Image forming apparatus with half-tone density control

Details Image forming apparatus with half-tone density control Image forming apparatus with half-tone density control

2000-04-07

2001-04-10

Pendegrass, Joan (Department: 2852)

Electrophotography

Control of electrophotography process

Of plural processes

C358S296000

Reexamination Certificate

active

06215968

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an image forming apparatus employing an electrophotographic technique, such as a copying machine, a laser beam printer, and a facsimile machine.
BACKGROUND OF THE INVENTION
A color electrophotographic device includes a plurality of photosensitive drums
1
as shown in
FIG. 2
explaining an image forming apparatus of the present invention. Each photosensitive drum
1
is supported rotatably and driven to rotate in a direction indicated by an arrow by means of a driving device.
Provided sequentially around each photosensitive drum
1
are: a charging device
2
for charging the surface of the photosensitive drum
1
uniformly; exposing means
3
for exposing the surface of the photosensitive drum
1
to form a latent image; a developing device
4
for developing the latent image to a toner image; a transferring device
5
for transferring the toner image onto a transfer material; and a cleaning device
6
for cleaning residual toner on the surface of the photosensitive drum
1
.
The four photosensitive drums
1
are aligned in series, and provided with developing bathes respectively containing color toners: Y (yellow), M (Magenta), C (Cyan), and Bk (Black).
The transferring device
5
is provided with a transfer belt
7
which is looped over a driving pulley and a slave pulley and run in a direction indicated by arrows. A recording medium as the transfer material is held electrostatically and thus transported by the transfer belt
7
.
Transfer chargers
8
are provided inside the loop of the transfer belt
7
so as to oppose the respective photosensitive drums
1
, thereby transferring toner images formed on their respective photosensitive drums
1
onto the recording medium.
The recording medium held by the transfer belt
7
passes by the four photosensitive drums
1
and further a fusing device
9
, whereby the toner image is fused onto the same.
In the electrophotographic device represented by the above color electrophotographic device, density characteristics vary with an applied voltage and a temperature rise caused by a series of charging, exposing, and developing actions in the electrophotographic process. For this reason, before input image data is outputted, the density characteristics are corrected as desired in most of the cases.
More specifically, a plurality of toner patterns each having a specific density are formed on the photosensitive drum
1
each time the power supply starts or a predetermined number of sheets are released. Then, the densities of these toner patterns are checked by a sensor, and differences between the checked densities and corresponding optimal densities, that is, the preset reference values, are found. Then, a density conversion table is created based on these differences. Thereafter, the density of the input image data is corrected based on the density conversion table thus created before the image is outputted.
Incidentally, an image forming apparatus, such as an electrophotographic device, outputs several kinds of images including solid (black-painted), line, half-tone, etc. Images vary when influenced by varying factors, namely, a series of charging, exposing, developing, and transferring actions in the electrophotographic process, and therefore, the density of an output image can not be maintained at a specific level without effecting a density correction. In addition, influence from the varying factors in the electrophotographic process varies with the kinds of images, and a density correction has to be controlled differently for each kind of images.
However, because the conventional image forming apparatus controls a quantity of toner to be adhered to the photosensitive drum
1
by detecting the density or a quantity of toner on a solid image, there rises a problem that a density of an entire output image can not be made uniform for each kind of images.
To solve the above problem, for example, Japanese Laid-open Patent Application No. 265571/1996 (Japanese Official Gazette, Tokukaihei No. 8-265571, publishing date: Oct. 11, 1996) discloses an image forming apparatus as follows.
That is, the image forming apparatus disclosed in the above publication forms two kinds of density detecting toner patterns, namely, a high density detecting toner pattern and a half-tone density toner pattern, by changing a developing bias, so that the density of an entire image having half-tones, etc. can be corrected adequately.
The high density detecting toner pattern is detected by toner quantity detecting means composed of a reflection sensor, and the maximum toner quantity on the photosensitive drum is controlled by density correcting means. The half-tone detecting toner pattern is also detected by the toner quantity detecting means, and a toner quantity on the photosensitive drum for a half-tone density portion is adjusted under control of the density correcting means. By effecting both the control of the maximum toner quantity using the high density detecting toner pattern and the control of the toner quantity for the half-tone density portion using the half-tone detecting toner pattern, the density of an entire image is maintained uniformly at a specific level.
More specifically, the density correcting means has the toner quantity detecting means detect the high density from the high density detecting toner pattern, compares the detected high density with the high density reference value, and effects the high density correction if there is a difference. Further, after the high density portion of the image is adjusted, the density correcting means has the toner quantity detecting means detect the half-tone density from the half-tone density detecting toner pattern, compares the detected half-tone density with the half-tone density reference value, and effects the half-tone density correction if there is a difference.
Also, Japanese Laid-open Patent Application No. 289148/1996 (Japanese Official Gazette, Tokukaihei No. 8-289148, publishing date: Nov. 1, 1996) discloses a half-tone density correction. According to this publication, a plurality of half-tone toner patterns of respective colors are formed on a transfer belt by changing a pulse width of a laser beam during the exposing action in the series of charging, exposing, developing, and transferring actions, and these patterns are checked sequentially by a density detecting sensor, whereby an optical density is detected from the checking results.
Then, the checked density values are compared with prestored target density values of their respective colors, and differences between the target density values and current density values are computed to update a half-tone table.
As has been discussed, the density correction using the toner patterns is effected by forming a plurality of toner patterns each time the power supply starts or a predetermined number of sheets are released.
Hence, the conventional image forming apparatus not only effects the high density correction, but also adjusts the half-tone density, and therefore, the density correction takes a considerably long time. Consequently, the conventional image forming apparatus keeps the user waiting longer compared with an image forming apparatus which effects the high density correction alone, thereby posing a problem as not being user-friendly.
In addition, because the half-tone density is adjusted in addition to the high density correction, a larger quantity of toner is consumed in forming the half-tone density detecting toner patterns for the half-tone density adjustment, thereby increasing the cost undesirably.
The following will explain more in detail the half-tone density correction method disclosed in Japanese Laid-open Patent Application No. 289148/1996 supra. Initially, a first density conversion table used as a reference is created at the time of maintenance. Then, when an image is outputted, a toner pattern is formed each time a predetermined number of copies are made, and the density of the toner pattern is checked, based on which a second density conversion table is created. S

Affiliated with

Also associated with

Rating

Image forming apparatus with half-tone density control 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 with half-tone density control, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus with half-tone density control will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2520643