JP2007232681A - Photoelectric encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric encoder which facilitates alignment control to enhance user-friendliness. <P>SOLUTION: In this encoder, light-receiving sections 22a-22a6 contain transmissive diffraction gratings equally-spaced from irradiation (core) section 21a, comprise light-receiving sections for displacement detection 22a2, 22a3, 22a5, 22a6 to detect measuring axial displacement towards scale 10, and light-receiving sections for tilt monitoring 22a1, 22a4 to detect pitch and roll of detector plane towards scale 10 centering on irradiation section 21a. Additionally signal processing section 30 uses light-receiving signal from the light-receiving sections for tilt monitoring 22a1, 22a4 to compensate light-receiving signal of the light-receiving sections for displacement detection 22a2, 22a3, 22a5, 22a6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectric encoder used in a displacement measuring device, a machine tool, and the like, and more particularly to an optical encoder capable of adjusting the alignment of a read head.

In a photoelectric encoder using a reflection type phase grating scale, interference fringes of diffracted light having scale position information are generated by irradiating the reflection type phase grating scale with coherent light from a point light source. And length measurement is attained by phase-detecting this interference fringe (refer patent document 1).
JP 2004-53605 A

  Conventionally, in this type of photoelectric encoder, a 90 ° phase difference two-phase signal is obtained by obtaining a differential signal of a 90 ° phase difference four-phase signal centered on a point light source and arranged in a 2 × 2 matrix around the point light source. Can be obtained. However, when the detection surface of the read head in which the light receiving unit is disposed is inclined with respect to the scale, the obtained differential signal varies. In this way, DC fluctuations occur in the phase difference two-phase signal accompanying fluctuations in straightness in the length measuring section, and errors in phase detection increase.

  When the amount of light received decreases due to scale contamination or the like, the light sensitivity can be made constant by feeding back the light amount adjustment (APC) of the light source to the DC component of the light reception signal. However, if there is an error in the mounting alignment, the feedback is not properly applied and an error occurs in the length measurement signal.

  In view of the above, an object of the present invention is to provide a photoelectric encoder that facilitates alignment adjustment and improves usability.

  A first photoelectric encoder according to the present invention includes a scale in which a diffraction grating is formed at a predetermined pitch in the measurement axis direction, and an irradiation unit that is arranged to be relatively movable with respect to the scale and irradiates the scale with coherent light. And a plurality of light receiving units arranged around the irradiation unit at a predetermined interval in the measurement axis direction and a direction orthogonal thereto, and receiving light emitted from the irradiation unit and reflected by the diffraction grating of the scale Read signal heads arranged on the same detection surface, and signal processing means for detecting a displacement of the read head in the measurement axis direction relative to the scale by processing a light reception signal from a light receiving unit of the read head. In the photoelectric encoder, the light receiving unit has a transmissive diffraction grating arranged at an equal distance from the irradiation unit on a light receiving surface, and the measurement with respect to the scale. A light receiving unit for detecting a displacement for detecting a displacement in an axial direction; and a light receiving unit for an inclination monitor for detecting a pitch and a roll of the detection surface with respect to the scale with the irradiation unit as a center. Is characterized in that the received light signal of the displacement detecting light receiver is corrected by the received light signal from the tilt monitor light receiving section.

  According to the present invention, the displacement detection light-receiving unit, the tilt monitor light-receiving unit, and the signal processing means are provided, and the light-receiving signal of the displacement detection light-receiving unit is corrected by the signal from the tilt monitor light-receiving unit. Therefore, it is possible to provide a photoelectric encoder that facilitates alignment adjustment and improves usability.

  Hereinafter, a photoelectric encoder according to an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment]
A photoelectric encoder according to a first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the photoelectric encoder includes a scale 10 having a diffraction grating formed at a predetermined pitch in the measurement axis direction, a reading head 20 that emits light and receives light, and a scale detected by the reading head 20. And a signal processing unit 30 that corrects the received light signal based on the received light signal. The longitudinal direction of the scale 10 is the measurement axis X. The read head 20 is disposed so as to be relatively movable in the X direction while maintaining a predetermined distance D with respect to the scale 10. Note that the read head 20 may be fixed and the scale 10 may be moved relatively. That is, it is only necessary that the reading head 20 and the scale 10 are relatively movable in the X direction.

