Developing apparatus

A developing apparatus is provided with a developing roller for carrying a toner thereon and an elastic blade pressed against the surface of the developing roller to apply the toner thereto. The toner is thus applied to the surface of the developing roller by the elastic blade to form a thin layer of the toner on the surface of the developing roller. The thin layer is opposed to a photosensitive drum at a predetermined space to deposit the toner on an electrostatic latent image on the photosensitive drum. Magnets and magnetic particles are provided to prevent the toner from leaking out.

BACKGROUND OF THE INVENTION 
The present invention relates to a developing apparatus for depositing a 
developing agent on an image carrier with a latent image thereon, thereby 
developing the latent image. 
Development is achieved, for example, when a developing agent (colored 
powder called toner or developer) which is charged with a polarity 
opposite to the electric charges forming an electrostatic latent image is 
electrostatically attracted to the electrostatic latent image. Developing 
agents include one-component developing agents which consist of a powdery 
toner only or a toner coated with SiO.sub.2 or another additive, and 
two-component developing agents which are composed of a powdery toner and 
a carrier as it is called, such as magnetic powder or fine resin powder, 
glass, etc. In the two-component developing agents, the toner is securely 
charged by friction with the carrier. To maintain a constant developing 
density, on the other hand, the mixture ratio between toner and carrier, 
i.e., toner density, must be kept constant. Requiring no such control of 
toner density, the one-component developing agents surpasses the 
two-component developing agents in easy handling. 
The one-component developing agents are classified into two types, magnetic 
and nonmagnetic. In general, a nonmagnetic developing agent is prepared by 
mixing resin powder with a color agent such as carbon, while a magnetic 
developing agent is a mixture of resin powder and magnetic powder. 
A prior art method using a one-component developing agent is an application 
of the so-called no-contact developing process stated in Japanese Patent 
Publication No. 9475/66. In this developing process, an image carrier is 
opposed to a layer of a developing agent on a developing agent carrier at 
a fixed space, and a suitable bias is applied to the developing agent 
layer to fly the developing agent to image portions of an electrostatic 
latent image on the image carrier. The no-contact developing process is 
superior to any other developing methods in the following points. Since a 
developing agent with electric insulating property or high resistance can 
be used in the process, there is no possibility of defective transfer. 
Moreover, the developing agent will not cause fog, since it will not be 
flown to the no-image portions of the electrostatic latent image. In 
developing an electrostatic latent image by the no-contact developing 
process, the distance between the image carrier and the developing agent 
carrier must be minimized for a visible image of higher quality. 
Naturally, therefore, the developing agent layer on the developing agent 
carrier needs to be very thin and uniform. 
In order to form such a thin layer of developing agent, a toner layer 
forming method is disclosed in Japanese Patent Disclosure No. 43037/79 in 
which a thin layer of a magnetic developing agent is formed on a 
developing agent carrier containing magnetic field generating means 
therein. According to this method, a uniformly thin layer of magnetic 
developing agent can be formed with high reliability. Thus, a satisfactory 
visible image may be obtained by the use of the no-contact developing 
process. 
The no-contact developing process, however, requires as indispensable 
requisites a magnetic field generating means, i.e., a magnet, and a 
magnetic developing agent composed of toner and magnetic powder dispersed 
therein. Thus, this developing process has the following drawbacks: 
(1) the use of the magnet in the developing agent carrier renders the 
apparatus complicated and expensive, constituting a hindrance to the 
reduction of the size and weight of the apparatus, 
(2) the magentic developing agent is more expensive than the nonmagnetic 
one, and 
(3) containing magnetic powder, the magnetic developing agent is poor in 
coloring capability and is unsuited for color print. 
Thus, the no-contact developing process using the magnetic developing agent 
has the substantial drawbacks attributed to the use of the magnetic 
developing agent, as well as many advantages. 
Meanwhile, a no-contact developing process using a nonmagnetic developing 
agent may be considered an ideal developing method which can settle all 
the problems related to the prior art method. 
In the noncontact developing method, which uses nonmagnetic toner, in order 
to charge the toner and form a stable layer, a toner layer forming an 
elastic member (hereinafter referred to as an elastic member), which can 
be pressed against the toner carrier, is used. This elastic member is 
elastically moved relative to the surface of the toner carrier by the flow 
of toner, etc. Accordingly, a gap must be provided between the ends of the 
elastic member and the side wall to allow for this movement. Also, the 
toner carrier is rotatable and a thin layer of toner is formed on its 
periphery so a gap must be provided around its end surfaces and side wall 
as well. But, because the particles of toner are in the 10 .mu.m range, 
they leak from these two gaps, which results in a dirty machine. 
