Electrophotographic apparatus having a cleaning device

In an image formation apparatus such as an electrophotographic printing apparatus, a cleaning device can effectively clean the peripheral surface of a photosensitive drum throughout the full length. The cleaning apparatus includes a fur brush 32 rotating while keeping contact with the entire periphery of a photosensitive drum 6. The cleaning characteristics of this fur brush 32 change between an outside portion R opposing gap roller contact portions at both end portions outside a print area of the photosensitive drum 6 and an inside portion inside this outside portion R.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electrophotographic apparatus having a 
cleaning device used for an image formation apparatus such as a printing 
apparatus using an electrophotographic system. 
2. Description of the Related Art 
In a conventional printing apparatus using an electrophotographic system, a 
cleaning system using a rubber blade, a fur brush, or the like, has gained 
wide acceptance for cleaning untransferred residual toner adhering to a 
photosensitive drum after transfer. A system using a rubber blade and a 
fur brush in combination has also been employed. Particularly, a fur brush 
cleaning system has been often used for high speed machines, and the 
residual toner on the photosensitive drum, which has not been transferred 
to a recording sheet, is removed by the fur brush. 
A cleaning fleece or blade has also been used to clean any contamination 
which has not been removed by the fur brush. 
In the printing apparatus of this kind, a gap producing roller for defining 
a gap between an exposure portion (using an LED array) for forming an 
electrostatic latent image and the peripheral surface of the 
photosensitive drum, and a gap producing roller for defining a gap between 
the peripheral surface of the photosensitive drum and a sheet entry guide 
at a transfer portion are arranged to rotate while maintaining contact 
with the peripheral surface of the photosensitive drum outside the print 
area. 
A film-like toner adheres to the peripheral surface at the end portions of 
the photosensitive drum, where the gap producing rollers keep contact, due 
to scattering toner during printing. This portion is also cleaned, with 
the print area portion of the photosensitive drum, by a combination of the 
fur brush cleaner with a cleaning fleece or a combination of the fur brush 
cleaner with a cleaning blade. 
In the case of the former combination, i.e. the fur brush cleaner with the 
cleaning fleece, the cleaning fleece portion corresponding to both end 
portions of the photosensitive drum, to which the film-like toner adheres, 
is made coarser than usual so as to improve the cleaning effect, but 
scratch and wear occur on the peripheral surface of the photosensitive 
drum. In the case of the latter combination, a push force of the blade can 
be changed, but flattering and feeding failure of the sheet may occur. 
Further, the cleaning effect drops at the portion where the amount of the 
toner is great, such as the gap producing roller contact portions, because 
adhesion of the toner to the blade is strong. 
As described above, since the conventional cleaning system cannot 
effectively clean the film-like toner adhering to the peripheral surface 
of the photosensitive drum, with which the gap producing rollers are in 
contact, the following problems occur. 
(1) The original gap cannot be secured. 
(2) When a large amount of the toner adheres to the drum, the toner may 
peel off at the contact portion with the gap producing rollers, may 
contaminate the peripheral portions, and may exert an adverse influence on 
printing. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an 
electrophotographic apparatus having a cleaning device which can 
effectively clean the peripheral surface of a photosensitive drum 
throughout its full length. 
According to the present invention, there is provided an 
electrophotographic printing apparatus having a cleaning device 
comprising: a rotatable photosensitive drum having an outer 
circumferential surface having, along an axial direction thereof, an 
inside area including at least a printing area and respective outside 
areas positioned outward of said inside area in an axial direction 
thereof; a rotatable fur brush being in contact with said outer surface of 
the photosensitive drum entirely in the axial direction of said drum; and 
said fur brush having, along its axial direction, an inner area opposite 
to said inside area of the drum and respective outer areas opposite to 
said respective outside areas of the drum, and the cleaning characteristic 
of the fur brush in said inner area is different from that in said 
respective outer areas. 
It is advantageous that said rotatable fur brush comprises a cylindrical 
substrate and hairs or fibers implanted on said cylindrical substrate, the 
hardness of the fibers implanted in said outer areas is greater than the 
hardness of the fibers implanted in said inner area of the fur brush. 
It is also advantageous that said rotatable fur brush comprises a 
cylindrical substrate and hairs of fibers implanted on said cylindrical 
substrate, a density or fibers implanted in said outer areas is greater 
than a density of fibers implanted in said inner area of the fur brush. 
It is further advantageous that said rotatable fur brush comprises a 
cylindrical substrate and hairs or fibers implanted on said cylindrical 
substrate, the hardness of fibers implanted in a part of said outer areas 
is greater than the hardness of fibers implanted in said inner area of the 
fur brush and the density of fibers implanted in the remaining part of 
said outer areas is greater than the density of fibers implanted in said 
inner area of the fur brush. 
