JP3185373B2 - Encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoder and, more particularly, to a method in which a coherent light beam such as a laser beam is made incident on a fine grating array such as a diffraction grating attached to a moving object (scale), and a predetermined order from the diffraction grating. Related to encoders such as rotary encoders and linear encoders that measure the movement information of a diffraction grating, that is, the movement information of a moving object, by forming interference fringes by causing diffracted light to interfere with each other and counting the light and dark fringes of the interference fringes. It is.

[0002]

2. Description of the Related Art Conventionally, there has been an encoder as a measuring instrument capable of measuring movement information such as a moving amount and a moving direction of a moving object in an NC machine tool or the like with high accuracy, for example, in a submicron unit. It is used.

In particular, as a high-precision and high-resolution encoder, a coherent light beam such as a laser is made incident on a diffraction grating provided on a moving object, and diffracted lights of a predetermined order generated from the diffraction grating interfere with each other. An encoder of the diffracted light interference type, which calculates a moving state such as a moving amount and a moving direction of the moving object by counting the brightness of the stripe, is well known.

FIG. 27 is a schematic view of a main part of a conventional linear encoder of the diffracted light interference type.

In FIG. 1, a single-color light beam emitted from a light source 1 is made incident on a fine grating array 5 having a grating pitch P composed of a diffraction grating or the like on a scale 5a to generate a plurality of diffracted lights. At this time, the order of the light beam going straight is defined as 0, and diffracted lights of the order such as ± 1, ± 2, ± 3... Are defined on both sides thereof, and the moving direction of the scale 5a is + and the opposite direction is −. Will be distinguished from each other. Then, the phase of the wavefront of the nth-order diffracted light is shifted by 2π · n · X / P with respect to the wavefront of the 0th-order light, where X is the amount of movement of the scale 5a.

[0006] Since diffracted lights of different orders have different wavefront phases from each other, if the optical paths of the two diffracted lights are overlapped and interfered by an appropriate optical system, a bright / dark signal is obtained.

For example, when the + 1st-order diffracted light and the -1st-order diffracted light are superimposed and interfered with each other using the mirrors 9a and 9b and the beam splitter 3, the phase of each other is 4π while the scale 5a moves by one pitch of the fine grating. It's going to shift 2
A light amount change of a period light and dark occurs. Therefore, by detecting a change in light amount between light and dark at this time, the movement amount of the scale 5a can be obtained.

FIG. 28 is a schematic diagram of a main part of a conventional linear encoder of the diffracted light interference type which detects not only the moving amount of the scale 5a but also the moving direction.

In the figure, as compared with the encoder of FIG. 27, at least two types of light and dark signals obtained from two diffracted lights accompanying the movement of the scale 5a are prepared, and their light and dark timings are shifted from each other. The moving direction has been detected.

That is, in FIG.
Before superimposing the diffracted light and the m-order diffracted light, the polarizing plate 8
By using a, 8b, etc., both light fluxes are converted into linearly polarized light fluxes whose polarization planes are orthogonal to each other. Then, the optical paths are overlapped via the mirrors 9a and 9b and the beam splitter 3a, and then transmitted through the quarter-wave plate 7a to be converted into linearly polarized light whose azimuth of the plane of polarization is determined by the phase difference between the two light beams.

[0011] Further, the non-polarizing beam splitter 3b
Are divided into two light fluxes, and the respective light fluxes are transmitted through polarizing plates (analyzers) 8c and 8d arranged so that the detection directions (directions of linearly polarized light that can be transmitted) are shifted from each other. Detectors 10a and 10b detect two types of light / dark signals with shifted timings.

For example, if the detection directions of the two polarizing plates are shifted from each other by 45 degrees, the timing of light and dark can be represented by a phase of 90.
Degree (π / 2). The encoder shown in FIG.
The movement information including the movement direction of the scale 5a is detected using the signals from the two detectors 10a and 10b.

[0013]

In general, a diffracted light interference type encoder is capable of detecting at a high resolution, but at the expense of reading a fine grid array at a high resolution, the movement or rotation of the scale at a slight speed is required. The frequency of the encoder signal is easily on the order of several MHz. For this reason, the size of the electric signal amplification and processing unit tends to be large, and it tends to be susceptible to noise.

Further, there has been a problem that the use of a semiconductor element such as a laser diode, a light receiving element, and an electric circuit used as a light source is restricted in a thermal environment or a strong electromagnetic field (noise environment).

On the other hand, there is also a method in which a light source and a light receiving element are separated from a moving object (under the environment of an object to be measured) by using an optical fiber. In this case, at least one light emitting fiber and two light receiving fibers are required.

In general, a three-dimensional precision alignment structure on the order of microns is required at a position where a light beam enters an optical fiber (connector portion). Therefore, when a plurality of optical fibers are used, there is a problem that the entire apparatus becomes complicated and large.

On the other hand, it is sufficient if the encoder can be constituted by one optical fiber. However, for example, in the case of an encoder of the diffracted light interference type using one optical fiber, at least two-phase signals having different phases are obtained. However, there is a problem that the light beam must be transmitted through the optical fiber so that it is difficult to realize the light beam.

Even if an encoder of such a system is constituted by only one optical fiber, light loss at the point where the light beam enters the optical fiber must be prepared to some extent, and the optical loss due to aging or disturbance may occur. There has been a problem that the amount of light that can be transmitted through the coupling unit also tends to vary, and that when transmitting an analog signal from the encoder, the signal information is likely to be lost.

According to the present invention, by appropriately constructing one polarization maintaining fiber and each element, the light flux from the light source means can be efficiently guided to an arbitrary position, and the entire apparatus can be controlled without being affected by the thermal environment. It is an object of the present invention to provide an encoder capable of detecting scale (moving object) movement information with high accuracy while simplifying.

In addition, the present invention utilizes the heterodyne interferometry and appropriately configures one polarization plane holding fiber and each element so that the light flux from the light source means can be reduced at any position to reduce light loss. It is an object of the present invention to provide an encoder that can efficiently guide light and detect scale (moving object) movement information with high accuracy while simplifying the entire apparatus without being affected by a thermal environment.

[0021]

The encoder according to the present invention comprises: (1-a) irradiating a light beam from a light source means to the fine grid array of a scale provided with a fine grid array through an optical unit; Are reflected by a mirror or a diffraction grating reflecting element, and the re-diffracted light generated by re-entering the fine grating array is guided to the optical means, and a part of the optical means. In the encoder to obtain the relative movement information of the scale by using the periodic signal obtained from the photoelectric conversion means, detecting the light and dark signal of the light flux based on the interference by using the periodic signal obtained from the photoelectric conversion means, The optical means has a polarization maintaining fiber in a part thereof, the polarization planes of two diffracted lights generated from the fine grating array are orthogonal to each other, and the direction of the polarization plane is f of the polarization maintaining fiber. It is characterized in that it is configured to be at 45 degrees with respect to the axis or the s axis.

(1-b) The light beam from the light source means is irradiated through the optical means to the fine grid row of the scale provided with the fine grid row, and the light beams of different orders generated from the fine grid row are generated.
The two diffracted lights are reflected by a mirror or a diffraction grating reflection element,
The re-diffracted light generated by re-entering the fine grating array is guided to the optical means, extracted through a part of the optical means, overlapped and interfered, and the light / dark signal of the light beam based on the interference is photoelectrically converted. An encoder for detecting relative movement information of the scale using a periodic signal detected by the conversion means and using a periodic signal obtained from the photoelectric conversion means, wherein the optical means has a polarization maintaining fiber in a part thereof, and The polarization planes of two diffracted lights generated from the row are orthogonal to each other, and the direction of the polarization plane is 45 degrees with respect to the f-axis or s-axis of the polarization-maintaining fiber.

In particular, in the present invention, the two diffracted lights generated from the fine grating array are returned to the original optical path by the mirror or the diffraction grating reflecting element, diffracted again by the fine grating array, and then guided to the optical means. It is characterized by light.

(1-c) Different frequencies (ν1, ν2) from the light source means for oscillating light beams of at least two frequencies
Irradiating, via optical means, the fine grating rows of the scale provided with the fine grating rows through the optical means, and the frequencies of the diffracted lights generated from the fine grating rows due to the incidence of the two light fluxes are different, and the polarization plane Are mutually different orders (m, n)
Of the two diffracted lights, one is a mirror and the other is λ /
Two sets (ν1m, ν2n) and (ν1n, ν2m) of re-diffracted light generated by being reflected by a mirror or a diffraction grating reflecting element via a four-phase plate and re-entering the fine grating row are formed, and are formed in the optical means. The two light beams are guided to each other, and the two diffracted light beams overlap each other and interfere with each other to form the two independent light and dark light beams (ν2n−ν1m) and (ν2m−ν1n), and the two light and dark light beams are photoelectrically converted. Means for detecting relative movement information of the scale using a periodic signal obtained from the photoelectric conversion means, the optical means has a polarization maintaining fiber in a part thereof, and the two light and dark light fluxes Is characterized in that the direction of the polarization plane is parallel to the f-axis or the s-axis of the polarization-maintaining fiber.

In particular, in the present invention, the signal obtained from the encoder of the diffracted light interference method is applied to a signal obtained by continuously generating a specific periodic signal (bright and dark signal) even when the scale to be measured is stopped by applying the principle of the heterodyne interferometry. Is generated and transmitted.

