Abstract:
A position sensing optical encoder includes an illumination source that operates by providing primary radiation having a first level of intensity uniformity to saturate at least a portion of a relatively broad phosphor area including uniformly distributed phosphor. The phosphor area absorbs the primary radiation and emits phosphor radiation to illuminate the encoder scale pattern. The scale pattern spatially modulates the phosphor light, and the spatially modulated pattern of phosphor light is sensed by a photodetector arrangement. Due at least partially to saturation of the phosphor, the phosphor light has a second level of phosphor light intensity uniformity that is more uniform than the first level of primary light intensity uniformity, which enhances the encoder accuracy. The uniform phosphor illumination intensity is economically provided over a broad area with few components and minimized optical path length, particularly for path length perpendicular to the scale.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to precision measurement instruments, and more particularly to a displacement encoder that utilizes a phosphor illumination source. 
     BACKGROUND OF THE INVENTION 
     Various optical displacement encoders are known that use a readhead having an optical arrangement that images a scale pattern to a photodetector arrangement in the readhead. The image of the scale pattern displaces in tandem with the scale member, and the movement or position of the displaced scale pattern image is detected with a photodetector arrangement. Conventional imaging, self-imaging (also called Talbot imaging), and/or shadow imaging may be used to provide the scale pattern image in various configurations. 
     Optical encoders may utilize incremental or absolute position scale structures. An incremental position scale structure allows the displacement of a readhead relative to a scale to be determined by accumulating incremental units of displacement, starting from an initial point along the scale. Such encoders are suitable for certain applications, particularly those where line power is available. However, in low power consumption applications (e.g., battery powered gauges, and the like), it is more desirable to use absolute position scale structures. Absolute position scale structures provide a unique output signal, or combination of signals, at each position along a scale. They do not require continuous accumulation of incremental displacements in order to identify a position. Thus, absolute position scale structures allow various power conservation schemes. A variety of absolute position encoders are known, using various optical, capacitive or inductive sensing technologies. U.S. Pat. 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 relevant to absolute position encoders, and are hereby incorporated herein by reference in their entirety. 
     One issue with regard to the design of optical encoders is that users generally prefer that the readheads and scales of the encoders be as compact as possible. A compact encoder is more convenient to install in a variety of applications. However, absolute optical encoders generally require a plurality of scale tracks, which tends to demand a relatively broader scale member, illumination system, and photodetector arrangement. One solution has been to minimize the width of absolute scale tracks. However, minimizing the width of scale tracks, the illumination system, and photodetector arrangement is generally detrimental to the signal to noise ratio(s) of an absolute encoder, reducing its potential accuracy. Furthermore, narrower scale tracks are relatively more sensitive to a given amount of contamination, misalignment, and other variations that may be expected in industrial environments, and are therefore less robust and stable in operation. Thus, in particular with regard to absolute optical encoders, it would be desirable to maintain relatively larger scale track widths, in order to maintain accuracy as robustly as possible, while otherwise maintaining as compact an optical encoder configuration as possible. However, the prior art fails to teach configurations which provide certain combinations of robustness, compact size, range-to-resolution ratio, and cost desired by users of encoders. Improved configurations of encoders that provide such combinations would be desirable. 
     SUMMARY OF THE INVENTION 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. In general, unless otherwise indicated by explicit description or context, when referring to the “phosphor” herein, the reference includes not only the light-emitting phosphor molecules, but also includes any carrier or substance that surrounds the phosphor molecules and facilitates their application and/or protection on a substrate. 
     The present invention is directed to improved displacement encoder configurations that provide improved combinations of compact size, robustness, range-to-resolution ratio, high resolution, and fabrication and assembly cost. 
     Ideally, in optical displacement encoders the shape of the area of the moving scale pattern, which determines the shape of the spatially modulated light pattern that overlaps the photodetector, should be the sole determinant of the displacement signal. In addition, in order to increase the robustness of the encoder operation, it is generally desirable to increase the area of the scale pattern that governs the spatially modulated light pattern to a practical maximum, such that any contamination that may be introduced on the scale disrupts as little as possible of the desired signal-generating light pattern. However, illumination non-uniformity may cause extraneous intensity variations within the spatially modulated light pattern on the photodetector, such that the accuracy of the displacement signal is degraded. Conventionally, lenses and/or diffusers are positioned axially along an optical path in order to expand the beam of a light source and provide a uniform intensity distribution across the portion of the scale pattern that is to be imaged. However, the required length of an optical path including such elements (e.g., a lens) prevents the encoder configuration from being made more compact along the optical axis, particularly as the area of the scale pattern that is included in the optical path is increased. 
     In accordance with one embodiment of the present invention, uniform light intensity is achieved without the use of a lens, by utilizing a primary light source to excite and saturate a phosphor area which then provides uniform illumination to a scale pattern. In one specific embodiment, the primary light source may provide non-uniform primary radiation that approximately saturates an area of uniformly distributed phosphor that absorbs the primary radiation at a first wavelength, the saturated phosphor then providing a “secondary” phosphor radiation at a second wavelength that illuminates the scale with a relatively uniform intensity to produce a scale pattern “image” (e.g., a shadow image) that is sensed by the photodetector. Due to saturation of the phosphor, the uniformity of the intensity of the secondary radiation may be similar to the uniformity of the saturated volume of the phosphor. Uniform illumination intensity may therefore be economically provided over a wide area with relatively few components, in a configuration that minimizes the path length and encoder size along a direction normal to the plane of the scale pattern. Other advantages include the ability to match the phosphor wavelength to the maximum sensitivity of the photodetector (e.g., for better signal-to-noise ratio and energy efficiency); patterning the phosphor to provide an economical source grating for self imaging type displacement encoders; and using the phosphor to provide diffuse illumination in applications where such is more desirable than directional illumination of the type typically provided by primary radiation sources (e.g., LEDs, laser diodes, etc.). 
     It will be appreciated that the intensity uniformity provided by the phosphor is improved over that obtained directly from a primary radiation source (e.g., a LED primary source, an interposed diffuser, etc.). In addition, the improved uniformity is achieved along a very short optical path. In other words, the saturated phosphor used in combination with a high divergence primary light source results in a configuration with a large illumination area and a very short optical path, which is desirable for achieving a more compact encoder configuration. 
     In accordance with another aspect of the invention, the uniformity of the phosphor light from the phosphor may depend on the phosphor thickness and how uniformly the light-emitting phosphor molecules are distributed within the phosphor volume. In one embodiment, the phosphor molecules are suspended in a well-mixed carrier (e.g., such that the phosphor molecules are uniformly distributed in the carrier volume) and then spin-coated onto a flat substrate, or else the phosphor is distributed using other known techniques, such that uniform thickness and density of the phosphor is achieved. In one embodiment, the absolute scale tracks may be illuminated by a continuous phosphor area, while the incremental scale track is illuminated by a patterned phosphor area (e.g., as may be formed through a photo-resist/etch process or a laser etch). The patterned phosphor may serve as a source grating that facilitates providing the detected image of the incremental scale track by using known self-imaging techniques. In another embodiment, the absolute scale tracks may also be illuminated by a phosphor area patterned to form a source grating (that is, a periodic array of line sources), even in embodiments where the absolute scale tracks are imaged using conventional or shadow imaging techniques. In some embodiments, the primary light source wavelength may be outside the range of the detector response, or eliminated from the detector response using a wavelength filter in the optical path, so as to have only the phosphor light from the phosphor be involved determining the encoder displacement signals. It will be appreciated that the phosphor response time may be very fast (e.g., on the order of microseconds), which is ideal for certain applications (e.g., a low power pulsed optical ABS encoder system). 
     In some embodiments, a scale configuration usable with the present invention comprises a scale element including an absolute scale pattern comprising a fine track pattern and at least a first absolute track pattern. The various track patterns are arranged to receive light from the phosphor and output respective track-specific spatially modulated light patterns along respective light paths to various corresponding detector portions of the detector electronics (e.g., a fine track detector portion and at least a first absolute track detector). The fine track pattern and its corresponding detector portion may be configured according to known techniques (e.g., using conventional imaging, shadow imaging, or self-imaging techniques and known detector structures to generate periodic displacement signals). As previously indicated, in some embodiments, the phosphor area for illuminating the fine track pattern may be patterned as a source grating (e.g., to provide spatially coherent light, as is desirable when using self-imaging techniques to generate a scale image from a grating-like scale pattern). 
