Electrophotography – Control of electrophotography process – Having temperature or humidity detection
Reexamination Certificate
2001-03-28
2002-10-08
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Control of electrophotography process
Having temperature or humidity detection
Reexamination Certificate
active
06463226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier or a printer which uses an electrophotographic system or an electrostatic recording system.
2. Related Background Art
When an image forming apparatus is used, and if an operating environment around the apparatus is different from a storage environment of paper as a recording material, or even if the operating environment is the same as the storage environment of the paper, it can be presumed that the image forming apparatus is operated in a state where a moisture amount in the atmosphere of the operating environment is different from a moisture absorption amount of the paper.
Generally speaking, when plain paper (neutral paper) used for copying or the like stands alone in each environment from a state of room temperature, the time required for allowing a sheet of paper to sufficiently adapt itself to the environment is about one hour. Even if the paper loaded in a cassette and supplied to an image forming apparatus adapts itself to the environment for a sufficiently long time, moisture is absorbed in and dehydrated from a portion near by the surface in each environment.
In the situation above, especially in a low humid environment in which an absolute moisture amount in a surrounding environment of an image forming apparatus is small, if a continuous image output or an intermittent image output within a fixed time is successively performed exceeding the fixed time (a pseudo continuous image output), the difference (moisture amount of apparatus surrounding environment<moisture amount of paper) of this moisture amount may cause trouble for the image forming process.
In case of an image forming apparatus of an electrophotographic method, although transferring means uses a transferring belt, a roller or the like as a transferring member to transfer a toner image formed on a photosensitive member to paper, this transferring member is frequently used in contact with the photosensitive member or with a fixed amount of small gap retained. The toner image on the photosensitive member is efficiently transferred to the paper by making the paper adhere to the photosensitive member in a certain amount of adhesion state with this contacting or non-contacting transferring member.
When a continuous image output including a pseudo continuous image output is performed, a latent image potential change on a photosensitive member that is considered as influences, such as exfoliation discharge at transfer, a transfer voltage and the difference in a moisture amount of paper and an image forming apparatus occurs, and an image density change occurs.
A phenomenon in which a latent image on a photosensitive member is changed due to such continuous image output is a transient change unlike a degraded change until the life of an image forming apparatus expires. Accordingly, since the phenomenon is recovered when a certain measure of time elapses, the corrective action is difficult.
Generally, as remedy means against a latent image potential change on a photosensitive member, detection of environmental data, such as temperature and humidity, detection of the potential on the photosensitive member or detection of the density on the photosensitive member, a transferring material, an intermediate transferring member or paper is performed, and the density correction of an output image is performed based on each result.
If a potential sensor and a density sensor is not mounted on an image forming apparatus, such a method is usually used that makes an estimate to the extent of a process life and performs density correction based on the detection data of environmental parameters, such as temperature and humidity, using a potential change table and a development contrast on a previously prepared photosensitive member.
Further, in case of an image forming apparatus having no potential sensor and density sensor, there is also a method for reading an image density (a gradation pattern) using external reading means, such as a scanner, concerning an output image, and making the image forming apparatus perform correction according to a gradation correction table using communication means, as a measure for a density change.
However, since the density change under continuous output is a transient decrease, it is difficult to take a sufficient measure as long as such an image forming apparatus that always detects the potential on a photosensitive member and performs feedback control is not used. Moreover, if the correction described above is made by the reading means in such a situation in which a transient potential change on the photosensitive member occurs, the correction runs into a situation in which density correction is further necessary (refer to Japanese Patent Application Laid-Open No. 10-28229).
Hence, a measure for a change of a latent image on a photosensitive member, especially a decrease of an exposure portion potential (light portion potential Vl) that is directly linked with a density change, caused by a continuous image output using paper in a low humid environment, is necessary.
FIG. 7
shows a transition of a Dmax density at the time when a continuous image output is performed in a low humid environment at a temperature of 23° C. and a humidity of 5%. This environment at the temperature of 23° C. and the humidity of 5% is a low humid environment in which a moisture amount is 0.89 g/1 kg (a unit indicates g of water/l kg of air), and the moisture amount is less than 1 g/l kg.
It is known from
FIG. 7
that density decreases when a continuous image output is performed, and the density is recovered when the continuous image output stops for a certain period.
A latent image potential change in a passed sheet portion on a photosensitive member at this time is shown in FIG.
8
. It is known from by
FIG. 8
that density decreases due to a continuous image output, and the density is recovered when the continuous image output stops for a fixed period. It is characteristic that while the potential (Vd) of the non-exposure portion is almost fixed, a change of the potential (Vl) of the exposure portion is large.
FIG. 9
shows an enlarged drawing of the exposure portion potential of FIG.
8
. It is well known from
FIG. 9
that a decrease amount of the exposure portion potential VI also reaches 40 to 50 V at a maximum. It is known that the potential Vl decreases even in the exposure portion in which no image is formed on paper.
Since a change of the exposure portion potential on this level has a great effect on a development contrast potential, it causes a density change of about &Dgr;D=0.1 or more as shown in FIG.
7
.
As causes of a decrease of the exposure portion potential as shown in
FIG. 9
, various influence factors are considered. For example, a transfer voltage, exfoliation discharge in a transfer unit, wear between a photosensitive member and paper, a sensitivity change of the photosensitive member due to a temperature change, a sensitivity change of the photosensitive member due to a moisture absorption amount of paper or the like.
Table 1 shows the result on which the difference in a change of the exposure portion potential Vl according to the presence of 200 continuation passed sheets and the presence (ON/OFF) of transfer is examined in a low humid environment at a moisture amount of 0.89 g/kg.
TABLE 1
Decrease Amount of V1 Potential at 200
Continuation Sheets in Environment at Moisture Amount
of 0.89 g/kg
Passed sheet
Present
None
Transfer
ON
−30 V
−5 V
OFF
−20 V
—
Further, a change amount from an initial value of the exposure portion potential VI at the time when a continuous output of 1,000 sheets was performed with transfer ON, and a pseudo continuous output for a total of 1,000 sheets, intermittently 500 times every two sheets, was performed are shown in FIG.
10
. Besides, two kinds of lots A and B of photosensitive members were prepared. The two kinds of the lots A and B were tested for the continuous output and the one kind of the lot B
Kitajima Ken-ichiro
Toyohara Yuichiro
Fitzpatrick ,Cella, Harper & Scinto
Lee Susan S. Y.
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