Patent Publication Number: US-2009232419-A1

Title: System for detecting markings

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 61/036,110, filed Mar. 13, 2008, herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to optoelectronic systems, and more particularly to an optoelectronic system for an optical mark reader that recognizes or detects marks, such as “bubbles” filled in on examination answer sheets. 
     BACKGROUND OF THE INVENTION 
     Automated inspection and tallying of man-made markings has widespread applications. For example, in multiple-choice tests, each test taker may be instructed to indicate his or her answer to each question by darkening a delineated area, commonly called a “bubble,” among a row of bubbles on a printed medium known as an answer sheet or card. A bubble sheet or card typically bears multiple rows of bubbles for multiple questions, with the bubbles also forming columns. After a test is completed, the answer sheets or cards are then fed through an optical mark reader (OMR), which optoelectronically detects the location of the darkened bubble in each row, thereby determining the answer that the test taker chose. Similar techniques can also be used for other applications and contexts including, for example, conducting polls and elections. 
       FIG. 1  illustrates an exploded view of one OMR, which is known in the art and described in U.S. Pat. No. 7,068,861 to Swanson et al. issued on Jun. 27, 2006. As shown in  FIG. 1 , the OMR  100  includes a top portion  110  that can be coupled to a base  150 . When the top portion  110  and base  150  are coupled together, a slot is defined therebetween to allow insertion and passage of a scan card or sheet through the OMR  100  for detecting the markings made thereon. 
     The top portion includes a top cover  112  and bottom cover  120 . They can be coupled together via the tabs  126  to house various internal components including a circuit board  114 , a stepper motor  118  and a computer interface cable  116 . The circuit board  114  has mounted thereon an optoelectric system including an array of light-emitting and light-sensing elements  130   a - j . This array  130   a - j  is shown as being mounted to the circuit board  114 , but any number of optoelectric elements can be used to suit particular applications (e.g., relative to the number of bubbles across an answer card or sheet). The circuit board  114  also has mounted thereon connectors for detachably connecting the computer interface cable  116  and stepper motor  118 , respectively, to the board  114 . When the top portion  110  is assembled, the motor  118  is positioned in a cradle  122  formed in the bottom cover  120  such that a driver roller  156  protrudes through a slot  158  formed on the bottom cover  120 . The circuit board  114  is positioned such that the array of optoelectric elements  130   a - j  is directly over a window  124  in the bottom cover  120  for reading scan card or sheet passed under the window  124 . A transparent window cover (e.g., made of scratch resistant material) can be mounted in or otherwise coupled with the window  124  to protect the optoelectric elements. 
     When the top portion  110  and base  150  are coupled together, a spring-loaded guide roller  154  is biased against the driver roller  156 . When a scan card or sheet is placed between the driver roller  156  and guide roller  154  and the motor  118  is energized, the motor  118  drives the driver roller  156  and guide roller  154  to move the scan card or sheet along a guide  152  formed in the base  150 . The different rows of bubbles are thus positioned to be read under the optoelectric elements  130   a - j . Each of the optoelectric elements  130   a - j  includes a light-emitting portion and a light-detecting portion. The optoelectronic elements  130   a - j  may be, for example, the EE-SY169 photo sensor package available from Omron Electronics, Schaumburg, Ill. This photo sensor package includes a red light-emitting diode (LED) that illuminates an area of the card, and a phototransistor that detects light emitted from the LED and reflected off the card or sheet. If the illuminated area is unmarked, the phototransistor outputs an unmarked voltage value (i.e., a voltage value indicative of an unmarked area) to a controller. Alternatively, if the phototransistor detects a blackened or partially marked area, the output voltage from the phototransistor will indicate how much light is being reflected back depending on how dark the mark is. 
