Electrophotographic apparatus of improved low image density

An electrophotographic apparatus includes a photoconductor drum, also known as an electrostatic latent image holding member, with a magnet placed therein. An electrostatic latent image is formed on the magnetic drum. Then, the drum is brought into contact with a magnetic developer, or toner, in a developer reservoir to have the magnetic developer attached to the photoconductor drum surface by a magnetic force. A removing roller, having an AC voltage applied thereto, is passed in close vicinity of the magnetic drum with the resultant development of images because toner remains at image areas only. In the electrophotographic apparatus, the photoconductor drum, the removing roller or both include two magnetic poles. A device for increasing friction force of the surface of the photoconductor drum, of the removing roller or both may also be provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electrophotographic apparatus which can 
be used in printers, facsimile equipment or similar equipment. 
2. Discussion of Related Art 
A two-component development method using a developer formed of a toner and 
a carrier has so far been widely used in electrophotography, but in recent 
years development of a mono-component development method has been in 
progress in order to make image forming units smaller and less costly. 
FIG. 28 shows the electrophotographic apparatus which uses such a 
mono-component development method, which was disclosed by the inventors of 
the present invention in the Japanese Patent Application "Heisei 
3-345990." In FIG. 28, an electrostatic latent image holding member of an 
organic photoconductor drum 1 has phthalocyanine dispersed in a binder 
resin of polyester group. A magnet 2 has the axis thereof fixed coaxially 
with the organic photoconductor drum 1. A corona charger 3 charges the 
organic photoconductor drum 1. A grid electrode 4 controls charge 
potential of the organic photoconductor drum 1. The electrophotographic 
apparatus also includes a signal light 5 (also referred to herein as 
"laser light"), and a developer reservoir 6. A magnetic one-component 
toner 7 (also referred to in this application as a "one component magnetic 
toner" or as "toner") serves as a developer. A damper 8 makes smooth the 
flow of the toner 7 inside the developer reservoir 6, and also prevents 
the toner 7 from being packed due to its own weight and filling between 
the organic photoconductor drum 1 and a removing roller 9. 
The magnet 2 forms a magnetic pole in an area of .theta.=10.degree. 
opposite to the developer reservoir 6. The removing roller 9 is made of 
aluminum and has a magnet 10 therein. An AC high voltage power source 11 
applies a voltage to the removing roller 9. A scraper 12 made of polyester 
film scrapes the toner from the removing roller 9. A transfer corona 
charger 13 transfers toner images formed on the organic photoconductor 
drum 1 to paper. 
With the help of FIG. 28, an explanation will be made hereunder of how the 
electrophotographic apparatus described above operates. The organic 
photoconductor drum 1 is charged to -500 V by means of the corona charger 
3 and the grid electrode 4. An electrostatic latent image is formed by 
irradiating the laser light 5 on the organic photoconductor drum 1. The 
toner 7 is deposited on the surface of the organic photoconductor drum 1 
by magnetic force in the developer reservoir 6. Next, the organic 
photoconductor drum 1 is caused to pass the front of the removing roller 
9. At this time, an AC voltage of 750.sub.O-p (1 kHz in frequency) with a 
DC voltage of -350 V superimposed thereon is applied to the removing 
roller 9 from the AC high voltage power source 11. Then, the toner 7 is 
removed from the organic photoconductor drum 1 to the removing roller 9, 
and toner images with a positive-negative picture reversal are left only 
on the image areas of the organic photoconductor drum 1. The toner 7 
deposited on the removing roller 9, which is rotating in the direction of 
the arrow, is scraped off by the scraper 12, and returned to the developer 
reservoir 6 for use in the image forming steps to follow. The toner images 
thus formed on the organic photoconductor drum 1 are transferred to paper 
(not shown in FIG. 28) by the transfer corona charger 13, and then 
thermally fixed by means of a fixing equipment (not shown in FIG. 28). 
However, when printing is performed by the electrophotographic apparatus, 
the image density of solid-image is low under a high temperature and high 
humidity environment (33.degree. C., 85% relative humidity (RH), for 
example), and background development is found to increase gradually on the 
printed images. 
None of the prior art electrophotographic apparatus produces high quality 
images having high image density, which are substantially free of 
non-uniformity in density. Similarly, most of the prior art 
electrophotographic apparatus exhibits unevenness in the force 
transporting the toner particles on the electrostatic image holding 
member. 
SUMMARY OF THE INVENTION 
One object of the present invention is to provide an electrophotographic 
apparatus for reproducing prints with high image density and excellent 
image quality which does not show any non-uniformity in image density and 
any background development. 
One embodiment of the present invention is directed to an 
electrophotographic apparatus comprising a magnetic developer, an 
electrostatic latent image holding member which rotates in a specified 
direction, and a removing roller which is placed at a position with a 
specified distance apart from the surface of said electrostatic latent 
image holding member and rotates in the direction opposite to the rotation 
of said electrostatic latent image holding member, a developer reservoir 
for supplying said magnetic developer to the surface of said electrostatic 
latent image holding member, a means for supplying an AC voltage to said 
removing roller to remove the developer retained on non-image areas of 
said electrostatic latent image holding member, and a magnetic field 
generating means, installed inside said electrostatic latent image holding 
member, for producing two magnetic poles having polarity different from 
each other on the surface of said electrostatic latent image holding 
member in the proximity to (also referred to interchangably in this 
application as "the vicinity of") image developing areas where said 
electrostatic latent image holding member comes closest to said removing 
roller. 
Thus, the invention makes it possible to realize an electrophotographic 
apparatus wherein the developer, e.g., the toner, attached on the 
electrostatic latent image holding member, is transported in abundance to 
the image development areas where the electrostatic latent image holding 
member and the removing roller are situated opposite to each other, 
resulting in an improvement in low image density (caused in prior art by 
insufficient supply of toner) and an achievement in gaining a high 
resolution picture of excellent quality in a stable manner even under the 
conditions of high temperature and high humidity, and further an 
achievement in realizing a picture of excellent quality even when operated 
under a high speed processing condition. 
Another embodiment of the present invention is directed to an 
electrophotographic apparatus comprising a magnetic developer, an 
electrostatic latent image holding member which rotates in a specified 
direction, a removing roller which is placed at position with a specified 
distance apart from the surface of said electrostatic latent image holding 
member and rotates in the direction opposite to the rotation of said 
electrostatic latent image holding member, a developer reservoir for 
supplying said magnetic developer to the surface of said electrostatic 
latent image holding member, a means for supplying an AC voltage to said 
removing roller to remove the developer retained on non-image areas of 
said electrostatic latent image holding member, and a magnetic field 
generating means installed inside said removing roller, for producing two 
magnetic poles with polarity different from each other on the surface of 
said removing roller in the vicinity of image development areas where said 
electrostatic latent image holding member comes closest to said removing 
roller. 
Thus, the invention makes it possible to realize an electrophotographic 
apparatus wherein the toner collected on the removing roller is quickly 
removed from the image developing areas with the resultant prevention of 
background developing caused by insufficient removal of the toner, 
consequently contributing to gaining a high resolution picture of 
excellent quality in a stabilized manner even under the conditions of high 
temperature and high humidity, and further realizing a picture of 
excellent quality even when operated under a high speed processing 
condition. 
Yet another embodiment of the present invention is directed to an 
electrophotographic apparatus comprising a magnetic developer, an 
electrostatic latent image holding member rotating in a specified 
direction, a removing roller which is placed at a position with a 
specified distance apart from the surface of said electrostatic latent 
image holding member and rotates in the direction opposite to the rotation 
of said electrostatic latent image holding member, a developer reservoir 
for supplying said magnetic developer to the surface of said electrostatic 
latent image holding member, a means for supplying an AC voltage to said 
removing roller to remove the developer retained on non-image areas of 
said electrostatic latent image holding member, and a magnetic field 
generating means, installed inside said electrostatic latent image holding 
member, for producing two magnetic poles, having different polarity from 
each other, on the surface of said electrostatic latent image holding 
member in the vicinity of image developing areas where said electrostatic 
latent image holding member comes closest to said removing roller, and a 
magnetic field generating means installed inside said removing roller for 
producing two magnetic poles having polarity different from each other on 
the surface of said removing roller in the vicinity of developing areas 
where said electrostatic latent image holding member comes closest to said 
removing roller. 
Yet another embodiment of the present invention is directed to an 
electrophotographic apparatus comprising a magnetic developer, an 
electrostatic latent image holding member which has on its surface a means 
for increasing friction force against said developer and rotates in a 
specified direction, a removing roller which is placed at a position with 
a specified distance apart from the surface of said electrostatic latent 
image holding member and rotates in the direction opposite to the rotation 
of said electrostatic latent image holding member, a developer reservoir 
for supplying said magnetic developer to the surface of said electrostatic 
latent image holding member, a means for supplying an AC voltage to said 
removing roller to remove the developer retained on non-image areas of 
said electrostatic latent image holding member, and a magnetic field 
generating means, installed inside said electrostatic latent image holding 
member, for producing a magnetic field on the surface of said 
electrostatic latent image holding member in the vicinity of image 
developing areas where said electrostatic latent image holding member 
comes closest to said removing roller. 
Thus, the invention makes it possible to realize an electrophotographic 
apparatus wherein the quantity of the toner to be deposited on the 
electrostatic latent image holding member is sufficiently secured with a 
resultant contribution to gaining a high resolution picture of excellent 
quality in a stabilized manner even under the conditions of high 
temperature and high humidity, and further realizing a picture of 
excellent quality even when operated under a high speed processing 
condition. 
