Electrophotography – Control of electrophotography process – Having temperature or humidity detection
Reexamination Certificate
2001-06-07
2002-12-10
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Having temperature or humidity detection
C399S053000, C399S082000
Reexamination Certificate
active
06493522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process and to a developing device used in the image forming apparatus. More particularly, the present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine, and to a developing device used in the image forming apparatus.
2. Related Background Art
In recent years, many image processing apparatuses have been proposed as a hardware unit for digital information communication through a data communication network and for outputting digital information.
This kind of apparatus comprises a copying machine, a printer and a facsimile machine.
FIG. 9
is a diagram schematically showing essential portions of a digital printer, which is an example of this kind of conventional image forming apparatus.
A photosensitive drum
1
provided as an image bearing member is formed of a cylindrical electroconductive base member and a photoconductive layer formed on the base member, and is supported so as to be rotatable in the direction indicated by the arrow A in FIG.
9
.
Around the photosensitive drum
1
are successively disposed, along the direction indicated by the arrow A, a primary charger
2
which uniformly charges the surface of the photosensitive drum
1
, an exposing device
3
which reads an original to obtain an image signal according to the density of an image and exposes the photosensitive drum
1
on the basis of the image signal to form an electrostatic latent image, a developing device
4
which attaches toner (developer) to the electrostatic latent image to form a toner image (developed image), a transfer-separation charger
5
which transfers the toner image formed on the photosensitive drum
1
onto a sheet S and separates from the photosensitive drum
1
the sheet S having the transferred toner image on its surface, a cleaning device
6
which removes residual toner on the photosensitive drum
1
after transfer of the toner image, and a pre-exposing device
7
which eliminates residual charge on the photosensitive drum
1
.
Sheet S having the transferred image on its surface is transported to a fixing device
8
after being separated from the photosensitive drum
1
. In the fixing device
8
, the toner image on the surface of sheet S is fixed and the desired printed image is formed by image forming means to be delivered to a place outside the image forming apparatus.
In a reader unit
91
, an original placed on an original glass stand
911
is irradiated with light emitted from an illumination lamp
912
, and reflected light from the original is imaged on a single-line photoelectric element array
913
provided as a photoelectric conversion element to be converted into an electrical signal in accordance with image information. Reflected light from the original irradiated with light from the illumination lamp
912
is guided by mirrors
914
a
and
914
b
and imaged on the photoelectric conversion device
913
by a lens
916
. The electrical signal output from the photoelectric conversion device
913
undergoes analog to digital conversion in an analog to digital (A/D) converter
915
to be converted into an 8-bit digital image data. This image data undergoes logarithmic conversion in a black signal generation circuit
917
to convert luminance information into density information, thereby obtaining image density data.
Eight-bit digital image data formed as described above is supplied to a laser drive circuit
301
, which is a well-known pulse-width modulation (PWM) circuit. The drive circuit
301
modulates the emission time of a semiconductor laser
304
according to the supplied image density signal so as to change the area grayscale level in each pixel area, thereby realizing a tint or tone.
Laser driving methods are generally grouped into those using a PWM circuit corresponding to that described above and those using a binary laser drive circuit. The PWM circuit modulates, according to the level of the input image density signal, a pulse width signal corresponding to the time period during which the semiconductor laser emits light, as described above. On the other hand, the binarizing circuit converts the image signal into a two-step signal consisting of particular emission-on and emission off signals and inputs this two-step signal to the laser drive circuit
301
, thereby turning on and off the semiconductor laser device
304
.
Laser light emitted by the above-described laser driving according to the image signal is led to the photosensitive drum
1
by a polygon mirror scanner
302
rotating at a high speed and by a mirror
303
to perform raster scan writing on the photosensitive drum
1
, thereby forming a digital electrostatic latent image as image information.
A number of electrophotographic methods, including the inventions patented as U.S. Pat. No. 2,297,961, Japanese Patent Publication (Kokoku) Nos. 42-23910 and 43-24748, etc., are known. Ordinarily, an electrical latent image is formed by one of various available means on a photosensitive drum provided as a recording medium using a photoelectric material and is developed by using toner (developer), and the obtained toner image is transferred onto a recording member such as paper selected as desired and is fixed on the recording member by heating or processing using a solvent vapor or the like to produce an image output.
Also, various development methods for visualizing an electric latent image by using a developer are known, which are, for example, magnetic brush development methods relating to U.S. Pat. No. 2,874,063, powder cloud methods relating to U.S. Pat. No. 2,221,776, fur brush development methods, and liquid development methods. In particular, among these development methods, magnetic brush development methods using a two-component developer having toner and a carrier as main components have been put into wide practical use. This kind of method makes it possible to obtain a good image with comparatively high stability, but entails drawbacks relating to the two-component developer, i.e., degradation of the carrier and variation in the toner/carrier mixture ratio.
To avoid these drawbacks, various development methods using a monocomponent developer composed of toner alone have been proposed. This kind of development method eliminates the need for control of the amount of toner with respect to the toner/carrier mixture ratio and has the advantage of simplifying the image forming apparatus.
Such a monocomponent development method is carried out in such a manner that a developer bearing member
41
of the developing device
4
is disposed so as to be opposed to the photosensitive drum
1
for bearing an electrostatic latent image in a noncontact relationship therewith, and a developing bias voltage E from a power supply
49
is applied between the developer bearing member
41
and the photosensitive drum
1
to perform development of the electrostatic latent image on the photosensitive drum (image bearing means)
1
(see FIGS.
6
and
7
).
Methods which have been widely used as a method for forming a developer layer on the surface of the developer bearing member
41
to perform the above-described development are a method in which a member
43
in the form of a plate is used as a developer layer forming means and a suitable pressure “P” is applied to the member
43
to maintain the same in contact with the developer bearing member
41
(FIG.
6
), and a method in which a developer layer forming member
43
is disposed with a suitable gap G
1
formed between the member
43
and the developer bearing member
41
(
FIG. 7
) and a developer is fed to the vicinity N of the plate-shaped member
43
by rotation of the developer bearing member
41
in the direction indicated by the arrow B. The latter method is suitable for a high-speed image forming apparatus.
Ordinarily, the peripheral speed Vdahm of the developer bearing member is set higher, more specifically 1.4 to 2.2 times higher than that of the image bearing me
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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