In this method, two light beams having different wavelengths (frequency) are guided to different optical paths to change their optical path lengths (phases), and then returned to the original optical paths to interfere with each other. At this time, as long as there is no phase change between the two optical paths, a beat signal (bright and dark signal) having a difference between the two oscillation frequencies is continuously generated. Then, when a phase shift occurs between the two optical paths due to a movement of the scale or the like, the frequency of the beat signal is up / down according to the direction of the change.

Then, by detecting the frequency shift Δν (or the phase shift ΔΦ), the speed of the phase change accompanying the movement of the scale (that is, including the sign indicating the moving speed and the moving direction of the scale) is detected. The phase shift is counted every 2π, for example, and the amount of phase change accompanying the movement of the scale (ie, the amount of movement of the scale, including the sign indicating the direction of movement)
Is detected.

In the present invention, a signal is treated as a frequency or phase shift utilizing this principle, so that even if noise is mixed during transmission of the signal or the amplitude fluctuates, the information is not easily damaged.

Further, in the present invention, the coupling system between the dual-frequency oscillation laser and the encoder of the diffracted light interference system is appropriately configured using the polarization maintaining fiber. Furthermore, the optical system is appropriately configured so that the (initial) oscillation frequencies of both light beams when diffracted lights of different orders interfere with each other are different from each other. As a result, light loss at the coupling unit when transmitting a signal relating to scale movement information is reduced, and transmission can be performed efficiently.

(1-d) A light beam is radiated from a light source means through an optical means to the fine grid array of the scale provided with the fine grid array, and two diffracted lights of different orders generated from the fine grid array are mirrored. Alternatively, the second diffracted light generated by being reflected by the diffraction grating reflection element and incident on the fine grating array again is guided to the optical means, and overlapped and interfered with each other. In the encoder which detects the relative movement information of the scale by using the periodic signal obtained by the photoelectric conversion means, the optical means has a polarization maintaining fiber in a part thereof. Out of the diffracted light from the micro-grating array, the two diffracted lights interfere with each other for each polarization plane orthogonal to each other to form two light / dark signal lights, and the direction of the polarization plane of the two light / dark signal lights is the polarization plane. Wave front It is characterized by being configured so as to be parallel to the f axis or the s-axis of the lifting fiber.

(1-e) Two light beams of different frequencies are radiated from the light source means for oscillating light beams of at least two frequencies to the fine grating rows of the scale provided with the fine grating rows via the optical means, Two diffracted lights having different frequencies and different orders from the fine grating array are reflected by a mirror or a diffraction grating reflecting element, and re-diffracted light generated by re-entering the fine grating array is guided to the optical means. Light, taken out through a part of the optical means, overlapped and interfered with each other, a light / dark signal of a light flux based on the interference was detected by a photoelectric conversion means, and the scale was obtained by using a periodic signal obtained from the photoelectric conversion means. The optical means has a polarization maintaining fiber in a part thereof, and the polarization planes of two diffracted lights generated from the fine grating array are orthogonal to each other. It is characterized in that the direction of the polarization plane is configured to be parallel to the f axis or the s-axis of the polarization-maintaining fiber.

In particular, in the present invention, the principle of the heterodyne interferometry is applied, and the signal obtained from the encoder of the diffracted light interference method is used as a signal in which a specific periodic signal (bright and dark signal) continues to be generated even when the scale, which is the object to be measured, is stopped. Generated and transmitted.

In this method, two light beams having different wavelengths (frequency) are guided to different optical paths, and the optical path lengths (phases) are changed. Then, the optical paths are returned to the original optical paths and interfere with each other. At this time, as long as there is no phase change between the two optical paths, a beat signal (bright and dark signal) having a difference between the two oscillation frequencies is continuously generated. When the phase shifts between the two optical paths due to the movement of the scale or the like, the frequency of the beat signal goes up / down according to the direction of the change.

Then, by detecting the frequency shift Δν (or the phase shift ΔΦ), the speed of the phase change accompanying the movement of the scale (that is, including the sign indicating the moving speed and the moving direction of the scale) is detected. Is counted, for example, at intervals of 2π, and the amount of phase change accompanying the movement of the scale (that is, the amount of movement of the scale, including the sign indicating the moving direction) is detected.

In the present invention, by utilizing this principle, a signal is handled as a frequency or phase shift, so that noise is not mixed during transmission of the signal or information is not easily damaged even if the amplitude fluctuates.

Further, in the present invention, the coupling system between the dual-frequency oscillation laser and the encoder of the diffracted light interference system is appropriately configured using the polarization maintaining fiber. Furthermore, the optical system is appropriately configured so that the (initial) oscillation frequencies of both light beams when diffracted lights of different orders interfere with each other are different from each other. As a result, light loss at the coupling unit when transmitting a signal relating to scale movement information is reduced, and transmission can be performed efficiently.

[0037]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention. In the figure, the arrow indicates the traveling direction of the light beam, and the sinusoidal symbol indicates the plane of polarization. Reference numeral 101 denotes a light source means, such as a laser beam or an LED that emits monochromatic light or coherent light.
And the like.

A divergent light beam (in this case, linearly polarized light) emitted from the light source 1 is converted into a substantially parallel light beam by a collimator lens 2a, passes through a non-polarizing beam splitter 3a, and enters a coupling lens 2b. The light beam from the coupling lens 2b is incident on the first end surface (incident surface) 6a of the polarization maintaining fiber 6. At this time, the position is adjusted so that one of the optical axes (s-axis and f-axis) of the polarization plane holding fiber 6 and the polarization plane of the incident light beam are parallel as shown in FIG.

(Here, the polarization maintaining fiber 6 propagates a light beam while maintaining the polarization state.
The optical axis of the polarization maintaining fiber 6 is defined as the f-axis in the direction in which the propagation speed of the light wave is fast, and the s-axis in the direction in which the propagation speed is slow. The light beam emitted from the second end face (emission surface) 6b of the polarization maintaining fiber 6 is a light beam having one of the s-axis component and the f-axis component. The light beam from the emission surface 6b of the polarization maintaining fiber 6 is converted into a substantially parallel light beam by the coupling lens 2c, and is incident on the fine grating array 5 composed of the diffraction grating on the scale 5a.

Each element 2a, 3a, 2b, 6, 2c constitutes one element of the optical means 102 for making the light beam from the light source means 101 incident on the scale 5a.

Then, of the plurality of diffracted lights generated from the fine grating array 5, for example, ± 1st-order diffracted lights are converted into polarizing plates 8a and 8b.
The light is reflected by the mirrors 9a and 9b through the optical path, returns to the original optical path, and is again incident on the fine grid array 5 of the scale 5a.

At this time, as shown in the figure, the ⁺ 1st-order diffracted light is linearly polarized light (s + f) ⁺¹ whose polarization plane has an angle relationship of 45 degrees with the s-axis, and the -1st-order diffracted light is converted by the polarizing plates 8a and 8b. Linearly polarized light (s
-F) It is set to be ^-1 . Each element 8a, 8b,
9a and 9b constitute each element of the detection optical system 103.

These two light beams (s + f) ⁺¹ , (s-f)
^-1 is diffracted again by the fine grating array 5 and only the ^{+ 1st-order} diffracted light (s + f) ^{+ 1 + 1} of the ^{+ 1st-order} diffracted light and the -1st-order diffracted light (s-f) ^{-1-1 of the -1st} -order diffracted light are cup- ^shaped. The light enters the ring lens 2c. Two light beams (s + f) ^{+ 1 + 1} , (s) re-entering the polarization maintaining fiber 6 by the coupling lens 2c
−f) ^-1-1 are linearly polarized planes that form 45 degrees with the s-axis and f-axis and are orthogonal to each other, and propagate through the polarization-maintaining fiber 6.

At this time, the light beam (s + f) ^{+ 1 + 1} becomes clockwise elliptically polarized light while propagating through the polarization maintaining fiber 6, and finally becomes clockwise circularly polarized light at the exit 6a. ^-1-1 eventually becomes counterclockwise elliptical polarization, and finally at the exit 6a, counterclockwise circular polarization. This phenomenon is caused by the difference in the propagation speed between the optical axes (s, f) of the polarization maintaining fiber 6, and the length L of the fiber is represented by the following relational expression. When the condition is satisfied, exchange between linearly polarized light and circularly polarized light is performed.

That is, the length and mode refractive index of the polarization maintaining fiber are L and β, and the wavelength of the light beam from the light source 1 is λ ₀ , n.
Is an integer when L = λ ₀ (（+ n) / ββ (a).

Therefore, in this embodiment, each element is set so as to satisfy the relational expression (a): 0.9 <(1/4 + n) · λ ₀ /(β·L)<1.1‥‥(b) are doing. As a result, the initial purpose is successfully achieved.

The two light beams emitted from the first end face 6a of the polarization maintaining fiber 6 are converted into substantially parallel light beams by the coupling lens 2b while the rotation directions of the circular polarization planes are reversed, and are converted by the non-polarizing beam splitter 3a. Reflecting.

When these two light beams are combined ^vectorwise , linearly polarized light whose polarization direction is uniquely determined by the phase difference between the light beam (s + f) ^{+ 1 + 1} and the light beam ( ^sf ) ^-1-1 Luminous flux. Therefore, while the scale 5a moves in one direction, the phase difference between the two light beams continuously shifts, so that the plane of polarization of linearly polarized light continues to rotate. And the phase difference between the two light beams is 2
The polarization direction of the linearly polarized light is rotated by 180 degrees every π.