  In the following, the direction parallel to the surface of the scale 10 and orthogonal to the X direction is defined as the Y direction, and the direction orthogonal to the X direction and the Y direction, that is, the direction orthogonal to the surface of the scale 10 is defined as the Z direction. Further, the inclination in the XZ plane between the scale 10 and the reading head 20 is the P (Pitch) direction, the inclination in the YZ plane is the R (Roll) direction, and the inclination in the XY plane. Is the Ya (Yaw) direction.

  The scale 10 has a lattice 11 extending in the Y direction and periodically arranged at a predetermined pitch along the X direction. The grating 11 is related to the wavelength of the light source so that the zero-order diffracted light is attenuated in the X direction on the detection surface of the read head 20 and a Gaussian distribution of two peaks by the first-order diffracted light is obtained. It is decided by. Moreover, the grating | lattice 11 reflects light so that the light quantity distribution of the Gaussian distribution of one mountain may be formed, for example with respect to the Y direction.

  The read head 20 mainly includes one light source optical fiber 21, six light receiver optical fibers 22 arranged around the light source optical fiber 21, and one light source optical fiber 21 and six light receiver optical fibers. 22, a cylindrical first ferrule 23 surrounding the optical fiber 21, 22 and 22, and a cap-type second ferrule 24 provided at the tip of the first ferrule 23.

  Next, with reference to FIGS. 2 to 4, the optical fibers 21 and 22 constituting the read head 20 and the first ferrule 23 formed around the optical fibers will be described. 2 is a front view of the read head 20, FIG. 3 is a cross-sectional view of a surface orthogonal to the optical axis of the read head 20, and FIG. 4 is a cross-sectional perspective view in which a part of the read head 20 is cut away. .

  As shown in FIGS. 2 to 4, the light source optical fiber 21 has a refractive index higher than that of the core 21 a that guides light formed at the center of the core and the core 21 a that is formed on the outer periphery of the core 21 a. The clad 21b is formed of a low clad 21b and a coating 21c formed on the outer periphery of the clad 21b. For the light source optical fiber 21, for example, a single mode fiber is used.

  Similarly, the optical fiber for receiver 22 includes a core 22a for guiding light formed at the center thereof, a clad 22b having a lower refractive index than the core 22a formed on the outer periphery of the core 22a, and an outer periphery of the clad 22b. And the coating 22c formed on the surface. In addition, for example, a multimode fiber is used for the optical fiber 22 for the light receiver.

  The light source optical fiber 21 and the light receiver optical fiber 22 are accommodated in an inner tube 201 having an inner diameter slightly larger than a circumscribed diameter (hereinafter referred to as a bundle diameter) in which they are bundled. The inner tube 201 preferably has a bundle diameter of 0.15 or less. However, due to the close contact bias when the bundle is inserted, the optical fibers 21 and 22 are not moved even by about 0.2 times.

  The diameter of the light source optical fiber 21 including the core 21a and the cladding 21b is smaller than the diameter of the light receiving optical fiber 22 including the core 22a and the cladding 22b.

  Accordingly, the coating 21c of the light source optical fiber 21 is formed to be thicker than the diameter of the coating 22c of the optical fiber 22 for the light receiver, and the combined diameter of the core 21a, the cladding 21b, and the coating 21c of the light source optical fiber 21 is large. And the diameter of the core 22a, the cladding 22b, and the coating 22c of the optical fiber 22 for the light receiver are combined to be the same. Thus, even if the thickness of the core and the clad is different for each optical fiber by forming the thickness of the coatings 21c and 22c based on the thickness of the core and the clad, the diameter of the optical fiber is the same. It can be a diameter.

  Therefore, it is possible to closely arrange several fibers having different characteristics as in this embodiment. Further, since the optical fiber is covered and protected, the possibility of breakage is very low when the first ferrule 23 is inserted, and there is no coating removal work with a single wire. easy. Therefore, the manufacturing cost when manufacturing the bundled optical fiber bundle is reduced, and the yield can be improved.

  For example, a light source such as an LD is provided at the end of the light source optical fiber 21 opposite to the second ferrule 24 (not shown). Light emitted from a light source such as an LD is guided through the core 21a of the light source optical fiber 21 and is irradiated from the tip of the core 21a. That is, the tip of the core 21a of the light source optical fiber 21 functions as the irradiation unit 21a. In addition, the light used as the light source is preferably light having a good directivity with a uniform phase, such as laser light such as an LD or a gas laser.