     Although the foregoing-described optoelectric elements have operated sufficiently well for OMRs, a new optoelectronic system would be an important improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exploded view of a conventional OMR; 
         FIG. 2  illustrates a perspective view of an embodiment of a system for detecting markings according to an aspect of the present invention; 
         FIG. 3  illustrates a partially exploded view of an example optical subsystem of the optoelectronic system of  FIG. 2 ; 
         FIG. 4  illustrates a cross-sectional view of the optical subsystem along the 3-3 plane labeled in  FIG. 2  in accordance with an aspect of the present invention; 
         FIG. 5  illustrates an example block diagram for an embodiment of an optoelectronic system of an OMR; and 
         FIG. 6  illustrates an example schematic showing details of an embodiment of a light-detecting circuit of an optoelectronic system of an OMR. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the Figures, an example optoelectronic system for an OMR is described. As shown in  FIG. 2 , the optoelectronic system  200  is configured to detect markings on a printed medium PM, particularly markings in bubbles that are provided on the printed medium PM. The illustrated embodiment of the optoelectronic system  200  is shown as including a circuit board  202  with a plurality of components thereon. But the present optoelectronic system need not include the circuit board  202 . Indeed, it should be appreciated that the present optoelectronic system provides improved optical and electronic subsystems that may retrofit, replace, etc., the optoelectronic elements  130   a - j  known in the prior art, including the control and detection circuitry thereof. The optoelectronic system  200  includes an optical subsystem  220  and an electronic subsystem  240  including circuitry, which may be embodied by, for example, wiring and electrical/electronic components on the circuit board  202 , for controlling operation of and detecting marks read by the optical subsystem  220 . 
     As shown in  FIG. 3 , the optical subsystem  220  includes a light-emitting part  222 , a light-detecting part  224  and a shroud  228 . The light-emitting part  222  includes ten light-emitting elements  222   a - j  as shown, however the light-emitting part  222  may include fewer or additional light-emitting elements. The light-emitting elements  222   a - j  are light emitting diodes (LEDs), for example surface-mount LEDs as shown to facilitate manufacture of the system  200 . The light-detecting part  224  includes ten light-detecting elements  224   a - j  as shown, however the light-detecting part  224  may include fewer or additional light-detecting elements. The light-detecting elements  224   a - j  are optical to electrical conversion elements such as photo-sensitive diodes or transistors, for example surface-mount elements as shown to facilitate manufacture of the system  200 . The light-emitting elements  222   a - j  and the light-detecting elements  224   a - j  are configured in a one to one relationship to define emitting/detecting pairs so that light emitted by one light-emitting element is reflected from the printed medium PM ( FIG. 2 ) and received by one light-detecting element. A first emitting/detecting pair is indicated by reference number  226   a  and the dashed line surrounding light-emitting element  222   a  and light-detecting element  224   a . Although only one pair  226   a  is indicated for clarity, further pairs may be defined by the other emitting and detecting elements  222   b  and  224   b ,  222   c  and  224   c , etc. 
     The shroud  228  is configured for housing the light-emitting and light-detecting parts  222 ,  224  and for separating the elements  222   a - j ,  224   a - j  to help define and optically isolate the emitting/detecting pairs. As will be explained hereinafter, the shroud  228  provides a monolithic waveguide that optically couples the light-detecting element and the light-emitting element of each emitting/detecting pair (e.g., pair  226 A). The shroud  228  may be made of various materials known in the art such as metal including aluminum, opaque plastic, etc. Furthermore, the shroud  228  may be formed by various methods known in the art including machining, casting, molding (e.g., injection molding), etc. Referring now to  FIGS. 3 and 4 , the shroud  228  is illustrated as including a generally rectangular parallelepiped-shaped body with a first surface  2280 , a second surface  2290 , and a plurality of apertures extending between the first and second surfaces  2280 ,  2290 . As can be appreciated from  FIG. 3 , the first surface  2280  may be referred to hereinafter as the top surface or reader surface for sake of convenience of explanation because of its proximity to the printed medium PM when detecting the markings thereon. Furthermore, the second surface  2290  may be referred to hereinafter as the bottom surface or board-contacting surface for sake of convenience of explanation because of its proximity to the circuit board  202  ( FIG. 4 ) when the optical subsystem  220  is coupled with the electrical subsystem  240  via the board  202 . 
     As shown in  FIG. 3  the plurality of apertures is defined by first apertures  226   a - j  and second apertures  228   a - j . The first apertures  226   a - j  are generally round cylindrical apertures in the top surface  2280  that extend a predetermined distance from the top surface  2280  toward the bottom surface  2290 . As shown in  FIG. 4 , each of the first apertures (first aperture  226   a  is shown in  FIG. 4 ) is in communication with a first recess ( 232   a  in  FIG. 4 ) formed in the bottom surface  2290 . The first recess  232   a  is generally square-shaped with the first aperture  226   a  being at approximate centers of the first recesses  232   a . The first aperture  226   a  extends between the recessed surfaces R 1  of the first recess  232   a  and the top surface  2280 . The recessed surface R 1  may be configured approximately halfway through the thickness of the shroud  228  such that the first apertures  226   a - j  also extend approximately halfway through the thickness of the shroud  228 . Light emitted by the light-emitting elements  222   a - j , which are configured in the first recesses  232   a - j , propagates through the first apertures  226   a - j  to illuminate bubble portions of the printed medium PM proximate the top surface  2280 . 
