Image developing device using a one-component toner

An elastic member for pressing is provided in a prescribed location in an area where the developer carrier comes in contact with the discharging member, in order to bring the discharging member into contact with the developer carrier so that mechanical peeling of the residual developer on the developer carrier is not caused, and the discharging member is provided with a bias power supply for setting bias in a direction imparting to the discharging member a force for electrically drawing the residual developer on the developer carrier away from the developer carrier, and after thus reducing the electric adhesion of the residual developer to the developer carrier, the developer feed member removes the residual developer on the developer carrier in the vicinity of disjunction area or in the contact area of the developer carrier and the developer feed member, thereafter applies new developer in a developer container to the developer carrier in the vicinity of approaching area or in the contact-starting area of the developer carrier and the developer feed member.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a developing device using one-component 
toner, more specifically, relates to a developing device used for an image 
forming device such as copying machines using electrophotography, printers 
and electrostatic recording devices. 
(2) Description of the Related Art 
The developing device using one-component toner is easy to reduce the size 
and easy to handle, but there is a problem in transferring and charging 
the toner and making the toner uniformly thin. A general developing device 
will now be described with reference to FIG. 1. 
As shown in FIG. 1, an electrostatic image is formed on the surface of a 
photosensitive drum 51, which is an electrostatic latent image carrier, by 
means of a latent image-forming means (not shown). A developing roller 100 
is disposed in a position opposite to the photosensitive drum 51 as a 
developer carrier, and on the surface of the developing roller 100, toner 
2 which is the developer is adhered. The development is carried out by 
adhering the toner 2 to the photosensitive drum 51 to visualize the 
electrostatic image. The charged toner 2 is formed in a thin layer on the 
developing roller 100. 
As for the means for forming toner in a thin layer, the toner 2 is first 
supplied and adhered on the developing roller 100 by a toner feed roller 
200 which is a developer feed member brought into contact with the 
developing roller 100 and is connected to a bias power supply 210 for 
feeding toner. Thereafter, the toner 2 on the developing roller 100 is 
formed uniformly in a thin layer by a blade 300 which is a developer 
regulating member, as the developing roller 100 rotates. Furthermore, 
voltage for the developing bias is impressed to the developing roller 100 
by a power supply 110 and blade bias voltage is impressed to the blade 300 
by a power supply 390. 
With such a developing device 1b using one-component developer, however, 
when the residual toner adhered to the developing roller 100 is not 
removed after the development, the developing pattern formed by the 
residual toner remains until the next development, resulting in a memory 
image. To solve this problem, a Mylar sheet 430 (a residual toner removing 
member) abutting to the developing roller 100 after the development is 
newly provided to scratch the residual toner on the developing roller 100. 
With the developing device using conventional non-magnetic developer 
(hereinafter referred to as "toner"), as a method for supplying the toner, 
there have been disclosed many methods, such as the one using an elastic 
foamed body which is disclosed in Japanese Unexamined Patent Publication 
No. Hei 2-191974. The one using the elastic foamed body as the method for 
supplying the toner is capable of supplying the toner to the developer 
carrier (hereinafter referred to as a "developing roller"), but it has 
been difficult to remove the residual toner on the developing roller which 
passed through the developing zone. In particular, when the supply voltage 
having the same polarity as the charging polarity of the toner is 
impressed in order to supply toner sufficiently and stably, removal of the 
residual toner on the developing roller becomes more difficult. As a 
result, in the toner layer on the developing roller, toner which was not 
consumed in the developing zone and toner newly supplied by the developing 
roller mingle together to deteriorate the developing properties and cause 
a development history (development unevenness). 
Therefore, as disclosed in Japanese Patent Publication No. Sho 60-7790, 
there is a method in which a roller for recovering the residual toner from 
the developing roller is provided in a prescribed location, and bias 
voltage having the opposite polarity to the charged polarity of the toner 
is impressed on the recovering roller to remove the residual toner on the 
developing roller after it passed through the developing zone. With this 
method, however, a roller for recovering the toner is separately required, 
and the cost increases. 