     In some embodiments an absolute track detector portion may be configured with individual photodetector areas that have a Y direction edge-to-edge dimension YDETABS along a Y direction that is perpendicular to a measuring axis direction, and these photodetector areas may be configured to spatially filter their received spatially modulated light pattern and output a plurality of respective position indicating signals that have respective spatial phases. In one embodiment, the absolute track pattern comprises geometrically congruent subtrack portions that extend along the measuring axis direction, and the geometrically congruent subtrack portions are arranged such that if one of the geometrically congruent portions is translated along the Y axis direction by the dimension YDETABS, then the geometrically congruent portions will nominally coincide. The geometrically congruent subtrack portions may furthermore be configured such that they are separated along the Y direction by a dimension YCENT that is less than YDETABS, and the geometrically congruent subtrack portions may each have a Y direction dimension YTOL, such that the dimensional quantity [YCENT+2(YTOL)] is greater than YDETABS. Thus, the detector portion for sensing the absolute track may be narrower than the absolute track pattern along the Y direction, but because the ends of the photodetectors are each nominally located over geometrically congruent subtrack portions (to sense geometrically congruent light patterns), the detected signal is not sensitive to misalignment of the detector portion along the Y direction. It will be appreciated that a narrower detector portion is more economical, and may also facilitate a compact device. In some such embodiments the absolute scale pattern may have a width less than 3.0 millimeters and still be used to provide a desirable range-to-resolution ratio in an economical absolute encoder configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a partially schematic exploded diagram of a representative encoder configuration that uses a light source to illuminate a scale pattern and produce a corresponding spatially modulated light pattern on a detector; 
         FIG. 2  is a partially schematic exploded diagram of a first embodiment of an encoder configuration utilizing a light source that includes a phosphor to provide illumination to a scale pattern and produce a corresponding spatially modulated light pattern on a detector in accordance with this invention; 
         FIG. 3  is a diagram of a cross-sectional end view of a second embodiment of an encoder configuration utilizing a light source that includes a phosphor to provide illumination to a scale pattern; 
         FIGS. 4A-4C  are diagrams of top and bottom views of components at different layers within the encoder configuration of  FIG. 3 ; 
         FIG. 5  is a diagram of a cross-sectional end view of a third embodiment of an encoder configuration utilizing a light source that includes a phosphor to provide illumination to a scale pattern; 
         FIGS. 6A-6D  are diagrams of top and bottom views of components at different layers within the encoder configuration of  FIG. 5 ; 
         FIG. 7  is a diagram of a cross-sectional end view of a fourth embodiment of an encoder configuration utilizing a light source that includes phosphor to provide illumination to a scale pattern; and 
         FIGS. 8A and 8B  are diagrams of top and bottom views of components at different layers within the encoder configuration of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a partially schematic exploded diagram illustrating an optical displacement encoder configuration  100 , which is a representative encoder configuration that uses a light source to illuminate a scale pattern and produce a corresponding spatially modulated light pattern on a detector. The encoder configuration  100  is described in more detail in copending and commonly assigned U.S. patent application Ser. No. 12/273,400, filed Nov. 18, 2008, (hereinafter “the &#39;400 Application”) which is hereby incorporated by reference in its entirety. The illumination system or portion  160  used in the encoder configuration  100  has certain disadvantages, which are remedied by encoder configurations that use novel illumination configurations described in greater detail below. Various other aspects of the design and operation of the encoder configuration  100  are particularly desirable in some applications. These aspects of the design and operation may be retained in various advantageous combinations with the novel illumination configurations disclosed below with reference to  FIGS. 2-8 , and these aspects are therefore outlined here so that embodiments disclosed further below may be understood by analogy. 
     As shown in  FIG. 1 , the encoder configuration  100  includes a scale element  110 , detector electronics  120  which is connected to signal generating and processing circuitry  190 , and an illumination system or portion  160  comprising a light source  130  for emitting visible or invisible wavelengths of light, a lens  140 , and an optional source grating  150 . The light source  130  may also be connected to the signal generating and processing circuitry  190  by power and signal connections (not shown). As will be described in more detail below, the configuration of the scale tracks on the scale element  110  can be formed in a compact configuration and provide certain advantages. 
     In the embodiment shown in  FIG. 1 , the scale element  110  includes an absolute scale pattern  115  including three scale track patterns: an incremental track pattern TINC, a first absolute track pattern TABS 1 , and a second absolute track pattern TABS 2 , as described in more detail in the previously incorporated &#39;400 Application. The track patterns TABS 1  and TABS 2  are referred to as absolute scale track patterns because they provide signals (e.g., a combination of signals) usable to determine an absolute position over an absolute measuring range determined by their configuration.  FIG. 1  also shows orthogonal X, Y and Z directions, according to a convention used herein. The X and Y directions are parallel to the plane of the absolute scale pattern  115 , with the X direction parallel to the intended measuring axis direction MA (e.g., perpendicular to elongated grating pattern elements that may be included in the incremental track pattern TINC). The Z direction is normal to the plane of the absolute scale pattern  115 . 
     The detector electronics  120  includes a detector configuration  125  comprising three detector tracks DETINC, DETABS 1  and DETABS 2  arranged to receive light from the three scale track patterns TINC, TABS 1  and TABS 2 , respectively. The detector electronics  120  may also include signal processing circuitry  126  (e.g., signal offset and/or gain adjustments, signal amplifying and combining circuits, etc.). In one embodiment, the detector electronics  120  may be fabricated as a single CMOS IC. 
     In operation, light  134  (e.g., primary light) emitted from the light source  130  may be partially or fully collimated by the lens  140 , over a beam area sufficient to illuminate the three scale track patterns.  FIG. 1  schematically shows three track-specific light paths  134 A,  134 B and  134 C, of the light  134 . Light path  134 A is a representative central path including light that illuminates the scale track pattern TINC. When the scale track pattern TINC is illuminated, it outputs a track-specific spatially modulated light pattern to the detector track DETINC of the detector electronics  120 . In some embodiments, for example those having a fine track wavelength of approximately 8-40 microns, the encoder configuration  100  may be configured according to known methods to produce a self image (e.g., a Talbot image or a Fresnel image) at the plane of the detector track DETINC. In some self-imaging configurations the light source  130  may be an LED. In some cases, depending on the characteristics of the light source  130 , the source grating  150  may be required in order to condition the light  134  in a manner that makes it suitable for self-imaging. In such a case, the light surrounding the representative light path  134 A passes through the grating structure of the source grating  150  to provide an array of spatially coherent illumination sources at the grating openings, which may be arranged with a pitch corresponding to the pitch or wavelength of the track pattern TINC (e.g., a pitch two times that of TINC), to illuminate the scale track pattern TINC according to known self-imaging illumination principles.  FIG. 1  shows an embodiment of the source grating  150  that allows the representative light paths  134 B and  134 C to pass through a transparent substrate of the source grating  150 , so that their intensity and degree of collimation, which contributes to the quality of the signals from the detector tracks DETABS 1  and DETABS 2 , is not disrupted by the grating structure of the source grating  150 . In other embodiments, the representative light paths  134 B and  134 C may also pass through a grating structure on the source grating  150 , however, in certain embodiments this is not the optimum configuration. 
