JP2020056786A - Optical rotary encoder - Google Patents

Abstract

To provide an optical encoder having contamination resistance and fault tolerance.SOLUTION: An optical encoder structure 1400 includes a detector array 1465 having a rotary scale 1410 having a grating bar GB, an illumination light source 1420, a structured illumination generation mechanism SIGA, and an optical detector 1460. The structured illumination generation mechanism SIGA is constituted so that light source light 1434 is inputted to a first illumination region IR1 on the rotary scale 1410 that causes light to be diffracted to a beam polarizer structure BDC that sends out diffraction light so as to give an interference fringe pattern in the vicinity of a second illumination region IR2 on the rotary scale. The scale outputs light that forms a detector interference fringe pattern composed of relatively narrow optical intensity band in a detection interference fringe movement direction DFMD that is long in a rotation measurement direction θ and intersects the rotation measurement direction θ. The optical detector 1460 detects the position of the optical intensity band as a function of displacement of the rotary scale 1410 and gives a corresponding displacement or position signal.SELECTED DRAWING: Figure 14A

Description

  The present invention relates generally to precision position or displacement measurement devices, and more particularly to an encoder that performs signal processing that is resistant to errors due to contaminated or defective portions of the scale.

  The optical position encoder determines the displacement of the readhead relative to a scale having a pattern detected by the readhead. Typically, a position encoder has at least one scale track with a periodic pattern. The signal resulting from the scale is periodic as a function of the displacement or position of the readhead along the scale track. By using a plurality of scale tracks, an absolute type position encoder can give a specific combination of signals at each position in a direction along the absolute scale.

  Optical encoders can use incremental or absolute position scale structures. In the incremental position scale structure, the displacement of the readhead relative to the scale can be determined by accumulating incremental units of displacement starting from an initial position in the direction along the scale. Such an encoder is suitable for certain applications, especially where commercial power is available. For low power applications (e.g., a gauge powered by a battery), it is more desirable to use an absolute position scale structure. The absolute position scale structure provides a specific output signal or combination of signals at each position along the scale. Therefore, various power saving methods can be applied to the absolute position scale structure. Patent Documents 1 to 11 disclose one or both of various encoder structures and signal processing techniques relating to an absolute position encoder. By reference to these documents, these documents are incorporated herein in their entirety.

  There are encoder structures that achieve certain advantages by using an illumination source diffraction grating in the illumination section. Patent Documents 12 to 15 disclose such an encoder structure. The structures disclosed in these patents can be characterized as utilizing super-resolution moiré imaging.

  In various applications, manufacturing defects or contamination of the scale, such as dust or oil on the scale track, disturb the pattern detected by the readhead, resulting in errors in the resulting position or displacement measurements. In general, the size of an error due to a defect or contamination depends on factors such as the size of the defect or contamination, the wavelength of the periodic pattern on the scale, the size of the detection area of the readhead, and the relationship between these sizes. Dependent. Various methods for responding to an abnormal signal in an encoder are known. Almost all of these methods are based on disabling the encoder signal, providing an "error signal" alerting the user, adjusting the light source intensity to amplify low level signals, and the like.

U.S. Pat. No. 3,882,482 U.S. Pat. No. 5,965,879 U.S. Pat. No. 5,279,044 U.S. Pat. No. 5,886,519 U.S. Pat. No. 5,237,391 U.S. Pat. No. 5,442,166 U.S. Pat. No. 4,964,727 U.S. Pat. No. 4,414,754 U.S. Pat. No. 4,109,389 U.S. Pat. No. 5,773,820 U.S. Pat. No. 5,010,655 US Patent No. 8,941,052 US Patent No. 9,018,578 US Patent No. 9,029,757 U.S. Patent No. 9,080,899 JP-A-2003-65803 US Patent No. 8,493,572

  However, the above-described method does not provide a means for continuing accurate measurement operation regardless of an abnormal signal due to a certain scale defect or contamination. Thus, these methods have limited applications. A known method for reducing the influence of scale contamination and defects on measurement accuracy is disclosed in Patent Document 16. Patent Document 16 proposes a method in which a plurality of photodetectors output a periodic signal having the same phase, and each of these signals is input to a signal stability determination unit. The signal stability determination means outputs only the signal determined to be "normal", and the "normal" signals are combined to form a basis for position measurement. "Abnormal" signals are removed from the position measurement operation. However, the method of determining “normal” and “abnormal” signals disclosed in Patent Document 16 has a disadvantage that the use of the disclosure of Patent Document 16 is limited.

  U.S. Pat. No. 5,077,086 discloses a contamination- and defect-resistant optical encoder structure that provides a means for selecting a signal from a photodetector that is not affected by contamination. However, the structure of U.S. Pat. No. 6,077,067 relies on complex signal processing that is undesirable in some applications.

  There is a need for an improved technique that provides a highly accurate measurement operation that does not require complicated signal processing and that prevents or mitigates abnormal signals due to certain types of scale defects or contamination.

  The present invention has been made in view of the above circumstances, and has as its object to provide an optical encoder having stain resistance and defect resistance.

  The optical rotary encoder has a rotary scale, an illumination light source, a structured illumination generation mechanism, and a photodetector array. In some embodiments, the optical rotary encoder may be configured to use a rotary scale that is a cylindrical scale. In some embodiments, the optical rotary encoder may be configured to use a rotary scale that is a flat scale (for example, circular).

In each case, the rotary scale extends along a rotation measurement direction about a rotation axis orthogonal to the rotation plane. The rotary scale has a rotary scale grid composed of scale grid bars disposed on a rotating surface extending along the rotational measurement direction. The scale grating bars, thin in the rotating measuring direction, the rotation measurement is elongated in the rotary scale grating bars a direction intersecting the direction and periodically arranged in nominal scale pitch P _SF to the rotation measurement direction. The illumination light source has a light source that outputs light source light to a structured illumination generation mechanism, and the structured illumination generation mechanism has a first illumination area on the rotary scale, at least first and second deflection elements. A beam deflector structure and a second illumination area on the rotary scale. The structured illumination generating mechanism is configured such that the light source light is input to the first illumination area, and the first illumination area diffracts the light source light to form the structured illumination light as structured illumination light. Outputting to the beam deflector structure, the beam deflector structure intersects the diffracted beams of the structured illumination light with each other, and intersects the structured illumination light after the intersection with the second illumination on the rotary scale. And transmitting the light to an area to form an illumination interference fringe pattern in the second illumination area and to make it incident on the detector. The illumination interference fringe pattern is composed of stripes that are thin in the rotation measurement direction and long in the illumination interference fringe direction that intersects the rotation measurement direction.

  Of course, "structured illumination light" as used herein may be referred to as light beams or rays that interfere to form interference fringes or structured illumination in any of its optical paths. At some point in the optical path, such a light beam or beam may be in one or both of a separated and non-interfering state and a state that does not actively provide "structured illumination". However, at any position, such a light beam or light beam may still be referred to as "structured illumination light", as the configuration disclosed herein is important to the purpose or function during operation. .

  Of course, as used herein, the term "intersection" with respect to the diffracted light beam or order of the diffracted light, as described below, refers to detector interference output to scale light from the second illumination area. It is intended to refer to the configuration of the optical path to cause diffraction of such a beam by the grating in the first and second illumination areas, which enhances or adds to the change in the spatial phase of the fringe pattern. The two divergent beams of diffracted light are converged (e.g., at or near one of the axis of rotation and the optical path) together before being further deflected to converge and overlap these beams in the second illumination region. The term "intersecting" is used to describe such an optical path, since by deflecting to "intersect" this requirement is met by various beam polarizer structures in the first and second illumination areas on different sides of the rotary scale. Used for the configuration of

  The detector array has a set of N spatial phase detectors that are periodically arranged at a detector pitch PD in the direction of the detected interference fringes that intersects the rotational measurement direction. Each of the spatial phase detectors is configured to provide a spatial phase detector signal, wherein at least a majority of the spatial phase detectors extend in the rotational measurement direction over a relatively long dimension and intersect the rotational measurement direction. Is relatively narrow in the moving direction of the detected interference fringes. The set of N spatial phase detectors has a photodetector structure arranged in a spatial phase sequence along the detected interference fringe moving direction. In various aspects, the optical rotary encoder and the elements described above may be configured as follows.

  The rotary scale has a rotary scale grating bar direction on the rotating surface that is oriented in a direction that makes a non-zero yaw angle に 対 し て with respect to a direction intersecting the measurement axis direction along the rotating surface. The structured illumination generating mechanism may be configured such that the illumination interference fringe direction of the illumination interference fringe pattern near the second illumination area on the rotary scale is equal to the scale grating near the second illumination area on the rotary scale. The nominal interference fringe direction is rotated by a yaw difference angle YDA that is not 0 with respect to the bar direction. The rotary scale grating receives the illumination interference fringe pattern in the second illumination region and forms a periodic scale light pattern having the detector interference fringe pattern in the photodetector structure on the photodetector structure. Scale light may be output. The detector interference fringe pattern extends in a direction parallel to the rotation measurement direction over a relatively long dimension, is relatively thin in the detection interference fringe movement direction that intersects the rotation measurement direction, and includes the rotation measurement direction. And a periodic high light intensity and low light intensity band having a periodicity of the detected interference fringe period PDF in the detection interference fringe moving direction intersecting with the above. The detected fringe period PDF and the detected fringe moving direction intersect with the rotational measurement direction and depend at least in part on the non-zero yaw angle ψ. The high light intensity and low light intensity bands move in the detected interference fringe movement direction that intersects the rotation measurement direction as the scale grating rotates about the rotation axis. The photodetector structure detects a displacement of the high light intensity and low light intensity bands in the detection interference fringe moving direction intersecting with the rotation measurement direction, and outputs a spatial phase displacement signal indicating a displacement of a rotary scale. give.

  In various aspects described above, the non-zero yaw difference angle YDA is nominally -2 °. In various aspects, each of the N spatial phase detectors has an even number of scale light receiving regions. In various aspects, the detected interference fringe period PDF may be 40 μm or more. In various aspects, the beam deflector structure has a transparent optical block, and the deflecting element of the beam deflector structure consists of, or is formed on or attached to, the surface of the transparent optical block. It may be composed of a given element.

  As described above, in one embodiment, the optical rotary encoder is a “cylindrical rotary encoder” using a cylindrical rotary scale. Cylindrical rotary scales nominally have a cylindrical rotating surface provided with scale grids. In such an embodiment, the first and second illuminated areas are located proximate each of the different diameter ends of the cylindrical rotary scale, and the illuminating light source is in a line passing through the first and second illuminated areas. The light source light is output to the first illumination area along the direction.

  In one aspect of such a cylindrical rotary encoder, the beam deflector structure is located in a space that is partitioned by projecting a cylindrical rotating surface along the direction of the axis of rotation.

  In one aspect of such a cylindrical rotary encoder, the beam deflector structure receives each beam of the diffracted light source light output from the first illumination area, and converts each received beam near the rotation axis. And deflected along a convergent beam path leading to a divergent beam path, receiving the deflected beams and superimposing them via the convergent beam path, so that the illumination interference was in the vicinity of the second illumination area. Each received beam is deflected to form a fringe pattern. In one embodiment, the beam deflector structure has a surface, which is arranged on a different side with respect to the rotation axis and extends parallel to a diameter of the cylindrical rotary scale passing through the first and second illumination regions. And having the first and second parallel plate mirrors or gratings facing each other in a direction to receive each beam of the diffracted light source light output from the first illumination area. The first and second parallel plate mirrors or gratings further receive each beam of the diffracted light source light output from the first illumination area, and intersect near the rotation axis to connect to the divergent beam path. Deflecting each beam along the convergent beam path, receiving each deflected beam and superimposing the beams via the convergent beam path to provide the illumination interference near the second illumination area; So as to form a pattern, deflecting the respective beams received. In another aspect, at least one of the illumination light source and the beam deflector structure is configured such that each beam of the diffracted light source light converges near an intersection near the rotation axis; At least one of the detector structure and the detector array forms the periodic scale light pattern having the detector interference fringe pattern, and the output reflected scale light is nominally collimated at the photodetector structure. It is configured to be.

  In one aspect of such a cylindrical rotary encoder, the optical rotary encoder has a first measurement channel, a second measurement channel similar to the first measurement channel, and the first and second measurement channels. Each of the spatial phase shift signals of the measurement channel, or a combination of the measurements derived therefrom, mitigate or compensate for potential misalignment errors occurring in the individual spatial phase shift signals or the measurements derived therefrom. In one aspect, the first measurement channel includes the scale grid bar arranged along a first scale track of the rotary scale to form the yaw angle ψ, the second measurement channel Has the scale grid bars arranged along a second scale track of the rotary scale spaced from the first scale track in the direction of the axis of rotation so as to form a yaw angle -ψ; One said beam deflector structure is shared by said first and second measurement channels.

  As described above, in one embodiment, the optical rotary encoder is a “flat rotary encoder” using a flat rotary scale (for example, a circular shape).

Such various flat rotary encoders may be in the form of a transmission or reflection flat rotary encoder. Flat circular rotary scale has a Taber surface reflective scale grating bars arranged at a regular angular pitch AP _SF is provided. In an embodiment of a reflection type flat plate rotary encoder, the illumination light source, the beam deflector structure and the detector array of the first measurement channel are all arranged on the same side of the rotary scale. The first and second illumination areas are disposed near respective ends of the rotary scale having different diameters, and the illumination light source is arranged along a plane passing through the first and second illumination areas. The light source light is output to the first illumination area so as to form an incident angle with respect to the plane rotating surface in the plane. The beam deflector structure receives each beam of the diffracted light source light reflected and output by the first illumination area, and moves each received beam along a converging beam path that intersects near the rotation axis. So that each deflected beam follows the divergent beam path, reflects each beam to the vicinity of the intersection near the rotation axis, and each beam overlaps via the convergent beam path to form the second beam. Each beam is deflected so as to form the illumination interference fringe pattern in the vicinity of the illumination area, and the second illumination area receives the illumination interference fringe pattern and receives the illumination interference fringe pattern in the photodetector structure. And outputting scale light reflected at an incident angle with respect to the plate rotating surface so as to form the periodic scale light pattern having the following.

  In the aspect of the reflection type flat plate rotary encoder, at least one of the illumination light source and the beam deflector structure is configured such that each beam of the diffracted light source light converges near an intersection near the rotation axis. Wherein at least one of the beam deflector structure and the detector array forms the periodic scale light pattern having the detector interference fringe pattern, wherein the output reflected scale light is coupled to the photodetector structure. Is nominally configured to be collimated.