  A light receiver such as a CCD is provided at the end of the light receiving optical fiber 22 opposite to the second ferrule 24 (not shown). Light received at the end of the core 22a of the optical fiber 22 for the light receiver on the second ferrule 24 side is guided through the core 22a, emitted from the opposite end of the core 22a, and received by the CCD. That is, the tips of the cores 22a of the six optical fibers 22 for the light receiver function as light receiving portions 22a1 to 22a6, respectively.

  As shown in FIG. 3, the centers of the six light receiving portions 22a1 to 22a6 are arranged in a hexagonal shape with the irradiation portion (core) 21a as the center so that the light receiving portions 22a1 and 22a4 are arranged in the Y direction. Yes. That is, the reading head 20 includes light receiving units 22a1 to 22a6 arranged on the same detection surface as the irradiation unit 21a with a predetermined interval around the irradiation unit 21a in the measurement axis direction and a direction orthogonal thereto. .

  The second ferrule 24 is provided at an opening 25 provided at a location corresponding to the core 21 a at the tip of one light source optical fiber 21 and at a location corresponding to the core 22 a at the tip of six optical fibers 22 for light receivers. And a slit 26 formed therein.

  The slit 26 includes a first slit 26a provided at a position corresponding to the light receiving portions 22a1 and 22a4 and a second slit 26b provided at positions corresponding to the other light receiving portions 22a2, 22a3, 22a5 and 22a6. Have.

  The first slit 26a is formed at a position shifted to one side in the X direction from the centers of the light receiving portions 22a1 and 22a4. As will be described later, the light receiving portions 22a1 and 22a4 whose incident light is blocked by the first slit 26a are used as light receiving portions for an inclination monitor for detecting the pitch of the detection surface relative to the scale 10 and the inclination in the roll direction. Is done.

  The second slit 26 b is a slit extending in the Y direction formed in a predetermined cycle in the X direction and forms a transmission type diffraction grating type corresponding to the grating 11 of the scale 10. Reflected light from the grating 11 of the scale 10 is received by the light receiving portions 22a2, 22a3, 22a5, and 22a6 through the second slits 26b. By measuring the amount of received light while moving the reading head 20 relative to the scale 10, it is possible to detect displacement in the measurement axis direction. That is, the light receiving units 22a2, 22a3, 22a5, and 22a6 are used as light receiving units for displacement detection for detecting displacement in the measurement axis direction with respect to the scale 10.

  Next, the intensity distribution of the reflected light from the scale 10 and the positions of the light receiving units 22a1 to 22a6 that receive the reflected light will be described with reference to FIG. In addition, since the light from the irradiation part 21a is a laser beam etc., it is irradiated with the intensity | strength which spreads in a Gaussian distribution (or Airy disk shape distribution) centering | focusing on an irradiation axis (Z direction).

  FIG. 5A shows the distribution of reflected light from the scale 10 in the X direction. The solid line shows an example of the alignment adjustment, and the broken line shows the alignment adjustment. This is an example in the case of not. As shown in FIG. 5A, in the X direction, the light irradiated from the irradiation unit 21a is affected by the unevenness of the grating 11 formed on the scale 10, and only ± first-order diffracted light is reflected. Is done. Therefore, the intensity of the reflected light is a superposition of two Gaussian distributions having a distribution center that is shifted from the center of the irradiation part 21a. By the first slit 26a, the light receiving portions 22a1 and 22a4 receive light at a position A1 between the peak P1 and the peak P2 of this distribution and shifted from the valley V of the distribution. Note that the shape of the Gaussian distribution of these reflected lights is determined by the light source wavelength, the period of the scale grating, the light source divergence angle, etc., so that the superposition of two Gaussian distributions necessarily has two peaks. I can't. Therefore, if the superposition of the Gaussian distribution has one peak, the light receiving units 22a1 and 22a4 are provided at positions that receive reflected light at positions shifted from the peak of the distribution.

