Method and apparatus for cleaning a color image forming apparatus by sticking developer on the photoconductor without forming an image

A developing unit which accommodates black toner is operated for developing process by black toner only at a proper time when color image forming operation is not performed by other developing units which accommodate other colored toners. Then, a cleaning blade is actuated without conducting transfer process of the developed image onto a transfer material, and residual toner is removed from the photoconductor.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
The present invention relates to a colored image forming apparatus such as 
color copying machine and color printer which is provided with developing 
units for use with colored toners other than black in addition to a 
developing unit which is used for black toner. 
2. Description of Related Art 
In a colored image forming apparatus, an electrostatic latent image which 
is to be developed by a predetermined color is formed on a photoconductor 
by optical system of copying machine or printer. Then, the electrostatic 
latent image is developed by a developing unit which accommodates a 
predetermined colored toner to be used for development. The developed 
image after development is transferred onto a transfer material, 
intermediate transfer belt or the like on the photoconductor. Thereafter, 
an electrostatic latent image which is to be developed by next 
predetermined color is formed on the photoconductor by optical system. The 
electrostatic latent image thus formed is developed by a developing unit 
which accommodates the next predetermined colored toner to be used for 
development. The developed image thus obtained is transferred onto the 
transfer material, intermediate transfer belt or the like on the 
photoconductor by overlaying it on the image previously transferred. After 
each transfer process, the developer remained on the photoconductor is 
cleaned by a cleaning device. 
However, when colored toners other than black toner are cleaned, residual 
developer on the photoconductor is not well cleaned compared with the case 
when black toner is cleaned, and it causes to readily produce filming on 
the photoconductor by colored toners other than black toner. The cause is 
not known yet, however, it may be attributed to dye or pigment which is a 
component of toners. A resin of low melting viscosity is often used for 
colored toners other than black toner in order to produce clearer color 
and also to have satisfactory permeability when image is transferred onto 
a sheet used for overhead projectors. In this case, however, it tends to 
further deteriorate cleaning capability. 
Japanese Patent Publications TOKKO SHO No. 51-1130, TOKKAI SHO No. 
57-204576 and TOKKAI SHO No. 55-89882 disclose ideas to solve these 
problems. 
In the first publication, there is disclosed an idea for improving toner 
cleaning efficiency by mixing toner with small amount of low adhesive 
polymeric additive in smaller average particle size than that of the toner 
of each developer. In the second publication, an idea is disclosed wherein 
each developer is mixed with an abrasive for removing a matter adhered to 
the photoconductor when cleaning process is conducted. In the third 
publication, there is disclosed an idea for removing a matter adhered to 
the photoconductor with said resin by providing a grinding device aside 
from a cleaning device. 
However, in the colored image forming apparatus, it takes labors to mix 
proper amount of suitable polymeric additive or abrasive with each 
developer and it eventually becomes expensive. Moreover, it is not 
preferable for use in forming a colored image which requires delicate tone 
since it badly affects the clearness of color and permeability when the 
additive or abrasive are mixed with colored toner other than black toner. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide a colored image 
forming apparatus which is capable of improving reliability on image by 
effectively preventing filming on the photoconductor by colored toners 
other than black toner wherein special additive or abrasive is not 
necessary to be mixed with colored toner other than black toner, and 
special device such as grinding device is not necessary either. 
The present invention has been brought about based on the knowledge of the 
inventors who studied to accomplish the above-mentioned object. That is a 
discovery that even there occurred filming on the photoconductor by 
colored toners other than black toner, a matter adhered to the 
photoconductor such as filming can be effectively removed if development 
is made by black toner and cleaning is conducted by the cleaning device 
without conducting transfer process. The reason why such sufficient 
cleaning can be made by use of black toner is not known clearly, however, 
it may be presumed that the carbon largely contained in black toner 
contribute to the cleaning efficiency. 
In the present invention, there are provided developing units by which 
other colored toners other than black toner are used in addition to a 
developing unit by which black toner is used, and the developing units are 
selectively used every time when an electrostatic latent image to be 
developed in a predetermined color is formed to develop into a colored 
image wherein development by the developing unit in which black toner is 
used is carried out at proper time when colored image is not formed and 
the photoconductor is cleaned without performing transfer process which is 
the characteristic of the present invention. 
