Title: Image forming apparatus and convey control method for recycle toner
Abstract: This invention relates to an image forming apparatus which employs a recycling scheme of recovering and reusing transfer residue toner, and a convey control method for recycle toner. In order to prevent a phenomenon such as fogging or character thickening, a toner recycle mechanism shares one driving source with a photosensitive body or fixing unit, and includes an electromagnetic clutch for switching driving force transmission to the recycling means when driving the photosensitive body or fixing unit, and a controller which controls power supply to the electromagnetic clutch. The convey control method for recycle toner includes the steps of starting copying, measuring a printing ratio of an image pattern per image, and suppressing a return amount of the recycle toner when the printing ratio of the image pattern is low.
Patent Number: 6,892,045 Issued on 05/10/2005 to Tokimatsu, et al.
| Inventors:
|
Tokimatsu; Hiroyuki (Tokyo, JP);
Ohtani; Junichi (Tokyo, JP)
|
| Assignee:
|
Konica Corporation (Tokyo, JP)
|
| Appl. No.:
|
439148 |
| Filed:
|
May 14, 2003 |
Foreign Application Priority Data
| May 24, 2002[JP] | 2002-150466 |
| Current U.S. Class: |
399/359 |
| Intern'l Class: |
G03G 021/00 |
| Field of Search: |
399/358,359,360,260
|
References Cited [Referenced By]
U.S. Patent Documents
| 5547795 | Aug., 1996 | Ochiai et al.
| |
| 5712072 | Jan., 1998 | Inaba et al.
| |
| Foreign Patent Documents |
| 06242681 | Sep., 1994 | JP.
| |
| 11084977 | Mar., 1999 | JP.
| |
| 2002162879 | Jun., 2002 | JP.
| |
Primary Examiner: Grimley; Arthur T.
Assistant Examiner: Gleitz; Ryan
Attorney, Agent or Firm: Frishauf, Holtz, Goodman & Chick, P.C.
Claims
1. An image forming apparatus comprising:
a latent image carrier for carrying a latent image;
a developing unit for developing the latent image carried on said latent image
carrier on a developing agent carrier which carries a developing agent formed of
nonmagnetic toner and a magnetic carrier;
a transfer unit for transferring a developing image on said latent image carrier
onto a transfer paper;
a fixing unit for fixing the toner on the transfer paper;
a cleaning unit arranged downstream of said transfer unit to recover the nonmagnetic
toner on said latent image carrier; and
a recycling unit which conveys the toner recovered by the cleaning unit to said
developing unit, and which shares one driving source with said latent image carrier;
wherein said recycling unit comprises;
an electromagnetic clutch for transmitting a driving force to said recycling
unit when driving said latent image carrier; and
a controller for controlling power supply to said electromagnetic clutch;
wherein said electromagnetic clutch comprises a normally closed electromagnetic
clutch which transmits the driving force in an OFF state thereof and which does
not transmit the driving force in an ON state thereof.
2. The image forming apparatus according to claim 1, wherein the power supply
to said electromagnetic clutch is controlled such that a time that the electromagnetic
clutch is maintained in the ON state is longer for lower printing ratios of an
image formation pattern.
3. The image forming apparatus according to claim 1, wherein power supply to
said electromagnetic clutch is controlled based on a length of time from when said
apparatus is stopped until driving of said apparatus is resumed.
4. The image forming apparatus according to claim 1, wherein the nonmagnetic
toner is polymerized toner having a volume average particle size which is not less
than 3 μm and not more than 9 μm.
5. The image forming apparatus according to claim 4, wherein a shape factor SF-
1
indicating a spherical degree of the nonmagnetic toner is 100 to 140, and a shape
factor SF-
2 indicating a degree of non-uniformity of the nonmagnetic toner
is 100 to 120;
wherein
where:
Lmax is the maximum particle diameter;
Laround is the particle circumferential length, and
A is the toner projection area.
6. The image forming apparatus according to claim 1, wherein the magnetic carrier
is a ferrite core carrier formed of magnetic particles with a volume average particle
size of 30 μm to 65 μm and a magnetization amount of 20 emu/g to 70 emu/g.
