Abstract:
An improved optical encoding apparatus for the detection of position and/or motion of a mechanical device includes a codescale having an alternating pattern of windows and bars, the windows and bars having a substantially equal width, an encoder housing having one or more portions, a light-emitting source embedded within the encoder housing, a light-detecting sensor embedded within the encoder housing, the light-detecting sensor having at least six light-detecting elements, wherein the encoder housing includes one or more optical elements configured to enable light generated by the light-emitting source to project the codescale&#39;s pattern of bars and windows onto the light-detecting sensor, and wherein the width of each light-detecting element is no more than ⅓ the width of the windows and bars projected onto the light-sensing detector.

Description:
BACKGROUND  
       [0001]     The present invention relates to an optical encoding device for the sensing of position and/or motion.  
         [0002]     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, 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  
         [0003]     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.  
         [0004]     While optical encoders have proved to be a reliable technology, there still exists substantial industry pressure to simplify manufacturing operations and decrease costs while improve spatial resolution and other performance issues. Accordingly, new technology related to optical encoders is desirable.  
       SUMMARY  
       [0005]     In a first sense, an optical encoding apparatus for the detection of position and/or motion of a mechanical device includes a codescale having an alternating pattern of windows and bars, the windows and bars having a substantially equal width, an encoder housing having one or more portions, a light-emitting source embedded within the encoder housing, a light-detecting sensor embedded within the encoder housing, the light-detecting sensor having at least six light-detecting elements, wherein the encoder housing includes one or more optical elements configured to enable light generated by the light-emitting source to project the codescale&#39;s pattern of bars and windows onto the light-detecting sensor, and wherein the width of each light-detecting element is no more than ⅓ the width of the windows and bars projected onto the light-sensing detector.  
         [0006]     In a second sense, an optical encoding apparatus for the detection of position and/or motion includes a codescale having an alternating pattern of windows and bars, the windows and bars having a substantially equal width, an encoder housing having one or more portions, a light-emitting source embedded within the encoder housing, a light-sensing means embedded within the encoder housing for use in the detection of codescale travel; and one or more optical elements configured to enable light generated by the light-emitting source to project the codescale&#39;s pattern of bars and windows onto the light-sensing means.  
         [0007]     In a third sense, a method for detecting both a distance and direction traveled for a codescale in an optical encoding apparatus includes projecting a first pattern of windows and bars from the codescale onto a light-sensing detector having at least six light-detection elements, the projected windows and bars each having a first width and the light-detection elements each having a second width, the second width being less than ⅓ the first width, sampling the state of each light-detection element a first time, moving the codescale at least one second width, projecting a second pattern of windows and bars from the codescale onto the light-sensing detector, sampling the state of each light-detection element a second time and determining at least the direction of codescale travel using the sensed states of the first and second samplings.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0008]     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.  
         [0009]      FIG. 1  shows a first reflection-based optical encoder;  
         [0010]      FIG. 2  shows a first conventional optical detector;  
         [0011]      FIG. 3  shows a second conventional optical detector;  
         [0012]      FIG. 4  shows a third conventional optical detector; and  
         [0013]      FIG. 5  shows an improved optical detector for use with the disclosed methods and systems. 
     
    
     DETAILED DESCRIPTION  
       [0014]     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.  
         [0015]     In the following embodiments, the novel systems and apparatus of the present disclosure can improve the spatial resolution of optical encoders over previously known devices. By incorporating detectors that use a high number of detection elements for a given distance as compared to the distance of a window and bar of a respective codescale, spatial resolution can be increased with a minimum of expense.  
         [0016]     Optical encoders are generally classified into two categories: transmission-based optical encoders and reflection-based optical encoders. The following disclosure is generally directed to reflection-based optical encoders. However, it should be appreciated that many of the various system, devices and processes described herein can apply to transmission-based encoders as well.  
         [0017]      FIG. 1  shows a first reflection-based optical encoder  100 . The reflection-based encoder  100  includes an optical emitter  122  and an optical detector  132  mounted on a substrate  110  and encapsulated in an optical housing  120 , which is typically made from some form of resin or glass. The exemplary optical housing  120  has two dome-shaped lenses  124  and  134 , with the first lens  124  directly above the optical emitter  122  and the second lens  134  directly above the optical detector  132 . A codescale  193 , i.e., a codewheel, codestrip or the like, is positioned above the housing  120  on body  190 , which for the present example can be a flat, linearly moving body or spinning disk. A link  140  is provided from the detector  134  to a post processor (not shown) in order that light signals reaching the detector  134  can be properly interpreted.  
         [0018]     In operation, light emitted by the optical emitter  122  can be focused by the first lens  124 , then transmitted to the codescale  193  along the light&#39;s path  150  at location  195 . Should the codescale  193  be positioned such that a reflective slot/bar is present at location  195 , the transmitted light can be reflected to the second lens  134 , then focused by the second lens  134  onto the optical detector  132  where it can be detected. Should the codescale  193  be positioned such that a reflective slot/bar is not present at location  195 , the transmitted light will be effectively blocked, and the optical detector  132  can detect the absence of light. Should the codescale  193  be configured and position such that a combination of reflective and non-reflective bars are simultaneously present at location  195 , the codescale  193  can reflect light commensurate with the pattern of reflective and non-reflective bars such that the pattern is effectively projected onto the optical detector  132 .  