     Light paths  134 B and  134 C are representative paths including light that illuminates the scale track patterns TABS 2  and TABS 1 , respectively. When the scale track patterns TABS 2  and TABS 1  are illuminated, they output track-specific spatially modulated light patterns (e.g., patterned light corresponding to their patterns) to the track-specific detector tracks DETABS 2  and DETABS 1 , respectively, of the detector electronics  120 . In various embodiments, the encoder configuration  100  may be configured such that the track patterns TABS 2  and TABS 1  produce a shadow image (e.g., a blurred or unblurred shadow image, depending on the degree of collimation provided by the lens  140 ) projected onto the detector tracks DETABS 2  and DETABS 1 , respectively, as described in greater detail in the previously incorporated &#39;400 Application. It will be appreciated that all of the spatially modulated light patterns move in tandem with the scale  110 . In optical and electronic signal channels corresponding to each of the detector tracks DETINC, DETABS 1  and DETABS 2 , individual photodetector areas are arranged to spatially filter their respective received spatially modulated light pattern to provide desirable position indicating signals (e.g., quadrature signals, or other periodic signals having a spatial phase relationship that is conducive to signal interpolation). In some embodiments, rather than individual photodetector areas, a spatial filter mask with individual apertures may mask relatively larger photodetectors to provide light receiving areas analogous to the individual photodetector areas illustrated, to provide a similar overall signal effect according to known techniques. 
     In various applications, the detector electronics  120  and illumination system  160  are mounted in a fixed relationship relative to one another, e.g., in a readhead or gauge housing (not shown), and are guided along the measuring axis relative to the scale  110  by a bearing system, according to known techniques. The scale may be attached to a moving stage, or a gauge spindle, or the like, in various applications. The configuration shown in  FIG. 1  is a transmissive configuration. The scale pattern  115  comprises light blocking portions and light transmitting portions (e.g., fabricated on a transparent substrate using known thin-film patterning techniques, or the like) that output the spatially modulated light patterns to the detector tracks by transmission. It will be appreciated that similar components may be arranged in reflective embodiments, wherein the illumination system  160  and the detector electronics are arranged on the same side of the scale  110 , and positioned for angled illumination and reflection if necessary, according to known techniques. In either transmissive or reflective scale patterns, the portions of the scale pattern that provide the light that is detected by the absolute detector tracks (e.g., DETABS 1  or DETABS 2 ), may be referred to as the signal producing portions of the scale pattern, and it will be understood that other portions of the scale pattern generally provide as little light as possible to the detector tracks and may be referred to as signal diminishing portions. It should be appreciated that the signal producing portions or the signal diminishing portions of the scale pattern may be patterned according to the teachings herein, in various embodiments. Stated another way, scale patterns which are “negatives” of each other may both produce useable signals, with the resulting signal variations also being approximately the “negative” of each other for a given reflective or transmissive arrangement. Thus, the scale patterns may be described in terms of “signal varying portions,” and it will be understood that in various embodiments, the signal varying portions may comprise either the signal producing portions or the signal diminishing portions of the scale pattern. 
     As previously outlined, ideally, the spatially modulated light pattern that overlaps the photodetector should vary only as a function of the scale pattern displacement, which should be the sole determinant of the displacement signal. Stated another way, the spatially modulated light pattern should move in tandem with the displaced scale pattern, and otherwise its spatially modulated intensity variations should remain stable. However, it will be appreciated that illumination non-uniformity causes extraneous intensity variations that are superimposed upon those caused by the displaced scale pattern within the spatially modulated light pattern, such that the accuracy of the displacement signal is degraded. Conventionally, as exemplified by the illumination system  160 , lenses and/or diffusers are positioned axially along an optical path in order to expand the beam of a light source and provide a uniform intensity distribution across the portion of the scale pattern that is to be imaged. However, the required length of an optical path including such elements (e.g., the divergence length between the light source and the lens, and the lens length) prevents the encoder configuration from being made more compact, particularly along the Z axis, and particularly as the area of the scale pattern that is illuminated is increased. As previously outlined, to provide robust operation, it is generally desirable to increase the area of the scale pattern that is illuminated to provide the spatially modulated light pattern to a practical maximum, such that any contamination that may be introduced on the scale pattern disrupts as little as possible of the detected spatially modulated light pattern. 
     In contrast to the encoder configuration  100 , the embodiments disclosed below with reference to  FIGS. 2 through 8  use novel illumination configuration including phosphors to provide uniform illumination intensity over a relatively broad illumination area of the scale pattern, while using a relatively small optical path length, particularly along the Z axis dimension. 
       FIG. 2  is a partially schematic exploded diagram of a first embodiment of an encoder configuration  200  utilizing a light source that includes a phosphor to provide illumination to a scale pattern that produces a corresponding spatially modulated light pattern on a detector in accordance with this invention. Except for the use of the phosphor to enhance the illumination uniformity and eliminate the requirement for an illumination lens, the components and operating principles of the encoder configuration  200  may be approximately similar to those of the encoder configuration  100  of  FIG. 1 , and may generally be understood by analogy. For example, 2XX series numbers in  FIG. 2  that have the same “XX” suffix as 1XX series numbers in  FIG. 1  may designate similar or identical elements, which may function similarly, except as otherwise described or implied below. 
     As shown in  FIG. 2 , the encoder configuration  200  includes a scale element  210 , detector electronics  220  which is connected to signal generating and processing circuitry  290 , and an illumination system or portion  260  comprising one or more primary light source(s)  230  (e.g., an LED) for generating visible or invisible wavelengths of light, an optical deflector and/or scattering element  232 , a transparent substrate  204  with a phosphor layer  205  (alternatively referred to as a phosphor area  205 ). An optional wavelength filter  270  may also be included. In various embodiments, the optical deflector and/or scattering element  232  and the transparent substrate  204  may be merged and/or indistinguishable, and/or the phosphor layer  205  may be applied directly to a surface of the optical deflector and/or scattering element  232 . The light sources  230  may be connected to the signal generating and processing circuitry  290  by power and signal connections (not shown). In various embodiments, the scale element  210  is positioned at a generally stable distance along the Z direction from the illumination system  260 , and from the detector electronics  220  (in particular, the detector configuration  225 ) within an encoder housing or gauge housing or a readhead assembly (not shown), according to known techniques. In the embodiment shown in  FIG. 2 , the scale element  210  is shown to be supported at its end by a bracket  212  and a rod  214 . In certain gauge applications (e.g., a spindle gauge) the rod  214  may be guided relative to the illumination portion  260  and detector configuration  225  (e.g., by bearings, not shown) and may project from the end of the gauge to contact a workpiece. The rod  214 , the bracket  212 , and the attached scale element  210  will then move relative to the gauge and follow the workpiece in order to measure its displacement. In some embodiments, spacers may be utilized to provide a desired gap or spacing between the illumination portion  260  and the detector configuration  225  along the Z direction, through which the scale element  210  moves along the direction of the measuring axis MA, as will be described in more detail below with respect to  FIG. 3 . 
     In the embodiment shown in  FIG. 2 , the scale element  210  includes an absolute scale pattern  215  including three scale track patterns similar to those of the scale pattern  115  of  FIG. 1 , an incremental track pattern TINC, and first and second absolute track patterns TABS 1  and TABS 2 , respectively, which provide a combination of signals usable to determine an absolute position over an absolute measuring range determined by their configuration. Such tracks are described in detail in the previously incorporated &#39;400 Application. The detector electronics  220  includes a detector configuration  225  comprising three detector tracks DETINC, DETABS 1  and DETABS 2  arranged to receive light from the three scale track patterns TINC, TABS 1  and TABS 2 , respectively. The detector electronics  220  may also include signal processing circuitry  226  (e.g., signal offset and/or gain adjustments, signal amplifying and combining circuits, etc.). In one embodiment, the detector electronics  220  and/or the signal generating and processing circuitry  290  may be fabricated as a single CMOS IC. 
