Developing device with shutter blade

A developing device for developing a latent image held on a latent image holding member by application of a developing agent, onto the latent image, which comprises a developing sleeve disposed in confrontation to the latent image holding member, a developer feeding device to feed the developer onto the surface of the developing sleeve, a regulating device to regulate thickness of a developer layer on the developing sleeve, and a shutter blade which is so provided as to be able to take a contact position with the surface of the developing sleeve and a withdrawal position away from the surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a developing device. More particularly, 
it is concerned with a developing device, in which a uniform thin layer of 
a single component developer is formed on a developer holding means, and 
then the thin layer of developer is disposed in confrontation to a latent 
image holding member to develop the latent image. 
2. Description of Prior Arts 
There have heretofore been known various types of developing devices, which 
utilize a single component developing agent. 
Of these various types, a toner transfer development has been known to be a 
unique method. According to this method, a single component developer is 
applied onto a developer holding means in the form of a uniform thin 
layer, then this thin developer layer is disposed in confrontation to the 
surface of an electrostatic latent image with a small space gap 
therebetween, and the developer is caused to migrate from the developer 
holding means to the electrostatic latent image surface by the 
electrostatic force of attraction, thereby developing the latent image 
(vide: U.S. Pat. No. 3,232,190). According to this method, since the 
developer is not attracted to a non-image portion where no latent image 
potential exists and also the developer is not in contact with the 
non-image portion, a favorable development free from fogging can be 
effected. Further, since no carrier particles are used, there is no 
possibility of variations in the mixing ratio of the developer, hence no 
possibility of deterioration in the property of the carrier particles. 
The assignee of the present invention has also filed U.S. Patent 
Application Ser. Nos. 938,101, 938,494, and 58,434, in which different 
types of the toner transfer development method are proposed. 
According to the former two methods, a single component magnetic developer, 
a developer holding means made of a non-magnetic material, and a magnetic 
field generating means are arranged in the order as mentioned, and, after 
the developer is fed onto the developer holding means, a uniform thin 
layer of the developer is formed on the developer holding means by the 
magnetic force generated by the magnetic field generating means and a 
developer layer thickness regulating member. This thin layer of the 
developer is disposed in confrontation to the surface of an electrostatic 
latent image with a small space gap being provided therebetween so as to 
avoid contact at their surfaces. The development is effected by stretching 
out the developer at positions facing the image portions due to the 
electrostatic force of attraction. In this case, too, since the 
development is done in a state of the developer not being in contact with 
the non-image portion, a developed image perfectly free from the fogging 
can be obtained. 
The latter development method is as follows. A single component magnetic 
developer, a developer holding means made of a non-magnetic material, and 
a magnetic field generating means are arranged in the order as mentioned. 
After the developer has been fed onto the developer holding means, a 
uniform thin layer of the developer is formed on the developer holding 
means by the magnetic force generated by the magnetic field generating 
means and a developer layer thickness regulating member. This thin layer 
of the developer is disposed in confrontation to the surface of an 
electrostatic latent image with a small space gap being provided 
therebetween so as to avoid contact at their surfaces. The development is 
effected by applying an alternating bias voltage as the developing bias 
voltage between the electrostatic latent image surface and the developer 
holding means, and by further changing the space gap with lapse of time. 
According to this development method, the developer is applied even to the 
non-image portion of the electrostatic latent image at the initial stage 
of the development, whereby a half tone portion of the latent image is 
developed, and, thereafter, the developer is applied only to the image 
portion with lapse of time. This latter method is effective in obtaining, 
in comparison with the former development method, a developed image having 
good reproducibility in the half tone portion and being perfectly free 
from the fogging. 
Thus, according to the developing method wherein the thin layer of the 
single component developer (hereinafter called also "toner") is disposed 
in confrontation to a latent image, there can be attained excellent 
effects in its developing capability, image reproducibility, life of the 
developer, and so forth, in comparison with the conventional developing 
method. 
However, even with these developing methods, there are various problems to 
be mentioned hereinbelow in putting them into practice. 