SUMMARY OF THE INVENTION 
The present invention has been made in consideration of the above 
situation, and has as its object to provide a developing apparatus wherein 
leakage and dropping of a developing agent from the two end portions of a 
developing agent carrier is prevented, and the contamination of the 
interior of a copying machine or the like is eliminated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One embodiment of a developing apparatus according to the present invention 
applied to an image forming apparatus will now be described in detail with 
reference to the accompanying drawings of FIGS. 1 to 6. 
First, the image forming apparatus, e.g., a copying machine, using the 
developing apparatus of the invention will be described. FIG. 1 is a 
sectional view schematically showing the copying machine. In FIG. 1, 
numeral 1 designates a housing of the copying machine. Rotatably disposed 
in the central portion of the housing 1 is an image carrier, e.g., a 
photoconductive drum 2 made of selenium, on the surface of which is formed 
an electrostatic latent image. The photoconductive drum 2 is surrounded by 
a lamp 4 and a convergent light transmitting member 5 for optically 
scanning an original paper put on a horizontally reciprocating original 
table 3 and for forming an electrostatic latent image corresponding to an 
image of the original paper on the surface of the photoconductive drum 2, 
a discharge lamp 6 for de-electrifying the surface of the photoconductive 
drum 2 before the formation of the original image, a charger 7 for 
uniformly charging the surface of the photoconductive drum 2 after the 
de-electrification, and a developing apparatus 8 according to the 
invention for selectively flying a developing agent to the electrostatic 
latent image on the surface of the photoconductive drum 2 to develop the 
electrostatic latent image. Thus, the developing apparatus 8 forms a 
visible image on the surface of the photoconductive drum 2. 
A one-component toner such as the nonmagnetic toner mentioned above is 
mainly used as a developing agent. However, two-component developer can be 
used where the diameter of a carrier contained in the two-component 
developer is substantially equal to or smaller than that of a toner 
contained in the two-component developer. 
A paper feeding section 10 is provided at one side portion (right-hand side 
portion of FIG. 1) of the housing 1. The paper feeding section 10 includes 
a paper cassette 11 removably attached to the one side portion of the 
housing 1, a paper supply roller 12 in rolling contact with the uppermost 
one of sheets P contained in the paper cassette 11 and capable of 
delivering the sheets P one by one into the housing 1, and a sheet-bypass 
guide 13 for manual paper supply. Each sheet P delivered from the paper 
feeding section 10 is regulated for feed timing by a pair of aligning 
rollers 15, and fed so as to be in rolling contact with the 
photoconductive drum 2 in a transfer section. 
The photoconductive drum 2 is also surrounded by a pre-transfer charger 9, 
a transfer charger 16 for transferring the developing agent to the sheet 
to form a visible image thereon, and a separation charger 17 for 
separating the sheet from the photoconductive drum 2 after transfer. The 
transfer section is defined between the photoconductive drum 2 and the 
transfer charger 16. After the developing agent image (visible image) is 
transferred to the sheet, the sheet is guided to a fixing unit 20 by a 
conveyor belt 19. The developing agent is fixed by the pressure and heat 
of a pair of heat rollers 21 which constitute the fixing unit 20. After 
the fixation, the sheet is discharged onto a tray 23 by a pair of exit 
rollers 22. After the transfer operation, the developing agent remaining 
on the surface of the photoconductive drum 2 is removed by a cleaning unit 
18. 
The developing apparatus 8 according to the first embodiment of the 
invention will now be described in detail. FIGS. 2 and 3 are a perspective 
view and a sectional view, respectively, schematically showing the 
developing apparatus 8. 
The developing apparatus 8 has a housing 34 which contains a nonmagnetic 
developing agent. The housing 34 is provided with a back frame 30 and a 
front frame 31 spaced from each other and side frames 32 and 33 attached 
to both side portions of the frames 30 and 31. The housing 34 is open at 
both the top and bottom and has a swingable cover member 41 at its top 
opening 34A. When the cover 41 is up, the developing agent is supplied 
through the top opening 34A. Disposed near a bottom opening 34B of the 
housing 34 is a rotatable developing agent carrier, e.g., an aluminum or 
stainless-steel developing roller 35, which carries the developing agent 
on its surface. The developing roller 35 is pivotally mounted on the two 
side frames 32 and 33. 
