Process control stabilizing system including a cleaning device for the corona wires

The present invention provides a process control stabilizing system including a cleaning device for the corona wires which allows the process control to be carried out optimally based on exact information which is obtained by certain sensors while a discharge from the main charger unit is kept uniform. The system is constructed so that an electrode cleaner is activated before the detection of the surface potential and/or the detection of the optical density, and in addition, the cleaning operation will be operated until the detection result falls within a predetermined range. Alternatively, the system causes detection of the surface potential and/or detection of the optical both before and after a cleaning operation by the electrode cleaner. The cleaning operation will be repeated until the difference between the first and second detections falls within a predetermined range. In the above operations, if the repetitions of the operations in excess of the predetermined number of times cannot make the detection result fall within the predetermined range, the system preferably activates a warning device and/or prohibits a copying operation.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a process control stabilizing system which 
is incorporated in an image forming apparatus and controls the 
electrophotographic process so as to provide an image in an optimum 
condition. 
(2) Description of the Related Art 
Generally, with regard to photoconductive members for use in image forming 
apparatuses, the surface potential of a photoconductive member varies 
largely dependent upon environmental conditions of the location where it 
is used. As regards OPC's (organic photoconductors), for example, the 
surface potential at low temperature environment is lower by 100 to 150 V 
than that at a normal temperature due to dependance of the mobility of 
photocarriers therein. With regard to Se-photoconductors, the amount of 
thermally excited carriers varies dependent upon temperatures, so that the 
potential increases by 50 v at a low temperature and decreases by 50 to 
100 volts at an elevated temperature. The temperature dependence is 
problematic. Further, the OPC's exhibit a tendency that the thickness of 
the photosensitive layer thereof is reduced by mechanical stresses (that 
is, scratching or abrasive effects by a cleaner blade and/or copy paper) 
with the total copy volume increased. The variations of the surface 
potential in a photoconductive member due to the aforesaid effects, would 
lower the density of an image copied or bring about other great 
deterioration to image quality. Further the variations would influence the 
toner consumption amount for development to give rise to a waste of toner. 
On the other hand, as to developers, the amount of frictionally generated 
static electric charges of toner varies depending on environment charges. 
Specifically, under a circumstance at a low temperature with low humidity, 
toner tends to acquire more charges resulting in lowering in image density 
(i.e. the halftone density lies within approximately 0.8.+-.0.4), while 
toner powders get less charges at an elevated temperature with a high 
humidity, to induce increase of the image density, deterioration of 
gradation reproduction behavior, and/or a waste of toner etc. 
Moreover, even if the copying mode were changed, the effect would sometimes 
fail to reflect due to the disadvantages stated above. That is, the image 
quality between different modes would not be clear or distinguishable, or 
the intention to lessen the toner consumption could not be achieved. In 
order to eliminate these defects and drawbacks, there are disclosed 
various proposals of process controls one of which is cited as Japanese 
Patent Publication Sho 61 No. 29502. A method of the publication includes 
the steps of measuring electric charges in both dark and light portions 
and then controlling the condition for charging based on the measurement 
in the dark portion while controlling the condition for exposure or 
development with reference to the measurement in the light portion, in 
order to provide exactly controlled images. 
Another method includes the steps of detecting a surface potential of a 
photoconductive member at proper times by surface potential meter provided 
inside copier and adjusting optimally based on the detected quantity the 
power of charger and/or the applied voltage for exposure lamp. Still 
another method includes the steps of exposing an image of a referential 
white board etc. onto a photoconductive member, developing the latent 
image into a visual image with toner, measuring the density of the 
toner-image by an optical sensor, and optimally adjusting based on the 
detected quantity the power of charger, the toner density of developer, 
the bias voltage for development, and the power voltage for exposure lamp. 
With the conventional arrangement described above, however, it has been 
impossible to get proper information on images from sensors due to a lack 
of uniformity in discharging by a charger. The charger is at all times 
exposed to and polluted with toner powders splashing inside the copier, an 
evaporated and splashed silicon oil used in heat-fixing process, and/or 
any other dirt outside the copier. This makes it very difficult to keep 
discharge of the charger uniform across the longitudinal direction of a 
photoconductive member. For this reason, unevenness in discharging occurs 
and this causes the photoconductive member to have an uneven distribution 
of its surface potential in the longitudinal direction thereof, or the 
toner-developed image on the photoconductive member for the referential 
white board to become uneven. If a surface potential meter or optical 
sensor samples the portion with such unevenness, the resultant measurement 
cannot represent a cross-section or typical value of the entire system, 
and the process of the system might disadvantageously be controlled based 
upon the erroneous measurement. This failure to control the process may 
possibly bring about various serious problems. That is, a process 
condition widely deviates from an optimally controlled condition might 
cause fluctuation of the quality of images. A defectively controlled 
process condition might damage the photoconductive member. Alternatively, 
an unusual increase in toner density fails to provide balanced frictional 
electrification charges to toner powders, yielding weakly charged toner 
which would make images foggy. Moreover, augment of toner might cause the 
toner powders to splash, polluting the inside of the copier. 
To overcome these problems, that is, to measure against the uneven 
distribution of static electric charges on the photoconductive member, 
various proposals have been made. For example, Japanese Patent Application 
Laid-Open Hei 2 No. 179659 discloses a corona charging device in an 
electro-copier able to detect the unevenness of charges and automatically 
executing cleaning operation of a corona charger when the charger causes 
uneven discharge. The device detects irregularity of toner density of the 
image on a photoconductor as an indicator for unevenness of discharging by 
the corona charger. More specifically, if a toner density sensor 
incorporated in the device exhibits an output power lower than a threshold 
level, the device recognizes occurrence of the unevenness in discharging. 