  In such an embodiment of the reflection-type flat plate rotary encoder, the first and second illumination regions are arranged near respective ends having different diameters passing through the rotation axis of the rotary scale, and the illumination light source includes: The light source light is applied to the first illumination area along a nominal illumination plane nominally perpendicular to the plate rotation plane and nominally parallel to the diameter and offset from the diameter by a nominal illumination plane offset. And the first and second illumination areas are each offset from the diameter by the nominal illumination plane offset, the nominal illumination plane offset being the direction in which the nominal illumination plane intersects the measurement axis direction In parallel to the nominal or average arrangement of the scale grid bars of the second illumination area making the non-zero yaw angle with respect to Rolling along the surface is configured to be placed, the nominal interference fringe direction yaw angle is rotated by the second yaw difference angle YDA not the 0 to the nominal illumination plane of the illumination area. In one embodiment, the non-zero yaw difference angle YDA is twice the non-zero yaw angle.

  In the aspect of the reflection type flat plate rotary encoder, the beam deflector structure includes first and second pairs of transmission type gratings and an intersection area reflector, and the first type of the transmission type gratings. Are arranged in a plane that is nominally parallel to the plane of rotation, and each grating of the first pair is a respective beam of the diffracted light source light reflected and output by the first illumination area. Wherein each grating of the first pair has a grating bar configured to deflect each light beam along the converging beam path that intersects near the axis of rotation; The area reflector is disposed near a position where the convergent beam path intersects near the rotation axis, reflects each beam from the intersection area reflector so as to follow the divergent beam path, and The pair of 2 Each grating of the second pair is arranged to receive each beam along the divergent beam path, and each grating of the second pair is arranged in a substantially parallel plane. A grating bar configured to overlap along the divergent beam path and form the illumination interference fringe pattern near the second illumination region. In one aspect, in the first pair of transmission gratings, each grating of the first pair receives collimated light of each beam and each beam along the convergent beam path converging near the axis of rotation. And a curved grating bar that deflects each beam near the axis of rotation, wherein in the second pair of transmission gratings, each grating of the second pair receives divergent light of each beam. A curve configured to collimate and deflect the light of each beam so that the beams of collimated light overlap along the convergent beam path to form an illumination interference fringe pattern near the second illumination area. Has a grid bar. In one embodiment, the intersection area reflector has a curved surface.

FIG. 2 is a partial and schematic three-dimensional exploded view of an optical encoder structure 100 having a stain resistance and a defect resistance that provides a displacement signal. FIG. 3 is a partial schematic view of an optical encoder structure 200 having a stain resistance and a defect resistance for providing a displacement signal. FIG. 4 is a partial schematic view of a photodetector structure 360 of the optical encoder structure 300 having stain resistance and defect resistance. It is a partial schematic diagram of the photodetector structure 460A of the optical encoder structure 400A having stain resistance and defect resistance. It is a partial schematic diagram of photodetector structure 460B of optical encoder structure 400B having stain resistance and defect resistance. FIG. 7 is a partial schematic view of an additional embodiment of an optical encoder structure 500 having a stain and defect resistance providing a displacement signal. 5 schematically illustrates scale light components SL1 and SL2 forming a detector interference fringe pattern 635 similar to or the same as detector interference fringe pattern 535 near photodetector structure 660 similar to light detector structure 560 of FIG. FIG. FIG. 14 is a second schematic diagram of scale light components SL1 and SL2 forming an interference fringe pattern 635. FIG. 7 is a graph 700 of characteristics of an optical encoder having contamination resistance and defect resistance similar to the optical encoder structure 500 shown in FIGS. 5 and 6. FIG. 7 is a schematic diagram 800 of an exemplary photodetector structure 860 that can be used in a contamination and defect resistant optical encoder similar to the optical encoder structure 500 shown in FIGS. 5 and 6. FIG. 9 is a schematic diagram illustrating a cross-section of another exemplary light detector structure 960A of the optical encoder 900A having contamination and defect resistance similar to the light detector structure shown in FIG. FIG. 9 is a schematic diagram illustrating a cross-section of another exemplary light detector structure 960B of the optical encoder 900B having contamination and defect resistance similar to the light detector structure 860 shown in FIG. FIG. 11 is a partial schematic view of an additional embodiment of an optical encoder structure 1000 having a stain resistance and a defect resistance for providing a displacement signal. It is a schematic diagram of the first illumination light source diffraction grating 1040. It is a schematic diagram of the 2nd illumination light source diffraction grating 1050. FIG. 14 is a partial schematic diagram of an additional embodiment of an optical encoder structure 1200 having stain and defect resistance to provide a displacement signal. FIG. 13 is a first schematic diagram of scale light components forming a scale light pattern 1235 proximate to a light detector structure similar to the light detector structure 1260 of FIG. FIG. 13 is a second schematic diagram of scale light components forming a scale light pattern 1235 proximate to a photodetector structure similar to the photodetector structure 1260 of FIG. 12. FIG. 13 is a third schematic diagram of scale light components forming a scale light pattern 1235 proximate to a light detector structure similar to the light detector structure 1260 of FIG. FIG. 13 is a fourth schematic diagram of scale light components forming a scale light pattern 1235 proximate to a photodetector structure similar to the photodetector structure 1260 of FIG. 12. FIG. 1 is a partial isometric view of a first embodiment of a stain and defect resistant optical rotary encoder structure using a cylindrical rotary scale to provide displacement signals. FIG. 14B is a partial view of the rotary scale grating of FIG. 14A showing further details of the illumination area on the rotary scale. FIG. 14A shows an embodiment of a contamination and defect resistant optical rotary encoder structure that can be similar or identical to the optical rotary encoder structure shown in FIG. 14A and that includes certain alternative elements. FIG. 2 is a partial schematic diagram when viewed along the line. A view along the axis of rotation showing a second embodiment of an optical rotary encoder structure using a cylindrical rotary scale and having a specific deformation element and providing a displacement signal and having contamination and defect resistance. FIG. FIG. 8 is a partial isometric view of a third embodiment of an optical rotary encoder structure having a stain resistance and a defect resistance using a flat rotary scale for providing a displacement signal. FIG. 17B is a partial view of the rotary scale grating of FIG. 17A showing further details of first and second illumination regions IR1 and IR2 on the rotary scale. FIG. 17B is a diagram schematically showing a grating pattern that can be used in one embodiment of a beam deflection structure that can be used for the rotary encoder structure shown in FIG. 17A.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and a repeated description will be omitted as necessary.

  In the following, a contamination and defect resistant optical encoder structure providing a displacement signal is disclosed. In the following, the stain and defect resistant optical encoder structure is to be understood as indicating the structure of the stain and defect resistant optical encoder.

  FIG. 1 is a partial, schematic, three-dimensional exploded view of an optical encoder structure 100 that provides a displacement signal and is resistant to contamination and defects. The encoder structure 100 has a scale grating 110, an illumination unit 120, and a photodetector structure 160.

  FIG. 1 shows an X direction, a Y direction, and a Z direction, which are orthogonal to each other, according to a custom. The X direction and the Y direction are parallel to the plane of the scale grating 110, and the X direction is parallel to the measurement axis direction MA (for example, the X direction is orthogonal to the elongated pattern elements of the scale grating 110). doing). The Z direction is perpendicular to the plane of the scale grating 110.

  In the embodiment shown in FIG. 1, the scale grating 110 is a transmission diffraction grating. The scale grating 110 extends in the measurement axis direction MA. The scale grating 110 is a periodic pattern composed of bars that are periodically arranged in the measurement axis direction MA, are thin in the measurement axis direction MA, and are long in a direction perpendicular to the measurement axis direction MA (that is, the Y direction). Having.

The illumination unit 120 includes an illumination light source 130, a first illumination grating 140, and a second illumination grating 150. The illumination light source 130 has a light source 131 and a collimating lens 132. The light source 131 is configured to output light source light 134 to the collimating lens 132. The collimating lens 132 is configured to receive the light source light 134 and output the collimated light source light 134 ′ to the first illumination grating 140. The first illumination grating 140 receives the source light 134 ′ and diffracts the source light 134 ′ toward the second illumination grating 150. The second illumination grating 150 receives the source light 134 ′ and further diffracts the source light 134 ′ toward the scale grating 110 via a path along the source light path SOLP. The scale grating 110 receives as input the source light 134 ′ along the source light path SOLP and outputs scale light having a periodic scale light pattern 135 to the photodetector structure 160 via a path along the scale light path SCLP. I do. Photodetector structure 160 receives periodic scale light pattern 135 from scale grating 110 via a path along the scale light path SCLP. The periodic scale light pattern 135 moves on the photodetector structure 160 in response to a relative displacement between the scale grating 110 and the photodetector structure 160 in the measurement axis direction MA. An example of a photodetector structure similar to photodetector structure 160 is shown in detail in FIG. The photodetector structure 160 has a set of N spatial phase detectors arranged in a spatial phase train along a direction intersecting the measurement axis direction MA (ie, the Y direction). Here, N is an integer of 6 or more. The spatial phase train consists of two outer spatial phase detectors located at the beginning and end of a direction intersecting the measurement axis direction MA, and an inner group of spatial phase detectors located between the two outer spatial phase detectors. And In the example shown in FIG. 1, the set of N spatial phase photodetectors has three spatial phase detector subsets S ₁ , S ₂ and S ₃ with the same subset spatial phase sequence.

  At least a majority of each of the spatial phase detectors is relatively long in the measurement axis direction MA and relatively thin in a direction orthogonal to the measurement axis direction MA (ie, the Y direction). At least a majority of each of the spatial phase detectors is spatially periodic scale light along the measurement axis direction MA, which is arranged corresponding to each of the spatial phases of the spatial phase detector according to the periodic scale light pattern. It has a light receiving area and is configured to provide a spatial phase detector signal. Within the spatial phase train, each of the inner group of spatial phase detectors is preceded and followed by a spatial phase detector having a different spatial phase than the spatial phase detector. The preceding and succeeding spatial phase detectors have different spatial phases. In other words, when attention is paid to one spatial phase detector, the spatial phase detector of interest is one or more succeeding spatial phase detectors and one or more preceding spatial phase detectors in a direction intersecting the measurement axis direction MA. With the spatial phase detector. However, when attention is paid to the spatial phase detector provided at the end in the direction crossing the measurement axis direction MA in the inner group, the noted spatial phase detector belongs to one outer phase detection and belongs to the inner group. It will be sandwiched by other spatial phase detectors.

  In various applications, the photodetector structure 160 and the illuminator 120 may be implemented to have a fixed relationship to each other, for example, in a readhead or gauge housing (not shown). According to known techniques, the photodetector structure 160 and the illuminator 120 are guided in the measurement axis direction MA with respect to the scale grating 110 by a bearing system. The scale grating 110 may be mounted on a movable stage, a gauge spindle, or the like in various applications.

  It will be appreciated that the stain and defect resistant optical encoder structure 100 is only one example of a stain and defect resistant optical encoder structure in accordance with the principles disclosed herein. In a variant, various optical components such as a telecentric imaging system and an aperture stop may be used. In a variant, the lighting section may have only one lighting grid.

  FIG. 2 is a partial schematic view of an optical encoder structure 200 having a stain resistance and a defect resistance for providing a displacement signal. The optical encoder structure 200 having stain resistance and defect resistance is similar to the encoder structure 100. 2XX and 1XX in FIG. 1 which are approximate codes indicate the same elements unless otherwise specified. The encoder structure 200 shown in FIG. 2 is a reflection type structure. Scale 210 is a reflective scale grating.

  FIG. 3 is a partial schematic view of a photodetector structure 360 of the optical encoder structure 300 having contamination resistance and defect resistance. The optical encoder structure 300 having contamination resistance and defect resistance is similar to the optical encoder structure 100 having contamination resistance and defect resistance or the optical encoder structure 200 having contamination resistance and defect resistance. Is also good. The photodetector structure 360 has a set of N spatial phase detectors arranged in a spatial phase array along a direction intersecting the measurement axis direction MA. Here, N is an integer of 6 or more. The spatial phase train consists of two outer spatial phase detectors located at the beginning and end of a direction intersecting the measurement axis direction MA, and an inner group of spatial phase detectors located between the two outer spatial phase detectors. And The majority of the spatial phase detectors are relatively long in the measurement axis direction MA and relatively thin in a direction orthogonal to the measurement axis direction MA. At least a majority of each of the spatial phase detectors is spatially periodic scale light along the measurement axis direction MA, which is arranged corresponding to each of the spatial phases of the spatial phase detector according to the periodic scale light pattern. It has a light receiving area and is configured to provide a spatial phase detector signal. Within the spatial phase train, each of the inner group of spatial phase detectors is preceded and followed by a spatial phase detector having a different spatial phase than the spatial phase detector. The preceding and succeeding spatial phase detectors have different spatial phases. In other words, when attention is paid to one spatial phase detector, the spatial phase detector of interest is one or more succeeding spatial phase detectors and one or more preceding spatial phase detectors in a direction intersecting the measurement axis direction MA. With the spatial phase detector. However, when attention is paid to the spatial phase detector provided at the end in the direction crossing the measurement axis direction MA in the inner group, the noted spatial phase detector belongs to one outer phase detection and belongs to the inner group. It will be sandwiched by other spatial phase detectors.

In an embodiment, the set of N spatial phase detectors may include at least M subsets of the spatial phase detectors. Here, M is an integer of 2 or more. Each of the M subsets has a spatial phase detector included in the set of N spatial phase photodetectors that provides a respective spatial phase. In the embodiment, M may be 3 or more. In the embodiment, M may be 6 or more. In an embodiment, each of the M subsets of spatial phase detectors may include spatial phase detectors providing the same spatial phase, arranged in the same spatial phase sequence subset. FIG. 3 shows an embodiment of the M subsets of the spatial phase detector denoted S ₁ -S _M. Subset S ₁ has spatial phase detectors SPD _1A , SPD _1B , SPD _1C and SPD _1D . The subset _{S 2} has a spatial phase detector _{SPD 2A, SPD 2B, SPD 2C} and _{SPD 2D.} The subset _SM has spatial phase detectors SPD _MA , SPD _MB , SPD _MC and SPD _MD . Each of the spatial phase detectors in FIG. 3 is represented as having K scale light receiving regions. As an example of the scale light receiving area, the spatial phase detector SPD _MD is labeled with scale light receiving areas SLRA _M1 and SLRA _MK . In the embodiment, K may be an even value.

