JP2008249456A - Optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact optical encoder provided with high resolution without needing additional composition such as a wavelength plate and a polarizing plate essential in the conventional optical encoder by including a novel optical element, and at the same time, easy in alignment of an optical element. <P>SOLUTION: The optical encoder lessens a condensing angle of two diffraction lights by enlarging a grating period of a diffraction grating coupling the two branched diffraction lights rather than the grating period of a scale formed on a measuring object. By the composition, the optical encoder makes the alignment very easy by enlarging an allowable range of a position of an optical axis direction installing the diffraction grating of a coupling side. Even in the composition, it is proved that highly precise resolution of the optical encoder is maintained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical encoder that optically measures the amount of movement of an object to be measured, and more particularly to an optical encoder that has a high degree of freedom in designing an optical system and allows easy alignment of optical elements.

  2. Description of the Related Art Conventionally, an optical encoder as a grating interference type displacement measuring apparatus that measures a moving amount of a measurement object with high accuracy on the order of μm or less using a scale on which a diffraction grating is formed has been put into practical use. In general, in an optical encoder, a light intensity signal obtained as a result of making two coherent lights of the same wavelength incident at an equal incident angle on a scale on which a diffraction grating is formed, and then combining the diffracted lights with each other. The amount of scale movement is derived from The conventional optical encoder disclosed in Japanese Patent Laid-Open No. 6-194189 (Patent Document 1) employs a configuration in which light from a light source is divided into two by a beam splitter and the two divided lights are incident on a scale. However, in the optical system composed of optical elements such as mirrors and lenses disclosed in Patent Document 1, alignment for making two lights incident at the same incident angle is not easy. In addition, since the optical encoder disclosed in Patent Document 1 employs a configuration in which two lights are generated by a beam splitter, the light amounts of the two lights cannot be made equal, resulting in high resolution. It was difficult to realize.

In this regard, Japanese Patent Application Laid-Open No. 6-229718 (Patent Document 2) uses a transmissive diffraction grating as means for dividing light from a light source into two parts, thereby allowing the light source light to have the same amount of light and the + 1st order and −1. A configuration is disclosed in which the light is separated into the next diffracted light and incident on the scale symmetrically with respect to the optical axis of the light source. Further, Patent Document 2 simultaneously discloses a configuration in which the above-described + 1st order and −1st order diffracted lights are combined by a diffraction grating. According to the principle of the multiplexing interferometry, the shorter the grating period of the scale, the more accurately the displacement can be measured. However, if the grating period of the diffraction grating on the side where the separated light is multiplexed is shortened accordingly, In this case, strict alignment accuracy of the diffraction grating on the side for multiplexing the separated light is required. In this regard, Patent Document 2 does not disclose any specific relationship regarding the relationship between the grating periods of the plurality of diffraction gratings constituting the optical system.
JP-A-6-194189 JP-A-6-229718

The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to provide an optical encoder having high resolution and easy alignment of optical elements. It is another object of the present invention to provide a compact optical encoder that includes a novel optical element and does not require additional components such as a wave plate and a polarizing plate that are essential in the conventional optical encoder.

  As a result of earnestly examining the configuration of the optical system of the optical encoder that can alleviate the difficulty of alignment of the optical elements without sacrificing the resolution, the present inventor has determined the grating period of the diffraction grating on the multiplexing side. Even if it is larger than the grating period of the scale, in addition to facilitating the alignment of the multiplexing interference section regardless of the displacement accuracy, the practical resolution with reproducibility even if the light illuminating the scale is one place. Has been found to be possible to achieve the present invention.

  That is, according to the present invention, an optical encoder including a diffracted light branching unit and a diffracted light combining / interfering unit, wherein the diffracted light branching unit and the diffracted light combining / interfering unit are configured by a planar diffraction grating, An optical encoder is provided in which the diffraction grating period of the diffracted light combining and interfering part is larger than the diffraction grating period of the light branching part. In the present invention, it is preferable that the width in the periodic direction of the diffraction grating that multiplexes the diffracted light of the diffracted light combining interference unit is not longer than the length for uniformly detecting the light and darkness of the interference fringes.

