JPH08327321A - Apparatus for detecting displacement data - Google Patents

Abstract

PURPOSE: To easily obtain a movement data of high resolution while avoiding a collision of a first and a second scales, by setting a distance between a phase grating and an amplitude grating to satisfy a specified condition when the relative displacement data of the first and second scales is obtained. CONSTITUTION: The luminous flux emitted from a light source LGT is turned to a parallel luminous flux R by a collimator lens CL and shed onto a first scale D. A transmitting-type phase grating GT1 is recorded on the scale D. The luminous flux entering the phase grating GT1 is diffracted and made incident on a second scale having amplitude gratings GT2A-GT2D. Interference lights based on diffraction lights diffracted at the amplitude gratings GT2A-GT2 D are detected by a photodetecting means S comprising photodetecting elements SA, SB, SC, SD. When a relative displacement data of the first scale D and the second scale is to be obtained, the distance (h) between the phase grating GT1 and the amplitude grating GT2A-GT2D is set to satisfy (Pl<2> -4λ<2> )/(8λ)<h.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement information detecting apparatus, and more particularly to irradiating a grating attached to two scales that move relative to each other with a light beam so as to obtain a phase- or intensity-modulated signal light obtained therefrom. It is suitable for an encoder or the like that detects displacement information such as position, displacement amount, displacement direction, speed, acceleration, and the like regarding the two scales by detecting.

[0002]

2. Description of the Related Art Conventionally, an incremental encoder is often used as a device for measuring relative displacement information (displacement amount, velocity, acceleration, etc.) of an object with high accuracy. The incremental encoder forms an amplitude grating (bright and dark grating) GT1 having a pitch of 100 microns on the first scale which moves relatively, illuminates the luminous flux on the amplitude grating GT1, and transmits the light transmitted thereat to the first scale. The light is guided to a second scale provided with an amplitude grating GT2 having the same pitch as the pitch, and the amplitude grating GT2 is transmitted therethrough. At this time, when the transmissive portions of the two gratings overlap, the transmitted light is maximized, and when the two gratings are shifted by 1/2 pitch and overlap, the transmitted light is minimized. The generated light flux is received by the light receiving means.

In the light receiving means, the 1 generated when the first scale and the second scale move relative to each other by one pitch of the grating.
The change in the light amount of the cycle is detected, and the cycle at this time is counted to obtain the incremental signal. In this incremental encoder, the measurement resolution of the relative movement amount is the same as the grating pitch.

[0004]

Recent encoders are required to have high resolution for detecting displacement information. In the conventional incremental type encoder described above,
The grating pattern (bright and dark striped pattern) formed by the transmitted light from the amplitude grating GT1 becomes blurred due to the diffraction phenomenon of light as the distance from the amplitude grating GT1 increases.

For this reason, when the transmitted light is detected by the light receiving means by superimposing it on the amplitude grating GT2, the contrast of the intensity modulation of the light quantity due to the relative movement decreases. Therefore, in order to reduce the influence of the diffraction phenomenon of light, the first amplitude grating and the second amplitude grating are arranged as close to each other as possible.

For example, in order to improve the resolution of the encoder (EX. Incremental signal period pitch 10 μm), the encoder of the conventional system is used by using the first 10 μm pitch amplitude grating and the second 10 μm pitch amplitude grating. , The interval between the first amplitude grating and the second amplitude grating is calculated by
It is necessary to make them close to each other to about 0 μm. However, since the two scales that move relative to each other are generally constrained by the stage including various guide mechanisms,
If the distance between the two is narrowed, the first
The scale and the second scale collide with each other, causing a damage accident.

Further, in order to increase the resolution of the encoder (EX. Incremental signal period pitch 0.5 μm),
When a signal is divided by a known electric interpolation circuit to improve the resolution, an encoder of a system using the first amplitude grating and the second amplitude grating forms a sinusoidal change in brightness of signal light. Therefore, there is a problem that the accuracy is poor and the number of divisions cannot be increased.

