Browse Prior Art Database

Automatic Tilt Correction for Scanning Rasters

IP.com Disclosure Number: IPCOM000094635D
Original Publication Date: 1965-Apr-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Garry, GA: AUTHOR

Abstract

Cathode ray tubes are used for optically scanning patterns such as printed characters. A vertical raster for scanning a line of printing is generated by applying a slow-speed sawtooth wave to the horizontal deflection system and a high-speed sawtooth to the vertical deflection system of the CRT scanner. However, each resulting vertical scan is slightly tilted because horizontal motion occurs during the vertical scan. To correct the tilt of each vertical scan, the horizontal sawtooth is modified to approximate a staircase waveform. Horizontal motion of the beam then occurs only during retrace.

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Automatic Tilt Correction for Scanning Rasters

Cathode ray tubes are used for optically scanning patterns such as printed characters. A vertical raster for scanning a line of printing is generated by applying a slow-speed sawtooth wave to the horizontal deflection system and a high-speed sawtooth to the vertical deflection system of the CRT scanner. However, each resulting vertical scan is slightly tilted because horizontal motion occurs during the vertical scan. To correct the tilt of each vertical scan, the horizontal sawtooth is modified to approximate a staircase waveform. Horizontal motion of the beam then occurs only during retrace.

Horizontal ramp generator 10 has positive-going and negative-going outputs when the digital scan-left and scan-right signals are applied, respectively. Vertical ramp generator 20 has positive-going and negative-going outputs when the digital scan-up and retrace signals are applied to it, respectively. Current switches 25 and 30 are controlled by the scan right and scan left signals, respectively. These switches, when operated, pass a portion of the output of 20 to amplifier 40.

Thus when scanning left, current switch 30 is operated. The outputs of generators 10 and 20 are positive-going when scanning left and up. However, the output of 10 is applied to a positive input of 40 while the signal from 20 is passed by 30 to a negative input of
40. The signal from 20, passed by 30, cancels in 40 the signal applied from 10. Therefore, t...