Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2002-12-18
2004-09-07
Lee, Susan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S248000, C347S262000, C399S394000, C399S395000
Reexamination Certificate
active
06788322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a LBP (laser beam printer) or a copying machine that uses electronic photographic technology, for example, and an image formation control method.
2. Description of the Related Art
A conventional image forming apparatus is shown in
FIGS. 26 and 27
.
FIG. 26
is a side view showing a print position adjusting mechanism in a conventional image forming apparatus.
FIG. 27
is a plan view showing a part of the print position adjusting mechanism in FIG.
26
. In the figures, there are shown a photosensitive drum
31
, a laser device
202
that forms latent images on the photosensitive drum
31
, a resist clutch (hereinafter, also referred to as “the resist roller”)
203
that determines the timing of feeding a sheet, a sheet sensor
1304
that detects a fed sheet, a deviation amount detection sensor
1305
that detects the amount of deviation of a side edge in a direction perpendicular to the direction in which a sheet is fed (hereinafter referred to as “the sheet feeding direction”), an output sheet
1401
, and a sheet feeding direction
1403
.
In the conventional print position adjusting mechanism having the above described configuration, a CPU, not shown, obtains the deviation amount of the side edge of the sheet detected by the deviation amount detection sensor
1305
and a sheet position in the sheet feeding direction detected by the sheet sensor
1304
, and transmits such information to an image control circuit, not shown. The image control circuit adjusts the timing of transferring image data that is to be transferred to a laser control circuit, not shown, that drives the laser device
202
, according to the obtained information.
After a position of starting writing an image by the laser device
202
(position of starting laser beam irradiation) is set, skew of the sheet is determined according to at least two positions of the side edge of the sheet detected by the deviation amount detection sensor
1305
, and thereafter displaying an error or the like is performed (for example, Japanese Laid-Open Patent Publication No. 9-219776).
However, the above described conventional print position adjusting mechanism of the image forming apparatus has a problem given below, and an improvement has been desired. That is, when sheet feeding is carried out at a high speed in order to increase printing speed, the reading capability of the sheet sensor particularly in the sheet feeding direction is insufficient; when a cheap mechanical sensor is used as a sheet sensor, the reading error is large, resulting in a deviation of the image position which is as large as the reading error.
Further, in the case that a single transparent or reflection type of optical sensor is used as a sensor that detects the leading edge of the sheet in the sheet feeding direction, when a sheet is fed with a skew, the leading edge may not be detected accurately. Therefore, it is very difficult to accurately correct the deviation of timing of feeding a sheet by a resist roller, using a single optical sensor.
Still further, the detection of the skew of a sheet is determined, according to the position of the side edge of the sheet detected by the deviation amount detection sensor
1305
during feeding of the sheet. Accordingly, image formation has already been carried out at the time a skew is detected. As a result, there is no other way but notifying the operator of the skew as an image output error.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide an image forming apparatus and an image formation control method which are capable of accurately detecting the position of a sheet in the sheet feeding direction to thereby obtain an accurate printing position even during high speed sheet feeding without an increase in the cost.
It is a second object of the present invention to provide an image forming apparatus and an image formation control method which are capable of accurately detecting skew of a sheet before formation of an image on the sheet to thereby prevent a sheet with an image formed with a low print quality due to skew of the sheet from being output.
To attain the first object, a first aspect of the present invention provides an image forming apparatus comprising an image forming section that forms an image of an original on a sheet, a resist roller that conveys the sheet to the image forming section in predetermined timing, a sheet reading section having a plurality of read pixels for reading an image of the sheet and disposed in an area which the sheet passes, between the image forming section and the resist roller in such a fashion that the plurality of read pixels are arranged in a direction perpendicular to a direction in which the sheet is fed, a leading edge detecting section that detects a leading edge of the sheet by repeatedly reading the plurality of read pixels with a predetermined period, and a start time determining section that determines timing for starting image formation by the image forming section, based on the leading edge of the sheet detected by the leading edge detecting section.
With the arrangement according to the first aspect of the present invention, the sheet reading section having a plurality of pixels is disposed between the image forming section and the resist roller in the direction perpendicular (hereinafter referred to as “the width direction”) to the sheet feeding direction to detect the leading edge of the sheet. As a result, the position of the sheet in the sheet feeding direction can be accurately detected even during feeding of the sheet at a high speed, which can achieve image formation based on an accurate print position.
To attain the first object, a second aspect of the present invention provides an image forming apparatus comprising an image forming section that forms an image of an original on a sheet, a resist roller that conveys the sheet to the image forming section in predetermined timing, a sheet reading section having a plurality of read pixels for reading the image of the sheet and disposed in an area which the sheet passes, in a such a fashion that the plurality of read pixels are arranged in a direction perpendicular to a direction in which the sheet is fed, a leading edge detecting section that detects a leading edge of the sheet by repeatedly reading the plurality of read pixels with a predetermined period, a start time determining section that is responsive to the leading edge of the sheet being detected by the leading edge detecting section, for determining timing for starting image formation in the direction in which the sheet is fed by the image forming section, a side edge detecting section that detects a side edge of the sheet by repeatedly reading the plurality of read pixels read by the leading edge detecting section, and a writing start position adjusting section that adjusts a writing start position in which the image of the original is written by the image forming section in the direction perpendicular to the direction in which the sheet is fed, based on the side edge of the sheet detected by the side edge detecting section.
With the arrangement according to the second aspect of the present invention, since the leading edge and side edge of the sheet are detected by the sheet reading section having a plurality of pixels arranged in the width direction, the sheet positions in the sheet feeding direction and the width direction can be accurately detected, to thereby enable realizing image formation based on accurate print positions. Further, no special leading edge detection sensor is required, which makes it possible to decrease the number of components and hence make an image forming apparatus more compact in size.
Preferably, the leading edge detecting section repeatedly reads a part of the plurality of read pixels.
Since the leading edge detecting section thus uses a part of the plurality of pixels of the sheet reading section, the reading period is shorter and hence the pixel data density
Canon Kabushiki Kaisha
Lee Susan
Rossi & Associates
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