7. An image forming apparatus comprising:
a latent image carrier for carrying a latent image;
a developing unit for developing the latent image carried on said latent image
carrier on a developing agent carrier which carries a developing agent formed of
nonmagnetic toner and a magnetic carrier;
a transfer unit for transferring a developing image on said latent image carrier
onto a transfer paper;
a fixing unit for fixing the toner on the transfer paper;
a cleaning unit arranged downstream of said transfer unit to recover the nonmagnetic
toner on said latent image carrier; and
a recycling unit which conveys the toner recovered by the cleaning unit to said
developing unit, and which shares one driving source with said fixing unit;
wherein said recycling means comprises:
an electromagnetic clutch for transmitting a driving force to said recycling
unit when driving said fixing unit; and
a controller for controlling power supply to said electromagnetic clutch;
wherein said electromagnetic clutch comprises a normally closed electromagnetic
clutch which transmits the driving force in an OFF state thereof and which does
not transmit the driving force in an ON state thereof.
8. The image forming apparatus according to claim 7, wherein the power supply
to said electromagnetic clutch is controlled such that a time that the electromagnetic
clutch is maintained in the ON state is longer for lower printing ratios of an
image formation pattern.
9. The image forming apparatus according to claim 7, wherein power supply to
said electromagnetic clutch is controlled based on a length of time from when said
apparatus is stopped until driving of said apparatus is resumed.
10. The image forming apparatus according to claim 7, wherein the nonmagnetic
toner is polymerized toner having a volume average particle size which is not less
than 3 μm and not more than 9 μm.
11. The image forming apparatus according to claim 10, wherein a shape factor
SF-
1 indicating a spherical degree of the nonmagnetic toner is 100 to 140,
and a shape factor SF-
2 indicating a degree of non-uniformity of the nonmagnetic
toner is 100 to 120;
wherein:
where:
Lmax is the maximum particle diameter;
Laround is the particle circumferential length, and
A is the toner projection area.
12. The image forming apparatus according to claim 7, wherein the magnetic carrier
is a ferrite core carrier formed of magnetic particles with a volume average particle
size of 30 μm to 65 μm and a magnetization amount of 20 emu/g to 70 emu/g.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for development by
using a two-component developing agent in accordance with electrophotography and,
more particularly, to an image forming apparatus which employs a recycling scheme
of recovering and reusing transfer residue toner and a convey control method for
recycle toner.
2. Description of the Related Art
According to an example of an image forming process of forming an image
by electrophotography, an electrostatic latent image is formed on a latent image
carrier such as a photosensitive body. The formed electrostatic latent image is
developed by a developing means to form a toner image on the latent image carrier.
The formed toner image is transferred onto transfer paper by a transfer means.
The transferred toner image is fixed on the transfer paper by a fixing means. Thus,
an image is formed on the transfer paper. According to another example, a toner
image on an image forming body such as a photosensitive body is transferred onto
an intermediate transfer body serving as an image carrier. The toner image is then
transferred from the intermediate transfer body onto transfer paper by a transfer
means, and is fixed. Thus, an image is formed on the transfer paper.
In the developing step of an image forming process, development using a two-component
developing agent containing nonmagnetic toner and a magnetic carrier is often employed,
and a DC-bias developing bias voltage is applied.
In development using the two-component developing agent, since only the toner
is consumed by development, an appropriate amount of new toner corresponding to
the consumed amount must be replenished. Thus, toner replenishment is performed.
The toner image formed on the latent image carrier is transferred onto the transfer
paper or intermediate transfer body by the transfer means. At this time, the transfer
residue toner which is not transferred but left on the latent image carrier is
cleaned by a cleaning means. A recycling scheme is employed in which the toner
cleaned by the cleaning means and recovered in a cleaning unit is conveyed to a
developing unit and is reused. When the recycling scheme is employed, a waste toner
box for collecting the recovered toner to dispose it is not necessary. In this
manner, the recycling scheme can be regarded as a scheme that reduces waste and
is accordingly friendly to the environment.
A dynamic torque required for conveying the toner recovered by the recycling
means
to the developing unit is as small as about {fraction (1/10)} that required for
driving the latent image carrier and fixing unit. To reduce the cost and to save
the space, the recycling means is driven by the same driving source as for the
latent image carrier or fixing unit.
In the cleaning unit, the toner (recycle toner) recovered by the cleaning means
has been conveyed after it is scraped by a cleaning blade or the like. The recycle
toner has accordingly been subjected to a mechanical stress. When the recycle toner
is compared to new toner, it has lower flowability, it is harder to mix with the
carrier, and its electrostatic properties also degrade. When the recycle toner
is developed again, it tends to pose a problem such as fogging or character thickening.