The front frame 31 is fitted with an elastic blade 36 by means of a blade 
holder 37. The elastic blade 36 is formed of, e.g., silicone-butadiene 
rubber (40 to 90 hardness), urethane rubber, stainless steel, phosphor 
bronze (approximately 0.01 to 0.5 mm in thickness), or urethane sheet. The 
elastic blade 36 is pressed against the surface of the developing roller 
35 to coat the surface with the developing agent T. The contact pressure 
between the elastic blade 36 and the developing roller 35 can be finely 
adjusted by controlling the position of the blade holder 37. 
Part of the surface of the elastic blade 36 opposed to the developing 
roller 35 is in surface contact with the developing roller 35. Therefore, 
the contact area between the elastic blade 36 and the developing roller 35 
is wider than in the case of the prior art construction in which the free 
end portion of the elastic blade is pressed against the developing roller. 
Thus, the fine adjustment of the contact pressure on the developing roller 
35 is easy, and the contact pressure can be made uniform. Also, the 
developing agent can enjoy friction under the contact pressure for a 
longer time, thus acquiring uniform and sufficient electric charges. 
Recovery blade 42 is provided on the lower end of back frame 30 for 
pressing against developing roller 35. The toner left on the developing 
roller 35 after the developing operation is recovered into housing 34 by 
this recovery blade 42. 
The developing apparatus 8 is located in a position such that the 
developing agent layer on the developing roller 35 is not in contact with 
the photoconductive drum 2. A gap G between the developing roller 35 and 
the photoconductive drum 2 mainly depends on the charge quantity, the 
particle size of the developing agent and the thickness of the developing 
agent layer. To ensure the flight of the developing agent for a visible 
image of good quality, it is necessary to minimize the gap G. The gap G 
can be narrowed only if the developing agent layer on the developing 
roller 35 is a thin layer. The range of the particle size of the 
developing agent used depends on the resolution of the desired image. This 
is usually a range of 7 to 20 mm. Thus, the practical gap G between the 
developing roller 35 and the photoconductive drum 2 ranges from 
approximately 50 to 400 microns. Here the thin layer may be a monolayer or 
a multilayer, including up to six or seven layers, of the developing 
agent. 
To maintain the accuracy of the gap G, a pair of gap control rollers 39 are 
mounted on the shaft of the developing roller 35 so as to be rotatable in 
a body. The gap control rollers 39 come into contact with both side 
portions of the peripheral surface of the photoconductive drum 2 or 
engaging rollers (not shown) mounted on the shaft of the photoconductive 
drum 2, thereby keeping the intercentral distance between the 
photoconductive drum 2 and the developing roller 35. A power source 40 is 
provided for applying a voltage to the developing roller 35 to form an 
electric field between the photoconductive drum 2 and the developing 
roller 35 and generally includes D.C. power source or deviated A.C. power 
source. The power source 40, which is not requisite for the developing 
apparatus 8 of the invention, serves to facilitate the flight of the 
developing agent on the developing roller 35 to the surface of the 
photoconductive drum 2 by forming the electric field between the two 
members 2 and 35. The developing agent frictionally charged on the 
developing roller 35 is transferred to the surface of the photoconductive 
drum 2 by only an electrostatic attraction attributed to latent image 
charges on the surface of the photoconductive drum 2. 
The following is a description, with reference to FIGS. 3 and 4, of the 
magnet 43 and the magnetic particles 44 which prevent the toner from 
leaking out. The magnet 43 is attached to each inside surface of the side 
frames 32 and 33, and faces the region which includes at least the 
triagular area 46 (shown by crisscross hatching in FIG. 3), which is 
surrounded by the end surfaces of the elastic blade 36 and the periphery 
of the developing roller 35. A magnetic toner or iron powder, for example, 
is used as the magnetic particles 44. These magnetic particles 44 are 
adhered to the inside surface of magnet 43 filling the gap between the 
side frames 32, 33 and the elastic blade 36, and the gap between the side 
frames 32, 33 and the developing roller 35, which arise in the triangular 
region 46. 
