Printer and method of correcting color registration error...

Details Printer and method of correcting color registration error... Printer and method of correcting color registration error...

1999-10-29

2001-03-06

Pendegrass, Joan (Department: 2852)

Incremental printing of symbolic information

Electric marking apparatus or processes

Electrostatic

C399S301000

Reexamination Certificate

active

06198490

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printer designed to be able to correct registration of images of different colors rendered at wrong areas, and a method of correcting a color registration error.
2. Description of the Related Art
FIG. 1
illustrates a cross-sectional view of a general liquid electrophotographic color printer. The printer operates by transporting developer by photoreceptor belt
14
onto paper
23
passing through a transfer device
20
.
Photoreceptor belt
14
follows a circulation path around a plurality of rollers
11
,
12
and
13
. Installed around the circulation path are a reset device
15
, optical scanning devices
30
,
40
,
50
,
60
, optical detectors
38
,
48
,
58
and
68
, developing devices
36
,
46
,
56
and
66
, a drying device
18
, and the transfer device
20
.
Chargers
15
b
,
37
,
47
, and
57
charge the photoreceptor belt
14
with a predetermined potential to prime the belt for the registration of a new electrostatic latent image. Yellow, magenta, cyan, and black each require the registration of a new electrostatic latent image. After transfer of the color images onto paper, an exposing device
15
a
erases any remaining electrostatic charge from the photoreceptor belt
14
.
The printing process begins when the leading edge of a designated image writing page area on the photoreceptor belt
14
reaches the scanning position of the first optical scanning device
30
. The first optical scanning device
30
projects light corresponding to yellow-color image information onto the photoreceptor belt
14
, which already carries a charge from charger
15
b
. An electrostatic latent image is formed on the photoreceptor belt
14
by the first optical scanning device
30
, and is developed by the first developing device
36
, which supplies yellow developer (Y).
The page area on the photoreceptor belt
14
is recharged by charger
37
so that the next electrostatic latent image can be written onto the page area. When the charged page area reaches the scanning position of the second optical scanning device
40
, the second optical scanning device
40
projects light corresponding to magenta-color image information. Another electrostatic latent image is formed on the photoreceptor belt
14
by the second optical scanning device
40
, and is developed by the second developing device
46
, which supplies magenta developer (M).
This process repeats as the page area continues through the third and fourth optical scanning devices
50
and
60
, projecting cyan-color and black image information, and through the third and fourth developing devices
56
and
66
, supplying cyan-color developer (C) and black developer (BK). Consequently, by passing through all four developing devices, a full color image can be formed within the page area on the receptor belt
14
.
The page area continues along the circulation path through the drying device
18
, which removes liquid carrier from the photoreceptor belt
14
.
The color image formed of developing material on the photoreceptor belt
14
is transferred to a transfer roller
21
, which rotates in contact with the photoreceptor belt
14
. The color image is transferred via the transfer roller
21
to a sheet of paper
23
entering between the transfer roller
21
and a fixing roller
22
.
This printer is susceptible to color registration error. Color registration error occurs when the image of an individual color is not registered at the correct pixel writing position in relation to the color images of the other colors. This occurs as optical scanning devices
30
,
40
,
50
and
60
sequentially write their respective color image information onto the same page area on the circulating photoreceptor belt
14
, when the respective color image information is inaccurately registered within the page area. As a result, the desired image cannot be obtained.
The conventional art corrects color registration error by printing an image of a predetermined test pattern, having an inspector measure the distance difference between adjacent test patterns of different colors output on the paper
23
, calculating the amount of color registration error, and adjusting the printing process to compensate for the error. However, this method is complicated, since the inspector must manually calculate the color registration error. Manual inspection has a high possibility of introducing extraneous error and imprecision into the calculation of the color registration error amount.
In another conventional method, color registration is corrected by printing test patterns for each color using all of the developing devices
36
,
46
,
56
and
66
by a normal printing method, and calculating the amount of color registration error by detecting information associated with the interval between the printed test patterns of the different colors. Detection is performed by an image information acquisition sensor such as a charge-coupled device (CCD). However, this method requires the installation of image information acquisition sensors for the respective colors to accurately measure a color registration error, thus complicating the installation.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a printer which can internally and accurately measure and correct a color registration error without adding a large number of components, and a method of correcting the color registration error.
Accordingly, to achieve the above objective, the present invention provides a printer including: a photoreceptor circulating along a path formed by a plurality of rollers; a plurality of optical scanning devices for emitting a scanning light toward the photoreceptor; a plurality of developing devices for supplying developing materials of different colors to the photoreceptor; a plurality of optical detectors for detecting part of the light emitted from the optical scanning devices; an engine controller for controlling a driving of the optical scanning devices, the developing devices, and the rollers, using received light output from the optical detectors so that test patterns for each optical scanning device set to detect a color registration error between the optical scanning devices is formed on the photoreceptor; a pattern position detector for detecting the positions of the test patterns formed from fixed positions through a developing process; and a color registration correction calculator for calculating a color registration error amount from the position information of the test patterns provided by the pattern position detector, and calculating color registration correction data from the calculated error amount and outputting the calculated correction data to the engine controller.
Preferably, the engine controller selects a single developing device to develop electrostatic latent images formed on the photoreceptor in response to the test patterns formed by the optical scanning devices, thereby using a single color developing material.
To achieve the above objective, the present invention provides a color registration error correcting method including the steps of: (a) forming electrostatic latent images corresponding to test patterns of different colors set for color registration error detection, on the photoreceptor by the optical scanning devices; (b) developing the different color electrostatic latent images with a single color developing material by one selected developing device; (c) detecting the positions of the test patterns formed of the single color developing material; (d) calculating color registration error amounts from the detected test pattern position information; and (e) obtaining color registration correction data from the error amounts calculated in step (d).


REFERENCES:
patent: 5115256 (1992-05-01), Miyagi et al.
patent: 5257037 (1993-10-01), Haneda et al.
patent: 5909235 (1999-06-01), Folkins
patent: 8-324028 (1996-12-01), None
patent: 11-237778 (1999-08-01), None

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