Based upon the detection, cleaning means is activated which comprises 
cleaning pads sandwiching the charging wires stretched in the charger and 
being slidable so as to be driven by a stepping motor. Thus, on the 
occasion of detecting uneven toner density, the stepping motor is 
activated to execute cleaning operation. 
Like the above disclosure, Japanese Utility Model Application Laid-Open Hei 
3 No. 20349, relating to an image forming apparatus equipped with an 
automatic cleaning mechanism in a corona charger, measures the density of 
a referential image on its photoconductive member by using detecting means 
comprising plural photosensors, and executes cleaning operation in the 
same manner as described of the above prior art by moving and sliding the 
cleaning mechanism when difference between the density values detected by 
the different photosensors is found to exceed a predetermined level. 
Another Japanese Utility Model Application Laid-Open Hei 2 No. 123947 
proposes a technology relates to an image recording apparatus comprising a 
plurality of developing units, wherein charging wires in the charger are 
cleaned by a cleaning means every time a different developing unit is 
selected. Here the cleaning means used is of slidable type with the same 
structure described above. The object of this apparatus is to conduct 
cleaning operation of the charging wires in accordance with the selection 
of the developers. 
Of these three publications, the first and second articles disclose the 
apparatuses all of which execute cleaning operation of the charging wires 
in the charger based on the comparison of the output power of the toner 
density sensor or sensors with a predetermined value. In consequence, it 
is true that the charging wires are cleaned effectively, but it is not 
that the process is controlled exactly based upon the density change, so 
that these cannot be thought of as the most suitable process control 
methods. 
The third article discloses a technology in which the charging wires in the 
charger are cleaned before a currently engaged developing unit is replaced 
by a different unit in order to change the developing process. Therefore, 
this method is not the one that keeps on controlling a certain developing 
unit with reference to its output information. 
On the other hand, Japanese Patent Application Laid-Open Hei 3 No. 105360 
discloses an image forming apparatus capable of performing automatic 
maintenance including cleaning operation of charger in parallel with the 
operations for attaching and detaching an IC card as a portable external 
memory means. Cleaning means disposed slidably with sandwiching 
corresponding electrodes is provided for each of a primary charger, a 
transfer charger and a separation charger, and is adapted to be driven by 
a respective motor supplied by a motor driving power source. The 
activation of these motors, in consequence the cleaning operation, is 
determined by a counter for total copy number. Here, the connector of the 
aforesaid IC card serves as a detecting means, being connected detachably 
to the apparatus body. 
The method is to control automatically certain subjects for maintaining the 
image forming apparatus using the IC card. Nevertheless, in this method, 
the wires of the chargers will not be cleaned until the detecting means 
sends out the order i.e, the signal for cleaning. In other words, the 
method is not the one that carries out an exact process control following 
the information from the photoconductive member. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a process 
control stabilizing system which allows the precess control to be carried 
out optimally based on exact information which is obtained by certain 
sensors with assuredly keeping uniform a discharge from the main charger 
unit. 
In order to achieve the above object, the present invention is constructed 
as follows. 
That is, in accordance with one aspect of the present invention, a process 
control stabilizing system for use in an image forming apparatus in which 
a visual image is formed by the steps of electrifying the surface of a 
photoconductive member by discharging electricity from a discharging 
electrode of a charger, exposing the photoconductive member to light 
corresponding to a pattern image to form an electrostatic latent image, 
and developing the latent image with toner, the system which allows 
process control means to control the electrophotographic process on the 
basis of the surface potential of the photoconductive member detected by 
potential detecting means, to thereby obtain an optimum image, is 
characterized in that the charger is provided with electrode cleaning 
means for cleaning the discharging electrode, and the process control 
means controls and activates the electrode cleaning means to clean the 
discharging electrode of the charger prior to detection of the surface 
potential of the photoconductive member by the potential detecting means. 
In accordance with another aspect of the invention, a process control 
stabilizing system for use in an image forming apparatus in which a visual 
image is formed by the steps of electrifying the surface of a 
photoconductive member by discharging electricity from a discharging 
electrode of a charger, exposing the photoconductive member to light 
corresponding to a pattern image to form an electrostatic latent image, 
and developing the latent image with toner, the system which process 
control means to control the electrophotographic process on the basis of 
the optical toner density of a toner image detected by density detecting 
means, to thereby obtain an optimum image, is characterized in that the 
charger is provided with electrode cleaning means for cleaning the 
discharging electrode, and the process control means controls and 
activates the electrode cleaning means to clean the discharging electrode 
of the charger prior to detection of the optical density by the density 
detecting means. 
In accordance with a further aspect of the invention, a process control 
stabilizing system for use in an image forming apparatus in which a visual 
image is formed by the steps of electrifying the surface of a 
photoconductive member by discharging electricity from a discharging 
electrode of a charger, exposing the photoconductive member to light 
corresponding to a pattern image to form an electrostatic latent image, 
and developing the latent image with toner, the system which comprises at 
least one or both of potential detecting means for detecting the surface 
potential of the photoconductive member and density detecting means for 
detecting the optical density of a toner image, and allows process control 
means to control the electrophotographic process on the basis of the 
detection result to thereby obtain an optimum image, characterized in that 
the charger is provided with electrode cleaning means for cleaning the 
discharging electrode; and the process control means controls and 
activates the electrode cleaning means to clean the discharging electrode 
of the charger if the detection result from the potential detecting means 
and/or the density detecting means falls out of a predetermined range, 
performs again the detection to obtain detection result from the potential 
detecting means and/or the density detecting means, and repeats the series 
of controlling operations until the detection result falls within the 
predetermined range. 