Still another embodiment of the present invention is an electrophotographic 
apparatus comprising a magnetic developer, an electrostatic latent image 
holding member which rotates in a specified direction, a removing roller 
which has on its surface a means for increasing friction force against 
said developer, and which is placed at a position with a specified 
distance apart from the surface of said electrostatic latent image holding 
member, and rotates in the direction opposite to the rotation of said 
electrostatic latent image holding member, a developer reservoir for 
supplying said magnetic developer to the surface of said electrostatic 
latent image holding member, a means for supplying an AC voltage to said 
removing roller for removing the developer retained on non-image areas of 
said electrostatic latent image holding member, and a magnetic field 
generating means, installed inside said electrostatic latent image holding 
member, for producing a magnetic field on the surface of said 
electrostatic latent image holding member in the vicinity of image 
developing areas where said electrostatic latent image holding member 
comes closest to said removing roller. 
Thus, the invention makes it possible to realize an electrophotographic 
apparatus wherein the toner collected on the removing roller is quickly 
removed from the image development areas with resultant prevention of 
background developing caused by insufficient collection of the toner, 
consequently contributing to gaining a high resolution picture of 
excellent quality in a stabilized manner even under the conditions of high 
temperature and high humidity, and further realizing a picture of 
excellent quality even when operated under a high speed processing 
condition. 
Another embodiment of the invention is directed to a method for forming an 
image by an electrophotographic apparatus comprising: forming an 
electrostatic latent image on a surface of an electrostatic latent image 
holding member; applying a magnetic developer to the surface of the 
electrostatic latent image holding member, thereby applying the magnetic 
developer to image and non-image areas of the surface of the electrostatic 
image holding member; attaching the magnetic developer to the surface of 
the electrostatic latent image holding member by a first magnetic field 
generating means installed inside the electrostatic latent image holding 
member, said magnetic field generating means producing two magnetic poles, 
having polarity different from each other, on the surface of the 
electrostatic latent image holding member; passing a removing roller, 
comprising a second magnetic field generating means installed therein, in 
the vicinity of the electrostatic latent image holding member to remove 
the magnetic developer from the non-image areas of the electrostatic 
latent image holding member; and transferring onto paper the magnetic 
developer from the image areas. 
Yet another embodiment of the invention is directed to an 
electrophotographic apparatus comprising a magnetic developer, an 
electrostatic latent image holding member rotating in a specified 
direction, a removing roller placed at a position with a specified 
distance apart from the surface of said electrostatic latent image holding 
member rotating opposite to said specified direction, a developer 
reservoir for supplying said magnetic developer to the surface of said 
electrostatic latent image holding member, a voltage source for applying 
an AC voltage to said removing roller to remove the magnetic developer 
retained on non-image areas of said electrostatic latent image holding 
member, and a magnetic field generator installed inside said electrostatic 
latent image holding member for producing two magnetic poles having 
polarity different from each other on the surface of said electrostatic 
latent image holding member in proximity to developing areas where said 
electrostatic latent image holding member comes closest to said removing 
roller. 
The electrophotographic apparatus of the invention has a number of 
advantages. The electrophotographic apparatus of the invention produces 
high quality images having high image density, which are substantially 
free of non-uniformity in density. The apparatus substantially eliminates 
the unevenness in the force transporting the toner particles on the 
electrostatic image holding member because the force is applied to a 
magnetic brush of the particles formed on the surface of the electrostatic 
image holding member, rather than to the individual particles. Without 
wishing to be bound by any theory of operability, it is believed that this 
feature of the apparatus contributes to the improved quality of images 
produced thereby.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The invention will be described in conjunction with exemplary embodiments 
thereof illustrated in the figures and the following examples. 
EXAMPLE 1 
An electrophotographic apparatus of the first exemplary embodiment of the 
present invention will be described with the help of FIG. 1 to FIG. 5. 
FIG. 1 is a schematic illustration showing the structure of Example 1 of 
the invention. 
With reference to FIG. 1, a cylindrical electrostatic latent image holding 
member 14 (30 mm in diameter), also referred to in this application as an 
"electrostatic latent image holding member" has disposed on its surface an 
organic photoconductor prepared by dispersing phthalocyanine in a binder 
resin of polyester group. The electrostatic latent image holding member 14 
rotates at a peripheral speed of 30 mm/s. A magnet 15 is fixed coaxially 
with said electrostatic latent image holding member 14. The magnet 15 is 
formed of non-rotary two poles, and it serves as a magnetic field 
generating means. The magnet 15 of this embodiment and any equivalent 
magnets or magnetic plates of all embodiments of the invention are 
stationary and do not rotate with the cylindrical electrostatic latent 
image holding member 14. Accordingly, the magnet 15 (and its equivalents, 
such as magnetic plates) may also be referred to herein as "non-rotary 
magnet" or "non-rotary magnetic plate." There are no particular 
restrictions imposed on the nature of the magnet 15 which can be any 
suitable magnet, such as a permanent magnet or an electromagnet. 
A corona charger 16 charges negatively the electrostatic latent image 
holding member 14. A grid electrode 17 controls the charge potential of 
the electrostatic latent image holding member 14. A signal light 18 forms 
electrostatic latent images. The electrophotographic apparatus also 
includes a developer reservoir 19 and a developer 20, e.g., a magnetic 
mono-component negatively chargeable toner with an average particle 
diameter of 12 .mu.m. A cylindrical removing roller 21 (16 mm in 
diameter), made of aluminum, serves as an electrode, which is installed at 
a specified distance apart from the electrostatic latent image holding 
member 14. The removing roller 21 rotates at a peripheral speed of 30 mm/s 
in the direction opposite to the rotation of the electrostatic latent 
image holding member 14. A non-rotary magnet 22 is fixed coaxially with 
the removing roller 21. The non-rotary magnet 22 serves as a magnetic 
field generating means. The magnet 22 of this embodiment and any 
equivalent magnets or magnetic plates of all embodiments of the invention 
are stationary and do not rotate with the removing roller 21. Accordingly, 
the magnet 22 (and its equivalents, such as magnetic plates) may also be 
referred to herein as "non-rotary magnet" or "non-rotary magnetic plate." 
There are no specific restrictions imposed on the nature of the magnet 22, 
which can be any suitable magnet, such as a permanent magnet or an 
electromagnet. 
An AC high voltage power source 23 applies voltage to the removing roller 
21. A scraper 24 made, for example, of a polyester film, scrapes off the 
toner attached on the removing roller 21. A transfer corona charger 25 
transfers the images, which are formed on the electrostatic latent image 
holding member 14 by deposition of the toner, onto paper. A cleaner 26 
removes the toner that remains on the electrostatic latent image holding 
member 14 after the images are transferred. 
FIG. 3 shows a chart of magnetic flux density distribution observed in the 
vertical direction on the surface of the electrostatic latent image 
holding member 14 in the vicinity of the magnet 15. The peak values of the 
magnetic flux density measure -700 Gs (S-pole), and 500 Gs (N-pole), 
respectively. The peak value of magnetic flux density of the magnet 22 
measures 600 Gs (N-pole) at the surface of the removing roller 21. 
FIG. 4 shows the positional relation between the magnets 15 and 22, both 
installed inside the electrostatic latent image holding member 14 and the 
removing roller 21, respectively. 
The angle .theta..sub.1 that the south pole of the magnet 15 installed 
inside the electrostatic latent image holding member 14 makes from the 
point where the surface of the electrostatic latent image holding member 
14 comes closest to that of the removing roller 21 was set in one 
embodiment to .theta..sub.1 =40.degree. in the direction opposite to the 
rotation of the electrostatic latent image holding member 14, while the 
angle .theta..sub.2 of the north pole was set to .theta..sub.2 =10.degree. 
in the same embodiment. 
In that same embodiment, the angle .theta..sub.3 that the north pole of the 
magnet 22, installed inside the removing roller 21, makes from the point 
where the surface of the removing roller 21 comes closest to that of the 
electrostatic latent image holding member 14 was set to .theta..sub.3 
=-15.degree. in the direction opposite to the rotation of the removing 
roller 21. 
In general, the range of the angle .theta..sub.1 is desirable to be 
15.degree.&lt;.theta..sub.1 &lt;50.degree., and the range of 
20.degree.&lt;.theta..sub.1 &lt;45.degree., in particular, is the most suitable 
range. 
The range of the angle .theta..sub.2 is desirable to be 
0.degree.&lt;.theta..sub.2 &lt;30.degree., and the range of 
5.degree.&lt;.theta..sub.2 &lt;20.degree., in particular, is the post suitable 
range. 
The range of the angle .theta..sub.3 is desirable to be 
-30.degree.&lt;.theta..sub.3 &lt;10.degree., and the range of 
-20.degree.&lt;.theta..sub.3 &lt;0.degree., in particular, is the most suitable 
range. 
The composition of the developer used in the present example, i.e., the one 
component magnetic toner, was 70% wt. of polyester resin, 25% wt. of 
ferrite, 3% wt. of carbon black, and 2% wt. of oxycarboxylic acid metal 
complex with 0.4% wt. of colloidal silica added further. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with reference to FIG. 1. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -4 kV and the grid electrode voltage was -500 V.). Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on the electrostatic latent image holding member 14. 
At this time, the exposure potential (V.sub.r) of the electrostatic latent 
image holding member 14 was -100 V. Next, the one-component magnetic toner 
was attached on the surface of the electrostatic latent image holding 
member 14 in the developer reservoir 19 by the magnetic force of the 
magnet 15. 