  Further, according to the present invention, there is provided an optical encoder in which a quarter wavelength plate is provided for each optical path of two diffracted lights diffracted by the diffracted light branching section. Furthermore, according to another configuration of the present invention, a half-wave plate is disposed in an optical path of one of the two diffracted lights diffracted by the diffracted light branching unit, and the diffracted light combined An optical encoder in which a quarter-wave plate is disposed behind the interference unit is provided.

  In addition, according to another configuration of the present invention, the diffraction grating that combines the diffracted lights of the diffracted light combining interference unit includes a first diffraction grating and a B phase signal for generating an A phase signal. , The grating period of the first diffraction grating and the grating period of the second diffraction grating are equal, and the diffraction of the first diffraction grating and the second diffraction grating An optical encoder is provided in which the grating positions are shifted from each other by 1/8 of the grating period relative to the period direction.

  As described above, according to the present invention, an optical encoder having high resolution and easy alignment of optical elements is provided. The present invention also provides a compact optical encoder that does not require an additional configuration such as a wave plate or a polarizing plate.

  Hereinafter, the present invention will be described with reference to embodiments shown in the drawings, but the present invention is not limited to the embodiments shown in the drawings.

  FIG. 1 shows a schematic diagram of an optical encoder 10 according to a first embodiment of the present invention. In FIG. 1, the optical path is indicated by an arrow in order to explain the function of the optical encoder 10 (hereinafter, the same applies to FIGS. 2 to 4). The optical encoder 10 of this embodiment includes a diffracted light branching section R for branching coherent light emitted from a light source 12 such as a helium-neon laser, a solid-state laser, and a semiconductor laser into + first order diffracted light and −1st order diffracted light, A diffracted light combining interference unit I for combining the branched diffracted light and a light detecting unit D for detecting the combined interference light are configured.

  The coherent light emitted from the light source 12 enters perpendicularly to the periodic direction of the scale 14 configured as a reflective diffraction grating, and is then diffracted by + 1st order and −1st order. The two + 1st order and −1st order diffracted lights a and b have a phase difference corresponding to the relative displacement of the scale 14 and are simultaneously interfered by the diffracted light combining interfering section I to cause interference. The light intensity is detected by the light detection unit D. From this signal, the relative displacement of the scale 14 can be measured. In FIG. 1, 0th-order light (straight-ahead light) from the scale 14 is not illustrated, but is blocked as necessary (hereinafter the same as in FIGS. 2 to 4).

  In this embodiment, the scale 14 is movable by a moving stage 15 and is configured as a planar diffraction grating having a grating structure perpendicular to the moving direction M, and incident light from the light source 12 is incident. They are arranged so as to be diffracted symmetrically with a diffraction angle θ with respect to the direction. However, in an actual configuration, it is preferable to slightly shift the angle in the vertical direction from the diffraction direction so that the return light from the scale 14 does not return directly to the light source 12.

  The two diffracted beams a and b reflected and diffracted by the scale 14 enter the diffraction grating 16a and the diffraction grating 16b, respectively. The diffraction gratings 16a and 16b are both configured as diffraction gratings having the same grating period as the scale 14, and the two diffraction gratings are arranged so that the periodic direction of the scale 14 and the periodic directions of the diffraction gratings 16a and 16b are parallel to each other. 16a and 16b are arranged. Since it is configured in this way, the two diffracted beams a and b become two parallel beams a 'and b' after passing through the diffraction gratings 16a and 16b, respectively. That is, in the present embodiment, the diffracted light branching portion R is configured by the scale 14 and the diffraction gratings 16a and 16b.