The present invention is directed to the first scale and the second scale which move relative to each other.
By properly setting the pitch of the grating provided on the scale, the type of the grating, and the interval between both gratings, and the characteristics of the light source means, the bright and dark fringes utilizing the diffraction interference phenomenon of light are firstly formed. By stably generating at a position relatively distant from the scale and providing the second grating there, collision information between the first scale and the second scale can be avoided and high-resolution movement information can be easily obtained. An object is to provide a displacement information detection device.

Another requirement is high reliability during high temperature operation. In particular, a rotary encoder used in combination with a motor aims to provide a displacement information detection device that can be used in an environment of about 80 ° C.

[0010]

DISCLOSURE OF THE INVENTION The displacement information detecting apparatus of the present invention comprises: (1-1) Injecting a light beam having a wavelength λ from a light source means into a phase grating having a grating pitch P1 provided on the first scale, The modulated light from the phase grating is made incident on the amplitude grating on the second scale arranged opposite to the first scale, the modulated light from the amplitude grating is received by the light receiving means, and the signal from the light receiving means is used to generate the modulated light. When the relative displacement information between the first scale and the second scale is obtained, the interval h between the phase grating and the amplitude grating is set to satisfy (P1 ² -4λ ² ) / (8λ) <h. It has a feature.

(1-2) A light flux having a wavelength λ from the light source means is made incident on a phase grating having a grating pitch P1 provided on the first scale, and the modulated light from the phase grating is arranged to face the first scale. The modulated light from the amplitude grating is incident on the amplitude grating on the second scale, the light receiving means receives the modulated light, and the relative displacement information between the first scale and the second scale is obtained using the signal from the light receiving means. At this time, the distance h between the phase grating and the amplitude grating is

[0012]

[Equation 2] It is characterized by setting so as to satisfy.

In addition, the configuration (1-1) or the configuration (1-
2), (1-1-1) The phase grating is composed of a phase diffraction grating having an uneven cross-sectional shape, and is set so that the phase difference between the light flux passing through the concave portion and the convex portion is λ / 2. That

(1-1-2) When the grating pitch of the amplitude grating is P2, P1 = 2 · P2.

(1-1-3) Both the phase grating and the amplitude grating are radial gratings, and the light receiving means obtains an incremental signal from the modulated light passing through the phase grating and the amplitude grating. , N1 = N2 / 2, where N1 and N2 are the number of gratings corresponding to one round of the amplitude grating, respectively.

(1-1-4) A light flux of wavelength λ from the light source means is made incident on a phase grating having a grating pitch P1 provided on the first scale, and the modulated light from the phase grating is gapped to the first scale. The modulated light from the amplitude grating is made incident on an amplitude grating on the second scale, which is opposed to the first scale and the second scale by using a signal from the light receiving means. When obtaining the relative displacement information of, the light source means has a surface emitting element and a collimator lens, the length of the component of the arrangement direction of the phase grating of the surface emitting element is d, and the focal length of the collimator lens is f. Then, d ≦ 0.375 · f · P1 / h.

(1-1-5) A periodic incremental signal is obtained from the light receiving means with the relative movement of the first scale and the second scale. And so on.

(1-6) A light flux of wavelength λ from the light source means is made incident on a phase grating having a grating pitch P1 provided on the first scale, and the modulated light from the phase grating has a gap h on the first scale. Through the amplitude grating on the second scale disposed opposite to each other, the modulated light from the amplitude grating is received by the light receiving means, and the signal from the light receiving means is used to make the relative between the first scale and the second scale. When the displacement information is obtained, the light source means has a surface emitting element and a collimator lens, where the length of the component of the arrangement direction of the phase grating of the surface emitting element is d and the focal length of the collimator lens is f. The feature is that d ≦ 0.375 · f · P1 / h.

Further, it is characterized in that a periodic incremental signal is obtained from the light receiving means in accordance with the relative movement of the first scale and the second scale.

[0020]

Embodiment 1 FIG. 1 is a perspective view of the essential portions of Embodiment 1 of the present invention. In this embodiment, two objects (GT1, G1
It shows a case where the invention is applied to a linear encoder that detects linear displacement information of T2).

In the figure, a light beam emitted from a light source means LGT having a low coherency such as an LED is converted into a parallel light beam R by a collimator lens CL and illuminated on a scale (first scale) D which moves relative (rotationally). It Hereinafter, the luminous flux component emitted from the center of the light emitting portion of the LED will be described.