Moreover, as disclosed in Japanese Patent No. 2557826 (issued in 1996), 
there is a method in which a thin plate having elasticity is brought into 
contact with the developing roller to remove the residual toner on the 
developing roller. Moreover, there is another method in which a thin plate 
is brought into contact with the developing roller and bias voltage is 
impressed to the thin plate to remove the residual toner on the developing 
roller. 
With these methods, when the residual toner on the developing roller is 
removed, it is necessary to bring the toner removing member into deep 
contact with the developing roller. Furthermore, in the case of removing 
the residual toner on the developing roller electrically, the discharging 
effect is increased by pressing the toner removing member into deep 
contact with the developing roller and enlarging the contact area. 
As a result, a mechanical stress is applied to the residual toner on the 
developing roller, and the toner is easily deteriorated, thus 
deterioration of the developing properties, such as filming of the toner 
on the surface of the developing roller may be caused. 
On the other hand, with the technique disclosed in Japanese Unexamined 
Patent Publication No. Hei 2-191974, it is described therein that the cell 
density of the elastic foamed body is preferably from 10 cells per 25 mm 
to 200 cells per 25 mm, and cells are brought into contact with each other 
so that the contact depth is from 0.5 mm to 2 mm and the contact width is 
from 0.2 mm to 5 mm, or cells are closely arranged so that the distance 
between the both surfaces is not larger than 2 mm. However, the 
above-mentioned cell density corresponds to the cell density of almost all 
foamed elastic body, and there may be a problem occurred at the time of 
actual use. For example, if the cell density is low, the toner easily 
penetrates into the foamed cell of the elastic foamed body to make the 
elastic foamed body hard. As a result, increase of the driving torque of 
the feed roller or decrease of the volume of toner transferred by the feed 
roller is caused. On the contrary, if the cell density is high, the toner 
cannot easily penetrate into the foamed cell of the elastic foamed body, 
but the volume of toner transferred by the feed roller decreases. As a 
result, the density necessary for development cannot be obtained, and 
since the hardness of the elastic foamed body itself is high, the torque 
increases, the contact pressure between the developing roller and the feed 
roller becomes high, and the toner is subjected to the mechanical stress 
and becomes easily deteriorated. 
Furthermore, since the contact conditions has a wide range, the feed 
properties differ largely. For example, if the contact depth is large, the 
contact pressure between the developing roller and the feed roller becomes 
high, the driving torque of both rollers increases, and the toner is 
subjected to the mechanical stress and easily deteriorated. On the 
contrary, if the contact depth is small, the capability of the feed roller 
to apply the toner to the developing roller decreases, and the feed roller 
cannot feed the toner sufficiently. In addition, the accuracy of the outer 
diameter of the feed roller is required, but the preparation thereof with 
the elastic foamed body is difficult. 
Furthermore, with a feeding method using an elastic foamed body as a feed 
member, the developing roller and the feed member are brought into contact 
with each other. In this case, the developing roller having hardness 
higher than that of the feed roller is normally used. For example, as a 
material of the developing roller, a metal sleeve or an elastic solid 
rubber is often used. Therefore, in the contact area of the developing 
roller and the feed roller, modified feed rollers using an elastic foamed 
body having hardness lower than that of the developing roller accounts for 
the majority thereof, and the state of the contact pressure between the 
developing roller and the feed roller is mostly determined by the hardness 
of the feed roller. That is to say, even if the contact depth of the 
developing roller and the feed roller is the same amount, if the hardness 
of the feed roller is high, the pressure in the contact area of the 
developing roller and the feed roller increases, on the contrary, if the 
hardness of the feed roller is low, the pressure in the contact area 
decreases. 