In the embodiment shown in FIG. 3, the spatial phase sequence is a spatial phase detector including subscripts A, B, C, and D (eg, spatial phase detectors SPD _1A , SPD _1B , SPD _1C and SPD _1D ). Is represented. The spatial phase detectors with subscripts A and D are the two outer spatial phase detectors located at the beginning and end of each instance of the spatial phase sequence. The spatial phase detectors with subscripts B and C are the inner group.

The spatial phase detectors SPD _1A , SPD _1B , SPD _1C and SPD _1D output spatial phase detector signals A ₁ , B ₁ , C ₁ and D ₁ respectively. The spatial phase detectors SPD _2A , SPD _2B , SPD _2C and SPD _2D output spatial phase detector signals A ₂ , B ₂ , C ₂ and D ₂ respectively. The spatial phase detectors SPD _MA , SPD _MB , SPD _MC and SPD _MD output spatial phase detector signals A _M , B _M , C _M and D _M , respectively.

  A stain and defect resistant optical encoder structure according to the principles disclosed herein can tolerate 100 μm size contamination (eg, wire bonding contamination) and 300 μm size scale defects. Provide a simple design. Contamination or imperfections on the scale typically result in common mode error components at adjacent spatial phase detectors that can be offset by signal processing (eg, quadrature processing). Spatial phase detectors that are relatively long in the measurement axis direction MA and relatively thin in a direction orthogonal to the measurement axis direction MA provide better contamination and defect resistance. By reducing the structural frequency of the spatial phase detector in the measurement axis direction MA, the change in the signal level can be made more gradual. Further, such an encoder does not need to perform complicated signal processing for providing stain resistance and defect resistance. The signal provided by the set of N spatial phase detectors may be processed according to standard techniques known to those skilled in the art.

  In the embodiment as shown in FIG. 3, N is greater than or equal to 8, and each of the spatial phase detector subsets may have four spatial phase detectors, each having a spatial phase separated by 90 degrees. In a variant, each of the spatial phase detector subsets may have three spatial phase detectors, each having a spatial phase separated by 120 degrees.

In the embodiment shown in FIG. 3, the photodetector structure 360 is configured to combine spatial phase detector signals corresponding to the same spatial phase and to output each of the combined signals as a spatial phase position signal. It has a connection part. The photodetector structure 360 is configured to output four spatial phase position signals corresponding to spatial phases separated by 90 degrees. Spatial phase signals (eg, A ₁ , A _2, and A _M ) with the same letter notation are combined (eg, added) to provide spatial phase signals ΣA, ΣB, ΣC, and ΣD. In a variant, the photodetector structure may be configured to output three spatial phase position signals corresponding to spatial phases separated by 120 degrees. In other cases, furthermore, the spatial phase position signal may be used to determine the displacement signal by, for example, quadrature signal processing or three-phase signal processing.

  In a variant, each of the spatial phase detectors is relatively long in the measurement axis direction MA and relatively thin in a direction perpendicular to the measurement axis direction MA. At least a majority of each of the spatial phase detectors is spatially periodic scale light along the measurement axis direction MA, which is arranged corresponding to each of the spatial phases of the spatial phase detector according to the periodic scale light pattern. It has a light receiving area and is configured to provide a spatial phase detector signal.

  In the embodiment, the dimension YSLRA of the scale light receiving area of each of the N spatial phase detectors in the Y direction can be 250 μm at the maximum. In embodiments, YSLRA may be 5 μm or more.

  In the embodiment, the distance YSEP in the Y direction between the scale light receiving regions in an adjacent pair of N spatial phase detectors can be set to 25 μm at the maximum.

  In the embodiment, the dimensions YSLRA of the scale light receiving regions of the N spatial phase detectors are the same in the Y direction. In the embodiment, the distance YSEP in the Y direction between the scale light receiving regions in the adjacent pair of N spatial phase detectors is the same.

  There is a trade-off relationship between increasing the value of N and increasing the value of N, while increasing the value of N decreases the signal level of each of the spatial phase detectors. Needless to say.

FIG. 4A is a partial schematic diagram of a photodetector structure 460A of an optical encoder structure 400A having stain resistance and defect resistance. For simplicity, FIG. 4A has two spatial phase detector _{SPD 1A} and _{SPD 1B,} shows only one spatial phase detector subsets _{S 1.} The photodetector structure 460A has at least six spatial phase detectors based on the principles disclosed herein, but of course only two are shown for simplicity. In the embodiment shown in FIG. 4A, each of the N spatial phase detectors (eg, spatial phase detectors SPD _1A and SPD _1B ) is covered with a spatial phase mask (eg, phase masks PM _1A and PM _1B ). It has a photodetector (eg, PD _1A and PD _1B indicated by broken lines). The spatial phase mask blocks the scale light pattern so that the photodetector does not receive the periodic scale light pattern, except for those that pass through an opening provided in the spatial phase mask. In this case, the scale light receiving region has a spatial phase mask (e.g., the spatial phase mask _{PM 1A} and _{PM 1B)} photodetectors exposed through the respective openings (e.g., photodetectors _{PD 1A} and _{PD 1B).} In the embodiment shown in FIG. 4A, the scale light receiving area (that is, the opening) of the phase mask PM _1B is offset by 90 degrees in the measurement axis direction MA with respect to the scale light receiving area of the phase mask PM _1A . In FIG. 4A, the spatial phase masks PM _1A and PM _1B are schematically shown as separated portions. However, in the embodiment, in order to eliminate a potential positioning error, the spatial phase masks PM _1A and PM _1B are appropriately manufactured using the same material and the same process. Needless to say, it is good.

FIG. 4B is a partial schematic diagram of a photodetector structure 460B of the optical encoder structure 400B having stain resistance and defect resistance. For simplicity, FIG. 4B shows only one spatial phase detector subset S ₁ ′ having two spatial phase detectors SPD _1A ′ and SPD _1B ′. The photodetector structure 460B has at least six spatial phase detectors based on the principles disclosed herein, but of course only two are shown for simplicity. In the embodiment shown in FIG. 4B, each of the N spatial phase detectors (eg, spatial phase detectors SPD _1A ′ and SPD _1B ′) are electrically and interconnected to receive a periodic scale light pattern. A periodic array of photodetector regions. In this case, the scale light receiving area has a photodetector area that is a periodic array of photodetectors. In the embodiment shown in FIG. 4B, the photodetector area of the spatial phase detector SPD _1B ′ is offset by 90 degrees in the measurement axis direction MA with respect to the photodetector area of the spatial phase detector SPD _1A ′.

  FIG. 5 is a partial schematic diagram of an additional embodiment of an optical encoder structure 500 that provides a displacement signal and is resistant to contamination and defects. In the encoder structure 500, the periodic scale light pattern 535 to be detected is constituted by the detector interference fringe pattern 535. The detector interference fringe pattern 535 is composed of a band arranged to extend in the measurement axis direction MA over a relatively long dimension, and along the detection interference fringe movement direction DFMD while the optical encoder is displaced. And move so as to intersect the measurement axis direction.

The optical encoder structure 500 has a scale 510, an illumination light source 520, and a photodetector structure 560. The scale 510 extends in the measurement axis direction MA. Scale 510 has a scale grating composed of grating bars GB arranged substantially parallel to measurement axis direction MA on scale surface SP. Grid bars GB is thin the measuring axis direction MA, measuring axis direction MA and long in the lattice bar direction GBD crossing, it is periodically arranged with a scale pitch P _SF to the measuring axis direction MA. The illumination light source 520 includes a light source 530 and a structured illumination generation unit 533. Light source 530 outputs light 534 '. The structured illumination generation unit 533 receives the light 534 ′ and outputs the structured illumination 534 ″ to the illumination area IR on the scale plane SP. The structured illumination 534 ″ is thin in the measurement axis direction MA, forms a non-zero illumination interference fringe yaw angle に 対 し て with respect to the grating bar direction GBD, and is long in the illumination interference fringe direction IFD that intersects the measurement axis direction MA. It is composed of an illumination interference fringe pattern IFP composed of interference fringes. The light source 530 has a point light source 531 and a collimating lens 532. Point light source 531 outputs light 534 to a collimating lens, which collimates light 534 to light 534 '. In various embodiments, the non-zero illumination fringe yaw angle ψ may be used to move one or more elements of structured illumination generator 533 (eg, one of elements 540 and 550) to a desired angle with respect to the Y axis. , Around the Z axis. In embodiments, a non-zero illumination interference fringe yaw angle ψ may be realized or increased by rotating the grating bar direction GBD about the Z axis by a desired angle with respect to the Y axis.

  As will be described in more detail below with reference to FIGS. 8, 9A and 9B, the photodetector structure 560 is periodic at the detector pitch PD (see FIG. 6) in the detected interference fringe movement direction DFMD that intersects the measurement axis direction MA. Has a set of N spatial phase detectors arranged in a matrix. Each of the spatial phase detectors is configured to provide a spatial phase detector signal. At least a majority of the spatial phase detectors extend in the measurement axis direction MA over a relatively long dimension and are relatively narrow in the detection fringe movement direction DFMD that intersects the measurement axis direction MA. The set of N spatial phase detectors is arranged in a spatial phase sequence along the detected interference fringe moving direction DFMD.

  The scale 510 receives the illumination interference fringe pattern in the illumination area IR and outputs the scale light component via the scale light path SCLP. As a result, a detector interference fringe pattern 535 is formed on the photodetector structure 560. As described later in detail with reference to FIG. 6, the detector interference fringe pattern 535 extends in the measurement axis direction MA over a relatively long dimension and moves in the detection interference fringe movement direction DFMD that intersects the measurement axis direction MA. It is composed of high light intensity and low light intensity bands which are relatively thin and have a periodicity of the detected interference fringe period PDF in the detected interference fringe movement direction DFMD. To show these orientations, here the band extends in the measurement axis direction MA over a relatively long dimension, but in various embodiments the bands must be arranged along the measurement axis direction MA. It does not mean that it must not. As described below with reference to FIG. 6, in various exemplary embodiments, the bands may be arranged at a moderate or small angle with respect to the measurement axis direction MA.

  As will be described later with reference to FIG. 7, the detected interference fringe period PDF and the detected interference fringe movement direction DFMD that intersects with the measurement axis direction MA partially, but partially depend on the illumination interference fringe yaw angle 以外 other than zero. As the scale 510 is displaced in the measurement axis direction MA, the high light intensity and low light intensity bands move in the detection interference fringe movement direction DFMD crossing the measurement axis direction MA. The photodetector structure 560 is configured to detect the displacement of the high light intensity and low light intensity bands in the detection interference fringe movement direction DFMD that intersects the measurement axis direction MA and to provide a spatial phase displacement signal indicating the displacement of the scale. Is done.

  In the embodiment shown in FIG. 5, the structured illumination generating unit 533 has a first illumination light source diffraction grating 540 and a second illumination light source diffraction grating 550. In an embodiment, the first illumination light source diffraction grating 540 and the second illumination light source diffraction grating 550 may be phase gratings. Phase gratings provide higher output efficiency by reducing light loss.

  The optical encoder structure having contamination resistance and defect resistance according to the principle described with reference to FIGS. 5 to 9B is resistant to contamination of 100 μm (for example, wire bonding contamination) and scale defect of 300 μm. Provide a simple design to have. Contamination or imperfections on a scale that is the same size or larger than the detected fringe period can typically be canceled by signal processing (eg, quadrature processing) common mode errors in adjacent spatial phase detectors. Produces an ingredient. That is, the effect of contamination traveling along the measurement axis direction is shared between adjacent spatial phase detectors, and as the scale or readhead structure is displaced in the measurement axis direction, the measurement axis travels between adjacent spatial phase detectors. Move in the direction. Since the contamination effect is a conmode effect between adjacent spatial phase detectors, and the spatial phase detector extends in the measurement axis direction MA over a relatively long dimension that is substantially greater than the contamination effect Therefore, the influence of contamination on the accuracy of the displacement signal is substantially reduced. In the case of unprocessed non-common mode errors, as the photodetector structure 560 is displaced with respect to the scale 510, the portion of the detector interference fringe pattern 535 corresponding to the defect may be shifted from one spatial phase detector to another. Another advantage is that it moves very slowly to the phase detector, which allows the spatial phase displacement signal to be more efficiently compensated. Such an encoder can provide resistance to contamination and defects without requiring complicated signal processing. The spatial phase displacement signal provided by the set of N spatial phase detectors may be processed according to standard techniques known to those skilled in the art.

  FIG. 6A shows a scale light component SL1 and a scale light component SL1 similar to or the same as the detector interference fringe pattern 535 in the vicinity of the light detector structure 660 similar to the light detector structure 560 of FIG. A first diagram of SL2 is shown schematically. The detector fringe pattern 635 may be provided by an optical encoder similar to the optical encoder structure 500 outlined with reference to FIG. As described above with reference to FIG. 5, FIG. 6A shows a cross section of scale light that forms a detector interference fringe pattern 635 on a plane defined by the measurement axis direction MA and the scale light path SCLP. As shown in FIG. 6A, the scale light component includes a first scale light component SL1 and a second scale light component SL2 (shown by broken lines representing a high light intensity band). The first scale light component SL1 and the second scale light component SL2 each include parallel light rays, and the parallel light rays of the first scale light component SL1 are along directions at opposite angles with respect to the scale light path SCLP. The first scale light component SL1 and the second scale light component SL2 overlap to form a detector interference fringe pattern 635 according to a known principle. The first scale light component SL1 and the second scale light component SL2 may be formed by diffracted lights of different diffraction orders from the structured illumination generator. The detector interference fringe pattern 635 includes a dark or low light intensity band 635D represented by a broken line and a bright or high light intensity band 635L represented by a thick line.

  FIG. 6B schematically shows a second diagram of the scale light components SL1 and SL2 forming the interference fringe pattern 635. FIG. 6B shows a cross section near the photodetector structure 660 of the detector interference fringe pattern 635 on the plane defined by the measurement axis direction MA and the Y direction described above with reference to FIG. As shown in FIG. 6B, the detector interference fringe pattern 635 includes a dark or low light intensity band 635D represented by a thick line and a bright or high light intensity band 635L represented by a broken line. The dark or low light intensity band 635D and the bright or high light intensity band 635L have a periodicity of the detected interference fringe period PDF in the detected interference fringe moving direction DFMD. In general, the direction of movement of the detected interference fringes intersects the directions of the interference bands 635D and 635L with a slight rotation equal to the non-zero illumination interference fringe yaw angle に 対 し て with respect to the Y direction.

