DE102015209716A1 - Optical encoder with customizable resolution - Google Patents

Optical encoder with customizable resolution

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Publication number
DE102015209716A1
DE102015209716A1 DE102015209716.1A DE102015209716A DE102015209716A1 DE 102015209716 A1 DE102015209716 A1 DE 102015209716A1 DE 102015209716 A DE102015209716 A DE 102015209716A DE 102015209716 A1 DE102015209716 A1 DE 102015209716A1
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Germany
Prior art keywords
scale
light
detector
section
grating
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Pending
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DE102015209716.1A
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German (de)
Inventor
Joseph Daniel Tobiason
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Mitutoyo Corp
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Mitutoyo Corp
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Priority to US14/290,846 priority Critical
Priority to US14/290,846 priority patent/US9080899B2/en
Application filed by Mitutoyo Corp filed Critical Mitutoyo Corp
Publication of DE102015209716A1 publication Critical patent/DE102015209716A1/en
Application status is Pending legal-status Critical

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01DMEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infra-red, visible, or ultra-violet light
    • G01D5/32Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infra-red, visible, or ultra-violet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infra-red, visible, or ultra-violet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/36Forming the light into pulses
    • G01D5/38Forming the light into pulses by diffraction gratings

Abstract

A flexible optical path measuring system configuration uses an output grating to illuminate a structured light scale so that light from the scale is modulated with a beat frequency envelope that may have a relatively coarse pitch that matches a desired detector pitch. An imaging configuration provides spatial filtering to remove the high spatial frequencies from the modulation envelope to provide a clean signal in the detected fringe pattern. This combination of elements allows for an incremental scale trace pattern with a relatively finer pitch (eg, 4, 5, 8 microns) to provide stripes at a coarser pitch (eg, 20 microns) to a detector. Various scale resolutions can use a corresponding output grid so that all combinations can produce detector strips that match the same inexpensive detector component.

Description

  • TERRITORY
  • The present application relates generally to precision measuring instruments, and more particularly to optical path measuring systems.
  • BACKGROUND
  • Various optical path measuring systems are known which use a read head having an optical arrangement which images a scale pattern on a photodetector array in the read head. The image of the scale pattern displaces along with the scale element, and the movement or position of the displaced scale pattern image is detected with a photodetector array. One can use conventional imaging, self-imaging (also called Talbot imaging), and / or shadow mapping to provide the scale pattern image in various configurations.
  • Optical encoders can use scale structures with incremental or absolute positions. A scale structure with incremental positions allows the displacement of a read head relative to a scale to be determined by summing incremental displacement units from a starting point along the scale. Such encoders are suitable for certain applications, especially those in which mains power is available. For low power applications (eg, battery powered meters and the like), it is more desirable to use absolute position scale structures. Absolute position scale structures provide a unique output signal or a combination of signals at each position along a scale. They do not require continuous summing of incremental relocations to identify a position. Thus, scale structures with absolute positions enable various energy-saving measures. Various absolute position encoders are known which use various optical, capacitive or inductive sensor technologies. The U.S. Patent Nos. 3,882,482 ; 5,965,879 ; 5,279,044 ; 5,886,519 ; 5,237,391 ; 5,442,166 ; 4,964,727 ; 4,414,754 ; 4,109,389 ; 5,773,820 and 5,010,655 disclose various encoder configurations and / or signal processing techniques that are of importance to absolute position encoders and are hereby fully incorporated by reference.
  • One type of configuration used in some optical encoders is a telecentric arrangement. The U.S. Patents No. 7,186,969 ; 7,307,789 and 7,435,945 , which are hereby incorporated by reference in their entirety, disclose various encoder configurations employing either single or dual telecentric imaging systems for imaging the periodic light pattern and detecting the displacement of the periodic scale structure. Telecentric imaging systems provide certain desirable features in such optical encoders.
  • A problem with the design of such optical encoders is that users generally prefer that the read heads and scales of the encoders be as space efficient as possible. A space-saving encoder is more convenient to install in a variety of applications. For certain precision measurement applications, high resolution is also required. However, the prior art does not teach configurations that provide certain combinations of high resolution, range / resolution ratio, robustness, space-saving size, and design features that enable a variety of encoder resolutions to be provided using shared manufacturing techniques and components, and the low Allow costs as desired by the users of the encoder. Improved configurations of encoders that provide such combinations would be desirable.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • The above aspects and many advantages thereof will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. Show it:
  • 1 a partially schematic exploded diagram of a coder configuration with a double telecentric arrangement and a scale with absolute, reference and incremental track patterns using conventional imaging techniques;
  • 2A to 2C Diagrams of the incremental scale trace pattern, the image intensity and the detector configuration of the encoder configuration 1 ;
  • 3 a partially schematic exploded diagram of a coder configuration with a double telecentric arrangement and a scale with absolute, reference and incremental track patterns using spatial filtering and imaging principles according to the principles disclosed herein;
  • 4A to 4D Diagrams of the illumination strip pattern, the incremental scale trace pattern, the resulting moiré Image Intensity and the detector configuration of the encoder configuration 3 ;
  • 5 a graph depicting modulation transfer functions corresponding to various sets of design parameters;
  • 6 a graph showing the dependence of the depth of field (% DOF), the spatial harmonic content and the optical signal power on the dimension of an aperture in the measuring axis direction;
  • 7 a partially schematic exploded diagram of an embodiment of the encoder configuration 1 ;
  • 8th a partially schematic exploded diagram of an embodiment of the encoder configuration 3 ;
  • 9 a diagram of an alternative configuration of the phase grating portion of the embodiment 8th ;
  • 10A and 10B Diagrams of the scale track pattern arrangements of the encoder configurations respectively 1 and 3 ;
  • 11 a table containing the parameters for various scale and detector track combinations for the encoder configuration 3 maps;
  • 12 a schematic cross-sectional diagram showing different light paths through a double-telecentric imaging encoder arrangement;
  • 13A and 13B a configuration that is another embodiment of a practical implementation of an encoder configuration according to the principles disclosed herein;
  • 14 an analysis of in 13 4, which indicates how a phase grating provides the operational diffraction orders that provide the optical intensity signals at the detector;
  • 15 a partially schematic exploded diagram of an encoder configuration comprising a first alternative embodiment of a lighting section;
  • 16 a schematic drawing of a coder configuration, which includes a second alternative embodiment of a lighting section, the elements in addition to those in 15 and which may be used in a reflective encoder configuration;
  • 17 Figure 5 is a drawing of a lighting section that may be used in a coder configuration according to the principles disclosed herein;
  • 18 Figure 5 is a drawing of a lighting section that may be used in a coder configuration according to the principles disclosed herein;
  • 19 Figure 5 is a drawing of a lighting section that may be used in a coder configuration according to the principles disclosed herein;
  • 20 Figure 5 is a drawing of a lighting section that may be used in a coder configuration according to the principles disclosed herein;
  • 21 Figure 5 is a drawing of a lighting section that may be used in a coder configuration according to the principles disclosed herein;
  • 22 Figure 5 is a drawing of a lighting section that may be used in a coder configuration according to the principles disclosed herein;
  • 23A an embodiment of a scale grid pattern comprising offset grid sections that may be used in an encoder configuration;
  • 23B schematically the alignment of combined intensity contributions of each scale grid section 23A in a scale image;
  • 23C the scale image representing the combined intensity contributions of each of the scale image sections 23B includes;
  • 24A a schematic diagram of a first encoder configuration 2400A configured to use an enlarged area of the scale grid according to the principles disclosed herein;
  • 24B 12 is a schematic diagram of a second encoder configuration configured to use an enlarged portion of the scale grid in accordance with the principles disclosed herein;
  • 25A FIG. 3 is a schematic diagram showing an encoder configuration including a scale element disposed at a roll angle to mitigate any self-image effects; FIG.
  • 25B 12 is a schematic diagram showing an encoder configuration comprising a scale element and a phase grating of a lighting section arranged at a roll angle to mitigate any self-image effects; and
  • 25C 12 is a schematic diagram showing an encoder configuration including a phase grating of a lighting section arranged at a roll angle to reduce any self-image effects.
  • DETAILED DESCRIPTION
  • 1 FIG. 12 is a partially schematic exploded diagram of an optical path measuring system configuration. FIG 100 with a double telecentric arrangement and a scale with absolute, reference and incremental track patterns and using conventional imaging techniques. Certain aspects of the encoder configuration 100 are similar to the encoder configurations described in copending and commonly assigned U.S. Patent Application Serial No. 12 / 535,561, filed August 4, 2009, now U.S. Patent No. 8,492,703 and U.S. Patent Application No. 12 / 273,400, filed November 18, 2008 (hereinafter '400 application), now U.S. Patent No. 7,608,813 which are hereby incorporated by reference in their entirety. Although the encoder configuration 100 is able to function accurately and effectively with an incremental scale track having a relatively coarse pitch (e.g., 20 microns), as discussed below with reference to FIG 3 In more detail, the methods disclosed herein may be used to enable the use of an incremental scale trace with a much finer pitch (eg, 4 microns) in a similar configuration.
  • As in 1 includes the encoder configuration 100 a scale element 110 , a lens 140 for directing visible or invisible wavelengths of light from a light source (not shown) and a double telecentric imaging configuration 180 , The double telecentric imaging configuration 180 includes a first lens 181 on a first lens plane FLP, an aperture 182 in an aperture component 182 ' on an aperture plane AP, a second lens 183 at a second lens plane SLP and a detector electronics 120 on a detector level DP. In at least one embodiment, the scale element is 110 separated from the first lens plane FLP by a distance d 0 , the first lens plane FLP is separated from the aperture plane AP by a focal length f, the aperture plane AP is separated from the second lens plane SLP by a focal length f ', and the second lens plane SLP is from the detector plane DP separated by a distance d 0 '. The detector electronics 120 can be used on circuits for generating and processing signals 190 be connected. The light source can also be connected to the circuits for generating and processing signals via energy and signal connections (not shown) 190 be connected.
  • At the in 1 embodiment shown comprises the scale element 110 a scale pattern 115 comprising three scale track patterns: an absolute scale track pattern TABS1, a reference scale track pattern TREF1 and an incremental scale track pattern TINC1. The track pattern TABS1 is called an absolute scale track pattern because it provides signals usable to determine an absolute position over an absolute measurement range. In at least one embodiment, any conventional absolute scale pattern may be used for the absolute scale track pattern TABS1. In at least one embodiment, the absolute scale track pattern TABS1 may have a very "coarse" ABS resolution of about the order of the detector dimension along the X-axis.
  • For the incremental scale trace pattern TINC1, in at least one embodiment, the incremental pitch may be relatively coarse (eg, 20 microns). As below with reference to 3 In more detail, a finer pitch (eg, 4 microns) can be made to operate in a similarly sized encoder configuration using the methods disclosed herein. The reference scale track pattern TREF1 is formed such that it can be resolved to a level that allows it to specify a particular incremental wavelength such that the incremental wavelength (eg, from the incremental scale track pattern TINC1) with respect to a absolute marking (eg of the absolute scale track pattern TABS1) is not ambiguous. As below with reference to 10A In more detail, in at least one embodiment, the reference scale track pattern TREF1 may comprise a series of reference marks. In at least one embodiment, the reference marks may be formed as a series of Barker patterns, which may also serve as vernier reference marks, and may be formed according to various known techniques.
  • 1 shows orthogonal X, Y and Z directions according to an agreement used here. The X and Y directions are parallel to the plane of the scale pattern 115 wherein the X-direction is parallel to the intended measuring axis direction MA 82 is (for example, perpendicular to elongated pattern elements included in the incremental scale trace pattern TINC1 may be included). The Z direction is perpendicular to the plane of the scale pattern 115 ,
  • The detector electronics 120 includes a detector configuration 125 comprising three detector tracks DETABS1, DETREF1 and DETINC1 arranged to receive light from the three scale track patterns TABS1, TREF1 and TINC1, respectively. The detector electronics 120 can also use signal processing circuits 126 include (eg, signal offset and / or gain adjustment circuits, signal amplification and combination circuitry, etc.). In at least one embodiment, the detector electronics 120 be made as a single CMOS IC.
  • As illustrated by the image channel for the incremental scale track pattern TINC1, the light from the illumination source becomes in operation from the lens 140 passed to the incremental scale track pattern TINC1 with output light 131 to illuminate. In some embodiments, the output light is 131 coherent light. The incremental scale track pattern TINC1 then gives the scale light 132 out. It is understood that the limiting aperture 182 , which has an aperture width AW in the X direction, serves as a spatial filter (as described below with reference to FIGS 2 described in more detail) to select or limit the beams of light passing through the incremental scale track pattern TINC1. 1 forms three such light rays, two outer rays and one middle ray. As in 1 shown, transmits the lens 181 the light rays towards the limiting aperture 182 , The limiting aperture 182 transmits the rays as spatially filtered image light 133 to the second lens 183 , and the second lens 183 transmits and focuses the spatially filtered image light to form an image of the scale trace pattern TINC1 on the detector trace DETINC1.