Furthermore, with a toner feeding method using an elastic foamed body, 
toner adhered on the surface of the feed roller and toner infiltrating 
shallowly into the inside of cells are transferred to the surface of the 
developing roller, as the feed roller rotates. The toner which has reached 
the contact area of the developing roller and the feed roller is 
frictionally charged and moves to the surface of the developing roller. At 
that time, however, the toner transferred to the surface of the developing 
roller is only the toner existing close to the outermost layer on the 
surface of the feed roller, and the quantity of toner mechanically applied 
to the developing roller decreases, hence poor supply of toner is easily 
caused on the developing roller. At the time of developing solid black, 
sufficient image density cannot be obtained. 
Therefore, when the followability of the image density at the time of 
printing solid black is kept during development, if supply bias having the 
same polarity as the charging polarity of the toner is applied to the 
toner feed roller in order to feed toner sufficiently and stably, the 
effect of discharging member obtained by mechanically removing the 
residual toner on the developing roller with the feed roller is hardly 
obtained. That is to say, the electric adhesion of the residual toner with 
the developing roller after passing through the developing zone is 
decreased by the discharging member, but by applying the supply bias to 
the feed roller, the residual toner removed by the mechanical force of the 
feed roller adheres again on the surface of the developing roller due to 
the electric field in the feeding direction of the toner, formed between 
the developing roller and the feed roller, in the vicinity of disjunction 
or in the contact area of the feed roller and the developing roller. As a 
result, there is a possibility to cause a difference in the charge 
quantity or a difference in the adhesion quantity per unit area between 
the residual toner on the developing roller and the newly supplied toner, 
and it appears as density unevenness (development history) on the output 
image. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a 
developing device which can carry a toner to a developing zone so that 
there is no development history on a developing roller. 
It is another object of the present invention to provide a developing 
device which can increase chances for discharging a toner in the contact 
area between the developing roller and a discharging member, and can be 
set so that the toner in the contact area is not mechanically removed. 
It is a further object of the present invention to provide a developing 
device which can maintain the capability of supplying a toner stably to a 
developing roller and the capability of removing the residual toner on the 
developing roller regardless of the lapse of time. 
It is still another object of the present invention to provide a developing 
device where a developer feed member has compatibly both capabilities of 
supplying a developer to and removing a residual developer from a 
developer carrier. 
It is a still further object of the present invention to provide a 
developing device which can obtain sufficient image density even at the 
time of developing solid black. 
To attain the above-mentioned objects, the gist of the present invention 
has the following constructon. 
The first gist of the present invention is an electrostatic latent image 
developing device comprising: a developer carrier for supporting and 
carrying one-component developer on the surface thereof; a developer feed 
member for abutting against the developer carrier and feeding the 
developer to the developer carrier; and a discharging member for 
discharging the developer on the developer carrier after development, in 
which residual developer on the developer carrier is removed, wherein an 
elastic member for pressing is provided in a prescribed location in an 
area where the developer carrier comes in contact with the discharging 
member, in order to bring the discharging member into contact with the 
developer carrier so that mechanical peeling of the residual developer on 
the developer carrier is not caused, the discharging member is provided 
with a bias power supply for setting bias in a direction imparting to the 
discharging member a force for electrically drawing the residual developer 
on the developer carrier away from the developer carrier, and after thus 
reducing the electric adhesion of the residual developer to the developer 
carrier, the developer feed member removes the residual developer on the 
developer carrier in the vicinity of disjunction area or in the contact 
area of the developer carrier and the developer feed member, thereafter 
applies new developer in a developer container to the developer carrier in 
the vicinity of approaching area or in the contact-starting area of the 
developer carrier and the developer feed member. 
The second gist of the present invention is a developing device according 
to the first gist, wherein the elastic member for pressing has the Asker F 
hardness of not higher than 70.degree.. 
The third gist of the present invention is a developing device according to 
the first gist, wherein the developer feed member comprises an elastic 
foamed body having the number of foaming cells of from 80/in. to 140/in., 
the developer feed member abuts against the developer carrier with a 
contact depth of from 0.5 mm to 1 mm, feeds the developer to the developer 
carrier in proximity to or in the contact area with the developer carrier, 
and removes the residual toner on the developer carrier in the disjunction 
or contact area thereof. 