According to the color copying machine of the present invention, developing 
process is carried out by only a developing unit in which black toner is 
used at a proper time when a colored image is not formed. Black toner is 
thus adhered to the surface of photoconductor. Then, the surface of the 
photoconductor is cleaned under the existence of black toner by the 
cleaning device without performing transfer process and a matter adhered 
to the photoconductor such as filming formed by colored toners other than 
black toner is removed together with black toner. 
These and other objects and features of the present invention will become 
more apparent from the following description taken in conjunction with the 
accompanying drawings which illustrate specific embodiments of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will now be described below referring 
to accompanying drawings. 
FIG. 1 shows a schematic constructional view of the main part of a color 
copying machine to which the present invention is applied as one of 
embodiments. 
The copying machine is provided with a photoconductive drum 8 in the 
central part, and the drum is rotatively driven in the direction of arrow 
A in the figure by an unillustrated driving means. Around the 
photoconductive drum 8, there are sequentially disposed a charger 1, 
developing units 4,5,6,7, a transfer charger 10, a blade-type cleaning 
device 140 and an eraser 21. 
In the developing units 4,5,6, colored toners other than black toner are 
accommodated. More particularly, magenta toner is accommodated in the 
developing unit 4, cyan toner in the unit 5 and yellow toner in the unit 6 
respectively. In the developing unit 7, there is accommodated black toner 
to which abrasive may be mixed. As the abrasive, the products such as 
follows may be named; i.e. ceria, silica, calcium carbonate, aluminum 
sulfate, barium sulfate, magnesium sulfate, aluminum oxide (alumina), 
strontium oxide and carborundum. Each toner is negatively charged against 
the electrifying polarity of charger. 
The transfer charger 10 is accommodated in a transfer drum 9 which is 
provided with an unillustrated transfer material holding means. 
Above the photoconductive drum 8, there are disposed an original glass 
table 301, an original illuminating lamp 302, an optical system 3 
comprising of first to fourth mirrors 303-306 for scanning an original and 
projecting and exposing an image on the photoconductive drum 8 and a 
projection lens 307. 
Under and on the side of the transfer drum 9, there is provided a paper 
feed cassette C. Transfer paper or transfer material T used for overhead 
projector accommodated in the cassette is sent out of the cassette C by 
paper feed rollers F and held on the drum 9 by an unillustrated holding 
means of the transfer drum 9 after paper feed timing is adjusted by a 
timing roller device 22. 
Above the transfer drum 9, there are sequentially disposed a transfer belt 
23 for transporting the transfer material conveyed from the transfer drum 
9, fixing rollers 11,12 provided with heaters therein, discharge rollers G 
and a discharge tray E. 
The cleaning device 140 includes a blade 14 which is pressed to come in 
contact with the surface of the photoconductive drum 8 to scrape off toner 
adhered to the surface of the drum 8. 
The copying machine in this embodiment is controlled and operated by a 
control circuit 15 which is centered around a microcomputer. The output 
port of the control circuit 15 is connected to the developing units 4,5,6 
and 7 through a developing unit driving circuit 151 and also to the 
charger 1 through a high voltage power source 152, the transfer charger 10 
through a high voltage power source 153 and the eraser 21 through a 
lighting circuit 154 respectively. 
The charger 1 is provided with a grid 2 which is maintained at a constant 
voltage. 
The output port of the control circuit 15 is also connected with a heater 
in the fixing roller 11 through a heater power source 155 and a heater in 
the fixing roller 12 through a heater power source 156 respectively, and 
is further connected to a total counter 17 which is arranged for counting 
the total number of sheets copied. 
To the input port of the control circuit 15, a power source 20 is connected 
through a power source switch 18, and a print switch 19 and temperature 
detector 16 of the fixing rollers 11,12 are also connected respectively. 
Input and output load of the optical system 3 and others are also 
connected to the control circuit 15. 
Now, the operational action of the apparatus will be described below. 
At the beginning, the power source switch 18 is turned on by which heaters 
in the fixing rollers 11,12 are turned on to start warming-up operation. 
During this warming-up operation, the photoconductive drum 8 is rotatively 
driven under a state that the original illuminating lamp is put off, and 
is electrified by the charger 1. At the same time, the developing unit 7 
which accommodates black toner is only operated or bias voltage is applied 
between the photoconductive drum 8 in addition to the operation of the 
developing unit 7 thereby producing solid image of black toner on the 
photoconductive drum 8. At this stage, the photoconductive drum 8 is 
cleaned by the cleaning blade 14 without operating the transfer charger 
10, and the eraser 21 is turned on according to requirement. 