This phenomenon does not substantially pose any problem when the ratio of the recycle
toner in the developing agent is low, but does when the ratio is high.
When toner having a small particle size or toner manufactured by a polymerization
method and having a sharp particle size distribution is used, an image quality
such as resolution, tone, character reproducibility, and the like is high. Therefore,
when the recycle toner described above is used, the above problem is obvious.
This problem of degradation in image quality occurs as follows. When the printing
ratio of an image formation pattern to be printed continuously is low, the amount
of new toner to be replenished becomes small, and accordingly the proportion of
the recycle toner in the developing agent increases. This causes obvious degradation
in image quality.
It is known that the problem of degradation in image quality tends to occur when
the image forming apparatus has been kept stopped for a long period of time, e.g.,
for 2 h or more, and then several hundred prints are output. This is because the
charges of the recycle toner damaged due to the long-time stop are decreased.
To solve this phenomenon, a single driving source may be employed as a driving
source for the recycling means, or the amount of recycle toner to be returned to
the developing unit may be controlled in accordance with the printing ratio of
an image formation pattern. Alternatively, while several hundred prints are output
after long-time stop, the amount of recycle toner to be returned to the developing
unit may be controlled. If, however, a single driving source is provided to the
recycling means in order to control the amount of recycle toner, cost reduction
and space saving cannot be achieved.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above situation of the prior
art, and has as its object to provide an image forming apparatus in which the supply
amount of recycle toner can be controlled so that, while the recycling means shares
one driving source with the latent image carrier or fixing unit, no degradation
in image quality occurs even when, e.g., the printing ratio of the image formation
pattern is low continuously or even in operation after long-time stop.
In order to achieve the above object, according to the first aspect of the present
invention, there is provided an image forming apparatus comprising a latent image
carrier for carrying a latent image, a developing unit for making visible the latent
image on the latent image carrier on a developing agent carrier carrying a developing
agent formed of nonmagnetic toner and a magnetic carrier, a transfer unit for transferring
a visible image on the latent image carrier onto transfer paper, a fixing unit
for fixing the toner on the transfer paper, a cleaning unit arranged downstream
of the transfer unit to clean the nonmagnetic toner on the latent image carrier,
recycling means for conveying the cleaned toner to the developing unit, and control
means, wherein the recycling means shares one driving source with the latent image
carrier, and comprises an electromagnetic clutch for switching driving force transmission
to the recycling means when driving the latent image carrier, and the control means
controls power supply to the electromagnetic clutch.
According to the second aspect of the present invention, there is provided
an image forming apparatus comprising a latent image carrier for carrying a latent
image, a developing unit for making visible the latent image on the latent image
carrier on a developing agent carrier carrying a developing agent formed of nonmagnetic
toner and a magnetic carrier, a transfer unit for transferring a visible image
on the latent image carrier onto transfer paper, a fixing unit for fixing the toner
on the transfer paper, a cleaning unit arranged downstream of the transfer unit
to clean the nonmagnetic toner on the latent image carrier, recycling means for
conveying the cleaned toner to the developing unit, and control means, wherein
the recycling means shares one driving source with the fixing unit, and comprises
an electromagnetic clutch for switching driving force transmission to the recycling
means when driving the fixing unit, and the control means controls power supply
to the electromagnetic clutch.
The electromagnetic clutch in the image forming apparatus according to the first
and second aspects transmits a driving force in an OFF state and does not in an
ON state.
Power supply to the electromagnetic clutch in the image forming apparatus according
to the first and second aspects is controlled such that the lower a printing ratio
of an image formation pattern, the longer an ON time.
Power supply to the electromagnetic clutch in the image forming apparatus according
to the first and second aspects is controlled in accordance with a time since the
apparatus is stopped until driving of the apparatus is resumed.
The recycling scheme is very excellent in that it does not dispose, as waste
toner, toner which is not transferred but recovered, and reuses it. As is apparent
from the above aspects, with the image forming apparatus of the present invention,
the problem of how the recycling means should be driven and the problem of the
phenomenon in which fogging or character thickening occurs during development due
to the recycle toner containing damaged toner can be solved without sacrificing
the cost or space, while an image with a high image quality can be maintained for
a long period of time.