The fourth gist of the present invention is a developing device according 
to the first gist, wherein the developer feed member comprises an elastic 
foamed body having the Asker F hardness of 60.degree. to the Asker C 
hardness of 30.degree.. 
The fifth gist of the present invention is a developing device according to 
the first gist, wherein the developer feed member is an electroconductive 
elastic foamed body having a resistance of from 10.sup.4 to 10.sup.7 
.OMEGA., and bias voltage of the same polarity as the charging polarity of 
the developer on the developer carrier is applied to the developer feed 
member. 
The sixth gist of the present invention is a developing device according to 
the first gist, wherein the following formula is satisfied: 
EQU .vertline.Vc.vertline.-50.ltoreq..vertline.Vt.vertline..ltoreq..vertline.Vc 
.vertline.+100 (V) 
with regard to the bias voltage Vt (V) impressed to the developer feed 
member and the bias voltage Vc (V) impressed to the discharging member. 
The seventh gist of the present invention is a developing device according 
to the first gist, wherein the discharging member is a thin plate-like 
member of an electroconductive elastic body, and bias voltage having a 
polarity opposite to the charging polarity of the developer is impressed 
to the discharging member. 
The eighth gist of the present invention is a developing device according 
to the seventh gist, wherein the discharging member in the thin plate-like 
member comprises polycarbonate, polybutyl terephthalate, and has carbon 
black a resistance of from 10.sup.3 to 10.sup.6 .OMEGA.. 
The ninth gist of the present invention is a developing device according to 
the first gist, wherein the discharging member and the developer carrier 
abut against each other in the contact area in the axial direction wider 
than the developer carrying area on the developer carrier. 
Herein after a developer carrier, a developer, a developer feed member, a 
residual developer, and elastic member are also called "developing 
roller", "toner", "feed roller", "residual toner" and "elastic foamed 
body", respectively. 
According to the first gist, it becomes possible to provide an elastic 
foamed body between the surface opposite to the contacting surface of the 
thin plate-like discharging member with the developing roller, and the 
developer container, for example, in a contact area of the thin plate-like 
discharging member and the developing roller, so that the abutting force 
between the developing roller and the thin-plate elastic body which is a 
discharging member can be reduced and the contact area between the 
developing roller and the discharging member can be sufficiently secured, 
to reduce the abutting force between the developing roller and the thin 
plate-like discharging member and to enlarge the contact area between 
them. Hence, electric discharging is performed in the contact area of the 
developing roller and the discharging member, without mechanically peeling 
off the residual toner on the developing roller, and after reducing the 
electric attraction working between the developing roller and the residual 
toner, the residual toner on the developing roller is mechanically removed 
in the contact area of the feed roller and the developing roller, or in 
the vicinity of disjunction of them, and the developing roller is provided 
with new toner in the area where the developing roller is close to the 
feed roller or in the contact area therewith. As a result, toner without 
having any development history onto the developing roller can be 
transferred and to the developing zone. 
According to the second gist, after one end of the ends of the thin-plate 
discharging member is fixed to the developing container, the free end 
thereof is brought into contact with the developing roller, and an elastic 
foamed body is provided on the opposite side of the contact surface of the 
discharging member and the developing roller in the contact area, and the 
sponge hardness of the elastic foamed body is set to be not higher than 
70.degree. as measured by the Asker F hardness, thereby the contact area 
between the developing roller and the thin-plate discharging member can 
the enlarged, without increasing the contact pressure between the 
developing roller and the thin-plate discharging member. As a result, a 
chance of discharging the toner in the contact area between the developing 
roller and the discharging member increases, without mechanically removing 
the toner in the contact area. 