     The second apertures  228   a - j  are generally rectangular-shaped apertures that include ledges or lands L therein when viewed from the top side  2280 . The cross-section of  FIG. 4  shows only the first pair of recesses  232   a  and  234   a , but the configuration of each successive pair is substantially similar. The second aperture  228   a  is in communication with a second recess  234   a  formed in the bottom surface  2290 . As shown, the second recesses  234   a - j  are generally rectangular-shaped with the second apertures  228   a - j  being laterally offset toward the first apertures  226   a - j  relative to the centers of the second recesses  232   a - j . The second apertures  228   a - j  extend between the recessed surfaces R 2  of the second recesses  234   a - j  and the top surface  2280 . The recessed surfaces R 2  may be configured approximately halfway through the thickness of the shroud  228  such that the second apertures  228   a - j  also extend approximately halfway through the thickness of the shroud  228 . As shown in  FIG. 4 , the second apertures (one second aperture  2286  being shown in cross-section) are generally defined by laterally offset, partially overlapping recesses, namely second recess  234   a , which has a recessed surface corresponding to lands or ledges L. As such, the second apertures  228   a - j  extend between lands or ledges L and recessed surfaces R 2  of second recesses  234   a - j.    
     As shown in  FIG. 4 , the light-emitting elements  222   a - j  are configured in the first recesses  232   a - j  (one first recess  232   a  being shown) so that light emitted by the light-emitting elements  222   a - j  propagates through the first apertures  226   a - j  (one first aperture  226   a  being shown) and illuminates bubbles on the printed medium, which translates along the reading plane RP. As further shown in  FIG. 4 , the light-detecting elements  224   a - j  (one element  224   a  being shown in  FIG. 8 ) are configured in the second recesses  234   a - j  (one second recess  234   a  being shown) so that light reflected from the printed medium proximate to the reading plane RP propagates to the light-detecting elements  224   a - j  angularly through the second apertures  228   a - j  (one second aperture  2286  being shown), which are defined by second recesses  234   a - j  (one second recess  234   a  being shown). In view of the foregoing, it can be appreciated that the first apertures  226   a - j  are generally aligned with the second apertures  228   a - j  (and vice versa). That is, centers of the generally round cylindrical-shaped first apertures  226   a - j  are configured on lengthwise axes extending laterally through centers of the generally rectangular-shaped second apertures  228   a - j.    
     In this way the shroud  228  provides a monolithic waveguide for: 1) ensuring that light emitted from the light-emitting elements  222   a - j  is guided to the printed medium PM on the reading plane RP; 2) ensuring that light reflected from the printed medium PM on the reading plane RP is guided to the light-detecting elements  224   a - j ; and 3) optically isolating the emitting/detecting pairs from each other. Although various dimensional and angular values are shown on  FIG. 4 , these values are to be understood as providing one example configuration for the illustrated embodiment of the optical subsystem  220 . Indeed, it should be understood that the values and configuration may be changed in various ways for various reasons including, for example, adapting the optical subsystem  220  to a motor (e.g., motor  118 ,  FIG. 1 ) having a faster or slower steady-state printed medium-feeding speed, adapting the optical subsystem  220  to a user-specific or application-specific printed medium bearing custom-configured or differently-configured indicia such as, for example, differently spaced-apart bubbles, etc. 
