Method and apparatus for finding media top-of-page in an optical image scanner

A method for sensing an edge of a medium in an image transfer device, the method comprising:

• (a) radiating a light source upon a surface of a processing path for the medium in the image transfer device;
• (b) increasing a contrast sensitivity level of a photo sensor array relative to a normal image processing sensitivity level;
• (c) detecting an amount of light reflected from the surface of the processing path;
• (d) comparing the amount of light detected with a threshold amount of light to produce a compare result, the threshold amount of light being indicative of a shadow being cast over at least a portion of the processing path in response to the edge of the medium being exposed to the light source in the processing path;
• and,
• (e) in the event the compare result is not less than the threshold level, then returning the contrast sensitivity level to a normal image processing sensitivity level and initiating an image transfer of the medium, otherwise, in the event the compare result is less than the threshold level, then repeating steps (a) through (e) until the threshold level is reached.

A medium processing device, comprising:

• (a) a support surface for supporting a medium to be processed in the medium processing device;
• (b) a light source directed upon the support surface;
• (c) a photo sensor array for sensing a shadow cast upon the support surface as a result of an edge of the medium being exposed to the light source;
• and,
• (d) processing means for processing signals produced by the photo sensor array such that the signals are processed and recognized as being indicative of the edge of the medium casting the shadow upon the support surface, and wherein the processing means includes:
• (i) memory apparatus for storing a plurality of line sum indicia, each line sum indicia being indicative of an amount of light reflected from the support surface as sensed by one or more zones of photo sensors of the photo sensor array for a given scanline;
• (ii) computational apparatus for computing a running average from the plurality of stored line sum indicia;
• (iii) differencing apparatus for differencing the running average with a most recent line sum indicia to produce a resultant value;
• and,
• (iv) compare apparatus for comparing the resultant value with a threshold value, the threshold value being indicative of the shadow being cast upon the support surface.

A system for detecting an edge of a medium in a medium processing device, the system comprising:

• (a) a support surface for supporting the medium;
• (b) a light source directed upon the support surface;
• (c) an array of photo sensors;
• and,
• (d) control apparatus for controlling the array of photo sensors such that at least one predefined window of the array of photo sensors senses a shadow cast upon the support surface as a result of the edge of the medium being exposed to the light source.

A method for sensing an edge of a medium in an image transfer device, the method comprising:

• (a) radiating a light source upon a surface of a processing path for the medium in the image transfer device;
• (b) detecting an amount of light reflected from the surface of the processing path and summing light impingement values associated with one or more separate zones of photo sensors of a photo sensor array to produce a line sum value that is indicative of an amount of light reflected from the surface of the processing path;
• (c) comparing the amount of light detected with a threshold amount of light to produce a compare result, the threshold amount of light being indicative of a shadow being cast over at least a portion of the processing path in response to the edge of the medium being exposed to the light source in the processing path;
• and,
• (d) in the event the compare result is not less than the threshold level, then initiating an image transfer of the medium, otherwise, in the event the compare result is less than the threshold level, then repeating steps (a) through (d) until the threshold level is reached.