This light beam is converted into a non-polarized beam splitter 3b.
After splitting the light into two light beams, the light is transmitted through polarizing plates (analyzers) 8c and 8d whose transmission polarization directions are shifted from each other. At this time, the plane of polarization of the linearly polarized light beam and the polarizing plate (8
The transmitted light amount becomes maximum at a timing when the polarization direction of (c, 8d) matches, and is converted into a light / dark signal light beam which becomes minimum at a timing orthogonal thereto. The light / dark timing between the two light / dark signals may be set by shifting the setting of the transmission polarization directions of the two polarizing plates.

The luminous flux of these light / dark signals is converted into photoelectric conversion means 1
The electric signals are converted into electric signals by the photoelectric elements 10a and 10b as 05, and a two-phase signal as an encoder is output from this (after the amplitude is amplified). In this embodiment, the movement information such as the movement amount and the movement direction of the scale 5a is detected by using the signal obtained by the photoelectric conversion means 105 (the photoelectric elements 10a and 10b) at this time.

As described above, in the present embodiment, by appropriately configuring one polarization-maintaining fiber and each element, that is, when transmitting two diffracted lights generated from the fine grating array of the scale to the polarization-maintaining fiber, The polarization planes of the two diffracted light beams are made orthogonal to each other so that the two light beams do not interfere with each other to produce a bright / dark signal, and the optical axes (f axis, s
Axis) so that they are incident at 45 degrees and transmitted. The difference in the propagation speed between the s-axis and the f-axis of the polarization-maintaining fiber is utilized at the exit of the polarization-maintaining fiber. The linearly-polarized light beam is converted into a circularly-polarized light beam in the opposite direction, and the vector-like combined light beam of the two light beams is converted from phase difference information of two light beams into information of the direction of the plane of polarization of linearly-polarized light. By transmitting the linearly polarized light beam, the movement information of the scale 5a is detected with high accuracy while simplifying the entire apparatus.

In the present invention, the following modifications of the elements in the first embodiment can be similarly applied.

(2-a) Use of a combination of diffracted lights of orders other than ± 1st-order diffracted light as diffracted light from a fine lattice array on a scale.

(2-b) A mirror type beam splitting unit having a similar function is used instead of the prism beam splitter.

(2-c) The two diffracted lights obtained from the fine grating array (diffraction grating) provided on the scale are not limited to the reflection type, but may be the transmission type diffraction light as shown in FIG. FIG. 2 shows only the vicinity of the scale 5a, and each corresponds to FIG. The same elements as those shown in FIG. 1 are denoted by the same reference numerals.

(2-d) As shown in FIG. 3, the light beam from the polarization-maintaining fiber 6 is first split into two light beams by using a prism 51 having a split surface BS, and then split into two fine grid lines 5 of a scale 5a. You may make it enter.

FIG. 3 is developed based on the optical system of the first embodiment. In the figure, the light beam emitted from the emission surface 6b of the polarization maintaining fiber 6 is only one of the components of the optical axis (s axis, f axis) of the polarization maintaining fiber 6.

Therefore, the dividing surface B of the prism 51 as shown in FIG.
A polarized beam splitter film deposited on S is used. For example, the reflected light beam on the split surface BS is a light beam on a polarization plane formed by 45 degrees with the f axis, and the transmitted light beam on the split surface BS is a light beam orthogonal to the same. Separated and taken out. After the + 1st-order or -1st-order diffraction, respectively, the original optical path is returned to obtain two light beams having the same properties.

When a normal non-polarizing beam splitter film is used in place of the polarizing film, the components of the polarization plane orthogonal to each other in the optical path irradiated from the prism shown in FIG. , F-axis and 45-degree polarization plane components can be selected. Note diffracted light (s + f) ^+1, instead of placing a common mirror 9 at a position of (s-f) ^-1, the diffracted light ^{(s + f) +1, (} s-
f) Each mirror may be arranged at the position of ^-1 .

(2-e) Instead of the mirrors 9a and 9b,
A cat's eye optical element, a diffraction grating reflecting element, a corner cube, or the like may be used.

According to this, it is possible to correct the optical path shift due to the wavelength variation of the light beam from the light source. If the diffraction grating reflection element is a reflection type diffraction grating, the original optical path can be returned by using a periodic grating having a pitch that is half the pitch of the fine grating row 5 of the scale. (2-f) The structure of the cross section of the polarization maintaining fiber is not only the so-called elliptical clad type shown in the figure but also an elliptical core type or PA
An NDA type or the like is applicable.

(2-g) The fine grid array provided on the scale is not limited to a linear one, and if a grid in which a radial grid is recorded on a rotating disk is used, it can be directly applied to a rotary encoder.

FIG. 4 is a schematic view of a main part of a second embodiment of the present invention. In the figure, the arrow indicates the traveling direction of the light beam, and the sinusoidal symbol indicates the plane of polarization. Reference numeral 101 denotes a light source means, such as a laser beam or an LED that emits monochromatic light or coherent light.
And the like.

A divergent light beam (in this case, linearly polarized light) emitted from the light source 1 is converted into a substantially parallel light beam by a collimator lens 2a, passes through a non-polarizing beam splitter 3a, and enters a coupling lens 2b. The light beam from the coupling lens 2b is incident on the first end surface (incident surface) 6a of the polarization maintaining fiber 6. At this time, the position is adjusted so that the angle between the optical axes (s-axis and f-axis) of the polarization maintaining fiber 6 and the polarization plane of the incident light beam is about 45 ° as shown in FIG.

(Here, the polarization maintaining fiber 6 propagates the light beam while maintaining the polarization state.
The optical axis of the polarization maintaining fiber 6 is defined as the f-axis in the direction in which the propagation speed of the light wave is fast, and the s-axis in the direction in which the propagation speed is slow. The light flux emitted from the second end face (emission face) 6b of the polarization maintaining fiber 6 is a light flux having an s-axis component and an f-axis component. The light beam from the exit surface 6b of the polarization maintaining fiber 6 is converted into a substantially parallel light beam by the coupling lens 2c,
The light is incident on a fine grating array 5 composed of a diffraction grating on a scale 5a.

Each element 2a, 3a, 2b, 6, 2c constitutes one element of the optical means 102 for causing the light beam from the light source means 101 to enter the scale 5a.

Then, of the plurality of diffracted lights generated from the fine grating array 5, for example, ± 1st-order diffracted lights are converted into polarizing plates 8a and 8b.
The light is reflected by the mirrors 9a and 9b through the optical path, returns to the original optical path, and is again incident on the fine grid array 5 of the scale 5a.

At this time, the + ^1st- order diffracted light is converted into linearly polarized light (s ⁺¹ ) parallel to the s-axis, and the next-order diffracted light is converted into linearly polarized light (f ⁻¹ ) parallel to the f-axis, as shown in FIG. I am trying to become. Each element 8a, 8b, 9a, 9b
Constitute each element of the detection optical system 103.

These two luminous fluxes (s ⁺¹ , f ^-1 ) are diffracted again by the fine grating array 5 and ^{+ 1st-order} diffracted light of the + ^1st-order diffracted light (s ^{+ 1} )
^{+ 1 + 1} ) and only the -1st-order diffracted light (f- ^1-1 ) of the -1st-order diffracted light enters the coupling lens 2c. In the coupling lens, the two light beams (s ^{+ 1 + 1} ) and (f ^{−1 -1} ) that have ^{entered the} polarization maintaining fiber 6 again by 2 c are the s axis, respectively.
It has a polarization plane parallel to the f-axis, and propagates independently (without mutual interference) in the polarization plane holding fiber 6.

First end face 6a of polarization maintaining fiber 6
The two light beams emitted from the light source are converted into substantially parallel light beams by the coupling lens 2b with their polarization planes orthogonal to each other, reflected by the non-polarizing beam splitter 3a, and transmitted through the quarter-wave plate 7a. At this time, the crystal axis of the quarter-wave plate 7a (the s-axis and the f-axis as in the case of the polarization maintaining fiber, but are shown as Pf-axis and Ps-axis in the drawing for the sake of simplicity) is polarized by two light beams. The light beam (s ^{+1 +1} ) is turned into a clockwise circularly polarized light beam, and the light beam (f ^-1-1 ) is turned into a counterclockwise circularly polarized light beam by being attached so as to be oriented at 45 ° to the wavefront. ing. (Or the inverse relation). Each element 3a,
7a constitutes one element of the superposition means 104.

When these two light beams are combined ^vectorwise, a linearly polarized light beam that uniquely determines the polarization direction based on the phase difference between the light beam (s ^{+ 1 + 1} ) and the light beam (f- ^1-1 ). become.
Therefore, while the scale 5a moves in one direction, the phase difference between the two light beams continuously shifts, so that the plane of polarization of linearly polarized light continues to rotate. Then, the polarization direction of the linearly polarized light is rotated by 180 ° every 2π in phase difference between the two light beams.

This light beam is converted to a non-polarized beam splitter 3b.
After splitting the light into two light beams, the light is transmitted through polarizing plates (analyzers) 8c and 8d whose transmission polarization directions are shifted from each other. At this time, the plane of polarization of the linearly polarized light beam and the polarizing plate (8
The transmitted light amount becomes maximum at a timing when the polarization direction of (c, 8d) matches, and is converted into a light / dark signal light beam which becomes minimum at a timing orthogonal thereto. The light / dark timing between the two light / dark signals may be set by shifting the setting of the transmission polarization directions of the two polarizing plates.