  • Thus, when the incremental scale track pattern TINC1 is illuminated, there is a track-specific spatially-modulated light pattern to the detector track DETINC1 of the detector electronics 120 out. An image of the spatially modulated light pattern is formed on an image plane IMGP, which may be configured to be coplanar with the detector trace DETINC1 (where the image plane IMGP in FIG 1 will be shown separately for explanation). As shown in the image plane IMGP, the pattern of the scale image SI has a modulated scale image pitch P SI , which may be relatively coarse in one specific embodiment (eg, 20 microns).
  • Similar to the imaging of the spatially modulated light pattern from the incremental scale track pattern TINC1 on the detector track DETINC1, when the scale track patterns TREF1 and TABS1 with the light from the lens 140 are illuminated, they give track-specific spatially modulated light patterns (eg patterned light that corresponds to their patterns) to the track-specific detector tracks DETREF1 and DETABS1 of the detector electronics 120 out. As noted previously, the reference scale track pattern TREF1 (eg, with Barker patterns) indicates a particular incremental wavelength such that the wavelength of the incremental scale track pattern TINC1 relative to the absolute mark is not ambiguous from the absolute scale track pattern TABS1. It is understood that all spatially modulated light patterns coincide with the scale 110 move.
  • As below with reference to. 11 described in more detail, individual photodetector surfaces are arranged in each of the detector tracks DETINC1, DETABS1 and DETREF1 to spatially filter their respective received spatially modulated light patterns to provide desirable positional indicative signals (eg, the incremental detector trace DETINC1 generates quadrature signals or other periodic signals, having a spatial phase relationship conducive to signal interpolation). In some embodiments, rather than discrete photodetector areas, a single-aperture spatial filter mask may mask relatively larger photodetectors to provide light-receiving areas similar to the individual photodetector areas to provide a similar overall signal effect in accordance with known techniques.
  • In various applications, the detector electronics and the light source are incorporated with respect to each other in a fixed relationship, e.g. In a read head or meter housing (not shown), and are used in accordance with known techniques by a storage system along the measurement axis with respect to the scale 110 guided. The scale may be attached to a moving stage or meter spindle or the like in various applications. It is understood that in 1 shown configuration is a transmissive configuration. Ie. the scale pattern 115 includes light blocking portions and light transmitting portions (eg, formed on a transparent substrate using known thin film patterning techniques or the like) which output the spatially modulated light patterns to the detector tracks by transmission. It is understood that similar components may be arranged in reflective embodiments, with the light source and detector electronics on the same side of the scale 110 are arranged and positioned for an optionally angular illumination and reflection according to known techniques.
  • With either transparent or reflective scale patterns, one can see the sections of the Scale patterns that provide the light detected by the detector tracks (eg, DETABS1, DETREF1, or DETINC1) as signal generating portions of the scale pattern, and it is understood that other portions of the scale pattern generally have as little light to the detector tracks as and can be referred to as signal-reducing sections. It is understood that the signal generating portions or the signal reducing portions of the scale pattern according to the present teachings may be patterned in various embodiments. In other words, scale patterns that are "negatives" of one another can both produce useful signals, and the resulting signal variations are also approximately "negative" from one another for a given reflective or transmissive array. Thus, the scale patterns may be described in terms of "signal varying sections", and it should be understood that in various embodiments, the signal varying sections may include either the signal generating sections or the signal reducing sections of the scale pattern.
  • 2A to 2C depict various aspects related to the optical signal channel corresponding to the incremental scale trace pattern TINC1 1 equivalent. More specifically, forms 2A the incremental scale track pattern TINC1 having a scale pitch P SL . 2 B FIG. 12 is a graph of the resulting image intensity signal IMG1 from the light from the incremental scale trace TINC1 at the detector plane DP. As in 2 B The resulting image intensity (for example, through the aperture 182 ) is spatially filtered to produce an approximately sinusoidal signal (eg, as opposed to a square wave signal as would be produced from an unfiltered signal from the incremental scale trace pattern TINC1), and has a signal period P ISC . 2C is a diagram of the incremental detector trace DETINC1, the explanation of an image of the image intensity signal IMG1 from 2 B was superimposed. As in 2C 4, the detector trace DETINC1 is connected to output quadrature signals, with four detector elements in a period of the detector track wavelength λ d , which also corresponds to a period P ISC of the image intensity signal IMG1.
  • 3 Figure 4 is a partially schematic exploded diagram of an encoder configuration 300 with a double telecentric arrangement and a scale with absolute, reference and incremental track patterns using spatial filtering and imaging techniques according to the principles disclosed herein. Some of the components and operating principles of the encoder configuration 300 are approximately similar to the encoder configuration 100 out 1 and are generally analogously understandable. For example, the 3XX serial numbers in 3 which have the same "XX" ending as the 1XX serial numbers in 1 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • As in 3 includes the encoder configuration 300 a scale element 310 , a lighting system or a section 360 and a double telecentric imaging configuration 380 , The lighting system or the lighting section 360 includes a light source 330 (eg, an LED) for emitting visible or invisible wavelengths of light, a lens 340 and a phase grating 350 , As will be described in more detail below, the phase grating 350 in at least one embodiment may be used to generate patterned light patterns, and may not be in the optical signal path channels for the incremental and reference scale track patterns TINC2 and TREF2, but not for the absolute scale track pattern TABS2. The double telecentric imaging configuration 380 includes a first lens 381 on a first lens plane FLP, an aperture 382 in an aperture component 382 ' on an aperture plane AP, a second lens 383 on a second lens plane SLP and a detector electronics 320 on a detector level DP. The detector electronics 320 can be used on circuits for generating and processing signals 390 be connected. The light source 330 also has power and signal connections (not shown) to circuits for generating and processing signals 390 be connected.
  • At the in 3 embodiment shown comprises the scale element 310 a scale pattern 315 comprising three scale track patterns: an absolute scale track pattern TABS2, a reference scale track pattern TREF2 and an incremental scale track pattern TINC2. In at least one embodiment, a conventional absolute scale track pattern may be used for the absolute scale track pattern TABS2. In at least one embodiment, the absolute scale track pattern TABS2 may have a relatively "coarse" ABS resolution on the order of the detector dimension along the X-axis.
  • As will be described in more detail below, the encoder configuration is 300 designed to use certain spatial filtering and imaging principles that allow a finely graduated scale to provide larger pitch stripes corresponding to the detector element pitch of a low cost detector that detects the scale displacement. To create the desired stripes, the phase grating is 350 one Illumination grating designed to have a pitch close to the pitch of the incremental scale trace pattern TINC2 and the reference scale trace pattern TREF2 (eg, a phase grating pitch of 5 microns compared to an incremental scale pitch of 4 microns and a reference scale pitch). Scale score of 4.1 microns). The resulting fringe period from the phase grating 350 and the incremental scale track pattern TINC2 may be relatively coarse (eg, 20 microns) and may be slightly different than the fringe period produced by the phase grating 350 and the reference scale track pattern TREF2 (eg, 22.77 microns) is generated.
  • As will be described in more detail below, the detected pattern with spatial filtering becomes the double telecentric imaging configuration 380 pictured which the aperture 382 which hides or removes high spatial frequencies corresponding to the incremental and reference scale trace patterns TINC2 and TREF2. In certain implementations, the parameters are chosen such that the resulting modulated image split of the spatially filtered pattern corresponds to the pitch of a predetermined given detector (eg, a detector designed for 20 micron incremental scale scoring). Suitable aperture dimensions can be chosen to achieve the desired spatial filtering effect which removes the high spatial frequencies and results in the desired pattern stripe period. Certain techniques relating to such aperture dimensions to achieve desired spatial wavelength filtering are taught in the commonly assigned US Pat U.S. Patent No. 7,186,969 described in more detail, which is hereby incorporated by reference in its entirety.
  • As below with reference to 10B In more detail, in at least one embodiment, the reference scale track pattern TREF2 may comprise a series of reference marks that may be formed as a Barker pattern. The reference marks may also serve as vernier reference marks. The reference scale track pattern TREF2 is designed so that it can be resolved to a level that allows it to specify a particular incremental wavelength for the incremental scale track pattern TINC2 such that the incremental wavelengths with respect to an absolute mark are different from the absolute scale track pattern TABS2 are not ambiguous. In at least one embodiment, the combination of the reference track pattern TREF2 (eg, a Barker pattern) and the incremental track pattern TINC2 may produce a synthetic wavelength whose measured synthetic phase points to the correct cycle of the incremental scale track pattern (eg a measured synthetic phase of zero indicates a proper incremental cycle corresponding to that phase).
  • As a specific example, compared to the incremental scale trace pattern TINC2 (eg, 4.0 microns, which gives a modulated and spatially filtered fringe pattern with a period of 20 microns), the reference scale trace pattern TREF2 may have a slightly different pitch (e.g. 4.1 microns, which gives a modulated and spatially filtered fringe pattern with a period of 22.77 microns), so that the phase of the reference scale track pattern coincides with the phase of the incremental scale track pattern only at a specific point along a given length (eg, coincides only at one point along a Barker pattern length in the reference scale track pattern). The position in which the phases match defines a particular incremental wavelength for the incremental scale trace pattern TINC2.
  • In a specific embodiment, Barker patterns may be provided in the reference scale track pattern TREF2 at selected intervals (eg, 0.6 millimeters). The phase of each Barker pattern (eg in the middle of the pattern) coincides with the phase of the incremental scale trace pattern TINC1 at the locations spaced by the predetermined distance (eg, 0.6 millimeter) (or has a constant phase shift with respect to it). The synthetic wavelength of the incremental scale trace pattern TINC2 and the reference scale trace pattern TREF2 is larger than the Barker pattern length. In at least one embodiment, this relationship may be expressed by indicating that the synthetic wavelength of the incremental scale track pattern and the reference (eg, Barker) scale track pattern is greater than the Barker pattern length L such that L <pp ' / (p'-p), where p is the pitch of the incremental scale track pattern TINC2, and p 'is the pitch of the Barker pattern in the reference scale track pattern TREF2.
  • As in 3 shown includes the detector electronics 320 a detector configuration 325 comprising three detector tracks, DETABS2, DETREF2 and DETINC2, arranged to receive light from the three scale track patterns, TABS2, TREF2 and TINC2, respectively. The detector electronics 320 can also use signal processing circuits 326 (eg, circuitry for signal offset and / or gain adjustments, signal amplification and combination, etc.). In at least one embodiment, the detector electronics 320 be made as a single CMOS IC.
  • In operation, the light can 331 (eg primary light) coming from the light source 330 is emitted, partially or completely from the lens 340 be collimated over a beam surface sufficient to illuminate the three scale track patterns TABS2, TREF2 and TINC2. The phase grating 350 is dimensioned to diffract the output light to diffracted structured light 331 ' for the reference and incremental scale track patterns TREF2 and TINC2 (but not for the absolute scale track pattern TABS2) to achieve the previously described modulated and spatially filtered imaging effects. Then, as illustrated by the image channel for the incremental scale track pattern TINC2, the incremental scale track pattern TINC2 provides scale light 332 for the lens 381 ready. It is understood that the limiting aperture 382 having an aperture width AW in the X-axis direction serves as a spatial filter (as described below with reference to FIGS 4 and 12 described in more detail) to select or limit the light rays passing through the image channels. 3 forms three such light rays, two outer rays and one middle ray. As in 3 shown, transmits the lens 381 the light rays towards the limiting aperture 382 , The limiting aperture 382 transmits the rays as spatially filtered image light 333 to the second lens 383 , and the second lens 383 transmits and focuses the spatially filtered image light to form a spatially modulated light pattern on the detector trace DETINC2. As previously noted and as discussed below with reference to 4 In more detail, according to the principles disclosed herein, the spatially modulated light pattern on the detector trace DETINC comprises a modulated and spatially filtered fringe pattern.
