical system for guiding the coherent light to the scale S can be simplified.

In the above embodiment, three grid patterns PT
_The diffraction grating G in which _1, PT _{2 and} PT ₃ are multiply formed is used.
If four or more grating patterns with different grating angles are multiplexed to form a diffraction grating and more information is obtained by increasing the number of optical systems, more accurate or more It is possible to detect the absolute position over a long stroke.

[0051]

According to the present invention, the scale can be scaled by one manufacturing technique, the detector does not become large and complicated, and the movement speed is not restricted, and the high resolution grating interference type displacement is provided. A detection device can be obtained. Moreover, the width dimension of the scale can be reduced, and the optical system for guiding the coherent light to the scale can be simplified.

[Brief description of the drawings]

FIG. 1 is a diagram showing a scale used in an embodiment of a grating interference type displacement detection device according to the present invention.

FIG. 2 is a perspective view showing a detection optical system used in the above embodiment.

FIG. 3 is a view of the detection optical system of FIG. 2 seen from above.

FIG. 4 is a perspective view showing the basic principle of a grating interference type displacement detection device according to the present invention.

FIG. 5 is a plan view of the scale used in FIG.

6 is a block diagram showing a detection circuit used in FIG. 4. FIG.

FIG. 7 is a diagram showing changes in phases θ _1, θ _{2 and} θ ₃ obtained in FIG.

[Explanation of symbols]

S scale G diffraction grating PT _1, PT _2, PT ₃ grating pattern PD ₁ laser diode (light source) HM _2, HM _3, HM ₄ half mirror (first light mixing means) HM ₅ half mirror and M _3, M ₄ Mirror (second light mixing means) HM ₆ half mirror and M _5, M ₆ mirror (second light mixing means) PD _1, PD _2, PD ₃ photoelectric conversion element (light receiving element)

Claims (1)

[Claims] 1. A scale having a diffraction grating in which a plurality of grating patterns having different grating angles and slightly different grating pitches are multiply formed, a light source for irradiating the diffraction grating of this scale with a light beam, and the diffraction First diffusing means for mixing diffracted light of different orders generated by one grating pattern among diffracted lights of different directions generated by each grating pattern of the grating to form interference fringes, and generating by the different grating pattern A second light mixing means for mixing the diffracted lights of the same order to form interference fringes, and a detector including a light receiving element for photoelectrically converting these interference fringes, and the relative displacement between the scale and the detector A grating interference type displacement detection device characterized in that it simultaneously generates a plurality of detection signals having different cycles.