The above and many other objects, features and advantages of the present invention
will become manifest to those skilled in the art upon making reference to the following
detailed description and accompanying drawings in which preferred embodiments incorporating
the principle of the present invention are shown by way of illustrative examples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view showing the arrangement of an image
forming apparatus;
FIG. 2 is a control block diagram of the image forming apparatus;
FIG. 3 is a control block diagram of the image forming apparatus;
FIG. 4 is a flow chart of the first embodiment;
FIG. 5 is a flow chart of the second embodiment; and
FIG. 6 is a flow chart of the third embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Several preferred practical examples and embodiments of an image forming
apparatus according to the present invention will be described with reference to
the accompanying drawings.
FIG. 1 shows a copying machine that utilizes the electrophotographic process
of forming a monochrome image as an image forming apparatus to which the present
invention is applied. Note that the image forming apparatus of the present invention
is not limited to the arrangement shown in FIG.
1.
Reference numeral
1 denotes a drum-like photosensitive body serving
as a latent image carrier. In the photosensitive body
1, as an organic semiconductor
layer to be negatively charged, a phthalocyanine pigment dispersed in polycarbonate
is applied to a cylinder-like metal substrate which is grounded. The thickness
of the photosensitive body layer including a charge transport layer is 30 μm.
The drum has a diameter of 80 mm, and is rotatably driven at a peripheral velocity
(Vp) of 280 mm/s in the direction of an arrow (t
1).
Reference numeral
2 denotes a scorotron charging means for uniformly
charging the outer surface of the rotating photosensitive body
1 to a predetermined
polarity and potential. The charging means
2 forms a charging electrode
arrangement in which the distance between the wire and grid is 7.5 mm, the distance
between the grid and photosensitive body is 1 mm, and the distance between the
wire and back plate is 12 mm. The charging means
2 applies a bias voltage
to the photosensitive body
1 with a grid application voltage of -730 V and
a charging current value of -800 μA, thus setting the charging potential
of the photosensitive body
1 to -750 V.
Reference numeral
3 denotes an image exposing means employing a
laser scanning scheme. The image exposing means
3 uses a semiconductor laser
(LD) having a laser wavelength of 780 nm, and its output power is 300 μW.
The image exposing means
3 emits a laser beam to scan and expose the uniformly
charged surface of the photosensitive body
1, thus forming an electrostatic
latent image.
A developing unit
4 has a magnet roller
42 as a developing stationary
magnet in it. A developing agent in which toner is attached to the carrier charged
by mutual friction is attached to the outer surface of a developing agent carrier
41 rotatable in the direction indicated by an arrow (t
2). After the
thickness of the developing agent is regulated by a layer thickness regulating
means
45, the developing agent is conveyed to a developing region opposing
the photosensitive body
1. Then, development is performed.
A pair of stirring convey screws
43A and
43B and a rotary paddle
44 are provided in a developing container
46, and convey toner NT
newly supplied from a toner hopper
42 or recycle toner RT to the developing
agent carrier
41 while mixing them with the developing agent in the container
46 and stirring them. The stirring convey screws
43A and
43B
are both rod-like screw members, of which one stirs the developing agent from the
front side to the deep side of the surface of drawing, and the other one from the
deep side to the front side, thus conveying the developing agent. The toners NT
and RT are dropped onto the developing agent which is being circulated by the stirring
convey screws
43A and
43B, so that they are mixed and stirred and
discharged toward the rotary paddle
44. The developing agent mixed with
the discharged toners NT and RT and stirred is further stirred by the rotary paddle
44 which is like a water wheel, and is supplied to the developing agent
carrier
41. The developing agent carrier
41 is formed by covering
the outer surface of a magnet roller with an aluminum sleeve having a surface coated
with stainless steel by flame spray coating. The developing agent carrier
41
having a roller diameter of 40 mm is rotated at a linear velocity (vs) of 560 mm/s,
so that its linear-velocity ratio (vs/vp) to the photosensitive body
1 is
2. The developing agent carrier
41 performs development upon reception of
a DC-component developing bias. Reverse development is performed by applying a
developing bias of -600 V as the DC component.
As the toner of the two-component developing agent containing the nonmagnetic
toner and magnetic carrier, polymerized toner having a volume average particle
size of 3 μm to 9 μm is preferable. When polymerized toner is used,
an image forming apparatus with high resolution and stable density, which causes
very few fogging becomes possible.