In the above case, in a case where the operation of the electrode cleaning 
means based on the detection result from the potential detecting means 
and/or density detecting means has been repeated up to a predetermined 
number of times in the aforementioned process control means, if the 
detection result after the predetermined times of detections does not fall 
within the predetermined range, it is effective that the system activates 
warning means and/or prohibits copying operation. 
In accordance with still another aspect of the invention, a process control 
stabilizing system for use in an image forming apparatus in which a visual 
image is formed by the steps of electrifying the surface of a 
photoconductive member by discharging electricity from a discharging 
electrode of a charger, exposing the photoconductive member to light 
corresponding to a pattern image to form an electrostatic latent image, 
and developing the latent image with toner, the system which comprises at 
least one or both of potential detecting means for detecting the surface 
potential of the photoconductive member and density detecting means for 
detecting the optical density of a toner image, and allows process control 
means to control the electrophotographic process on the basis of the 
detection result to thereby obtain an optimum image, characterized in that 
the charger is provided with electrode cleaning means for cleaning the 
discharging electrode; and the process control means controls and 
activates the electrode cleaning means to clean the discharging electrode 
of the charger after the detection step in which the surface potential is 
detected by the potential detecting means and/or the optical density is 
detected by the density detecting means, thereafter performs again the 
detection to obtain detection result from the potential detecting means 
and/or the density detecting means, takes a difference of the detection 
result between before and after the cleaning of the discharging electrode, 
and repeats the series of controlling operations until the difference of 
the detection result falls within a predetermined range. 
In the above case, in a case where the operation of the electrode cleaning 
means based on the difference of the detection result from the potential 
detecting means and/or density detecting means has been repeated up to a 
predetermined number of times in the aforementioned process control means, 
if the difference of the detection result after the predetermined times of 
the detections does not fall within the predetermined range, it is 
effective that the system activates warning means and/or prohibits copying 
operation. 
Since the present invention is constructed as stated above, it is possible 
to perform detection of the surface potential by the potential detecting 
means and/or detection of the optical density by the density detecting 
means while a discharge from the main charger unit is assured to be 
uniform. In addition, the controlling operation can be repeated until the 
difference between the detections before and after the cleaning of the 
electrode falls within a predetermined range. In the above operations, if 
an abnormal state occurs, the system is adapted to activate warning means 
and/or prohibit copying operation, thus making it possible to effect an 
optimum process control on the basis of the exact information.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One embodiment of the present invention will hereinafter be described with 
reference to FIGS. 1 to 11. This embodiment will be illustrated in a case 
where a process control stabilizing system is applied to a copying 
machine. 
The copying machine to which the embodiment is applied comprises, as show 
in FIG. 1, a cylindrical photoconductive drum 1 rotatable in a direction 
of arrow A in the apparatus. The photoconductive drum 1 is structured with 
a drum substrate of, for example, an aluminum prime tube with the wall 
thickness of 2 mm, 100 mm in diameter, and 340 mm in length. Typically, an 
electric carrier generating layer of 1 .mu.m thick and an electric carrier 
transporting layer of 34 .mu.m thick are coated on the outside 
circumferential surface of the drum substrate uniformly successively in 
that order to form an organic semiconductor material. Disposed above the 
photoconductor drum 1 is a transparent original setting table 2 on which 
an original M is put. Disposed between the original setting table 2 and 
the photoconductive drum 1 is an exposure optical system 3 comprising an 
exposure lamp 4, a plurality of mirrors 5 and a lens 6. 
In the exposure optical system 3, light emitted from the exposure lamp 4 
optically scans the original M on the original setting table 2, and the 
reflected light is focused to irradiate at an exposure point B the surface 
of the photoconductive drum 1 through mirrors 5 and lens 6 as shown with a 
chain line in FIG. 1. The surface of the photoconductive drum 1 having 
been electrified uniformly by a main charger unit 7 which will be referred 
to hereinafter is thus exposed to form an electrostatic latent image 
thereon in accordance with the pattern image of the original M. 
Disposed around the photoconductive drum 1 are the main charger unit 7 as 
stated above for charging or electrifying the surface of the 
photoconductive drum 1 at a predetermined voltage; a blank lamp 8 for 
erasing charges from the non-image area on the surface of the 
photoconductive drum 1; a developing unit 9 for developing with a toner 
the electrostatic latent image into a toner-developed image; an advance 
charge-removing lamp 10 for removing residual charges from the surface of 
the photoconductive drum 1 before transferring the toner-image; a transfer 
charger 11 for transferring the toner-image formed on the surface of the 
photoconductive drum 1 to a sheet of paper P to be transferred; a 
separation charger 12 for separating the copy paper P having the 
toner-image thereon from the surface of the photoconductive drum 1; a 
cleaner unit 13 for collecting residual toner on the surface of the 
photoconductive drum 1; a charge removing lamp 14 for removing residual 
electric charges on the surface of the photoconductive drum 1. The copy 
paper P separated from the photoconductive drum 1 with the help of the 
separation charger 12 is conveyed through an unillustrated moving path to 
a fixing unit 15 disposed on paper-discharging side. The fixing unit 15 
fixes the toner image on the copy paper. 