A transmission type phase grating GT1 is provided on the scale D.
(Lattice pitch P1) is recorded. Phase grating GT1
The cross-sectional shape of is a lamella lattice, and the unevenness ratio is 1: 1,
Refractive index n of constituent materials, wavelength λ of light source, step Δ = λ / (2
X (n-1)). The amount of transmitted light due to unevenness is the same.

The light beam incident on the phase grating GT1 is transmitted and diffracted, and diffracted lights of a predetermined order interfere with each other and enter a second scale (not shown) provided with an amplitude grating (slit grating) GT2 having a grating pitch P2. To do. The first scale and the second scale are arranged opposite to each other at an interval h that satisfies the condition described later. The amplitude grating GT2 has a phase of 1 /
Two amplitude gratings GT2A, GT arranged with a shift of 4 periods
2B and four amplitude gratings GT2C and GT2D each having a half-cycle phase difference from them.

The interference light based on the diffracted light diffracted by each of the amplitude gratings GT2A to GT2D is received by the light receiving means S composed of four light receiving elements SA, SB, SC, SD provided correspondingly. Light receiving element SA, SB, SC, SD
From, sinusoidal analog signals are obtained by shifting each other by ¼ cycle. A sinusoidal analog signal (incremental signal) is processed by a processing circuit (not shown) to shift the four phases, and the first scale (phase grating GT1) and the second scale are processed.
Movement information such as relative movement amount and movement direction of the scale (amplitude grating GT2) is obtained. As a signal processing method at this time, for example, the method proposed by the present applicant in Japanese Patent Laid-Open No. 7-83612 can be applied.

Next, a method of setting the interval h between the first scale (phase grating GT1) and the second scale (amplitude grating GT2) in this embodiment will be described. In this example,
The phase of the wavefront of the parallel light flux that passes through the transmission type phase grating GT1 is modulated (optically modulated) by the unevenness of the phase grating. 2A and 2B show the phase grating GT1 at this time.
FIG. 3 is an explanatory diagram showing a state in which the phase of a wavefront is modulated by a concavo-convex light beam incident on a and a light amount distribution due to a change in the wavefront as gradation density.

In FIG. 2, the optical path length difference from the unevenness of the phase grating GT1 is 0 at the upper part of the uneven boundary portion near the phase grating GT1. Therefore, at the upper part of the uneven boundary, the phase grating G
The wavefronts overlap and interfere with each other due to the phase difference of π due to T1.
For this reason, when the light fluxes from both the irregularities reach, interference causes a light quantity lowering portion.

Further away from the phase grating GT1, at the upper part of each of the concave and convex boundary portions at a specific distance h0, the light fluxes from the concave and convex parts reach under the condition of the optical path length difference λ due to the diffraction phenomenon. As a result, they cancel each other out due to interference and become dark. Naturally, the difference in optical path length is 0 at the upper part of the uneven boundary.
Therefore, it is a light quantity lowering portion. The contrast of the light-dark pattern at this position is very low.

Further away from the phase grating GT1 and above each concave and convex boundary portion at a specific distance h1, the light fluxes from the concave and convex portions have an optical path length difference of 0.5 due to the diffraction phenomenon.
They will arrive under the condition of λ, and they will be strengthened by interference and become brighter. Since the difference in optical path length is 0 at the upper part of the uneven boundary portion, it is a light amount lowering portion. The cycle of the light-dark pattern is half the grating pitch P1 of the phase grating GT1, and the intensity distribution of the light-dark pattern has a sine wave shape.

Further away from the phase grating GT1, interference of emitted light from a wide range of unevenness is increased due to a diffraction phenomenon, and the light quantity on the upper and lower parts of the unevenness due to cancellation due to phase shift becomes remarkable, and eventually a sinusoidal bright and dark pattern. Disappears.

Therefore, in the present embodiment, as shown in FIG. 1, at a position h1 where the contrast of the bright and dark pattern generated in the phase grating GT1 is highest, a fixed transmission type amplitude grating (having a grating pitch P2 = P1 / 2) ( Slit grid) GT2 is arranged.