At this time, the toner was charged to about -3 .mu.C/g. The toner attached 
on the electrostatic latent image holding member 14 was then formed into a 
brush-like shape along the magnetic force which was produced by the magnet 
15 and disposed in the peripheral direction of the electrostatic latent 
image holding member 14. The toner attached in the brush-like shape was 
transported by the frictional force caused by rotation of the 
electrostatic latent image holding member 14. Thus, the magnetic toner 
which was aligned along the magnetic force lines produced by magnetic 
field looked like a brush, and is referred to as a "magnetic brush." The 
electrostatic latent image holding member 14 having a toner layer attached 
thereto passed the front of the removing roller 21, the surface of which 
was located at a distance of 300 .mu.m from that of the electrostatic 
latent image holding member 14. 
An AC voltage (1 kHz in frequency) of 750 V.sub.O-p superimposed with a DC 
voltage of -300 V having a waveform as shown in FIG. 5 was applied to the 
removing roller 21 from the AC high voltage power source 23. While the 
toner layer on the electrostatic latent image holding member 14 was 
traveling by passing between the electrostatic latent image holding member 
14 and the removing roller 21, the toner attached to the non-image areas 
of the electrostatic latent image holding member 14 was gradually removed 
to the side of the removing roller 21. Only the toner images with a 
positive-negative picture reversal remained at the image areas of the 
electrostatic latent image holding member 14. 
The toner attached on the removing roller 21 was formed into a brush-like 
shape along the magnetic force which was produced by the magnet 22 and 
disposed in the peripheral direction of the removing roller. The toner 
attached on the removing roller 21 was transported by the frictional force 
caused by rotation of the removing roller 21, in the direction indicated 
by an arrow in FIG. 1, scraped off by the scraper 24, and returned into 
the developer reservoir 19. It was observed at the upper area of the 
S-pole on the surface of the electrostatic latent image holding member 14 
that the toner was in a fierce turbulence. The toner images thus formed on 
the electrostatic latent image holding member 14 were transferred onto 
paper (not shown in FIG. 1) by means of the transfer corona charger 25. 
Then, after thermal fixing by means of a fixing equipment (not shown in 
FIG. 1), printed images were obtained. On the other hand, the toner left 
on the electrostatic latent image holding member 14, after transferring 
the toner images onto paper, was transported by the rotation of the 
electrostatic latent image holding member 14, and collected by the cleaner 
26. As a result, sharp images of high image density without showing any 
non-uniformity of density were obtained. 
Accordingly, this particular exemplary embodiment of the present invention 
features a structure comprising a fixed and non-rotary magnet, i.e., a 
magnetic field generating means, which is installed inside a rotary 
electrostatic latent image holding member, and produces two magnetic poles 
having polarity opposite to each other on the surface of the electrostatic 
latent image holding member in the vicinity of the developing areas where 
the electrostatic latent image holding member comes closest to the 
removing roller. 
The operation of the electrophotographic apparatus of the present example 
and the effects thereof will be explained in a greater detail with 
reference to FIG. 2. FIG. 2 is an enlarged view showing schematically the 
vicinity of the developing areas of the electrophotographic apparatus 
illustrated in FIG. 1. As shown in FIG. 2, the toner is aligned in a 
brush-like shape along the magnetic force lines generated by the magnet 15 
in the peripheral direction of the electrostatic latent image holding 
member 14 to form a magnetic brush 20a. Therefore, the transporting force 
applied to the toner 20 (or "developer 20") exerted by the electrostatic 
latent image holding member 14 does not work on the individual particles 
of the toner, which are forming the first layer of the toner and are in 
direct contact with the surface of the electrostatic latent image holding 
member. Instead, the transporting force applied to the toner 20 works on 
the entire magnetic brush which is a collection of the toner particles 
arranged together by the magnetic force, and therefore the transporting 
force to carry the toner is remarkably intensified. Besides, the 
unevenness in transporting force due to the non-uniformity in frictional 
force among the individual toner particles is also rectified. As a result, 
the toner furnished to the electrostatic latent image holding member 14 is 
supplied to the developing areas in abundance and in a stabilized manner, 
thereby producing an excellent picture quality showing a high image 
density, which is substantially free of any non-uniformity in density. 
EXAMPLE 2 
A second exemplary embodiment of the present invention for an 
electrophotographic apparatus will be explained with reference to FIG. 6, 
FIG. 7, and FIG. 8. 
The present example is a modification of the previous exemplary embodiment, 
illustrated, e.g., in Example 1, and the structure thereof is illustrated 
in FIG. 6. The structure shown in FIG. 6 differs from that of FIG. 1 in 
the magnetic field generating means. More specifically, the magnet 15 
installed inside the electrostatic latent image holding member has one 
magnetic pole, and a magnetic plate 27 has been added, instead, to the 
magnet 15 at the side opposite to the direction of rotation thereof. The 
magnetic plate 27 can be made of any substance readily magnetized by an 
external magnetic field, such as iron or similar substances. The remaining 
parts of FIG. 6 are the same as those in FIG. 1. Therefore, the function 
of the various components and the operation of the electrophotographic 
apparatus of FIG. 6 is substantially the same as those of FIG. 1, 
described in detail above. 
FIG. 7 shows a chart of the magnetic flux density distribution of the 
magnet 15 and the magnetic plate 27 observed in the vertical direction on 
the surface of the electrostatic latent image holding member 14 in this 
Example. The peak values of the magnetic flux density measured -300 Gs 
(magnetic plate), and 500 Gs (N-pole), respectively. The magnetic plate 27 
is magnetized by the magnet 15, and a magnetic pole opposite to the one 
formed on the surface of the magnet 15 is produced on the surface of the 
magnetic plate 27. FIG. 8 shows the arrangement of the magnet 15 and the 
magnetic plate 27 both installed inside the electrostatic latent image 
holding member 14, and the magnet 22 inside the removing roller 21. The 
angle .theta..sub.1 that the magnetic plate 27 installed inside the 
electrostatic latent image holding member 14 makes from the point where 
the surface of the electrostatic latent image holding member 14 comes 
closest to that of the removing roller 21 was set to .theta..sub.1 
=40.degree. in the direction opposite to the rotation of the electrostatic 
latent image holding member 14, while the angle .theta..sub.2 of the north 
pole of the magnet 15 inside the electrostatic latent image holding member 
14 was set to .theta..sub.2 =10.degree.. The angle .theta..sub.3 that the 
north pole of the magnet 22 installed inside the removing roller 21 makes 
from the point where the surface of the removing roller 21 comes closest 
to that of the electrostatic latent image holding member 14 was set to 
.theta..sub.3 =-15.degree. in the direction opposite to the rotation of 
the removing roller 21. 
The range of said angle .theta..sub.1 is desirable to be 
15.degree.&lt;.theta..sub.1 &lt;50.degree., and the range of 
20.degree.&lt;.theta..sub.1 &lt;45.degree. in particular, is the most suitable 
range. The range of said angle .theta..sub.2 is desirable to be 
0.degree.&lt;.theta..sub.2 &lt;30.degree., and the range of 
5.degree.&lt;.theta..sub.2 &lt;20.degree. in particular, is the most suitable 
range. The range of said angle .theta..sub.3 is desirable to be 
-30.degree.&lt;.theta..sub.3 &lt;10.degree., and the range of 
-20.degree.&lt;.theta..sub.3 &lt;0.degree. in particular, is the most suitable 
range. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with reference to FIG. 6. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -4 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential (V.sub.r) of the electrostatic latent image 
holding member 14 was -100 V. Next, the mono-component magnetic toner was 
attached on the surface of said electrostatic latent image holding member 
14 in the developer reservoir 19 by the magnetic force of both the magnet 
15 and the magnetic plate 27. The toner attached on the electrostatic 
latent image holding member 14 was then formed into a brush-like shape 
along the magnetic force, which was produced by both the magnet 15 and the 
magnetic plate 27, and disposed in the peripheral direction of the 
electrostatic latent image holding member 14. The toner attached in the 
brush-like shape was transported by the frictional force caused by 
rotation of the electrostatic latent image holding member 14. The 
electrostatic latent image holding member 14 with the toner layer attached 
passed the front of the removing roller 21, the surface of which was 
located at a distance of 300 .mu.m from that of the electrostatic latent 
image holding member 14. An AC voltage (1 kHz in frequency) of 750 
V.sub.O-p, superimposed with a DC voltage of -300 V having a waveform as 
shown in FIG. 5, was applied to the removing roller 21 from the high 
voltage power source 23. 
While the toner layer on the electrostatic latent image holding member 14 
was traveling by passing between the electrostatic latent image holding 
member 14 and the removing roller 21, the toner attached on the non-image 
areas of the electrostatic latent image holding member 14 was gradually 
removed to the side of the removing roller 21. Only the toner images with 
a positive-negative picture reversal remained at the image areas of the 
electrostatic latent image holding member 14. 
The toner attached on the removing roller 21 was formed into a brush-like 
shape along the magnetic force which was produced by the magnet 22 and 
disposed in the peripheral direction of the removing roller. The toner 
attached in the brush-like shape was transported by the frictional force 
caused by rotation of the removing roller 21, scraped off by the scraper 
24, and returned into the developer reservoir 19. It was observed at the 
upper area of the magnetic plate 27, on the surface of the electrostatic 
latent image holding member 14, that the toner was in a fierce turbulence. 