(1) Foreign substances get in between the non-magnetic developer holding 
means and the developer layer thickness regulating member, and the portion 
where the foreign substances exist do not allow the toner to pass 
therethrough, whereby no toner can be fed to this portion and streaky 
irregularity occurs in the toner layer. Most of these foreign substances 
are paper dust and thread dust which have intruded from outside. In other 
cases, such foreign substance might be agglomerated mass of the toner 
particles. Further, depending upon the quality of the toner, it tends to 
be fused onto the surface of the magnetic blade as the developer layer 
thickness regulating member, and to grow bigger with lapse of time to 
cause an irregular surface on the edge part of the magnetic blade. 
Although the occurrence of this fusion of the toner is largely governed by 
the material quality of the toner, when the number of revolutions of the 
non-magnetic sleeve as the developer holding means increases, the force of 
the toner to collide against the magnetic blade also increases with the 
consequence that the toner tends to be readily fused to the blade surface. 
While intrusion of such foreign substances and occurrence of the 
agglomerated toner due to its fusion are not so high in their frequency of 
generation, such intrusion and agglomeration, however small in quantity 
they may occur at one time, accumulate in the developing device little by 
little during use of the device over a long period of time, and such 
accumulated effect appears on the developed image. 
As measures against such unfavorable phenomena, there has heretofore been 
made a proposal, if any, to merely construct the developing device in a 
closed structure to prevent dust, etc. from entering into the device. In 
most cases, the toner within the developing device is totally taken 
outside the device, and the dust accumulated on the blade is removed every 
time the intrusion of the foreign substances and the fusion of the toner 
occur. Such method, however, not only takes time, but also causes 
considerable staining of the device, etc. due to scattering of the toner 
particles here and there, hence an improvement in this respect has been 
desired. 
On the other hand, when the foreign substances accumulated on the edge of 
the magnetic blade are going to be removed by an external mechanical means 
without taking the developer out of the container vessel, there often 
takes place such a situation that the toner is often urged toward the 
surface of the developing sleeve which is the developer holding means with 
the consequence that the toner particles are agglomerated, or the toner 
mass is tightly adhered onto the sleeve surface to invite adverse effects. 
(2) During a long period of developing operation, a thin layer of the 
developer is formed on the surface of the developer holding means to lower 
the developing capability. 
At the time of the developing operation, the developer constantly repeats 
contact and separation to and from the surface of the developer holding 
means, on account of which the surface of the developer holding means 
tends to be stained with the developer, or a film layer of the developer 
tends to be formed. This thin layer of developer may be sometimes a 
resinous component of a low molecular weight contained in the developer, 
or in other cases, a controlling agent to impart the triboelectricity to 
the developer, or, in still other cases, very fine particles of the toner 
that have not contributed to the development. In any event, when these 
components cover the surface of the developer holding means, in 
particular, when the developing method which utilizes the charge of the 
developer, the charge quantity of the developer falls short to cause a 
lowering in the developing density, deterioration in the image 
reproducibility, and various other problems. 
(3) During a long developing operation, the developer particles agglomerate 
to increase the adhesive force between the developer and the surface of 
the developer holding means, whereby formation of the developer layer in 
the uniform thickness becomes difficult, and irregularity in the image 
development takes place thereby. 
No problem occurs so far as the developer coated on the developer holding 
means contributes to the development within a short period of time and 
then separates from the surface of the developer holding means. However, 
when the developer which has not contributed to the development due to low 
image density, and other reasons remains on the surface of the developer 
holding means for a long period of time, the developer particles increase 
their mutual agglomerating force to partially form a thicker coated layer 
on the surface, thereby causing irregularity in the developed image. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
developing device which has entirely solved the problems inherent in the 
conventional developing devices as mentioned in the foregoing. 
It is another object of the present invention to provide an improved 
developing device of good image reproducibility. 
It is still another object of the present invention to provide an improved 
developing device capable of easily removing various foreign substances 
such as paper dust, thread dust, agglomerated toner particles, and others 
accumulated on the developer holding means. 
It is yet another object of the present invention to provide an improved 
developing device capable of preventing a decrease in the development bias 
effect due to filming of the toner on the developer holding means, 
shortage in the charge quantity of the toner, and a decrease in the 
development density. 