  • When the scale track patterns TREF2 and TABS2 are illuminated, they respectively give track-specific spatially modulated light patterns (eg patterned light corresponding to their patterns) to the track-specific detector tracks DETREF2 and DETABS2 of the detector electronics 320 out. As noted previously, the spatially modulated light pattern on detector trace DETREF2 also includes a modulated and spatially filtered imaged fringe pattern. It is understood that all spatially modulated light patterns coincide with the scale 310 move. In optical signal channels corresponding to each of the detector tracks DETINC2, DETABS2 and DETREF2, individual photodetector areas are arranged to spatially filter their respective received spatially modulated light patterns to provide desirable positional indicative signals (eg, for the incremental scale track pattern TINC2 which generates quadrature signals , or other periodic signals having a spatial phase relationship conducive to signal interpolation). In some embodiments, rather than discrete photodetector areas, a single aperture spatial filter mask may mask relatively larger photodetectors to provide light receiving areas similar to the imaged individual photodetector areas to provide a similar overall signal effect according to known techniques.
  • In various applications, the detector electronics 320 and the light source 330 incorporated with respect to each other in a fixed relationship, e.g. In a read head or meter housing (not shown), and are used in accordance with known techniques by a storage system along the measurement axis with respect to the scale 310 guided. The scale may be attached to a moving stage or to a gauge spindle or the like in various applications.
  • 4A to 4D depict various aspects related to the optical signal channel that corresponds to the incremental scale trace pattern TINC2 3 equivalent. More specifically, forms 4A the illumination strip pattern IFP from that of the phase grating 350 is produced. The illumination stripe pattern IFP is shown as having a pitch P MI (eg, 5 microns). 4B maps the incremental scale track pattern TINC2, which has a scale pitch P SF (eg, 4 microns). 4C FIG. 12 is a graph of the resulting image intensity signal IMG2 from the light from the combination of the stripe grating 350 and the incremental scale trace TINC2 at the detector level DP. As in 4C As shown, the resulting image intensity comprises moire fringes having a beat frequency with an overall sinusoidal envelope pattern having a modulated image pitch P IMESF (eg, 20 microns). As previously described, the image intensity (eg, through the aperture 182 ) spatially filtered to the high frequency signals HFS from the phase grating 350 and the incremental scale track pattern TINC2 to produce the approximately sinusoidal envelope signal for the imaged moiré fringes with the resulting modulated image pitch P IMESF .
  • In various embodiments, the aperture is 350 is configured such that the aperture width AW = F · λ · (a / (P MI P SE / (P MI - P SF ))), where a is greater than 2.0 and less than 6.0. The spatially modulated image light includes stripes (in 4C shown in detail) resulting from the interference of two diffraction orders which differ by a value Δn. For example, in some embodiments, if the moiré image intensity signal IMG2 is from the overlap of a component of the scale light 332 of a diffraction order +1 and -1, then the value of Δn = 2. In other embodiments, the value of Δn may be 1 or 4.
  • It is understood that in coder configurations that include a light source that outputs coherent light, the variable a must have a value greater than 0.5. For embodiments that use coherent light, the value of a may be greater than 0.5 and less than 1.5. In one embodiment that uses coherent light, the value of a is 1. For embodiments that use incoherent light, the value of a may be greater than 1 and less than 4. In one embodiment using incoherent light, the value of a is equal to 2.
  • The image intensity signal IMG2 is modulated with an intensity modulation envelope having a spatial wavelength P IMESF that depends on the scale pitch P SF and the illumination stripe pitch P MI , and P SF and P MI are selected to cooperate with a detector pitch P d of the detector trace DETINC2 in that ΔnP MI P SF / (ΔnP MI -P SF ) = P IMESF = m × P d / k when the light source outputs incoherent light and ΔnP MI P SF / (2ΔnP MI -P SF ) = P IMESF = m · P d / k when the light source outputs incoherent light, where m is a number of phase signals output from the detector configuration, and k is an odd integer, where the spatial wavelength P IMESF is greater than the graduation P SF .
  • A series of vertical reference lines VRL, between 4A . 4B and 4C are drawn, provide an indication of the signal levels from the illumination strip pattern 4A ready by the incremental scale track pattern TINC2 off 4B and appear as corresponding signal intensities in the resulting moiré image intensity 4C , 4D is a diagram of the incremental detector trace DETINC2, which is illustratively an image of the beat frequency envelope of the moiré image intensity signal IMG2 4C is superimposed. As in 4D 4, the detector trace DETINC2 is connected to output quadrature signals, four detector elements being within one period of the detector pitch P d , which also corresponds to a period P IMESF of the moiré image intensity signal IMG2.
  • 5 and 6 show basic design reference information, each in 26 and 27 of the previously adopted U.S. Patent No. 7,186,969 are included. The usage of 5 and 6 With regard to the selection of aperture sizes in various embodiments, one may understand based on the disclosure of the '969 patent and will not be described in detail here. However, the teachings herein may be used in conjunction with the present disclosure. Much of the description of the '969 patent relates to incoherent illumination. One skilled in the art will make appropriate adjustments to his teachings based on known considerations regarding the differences between incoherent and coherent illumination in imaging systems.
  • 7 Figure 4 is a partially schematic exploded diagram of an encoder configuration 700 showing an embodiment of a practical implementation of the encoder configuration 100 out 1 is. Some of the components and operating principles of the encoder configuration 700 are approximately similar to the encoder configuration 100 out 1 and are generally analogously understandable. For example, the 7XX serial numbers in 7 which have the same "XX" ending as the 1XX serial numbers in 1 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • As in 7 includes the encoder configuration 700 a scale element 710 , a lighting system or a lighting section 760 and a double telecentric imaging configuration 780 , The lighting system or the lighting section 760 includes a light source 730 (eg, an LED) for emitting visible or invisible light wavelengths, a lens 740 and a beam splitter 755 , The double telecentric imaging configuration 780 includes a first lens array 781 on a first lens plane FLP, an aperture array 782 in an aperture component 782 ' on an aperture plane AP, a second lens array 783 on a second lens plane SLP and a detector electronics 720 on a detector level DP. The detector electronics 720 may be connected to circuits for generating and processing signals (not shown). The light source 730 may also be connected to the circuits for generating and processing signals via power and signal connections (not shown).
  • With respect to the lens arrays 781 and 783 and the aperture array 782 It is understood that each of them includes individual elements that are similar to the first lens 181 , the aperture 182 and the second lens 183 the encoder configuration 100 out 1 are. In 7 In each of the arrays, each of the individual elements cooperates similarly to provide a single image path or channel, which may be referred to as an image channel or image channel configuration. Each of the image channels works in a similar way to the image channel for each lens and the aperture previously described 1 described encoder configuration 100 , In the embodiment of 7 The multiple image channels are used to provide additional robustness levels to the system against contamination, defects, scale ripple etc., in that if a single image channel is contaminated or otherwise compromised, the remaining image channels may further provide accurate imaging of the scale pattern.
  • At the in 7 embodiment shown comprises the scale element 710 a scale pattern 715 comprising the three scale track patterns previously described with reference to 1 comprising: the absolute scale track pattern TABS1, the reference scale track pattern TREF1 and the incremental scale track pattern TINC1. In at least one embodiment, the absolute scale track pattern TABS1 may have a very "coarse" ABS resolution on the order of the detector dimension along the X-axis.
  • For the incremental scale trace pattern TINC1, in at least one embodiment, the incremental pitch may be relatively coarse (eg, 20 microns). As below with reference to 8th described in more detail, a finer pitch (eg, 4 microns) may be implemented with a similarly sized encoder configuration in accordance with the principles disclosed herein. As below with reference to 10A In more detail, in at least one embodiment, the reference scale track pattern TREF1 may comprise a series of reference marks which may be formed as a series of Barker patterns which may also serve as vernier reference marks and which may be formed according to various known techniques ,
  • The detector electronics 720 includes a detector configuration 725 comprising the three detector tracks DETABS1, DETREF1 and DETINC1 arranged to receive light from the three scale track patterns TABS1, TREF1 and TINC1, respectively. The detector electronics 720 may also include signal processing circuitry (eg, circuitry for signal offset and / or gain adjustments, signal amplification and combination, etc.). In at least one embodiment, the detector electronics 720 be made as a single CMOS IC.
  • In operation, the light can 731 (eg primary light) coming from the light source 730 is emitted, partially or completely from the lens 740 be collimated and is through the beam splitter 755 passed over a beam surface sufficient to illuminate the three scale track patterns TABS1, TREF1 and TINC1. Then, as illustrated by the image channel for the incremental scale track pattern TINC1, the incremental scale track pattern TINC1 provides scale light 732 ready, that of the beam splitter 755 towards the lens array 781 is redirected. It is understood that any limiting aperture of the aperture array 782 , each of which has an aperture width ΔN in the X direction, serves as a spatial filter (as previously described with reference to Figs 2 discussed) to select or limit the light rays passing through the given image channel for the incremental scale trace pattern TINC1. As in 7 shown, transmit the corresponding lenses of the lens array 781 for each image channel, the light rays in the direction of the corresponding apertures of the limiting aperture array 782 , The corresponding apertures of the bounding aperture array 782 then transmit the rays as spatially filtered image light 733 to the respective lenses of the second lens array 783 , and the respective lenses of the second lens array 783 transmit and focus the spatially filtered image light to form respective spatially modulated light patterns that correspond to the respective portions of the incremental scale trace pattern TINC1 at the respective portions of the detector trace DETINC1.
  • Thus, when the incremental scale track pattern TINC1 is illuminated, there are a number of track-specific spatially modulated light patterns at the respective portions of the detector track DETINC1 of the detector electronics 720 from which correspond to the respective image channel. An image of the spatially modulated light pattern is formed on an image plane IMGP, which may be configured to be coplanar with the detector trace DETINC1.
  • Similar to the imaging of the spatially modulated light patterns from the incremental scale track pattern TINC1 on the detector track DETINC1 when the scale track patterns TREF1 and TABS1 are illuminated by the light from the lens 740 are illuminated, they give track-specific spatially modulated light patterns (eg patterned light that corresponds to their patterns) to the track-specific detector tracks DETREF1 and DETABS1 of the detector electronics 720 out. As previously noted, the reference scale track pattern TREF1 (eg, with Barker patterns) may be resolved to indicate a particular incremental wavelength such that the wavelength of the incremental scale track pattern TINC1 relative to the absolute mark is different from the absolute scale track pattern TABS1 is not ambiguous. It is understood that all spatially modulated light patterns coincide with the scale 710 move. Discrete photodetector areas are arranged on each of the detector tracks DETINC1, DETABS1 and DETREF1 to filter their respective received spatially modulated light patterns to provide desirable positional indicative signals (eg, the incremental detector trace DETINC1, the quadrature signals or other periodic signals having a spatial phase relationship , which is conducive to signal interpolation).
  • In various applications, the detector electronics and the light source are incorporated with respect to each other in a fixed ratio, e.g. In a read head or meter housing (not shown), and are used in accordance with known techniques by a storage system along the measurement axis with respect to the scale 710 emotional. The scale may be attached to a moving stage or to a gauge spindle or the like in various applications. In the 7 The configuration shown is a reflective configuration. Ie. the light source and the detector electronics are on the same side of the scale 710 arranged and positioned according to known angular illumination and reflection techniques. Thus, the scale pattern includes 715 light absorbing portions and light reflecting portions (eg, fabricated on a substrate using known reflection techniques) which output the spatially modulated light patterns by reflection to the detector tracks. It is understood that similar components may be arranged in transmissive embodiments (see, eg, FIG. 1 ).
  • 8th Figure 4 is a partially schematic exploded diagram of an encoder configuration 800 showing an embodiment of a practical implementation of the encoder configuration 300 out 3 is. Some of the components and operating principles of the encoder configuration 800 are approximately similar to the encoder configuration 300 out 3 and are generally analogously understandable. For example, the 8XX serial numbers in 8th which have the same "XX" extension as the 3XX serial numbers in 3 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • As in 8th includes the encoder configuration 800 a scale element 810 , a lighting system or a lighting section 860 and a double telecentric imaging configuration 880 , The lighting system or the lighting section 860 includes a light source 830 (eg, an LED) for emitting visible or invisible light wavelengths, a lens 840 , a phase grid 850 and a beam splitter 855 , As will be described in more detail below, the phase grating 850 however, in at least one embodiment, the image channels for the incremental and reference scale track patterns TINC2 and TREF2 are not set and dimensioned for the absolute scale track pattern TABS2. The double telecentric imaging configuration 880 includes a first lens array 881 on a first lens plane FLP, an aperture array 882 on an aperture plane AP, a second lens array 883 on a second lens plane SLP and a detector electronics 820 on a detector level DP. It is understood that the lens arrays 881 and 883 and the aperture array 882 are arranged and work like the lens arrays 781 and 783 and the aperture array 782 previously referring to 7 have been described. The detector electronics 820 may be connected to circuits for generating and processing signals (not shown). The light source 830 may also be connected to the circuits for generating and processing signals via power and signal connections (not shown).
