Electrophotography – Control of electrophotography process – Responsive to copy media characteristic
Reexamination Certificate
2000-07-31
2002-04-30
Brase, Sandra (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to copy media characteristic
C399S068000, C399S069000, C399S389000
Reexamination Certificate
active
06381422
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus applicable to a copier, a printer and the like, and more particularly to an image forming apparatus for fine-adjusting a fixation speed of a development material in accordance with temperature control for fusing and fixing the development material.
DESCRIPTION OF THE PRIOR ART
In general, an image forming apparatus prints and records image information supplied from an image information supplying device such as a personal computer (which will be referred to as PC hereinafter) or a digital camera onto paper such as plain paper or an OHP sheet and can be applied to, for example, a color plain paper copy machine (which will be referred to as PPC hereinafter) or a printer. It is to be noted that paper may be referred to as “an image forming medium” in this specification according to circumstances.
The image forming apparatus for the above-described usage comprises: an image forming unit for forming an image by using a development material such as toner; a paper feeding portion for supplying paper to this image forming unit; a paper carrying portion for carrying the supplied paper; and a paper feed/paper carriage controlling portion for controlling supply/carriage of the paper to the image forming unit by the paper feeding portion and the paper carrying portion. The image forming unit includes: an image bearer for accreting the development material to be borne as an image after obtaining a latent image of an optical image formed through an optical system; a development unit for developing the latent image borne by this image bearer as an image by the development material; a transfer unit for transferring the developed image onto the paper; and a fixation unit for fixing the transferred image.
The fixation unit includes a heat roller and a press roller which sandwich the image forming medium carried by the transfer unit on the upstream side and rotate. A heat lamp for heating is provided in each of the heat roller and the press roller, and thermistors for detecting a surface temperature of each roller are provided in the vicinity of the both rollers.
The control operation for a temperature for fixing the development material in the image forming apparatus having the above-described structure will now be schematically described with reference to a flowchart of FIG.
1
. In
FIG. 1
, the processing operation for selecting a type of the image forming medium is first carried out in accordance with a user's choice (step ST
1
). In the step ST
2
, the type of the image forming medium is then determined, and a set temperature T is set in the fixation unit in accordance with the paper type in the step ST
3
. When the fixation temperature is set, a fixation temperature control sequence is started so that the temperature management is performed in accordance with a predetermined sequence in the step ST
4
.
In
FIG. 1
, as to the set temperature T, a set value is adjusted by using an adjustment sequence in the adjustment mode. The step ST
10
in this adjustment sequence includes the adjustment mode step ST
11
for setting the fixation temperature and the adjustment mode step ST
13
for setting a fixation drive speed. When setting of the fixation temperature starts in the step ST
11
, the set value is stored in the step ST
12
and the value is supplied as the set temperature T in the step ST
3
.
Upon starting control of the adjustment mode step ST
13
, the set value of the fixation drive speed is set in the step ST
13
, and the set value is stored in the step ST
14
. This set value is used for setting a standard speed S of the fixation drive speed in the step for setting the fixation drive speed S in the step ST
15
. The standard speed S of the drive speed is set separately from setting of the fixation temperature T in the step ST
3
. In the adjustment sequence in the step ST
10
, the fixation temperature T and the drive speed S are separately set without correlation, and only the set value of the fixation temperature T is taken in the control sequence. Therefore, the set value for the fixation drive speed is not used in the conventional control sequence.
Although the fixation unit fuses and fixes onto the paper the toner electrostatically absorbed on the paper, an appropriate temperature for fixation varies depending on a thickness of the paper. In case of a color image formed by using a color development material, a color having a predetermined gradation is formed by superimposing toners having different colors, e.g., yellow (Y), magenta (M), cyan (C). That is, toners having different colors are superimposed and fused to be mixed, thereby obtaining a desired color. Therefore, a temperature for fusing this color toner and a speed for fixing the toner are not separately controlled, but a technique for correlating them with each other to be fine-adjusted is demanded.
In particular, when forming an image on the surface of such as a transparent sheet used for an OHP (Over-Head Projector) and the like or forming an image on thicker paper than the plain paper, the optimum temperature management is required. Therefore, when forming an image on the image forming medium such as the thick paper or the transparent sheet, a fixation temperature optimum for the image forming medium chosen in the paper selection is fine-adjusted in advance, and an optimum temperature for each medium is set.
As a prior art relating to control over the fixation temperature and the fixation speed in such a fixation device, there are image forming apparatuses disclosed in Japanese patent application laid-open No. 138789-1994, Japanese patent application laid-open No. 219292-1995, Japanese patent application laid-open No. 220928-1996 and others. The first prior art is a technique for preventing a non-paper passing portion of the fixation roller from being unnecessarily heated; the second prior art, a technique for adjusting the fixation speed and the transfer speed in a transfer drum in accordance with each paper type; and the third prior art, a technique for preventing the fixation temperature from falling when passing the long recording paper.
In the prior art including the above-described literatures, since the heat roller and the press roller which are provided to the fixation unit thermally expand so that diameters of them increase when the fixation temperature becomes high, the speed for carrying the paper increases. When this speed exceeds the transfer speed of the transfer belt on the upstream side, the paper being carried is pulled, which generates a minute displacement at a part where transfer is carried out on the paper. Therefore, even if displacement or color shift is not generated on the part of paper where image formation was carried out earlier, displacement or color shift occurs on the part of paper where image formation was performed later, and the image formation accuracy in the entire one sheet of paper is deteriorated.
In particular, in a color image forming apparatus in which both an exposure device and a photosensitive body are united as one and multiple kinds of development materials are held in each development unit and copulatively changed over so that superimposed images are formed on the photosensitive drum, since supply positions of development materials supplied from a plurality of development units provided in accordance with respective colors are subtly displaced for example, there is a problem that displacement or color shift becomes prominent at the part of the paper where the image formation is delayed.
Further, in cases where the speed for carrying the image forming medium in the fixation unit increases even in an image forming apparatus which holds only the black development material and develops and fixes a monochrome image and there is a difference between the carriage speed and the development speed in the development unit, there occurs blur of an image or displacement of an image formation position on the part of paper where image formation is delayed, which leads to a problem such that a desired
Brase Sandra
Toshiba Tec Kabushiki Kaisha
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