At this time, the amplitude grating GT2 outputs a transmitted light having a sine wave shape and a bright / dark signal light with a high contrast. At this time, the light-dark cycle is two cycles for each movement amount P1 of the scale D. In the present embodiment, the transmitted light at this time is detected by the light receiving means S to obtain relative movement information of the phase grating GT1 and the amplitude grating GT2.

The interval h between the phase grating GT1 and the amplitude grating GT2 is set as follows. For example, if the grating pitch P1 of the scale is 20 μm and the grating pitch P2 of the fixed grating is 10 μm, the encoder has a resolution of 10 μm, and the gap between the scale and the fixed grating at that time can be set to about 200 μm. . With this value, the problem of collision during relative movement of the scale is unlikely to occur.

Next, this phenomenon will be described in detail. The light flux emitted from the convex portion and the concave portion of the phase grating GT1 made of a refractive index medium is such that the concave portion is π relative to the convex portion with reference to the convex surface.
Only the phase of the wavefront is advanced.

The circular arc shape wa in FIG. 2 indicates a wavefront. Focusing on the light flux component at the center of each uneven portion,
The wavefront w1 emitted from the concave portion and the wavefront w2 emitted from the convex portion are
As the distance increases, they spread out in an arc and interfere with each other.
And, the overlap of the wavefronts is always λ /
Two shifts. That is, the upper part of the boundary portion of the unevenness becomes dark because the light flux intensity is weakened by the interference.

On the other hand, in the upper part of the concave part, the wave fronts of the convex parts are regularly strengthened or weakened. Similarly, in the upper part of the convex part, the wave fronts of the concave parts are regularly strengthened or weakened.

(A) When the distance h from the surface of the phase grating GT1 (the surface of the convex portion) satisfies h = (P1 ² −λ ² ) / (4π) (1), the linear movement from the concave portion is performed. The difference between the optical path length of the light beam w1a component and the optical path length of the obliquely traveling light beam w2b component from the convex portion is 0.5λ. The phase of the wave front of the light flux reaching from the concave portion is 2π · h1 / λ−π The phase of the wave front of the light flux reaching from the convex portion is 2π {h1 + (0.5λ)} / λ, and the phase difference between the two is 2π. Then, the interference strengthens each other and the strength becomes maximum.

At the same time, the difference between the optical path length of the straight light beam w2a component from the convex portion and the optical path length of the oblique light beam w1b component from the concave portion becomes λ / 2. The phase of the wave front of the light flux reaching from the convex portion is 2π · h1 / λ The phase of the wave front of the light flux reaching from the concave portion is 2π {h1 + (0.5λ)} / λ−π, and the phase difference between them is 0. Intense interference with each other, maximizing the strength. As a result, the contrast of the light-dark pattern at the position h1 is maximized, and the light-dark pattern has a sinusoidal distribution.

(B) In a place where the distance h from the surface (the surface of the convex portion) of the phase grating GT1 satisfies h = (P1 ² -4λ ² ) / (8λ), the optical path length of the straight light flux w1a component from the concave portion. And the optical path length of the oblique light flux w2b component from the convex portion becomes λ. The phase of the wave front of the light flux reaching from the concave portion is 2π · h0 / λ−π The phase of the wave front of the light flux reaching from the convex portion is 2π (h0 + λ) / λ, and the phase difference between them becomes 3π, which is weakened by interference. However, the strength is extremely small. At the same time, the difference between the optical path of the straight light flux w2a component from the convex portion and the optical path of the oblique light flux w1b component from the concave portion becomes λ. The phase of the wavefront of the light flux reaching from the convex portion is 2π · h0 / λ The phase of the wavefront of the light flux reaching from the concave portion is 2π (h0 + λ) / λ−π, and the phase difference between the two becomes π and is weakened by interference. However, the strength is extremely small. As a result, the contrast of the bright-dark pattern at this position h0 becomes minimal.

