Abstract:
This invention relates to an apparatus for determining a media feature, comprising: a plurality of light filters such that the filters include a media measurement aperture and a calibration aperture and wherein the filters are spaced a predetermined distance apart to allow media to be introduced between the filters; a light source located substantially adjacent to one of the filters; and a light detector located substantially adjacent to another of the filters.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an apparatus for determining a media feature, comprising: a plurality of light filters such that the filters include a media measurement aperture and a calibration aperture and wherein the filters are spaced a predetermined distance apart to allow media to be introduced between the filters; a light source located substantially adjacent to one of the filters; and a light detector located substantially adjacent to another of the filters. 
   2. Description of the Related Art 
   Prior to the present invention, as set forth in general terms above and more specifically below, it is known, that image forming devices are capable of printing images on media sheets of varying widths. Printing beyond the edges of a media sheet can cause a number of problems. It wastes imaging material such as ink and/or toner. The wasted imaging material can damage or decrease the life span of the image forming device. Also, the wasted imaging material can be inadvertently transferred to another media sheet thereby degrading print quality. 
   It is also known, that sensors can be employed to detect a variety of media and media defects. Such sensors include sensors attached to moving carriages that scan across the media and fixed/stationary sensors. While these sensors are capable of detecting a variety of media and media defects, these sensors either require time to move which results in coordination complexity and loss of throughput (time lost while moving the sensor) or relatively small sensors that are expensive and may not provide enough resolution. Finally, none of these sensors detect media features, such as tabs and are self-calibrating. 
   It is apparent from the above that there exists a need in the art for a media sensing device which is capable of detecting media, media defects, and media features, such as tabs, but which at the same time is self-calibrating. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure. 
   SUMMARY OF THE INVENTION 
   Generally speaking, an embodiment of this invention fulfills these needs by providing an apparatus for determining a media feature, comprising: a plurality of light filters such that the filters include a media measurement aperture and a calibration aperture and wherein the filters are spaced a predetermined distance apart to allow media to be introduced between the filters; a light source located substantially adjacent to one of the filters; and a light detector located substantially adjacent to another of the filters. 
   In certain preferred embodiments, the media measurement aperture and calibration aperture of each of the filters are in alignment with each other. Also, the light source is comprised of a uniform light source, such as an electroluminescent panel. Finally, the light detector is comprised of a photovoltaic cell. 
   In another further preferred embodiment, the apparatus for determining a media feature is capable of detecting media, media defects, and media features, such as tabs, but which at the same time is self-calibrating. 
   The preferred apparatus for determining a media feature, according to various embodiments of the present invention, offers the following advantages: ease-of-use; ease of detecting media; ease of detecting media defects; and ease of detecting media features. In fact, in many of the preferred embodiments, these factors of ease of detecting media, ease of detecting media defects, and ease of detecting media features are optimized to an extent that is considerably higher than heretofore achieved in prior, known apparatus for determining media features. 
   The above and other features of the present invention, which will become more apparent as the description proceeds, are best understood by considering the following detailed description in conjunction with the accompanying drawings, wherein like characters represent like parts throughout the several views and in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an exemplary image forming device in which various embodiments of the present invention may be implemented; 
       FIG. 2  is a schematic illustration of an apparatus for determining a media feature, according to one embodiment; 
       FIG. 3  is an exemplary block diagram illustrating the logical program elements for implementing various embodiments of the present invention; 
       FIG. 4  is an exemplary two-dimensional graph charting voltage level change as a media sheet with no holes passes a sensor, according to an embodiment of the present invention; 
       FIG. 5  is an exemplary chart illustrating how detected voltage level can vary based on media width, according to an embodiment of the present invention; 
       FIG. 6  is an exemplary flow diagram illustrating steps taken to identify a media width, according to an embodiment of the present invention; 
       FIG. 7  is an exemplary two-dimensional graph charting voltage level as a media sheet with three holes passes a sensor, according to an embodiment of the present invention; 
       FIG. 8  is an exemplary two dimensional graph charting a change in voltage level caused by a hole, according to an embodiment of the present invention; 
       FIG. 9  is an exemplary flow diagram illustrating steps taken to identify a hole, according to an embodiment of the present invention; 