The luminous flux of these light / dark signals is converted into photoelectric conversion means 1
The electric signals are converted into electric signals by the photoelectric elements 10a and 10b as 05, and a two-phase signal as an encoder is output from this (after the amplitude is amplified).

In this embodiment, the photoelectric conversion means 10 at this time is
The movement information such as the movement amount and the movement direction of the scale 5a is detected using the signals obtained by the photoelectric conversion elements 5 (photoelectric elements 10a and 10b).

As described above, in this embodiment, by appropriately configuring one polarization-maintaining fiber and each element, that is, when transmitting two diffracted light beams generated from the fine grating array of the scale through the polarization-maintaining fiber, The polarization planes of the two diffracted light beams are made orthogonal to each other so that the two light beams do not interfere with each other to produce a bright / dark signal, and the optical axes (f axis, s
(Axis) so as to be incident on the axis 5 so as to be parallel to each other, and transmit the signal. Thus, the movement information of the scale 5a is detected with high accuracy while simplifying the entire apparatus.

FIG. 5 is a schematic view of a main part of a third embodiment of the present invention.

In this embodiment, the plane of polarization of the light beam from the light source means 101 is made incident parallel to the optical axis of the polarization maintaining fiber 6, propagated, and then incident on the fine grid array 5 of the scale 5 a. The difference is that the polarization plane of one of the two diffracted lights from the fine lattice array 5 is rotated by 90 degrees by the crystal optical element (λ / 4 plate) 7b and is incident on the polarization plane holding fiber 6. The other configuration is the same as that of the second embodiment shown in FIG.

That is, the divergent light beam (in this case, linearly polarized light) emitted from the light source 1 is converted into a substantially parallel light beam by the collimator lens 2a, passes through the non-polarizing beam splitter 3a, and enters the coupling lens 2b. The light beam from the coupling lens 2b is incident on the first end surface (incident surface) 6a of the polarization maintaining fiber 6. At this time, the position is adjusted such that one of the optical axes (s-axis, f-axis) of the polarization plane holding fiber 6 and the polarization plane of the incident light beam coincide as shown in FIG.

Here, it is assumed that the s-axis is coincident with the s-axis. Then, the second end face (outgoing face) 6 of the polarization maintaining fiber 6
The light beam emitted from b is a light beam having an s-axis component. The light beam from the emission surface 6b of the polarization maintaining fiber 6 is converted into a substantially parallel light beam by the coupling lens 2c, and is incident on the fine grating array 5 composed of the diffraction grating on the scale 5a.

Then, of a plurality of diffracted lights generated from the fine grating array 5, for example, one of the ⁺ 1st-order diffracted light s ⁺¹ and the -1st-order diffracted light s ^-1 is converted into one diffracted light (s ^-1 ) The light is reflected by the mirrors (9a, 9b) via the crystal optical element (λ / 4 plate) 7b, returns to the original optical path, and is again incident on the fine lattice array 5 of the scale 5a.

At this time, the crystal axis (Ps axis) of the λ / 4 plate 7b
Are arranged at 45 degrees with respect to the polarization plane of the light flux s ^-1 . And thereby forces the light re-enter into the light beam (s ^-1) the light beam (s ^-1) and polarizing beam (f ^-1) is converted into a fine lattice columns 5 wavefront perpendicular.

These two luminous fluxes (s ⁺ , f ^-1 ) are diffracted again by the fine grating array 5, and the + ^1st-order diffracted light of the + ^1st-order diffracted light (s
^{+ 1 + 1} ) and only the -1st-order diffracted light (f- ^1-1 ) of the -1st-order diffracted light ^{enter the} coupling lens 2c. The two light beams (s ^{+ 1 + 1} ) and (f- ^1-1 ) that have ^{reentered the} polarization maintaining fiber 6 by the coupling lens 2c have polarization planes parallel to the s-axis and f-axis, respectively, so that the polarization plane is maintained. The light propagates independently (without mutual interference) in the fiber 6.

First end face 6a of polarization maintaining fiber 6
The two light beams emitted from the light source are converted into substantially parallel light beams by the coupling lens 2b with their polarization planes orthogonal to each other, reflected by the non-polarizing beam splitter 3a, and transmitted through the quarter-wave plate 7a. At this time, the crystal axis of the quarter-wave plate 7a (the s-axis and the f-axis as in the case of the polarization maintaining fiber, but are shown as Pf-axis and Ps-axis in the drawing for the sake of simplicity) is polarized by two light beams. The light beam (s ^{+1 +1} ) is turned into a clockwise circularly polarized light beam, and the light beam (f ^-1-1 ) is turned into a counterclockwise circularly polarized light beam by being attached so as to be oriented at 45 ° to the wavefront. ing. When these two light beams are combined ^vectorwise , the polarization direction is uniquely determined by the phase difference between the light beam (s ^{+ 1 + 1} ) and the light beam (f- ^1-1 ). Which determines the linearly polarized light flux. Therefore, while the scale 5a moves in one direction, the phase difference between the two light beams continuously shifts, so that the plane of polarization of linearly polarized light continues to rotate. Then, the polarization direction of the linearly polarized light is rotated by 180 ° every 2π in phase difference between the two light beams.

This light beam is converted to a non-polarized beam splitter 3b.
After splitting the light into two light beams, the light is transmitted through polarizing plates (analyzers) 8c and 8d whose transmission polarization directions are shifted from each other. At this time, the plane of polarization of the linearly polarized light beam and the polarizing plate (8
The transmitted light amount becomes maximum at the timing when the polarization orientations a and 8b) coincide with each other, and is converted into the light / dark signal light flux which becomes minimum at the timing orthogonal thereto. The light / dark timing between the two light / dark signals may be set by shifting the setting of the transmission polarization directions of the two polarizing plates.

The luminous flux of these light / dark signals is converted into photoelectric conversion means 1
The electric signals are converted into electric signals by the photoelectric elements 10a and 10b as 05, and a two-phase signal as an encoder is output from this (after the amplitude is amplified).

In this embodiment, similarly to the second embodiment, the movement information such as the movement amount and the movement direction of the scale 5a is detected by using the signal obtained by the photoelectric conversion means 105 (photoelectric elements 10a and 10b) at this time. I have.

In the present invention, the above-described Embodiment 2 and Embodiment 2
In 3, the following changes of each element can be similarly applied.

(3-a) Use of a combination of diffracted lights of orders other than ± 1st-order diffracted light as the diffracted light from the fine lattice array on the scale.

(3-b) A mirror-type beam splitting unit having a similar function is used in place of the prism beam splitter.

(3-c) The two diffracted lights obtained from the fine grating array (diffraction grating) provided on the scale are not limited to the reflection type but may be the transmission type diffraction light as shown in FIGS. good. 6 and 7 show only the vicinity of the scale 5a,
4 and 5 respectively correspond to FIGS. The same elements as those shown in FIGS. 4 and 5 are denoted by the same reference numerals.

(3-d) As shown in FIG. 8, the light beam from the polarization-maintaining fiber 6 is first split into two light beams by using a prism 51 having a split surface BS, and then split into two fine grid lines 5 of a scale 5a. You may make it enter.

FIG. 8 is developed based on the optical system of the second embodiment. In the figure, the light beam emitted from the emission surface 6b of the polarization maintaining fiber 6 contains an equal amount of the component of the optical axis (s-axis, f-axis) of the polarization maintaining fiber 6.

Therefore, the divided surface B of the prism 51 as shown in FIG.
A polarization beam splitter film deposited on S is used. For example, the reflected light beam at the split surface BS is separated and extracted as an f-axis component light beam, and the transmitted light beam at the split surface BS is extracted as an s-axis component light beam. After the + 1st-order or -1st-order diffraction, respectively, the original optical path is returned to obtain two light beams having the same properties.

When a normal non-polarizing beam splitter film is used in place of the polarizing film, the s-axis component and the f-axis component are respectively orthogonal to each other in the optical path irradiated from the prism in the figure to the scale. What is necessary is just to arrange a polarizing plate so that it can be performed. Instead of arranging the common mirror 9 at the positions of the diffracted lights s ^-1 and f ⁺¹ , respective mirrors may be arranged at the positions of the diffracted lights s ⁺¹ and f ^-1 .

(3-e) Instead of the mirrors 9a and 9b, cat's eye optical elements 9c and 9d shown in FIG. 9 or diffraction grating reflecting elements 9e and 9f shown in FIG. 10 or corner cubes may be used.

According to this, it is possible to correct the optical path shift due to the wavelength variation of the light beam from the light source. Incidentally, if the diffraction grating reflection elements 9e and 9f are reflection type diffraction gratings, the original optical path can be returned by setting them to a periodic grating having a pitch which is half the pitch of the fine grating row 5 of the scale.

(3-f) The structure of the cross section of the polarization maintaining fiber may be an elliptical core type, a PANDA type, or the like, in addition to the so-called elliptical cladding type shown in the figure.

(3-g) The fine grating array provided on the scale is not limited to a linear one, and if a radial grating is recorded on a rotating disk, for example, it can be directly applied to a rotary encoder.

FIG. 11 is a schematic view of a main part of a fourth embodiment of the present invention. In the figure, the arrow indicates the traveling direction of the light beam, and the sinusoidal symbol indicates the plane of polarization. 101 is a light source means,
It has a light source 1 such as a two-frequency oscillation laser that oscillates a light beam of at least two frequencies (ν ₁ , ν ₂ ) (wavelength).