According to this embodiment, the copier is equipped with a process control 
stabilizing system 20 which comprises a CPU (central processing unit) 21 
as process controlling means for optimally regulating the voltage applied 
to the exposure lamp 4, the output power of the main charger unit 7, the 
developing bias voltage for developing unit 9 and the toner density of a 
developer; a surface potential sensor 22 as potential detecting means for 
detecting the surface potential of the photoconductive drum 1 and 
controlling the CPU 21 based on the detection result; and an optical 
sensor 23 as density detecting means for detecting the optical density of 
a referential toner image formed on the surface of the photoconductive 
drum 1 and controlling the CPU 21 based on the detection result. The 
referential toner image is created by scanning a referential white board 
24 disposed at an end of the original setting table 2 with light emitted 
from the exposure lamp 4 so as to form an electrostatic latent image upon 
the surface of the photoconductive drum 1, and developing the latent image 
into a toner-image by the developing unit 9. 
The surface potential sensor 22 is used of an oscillating sector type, and 
disposed in the periphery of the photoconductive drum 1 on the upstream 
side of the developing unit 9. The optical sensor 23 comprises, as shown 
in FIG. 2, an 890 nm-infrared LED (light emitting diode) 23a, a 
phototransistor 23b and holder 23c for supporting the both, and is 
disposed in the periphery of the photoconductive drum 1 on the upstream of 
the cleaner unit 13. As shown in FIG. 3, the LED 23a is connected at its 
cathode to a power voltage Vcc and grounded at its anode through a 
resistance R.sub.1 to form a light emitting section. On the other hand, 
the phototransistor 23b is connected at its collector to a power voltage 
Vcc and grounded at its emitter through a resistance R.sub.2 to form a 
light receiving section. An output terminal for extracting the detection 
signal is taken out from a joint between the emitter of the 
phototransistor 23b and the resistance R.sub.2. 
The optical sensor 23 senses the optical density of a referential toner 
image T formed on the surface of the photoconductive drum 1 such that the 
LED 23a of the light emitting section emits light onto the referential 
toner image T, and the light reflected therefrom is picked up and detected 
by the phototransistor 23b of the light receiving section. The optical 
sensor 23 outputs the thus sensed optical density as a detection signal. 
The surface potential sensor 22 detects the surface potential of the 
photoconductive drum 1 and outputs the detected value as a detection 
signal in the same manner as does the optical sensor 23. 
The above sensors 22, 23 are connected at their respective output terminals 
to the same CPU 21 through individual amplifiers 25, 25 and individual A/D 
converters 26, 26. The output terminals of the CPU 21 are connected to the 
main charger unit 7 through a power source 28, the developing unit 9 
through a developing bias source 29 and the developing unit 9 through a 
toner supply driving unit 30. 
Meanwhile, the main charger unit 7, which electrifies the surface of the 
photoconductive drum 1 at a predetermined voltage as already described, 
comprises an elongated rectangular supporting member 7a and two parallel 
discharging wires 7b, 7b (discharging electrode) stretched in the 
longitudinal direction of the supporting member 7a. The discharging wires 
7b, are made of a tungsten wire of 70 .mu.m in diameter. The wires 7b, are 
fixed at their one ends with a screw 7c to the supporting member 7a, while 
the other ends are attached to the supporting member 7a via a spring 7d so 
that the tension of the wires is adjustable. 
The main charger unit 7 is provided with electrode cleaning means for 
cleaning the discharging wires 7b, 7b. The cleaning means includes a 
frictionally slidable piece 31 for slidably wiping the discharging wires 
7b. As is shown in FIGS. 5 and 6, the frictionally slidable piece 31 is 
fixedly attached to a driving wire 32 such that the engaging ends 32a, 32a 
are each accepted by respective catching members 31a, 31a and the engaging 
portion is covered with a holder 33 which is fixed by a screw 34 fitting 
in an internal thread 31b. The driving wire 32 with the frictionally 
slidable piece 31 is wound around driving and idler pulleys 35 and 36 
disposed at both extremities in the longitudinal direction of the 
supporting member 7a. In this arrangement, the driving pulley 35 is 
rotated by an unillustrated motor, to cause the frictionally slidable 
piece 31 to move back and forth in a direction of C.sub.1 -C.sub.2 across 
which the discharging wires 7b are extended, whereby the discharging wires 
7b, 7b are wiped and cleaned. The driving motor as a driver for the 
frictionally slidable piece 31 is driven by the control of the CPU 21 
before the detection performed by the above-mentioned sensors 22 and 23. 
In the configurations described above, referring to a flowchart of FIG. 7, 
description will be made hereinafter about the control of 
electrophotographic process achieved by the CPU 21 in the process control 
stabilizing system 20 of this embodiment. 
First of all, when the power switch of the copy machine is tuned on (S1), 
the CPU 21 controls the driving motor so as to move the frictionally 
slidable piece 31 back and forth three rounds in the direction C.sub.1 
-C.sub.2, thus wiping and cleaning the discharging wires 7b in the main 
charger unit 7 (S2). 
Next, the surface potential sensor 22 detects the surface potential of the 
photoconductive drum 1, while the optical sensor 23 detects the optical 
density of the reference toner image formed on the surface of the 
photoconductive drum 1. The thus detected signals are inputted to the CPU 
21 through the respective amplifiers 25, 25 and the respective A/D 
converters 26, 26 (S3). 
Based on the detection signals from the sensors 22 and 23, the CPU 21 sends 
out output signals to the power sources 27, 28, 29 and the toner supply 
driving unit 30, so as control optimally the voltage to the exposure lamp 
4, the power of the main charger unit 7, the development bias voltage in 
the developing unit 9 and the toner density of the developer (S4). 
