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Browse Prior Art Database

INTENSITY CONTROL FOR RASTER OUTPUT SCANNERS

IP.com Disclosure Number: IPCOM000025231D
Original Publication Date: 1984-Feb-29
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 169K

Publishing Venue

Xerox Disclosure Journal

Abstract

Referring to Figure 1, Raster Output Scanners (ROS) suffer from intensity variations in the writing beam 3 which may degrade performance on the recording media such as photoreceptor 4 of a xerographic system. In particular, raster spot intensity decreases at both ends of scan in conventional overfilled polygon illumination as well as in facet tracking illumination. This fall-off of raster intensity may be a problem in attempting to faithfully reproduce the images scanned. Similarily, intensity non-uniformities caused by other ROS related components can occur from raster line to raster line due to differences in the facet reflectivity of polygon 5 or over groups of raster lines due for example to power degradation of laser 6, dirt collection on optical surfaces such as mirror 7, or loss of efficiency of modulator 8.

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Page 1 of 4

XEROX DISCLOSURE JOURNAL

INTENSITY CONTROL FOR RASTER OUTPUT SCANNERS U.S. C1. 358/293 James C. Traino

Proposed Classification Int. Cl. H04n 1/10

Felice A. Micco
Douglas L. Keene

v POWER FIG I

1 I-

LASER OPTIC

M OD UL ATOR 7

BEAM INTENSITY CONTROL SIGNAL

7-

IMAGE DATA

FIG 2

BEAM INTENSITY CONTROL SIGNAL

+5 V

b

t

390r

222r -5v

-5 v

Volume 9 Number 1 January/February 1984 77

[This page contains 1 picture or other non-text object]

Page 2 of 4

INTENSITY CONTROL FOR RASTER OUTPUT SCANNERS (Cont'd)

Referring to Figure 1, Raster Output Scanners (ROS) suffer from intensity variations in the writing beam 3 which may degrade performance on the recording media such as photoreceptor 4 of a xerographic system. In particular, raster spot intensity decreases at both ends of scan in conventional overfilled polygon illumination as well as in facet tracking illumination. This fall-off of raster intensity may be a problem in attempting to faithfully reproduce the images scanned. Similarily, intensity non-uniformities caused by other ROS related components can occur from raster line to raster line due to differences in the facet reflectivity of polygon 5 or over groups of raster lines due for example to power degradation of laser 6, dirt collection on optical surfaces such as mirror 7, or loss of efficiency of modulator 8.

In previous applications of laser raster scanning, static adjustment of writing beam intensity was applied to compensate for laser power degradation and dirt collection on optical surfaces. Static adjustment was implemented by incorporating the laser into a feedback loop and electronically controlling its excitation current. Stability criteria were met by including in the feedback loop a photosensor which monitored laser power and issued error information to a variable laser power supply. The laser output power was then adjustable, stable and quiet over the frequency range of DC to several kilohertz.

Later, techniques to reduce the raster intensity fall-off by dynamically adjusting the spot intensity during scanning were devised. Dynamic intensity control provided more rapid correction of the raster spot intensity than was possible with the previous static adjustment techniques. The speed requirement, coupled with advances in laser technology which reduced the need to externally compensate for laser instability and noise, led to performing raster scanning intensity control using an acousto-optic modulator. driver with two input ports substituted for a conventional one input port driver in the acousto-optic modulator was used. The dual port driver accepted image data through one port (digital signal) and intensity correction data through other port (analog signal). Thus, it was possible to correct during scan ROS intensity variations by electronically controlling the analog input port of the dual port acousto-optic modulator R.F. driver.

For this purpose, a specially modified R.F.

It is here proposed that the intensity within a sing...