  FIG. 5B shows the distribution of reflected light from the scale 10 in the Y direction. The solid line shows an example of the alignment adjustment, and the broken line shows the alignment adjustment. This is an example in the case of not. As shown in FIG. 5B, the reflected light is not affected by the grating 11 formed on the scale 10 in the Y direction. Therefore, the intensity distribution of the reflected light becomes one Gaussian distribution centering on the irradiation part 21a. The light receiving portions 22a1 and 22a4 are provided at positions where the reflected light is received at the skirts A2 and A3 of the Gaussian distribution that is symmetrically shifted from the peak P3 of the Gaussian distribution.

  The light receiving units 22a2, 22a3, 22a5, and 22a6 for detecting the displacement receive signals of a phase, bb phase, b phase, and ab phase that are different from each other due to the spatial phase of the slit 26b formed on the front surface thereof. To do. Here, the a phase and the b phase are 90 ° out of phase, the inverted signal of the a phase is the ab phase, and the inverted signal of the b phase is the bb phase. From these four-phase signals, two-phase A-phase signals (a-ab) and B-phase signals (b-bb) having a 90 ° phase difference can be obtained.

  Now, assuming that the scale 10 and the read head 20 are in an ideal alignment state, as shown in FIG. 6, the Lissajous waveform obtained from the A phase signal and the B phase signal is represented by the A phase axis and the B phase axis. It becomes an ideal circle centered on the intersection.

  On the other hand, when the reading head 20 includes an alignment error in the P (pitch) direction with respect to the scale 10, the Lissajous waveform generates a DC error and a phase error as shown in FIG. However, the center position varies over the second quadrant and the fourth quadrant, and the Lissajous waveform also becomes an ellipse. When the reading head 20 includes an alignment error in the R (roll) direction with respect to the scale 10, the Lissajous waveform generates a DC error and a phase error as shown in FIG. The center position fluctuates over the first quadrant and the third quadrant, and the Lissajous waveform also becomes an ellipse. Further, when the reading head 20 includes an alignment error in the Ya (yaw) direction with respect to the scale 10, the Lissajous waveform generates an amplitude error as shown in FIG. The radius becomes smaller. However, in this case, the Lissajous waveform itself is not distorted.

  Therefore, the alignment errors in the P direction and the R direction described above are detected and corrected by the light receiving units 22a1 and 22a4 for tilt monitoring.

  Next, with reference to FIG. 8, a functional block diagram of the signal processing unit 30 that corrects the alignment error based on the received light intensity will be described.

  The respective signals received by the light receiving units 22a1 and 22a4 are amplified by the amplifiers 31 and 32, respectively. The amplified signal is input to the first differentiator 33 and output as the difference signal. The first control unit 34 performs alignment adjustment of the photoelectric encoder, automatic adjustment of the light source power, and dynamic DC correction so that the difference signal is zero. That is, correction in the R direction is performed.

  The signals amplified in the amplifiers 31 and 32 are input to the first adder 36 from the branch portions 35a and 35b and added. On the other hand, the second adder 37 adds the signals received by the light receiving units 22a2, 22a3, 22a5 and 22a6. The second subtractor 38 calculates and outputs the difference between the addition signals input from the first adder 36 and the second adder 37. The second controller 39 performs alignment adjustment of the photoelectric encoder, automatic adjustment of the light source power, and dynamic DC correction so that the difference signal obtained by the second differentiator 38 becomes a predetermined value. That is, correction in the P direction is performed.

  As described above, the photoelectric encoder according to the first embodiment of the present invention uses the light receiving units 22a2, 22a3, 22a5, and 22a6 as the light receiving unit for detecting the displacement for detecting the displacement in the measurement axis direction with respect to the scale 10. The light receiving portions 22a1 and 22a4 are used as light receiving portions for an inclination monitor for detecting the pitch and roll of the detection surface. Furthermore, the displacement measurement value in the measurement axis direction obtained by the light receiving parts 22a2, 22a3, 22a5, 22a6 by the signal processing part 30 can be corrected based on the signals obtained by the light receiving parts 22a1, 22a4.

  With such a configuration, conventionally, alignment adjustment is performed by a Lissajous signal while relatively moving the reading head 20, but optimum alignment adjustment is possible even in a stationary state. Dynamic DC correction is also possible.