The toner images thus formed on the electrostatic latent image holding 
member 14 were transferred onto paper (not shown in FIG. 6) by means of 
the transfer corona charger 25. Then, after thermally fixing by means of a 
fixing equipment (not shown in FIG. 6), printed images were obtained. On 
the other hand, the toner left on the electrostatic latent image holding 
member 14, after transferring the toner images to paper, was transported 
by the rotation of the electrostatic latent image holding member 14, and 
collected by the cleaner 26. 
As a result, sharp images of high image density without showing any 
non-uniformity of density were obtained. 
The remaining properties and features of the electrophotographic apparatus 
of this Example are the same as explained above in conjunction with the 
apparatus of Example 1. 
EXAMPLE 3 
An electrophotographic apparatus of a third exemplary embodiment of the 
this invention will be described with reference to FIGS. 9-12. 
FIG. 9 is a schematic illustration showing the structure of another 
exemplary embodiment of the present invention of an electrophotographic 
apparatus of this invention. In FIG. 9, a cylindrical electrostatic latent 
image holding member 14 (30 mm in diameter), has its surface disposed with 
an organic photoconductor prepared by dispersing phthalocyanine in a 
binder resin of polyester group, and rotates at a peripheral speed of 30 
mm/s. A non-rotary magnet 15 is fixed coaxially with said electrostatic 
latent image holding member 14. The magnet 15 can be any suitable magnet, 
such as a permanent magnet or an electromagnet. The peak value of the 
magnetic flux density on the surface of the electrostatic latent image 
holding member 14 is -800 Gs (S-pole). A corona charger 16 charges 
negatively the electrostatic latent image holding member 14. A grid 
electrode 17 controls the charge potential of the electrostatic latent 
image holding member 14. A signal light 18 (also referred to herein as a 
"laser light" or a "laser signal light") forms electrostatic latent 
images. The electrophotographic apparatus of this embodiment also 
comprises a developer reservoir 19, a developer 20, e.g., a magnetic 
mono-component negatively chargeable toner with an average particle 
diameter of 12 .mu.m, and a cylindrical removing roller 21 (also referred 
to herein as a "removing roller") (16 mm in diameter), made of aluminum, 
serving as an electrode and rotating at a peripheral speed of 30 mm/s in 
the direction opposite to the rotation of the electrostatic latent image 
holding member 14. A non-rotary magnet 22 is fixed coaxially with the 
removing roller 21 and formed of two magnetic poles. The magnet 22 can be 
any suitable magnet, such as a permanent magnet or an electromagnet. An AC 
high voltage power source 23 applies voltage to the removing roller 21. A 
scraper 24, made of polyester film, scrapes off the toner attached on the 
removing roller 21. A transfer corona charger 25 transfers the images, 
which were formed on the electrostatic latent image holding member 14 by 
deposition of toner, onto paper. A cleaner 26 removes the toner that 
remains on the electrostatic latent image holding member 14 after 
transferring the images. 
FIG. 11 is a chart of the magnetic flux density distribution observed on 
the surface of the removing roller 21 in the vertical direction of the 
magnet 22. The peak values of the magnetic flux density measure -600 Gs 
(N-pole), and -350 Gs (S-pole), respectively. FIG. 12 shows the positional 
relation between the magnets 15 and 22 both installed inside the 
electrostatic latent image holding member 14 and the removing roller 21, 
respectively. The angle .theta..sub.1 that the magnet 15, installed inside 
the electrostatic latent image holding member 14, makes from the point 
where the surface of the electrostatic latent image holding member 14 
comes closest to that of the removing roller 21 was set to .theta..sub.1 
=35.degree. in the direction opposite to the rotation of the electrostatic 
latent image holding member 14, while the angle .theta..sub.2 of the north 
pole of the magnet 22 inside the removing roller 21 was set to 
.theta..sub.2 =-15.degree. and the angle .theta..sub.3 of the south pole 
to .theta..sub.3 =+20.degree.. The range of said angle .theta..sub.1 is 
desirable to be 0.degree.&lt;.theta..sub.1 &lt;45.degree., and the range of 
10.degree.&lt;.theta..sub.1 &lt;40.degree., in particular, is the most suitable 
range. The range of said angle .theta..sub.2 is desirable to be 
-20.degree.&lt;.theta..sub.2 &lt;0.degree., and the range of -15&lt;.theta..sub.2 
&lt;-10.degree., in particular, is the most suitable range. The range of said 
angle .theta..sub.3 is desirable to be 0.degree..theta..sub.3 &lt;90.degree., 
and the range of 10.degree.&lt;.theta..sub.3 &lt;50.degree., in particular, is 
the most suitable range. 
The composition of the developer used in the present example, i.e., the one 
component magnetic toner, was 70% wt. of polyester resin, 25% wt. of 
ferrite, 3% wt. of carbon black, and 2% wt. of oxycarboxylic acid metal 
complex with 0.4% wt. of colloidal silica added further. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with reference to FIG. 9. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -4 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential (V.sub.r) of the electrostatic latent image 
holding member 14 was -100 V. Next, the mono-component magnetic toner was 
attached on the surface of said electrostatic latent image holding member 
14 in the developer reservoir 19 by the magnetic force of the magnet 15. 
At this time, the toner was charged to about -3 .mu.C/g. The electrostatic 
latent image holding member 14 attached with a toner layer passed the 
front of the removing roller 21, the surface of which was located at a 
distance of 300 .mu.m from that of the electrostatic latent image holding 
member 14. 
An AC voltage (1 kHz in frequency) of 750 V.sub.O-p superimposed with a DC 
voltage of -300 V having a waveform as shown in FIG. 5 was applied to the 
removing roller 21 from the high voltage power source 23. While the toner 
layer on the electrostatic latent image holding member 14 was traveling by 
passing between the electrostatic latent image holding member 14 and the 
removing roller 21, the toner attached on the non-image areas of the 
electrostatic latent image holding member 14 was gradually removed to the 
side of the removing roller 21. Only the toner images with a 
positive-negative picture reversal remained at the image areas of the 
electrostatic latent image holding member 14. 
The toner attached on the removing roller 21 which was rotating in the 
direction of the arrow in FIG. 9 was formed into a brush-like shape along 
the magnetic force which was produced by the magnet 22 and disposed in the 
peripheral direction of the removing roller 21. The toner attached on the 
removing roller 21 in a brush-like shape was transported by the friction 
force due to the rotation of the removing roller 21, scraped off by the 
scraper 24, and returned into the developer reservoir 19. 
It was observed at the upper area of the S-pole on the surface of the 
removing roller 21 that the toner was in a fierce turbulence. The toner 
images thus formed on the electrostatic latent image holding member 14 
were transferred onto paper (not shown in FIG. 9) by means of the transfer 
corona charger 25. Then, after thermally fixing the images by means of a 
fixing equipment (not shown in FIG. 9), printed images were obtained. On 
the other hand, the toner left on the electrostatic latent image holding 
member 14, after transferring the toner images to paper, was transported 
by the rotation of the electrostatic latent image holding member 14, and 
collected by the cleaner 26. 
As a result, sharp images of high image density without showing any 
non-uniformity of density were obtained. 
Accordingly, this particular exemplary embodiment of the present invention 
features a structure comprising a fixed and non-rotary magnet, i.e., a 
magnetic field generating means, which is installed inside a rotary 
removing roller, and produces two magnetic poles having polarity opposite 
to each other on the surface of the removing roller in the vicinity of the 
development areas where the electrostatic latent image holding member 
comes closest to the removing roller. 
The operation of the electrophotographic apparatus of this exemplary 
embodiment of the invention and features thereof will be explained in a 
greater detail with reference to FIG. 10. FIG. 10 is an enlarged view 
showing schematically the vicinity of the development areas of the 
electrophotographic apparatus illustrated in FIG. 9. As shown in FIG. 10, 
the toner serving as the developer is aligned in a brush-like shape along 
the magnetic force lines generated by the magnet 22 in the peripheral 
direction of the removing roller 21 to form a magnetic brush 20b. 
Therefore, the transporting force applied to the toner 20 exerted by the 
removing roller 21 does not only work on the individual particles of the 
toner, which are forming the first layer of the toner and in direct 
contact with the surface of the removing roller 21. Instead, the 
transporting force applied to the toner 20 also works on the entire 
magnetic brush which is a collection of the toner particles put together 
by the magnetic force, and therefore the transporting force to carry the 
toner is remarkably intensified. Besides, the unevenness in transporting 
force due to the scattering in frictional force among the individual toner 
particles is also rectified. 
As a result, since the low charged toner collected by the removing roller 
21 can be removed from the areas vibrated by an AC bias voltage in a 
forceful and stable manner, excellent picture quality without any 
background development and non-uniformity of density is obtained even 
under the conditions of high temperature and high humidity or high speed 
processing. 
EXAMPLE 4 
A fourth exemplary embodiment of the present invention for an 
electrophotographic apparatus will be described with the help of FIG. 13, 
FIG. 14, and FIG. 15. 
The present example is a modification of the previous exemplary embodiment, 
e.g., Example 3, and the structure of this example is illustrated in FIG. 
13. 
The structure shown in FIG. 13 differs from that of FIG. 9 in the 
construction of the non-rotary magnet 22. More specifically, the magnet 22 
has one magnetic pole, and a non-rotary magnetic plate 28 is mounted on 
the upper side of the magnet 22. 