After the photoconductive drum 8 is scraped by the cleaning blade 14 for a 
predetermined period of time and when the temperature of the fixing 
rollers 11,12 detected by the detector 16 has reached a fixed temperature, 
the warming-up operation is completed to be ready for printing. At this 
time, a matter adhered to the drum 8 such as filming caused by colored 
toners other than black toner 8 is removed by the solid development of 
black toner and succeeding cleaning operation by the cleaning blade 14. 
After the warming-up operation is completed, succeeding color copying 
operation is started upon a print switch 19 is turned on. Firstly, an 
electrostatic latent image to be developed by magenta toner is formed on 
the photoconductive drum 8 by the optical system 3. This electrostatic 
latent image is developed by the developing unit 4 using magenta toner, 
and the toner image obtained by this development is transported to the 
transfer charger 10. 
On the other hand, a transfer material T is fed from the paper feed 
cassette C and is held on the transfer drum 9 after passing through the 
timing roller device 22. The transfer material T held thereat is 
rotatively conveyed in the direction of arrow B together with the transfer 
drum 9 at an equal velocity of the photoconductive drum 8. The tip of 
magenta toner image formed on the photoconductive drum 8 and the tip of 
the transfer material T on the transfer drum 9 coincide with each other at 
the location of the transfer charger 10 and the image is transferred on 
the transfer material T thereafter. 
In this manner, electrostatic latent images to be developed by cyan toner, 
yellow toner and black toner are successively formed on the 
photoconductive drum 8 by the optical system 3. These electrostatic latent 
images are successively developed by the developing units 5,6,7 every time 
when respective images are formed, and finally each toner image by cyan, 
yellow and black are produced respectively. Each colored toner image 
produced by this developing procedure is successively transferred onto the 
transfer material T on the transfer drum 9 from the photoconductive drum 8 
by overlaying on top the other. The transfer material T on which toner 
images in different colors are repeatedly and multiplicatively transferred 
is transported to the fixing rollers 11,12 by the transfer belt 23 after 
it is released from the transfer drum 9. The toners on the transfer 
material T is melted together thereat into predetermined colors and the 
image is fixed on the transfer material T. After the fixing process, the 
transfer material T is discharged onto the discharge tray E by the 
discharge rollers G. 
Every time when the toner images obtained by each developing units 4,5,6 
and 7 are transferred onto the transfer material T on the transfer drum 9, 
the residual toner on the photoconductive drum 8 is scraped by the 
cleaning blade 14 of the cleaning device 140 into a cleaner housing 13 and 
is accommodated in an unillustrated collection box. The charge remained on 
the photoconductive drum 8 is erased by the eraser 21 to be ready for next 
process. 
The operation of the control circuit 15 for controlling a series of the 
above described action of the copying machine will now be described below 
with reference to FIGS. 2 and 3. 
FIG. 2 shows the main routine of control by the control circuit 15. 
According to this routine, an initialization is set at step #1 when the 
power source of the copying machine is turned on or when the program is 
returned after the trouble such as jamming is cleared. Then, an internal 
timer is started at step #2. The internal timer is arranged for 
determining the length of the main routine and the value is set in advance 
at step #1 when initialization is set. At step #3, judgement is made 
whether flag F.sub.1 which indicates the completion of cleaning operation 
of the photoconductive drum 8 is `0` or not. The flag F.sub.1 is set at 
`0` when initialization is made at step #1. If the flag F.sub.1 is `0` at 
step #3, a subroutine for processing photoconductor (cleaning process) to 
be described later is called at step #4. If the flag F.sub.1 is `1`, a 
copying process subroutine for conducting ordinary copying operation is 
called at step #5. As this copying process subroutine is known well by the 
conventional copying machine, description on the subroutine will be 
omitted. After other process are conducted at step #6, one cycle of 
routine is finished at step #7 with time limit of the internal timer. By 
utilizing the length of time set for one cycle of this routine, various 
timers appearing in various subroutine are counted. 
A photoconductor processing subroutine will be described below referring to 
FIG. 3. 