From the light source 1, two light beams (ν ₁ , ν ₂ ) having substantially the same frequency and mutually different polarization planes whose polarization planes are orthogonal to each other are emitted in an overlapping manner. These two light fluxes (ν ₁ ,
ν ₂ ) passes through the non-polarizing beam splitter 3a, is condensed by the coupling lens 2b, and is incident on the first end surface (incident surface) 6a of the polarization maintaining fiber 6. At this time, the optical axes (s-axis, f-axis) of the polarization maintaining fiber 6 and 2
The two light beams (ν ₁ , ν ₂ ) are aligned with the plane of polarization. (Either combination may be used.) (Here, the polarization maintaining fiber 6 propagates the light beam while maintaining the polarization state. The optical axis of the polarization maintaining fiber 6 is in the direction in which the propagation speed of the light wave is higher. To the f axis,
The slow direction is the s-axis. ) The s-axis component light beam and the f-axis component light beam of the light beam emitted from the second end face (outgoing surface) 6b of the polarization maintaining fiber 6 correspond to the light beam ν ₁ and the light beam ν ₂ , respectively.

The two luminous fluxes (ν ₁ , ν ₂ ) from the exit surface 6b of the polarization maintaining fiber 6 are coupled to the coupling lens 2c.
, And is incident on a fine grating array 5 composed of a diffraction grating on a scale 5a.

Each of the elements 3a, 2b, 6, 2c constitutes one element of the optical means 102 for causing the light beam from the light source means 101 to enter the scale 5a.

Then, of a plurality of diffracted lights generated from the fine grating array 5, for example, ± 1st-order diffracted lights are converted into mirrors 9a and 9b.
Then, the light is returned to the original optical path, and is again incident on the fine grid array 5 of the scale 5a.

At this time, the λ / 4 plate 11 is arranged in one optical path in the optical path of the -1st-order diffracted light in FIG. Then, the -1st-order diffracted light before passing through the λ / 4 plate 11 is linearly polarized light parallel to the s-axis (s ⁻¹ ) = (ν ₁ ⁻¹ ) linearly polarized light parallel to the f-axis (f ⁻¹ ) = (ν ₂ ^-1) what was the lambda / 4 plate a reciprocating transmission to the s-axis parallel to the linearly polarized light _{^{(s -1) = (ν 2}} -1) parallel to the f axis linearly polarized light (f ^-1) = (Ν ₁ ^-1 ).

On the other hand, the + 1st-order diffracted light is linearly polarized light parallel to the s-axis (s ⁺¹ ) = (ν ₁ ⁺¹ ) Linearly polarized light parallel to the f-axis (f ⁺¹ ) = (ν ₂ ⁺¹ )

These four light beams are diffracted again by the fine grating row 5a. Among them, ^{+ 1st-order} diffracted light (s ^{+ 1 + 1} ) and (f ^{+ 1 + 1} ) of the ^{+ 1st-order} diffracted light and -1st-order diffracted light (s- ^1-1 ) and (f- ^1-1 ) of the -1st-order diffracted light Only the coupling lens 2
c. That is, linearly polarized light parallel to the s-axis (s ^{+ 1 + 1} ) = (ν ₁ ^{+ 1 + 1} ) Linearly polarized light parallel to the f-axis (f ^{+ 1 + 1} ) = (ν ₂ ^{+ 1 + 1} ) s-axis Linearly polarized light (s- ^1-1 ) = (ν ₂ ^-1-1 ) parallel to the f axis Linearly polarized light (f ^-1-1 ) = (ν ₁ ^-1-1 ) parallel to the f-axis.

At this time, the light beams having the same polarization plane interfere with each other and are converted into two types of light / dark signal light beams. That is, the light and dark signal light flux IS =
(Ν ₂ ^-1-1 ) − (ν ₁ ^{+ 1 + 1} ) Linearly polarized light / dark signal light flux IF parallel to the f-axis =
(Ν ₂ ^{+ 1 + 1} ) − (ν ₁ ^-1-1 ). Here, ν ₂ > ν ₁ . Here, if the frequency shift due to ± first-order diffracted light is described as ± Δν, (ν ₂ ^-1-1 ) − (ν ₁ ^{+ 1 + 1} ) = (ν ₂ −ν ₁ ) −4Δν (ν ₂ ^{+ 1 + 1)} ) − (Ν ₁ ^−1-1 ) = (ν ₂ −ν ₁ ) + 4Δν. (The frequency shifts of the two light / dark signal light fluxes are opposite to each other and have the same amount.) The two light / dark signal light fluxes IS and IF incident on the second end face 6b of the polarization maintaining fiber 6 again by the coupling lens 2c are respectively obtained. The plane of polarization is parallel to the s-axis and the f-axis. The laser beam is made incident on the polarization maintaining fiber so as to coincide with the optical axis of the polarization maintaining fiber, and propagates independently (without mutual interference) in the polarization maintaining fiber 6.

The two light / dark signal light beams IS and IF emitted from the first end face 6a of the polarization plane holding fiber 6 are converted into substantially parallel light beams by the coupling lens 2b while keeping their polarization planes orthogonal to each other, and are converted into a non-polarized light beam. The light is reflected by the splitter 3a and further separated by the polarization beam splitter 12 for each polarization component. As a result, the light beam is returned to two light / dark signal light fluxes which repeat light / dark at substantially the difference frequency between the two oscillation frequencies, and is converted into an electric signal by the photoelectric elements 10a and 10b as the photoelectric conversion elements 105 (after the amplitude is amplified). It outputs a modulated two-phase signal as an encoder using interference.

In this embodiment, the photoelectric conversion means 10 at this time is
The movement information such as the movement amount and the movement direction of the scale 5a is detected using the signals obtained by the photoelectric conversion elements 5 (photoelectric elements 10a and 10b).

As described above, in this embodiment, by appropriately configuring the two-frequency oscillation laser, one polarization-maintaining fiber, and each element, that is, the two-order diffracted light generated from the fine grating array of the scale is polarized. Before returning to the wavefront holding fiber, a crystal optical element 11 for exchanging the polarization plane is inserted into at least one of the optical paths having different diffraction orders (m, n) to convert the mth-order diffraction light and the nth-order diffraction light into different oscillation frequencies ( ν ₁ , ν ₂ ) corresponding to the light flux, convert the polarization plane into an interference signal by aligning the polarization planes, and further make the polarization plane parallel to one of the optical axes (s-axis, f-axis) of the polarization maintaining fiber. The movement information of the scale 5a is detected with high accuracy while simplifying the entire apparatus.

In this embodiment, as shown in FIG. 12, a non-polarizing beam splitter 3a is used as a reference light / dark signal (signal not subjected to phase modulation due to movement of the scale 5a = difference signal of oscillation frequency of a two-frequency laser). The reflected light flux from the light source may be used.

That is, as shown in FIG. 12, two light beams (ν
₁ , ν ₂ ) is transmitted through a polarizing plate (analyzer) 8 d set to have a transmission characteristic in an azimuth of 45 ° with respect to the polarization azimuth, and an interference phenomenon occurs between the common polarization components of both light fluxes. .

Then, the light beam is converted into a light / dark signal light beam that repeats light / dark at the difference frequency between the oscillation frequencies of the two light beams (ν ₁ , ν ₂ ).
This light / dark signal light beam may be converted into an electric signal by the photoelectric element 10c (after its amplitude has been amplified), and a reference phase signal as an encoder utilizing heterodyne interference may be output and used.

In the present invention, the following modifications of the elements in the fourth embodiment can be similarly applied.

(4-a) Use of a combination of diffracted lights of orders other than ± 1st-order diffracted light as the diffracted light from the fine lattice array on the scale.

(4-b) A mirror type beam splitting unit having a similar function is used in place of the prism beam splitter.

(4-c) The two diffracted lights obtained from the fine grating array (diffraction grating) provided on the scale are not limited to the reflection type, but may be the transmission type diffraction light as shown in FIG.
FIG. 13 shows only the vicinity of the scale 5a. Also, FIG.
The same elements as those shown in FIG. 1 are denoted by the same reference numerals.

(4-d) The two light beams from the polarization-maintaining fiber 6 may be first split into two light beams by using a prism having a split surface BS, and then may be incident on the fine grid array 5 of the scale 5a. .

(4-E) Instead of the mirrors 9a and 9b, the cat's-eye optical elements 9c and 9d shown in FIG.
The diffraction grating reflection elements 9e and 9f shown in FIG. According to this, it is possible to correct the optical path shift due to the wavelength variation of the light beam from the light source. Incidentally, if the diffraction grating reflection elements 9e and 9f are reflection type diffraction gratings, the original optical path can be returned by setting them to a periodic grating having a pitch which is half the pitch of the fine grating row 5 of the scale.

(4-f) The structure of the cross section of the polarization maintaining fiber may be an elliptical core type, a PANDA type, or the like, in addition to the so-called elliptical cladding type shown in the figure.

(4-g) The fine grating array provided on the scale is not limited to a linear one, and if a radial grating is recorded on a rotating disk, for example, it can be directly applied to a rotary encoder.

FIG. 16 is a schematic view of a main part of a fifth embodiment of the present invention. In the figure, the arrow indicates the traveling direction of the light beam, and the sinusoidal symbol indicates the plane of polarization. 101 is a light source means,
Laser light or LE that emits monochromatic light or coherent light
D and the like.