       FIG. 10  is an exemplary flow diagram illustrating steps taken to determine if a change in voltage level data represents a hole, according to an embodiment of the present invention; 
       FIG. 11  illustrates an exemplary media sheet having variously placed and sized holes; 
       FIG. 12  is an exemplary two dimensional graph charting a change in voltage level caused by variously placed and sized holes as the media sheet of  FIG. 11  passes between the apparatus of  FIG. 2 , according to an embodiment of the present invention; 
       FIG. 13  is an exemplary flow diagram illustrating steps taken to locate a hole, according to an embodiment of the present invention; 
       FIG. 14  is an exemplary flow diagram illustrating steps taken to identify a location and size of a hole based on a change in voltage level caused by that hole, according to an embodiment of the present invention; 
       FIG. 15  illustrates an exemplary media sheet having variously placed and sized tabs; 
       FIG. 16  is an exemplary two dimensional graph charting a change in voltage level caused by variously placed and sized tabs as the media sheet of  FIG. 15  passes between the apparatus of  FIG. 2 , according to an embodiment of the present invention; 
       FIG. 17  is an exemplary flow diagram illustrating steps taken to locate a tab, according to an embodiment of the present invention; and 
       FIG. 18  is an exemplary flow diagram illustrating steps taken to identify a location and size of a tab based on a change in voltage level caused by that tab, according to an embodiment of the present invention 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   INTRODUCTION: A given image forming device can be capable of printing on media having varying features. Examples of features include width as well as the presence and location of holes and tabs, and defects such as tears. To extend the life of the device, help reduce waste of imaging material such a toner or ink, and to help achieve a desired level of print quality, the image forming device may be made aware of the features of the media on which it is about to print. Various embodiments function to identify the width and other features of a sheet of print media. 
   The following description is broken into sections. The first section, labeled “components,” describes an example of the physical and logical components of an image forming device in which various embodiments of the invention may be implemented. The second section, labeled “Media Width” describes an exemplary series of method steps and examples for detecting the width of a sheet of print media. The third section, labeled “Identifying Holes” describes an exemplary series of method steps and examples for detecting the presence of a hole in a sheet of print media. The fourth section, labeled “Locating Holes,” describes an exemplary series of method steps and examples for identifying the location and size of a hole in a sheet of print media. The fifth section, labeled “Locating Tabs,” describes an exemplary series of method steps and examples for identifying the location and size of media tabs. 
   COMPONENTS:  FIG. 1  illustrates an exemplary image forming device  10  in which various embodiments of the present invention may be implemented. Image forming device  10  represents generally any device capable of forming an image on a sheet of paper or other print media. Image forming device  10  includes print engine  12 , sensor  50 , media drive  16 , media path  18 , device memory  20 , and processor  22 . 
   Print engine  12  represents generally the hardware components capable of forming an image on print media. Where, for example, image forming device  10  is a laser printer, print engine  12  may include a laser, a fuser, and a toner cartridge housing a toner reservoir, a photoconductive drum, a charging device, and a developer. In operation, the charging device places a uniform electrostatic charge on a photoconductive drum. Light from the laser is scanned across the photoconductive drum in a pattern of a desired print image. Where exposed to the light, the photoconductive drum is discharged creating an electrostatic version of the desired print image. The developer transfers charged toner particles from the toner reservoir to the photoconductive drum. The charged toner particles are repelled by the charged portions of the photoconductive drum but adhere to the discharged portions. The charge roller charges or discharges the print media sheet. As the media sheet passes across the photoconductive drum, toner particles are then transferred from the photoconductive drum to the media sheet. The fuser thermally fixes the transferred toner particles to the media sheet. 
   Where, for example, image forming device  10  is an ink printer, print engine  12  might include a carriage and an ink cartridge housing an ink reservoir and one or more print heads. In operation, the print heads selectively eject ink from the ink reservoir onto a media sheet, according to a desired print image. The carriage selectively moves and positions the print head relative to a media sheet such that the ejected ink forms the desired print image. 
   Sensor  50 , described in more detail below with reference  FIG. 2 , represents hardware components capable of being used to identify one or more print media features by detecting the change in voltage level resulting from a change in light detected by the photovoltaic cell as the media passes through sensor  50 . Media drive  16  represents the hardware components capable of urging print media along media path  18 . Media path  18  represents generally the path along which print media flow through image forming device  10  during a printing operation. 
