Abstract:
A reflection-based optical encoding apparatus for the detection of position and/or motion of a mechanical device includes an encoding medium having at least a first reflective portion, and an encoder housing having a light-emitting source and a light-detecting sensor embedded within, the encoder housing being placed in proximity to the encoding medium such that a functional light path can be established from the light-emitting source to the light-detecting sensor via the first reflective portion of the encoding medium. The encoder housing includes a first flat facet positioned between the light-emitting source and the encoding medium, the first flat facet having a first angle relative to a common geometric plane such that light passing from the light-emitting source to the encoding medium is refracted along a first angled path in a manner that the refracted light strikes a desired location of the encoding medium.

Description:
BACKGROUND 
   The present disclosure relates to an optical encoding device for the sensing of position and/or motion. 
   Optical encoders are used in a wide variety of contexts to determine position and/or movement of an object with respect to some reference. Optical encoding is often used in mechanical systems as an inexpensive and reliable way to measure and track motion among moving components. For instance, machines such as printers, scanners, photocopiers, fax machines, plotters, and other imaging systems often use optical encoders to track the movement of an image media, such as paper, as an image is printed on the media or an image is scanned from the media. 
   Generally, an optical encoder includes some form of light emitter/detector pair working in tandem with a “codewheel” or a “codestrip”. Codewheels are generally circular and can be used for detecting rotational motion, such as the motion of a paper feeder drum in a printer or a copy machine. In contrast, codestrips generally take a linear form and can be used for detecting linear motion, such as the position and velocity of a print head of the printer. Such codewheels and codestrips generally incorporate a regular pattern of slots and bars depending on the form of optical encoder. 
   While optical encoders have proved to be a reliable technology, there still exists substantial industry pressure to simplify manufacturing operations, reduce the number of manufacturing processes, minimize the number of parts and minimize the operational space. Accordingly, new technology related to optical encoders is desirable. 
   SUMMARY 
   In a first sense, a reflection-based optical encoding apparatus for the detection of position and/or motion of a mechanical device includes an encoding medium having at least a first reflective portion, and an encoder housing having a light-emitting source and a light-detecting sensor embedded within, the encoder housing being placed in proximity to the encoding medium such that a functional light path can be established from the light-emitting source to the light-detecting sensor via the first reflective portion of the encoding medium. The encoder housing includes a first flat facet positioned between the light-emitting source and the encoding medium, the first flat facet having a first angle relative to a common geometric plane such that light passing from the light-emitting source to the encoding medium is refracted along a first angled path in a manner that the refracted light strikes a desired location of the encoding medium. 
   In a second sense, a reflection-based optical encoding apparatus for the detection of position and/or motion of a mechanical device includes an encoding medium having at least a first reflective portion, and an encoder housing having a light-emitting source and a light-detecting sensor embedded within, the encoder housing being placed in proximity to the encoding medium such that a functional light path can be established from the light-emitting source to the light-detecting sensor via the first reflective portion of the encoding medium. The encoder housing includes a first flat facet positioned between the light-detecting sensor and the encoding medium, the first flat facet having an angle such that light passing from a desired location of the encoding medium is refracted along an angled path in a manner that the refracted light is directed to the light-detecting sensor. 
   In a third sense, a reflection-based optical encoding apparatus for the detection of position and/or motion of a mechanical device includes an encoding medium having at least a first reflective portion, an encoder housing having a light-emitting source and a light-detecting sensor embedded within, the encoder housing being placed in proximity to the encoding medium such that a functional light path can be established from the light-emitting source to the light-detecting sensor via the first reflective portion of the encoding medium and a first refractive means positioned between the encoder body and the encoding medium for advantageously refracting light along an angled path in a manner to establish the functional light path. 

   
     DESCRIPTION OF THE DRAWINGS 
     The example embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements. 
       FIG. 1  shows a 1 transmission-based optical encoder; 
       FIG. 2  shows a reflection-based optical encoder; 
       FIG. 3  shows a novel flat-top reflection-based optical encoder; 
       FIG. 4  shows a first variant of the novel reflection-based optical encoder of  FIG. 3 ; 
       FIG. 5  shows a second variant of the novel reflection-based optical encoder of  FIG. 3 ; and 
       FIG. 6  shows a variant of the novel reflection-based optical encoder of  FIG. 5 . 