     Briefly outlining the operation of the encoder configuration  200 , the primary light source(s)  230  generate and emit the primary light PRL which enters the optical deflector and/or scattering element  232  and is thereby distributed over a broad area through the transparent substrate  204  to the phosphor area  205 , which has a light emitting area large enough to illuminate the three scale track patterns TINC, TABS 1  and TABS 2  with phosphor light PHL. For example, in some embodiments, the phosphor area  205  has a phosphor area dimension along the Y direction that is at least as large as the overall dimension of the scale pattern  215  along Y direction. The operation of the optical deflector and/or scattering element  232  and the phosphor area  205  are described in greater detail below. The three scale track patterns TINC, TABS 1  and TABS 2  output (e.g., transmit) the phosphor light PHL as track-specific spatially modulated phosphor light patterns SMPHLINC, SMPHLABS 1 , and SMPHLABS 2  to the track-specific detector tracks DETINC, DETABS 1  and DETABS 2 , respectively. It will be appreciated that in some embodiments, some of the primary light PRL may be transmitted through the phosphor area  205  and transmitted by the scale track patterns with the spatially modulated phosphor light patterns SMPHL. However, as outlined elsewhere herein, this may be undesirable in that the primary light PRL may be less uniform than the phosphor light PHL. Thus, some embodiments may include a wavelength filter  270  that removes the wavelengths corresponding to the primary light PRL from the signal light SL that reaches the detector tracks  225 . Alternatively, in some embodiments, the detector tracks  225  are substantially insensitive to the wavelength range associated with the primary light PRL, and the wavelength filter is not needed in such embodiments. It will be appreciated that the illumination system  260  of the encoder configuration  200  provides illumination over a relatively broad area of the scale track patterns (e.g., corresponding to the phosphor area  205 ) while being very compact along the Z direction. The illumination system  260  overcomes intensity non-uniformities which are difficult to overcome in the primary light in this broad-area, yet compact-Z, illumination system arrangement by using the phosphor area  205  to output phosphor light PHL that has a more uniform intensity than the primary light PRL would have at a similar location along the optical path, due to effects and techniques described in greater detail below. 
     Examining the encoder configuration  200  further,  FIG. 2  schematically shows three track-specific light paths  234 A,  234 B and  234 C, of the phosphor light PHL. Light path  234 A is represented by central ray in  FIG. 2 , and generally includes any light that both illuminates the scale track pattern TINC and reaches the detector track DETINC of the detector electronics  220 . In particular, then the scale track pattern TINC is illuminated along the light path  234 A, it outputs a track-specific spatially modulated light pattern to the track-specific detector track DETINC. In some embodiments, for example those having a fine track wavelength LINC of approximately 8-40 microns, the encoder configuration  200  may be configured to produce a self image (e.g., a Talbot image or a Fresnel image) at the plane of the detector track DETINC. In such fine track self-imaging configurations the phosphor area  205  may be patterned to provide a phosphor area source grating. That is, it may be patterned as fine stripes of phosphor material separated by spaces, at least in the phosphor area region  205 -INC which produces phosphor light PHL that illuminates the scale track pattern TINC and subsequently reaches the detector track TINC, as represented in  FIG. 2 . Alternatively, a uniform phosphor may be masked to emit light through analogous fine slits. In either case, the phosphor area source grating provides an array of spatially coherent illumination sources, which may be arranged with a pitch approximately matching the pitch or wavelength of the track pattern TINC, to illuminate the scale track pattern TINC according to known self-imaging illumination principles. 
     Track-specific light paths  234 B and  234 C are represented by central rays in  FIG. 2 . Light path  234 C generally includes any light that both illuminates the scale track pattern TABS 1  and reaches the detector track DETABS 1 , and light path  234 B generally includes any light that both illuminates the scale track pattern TABS 2  and reaches the detector track DETABS 2 . When the scale track patterns TABS 2  and TABS 1  are illuminated, they output track-specific spatially modulated light patterns (e.g., patterned light corresponding to their patterns) to the track-specific detector tracks DETABS 2  and DETABS 1 , respectively. In various embodiments, the encoder configuration  200  may be configured such that the track patterns TABS 2  and TABS 1  produce a shadow image (e.g., a blurred shadow image) on the detector tracks DETABS 2  and DETABS 1 , as described in the previously incorporated &#39;400 Application. In the embodiments shown in  FIG. 2 , the phosphor light PHL included in the light paths  234 B and  234 C originates from regions of the phosphor area  205  that are source grating structured. However, this is not significant to the signal generating operation of the corresponding tracks, and the regions of the phosphor area  205  that are outside of the region  205 -INC may comprise uniform and/or unpatterned phosphor material, in various embodiments. Similarly, if self-imaging is not used to generate the fine track spatially modulated light pattern (e.g., if the fine track wavelength LINC is large enough to provide a detectable shadow image of the fine track TINC at the detector track DETINC), then the region  205 -INC may also comprise uniform and/or unpatterned phosphor material. It will be appreciated that the sequence of the scale tracks along the Y direction in  FIG. 2  is exemplary only, and not limiting. For example, in other embodiments, the absolute track patterns TABS 1  and TABS 2  may be arranged adjacent to one another with the fine track pattern TINC located to one side of them, provided that the detector tracks and source grating structure (if any) are arranged along the proper corresponding light paths according to the teachings outlined above. 
     In contrast to the light used to illuminate the scale tracks in the encoder configuration  100  shown in  FIG. 1 , in the encoder configuration  200  the phosphor light PHL that illuminates the scale may be quite diffuse. Thus, when shadow images provide the spatially modulated phosphor light patterns that are detected, the shadow images may be significantly blurred. The amount of blur will depend on the Z direction spacing or gap between phosphor area  205  and the scale pattern  215 , and particularly on the Z direction spacing or gap between the scale pattern  215  and the detector configuration  225 . It will be appreciated that  FIG. 2  is an exploded view, where the Z direction spacing is greatly exaggerated. In various embodiments, the Z-direction spacings or gaps are selected to provide an amount of blur corresponding to desirable signal characteristics. It should be appreciated that some amount of blur may be advantageous, in that it may remove higher spatial frequencies from the spatially modulated phosphor light pattern that is detected, which may provide a more ideal sinusoidal displacement signal in some embodiments. One advantage of an absolute track pattern according to this invention, approximately as illustrated and/or as taught in the &#39;400 Application, is that the spatial harmonic content in the resulting detector signal does not vary substantially at various Z direction spacings between the illumination system  260 , the absolute scale pattern  215 , and the detector configuration  225 , and is thus a single absolute track pattern design can accommodate a variety of fine track techniques and adjustments without imposing additional design constraints. 
     As shown in  FIG. 2 , in various embodiments, the absolute track detector portion of  FIG. 2  may be configured with individual photodetector areas that have a Y direction edge-to-edge dimension YDETABS along a Y direction that is perpendicular to a measuring axis direction, and these photodetector areas may be configured to spatially filter their received spatially modulated light pattern and output a plurality of respective position indicating signals that have respective spatial phases. The absolute track pattern may comprise geometrically congruent subtrack portions that extend along the measuring axis direction, and the geometrically congruent subtrack portions may be arranged such that if one of the geometrically congruent portions is translated along the Y direction by the dimension YDETABS, then the geometrically congruent portions will nominally coincide. The geometrically congruent subtrack portions may furthermore be configured such that they are separated along the Y direction by a dimension YCENT that is less than YDETABS, and the geometrically congruent subtrack portions may each have a Y direction dimension YTOL, such that the dimensional quantity [YCENT+2(YTOL)] is greater than YDETABS. Thus, the detector portion for sensing the absolute track may be narrower than the absolute track pattern along the Y direction, but because the ends of the photodetectors are each nominally located over geometrically congruent subtrack portions (to sense geometrically congruent light patterns), the detected signal is not sensitive to misalignment of the detector portion along the Y direction. It will be appreciated that a narrower detector portion is more economical, and may also facilitate a more compact device. These aspects of the encoder configuration  200 , as well as alternative scale pattern track configurations that may be used, are described in greater detail in the previously incorporated &#39;400 Application. 