  Next, the beams a 'and b' branched into parallel light beams are diffracted by the diffraction grating 20 and collected after passing through quarter-wave plates 18a and 18b used as phase adjusting devices. The diffraction grating 20 is arranged so that the periodic direction of the scale 14 and the diffraction gratings 16a and 16b are parallel to the periodic direction. Here, the optical axes of the quarter wave plates 18a and 18b are arranged at angles of + 45 ° and −45 ° with respect to the polarization directions of the beams a ′ and b ′, respectively, and the beams a ′ and b ′. Is diffracted by the diffraction grating 20 after passing through quarter-wave plates 18a and 18b, respectively, to become clockwise circularly polarized light a "and counterclockwise circularly polarized light b". A diffraction grating 22 is disposed at a position where the two diffracted beams a ″ and b ″ are collected and overlapped with each other, and are combined by the diffraction grating 22 to cause interference. The diffraction grating 22 is arranged so that the periodic direction of the scale 14, the diffraction gratings 16 a and 16 b, and the diffraction grating 20 is parallel to the periodic direction. In other words, in the present embodiment, the diffraction grating 20 and the diffraction grating 22 constitute a diffracted light combining interference unit I.

  Next, after the combined interference light c subjected to the combined interference is limited in beam width in the diffraction direction by the slit 24 arranged to extract a portion where the brightness and darkness of the interference fringes are uniform, a part of A polarized light component that passes through a transmission / reflecting plate 26 constituted by a half mirror or a beam splitter and enters a polarizing plate 28, and is polarized in the same direction as the polarized light of the diffracted light a and b by the polarizing plate 28 or shifted by 45 °. Is extracted and detected by the photodetector 30 as an A / B phase signal. The other part of the light is reflected by the transmission / reflection plate 26 and then enters the polarizing plate 28. The polarization of the A / B phase signal detected by the detector 30 by the polarizing plate 28 is deviated by 45 °. The polarized component is extracted and detected by the photodetector 32 as an A / B phase signal. That is, in the present embodiment, the light detection unit D is configured by the transmission / reflection plate 26, the polarizing plate 28, and the photodetectors 30 and 32.

  Note that the two A / B phase signals detected by the light detection unit D are detected as sine wave signals that are 90 ° out of phase with respect to the moving direction M of the scale 14. The detection signal whose phase is delayed by 90 ° with respect to the predetermined moving direction of the moving stage 15 may be determined as the B phase signal, and the reference detection signal may be determined as the A phase signal. The A phase signal and the B phase signal are fixed. It is important that the phase difference between the A / B phase signals is 90 °. By using these two signals for the A-phase signal and the B-phase signal, the displacement of the scale 14 including the moving direction and the like is measured with high accuracy. As described above, the physical configuration of the optical encoder 10 of the present embodiment has been described together with the function thereof. Further, the characteristics of the optical encoder 10 of the present embodiment will be described below.

  As shown in FIG. 1, in the optical encoder 10 of the present embodiment, all means for branching, condensing, and interfering light are configured by a planar diffraction grating. With such a configuration, the alignment becomes much easier as compared with an optical system using a conventional lens or mirror. In other words, when designing a desired optical path, a desired optical path can be uniquely realized simply by designing the grating period for the scale 14, diffraction grating 16, diffraction grating 20, and diffraction grating 22 described above. In the optical encoder 10 of this embodiment, since the grating period of the scale 14 and the grating period of the diffraction grating 16 are designed to be equal, the two diffracted lights a and b reflected and diffracted by the scale 14 are Each of the diffraction gratings 16a and 16b automatically becomes parallel light a′b ′. In this embodiment, the optical system of the optical encoder 10 is constructed symmetrically with respect to the optical axis of the light source 12 by adopting a configuration in which the two diffracted lights branched in this way are diffracted into parallel light. In addition, the separation distance S between the diffracted light branching portion R and the diffracted light combining / interfering portion I can be freely designed, so that the degree of freedom in device design increases.