         [0019]     Generally, it should be appreciated that conventional optical encoders use either single-element detectors or detectors having a low number of optical detection elements. By way of example,  FIG. 2  shows such a first conventional detector  234  for use in an optical encoder, such as the encoder  100  of  FIG. 1 . As shown in  FIG. 2 , the optical encoder  234  has a single optical detection element {A} having a width W 1  and being capable of producing two discrete states: 0 and 1. A projected codescale pattern having alternating windows and bars is superimposed over the optical detector  234 . Assuming that the width of the windows W 1  and the bars B 1  is approximately equal, a moving codescale producing the projected codescale pattern can cause the detection element {A} to produce an alternating 1-0-1-0-1-0 output. While the detector  234  of  FIG. 2  can be used to sense a change in codescale position to a resolution of W 1 , the detector  234  cannot be used to sense the direction of codescale travel.  
         [0020]      FIG. 3  shows a second conventional detector  334  that can be used with optical encoders. As shown on  FIG. 3 , the detector  334  has two light-detecting elements {A, /A}. Given the series of windows and bars shown superimposed over the light-sensing elements {A, /A}, the states produced by detection elements {A, /A} can alternate between {1, 0} and {0, 1} for every interval W 1  traveled by the codescale. Although the second detector  334  shares a limitation with the detector  234  of  FIG. 2  in that it cannot be used to detect the direction of codescale travel, the detector  334  has an advantage in that it can provide a differential output and thus improve the signal-to-noise ratio of an optical detection system  
         [0021]     Continuing to  FIG. 4 , a detector  434  is shown that can be used to detect the direction that a codescale travels as well as a distance traveled. This directional sensing advantage can be gained by increasing the number of detection elements to four with each detection element having a width half that of the codescale&#39;s projected bars and windows. As shown in  FIG. 4 , the optical detector  434  has four detection elements {A, B, /A, /B}, which can produce a set of four distinct states: {1, 1, 0, 0} {0, 1, 1, 0} {0, 0, 1, 1} and {1, 0, 0, 1}. Assuming that the detection elements {A, B, /A, /B} each have a width W 2 , (W 2  being half the width of W 1 ), the detector  434  can not only sense the direction of travel for a codescale, but it can sense a distance of codescale travel to a resolution W 2 , which is twice the distance resolution available to that of the previously described detectors  234  and  334  of  FIGS. 2 and 3 .  
         [0022]     Keeping  FIG. 4  in mind, it should be appreciated that a conventional approach to increasing resolution for optical encoders while maintaining direction sensing capacity would be to continue using the four-element architecture while incorporating finer geometries in both detection elements and codescales.  
         [0023]     However, as will be demonstrated below, the inventor of the disclosed methods and systems has devised a different approach to optical encoders where the cost tradeoffs differ substantially from conventional approaches.  
         [0024]      FIG. 5  shows an improved optical detector  534  that can be used with optical encoders, such as the encoder  100  of  FIG. 1 . As shown in  FIG. 5 , the improved optical detector  532  includes eight separate detection elements {A, B, C, D, /A, /B, /C, /D}, which is far more than the four detections element required to sense both distance and direction traveled. The output states for the detection elements {A, B, C, D, /A, /B, /C, /D are: {1,1,1,1,0,0,0,0}, {0,1,1,1,1,0,0,0}, {0,0,1,1,1,1,0,0}, {0,0,0,1,1,1,1,0}, {0,0,0,0,1,1,1,1}, {1,0,0,0,0,1,1,1}, {1,1,0,0,0,0,1,1} and {1,1,1,0,0,0,0,1}. The improved resolution can be attributed at least in part to the width of each detection element W 3 , which is one-fourth the width W 1  of the windows and bars of the previously discussed codescale pattern.  
         [0025]     While the exemplary detector  534  has eight detection elements of width W 3  (=W 1 /4), it should be appreciated the concepts of  FIG. 5  can extend to detectors having other numbers of detection elements. For example, a detector with six detection elements with each element having a width of W 1 /3 can be used. Similarly, a detector with ten detection elements with each element having a width of W 1 /5 also can be used, and so on.  
         [0026]     Returning to  FIG. 5 , while the conventional approach to making a detection device with finer resolution might be a matter of merely shrinking the geometries of the detector  434  of  FIG. 4 , the inventor of the improved optical detector  134  has created a device that can provide finer spatial resolution using relatively coarser resolution codescale. Accordingly, any expenses incurred due to the increased number of detection elements can be offset by: (1) a manufacturing advantage in that existing codescales can be used, (2) a manufacturing advantage in that retooling a production line to produce different codescales might be avoided and (3) that new manufacturing problems arising due to the finer resolution issues will not be incurred. For example, a codewheel for a transmission-type optical encoder can avoid the various manufacturing flaws that might arise by doubling the number of windows and bars using conventional approaches.  
         [0027]     Again returning to  FIG. 5 , while the exemplary detector  134  of  FIG. 5  can detect discrete 0/1 states for each detector, it should be appreciated that further resolution might be gained from the present detector  534  by taking advantage of the analog (and presumably linear or somewhat linear) transfer function of the individual detection elements {A, B, C, D, /A, /B, /C or /D}. That is, by sampling each detection element output using an analog-to-digital converter and then applying optionally some linearization algorithm to the digitized data, distance resolution can be extended to a distance substantially less that W 3 .  
         [0028]     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.