     In some embodiments, the overall width of the scale pattern  215  may be 6.0 millimeters or significantly less (e.g., approximately 3.0 millimeters, or less, in some embodiments), the Y direction dimensions of the scale pattern tracks TINC, TABS 1  and TABS 2  may each be less than 2.0 millimeter or 1 or significantly less (e.g., 0.8 millimeters, in some embodiments), and the Y direction dimensions of the detector tracks DETINC, DETABS 1  and DETABS 2  may each be less than the scale pattern track dimension, (e.g., 0.5 millimeters when the scale pattern track dimensions are 0.8 millimeters). The Y direction dimensions YTOL may extend along the Y direction beyond the Y direction dimensions of the detector tracks DETINC, DETABS 1  and DETABS 2  by an amount that allows for both misalignment and to prevent blurred spatially modulated light from bleeding onto the detectors of an adjacent track (e.g., by 0.15-0.50 millimeters, or as otherwise required, in some embodiments). More generally, it is desirable in various embodiments to arrange the components so as to avoid “image crosstalk” (i.e., it is generally desirable that transmitted light from one track should not significantly reach a detector that is intended to detect light from a different track), as will be described in more detail below. The wavelength LABS 2  of the absolute track pattern TABS 2  may be L 2 =720 microns and the wavelength LABS 1  of the absolute track pattern TABS 1  may be L 1 =700 microns. The wavelength LINC of the fine track pattern TINC may be 20 microns. Using a signal processing technique that compares the phases of the LABS 1  and LABS 2  signals, this provides an absolute range of approximately 25.2 mm, and allows reasonable interpolation ratios to be used. Such compact dimensions are particularly advantageous in a number of applications (e.g., linear gauges and the like), both in relation to size and in relation to cost. It will be understood that the configuration and dimensions outlined in the example above, are exemplary only, and not limiting. 
     It will be appreciated that all of the spatially modulated light patterns move in tandem with the scale  210 . In optical and electronic signal channels corresponding to each of the detector tracks DETINC, DETABS 1  and DETABS 2 , individual photodetector areas, or masked areas on the photodetectors, are arranged to spatially filter their respective received spatially modulated light pattern to provide desirable position indicating signals (e.g., quadrature signals, or other periodic signals having a spatial phase relationship that is conducive to signal interpolation). 
     Examining the illumination system  260  further, as previously implied, the primary light PRL may comprise light concentrated in a first wavelength range, and may be emitted from light sources  230  (e.g., LED&#39;s, laser diodes) that have a relatively small light emitting area. The optical deflector and/or scattering element  232  is used to expand the primary light PRL from the relatively small light emitting area to cover a larger, relatively broad, light emitting area of the phosphor area  205 ) while traversing only a relatively short optical path length and, in particular, within a compact dimension along the Z direction (e.g., less than 5, 4 or 3 mm along the Z direction). In one embodiment the optical deflector and/or scattering element  232  may comprise a wedge shaped diffusing light guide panel analogous to that disclosed in U.S. Pat. No. 6,347,874, which is hereby incorporated herein by reference in its entirety. The optional wavelength filter  270  (if used) may generally be located at any location between the phosphor area  205  and the detector tracks of the detector portion  225 . In some embodiments, it is located adjacent to the phosphor area  205  (to filter and output the phosphor light PHL), and may be part of the illumination system  260 . In some embodiments, the phosphor area  205  may be located at the interface between the transparent substrate  204  the optical deflector and/or scattering element  232 , where it is protected, and the optional wavelength filter  270  may be applied to the output surface of the transparent substrate  204 . In various embodiments, the optical deflector and/or scattering element  232  and the transparent substrate  204  may be merged and/or indistinguishable, and/or the phosphor layer  205  may be applied directly to a surface of the optical deflector and/or scattering element  232 . As previously indicated, in some embodiments the optical deflector and/or scattering element  232  and the transparent substrate  204  may be merged and/or indistinguishable, and/or the phosphor layer  205  may be applied directly to a surface of the optical deflector and/or scattering element  232 . In other embodiments an illumination system comprising the light sources  230 , the optical deflector and/or scattering element  232 , and the phosphor area  205  may included interference filters (e.g., the filter  270 ) and/or reflectors, and/or may otherwise be arranged in a manner analogous to configurations disclosed in U.S. Pat. No. 7,357,554, which is hereby incorporated herein by reference in its entirety. 
     As previously outlined, it is a desirable feature of an encoder configuration according to this invention that the illumination system (e.g., the illumination system  260 ) provides phosphor light PHL that illuminates the scale track patterns with better intensity uniformity than would otherwise be provided by the primary light PRL in the absence of the phosphor area  205 . For example, in concrete terms, the illumination system provides phosphor light PHL that illuminates the scale track patterns with better intensity uniformity than is provided by the primary light PRL proximate to the phosphor area  205 . One advantage of using a phosphor area in a configuration according to this invention (e.g., the phosphor area  205 ) is that the primary light PRL is scattered in the phosphor medium, improving its intensity uniformity within the phosphor area. Furthermore, the phosphor light PHL emitted by the phosphor is emitted omni-directionally by the phosphor molecules, such that the phosphor light primary light PRL is a spatially averaged diffuse light, improving its intensity uniformity beyond that of the primary light PRL, particularly at a distance from the phosphor area  205  (e.g., at the location of the scale patterns  215 ). 
     A further advantage of the phosphor area (e.g., the phosphor area  205 ) is provided when the phosphor area is configured to include a “saturation” intensity level and the primary light PRL is distributed to the phosphor area with a primary light intensity that exceeds the saturation intensity level proximate to the phosphor area, for at least a portion of the phosphor area. By a saturation intensity level, we mean that above the saturation intensity level the ratio of phosphor light intensity increase to primary light intensity increase decreases significantly relative to that ratio below the saturation intensity level. This non-linear phosphor area response may arise from one or more fundamental mechanisms, including known concentration quenching and/or luminescence saturation processes such as ground state depletion and energy transfer between excited phosphor ions, additional quenching pathway energy transfer, and/or a slow radiative relaxation rate of the phosphor material (e.g., slow relative to the excitation pulse of primary light), for example. 
     Due to the aforementioned nonlinear response in the phosphor area, intensity peaks in the primary light PRL intensity distribution that exceed the saturation intensity level at the phosphor area are relatively reduced or eliminated in the resulting phosphor light PHL intensity distribution that is output from the phosphor area in the wavelength range of the phosphor light PHL. As a result the phosphor light PHL intensity uniformity may be significantly more uniform than the level of primary light PRL intensity uniformity proximate to the phosphor area. In various embodiments, it may be desirable if a majority or all of the phosphor area is illuminated with a primary light intensity that exceeds its saturation intensity level. It will be appreciated that in order to best exploit this effect to achieve uniform intensity in the phosphor light PHL, it is advantageous to make the density and thickness of the light emitting regions of the phosphor area material substantially uniform, or as uniform as possible. 
     The uniform diffuse light from the phosphor area  205  works well in cooperation with the scale and detection concepts outlined above. The foregoing features, separately and in combination, allow for a relatively small primary light emitting area to be expanded to a relatively large phosphor light illumination area in relatively short illumination path length, and still provide a relatively uniform illumination intensity (the phosphor light illumination intensity) to the scale track pattern over the relatively large area, to enhance robustness and accuracy in a compact configuration. In some embodiments, the phosphor light PHL intensity may vary less than 10%, 5% or even 1% proximate to the portions of the scale pattern that provide the detected portions of spatially modulated light pattern. 
     Another advantage of a phosphor area is that phosphors can respond to very short primary light PRL pulses (e.g., pulse durations of 5 microseconds or less, or 1 microsecond or less, in some embodiments) and output phosphor light PHL very quickly (e.g., on the order of less than a microsecond to hundreds of microseconds, depending on the phosphor composition and the primary light pulse duration), and can be fairly energy-efficient. Therefore, they are compatible with pulsed low power (e.g., battery-powered) optical encoder configurations (e.g., absolute encoder gauge operations), where each pulse may exceed the saturation level over some or all of the phosphor area, if desired, while maintaining a low average power level. General design considerations for the use of phosphors are described in U.S. Patent Publication Nos. 2008/0231911, and 2009/0101930, each of which are hereby incorporated by reference herein in their entireties. 
       FIG. 3  is a diagram of a cross-sectional end view of a second embodiment of an encoder configuration  300  utilizing a light source that includes a phosphor area to provide illumination to a scale pattern, and  FIGS. 4A-4C  are diagrams of top and bottom views of selected components at different layers within the encoder configuration  300  of  FIG. 3 , with alignment along the Y direction approximately maintained throughout all these figures. In one embodiment, the encoder configuration  300  may be similar to the encoder configuration  200  of  FIG. 2 , and elements having 3XX reference numbers may generally be analogous to elements having 2XX reference numbers in  FIG. 2 , and may generally be similarly understood and configured in an analogous manner, unless otherwise indicated by description or context. As shown in  FIG. 3 , the encoder configuration  300  includes a scale member  310  including a scale pattern  315 , a circuit assembly  395  (e.g., a printed circuit board and associated signal processing circuitry) including a detector electronics  320 , and an illumination system or portion  360 , which in this embodiment comprises one or more primary light source(s)  330  (e.g., an LED) for generating visible or invisible wavelengths of light, an optical deflector element  332 , a transparent substrate  304  with a phosphor layer or area  305 . 
