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Form Detection Mechanism on a Serial Printer

IP.com Disclosure Number: IPCOM000040143D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Chohsa, H: AUTHOR [+2]

Abstract

The vertical ends of a sheet or a form on a platen are detected by a reflection-type photo-sensor mounted on a horizontally movable printhead carrier and a form detection logic. When the carrier moves along a print line or a horizontal line inside a blank form or a pre-print form, the ratio of black data to total black/white data sensed by the sensor is low. When the carrier moves outside of the form on the black platen, the ratio is high. The first detection of the higher ratio shows a vertical end of the form. As shown in the figure, a printhead 1 and a reflection-type photo- sensor 2 are mounted on a carrier 3 or on its ribbon shield which is moved along a print line of a form 4 on a black platen 5 by a DC motor 6 through a timing belt 7.

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Form Detection Mechanism on a Serial Printer

The vertical ends of a sheet or a form on a platen are detected by a reflection- type photo-sensor mounted on a horizontally movable printhead carrier and a form detection logic. When the carrier moves along a print line or a horizontal line inside a blank form or a pre-print form, the ratio of black data to total black/white data sensed by the sensor is low. When the carrier moves outside of the form on the black platen, the ratio is high. The first detection of the higher ratio shows a vertical end of the form. As shown in the figure, a printhead 1 and a reflection-type photo- sensor 2 are mounted on a carrier 3 or on its ribbon shield which is moved along a print line of a form 4 on a black platen 5 by a DC motor 6 through a timing belt 7. An encoder 8 mounted on the DC motor 6 provides interrupt signals corresponding to various carrier positions along a print line. An interrupt controller 9 invokes interrupt in a microcode when each interrupt signal is generated. In an interrupt routine of the microcode, an absolute print position is updated and also the output of a comparator 10 is monitored. The comparator 10 compares analog output voltage from the photo-sensor 2 with threshold voltage supplied by a threshold selection circuit 11, and provides a black or white signal. Also in the interrupt routine, counts of black signals and white signals are accumulated for a single print scan, and used to calculate "End of For...