(C) At a place where the distance h from the surface (the surface of the convex portion) of the phase grating GT1 satisfies h = (P1 ² -9λ ² ) / (12λ), the optical path length of the straight light flux w1a component from the concave portion. Immediately after that, the difference from the optical path length of the oblique light flux w2b component from the convex portion becomes 1.5λ. The phase of the wave front of the light flux reaching from the concave portion is 2π · h1 / λ−π The phase of the wave front of the light flux reaching from the convex portion is 2π {h1 + (1.5λ)} / λ, and the phase difference between them is 4π. , Interference strengthens each other and maximizes the strength. At the same time, the difference between the optical path length of the straight light flux w2a component from the convex portion and the optical path length of the oblique light flux w1b component from the concave portion becomes 1.5λ. The phase of the wave front of the light flux reaching from the convex portion is 2π · h1 / λ The phase of the wave front of the light flux reaching from the concave portion is 2π {h1 + (1.5λ)} / λ−π, and the phase difference between them is 2π. Then, the interference strengthens each other and the strength becomes maximum. However, due to the interference of the light flux from the adjacent uneven portion, the maximum of the contrast of the light-dark pattern at the position h2 is deviated, and the light-dark distribution is not sinusoidal.

Therefore, in this embodiment, (P1 ² -4λ ² ) /
If (8λ) <h is satisfied, a practical contrast can be obtained. Specifically, it is set so as to satisfy the expression (1).

By the way, the wavelength λ of the light beam from the light source LGT
= 0.66 μm, pitch P1 of the phase grating GT1 = 25 μm
Assuming m, the distances h1 and h0 are h1 = 236 μm and h0 = 118 μm. That is, the maximum contrast can be obtained by setting the gap with the amplitude grating GT2 to h1.

Next, the luminous flux components emitted from the periphery of the light emitting portion of the LED will be described. The phase of the wavefront of the parallel light flux R transmitted through the transmission phase grating GT1 is modulated by the unevenness similarly to the LED central portion light flux component. However, the light flux travels slightly obliquely depending on the focal length f of the collimator lens CL and the amount of deviation from the center of the light emitting portion.

FIGS. 3A and 3B are explanatory diagrams showing the gradation of the phase of the wavefront of the parallel light beam incident on the phase grating GT1 and the light quantity distribution due to the wavefront change, which are represented by gradation density. is there.

As shown in FIG. 3, in the upper part of the uneven environment portion near the grating GT1, when the light fluxes from both of the unevenness reach, the optical path length difference from the unevenness of the phase grating is 0, so the phase difference of π by the phase grating is Since the wavefronts overlap and interfere with each other, the interference causes a light quantity lowering portion.

Further away from the grating GT1, on the upper part of each unevenness of a certain specific distance h0, the light fluxes from the unevenness arrive under the condition of the optical path length difference λ due to the diffraction phenomenon, and they cancel each other out due to interference and become dark. Since the difference in optical path length is 0 at the upper part of the uneven boundary portion, it is a light amount lowering portion. The contrast of the light-dark pattern at this position is very low.

Further away from the grating GT1, the light fluxes from both of the irregularities at a specific distance h1 reach each other due to the diffraction phenomenon under the condition that the optical path length difference is 0.5λ, and they are strengthened by interference. Get brighter. Since the difference in optical path length is 0 at the upper part of the uneven boundary portion, it is a light amount lowering portion. The period of this light-dark pattern is the phase grating GT
At a half of the grating pitch P1 of 1, the intensity distribution of light and dark becomes sinusoidal.

Further, if the distance from the grating GT1 is increased, interference of the light emitted from the uneven surface in a wide range is increased due to the diffraction phenomenon, and the light quantity on the upper surface of the uneven surface is significantly reduced due to the cancellation due to the phase shift, and the sinusoidal bright-dark pattern disappears.

Comparing FIG. 2 and FIG. 3, the interference fringes are displaced in the space of the distance of the gap h1. This shift amount s is the gap h
And the inclination of the obliquely traveling light flux. Therefore, the interference fringes projected onto the space have a periodical change in contrast with the distance from the phase grating GT1 as shown in FIG. 4 in which the light amount distribution is represented by gradation density as in FIG. 3B, but the contrast decreases as the distance increases. Becomes noticeable.

Then, at the position of the gap h, the slit grating G
The brightness modulation contrast of the transmitted light when T2 is arranged decreases as the shift amount s increases. The contrast becomes 0 when the shift amount becomes 1/2 of the interference fringe pitch.