     The light source(s)  330  may be connected to signal generating and processing circuitry of the circuit assembly  395  by power and signal connections  331 . In various embodiments, the scale element  310  is positioned and guided at a generally stable distance along the Z direction from the illumination system  360 , and from the detector electronics  320  (in particular, the detector configuration  325 ) within an encoder housing or gauge housing according to known techniques. In the embodiment shown in  FIG. 3 , spacers  318  may be utilized to provide a desired gap or spacing between the illumination portion  360  and the detector configuration  325  along the Z direction, through which the scale element  310  moves along the direction of the measuring axis MA. 
     Briefly outlining the operation of the encoder configuration  300 , the primary light source(s)  330  generate and emit the primary light PRL which enters the optical deflector element  332  and is thereby distributed over a broad area through the transparent substrate  304  to the phosphor area  305 , which has a light emitting area large enough to illuminate the scale track patterns included in the scale pattern  315  with phosphor light PHL. The primary light PRL may have a first wavelength range, and the phosphor light PHL may have a second wavelength range different than the first wavelength range, as previously outlined. The scale pattern  315  outputs (e.g., transmits) the phosphor light PHL as a spatially modulated phosphor light pattern to the detector tracks of the detector configuration  325 , according to principles previously outlined with reference to  FIG. 2 . In some embodiments, the encoder configuration may include a wavelength filter (not shown) located at a convenient location along the optical path between the phosphor area  305  and the detector configuration  325  to remove the wavelengths corresponding to the primary light PRL from the signal light SL that reaches the detector configuration  325 , according to previously outlined principles. Alternatively, in some embodiments, the detectors of the detector configuration  325  are substantially insensitive to the wavelength range associated with the primary light PRL, and the wavelength filter is not needed in such embodiments. In any case, the optical and electronic signal channels corresponding to each of the detector tracks of the detector configuration  325 , are arranged to spatially filter their respective received spatially modulated light pattern to provide desirable position indicating signals (e.g., quadrature signals, or other periodic signals having a spatial phase relationship that is conducive to signal interpolation), according to previously described principles. 
       FIG. 4A  is a diagram illustrating a bottom view of elements associated with the illumination system  360 .  FIG. 4A  shows the footprint of joining areas  318 ′ where the transparent substrate  304  may be fastened to the spacers  318  (shown in  FIG. 3 ), to establish a desired gap between the various elements of the encoder configuration  300 . As shown in  FIG. 4A , the phosphor area  305  may include track-specific phosphor areas  305 A,  305 B and  305 C. However, in other embodiments these track-specific areas may be merged and or indistinguishable. In one embodiment the phosphor area  305 A may be formed as an incremental illuminating portion which is source grating structured in order to support self-imaging of the track TINC, and the other phosphor areas  305 C and  305 B may or may not be source grating structured, depending on whether phosphor light PHL from them reaches the incremental track of the scale and the incremental detector array, all according to principles previously outlined with reference to  FIG. 2 . In one embodiment, a cover  308  (e.g., a material sheet or an encapsulant) covers and surrounds the phosphor area  305  for environmental and/or abrasion protection. In one embodiment that cover  308  may include a wavelength filter that blocks the primary light PRL. More generally, in various embodiments the illumination system  360  may have alternative configurations including any compatible combination of the various alternative illumination system features previously outlined with reference to  FIG. 2 . As previously outlined, it is generally advantageous to make the phosphor area  305  be as uniform as possible. It is also advantageous when the phosphor area  305  is configured to include a “saturation” intensity level and the primary light PRL is distributed to the phosphor area with a primary light intensity that exceeds the saturation intensity level proximate to the phosphor area  305 , for at least a portion of the phosphor area  305 , according to previously outlined principles. Both of the aforementioned factors tend to improve the uniformity of the phosphor light PHL that illuminates the scale pattern  315  and provides the signal light SL, which generally improves the potentially accuracy of the encoder configuration  300 . The encoder configuration  300  provides phosphor light PHL that has better intensity uniformity proximate to the scale pattern  315  than the primary light intensity uniformity proximate to the phosphor area  305 . In various embodiments, the phosphor light intensity may vary less than 10%, 5% or even 1% proximate to the portions of the scale pattern  315  that provide the detected portions of the spatially modulated light pattern included in the signal light SL. 
       FIG. 4B  is a diagram of a bottom view of the scale member  310 . As shown in  FIG. 4B , the scale member  310  includes the scale pattern  315 , which may include an incremental track TINC and two absolute tracks TABS 1  and TABS 2 . In one embodiment, the scale pattern  315  may be similar to the scale pattern  215  of  FIG. 2 . 
       FIG. 4C  is a diagram of a top view of the circuit assembly  395 . As shown in  FIG. 4C , the circuit assembly  395  (e.g., a printed circuit board) includes the detector electronics  320  (e.g., an integrated circuit as previously described with reference to the detector electronic  120  and/or  220 ). The detector electronics  320  may comprise signal processing circuitry  326  (e.g., signal offset and/or gain adjustments, signal amplifying and combining circuits, etc.) and the detector configuration  325 , which may comprise three detector tracks DETINC, DETABS 1  and DETABS 2  arranged to receive light from the three scale track patterns TINC, TABS 1  and TABS 2 , respectively, and provide desirable signals, all according to previously described principles. All of the foregoing elements may be interconnected by circuit connections  327  and  329  (e.g., circuit traces and wirebonds, which are represented in a symbolic manner). The circuit assembly  395  may include additional signal processing and/or interface circuitry (not shown) as needed to support the operation of the light sources and a host system, display, or the like.  FIG. 4C  also shows the footprint of joining areas  318 ″ where the circuit assembly  395  may be fastened to the spacers  318  (shown in  FIG. 3 ), to establish a desired gap between the various elements of the encoder configuration  300 , as outlined above. 
     As previously indicated, it is desirable in various embodiments to arrange the various elements shown and described so as to avoid “image crosstalk” between the various tracks (i.e., it is generally desirable that a significant amount of light from one track should not reach a detector that is intended to detect light from a different track). It is furthermore desirable to set the spacings along the optical path to avoid excessive blur in the spatially modulated phosphor light that provides the signal light SL that is detected by the detector configuration  325 . It will be understood that various dimensions in FIGS.  3  and  4 A- 4 C are necessarily exaggerated for purposes of illustration, and that desirable configurations and/or spacings may be established by analysis or experiment based on the principles outlined herein. Thus, it will be understood that the configurations illustrated herein are exemplary only, and not limiting. 
       FIG. 5  is a diagram of a cross-sectional end view of a third embodiment of an encoder configuration  500  utilizing a light source that includes a phosphor area to provide illumination of a scale pattern, and  FIGS. 6A-6D  are diagrams of top and bottom views of selected components at different layers within the encoder configuration of  FIG. 5 , with alignment along the Y direction approximately maintained throughout all these figures. In one embodiment, certain of the components of the encoder configuration  500  may be similar to their counterparts in the encoder configuration  300  of FIGS.  3  and  4 A- 4 C, and elements having 5XX reference numbers may generally be analogous to elements having 3XX reference numbers in FIGS.  3  and  4 A- 4 C, and may generally be similarly understood and configured in an analogous manner, unless otherwise indicated by description or context. As shown in  FIG. 5 , the encoder configuration  500  includes a scale member  510  including a scale pattern  515 , a circuit assembly  595  (e.g., a printed circuit board and associated signal processing circuitry) including a detector electronics  520 , and an illumination system or portion  560 , which in this embodiment comprises a primary light source assembly  565  including one or more primary light source(s)  530  (e.g., an LED) for generating visible or invisible wavelengths of light, and a phosphor area  505 . The light source(s)  530  may be connected to signal generating and processing circuitry of the circuit assembly  595  by power and signal connections  531 . In contrast to previously described illumination systems, in the present embodiment the phosphor area  505  is located on a surface  510 A of the scale member  510 , as described in greater detail below. The scale element  510  may be guided at a generally stable distance along the Z direction from the detector electronics  520  (in particular, the detector configuration  525 ) within an encoder housing or gauge housing according to known techniques. Spacers  518  may provide a desired gap between the primary light source assembly  565  and the detector configuration  525  along the Z direction, through which the scale element  510  moves along the direction of the measuring axis MA. 