  • At the in 8th embodiment shown comprises the scale element 810 a scale pattern 815 comprising the three scale track patterns previously described with reference to 3 which includes the absolute scale track pattern TABS2, the reference scale track pattern TREF2 and the incremental scale track pattern TINC2. In at least one embodiment, the absolute scale track pattern TABS2 may have a relatively "coarse" ABS resolution on the order of the detector dimension along the X-axis. As before with reference to 3 described, the reference scale track pattern TREF2 and the incremental scale track pattern TINC2 are used and mapped in accordance with the spatial filtering and imaging principles disclosed herein.
  • As in 8th shown includes the detector electronics 820 a detector configuration 825 comprising the three detector tracks DETABS2, DETREF2 and DETINC2 arranged to receive light from the three scale track patterns TABS2, TREF2 and TINC2, respectively. The detector electronics 820 may also include signal processing circuitry (eg, circuitry for signal offset and / or gain adjustments, signal amplification and combination, etc.). In at least one embodiment, the detector electronics 820 be made as a single CMOS IC.
  • In operation, the light can 831 (eg primary light) coming from the light source 830 is emitted, partially or completely from the lens 840 be collimated and through the beam splitter 855 over a beam surface sufficient to illuminate the three scale track patterns TABS2, TREF2 and TINC2. The phase grating 850 is dimensioned to diffract the output light to diffracted structured light 831 ' for the reference and incremental scale track patterns TREF2 and TINC2 (but not for the absolute scale track pattern TABS2). As illustrated by the image channel for the incremental scale track pattern TINC2, the incremental scale track pattern TINC2 then gives scale light 832 from the beam splitter 855 towards the lens array 881 is redirected. It is understood that any limiting aperture of the aperture array 882 , each of which has an aperture width AW in the X direction, serves as a spatial filter (as previously with reference to 4 described) to select or limit the light rays passing through the given image channels. In other words, as described above, the spatial filtering effectively fades out the high-frequency portions of the images generated by the phase grating and the incremental scale pattern patterns, so that the remaining signal consists mainly of the modulation, which is called the beat frequency between the stripe division of the structured lighting and the division of the scale grid. The resulting modulated image pitch is a measure of the period of this beat frequency envelope.
  • As in 8th shown, transmit the corresponding lenses of the lens array 881 for each image channel, the light rays in the direction of the corresponding apertures of the limiting aperture array 882 , The corresponding apertures of the bounding aperture array 882 transmit the rays as spatially filtered image light 833 to the respective lenses of the second lens array 883 , and the respective lenses of the second lens array 883 transmit and focus the spatially filtered image light to form respective spatially modulated light patterns corresponding to the respective portions of the incremental scale trace pattern TINC2 at the respective portions of the detector trace DETINC2. As before with reference to 4 and according to the principles disclosed herein, the spatially modulated light patterns on the detector trace DETINC2 comprise modulated and spatially filtered imaged fringe patterns.
  • If the scale track patterns TREF2 and TABS2 are similarly illuminated, they input track-specific spatially modulated light patterns respectively to the track-specific detector tracks DETREF2 and DETABS2 of the detector electronics 820 out. As previously noted, the spatially modulated light patterns on the reference detector track DETREF2 also include modulated and spatially filtered imaged fringe patterns. It is understood that all spatially modulated light patterns coincide with the scale 810 move. In optical signal channels corresponding to each of the detector tracks DETINC2, DETABS2 and DETREF2, individual photodetector areas are arranged to spatially filter their respective received spatially modulated light patterns for desirable positional indicative signals (eg, the incremental detector trace DETINC2, the quadrature signals, or other periodic signals) Signals having a spatial phase relationship conducive to signal interpolation).
  • In various applications, the detector electronics 820 and the light source 830 built with respect to each other in a fixed ratio, z. In a read head or meter housing (not shown), and are used in accordance with known techniques by a storage system along the measurement axis with respect to the scale 810 guided. The scale may be attached to a moving stage or to a gauge spindle or the like in various applications. In the 8th The configuration shown is a reflective configuration. Ie. the light source 830 and the detector electronics 820 are on the same side of the scale 810 arranged and positioned according to known techniques for angular illumination and reflection. Thus, the scale pattern includes 815 light absorbing portions and light reflecting portions (made, for example, on a substrate using known techniques) which output the spatially modulated light patterns to the detector traces by reflection. It is understood that similar components may be arranged in transmissive embodiments (see, eg, FIG. 3 ).
  • 9 is a diagram of an encoder configuration 900 , which is an alternative embodiment of the phase grating portion of the encoder configuration 800 out 8th maps. As in 9 includes the encoder configuration 900 a scale element 910 , a light source 930 , a lens 940 , two phase grids 950A and 950B and a beam splitter 955 , A major difference over the encoder configuration 800 out 8th is that instead of using a single phase grating 850 the encoder configuration 900 two phase grids 950A and 950B used. In a specific embodiment, the phase grating 950A a 0.92 micron phase grating, whereas the phase grating 950B a 0.84 micron phase grating with air gap (without coupling) can be. This configuration allows a space-saving design by using the phase grating 950B does not require that the light rays coming from the phase grating 950A be completely discharged. In a specific embodiment, after the transmission of the light through the phase gratings 950A and 950B Generates light stripes of a predetermined period (eg, 5 microns) which, combined with the division of the incremental scale trace pattern TINC2 (eg, 4 microns) produces modulated and spatially filtered stripes having a predetermined period (eg, 20 microns) ,
  • 10A and 10B For example, diagrams of the scale track pattern arrangements of the encoder configurations are respectively 1 and 3 , As in 10A includes the scale track pattern arrangement 1000A the absolute scale track pattern TABS1, the reference scale track pattern TREF1, and the incremental scale track pattern TINC1. As described above, the absolute scale track pattern TABS1 provides signals that are usable to to determine an absolute position over an absolute measuring range, which in the embodiment of 10A are depicted as comprising coded signal sections indicating absolute positions along the scale track pattern.
  • For the incremental scale trace pattern TINC1, the incremental pitch is mapped as it is relatively coarse (eg, 20 microns). In the section of the reference scale trace TREF1 which is in 10A 4, four reference marker patterns RM1A to RM1D are shown and shown as occurring at predetermined intervals. In at least one embodiment, the reference marks may be formed as Barker patterns that may be formed according to various known techniques. The reference marker patterns can also serve as vernier reference marks. As described above, the reference scale track pattern TREF1 can be resolved to a level that allows it to specify a particular incremental wavelength such that the incremental wavelength (eg, from the incremental scale track pattern TINC1) with respect to an absolute mark (eg, from the absolute scale track pattern TABS1) is not ambiguous. As in 10A 4, the scale has an overall width dimension X1, while the area covered by the scale track patterns TABS1, TREF1 and TINC1 has a width dimension X2. In a specific embodiment, dimension X1 is equal to 13 millimeters while dimension X2 is equal to 3.9 millimeters.
  • As in 10B includes the scale track pattern arrangement 1000B the absolute scale track pattern TABS2, the reference scale track pattern TREF2 and the incremental scale track pattern TINC2. The various possible dimensions and configurations for the scale trace patterns will be described below with reference to FIG 11 described in more detail. In general, it is understood that the scale track pattern arrangement 1000B is designed to be about as large as the scale track pattern arrangement 1000A out 10A so that the scale track pattern arrangement 1000B can be used in an encoder configuration otherwise for the scale track pattern arrangement 1000A is designed. As in 10B 1, the absolute scale track pattern TABS2 provides signals usable to determine an absolute position over an absolute measurement range, and may include coded portions similar to those of the absolute scale track pattern TABS1 10A are. In at least one embodiment, the absolute scale track pattern TABS2 may have a very coarse ABS resolution on the order of the detector dimension along the X-axis.
  • As in 10B As shown, the incremental scale track pattern TINC2 is imaged as is a much finer pitch (eg, 4 microns) compared to the pitch of the incremental scale track pattern TINC1 10A (eg 20 microns). The in 10B The portion of the reference scale trace TREF2 shown is depicted as having a series of four reference mark patterns RM2A to RM2D. The reference marker patterns RM2A to RM2D may be formed as a Barker pattern according to various known techniques. The reference marker patterns can also serve as vernier reference marks. The reference scale track pattern TREF2 is designed so that it can be resolved to a level that allows it to specify a particular incremental wavelength for the incremental scale track pattern TINC2 such that the incremental wavelengths with respect to an absolute mark are different from the absolute scale track pattern TABS2 are not ambiguous. In at least one embodiment, the combination of the modulated and spatially filtered images of the reference track pattern TREF2 and the incremental track pattern TINC2 creates a synthetic wavelength for which the measured synthetic phase points to the correct incremental scale track pattern cycle (eg, a measured synthetic phase of indicate zero a correct incremental cycle corresponding to this phase).
  • As an example, in the embodiment 10B each of the reference marker patterns RM2A to RM2D is shown as having a corresponding phase marker PHS2A to PHS2D indicating a point at which a perfectly-derived phase would occur for each position. In other words, in the reference scale track pattern TREF2, the reference mark patterns (eg, patterns RM2A to RM2D) are provided at selected intervals (eg, 0.6 millimeters). The phase of each reference marker pattern (eg, in the middle of each pattern where the PHS2A to PHS2D phase markers occur) coincides with the phase of the incremental scale trace pattern TINC2 at the locations that are spaced by the predetermined distance (eg, 0.6 Millimeter), (or has a constant phase offset thereto). The synthetic phase of the incremental scale trace pattern TINC2 and the reference scale trace pattern TREF2 is greater than the length of the reference mark pattern (ie, greater than the length of each of the individual Barker patterns).
  • As previously described, the reference scale track pattern TREF2 (with the reference marker patterns) is designed to produce the same type of modulated and spatially filtered pictures as the incremental scale track pattern TINC2. To the modulated and spatially filtered imaging For example, a phase grating having a pitch close to the pitch of the incremental scale trace pattern TINC2 and the reference scale trace pattern TREF2 is used (e.g., a phase grating pitch of 5 microns as compared to an incremental scale pitch of 4 microns and a reference) -Scale pitch of 4.1 microns). The resulting modulated and spatially filtered imaged fringe period from the phase grating and the incremental scale trace pattern TINC2 may be relatively coarse (e.g., 20 microns) and may be slightly different than the modulated and spatially filtered imaged fringe period from the phase grating and the reference Scale trace pattern TREF2 is generated (eg 22.77 microns).
  • By making the reference scale track pattern TREF2 slightly different in pitch (eg, 4.1 micrometers) compared to the pitch of the incremental scale track pattern TINC2 (eg, 4.0 micrometers), the phase of the reference scale track pattern is the same Phase of the incremental scale trace pattern only at a given point along a given length (eg, it coincides only at one point along a barker pattern length within the reference scale trace TREF2 as indicated by the phase markers PHS2A to PHS2D). This position, in which the phases match, defines a particular incremental wavelength for the incremental scale trace pattern TINC2.
  • As previously described, the use of an incremental scale trace pattern with a relatively fine pitch (e.g., 4 microns) imaged by patterned light produced by a phase grating at a selected pitch (e.g., 5 microns) , a modulated and spatially filtered pattern with a relatively coarse modulated image split (eg, 20 microns) can be generated. It is understood that in such an embodiment, a selected ratio (eg, 5 to 1) exists between the modulated image split (eg, 20 microns) and the pitch of the incremental scale trace pattern (eg, 4 microns). In selected embodiments, ratios of approximately 5 to 1 or more (eg, 10 to 1, 20 to 1, etc.) may be desirable to enable an incremental scale trace pattern to be used with a higher resolution in a coder configuration previously designed for coarse incremental scale scoring.
  • 11 is a table 1100 which outputs the parameters for various scale and detector track combinations for the encoder configuration 3 maps. As in 11 For a first implementation, the incremental scale trace pattern TINC2 is indicated as having a pitch of p = 4 microns, and the associated phase grating produces structured light of a stripe period S = 5 microns. The imaged fringe period resulting from the modulated and spatially filtered imaging is f = 20 microns. An interpolation factor (indicating the necessary interpolation level) is K = 40. The detector elements are designed to have a pitch of d = 15 microns. It should be understood that in certain embodiments, the detector element pitch may be designated 1/4, 1/3, 2/3 or 3/4 of the stripe period f. For at least one embodiment, the detector element pitch for a 20 micron strip may be 3/4 (as for the detector element pitch d = 15 microns in the present example).
