Toner remixing developing unit

A developing unit for an electrophotographic apparatus that uses a cleaning roll, oppositely charged from the toner remaining on the developing roller, to clean a developing roller after a latent electrostatic image has been developed into a latent toner image. The ink is removed from the developing roller and mixed with fresh toner from the toner cartridge to maintain a uniform charge throughout the toner that is applied to the developing roller and to increase the quality of resolution obtained when printing for an extended period of time.

CLAIM OF PRIORITY 
This application makes reference to, incorporates the same herein, and 
claims all rights accruing thereto under 35 U.S.C. .sctn.119 through my 
patent application entitled Developing Unit of an Electrophotographic 
Apparatus earlier filed in the Korean Industrial Property Office on the 
Oct. 22, 1996 and there duly assigned Serial No. 1996/35004. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a device for an electrophotographic 
apparatus and, more particularly, to a device for improving the quality of 
ink supplied to the photoconductive drum in an electrophotographic 
apparatus. 
2. Background Art 
Supplying a consistently high quality of toner to a photoconductive drum is 
crucial for the proper operation of an electrophotographic apparatus 
during the printing process. An electrophotographic apparatus can be 
either one of a laser printer, an electronic copier, a facsimile machine, 
or any versatile office machine. The general operation of an 
electrophotographic apparatus starts with paper being loaded from a supply 
tray and then transported through to a high pressure transfer roller. The 
high pressure transfer roller transfers the toner image from the 
photoconductive drum onto the sheet of paper. Subsequently, the paper is 
transported to a fixing device that fuses the toner image onto the paper 
using both heat and pressure rollers. 
To prepare the toner image for the high pressure transfer roller, it is 
necessary to attach toner particles to the latent electrostatic image on 
the photoconductive drum. The toner particles are applied by the 
developing unit and transform the latent electrostatic image into a latent 
toner image. 
A toner cartridge charged with a static voltage is contained in the 
developing unit and supplies toner to the supply roller. The toner is 
stirred by an agitator that keeps the toner evenly charged and mixed. The 
electrostatically charged toner is transferred to the supply roller by the 
rotation of the agitator. The rotation of the supply roller then transfers 
the toner to a developing roller. The toner deposited on the developing 
roller is uniformly applied due to a doctor-blade that maintains a 
constant level of thickness of toner on the developing roller. 
A photoconductive drum is charged by a charger roller with a static 
negative voltage. Then, the photoconductive drum is rotated and exposed to 
the light from a light emitting device. The parts of the photoconductive 
drum surface exposed to the light generate an latent electrostatic image. 
This latent electrostatic image is transformed into a latent toner image 
when toner particles are attached to the latent electrostatic image by the 
developing roller. A sheet of paper loaded from a paper tray is fed into 
the electrophotographic apparatus by a pickup roller. The paper is then 
transferred to a high pressure transfer roller that presses the paper 
against the photoconductive drum to transfer the toner image onto the 
sheet of paper from the drum. Then the paper, and applied toner image, is 
transported between the heating roller and the pressure roller of a fixing 
unit to fuse the toner image into the sheet using both heat and pressure. 
More specifically, the developing roller is mounted between the 
photoconductive drum and the toner supply roller. Toner is stirred by the 
agitator and fed to the developing roller. A doctor-blade contacts the 
developing roller and controls the thickness of the toner applied to the 
developing roller. Then, the photoconductive drum rotates and brings the 
latent electrostatic image into contact with the layer of toner formed on 
the developing roller, thus developing a latent toner image. After 
developing the latent toner image, the toner that remains on the 
developing roller is partially recovered and mixed with the reservoir of 
ink supplied by the toner cartridge while most of the remaining toner 
stays attached to the surface of the developing roller. This re-using of 
toner can lower the quality of printed images. 
Different innovations have been developed to regulate the toner used in an 
electrophotographic apparatus. By way of example, U.S. Pat. No. 5,317,370 
to Kohyama entitled Developing Apparatus Including Means for Collecting 
Used Developing Agent, shows the removal of used toner from the toner 
supply roll. Both U.S. Pat. No. 4,989,037 to Nagatsuna entitled Device for 
Driving a Rotary Body and U.S. Pat. No. 3,918,808 to Narita entitled 
Photorecptor Cleaning Device for Electrophotographic Copying Apparatus of 
the Dry Cleaning Agent Type, mention devices for cleaning excess toner 
from a photoconductive drum. 