     Briefly outlining the operation of the encoder configuration  500 , the primary light source(s)  530  generate and emit the primary light PRL over a broad area to illuminate through the intervening gap to the phosphor area  505 , which extends along the measuring axis direction of the scale surface  510 A. The phosphor area  505  has a light emitting area large enough to illuminate the scale track patterns included in the scale pattern  515  through the transparent scale member  510  with the phosphor light PHL. The primary light PRL may have a first wavelength range, and the phosphor light PHL may have a second wavelength range, as previously outlined. The scale pattern  515  outputs (e.g., transmits) the phosphor light PHL as a spatially modulated phosphor light pattern to the detector tracks of the detector configuration  525 , according to principles previously outlined with reference to  FIGS. 2 and 3 . In some embodiments, the encoder configuration may include a wavelength filter (not shown) located at a convenient location along the optical path between the phosphor area  505  and the detector configuration  525  to remove the wavelengths corresponding to the primary light PRL from the signal light SL that reaches the detector configuration  525 , according to previously outlined principles. Alternatively, in some embodiments, the detectors of the detector configuration  525  are substantially insensitive to the wavelength range associated with the primary light PRL, and the wavelength filter is not needed in such embodiments. The optical and electronic signal channels corresponding to each of the detector tracks of the detector configuration  525 , are arranged to spatially filter their respective received spatially modulated light pattern to provide desirable position indicating signals (e.g., quadrature signals, or other periodic signals having a spatial phase relationship that is conducive to signal interpolation), according to previously described principles. 
       FIG. 6A  is a diagram illustrating a bottom view of elements associated with the primary light source assembly  565 , which may be a printed circuit board.  FIG. 6A  shows the footprint of joining areas  518 ′ where the primary light source assembly  565  may be fastened to the spacers  518  (shown in  FIG. 5 ), to establish a desired gap between the various elements of the encoder configuration  500 . The primary light source(s)  530  may be arranged in any desired pattern provided that the phosphor area  505  is illuminated according to previously outlined principles. More generally, in various embodiments the primary light source assembly  565  may have alternative configurations including any compatible combination of functionally similar illumination system features previously outlined with reference to  FIG. 2  or  3 , or the like. For example, in one alternative embodiment the primary light source assembly  565  may include components arranged approximately as the components  330  and  332  are arranged in the encoder configuration  300  (shown in  FIG. 3 ). 
       FIG. 6B  is a diagram of the upper surface  510 A of the scale member  510 , including the phosphor area  505 . In this embedment, the phosphor area  505  extends along the measuring axis direction of the scale member  510  over a length commensurate with the scale pattern  515 , and different parts of the phosphor area  505  are illuminated and emit light, depending on which part of the scale member  510  is located adjacent to the primary light PRL and the detector configuration  525 . As shown in  FIG. 6B , the phosphor area  505  may include track-specific phosphor areas  505 A,  505 B and  505 C. However, in other embodiments these track-specific areas may be merged and or indistinguishable. In one embodiment the phosphor area  505 A may be formed as an incremental illuminating portion which is source grating structured in order to support self-imaging of the track TINC, and the other phosphor areas  505 C and  505 B may or may not be source grating structured, depending on whether phosphor light PHL from them reaches the incremental track of the scale and the incremental detector array, all according to principles previously outlined with reference to  FIG. 2 . In one embodiment, a cover  508  (e.g., a material sheet or an encapsulant) covers and surrounds the phosphor area  505  for environmental and/or abrasion protection. As previously outlined, it is generally advantageous to make the phosphor area  505  be as uniform as possible. It is also advantageous when the phosphor area  505  is configured to include a “saturation” intensity level and the primary light PRL is distributed to the phosphor area with a primary light intensity that exceeds the saturation intensity level proximate to the phosphor area  505 , for at least a portion of the phosphor area  505 , according to previously outlined principles. Both of the aforementioned factors tend to improve the uniformity of the phosphor light PHL that illuminates the scale pattern  515  and provides the signal light SL, which generally improves the potentially accuracy of the encoder configuration  500 . 
       FIG. 6C  is a diagram of a bottom view of the scale member  510 . As shown in  FIG. 6C , the scale member  510  includes the scale pattern  515 , which may include an incremental track TINC and two absolute tracks TABS 1  and TABS 2 . In one embodiment, the scale pattern  515  may be similar to the scale pattern  215  of  FIG. 2 . 
       FIG. 6D  is a diagram of a top view of the circuit assembly  595 , and associated elements. The elements of  FIG. 6D  are analogous to counterparts shown in  FIG. 4C , and may be similarly understood. 
     As previously indicated, it is desirable in various embodiments to arrange the various elements to avoid “image crosstalk” between the various tracks. It is furthermore desirable to set the spacings along the optical path to avoid excessive blur in the spatially modulated phosphor light that provides the signal light SL that is detected by the detector configuration  525 . It will be understood that various dimensions in FIGS.  5  and  6 A- 6 D are necessarily exaggerated for purposes of illustration, and that desirable configurations and/or spacings may be established by analysis or experiment based on the principles outlined herein. Thus, it will be understood that the configurations illustrated herein are exemplary only, and not limiting. 
       FIG. 7  is a diagram of a cross-sectional end view of a fourth embodiment of an encoder configuration  700  utilizing a light source that includes phosphor areas to provide illumination to a scale pattern, and  FIGS. 8A and 8B  are diagrams of top and bottom views of selected components at different layers within the encoder configuration of  FIG. 7 , with alignment along the Y direction approximately maintained throughout all these figures. As will be described in more detail below, the encoder configuration  700  illustrates a reflective-type configuration. Despite this difference from previous embodiments, certain of the components of the encoder configuration  700  may be similar to their counterparts in the encoder configuration  300  of FIGS.  3  and  4 A- 4 C, and elements having 7XX reference numbers may generally be analogous to elements having 3XX reference numbers in FIGS.  3  and  4 A- 4 C, and may generally be similarly understood and configured in an analogous manner, unless otherwise indicated by description or context. 
     As shown in  FIG. 7 , the encoder configuration  700  includes a scale member  710  including a scale pattern  715 , a circuit assembly  795  (e.g., a printed circuit board and associated signal processing circuitry) including a detector electronics  720  and an illumination system or portion  760 . In this embodiment the illumination system  760  comprises three track-specific illumination systems,  760 A,  760 B, and  760 C, as described in greater detail below. Each of the track-specific illumination systems comprises a primary light source  730 A,  730 B, or  730 C (e.g., an LED) for generating visible or invisible wavelengths of light, and a corresponding phosphor area  705 A,  705 B or  705 C, respectively. The phosphor areas  705 A,  705 B or  705 C may be fabricated on one or more transparent substrates that are fastened to the circuit assembly  795 . The light sources  730  may be connected to signal generating and processing circuitry of the circuit assembly  795  by power and signal connections (not shown). The scale element  710  may be guided at a generally stable distance along the Z direction from the circuit assembly  795  (in particular, the illumination systems  730  and detector configuration  725 ) within an encoder housing or gauge housing according to known techniques. 