  • For the reference scale track pattern TREF2 in the first implementation, the pitch of the elements in each of the Barker patterns p '= 4.1 microns, while the associated phase grating produces patterned light with a stripe period of S = 5 microns (similar to that for the incremental scale track pattern). The imaged fringe period produced by the combination of the patterned light from the phase grating through the reference scale track pattern produces a modulated and spatially filtered imaged fringe period of f '= 22.77 microns. The interpolation factor is K = 40. The pitch of the detector elements is d '= 17 microns. For the combined use of the incremental and reference scale track patterns, the synthetic vernier wavelength (f f '/ (f - f')) is equal to 164 microns. The length of each of the Barker patterns in the reference scale track pattern is L = 136 microns (with 33 lines with the pitch p '= 4.1 microns). It will be understood that in certain embodiments, the number of lines in the Barker pattern may be required to form an appropriately visible stripe (ie, a sufficient portion of the beat frequency envelope) to be included as part of the modulated and spatially filtered image, generated on the detector tracks can be detected correctly. With respect to the number of detector elements in the image array per track and area and their total length for the incremental detector track DETINC1, there are 8 elements in each set (with a total length of 120 microns), and for the reference detector track DETREF1 there are 8 Elements in each set (with a total length of 136 microns). The number of incremental cycles between the Barker patterns is 150.
  • As in 11 For a second conversion, the incremental scale trace pattern TINC2 is indicated as having a pitch of p = 8 microns, and the associated phase grating produces structured light with a stripe period of S = 10 microns. The pictured stripe period, resulting from the modulated and spatially filtered imaging yields f = 40 microns. The interpolation factor is K = 27.6. The detector elements are designated to have a pitch of d = 10 microns. In at least one embodiment, the detector element pitch for a 40 micron strip may be 1/4 (as for the detector element pitch d = 10 microns in the present example).
  • For the reference scale track pattern TREF2 at the second conversion, the pitch of the element in each of the Barker patterns is p '= 8.3 microns, while the associated phase grating produces structured light with a stripe period S = 10 microns (similar to that for the incremental scale track pattern). The imaged fringe period produced by the combination of the patterned light from the phase grating through the reference scale track pattern produces a modulated and spatially filtered imaged fringe period of f '= 48.8 microns. The interpolation factor is K = 27.6. The pitch of the detector elements is d '= 12.2 microns. For the combined use of the incremental and reference scale track patterns, the synthetic vernier wavelength (f f '/ (f-f')) is equal to 221.3 microns. The length of each of the Barker patterns in the reference scale trace pattern is L = approximately 195 microns (with approximately 23 lines with the pitch p '= 4.1 microns). With respect to the number of detector elements in the image array per track and area and their total length, for the incremental detector track DETINC2 there are 16 elements in each set (with a total length of 160 microns), and for the reference detector track DETREF2 there are 16 Elements in each set (with a total length of 195 microns). The number of incremental cycles between the Barker patterns is 75.
  • 12 is essentially a copy of a figure contained in U.S. Patent Application No. 12 / 535,561 ('561 application), which is referred to as U.S. Prior Publication No. US Pat. US 2011/0031383 (Publication '383), which is hereby incorporated by reference in its entirety. 12 is to be understood based on the disclosure of the '561 application and will not be described in more detail here. However, the related techniques may be used in conjunction with the principles disclosed herein.
  • Short is 12 a schematic cross-sectional diagram 1200 , the different light paths through a picture channel 1280-1 a double telecentric encoder imaging arrangement 1270-1 shows similar to the double telecentric imaging configurations shown here 380 . 880 and 1380 is. The U.S. Patent No. 7,307,789 ('789 patent), which is hereby incorporated by reference, discloses various embodiments of dual telecentric encoder configurations employing a second lens (or lens array) whose shape is similar to that of a first lens (or lens array) and which is reversed with respect to the first lens along an optical axis such that lens aberrations of the two similar lenses approximately balance each other to reduce aberrations in the resulting image. It will be understood that the teachings of the '789 patent address only the compensation of lens aberrations that cause spatial distortions in an image of a scale pattern; ie a distortion of the location of pattern features in the image. In the 12 The illustrated embodiment may provide a similar type of spatial distortion correction in an image when the first lens 1210-1 and the second lens 1210-1 ' have similar aberrations. However, there may be a more subtle problem associated with interference effects that can occur in the image due to lens aberrations. The '789 patent does not address this problem. The '561 application addresses this problem and its teachings are applicable to various present embodiments, particularly those concerning the diffraction order beam blocking and aperture dimensions that may be applied with appropriate adjustments in some embodiments according to the principles disclosed herein.
  • 13A and 13B show a configuration 1300 , which is another embodiment of a practical implementation of the encoder configuration according to the principles disclosed herein. Some of the components and operating fundamentals of the encoder configuration 1300 are approximately similar to the encoder configuration 300 out 3 and or 800 out 8th and are generally analogously understandable. For example, the 13XX serial numbers in 13 which have the same "XX" extension as the 3XX serial numbers in 3 denote similar or identical elements that may function similarly as far as below or below 13A and 133 not otherwise described or suggested. In at least one embodiment, the dimensional relationships of in 13A and 13B shown in realistic exemplary proportions with respect to each other, although such relationships may be changed in various other embodiments. In at least one embodiment, for reference, the dimension DIMZ may be approximately 26.5 mm, and the dimension DIMY may be approximately 48 mm. The dimension GAP can be about 1 mm. Other suitable dimensions may be scaled in one embodiment based on these dimensions. It is understood that this embodiment is purely exemplary and not restrictive.
  • As in 13A includes the encoder configuration 1300 in one embodiment, a scale element 1310 , a lighting system or a lighting section 1360 and a double telecentric imaging configuration 1380 , The lighting system or the lighting section 1360 includes a light source 1330 (eg, a laser diode, LED, or the like) for emitting visible or invisible wavelengths of light 1331 (eg, a wavelength of 655 microns for a laser in at least one embodiment), an aperture 1335 , a collimating (or approximately collimating, at least in the XY plane) lens 1340 , a polarizing beam splitter 1390 , a jet trap 1392 , a reflector 1342 , an aperture element 1345 , a reflector 1344 , a phase grid 1350 and a beam splitter 1355 , The double telecentric imaging configuration 1380 includes a first lens 1381 on a first lens plane, an aperture 1382 in an aperture component 1382 ' on an aperture plane, a second lens 1383 on a second lens level and detector electronics 1320 on a detector level. The detector electronics 1320 may be connected to circuits for generating and processing signals (not shown). The light source 1330 may be connected to the circuits for generating and processing signals via power and signal connections (not shown).
  • In operation becomes light 1331 (eg primary light) coming from the light source 1330 is emitted through the aperture 1335 transferred, the isolated sections of the light 1331 can block. In at least one embodiment, the aperture 1335 have a diameter of 4 mm. The transmitted light can be from the lens 130 be almost or completely collimated and is through the beam splitter 1390 directed. Z polarized light is emitted from the polarizing beam splitter 1390 as light 1331Z pass through. The polarizing beam splitter 1390 is configured to prevent stray light in the light source 1330 is reflected back. Such scattered light is from the polarizing beam splitter 1390 as a ray 1391 which turns into a ray trap 1392 is directed.
  • The light 1331Z goes through a quarter wave plate 1393 , the Z-polarized incident light in R-circle polarized light 1331C transforms. Light that can be reflected by subsequently encountered elements along the optical path returns as L-polarized light and becomes X-polarized as it travels through the quarter wavelength plate 1393 goes. Such X-polarized reflected light is from the polarizing beam splitter 1390 blocked and to the jet trap 1392 directed so that it does not return to the light source 1330 to disturb or create other extraneous light rays.
  • The light 1331C is from the reflector 1342 reflected and through the aperture element 1345 directed the light beam 1331C shaped to have a desired portion (eg, a desired track portion) of the scale 1310 Illuminates after removing it from the reflector 1344 was reflected and through the phase grating 1350 gone to the diffracted structured light 1331 ' to become. In at least one embodiment, the aperture 1345 have an X dimension of 6 mm and a Y dimension of 1.5 mm.
  • In at least one embodiment wherein the light source 1330 For example, if a laser diode emits light at a wavelength of 655 microns, the scale element may have a grating pitch of 4.00 microns, and the phase grating 1350 may have a 4.44 micron grating pitch and may be configured to block zeroth-order light. The resulting amplitude modulation may have a period of approximately 20 microns.
  • Then the scale element reflects 1310 the diffracted structured light from its scale grid elements around the scale light 1332 to provide the modulation described above, and is provided by the beam splitter 1355 headed to the detector 1320 through the double telecentric imaging configuration 1380 to be imaged, which according to the above-mentioned principles can work to the scale light 1332 spatially filter such that the period of the amplitude modulation, approximately the spatial filter period of the detector elements of the detector 1320 corresponds to the primary intensity modulation of the scale light 1332 That is, finally, the signal variation of the signals of the detector 1320 causes. In at least one embodiment, the aperture 1382 the double telecentric imaging configuration 1380 have a diameter of about 1 mm to zeroth-order components of the scale light 1332 to block and the desired filtering of the spatial frequency components of the scale light 1332 to provide a higher spatial frequency than the amplitude modulation component. Another way to describe this is to use the aperture 1382 is configured to prevent imaging of the phase grating and / or the scale grating.
  • 14 shows a reference diagram of various beam paths in one embodiment of an encoder configuration 1400 which comprises a coherent light source. Some of the components and operating principles of the encoder configuration 1400 are approximately similar to the encoder configuration 300 out 3 and or 800 out 8th and are generally analogously understandable. For example, the 14XX serial numbers in 14 , Which the same "XX" extension as the 3XX serial numbers in 3 denote similar or identical elements that may function similarly as far as below or below 14 not otherwise described or suggested. As in 14 As shown, the light source emits output light 1431 , A phase grid 1450 divides the output light into a structured lighting 1431 ' comprising beams of various diffraction orders. 14 shows the beam 1431p of order +1 and the beam 1431N of order -1, which interfere to provide a lighting stripe division P i . It is understood that additional orders of bundles of rays in the structured illumination 1431 ' available. For the sake of clarity, in 14 however, only the order +1 and the order -1 are shown. The scale 1410 comprises a graduation P g . The scale 1410 receives the structured lighting 1431 ' and gives the scale light 1432 which comprises stripes with an envelope comprising a period P e . The period P e can be derived with respect to the graduation scale P i and the graduation P g with P e = P g P i / (2P i -P g ). It should be understood that the denominator includes a term 2P i that is P i for the case of incoherent light.
  • 15 Figure 4 is a partially schematic exploded diagram of an encoder configuration 1500 , which is an alternative embodiment of a lighting section 1560 includes. With the exception of the lighting section 1560 are the components and operating principles of the encoder configuration 300 similar to the encoder configuration 300 out 3 and are generally analogously understandable. For example, the 15XX serial numbers in 15 which have the same "XX" extension as the 3XX serial numbers in 3 , denote similar or identical elements that may function similarly unless otherwise described or suggested below. At the in 15 The embodiment shown is the encoder configuration 1500 configured such that the lighting section 1560 (more specifically, the aperture configuration 1572 ) the transmission of unwanted orders of light onto the scale grid 1510 suppressed or eliminated and allows only the desired orders (eg, only ± 1 orders). This improves the signal quality of the encoder configuration 1500 in comparison with previously disclosed configurations. The inventors have determined that, for the encoder configurations disclosed herein, residual orders of light result in periodic irregularities in the resulting signals at the detectors, including irregularities associated with zeroth-order light in the structured illumination that interacts with the scale grid. It has been found that such irregularities can occur in alternating periods of the signals at the detectors, rather than occurring in each period of the signal, reducing the possibility of accurately compensating and / or interpolating the resulting signals. The illumination configurations disclosed below are therefore of particular value in combination with the encoder configurations taught herein, although their utility is not limited to such configurations.
  • In addition to the components 1530 . 1540 and 1550 , whose operation is understandable based on the foregoing description of analogous components, includes the lighting section 1560 Further, a first filter lens 1571 , a spatial filter aperture configuration 1572 at about a focal plane of the first filter lens 1571 is positioned, a second filter lens 1573 positioned on a plane approximately at a distance equal to its focal length from the spatial filter aperture configuration 1572 located. In operation, the lighting grid gives 1550 diffracted structured light 1531 ' similar to in 3 out. The diffracted structured light 1531 ' is from the first illumination lens 1571 at a level of spatial filter aperture configuration 1572 focused. The spatial filter aperture configuration 1572 is configured to diffract zero order diffracted light from the diffracted structured light 1531 ' using a middle section 1572c and diffracted light of higher order with edges of the aperture configuration 1572 to block and a spatially filtered structured lighting 1531 '' comprising only + 1 and -1 diffracted light components using an open aperture section 1572op transferred to. At the in 15 The embodiment shown is the spatial filter aperture configuration 1572 with the middle section 1572c configured from the open aperture section 1572op surrounded, which comprises symmetrically arranged slots. In some alternative embodiments, a spatial filter aperture configuration may include a central circular aperture surrounded by an annular aperture. The second illumination lens 1573 receives the spatially filtered structured light 1531 and gives the spatially filtered structured lighting 1531 '' , which consists of the diffracted light components of order +1 and -1, to the scale pattern 1515 on the level, with the scale grid 1510 coincides. The dimensions in the measuring axis direction of the middle section 1572c and the open aperture section 1572op may be determined by analysis or experimentation and are generally selected to block zero-order light in each particular example, as previously discussed, and transmit +/- first-order diffracted light.