Then, a timer (not shown) in the system is reset or initialized and then 
turned on (S5). At a next step (S6), judgment is made on whether thirty 
minutes has elapsed after the timer was turned on. At S6, if the lapse of 
time is less than thirty minutes, the main routine is executed (S7), and 
then the operation again returns to S6. On the other hand, if the time has 
elapsed thirty minutes or more, the process goes back to S2, and the 
discharging wires 7b are cleaned by the electrode cleaning means in the 
same manner described above. 
A practical copying operation for 50k sheets of paper was made in the 
system for evaluating the aging behavior without operating the 
aforementioned electrode cleaning means. After the operation, measurement 
was made on the surface potential (or unevenness of the surface potential) 
in the longitudinal (or axial) direction of the photoconductive drum 1. 
FIG. 8 shows a graph of the result. In this graph, an upper curve shows a 
variation of the potential in the solid area, whereas a lower curve 
represents a variation of the potential in the blank area. 
As is apparent from FIG. 8, the potential in the solid area varies within a 
range of 700.+-.100 v and the potential in the blank area varies within a 
range of 150.+-.70. "As may be seen both areas exhibit great unevenness in 
potential". 
In the same condition, an original M with a uniform halftone density (about 
0.4 in the optical reflection density) was subjected to a copying 
operation, and the density (or the density unevenness) was evaluated in 
the longitudinal direction of the photoconductive drum 1. FIG. 9 shows a 
graph of the result. As will be appreciated from the result of FIG. 9, the 
density unevenness which can be attributed to the unevenness of the 
surface potential exhibits a markedly great unevenness, specifically a 
variation of 0.8.+-.0.3 in reflection density. 
In order to find the cause, the discharging wire 7b was observed in its 
surface using an optical microscope and an electron microscope. As a 
result, needle-like formation was observed. From a qualitative composition 
analysis for the formation, a large amount of Si-element was detected, 
from which it was assumed that the needle-like formation was provably 
created by evaporation and splash of the silicon oil used in the 
heat-fixing step. It will be apparently understood that an erroneous 
process control must be made if such a portion with unevenness is detected 
as a reference by the surface potential sensor 22 and the optical sensor 
23. Since the surface potential of the photoconductive drum 1 varies or 
fluctuates to a degree of 100 to 150 v, if the precision in detecting for 
the process to be regulated includes .+-.100 v due to the surface 
potential unevenness, the control itself will lose its meaning. The 
process control by means of the optical sensor 23 is also likely to be 
effected based upon information not representing a typical value for the 
photoconductive drum 1, in consequence the control itself not only becomes 
meaningless, but also gives rises to a fear of increasing the unstablity. 
Next, after another real copying operation for 50k sheets of paper in the 
system for evaluating the aging, evaluation was made of the unevenness of 
the surface potential and the unevenness of the halftone image density in 
the longitudinal direction of the photoconductive drum 1. Then, the 
discharging wires 7b were cleaned by activating the electrode cleaning 
means, and the surface potential and the halftone image density were 
measured in this condition. FIGS. 10 and 11 show graphs of the result. 
Upon the measurement, the cleaning operation of the discharging wires 7b 
was effected by slidably wiping the wires 7b with the frictionally 
slidable piece 31 constituting the electrode cleaning means being traveled 
three rounds. The surface potential and the halftone image density were 
measured after each round of the frictionally slidable piece 31. In FIGS. 
10 and 11, a dashed line represents result immediately after the practical 
copying operation for aging. A double-dots chain line indicates a result 
after the first round travel of the frictionally slidable piece 31. A 
single dot chain line and a solid line represent results after the second 
and third round travels, respectively. 
As is clearly shown in FIGS. 10 and 11, the unevenness of the surface 
potential and the halftone image density is reduced by the operation of 
the electrode cleaning means. Specifically, after the three rounds 
operation of the frictionally slidable piece 31, the former reduces to a 
range of .+-.15 v, and the latter to a range of .+-.0.1 to present 
substantially eliminated unevenness. The detection of the surface 
potential by the surface potential sensor 22, or the detection of the 
reflection density by the optical sensor 23 in such a condition, can be 
considered as sufficiently representing a state of the photoconductive 
drum 1. Therefore, the process control performed based on the detection 
result can achieve the desired object, in particular, properly compensate 
or correct the fluctuation of the surface potential of the photoconductive 
drum 1 and the instability of the developer used. 
As detailed heretofore, this process control stabilizing system 20 controls 
the photoelectrographic process by the CPU 21 with reference to the 
detection signals from the surface potential sensor 22 and the optical 
sensor 23. Additionally, the above CPU 21 activates the electrode cleaning 
means provided for the main charger unit 7 automatically to clean the 
discharging wires 7b before the detection steps of the sensors 22, 23, so 
that a uniform discharge from the main charger unit 7 may be expected. 
Consequently, the photoelectrographic process control is executed by the 
CPU 21 as described above, based on the proper information from the 
sensors 22, 23, thus making it possible to provide an optimum image to a 
copy paper sheet P in the copy operation. 
Referring next to FIG. 12, another embodiment of the present invention will 
be described hereinafter. In this embodiment, all the configurations are 
the same with those of the previous embodiment except the function of the 
CPU 21 as a part of the process control stabilizing system 20 of the 
previous embodiment. Therefore, descriptions for other than the copying 
process control effected by a CPU will be abbreviated. Further, like 
reference numerals will be allotted for identical members having similar 
functions to those in the previous embodiment. The CPU used here is also 
designated by the same reference numeral 21 as in the previous embodiment 
for convenience (see FIG. 1). 