When the intensity distribution of the interference fringes in the space is set to I = Σ (sin (πx / P1)) ² and the LED light emitting portion emits light with substantially uniform luminance, the dark portion: Imin = ∫ _{-s / 2} ^{+ s / 2} (Sin (πx / P1)) ² dx bright part: Imax = ∫ _{−s / 2} ^{+ s / 2} (cos (πx / P1)) ² dx. However, P1 is the period (μm) of the irregularities of the grating GT1. Assuming that the practical contrast is 0.3 or more, the shift amount s at which contrast = (Imax−Imin) / (Imax + Imin) = (P1 / 2πd) sin (2πd / P1) = 0.3 is approximately 0. It becomes 375P.

That is, the deviation amount s of the interference fringes in the installation space of the slit grating GT2 is allowed to be ± 0.375P / 2.

Now, when the focal length of the collimator lens is f and the light emitting portion size of the surface light emitting element such as an LED (the length of the diffraction grating GT1 with respect to the arrangement direction of the grating) is d (μm), the deviation amount is s. Since s: h = d: f, d = f · s / f Therefore, the admissible d of the light emitting element size that allows a contrast of 0.3 is d ≦ 0.375 · f · P1 / h Become. In this embodiment, the design value is set in this range.
Incidentally, assuming that the optimum gap h when a point light source is used is h = (P1 ² −λ ² ) / (4λ) and the center wavelength λ of the light source used is = 0.66 μm, and the period P1 of the concavo-convex grating GT1 is 25 μm, h = 236 Since it is 0.6 μm, the focal length f of the collimator lens is f = 200.
If 0 μm is determined, d ≦ 79.2 μm is obtained.

When d = 0.5 · f · P1 / h, the spatial contrast becomes 0 in calculation. The light source size d
Is the length of the array orientation component of the grating GT1 when the shape of the light emitting portion is rectangular, square, circular, or elliptical.

FIG. 5 shows an example of measuring the contrast of the transmission modulated light from the slit grating by making an encoder utilizing these phenomena and changing the distance between the phase grating GT1 and the amplitude grating GT2. The wavelength of the light source λ = 0.66μ
m, the light emitting portion is 20 μm × 20 μm, and the focal length of the collimator lens is 2 mm. The minimum position and the maximum position of the contrast almost match the above description.

In the present embodiment, as described above, the phase grating GT
By setting the interval h between the 1 and the amplitude grating GT2 as in the equation (1) and by defining the light source size, high-contrast spatial interference light is obtained, which results in the first scale (phase grating GT1) and the second scale. The relative displacement information with the (amplitude grating GT2) is detected with high accuracy.

In this embodiment, the phase grating GT1 and the amplitude grating G are used.
Even if the interval h of T2 does not completely satisfy the expression (1),
Both distance h,

[0057]

(Equation 3) By setting as described above, a bright and dark pattern having a relatively good contrast can be obtained, and the object of the present invention can be substantially achieved.

In this embodiment, each element may be constructed as follows.

(A1) Phase grating GT1 and amplitude grating GT2
A radial phase grating recorded on a disk that rotates relative to the disk, and a radial amplitude grating, and a combination of these to form a rotary encoder.

(A2) The structure in which each amplitude grating of the amplitude grating GT2 is divided into a plurality of parts and the phases thereof are shifted from each other to shift the bright and dark timings of the transmission modulated light is changed.

(A3) Fixing the phase grating GT1 and moving the amplitude grating GT2.

(A4) Change the amplitude grating GT2 to another amplitude grating (reflection slit grating, prism array grating) instead of the slit grating.

(A5) Change the phase grating of the phase grating GT1 to one that gives a high and low distribution of the refractive index periodically, instead of a lamellar grating having irregularities.

[0064]

As described above, according to the present invention, by appropriately setting the grating pitches of the diffraction gratings provided on the first scale and the second scale that move relative to each other, and the distance between the two diffraction gratings, or By setting the characteristics of the light emitting element or the optical system, the pitch of the diffraction grating, and the spacing between both diffraction gratings, collision information between the first scale and the second scale can be avoided and high-resolution movement information can be easily obtained. A displacement information detection device can be achieved.