Thus, according to the present invention, since the cleaning characteristic 
of fur brush in the inner area thereof is different from that in said 
respective outer areas, i.e., the outside areas of the photosensitive 
drum, to which toner may more readily adhered as mentioned above, can be 
more strongly cleaned than the inside area of the drum. Therefore, a 
variation of gap clearance between the drum and the LED array or the like 
will no longer occur and no toner will be scattered from the drum.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, preferred embodiments of the present invention will be 
described with reference to the accompanying drawings. 
FIG. 1 shows the appearance of an electrophotographic printing apparatus to 
which the present invention is applied, and FIG. 2 is an explanatory view 
showing an internal conveying path. In the drawings, reference numeral 1 
denotes a hopper portion, 2 is a printer portion, 3 is a stacker portion, 
and 4 is an operation display portion. Hoppers 1.sub.1, 1.sub.2 and 
1.sub.3 are disposed at upper, intermediate and lower stages inside the 
hopper portion 1, respectively, and stackers 3.sub.1 and 3.sub.2 are 
vertically disposed in the stacker portion 3. Reference, numeral 5 in FIG. 
2 denotes a reversible conveyor portion (the operation of which will be 
later described). 
As shown in detail in FIG. 3, the printer portion 2 includes a 
photosensitive drum 6, a pre-charging device 7, an exposure portion 8, a 
developing unit 9, a sheet entry guide 10, a transfer charging device 11, 
an AC charge eliminator 12, a surface potential sensor 15, a pre-transfer 
charge eliminator 16 and an LED charge eliminator 17 that are disposed 
around the photosensitive drum 6. 
As shown in detail in FIG. 4, the exposure portion 8 is constituted by 
juxtaposing an LED array 8.sub.1 of 240 dpi and an LED array 8.sub.2 of 
300 dpi. FIG. 5A is a plan view of the fitting structure of the LED array 
8.sub.1 (8.sub.2) and FIG. 5B is a front view thereof. FIG. 6A is an 
enlarged plan view of the principal portions of FIGS. 5A and 5B and FIG. 
6B is a front view thereof. The LED array 8.sub.1 (8.sub.2) is supported 
by a frame 18 of the exposure portion 8 through a pair of leaf springs 19. 
Both of the upper and lower leaf springs 19 are made of the same material. 
Each leaf spring 19 is equipped with a slit 19a, and an intermediate leaf 
portion 19b is so formed as to be capable of displacement with respect to 
an outer frame portion 19c. Reference numeral 20 denotes a hole for a 
screw which fixes the outer frame portion 19c of the leaf spring 19 to a 
block 22 on the side of the frame 18. Reference numeral 21 denotes a hole 
for a screw which fixes the intermediate portion 19b of the leaf spring 19 
to a block 23 on the side of the LED array 8.sub.1 (8.sub.1). 
A pair of gap producing rollers 24, which come into contact with portions 
other than print area at both end portions of the photosensitive drum 6, 
are rotatably supported by the LED array 8.sub.1 (8.sub.2), as shown in 
FIG. 6B. The contact force of the gap producing rollers 24 to the 
photosensitive drum 6 is imparted by the leaf springs 19. Accordingly, 
even when any eccentricity resulting from accuracy of components occurs in 
the photosensitive drum 6, this eccentricity is absorbed by the leaf 
springs 19, and the gap between the LED array and the surface of the 
photosensitive drum 6 is kept constant. FIG. 7A is a detailed side view of 
the support portion of the gap producing roller 24 and FIG. 7B is a front 
view thereof. 
As shown in detail in FIG. 8, the sheet entry guide 10 is equipped with a 
lower conveyor guide 25 and an upper conveyor guide 26 opposing the 
former. These conveyor guides 25 and 26 have a width somewhat greater than 
the width of a sheet so as to completely guide the sheet 100 conveyed to a 
transfer position, and are formed by a rigid plate such as a stainless 
steel. However, only the distal end portion 25a of the lower conveyor 
guide 25 made of a material having flexibility and higher stiffness than 
paper, such as a metal or a resin, such as a plastic sheet. 
The base portion of the lower conveyor guide 25 is rotatably supported by a 
shaft 29 which is in turn supported by a side plate 28 of a fixed portion 
27. A pair of gap producing rollers 30 are rotatably supported in the 
proximity of the distal end of the lower conveyor guide 25. The gap 
producing rollers 30 exist in the proximity of the right end of the 
transfer charger 11. The lower conveyor guide 25 is biased clockwise by a 
coil spring 31 wound on a shaft 29, so that the gap producing rollers 30 
are brought into pressure contact with the photosensitive drum 6. FIG. 9 
is an explanatory view of the relationship between the gap producing 
rollers 30 and the photosensitive drum 6 in the longitudinal direction. 