     Briefly outlining the operation of the encoder configuration  700 , each primary light source  730  generates and emits the primary light PRL to cover the relatively broad area of their corresponding phosphor area  705 . For example, the primary light PRL diverges very strongly from a relatively small emitting area of the primary light source  730  to illuminate its corresponding phosphor area  705 , with or without the aid of a miniature lens (not shown). In the embodiment shown in  FIGS. 7 ,  8 A and  8 B, the primary light source  730  may be mounted into a circuit board of the circuit assembly  795 , which may include a pocket  732  (shown in dashed outline in  FIGS. 8A and 8B ) between the primary light source and the phosphor area  705  to allow a clearance path for the primary light PRL. In one embodiment, the pocket  732  may include (e.g., be filled with) a scattering or diffusing element (e.g., a molded scattering or diffusing element or a scattering or diffusing medium) to aid the divergence of the primary light PRL, if needed. In other embodiments, a plurality of primary sources  730  (e.g., a plurality of primary light sources  730 A) may illuminate a single one of the track-specific phosphor areas  705  (e.g., the phosphor area  705 A), to reduce the amount of divergence that is required for the primary light PRL. 
     Each phosphor area  705  has a light emitting area large enough to illuminate its corresponding nearby scale track pattern, which is included in the scale pattern  715  on the transparent scale member  710 , with phosphor light PHL. Because the phosphor light PHL is generally diffuse, each illumination system  705  includes light that reaches the corresponding nearby scale track at an angle and then reflects at an angle to reach the corresponding nearby detector track of the detector configuration  725 . The primary light PRL may have a first wavelength range, and the phosphor light PHL may have a second wavelength range, as previously outlined. The scale pattern  715  includes reflective pattern portions that output (reflect) the phosphor light PHL as a spatially modulated phosphor light pattern to the detector tracks of the detector configuration  725 , according to principles previously outlined with reference to  FIGS. 1-3 . In some embodiments, the encoder configuration  700  may include a wavelength filter (not shown) located to cover the detector tracks of the detector configuration  725 , to remove the wavelengths corresponding to the primary light PRL from the signal light SL that reaches the detector configuration  725 , according to previously outlined principles. Alternatively, in some embodiments, the detectors of the detector configuration  725  are substantially insensitive to the wavelength range associated with the primary light PRL, and the wavelength filter is not needed in such embodiments. The optical and electronic signal channels corresponding to each of the detector tracks DETINC, DETABS 1  and DETABS 2  of the detector configuration  725 , are arranged to spatially filter their respective received spatially modulated light pattern to provide desirable position indicating signals (e.g., quadrature signals, or other periodic signals having a spatial phase relationship that is conducive to signal interpolation), according to previously described principles. 
       FIG. 8A  is a diagram of a bottom view of the scale member  710 . As shown in  FIG. 8A , the scale member  710  includes the scale pattern  715 , which may include an incremental track TINC and two absolute tracks TABS 1  and TABS 2 . In one embodiment, except for their location relative to one another on the scale member  710 , the individual scale tracks TINC, TABS 1  and TABS 2  may be similar to those previously described with reference to  FIG. 2 . The scale tracks TABS 1 , TABS 2  and TINC may comprise high reflectance portions (e.g., bright chrome) that output the spatially modulated light pattern to the detector tracks DETABS 1 , DETABS 2  and DETINC, respectively, by reflection, as well as having low reflectance portions or transmissive portions that absorb the phosphor light PHL or transmit it away from the detector tracks. 
       FIG. 8B  is a diagram of a top view of the circuit assembly  795 , and associated elements. The elements  720 ,  725 ,  726 ,  727 , and  729  of  FIG. 8B  are analogous to counterparts shown in  FIG. 4C , and may be similarly understood. The elements and operation illumination systems  760 A- 760 C may be understood based on previous description. In one embodiment the phosphor area  705 A may be formed as an incremental illuminating portion which is source grating structured in order to support self-imaging of the track TINC, and the other phosphor areas  705 C and  705 B may or may not be source grating structured, depending on whether phosphor light PHL from them reaches the incremental track TINC of the scale and the incremental detector array DETINC, all according to principles previously outlined with reference to  FIG. 2 . In one embodiment, a cover (e.g., a material sheet or an encapsulant, not shown) may cover or surround each the phosphor areas  705 A- 705 C for environmental and/or abrasion protection. As previously outlined, it is generally advantageous to make each of the phosphor areas  705 A- 705 C as uniform as possible. It is also advantageous when each of the phosphor areas  705 A- 705 C is configured to include a “saturation” intensity level and the primary light PRL is distributed to the phosphor area with a primary light intensity that exceeds the saturation intensity level proximate to the phosphor area, according to previously outlined principles. Both of the aforementioned factors tend to improve the uniformity of the phosphor light PHL that illuminates the scale pattern  715  and provides the signal light SL, which generally improves the potentially accuracy of the encoder configuration  700 . 
     Regarding the overall arrangement of the tracks of the encoder configuration  700 , as previously indicated, it is desirable in various embodiments to arrange the various elements to avoid “image crosstalk” between the various tracks. It will be appreciated that the illumination system  760 A illuminates the scale track TINC with phosphor light that is incident on, and reflects from, the scale track TINC with a significant component of travel along the Y direction (that is, perpendicular to the measuring axis direction MA and parallel to the grating bars of the scale track TINC. Therefore, the scale track TINC and the detector track DETINC are separated along the Y direction from the other detector tracks by a distance that prevents them from receiving a significant amount of the light reflected from the scale track TINC along the Y direction. Of course this also prevents light from the scale tracks TABS 1  and TABS 2  from reaching the detector DETINC. Illuminating the scale track TINC along the Y direction (e.g., approximately at shown in FIGS.  7  and  8 A- 8 B) may allow relatively uniform illumination to be provided along the illuminated length of the detector track DETINC, despite the reflective configuration and the angled illumination and reflection. In one embodiment, the phosphor area  705 A may be source grating structured, and may be fabricated on a transparent substrate. The edge of the transparent substrate may be fabricated perpendicular to the bars of the source grating structure. Similarly the adjacent edge of the detector electronics  720  may be fabricated perpendicular to the elongated individual sensing areas of the detector track DETINC (shown in  FIG. 2 , for example). The adjacent edges of the transparent substrate of the phosphor area  705 A and the detector electronics  720  may then be assembled to abut one another, which aligns the source grating structure to detector structure so that both may be aligned to the grating structure of the scale track TINC, in order to optimize self-imaging of the scale track TINC on the detector track DETINC. Since the signals from the detector track DETINC provide the highest resolution and accuracy in the encoder configuration  700 , these features may be advantageous, either separately or in combination. 
     In contrast, in the embodiment shown in FIGS.  7  and  8 A- 8 B, the illumination systems  760 C and  760 B illuminate the scale tracks TABS 1  and TABS 2 , respectively, with phosphor light that is incident on, and reflects from, the scale tracks with a primary component of travel along the X direction (and only a relatively small component of travel along the Y direction). Therefore, in order to prevent image crosstalk it is sufficient to separate the illumination system  760 C and the detector track DETABS 1  (which are associated with the scale track TABS 1 ) primarily along the X direction from the illumination system  760 B and the detector track DETABS 2  (which are associated with the scale track TABS 2 ), e.g., as shown in  FIG. 8A-8B . It will be understood that various dimensions in FIGS.  7  and  8 A- 8 B are necessarily altered or exaggerated for purposes of illustration, and that desirable configurations and/or spacings may be established by analysis or experiment based on the principles outlined herein. 
     The encoder configuration  700  shown in FIGS.  7  and  8 A- 8 B is suitable for simultaneous operation of all signal channels, which may be advantageous in applications that measure high speed motion. However, there are a number of applications in which the signals from the various signal channels (e.g., signals from the detector tracks DETINC, DETABS 1  and DETABS 2 ) may be obtained sequentially without detrimentally affecting the measurement accuracy. In such applications the illumination systems  760 A,  760 B and  760 C may be operated at different times, in which case image crosstalk may be prevented by using exclusive circuit timing for activating the various illumination systems (e.g., to provide individual light pulses) and for acquiring the signals from the various detector tracks. Thus, in embodiments that activate individual illumination systems and acquire signals sequentially, the configuration of illumination systems, scale tracks, and detector tracks need not consider image crosstalk, and may therefore be made considerably more compact than the configurations illustrated and described above. Thus, it will be understood that the configurations illustrated herein are exemplary only, and not limiting. 
     While the preferred embodiment of the invention has been illustrated and described, numerous variations in the illustrated and described arrangements of features and sequences of operations will be apparent to one skilled in the art based on this disclosure. Thus, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.