The magnetic plate 28 may be made from any substance readily magnetized by 
an external magnetic field, e.g., iron or similar substances. The other 
parts of FIG. 13 are the same as those in FIG. 9. Therefore, the same 
explanation as was made regarding the symbols used in FIG. 9 applies to 
those of FIG. 13, and a separate explanation of the symbols is omitted 
here. 
FIG. 14 shows a chart of the magnetic flux density distribution of the 
magnet 22 and the magnetic plate 28 observed on the surface of the 
removing roller 21 in the vertical direction. The magnetic plate 28 is 
magnetized by the magnet 22, and a magnetic pole opposite to the one 
formed on the surface of the magnet 22 is produced on the surface of the 
magnetic plate 28. The peak values of the magnetic flux density measure 
600 Gs (N-pole), and -200 Gs (magnetic plate), respectively. FIG. 15 shows 
the positional relation between the magnet 22 inside the removing roller 
21 and the magnet 15 inside the electrostatic latent image holding member 
14. The angle that the magnet 15 installed inside the electrostatic latent 
image holding member 14 makes from the point where the surface of the 
electrostatic latent image holding member 14 comes closest to that of the 
removing roller 21 was set to .theta..sub.1 =35.degree. in the direction 
opposite to the rotation of the electrostatic latent image holding member 
14, while the angle .theta..sub.2 of the north pole of the magnet 22 
inside the removing roller 21 and the angle .theta..sub.3 of the magnetic 
plate 28 were set to .theta..sub.2 =-15.degree. and .theta..sub.3 
=+15.degree., respectively. The range of said angle .theta..sub.1 is 
desirable to be 0.degree.&lt;.theta..sub.1 &lt;45.degree., and the range of 
10.degree.&lt;.theta..sub.1 &lt;40.degree., in particular, is the most suitable 
range. The range of .theta..sub.2 is desirable to be 
-20.degree.&lt;.theta..sub.2 &lt;0.degree., and the range of 
-15.degree.&lt;.theta..sub.2 &lt;-10.degree., in particular, is the most 
suitable range The range of .theta..sub.3 is desirable to be 
0.degree.&lt;.theta..sub.3 &lt;90.degree., and the range of 
10.degree.&lt;.theta..sub.3 &lt;50.degree., in particular, is the most suitable 
range 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with the help of FIG. 13. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -4 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential of the electrostatic latent image holding 
member 14 was -100 V. The mono-component magnetic toner was attached on 
the surface of said electrostatic latent image holding member 14 in the 
developer reservoir 19 by the magnetic force of the magnet 15. Next, the 
electrostatic latent image holding member 14 attached with said toner 
layer passed the front of the removing roller 21. An AC voltage (1 kHz in 
frequency) of 750 V.sub.O-p superimposed with a DC voltage of -300 V 
having a waveform as shown in FIG. 5 was applied to the removing roller 21 
from the high voltage power source 23. The toner layer on the 
electrostatic latent image holding member 14 traveled between the 
electrostatic latent image holding member 14 and the removing roller 21. 
The toner attached on the non-image areas of the electrostatic latent 
image holding member 14 was gradually removed to the side of the removing 
roller 21. Consequently, only the toner images with a positive-negative 
picture reversal remained at the image areas of the electrostatic latent 
image holding member 14. The toner attached on the removing roller 21, 
which was rotating in the direction of the arrow, was formed into a 
brush-like shape along the magnetic force which was produced by the magnet 
22 and the magnetic plate 28 and disposed in the peripheral direction of 
the removing roller 21. The toner attached on the removing roller 21 in a 
brush-like shape was transported by the frictional force due to the 
rotation of the removing roller 21, scraped off by the scraper 24, and 
returned into the developer reservoir 19. 
It was observed in the upper area of the magnetic plate 28 on the surface 
of the removing roller 21 that the toner was in a fierce turbulence. The 
toner images thus formed on the electrostatic latent image holding member 
14 were transferred onto paper (not shown in FIG. 13) by means of the 
transfer corona charger 25. Then, after thermally fixing by means of a 
fixing equipment (not shown in FIG. 13), printed images were obtained. On 
the other hand, the toner left on the electrostatic latent image holding 
member 14, after transferring of the images onto paper, was transported by 
the movement of the electrostatic latent image holding member 14, and 
collected by the cleaner 26. 
As a result, sharp images without showing any background development or 
non-uniformity of images were obtained. 
The operation and features of the electrophotographic apparatus of the 
present example are substantially the same as above explained in Example 
3. 
EXAMPLE 5 
A fifth exemplary embodiment of an electrophotographic apparatus of the 
present invention will be described with the help of FIG. 16 and FIG. 17. 
FIG. 16 is a schematic illustration showing the structure of the present 
example. The structure shown in FIG. 16 differs from that of FIG. 1 in the 
means employed to produce magnetic fields on the surface of the removing 
roller. 
More specifically, a non-rotary magnet 22 installed inside the removing 
roller 21 and fixed thereto coaxially has two poles. The magnet 22 can be 
any suitable magnet, such as a permanent magnet or an electromagnet. FIG. 
3 shows a chart of the distribution of the magnetic fluxes produced by a 
non-rotary magnet 15 and observed on the surface of the electrostatic 
latent image holding member 14 in the vertical direction. FIG. 11 shows a 
chart of the distribution of the magnetic fluxes produced by the magnet 22 
and observed on the surface of the removing roller 21 in the vertical 
direction. FIG. 17 shows the positional relation between the magnet 15 
inside the electrostatic latent image holding member 14 and the magnet 22 
inside the removing roller 21. The angle that the S-pole of the magnet 15 
installed inside the electrostatic latent image holding member 14 makes 
from the point where the surface of the electrostatic latent image holding 
member 14 comes closest to that of the removing roller 21 was set to 
.theta..sub.1 40.degree. in the direction opposite to the rotation of the 
electrostatic latent image holding member 14, while the angle 
.theta..sub.2 of the N-pole of the magnet 15 was set to .theta..sub.2 
=10.degree.. The angle that the N-pole of the magnet 22 installed inside 
the removing roller 21 makes from the point where the surface of the 
removing roller comes closest to that of the electrostatic latent image 
holding member 14 was set to .theta..sub.3 =-15.degree. in the direction 
opposite to the rotation of the removing roller, while the angle 
.theta..sub.4 of the S-pole of the magnet 22 was set to .theta..sub.4 
=20.degree.. 
The range of said angle .theta..sub.1 is desirable to be 
15.degree.&lt;.theta..sub.1 &lt;50.degree., and the range of 
20.degree.&lt;.theta..sub.1 &lt;45.degree., in particular, is the most suitable 
range. The range of .theta..sub.2 is desirable to be 
0.degree.&lt;.theta..sub.2 30.degree., and the range of 
5.degree.&lt;.theta..sub.2 &lt;20.degree., in particular, is the most suitable 
range. The range of .theta..sub.3 is desirable to be 
-30.degree.&lt;.theta..sub.3 &lt;10.degree., and the range of 
-20.degree.&lt;.theta..sub.3 &lt;0.degree., in particular, is the most suitable 
range. The range of .theta..sub.4 is desirable to be 
0.degree.&lt;.theta..sub.4 &lt;30.degree., and the range of 
5.degree.&lt;.theta..sub.4 &lt;25.degree., in particular, is the most suitable 
range. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with the help of FIG. 16. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -4 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential of the electrostatic latent image holding 
member 14 was -100 V. Mono-component magnetic toner was attached on the 
surface of said electrostatic latent image holding member 14 in the 
developer reservoir 19 by the magnetic force of the magnet 15. Next, the 
toner attached on the electrostatic latent image holding member 14 was 
aligned in the peripheral direction of the electrostatic latent image 
holding member 14 along the magnetic field produced by the magnet 15 to 
form a magnetic brush, and the brush-like toner was transported by the 
friction force produced by the rotation of the electrostatic latent image 
holding member 14. Then, the electrostatic latent image holding member 14 
attached with said toner layer passed the front of the removing roller 21. 
An AC voltage (1 kHz in frequency) of 750 V.sub.O-p superimposed with a DC 
voltage of -300 V having a waveform as shown in FIG. 5 was applied to the 
removing roller 21 from the high voltage power source 23. 
The toner layer on the electrostatic latent image holding member 14 
traveled between the electrostatic latent image holding member 14 and the 
removing roller 21, and the toner attached on the non-image areas of the 
electrostatic latent image holding member 14 was gradually removed to the 
side of the removing roller 21. Only the toner images with a 
positive-negative picture reversal remained at the image areas of the 
electrostatic latent image holding member 14. 
On the other hand, the toner attached on the removing roller 21 was formed 
into a brush-like shape along the magnetic field produced in the 
peripheral direction of the removing roller. The toner attached in a 
brush-like shape was transported by the frictional force due to the 
rotation of the removing roller 21, scraped off by the scraper 24, and 
returned into the developer reservoir 19. 
Besides, it was observed in the upper area of the magnet 22 on the surface 
of the removing roller 21 that the toner was in a fierce turbulence. The 
toner images thus formed on the electrostatic latent image holding member 
14 were transferred onto paper (not shown in FIG. 16) by means of the 
transfer corona charger 25. Then, after thermally fixing by means of a 
fixing equipment (not shown in FIG. 16), printed images were obtained. On 
the other hand, the toner left on the electrostatic latent image holding 
member 14 after transferring of the images to the paper was transported by 
the movement of the electrostatic latent image holding member 14, and 
collected by the cleaner 26. 