  In the dynamic range signal adjustment, the differential signal can be corrected in real time by adjusting the sensitivity and using it as a DC adjustment signal. Furthermore, since the straightness variation and the detection sensitivity can be DC-corrected in a linear proportional region, the range of variation can be expanded by performing linearization correction. In addition, accurate APC feedback is possible with respect to a decrease in the amount of received light due to dirt on the scale 10 or the like.

[Second Embodiment]
Next, a photoelectric encoder according to a second embodiment of the present invention will be described with reference to FIGS.

  The difference from the first embodiment of the photoelectric encoder according to the second embodiment is mainly in addition to the light receiving portions 22a1 to 22a6 of the six optical fibers 22 for the first embodiment as shown in FIG. The light receiving portions 22a7 and 22a8 by two light receiving optical fibers 22 are provided on the left and right sides (both sides in the X direction).

  Specifically, the read head 20 ′ according to the second embodiment includes one light source optical fiber 21 and eight light receiving optical fibers 22 arranged around the optical fiber 21 in a rectangular ferrule 23 ′. This is the structure formed. The ferrule 23 'is provided with a left V-groove alignment element 23'a and a right V-groove alignment element 23'b at its end. Eight light receiving optical fibers 22 are arranged so as to be adjacent to the interface between the left V-groove matching element 23'a and the right V-groove matching element 23'b. The light receiving portions 22a2, 22a3, 22a5, and 22a6 except for the light receiving portions 22a1, 22a4, 22a7, and 22a8 at the upper, lower, left, and right ends of the bundle of these eight optical fibers 22 for light receiving devices have a transmission having a groove parallel to the Y direction. A mask 26'b on which a type diffraction grating is formed is provided.

  In the read head 20 ′ according to the second embodiment, the light receiving portions 22 a 1 and 22 a 4 are provided so as to receive reflected light at locations located at equal distances in the Y direction from the center of the irradiation portion 21 a. In addition, the light receiving portions 22a7 and 22a8 are provided so as to receive reflected light at locations that are located at an equal distance in the X direction from the center of the irradiation portion 21a. The light receiving portions 22a2, 22a3, 22a5 and 22a6 are configured such that reflected light is received as interference fringes by the mask 26b '.

  In the light receiving units 22a1 to 22a8 arranged in this way, the signals obtained from the light receiving units 22a2, 22a3, 22a5, and 22a6 are used as signals for detecting the displacement in the measurement axis direction with respect to the scale 10 as in the first embodiment. . Further, the signal obtained from the light receiving units 22a7 and 22a8 is a signal for correcting the P direction of the light receiving unit with respect to the scale 10, and the signal obtained from the light receiving units 22a1 and 22a4 is corrected in the R direction of the light receiving unit with respect to the scale 10. Use as a signal for. That is, the respective light receiving portions 22a1 to 22a8 and the distribution of the reflected light in the X direction and the Y direction have the relationship shown in FIGS. 10A and 10B, which is different from FIG. 5 in the first embodiment. The light intensities A1 ′, A1 ′ and A2 ′, A2 ′ at both ends of the Gaussian distribution are detected in both the direction and the Y direction.

  Next, a signal processing unit 30 'of the photoelectric encoder according to the second embodiment will be described with reference to FIG. In the photoelectric encoder according to the second embodiment, the control in the P direction and the R direction is executed based on independent signals. Signals from the light receiving units 22a1 and 22a4 (light intensity distribution in the X direction) are amplified via amplifiers 31 'and 32', respectively, and a difference signal is generated by a differencer 33 '. The first control unit 34 ′ controls the photoelectric encoder so that the difference signal from the subtractor 33 ′ becomes zero, and performs correction in the P direction.

  Similarly, signals from the light receiving units 22a1 and 22a4 (light intensity distribution in the Y direction) are amplified through the amplifiers 31 ″ and 32 ″, respectively, and a difference signal is generated by the difference unit 33 ″. Then, the second control unit 39 ′ controls the photoelectric encoder so that the difference signal from the differentiator 33 ″ becomes zero, and corrects in the R direction.

  As mentioned above, although several embodiment of this invention was described, this invention is not limited to these, A various change, addition, substitution, etc. are possible within the range which does not deviate from the meaning of invention. For example, the light source is not limited to the one that guides laser light or the like by an optical fiber, and may be a surface light emitting diode or the like. Further, the circular light-receiving portion of the optical fiber is covered with a shielding object. However, the invention is not limited to using a light-receiving optical fiber, and a striped array CCD or the like can also be directly formed.

