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MULTIPLE-SPOT BEAM CONTROL FOR A RASTER OUTPUT SCANNER

IP.com Disclosure Number: IPCOM000026587D
Original Publication Date: 1992-Oct-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 8 page(s) / 518K

Publishing Venue

Xerox Disclosure Journal

Abstract

Electrophotographic printers wherein a laser scan line is projected onto a photoconductive surface are well known. In the case of laser printers, facsimile machines, and the like, it is common to employ a raster output scanner (ROS) as a source of signals to be imaged on a pre-charged photoreceptor (a photosensitive plate, belt, or drum) for purposes of xerographic printing. The ROS provides a laser beam which is modulated (switched on and off, or otherwise controlled, selectively) as it moves, or scans, across the photoreceptor. This small scale of the individual scan line necessarily requires very precise tolerances in coordinating the motion of the surface of the photoreceptor 18 and the spot 16 transverse thereto. In a typical imaging system using a servo motor with feedback control for velocity regulation of a drum photoreceptor, low frequency velocity errors are generally removed by the regulating action of the servo system, but because feedback bandwidth is limited, passive damping from the drive motor and drum inertia must be relied upon to suppress higher frequenc errors. The result on the

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Page 1 of 8

XEROX DISCLOSURE JOURNAL

MULTIPLE-SPOT BEAM CONTROL Proposed Classification FOR A RASTER OUTPUT SCANNER
U.S. Frank C. Genovese C1.359/204
Int.
C1. G02B 26/08

18 D1 D2 D3 D4 D1 D2 D3 D4 18

FIG. IA FIG. I6

18 D1 D2 D3 D4

FIG. IC

XEROX DISCLOSURE JOURNAL - Vo1.17 No. 5 SeptembedOctober 1992 393

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Page 2 of 8

MULTIPLE-SPOT BEAM CONTROL FOR A RASTER OUTPUT SCANNER( Cont'd)

  8 MHZ OSCILLATOR

FIG. 2 J

0.5MHZ 8-B1T

(1 28)

  c 16
COUNTER

7 COUNTER

I

LATCH

C

-

32

- 7: 50ms RC= - +


B

n

46

                       D4 (DOWNSTREAM) (UPSTREAM)

PIXEL DATA

48

FIG. 3

394 XEROX DISCLOSURE JOURNAL - Vo1.17 No. 5 September/October 1992

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Page 3 of 8

MULTIPLE-SPOT BEAM CONTROL FOR A RASTER OUTPUT SCANNER( Cont'd)

Electrophotographic printers wherein a laser scan line is projected onto a photoconductive surface are well known. In the case of laser printers, facsimile machines, and the like, it is common to employ a raster output scanner (ROS) as a source of signals to be imaged on a pre-charged photoreceptor (a photosensitive plate, belt, or drum) for purposes of xerographic printing. The ROS provides a laser beam which is modulated (switched on and off, or otherwise controlled, selectively) as it moves, or scans, across the photoreceptor. This small scale of the individual scan line necessarily requires very precise tolerances in coordinating the motion of the surface of the photoreceptor 18 and the spot 16 transverse thereto. In a typical imaging system using a servo motor with feedback control for velocity regulation of a drum photoreceptor, low frequency velocity errors are generally removed by the regulating action of the servo system, but because feedback bandwidth is limited, passive damping from the drive motor and drum inertia must be relied upon to suppress higher frequenc errors. The result on the

is error velocity this of document printed "strobing," or ?hue rainbows" in a color system. re F erred to as "banding" or

The actual positional error is typically on the order of a few microns or less, much smaller than the cross section of the typical scan line, allowing for correction by shifting the effective center of spot 16 in compensation . This shifting of the s ot 16 relative to moving photoreceptor surface 18 in order to

known as %earn steering." Accordingly, the present invention uses beam steering to adjust the intensity of at least one of a plurality of light beam elements to adjust the relative position of the effective center of exposure of the composite spot on the charged photosensitive surface in the process direction.

Figures lA, lB, and 1C show intensity profiles of spot 16 forming a scan line, illustrating how the present invention accomplishes the beam steering. Spot 16 is created as a composite of a plurality of overlapping, convergent elements (smaller spots) shown in the Figures as Dl-D4. (In the following description, elements Dl-D4 are referred...