It is another object of the present invention to provide an improved 
developing device which does not cause irregularity in the developed 
image. 
According to the present invention, generally speaking, there is provided a 
developing device for developing a latent image on a latent image holding 
member by application of a developing agent to the latent image, which 
comprises developer holding means disposed in confrontation to the latent 
image holding member, developer feeding means to feed the developer to the 
surface of the developer holding means, regulating means to regulate the 
thickness of a developer layer on the developer holding means, and shutter 
blade means which is so provided as to be able to take a contact position 
with the surface of the developing sleeve and a withdrawal position away 
from the sleeve surface. 
The foregoing objects, other objects, the construction and operation of the 
developing device according to the present invention will become more 
apparent from the following detailed explanations thereof when read in 
conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows the developing device, to which the present invention is 
applicable. In the drawing, a numeral 1 refers to an electrostatic latent 
image holding member consisting of a photosensitive member, an insulating 
member, etc., on which an electrostatic latent image has been formed. The 
latent image holding member moves in the direction of an arrow a. A 
numeral 2 refers to a developing sleeve of a non-magnetic material such 
as, for example, stainless steel, brass, etc.. The developing sleeve is 
disposed in confrontation to the latent image holding member with a small 
space gap (0.5 mm or so) therebetween and rotates in the direction of an 
arrow b. This small space gap is set wider than the thickness of the 
developer layer to be formed on the developing sleeve. Inside this 
developing sleeve, there is fixedly provided a magnetic roll 3 which is 
magnetized as illustrated. By the magnetic force of this magnetic roll 3, 
a layer of a developer T (having a mean particle diameter of approximately 
30 microns) is formed on the surface of the developing sleeve 2. Thickness 
of the developer layer is regulated by a doctor blade 4 made of, for 
example, iron and disposed in contiguity to the surface of the developing 
sleeve. A space gap between the edge of the doctor blade 4 and the 
developing sleeve 2 is set at, for example, 0.3 mm. In order to perform 
thickness regulation of the developer layer accurately and securely, 
magnetic poles of approximately 600 gausses are disposed within the 
developing sleeve 2, whereby the developer layer is controlled to its 
thickness of approximately 70 microns. The thickness regulated developer 
layer then reaches a developing position facing the surface of the latent 
image holding member 1, thereby performing the image development in any of 
the developing methods as mentioned in the foregoing. 
Here, if the developing operation is performed with the construction as 
shown in FIG. 1 as it is, the defects as listed in the above (1) to (3) 
would arise. The present invention is to remove these detects, according 
to which the construction of the developing device is improved as shown in 
FIGS. 2A to 2C. 
Explaining the present invention in reference to FIG. 2A, a numeral 4 
refers to the doctor blade as also shown in FIG. 1. In this embodiment, 
the shutter blade 5 is provided at the side surface of the doctor blade, 
through which the developer is fed. This shutter blade 5 is so provided as 
to be movable in the arrow direction c along slide rails 6, 6. The shutter 
blade is maintained in its non-operative position in FIGS. 2A and 2B. In 
this non-operative state of the shutter blade 5, if and when foreign 
substances such as dusts, agglomerated toner particles, etc. intervene 
into the doctor blade 4 during the developing operation, or when carrying 
out periodical inspection of the device, the shutter blade 5 is brought 
into contact with the surface of the developing sleeve by means of a bar 
handle 7 provided on the top end part of the blade as shown in FIG. 2C, 
and by rotating the developing sleeve either manually or automatically, 
cleaning of the sleeve surface is carried out. 
The shutter blade 5 as used here may be made of any kind of material. It 
has been found out experimentally that a relatively thin blade of metal 
material such as phosphor bronze of the thickness of 100 microns is 
effective. It has also been verified that a relatively thin sheet of 
rubber, plastic, and like other materials may be satisfactorily used for 
the purpose. An angle of contact of the shutter blade 5 to the developing 
sleeve should preferably be made such that an angle .alpha. at the 
developer feeding side constitutes an obtuse angle as shown in FIG. 2C, 
which is favorable from the aspects of the cleaning efficiency and 
prevention of the shutter blade from inverting its direction of contact. 