In this routine, judgement is made whether flag F.sub.2 which indicates the 
cleaning of the photoconductor 8 is being processed is `0` or not at step 
#10. The flag F.sub.2 is also set at `0` when initialization is set at 
step #1. If the flag F.sub.2 is `0` at step #10, the flag F.sub.2 is set 
at `1` at step #11 and timer TA is set at step #12. The time set by timer 
TA is the time sufficient enough for forming solid image on the 
photoconductive drum 8 by black toner. Then, the photoconductive drum 8 is 
rotated at step #13, and solid development by black toner is carried out 
at step #14. If the flag F.sub.2 is `1` at step #10 or when solid 
development by black toner is finished at step #14, judgement is made 
whether timer TA is up or not at step #15. If the timer TA is counted up, 
the developing operation is stopped and cleaning process is started at 
step #16, then timer TB is set at step #17. 
If the timer TA is not counted up or steps #16 and #17 are passed through 
after timer TA is set at step #15, the program proceeds to step #18. The 
time set by timer TB is the time sufficient enough for cleaning solid 
image of black toner on the photoconductive drum 8. At step #18, judgement 
is made whether the timer TB is counted up or not, and if the time is 
counted up, cleaning operation is stopped at step #19 and flag F.sub.1 is 
set at `1` and flag F.sub.2 is reset at `0` (step #20 and #21). 
According to the embodiment described above, the photoconductive drum 8 is 
cleaned by the solid development by black toner and the cleaning process 
until the warming-up time in the fixing rollers 11,12 is completed after 
the power source switch 18 is turned on, and even if there is a matter 
such as filming adhered to the photoconductive drum 8 by colored toners 
other than black toner, it will be removed. 
The present invention is not limited to the embodiment described above and 
may be applied to various modes. Particularly, in place of the solid 
development by black toner and the cleaning process which follows, it may 
be considered to carry out the cleaning operation after a series of 
copying operation is conducted wherein the total number of copy sheets 
have exceeded a predetermined number or before or after the copying 
operation is conducted. 
In case when the cleaning process is conducted after a series of copying 
operation is completed wherein the total number of copy sheets have 
exceeded a predetermined number, it may be considered to carry out the 
solid development and cleaning process when the number of printing sheets 
have exceeded, for instance, 100 sheets of paper. 
If such process under which the cleaning process is conducted every 100 
sheets of paper is described as a second embodiment of the present 
invention, the main routine of control by the control circuit 15 comes as 
illustrated in FIG. 4. 
In the flow chart of FIG. 4, N represents the number of printing sheets. In 
this case, the number of sheets copied so far are read from non-volatile 
memory at step #1 of initialization, and when the copying operation at 
step #5 is completed (step #51), the number of sheets copied are counted 
at step #52. When the number of sheets reach 100 sheets (step #53), the 
counter is cleared `0` at step #54, and flag F.sub.1 is reset `0` at step 
#55. In this case, the flag F.sub.1 is set `1` at initialization (step 
#1). 
It may be arranged to carry out solid development by black toner and the 
cleaning process every time when successive copying operation is conducted 
since copying efficiency is largely lowered if the photoconductive drum 8 
is developed by black toner followed by cleaning process before or after 
every copying operation is conducted. 
If the case when cleaning process is conducted after printing is over or at 
the time of printing is described as third embodiment of the present 
invention, the main routine of control by the control circuit 15 comes as 
illustrated in FIG. 5. In this case, flag F.sub.1 is set at `1` at step #1 
of initialization and when copying operation is finished at step #5 (step 
#501), the flag F.sub.1 is reset `0` at step #502. The flag F.sub.1 thus 
reset at `0` is set "1" at step #20 of photoconductor process subroutine 
shown in FIG. 3. 
In an apparatus described in the above embodiment, the so-called 
positive-to-positive method is disclosed wherein an image is formed by 
using a toner negatively charged against the electrifying polarity of 
charger, however, the so-called negative-to-positive method can also be 
applied to the present invention wherein an image is formed by a toner 
positively charged against the electrifying polarity of charger. However, 
when a solid image is to be formed in an apparatus to which the 
negative-to-positive method is applied, black developing unit is operated 
under a state the charger is turned off. 
Although the present invention has been fully described by way of examples 
with reference to the accompanying drawings, it is to be noted that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.