FIG. 7 is a graph 700 of the characteristics of an optical encoder having stain and defect resistance similar to the optical encoder structure 500 shown in FIGS. This graph shows the detected interference fringe period PDF with respect to the illumination interference fringe yaw angle ψ. Graph 700 includes a first illumination source diffraction grating of the grating pitch P _1, the second illumination source grating and stain resistance and defect resistance with structured illumination generating unit having a scale of the scale pitch P _SF of the grating pitch P ₂ 2 shows data of an optical encoder having the following. The above-mentioned pitches P ₁ , P ₂ and P _SF satisfy the following equations.

By the following equation, the detected interference fringe period PDF is linked to the illumination interference fringe yaw angle ψ.

  In general, for a contamination- and defect-resistant optical encoder, the detection fringe period PDF is configured to be large (for example, larger than 7 μm, or larger than 40 μm in some embodiments). Is desirable. In this case, the illumination interference fringe yaw angle ψ needs to be a small value (for example, less than 7 μm). A large value of the detected fringe period PDF provides good resistance to measurement errors due to misalignment between the scale, the photodetector structure and the illumination source. Errors due to pitch or rolling of the scale for one or both of the illumination light source and the photodetector structure are inversely proportional to the detected fringe period PDF. Therefore, the detection fringe period PDF having a large value provides good robustness against measurement errors caused by undulation of the scale.

  FIG. 8 is a schematic diagram 800 of an exemplary photodetector structure 860 that can be used in a contamination and defect resistant optical encoder similar to the optical encoder structure 500 shown in FIGS. 5 and 6. . Here, the photodetector structure has spatial phase detectors that extend in proximity to or approximately along the measurement axis direction and are periodically arranged crossing the measurement axis direction. 8XX of FIG. 8 and 5XX of FIG. 5, which are similar symbols, indicate similar elements unless otherwise specified.

  The photodetector structure 860 has a set of N spatial phase detectors arranged in a spatial phase sequence along the detected interference fringe movement direction DFMD. N is an integer of 6 or more. The spatial phase train consists of two outer spatial phase detectors located at the beginning and end of a direction intersecting the measurement axis direction MA, and an inner group of spatial phase detectors located between the two outer spatial phase detectors. And Each of the inner group of spatial phase detectors is preceded and followed by a spatial phase detector having a different spatial phase from the spatial phase detector in the spatial phase sequence. The preceding and succeeding spatial phase detectors have different spatial phases. In other words, when attention is paid to one spatial phase detector, the spatial phase detector of interest is one or more succeeding spatial phase detectors and one or more preceding spatial phase detectors in a direction intersecting the measurement axis direction MA. With the spatial phase detector. However, when attention is paid to the spatial phase detector provided at the end in the direction crossing the measurement axis direction MA in the inner group, the noted spatial phase detector belongs to one outer phase detection and belongs to the inner group. It will be sandwiched by other spatial phase detectors. Each of the spatial phase detectors has a spatial periodicity of the detected interference fringe moving direction DFMD, and is arranged corresponding to each of the spatial phases of the spatial phase detector according to the periodic scale light pattern. It has a scale light receiving area.

In an embodiment, the set of N spatial phase detectors may include at least M subsets of the spatial phase detectors. Here, M is an integer of 2 or more. Each of the M subsets has a spatial phase detector included in the set of N spatial phase photodetectors that provides a respective spatial phase. In the embodiment, M may be 4 or more. In the embodiment, M may be 6 or more. In an embodiment, each of the M subsets of spatial phase detectors may include spatial phase detectors providing the same spatial phase, arranged in the same spatial phase sequence subset. FIG. 8 shows an embodiment of the M subsets of the spatial phase detector denoted S ₁ -S _M. Subset S ₁ has spatial phase detectors SPD _1A , SPD _1B , SPD _1C and SPD _1D . The subset _{S 2} has a spatial phase detector _{SPD 2A, SPD 2B, SPD 2C} and _{SPD 2D.} The subset _SM has spatial phase detectors SPD _MA , SPD _MB , SPD _MC and SPD _MD .

In the embodiment shown in FIG. 8, the spatial phase sequence is a spatial phase detector including subscripts A, B, C, and D (eg, spatial phase detectors SPD _1A , SPD _1B , SPD _1C and SPD _1D ). Is represented. The spatial phase detectors with subscripts A and D are the two outer spatial phase detectors located at the beginning and end of each instance of the spatial phase sequence. The spatial phase detectors with subscripts B and C are the inner group.

The spatial phase detectors SPD _1A , SPD _1B , SPD _1C and SPD _1D output spatial phase detector signals A ₁ , B ₁ , C ₁ and D ₁ respectively. The spatial phase detectors SPD _2A , SPD _2B , SPD _2C and SPD _2D output spatial phase detector signals A ₂ , B ₂ , C ₂ and D ₂ respectively. The spatial phase detectors SPD _MA , SPD _MB , SPD _MC and SPD _MD output spatial phase detector signals A _M , B _M , C _M and D _M , respectively.

  In the embodiment as shown in FIG. 8, N is greater than or equal to 8, and each of the spatial phase detector subsets may have four spatial phase detectors, each having a spatial phase separated by 90 degrees. In a variant, each of the spatial phase detector subsets may have three spatial phase detectors, each having a spatial phase separated by 120 degrees.

In the embodiment shown in FIG. 8, the photodetector structure 860 is configured to combine spatial phase detector signals corresponding to the same spatial phase and to output each of the combined signals as a spatial phase position signal. It has a connection part. The photodetector structure 860 is configured to output four spatial phase position signals corresponding to spatial phases separated by 90 degrees. Spatial phase signals (eg, A ₁ , A _2, and A _M ) with the same letter notation are combined (eg, added) to provide spatial phase signals ΣA, ΣB, ΣC, and ΣD. In a variant, the photodetector structure may be configured to output three spatial phase position signals corresponding to spatial phases separated by 120 degrees. In other cases, furthermore, the spatial phase position signal may be used to determine the displacement signal by, for example, quadrature signal processing or three-phase signal processing.

  In the embodiment, the distance YSEP in the detection interference fringe moving direction DFMD between the respective scale light receiving regions of the adjacent pairs of the N spatial phase detectors may be 25 μm or less. In the embodiment, the distance YSEP in the detection interference fringe moving direction DFMD between the respective scale light receiving regions of the adjacent pairs of N spatial phase detectors is the same.

  FIG. 8 further shows the detector axis DA in the measurement axis direction MA. The detector axis is the direction parallel to the particular extension direction of the spatial phase detector. In general, it is desirable that the detector axis DA is orthogonal (substantially orthogonal) to the detected interference fringe moving direction DFMD. However, if a good displacement signal can be obtained, it is not strictly limited to this example. Therefore, in the embodiment, especially when the detection interference fringe movement direction DFMD is not orthogonal to the measurement axis direction MA, the detector axis may be rotated by the angle α with respect to the measurement axis direction MA. Since it is desirable to use a small illumination fringe yaw angle ψ (as described with respect to FIG. 7), the angle α may be significantly smaller. If the illumination fringe yaw angle ψ is a very small value, it is not necessary to rotate the detector axis DA with respect to the measurement axis direction MA.

FIG. 9A is a schematic diagram illustrating a cross-section of another exemplary photodetector structure 960A having an optical encoder 900A having contamination and defect resistance similar to the photodetector structure shown in FIG. For simplicity, FIG. 9A has two spatial phase detector _{SPD 1A} and _{SPD 1B,} shows only one spatial phase detector subsets _{S 1.} The photodetector structure 960A has more spatial phase detectors based on the principles disclosed herein, but of course only two are shown for simplicity. In the embodiment shown in FIG. 9A, each of the N spatial phase detectors (eg, spatial phase detectors SPD _1A and SPD _1B ) is covered with a spatial phase mask (eg, phase masks PM _1A and PM _1B ). It has a photodetector (eg, PD _1A and PD _1B indicated by broken lines). The spatial phase mask blocks the scale light pattern so that the photodetector does not receive the periodic scale light pattern, except for those that pass through an opening provided in the spatial phase mask. In this case, the scale light receiving area has photodetector areas (eg, photodetectors PD _1A and PD _1B ) exposed through respective openings of a spatial phase mask (eg, spatial phase masks PM _1A and PM _1B ). . In the embodiment shown in FIG. 9A, the scale light receiving area (that is, the opening) of the phase mask PM _1B is offset by 90 degrees in the detection interference fringe moving direction DFMD with respect to the scale light receiving area of the phase mask PM _1A . . In FIG. 9A, the spatial phase masks PM _1A and PM _1B are schematically shown as separated portions. However, in the embodiment, in order to eliminate a potential positioning error, the spatial phase masks PM _1A and PM _1B are appropriately formed of the same material and the same process. Needless to say, it is good.

FIG. 9B is a schematic diagram illustrating a cross-section of another exemplary photodetector structure 960B of the optical encoder 900B having contamination and defect resistance similar to the photodetector structure 860 shown in FIG. For simplicity, FIG. 9B shows only one spatial phase detector subset S ₁ ′ with two spatial phase detectors SPD _1A ′ and SPD _1B ′. The photodetector structure 960B has more spatial phase detectors based on the principles disclosed herein, but of course only two are shown for simplicity. In the embodiment shown in FIG. 9B, each of the N spatial phase detectors (eg, spatial phase detectors SPD _1A ′ and SPD _1B ′) are electrically and interconnected to receive a periodic scale light pattern. A periodic array of photodetector regions. In this case, the scale light receiving area has a photodetector area that is a periodic array of photodetectors. In the embodiment shown in FIG. 9B, the photodetector region of the spatial phase detector SPD _1B ′ has a 90 ° spatial phase in the detection interference fringe movement direction DFMD with respect to the photodetector region of the spatial phase detector SPD _1A ′. Offset by shift.

  In an embodiment of a photodetector structure similar to photodetector structures 960A and 960B, it is advantageous for each of the N spatial phase detectors to have an even number of scaled light receiving areas. The 0th-order diffracted light component of the scale light can fluctuate the light intensity of the fringes alternately appearing in the scale light. Therefore, this variation is averaged by using an even number of scale light receiving regions.

  FIG. 10 is a partial schematic view of an additional embodiment of an optical encoder structure 1000 having a contamination resistance and a defect resistance for providing a displacement signal. In the encoder structure 1000, the periodic scale light pattern 1035 to be detected is constituted by the detector interference fringe pattern 1035. The detector interference fringe pattern 1035 is composed of bands arranged to extend in the measurement axis direction MA over a relatively long dimension, the direction intersecting the measurement axis direction during displacement of the optical encoder. It moves along the interference fringe moving direction DFMD.

The encoder structure 1000 has a scale 1010, an illumination light source 1020, and a photodetector structure 1060. The scale 1010 has a scale grid composed of grid bars GB arranged on a scale plane SP substantially parallel to the measurement axis direction MA. Scale grating bar GB is thin the measuring axis direction MA, long scale grating bar direction SGBD perpendicular to the measuring axis direction MA, it is periodically arranged with a scale pitch P _SF to the measuring axis direction MA. The illumination light source 1020 includes a light source 1030 and a structured illumination generation unit 1033. Light source 1030 outputs light 1034 '. The structured illumination generation unit 1033 receives the light 1034 ′ and outputs the structured illumination 1034 ″ to the illumination area IR on the scale plane SP via the light source optical path SOLP. The structured illumination 1034 ″ is an illumination interference pattern IFP that is thin in the measurement axis direction MA, is oriented in a direction intersecting the measurement axis direction MA, and is composed of long stripes in the illumination interference fringe direction IFD. The light source 1030 has a point light source 1031 and a collimating lens 1032. Point light source 1031 outputs light 1034 to a collimating lens, which collimates light 1034 to light 1034 '.

  As described above in detail with reference to FIGS. 8, 9A and 9B, the photodetector structure 1060 has a detector pitch PD (see FIGS. 6A and 6B) in a detection interference fringe movement direction DFMD that intersects the measurement axis direction MA. ) Has a set of N spatial phase detectors arranged periodically. The spatial phase detectors are each configured to provide a phase detection signal. At least a majority of the spatial phase detectors each extend in the measurement axis direction MA over a relatively long dimension and are relatively narrow in the detection fringe movement direction DFMD that intersects the measurement axis direction MA. The set of N spatial phase detectors is arranged in a spatial phase sequence along the detected interference fringe moving direction DFMD.

  As in the case of the encoder structure 500, the scale 1010 receives the illumination interference fringe pattern in the illumination region IR and outputs the scale light component via the scale light path SCLP. As a result, a detector interference fringe pattern 1035 is formed on the photodetector structure 1060. As described above with reference to FIG. 6, the detector interference fringe pattern 1035 extends in the measurement axis direction MA over a relatively long dimension and extends in the detection interference fringe movement direction DFMD orthogonal to the measurement axis direction MA. It is relatively thin and has high intensity and low intensity bands that are periodic with the detected interference fringe period PDF.

The scale grating bar direction SGBD points in a direction forming a non-zero yaw angle ψ _SC with respect to the read head surface RHP defined by the light source light path SOLP and the scale light path SCLP.

  The structured illumination generation unit 1033 includes a first illumination light source diffraction grating 1040 and a second illumination light source diffraction grating 1050. These are shown in more detail in FIGS. 11A and 11B. In an embodiment, the first illumination light source diffraction grating 1040 and the second illumination light source diffraction grating 1050 may be phase gratings.

As described above with reference to FIG. 7, the detected interference fringe period PDF and the detected interference fringe movement direction DFMD that intersects with the measurement axis direction MA are partially, but not zero, the illumination interference fringe yaw angle _{ＳＣ SC} . Dependent. As the scale 1010 is displaced in the measurement axis direction MA, the high intensity and low intensity bands move in the detection interference fringe movement direction DFMD that intersects the measurement axis direction MA. The photodetector structure 1060 is configured to detect high and low intensity band displacements in a detected interference fringe movement direction DFMD that intersects the measurement axis direction MA, and outputs a spatial phase displacement signal indicating scale displacement, respectively. give.

  FIG. 11A is a schematic diagram of the first illumination light source diffraction grating 1040. FIG. 11B is a schematic diagram of the second illumination light source diffraction grating 1050. In various embodiments, the optical encoder 1000 is desirably configured to minimize errors in the displacement signal caused by variations in the gap between the scale 1010, the illumination source 1020, and the photodetector structure 1060.

