Electrophotography – Internal machine environment – Forced air circulation
Reexamination Certificate
2001-07-25
2003-07-15
Grainger, Quana M. (Department: 2852)
Electrophotography
Internal machine environment
Forced air circulation
C399S044000, C399S094000
Reexamination Certificate
active
06594456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image forming apparatus for effecting image recording by way of an electrophotographic process. The invention also relates to an image forming apparatus having a temperature detecting sensor for controlling image forming conditions.
2. Description of the Related Art
An image forming apparatus such as a laser printer or a copier has heretofore detected the outside air temperature by a temperature detecting element such as a thermistor disposed therein, and has appropriately determined a process parameter such as the temperature of a heat-fixing device by outside air temperature information.
However, the temperature detecting element such as a thermistor is disposed in the apparatus, and this leads to the problem that the outside air temperature cannot be accurately detected under the influence of the self temperature rise of the apparatus.
Also, as an image forming apparatus of this kind, there is an image forming apparatus of the electrophotographic type such as a laser printer or a copier. The image forming apparatus of the electrophotographic type according to the related art will hereinafter be described with reference to
FIG. 10
of the accompanying drawings.
FIG. 10
is a typical cross-sectional view of the image forming apparatus according to the related art.
A recording medium
2
set in a sheet feeding cassette
3
a
is conveyed to a transferring position by a pickup roller
3
b
, a pair of feed and retard rollers
3
c
, a pair of conveying rollers
3
d
and a pair of conveying rollers
3
e
. A transferring roller
4
as transferring means is disposed at the transferring position, and by a voltage being applied thereto, the transferring roller
4
transfers a toner image on a photosensitive drum
7
to the recording medium
2
.
The photosensitive drum
7
is charged by charging means
8
, and then a laser beam is applied thereto from optical means
1
, whereby a latent image conforming to image information is formed on the photosensitive drum
7
. This latent image is developed into a visible image, i.e., a toner image, by developing means
9
.
The recording medium
2
to which the toner image has been transferred is conveyed to fixing means
5
via a conveying belt
3
f
. The fixing means
5
applies heat and pressure to the recording medium
2
passing therethrough to thereby fix the transferred toner image on the recording medium
2
.
Particularly, if the fixing means is of a film heating type (disclosed in Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 2-157878, Japanese Patent Applications Laid-Open Nos. 4-44075 through 44083, Japanese Patent Applications Laid-Open Nos. 4-204980 through 204984, etc.), heat-resistant film (heat-resistant fixing film) which is a heating rotary member is brought into close contact with a heat generating member by a pressurizing rotary member (elastic roller).
A pressure contact nip portion is formed with the heat-resistant fixing film nipped between the heating member and the pressurizing member, and the recording medium bearing an unfixed image thereon is introduced into between the heat-resistant fixing film and the pressurizing member and is conveyed with the heat-resistant fixing film, and by the heat from the heating member imparted through the heat-resistant fixing film and the pressure of the pressure contact nip portion, the unfixed image is fixed as a permanent image on the recording medium.
Thereafter, the recording medium is conveyed and discharged onto a discharge tray
6
by a pair of discharge rollers
3
g
and a pair of discharge rollers
3
h.
A thermistor (not shown) is provided in the fixing means
5
, and on the basis of detected temperature information, a suitable fixing temperature is determined and temperature adjustment is effected. Also, appropriate transfer control is effected on the basis of an electric current or a voltage in the transferring roller
4
when the recording medium
2
is or is not nipped between the photosensitive drum
7
and the transferring roller
4
.
As described above, there is adopted a process of applying feedback on the basis of the information in the control device chiefly from a point of time at which the recording medium
2
has arrived at the fixing means
5
or the control means of the transferring roller
4
.
Also, a fan
10
is provided on the side surface of the main body of the image forming apparatus. The fan
10
takes in the outside air into an air trunk formed in the apparatus to prevent the inside air of the apparatus from rising.
In the case of the related art as described above, however, there have arisen the following problems.
In the image forming apparatus as described above, particularly, if the fixing means is of the film heating type, a linear heating member of low heat capacity is used as the heating member and a thin film material of low heat capacity is used as the film and therefore, the saving of electric power and the shortening of the waiting time become possible, but there is also a side in which the image forming apparatus is liable to be affected by the temperature environment under which the apparatus is used. Accordingly, the amount of heat is liable to become excessive or deficient.
When the amount of heat is excessive, a portion of the toner image remains on the fixing film side and after one revolution of the film, a bad image in which that toner is transferred to the recording medium may occur. Also, when the amount of toner is deficient, there is the possibility of causing bad fixing.
As described above, the outside air temperature cannot be detected with good response and accurately and therefore, it has not been possible to effect appropriate fixing temperature control taking even the outside air temperature into account.
Also, when control of a transfer bias is performed, the outside air temperature cannot be detected with good response and accuracy, similar to the fixing temperature control. Therefore, it has not been possible to effect appropriate transfer bias control taking even the outside air temperature into account. This also may cause a bad image.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-noted problems and an object thereof is to provide an image forming apparatus in which the outside air temperature can be detected with high accuracy and a process parameter can be set appropriately.
To achieve the above object, the present invention is an image forming apparatus for effecting image recording on a recording sheet by the electrophotographic process. In one aspect, the apparatus comprises a cooling fan, a temperature sensor disposed in the vicinity of the cooling fan, and outside air temperature calculating means for calculating the outside air temperature on the basis of temperature information from the temperature sensor, wherein the parameter of the electrophotographic process is changed on the basis of outside air temperature information from the outside air temperature calculating means, characterized in that the outside air temperature calculating means finds an average value obtained by averaging temperatures detected by the temperature sensor during the non-recording operation for a predetermined time period, and a value obtained by subtracting a predetermined value from the average value is the outside air temperature.
Preferably, the image forming apparatus is characterized in that when a power source switch is ON, the outside air temperature calculating means judges a temperature detected by the temperature sensor immediately after the closing of the power switch as the outside air temperature, and retains the detected temperature as the outside air temperature for a predetermined time period.
Preferably, the image forming apparatus is characterized in that during the non-recording operation, the cooling fan is intermittently driven at a predetermined cycle period, and the outside air temperature calculating means judges a value obtained by subtracting a
Hashimoto Hiroshi
Kimizuka Eiichiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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