Electrophotography – Image formation – Development
Reexamination Certificate
1999-11-03
2001-04-17
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
C399S175000
Reexamination Certificate
active
06219514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying apparatus, for example, a copying apparatus or a laser beam printer, and an electrostatic recording apparatus. More particularly, the present invention relates to an image forming apparatus for obtaining an image by developing an electrostatic latent image formed onto an image bearing member by toner.
2. Related Background Art
FIG. 5
is a schematic block diagram showing an image forming apparatus, and the operation thereof will be simply described.
First, an original G is put on an original mount
10
so that the surface to be copied of the original G faces downward. Next, a copy button is pressed, thereby starting the copying operation. The original G is scanned in the direction of an arrow by a unit
9
constructed integrally by a lamp for irradiating the original, a short focus lens array, and a CCD sensor while being irradiated by the unit
9
. The short focus lens array forms an image of original surface reflection light of the irradiation scanning light, and the formed image is inputted to the CCD sensor.
The CCD sensor is made up of: a light receiving unit; a transfer unit; and an output unit.
An optical signal is converted into a charged signal by the CCD light receiving unit, and the charged signal is synchronized with a clock pulse and sequentially transferred to the output unit by the transfer unit. In the output unit, the charged signal is converted into a voltage signal and amplified, and the impedance of the amplified signal is decreased, thereby outputting the signal. The voltage signal (analog signal) obtained in the above-mentioned manner is subjected to well-known image-processing, converted into a digital signal, and transmitted to a printer unit.
In the printer unit, the foregoing image signal is received and an electrostatic latent image is formed as follows. A photosensitive drum
1
is driven to rotate at a predetermined circumferential velocity in the direction of an arrow A while setting a spindle la as a center. In the rotating process, the surface is first subjected to a charging process uniformly so as to have a voltage of about −650 V by a charger
3
. The uniformly charged surface is scanned by light of a solid laser element for emitting light switched on/off in reply to the image signal with a rotary polygon mirror
104
(in
FIG. 6
) that rotates at a high speed, and thereby sequentially forms an electrostatic latent image for which the surface potential is attenuated to about −200 V in correspondence with the original image onto the surface of the photosensitive drum
1
.
FIG. 6
is a schematic block diagram showing the structure of a laser scanning unit
100
for scanning laser beams in the image forming apparatus. When scanning the laser beams with the laser scanning unit
100
, a solid laser element
102
is first flickered at a predetermined timing on the basis of an inputted image signal by a light emitting signal generating device
101
.
The laser beams irradiated from the solid laser element
102
are converted into luminous flux that are substantially in parallel to each other with a collimator lens system
103
. Further, the beams are scanned toward the direction of an arrow C with the rotary polygon mirror
104
rotating in the direction of an arrow B. The image is also formed onto a spot of a surface to be scanned
106
of a photosensitive drum or the like through an f&thgr;-lens group of
105
a,
105
b,
and
105
c.
The laser beams are scanned as mentioned above and, therefore, exposure distribution corresponding to one scanning of the image is formed on the surface to be scanned
106
. Further, if the surface to be scanned
106
is scrolled in the direction vertical to the scanning direction by a predetermined quantity in every scanning, exposure distribution can be obtained on the surface to be scanned
106
in response to the image signal.
Next, a developing step will now be described. Generally, there are four kinds of developing methods as follows.
(1) A method of coating non-magnetic toner onto a sleeve by a blade or the like, and coating magnetic toner onto the sleeve by magnetic force and carrying them, thereby developing the toner to the photosensitive drum
1
in a non-contact state (one-component non-contact developing)
(2) A method of developing the toner coated as mentioned above to the photosensitive drum in a contact state (one-component contact developing)
(3) A method of mixing magnetic carriers with toner particles, using them as the developer, and carrying them by magnetic force, thereby developing an image to a photosensitive drum in a contact state (two-component contact developing)
(4) A method of developing the foregoing two-component developer in a non-contact state (two-component non-contact developing)
It is easy to obtain a halftone image having high resolution. Consequently, there has been frequently used, for an image forming apparatus requiring a high picture quality, the two-component contact developing method such that the mixture of the toner particles and the magnetic carriers are used as the developer, and the image is developed in the contact state with the photosensitive drum such as a full-color copying apparatus.
A developing device
4
has a developer container
16
as shown in FIG.
7
. The inside of the developer container
16
is partitioned to a developing chamber (first chamber) R
1
and an agitating chamber (second chamber) R
2
by a partitioning wall
17
. Supply toner (non-magnetic toner)
18
is contained in a toner storage chamber R
3
. A supply port
20
is provided to the partitioning wall
17
, and the supply toner
18
in an amount corresponding to consumed toner is dropped and supplied into the agitating chamber R
2
through the supply port
20
.
On the other hand, a developer
19
is contained in the developing chamber R
1
and agitating chamber R
2
. The developer
19
is a two-component developer having non-magnetic toner and magnetic particles (carriers) (as a mixing ratio, the ratio of the non-magnetic toner is set to about 4% to 10% by weight). The non-magnetic toner has a volume mean particle diameter of about 5 to 15 &mgr;m. The magnetic particles are comprised of ferrite particles that have been resin-coated, resin particles to which a magnetic substance has been dispersed, or the like. As for the magnetic particles, the weight mean particle diameter is equal to 25 to 60 &mgr;m, the volume resistivity is equal to 10
6
to 10
13
&OHgr;·cm, and the transmittivity of the magnetic particles is equal to 2.5 to 5.0.
An opening portion is provided to a region that is close to the photosensitive drum
1
of the developer container
16
, and a developing sleeve
11
is provided so as to be projected toward the outer side from the opening portion. The developing sleeve
11
is rotatably assembled in the developer container
16
. The outer diameter dimension of the developing sleeve
11
is equal to 32 mm. The circumferential velocity of the developing sleeve
11
is equal to 280 mm/sec and the developing sleeve
11
is rotated in the direction of an arrow in the drawing. An interval Da between the developing sleeve
11
and the photosensitive drum
1
is arranged so as to have a distance of almost 500 &mgr;m. The developing sleeve
11
is made of non-magnetic material, and a magnet
12
serving as magnetic field generating means is fixed into the developing sleeve
11
.
The magnet
12
has: a developing magnetic pole S
1
; a magnetic pole N
3
located downstream from the developing magnetic pole S
1
; and magnetic poles N
2
, S
2
, and N
1
for carrying the developer
19
. The magnet
12
is arranged in the developing sleeve
11
so that the developing magnetic pole S
1
almost faces to the photosensitive drum
1
. The developing magnetic pole S
1
forms a magnetic field near a developed portion between the developing sleeve
11
and photosensitive drum
1
, and a magnetic brush is formed by the formed magnetic fi
Hibino Masaru
Kobayashi Yoshiaki
Ozawa Ichiro
Shida Masanori
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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