According to the third gist of the present invention, the foamed cell 
density is limited to a range of from 80 cells per in. to 140 cells per 
in., and the contact depth of the developing roller and the feed roller is 
limited to a range of from 0.5 mm to 1 mm, thereby stable feed capability 
and removal capability of the residual toner on the developing roller can 
be maintained for a long period of time. 
According to the fourth gist, by limiting the hardness of the elastic 
foamed body used for the feed roller in the range of from the Asker F 
hardness of 60.degree. to the Asker C hardness of 30.degree., the residual 
toner on the developing roller can be removed, and at the same time, new 
toner can be supplied onto the surface of the developing roller. That is, 
the removal capability and the feed capability can be compatible in the 
feed roller. 
According to the fifth gist, by using an electriconductive elastic foamed 
body as the developer feed member, limiting the resistance value thereof 
in a range of from 10.sup.4 to 10.sup.7 .OMEGA., and impressing bias 
voltage of the same polarity as the charging polarity of the toner on the 
developing roller to the developer feed roller, the above-mentioned bias 
voltage is impressed in the contact area of the developing roller and the 
feed roller, an electric field is formed in the moving direction of the 
charged toner toward between the developing roller and the feed roller. As 
a result, it becomes possible to apply the frictionally charged toner 
sufficiently onto the developing roller, in the vicinity of the contact 
area of the developing roller and the feed roller, hence sufficient image 
density can be obtained even at the time of developing solid black. 
According to the sixth gist of the present invention, by deciding the 
conditions of impressing the supply bias voltage and the discharging bias 
voltage within the range of the above-mentioned formula, with regard to 
the discharging bias applied to the discharging member and the supply bias 
for sufficiently supplying the toner to the developing roller, stable 
toner supply to the developing roller from which the residual toner has 
been removed can be realized, and the effect of removing the residual 
toner on the developing roller and the feed roller by discharging them 
after passing through the developing zone can be improved, without causing 
a development history. 
According to the seventh gist of the present invention, by using an 
electriconductive material for the thin-plate discharging member, 
discharging of the residual toner on the developing roller can be easily 
performed. 
According to the eighth gist of the present invention, the discharging 
member in a thin plate-like form comprises polycarbonate, polybutyl 
terephthalate, and carbon black, thereby the discharging member having 
electroconductivity and excellent wear resistance can be used for the 
elastic thin plate-like member. 
According to the ninth gist of the present invention, the length of the 
discharging member in the axial direction of the developing roller is made 
longer than the area where the developing roller carries toner to the 
electrostatic latent image, in other word, the adhesion area of the toner 
which adheres in the axial direction of the developing roller, thereby the 
discharging member can be brought into contact with the developing roller 
so that the discharging effect can be obtained with respect to the entire 
toner on the developing roller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiments of the present invention will now be described with 
reference to the accompanying drawings. 
FIG. 2 is a schematic sectional view showing diagram of a reversal 
developing device using negatively charged non-magnetic one component 
toner according to an embodiment of the present invention, wherein a 
developing device (developing unit) 1 is so disposed as to oppose a 
photosensitive drum (OPC drum) 51 on which an electrostatic latent image 
is formed by a latent image forming means (not shown). 
The developing device 1 has a developing roller 100 which is a developer 
carrier, a toner feed roller 200 which is a developer feed member, a toner 
layer restraining blade 300 which is a developer restraining member, a 
developer container 20 for accommodating toner 10, and respective power 
supplies (a power supply 110 for developing bias which applies developing 
bias voltage to the developing roller 100, a power supply 210 for toner 
supply bias which supplies bias power to the toner feed roller 200, and a 
power supply 390 for blade bias which applies blade bias voltage to the 
blade 300). 
In the developing device 1, the toner feed roller 200 is pressed to come in 
contact with the developing roller 100, and the rotation direction of the 
toner feed roller 200 is so set that it is in the opposite direction to 
the rotation (proceeding) direction of the developing roller 100 at the 
portion where it faces the developing roller 100. Therefore, the 
developing roller 100 and the toner feed roller 200 slide in contact with 
each other at the opposing portion. 