  • It is understood that zeroth-order light, that of the scale grid 1510 is issued by the imaging section 1580 can be suppressed or eliminated, or more precisely, the aperture 1582 , which limits the aperture configuration, may be configured to spatially filter zero-order light. In embodiments, the first filter lens 1571 however, light on the spatial filter aperture configuration 1572 focus at an angle (eg 1 °) that is about ten times the angle at the limiting aperture 1582 (eg 0.1 °). In such embodiments, the limiting aperture is 1582 much more sensitive to misalignment than the spatial filter aperture configuration 1572 , Therefore, it is more advantageous to have zero order light in the illumination section 1560 instead of in the imaging section 1580 to block. Furthermore, at the in 15 embodiment shown, the illumination grid 1550 be an amplitude grating (in contrast to the phase grating 350 ), which costs the production of the encoder configuration 1500 reduced. At the in 3 The embodiment shown has the encoder configuration 300 a practical limit on how far the scale pattern 315 from the phase grating 350 can be arranged. If the scale pattern 315 too far from the phase grid 350 is removed, then two diffraction orders (eg, orders +1 and -1) can not overlap and do not interfere with diffracted structured light 331 ' provide. The lighting section 1560 however, is configured to diffract structured light 1531 ' from a plane that approximates the illumination grid 1550 coincides. This allows for a larger operating gap than the encoder configuration 300 , This also allows the lighting section 1560 Output light provides more efficient, because the interfering orders most at the level of the illumination grid 1550 overlap. If desired, the modulated image pitch P IMESF can be adjusted by using an appropriate combination of the first filter lens 1571 and the second filter lens 1573 is selected with focal lengths selected to give a desired pitch P MI of the illuminated stripe division pattern IFP. Compared to the configuration disclosed in U.S. Patent Application No. 13 / 717,586, this provides additional design freedom for configuring the encoder 1500 so that the resulting modulated image division of the spatially filtered pattern matches the pitch of a given given detector. The modulated image pitch P MI may, for example, be chosen to provide desired relationships between the scale pitch P SF and the modulated image pitch P IMESF, according to the methods of FIG 4A to 4D provided basics.
  • 16 is a drawing of a lighting section 1660 in the case of a reflective encoder configuration 1600 can be used according to the principles disclosed herein. The components and operating principles of the encoder configuration 1600 are approximately similar to the encoder configuration 1500 out 15 and are generally analogously understandable. For example, the 16XX serial numbers in 16 which have the same "XX" extension as the 15XX serial numbers in 15 , denote similar or identical elements that may function similarly unless otherwise described or suggested below. At the in 16 In the embodiment shown, the lighting section comprises 1660 in addition a polarizer 1676 , a polarizing beam splitter 1677 and a quarter wave plate 1678 , In contrast to the encoder configuration 1500 , which is a transmissive configuration, is the encoder configuration 1600 a reflective configuration. The permeable configuration 1500 can readily be adapted to a reflective configuration similar to that described with reference to FIG 16 or similar to other reflective configurations disclosed herein. Adding the polarizer according to the basics, with reference to 16 however, provides more efficient use of light, as described in more detail below. Such use of polarizers may be adapted for use in conjunction with any compatible embodiment described herein.
  • In operation, the polarizer gives 1676 coherent collimated light 1631 from a lens 1640 and outputs collimated light that is linearly polarized. The polarizing beam splitter 1677 reflects a spatially filtered structured lighting 1631 '' from the second filter lens 1673 on the quarter wave plate 1678 , The quarter wave plate 1678 circularly polarizes the spatially filtered structured illumination 1631 '' from the second filter lens 1673 and give it to the scale pattern 1615 out. The scale pattern 1615 reflects spatially modulated picture light 1632 with a circular polarization on the quarter wave plate 1678 , The quarter wave plate 1678 gives the spatially modulated picture light 1632 with a circular polarization and gives the spatially modulated image light 1632 at the polarizing beam splitter 1677 with a linear polarization out in proportion to the structured lighting 1631 '' coming from the second filter lens 1673 is entered, rotated 90 degrees. The polarizing beam splitter 1677 transmits the spatially modulated picture light 1632 with a linear polarization on the imaging section 1680 , Because the quarter wave plate 1678 the spatially modulated picture light 1632 at the polarizing beam splitter 1677 with a polarization rotated 90 degrees (and thus coincident with the direction of polarization passing through the beam splitter 1677 is to be transferred), this increases the amount of light that goes to the imaging section 1680 is output by a factor of four compared to a configuration without quarter wavelength plates 1678 ,
  • 17 is a drawing of a lighting section 1760 which is at a coder configuration 1700 can be used according to the principles disclosed herein. The components and operating principles of the encoder configuration 1700 are approximately similar to the encoder configuration 300 out 3 and are generally analogously understandable. For example, the 17XX serial numbers in 17 which have the same "XX" extension as the 3XX serial numbers in 3 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • At the in 17 The embodiment shown is the encoder configuration 1700 configured such that the lighting section 1760 only desired orders (eg, only ± 1 orders) to a section of a scale track 1715 that transmits from an imaging configuration 1780 on a detector configuration 1725 is shown. As in 17 shown is a light source 1730 configured to output light 1731 output at a wavelength λ. In some embodiments, the light source 1730 one of a laser diode, a spatially coherent LED and a series of independent linear sources perpendicular to the measuring axis direction 82 are arranged (eg, an LED point source masked with slits, or a grating with spacing, or a period, the spatially coherent output light 1731 providing linear sources cumulatively contributing to an interference fringe pattern IFP). A collimation section 1740 (ie, a collimating lens) is arranged around the output light 1731 to collapse. A structured lighting generating section 1770 is configured to the output light 1731 to enter and a structured lighting 1731 ' to provide the structured lighting 1731 ' an illumination strip pattern IFP, which is transverse to the measuring axis direction 82 is oriented and in which the scale trace 1715 is entered. The scale track 1715 is configured to spatially modulate the input illumination strip pattern IFP and output scale light comprising spatially modulated image light. The detector configuration 1725 and the imaging configuration 1780 are configured so that only scale light, which consists of an imaged area IR of the scale track 1715 comes to the detector configuration 1780 is shown. The modes of operation of the imaging configuration 1780 and the detector configuration 1725 are analogous to those of the imaging configuration 380 and the detector configuration 325 and are analogous to the descriptions of the same understandable. The a structured lighting generating section 1770 includes a beam separating section 1771 and a lighting grid 1750 , The beam separating section comprises a beam splitter 1777 and a reflector 1778 , At the in 17 the particular embodiment shown is the Kollimationsabschnitt 1740 between the light source 1730 and the beam-separating section 1771 However, in other embodiments, a collimating section may be in other positions between a light source and a lighting grid. For example, in alternative embodiments, the collimation section 1740 between the beam-separating section 1771 and the lighting grid 1750 are located. In some embodiments, a collimating section may be arranged to collimate the first output light section and the second output light section output to the illumination grid. The beam-separating. section 1771 is arranged to the output light 1731 and is configured to generate a first output light section 1731A and a second output light portion 1731B to the lighting grid 1750 output, so that the first output light section 1731A and the second output light section 1731B Forming rays in the measuring axis direction 82 spaced apart from each other. More specifically, it is a beam splitting surface 1775 of the beam splitter 1777 configured to the output light 1731 to receive and the first output light section 1731A along a first beam path and the second output light section 1731B towards the reflector 1778 transferred to. The reflector 1778 is configured to the second output light section 1731B along a second beam path, which is spaced from the first beam path to reflect. At the in 17 Shown embodiment, the beam splitting surface 1775 and the reflector 1778 parallel and are surfaces of separate elements. Being parallel, they are the first output light section 1731A and the second output light section 1731B parallel on a plane near the lighting grid 1750 , In some embodiments (eg, the in 19 shown embodiment), the beam-splitting surface 1775 and the reflector 1778 Be surfaces of the same beam-splitting element. At the in 17 In the embodiment shown, the first and second beam paths are approximately perpendicular to the illumination grating. The lighting grid 1750 is configured to the first and second output light sections 1731A and 1731B over an operating gap on the scale track 1715 to bow so that only two orders of diffracted light (ie a diffracted light section 1731A ' a first + order of the first output light portion 1731A and a diffracted light section 1731B ' a first order of the second output light portion 1731B at the in 17 in an imaged region IR on a plane corresponding to the scale trace 1715 coincides, overlap, and to provide the illumination strip pattern IFP in the imaged region IR. Unlike the in 15 and 16 the embodiments shown, the lighting section 1760 light sections 1731ZA ' and 1731ZB ' zeroth order off which the scale trace 1715 to reach. The light sections 1731ZA ' and 1731ZB ' However, zeroth order drops entirely outside the imaged IR range, which depends on the detector configuration 1725 is shown. Therefore, carry the light sections 1731ZA ' and 1731ZB ' 0th order, though not blocked, does not contribute zero order undesired light to the operating signals associated with the illumination fringe pattern IFP in the imaged area of the scale trace 1715 linked by the imaging configuration 1780 on the detector configuration 1725 is shown.
  • At the in 17 In the embodiment shown, the beam-separating section 1771 in addition an optional double-jet aperture element 1772 include. The two-beam aperture element 1772 includes two apertures configured to the first output light portion 1731A and the second output light portion 1731B whereas the two-beam aperture element 1772 unwanted stray light and also reduces the location and the spacing of the first output light section 1731A and the second output light portion 1731B showing the scale track 1715 reach, can reduce.
  • As in 17 1, the imaged area IR has a dimension D in the measuring axis direction, the first output light portion 1731A and the second output light section 1731B are in the measuring axis direction 82 at the level near the lighting grid 1750 spaced apart by a separation distance B, and the separation distance B is equal to or greater than the dimension D of the imaged area. The first output light section 1731A has a width W1, and the second output light portion 1731B has a width W2 on the plane near the illumination grating 1750 on. Both W1 and W2 are larger than the dimension of the imaged area. Thereby, the imaged area can be filled with a spatially modulated illumination strip pattern according to the above-described principles, whereas the zero order light sections 1732ZA and 1732ZB by a sufficient distance on a plane near the scale track 1715 are separated, so they do not +1 with the section of the order 1732A and the section of order -1 1732B can not overlap, and more importantly, fall outside of the pictured range.
  • At the in 17 the embodiment shown are the first output light section 1731A and the second output light section 1731B parallel to a plane near the lighting grid. It is understood that in some embodiments, both are not parallel, but a gap distance between the illumination grid 1750 and the scale track 1715 and / or periods of the illumination grid 1750 or the grid of the scale track 1715 can be adjusted to achieve a desired fringe period of the interference fringe pattern IFP that is sensitive to the detector configuration 1725 is shown.
  • 18 is a drawing of a lighting section 1860 which is at a coder configuration 1800 can be used according to the principles disclosed herein. The components and operating principles of the encoder configuration 1800 are approximately similar to the encoder configuration 1700 out 17 and are generally analogously understandable. For example, the 18XX serial numbers in 18 which have the same "XX" ending as the 17XX serial numbers in 17 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • At the in 18 embodiment shown is a light source 1830 configured to output light 1831 to a collimating lens 1840 output, which is configured to the output light 1831 to collapse. The lighting section 1860 includes a beam separating section 1871 made of an aperture element 1872 consists of an open double aperture section 1872op includes. The aperture element 1872 is configured to be a first output light section 1831a and a second output light portion 1831B of the output light 1831 disconnect and attach it to the lighting grid 1850 output so that they form rays in the measuring axis direction 82 spaced apart, according to the previously discussed bases. In particular, they are configured such that only two orders of diffracted light (ie, a +1 order portion 1831a ' and a section of the order -1 1831B ' ) in the mapped area overlap IR on a plane that aligns with the scale track 1815 coincides. The light sections of zero order 1832ZA and 1832ZB do not contribute unwanted zeroth-order light to the operating signals that illuminate with stripe pattern IFP at the imaged area of the scale track 1815 are linked.