The CPU 21 of this embodiment sends out output signals, based upon the 
surface potential sensor 22 and the optical sensor 23 in the similar 
manner to the previous embodiment, to the power sources 27, 28, 29 and the 
toner supply driving unit 30, to effect an optimum copying process 
control. 
In the above optimum control in the copying process, the CPU 21 determines 
whether or not the measurement obtained from the sensors 22, 23 fall 
within predetermined ranges before the process control. If a detection 
value falls out of the range, the CPU 21 controls to activate the driving 
motor for the electrode cleaning means, which in turn drives the 
frictionally slidable piece 31 to slidably wipe the discharging wires 7b. 
The series of the operations, that is, the above judgement on each of the 
detection results and the cleaning of the discharging wires 7b, will be 
repeated in a predetermined number of times until the detection results 
fall within the predetermined ranges. 
Even after the cleaning operations of the discharging wires 7b have been 
repeated up to the predetermined number of times, if each of the detection 
results does not fall within the predetermined range, the CPU 21 activates 
an unillustrated warning means so as to inform the user that the apparatus 
is out of order. At the same time, the CPU 21 stops each of the 
constituents from functioning, to thereby prohibit the copying operation. 
With the arrangement of the process control stabilizing system 20 described 
above, description will be made on a controlling operation of the 
electro-photographic process effected by the CPU 21 with reference to a 
flowchart shown in FIG. 12. 
First, when the power switch of the copier is turned on (S11), the number K 
of operation times of the cleaning means is initialized, or set at zero 
(S12). Then the surface potential sensor 22 detects the surface potential 
of the photoconductive drum 1, while the optical sensor 23 detects the 
optical density of the reference toner image formed on the surface of the 
photoconductive drum 1. The thus detected signals are inputted to the CPU 
21 through the respective amplifiers 25, 25 and the respective A/D 
converters 26, 26 (S13). 
Next, judgement is made by the CPU as to whether or not the detected 
results from the sensors 22, 23 fall within predetermined ranges (S14). 
At S14, if each detection result falls within the predetermined range, the 
CPU 21, based on the detected signals from the sensors 22, 23, sends out 
output signals to the power sources 27, 28, 29 and the toner supply 
driving device 30, so as to optimally control the voltage of the exposure 
lamp 4, the power of the main charger unit 7, the development bias voltage 
for the developing unit 9, and the toner density of the developer (S15). 
Then, a timer (not shown) in the system is reset or initialized and 
thereafter activated (S16). In a next step (S17), judgment is made on 
whether thirty minutes has elapsed after the timer was turned on. At S17, 
if the lapse of time is less than thirty minutes, the main routine is 
executed (S18), and then the operation again returns to S17. On the other 
hand, if the time elapsed is judged to be thirty minutes or more at S17, 
the process goes back to S12, and the number K of times when the electrode 
cleaning means was operated is reset at zero as described above. 
On the other hand, if the detected results fall out of the predetermined 
ranges, judgement is made at S19 as to whether or not the number K of 
times when the electrode cleaning means was operated is equal to or larger 
than the predetermined value (number of times) at S19. When the number K 
of the operation times is judged at S19 as to be less than the 
predetermined value, namely, the electrode cleaning means has not yet 
operated the predetermined times, the CPU 21 controls the driving motor so 
as to move the frictionally slidable piece 31 back and forth three rounds 
in the direction C.sub.1 -C.sub.2, thus wiping and cleaning the 
discharging wires 7b in the main charger unit 7 (S20). Thereafter, the 
number K of the operation times is increased by one (S21), then the 
process goes back to S13 again. 
When the number K of the operation times is not less than the predetermined 
value, or electrode cleaning means has operated the predetermined times, 
the CPU 21 activates the warning means to inform the user that the 
apparatus is out of order (S22). Then, each of the constituents are 
stopped from functioning, to prohibit the copying operation (S23). 
Here, the criteria or the predetermined ranges based on which the CPU 21 
judges as to the surface potential and the optical density, are not to be 
specified particularly, since the criteria are dependent upon the types of 
the photoconductive drum 1 and the developer used, environment in which 
the apparatus is used, and other factors. But in this embodiment, the 
surface potential is limited within 700.+-.150 v, and the optical density 
is limited within 0.8.+-.0.4, to obtain an appropriate operation result. 
As detailed heretofore, in this process control stabilizing system 20, the 
CPU 21 determines whether or not each of the detection results from the 
sensors 22, 23 lies within the predetermined ranges, and if the detected 
results fall out of the ranges, the CPU controls the electrode cleaning 
means to cleans the discharging wires 7b before the control of the copying 
process is executed. Further, if, despite that the CPU 21 has repeated the 
predetermined times the series of the operations described above, the 
detection results will not fall within the predetermined ranges, the CPU 
judges that something wrong happens in the apparatus. With this judgement, 
the CPU 21 activates the warning means and stops each of the constituents 
from functioning, to thereby inform the user that the apparatus is out of 
order, and to prohibits the copying operation. 
Accordingly, based upon each of the detection results from the surface 
potential sensor 22 and the optical sensor 23, it is possible to clean the 
discharging wires 7b effectively. In addition, the system automatically 
judges an abnormal or defective state of the apparatus, so that it is 
possible to obviate a serious accident. 
Next, referring to FIG. 13, still another embodiment of the invention will 
hereinafter be described. 