A gap b is defined between the distal end portion 25a of the lower conveyor 
guide 25 and the photosensitive drum 6, and the size of this gap is 
smaller than the thickness t of a recording medium 100. Accordingly, when 
the leading edge of the recording paper 100 entering the gap between the 
lower and upper conveyor guides 25, 26 and conveyed to the transfer 
position reaches the gap producing roller 30, the recording paper 100 
pushes down the gap producing roller 30 against the force of the coil 
spring 31. The paper 100 is clamped between the photosensitive drum 6 and 
the gap producing roller 30 and is conveyed forward. 
Vibration occurring due to eccentricity of the photosensitive drum 6 during 
this conveying operation is absorbed by the coil spring 31. The recording 
paper 100 is pushed to the surface of the photosensitive drum 6 by the gap 
producing roller 30 when it passes the roller 30 and is in close contact 
with the surface of the photosensitive drum 6. Moreover, since this close 
contact portion exists in the proximity of the transfer position, the 
occurrence of print fall-off and print non-uniformity (which becomes a 
problem particularly in the case of double-face printing) can be prevented 
when the toner image is transferred from the surface of the photosensitive 
drum to the sheet 100. 
The cleaning device 13 is equipped with a fur brush 32 (see FIG. 3) which 
rotates while keeping contact with the photosensitive drum 6 throughout 
the entire length of the latter. 
When printing is made, the photosensitive drum 6 is turned clockwise as 
represented by arrows in FIGS. 2 and 3. The surface of the drum 6 is 
uniformly charged by the pre-charger 7. Next, exposure of the surface is 
effected by the exposure portion 8 in the pattern corresponding to the 
data, thereby forming an electrostatic latent image on the drum 6. This 
electrostatic latent image is developed to a toner image by the developing 
unit 9. Reference numerals 9.sub.1, 9.sub.2 and 9.sub.3 in FIG. 3 denote a 
first development magnetic roller, a second development magnet roller and 
a recovery magnet roller disposed in the developing unit 9, respectively. 
On the other hand, the sheet 100 is delivered from a predetermined hopper 
of the hopper portion 1 and is sent to the transfer position while being 
guided by the sheet entry guide 10. The toner image on the photosensitive 
drum 6 is transferred to the sheet 100 by the transfer charger 11 opposing 
the photosensitive drum 6 through the sheet. Thereafter, the image is 
fixed to the sheet 100 by the fixing device 33 (see FIG. 2). In the case 
of one-side printing, the sheet after fixation is discharged into any of 
the stackers 3.sub.1, 3.sub.2 of the stacker portion 3. 
In the case of double-side printing, the conveyor path is changed and the 
sheet after completion of fixation of one side is sent to the reversal 
transfer portion 5, and is thereafter conveyed to the photosensitive drum 
6 while its front and back are reversed. Printing is then made to the back 
in the same way as printing of the front surface, and the sheet is 
discharged into the stacker portion 3 after the toner image on the back is 
fixed. 
Symbol .times. in FIG. 2 represents a sheet sensor and symbol .smallcircle. 
represents a conveyor roller. The sheet sensor measures the timing of the 
sheet being conveyed to form the latent image or the visible image on the 
photosensitive drum 6, and detects any abnormality of the passage of the 
sheet. This abnormality of sheet passage is displayed in the operation 
display portion 4, so that an operator watches this display to take 
necessary measures. 
Any residual charge on the surface of the photosensitive drum 6 is removed 
by the LED charge eliminator 17 and the AC charge eliminator 12. The 
surface of the drum 6 is cleaned by the fur brush 32 of the cleaning 
device 13. A cleaning fleece 14 periodically cleans the surface of the 
photosensitive drum 6. Thereafter, printing operations described above are 
repeated. 
FIG. 10 shows the structure of the fur brush 32 for cleaning the surface of 
the photosensitive drum after transfer as described above. The fur brush 
32 is produced by bonding a brush 42 and brushes 43, 43 to the surface of 
a cylindrical substrate 41. The brush 42 is bonded to an inside portion Q 
of a range greater than the print area, and the brushes 43 are bonded to 
outside portions R outside the inside portion Q. A gap C of 3 to 5 mm 
exists between the brush 42 and the brushes 43. Each brush is formed by 
implanting fibers of nylon, rayon, etc, to a tape substrate. 
The relative positions of the fur brush 32 and the photosensitive drum 6 in 
the longitudinal direction are set as shown in FIG. 11. The brushes 43 
oppose the gap producing rollers 24, 30 which come into contact with the 
photosensitive drum 6 at both end portions outside the print area. 
In the present invention, the cleaning characteristics of the fur brushes 
are changed between the outside portion R and the inside portion Q so as 
to obviate the problems with the prior art already described. More 
definitely, any one of the following three constructions will be 
effective. 