  Furthermore, the optical encoder 10 of the present embodiment has the characteristics described below. Conventionally, in a configuration in which two branched diffracted lights are combined, the grating period of the diffraction grating on the side where the diffracted light is branched is designed to be equal to the grating period of the diffraction grating on the side where the diffracted light is combined. That was common sense. In general, it is possible to configure the apparatus more compactly by shortening the period as much as possible, and at the same time, when the parallel beams a ′ and b ′ are diffracted by the diffraction grating having the same period, the average disturbance of the spatial phase This is because it is intended to obtain a highly accurate combined interference signal by combining the beams a ″ and b ″ with less wavefront aberration. However, as a result of examining the alignment of the optical encoder 10, the present inventor has found that the optical encoder 10 shown in FIG. 1 has a grating period of the scale 14 and the diffraction grating 16 constituting the diffracted light branching section R, and a diffracted light multiplexing interference section. The idea that the grating periods of the diffraction gratings 20 and 22 constituting I are intentionally made different is obtained, and even if the grating periods of both are actually made different and the alignment accuracy of the diffraction grating 22 is relaxed, the detection signal does not deteriorate. It was proved that high-precision displacement can be measured.

  That is, in the optical encoder 10 of the present embodiment, the grating period of the diffracted light multiplexing interference unit I is designed to be larger than the periodic grating of the diffracted light branching part R. With such a configuration, the diffraction grating 20 with respect to the diffraction angle θ of the scale 14 which must be very large as the grating period of the diffracted light branching section R is shortened in order to improve the measurement accuracy. , 22 is designed to be larger than the grating period of the diffracted light branching section R, so that the beams a ″ and b ″ that are diffracted by the diffraction grating 20 and condensed / combined into the diffraction grating 22 can be obtained. It is possible to reduce the condensing angle θ ″. As a result, the smaller the condensing angle θ ″, the wider the overlapping area in the optical axis direction of the condensed beams a ″ and b ″. The allowable range of the position in the optical axis direction increases, and the alignment of the optical encoder 10 becomes much easier. That is, according to the present invention, an extremely practical length measuring device is constructed that can perform reproducible alignment without sacrificing measurement accuracy.

  The present invention has been described above with reference to the embodiment shown in FIG. 1, but the present invention is not limited to the above-described embodiment, and it goes without saying that various design changes are possible. Absent. This will be described below with reference to FIG. 2 and FIG.

  FIG. 2 shows an optical encoder 40 according to the second embodiment of the present invention. 2, the same reference numerals are used for components common to the optical encoder 10 shown in FIG. 1, and the description of the parts already described for the optical encoder 10 is omitted (hereinafter, FIG. 3 and FIG. 3). The same applies to 4).

  In the optical encoder 40 according to the second embodiment, the beam a ′ passes through the half-wave plate 42 used as a phase modulation device, and the polarization of linearly diffracted light is rotated by 90 °, and then the diffraction grating. On the other hand, the beam b ′ is incident on the diffraction grating 20 as it is. As a result, the polarization directions of the two diffracted lights of the beam a ′ and the beam b ′ are configured to be orthogonal to each other. Furthermore, in the optical encoder 40 according to the second embodiment, after the interference light combined by the diffraction grating 22 passes through the quarter-wave plate 44 that forms an angle of 45 ° with the polarization direction, a part of the interference light. Then, the light passes through the transmission / reflection plate 26 and is incident on the polarizing plate 28, and the polarizing component 28 takes out the polarized light component in the same direction as the polarized light of the diffracted light a and b or deviates from this by 45 ° to obtain the A / B phase. It is detected by the photodetector 30 as a signal. Another part of the light is reflected by the transmission / reflection plate 26 and then enters the polarizing plate 28, and the polarizing component 28 takes out a polarized light component whose 45 ° polarization is shifted from the diffracted light of the light. It is detected by the photodetector 32 as a phase signal. Also in this case, the two A / B phase signals detected by the photodetectors 30 and 32 are detected as two sine wave signals that are 90 ° out of phase with respect to the moving direction M of the scale 14. In this way, the optical encoder 40 functions as a highly accurate linear displacement meter, like the optical encoder 10 shown in FIG. It should be noted that the diffracted light branching portion in the present invention is not limited to the configuration shown in FIGS. This point will be further described with reference to FIG. 3 as a third embodiment of the present invention.