As a result, sharp images of high image density and free of non-uniformity 
in image density without showing any background development or image 
hysteresis were obtained. 
Accordingly, this example of one embodiment of the invention features a 
structure comprising a magnetic field generating means installed inside an 
electrostatic latent image holding member for producing two magnetic 
poles, having polarity different from each other, on the surface of said 
electrostatic latent image holding member in the vicinity of developing 
areas where the electrostatic latent image holding member comes closest to 
a removing roller. The structure of this embodiment also comprises a 
magnetic field generating means installed inside the removing roller for 
producing two magnetic poles, having polarity different from each other, 
on the surface of the removing roller in the vicinity of the developing 
areas where the electrostatic latent image holding member comes opposite 
to the removing roller. 
Therefore, because the toner supplied to the electrostatic latent image 
holding member 14 can be fed abundantly and in a stabilized manner to the 
development areas and further the toner collected by the removing roller 
21 can be removed sufficiently and in a stabilized manner from the area 
vibrating due to an AC bias voltage, there are produced images of 
excellent picture quality with a high image density and substantially free 
of any background development or non-uniformity of density even under the 
conditions of high temperature, high humidity, and high speed processing. 
EXAMPLE 6 
A sixth exemplary embodiment of an electrophotographic apparatus of the 
present invention will be described with the help of FIG. 18 and FIG. 19. 
This embodiment is a modification of the previous exemplary embodiment, 
e.g., Example 5, and the structure of this embodiment is illustrated in 
FIG. 18. 
The structure shown in FIG. 18 differs from that of FIG. 1 in the means to 
produce magnetic field on the surface of the removing roller 21. More 
specifically, the difference is in having a magnetic plate 28 mounted on 
the upper side of the non-rotary magnet 22 installed inside the removing 
roller 21 and fixed thereto coaxially. FIG. 3 shows a chart of the 
distribution of the magnetic fluxes produced by the non-rotary magnet 15 
and observed on the surface of the electrostatic latent image holding 
member 14 in the vertical direction. FIG. 14 shows a chart of the 
distribution of the magnetic fluxes produced by the magnet 22 and observed 
on the surface of the removing roller 21 in the vertical direction. FIG. 
19 shows the positional relation between the magnet 15 inside the 
electrostatic latent image holding member 14 and the magnet 22 inside the 
removing roller 21. The angle .theta..sub.1 that the S-pole of the magnet 
15 installed inside the electrostatic latent image holding member 14 makes 
from the point where the surface of the electrostatic latent image holding 
member 14 comes closest to that of the removing roller 21 was set to 
.theta..sub.1 =40.degree. in the direction opposite to the rotation of the 
electrostatic latent image holding member 14, while the angle 
.theta..sub.2 of the N-pole of the magnet 15 was set to .theta..sub.2 
=10.degree.. The angle that the N-pole of the magnet 22 installed inside 
the removing roller 21 makes from the point where the surface of the 
removing roller comes closest to that of the electrostatic latent image 
holding member 14 was set to .theta..sub.3 =-15.degree. in the direction 
opposite to the rotation of the removing roller, while the angle 
.theta..sub.4 of the magnetic plate was set to .theta..sub.4 =15.degree.. 
The range of said angle .theta..sub.1 is desirable to be 
15.degree.&lt;.theta..sub.1 &lt;50.degree., and the range of 
20.degree.&lt;.theta..sub.1 &lt;45.degree., in particular, is the most 
The range of .theta..sub.2 is desirable to be 0.degree.&lt;.theta..sub.2 
&lt;30.degree., and the range of 5.degree.&lt;.theta..sub.2 &lt;20.degree., in 
particular, is the most suitable range. The range of .theta..sub.3 is 
desirable to be -30.degree.&lt;.theta..sub.3 &lt;10.degree., and the range of 
-20.degree.&lt;.theta..sub.3 &lt;0.degree., in particular, is the most suitable 
range. The range of .theta..sub.4 is desirable to be 
0.degree.&lt;.theta..sub.4 &lt;30.degree., and the range of 
5.degree.&lt;.theta..sub.4 &lt;25.degree., in particular, is the most suitable 
range. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with the help of FIG. 18. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -4 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential of the electrostatic latent image holding 
member 14 was -100 V. One-component magnetic toner was attached on the 
surface of said electrostatic latent image holding member 14 in the 
developer reservoir 19 by the magnetic force of the magnet 15. 
Next, the toner attached on the electrostatic latent image holding member 
14 was aligned in the peripheral direction of the electrostatic latent 
image holding member 14 along the magnetic field produced by the magnet 15 
to form a magnetic brush (or a "brush-like shaped toner"), and the 
brush-like shaped toner was transported by the friction force due to the 
rotation of the electrostatic latent image holding member 14. Then, the 
electrostatic latent image holding member 14 attached with said toner 
layer passed the front of the removing roller 21. An AC voltage (1 kHz in 
frequency) of 750 V.sub.O-p superimposed with a DC voltage of -300 V 
having a waveform as shown in FIG. 5 was applied to the removing roller 21 
from the high voltage power source 23. The toner layer on the 
electrostatic latent image holding member 14 traveled between the 
electrostatic latent image holding member 14 and the removing roller 21, 
and the toner attached on the non-image areas of the electrostatic latent 
image holding member 14 was gradually removed to the side of the removing 
roller 21. 
Only the toner images with a positive-negative picture reversal remained at 
the image areas of the electrostatic latent image holding member 14. The 
toner attached on the removing roller 21 was formed into a brush-like 
shape along the magnetic field produced by the magnet 22 inside the 
removing roller in the peripheral direction of the removing roller. The 
toner attached in a brush-like shape was transported by the friction force 
due to the rotation of the removing roller 21, scraped off by the scraper 
24, and returned into the developer reservoir 19. 
Besides, it was observed in the upper areas of both the S-pole inside the 
electrostatic latent image holding member 14 and the magnetic plate inside 
the removing roller 21 that the toner was in a fierce turbulence. The 
toner images thus formed on the electrostatic latent image holding member 
14 were transferred onto paper (not shown in FIG. 18) by means of the 
transfer corona charger 25. Then, after thermally fixing by means of a 
fixing equipment (not shown in FIG. 18), printed images were obtained. On 
the other hand, the toner left on the electrostatic latent image holding 
member 14, after transferring of the images onto paper, was transported by 
the rotation of the electrostatic latent image holding member 14, and 
collected by the cleaner 26. 
As a result, sharp images of high image density and substantially free of 
non-uniformity in density without showing any background development or 
image hysteresis were obtained. 
The operation and features of the electrophotographic apparatus of the 
present example are substantially the same as described above in Example 
5. 
EXAMPLE 7 
A seventh exemplary embodiment of an electrophotographic apparatus of the 
present invention will be described with the help of FIG. 20 and FIG. 21. 
This embodiment is a modification of the previous exemplary embodiment, 
e.g., Example 5, and the structure of this embodiment is illustrated in 
FIG. 20. 
The structure shown in FIG. 20 differs from that of FIG. 6 in the use of a 
different device to produce magnetic field on the surface of the removing 
roller 21. More specifically, the difference is in having a non-rotary 
magnet 22 installed inside the removing roller 21 formed of two magnetic 
poles. 
FIG. 7 shows a chart of the distribution of the magnetic fluxes produced by 
the magnet 15 and the magnetic plate 27 and observed on the surface of the 
electrostatic latent image holding member 14 in the vertical direction. 
FIG. 11 shows a chart of the distribution of the magnetic fluxes produced 
by the magnet 22 and observed on the surface of the removing roller 21 in 
the vertical direction. FIG. 21 shows the positional relation between the 
magnet 15 inside the electrostatic latent image holding member 14 and the 
magnet 22 inside the removing roller 21. The angle .theta..sub.1 that the 
magnetic plate 27 installed inside the electrostatic latent image holding 
member 14 makes from the point where the surface of the electrostatic 
latent image holding member 14 comes closest to that of the removing 
roller 21 was set to .theta..sub.1 =40.degree. in the direction opposite 
to the rotation of the electrostatic latent image holding member 14, while 
the angle .theta..sub.2 of the N-pole of the magnet 15 inside the 
electrostatic latent image holding member 14 was set to .theta..sub.2 
=10.degree.. The angle .theta..sub.3 that the N-pole of the magnet 22 
installed inside the removing roller 21 makes the point where the surface 
of the removing roller comes closest to that of the electrostatic latent 
image holding member 14 was set to .theta..sub.3 =15.degree. in the 
direction opposite to the rotation of the removing roller, while the angle 
.theta..sub.4 of the S-pole of the magnet 22 was set to .theta..sub.4 
=+20.degree.. 