As shown in FIG. 11A, the first illumination source grating 1040 is composed of a first index grating bars which are periodically arranged in the first index pitch P ₁ in the first index plane. The first index grating bar is narrow in the measurement axis direction, intersects with the measurement axis direction, and is long in the direction of the first index grating bar rotated by an angle に 対 し て_{1 with} respect to the read head surface RHP. As shown in FIG. 11B, the second illumination source grating 1050 is composed of a second index grating bars which are periodically arranged in the second index pitch P ₂ in the second index plane parallel to the first index plane . Second index grating bars, thin the measurement axis direction, intersects the measuring axis direction, and long in the second index grating bars direction being rotated by an angle [psi ₂ to the read head surface RHP.

In various embodiments, such as optical encoder 500, the dynamic gap error is caused by scale waviness, which is a variation in the distance between illuminator 520 and scale 510 along the source light path SOLP. . When the optical path length in the direction along the scale optical path SCLP changes, the relative phase of the interference light beam forming the detector interference fringe pattern 1035 changes.
In various embodiments, _{１ 1} and ψ ₂ may be selected to provide dynamic gap errors of the same magnitude and different codes. Two interference light phase of the interference light beams forming a detector fringe pattern 1035, [Phi ₊ and [Phi _- may be represented by. The wavelength of the light output from the light source 1030 is λ. The dynamic gap error DGE is related to the gap variation Δg in a direction perpendicular to the measurement axis direction MA and the scale grid bar direction SGBD (ie, the Z direction). The dynamic gap error DGE is expressed by the following equation.

More specifically, the differential term in the above equation is represented by the following equation.
Here, the coefficient Ω is defined by the following equation.

は、第１照明光源回折格子１０４０ 及び第２照明光源回折格子１０５０のそれぞれのヨーイングに起因する誤差成分である。
第２項の

は、ヨー角ψ_ＳＣに起因する誤差成分である。角度ψ_１及びψ_２で規定される誤差を意図的に導入することで、第２項に起因する誤差を補償することができる。 In Equation 4, the first term

Is an error component caused by yawing of each of the first illumination light source diffraction grating 1040 and the second illumination light source diffraction grating 1050.
The second term

Is an error component caused by the yaw angle _{ＳＣ SC} . By intentionally introduced errors defined by an angle [psi ₁ and [psi _2, it is possible to compensate for the error caused by the second term.

In the embodiment, the scale 1010 is configured by a scale grating made of a reflective grating. As shown in FIG. 10, the light source light path SOLP may be oriented in a direction forming an angle V with respect to a direction perpendicular to the scale surface. To give the desired detected fringe period PDF, the yaw angle ψ _SC satisfies the following equation:

To cancel the dynamic gap error DGE shown in Formula 3, the angle [psi ₁ and [psi ₂ satisfies the following equation.

Configured similarly to the optical encoder structure _{500, P SF} is 2 [mu] m, _{P 1} is 2 [mu] m, _{P 2} is 1 [mu] m, V is 30 °, lambda is 660 nm, the typical example of an optical encoder of the PDF is 120 [mu] m, [psi _SC May be 0.48 °. In this case, the position measurement error has a dynamic gap error of 4.8 nm per 1 μm gap variation Δg. In a typical example of an optical encoder configured similarly to the optical encoder structure 1000 and having the same parameters as above, ψ _SC may be 0.94 °, ψ ₁ may be −0.46 °, and, [psi ₂ may be 0.0 °. The yaw angle _{１ 1} causes a dynamic gap error of −9.4 nm per 1 μm gap variation Δg in position measurement error. The yaw angle ψ ₂ causes a dynamic gap error of 9.4 nm per 1 μm gap variation Δg in position measurement error. By balancing the two dynamic gap errors, the dynamic gap error is net to zero.

  FIG. 12 is a partial schematic diagram of an additional embodiment of an optical encoder structure 1200 having a stain and defect resistance providing a displacement signal. In the encoder structure 1200, the periodic scale light pattern 1235 to be detected is constituted by a detector interference fringe pattern. The detector fringe pattern is comprised of bands arranged to extend in the measurement axis direction MA over a relatively long dimension, and along the detected fringe movement direction DFMD while the optical encoder is displaced. , And crosses the measurement axis direction MA. The scale light pattern 1235 may be provided by an optical encoder similar to the optical encoder structure 1000 described with reference to FIG.

The optical encoder structure 1200 has a scale 1210, an illumination light source 1220, and a light detector structure 1260. The scale 1210 extends in the measurement axis direction MA. The scale 1210 has a scale grid composed of grid bars GB arranged on a scale plane SP substantially parallel to the measurement axis direction MA. Scale grating bar GB is thin the measuring axis direction MA, long scale grating bar direction SGBD intersecting the measuring axis direction MA, it is periodically arranged with a scale pitch P _SF to the measuring axis direction MA. The illumination light source 1220 includes a light source 1230 and a structured illumination generation unit 1233. Light source 1230 outputs light 1234 '. The structured illumination generation unit 1233 receives the light 1234 ′ and outputs the structured illumination 1234 ″ to the illumination area IR on the scale plane SP via the light source light path SOLP. The structured illumination 1234 ″ has an illumination interference fringe pattern IFP that is thin in the measurement axis direction MA and long in the illumination interference fringe direction IFD (see FIG. 5) intersecting the measurement axis direction MA. The light source 1230 has a point light source 1231 and a collimating lens 1232. Point light source 1231 outputs light 1234 to a collimating lens, which collimates light 1234 into light 1234 '.

  As described in more detail with reference to FIGS. 8, 9A and 9B, the photodetector structure 1260 has a detector pitch PD (detailed in FIG. 8) in a detection interference fringe movement direction DFMD that intersects the measurement axis direction MA. (Similar to the illustrated photodetector structure 860) with a set of N spatial phase detectors arranged periodically. Each of the spatial phase detectors is configured to provide a phase detection signal. At least a majority of the spatial phase detectors extend in the measurement axis direction MA over a relatively long dimension and are relatively narrow in the detection fringe movement direction DFMD that intersects the measurement axis direction MA. The set of N spatial phase detectors is arranged in a spatial phase sequence along the detected interference fringe moving direction DFMD.

  As in the case of the encoder structure 500, the scale 1210 receives the illumination interference fringe pattern in the illumination area IR and outputs the scale light component via the scale light path SCLP. This forms a scale light pattern 1235 on the photodetector structure 1260. As described in detail with reference to FIGS. 6A and 6B, the scale light pattern 1235 extends in the measurement axis direction MA over a relatively long dimension and moves in the detection interference fringe movement direction DFMD that intersects the measurement axis direction MA. It is composed of high light intensity and low light intensity bands which are relatively thin and have a periodicity of the detected interference fringe period PDF in the detected interference fringe movement direction DFMD.

The scale grating bar direction SGBD points in a direction forming a yaw angle _{ＳＣ SC} other than 0 with respect to the read head surface RHP defined by the light source light path SOLP and the scale light path SCLP.

As described above with reference to FIG. 7, the detection interference fringe period PDF and the detection interference fringe movement direction DFMD intersecting with the measurement axis direction MA partially, but partially depend on the yaw angle ψ _SC other than 0. As the scale 1210 is displaced in the measurement axis direction MA, the high light intensity and low light intensity bands move in the detection interference fringe movement direction DFMD crossing the measurement axis direction MA. The photodetector structure 1260 is configured to detect displacement of the high light intensity and low light intensity bands in the detected interference fringe movement direction DFMD that intersects the measurement axis direction MA, and outputs a spatial phase displacement signal indicative of the scale displacement. give.

  The normal line RHPN of the read head surface RHP is oriented in a direction forming a pitch angle φ other than 0 with respect to the measurement axis direction MA.

  FIG. 13A schematically illustrates a first view of scale light components forming a scale light pattern 1235 proximate to a photodetector structure similar to the photodetector structure 1260 of FIG. More specifically, FIG. 13A shows a cross-section of a portion SIG of scale light pattern 1235 in a plane defined by measurement axis direction MA and Y direction proximate to photodetector structure 1260. The portion SIG of the scale light pattern 1235 is a set of interference fringes formed by the overlap of the scale light components SL1 and SL2 understood with reference to FIG. 6B. The portion SIG of the scale light pattern 1235 includes a dark or low light intensity interference band 1235SIGD indicated by a thick line and a bright or high light intensity interference band 1235SIGL indicated by a broken line. The partial SIG is similar to the detector interference fringe pattern 635 and is a portion of the scale light pattern 1235 that provides a spatial phase displacement signal indicating the scale displacement. More specifically, the photodetector structure 1260 detects the displacement of the interference bands 1235SIGD and 1235SIGL in the detected interference fringe movement direction DFMD that intersects the measurement axis direction MA, and provides a spatial phase displacement signal indicating the scale displacement. It is configured as follows.

  In various embodiments, the detector fringe pattern 635 may further include zero order light that causes a variation in light intensity of the high light intensity interference band 635L. More specifically, the interference between the zero-order scale light and the scale light components SL1 and SL2 causes a low light intensity or high light intensity interference band parallel to the low light intensity interference band 635D and the high light intensity interference band 635L. Is generated. As a result, in the detector interference fringe pattern 635, interference fringes having a variation pattern occur in alternating fringes, and a short range error occurs in the spatial phase displacement signal. As described below, the contamination and defect resistant optical encoder structure 1200 is configured to suppress these errors. More specifically, the interference between the zero-order scale light and the light corresponding to the scale light components SL1 and SL2 shown in FIG. 6B causes the optical encoder to be parallel to the light corresponding to the scale light components SL1 and SL2. During the displacement, an interference fringe in a band of dark or bright light intensity that moves in the detection interference fringe movement direction DFMD occurs.

  It should be understood that FIGS. 13A-13D show a portion of the scale light pattern 1235 in a reference frame, side by side with the photodetector structure 1260. In general, a photodetector structure, such as photodetector structure 1260, has a spatial phase detector in a detection interference fringe movement direction DFMD that intersects measurement axis direction MA and does not exactly match Y direction. Should be oriented parallel to the fringe pattern defined by the low or high light intensity interference bands 1235SIGD and 1235SIGL along.

  FIG. 13B is a second diagram schematically illustrating scale light components forming a scale light pattern 1235 proximate to a photodetector structure similar to the photodetector structure 1260 of FIG. More specifically, FIG. 13B shows a cross section of the portion PZ of the scale light pattern 1235 in a plane defined by the measurement axis directions MA and the Y direction close to the photodetector structure 1260. The portion PZ of the scale light pattern 1235 is a set of interference fringes formed by the overlap of the zero-order scale light and the scale light component SL1. The portion PZ of the scale light pattern 1235 includes a dark or low light intensity interference band 1235PZD indicated by a thick line and a bright or high light intensity interference band 1235PZL indicated by a broken line.

  Since the pitch angle φ is other than 0, the interference bands 1235PZD and 1235PZL are arranged so as not to be parallel to the detected interference fringe moving direction DFMD, that is, not to be parallel to the interference bands 1235SIGD and 1235SIGL.

  FIG. 13C is a third diagram schematically illustrating scale light components forming a scale light pattern 1235 proximate to a photodetector structure similar to the photodetector structure 1260 of FIG. More specifically, FIG. 13C shows a cross section of the portion MZ of the scale light pattern 1235 in a plane defined by the measurement axis directions MA and the Y direction close to the photodetector structure 1260. The portion MZ of the scale light pattern 1235 is a set of interference fringes formed by the overlap of the zero-order scale light and the scale light component SL2. The portion MZ of the scale light pattern 1235 includes a dark or low light intensity interference band 1235MZD indicated by a thick line and a bright or high light intensity interference band 1235MZL indicated by a broken line.

  Since the pitch angle φ is other than 0, the interference bands 1235MZD and 1235MZL are arranged so as not to be parallel to the detected interference fringe moving direction DFMD, that is, not to be parallel to the interference bands 1235SIGD and 1235SIGL.

  FIG. 13D is a fourth diagram schematically illustrating scale light components forming a scale light pattern 1235 proximate to a photodetector structure similar to the photodetector structure 1260 of FIG. More specifically, FIG. 13D illustrates a cross section of each of the portions PZ, MZ, and SIG of the scale light pattern 1235. If the pitch angle φ is 0, the interference bands of the portions PZ and MZ will be directed at different angles with respect to the detected interference fringe movement direction DFMD, but instead, the interference bands 1235SIGD and 1235SIGL Become parallel to. As a result, the light intensity varies between the alternate interference band and the interference band 1235SIGL having a high light intensity of the partial SIG, and a short range error occurs in the spatial phase displacement signal. However, as shown in FIG. 13D, when the pitch angle φ is not 0, the low light intensity interference bands 1235PZD and 1235MZD of the portions PZ and MZ overlap in the low interference region LO, and the high light intensity interference bands 1235PZL and 1235MZL Overlap in the high interference area HI. The regions LO and HI are arranged in a direction that intersects the detection interference fringe movement direction DFMD. The light intensity of 1235 in the regions LO and HI is averaged in a direction intersecting the detected interference fringe movement direction DFMD, and the light intensity fluctuation in the detected interference fringe movement direction DFMD between the alternating fringes in the scale light 1235. Is suppressed. This averaging reduces the short range error of the spatial phase displacement signal caused by the zero-order scale light that interferes with the partial SIG of the scale light 1235.

  In an embodiment of the optical encoder structure 1200 having stain and defect resistance, φ may be greater than 0.3 ° and less than 2.0 °.

  In an embodiment of the optical encoder structure 1200 having contamination resistance and defect resistance, each of the N phase detectors may have an even number of scale light receiving regions.

In an embodiment of the contamination- and defect-resistant optical encoder structure 1200, the structured illumination generator 1233 includes a first illumination source diffraction grating (eg, a first illumination source diffraction grating 1040) and a second illumination. A light source diffraction grating (for example, the second illumination light source diffraction grating 1050) may be provided. The first illumination source grating may be constituted by a first illumination source grating bar in the first index plane are periodically arranged in the first index pitch P _1. First illumination source grating bars, thin the measurement axis direction, intersects the measuring axis direction, and long in the first index grating bar direction is rotated by an angle [psi ₁ with respect to the read head surface RHP. The second illumination source grating may be constituted by the second illumination source grid bars which are periodically arranged in the second index pitch P ₂ in the first index plane parallel to the second index plane. Second illumination source grating bars, thin the measurement axis direction, intersects the measuring axis direction, and long in the second index grating bars direction being rotated by an angle [psi ₂ to the read head surface RHP. In an embodiment (eg, as described in detail with respect to FIG. 10), scale 1210 may include a scale grating that is a reflective grating. The light source light path SOLP may be oriented in a direction forming an angle V with respect to a direction perpendicular to the scale plane SP. The yaw angle _{ＳＣ SC} may satisfy Expression (6). In the embodiment, the wavelength of the light output from the light source 1230 may be λ, the coefficient Ω may be defined by Expression (5), and the angles _{１ 1} and ψ ₂ satisfy Expression (7). Is also good. In an embodiment, the first illumination light source diffraction grating and the second illumination light source diffraction grating may be phase gratings. In the embodiment, the detected interference fringe period PDF may be 40 μm or more.