I have observed that what is needed, but has so far been neglected in the 
art, is a developing unit that removes the toner remaining on the 
developing roller after the developing process is finished. This will 
avoid continuously stressing the re-used toner with pressures applied 
between the photoconductive drum and the developing roller and with the 
pressures applied between the developing roller and the doctor-blade. 
Thus, the degradation of printing quality, especially when a great number 
of sheets are being printed or after a long time has passed without 
operating the electrophotographic apparatus, can be eliminated. I believe 
that this inadvertent re-using of toner also causes the toner on the 
developing roller to have a non-uniform electrical charge. Consequently, 
images printed under some circumstances lack the high resolution otherwise 
possible. I expect that a developing roller that does not re-use toner 
that has been on the developing roller during a development process will 
improve the resolution of printed images and the usefulness of the 
associated electrophotographic apparatus. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
improved developing unit for an electrophotographic apparatus. 
It is another object to provide a developing unit that can remove the toner 
that remains on the developing roller after a latent toner image is 
developed. 
It is still another object to provide a developing unit that can print 
images having a high resolution. 
It is yet another object to provide a developing unit that mixes the toner 
that remains on the developing roll after developing a latent toner image 
with fresh toner. 
It is still yet another object to provide a developing unit that maintains 
a uniform electrostatic potential throughout the toner on the developing 
roll. 
It is a further object of the present invention to provide a developing 
unit that can reduce the degradation of print quality after long term 
operation of the electrostatic apparatus. 
To achieve these and other objects, a developing unit for an 
electrophotographic apparatus may be constructed with a developing roller, 
a toner supply roller, a doctor-blade, and a cleaning roller that removes 
the toner that remains on the developing roller after developing the 
latent toner image. A cleaning voltage charger may also be used to charge 
the cleaner roll with a static electricity of the opposite polarity from 
that of the toner remaining on the developing roll. Thus, the remaining 
toner is attracted by the cleaning roller and removed from the developing 
roller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawings, particularly FIG. 1, which illustrates the 
operation of a versatile office machine 100. A sheet of paper 60 is loaded 
from document tray 62 and transported to a contact image sensor (CIS) 68, 
by automatic document supplying roller 64 and transfer roller 66. Then, 
CIS 68 generates a light beam to scan sheet of paper 60. The light beam 
passes through the document reflected by white roller 74. The reflected 
light beam is detected by an optical sensor that translates the 
corresponding image into computer readable binary information. 
Subsequently, paper 60 is transported by transfer roller 76 and passes by 
photoconductive drum 12 and is then fixed by a fixing unit. Then, pickup 
roller 86 and discharging roller 84 eject paper 88. Alternatively, paper 
80 can be fed from cassette 78 by roller 72. 
During the beginning of a printing operation the surface of photoconductive 
drum 12 is uniformly charged by a charging unit provided in versatile 
office machine 100. Then, the surface of photoconductive drum 12 is 
exposed to light produced by an exposing unit, thus forming a latent 
electrostatic image. The electrostatic image is then transformed to a 
latent toner image by fine tone particles that are attached by developing 
unit 69. The toner image formed on photoconductive drum 12 is transferred 
to the paper by high pressure transfer roller 38. The toner image is fused 
onto paper 60 at fixing unit 82 by heating roller 82a and pressure roller 
82b. Then, the sheet 60 is discharged by discharging roller 84 and ejected 
from the electrophotographic machine. 
As shown in FIG. 2, a toner cartridge 7 or reservoir, 20 charged with a 
static voltage is contained in the developing unit and supplies toner to 
the supply roller. The toner is stirred by agitator 34 to keep the toner 
evenly charged and mixed. The electrostatically charged toner 24a is 
transferred to the supply roller by the rotation of agitator 34. The 
rotation of supply roller 18 then transfers toner 24a to developing roller 
16. The toner 24c deposited on developing roller 16 is uniformly applied 
due to doctor-blade 14 that maintains a constant toner thickness on the 
developing roller. 