The divergent light beam (in this case, linearly polarized light) emitted from the light source 1 is converted into a substantially parallel light beam by the collimator lens 2a, and is transmitted through the non-polarizing beam splitter 3a to enter the coupling lens 2b. The light beam from the coupling lens 2b is incident on the first end surface (incident surface) 6a of the polarization maintaining fiber 6. At this time, the position is adjusted so that the angle between the optical axes (s-axis and f-axis) of the polarization maintaining fiber 6 and the polarization plane of the incident light beam is about 45 ° as shown in FIG.

(Here, the polarization maintaining fiber 6 propagates a light beam while maintaining the polarization state.
The optical axis of the polarization maintaining fiber 6 is defined as the f-axis in the direction in which the propagation speed of the light wave is fast, and the s-axis in the direction in which the propagation speed is slow. The light flux emitted from the second end face (emission face) 6b of the polarization maintaining fiber 6 is a light flux having an s-axis component (polarization component s) and an f-axis component (polarization component f). The light beam from the emission surface 6b of the polarization maintaining fiber 6 is converted into a substantially parallel light beam by the coupling lens 2c, and is incident on the fine grating array 5 composed of the diffraction grating on the scale 5a.

Each element 2a, 3a, 2b, 6, 2c constitutes one element of the optical means 102 for making the light beam from the light source means 101 incident on the scale 5a.

Then, of the plurality of diffracted lights generated from the fine grating array 5, for example, ± 1st-order diffracted lights are converted into mirrors 9a and 9b.
Then, the light is reflected back to the original optical path, and is again incident on the fine lattice array 5 of the scale 5a.

At this time, the ８ wavelength plate 1 is provided in one optical path.
1 so that the optical path length shift between the polarized light component S and the polarized light component f of the diffracted light from the fine grating array 5 is equivalent to １ ／ wavelength. Then, by diffracting the diffracted light back and forth through the ８ wavelength plate 11, the optical path length is shifted by １ ／ wavelength. For example, in the figure, the optical path length of linearly polarized light (s ⁻¹ ) parallel to the s-axis is inserted into the optical path of the −1st-order diffracted light to reduce the optical path length to １ ／
It is elongated by the wavelength (corresponding to delaying the phase by π / 2). Then, of the + 1st-order diffracted light, the phase of linearly polarized light (s ^{+ 1} ) parallel to the s-axis = 2π · 1 · X /
Phase of linearly polarized light (f ⁺¹ ) parallel to the P-f axis = 2π · 1 · X /
Phase of linearly polarized light (s ^-1 ) parallel to the s-axis of P-1 order diffracted light = -2π · 1 · X
/ P + π / 2 Phase of linearly polarized light (f ⁻¹ ) parallel to the f-axis = −2π · 1 · X
/ P.

The four light beams are reflected by the mirrors 9a and 9b and diffracted again by the fine grating array 5. +1 of these
^{+ 1st order} diffracted light (s ^{+ 1 + 1} ), (f ^{+ 1 + 1} ) of the second order diffracted light, and-
Only the -1st-order diffracted light (s- ^1-1 ) and (f- ^1-1 ) of the first-order diffracted light ^{enter the} coupling lens 2c.

The four light beams (s ^{+1 +1} ), (s ^{-1 -1} ), (f ^{+1 +1} ), (f ^{+1 +1} ), (f ^{+1 +1} ), which ^{again enter} the second end face 6b of the polarization maintaining fiber 6 by the coupling lens 2c. f ^-1-1 ) is a plane of polarization parallel to either the s-axis or the f-axis. The phase of each light beam at this time is (s ^{+ 1 + 1} ) phase = ^4.pi.X / P (s- ^1-1 ) phase = ^-4.pi.1.X / P + .pi. / 2 (f ^{+ 1 +1} ) = 4π · 1 · X / P (f ^−1-1 ) = − 4π · 1 · X / P

Therefore, in this embodiment, the light components of the s and f polarization planes interfere with each other. At this time, the light / dark signal IF of the f-polarized light component of the first set of the light beam f ^{+ 1 + 1} and the light beam f- ^1-1 is given by: IF = ｛sin (ωt + 4π · 1 · X / P) + sin (ωt−4π · 1 · X / P)｝ ² = （2 sin (ωt) · cos (4π · 1 · X / P)｝ ² = 4 · sin ² (ωt) · cos ² (4π · X / P) = 2 · sin ² (ωt) · ｛cos (8π ・ X / P) +1｝ = 2 ・ sin ² (ωt) ｛{1 + cos (8πＸX / P)｝ ... 4 cycles of cos per movement of one grid pitch The light-dark signal IS of the s-polarized light component of the second set of the wavy light-dark signal or the light flux s ^{+ 1 + 1} and the light flux s- ^1-1 is given by: IS = ｛sin (ωt + 4π · 1 · X / P + π / 2) + sin (ωt− 4π · 1 · X / P) } 2 = [{sin (ωt) + cos (ωt)} · {-sin (4π · X / P) + cos (4π · X / ^{)}] 2 = 2 · sin} 2 (ωt + π / 4) · {1-cos (8π · X / P-π / 2)} = 2 · sin 2 (ωt + π / 4) · {1-sin (8π · X / P)｝ …… Sine wave light / dark signal of four periods per movement of one pitch of the grating. As is clear from the equation, the two light and dark signals IF and IS of the f-polarized light component and the s-polarized light component have light and dark timings shifted from each other by π / 2.

In this embodiment, these two light-dark signals I
The optical axes (s-axis, f-axis) of the polarization plane maintaining fiber 6 whose polarization planes respectively represent the light and dark signal light beams LF and IS based on F and IS
And the beam is made to propagate so as to be parallel to. That is, the two light / dark signal light beams LF and LS propagate independently (without mutual interference) in the polarization plane maintaining fiber 6.

The two light and dark signal light beams LF and LS emitted from the first end face 6a of the polarization maintaining fiber 6 are converted into substantially parallel light beams by the coupling lens 2b while keeping their polarization planes orthogonal to each other, and are converted into non-polarized light beams. The light is reflected by the splitter 3a. The two light and dark signal light beams LF and LS are extracted by separating the two light and dark signal light beams LF and LS by the polarization beam splitter 12 for each polarization component.

The light / dark signal light flux is converted into an electric signal by the photoelectric elements 10a and 10b as the photoelectric conversion means 105 (after the amplitude is amplified), and a two-phase signal as an encoder is output from this.

In this embodiment, the photoelectric conversion means 10 at this time is
The movement information such as the movement amount and the movement direction of the scale 5a is detected using the signals obtained by the photoelectric conversion elements 5 (photoelectric elements 10a and 10b).

As described above, in this embodiment, by appropriately configuring one polarization plane holding fiber and each element, that is, two sets of diffracted light beams generated from the minute grating array of the scale interfere with each other for each polarization plane. When the light and dark signals IF and IS (the light and dark timings are shifted from each other) and the polarization plane maintaining fiber 6 is further transmitted, the light and dark signals LF and LS further interfere and the light and dark signals In order not to be disturbed, the polarization planes of the two light / dark signal light beams LF and LS are transmitted while being incident so as to be parallel to one of the optical axes (f-axis and s-axis) of the polarization maintaining fiber 6. Thus, the movement information of the scale 5a is detected with high accuracy while simplifying the entire apparatus.

In the present invention, the following modifications of the elements in the fifth embodiment described above can be similarly applied.

(5-a) Use of a combination of diffracted lights of orders other than ± 1st-order diffracted light as the diffracted light from the fine grating array on the scale.

(5-b) A mirror type beam splitting means having the same function is used instead of the prism beam splitter.

(5-c) The two diffracted lights obtained from the fine grating array (diffraction grating) provided on the scale are not limited to the reflection type, but may be the transmission type diffraction light as shown in FIG.
FIG. 17 shows only the vicinity of the scale 5a.
6 is supported. The same elements as those shown in FIG. 16 are denoted by the same reference numerals.

(5-d) Cat's eye optical elements 9c and 9d shown in FIG. 18 or FIG.
The diffraction grating reflection elements 9e and 9f shown in FIG.

According to this, it is possible to correct the optical path shift due to the wavelength fluctuation of the light beam from the light source. Incidentally, if the diffraction grating reflection elements 9e and 9f are reflection type diffraction gratings, the original optical path can be returned by using a periodic grating having a pitch which is half the pitch of the fine grating row 5 of the scale.

(5-E) As the cross-sectional structure of the polarization maintaining fiber, an elliptical core type, a PANDA type, or the like can be applied in addition to the so-called elliptical cladding type shown in the figure.

(5-f) The fine grid array provided on the scale is not limited to a linear one, but if a grid in which a radial grid is recorded on a rotating disk is used, it can be directly applied to a rotary encoder.

(5-g) Instead of the ８ wavelength plate, another wavelength plate or a crystal optical element having the same function may be used as long as a phase difference of 90 degrees can be provided between the two-phase signals. .

FIG. 20 is a schematic view of a main part of a sixth embodiment of the present invention. In the figure, the arrow indicates the traveling direction of the light beam, and the sinusoidal symbol indicates the plane of polarization. 101 is a light source means,
It has a light source 1 such as a two-frequency oscillation laser that oscillates light beams of at least two frequencies (wavelengths).