  FIG. 14A is a partial isometric view of a first embodiment of a contamination and defect resistant optical rotary encoder structure 1400 using a cylindrical rotary scale 1410 to provide a displacement signal. The encoder structure 1400 has a rotary array 1410, an illumination light source 1420, a detector array 1465 that includes a structured illumination generator SIGA and a photodetector structure 1460. In the embodiment shown in FIG. 14A, the rotary scale 1410 has a transmission grating. FIG. 14B is a partial view of the rotary scale grating 1410 of FIG. 14A showing further details of the second illumination region IR2 on the rotary scale 1410. The pitch and angle of each of the grating bars and interference fringes shown in FIGS. 14A and 14B are for illustration purposes and need not be to scale, and should be interpreted according to the associated description. Needless to say,

  In some respects, the optical rotary encoder structure 1400 may be understood to operate based on the concept of specific interference fringe generation and detection similar to that described above with reference to FIGS. 10-13D. In the encoder structure 1400, using a similar concept, the periodic scale light pattern 1435 to be detected is constituted by the detector interference fringe pattern 1435 '. The detector interference fringe pattern 1435 ′ is composed of bands (or interference fringes) arranged to extend in the rotational measurement axis direction MA over a relatively long dimension, and is rotated while the rotary scale 1410 is displaced. It moves along the detection interference fringe movement direction DFMD that intersects the measurement axis direction. Thus, the operation of the optical rotary encoder structure 1400 may be understood primarily by analogy to the one described above, and only certain aspects will be described below.

As shown in FIGS. 14A and 14B, the rotary scale 1410 extends along (or around) the rotation measurement direction θ about the rotation axis RA and is orthogonal to the rotation axis RA. Rotate parallel to the plane of rotation. The rotary scale 1410 has a rotary scale grating having scale grating bars GB arranged on the cylindrical rotating surface or on the cylindrical rotating surface along the rotation measuring direction θ. Scale grating bar GB is thin in the rotation measurement direction theta, long rotary scale grating bar direction RSGBD intersecting the rotation measurement direction theta, are periodically arranged at a nominal scale pitch P _SF in the rotation measurement direction theta. The illumination light source 1420 has a light source that outputs the light source light 1434 to the structured illumination generation mechanism SIGA. In the various rotary encoder structures disclosed in this specification, the structured illumination generation mechanism SIGA includes a first illumination area on a rotary scale, a beam deflector structure having at least first and second deflection elements, and A second illumination area on a rotary scale. In the specific embodiment shown in FIG. 14A, the structured illumination generation mechanism SIGA is configured such that the source light 1434 is input to the first illumination region IR1 on the rotary scale 1410. The first illumination region IR1 diffracts the source light and emits structured illumination light 1434 'consisting of a diffracted light beam (indicated by two different dashed lines in FIG. 14A) along the optical path LP. The light is output to a beam deflector structure BDC having a first mirror 1471 and a second mirror 1472. The beam deflector structure BDC crosses the diffracted light beams of the structured illumination light 1434 ′ with each other, and the structured illumination light (ie, the diffracted light beam) after the crossing is crossed in the second illumination region IR 2 on the rotary scale 1410. The structured illumination light 1434 'after the intersection is transmitted so as to overlap. In the second illumination region IR2, the diffracted light beams of the structured illumination light 1434 'interfere with each other so that the structured illumination light 1434' has the illumination interference fringe pattern IFP in the second illumination region IR2. An illumination interference fringe pattern IFP adjacent to the second illumination region IR2 is formed. The interference fringe pattern IFP is composed of interference fringes that are thin in the rotation measurement direction θ and long in the illumination interference fringe direction IFD that intersects the rotation measurement direction θ. As shown in FIG. 14A, a detector having an interference fringe having a relatively long dimension along the rotation measurement axis direction MA and moving along the detected interference fringe movement direction DFMD while the rotary scale 1410 is displaced. The angular difference between the illumination fringe direction IFD and the rotary scale grating bar direction RSGBD direction (shown in FIG. 14B) is such that a periodic scale light pattern 1435 having an interference fringe pattern 1435 'is provided. Provided.

  As shown in FIG. 14A, a first mirror 1471 and a second mirror 1472 direct the diffracted light beam of the structured illumination light 1434 'along the general direction of the optical path LP to a second illumination region IR2. To reflect. In the particular embodiment shown in FIG. 14A, a first mirror 1471 and a second mirror 1472 of the beam deflector structure BDC receive and receive each beam of diffracted light source light output from the first illumination region IR1. Deflects each received beam to follow a diverging beam path via a converging beam path where each beam intersects near the rotation axis RA, and then receives each deflected beam, and each received beam deflects the convergent beam path. Each received beam is deflected so as to overlap and form an illumination interference fringe pattern IFP near the second illumination region IR2. In some embodiments, structured illumination light 1434 'passes through free space between first mirror 1471 and second mirror 1472. In another embodiment, first mirror 1471 and second mirror 1472 may be provided on the surface of a monolithic optical material, and structured illumination light 1434 'is reflected by internal reflection within the monolithic optical material. You may. In some embodiments, the source light 1434 and the diffracted light beam are nominally collimated (eg, by providing a collimating lens in the illumination light source 1420). However, in another embodiment, at least one of the illumination light source 1420 and the beam deflector structure BDC is such that each beam of diffracted light source light from the first illumination region IR1 converges to an intersection near the rotation axis RA. It is configured to be. In such an embodiment, errors due to small component deviations can be reduced or eliminated. In such an embodiment, a lens included in illumination light source 1420 may provide convergent light source light 1434 that converges near rotation axis RA. In some embodiments, the scale light from the second illumination region IR2 forming a periodic scale light pattern 1435 having a detector fringe pattern 1435 'is nominally collimated at the detector structure 1460. , At least one of a beam deflector structure BDC and a detector array 1465. For example, in one such embodiment, the detector array 1465 has complementary characteristics to a lens that focuses the source light 1434 near the rotation axis RA, and a periodic scale light pattern 1435. May include a lens that collimates the light contained in the periodic scale light pattern 1435 before reaching the light detector 1460. Naturally, in the embodiment shown in FIG. 14A, the beam deflector structure BDC has first and second parallel plane mirrors 1471 and 1472 opposed to each other with respect to the rotation axis RA, and the first and second The parallel plane mirrors 1471 and 1472 have surfaces extending substantially parallel to the diameter of the cylindrical rotary scale 1410 passing through the first and second illumination regions IR1 and IR2, respectively. The first and second mirrors 1471 and 1472 are arranged to receive the respective beams of the diffracted light source light output from the first illumination region IR1. Of course, those surfaces are shown as rotated with respect to the line indicated as optical path LP, and this rotation provides the desired angle or direction to the illumination fringe direction IFD, in accordance with the principles described above. . It is needless to say that in some embodiments, the deflection by the mirrors 1471 and 1472 may be realized by separately providing various gratings instead of the mirrors.

  As described above, the rotary scale 1410 is a periodic scale having the illumination interference fringe pattern IFP input to the second illumination region IR2 and having the detector interference fringe pattern 1435 'in the photodetector structure 1460 of the detector array 1465. The light pattern 1435 is configured to output scale light. The detector interference fringe pattern 1435 ′ extends in the rotation measurement direction θ over a relatively long dimension, is relatively thin in the detection interference fringe movement direction DFMD that intersects (orthogonally) intersects (orthogonally) with the rotation measurement direction θ, and has a relatively small width. It has periodic high light intensity and low light intensity bands having the periodicity of the detected interference fringe period PDF in the direction DFMD.

As shown in detail in FIG. 14B, the rotary scale grating bar direction RSGBD of the grating bar GB along the rotating surface of the rotary scale 1410 has a non-zero yaw angle _{１ 1} with respect to a direction intersecting the measurement axis direction MA. It is facing in the direction you take. In general, the illumination interference fringe direction IFD of the interference fringe pattern 1435 'near the second illumination region IR2 on the rotary scale 1410 is the same as the rotary scale grating bar direction RSGBD near the second illumination region IR2 on the rotary scale 1410. 0 to face the direction to take nominal interference fringe direction yaw angle [psi ₂ which are rotated by the yaw difference angle YDA not respect, it is configured structured illumination generating mechanism SIGA. According to the display of FIG. 14B, YDA = (ψ ₁ −ψ ₂ ). [psi ₂ is intended to be measured from the reference point in the counterclockwise direction, that is considered a negative angle.

The detection interference fringe period PDF and the detection interference fringe movement direction DFMD that intersects the rotation measurement direction θ depend on the yaw difference angle YDA, which is partial but not zero (for example, as described with reference to FIG. 7, It depends on the yaw angle ψ _1). As the rotary scale 1410 rotates about the rotation axis RA, the high light intensity and low light intensity bands move in the detection interference fringe movement direction DFMD that intersects the rotation measurement direction θ. The photodetector array 1465 is configured to detect the displacement of the high light intensity and low light intensity bands in the detection interference fringe movement direction DFMD that intersects the rotation measurement direction θ, and the spatial phase displacement indicates the displacement of the rotary scale. Give a signal. In one embodiment, the light detector structure 1460 of the light detector array 1465 is similar to the light detector 560 and may be understood with reference to FIGS. 6A and 6B. The photodetector structure 1460 includes N spatial phase detectors periodically arranged at a detector pitch PD in a detector interference fringe movement direction DFMD that intersects the rotational measurement direction θ (as shown in FIGS. 6A and 6B). It may have a set of vessels. Each spatial phase detector may be configured to individually provide a spatial phase detector signal, wherein at least a majority of the spatial phase detectors have relatively long dimensions in the rotational measurement direction θ, and the rotational measurement direction θ And the detector fringe movement direction DFMD may be configured to have a relatively narrow dimension in the orthogonal direction, and the set of N spatial phase detectors, according to the principles described above, may be configured to detect detectors in a spatial phase train. They may be arranged in the interference fringe moving direction DFMD. In various embodiments, if the detected fringe period PDF is greater than or equal to 40 μm, there may be advantages in performance and / or cost. In various embodiments, if each of the N spatial phase detectors has an even number of scaled light receiving areas, it may be advantageous in performance and / or cost.

In some embodiments, Equation 6 may be applied to an optical rotary encoder structure, such as optical rotary encoder structure 1400. In this case, the rotary scale 1410, resulted in the equivalent of the first illumination light source grating 540 and the second illumination source grating 550, _{P 1} and _{P 2} is equal to the scale pitch _{P SF.} In some embodiments, it is advantageous equal [psi ₂ is the [psi _1. Since the light of source light 1434 and the structured illumination light 1434 'only pass through the two diffraction gratings, in optical encoder structure 1400, Equation 6 becomes the equation relating yaw angle _{１ 1} to the detected fringe period PDF. Simplified.

  The source light 1434 and the structured illumination light 1434 'that are incident twice on the rotary scale 1410 (i.e., incident on the first illumination region IR1 and the second illumination region IR2) provide a high resolution displacement measurement (i.e., as described above). The resolution is doubled by introducing the beam intersection as a combination of the two diffracted lights on different sides of the rotary scale 1410) and a line passing through the first illumination region IR1 and the second illumination region IR2. Correction of the orthogonal rotation offset can be performed.

  FIG. 15 is a partial schematic view showing one embodiment of an optical rotary encoder structure 1500 having stain resistance and defect resistance when viewed along the rotation axis direction. The optical rotary encoder structure 1500 may be similar or identical to the first of the various embodiments of the optical rotary encoder structure 1400 shown in FIG. Contains. Like numerals in FIGS. 15 and 14 may be understood to refer to like or similar elements unless otherwise indicated. Accordingly, only different or modified specific aspects of FIG. 15 will be described. In FIG. 15, two different variants of the beam polarizer structure BDC are shown. In particular, the first and second mirrors 1471 and 1472 are one embodiment of the first and second beam deflecting elements of the beam polarizer structure BDC, and the first and second beam deflecting elements are mirrors (1471 and 1471). 1472) or, as described above with reference to FIG. 14A, a grating (indicated by two different dashed lines) that deflects the diffracted light beam approximately as shown. First and second gratings 1473 and 1474, instead of first and second mirrors 1471 and 1472, are another embodiment of the first and second beam deflecting elements of the beam polarizer structure BDC. In one embodiment, the first grating 1473 has a first transmission grating structure and the second grating 1474 has a second transmission grating structure. Each of these gratings deflects each diffracted light (indicated by two different dashed lines) substantially as shown, according to the principles described above. In various embodiments, depending on the principles described above, the grating provides a focused and deflected beam or a collimated and deflected beam. In any case, a suitable grating can be determined through some or all of the design, simulation, and experiment based on a commercially available optical design program or a known grating design principle. Of course, in the grating 1473 (1474), the regions 1473A (1474A) and the regions 1473B (1474B) may not be identical or continuous in some embodiments. For example, in one embodiment, regions 1473A (1474A) and regions 1473B (1474B) may be mirror symmetric (eg, with respect to optical path LP) to provide the desired deflection for each beam.

  FIG. 16 shows a second embodiment of an optical rotary encoder structure 1600 having a stain and defect resistance providing a displacement signal using a cylindrical rotary scale 1610 having a reflection grating instead of a transmission grating. FIG. 3 is a partial schematic view when viewed along the rotation axis direction, and includes a specific deformation element. Encoder structure 1600 is similar to encoder structure 1500 shown in FIG. 15, except for the easily understandable changes caused by using the reflective grating of rotary scale 1610. Like numbers in FIGS. 16 and 15 (eg, having similar suffixes, such as 16XX and 15XX) may be understood to refer to like or similar elements unless otherwise indicated. Of course, the embodiment shown in FIG. 16 allows the illumination light source 1620, the beam deflector structure BDC and the detector array 1665 to all be located on a single component inside the rotary scale 1610.

  Of course, in the various encoder configurations described above, the rotary scale is a cylindrical scale having a nominal cylindrical rotating surface on which the scale grid is arranged, based on the principles described above. The first and second illumination regions IR1 and IR2 are located near different diameter ends of the cylindrical rotary scales 1410, 1610, respectively. Illumination light sources 1420, 1620 are configured to output source light 1434, 1634 to a first illumination region IR along a line that crosses the first and second illumination regions IR1 and IR2. The beam deflector structure BDC may be arranged in a space partitioned by projecting the cylindrical rotating surfaces of the rotary scales 1410, 1610 along the direction of the rotation axis RA.

