Browse Prior Art Database

Raster Search Control for Curve Follower

IP.com Disclosure Number: IPCOM000073606D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Keillor, RD: AUTHOR [+3]

Abstract

A problem common to all optical character recognition machines is misregistration of data with respect to the intended address or location on the document. The use of an expanded search pattern allows relaxation of the misregistration specification and results in a significant performance improvement. The expanded search pattern is achieved by causing the artificial follow to search in a sawtooth rather than a straight line pattern as shown in A. Alternate logical implementations for causing the circle follower to traverse a sawtooth trajectory are shown in B and C.

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Raster Search Control for Curve Follower

A problem common to all optical character recognition machines is misregistration of data with respect to the intended address or location on the document. The use of an expanded search pattern allows relaxation of the misregistration specification and results in a significant performance improvement. The expanded search pattern is achieved by causing the artificial follow to search in a sawtooth rather than a straight line pattern as shown in A. Alternate logical implementations for causing the circle follower to traverse a sawtooth trajectory are shown in B and C.

The actual operation of both circuits is quite similar. The sawtooth trajectory is accomplished by attenuating the circle at a given phase angle. A phase angle giving follow upward and to the left and a phase angle giving follow downward and to the left are necessary. A latch accomplishes the switching of phase angles and is controlled by the limits of a band established around the vertical coordinate. The upper and lower limits of the sawtooth are determined by the reference voltages generated at VC1 and VC2. The reference voltages generated are the result of a voltage comparison between a set voltage limit and the vertical character voltage input.

The slope of the two portions of the sawtooth are controlled by time delays TD1 and TD2. The waveforms in D demonstrate the effect of the time delays upon the phase inputs. Note that other arbitrary trajectories are...