  FIG. 3 shows an optical encoder 50 according to the third embodiment of the present invention. The present invention is not limited to the case where the light from the light source 12 is directly perpendicularly incident on the scale as shown in FIGS. 1 and 2, but the light from the light source 12 as shown in FIG. The light is vertically incident on the transmission type diffraction grating 52, the two branched diffracted lights are made incident on two spaced points on the scale 54, and the diffracted light from the diffracted light is combined in the diffracted light combining interference unit I. It is a concept including the structure to be made. In FIG. 3, for the convenience of explanation, the half-wave plate and the quarter-wave plate are omitted. However, as described above with respect to the first and second embodiments, the beam a ′, It should be understood that a half-wave plate or a quarter-wave plate is appropriately disposed at predetermined positions on the optical paths of the beam b ′ and the beam c.

  Furthermore, the 4th Embodiment of this invention is described with reference to FIG. FIG. 4 shows an optical encoder 60 according to the fourth embodiment of the present invention. As shown in FIG. 4, in the optical encoder 60, an A / B phase signal such as a half-wave plate, a quarter-wave plate, a polarizing plate, etc. used in the first to third embodiments described above. Does not require additional configuration to generate In the present embodiment, the diffraction grating 62 also has a function of generating an A / B phase signal. Hereinafter, the diffraction grating 62 in the present embodiment will be described with reference to FIG.

  FIG. 5 is a schematic view showing the diffraction grating 62 and the transmission / reflection plate 26 arranged behind the diffraction grating 62 in the present embodiment. The diffraction grating 62 is composed of two diffraction gratings, that is, a diffraction grating A for generating an A / B phase signal and a diffraction grating B for generating an A / B phase signal. The diffraction grating A and the diffraction grating B are both Are arranged with a distance d in a direction perpendicular to the common periodic structure direction X. The diffraction grating A and the diffraction grating B have the same grating period P, and the diffraction grating A and the diffraction grating B are arranged with their diffraction grating positions shifted by 1/8 of the grating period P. Yes. As a result of the diffraction grating A and the diffraction grating B being arranged in this way, the light intensity combined and interfered by the diffraction grating A and the light intensity combined and interfered by the diffraction grating B are out of phase with each other by 90 °. It becomes a sinusoidal A / B phase signal.

  The combined interference light that has passed through the diffraction grating A passes through a transmission portion t of the transmission / reflection plate 26 through a slit (not shown), and is then detected as an A / B phase signal by a photodetector (not shown). The combined interference light passing through B is reflected by the reflection part r of the transmission / reflection plate 26 and then detected as an A / B phase signal by a photodetector (not shown). In this embodiment, in order to prevent the combined interference light from the diffraction grating A and the combined interference light from the diffraction grating B from mixing with each other, the separation distance d between the diffraction grating A and the diffraction grating B is set to 100 to 150 μm. It is preferable that

  FIG. 4 shows a configuration in which the slit 24 is disposed behind the diffraction grating 62. In this embodiment, the lateral width W of the diffraction grating 62 shown in FIG. 5 is the same as the width of the opening of the slit 24. By setting the size, it is possible to select a region where the interference light intensity changes uniformly, and as a result, the slit 24 can be omitted. Needless to say, this configuration is not limited to the above-described fourth embodiment, but can also be applied to the diffraction grating 22 in the embodiment shown in FIGS. 1 to 3. That is, the slit 24 can be omitted by making the width of the region where the grating structure of the diffraction grating 22 is formed the same as the width of the opening of the slit 24.