In various encoder configurations, such as the rotary scale which is a cylindrical rotary scale described above, the illustrated track of the scale grid bar GB around the rotary scale interlocks with other accompanying optics that generate position signals from the track. And may be considered a first measurement channel. Of course, in such a "cylindrical scale" structure, it is particularly easy to add a second measurement channel similar or identical to the first measurement channel, if desired. For example, the second track of the grating bar GB may be provided on the rotary scale at a distance from the first scale track in the direction of the rotation axis RA. Some or all of the illumination source, beam deflector structure and detector array may be duplicated for the second measurement channel or shared between the two measurement channels. The advantage of such an arrangement is that by using a respective combination of the spatial phase displacement signals of the first and second measurement channels or the measurements derived therefrom, the individual spatial phase displacement signals derived from one measurement channel Or, it can be used to mitigate or compensate for errors due to potential deviations that can occur in measurement. Particularly advantageous one such embodiment, the first measurement channel comprises a scale grating bars GB arranged in the yaw angle [psi ₁ along the first scale track the rotary scale, the second measurement channel has spaced apart in the direction of the axis of rotation RA from the first scale track, the scale grating bars GB arranged in yaw angle -Pusai ₁ opposite along a second scale track rotary scale. In one embodiment, the first and second measurement channels may have different scale pitches, and the spatial phase difference between these signals may be determined in a known manner by an absolute measurement position along the measurement axis. May be used to indicate. In some embodiments, one beam deflector structure (eg, two parallel mirrors) may be suitably shared between the first and second measurement channels. In other embodiments, the first and second measurement channels may have substantially orthogonal optical paths, and a combination of these signals may have a particular misalignment error (both X and Y offset or eccentricity error). May be used for compensation.

  FIG. 17A is a partial isometric view of a third embodiment of a stain and defect resistant optical rotary encoder structure 1700 using a flat rotary scale 1710 to provide displacement signals. The encoder structure 1700 has a detector array 1765 including a rotary scale 1710, an illumination light source 1720, a structured illumination generator SIGA, and a photodetector structure 1760. In the embodiment shown in FIG. 17A, the rotary scale 1710 has a reflective grating. FIG. 17B is a partial view of the rotary scale (grating) 1710 of FIG. 17A, showing further details of the first and second illumination regions IR1 and IR2 on the rotary scale 1710. The pitches and angles of the grating bars and interference fringes shown in FIGS. 17A and 17B are for illustrative purposes only, do not need to be to scale, and should be interpreted according to the associated description. Needless to say, it should be.

  In some respects, the optical rotary encoder structure 1700 may be understood to operate based on the concept of the generation and detection of certain fringes similar to that described above with reference to FIGS. 10-14B. In the encoder structure 1700, using a similar concept, the periodic scale light pattern 1735 to be detected has a detector interference fringe pattern 1735 '. The detector interference fringe pattern 1735 ′ is composed of bands (or interference fringes) arranged to extend in the rotational measurement axis direction MA over a relatively long dimension, and to detect while the rotary scale 1710 is displaced. It moves along the interference fringe movement direction DFMD so as to intersect the rotation measurement axis direction. Thus, even if the flat rotary scale 1710 is used instead of the cylindrical rotary scale shown in FIG. 14A, the operation of the optical rotary encoder structure 1700 is mainly the same as that described above (particularly with respect to FIGS. 14A and 14B). Similar aspects may be understood, and only certain aspects are described below.

As shown in FIGS. 17A and 17B, the flat plate rotary scale 1710 may be circular, and extends along (or around) the rotation measurement direction θ about the rotation axis RA. Rotate in parallel to the plane of rotation orthogonal to RA. The rotary scale 1710 has a rotary scale grating having a reflective scale grating bar GB arranged on the plate rotating surface or on the plate rotating surface along the rotation measurement direction θ. Scale grating bar GB is thin in the rotation measurement direction theta, long rotary scale grating bar direction RSGBD intersecting the rotation measurement direction theta, are periodically arranged at a nominal angular pitch AP _SF in the rotation measurement direction theta. The detector array 1765 including the illumination light source 1720, the beam deflector structure BDC of the structured illumination generator SIGA, and the photodetector structure 1760 are all located on the same side of the rotary scale 1710. Of course, by multiplying the nominal or average radius from the rotation axis RA to the center of the illumination areas IR1 and IR2 by the angular pitch AP _SF , the nominal angular pitch AP _SF is determined with reference to FIGS. it may be converted into functionally equivalent to the scale pitch P _SF with the respect to formula and relationships) already mentioned disclosed herein "linear pitch".

  The illumination light source 1720 has a light source that outputs light source light 1734 to the structured illumination generation mechanism SIGA. The structured illumination generation mechanism SIGA includes a first illumination area IR1 on a rotary scale, a beam deflector structure BDC having first and second deflection elements 1773 and 1774, and a second illumination area on a rotary scale 1710. Has IR2. In the embodiment shown in FIG. 17A, the first and second illumination regions IR1 and IR2 are located near (but not entirely on) each of the different diameter ends of the rotary scale 1710. The illumination light source 1720 directs the source light 1734 at an angle of incidence to the first illumination region IR1 along a plane NIP intersecting the first and second illumination regions, with respect to the flat plate rotating surface in this plane. It is configured to output. The structured illumination generation mechanism SIGA is configured such that the light source light 1734 is input to the first illumination region IR1 on the rotary scale 1710. The first illumination region IR1 reflects the source light 1734 and diffracts it, and the structured illumination light 1734 '(shown by two different broken lines in FIG. 17A) consisting of the diffracted light beam travels along the optical path. Thus, it is configured to output to a beam deflector structure BDC having a first polarizing element 1773, a second polarizing element 1774, and an intersection area reflector 1780. The beam deflector structure BDC intersects the diffracted light beams of the structured illumination light 1734 ′ with each other so that the structured illumination light (ie, the diffracted light beam) crossed in the second illumination region IR 2 on the rotary scale 1710. The structured illumination light after the intersection is transmitted so as to overlap. In the embodiment of FIG. 17A, the first polarizing element 1773 of the beam deflector structure BDC is configured to receive each beam of the source light that has been diffracted and output from the first illumination region IR1. It is configured to deflect each received beam such that the beams follow a converging beam path that intersects at an intersection area reflector 1780 near the axis of rotation RA. The intersection area reflector 1780 reflects each beam near the intersection near the rotation axis RA, and each reflected beam follows a diverging beam path toward the second deflection element 1774 of the beam deflector structure BDC. The second deflecting element 1774 receives and deflects each beam such that the beams overlap along a convergent beam path and form an illumination interference fringe pattern IFP near the second illumination region IR2.

  The second illumination region IR2 receives the illumination interference fringe pattern IFP and forms a periodic scale light pattern 1735 having a detector interference fringe pattern 1735 'in the photodetector structure 1760 of the detector array 1765. Then, the reflected scale light is output so as to form an incident angle with respect to the rotating plane surface of the rotary scale 1710. In particular, in the second illumination region IR2, the diffracted light beams of the structured illumination light 1734 'interfere with each other so that the structured illumination light 1734' includes the illumination interference fringe pattern IFP in the second illumination region IR2. The illumination interference fringe pattern IFP near the illumination region IR2 is formed. The interference fringe pattern IFP is composed of interference fringes that are thin in the rotation measurement direction θ and long in the illumination interference fringe direction IFD that intersects the rotation measurement direction θ. As shown in FIG. 17A, a detector having an interference fringe having a relatively long dimension along the rotation measurement axis direction MA and moving along the detected interference fringe movement direction DFMD while the rotary scale 1710 is displaced. An angular difference between the illumination fringe direction IFD and the rotary scale grating bar direction RSGBD direction (shown in FIG. 17B) is provided so as to provide a periodic scale light pattern 1735 having an interference fringe pattern 1735 '. .

  In the particular embodiment shown in FIG. 17A, the first deflecting element 1773 has a first pair of transmissive gratings 1773A and 1773B, and the second deflecting element 1774 is a transmissive grating 1774A, as described in more detail below. And 1774B. A first pair of transmissive gratings 1773A and 1773B is arranged on a surface (eg, of optical block 1770) that is nominally parallel to the plane of rotation, and each grating in the pair is reflected in first illumination region IR1. It is arranged to receive each beam of the diffracted light source light 1734 ′ (also referred to as structured illumination light 1734 ′) output. Of course, each grating in the pair has a grating bar (described in detail below) configured to deflect each beam along an intersecting convergent beam path near the rotation axis RA, as described above. Intersecting region reflector 1780 is positioned such that the converging beam paths are close to the intersections near axis of rotation RA, and reflect each beam to follow a diverging beam path from intersecting region reflector 1780. Be composed. A second pair of transmission gratings 1774A and 1774B are also arranged on a surface that is nominally parallel to the plane of rotation (coplanar with the first pair of oversized gratings 1773A and 1773B), and each grating in this pair It is arranged to receive each beam following the divergent beam path from the area reflector 1780. Each grating in the pair is configured to deflect and superimpose each beam along a convergent beam path to form an illumination interference fringe pattern IFP near the second illumination region IR2 (described in detail below). And operate as described above.

  In some embodiments, the intersection area reflector 1780 may be a flat mirror. In other embodiments, the cross-region reflector 1780 has a radius of curvature on the order of a separation in the direction of the axis of rotation RA from the plane of the curved surface (eg, in other embodiments, the rotary scale 1710 having the grating bars GB). (Curved surface). In some embodiments, the source light 1734 and the diffracted light beam may be nominally collimated (eg, by providing a collimating lens in the illumination light source 1720). However, in other embodiments, at least one of the illumination light source 1720 and the beam deflector structure BDC is such that each beam of diffracted light source light from the first illumination region IR1 is near an intersection near the rotation axis RA. More preferably, it is configured to converge to the intersection area reflector 1780. In such a "beam convergence" configuration, specific errors due to small component deviations can be mitigated or eliminated.

  In such a “beam converging” configuration in the configuration shown in FIG. 17A, in a first pair of transmission gratings 1773A and 1773B, each grating of the pair receives collimated light of each beam. And may be configured to deflect each beam along a converging beam path that intersects near the axis of rotation and converges each beam near the axis of rotation RA, and more desirably to the intersection area reflector 1780. May have a curved grid bar. In the second pair of transmission gratings 1774A and 1774B, each grating of the pair may be configured to receive the dispersed light of each beam, collimating and deflecting the light of each beam. May have a curved grating bar configured to provide a collimated light beam along a converging beam path that overlaps near the second illumination region IR2 to form an interference fringe pattern IFP. An example of such a lattice pair will be described with reference to FIG. In this different "beam convergence" configuration, the lens included in illumination light source 1720 provides convergent light source light 1734 that converges near rotation axis RA. In one embodiment, the scale light from the second illumination region IR2 forming a periodic scale light pattern 1735 having a detector interference fringe pattern 1735 'is nominally collimated at the photodetector structure 1760. , One or both of the beam deflector structure BDC and the detector structure 1765 are configured. For example, in one embodiment, the detector array 1765 has complementary characteristics to the lens that converges the source light 1734 near the axis of rotation RA, and the periodic scale before reaching the photodetector 1760. A lens for collimating the light included in the light pattern 1735 may be included.

  As described above, the rotary scale 1710 receives the illumination interference fringe pattern IFP in the second illumination region IR2 and has the periodic scale light pattern having the detector interference fringe pattern 1735 ′ in the photodetector structure 1760 of the detector array 1765. As 1735, it is configured to output scale light. The detector interference fringe pattern 1735 'extends in the rotation measurement direction θ over a relatively long dimension, is relatively thin in the detection interference fringe movement direction DFMD that intersects the rotation measurement direction θ, and is in the detection interference fringe movement direction DFMD. It has periodic high light intensity and low light intensity bands having the periodicity of the detected interference fringe period PDF.

As shown in detail in FIG. 17B, the rotary scale grating bar direction RSGBD of the grating bar GB along the rotating surface of the rotary scale 1710 has a non-zero yaw angle _{１ 1} with respect to a direction intersecting the measurement axis direction MA. It is facing in the direction you take. In FIG. 17B, the direction orthogonal to the measurement axis direction MA is indicated by a radial straight line defined as extending radially from the rotation axis RA at the position of each grating bar GB. In general, the illumination interference fringe direction IFD of the interference fringe pattern 1735 ′ on the rotary scale 1710 near the second illumination area IR2 is nominally or averaged near the second illumination area IR2 on the rotary scale 1410. The structured illumination generation mechanism SIGA is configured so as to face a direction in which the yaw angle is a direction of a nominal interference fringe rotated by a yaw difference angle YDA that is not 0 with respect to the rotary scale grating bar direction RSGBD. In the particular embodiment shown in FIGS. 17A and 17B, the first and second illumination regions IR1 and IR2 are located near respective ends of different diameters passing through the rotary scale rotation axis RA, and the illumination light source 1720 comprises: Source light 1734 is directed to first illumination region IR1 along a nominal illumination plane NIP that is nominally parallel to the plate rotation surface and nominally parallel to its diameter, and is offset from the diameter by a nominal illumination plane offset IPOff. It is configured to output. The first and second illumination regions IR1 and IR2 are each offset from the diameter by a nominal illumination plane offset IPOff. The nominal illumination plane offset IPOff may be configured to be parallel to a nominal illumination plane NIP that is parallel to the nominal or average arrangement of the scale grid bar GB in the first illumination region IR1. Scale grating bar GB is anywhere rotary scale 1710 that includes a second illumination region IR2, taking the yaw angle [psi ₁ not 0 with respect to a direction perpendicular to the measuring axis direction MA. According to the above design principle, the illumination fringe direction IFD rotates in the second illumination region IR2 with a non-zero yaw difference angle YDA with respect to the nominal or average rotary scale grating bar direction RSGBD. According to the notation shown in FIG. 17B, YDA = (ψ ₁ −ψ ₂ ). [psi ₂ is intended to be measured from the reference point in the counterclockwise direction, that is considered a negative angle. In such an embodiment, preferably, the yaw difference angle YDA not zero is double the yaw angle [psi ₁ not zero.