   Device memory  20  represents generally any computer readable medium or media capable of storing programs and data for controlling the operation of print engine  12 , sensor  50 , and media drive  16 . Examples of programs stored by device memory  20  are described below with reference to  FIG. 3 . Processor  22  represents generally any processor capable of executing programs contained in device memory  20 . 
   As shown, media drive  16  includes pick roller  16 A and pinch rollers  16 B. Pick roller  16 A is responsible for selectively feeding print media from media source  24  into media path  18 . Pinch rollers  16 B are responsible for urging print media along media path  18  past sensor  50  and print engine  12 . As shown, sensor  50  is located upstream from print engine  12  along media path  18 . In this manner sensor  50  can be used to identify a print media feature and then the operation of print engine  12  can be directed, according to the identified feature. For example, where the feature is a width of the print media, print engine  12  can be directed not to print beyond the edges of the print media. 
   With respect to  FIG. 2 ,  FIG. 2  illustrates sensor  50 . Sensor  50  includes, in part, uniform light source  52 , conventional AC power source  54 , a plurality of light filters  56 ,  58 , a calibration aperture  60  located in each of the light filters  56 ,  58 , a media measurement aperture  62  located in each of the light filters  56 ,  58 , a light detector  61  which detects a sensed DC voltage  66 , and a media  68 . Preferably, the uniform light source  52  includes, but is not limited to, an electroluminescent panel. Also, the light detector  61  includes, but is not limited to, a photovoltaic cell. Detector  61  is used to measure the change in light brightness and creates a change in the emitted voltage level as the light brightness changes. 
   As shown in  FIG. 2 , light source  52  is located opposite light detector  61 . As different sizes of media  68  pass (in the direction of arrow B) between light filters  56  and  58 , different amounts of light arrive at light detector  61  (along the directions of arrows A) thereby creating a corresponding and proportional DC voltage. It is to be understood that larger media  68  will block more light and produce a lesser DC voltage than smaller media  68 . 
   Filters  56  and  58  with matching apertures  60  and  62  are used to calibrate and measure the media  68  as media  68  passes between filters  56  and  58 . Calibration aperture  60  is located in the media path so that it is always blocked by media  68  (before media  68  arrives at measurement aperture  62 ) regardless of the dimensions of media  68 . This allows sensor  50  to measure the translucence of the media and use it with the measurement aperture  62 . The leading edge of the media  68  first passes across the calibration aperture  60  and a translucence factor is computed based on the voltage measured at that moment and the known size of the calibration aperture  60 . Next, as the leading edge of media  68  passes through measurement aperture  62  (different sizes of media will block more or less of the measurement aperture  62 ), the actual size of the media  68  is computed based on the voltage measured and the previously computed calibration factor. Precise positioning control of media  68 , as it is transported through sensor  50 , allows for straightforward sampling times to measure the DC voltage by light detector  61 . It is to be understood that multiple configurations are possible. For example, some printing devices will justify the media to one side, thereby requiring only one sensor  50 . For center justified media, two sensors  50  would likely be needed to simultaneously observe both edges of the media  68 . 
   Turning now to  FIG. 3 , device memory  20  includes printing logic  100 , sensor logic  102 , evaluation logic  104 , and LUT (Look Up Table)  106 . Printing logic  100  represents generally any program or programs capable of directing media drive  16  ( FIG. 1 ) to urge a print media sheet along paper path  18  past print engine  12  as well as any program or programs capable of directing print engine  12  to form or to not form a desired image on the print media. 
   Sensor logic  102  represents generally any program or programs capable of collecting voltage level change data from sensor  50  ( FIG. 1 ). At discrete points in time, sensor  50  generates a signal corresponding to a measured change in voltage level. The value of the signal at each point in time is referred to as voltage level data. Also, a series of such values obtained over a time period is also referred to as voltage level change data. 
   Evaluation logic  104  represents generally any program or programs capable of analyzing voltage level change data to identify a print media feature. Examples of such features include print media width, the presence of a hole, the size and location of a hole, and media extensions, such as tabs. When performing its function, evaluation logic  104  may access and use data contained in LUT  106 . For example, evaluation logic  104  may access an entry in LUT  106  that corresponds to voltage level change data collected by sensor logic  102 . That entry might then contain data identifying a print media feature or data to be used to calculate the print media feature. 