   

   DETAILED DESCRIPTION 
   In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparatus and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparatus are clearly within the scope of the present teachings. 
   Optical encoders are generally classified into two categories: transmission-based optical encoders and reflection-based optical encoders. 
     FIG. 1  shows a transmission-based optical encoder  100 . As shown in  FIG. 1 , the encoder  100  includes an optical emitter  101  and an optical detector  102  encased in a housing  104 . An optical lens  106  can be incorporated into the housing  104  below the optical emitter  101  to collimate light emitted by the optical emitter  101  into parallel light  105 . A free area  107  is provided between the optical emitter  101  and the optical detector  102  and a codewheel/codestrip  103  is free to rotate or move inside the free area  107 . 
   In operation, light emitted by the optical emitter  101  can be collimated by the optical lens  106 , then transmitted through the free area  107  and the codewheel/codestrip  103 . Should the codewheel/codestrip  103  be positioned such that a slot/opening is present along the path of the transmitted light, such light can continue to the optical detector  102  where it can be detected. Should the codewheel/codestrip  103  be positioned such that a no slot/opening is present along the path of the transmitted light, the transmitted light will be blocked and the optical detector  102  can detect the absence of light. 
   In contrast to the transmission-based device of  FIG. 1 , a reflection-based optical encoder  200  is shown in  FIG. 2 . The reflection-based encoder  200  includes an optical emitter  201  and an optical detector  202  mounted on a leadframe  207  and encapsulated in an optical housing  204 , which is typically made from some form of resin or glass. The exemplary optical element  204  has two dome-shaped surfaces, with the first dome-shaped surface  205  directly above the optical emitter  201  and the second dome-shaped surface  206  directly above the optical detector  202 . 
   In operation, light emitted by the optical emitter  201  can be focused or collimated by the first dome-shaped surface  205  (which can act as a lens), then transmitted to the codewheel/codestrip  203 . Should the codewheel/codestrip  203  be positioned such that a reflective slot/bar is present along the path of the transmitted light, the transmitted light will be reflected to the second dome-shaped surface  206  (which also can act as a lens) and focused onto the optical detector  202  where it can be detected. Should the codewheel/codestrip  203  be positioned such that a no reflective slot/bar is present along the path of the transmitted light, the transmitted light will be effective blocked, and the optical detector  202  can detect the absence of light. 
     FIG. 3  shows a novel flat-top reflection-based optical encoder  300 . As shown in  FIG. 3 , the optical encoder  300  includes an optical emitter  301  and an optical detector  302  both mounted on substrate  307  and encapsulated in an optical housing  304 . The housing  304  has a single flat surface/facet  305  positioned over both the emitter  301  and detector  302  with the facet  305  being parallel relative to the substrate  307 . A codewheel/codestrip  303  is positioned above the facet  305  at an appropriate distance. 
   In operation, light emitted by the optical emitter  301  can be refracted as it passes the facet  305 , where the light can be further transmitted to the codewheel/codestrip  303  along the various light paths  308  shown in  FIG. 3 . Should the codewheel/codestrip  303  be positioned such that a reflective strip/slot/bar is present along the light paths  308 , the transmitted light can be intercepted at location  313 , reflected back to the encoder housing  304 , refracted a second time as it passes the boundary of the facet  305  and then directed to the optical detector  302  where it can be sensed/detected. Should the codewheel/codestrip  303  be positioned such that a no reflective strip/slot/bar is present along the light path  308  and at location  313 , the transmitted light can be effectively blocked and the optical detector  302  can detect the absence of light. Further, should the codewheel/codestrip  303  be configured such that a combination of reflective and non-reflective bars are simultaneously present along the light path  308  and at location  313 ; the codewheel/codestrip  203  can reflect light commensurate with the pattern of reflective and non-reflective bars such that the pattern is effectively projected onto the optical detector  301 . 
