Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-01-20
2002-09-17
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S559290, C399S394000
Reexamination Certificate
active
06452147
ABSTRACT:
This application is based on an application No. 10-9426 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus which forms toner patterns and detects them using a sensor to correct image forming positions in accordance with detection results, and particularly relates to an adjustment to a toner pattern detecting mechanism provided in the image forming apparatus.
(2) Description of the Related Art
A so-called “tandem-type” image forming apparatus, as one example of a conventional full-color image forming apparatus, has image holding components (photosensitive drums, for example) set in line corresponding to reproduction colors cyan, magenta, yellow, and black. The reproduction colors are respectively referred to as C, M, Y, and K hereinafter and components related to these colors are assigned numerals with a corresponding C, M, Y, or K. Toner images for different colors formed on the image holding components are sequentially transferred onto a transfer material (a recording sheet, for example) which is transported on a transfer belt or onto the transfer belt as a transfer intermediate component. The toner images are superimposed to form a color image.
In general, for the tandem-type image forming apparatus having the stated construction, a so-called “registration correction” is performed to correct forming positions of images formed on surfaces of the image holding components corresponding to the reproduction colors. By means of the registration correction, deterioration in the image quality caused by color deviations is prevented.
The following is a brief description of a method of the registration correction, with reference to
FIGS. 1A and 1B
.
FIG. 1A
is a diagrammatic illustration of a tandem-type image forming apparatus which has a registration correction mechanism. For the registration correction performed in this image forming apparatus, an optical sensor
925
for optically detecting a toner density is set after photosensitive drums
941
C to
941
K in the transportation direction of a transfer material, as shown in FIG.
1
A. The photosensitive drums
941
C to
941
K are set along a transfer belt
931
. Registration marks
960
C to
960
K, for example, corresponding to the photosensitive drums
941
C to
941
K are formed on the transfer belt
931
as shown in FIG.
1
B.
The registration marks
960
C to
960
K are formed in the same shape, and are V-shaped in FIG.
1
B. Each of the V-shaped registration marks is composed of a standard line making a right angle with a transportation direction when no deviation is detected and a sloped line forming a 45° angle with the standard line. When image writing positions on the photosensitive drums
941
C to
941
K are correct and transfer positions are also correct, this means that no color deviations occur. In this case, the registration marks
960
C to
960
K are formed on the exactly same line that is parallel to the transportation direction as shown in
FIG. 1B
, with the standard lines being formed with a distance D between them in the transportation direction.
The optical sensor
925
set after the photosensitive drums
941
C to
941
K detects the registration marks
960
C to
960
K. Due to its detection characteristics, the optical sensor
925
detects a toner density of a point located directly under the optical sensor
925
. More specifically, the optical sensor
925
sequentially detects toner densities of points on a dash line shown in FIG.
1
B. Here, a high density value is detected at each point of intersection of the dash line and the standard line or the sloped line of the corresponding registration mark
960
C to
960
K.
If the registration marks
960
C to
960
K are formed on the transfer belt
931
at respective correct positions, a time period taken from the detection of the standard line to the detection of the next standard line is obtained by dividing the distance D by a moving speed of the transfer belt
931
. In addition, time periods respectively taken from the detection of the standard line to the detection of the sloped line of the registration marks
960
C to
960
K are the same.
Meanwhile, if a timing at which a registration mark is formed is different between the photosensitive drums
941
C to
941
K, the distance D varies according to the different timings. This means that the time period taken from the detection of the standard line to the detection of the next standard line varies. In this case, an address of image data read from an image memory in the sub-scanning direction is corrected for each pixel so that deviations of the registration marks
960
C to
960
K are corrected.
If the image forming positions on the photosensitive drums
941
C to
941
K are deviated in the main scanning direction, the time period taken between the detections the standard line and the sloped line varies with the registration marks
960
C to
960
K. Since the standard line and the sloped line of each of the registration marks
960
C to
960
K intersect at a 45° angle, relative differences in time periods between the detections of the standard line and the sloped line correspond with deviations of the registration marks
960
C to
960
K in the main scanning direction. In this case, an address of image data read from the image memory in the main scanning direction is corrected for each pixel, with one of the registration marks
960
C to
960
K being set as a standard mark. As a result, the time periods respectively taken between the detections of the standard lines and the sloped lines of the registration marks
960
C to
960
K are the same.
The above operations are performed by a pattern position determining unit
916
a
, a color deviation calculating unit
916
b
, and an address correcting unit
916
c
shown in FIG.
1
A. The pattern position determining unit
916
a
determines timings at which the registration marks
960
C to
960
K are respectively detected. The color deviation calculating unit
916
b
calculates the color deviations. In doing so, the color deviation calculating unit
916
b
obtains the color deviations in the main scanning direction from the relative differences in the time periods respectively taken between the detections of the standard lines and the sloped lines of the registration marks
960
C to
960
K, and obtains the color deviations in the sub-scanning direction from the relative differences in the time periods respectively taken between the detections of the standard line and the corresponding next standard line. The address correcting unit
916
c
corrects an address value for each pixel in accordance with the color deviations in the main scanning and sub-scanning directions.
Here, the optical sensor
925
should reliably detect the registration marks
960
C to
960
K so that the registration correction is correctly performed as stated above. In general, a registration mark has a width equal to or shorter than 8 mm in the main scanning direction. To obtain a valid detection value, about 4 mm middle short part of the 8 mm-wide registration mark needs to be detected. Meanwhile, since tolerances are established for an installation position of the optical sensor
925
, a timing at which the optical sensor
925
detects the registration marks
960
C to
960
K varies according to the position of the optical sensor
925
. Also, deviations of the image forming positions of the registration marks
960
C to
960
K and magnification deviations in the main scanning and sub-scanning directions may be initially great.
When the registration correction is performed, the optical sensor
925
may not be able to reliably detect the registration marks
960
C to
960
K due to the deviated installation position of the optical sensor
925
and the variations in the image forming positions of the registration marks
960
C to
960
K which have been determined before the registration correction is performed.
To avoid this problem, the registration mark can be formed in a large
Le Que T.
Minolta Co. , Ltd.
LandOfFree
Image forming apparatus which corrects image forming... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus which corrects image forming..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus which corrects image forming... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2903562