Also, there is provided a cleaner pad 8 to remove the foreign substances 
agglomerated and adhered between the doctor blade 4 and the developing 
sleeve, 2, particularly on the edge of the doctor blade 4, even after 
removal of the foreign substances within the developing device by the 
shutter blade 5. The cleaner pad 8 is slidable breadthwise in the arrow 
direction d from end to end of the doctor blade 4 by a handle 9 provided 
thereon along its bottom edge, thereby removing the foreign substances 
remaining on the edge of the doctor blade. The pad 8 may always be 
positioned at one side end of the doctor blade and used by laterally 
sliding the same when necessity arises. The requirement which this cleaner 
pad 8 should satisfy is also not so stringent. As a rule, any material 
that does not damage the surface of the electrostatic image holding 
member, e.g., ordinary rubber material, etc., is sufficient to remove the 
foreign substances accumulated on the edge of the magnetic blade. 
FIGS. 3A and 3B show partial cross-sections of another embodiment of the 
present invention, in which the shutter blade is manually brought into 
contact with and separated from the surface of the developing sleeve, the 
same as the embodiment shown in FIG. 2. FIG. 3A shows a case, wherein the 
shutter blade is separated from the surface of the photosensitive member, 
and FIG. 3B shows a case, wherein the blade is in contact with the 
photosensitive member. Incidentally, it is to be noted that those parts 
which are the same as those in the FIG. 2 embodiment are designated by the 
same reference numerals. 
Two notches 10a and 10b for locking the shutter blade 5 are formed on 
either the doctor blade 4 or the supporting member 10 at both end parts 
thereof in the vertical direction. At both ends of the supporting member 
11 for the shutter blade 5, there are provided rotatable levers 12. When 
the lever 12 is fitted into any of the notches 10a and 10b, the shutter 
blade can be fixed at its position. In the ordinary state, the lever 12 is 
engaged with the upper notch 10a as shown in FIG. 3A, whereby the shutter 
blade 5 is away from the surface of the developing sleeve 2. In case the 
foreign substances such as dusts, agglomerated toner, etc. are adhered 
between the doctor blade 4 and the sleeve 2, the lever 12 is moved down 
from the upper notch 10a to the lower notch 10b so that the shutter blade 
5 may be locked in the state of its being in contact with the surface of 
the developing sleeve. In this state, when the sleeve 2 is rotated, only 
the foreign substances remain between the doctor blade 4 and the sleeve 2. 
These foreign substances are removed by the cleaning device such as 
cleaner pad 8, etc. as shown in FIG. 2. Fine particles of the toner which 
have been adhered onto the sleeve surface and formed a film layer can also 
be removed by this shutter blade 5. 
FIGS. 4A and 4B are also partial cross-sections of still another embodiment 
of the present invention. The device in this embodiment is so constructed 
that the shutter blade 5 may be automatically operated upon receipt of a 
signal from an image forming device such as an electrophotographic 
reproduction apparatus. 
In this embodiment, the shutter blade 5 is made of a magnetic material such 
as iron, nickel, and others, or a magnet. Inside the sleeve 2, there is 
fixedly provided a magnet roller 13. A magnetic pole 13a is disposed at a 
position facing the magnetic blade 4 made of the magnetic material or 
magnet. The shutter blade 5 is constantly subjected to a force in the 
direction of its contact with the sleeve surface due to the magnetic force 
of attraction from the magnetic pole 13a (FIG. 4B). When a signal to open 
the shutter blade is imparted, a plunger 14 connected with the supporting 
member 11 of the shutter blade 5 is actuated, and the shutter blade 5 is 
pulled upward. In this case, a resin member may be fitted at the edge 
portion of the shutter blade, or a resinous coating may be applied thereon 
to prevent the sleeve from being damaged. 