The following is a description of the operation of this developing 
apparatus 3 with reference to FIG. 8. The housing 34 of the developing 
apparatus 8 is filled with toner and the developing roller 35 rotates 
counterclockwise as shown by arrow A in FIG. 3. The toner T is conveyed by 
the developing roller 35 in the direction A and is charged by friction 
between the elastic blade 36 and the roller. At this time, the magnetic 
particles 44 adhering to the magnetic 43 fill the gaps which arise in the 
triangular region 46 between the side frames 32, 33 and the elastic blade 
36, and between the side frames 32, 33 and the developing roller 35. These 
gaps are sealed by these magnetic particles 44 and the toner is prevented 
from leaking out. 
The magnetic particles 44 adhering to the magnet 43 are given a shape which 
follows the shape of the gaps and thus an elastic shield member is 
provided to vary this shape. Consequently, the shield can be made to 
reliably follow the changes in shape of the elastic blade 36. 
Also, if the magnet 43 is arranged with the S and N poles alternating, as 
is shown in FIG. 5, the magnetic particles 44 will be connectedly arranged 
along the magnetic line 45 to fill the gap. In this way, the magnetic 
particles 44 form a so-called magnetic brush which abuts against the 
elastic blade 36 and, accordingly, toner leakage is prevented and the 
elastic deformation of the elastic blade 36 is not obstructed. When the 
magnetic particles 44 are flown to the developing area, no problem occurs 
as long as magnetic toner is used as the magnetic particles 44. 
This invention is not limited to the structure described in the first 
embodiment, and may be made in various ways while keeping within the scope 
and spirit of the invention. 
For example, the magnets 43 are not restricted to being fastened to the 
side frames 32, 33. As shown in FIG. 6, in a second embodiment of the 
invention, the magnets 43 may also be provided at both ends of the elastic 
blade 36 on the reverse side, which presses against the developing roller 
35. In this case, the magnetic particles 44 adhering to the magnets 43, 
are held at one location regardless of the rotation of the developing 
roller 35 so it is possible to prevent the leakage of toner at the ends of 
the elastic blade 36 and the developing roller 35. This effect can be 
realized providing the magnets 43 inside the elastic blade 36. 
As means for stopping the magnetic particles 44 at the ends of the elastic 
blade 36 by pressure to prevent the leakage of toner the magnets may be 
arranged on the side of the developing roller, as in a third embodiment, 
which is shown in FIG. 7. Here, a magnet roller 47, which has the same 
diameter as the developing roller 35, is arranged on both ends of 
developing roller 35. This magnet roller 47 is hollow in the center, and a 
hollow projecting journal 47a is provided at one end communicating with 
the hollow of the magnet roller 47. This projecting journal 47a is 
attached to the side frames 32, 33. Central journal 35a of developing 
roller 35 is rotatably supported in the hollow portion of magnet roller 
47. In this way, with the structure of the third embodiment, it is 
possible to keep the magnetic particles at both ends of the elastic blade 
36 under the pressure of the blade using the magnet roller 47 attached to 
the side frames 32, 33 and, consequently, the leakage of toner from the 
ends of the elastic blade 36 and the developing roller 35 can be 
prevented. 
Also, the magnet roller 47, according to a fourth embodiment of this 
invention as shown in FIGS. 8A and 8B, has a smaller diameter than the 
developing roller 35 and may rotate as one unit with it. Magnet roller 47, 
on the surface of which the magnetic particles 44 are adhered, is attached 
to the central journal 35a of developing roller 35. A magnetic particle 
shield cover 48, which is a thin cylinder, surrounds the magnet roller 47 
and has a diameter slightly smaller than that of the developing roller 35. 
The shield cover 48 has a gap, which covers the area from the edge of 
recovery blade 42 to the free end of elastic blade 36. With this kind of 
construction, the magnetic particles are displaced in a flow by the 
rotation of magnet roller 47, and the ends of the elastic blade 36 and the 
developing roller 35 are shielded by the magnetic powder 44 which flows 
out of the opening in the magnetic shield cover 48 due to the pressure of 
elastic roller 36, thereby preventing the leakage of toner. 
As was described above, according to this invention, it is possible to 
provide a developing apparatus in which the leakage of toner from the gaps 
between the ends of the layer forming elastic member and the toner carrier 
and the facing side walls, thereby keeping the machine clean. Moreover, 
because the shield is formed by magnetic particles, it is possible to 
reliably make the magnetic particles follow the deflections of the toner 
layer forming an elastic member.