In this embodiment, all the configurations are the same with those of the 
first embodiment except the function of the CPU 21 as a part of the 
process control stabilizing system 20 of the first embodiment. Therefore, 
descriptions for other than the copying process control effected by a CPU 
will be abbreviated. Further, like reference numerals will be allotted for 
identical members having similar functions with those in the first 
embodiment. The CPU used here is also designated by the same reference 
numeral 21 as in the first embodiment for convenience (see FIG. 1). 
The CPU 21 of this embodiment sends out output signals, based upon the 
surface potential sensor 22 and the optical sensor 23 in the similar 
manner to the first embodiment, to the power sources 27, 28, 29 and the 
toner supply driving unit 30, to effect an optimum copying process 
control. 
In the above optimum control in the copying process, the CPU 21 executes 
the detections of the surface potential by the surface potential sensor 22 
and the optical density by the optical sensor 23. Then, the CPU 21 
activates and controls the driving motor constituting the electrode 
cleaning means so as to wipe and clean the discharging wires 7b by the 
frictionally slidable piece 31. Thereafter, the CPU 21 again executes the 
detections using the sensors 22, 23, and compares the detected values 
before a cleaning of the wires 7b with those after the cleaning, and finds 
respective differences for each detection item. The CPU 21 repeats the 
control up to a predetermined number of times until the differences fall 
within the predetermined ranges. 
Even after the cleaning operations of the discharging wires 7b have been 
repeated the predetermined number of times, if each difference of the 
detection results does not fall within the predetermined range, the CPU 21 
activates an unillustrated warning means so as to inform the user that the 
apparatus is out of order. At the same time, the CPU 21 stops each the 
constituents from functioning to thereby prohibit the copying operation. 
With the arrangement of the process control stabilizing system 20 described 
above, description will be made on a controlling operation of the 
electro-photographic process effected by the CPU 21 with reference to a 
flowchart shown in FIG. 13. 
First, when the power switch of the copier is turned on (S31), the number K 
of operation times of the cleaning means is initialized, or set at zero 
(S32). Then the surface potential sensor 22 detects the surface potential 
of the photoconductive drum 1, while the optical sensor 23 detects the 
optical density of the reference toner image formed on the surface of the 
photoconductive drum 1. The thus detected signals are inputted to the CPU 
21 through the respective amplifiers 25, 25 and the respective A/D 
converters 26, 26 (S33). The thus detected process information will be 
referred to as 1. 
The CPU 21 controls the driving motor so as to move the frictionally 
slidable piece 31 back and forth three rounds in the direction C.sub.1 
-C.sub.2, thus wiping and cleaning the discharging wires 7b in the main 
charger unit 7 (S34). Thereafter, the sensors 22, 23 again execute the 
detection operations of the surface potential and the optical density, 
respectively and the resultant signals are inputted into the CPU 21 (S35). 
The thus detected process information at S35 will be referred to as 2. 
Next, differences are taken by subtracting the process information 2 from 
the process information 1, and judgement is made as to whether or not the 
differences fall within predetermined ranges (S36). 
At S36, if each of the differences between the process information 1 and 2 
falls within the predetermined range, the CPU 21, based on the detected 
signals from the sensors 22, 23, sends out output signals to the power 
sources 27, 28, 29 and the toner supply driving device 30, so as to 
optimally control the voltage of the exposure lamp 4, the power of the 
main charger unit 7, the development bias voltage for the developing unit 
9, and the toner density of the developer (S37). Then, a timer (not shown) 
in the system is reset or initialized and thereafter activated (S38). In a 
next step (S39), judgment is made on whether thirty minutes has elapsed 
after the timer was turned on. At S39, if the lapse of time is less than 
thirty minutes, the main routine is executed (S40), and then the operation 
returns to S39 again. On the other hand, if the time elapsed is judged to 
be thirty minutes or more at S39, the process goes back to S32 again, and 
the number K of times when the electrode cleaning means was operated is 
reset at zero as described above. 
On the other hand, if each of the differences between the process 
information 1 and 2 falls out of the predetermined range at S36, judgement 
is made at S41 as to whether or not the number K of times when the 
electrode cleaning means was operated is equal to or larger than the 
predetermined value (number of times). When the number K of the operation 
times is judged at S41 as to be less than the predetermined value, namely, 
the number of the operations of the electrode cleaning means does not 
reach the predetermined number of times, the number K of the operation 
times is increased by one (S42), then the process goes back to S33 again. 
When the number K of the operation times is not less than the 
predetermined value, or the electrode cleaning means has operated the 
predetermined number of times, the CPU 21 activates the warning means to 
inform the user that the apparatus is out of order (S43). Then, each of 
the constituents are stopped from functioning to prohibit the copying 
operation (S44). 
Here, the ranges within which the differences between the process 
information 1 and 2 are limited by the CPU 21 are not to be specified 
particularly, but in this embodiment, the difference of the surface 
potential between the information 1 and 2 is limited within 15 v, while 
the difference of the optical density is limited within 0.05 to 0.08, to 
obtain an appropriate operation result. 
As detailed heretofore, in this process control stabilizing system 20, the 
first and second sampling of the process control information, or the first 
and second detections of the surface potential by the sensor 22 and the 
optical image density by the sensor 23, are executed before and after the 
cleaning operation of the wire 7b. Then based upon the detected result, 
the CPU 21 determines whether or not each of the differences of the first 
and second process control information from the sensors 22, 23 lies within 
the predetermined ranges, and if the differences fall out of the ranges, 
the CPU controls the electrode cleaning means to clean the discharging 
wires 7b before the control of the copying process is executed. Further, 
if, despite that the CPU 21 has repeated the predetermined times the 
series of the operations described above, the differences will not fall 
within the predetermined ranges, the CPU judges that something wrong 
happens in the apparatus. With this judgement, the CPU 21 activates the 
warning means and stops each of the constituents from functioning, to 
thereby inform the user that the apparatus is out of order, and to 
prohibits the copying operation. 