According to the experiments done by the present inventors, the shutter 
blade made an iron sheet of 50 to 150 microns thick and treated for rust 
prevention could be satisfactorily attracted to the surface of the 
developing sleeve upon application of the magnetic field of approximately 
800 gausses from the magnetic pole 13a, whereby the cleaning of the toner 
could be done successfully. It is of course possible that, when the 
contact pressure is low, a spring is used together to increase the 
cleaning effect. Besides the magnetic material, sheets of rubber or 
plastic material as in the previous embodiment can also be used as the 
shutter blade for the purpose of the present embodiment. In this case, it 
is preferable to use a pressure member S (shown in dotted line in the 
drawing) such as spring, etc. for securing the contact of the shutter 
blade to the sleeve surface. 
FIGS. 5A and 5B illustrate yet another embodiment of the present invention, 
wherein a spring 15 is hooked at one end of the supporting member 11 for 
the shutter blade 5, by which the blade 5 is drawn upward (FIG. 5A). When 
a signal to cause the shutter blade 5 to contact the sleeve 2 is imparted, 
a cam 16 is rotated a half turn by means of a motor of a plunger (not 
shown) to pull down the shutter blade 5 against force of the spring 15, 
thereby bringing the same into contact with the sleeve surface. 
In this instance, the shutter blade 5 may be made of any appropriate 
material selected from a wide variety of materials such as metals, 
plastics, rubbers, and so forth. Also, the shutter blade can be contacted 
sufficiently vigorously to the sleeve surface by force of the cam, whereby 
stains adhered onto the sleeve surface, filming due to the resinous 
component contained in the toner, or adhesion of fine particles on the 
sleeve surface can be sufficiently cleaned. 
Even in this embodiment, the shutter blade 5 can be closely contacted to 
the sleeve surface by use of the magnetic material or magnet for the 
blade, and by providing the magnetic pole 13b in the magnet roller 13 at a 
position opposite to the sleeve surface. The same thing can be said of the 
embodiments in FIGS. 2 and 3. Incidentally, the filming on the sleeve 
surface and irregularity in the toner coating can be prevented even when 
the shutter blade is disposed at a position other than the position of the 
doctor blade for regulating the toner layer thickness. 
FIG. 6 shows one embodiment of the developing device, in which the present 
invention has been adopted. In this illustrated embodiment, the 
multi-polar permanent magnet 13 of the developing device (generally 
designated by a reference numeral 17) is fixed in position, and the sleeve 
2 rotates in the arrow direction at the surface adjacent to the 
electrostatic image holding member 1. By the rotation of the developing 
sleeve 2, one component insulative ferromagnetic toner 19 fed from the 
toner container 18 is coated on the sleeve surface. In this instance, the 
charging system for the sleeve surface and the toner particles is so 
selected that, by friction between the sleeve surface and the toner 
particles, the toner particles may be charged in the opposite polarity as 
that of the electrostatic image charge. Furthermore, the doctor blade 4 
made of iron material is disposed in contiguity to the sleeve surface (an 
interval of from 50 to 500 microns). The doctor blade 4 is in the form of 
a thin plate with the direction of the generatrix of the sleeve as its 
lengthwise direction. It is in the shape as shown in FIG. 2 for one 
example. By disposing this doctor blade at a position opposite to one 
magnetic pole 13a of the multi-polar permanent magnet 13 (the pole S.sub.3 
in the illustrated example), the thickness of the toner layer is regulated 
thinly and uniformly (in a range of from 30 to 300 microns, or preferably 
from 30 to 200 microns). A numeral 5 refers to the shutter blade according 
to the present invention, which performs cleaning of the surface of the 
sleeve or removal of dusts between the doctor blade 4 and the sleeve 2 by 
moving the same in the direction c. By adjusting the sleeve rotating 
speed, the surface layer speed of the toner layer, or preferably the inner 
speed of the toner layer may be made substantially equal to, or in the 
vicinity of, the speed of the surface of the electrostatic image holding 
member. In place of iron, other magnetic material may be used for the 
doctor blade 4, and an opposite magnetic pole may be formed. A magnet may 
also be used. A reference numeral 20 designates a power source to apply an 
alternating voltage across the non-magnetic cylinder 2 and the 
electrostatic image holding member 1. The blade 4 is maintained at the 
same potential as that of the toner holding member to prevent irregularity 
in the toner application. 