   MEDIA WIDTH:  FIG. 4-6  helps illustrate a method for identifying a media width based on a change in voltage level measured by sensor  50  ( FIG. 1 ).  FIG. 4  is a two-dimensional graph  140  illustrating a measured voltage level as a media sheet passes through sensor  50 . Initially, the measured voltage level is at a relatively high value  142 . When a leading edge of the media sheet enters calibration aperture  60 , the measured voltage level drops to a lower value  144 . When the leading edge enters measurement aperture  62 , the measured voltage level drops to a relatively low value  146 . When the trailing edge of media enters the calibration aperture  60 , the measured voltage level rises to a higher value  148 . Once the trailing edge enters the measurement aperture  62 , the measured voltage level returns to a relatively high value  149 . The width of the print media can be calculated as a function of the measured voltage level change. The presence of relatively low level  146  indicates a media width of a discernable value. 
   Media width sensor chart  150  of  FIG. 5  helps illustrate how detected light intensity can vary based on media width. LUT  106  ( FIG. 3 ) may include ten entries identifying different media widths A-J. Each entry can be identified by data corresponding to a different voltage level value. For example, the entry identifying media width (A) can be identified by data corresponding to voltage level change value (a) and so on. When voltage level data collected by sensor logic  102  indicates a change in measured voltage level from a relatively high value to a relatively low value, the voltage level data corresponding to that relatively low value can be used by evaluation logic  104  to access an entry in LUT  106  that identifies a media width. 
     FIG. 6  is an exemplary flow diagram illustrating method steps for identifying print media width. Light is directed toward a media path (step  160 ). The light beam is directed from a first side of the media path such that the beam spans at least a portion of a width of a media path. The light is filtered prior to converging on a light detector (step  161 ). Voltage change data is collected from the light detector (step  162 ). The voltage change data collected corresponds to a voltage change measured from a second side of the media path opposite the first side as print media is urged along the media path. The voltage change data is analyzed to identify a width of the print media (step  164 ). 
   IDENTIFYING HOLES:  FIG. 7-10  help illustrate a method for identifying holes in print media based on collected voltage change data.  FIG. 7  is a two-dimensional graph  170  illustrating a measured voltage level as a media sheet with three holes passes through sensor  50  ( FIG. 1 ). Initially, the measured voltage level is at a relatively high value  171 . When a leading edge of the media sheet enters the calibration aperture  60 , the measured voltage level drops to a lower value  175 . When a leading edge of a media sheet enters measurement aperture  62 , the measured voltage level drops to a relatively low value  172 . Voltage changes  173  correspond to the three holes. As a segment of the media sheet with a hole enters, passes through, and then exits sensor  50 , the measured voltage increases and then decreases back to the relatively low value  172 . When the trailing edge of media enters the calibration aperture  60 , the measured voltage level rises to a higher value  176 . Once the trailing edge exits calibration sensor  62 , the measured intensity returns to a relatively high value  174 . 
   The existence of a hole can be identified by noting a first change in voltage from the relatively high value  171  to the relatively low value  172  and then a second change in which the measured voltage increases to a value less than the relatively high value and returns to the relatively low value. Analyzing the second change can reveal whether or not the second change resulted from a hole rather than a tear or other defect. Voltage change graph  180  of  FIG. 8  helps illustrate. 
   Graph  180  charts a change in measured voltage resulting from a hole. Chart  180  includes a series of segments  182  each corresponding to a measured voltage at a given point in time. A curve  184  is defined by a series of points representative of the voltage change indicated by each segment  182  as a function of time. Curve  184  has a magnitude and a duration, as indicated in  FIG. 8 . The indicated duration is the duration for which the voltage change is equal to or greater than fifty percent of the magnitude. A suspected diameter can be determined based on the magnitude—a particular magnitude indicates a corresponding diameter. Using the velocity at which the print media travels through sensor  50  ( FIG. 1 ), a width corresponding to the indicated duration can be calculated. The cause of the voltage change represented by curve  184  can then be confirmed to be a hole if that width equals approximately eighty-six percent of the suspected diameter. 