  Further, in the present embodiment, signals corresponding to the A phase and the B phase are directly detected by using the light receiver divided into two so as to correspond to the arrangement positions and directions of the diffraction grating A and the diffraction grating B, respectively. If so, the transmission / reflection plate 26 can be omitted, and the optical encoder 60 can be made more compact.

  In addition, the planar diffraction grating in the present invention directly etches a substrate such as soft glass, Pyrex (registered trademark), quartz glass, and zero-expansion glass using a mask pattern produced by photolithography or electron beam lithography, Alternatively, it is possible to create a replica (replica) using a mold made of quartz glass, silicon, etc. to form the periodic structure, and when producing this as a reflective diffraction grating The surface of these diffraction gratings is coated with a light reflective film such as a dielectric multilayer film or a reflective metal film, or the substrate is coated with a light reflective film such as a dielectric multilayer film or a reflective metal film, It can be manufactured by forming a periodic structure with the materials described above. In the present invention, the diffraction grating 16 and the diffraction grating 20 in the first to fourth embodiments can be blazed diffraction gratings. Employing a blazed diffraction grating in the diffraction grating 16 and the diffraction grating 20 improves the diffraction efficiency and increases the light utilization efficiency. Therefore, a low-power, small-sized and inexpensive semiconductor laser can be used, and a compact device can be used. Can be configured.

  Hereinafter, the optical encoder of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples described later.

Example 1
The optical encoder 10 according to the first embodiment shown in FIG. 1 was actually constructed under the following conditions and performance evaluation was performed. In this embodiment, a diffraction grating of 1200 lines / mm (period: 0.833 μm) is used for the scale 14 and the diffraction grating 16, and a diffraction grating of 110 lines / mm (period: 0.909 μm) is used for the diffraction grating 20 and the diffraction grating 22. Was used. The opening width of the slit 24 was 100 μm. In the present embodiment, a 635 nm semiconductor laser was used as the light source 12 and a piezo stage was used as the moving stage 15 to move the scale 14 in about 10 nm steps. A Si photodiode was used for the photodetector (hereinafter, the same applies to Example 2).

  FIG. 6 shows A-phase and B-phase output signals, and FIG. 7 shows a Lissajous figure. One period of the sine wave signal shown in FIG. 6 corresponds to 0.4166 μm, which is half of the scale period, and has a resolution of 0.01 μm in about 40 divisions, and it was shown that a resolution of the order of nm or less can be obtained. .

(Example 2)
The optical encoder 60 according to the fourth embodiment shown in FIG. 4 was actually constructed under the following conditions and performance evaluation was performed. In this example, a diffraction grating of 1200 lines / mm (period: 0.833 μm) was used for the scale 14 and the diffraction grating 16, and a diffraction grating of 110 lines / mm (period: 0.909 μm) was used for the diffraction grating 20. In addition, a diffraction grating of 110 lines / mm (period: 0.909 μm) is used for each of the diffraction grating A and the diffraction grating B of the diffraction grating 62, and the gap d between the diffraction grating A and the diffraction grating B is 150 μm. The opening width of the slit 14 was 100 μm.

  FIG. 8 shows A-phase and B-phase output signals, and FIG. 9 shows a Lissajous figure. One period of the sine wave signal shown in FIG. 8 corresponds to 0.4166 μm, which is half of the scale period, and the resolution is 0.01 μm in about 40 divisions. .

In addition, the slit 14 was removed from the configuration shown in FIG. 4, and the grating width W of the diffraction grating 62 (diffraction grating A and diffraction grating B) was set to 100 μm, and measurement was performed in the same manner as described above. As a result, it was shown that the same high resolution could be obtained even though the slit 14 was removed. The actual condensing angle: θ ″ for these diffraction gratings is represented by θ ″ = sin ⁻¹ (λ / P), where λ is the wavelength used and P is the period of the diffraction grating. In other words, assuming that the wavelength used is 0.635 μm, the diffraction grating has a period of 0.833 μm (1200 lines / mm), 1.6 μm (625 lines / mm), 3.33 μm (300 lines / mm), and 9.09 μm (110 lines / mm) The focusing angle with respect to the angle: θ ″ is 49.7 °, 23.4 °, 11.0 °, and 4 °, respectively. Therefore, it can be seen that the alignment accuracy can be relaxed almost proportionally as the diffraction grating period increases.

