Browse Prior Art Database

Continuously Variable Resolution Document Scanner and Film Plotter

IP.com Disclosure Number: IPCOM000084854D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Childress, LS: AUTHOR

Abstract

An arrangement is shown which improves positional accuracy of scan/plot data on a document which may be subject to stretching or shrinkage.

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Continuously Variable Resolution Document Scanner and Film Plotter

An arrangement is shown which improves positional accuracy of scan/plot data on a document which may be subject to stretching or shrinkage.

The scanner/plotter consists of a cylindrical drum 2 upon which is mounted a document 4 to be scanned and digitized or photofilm to be exposed (printed), an optical assembly 6 including optical sensors and plotter light sources, coupled to a lead screw 8 and drive motor 10 combination, and control electronics 12.

Data is scanned/plotted along a circumferential track as the drum 2 revolves through a complete revolution, after which the optical assembly 6 is stepped to the next circumferential track to continue the scan/plot operation. The system utilizes a shaft angle encoder 14 coupled to the drum 2 and drum motor 38, whose velocity of revolution is controlled by the rate of the shaft encoder pulse train. This feedback technique keeps the drum surface velocity constant within a very close tolerance.

The shaft encoder 14 also emits a once per revolution index pulse which is applied to a loop including a delay line 16, pulse position modulator circuit 18 and gate 20. Delay line 16 is set to a nominal delay relative to the nominal drum speed and nominal scan/plot spacing, thereby providing a major delay in accordance with the system resolution desired.

Pulse position modulation circuit 18 provides a variable minor delay, which is used to compensate for the deviation of the drum speed from the norm. Gate 20 is controlled by a counter 40-decoder 42 combination which monitors the number of pulses desired as set by the required system resolution. The sum of the major and minor delays equal the pulse timing of the scan/plot pulse train applied from the modulator 18 to the control...