From the light source 1, two light beams (ν ₁ , ν ₂ ) of substantially parallel and mutually different frequencies having mutually orthogonal polarization planes are provided.
) Overlap and emit. These two light fluxes (ν
₁ , ν ₂ ) passes through the non-polarizing beam splitter 3a, is condensed by the coupling lens 2b, and is incident on the first end surface (incident surface) 6a of the polarization maintaining fiber 6. At this time, the optical axis (s axis,
The positions are aligned so that the polarization planes of the _two light beams (v ₁ , v ₂ ) coincide with each other. (Any combination may be used.) (Here, the polarization maintaining fiber 6 propagates the light beam while maintaining the polarization state. The optical axis of the polarization maintaining fiber 6 has a high propagation speed of the light wave. The direction is the f-axis and the slower direction is the s-axis.) Then, the s-axis component light beam and the f-axis component light beam of the light beam emitted from the second end surface (emission surface) 6b of the polarization maintaining fiber 6 are the light beam ν _1.
And light flux ν ₂ . Two light beams (ν ₁₎ from the exit surface 6b of the polarization maintaining fiber 6
, Ν ₂ ) are converted into substantially parallel light beams by the coupling lens 2 c, and a fine grating array 5 composed of a diffraction grating on the scale 5 a is formed.
Incident on

Each of the elements 3a, 2b, 6, 2c constitutes one element of the optical means 102 for causing the light beam from the light source means 101 to enter the scale 5a.

Of the plurality of diffracted lights generated from the fine grating array 5, for example, ± 1st-order diffracted lights (ν ₁ ⁺¹ and ν ₂ ^-1)
Is reflected by the mirrors 9a and 9b via the polarizing plates 8a and 8b, returned to the original optical path, and made incident again on the fine grid array 5 of the scale 5a.

At this time, the + 1st-order diffracted light is converted into linearly polarized light (s ^{+ 1} ) parallel to the s-axis by the polarizing plates 8a and 8b as shown in FIG.
= (Ν ₁ ⁺¹ ), the ^-1st -order diffracted light is linearly polarized light (f ⁻¹ ) = (ν ₂ ⁻¹ ) parallel to the f-axis. The components 8a, 8b, 9a, 9b constitute the components of the detection optical system 103.

These two luminous fluxes (s ⁺¹ , f ^-1 ) are diffracted again by the fine grating array 5 and ^{+ 1st-order} diffracted light of the + ^1st-order diffracted light (S
^{+ 1 + 1} ) = (ν ₁ ^{+ 1 + 1} ) and only the -1st-order diffracted light (f- ^1-1 ) = (ν ₂ ^-1-1 ) of the -1st-order diffracted light enters the coupling lens 2c. I do. The two light beams (s ^{+ 1 + 1} ) incident on the polarization maintaining fiber 6 again by the coupling lens 2c,
(F- ^1-1 ) has a polarization plane parallel to the s-axis and the f-axis, respectively, and propagates independently (without mutual interference) in the polarization-maintaining fiber 6.

First end face 6a of polarization maintaining fiber 6
The two light beams emitted from the light source are converted into substantially parallel light beams by the coupling lens 2b with their polarization planes orthogonal to each other, reflected by the non-polarizing beam splitter 3a, and are reflected by the two light beams (ν ₁ ^{+ 1 + 1} ,
ν ₂ ^-1-1 ) Polarizing plate (analyzer) 8 set to have transmission characteristics at an angle of 45 ° with respect to the polarization direction 8
c, which causes an interference phenomenon between the common polarization components of both light beams. Then, the light beam is converted into a light / dark signal light beam which repeats light / dark at the difference frequency between the oscillation frequencies of the two light beams.

The light / dark signal light beam is converted into photoelectric conversion means 105.
Is converted into an electric signal by the photoelectric element 10a, and a modulated phase signal as an encoder using heterodyne interference is output (after the amplitude is amplified).

In this embodiment, the photoelectric conversion means 10 at this time is
The movement information such as the movement amount and the movement direction of the scale 5a is detected using the signal obtained by the photoelectric conversion element 5 (photoelectric element 10a).

As described above, in the present embodiment, by appropriately configuring the two-frequency oscillation laser, one polarization-maintaining fiber, and each element, that is, the frequency generated from the fine grating array of the scale is different, and the diffraction order is small. When transmitting two different diffracted lights through the polarization maintaining fiber, the polarization planes of the two diffracted lights are made orthogonal to each other so that the two light beams do not interfere with each other to generate a bright and dark signal, and the optical axis (f
(Axis, s-axis) so as to be parallel to each other and transmit the signal, thereby detecting the movement information of the scale 5a with high accuracy while simplifying the entire apparatus.

In this embodiment, as a reference light / dark signal (signal not subjected to phase modulation due to movement of the scale 5a = difference signal of oscillation frequency of a two-frequency laser) from the non-polarizing beam splitter 3a as shown in FIG. May be used.

That is, as shown in FIG. 21, two light beams (ν
₁ , ν ₂ ) is transmitted through a polarizing plate (analyzer) 8 d set so as to have a transmission characteristic at an angle of 45 ° with respect to the polarization direction, causing an interference phenomenon between the common polarization components of both light beams. I have. Then, the light beam is converted into a light / dark signal light beam which repeats light / dark at a difference frequency between the oscillation frequencies of the two light beams (ν ₁ , ν ₂ ).

The light / dark signal light beam may be converted into an electric signal by the photoelectric element 10b (after its amplitude has been amplified), and a reference phase signal as an encoder utilizing heterodyne interference may be output and used.

In the present invention, the following modifications of the elements in the sixth embodiment can be similarly applied.

(6-a) Use of a combination of diffracted lights of orders other than ± 1st-order diffracted light as the diffracted light from the fine lattice array on the scale.

(6-b) A mirror type beam splitting unit having a similar function is used in place of the prism beam splitter.

(6-c) The two diffracted lights obtained from the fine grating array (diffraction grating) provided on the scale are not limited to the reflection type, but may be the transmission type diffraction light as shown in FIG.
FIG. 22 shows only the vicinity of the scale 5a. FIG. 20
Elements that are the same as the elements indicated by are given the same reference numerals.

(6-d) As shown in FIG. 23, the light beam from the polarization-maintaining fiber 6 is first split into two light beams using a prism 51 having a split surface BS, and then the scale 5a.
May be made incident on the fine lattice row 5.

FIG. 23 is developed based on the optical system of the sixth embodiment. In the figure, two light beams (ν ₁ , ν ₂ ) emitted from the exit surface 6b of the polarization maintaining fiber 6 correspond to the optical axis (s-axis, f-axis) directions of the polarization maintaining fiber 6, respectively. .

Therefore, the divided surface B of the prism 51 as shown in FIG.
A polarization beam splitter film deposited on S is used. For example, the reflected light beam on the division surface BS is an f-axis component light beam (ν
₂ ), the light beam transmitted through the division surface BS is separated and extracted like the s-axis component light beam (ν ₁ ). After the + 1st-order or -1st-order diffraction, respectively, the original optical path is returned to obtain two light beams having the same properties.

When a normal non-polarizing beam splitter film is used instead of the polarizing film, the s-axis component and the f-axis component are respectively orthogonal to each other in the optical path irradiated from the prism in the figure to the scale. What is necessary is just to arrange a polarizing plate so that it can be performed.

Instead of arranging the common mirror 9 at the positions of the diffracted lights s ^-1 and f ⁺¹ , respective mirrors may be arranged at the positions of the diffracted lights s ⁺¹ and f ^-1 .

(6-E) Instead of the mirrors 9a and 9b, the cat's-eye optical elements 9c and 9d shown in FIG.
The diffraction grating reflection elements 9e and 9f shown in FIG.

According to this, it is possible to correct the optical path shift due to the wavelength fluctuation of the light beam from the light source. Incidentally, if the diffraction grating reflection elements 9e and 9f are reflection type diffraction gratings, the original optical path can be returned by using a periodic grating having a pitch which is half the pitch of the fine grating row 5 of the scale.

(6-f) The structure of the cross section of the polarization maintaining fiber may be an elliptical core type, a PANDA type or the like in addition to the so-called elliptical cladding type shown in the figure.

(6-g) The fine grid array provided on the scale is not limited to a linear one, and if a grid in which a radial grid is recorded on a rotating disk is used, it can be applied to a rotary encoder as it is.

FIG. 26 is an embodiment showing an application example of the encoder of the present invention, and is a system configuration diagram of a drive system using the encoder. A drive output unit of a drive unit 200 having a drive source such as a motor, an actuator, and an engine;
Alternatively, the encoder 201 is provided in the moving part of the driven object.
Is attached to detect a displacement state such as a displacement amount and a displacement speed. The detection output of the encoder 201
The driving means 20 is controlled by the control means 202 so that the state set by the setting means 203 is obtained.
0 is transmitted to the drive signal. By configuring such a feedback system, the driving state set by the setting unit 203 can be obtained. Such a drive system is, for example, office equipment such as a typewriter, printer, copy machine, facsimile, etc., cameras, video equipment such as video equipment, further information recording and reproducing equipment, robots, machine tools,
The present invention can be widely applied not only to manufacturing apparatuses and transport machines, but also to general apparatuses having driving means, not limited thereto.

[0172]

According to the present invention, as described above, (7-a) by appropriately configuring one polarization maintaining fiber and each element, the light beam from the light source means can be efficiently moved to an arbitrary position. It is possible to achieve an encoder that can guide light and detect movement information of a scale (moving object) with high accuracy while simplifying the entire apparatus without being affected by a thermal environment.

In particular, in the present invention, a single polarization maintaining fiber is used, and the connection portion of the fiber is set to one place.
This facilitates transmission reliability and simplification of the entire device.