The toner feed roller 200 is formed using the same material as that of the 
developing roller 100, and it is possible to adjust the electric 
resistance by using a resistance-adjusting material similar to that for 
the developing roller 100. To further increase the elasticity of the toner 
feed roller 200, a foamed material is used for the toner feed roller 200, 
and the amount of the foaming agent used to prepare the feed roller 200 is 
larger than the amount used for the developing roller 100. Voltage is 
applied to the toner feed roller 200 from the bias power supply 210, and 
in general, large bias voltage is applied to the feed roller 200 in the 
direction pushing the toner toward the developing roller 100, for example, 
if an negative toner is used, large bias voltage is applied to the toner 
feed roller 200 on the negative electrode side. The toner 10 supplied to 
the developing roller 100 by the toner feed roller 200 is transferred to a 
position where the blade 300 which is a member for restraining the 
thickness of the toner layer abuts against the developing roller 100 with 
the rotation of the developing roller 100. 
The blade 300 made of a plate-like metal material is pressed to the 
developing roller 100 at the inner portion near the tip thereof. The toner 
10 supplied to the developing roller 100 is restrained to a predetermined 
charge quantity and thickness depending upon a predetermined set pressure 
and set position of the blade 300, transferred to the developing zone (a 
portion T facing the photosensitive material) and comes into the 
developing process. Furthermore, voltage is impressed to the blade 300 
from the bias power supply 390, and there are cases where large bias 
voltage is impressed to the blade 300 in the direction pressing the toner 
10 to the developing roller 100, for example, if an negative toner is 
used, on tile negative electrode side, and where bias voltage is impressed 
so that the blade has the same potential as that of the developing roller 
100. 
For example, with this embodiment, an negative toner (negatively charged 
toner) is used as the toner, and the surface potential of the toner layer 
is from about -30 (V) to about -50 (V), though it depends upon the kind of 
toner (the difference of the saturated charge quantity of the toner). 
With regard to the discharging bias and the supply bias, respective effects 
can be obtained by having a potential difference with the developing 
roller 100. Therefore, when -500 (V) of the developing bias is applied 
between the photosensitive material 51 and the developing roller 100, 
other bias conditions will be as described below. That is, Discharging 
bias=-300 (V) (potential difference with the developing roller=+200 (V)), 
Supply bias=-700 (V) (potential difference with the developing roller=-200 
(V)), and blade bias=-600 (V) (potential difference with the developing 
roller=-100 (V)). 
The undeveloped toner on the developing roller 100 which has not been used 
in the developing process returns to the developing device 1 with the 
rotation of the developing roller 100. However, the charging force is 
removed by a toner discharging device/means on the developing roller 100 
installed after the developing zone and before the feed roller 200, and 
thereby, the undeveloped toner is peeled and recovered to a hopper by 
pressing at the entrance of the feed roller 200 and reused. 
The blade 300 used for forming the toner layer is phosphor bronze plate 
having a plate thickness of 0.1 mm, and abuts against the developing 
roller 100 at about 30 gf/cm. As the blade material, stainless, copper, 
brass or the like may be used. It is also possible to apply a material 
contributing to the toner charging and having excellent wear resistance on 
the blade 300, and bring it into contact with the developing roller. 
The toner 10 is a non-magnetic one component type, and a negatively charged 
toner having a composition of 80 to 90 parts by weight of styrene-acrylic 
copolymer, 5 to 10 parts by weight of carbon black, 0.5 to 1.5 parts by 
weight of SiO.sub.2 as an externally added agent, and 0 to 5 parts by 
weight of a charge control agent, and having an average particle size of 
from 5 to 10 .mu.m is preferably used. In addition, the toner may be a 
positively charged toner, and it is a matter of course that the toner can 
be used not only as a black toner for monochrome copying machines and 
printers, but also as a color toner for color copying machines and 
printers. 
Moreover, the non-magnetic one component toner 10 is not limited to the 
above-mentioned composition, but the composition as shown below may be 
used for the present invention. 