   As mentioned above, as light passes between the optical housing  304  and the air, the light will be refracted at the air/housing boundary, i.e., facet  305 . This refraction can be a function of the refractive index I F1  of the material of the housing  304 , the refractive index I FA  of air, and the angle at which the light intercepts the facet  305 . Accordingly, it should be appreciated that the design choice of material for housing  304  as well as the relative positions of the emitter  301  and detector  302  (as well as various other special distances and geometries) can impact the desired performance of the optical encoder  300  as a whole. As such, it should be appreciated that the various design choices for materials and geometries/spacing can vary from embodiment to embodiment as may be found desirable or useful. 
   An advantage to the approach of flat-topped optical detectors is that they eliminate the need for external domes, which constrain package height and can make an encoder unnecessarily sensitive to mechanical alignment. By incorporating a flat-topped encoder package, package height can be reduced, alignment issues can be relaxed and manufacturing can be simplified. While flat-topped optics generally may not achieve the theoretical resolution of a domed lens, optical encoders using flat-topped bodies can nonetheless be used for codestrips/codewheels having more than 75 lines-per-inch, which satisfies a great deal of industry needs. 
     FIG. 4  shows a first variant of the novel reflection-based optical encoder of  FIG. 3 . As is depicted in  FIG. 4 , the variant optical encoder  400  is similar in structure to the encoder  300  of  FIG. 3 , but has a different body structure. That is, encoder housing  404  incorporates a trench  410 , which effectively forms two separate facets  405  and  406  through which light can pass. The trench  410  is an isolating structure that serves to improve isolation between the emitter  301  and detector  302  such that light is less likely to propagate from the emitter  301  to the detector  302  without being reflected via the codewheel/codestrip  303 . 
   While the detectors  202 / 302  and emitters  201 / 301  of the flat-topped encoders  200 / 300  depicted in  FIGS. 3 and 4  are shown mounted on a common substrate, it should be appreciated that in various embodiments detectors and emitters may be mounted on different substrates as may be required or advantageous in various situations, and that the facets for the detectors and emitters may or may not run along the same plane or along parallel planes. 
     FIG. 5  shows yet another variant of the novel reflection-based optical encoder of FIG.  3 . As is depicted in  FIG. 5 , the variant optical encoder  500  includes an optical emitter  301  and an optical detector  302  both mounted on substrate  307  and encapsulated in housing  504 . The housing  504  has two flat facets  505  and  506  positioned over the emitter  301  and detector  302 , respectively, with the facets  305  and  306  each having a respective angle θ 1 /θ 2  relative to the substrate  307 . An optical isolation trench  510  is provided between the optical emitter  301  and the optical detector  302 , and a codewheel/codestrip  303  is positioned above the facets  305  and  306  at an appropriate distance. 
   The operation of the encoder  500  of  FIG. 5  is essentially the same as with the previous examples. However, as light passes through the facets  505  and  506 , such light can be refracted as a function of angles θ 1  and θ 2  as well as the various refractive indexes I F1 /I FA  and the relative spatial distances and geometries of the emitter  301 , the detector  302  and other components. While it is envisioned that θ 1  and θ 2  will be equal in many embodiments, other encoder embodiments can take the form of asymmetric optical arrangements having different θ 1  and θ 2  angles, and still other encoder embodiments can take the form of one angle being zero degrees with the other angle being a non-zero degree angle. 
   Analysis indicated that the use of angled facets may improve the resolution of an optical encoder as compare to the optical encoders depicted in  FIGS. 3 and 4 . However, whether or not an angled facet is the best design choice for a particular optical encoder can depend on a variety of other design considerations. 
     FIG. 6  shows a variant of the optical encoder of  FIG. 5 . As is depicted in  FIG. 6 , the variant optical encoder  600  has a number of separate and independent differences. The first difference is that the trench  510  of  FIG. 5  can be replaced with an optional opaque structure  610  to further improve isolation. The second difference is that the encoder  600  has a bifurcated body with an emitter side  604 - 1  and a detector side  604 - 2 . The separate encoder body sides  604 - 1  and  604 - 2  optionally can be made of different materials having different refractive indexes I F1 /I F2 , and as mentioned above with respect to  FIG. 5 , θ 1  and θ 2  can vary relative to one another with the understanding that other design criteria, such as the positioning of the emitter  301  and/or detector  302  may vary accordingly. 
   While example embodiments are disclosed herein, one of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claims. The embodiments therefore are not to be restricted except within the scope of the appended claims.