Photoconductive drum 12 is charged by charger roller 30 with a static 
negative voltage. Then, the photoconductive drum is rotated and exposed to 
light emitting device 32. The parts of the photoconductive drum surface 
exposed to light generate a latent electrostatic image. This latent 
electrostatic image is transformed into a latent toner image when toner 
particles are attached to the latent electrostatic image by developing 
roller 16. A sheet of paper 60 is loaded from a paper tray and is fed into 
the electrophotographic apparatus by a pickup roller. The paper is then 
transferred to high pressure transfer roller 38 that presses the paper 
against the photoconductive drum to transfer the toner image onto the 
sheet of paper from the drum. Then the paper, and applied toner image, is 
transported between the heating roller and the pressure roller of a fixing 
unit to fuse the toner image into the sheet using both heat and pressure. 
More specifically, as shown in FIG. 3, developing roller 16 is mounted 
between photoconductive drum 12 and toner supply roller 18. Toner 24a is 
stored in reservoir 20, stirred by agitator 34 and fed to the developing 
roller. Doctor-blade 14 contacts developing roller 16 and controls the 
thickness of toner 24b applied to the developing roller. Then, 
photoconductive drum 12 rotates and brings the latent electrostatic image 
into contact with the layer of toner 24c formed on developing roller 16, 
thus developing the latent toner image. After developing the latent toner 
image, the toner that remains on developing roller 16 is partially 
recovered and mixed with the reservoir of ink supplied by the toner 
cartridge while most of remaining toner 24d stays attached to the surface 
of developing roller 16. Lower frame 22 is part of the developer frame of 
the present invention. 
FIG. 4 illustrates a developing unit as constructed according to the 
principles of the current invention. Developing roller 16 is positioned 
adjacent to photoconductive drum 12 to apply the negatively charged toner 
particles 24c necessary to develop the latent electrostatic image into a 
latent toner image. Toner supply roller 18 feeds toner, from reservoir 20, 
that has been stirred by agitator 34, to developing roller 16. 
Doctor-blade 14 is positioned to contact developing roller 16 and to 
regulate the thickness of toner 24b applied to the developing roller. 
A cleaning roller 10 is positioned in a groove 33 in lower frame 22 to 
contact the bottom of developing roller 16. Pressure from the cleaning 
roller combined with its opposite charge from the toner combine to remove 
the toner that remains on the developing roller. Cleaning voltage charger 
26 applies a positive electrostatic voltage to cleaning roller 10 to 
attract negatively charged toner particles 24d that remain on the 
developing roller after a latent toner image has been developed. Cleaner 
roller 10 is mounted within groove 31 formed at a corner 33 of surface 35 
of frame 22. The simplicity of using corner 33 eliminates the need for 
extra components. 
During the operation of the electrophotographic apparatus, toner 24a is 
transported by the rotation of toner supply roller 18 to developing roller 
16, where toner 24b is deposited with a uniform thickness due to the 
regulation of doctor-blade 14. Photoconductive drum 12 is rotated 
clockwise to contact the latent electrostatic image with the toner layer 
24c on the developing roller 16. This causes the latent electrostatic 
image to be transformed into a latent toner image. 
Then, the toner 24d remaining on developing roller 16 is removed by 
cleaning roller 10 and mixed with fresh toner 24a, as shown in FIG. 4. The 
toner obtained by mixing fresh toner 24a and remaining toner 24d is then 
fed to the developing roller by toner supply roller 18. 
Thus, the inventive developing unit uses a cleaning roller to remove 
remaining toner from the developing roller after the developing process. 
This causes the developing roller to always receive fresh uniformly 
charged toner. Hence, the difficulties caused by continuously stressing 
the remaining toner on the developing roller are eliminated along with the 
concurrent degradation of print quality. This increases the resolution and 
quality of printed images that can be obtained when printing for an 
extended period of time. 
Although this preferred embodiment of the present invention has been 
disclosed for illustrative purposes, those skilled in the art will 
appreciate that various modifications, additions and substitutions are 
possible, without departing from the scope and spirit of the invention as 
disclosed in the accompanying claims. It is also possible that other 
benefits or uses of the currently disclosed invention will become apparent 
over time.