  • 19 is a drawing of a lighting section 1960 which is at a coder configuration 1900 can be used according to the principles disclosed herein. The components and operating principles of the encoder configuration 1900 are approximately similar to the encoder configuration 1700 out 17 and are generally analogously understandable. For example, the 19XX serial numbers in 19 which have the same "XX" ending as the 17XX serial numbers in 17 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • At the in 19 The illustrated embodiment includes a structured illumination generating section 1970 a beam separating section 1971 that a crushing plate 1977 includes. The crushing plate 1977 is configured to be a first output light section 1931A at a first area of a first surface 1977a to reflect and a second output light section 1931B to transfer that from a second surface 1977b is reflected, and at a second area of the first surface 1977a issue. A lighting grid 1950 is configured to the first output light section 1931A and the second output light portion 1931B to input such that the first output light section 1931A and the second output light section 1931B Forming rays in the measuring axis direction 82 spaced apart, according to the previously discussed bases. The reflectance values of the first surface 1977a and the second surface 1977b can be adjusted to approximately equal intensities in the first output light section 1931A and the second output light portion 1931B to surrender. For example, the first surface 1977a have about 25% reflectance and the second surface 1977b may have about 100% reflectivity. In another embodiment, the first surface 1977a 50% reflectivity, the second surface 1977b can have 100% reflectivity, and a front surface 1977c can have 0% reflectivity, where the second output light section 1931B the crushing plate 1977 leaves. The beam-separating section 1971 is configured to have only two orders of diffracted light (ie, a first portion of the + order 1931A ' and a first section of the order 1931B ' ) in the mapped area overlap IR on a plane that aligns with the scale track 1915 coincides. The light sections of zero order 1931ZA ' and 1931ZB ' do not contribute zero order undesired light to the operating signals associated with the illumination strip pattern IFP at the imaged area of the scale track 1915 are linked.
  • 20 is a drawing of a lighting section 2060 which is at a coder configuration 1900 can be used according to the principles disclosed herein. The components and operating principles of the encoder configuration 1900 are approximately similar to the encoder configuration 1900 out 19 and are generally analogously understandable. For example, the 20XX serial numbers in 20 which have the same "XX" extension as the 19XX serial numbers in 19 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • At the in 20 In the embodiment shown, the lighting section comprises 2060 a beam separating section 2071 , which is a first radiation-conducting element 2077 and a second radiation-conducting element 2078 includes. The first radiation-guiding element 2077 is configured to be a first output light section 2031a from a first surface 2077A to reflect and a second output light section 2031 B to transfer that from a second surface 2077B is reflected and the second radiation-conducting element 2078 is issued. The second radiation-guiding element 2078 is configured to the second output light section 2031 B from a surface 2078A on the lighting grid 2050 to reflect and the first output light section 2031a from a surface 2078C on the lighting grid 2050 to reflect. In some embodiments, the first radiation-guiding element is 2077 a crushing plate. In some embodiments, the second radiation-guiding element is 2078 a crushing plate. In some embodiments, the surface comprises 2078A a reflective coating useful in embodiments in which the radiation-conducting element 2078 is a crushing plate, as this prevents an additional exit light portion from passing through the surface 2078A is transmitted, and thus prevents the second output light section 2031 B divides into two output light sections. In some embodiments, the second radiation-guiding element is 2078 configured to the first output light section 2031a through an anti-reflective surface 2078B transferred to. In some embodiments, the surface may be 2078A and the anti-reflective surface 2078B according to similar combinations of reflectivity values as those with respect to the first surface 1977a and the second surface 1977b in 19 be configured. The anti-reflective surface 2078B is useful if the radiating element 2078 a crushing plate is because this avoids that one additional output light section from the radiating element 2078 is reflected, and thus prevents the first output light section 2031a divides into two output light sections. Instead of a 100% reflective coating on the anti-reflective surface 2078B may have an aperture similar to the two-ray aperture element 1772 out 17 be used to block unwanted light from a split light section. The lighting section 2060 is advantageous in that the first output light section 2031a and the second output light section 2031 B have the same optical path lengths and wavelength dependence.
  • In some embodiments, the second radiation-guiding element 2078 the reflective surface 2078A and a compensation prism 2078D include (shown in phantom). In such embodiments, the reflective surface 2078A be a mirror, and the compensation may be configured such that the first output light portion 2031a and the second output light section 2031 B have the same optical path lengths and wavelength dependence.
  • 21 is a drawing of a lighting section 2160 which is at a coder configuration 2100 can be used according to the principles disclosed herein. The components and operating principles of the encoder configuration 2100 are approximately similar to the encoder configuration 1700 out 17 and are generally analogously understandable. For example, the 21XX serial numbers in 21 which have the same "XX" ending as the 17XX serial numbers in 17 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • At the in 21 In the embodiment shown, the lighting section comprises 2160 a beam separating section 2171 who has a first grid 2190 , a second grid 2191 , a blocking element 2192 and an aperture element 2193 includes. The first grid 2190 is configured to the output light 2131 in a first output light section 2131A and a second output light portion 2131b to divide, which have the orders +1 and -1 (or higher symmetric matching orders) of light, that of the first grid 2190 is bent. The blocking element 2192 is configured to identify any zeroth order components from the first grid 2190 to block. The second grid 2191 (In some embodiments, the same period as the first grid 2190 is) configured to the first output light section 2131A and the second output light portion 2131b to receive and a first parallel collimated light section 2131A and a second parallel collimated light section 2131b ' output, which are parallel to each other. The aperture element 2193 is configured to be the first parallel collimated light section 2131A ' and the second parallel collimated light section 2131b ' to receive them and to the lighting grid 2150 whereas any additional orders of light transmitted by the second grid 2191 is bent, filtered out. In some embodiments, the first grid 2190 and the second grid 2191 be for the highest efficiency phase grating.
  • 22 is a drawing of a lighting section 2260 in the case of a reflective encoder configuration 2200 can be used according to the principles disclosed herein. The components and operating principles of the encoder configuration 200 are approximately similar to the encoder configuration 2100 out 21 and are generally analogously understandable. For example, the 22XX serial numbers in 22 which have the same "XX" extension as the 21XX serial numbers in 21 , denote similar or identical elements that may function similarly unless otherwise described or suggested below.
  • The lighting section 2260 includes many of the same elements of the 21 shown illumination section 2160 in a space-saving optical arrangement using reflective rather than transmissive grating elements.
  • At the in 22 In the embodiment shown, the lighting section comprises 2260 a light source 2230 , a collimation lens 2240 and a structured lighting generating section 2270 , which is a beam-separating section 2271 which includes a first grid 2290 , a second grid 2291 , a blocking element 2292 , an aperture element 2293 and a reflector 2241 includes. The light source 2230 is configured to output light 2231 to the collimating lens 2240 issue. The collimation lens 2240 is configured to the output light 2231 to collapse and attach it to the reflector 2241 issue. The reflector 2241 is configured to the output light 2231 on the first grid 2290 to reflect. The first grid 2290 is configured to the output light 2231 in a first output light section 2231A and a second output light portion 2231B to divide the orders +1 and -1 (or higher symmetric matching orders) of light coming from the first grid 2290 is bent. The blocking element 2292 is configured to identify any zeroth order components from the first grid 2290 to block. The second grid 2291 is configured to the first output light section 2231A and the second output light portion 2231B to receive and a first parallel collimated light section 2231AP and a second parallel collimated light section 2231BP output, which are parallel to each other. The aperture element 2293 is configured to be the first parallel collimated light section 2231AP and the second parallel collimated light section 2231BP to receive them and to the lighting grid 2250 whereas any additional orders of light transmitted by the second grid 2291 is bent, filtered out.
  • The imaging configuration 2280 includes a first lens 2281 , an aperture 2282 , a second lens 2283 and a reflector 2284 , The reflector 2284 is configured to scale light 2232 on the imaging configuration 2280 to reflect.
  • 23A shows an embodiment of a scale pattern 2315 comprising offset grid sections that may be used in an encoder configuration according to the principles disclosed herein. It has been determined that suboptimal fabrication and / or alignment of the optical components in various embodiments disclosed herein may result in a nonuniform amplitude of alternating stripes on the detector. The scale pattern 2315 mitigates this problem, as previously with reference to 23B and 23C discussed. The scale pattern 2315 includes a scale grid 2310 , The scale grid 2310 includes a first scale grating section 2310A and a second scale grating section 2310B which are arranged in the measuring axis direction MA parallel to each other. The first scale grid section 2310A and the second scale grating section 2310B each have a scale pitch P SF . The second scale grid section 2310B has a spatial phase offset of 0.5 * P SF with respect to the first scale grating section. The scale grid 2310 also includes a third scale grid section 2310C and a fourth scale grating section 2310D , The third scale grid section 2310C and the fourth scale grid section 2310D each have a scale pitch P SF and are also arranged with a spatial phase offset of 0.5 · P SF . The third scale grid section 2310C has the same phase in the measuring axis direction MA as the first scale grating section 2310A , Each of the scale grid sections 2310A to D can be illuminated and mapped simultaneously for a single position measurement, z. B. similar to that in 3 shown incremental track pattern TINC2.
  • 23B schematically shows the alignment of combined intensity contributions of each scale grating section 23A to a scale image SI. The scale grid sections 2310A to D (or any single-phase grid) may individually contribute irregular scale image intensity contribution sections SIA to D as previously discussed, which may result in displacement measurement errors if used alone for displacement measurements. 23C shows the intensity in a scale image SI that includes the combined intensity contributions of each of the scale image sections SIA through D. As in 23C 4, the alignment of the contributions of the scale image sections SIA to D produces a contiguous intensity amplitude in the scale image SI despite the irregularity of the various contributions.
  • It is understood that in a particularly simple embodiment according to the principles made with reference to 23A have been described, a similar scale grating having offset portions may comprise only first and second scale grating portions (or additionally a third scale grating portion) having a phase offset of 0.5 * P SF with respect to each other. Alternatively, a similar scale grid may include more than two pairs of scale grid sections (eg, narrower along the Y direction), each pair having a phase offset of 0.5 * P SF with respect to each other. In any event, the y-direction dimension of the sections is to be adjusted such that the offset intensity contributions from the imaged regions of the offset grating sections contribute approximately the same amount to produce the approximately constant amplitude signal that is present in FIG 23C will be shown.
  • 24A and 24B show a schematic diagram of first and second encoder configurations 2400A and 2400B which are configured to use an enlarged area of the scale grid to mitigate any source of error. Except as discussed above, the in 24A and 24B In the embodiments shown, similar elements and dimensions as the embodiments shown in the preceding figures.
  • Microscopic variations of a scale period P SF can result from various manufacturing process errors. This can lead to errors in mid-range displacement measurements along a scale element, such as the scale element 2410A (or 2410B ). One solution to mitigating this type of error is to increase the area of the scale grid that contributes to the signal generating image of an imaging configuration to better average such errors, as in the first and second encoder configurations 2400A and 2400B , For comparison, at the in 3 embodiment shown, the scale element 110 separated from the first lens plane FLP by a distance d 0 , nominally equal to the focal length f of the first lens 181 which causes scale light rays corresponding to the dimension FR to be in the signal generating image of the Encoder configuration off 3 are included. In contrast, the imaging configuration 2480A ( 2480B ) configured such that a scale element 2410A ( 2410B ) is separated from the first lens plane FLP by a distance d 0 , that of the focal length f of the first lens 2481A ( 2481B ) deviates. More specifically, the scale element becomes 2410A ( 2410B ) in a position along an optical axis of the imaging configuration 2480A ( 2480B ), which is smaller than the focal length f of the imaging configuration 2480A ( 2480B ). Compared to the in 3 This may result in additional scale light beams corresponding to the dimensions ER in the signal generating image of the encoder configuration 2400A ( 2400B ) are included.
  • An embodiment such as that in FIG 3 can display an effective field of view on the 4 mm scale, whereas an embodiment such as the one shown in FIG 24A ( 24B ), can image an effective field of view on the 5 mm scale. In addition, decreasing the separation between the imaging configuration allows 2480A ( 2480B ) and the scale element 2410A ( 2410B ) a more space-saving encoder configuration.
  • 24A shows a transmissive scale configuration. In various embodiments that use a transmissive scale configuration, the scale element is 2410A arranged so that it from the phase grating 2450A separated by a distance d 1 , which is at most 2 mm. In alternative configurations using a reflective scale, a scale element may be arranged to be separated from a phase grating of a lighting section along a light path of an imaging configuration by a distance d 1 that is at most 6 mm. In some embodiments, the in 24A shown configuration, the scale element 2410A comprise a scale division, which is 4 microns, and the phase grating 2450A may include a pitch that is 4,444 microns. In some embodiments, the in 24B configuration shown may be a scale element 2410B comprise a graduation of 4 microns and a phase grating 2450B a lighting section 2460B may include a pitch that is 3,635 microns. Selecting a smaller pitch for the phase grating 2450A as that of the phase grating 2460B allows a smaller distance d 0 between the phase grating 2460B and the scale element 2410B for a given value of image division P IMESF .