Accordingly, the system of this embodiment can detect the unevenness of 
charging by the main charger unit 7 with an increased exactness, and 
assures to remove adverse influences of the disturbances and noises caused 
by the charging unevenness. In addition, the system can effect an exact 
detection of the charging unevenness as stated above, so that it is 
possible to make a sever decision about the abnormality of the apparatus. 
The present invention is not limited to the three embodiment presented 
heretofore, but various changes and modification can be made within the 
scope of the invention. For example, in the second and third embodiments, 
the frictionally slidable piece 31 for cleaning the discharging wire 7b is 
moved back and forth three rounds with respect to the discharging wires 
7b, but the number of times for wiping is not in particular limited. The 
parts and constituents of the surface sensor 22 or the optical sensor 23 
which constitutes the process control stabilizing system 20 are not 
specified. The control of the exposure lamp 4, main charger unit 7 and 
developing unit 9 accompanied with the system is not limited by the 
embodiments, either. 
Moreover, in the second and third embodiment, if the detection results or 
the difference of the detected results fall out of the predetermined 
ranges after the predetermined number of times of cleaning the discharging 
wires 7b, the system is constructed such as to both activate the warning 
means and prohibit the copying operation. But it is not necessary to 
effect both the operations, provision of either one alone will still work. 
As is apparent from these embodiments, the process control stabilizing 
system of the invention includes various novel features which have not 
been realized before, so that the system of the present invention can 
achieve excellent effects as follows. 
In accordance of one aspect of the present invention, the system is 
constructed such that the charger is provided with electrode cleaning 
means for cleaning the discharging electrode, and the process control 
means controls and activates the electrode cleaning means to clean the 
discharging electrode of the charger prior to detection of the surface 
potential of the photoconductive member by the potential detecting means. 
With this construction, the surface potential can be detected by the 
potential detecting means with the discharge from the charger kept 
assuredly uniform, in consequence, it is possible to effect an optimum 
process control based on the exact information. 
In accordance with another aspect of the present invention, the system is 
constructed such that the charger is provided with electrode cleaning 
means for cleaning the discharging electrode, and the process control 
means controls and activates the electrode cleaning means to clean the 
discharging electrode of the charger prior to detection of the optical 
density by the density detecting means. With this construction, the 
surface potential can be detected by the potential detecting means with 
the discharge from the charger kept assuredly uniform, in consequence, it 
is possible to effect an optimum process control based on the exact 
information. 
In accordance with further aspect of the present invention, the system is 
constructed such that the charger is provided with electrode cleaning 
means for cleaning the discharging electrode, and the process control 
means controls and activates the electrode cleaning means to clean the 
discharging electrode of the charger if the detection result from the 
potential detecting means and/or the density detecting means falls out of 
a predetermined range, performs again the detection to obtain detection 
result from the potential detecting means and/or the density detecting 
means, and repeats the series of controlling operations until the 
detection result falls within the predetermined range. With this 
arrangement, the cleaning of the discharge electrode of the charger can be 
effectively carried out based on the detection result from the potential 
detecting means and/or the density detecting means, in consequence, it is 
possible to assuredly eliminate cause for the charging unevenness brought 
about by the charger, thus making it to effect an optimum process control 
based on more exact information. 
In the above process control stabilizing system, the process control means 
is constructed such that, in a case where the operation of the electrode 
cleaning means based on the detection result from the potential detecting 
means and/or density detecting means has been repeated up to a 
predetermined number of times, if the detection result after the 
predetermined times of detections does not fall within the predetermined 
range, the system activates warning means and/or prohibits copying 
operation. With this construction, an abnormal or defective state in the 
apparatus can be automatically recognized, so that it is possible to 
prevent a serious accident from occurring. 
In accordance with still another aspect of the invention, the system is 
constructed such that the charger is provided with electrode cleaning 
means for cleaning the discharging electrode, and the process control 
means controls and activates the electrode cleaning means to clean the 
discharging electrode of the charger after the detection step in which the 
surface potential is detected by the potential detecting means and/or the 
optical density is detected by the density detecting means, thereafter 
performs again the detection to obtain detection result from the potential 
detecting means and/or the density detecting means, takes a difference of 
the detection result between before and after the cleaning of the 
discharging electrode, and repeats the series of controlling operations 
until the difference of the detection result falls within a predetermined 
range. With this construction, it is possible to detect the charging 
unevenness caused by the charger exactly, and to assuredly eliminate the 
influence of disturbances and noises caused by the charging unevenness. In 
consequence, it is possible to assuredly eliminate the cause of the 
charging unevenness brought about by the charger, thus making it possible 
to effect an optimum process control based on more exact information. 
In the above process control stabilizing system, the process control means 
is constructed such that, in a case where the operation of the electrode 
cleaning means based on the difference of the detection result from the 
potential detecting means and/or density detecting means has been repeated 
up to a predetermined number of times in the process control means, if the 
difference of the detection result after the predetermined times of the 
detections does not fall within the predetermined range, the system 
activates warning means and/or prohibits copying operation. With this 
arrangement, an abnormal or defective state in the apparatus can be 
recognized more severely, so that it is possible to assuringly prevent an 
accident from occurring.