1 is a perspective view of a photoelectric encoder according to a first embodiment of the present invention. It is a front view of the read head concerning a 1st embodiment of the present invention. It is sectional drawing of the read head which concerns on 1st Embodiment of this invention. FIG. 2 is a perspective view in which a part of the read head according to the first embodiment of the present invention is cut away. It is a figure which shows the positional relationship of the read head which concerns on 1st Embodiment of this invention, and the spatial distribution of reflected light. It is a Lissajous waveform in the ideal alignment state. It is a Lissajous waveform when an alignment error is included. It is a functional block diagram of the signal processing part which concerns on 1st Embodiment of this invention. It is a front view of the read head concerning a 2nd embodiment of the present invention. It is a figure which shows the positional relationship of the read head which concerns on 2nd Embodiment of this invention, and the spatial distribution of reflected light. It is a functional block diagram of the signal processing part which concerns on 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Scale, 11 ... Grating, 20 ... Reading head, 21 ... Optical fiber for light source, 21a ... Core (irradiation part), 21b ... Cladding, 21c ... Coating | cover, 22 ... Optical fiber for light receivers, 22a1-22a6 ... Core (light reception) Part), 22b ... cladding, 22c ... coating, 23 ... first ferrule, 23 '... ferrule, 23'a ... left V-groove matching element, 23'b ... right V-groove matching element, 24 ... second ferrule, 26 ... Slit, 26a ... first slit, 26b ... second slit, 26b '... mask, 30, 30' ... signal processing unit, 31, 32, 31 ', 32', 31 '', 32 '' ... amplifier, 33, 33 ′, 33 ″, 38... Difference unit, 34, 34 ′... First control unit, 36, 37... Adder, 39, 39 ′.

Claims (4)

A scale in which diffraction gratings are formed at a predetermined pitch in the measurement axis direction;
Arranged so as to be relatively movable with respect to the scale, an irradiation unit that irradiates the scale with coherent light, and the irradiation unit is arranged around the irradiation unit with a predetermined interval in the measurement axis direction and a direction perpendicular thereto. A reading head in which a plurality of light receiving parts that receive light emitted from the irradiation part and reflected by the diffraction grating of the scale are arranged on the same detection surface;
In a photoelectric encoder including a signal processing unit that processes a light reception signal from a light receiving unit of the reading head and detects a displacement of the reading head in the measurement axis direction with respect to the scale.
The light receiving unit is
A displacement-detecting light-receiving unit for detecting a displacement in the measurement axis direction with respect to the scale having a transmission type diffraction grating arranged at an equal distance from the irradiation unit on a light-receiving surface;
An inclination monitor light receiving unit for detecting a pitch and a roll of the detection surface with respect to the scale around the irradiation unit;
The signal processing means includes
The photoelectric encoder, wherein the light reception signal of the displacement detection light receiver is corrected by a light reception signal from the inclination monitor light receiver. The light receiving part for tilt monitor is
A pair of first light-receiving units for monitoring that are equally arranged in the measurement axis direction around the irradiation unit;
A pair of second light receiving units for monitoring that are equally arranged in a direction perpendicular to the measurement axis with the irradiation unit as a center,
The signal processing means detects the pitch of the detection surface based on the difference value of the light reception signal of the first monitor light receiving unit and detects the roll based on the difference value of the light reception signal of the second monitor light receiving unit. The photoelectric encoder according to claim 1, wherein: The light receiving part for tilt monitor is
It consists of a pair of light receiving parts for monitoring that are shifted from the irradiation part to one side in the measurement axis direction and that are evenly arranged in the direction perpendicular to the measurement axis with the irradiation part at the center,
The signal processing means detects the pitch of the detection surface based on an addition value of the light reception signals of the monitor light receiving unit, and detects a roll based on a difference value of the light reception signals of the monitor light reception unit. The photoelectric encoder according to claim 1. The read head is
A first optical fiber having the irradiation section at the tip;
A second optical fiber disposed around the first optical fiber and having the light receiving portion at the tip;
2. The photoelectric encoder according to claim 1, further comprising: a cylindrical ferrule that tightly bundles the tip ends of the first and second optical fibers while being covered with a coating material.

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