The polymerized toner is manufactured by the following manufacturing method.
A toner binder resin is produced and its toner shape is formed by polymerization
of a material monomer or prepolymer for the binder resin and a subsequent chemical
process. More specifically, the toner binder resin is obtained by polymerization
reaction such as suspension polymerization or emulsion polymerization, and a subsequent
particle fusing step which is performed when necessary. Regarding the polymerized
toner, the material monomer or prepolymer is uniformly dispersed in a water system
and is thereafter polymerized, thus manufacturing the toner. As a result, spherical
toner having a uniform particle size distribution and uniform shape can be obtained.
A shape factor SF-
1 indicating the spherical degree of the toner is preferably
between 100 and 140, and a shape factor SF-
2 indicating the degree of non-uniformity
of the toner is preferably between 100 and 120. The shape factors SF-
1 and
SF-
2 are given by the following equations:
where Lmax is the maximum diameter, Laround is the circumferential length,
and A is the toner projection area.
When the volume average particle size of the toner becomes less than 3 μm,
fogging or toner scattering tends to occur. The upper limit of 9 μm is the
upper limit of the particle size that enables high image quality that this embodiment
is aimed at.
As the carrier, a ferrite core carrier formed of magnetic particles with a volume
average particle size of 30 μm to 65 μm and a magnetization amount
of 20 emu/g to 70 emu/g in saturation magnetization is preferable. With a carrier
having a particle size smaller than 30 μm, carrier attaching tends to occur.
With a carrier having a particle size larger than 65 μm, an image with a
uniform density may not be formed.
Reference numeral
5 denotes a pre-transfer exposure light source
for irradiating the toner image in order to improve its transfer performance. Irradiation
is performed with an LED having a light wavelength of 700 nm at a light output
of 10 lux.
Reference numeral
6 denotes a corotron transfer electrode. With
the transfer electrode
6, the distance between the wire and photosensitive
body
1 is 8 mm and the distance between the wire and back plate is 12 mm.
The transfer electrode
6 transfers the toner image on the photosensitive
body
1 onto the transfer paper by constant current control with a transfer
current of 200 μA.
Reference numeral
7 denotes a corotron separation electrode. with
the separation electrode
7, the distance between the wire and photosensitive
body
1 is 8 mm and the distance between the wire and back plate is 12 mm.
The separation electrode
7 promotes separation of the transfer paper from
the photosensitive body
1 by a separation current with an AC component of
1,000 μA and a DC component of -200 μA.
Transfer paper P supplied from a paper supply unit (not shown) is supplied
by registration rollers
21 in synchronism with the toner image formed on
the photosensitive body
1, and the toner image is transferred to it at a
transfer nip portion (not shown) by the transfer electrode
6. The transfer
paper P passing through the transfer nip portion is separated from the surface
of the photosensitive body
1 by the separation electrode
7, and is
conveyed to a fixing unit
23 by a conveyor belt
22.
The fixing unit
23 consists of a heat roller
23a incorporating
a heater, and a press roller
23b. The transfer paper P bearing the
toner image on its surface is heated and pressurized between the heat roller
23a
and press roller
23b, so that the toner image is fixed. The transfer
paper P to which the toner image is fixed is delivered by delivery rollers
24
onto a delivery tray outside the copying machine.
The surface of the photosensitive body
1, from which the toner image has
been transferred to the transfer paper P, is cleaned by a cleaning unit
8
to remove the transfer residue toner. In this embodiment, a blade made of urethane
rubber is used as the cleaning means. The cleaning blade is of a counter type which
comes into slidable contact with the outer surface of the photosensitive body
1
to clean it. The outer surface of the photosensitive body
1, which has been
cleaned while passing through the cleaning unit
8, is irradiated by a pre-charging
exposing (PCL) means
9 using a light source having a light wavelength of
700 nm and a light output of 10 lux, so the residual potential is decreased. After
that, the process moves to the next image formation cycle.
The toner recovered by the cleaning unit
8 is dropped onto the bottom
of the cleaning unit
8 having a capacity of, e.g., about 100 g. The recovered
toner collected at the bottom of the cleaning unit
8 is recovered in the
developing unit
4 by a toner recycling means (unit)
81 which conveys
the toner by rotation of a convey screw provided in a toner convey path (to be
described later), and is reused as recycle toner for development.
