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Electrical Read Out of Printed Characters

IP.com Disclosure Number: IPCOM000079468D
Original Publication Date: 1973-Jul-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 4 page(s) / 46K

Publishing Venue

IBM

Related People

Sambucetti, CJ: AUTHOR

Abstract

A key problem in automatic machine processing of printed documents, is the ability to combine the printing effect with a form of discernible intelligence that makes the mark different from the surrounding medium. In one case, hard copy information is only machine readable (e.g. magnetic marking of perforated tape or cards). In a more significant case, a document is printed in both human and machine readable form, where only mark-sense and optical recognition of printed characters have been successful.

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Electrical Read Out of Printed Characters

A key problem in automatic machine processing of printed documents, is the ability to combine the printing effect with a form of discernible intelligence that makes the mark different from the surrounding medium. In one case, hard copy information is only machine readable (e.g. magnetic marking of perforated tape or cards). In a more significant case, a document is printed in both human and machine readable form, where only mark-sense and optical recognition of printed characters have been successful.

A detectable electrical signal difference can occur when the printed material is passed by a reading head containing sensitive indicator electrodes. The method recognizes marks printed in electrochromic (chemically treated) paper, and other forms of printing.

In printing marks (dots, bars or full characters) using the (silver/ paper with KF + ascorbic/reference electrode) system, the reason the black marking appears on the white paper background is that silver ions from the marking anode electrically dissolve and are reduced on the spot to finely divided silver (covered with a layer of silver oxide). This phenomenon is characterized in that the mark created "is electrically active". A chemical and physical discontinuity has been created by the appearance of the mark detectable by electrochemical techniques such as: potentiometry, amperometry and conductimetry.

In potentiometric sensing, printed paper and a pair of sensing electrodes act as a battery yielding a voltage signal varying in magnitude, depending on whether the sensing probe touches unprinted paper or a mark. To obtain reproducible differential voltage readings one of the electrodes of such sensing battery is of large surface area, to act as a reference electrode whose potential remains sensibly constant through the measurements.

The "sensing or indicator probe" is of very small dimensions (a wire of few mills cross section) so it is easily depolarized by chemical discontinuities on paper, which makes the sensing device much more sensitive. The small sensing probe, easily discriminates between closely spaced lines or dots.

The paper is slightly moist, because the sensing mechanism is an electrochemical cell and greater paper conductivity yields greater voltage differential between the mark and background. The signal differential obtained with the sensing cell described below is of such magnitude that marks can be detected on almost dry paper.

To make the differential voltage signal more reproducible and sensitive, it is convenient to place the two basic elements of the sensing battery (large common reference electrode and indicator probes) on opposite sides of the paper, so that the signal is measured through a layer of relatively constant thickness. An array of sensing probes on the marked side of the paper functions with a single, common reference electrode on the other side.

Marking paper has been chemically treated by impregnati...