The range of said angle .theta..sub.1 is desirable to be 
15.degree.&lt;.theta..sub.1&lt; 50.degree., and the range of 
20.degree.&lt;.theta..sub.1 &lt;45.degree. in particular, is the most suitable 
range. The range of said angle .theta..sub.2 is desirable to be 
0.degree.&lt;.theta..sub.2 &lt;30.degree., and the range of said angle 
5.degree.&lt;.theta..sub.2 &lt;20.degree. in particular, is the most suitable 
range. The range of said angle .theta..sub.3 is desirable to be 
-30.degree.&lt;.theta..sub.3 &lt;10.degree., and the range of 
-20.degree.&lt;.theta..sub.3 &lt;0.degree., in particular, is the most suitable 
range The range of said angle .theta..sub.4 is desirable to be 
0.degree.&lt;.theta..sub.4 &lt;30.degree., and the range of said angle 
5.degree.&lt;.theta..sub.4 &lt;25.degree., in particular, is the most suitable 
range. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with the help of FIG. 20. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -4 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential of the electrostatic latent image holding 
member 14 was -100 V. A mono-component magnetic toner 20 was attached on 
the surface of said electrostatic latent image holding member 14 in the 
developer reservoir 19 by the magnetic force of the magnet 15 installed 
inside the electrostatic latent image holding member 14. Next, the toner 
attached on the electrostatic latent image holding member 14 was aligned 
in the peripheral direction along the magnetic field produced by the 
magnet 15 inside the electrostatic latent image holding member 14 to form 
a magnetic brush, and the resulting brush-like toner was transported by 
the friction force produced by the rotation of the electrostatic latent 
image holding member 14. Then, the electrostatic latent image holding 
member 14, having said toner layer attached to it, passed the front of the 
removing roller 21. An AC voltage (1 kHz in frequency) of 750 V.sub.O-p 
superimposed with a DC voltage of -300 V having a waveform as shown in 
FIG. 5 was applied to the removing roller 21 from the high voltage power 
source 23. The toner layer on the electrostatic latent image holding 
member 14 traveled between the electrostatic latent image holding member 
14 and the removing roller 21, and the toner attached on the non-image 
areas of the electrostatic latent image holding member 14 was gradually 
removed to the side of the removing roller 21. Only the toner images with 
a positive-negative picture reversal remained at the image areas of the 
electrostatic latent image holding member 14. The toner attached on the 
removing roller 21 was formed into a brush-like shape along the magnetic 
field produced by the magnet 22 inside the removing roller in the 
peripheral direction of the removing roller. The toner attached in a 
brush-like shape was transported by the friction force produced by the 
rotation of the removing roller 21, scraped off by the scraper 24, and 
returned into the developer reservoir 19. It was also observed in the 
upper areas of both the magnetic plate 27 inside the electrostatic latent 
image holding member 14 and the S-pole, inside the removing roller 21, 
that the toner was in a fierce turbulence. The toner images thus formed on 
the electrostatic latent image holding member 14 were transferred onto 
paper (not shown in FIG. 20) by means of the transfer corona charger 25. 
Then, after thermally fixing by means of a fixing equipment (not shown in 
FIG. 20), printed images were obtained. As a result, sharp images of high 
image density and substantially lacking in non-uniformity in density 
without showing any background development or image hysteresis were 
obtained. On the other hand, the toner left on the electrostatic latent 
image holding member 14 after transferring of the toner images onto paper 
was transported by the rotation of the electrostatic latent image holding 
member 14, and collected by the cleaner 26. 
The operation and features of the electrophotographic apparatus of the 
present example are substantially the same as explained above in Example 
5. 
EXAMPLE 8 
An electrophotographic apparatus whereby excellent images of high image 
density without showing any non-uniformity of image density even at a 
higher printing speed are obtainable will be described as an exemplary 
eighth embodiment of the present invention with the help of FIG. 22. 
FIG. 22 shows the structure of an electrophotographic apparatus having a 
processing speed of 180 mm/s. The structure of FIG. 22 differs from that 
of FIG. 1 in the number of magnetic poles of the magnet 15 installed 
inside the electrostatic latent image holding member 14 and the roughness 
of the surface of the electrostatic latent image holding member 14. More 
specifically, the number of magnetic poles of the magnet 15 is one, and 
further the surface of the electrostatic latent image holding member 14 is 
made rough, e.g., by sand blasting, to have roughness of 0.8 .mu.m with 
the present example. 
Because of said blasting treatment, the friction force between the surface 
of the electrostatic latent image holding member 14 and the developer, 
e.g., the toner, has been effectively increased. Other parts of the 
structure shown in FIG. 22 are the same as those of FIG. 1, and the same 
explanation made with reference to the symbols of FIG. 1 applies to the 
ones of FIG. 22. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with the help of FIG. 22. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -6 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential of the electrostatic latent image holding 
member 14 was -100 V. Mono-component magnetic toner was attached on the 
surface of said electrostatic latent image holding member 14 in the 
developer reservoir 19 by the magnetic force of the magnet 15. The toner 
attached on the electrostatic latent image holding member 14 was 
transported without any slipping by the strong friction force working 
between the toner and the surface of the electrostatic latent image 
holding member 14. Then, the electrostatic latent image holding member 14, 
having said toner layer attached thereto, passed the front of the removing 
roller 21. An AC voltage (1 kHz in frequency) of 750 V.sub.O-p 
superimposed with a DC voltage of -300 V having a waveform as shown in 
FIG. 5 was applied to the removing roller 21 from the high voltage power 
source 23. The toner layer on the electrostatic latent image holding 
member 14 traveled between the electrostatic latent image holding member 
14 and the removing roller 21, and the toner attached on the non-image 
areas of the electrostatic latent image holding member 14 was gradually 
removed to the side of the removing roller 21. Only the toner images with 
a positive-negative picture reversal remained at the image areas of the 
electrostatic latent image holding member 14. The toner attached on the 
removing roller 21 was transported by the rotation of the removing roller 
21 in the direction of the arrow shown in FIG. 22, scraped off by the 
scraper 24, and returned into the developer reservoir 19. The toner images 
thus formed on the electrostatic latent image holding member 14 were 
transferred onto paper (not shown in FIG. 22) by means of the transfer 
corona charger 25. Then, after thermally fixing by means of a fixing 
equipment (not shown in FIG. 22), printed images were obtained. On the 
other hand, the toner left on the electrostatic latent image holding 
member 14 after transferring of the toner images onto paper was 
transported by the rotation of the electrostatic latent image holding 
member 14, and collected by the cleaner 26. 
As a result, sharp images of high image density and free of non-uniformity 
in image density were obtained. 
As explained above, the structure of the present example features a means 
to multiply the friction force between the surface of the electrostatic 
latent image holding member 14 and the developer. 
Accordingly, because of the increased friction force between the 
electrostatic latent image holding member and the toner, the toner can be 
transported by the rotation of the electrostatic latent image holding 
member without any slipping, and the capability of supply and 
transportation of toner can be greatly enhanced, and further the problem 
of uneven transportation of toner due to slippage can be eliminated. 
Therefore, because the toner supplied to the surface of the electrostatic 
latent image holding member can be fed to development areas in abundance 
and in a stabilized manner, excellent image quality of high image density 
and free of non-uniformity in image density can be realized even under the 
conditions of high temperature, high humidity, and high speed processing. 
Besides, even when the surface roughness of the electrostatic latent image 
holding member 14 is 0.5, it was possible to gain the same excellent 
results as described above. 
Further, although the surface of the electrostatic latent image holding 
member 14 was treated by blasting in the present example, it is also 
possible to gain the same effect by making fine grooves on the surface of 
the electrostatic latent image holding member 14 or by increasing 
roughness of that surface by any other suitable method. More specifically, 
the friction force between the surface of the electrostatic latent image 
holding member 14 and the toner is increased remarkably by grooving. As a 
result, the toner supplied is transported without slippage and sharp 
images of high image density and free of non-uniformity in image density 
are obtained. 
EXAMPLE 9 
Next, an electrophotographic apparatus whereby excellent images of high 
image density without showing any non-uniformity of image density even at 
a higher printing speed are obtainable will be described as another 
exemplary embodiment (the ninth embodiment) of the present invention with 
the help of FIG. 23 and FIG. 24. 
FIG. 23 shows the structure of an electrophotographic apparatus having a 
processing speed of 180 mm/s. FIG. 24 is an enlarged cross-sectional view 
of the rise and fall of the surface of the removing roller 21 which is 
included in the electrophotographic apparatus shown in FIG. 23. The 
structure of the apparatus of FIG. 23 differs from that of FIG. 9 in the 
number of magnetic poles of the magnet 22 installed inside the removing 
roller 21 and the roughness of the surface of the removing roller 21. More 
specifically, the number of magnetic poles of the magnet 22 is one and 
further the surface of the removing roller 21 has fine grooves running in 
parallel with the axial direction on the surface of the removing roller as 
shown in FIG. 24. 
The operation of the electrophotographic apparatus constructed as described 
above will be explained hereunder with the help of FIG. 23. 
The electrostatic latent image holding member 14 was charged to -500 V by 
means of the corona charger 16 and the grid electrode 17. (The applied 
voltage was -6 kV and the grid electrode voltage was -500 V.) Then, an 
electrostatic latent image was formed by irradiation of the laser signal 
light 18 on said electrostatic latent image holding member 14. At this 
time, the exposure potential of the electrostatic latent image holding 
member 14 was -100 V. Mono-component magnetic toner was attached on the 
surface of said electrostatic latent image holding member 14 in the 
developer reservoir 19 by the magnetic force of the magnet 15. Then, the 
electrostatic latent image holding member 14, having said toner layer 
attached thereto, passed the front of the removing roller 21. An AC 
voltage (1 kHz in frequency) of 750 V.sub.O-p superimposed with a DC 
voltage of -300 V having a waveform as shown in FIG. 5 was applied to the 
removing roller 21 from the high voltage power source 23. The toner layer 
on the electrostatic latent image holding member 14 traveled between the 
electrostatic latent image holding member 14 and the removing roller 21, 
and the toner attached on the non-image areas of the electrostatic latent 
image holding member 14 was gradually removed to the side of the removing 
roller 21. Only the toner images with a positive-negative picture reversal 
remained at the image areas of the electrostatic latent image holding 
member 14. The toner attached on the removing roller 21 was transported by 
the rotation of the removing roller 21 in the direction of the arrow, 
shown in FIG. 23, without slippage because of the strong friction force 
caused by the grooves made on the surface of the removing roller 21, 
scraped off by the scraper 24, and returned into the developer reservoir 
19. The toner images thus formed on the electrostatic latent image holding 
member 14 were transferred onto paper (not shown in FIG. 23) by means of 
the transfer corona charger 25. Then, after thermally fixing by means of a 
fixing equipment (not shown in FIG. 23), printed images were obtained. On 
the other hand, the toner left on the electrostatic latent image holding 
member 14, after transferring of the images onto paper, was transported by 
the rotation of the electrostatic latent image holding member 14, and 
collected by the cleaner 26. As a result, sharp images of high image 
density and free of non-uniformity in image density were obtained. 