In the image forming apparatus of the present invention described above, the
toner
recycling means
81 is driven by the same driving source as that for driving
the photosensitive body
1 or fixing unit
23.
FIG. 2 is a control block diagram of an image forming apparatus in which the
toner recycling means
81 is driven by the same driving motor MA as for the
photosensitive body
1.
In a controller C
1A, the return amount of the recycle toner is controlled
appropriately by an electromagnetic clutch CLA so as to suppress occurrence of
a problem such as fogging or character thickening caused by the recycle toner.
When it is detected that the above problem can be caused easily because the printing
ratio of the image pattern is low or the apparatus has been stopped for a long
period of time, the controller C
1A calls an electromagnetic clutch operation
program stored in a memory C
4 to cope with these situations and turns on/off
the electromagnetic clutch CLA. Thus, the return amount of the recycle toner is suppressed.
The recycle toner to be recovered by the cleaning unit
8 occurs in accordance
with the apparatus driving time during image formation, and must accordingly be
basically returned to the developing unit
4 in accordance with the driving
operation of the apparatus. For this purpose, as the electromagnetic clutch CLA
used for driving the toner recycling means
81, one which performs driving
when it is OFF to convey the recycle toner and which stops driving when it is ON
to stop conveying the recycle toner, that is, a normally closed electromagnetic
clutch is used.
FIG. 3 is a control block diagram of an image forming apparatus in which the
toner recycling means
81 is driven by the same driving motor MB as for the
fixing unit
23.
In a controller C
1B, the return amount of the recycle toner is controlled
appropriately by an electromagnetic clutch CLB so as to suppress occurrence of
a problem such as fogging or character thickening caused by the recycle toner.
When it is detected that the above problem can be caused easily because the printing
ratio of the image pattern is low or the apparatus has been stopped for a long
period of time, the controller C
1B calls an electromagnetic clutch operation
program stored in the memory C
4 to cope with these situations and turns
on/off the electromagnetic clutch CLB. Thus, the return amount of the recycle toner
is suppressed.
The recycle toner to be recovered by the cleaning unit
8 is produced with
the lapse of the apparatus driving time during image formation, and must accordingly
be basically returned to the developing unit
4 in accordance with the driving
operation of the apparatus. For this purpose, as the electromagnetic clutch CLB
used for driving the toner recycling means
81, one which performs driving
when it is OFF to convey the recycle toner and which stops driving when it is ON
to stop conveying the recycle toner, that is, a normally closed electromagnetic
clutch is used.
Preferred operation examples of the present invention will be described.
Many types of programs are available by combining electromagnetic clutch operation
programs stored in the memory C
4 described in the control block diagrams
of FIGS. 2 and 3, or by changing the threshold, and many operation examples are
available. Three operation examples will now be described.
OPERATION EXAMPLE 1
According to convey control for the recycle toner to be described in operation
example 1, control operation is performed to suppress the return amount of the
recycle toner when the printing ratio of the image pattern is low. FIG. 4 shows
a flow chart of this control.
In an image processor C2, when image data is to be subjected to image processes
such as tone correction, the printing ratio of an image pattern: per image is measured
and is stored in the memory.
When copying is started (F11), the controller C1A (C1B)
calculates a 20-copy average printing ratio of preceding 20 copies stored in the
memory, and checks whether the obtained average printing ratio is 10% (as a low
printing ratio) or more (F12).
If the average printing ratio of the 20 copies is 10% or more, the electromagnetic
clutch CLA (CLB) maintains OFF, and transmits the driving force to return the recycle
toner to the developing unit 4 (F13).
If the average printing ratio of the 20 copies is less than 10%, the electromagnetic
clutch CLA (CLB) is turned on and does not transmit the driving force, so the recycle
toner is not returned to the developing unit 4 (F14).
When copy operations including many image patterns with low printing ratios
are to be performed continuously by continuously performing the above control operation
while shifting it every copy operation, return of the recycle toner to the developing
unit 4 is suppressed, and the problem such as fogging or character thickening
does not occur in the printed image.
OPERATION EXAMPLE 2
In the flow of operation example 1, when the space in the cleaning unit 8
for storing the recovery toner recovered by the cleaning means is small, the recovery
toner which is not conveyed but left may fill the cleaning unit 8 to overflow.