     FIG. 9  is an exemplary flow diagram illustrating method steps for identifying a hole. Light beam is directed toward a media path (step  190 ). The light beam is directed from a first side of the media path such that the beam spans at least a portion of a width of a media path. The light is filtered and then impinges upon a light detector (step  191 ). Voltage change data is collected from the light detector (step  192 ). The voltage change data collected corresponds to a voltage change measured from a second side of the media path opposite the first side as print media is urged along the media path. The voltage change data is analyzed to identify the presence of a hole (step  193 ). 
     FIG. 10  is an exemplary flow diagram expanding on step  193 . A first change in voltage data collected is noted (step  200 ). The first change, for example, may be a change from a relatively high value to a relatively low value indicating that the leading edge of a media sheet has been detected. A second change in the collected voltage data is then noted (step  202 ). The second, change, for example, may be an increase from the relatively low value to a value less than the relatively high value. The magnitude of the second change and a duration for which the second change is equal to or greater than fifty percent of the magnitude measured (step  204 ). A suspected diameter corresponding to the magnitude and a width corresponding to the duration are ascertained (step  206 ). The suspected diameter and the width are compared to determine if the second change was caused by a hole (step  208 ). Where the width is approximately equal to eight-six percent of the suspected diameter, it can be presumed that the second change was caused by a hole. 
   LOCATING HOLES:  FIG. 11-14  help illustrate a method for locating holes in print media based on collected voltage change data.  FIG. 11  illustrates media sheet  210  having variously sized and located holes  212 - 216 . Hole  212  has a diameter D 1 . Hole  214  has a diameter D 2 , and hole  216  has a diameter D 3 . Measured from its center, hole  212  has a side edge distance D 4  (distance from side edge  219 ) and is located a distance D 5  from leading edge  219 . Hole  214  has a side edge distance D 6  and is located a distance D 7  from leading edge  219 . Hole  216  has a side edge distance D 8  and is located a distance D 9  from leading edge  219 . 
     FIG. 12  is a two-dimensional graph  220  illustrating a measured voltage level as a media sheet  210  ( FIG. 11 ) with three variously sized and located holes passes through sensor  50  ( FIG. 1 ). Initially, the measured voltage level is at a relatively high value  221 . When a leading edge of the media sheet enters the calibration aperture  60 , the measured voltage level drops to a lower value  222 . When a leading edge of a media sheet  94  enters measurement aperture  62 , the measured intensity level drops to a relatively low value  223 . Voltage level change  224  corresponds to hole  212  ( FIG. 11 ). Voltage level change  225  corresponds to hole  214  ( FIG. 11 ), and voltage level change  226  corresponds to hole  216  ( FIG. 11 ). When the trailing edge of the media  210  enters the calibration aperture  60 , the measured voltage level rises to a higher value  227 . Once the trailing edge exits sensor  50  ( FIG. 1 ), the measured intensity returns to a relatively high value  228 . 
   Focusing on  FIG. 12 , voltage level change  224  has dimensions D 4 ′, D 1 ′ and D 5 ′. D 4 ′ corresponds to fifty percent of its magnitude. D 1 ′ corresponds to its width at the fifty-percent magnitude level. D 5 ′ corresponds to the time between when the leading edge of the media sheet entered measurement aperture  62  and when voltage level change  224  reached its peak magnitude. 
   Referring back to  FIG. 11 , side edge distance D 4  can be calculated as a function of D 4 ′ ( FIG. 12 ). The two will vary by a linear factor that depends primarily on the known size of calibration filter  60  ( FIG. 1 ) and the measured change in voltage level. 
   Where the velocity of media sheet  94  is known, D 1 ′ and D 5 ′ can be converted to linear distances D 1 ″ and D 5 ″. Referring to  FIG. 11 , hole diameter D 1  can be calculated as a function of D 1 ″. D 1 ″ equals approximately eighty-six percent of D 1 . Leading edge distance D 5  then equals D 5 ″. 