(1) The fibers of the outside portion R of the fur brush 32 are made harder 
by at least 10% than the fibers of the inside portion Q. Methods of making 
the fibers harder include 1 the use of fibers having higher hardness, 2 
the use of thick fibers, 3 the use of short fibers, and so forth. 
(2) The density of the fibers of the outside portion R of the fur brush 32 
is made higher by at least 10% than the density of the fibers of the 
inside portion Q. 
(3) The hardness of a part of the fibers of the outside portion R of the 
fur brush 32 is made higher by at least 10% than that of the fibers of the 
inside portion Q, and the density of the remaining fibers of the outside 
portion R is made higher by at least 10% than that of the fibers of the 
inside portion Q. 
In any of the constructions described above, the brush 42 of the inside 
portion is the same as the brush of the prior art. 
Next, the bonding method of the brushes 42, 43 in the fur brush 32 having 
the structure described above will be explained with reference to FIGS. 
12A and 12B. 
The brush 42 is formed by spirally winding an 80 mm-wide tape substrate, to 
which fibers of nylon, etc, are implanted, onto the inside portion of the 
surface of the substrate 41 as shown in FIG. 12A. The fibers have a 
thickness of 0.02 mm, for example, and is implanted in a density of 11,220 
fibers/inch.sup.2, for example. The brush 43 is similarly formed by 
spirally winding a 3 mm-wide tape substrate, to which fibers having 
different density are implanted, onto the surface of the substrate 41. A 
gap C of 3 to 5 mm exists at the boundary between the brushes 42 and 43 
having different fiber densities. However, no problem will occur because 
the gap exists outside the print area. 
Though, in the later-appearing Experimental Example, nylon was used as the 
material of the fibers of the brush 42, rayon or other fibers can be used. 
Because the cleaning characteristics of the fur brush change between the 
inside portion and the outside portion as described above, even the fixing 
toner at the gap producing roller contact portion outside the print area 
of the photosensitive drum can be cleaned. Therefore, deviation of the gap 
due to the toner can be eliminated and scattering of the toner does not 
occur. 
Experimental results to evidence this effect (the number of printed sheets 
and the condition of occurrence of toner filming at gap producing roller 
contact portion) are illustrated in Table 1 below. Nylon was used as the 
fiber material. Symbol represents no filming, and symbol .times. 
represents that filming occurred. 
TABLE 1 
__________________________________________________________________________ 
.circleincircle. hair material: nylon 
hair No. of print 
density of 
thickness (.phi.) 
outside 
and length 
A4 (printing ratio 4%) 
portion 
(mm) of fiber 
100,000 
200,000 
300,000 
400,000 
500,000 
(pcs/inch.sup.2) 
of brush start 
sheets 
sheets 
sheets 
sheets 
sheets 
__________________________________________________________________________ 
11,220 .phi. 0.10 .times. 10 mm 
.circleincircle. 
.circleincircle. 
X -- -- -- 
(same as 
.phi. 0.10 .times. 11 mm 
.circleincircle. 
X -- -- -- -- 
inside .phi. 0.10 .times. 12 mm 
X -- -- -- -- -- 
portion) 
12,342 .phi. 0.10 .times. 10 mm 
.circleincircle. 
.circleincircle. 
.circleincircle. 
X -- -- 
(10% higher 
.phi. 0.10 .times. 11 mm 
.circleincircle. 
.circleincircle. 
X -- -- -- 
than inside 
.phi. 0.10 .times. 12 mm 
.circleincircle. 
X -- -- -- -- 
portion) 
13,464 .phi. 0.10 .times. 10 mm 
.circleincircle. 
.circleincircle. 
X -- -- -- 
(20% higher 
.phi. 0.10 .times. 11 mm 
.circleincircle. 
X -- -- -- -- 
than inside 
.phi. 0.10 .times. 12 mm 
X -- -- -- -- -- 
portion) 
__________________________________________________________________________ 
.circleincircle.: no filming 
X: filming occurred 
The following can be understood from the results tabulated in Table 1. 
(1) The best result can be obtained by increasing the fiber density by 10%. 
(2) The shorter the length of the fibers, the better becomes the results 
(12 mm.fwdarw.10 mm). 
The advantages of the present invention are obvious from the Experimental 
Results given above. 
As described above, in the present invention, the cleaning characteristic 
of the fibers of the fur brush is changed at the outside portion outside 
the print area of the photosensitive drum to which the toner attaches due 
to the pressure of the gap producing rollers on the photosensitive drum. 
Accordingly, the toner can be cleaned, and deviation of the gap resulting 
from the toner can be eliminated. Scattering of the toner can also be 
eliminated. 
It should be understood by those skilled in the art that the foregoing 
description relates to only a preferred embodiment of the disclosed 
invention, and that various changes and modifications may be made to the 
invention without departing from the spirit and scope thereof.