     Turning now to  FIGS. 5 and 6 , the electronic subsystem  240 , which controls operation of the optical subsystem  220  and which detects marks read by the optical subsystem  220 , will be described. As shown in  FIG. 5 , the electronic subsystem  240  is connected with the motor  118 , a power supply  222  and the optical subsystem  220 . Although the electronic subsystem  240  is shown being connected to the power supply  222 , alternatively the electronic subsystem  240  (and the optical subsystem  220 ) may be powered via the interface  116  (e.g., a USB interface that provides power and data transceiving). Furthermore, although the optical subsystem  220  is shown in  FIG. 5  as being separate or distinct from the electronic subsystem  240  and connected thereto, alternatively, the subsystems  220 ,  240  may be combined, integral, unitary or the like (e.g., mounted to the same board  202  as shown in  FIG. 2 ). The subsystem  240  includes a controller  242  such as a microprocessor or microcontroller as shown. The controller  242  is in communication with a digital-to-analog converter (DAC) module  244 , a gain module  246 , a communications module  248  and a motor drive module  250 . The controller is in communication with the motor drive module  250  (e.g., motor drive darlington array as shown) to operate the motor  118  (e.g., controlling turning on, turning off, shaft speed, etc.) via the motor interface  117  (e.g., stepper motor connector as shown). The controller  242  is in communication with the communications module  248  (e.g., USB controller as shown) to transceiver data, signals, etc. with an external device such as a PC via the communications interface  116  (e.g., USB connector as shown). For example, communications module  248  may enable the controller  242  to output data to a PC relative to markings that were detected on a score sheet or card so that the data can be stored, compared with an answer key or otherwise analyzed, etc. Similarly, the communication module  248  may enable a user to test, troubleshoot, run diagnostics, calibrate, etc. the OMR and various components thereof such as the optical subsystem  220 . 
     The DAC module  244  as shown is in communication with an LED drive module  252 . The DAC module  244  and the LED drive module  252  (which in some embodiments may be combined as a DAC/LED drive module) cooperate to provide a power source and driver for the light-emitting elements  242 A-J ( FIG. 4 ) of the optical subsystem  220 . The DAC and LED drive modules  244 ,  252  cooperate to apply variable voltages or currents to the light-emitting elements  222   a - j  according to a control signal output from the controller  242 . The controller  242  is additionally in communication with the light-detecting elements  224   a - j  of the optical subsystem  220  via the gain module  246 . The gain module  246  receives voltages that are output from the light-detecting elements  224   a - j , processes (e.g., amplifies and/or filters) the voltages, and outputs the processed voltages to the controller  242 . In some embodiments the gain module  246  may include a gain/spread circuit to achieve higher resolution for the controller&#39;s analog to digital converter (ADC). 
     Although not shown in  FIG. 5 , the controller  242  may also be in communication with a memory module such as an electrically erasable programmable read-only memory (EEPROM) module. The memory module may be used to store executable instructions (e.g., firmware) for operating various functions of the OMR such as, for example, the optical subsystem  220  or the motor  118 , calibration data and other data known in the art. The memory module may also be in communication with the DAC module  244  and the communications module  248 . 
       FIG. 6  illustrates an example schematic diagram showing an embodiment of a circuit for two channels (i.e., two emitting/detecting pairs) of the optical subsystem  220  and two channels of a gain module  246  ( FIG. 4 ) with a gain/spread circuit. As shown in  FIG. 6 , a first channel  260  includes a light-emitting element  262  (an LED D 11  as shown), a light-detecting element  264  (a light-to-voltage converter integrated circuit package U 20  as shown), and an amplifying circuit  266 . The amplifying circuit  266  includes op-amp U 22 -B and various passive components for voltage division, RC filtering etc. of the voltage output from light-detecting element  264 . Similarly, a second channel  270  includes a light-emitting element  272  (an LED D 12  as shown), a light-detecting element  274  (a light-to-voltage converter integrated circuit package U 21  as shown), and an amplifying circuit  276 . The amplifying circuit  276 , which as shown is substantially similar to amplifying circuit  266 , includes op-amp U 22 -D and various passive components for voltage division, RC filtering etc. of the voltage output from light-detecting element  274 . Furthermore as shown in  FIG. 6 , a gain/spread circuit  280  couples the amplifying circuits  266 ,  276 . Although component values and part numbers of various elements of the circuit are shown in  FIG. 6 , it should be appreciated that the values and part numbers are provided as examples and are not to be taken as limiting the present system and method to any specific component values, elements or interconnections thereof. Indeed, the circuit is flexible so that it may be adapted, changed, and/or configured with various different component values and elements for various reasons including, for example changing performance characteristics, etc. 
     In view of the foregoing it can be appreciated that the electronic subsystem  240  is configured to derive, from the signals generated by the light-detecting elements relative to light emitted by the light-emitting elements, signals indicative of the reflectance of the portions of the printed medium so that the OMR can output data regarding marking made in bubbles of the printed medium by test takers, voters and the like. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Various example embodiments of this invention are described herein. It should be understood that the illustrated and described embodiments are exemplary only, and should not be taken as limiting the scope of the invention.