In addition, according to the present invention, good incremental signal light can be obtained even if the scale on which the first grating of 10 micron order is recorded and the second grating are arranged to face each other with a gap of 100 micron order. Obtained, small,
A displacement information detection device with high resolution, stability, and simple structure can be achieved. Further, since the signal light has a good sine wave shape, the resolution can be improved by a known electrical interpolation circuit to achieve a high resolution displacement information detecting device.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of the light-dark distribution generation by the light transmitted through the phase grating of FIG.

FIG. 3 is an explanatory diagram of the light-dark distribution generation by the phase grating transmitted light in FIG.

FIG. 4 is an explanatory diagram of the light-dark distribution generation by the phase grating transmitted light in FIG.

FIG. 5 is an explanatory diagram of a measurement example of signal light contrast according to the first embodiment of the present invention.

[Explanation of symbols]

 LGT light source means CL collimator lens D first scale GT1 phase grating GT2 amplitude grating S light receiving means R luminous flux

Claims (8)

[Claims] 1. A light flux of wavelength λ from a light source means is made incident on a phase grating having a grating pitch P1 provided on the first scale,
The modulated light from the phase grating is made incident on the amplitude grating on the second scale arranged opposite to the first scale, the modulated light from the amplitude grating is received by the light receiving means, and the signal from the light receiving means is used. When obtaining the relative displacement information between the first scale and the second scale, the interval h between the phase grating and the amplitude grating is set so as to satisfy (P1 ² -4λ ² ) / (8λ) <h Displacement information detection device characterized by. 2. A light flux having a wavelength λ from a light source means is made incident on a phase grating having a grating pitch P1 provided on the first scale,
The modulated light from the phase grating is made incident on the amplitude grating on the second scale arranged opposite to the first scale, the modulated light from the amplitude grating is received by the light receiving means, and the signal from the light receiving means is used. When obtaining the relative displacement information between the first scale and the second scale, the interval h between the phase grating and the amplitude grating is calculated as follows. Displacement information detecting device, characterized in that it is set so that 3. The phase grating is composed of a phase diffraction grating having a concave-convex cross-sectional shape, and is set so that a phase difference between light beams passing through the concave portion and the convex portion is λ / 2. The displacement information detecting device according to claim 1. 4. The displacement information detecting device according to claim 1, wherein P1 = 2 · P2 when the grating pitch of the amplitude grating is P2. 5. The phase grating and the amplitude grating are both radial gratings, and the light receiving means obtains an incremental signal from the modulated light passing through the phase grating and the amplitude grating,
The number of gratings corresponding to one round of the phase grating and the amplitude grating is N
The displacement information detecting device according to claim 1 or 2, wherein N1 = N2 / 2 when 1 and N2. 6. A light flux having a wavelength λ from a light source means is made incident on a phase grating having a grating pitch P1 provided on the first scale,
The modulated light from the phase grating is applied to the first scale with a gap h.
Is incident on the amplitude grating on the second scale, which is arranged opposite to each other, and the modulated light from the amplitude grating is received by the light-receiving means, and the signal from the light-receiving means is used to convert the first scale and the second scale. When obtaining the relative displacement information, the light source means has a surface emitting element and a collimator lens, and the length of the arrangement direction component of the phase grating of the surface emitting element is d, and the focal length of the collimator lens is f. When: d ≦ 0.375 · f · P1 / h Displacement information detecting device characterized in that 7. A light flux having a wavelength λ from a light source means is made incident on a phase grating having a grating pitch P1 provided on the first scale,
The modulated light from the phase grating is applied to the first scale with a gap h.
Is incident on the amplitude grating on the second scale, which is arranged opposite to each other, and the modulated light from the amplitude grating is received by the light-receiving means, and the signal from the light-receiving means is used to convert the first scale and the second scale. When obtaining the relative displacement information, the light source means has a surface emitting element and a collimator lens, the length of the component of the arrangement direction of the phase grating of the surface emitting element is d, and the focal length of the collimator lens is f. The displacement information detecting device according to claim 2, wherein d ≦ 0.375 · f · P1 / h. 8. The periodic incremental signal is obtained from the light receiving means in accordance with the relative movement of the first scale and the second scale.
4, 5, 6 or 7 displacement information detection device.