Self-adjusting optical sensing system for financial and retail printers

A self-adjusting, optical-sensing system for providing an appropriate length for a receipt from a printer of a retail or financial machine, comprising:

• light-emitting means electrically connected to a programmable microprocessor for emitting and directing a light beam towards a media strip having black marks periodically disposed along an edge thereof, said light beam being reflected from said media strip when a black mark is not present, said light beam being reflected towards a photo-sensor;
• a D/A converter electrically connected to said light-emitting means for supplying said light-emitting means with a supply voltage;
• a photo-sensor in close proximity to said media strip and said light-emitting means, for sensing the reflected light beam from said media strip and providing a voltage signal indicative thereof, with said black mark substantially absorbing said light beam from said light-emitting means and thereby changing said voltage signal, which is then indicative of said media strip having advanced a length required to provide a receipt;
• and
• a programmable microprocessor comprising an A/D converter electrically connected to said photo-sensor for receiving said voltage signal from said photo-sensor, said programmable microprocessor being electrically connected to said D/A converter for receiving said input and for producing a supply voltage for energizing said light-emitting means, said input of said A/D converter being influenced by said voltage signal provided by said photo-sensor, with a calibration program contained in said microprocessor for assessing said input of said A/D converter when said media strip passes adjacent to said photo-sensor, and with supply voltages required to be fed to said light-emitting means by said D/A converter in order for said light-emitting means to direct said light beam towards said media strip, said calibration program providing a self-adjustment calibration by virtue of a relationship between said supply voltage fed to said light-emitting means under the control of said microprocessor and the voltage signal that is provided by said photo-sensor, said voltage signal influencing the control of said supply voltage by said microprocessor.

A method of automatically calibrating the photo-sensing of a media strip having black marks periodically disposed along an edge thereof, said media strip being advanced through a printer of a financial or retail machine until a black mark is sensed, wherein said media strip is cut to provide a receipt, said method comprising the steps of:

• a) sampling a first voltage corresponding to sensed ambient-light conditions;
• b) sampling a second voltage corresponding to an output voltage of a photo-reflective device sensing a media strip;
• c) determining a value representative of a threshold voltage being supplied to said photo-reflective device;
• d) subtracting said first voltage of step (a) from said second voltage of step (b), and comparing the difference voltage value with said threshold voltage value determined in step (c);
• and
• e) storing said threshold voltage value in memory, said threshold voltage value corresponding to a voltage calibration value when said difference voltage value of step (d) is greater than said threshold voltage value of step (c).

A method of automatically calibrating the photo-sensing of a media strip having black marks periodically disposed along an edge thereof, said media strip being advanced through a printer of a financial or retail machine until a black mark is sensed, wherein said media strip is cut to provide a receipt, said method comprising the steps of:

• a) sampling a voltage corresponding to an output voltage of a photo-reflective device sensing a media strip;
• b) nulling a portion of said output voltage in accordance with step (a), said portion corresponding to ambient light, in order to provide a first voltage value;
• c) determining a value representative of a threshold voltage being supplied to said photo-reflective device;
• d) comparing said first voltage value of step (b) with said threshold voltage value determined in step (c), to produce a difference voltage;
• e) storing said threshold voltage value in memory, said threshold voltage value corresponding to a voltage calibration value when said difference voltage value of step (d) is greater than said threshold voltage value of step (c).

A method of calibrating a sensing system for dispensing receipts from a printing machine, comprising the steps of:

• a) after assuming that a photo-sensing device is seeing white paper, iteratively increasing a voltage supply signal for energizing a light-emitting device having a beam that is reflected from a media strip towards said photo-sensing device, while measuring a voltage output corresponding to said photo-sensing device;
• b) determining whether said voltage output of said photo-sensing device has reached a maximum value before the voltage supply signal for said light-emitting device has reached a given, predetermined threshold value;
• and
• c) if the voltage output has reached a maximum value before the voltage supply signal has reached said predetermined threshold value, then choosing another threshold value that is representative of a reliable white-paper signal.