Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2000-02-23
2002-08-27
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S060000, C399S062000
Reexamination Certificate
active
06442355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus of electrophotographic type or electrostatic recording type embodied as a copying machine, a printer and the like, and a developer density controlling apparatus used with such an image forming apparatus, and more particularly it relates to an image forming apparatus having a density controlling apparatus for controlling toner density or image density of the developer developing agent through toner replenishing control of two-component developer.
2. Related Background Art
In general, in developing devices of an image forming apparatuses of electrophotographic type or electrostatic recording type, one-component developer mainly including magnetic or non-magnetic toner, or two-component developer mainly including non-magnetic toner and magnetic carrier is used. Particularly, in color image forming apparatuses for forming a full-color or multi-color image by an electrophotographic system, many developing devices utilize two-component developer in consideration of color tone and image quality of an image.
As is well-known, toner density (ratio of a weight of toner with respect to a total weight of carrier and toner) of the two-component developer is a very important factor for stabilizing image quality. During development, the toner in the developer is gradually consumed to reduce the toner density. Thus, it is required that the toner density or image density is always detected by using a toner density controlling apparatus (toner density detecting means) or image density detecting means and toner is replenished in accordance with the change in density to keep the toner density or image density constant, thereby maintaining the image quality.
FIG. 7
shows an example of an image forming apparatus (digital copying machine of electrophotographic type in this example) having a conventional toner density controlling apparatus.
First of all, an image on an original G is read by a CCD
1
, and a read analogue image signal is amplified to a predetermined level by an amplifier
2
and then is converted into an 8-bit (0 to 255 gradations) digital image signal by an analogue/digital converter (AID converter)
3
, for example.
Then, the digital image signal is sent to a &ggr;-converter
5
(converter for effecting density conversion by a look-up table system constituted by a 256-byte RAM, in this example), where the signal is subjected to &ggr;-correction. Thereafter, the signal is inputted to a digital/analogue converter (D/A converter)
9
.
The digital image signal is converted into an analogue image signal again by the converter
9
and then is inputted to one of inputs of a comparator
11
. A triangular wave signal having predetermined period generated from a triangular wave generating circuit
10
is inputted to the other input of the comparator
11
, so that the analogue image signal supplied to the one input of the comparator
11
is compared with the triangular wave signal and is subjected to pulse width modulation. The pulse width modulated binary image signal is inputted to a laser driving circuit as it is, and is used as an ON/OFF control signal for light emission of a laser diode
13
. A laser beam emitted from the laser diode
13
is scanned by a known polygon mirror
14
in a main scanning direction and is illuminated onto a photosensitive drum
40
as an image bearing member (rotated in a direction shown by the arrow) through an f&thgr; lens
15
and a reflection mirror
16
, thereby forming an electrostatic latent image.
On the other hand, the photosensitive drum
40
is subjected to uniform electricity removal by an exposure device
18
and then is uniformly charged, for example negatively, by a primary charger
19
. Thereafter, the laser beam is illuminated onto the photosensitive drum, thereby forming the electrostatic latent image corresponding to an image signal. The electrostatic latent image is developed by a developing device
20
as a visualized image (toner image). A toner replenishing hopper (tank)
8
containing replenishing toner
29
is attached to an upper part of the developing device
20
, and a toner carrying screw (toner replenishing means)
30
rotated by a motor to carry the toner
29
and supply it into the developing device
20
is disposed at a lower part of the hopper
8
.
The toner image formed on the photosensitive drum
40
is transferred, by a transfer charger
22
, onto a transfer material P conveyed to the photosensitive drum
40
by a transfer material bearing belt
17
. The transfer material bearing belt
17
is mounted and extending between two rollers
25
a
and
25
b
and is driven in a direction shown by the arrow in an endless fashion; meanwhile, the transfer material P borne on the belt is conveyed to the photosensitive drum
40
. Residual toner remaining on the photosensitive drum
40
is scraped by a cleaner
24
.
Incidentally, for simplifying the explanation, although only a single image forming station (comprised of latent image forming means including the exposure device
18
and the primary charger
19
, the photosensitive drum
40
, the developing device
20
and the like) is shown, in case of a color image forming apparatus, image forming stations corresponding to various colors (for example, cyan, magenta, yellow and black) are arranged in series above the transfer material bearing belt
17
along the shifting direction thereof.
The image forming apparatus is designed so that, in order to keep the toner density of developer or image density constant by effecting control for replenishing the toner to the developer
21
(toner density thereof is decreased) within the developing device
20
, by controlling rotation of a motor
28
by a CPU
6
through a motor driving circuit
7
on the basis of an output value a toner density sensor
23
provided within the developing device
20
, the control for replenishing the toner to the developer
21
within the developing device
20
, thereby keeping the toner density of developer or image density constant. Control data supplied to the motor driving circuit
7
is stored in a RAM
90
connected to the CPU
6
.
In order to control the toner density of developer or image density to be kept constant by effecting control for replenishing the toner to the developer
21
(toner density thereof is decreased) within the developing device
20
, one of density controlling apparatuses (ATR) of various types is provided within the image forming apparatus.
More specifically, regarding the toner density sensor
23
provided within the developing device
20
, an auto-toner replacement (ATR) control system (developer reflection ATR) in which the toner density of the developer
21
within the developing device
20
is detected as a reflected light amount, a control system (inductance ATR) in which permeability of magnetic carrier of the developer
21
within the developing device
20
is detected, or a control system (patch detection ATR) in which a reference patch image
26
is formed on the photosensitive drum
40
and image density of the patch image is detected by a sensor
27
such as a potential sensor opposed to the photosensitive drum
40
can be used.
However, since each of the above-mentioned ATRs by itself detects only the image density or toner density, countermeasure to change in environment or change in developing ability due to degradation of developer cannot be effected, so that the image may be deteriorated. Thus, a technique in which two or more ATRs are combined to compensate for the respective defects thereby to permit toner replenishing control has been proposed, as disclosed in Japanese Patent Application Laid-Open No. 9-127757.
According to this patent document, the toner is replenished by the developer reflection ATR, and, in this case, a toner excess/deficiency amount required for returning patch image density to initial density is calculated from output signals representative of difference in density of the patch image, and the toner replenishing amount is corrected by a
Hasegawa Kazuhiro
Hirobe Fumitake
Kimura Shigeo
Masuda Koji
Ogata Takao
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
LandOfFree
Developer density controlling apparatus including target... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Developer density controlling apparatus including target..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Developer density controlling apparatus including target... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2885191