(7-b) By using the heterodyne interferometry and appropriately configuring one polarization maintaining fiber and each element, the light flux from the light source means can be reduced to an arbitrary position at the optical coupling section. Guides light efficiently so as to reduce
It is possible to achieve an encoder capable of detecting scale (moving object) movement information with high accuracy while simplifying the entire apparatus without being affected by a thermal environment.

Further, according to the present invention, since a signal can be transmitted as a heterodyne signal, loss of signal information due to fluctuations in signal light amount due to disturbance or instability of an optical fiber connection portion is very small, so that high precision and high resolution can be achieved. An encoder becomes feasible.

Further, a two-phase heterodyne signal is generated.
^Luminous flux (ν ₂ ^{+ 1 + 1} ) − (ν ₁ ^-1-1 ) ⁺¹ , (ν ₂ ^-1-1 ) −
Since (ν ₁ ^{+ 1 + 1} ) is subjected to the same amount of frequency modulation in the opposite direction, a difference between the two signals is obtained to obtain twice the sensitivity, so that high resolution can be easily achieved.

In addition, in the present invention, one polarization maintaining fiber is used, and the connection portion of the fiber is provided at one place, thereby facilitating transmission reliability and simplifying the entire apparatus.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view when a part of FIG. 1 is modified.

FIG. 3 is an explanatory view when a part of FIG. 1 is modified.

FIG. 4 is a schematic diagram of a main part of a second embodiment of the present invention.

FIG. 5 is a schematic view of a main part of a third embodiment of the present invention.

FIG. 6 is an explanatory view when a part of FIG. 4 is modified.

FIG. 7 is an explanatory view when a part of FIG. 5 is modified.

FIG. 8 is an explanatory view when a part of FIG. 4 is deformed.

FIG. 9 is an explanatory view when a part of FIG. 4 is deformed.

FIG. 10 is an explanatory view when a part of FIG. 4 is modified.

FIG. 11 is a schematic diagram of a main part of a fourth embodiment of the present invention.

FIG. 12 is an explanatory view when a part of FIG. 11 is modified.

FIG. 13 is an explanatory view when a part of FIG. 11 is modified.

FIG. 14 is an explanatory view when a part of FIG. 11 is modified.

FIG. 15 is an explanatory view when a part of FIG. 11 is modified.

FIG. 16 is a schematic view of a main part of a fifth embodiment of the present invention.

FIG. 17 is an explanatory view when a part of FIG. 16 is modified.

FIG. 18 is an explanatory view when a part of FIG. 16 is modified.

FIG. 19 is an explanatory view when a part of FIG. 16 is modified.

FIG. 20 is a schematic view of a main part of a sixth embodiment of the present invention.

FIG. 21 is an explanatory view when a part of FIG. 20 is modified.

FIG. 22 is an explanatory view when a part of FIG. 20 is modified.

FIG. 23 is an explanatory view when a part of FIG. 20 is modified.

FIG. 24 is an explanatory view when a part of FIG. 20 is deformed.

FIG. 25 is an explanatory view when a part of FIG. 20 is deformed.

FIG. 26 is an explanatory diagram of a drive system using the encoder of the present invention.

FIG. 27 is a schematic diagram of a main part of a conventional diffracted light interference type encoder.

FIG. 28 is a schematic view of a main part of a conventional diffracted light interference type encoder.

[Explanation of symbols]

 Reference Signs List 101 light source means 102 optical means 103 detection optical system 105 photoelectric conversion means 1 light source 2a collimator lens 2b, 2c coupling lens 3a, 3b beam splitter 5 micro lattice array 5a scale 6 polarization plane holding fiber 7a, 7b crystal optical element 8a, 8b, 8c, 8d Polarizer 9a, 9b Mirror 10a, 10b Photoelectric element 104 Superposition means 12 Beam splitter 11 1/8 wavelength plate

──────────────────────────────────────────────────続 き Continued on front page (31) Priority claim number Japanese Patent Application No. 3-283584 (32) Priority date October 3, 1991 (Oct. 10.3) (33) Priority claim country Japan (JP) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01D 5/26-5/38 G01B 11/00-11/30

Claims (8)

(57) [Claims] 1. A light beam from a light source means is radiated to the fine grid row of a scale provided with a fine grid row through an optical means,
Two diffracted lights of different orders generated from the fine grating array are reflected by a mirror or a diffraction grating reflecting element,
The diffracted light generated by re-entering the sub-array
Light is guided to the stage, taken out through a part of the optical means, overlapped and interfered with each other, a light / dark signal of a light beam based on the interference is detected by the photoelectric conversion means, and a periodic signal obtained from the photoelectric conversion means is used. In the encoder for obtaining relative movement information of the scale, the optical means has a polarization maintaining fiber in a part thereof, and the polarization planes of two diffracted lights generated from the fine grating array are orthogonal to each other, and the polarization An encoder characterized in that the direction of the wavefront is 45 degrees with respect to the f-axis or s-axis of the polarization maintaining fiber. 2. When the length and mode refractive index of the polarization maintaining fiber are L and β, respectively, the wavelength of the light beam from the light source means is λ ₀ , and n is an integer, 0.9 <(１ ／ + n) · 2. The encoder according to claim 1, wherein the following condition is satisfied: λ ₀ /(β·L)<1.1. 3. A light beam from a light source means is radiated to the fine grid row of the scale provided with the fine grid row through an optical means,
Two diffracted lights of different orders generated from the fine grating array are reflected by a mirror or a diffraction grating reflecting element,
The diffracted light generated by re-entering the sub-array
Light is guided to the stage, taken out through a part of the optical means, overlapped and interfered with each other, a light / dark signal of a light beam based on the interference is detected by the photoelectric conversion means, and a periodic signal obtained from the photoelectric conversion means is used. In the encoder for obtaining relative movement information of the scale, the optical means has a polarization maintaining fiber in a part thereof, and the polarization planes of two diffracted lights generated from the fine grating array are orthogonal to each other, and the polarization An encoder characterized in that the direction of the wavefront is 45 degrees with respect to the f-axis or s-axis of the polarization maintaining fiber. 4. A former by two of the mirror about the diffracted light <br/> or the diffraction grating reflective elements arising from the fine lattice columns
4. The encoder according to claim 3, wherein the light is guided to the optical unit after returning to the optical path, and diffracted again by the fine grating array. 5. A light source unit that oscillates light beams of at least two frequencies irradiates two light beams of different frequencies (ν1, ν2) to the fine grating rows of a scale provided with fine grating rows via optical means. and, different frequency among diffracted light generated from <br/> the fine lattice columns with the two light beams incident,
For two diffracted lights of different orders (m, n) whose polarization planes are orthogonal to each other , one is a mirror and the other is a λ / 4 phase plate
Reflected by a mirror or a diffraction grating reflecting element through
Re diffracted light produced by causing incident again on the lattice column 2 pairs (ν1m, ν2n), (ν1n , ν2m) formed, the
The light is guided to an optical means, and each set of the two diffracted lights is superimposed on each other and interferes with each other, and the two independent light and dark luminous fluxes (ν
2n−ν1m) and (ν2m−ν1n), the two light and dark luminous fluxes are detected by the photoelectric conversion unit, and the relative movement information of the scale is obtained by using the periodic signal obtained from the photoelectric conversion unit. The optical means has a polarization maintaining fiber in a part thereof, and the direction of the polarization plane of the two bright and dark light beams is configured to be parallel to the f-axis or the s-axis of the polarization maintaining fiber. And the encoder. 6. A light source unit irradiates a light beam from a light source means via an optical means to the fine grid array of a scale provided with the fine grid array, and two diffracted lights of different orders generated from the fine grid array are mirrored or diffraction grating. The light is reflected by the reflective element, and
The second diffracted light generated by being incident on the fine lattice
The light is guided to the optical means, overlapped and interfered, and a light / dark signal light beam based on the interference is detected by the photoelectric conversion means via the optical means, and a relative signal of the scale is obtained using a periodic signal obtained from the photoelectric conversion means. In the encoder for obtaining the movement information, the optical means has a polarization maintaining fiber in a part thereof, and causes two diffracted lights of each of the mutually orthogonal polarization planes among the diffracted lights from the fine grating array to interfere with each other. An encoder characterized in that two light / dark signal light beams are formed, and the directions of the polarization planes of the two light / dark signal light beams are parallel to the f-axis or the s-axis of the polarization-maintaining fiber. 7. A light source means for oscillating light beams of at least two frequencies irradiates two light beams of different frequencies to each of the fine grid rows of a scale provided with fine grid rows via optical means, and The frequencies resulting from the rows are different,
Mirror or diffract two diffracted lights of different orders
The light is reflected by the grating reflection element and re-enters the fine grating row.
Guiding the re-diffracted light generated by the light to the optical means, taken out through a part of the optical means, overlapped and interfered,
An encoder for detecting a light / dark signal of a light beam based on the interference by a photoelectric conversion unit and obtaining relative movement information of the scale using a periodic signal obtained from the photoelectric conversion unit; The polarization plane of the two diffracted lights generated from the fine grating array is orthogonal to each other, and the direction of the polarization plane is parallel to the f-axis or the s-axis of the polarization plane holding fiber. An encoder characterized by the above. 8. Two diffracted light beams generated from the fine grating array
About the mirror or the diffraction grating reflecting element.
8. The encoder according to claim 7, wherein the light is returned to the optical path, and is diffracted again by the fine grating array, and then guided to the optical unit.