  • 25A to 25C show schematic diagrams of embodiments of encoder configurations 2500A . 2500B and 2500C , Conceptually, with each of the encoder configurations 2500A . 2500B and 2500C a scale member is disposed at a roll angle α about the measurement axis, and a phase grating of an illumination portion is disposed at a roll angle β around the measurement axis, parallel with respect to a plane to the measurement axis and perpendicular to an optical axis of the imaging portion. In various embodiments, as discussed with reference to previous figures, undesired zero order residual light received by an imaging section may cause effects that interfere with the desired position signals and cause near-field errors. One way in which this can be shown is by weak self-image planes that carry an image of the scale grid that is incident on a detector section. One means to mitigate this effect is to arrange a scale element or a phase grating of a lighting section with a small revolution or pitch with respect to a measuring axis. This causes multiple self-image planes to fall onto the detector section with a phase offset with respect to each other, which may average out their near-field errors. To do so, in some embodiments, it may be desirable to introduce a non-zero rotational or pitch angle such that at least one self-image plane and one reverse image plane fall on the detector section, as discussed below. In embodiments, the scale grating may be positioned with respect to the imaging section such that the light path of the imaging section about the measurement axis is at least 0 at a rotation or pitch angle that is in relation to a plane parallel to the scale grating and parallel to the measurement axis , 1 degree, is rotated. In some embodiments, the phase grating of the illumination section may be positioned with respect to the scale grating such that a roll angle between the plane of the phase grating and the plane of the scale grating in a plane perpendicular to the scale grating and parallel to the measurement axis is equal to (2 * B * M * P PG ^ 2) / (H · λ), where B is a number between 0.75 and 1.25, M is an enlargement of the imaging section, P PG is a pitch of the phase grating of the illumination section, H is a height of the field of view of the detector section is perpendicular to the measuring axis direction, and λ is a wavelength of illumination. In one embodiment, an encoder configuration may include a phase grating pitch P PG that is 4.444 microns, a magnification M that is 1X, and a height H that is 1000 microns, and therefore, a roll angle may be 3.5 degrees. In some embodiments, the phase grating of the illumination section may be positioned with respect to the scale grating such that a pitch angle between the plane of the phase grating and the plane of the scale grating in a plane perpendicular to the scale grating and parallel to the measurement axis is equal to (2 * B * M * P PG ^ 2) / (V · λ), where V is a length of a field of view of the Detector section in the measuring axis direction and B is a number between 0.75 and 1.25.
  • For example, show 25A to 25C three embodiments comprising a 3.5 degree roll angle between the phase grating and the scale element. The encoder configurations 2500A . 2500B and 2500C each include the scale element 2510A . 2510B and 2510C which are arranged at a roll angle α around the measurement axis with respect to a plane parallel to the measurement axis MA (ie, the X direction) and to the optical axis of the respective imaging sections 2580A . 2580B and 2580C is vertical. The lighting sections 2560A . 2560B and 2560C include the respective phase gratings 2550A . 2550B and 2550C which are arranged at a roll angle β around the measurement axis with respect to a plane parallel to the measurement axis MA (ie, the X direction) and to the optical axis of the imaging sections 2580A . 2580B and 2580C is vertical. In the encoder configuration 2500A is α 3.5 degrees and β is zero degrees. In the encoder configuration 2500B α is 1.75 degrees and β is -1.75 degrees. In the encoder configuration 2500C α is zero degrees and β is 3.5 degrees. In any event, the net rolling angle between the elements is 3.5 degrees, such that a self-imaging plane SIMG and reverse (reversal phase) image plane IIMG fall on a detector section indicated by a detector plane DP for self-image effects resulting from undesirable residual light zeroth order, about to pick up. Each of the encoder configurations 2500A . 2500B and 2500C includes visual fields having a height H perpendicular to the measuring axis direction and a length V in the measuring axis direction, which determine an optimum roll angle or pitch angle, as described above. The length V is not shown because its direction goes into the page, ie in the X direction.
  • Although the in 25A to 25C It should be understood that a pitch angle (around an axis that is perpendicular to the measurement axis and parallel to the scale grid, eg, the Y axis) also provides the desired effect can provide. In various embodiments, either the scale grating or a phase grating of the illumination section or both is arranged at a pitch angle relative to a plane that is parallel to the measurement axis and perpendicular to an optical axis of the imaging section by about 0.1 degrees of relative pitch between the elements or to provide more. In any event, the relative pitch angles should be chosen such that at least one self-imaging plane SIMG and reverse (reversal phase) image plane IIMG fall on a detector section on detector plane DP to cancel out approximately self-image effects resulting from undesirable zero-order residual light.
  • While various embodiments have been illustrated and described, many variations of the illustrated and described arrangements of features and operations will be apparent to those skilled in the art based on the present disclosure. It is therefore to be understood that various changes may be made therein without departing from the spirit and scope of the invention.
  • QUOTES INCLUDE IN THE DESCRIPTION
  • This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.
  • Cited patent literature
    • US 3882482 [0003]
    • US 5965879 [0003]
    • US 5279044 [0003]
    • US 5886519 [0003]
    • US 5237391 [0003]
    • US 5442166 [0003]
    • US 4964727 [0003]
    • US 4414754 [0003]
    • US 4109389 [0003]
    • US 5773820 [0003]
    • US 5010655 [0003]
    • US 7186969 [0004, 0054, 0067]
    • US 7307789 [0004, 0100]
    • US 7435945 [0004]
    • US 8492703 [0037]
    • US 7608813 [0037]
    • US 2011/0031383 [0099]

Claims (25)

  1. The embodiments of the invention claiming exclusive property or privilege are defined as follows: 1. Apparatus for measuring the relative displacement between two elements, the apparatus comprising: a scale grating extending along a measuring axis direction and a graduation P SF ; an illumination source comprising a light source emitting light having a wavelength λ; and a structured illumination generating portion for inputting the light and outputting structured illumination to the scale grating, the structured illumination including an illumination stripe pattern transverse to the light source Oriented measuring axis direction and having a illumination strip pitch P MI in the measuring axis direction on a plane coincident with the scale grid; an imaging section positioned to receive operative spatially modulated image light output from the scale grating and to output an operable periodic image of the spatially modulated image light as the scale grating is illuminated by the structured illumination from the illumination source; and a detector section including a set of respective optical detectors positioned to respectively receive different phases of the operable periodic image, the set of respective optical detectors having a detector pitch P d in the measuring axis direction, the detector pitch P d of one Corresponds to division between the detector elements corresponding to a particular detector signal phase, wherein: the imaging section comprises: the detector section positioned at a distance Z from the imaging section along a light path of the imaging section; a first lens positioned to receive the spatially modulated image light transmitted from the scale grating, the first lens having a focal length F defining a focal point located between the first lens and the detector portion; and an aperture positioned approximately at the focal length F between the first lens and the detector section; the spatially modulated image light comprises stripes resulting from the interference of two diffraction orders which differ by a value Δn; the aperture having a dimension W along the measuring axis direction is configured such that AN = Z · λ · (a · (Δn + 1) / (P MI P SF / ((P MI - P SF ) · M)), where M is an enlargement value of the imaging section, and the value of a is greater than 0.5 and less than 4.0, and the scale grating inputs the structured illumination and outputs the spatially modulated image light comprising the structured illumination modulated with an intensity modulation envelope having a spatial wavelength P IMESF , which depends on the scale pitch P SF and the illumination stripe pitch P MI , and P SF and P MI are selected to cooperate with the detector pitch P d such that ΔnP MI P SF / (ΔnP MI -) P SF ) = P IMESF = m × P d / k when the light source outputs incoherent light and ΔnP MI P SF / (2ΔnP MI -P SF ) = P IMESF = m × P d / k when the light source is coherent light where m is a number of phase signals received from the Detector section are output, and k is an odd integer, and wherein the spatial wavelength P IMESF is greater than the scale pitch P SF .
  2. Apparatus according to claim 1, wherein Δn = 2.
  3. Apparatus according to claim 1, wherein Δn = 1.
  4. Apparatus according to claim 1, wherein Δn = 4.
  5. The device of claim 1, wherein the imaging section further comprises a second lens having a focal length Fs, the second lens being positioned and configured between the aperture and the detector section at the focal length Fs from the aperture and at the distance Z from the detector section to receive light from the aperture and form the operable periodic image.
  6. The device of claim 5, wherein the second lens has the same nominal optical properties as the first lens, Fs = F, Z = Fs, and the first and second lenses are symmetrically oriented about the position of the aperture.
  7. The device of claim 1, wherein the aperture is at the distance Z from the detector section.
  8. The device of claim 1 wherein m is equal to one of 3 and 4 and k is equal to one of 1, 3 and 5.
  9. The device of claim 1, wherein the graduation P SF is less than 8 microns.
  10. The device of claim 1, wherein the illumination stripe pitch P MI is less than 8 microns.
  11. The apparatus of claim 1, further comprising a beam splitter located between the illumination portion and the scale grating. which is configured to transmit the structured illumination to the scale grid, to receive spatially modulated image light output from the scale grid, and to output the spatially modulated image light to the imaging section.
  12. The device of claim 1, wherein the interference fringe generating portion comprises a first phase grating which blocks or suppresses zero order light in the structured illumination.
  13. The apparatus of claim 12, wherein the interference fringe-generating portion further comprises a second phase grating configured to input light output from the first grating and output structured light including converging rays.
  14. The apparatus of claim 1, further comprising a reference scale track configured to receive the structured illumination and output reference interference fringes to the detector section.
  15. The apparatus of claim 14, wherein the reference scale track comprises reference marks that are vernier reference marks.
  16. The apparatus of claim 14, wherein the reference scale track comprises reference mark patterns having phases that provide a synthetic wavelength with respect to the scale grid.
  17. The apparatus of claim 1, further comprising an absolute scale trace comprising an absolute scale trace pattern configured to receive the structured illumination and output absolute scale light to the detector portion to provide signals useable to an absolute position over an absolute one To determine the measuring range.
  18. Apparatus according to claim 1, wherein: the imaging portion further comprises a second lens having a focal length Fs, the second lens positioned between the aperture and the detector portion at the focal length Fs of the aperture and being configured to receive light from the aperture and to acquire the operable periodic image to shape; and an enlargement M of the operable periodic image in the measuring axis direction is approximately M = Fs / F, and is set only by selecting the distances Fs and F.
  19. The device of claim 1, wherein the light source outputs coherent light and the value of a is greater than 0.5 and less than 1.5.
  20. The apparatus of claim 1, wherein the scale grating comprises a first scale grating portion and a second scale grating portion arranged in parallel in the measuring axis direction, the second scale grating portion having a spatial phase offset of 0.5 * P SF relative to the first scale grating portion in the measuring axis direction, and both the first scale grating portion and the second scale grating portion contribute to the operable spatially modulated image light output from the scale grating and the operable periodic image.
  21. The device of claim 1, wherein the scale grating is positioned by the imaging section at a distance less than the focal length F.
  22. The device of claim 1, wherein the scale grating is positioned relative to the imaging section such that the light path of the imaging section is rotated about the measurement axis at a roll angle that is at least zero with respect to a plane that is perpendicular to the scale grid and parallel to the measurement axis , 1 degree.
  23. The device of claim 1, wherein the scale grating is positioned relative to the imaging portion such that the light path of the imaging portion is rotated about an axis parallel to the measurement axis and parallel to the scale grating at a pitch angle with respect to a plane that is opposite to that of FIG Scale grids parallel, is at least 0.1 degrees.
  24. The apparatus of claim 1, wherein the phase grating of the illumination section is positioned with respect to the scale grating such that a roll angle between the plane of the phase grating and the plane of the scale grating in a plane perpendicular to the measurement axis equals (2 · B · M · P PG ^ 2) / (H · λ), where B is a number between 0.75 and 1.25, M is the magnification value of the imaging section, P PG is a pitch of the phase grating of the illumination section, and H is a height of a field of view of the detector section which is perpendicular to the measuring axis direction.
  25. The device of claim 1, wherein the phase grating of the illumination section is positioned relative to the scale grating such that a pitch angle between the plane of the phase grating and the plane of the scale grating in a plane perpendicular to the scale grating and parallel to the measurement axis equals (2 · B · M × P PG ^ 2) / (V × λ), where B is a number between 0.75 and 1.25, M is the magnification value of the imaging section, P PG is a pitch of the phase grating of the illumination section, and V is the length of a field of view of the detector section in the measuring axis direction.
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