Browse Prior Art Database

Scanning Error Detection and Recovery

IP.com Disclosure Number: IPCOM000094380D
Original Publication Date: 1966-Oct-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Cutaia, A: AUTHOR

Abstract

When scanning lines of characters in a character page reading machine, sometimes the scanning raster goes astray and lines are reread or skipped or the raster becomes lost. These error conditions can be detected by storing the vertical position of the raster at the start of each line and comparing this position with the vertical position of the raster after each line is read. The difference between the vertical coordinate position of the raster before and after reading a line should be bounded such that the direction and magnitude of this difference provides a basis for determining the types of error conditions. If the beam becomes lost, it always can be returned to the initial position established prior to reading a line.

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Scanning Error Detection and Recovery

When scanning lines of characters in a character page reading machine, sometimes the scanning raster goes astray and lines are reread or skipped or the raster becomes lost. These error conditions can be detected by storing the vertical position of the raster at the start of each line and comparing this position with the vertical position of the raster after each line is read. The difference between the vertical coordinate position of the raster before and after reading a line should be bounded such that the direction and magnitude of this difference provides a basis for determining the types of error conditions. If the beam becomes lost, it always can be returned to the initial position established prior to reading a line.

Several modes of operation are involved when scanning lines of characters. Mode 0 is a line search mode in which the raster is looking for data to be read. Mode 1 occurs when significant data is encountered and the raster starts to line center on this data. Mode 2 is a line centering mode and the raster is servoing on the line at high speeds. The actual reading of the characters occurs during Mode 3.

Control 10 provides an initial control signal to beam deflection circuit 15, line centering circuit 20, data register 25 and character recognition circuit 30. Circuit 15 provides horizontal and vertical deflection voltages to cathode ray tube 16 and drives its beam in the desired raster pattern. The light reflected from the background of document 17 and from the characters on it is picked up by photomultiplier tube 18. The output of 18 is the raw video signal which is amplified and digitized by circuit 19. The digitized data is entered into register
25. The data in 25 is applied to line centering 20 and recognition circuit 30.

Circuit 20 provides Up Space and Down Space drive signals to 15 so as to cause the raster to center upon the line of characters on 17. During this line centering operation, bidirectional counter 35 which is reset upon detecting the left precision discriminator LPD of the scan area is advanced one unit for each Up Space drive signal...