For the magnetic toner used, there is such one, for example, consisting of 
75 parts of polystyrene, 15 parts of magnetite, 3 parts of charge 
controlling agent, and 6 parts of carbon. These components are uniformly 
mixed by the well known method, and made into an average particle diameter 
of from 5 to 30 microns. Any other well known magnetic toner having the 
abovementioned particle size distribution and containing magnetic powder 
in the range of from 15 to 50 wt% may, of course, be used for the purpose 
of the present invention. 
The reason for limiting the average particle size of the toner and the 
content of the magnetic powder in the abovementioned ranges is as follows. 
When the average particle diameter of the toner particles becomes smaller 
than 5 microns, the toner particles rigidly adhere onto the surface of the 
non-magnetic cylinder due to the electrostatic force to become difficult 
to be separated from the drum surface, whereby no satisfactory development 
cannot be effected. Further, there is formed on the surface of the 
non-magnetic drum a layer of fine toner particles to hinder the contact 
charging action between the newly fed toner particles and the drum 
surface, thereby causing lowering in the developing density due to 
insufficient toner transfer. On the other hand, when the average particle 
diameter of the toner particles becomes larger than 30 microns, the image 
as developed becomes disadvantageously coarse. 
When the content of the magnetic powder becomes less than 15 wt%, there is 
obtained toner particles with less content of the magnetic powder as the 
result of pulverizing the toner components for producing the toner 
particles. And, when the toner particles containing a smaller amount of 
the magnetic powder are mixed in the developer, they tend to become easily 
agglomerated with the consequence that the resulting developer is inferior 
in its fluidity, and uniform charging of the toner particles becomes 
difficult, which causes fogging to occur readily. Also, the magnetic force 
of the toner particles to be attracted back to the magnet becomes lowered, 
which also causes fogging to occur, making it difficult to produce an 
image of good image quality. Further, the magnetic conveyance becomes 
difficult. On the other hand, when the content exceeds 50%, the resin 
component becomes less in quantity to deteriorate the image fixing 
property with the consequence that the quality of the resulting image 
becomes coarse and inferior for the practical use. 
FIG. 7 illustrates one embodiment of an electrophotographic reproduction 
apparatus, in which the developing device of the present invention has 
been incorporated. In the drawing, the reproduction apparatus which adopts 
the process as described in U.S. Pat. No. 3,666,363, wherein the 
three-layered photosensitive member consisting of an electrically 
conductive substrate, a photoconductive layer formed on the substrate, and 
an insulating layer over the photoconductive layer is used, is 
schematically shown. In this embodiment, the photosensitive drum 21 made 
of the above-mentioned photosensitive member shaped in a drum form is 
rotated in the direction of an arrow mark by a driving means (not shown). 
The photosensitive drum 21 is subjected to a uniform corona discharge by 
the primary charger 22, and then to the corona discharge by means of a 
corona discharger 23 in the secondary a.c. or in the polarity opposite to 
the of the primary charger 22. Simultaneously, the photosensitive drum is 
subjected to the image exposure through an optical system 24, and then to 
a uniform exposure over the entire surface of the photosensitive drum 21 
by an overall exposure lamp 26. In this manner, an electrostatic latent 
image of high image contrast is obtained on the surface of the 
photosensitive drum 21. The thus obtained electrostatic latent image is 
developed by a developer 17, and this developed image is transferred by a 
transfer charger 29 onto an image transfer paper 28 fed from a paper 
feeding cassette 27. The image transfer paper 28, onto which the image has 
been transferred, is then separated from the photosenitive drum 21 by a 
paper separation charger 30, and conveyed by a conveyor belt 31. 
Thereafter, the developed image transferred onto the image transfer paper 
28 is fixed thereon by an image fixing device 32. On the other hand, the 
surface of the photosensitive drum 21 is wiped by a cleaning device 33 to 
remove residual toner thereon. It is to be noted incidentally that, in the 
illustrated embodiment, the light 34 to be irradiated onto the 
photosensitive drum 21 simultaneously with the image exposure 25 is a 
blank exposure light which is imparted to the drum simultaneously with the 
secondary corona discharge for preventing unnecessary amount of the 
developer from adhering onto the photosensitive drum. 