   Focusing again on  FIG. 12 , intensity change  114  has dimensions D 2 ′, D 6 ′ and D 7 ′. D 6 ′ corresponds to fifty percent of its magnitude. D 2 ′ corresponds to its width at the fifty-percent magnitude level. D 7 ′ corresponds to the time between when the leading edge of the media sheet entered sensor  14 ′ and when intensity change  114  reached its peak magnitude. 
   Referring back to  FIG. 11 , side edge distance D 6  can be calculated as a function of D 6 ′ ( FIG. 19 ). The two will vary by a linear factor that depends primarily on the known size of calibration aperture  60  ( FIG. 1 ) and the measured change in voltage level. 
   Where the velocity of media sheet  210  is known, D 2 ′ and D 7 ′ can be converted to linear distances D 2 ″ and D 7 .″ Referring to  FIG. 11 , hole diameter D 2  can be calculated as a function of D 2 ″. D 2 ″ equals approximately eighty-six percent of D 2 . Leading edge distance D 7  then equals D 7 ″. 
   Focusing once again on  FIGS. 11 and 12 , voltage level change  226  has dimensions D 8 ′, D 3 ′ and D 9 ′. D 8 ′ corresponds to fifty percent of its magnitude. D 3 ′ corresponds to its width at the fifty-percent magnitude level. D 9 ′ corresponds to the time between when the leading edge of the media sheet entered measurement aperture  62  and when the voltage level change  226  reached its peak magnitude. 
   Referring back to  FIG. 11 , side edge distance D 8  can be calculated as a function of D 8 ′ ( FIG. 12 ). The two will vary by a linear factor that depends primarily on the known size of the calibration aperture  60  ( FIG. 1 ) and the measured change in voltage level. 
   Where the velocity of media sheet  210  is known, D 3 ′ and D 9 ′ can be converted to linear distances D 3 ″ and D 9 ″. Referring to  FIG. 11 , hole diameter D 3  can be calculated as a function of D 3 ″. D 3 ″ equals approximately eighty-six percent of D 3 . Leading edge distance D 9  then equals D 9 ″. 
   Moving on,  FIG. 13  is an exemplary flow diagram illustrating method steps for locating a hole. Light is directed toward a media path (step  230 ). The light is directed from a first side of a media path such that the light spans at least a portion of a width of the media path. The light is filtered (step  232 ). The light impinges upon a light detector (step  233 ). Voltage level change data is collected from the light detector (step  234 ). The voltage level change data collected corresponds to a voltage level change measured from a second side of the media path opposite the first side as print media is urged along the media path. The voltage level change data is analyzed to locate a hole (step  236 ). 
     FIG. 14  is an exemplary flow diagram expanding on step  236 . A first change in voltage data collected is noted (step  240 ). The first change, for example, may be a change from a relatively high value to a relatively low value indicating that the leading edge of a media sheet has been detected. A second change in the collected voltage level data is then noted (step  242 ). The second change, for example, may be an increase from the relatively low value to a value less than the relatively high value and then a return to the relatively low value. The magnitude of the second change and a duration of the second change at fifty percent of its magnitude are measured (step  244 ). An edge distance is calculated as a function of the measured magnitude (step  246 ). A diameter is calculated as a function of the measured duration (step  248 ). 
   Locating Tabs:  FIG. 15-18  help illustrate a method for locating holes in print media based on collected voltage change data.  FIG. 15  illustrates media sheet  250  having variously sized and located tabs  251 - 254 . Tab  251  has a length L 1 . Tab  252  has a length L 2 . Tab  253  has a length L 3 . Tab  253  has a length L 4 . Measured from length L 1 , tab  251  has a side edge distance M 1  (distance from side edge  255 ). Tab  252  has a side edge distance M 2 . Tab  253  has a side edge distance M 3 . Tab  254  has a side edge distance M 4 . 
     FIG. 16  is a two-dimensional graph  260  illustrating a measured voltage level as a media sheet  250  ( FIG. 15 ) with four variously sized and located tabs pass through sensor  50  ( FIG. 1 ). Initially, the measured voltage level is at a relatively high value  261 . When a leading edge of the media sheet enters the calibration aperture  60 , the measured voltage level drops to a lower value  268 . When a leading edge of a media sheet  250  enters measurement aperture  62 , the measured intensity level drops to a relatively low value  262 . Voltage level change  263  corresponds to tab  251  ( FIG. 15 ). Voltage level change  264  corresponds to tab  252  ( FIG. 15 ). Voltage level change  265  corresponds to tab  253  ( FIG. 15 ). Voltage level change  266  corresponds to tab  254  ( FIG. 15 ). When the trailing edge of the media  250  enters the calibration aperture  60 , the measured voltage level rises to a higher value  269 . Once the trailing edge exits sensor  50  ( FIG. 1 ), the measured intensity returns to a relatively high value  267 . 