As explained in the foregoing, the structure of the present example 
features a means to multiply the friction force between the surface of the 
electrostatic latent image holding member 14 and the toner, i.e., the 
developer. 
Accordingly, because of the increased friction force of the removing roller 
against the toner, the toner can be transported by the rotation of the 
removing roller without any slipping, and the collection capability of the 
toner can be greatly enhanced, and further the problem of uneven 
transportation of toner due to slippage can be solved. Therefore, because 
the slightly charged toner collected by the removing roller can be removed 
from the areas vibrated by an AC bias voltage sufficiently and in a 
stabilized manner, excellent image quality of high image density and free 
of non-uniformity in image density can be realized even under the 
conditions of high temperature, high humidity and high speed processing. 
Besides, it is possible to make the roughness of the surface of the 
removing roller 21 more than 0.5 .mu.m by blasting or to have the surface 
of the removing roller 21 lined with a conductive layer of resin mulled 
together with carbon to remarkably increase the friction force between the 
surface of the removing roller 21 and the toner. As a result, the toner 
collected is transported without slippage, and sharp images free of 
background development and non-uniformity in image density are obtained. 
EXAMPLE 10 
Next, an electrophotographic apparatus whereby excellent images of high 
image density without showing any non-uniformity of image density even at 
a higher printing speed are obtainable will be described as another 
exemplary embodiment (the tenth embodiment) of the present invention with 
the help of FIG. 25. 
FIG. 25 shows the structure of an electrophotographic apparatus having a 
processing speed of 180 mm/s. The structure of the apparatus of FIG. 25 
differs from that of FIG. 1 in the roughness of the surface of the 
electrostatic latent image holding member 14. More specifically, the 
surface of the electrostatic latent image holding member 14 is treated by 
blasting to have roughness of 0.5 .mu.m. Because of said blasting 
treatment, the friction force between the surface of the electrostatic 
latent image holding member 14 and the developer, e.g., the toner, is 
effectively increased. 
Other parts of the structure shown in FIG. 25 are the same as those of FIG. 
1, and the same explanation as made regarding the symbols of FIG. 1 
applies to those of FIG. 25. 
The structure of the present example comprises a magnetic field generating 
means installed inside the electrostatic latent image holding member 14 
for producing two magnetic poles, and a means for increasing the friction 
force between the surface of the electrostatic latent image holding member 
14 and the developer disposed on the electrostatic latent image holding 
member. 
Accordingly, because the toner attached on the electrostatic latent image 
holding member can be transported sufficiently to the developing areas by 
magnetic force and the toner can be transported by the rotation of the 
electrostatic latent image holding member without any slipping due to the 
increased friction force between the electrostatic latent image holding 
member and the toner, the capability of supply and transportation of toner 
can be greatly enhanced, and further the problem of uneven transportation 
of toner due to slippage can be solved. 
Therefore, because the toner supplied to the surface of the electrostatic 
latent image holding member can be fed to developing areas in abundance 
and in a stabilized manner, excellent image quality of high image density 
and free of non-uniformity in image density can be realized even under the 
conditions of high temperature, high humidity, and high speed processing. 
EXAMPLE 11 
Next, an electrophotographic apparatus whereby excellent images of high 
image density without showing any non-uniformity of image density even at 
a higher printing speed are obtainable will be described as still another 
exemplary embodiment (the eleventh embodiment) of the present invention 
with the help of FIG. 26. 
FIG. 26 shows the structure of an electrophotographic apparatus having a 
processing speed of 180 mm/s. The structure of the apparatus of FIG. 26 
differs from that of FIG. 9 in the roughness of the surface of the 
removing roller 21. More specifically, the surface of the removing roller 
21 is treated by sand blasting to provide that surface the roughness of 
0.5 .mu.m. Aside from this modification, the structure and operation of 
this embodiment is substantially the same as that of the embodiment of 
FIG. 9. 
The structure of the apparatus of the present example comprises a magnetic 
field generating means installed inside the removing roller for producing 
two magnetic poles, and a means for increasing the friction force between 
the surface of the removing roller and the toner, i.e., the developer, 
disposed on the removing roller. 
Accordingly, the toner collected to the removing roller can be removed 
sufficiently from the developing areas by magnetic force and further the 
capability of toner collection can be greatly enhanced because the 
friction force between the removing roller and the toner is increased and 
the toner is transported by the rotation of the removing roller without 
slippage, and still further the problem of uneven transportation of the 
toner due to slippage can be solved. Therefore, because the slightly 
charged toner collected by the removing roller can be removed from the 
areas vibrated by an AC bias voltage, the toner can be removed 
sufficiently and in a stabilized manner. Additionally, excellent image 
quality of high image density and free of non-uniformity in image density 
can be realized even under the conditions of high temperature, high 
humidity, and high speed processing. 
EXAMPLE 12 
Next, an electrophotographic apparatus whereby excellent images of high 
image density without showing any non-uniformity of image density even at 
a higher printing speed are obtainable will be described as still another 
exemplary embodiment (the twelfth embodiment) of the present invention 
with the help of FIG. 27. 
FIG. 27 shows the structure of an electrophotographic apparatus having a 
processing speed of 180 mm/s. The structure of the apparatus of FIG. 27 
differs from that of FIG. 16 in the roughness of the surfaces of the 
electrostatic latent image holding member 14 and the removing roller 21. 
More specifically, the surfaces of the electrostatic latent image holding 
member 14 and the removing roller 21 are treated by blasting to have 
roughness of 0.5 .mu.m, respectively. 
The structure of the apparatus of the present example comprises a magnetic 
field generating means for producing two magnetic poles of polarity 
different from each other on the surface of the electrostatic latent image 
holding member, a means for increasing the friction force of the surface 
of the electrostatic latent image holding member, a magnetic field 
generating means installed inside the removing roller 21 for producing two 
magnetic poles, and a means for increasing the friction force between the 
surface of the removing roller and the developer, e.g., the developer 
disposed on the removing roller. 
Accordingly, because the toner attached on the electrostatic latent image 
holding member can be transported sufficiently to the developing areas by 
magnetic force and the toner can be transported by the rotation of the 
electrostatic latent image holding member without any slipping because of 
the increased friction force between the electrostatic latent image 
holding member and the toner, the capability of supply and transportation 
of toner can be greatly enhanced. 
Further, the capability of toner collection can be greatly enhanced because 
the friction force between the removing roller and the toner is increased 
and the toner is transported by the rotation of the removing roller 
without slipping, and the problem of uneven transportation of toner due to 
slippage can also be solved. 
Therefore, because the toner supplied to the surface of the electrostatic 
latent image holding member can be fed to developing areas in abundance 
and in a stabilized manner, the slightly charged toner collected by the 
removing roller can be removed from the areas vibrated by an AC bias 
voltage sufficiently and in a stabilized manner, excellent image quality 
free of background development and non-uniformity in image density can be 
realized even under the conditions of high temperature, high humidity, and 
high speed processing. 
The embodiments described above are merely exemplary in nature and should 
not be considered to limit the scope of the invention, which is directed 
to any and all possible modifications falling within the spirit and scope 
of the invention described and claimed herein. 
For example, the invention encompasses an electrophotographic apparatus 
appropriately combining such a variety of means as producing magnetic 
field from two magnetic poles having polarity different from each other on 
the surface of an electrostatic latent image holding member, increasing 
the friction force of the surface of said electrostatic latent image 
holding member, producing two magnetic poles having polarity different 
from each other on the surface of a removing roller, increasing the 
friction force of the surface of the removing roller, and any other 
suitable combination of features described above. 
The embodiments described above provide a number of significant advantages. 
Since the magnetic force, generated by the magnetic field generating means 
having two opposing magnetic poles, in the electrostatic latent image 
holding member 14 and/or the removing roller 21, forces the toner to align 
in a brush-like shape (also referred to herein as a "magnetic brush"), the 
transporting force is applied to the entire brush-like shape, which 
substantially intensifies the transporting force. Additionally, the 
unevenness in the transporting force, due to non-uniformity of frictional 
forces among the individual toner particles is substantially eliminated. 
The provision of a means for increasing the friction force against the 
developer on the electrostatic image holding member 14 and/or the removing 
roller 21 intensifies these advantages. All of these improvements 
contribute to the production of improved images having relatively high 
resolution which are substantially free of non-uniformity in image 
density. 
Of course, it should be understood that a wide range of changes and 
modifications can be made to the preferred embodiments described above. It 
is therefore intended that the foregoing detailed description be regarded 
as illustrative rather than limiting, and that it be understood that it is 
the following claims, including all equivalents, which are intended to 
define the scope of this invention.