In either case, the detected interference fringe period PDF and the detected interference fringe movement direction DFMD intersect with the rotation measurement direction θ, and at least partially have a non-zero yaw difference angle YDA (eg, with respect to FIG. 7). As described, it depends on the non-zero yaw angle { ₁ ). The bands of high light intensity and low light intensity move in the detection interference fringe movement direction DFMD that intersects the rotation measurement direction θ as the scale 1710 rotates around the rotation axis RA. The detector array 1765 detects the displacement of the high light intensity and low light intensity bands in the detected interference fringe movement direction DFMD that intersects the rotation measurement direction θ and provides a spatial phase displacement signal indicating the displacement of the rotary scale. It is composed of In one embodiment, the light detector structure 1760 of the detector array 1765 is similar to the light detector 560 and may be understood with reference to FIGS. 6A and 6B. The photodetector structure 1760 includes N spatial phase detectors periodically arranged at a detector pitch PD in a detector interference fringe movement direction DFMD that intersects the rotational measurement direction (as shown in FIGS. 6A and 6B). It may have a set of vessels. Each spatial phase detector may be individually configured to provide a spatial phase detector signal, wherein at least a majority of the spatial phase detectors have a relatively long dimension in the rotational measurement direction and are orthogonal to the rotational measurement direction. The set of N spatial phase detectors may be configured to have a relatively narrow dimension in the direction of detector fringe movement, and the set of N spatial phase detectors may be moved in the spatial phase train according to the principles described above. It may be arranged in a direction. In various embodiments, if the detected fringe period PDF is greater than or equal to 40 μm, there may be advantages in performance and / or cost. In various embodiments, if each of the N spatial phase detectors has an even number of scaled light receiving areas, it may be advantageous in performance and / or cost.

In some embodiments, Equation 6 may be applied to an optical rotary encoder structure, such as optical rotary encoder structure 1700. In this case, the rotary scale 1710, resulted in the equivalent of the first illumination light source grating 540 and the second illumination source grating 550, _{P 1} and _{P 2} is equal to the effective scale pitch _{P SF.} As described above, the effective scale pitch P _SF is the angular pitch AP _SF (in radians) multiplied by the nominal or average radius from the axis of rotation RA to the center of one or both of the illumination regions IR1 and IR2. Is also good. Since the light of the source light 1734 and the structured illumination light 1734 ′ pass through two gratings similar to the optical encoder structure 1400, also for the optical encoder structure 1700, Equation 6 is simplified to Equation 8 described above, The yaw angle _１1 is related to the detected interference fringe period PDF.

With the light of the source light 1734 and the structured illumination light 1734 ′ incident on the rotary scale 1710 twice (ie, incident on the first illumination region IR1 and the second illumination region IR2),
In addition to correcting various potential misalignments in the rotary encoder structure 1700, high-resolution displacement measurement can be performed.

  FIG. 18 is a diagram schematically and qualitatively showing a grating pattern that can be used as the first pair of the transmission gratings 1773A and 1773B and the second pair of the transmission gratings 1774A and 1774B described with reference to FIG. 17A. It is. In the particular embodiment shown in FIG. 18, in a first pair of transmissive gratings 1773A and 1773B, each grating in the pair receives the collimated light of each beam and, as shown in FIG. It is configured to have a curved grid bar that deflects each beam along a converging beam path that intersects near RA and converges each beam near the rotation axis RA. In the second pair of transmissive gratings 1774A and 1774B, each grating in the pair receives the diverging light of each beam and, as shown in FIG. 17A, along a converging beam path that intersects near rotation axis RA. To collimate and deflect the light of each beam to produce a collimated light beam along a convergent beam path that overlaps and forms an illumination interference fringe pattern IFP near the second illumination region IR2. However, more generally, in various embodiments, alternative gratings that provide collimated and deflected beams everywhere may be constructed in accordance with the principles described above. In any case, a suitable grating can be determined through some or all of the design, simulation, and experiment based on a commercially available optical design program or a known grating design principle.

  While the preferred embodiment of the disclosure has been illustrated and described, it will be apparent to those skilled in the art, based on the present disclosure, that various modifications of the arrangement and process sequences of the illustrated and described components may be made. Various modifications may be used to implement the principles disclosed herein. Further, the various embodiments described above can be combined to provide further embodiments. The patent documents referred to herein are hereby incorporated by reference in their entirety. If desired, aspects of the embodiments can be modified to apply further patent and patent application concepts to provide further embodiments.

  These and other variations can be applied to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed as limiting the scope of the claims to the specific embodiments disclosed in the specification and claims, but rather by the following claims. It should be construed to include all possible embodiments, together with all ranges that are considered equivalents.

Claims (19)

A rotary scale extending in a rotation measurement direction about a rotation axis orthogonal to a rotation plane, the rotary scale being thin in the rotation measurement direction, being long in a rotary scale lattice bar direction intersecting with the rotation measurement direction, and being in the rotation measurement direction. the rotation surface extending toward, with a rotary scale grating consists of periodically arranged scale grating bar nominal scale pitch P _SF to the rotation measurement direction, and a rotary scale,
An illumination light source having a light source that outputs light source light to a structured illumination generating mechanism, wherein the structured illumination generating mechanism has a first illumination area on the rotary scale, at least first and second deflection elements. A first illumination area having a beam deflector structure and a second illumination area on the rotary scale, wherein the structured illumination generation mechanism diffracts the source light and outputs the diffracted light to the beam deflector structure as structured illumination light. Inputting the light source light to the illumination area, crossing the diffracted beams of the structured illumination light with each other, and transmitting the structured illumination light after the intersection to the second illumination area on the rotary scale. Forming an illumination interference fringe pattern in the second illumination region, wherein the illumination interference fringe pattern is formed of stripes that are thin in the rotation measurement direction and long in the illumination interference fringe direction that intersects the rotation measurement direction. It is an illumination light source,
A set of N spatial phase detectors periodically arranged at a detector pitch PD in a detection interference fringe moving direction intersecting with the rotational measurement direction, wherein each of the spatial phase detectors is a spatial phase detector; At least a majority of the spatial phase detectors extend in the rotational measurement direction over a relatively long dimension and are relatively narrow in the direction of the detected fringe movement that intersects the rotational measurement direction. A set of the N spatial phase detectors includes a detector array having a photodetector structure, arranged in a spatial phase sequence along the detection interference fringe moving direction;
The direction of the rotary scale grating bar is a direction on the rotating surface that forms a non-zero yaw angle に 対 し て with respect to a direction intersecting the direction of the measurement axis along the rotating surface;
The structured illumination generating mechanism may be configured such that the illumination interference fringe direction of the illumination interference fringe pattern near the second illumination area on the rotary scale is the same as the rotary scale near the second illumination area on the rotary scale. A nominal interference fringe direction rotated by a yaw difference angle YDA that is not 0 with respect to the lattice bar direction, and is configured to face a direction forming a yaw angle;
The rotary scale grating receives the illumination interference fringe pattern in the second illumination region and forms a periodic scale light pattern having the detector interference fringe pattern in the photodetector structure on the photodetector structure. Outputting scale light, the detector interference fringe pattern extends in a direction parallel to the rotation measurement direction over a relatively long dimension, and is relatively narrow in the detection interference fringe movement direction crossing the rotation measurement direction; And, having a periodicity of the detection interference fringe period PDF in the detection interference fringe movement direction intersecting with the rotation measurement direction, is configured by a periodic high light intensity and low light intensity band,
The detected interference fringe period PDF and the detected interference fringe movement direction intersect with the rotation measurement direction, and depend at least in part on the non-zero yaw angle 、;
The high light intensity and low light intensity bands move in the detection interference fringe moving direction that intersects the rotation measurement direction as the rotary scale grating rotates around the rotation axis,
The photodetector structure detects a displacement of the high light intensity and low light intensity bands in the detection interference fringe moving direction intersecting with the rotation measurement direction, and outputs a spatial phase displacement signal indicating a displacement of a rotary scale. give,
Optical rotary encoder. The non-zero yaw difference angle YDA is nominally -2 °.
The optical rotary encoder according to claim 1. Each of the N spatial phase detectors has an even number of scale light receiving regions,
The optical rotary encoder according to claim 1. The detection interference fringe period PDF is 40 μm or more;
The optical rotary encoder according to claim 1. The yaw angle ψ is given by the following equation:

Satisfy the relationship shown by
The optical rotary encoder according to claim 1. The rotary scale is a cylindrical rotary scale having a nominally cylindrical rotating surface on which the scale grid bars are arranged,
Each of the first and second illumination areas is located at a different diameter end of a cylindrical rotary scale, and the illumination light source is arranged along a line passing through the first and second illumination areas. Outputting light source light to the first illumination area, wherein the beam deflector structure is disposed in a space partitioned by projecting the cylindrical rotating surface along the direction of the axis of rotation.
The optical rotary encoder according to claim 1. The beam deflector structure receives each beam of the diffracted light source light output from the first illumination area, and converges each received beam crossing near the rotation axis to a diverging beam path. Each beam received to deflect along a path, receive each deflected beam, and superimpose via the convergent beam path to form the illumination interference fringe pattern near the second illumination area; Deflect,
The optical rotary encoder according to claim 6. At least one of the illumination light source and the beam deflector structure is configured such that each beam of the diffracted light source light converges near an intersection near the rotation axis,
At least one of the beam deflector structure and the detector array forms the periodic scale light pattern having the detector interference fringe pattern, and the output reflected scale light is nominally in the photodetector structure. Configured to be collimated on,
The optical rotary encoder according to claim 7. The beam deflector structure has surfaces that extend in parallel to the diameter of the cylindrical rotary scale that passes through the first and second illumination regions, respectively, and is disposed to face each other across the rotation axis, and First and second parallel plate mirrors or gratings oriented in a direction to receive each beam of the diffracted light source light output from one illumination area;
The first and second parallel plate mirrors or gratings further receive respective beams of the diffracted light source light output from the first illumination area, intersect near the rotation axis, and cross the divergent beam path. Deflecting each beam along the convergent beam path leading to and receiving the deflected beams and superimposing them via the convergent beam path to form the illumination interference fringe pattern near the second illumination area Deflect each received beam so that
The optical rotary encoder according to claim 7. A first measurement channel;
Having a second measurement channel similar to the first measurement channel;
Each of the spatial phase displacement signals of the first and second measurement channels, or a combination of the measurements derived therefrom, mitigates potential deviation errors in individual spatial phase displacement signals or the measurements derived therefrom. Or compensate,
The optical rotary encoder according to claim 7. The first measurement channel has the scale grid bar arranged along a first scale track of the rotary scale to form the yaw angle ψ;
The second measurement channel is arranged along a second scale track of the rotary scale, spaced apart from the first scale track in a direction of the rotation axis so as to form a yaw angle −ψ. Has a grid bar,
One said beam deflector structure is shared by said first and second measurement channels;
The optical rotary encoder according to claim 10. The rotary scale is a flat circular rotary scale having a flat rotating surface provided with reflection scale grating bars arranged at a constant angle pitch AP _SF ,
The illumination light source, the beam deflector structure and the detector array are all located on the same side of the rotary scale,
The first and second illumination areas are disposed near respective ends of the rotary scale having different diameters, and the illumination light source is arranged along a plane passing through the first and second illumination areas. Outputting the light source light to the first illumination area so as to form an angle of incidence with respect to the flat plate rotating surface in the plane;
The beam deflector structure receives each beam of the diffracted light source light reflected and output by the first illumination area, and moves each received beam along a converging beam path that intersects near the rotation axis. And deflects each beam toward an intersection near the axis of rotation such that each deflected beam follows a divergent beam path, and each beam overlaps through the convergent beam path to produce a second illumination. Deflecting each beam so as to form the illumination interference fringe pattern near the region,
The second illumination area is incident on the plate rotating surface such that the illumination interference fringe pattern is input and forms the periodic scale light pattern having the illumination interference fringe pattern in the photodetector structure. Outputs scaled light reflected at an angle,
The optical rotary encoder according to claim 1. At least one of the illumination light source and the beam deflector structure is configured such that each beam of the diffracted light source light converges near an intersection near the rotation axis,
At least one of the beam deflector structure and the detector array forms the periodic scale light pattern having the detector interference fringe pattern, and the output reflected scale light is nominally in the photodetector structure. Top, configured to be collimated,
An optical rotary encoder according to claim 12. The beam deflector structure includes first and second pairs of transmissive gratings and a cross-region reflector;
The first pair of transmission gratings are arranged in a plane that is nominally parallel to the rotating surface, and each grating of the first pair is reflected and output by the first illumination area. Each grating of the first pair is arranged to receive each beam of diffracted light source light, and each grating of the first pair is configured to deflect each light beam along the convergent beam path intersecting near the axis of rotation. Has a grid bar,
The intersection area reflector is disposed near a position where the convergent beam path intersects near the rotation axis, and reflects each beam from the intersection area reflector to follow the divergent beam path;
The second pair of transmission gratings is arranged in a plane that is nominally parallel to the rotating surface, and each grating of the second pair is arranged to receive each beam along the divergent beam path. Wherein each grating of the second pair has a grating bar configured such that each beam overlaps following the divergent beam path to form the illumination interference fringe pattern near the second illumination region. ,
An optical rotary encoder according to claim 12. In the first pair of transmission gratings, each grating of the first pair receives collimated light of each beam and deflects each beam along the convergent beam path that converges near the rotation axis; Having a curved grid bar to converge each beam near the rotation axis;
In the second pair of transmissive gratings, each grating of the second pair receives divergent light of each beam, collimates and deflects the light of each beam, and the collimated light beam is Having a curved grid bar configured to overlap along a path and form the illumination interference fringe pattern near the second illumination area;
The optical rotary encoder according to claim 14. The intersection area reflector has a curved surface,
The optical rotary encoder according to claim 14. The first and second illumination areas are arranged near respective ends of different diameters passing through the rotation axis of the rotary scale,
The illumination light source is configured to illuminate the first illumination along a nominal illumination plane nominally perpendicular to the plate rotation surface and nominally parallel to the diameter and offset from the diameter by a nominal illumination plane offset. Outputting the light source light to the area,
The first and second illumination areas are each offset from the diameter by the nominal illumination plane offset;
The nominal illumination plane offset is the nominal or average of the scale grid bars of the second illumination area where the nominal illumination plane makes the non-zero yaw angle with respect to the direction intersecting the measurement axis direction. The nominal interference fringe direction yaw angle is non-zero with respect to the nominal illumination plane of the second illumination area. Rotated by the yaw difference angle YDA,
An optical rotary encoder according to claim 12. The non-zero yaw difference angle YDA is twice the non-zero yaw angle,
An optical rotary encoder according to claim 17. The beam deflector structure has a transparent optical block, and the deflecting element of the beam deflector structure comprises a surface of the transparent optical block, or comprises an element formed or attached to a surface of the transparent optical block. ,
The optical rotary encoder according to claim 1.

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