   Focusing on  FIG. 16 , voltage level change  263  has dimensions L 1  and M 1 . M 1  corresponds to the time between when the leading edge of the media sheet entered measurement aperture  62  and when voltage level change  263  reached its peak magnitude. 
   Referring back to  FIG. 15 , side edge distance L 1  can be calculated by a linear factor that depends primarily on the known size of calibration aperture  60  ( FIG. 1 ) and the measured change in voltage level. 
   Where the velocity of media sheet  250  is known, L 1  can be converted to a linear distances. Referring to  FIG. 15 , the size of tab  251  can be calculated as a function of L 1  and M 1 . With respect to tabs  252 - 254 , their sizes can be calculated in a similar fashion using L 2 -L 4  and M 2 -M 4 , respectively 
   Moving on,  FIG. 17  is an exemplary flow diagram illustrating method steps for locating a tab. Light is directed toward a media path (step  270 ). The light is directed from a first side of a media path such that the light spans at least a portion of a width of the media path. The light is filtered (step  272 ). The light impinges upon a light detector (step  273 ). Voltage level change data is collected from the light detector (step  274 ). The voltage level change data collected corresponds to a voltage level change measured from a second side of the media path opposite the first side as print media is urged along the media path. The voltage level change data is analyzed to locate a hole (step  275 ). 
     FIG. 18  is an exemplary flow diagram expanding on step  275 . A first change in voltage data collected is noted (step  280 ). The first change, for example, may be a change from a relatively high value to a relatively low value indicating that the leading edge of a media sheet has been detected. A second change in the collected voltage level data is then noted (step  282 ). The second change, for example, may be an increase from the relatively low value to a value less than the relatively high value and then a return to the relatively low value. The magnitude of the second change and a duration of the second change at fifty percent of its magnitude are measured (step  284 ). An edge distance is calculated as a function of the measured magnitude (step  286 ). A magnitude is calculated as a function of the measured duration (step  208 ). 
   CONCLUSION: The illustrations of the Figures show the architecture, functionality, and operation of an exemplary environment in which various embodiments of the present invention may be implemented. Some of the Figures illustrate various embodiments of a sensor. The claimed subject matter is not limited to the embodiments shown. The sensor may be able to detect the change in voltage level as a result of the change in the intensity of a light directed across a portion of a width of a media path. The various block diagrams illustrate an example of the logical components that can be used to implement the various embodiments. Each block in the block diagrams may represent in whole or in part a module, segment, or portion of code that comprises one or more executable instructions to implement the specified logical function(s). Each block may represent a circuit or a number of interconnected circuits to implement the specified logical function(s). 
   Also, embodiments of the present invention can include any computer-readable medium for use by or in connection with an instruction execution system such as a computer/processor based system or an ASIC (Application Specific Integrated Circuit) or other system that can fetch or obtain the logic from computer-readable media and execute the instructions contained therein. “Computer-readable medium” can be any of one or more computer readable media that can contain, store, or maintain programs and data for use by or in connection with the instruction execution system. Computer readable media can comprise any one of many physical media such as, for example, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor media. More specific examples of suitable computer-readable media include, but are not limited to, a portable magnetic computer diskette such as floppy diskettes or hard drives, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory, or a portable compact disc. 
   Although the various flow diagrams show specific orders of execution, the orders of execution may differ from that which is depicted. For example, the order of execution of two or more blocks may be scrambled relative to the orders shown. Also, two or more blocks shown in succession may be executed concurrently or with partial concurrence. All such variations are within the scope of the claimed subject matter. 
   Embodiments of the present invention have been shown and described with reference to the foregoing exemplary embodiments. It is to be understood, however, that other forms, details, and embodiments may be made without departing from the spirit and scope of the invention which is defined in the following claims.