  In addition, when 300 lines / mm (period: 3.33 μm) are used for the diffraction grating 20 and the diffraction grating 62, the accuracy to match the combined position becomes stricter than that of 110 lines / mm, but 625 lines / mm ( It was difficult to align with good reproducibility with a diffraction grating with a period of 1.6 μm), but it was shown that reproducible alignment was sufficiently possible with this 300 grating / mm diffraction grating. .

  As described above, according to the present invention, an optical encoder having high resolution and easy alignment of optical elements is provided. The present invention also provides a compact optical encoder that does not require an additional configuration such as a wave plate or a polarizing plate. The optical encoder of the present invention is expected to contribute to the compactness of the optical device and the reduction of the manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic of the optical encoder which is the 1st Embodiment of this invention. Schematic of the optical encoder which is the 2nd Embodiment of this invention. Schematic of the optical encoder which is the 3rd Embodiment of this invention. Schematic of the optical encoder which is the 4th Embodiment of this invention. Schematic which shows the diffraction grating in the optical encoder which is the 4th Embodiment of this invention, and the permeation | transmission / reflection board arrange | positioned behind it. FIG. 3 is a diagram illustrating output signals of an A phase and a B phase of the optical encoder according to the first embodiment. The figure which made the Lissajous figure for one period of the output signal of the optical encoder of Example 1. FIG. FIG. 10 is a diagram illustrating output signals of A phase and B phase of the optical encoder according to the fourth embodiment. The figure which made the Lissajous figure for one period of the output signal of the optical encoder of Example 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical encoder, 12 ... Light source, 14 ... Scale, 15 ... Moving stage, 16 ... Diffraction grating, 18 ... 1/4 wavelength plate, 20 ... Diffraction grating, 22 ... Diffraction grating, 24 ... Slit, 26 ... Transmission / reflection Plates 28: Polarizing plate 30 ... Photo detector 32 ... Photo detector 40 ... Optical encoder 42 ... 1/2 wavelength plate 44 ... 1/4 wavelength plate 50 ... Optical encoder 52 ... Diffraction grating 54 ... Scale, 60 ... Optical encoder, 62 ... Diffraction grating

Claims (5)

An optical encoder including a diffracted light branching unit and a diffracted light combining unit,
The diffracted light branching unit and the diffracted light combining unit are configured with a planar diffraction grating,
An optical encoder in which a diffraction grating period of the diffracted light multiplexing interference part is larger than a diffraction grating period of the diffracted light branching part. The width in the periodic direction of the diffraction grating that multiplexes the diffracted light of the diffracted light combining interference section is equal to or less than the length for uniformly detecting the brightness of the interference fringes
The optical encoder according to claim 1. A quarter wavelength plate is disposed for each optical path of the two diffracted lights diffracted by the diffracted light branching section,
The optical encoder according to claim 1. Of the two diffracted lights diffracted by the diffracted light branching section, a half-wave plate is disposed in the optical path of one of the diffracted lights, and a quarter-wave plate is disposed behind the diffracted light combining interference section. Arranged,
The optical encoder according to claim 1. The diffraction grating for combining the diffracted light of the diffracted light combining interference unit comprises a first diffraction grating for generating an A phase signal and a second diffraction grating for generating a B phase signal,
The grating period of the first diffraction grating and the grating period of the second diffraction grating are equal,
The diffraction grating positions of the first diffraction grating and the second diffraction grating are shifted from each other by 1/8 of the grating period with respect to the periodic direction.
The optical encoder according to claim 1.

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