FIG. 8 shows an example of the timing chart to operate the shutter blade in 
the electrophotographic reproduction apparatus shown in FIG. 7. The 
shutter blade should be operated, as a rule, when no image reproduction is 
being conducted, because, while the shutter blade is in contact with the 
surface of the developing sleeve, no toner can be fed to the sleeve. 
The first embodiment is to actuate the shutter blade in synchronism with 
"on" and "off" of the main switch in the reproduction apparatus. As soon 
as the main switch is "on", the developing sleeve is rotated and the 
shutter blade is caused to contact onto the sleeve surface (T.sub.1). In 
the same manner, the sleeve is also rotated when the main switch is "off" 
to actuate the shutter blade (T.sub.2). In practice, the solenoid or the 
cam as shown in FIGS. 4 or 5 is actuated upon receipt of the signals 
T.sub.1, T.sub.2. It is preferable that the shutter blade be maintained in 
contact with the surface of the developing sleeve while the sleeve is 
performing at least one rotation. 
After the reproduction apparatus has been in an inoperative state for a 
long period of time, when the shutter blade is actuated in synchronism 
with the main switch closure, if functions to remove from the sleeve 
surface the toner particles which are prone to be agglomerated on the 
sleeve due to their moisture absorption, etc. as the result of their 
having remained on the sleeve surface for a long time, whereby uniform 
toner coating can be done. When the shutter blade is operated after 
completion of the copying operation (i.e., after opening of the main 
switch), it serves to remove the toner on the sleeve surface, whereby its 
scattering outside the apparatus and its moisture absorption can be 
prevented. Since the shutter blade has less opportunity to contact the 
sleeve, no remarkable damage is caused the blade, hence selection of the 
material for the blade is easy. 
The second embodiment is as follows. Prior to entering into the actual 
copying operation, or after completion of the copying operation, it 
sometimes occurs that the electrophotographic reproduction apparatus does 
not perform the image original exposure alone, but operates all the other 
constituent devices. Usually, the former is called "pre-rotation", and the 
latter "post-rotation". In synchronism with these pre- and post-rotations, 
the shutter blade is actuated (T.sub.3). Immediately before starting or 
after completion of the copying operation, the surface of the developing 
sleeve is cleaned to secure a predetermined toner coating. At the time of 
both pre- and post-rotations, the surface of the photosensitive member has 
been subjected to the charging and exposure, hence adhesion of the toner 
onto the drum surface is usually observed to some extent. However, by 
closing the shutter blade, the toner adhesion can be prevented. 
The third embodiment is concerned with a method of operating the shutter 
blade during the copying operation. No image formation is effected during 
a period from an image original exposure to the subsequent image original 
exposure. On account of this, light is irradiated onto the photosensitive 
drum from the blank exposure lamp 34 to remove the charge on the drum. 
During this non-forming period (T.sub.4), the shutter blade is closed to 
clean the sleeve surface. In this way, the sleeve surface can always be 
maintained in its cleaned state. Also, since the shutter blade is closed, 
except for the developing process step, scattering of the toner from the 
developing device can be kept to the minimum possible extent. 
The developing device according to the present invention can be utilized in 
other types of the reproduction apparatuses than that as mentioned above, 
wherein the three-layered photosensitive member is used, such as the 
reproduction apparatus based on the Carlson process using a double-layered 
photosensitive member, or in an electronic photo-printer using a laser 
beam, a magnetic printer using a magnetic latent image, and others. 
As described in the foregoing, since the present invention provides the 
shutter blade in the developing device so that it may take a contact 
position with the surface of the developer holding means, and a withdrawal 
position away from the surface, cleaning of dust, agglomerated toner 
particles, and so on accumulated between the developer layer thickness 
regulating means and the developer holding means becomes easy. Also, 
undesirable filming phenomenon of the toner on the surface of the 
developer holding means can be prevented, which contributes to prevention 
of the lowering in the developing bias effect, shortage in the frictional 
charging quantity of the toner, lowering in the developing density, 
irregularity in the developed image, deterioration in the image 
reproducibility, etc. Furthermore, since the surface of the developer 
holding means can be constantly kept clean, the uniform coating of the 
toner on the surface is secured.