Hence, when an image pattern with a high printing ratio with which a large amount
of recovery toner may be produced is to be output, the electromagnetic clutch CLA
(CLB) is controlled to perform recycling in combination with the flow of operation
example 1. This is operation example 2. FIG. 5 shows a flow chart of this control.
In the image processor C2, when an image data process is to be performed,
the printing ratio of an image pattern per image is measured and is stored in the memory.
When copying is started (F21), the controller C1A (C1B)
calculates a 20-copy average printing ratio of preceding 20 copies stored in the
memory, and checks whether the obtained printing ratio is 10% (as a low printing
ratio) or more (F22).
If the average printing ratio of the 20 copies is 10% or more, the electromagnetic
clutch CLA (CLB) maintains OFF, and transmits the driving force to return the recycle
toner to the developing unit 4 (F23).
If the average printing ratio of the 20 copies is less than 10%, whether a 5-copy
average printing ratio of preceding 5 copies is 20% (as a high printing ratio)
or more, is checked (F24).
If the 5-copy average printing ratio is 20% or more, that is, if the image currently
being printed has a high printing ratio and new toner is being replenished, the
electromagnetic clutch CLA (CLB) is turned off, and transmits a driving force to
return the recycle toner to the developing unit 4 (F25).
If the 5-copy average printing ratio is less than 20%, the electromagnetic clutch
CLA (CLB) is turned on and does not transmit the driving force, so the recycle
toner is not returned to the developing unit 4 (F26).
When copy operations including many image patterns with low printing ratios
are to be performed continuously by continuously performing the above control operation
while shifting it every copy operation, return of the recycle toner to the developing
unit 4 is suppressed. If an image pattern with a high printing ratio mixes
in the continuous copy operations, control operation is performed to return the
recycle toner, so that an appropriate recycle operation is performed. Thus, the
recycle toner does not excessively accumulate in the cleaning unit, and the problem
such as fogging or character thickening does not occur in the printed image.
OPERATION EXAMPLE 3
When the image forming apparatus resumes operation after it has been stopped
for a long period of time, an inconvenience such as fogging or character thickening
tends to occur in the print image while several hundred copies are output. According
to operation example 3, the amount of recycle toner to be returned to the developing
unit 4 is controlled while the several hundred copies are output after the
long-time stop. FIG. 6 shows a flow chart of this control.
The fixing unit 23 has a temperature sensor for measuring the temperature
of the fixing unit 23. When the power supply is turned on (F31),
the controller C1A (C1B) checks whether the fixing unit temperature
detected by the temperature sensor is 50° C. or more (F32).
If the fixing unit temperature is 50° C. or more, that is, if the stop time
since the last copy is output is not very long, the electromagnetic clutch CLA
(CLB) is turned off to transmit the driving force, and the recycle toner is returned
to the developing unit 4 (F33).
If the fixing unit temperature is less than 50° C., that is, after the copying
machine is stopped for a long period of time, the electromagnetic clutch CLA (CLB)
is kept on until 50 copies are output since the resumption of operation and does
not transmit the driving force, so the recycle toner is not returned to the developing
unit 4 (F34).
Between 51st and 100th copies, the electromagnetic clutch CLA (CLB) is turned
on and off alternately for each print, and returns the recycle toner to the developing
unit 4 intermittently with a ½ convey time once for every 2 copies (F35).
After 101 copies, the electromagnetic clutch CLA (CLB) maintains OFF and transmits
the driving force to return the recycle toner to the developing unit 4.
When the above control operation is performed, even after the image forming
apparatus is stopped for a long period of time, an inconvenience such as fogging
or character thickening does not occur in the print image. Flows F33 and
F36 of this example may be replaced by the flow chart shown in FIG. 5 described
in example 2. Then, control operation free from a phenomenon such as fogging or
character thickening is performed both in image formation after the image forming
apparatus is stopped for a long period of time and in image formation including
many image patterns with low printing ratios.
In the practical examples described above, a case wherein the recycling means
shares one driving source with the latent image carrier and a case wherein the
recycling means shares one driving source with the fixing unit are described. Note
that the recycling means can share one driving source with the developing unit
or with the registration rollers of the sheet feed means. In such driving arrangement,
if the electromagnetic clutch described above is provided and control operation
is performed, the same effect as that described above can be obtained.
*