As a thermoplastic resin which is the main resin, there can be mentioned 
polystyrene, polyethylene, polyester, low-molecular weight polypropylene, 
epoxy resin, polyamide, polyvinyl butyral or the like, other than 
styrene-acrylic copolymer. 
As a coloring agent, there can be mentioned, other than carbon black as 
mentioned above, furnace black, nigrosine-type dyes, and metallized dyes 
and the like, and for the color toner, there can be mentioned 
yellow-coloring agents such as benzidine-type yellow pigment, phorone 
Yellow, acetoacetic acid anilide type non-soluble azo pigments, monoazo 
pigments and azomethine pigments and the like, magenta coloring agents 
such as xanthene-type magenta dyes, phosphotungsten molybdate lake 
pigments, anthraquinone dyes, coloring materials comprising a xanthene dye 
and an organic carboxylic acid, thioindigo, naphthol-type insoluble azo 
pigments and the like, and cyan coloring agents such as copper 
phthalocyanine pigments and the like. 
As the externally added agents, there can be mentioned, other than 
SiO.sub.2 as mentioned above, colloidal silica, titanium oxide, alumina, 
zinc stearate, polyvinylidene fluoride, and mixtures thereof. 
As the charge control agent, there can be used azo-type metallized dyes, 
organic acid metal complex, chlorinated paraffin and the like for 
negatively charged toners, and nigrosine-type dyes, fatty acid metal salt, 
amines, quarternary ammonium salts and the like for positively charged 
toners. 
Furthermore, as the developing roller 100, there can be used an 
electroconductive elastic developing roller of 27 mm in diameter (Db), 
composed of an electroconductive urethane rubber containing an electric 
conduction imparting agent such as carbon black and the like and having a 
volume resistivity of about 10.sup.7 .OMEGA.cm and JIS-A hardness of from 
60.degree. to 70.degree., and the surface roughness R.sub.z of the 
developing roller being from 3 to 6 .mu.m (according to JISB-0601). The 
developing roller 100 rotates at a peripheral speed Vb of 200 mm/s in the 
direction of an arrow b in the figure, and developing bias voltage E.sub.1 
of -500 (V) is impressed to the developing roller 100 via a stainless 
shaft having a diameter Ds of 10 mm. 
The toner feed roller 200 is obtained by forming an elastic foamed body 
having a foamed cell density of from 80 cells per in. to 140 cells per 
in., and Asker F hardness of 60.degree. to Asker C hardness of 30.degree. 
in a form of roller onto a electroconductive shaft made of metals such as 
stainless. Asker C hardness is measured in accordance with JIS S 6050 
(spring type durometer). Asker F hardness is measured by using a hardness 
tester (manufactured by KOBUNSHI KEIKI CO., LTD, in Japan) according to 
procedure of JIS S 6050 under the following particular conditions that the 
pressing rod is a cylinder type of 25.2 mm in diameter, the spring load is 
55 g at 0.degree. and 455 g at 100.degree., and the pressing surface size 
and shape is a circle of 80 mm in diameter. The toner feed roller 200 
comes in contact with the developing roller 100 with a contact depth of 
from 0.5 to 1 mm. 
The discharging member 400 is an electroconductive thin-plate elastic body, 
and bias voltage of a polarity opposite to the charging polarity of the 
developer is impressed thereto by a power supply 410 for discharging bias. 
The discharging bias member 400 contains carbon black in a thin plate-like 
member made by mixing, for example, polycarbonate and polybutyl 
terephthalate, and the resistance value thereof can be set to be 10.sup.3 
to 10.sup.6 .OMEGA.. 
One end of the discharging member 400 is bonded to a part of the developing 
device 1, and the other end thereof is free and abuts against the 
developing roller 100. In the contact area P between the developing roller 
100 and the discharging member 400, an elastic member for abutment 420 is 
provided in such a manner that it abuts on the back face of the 
discharging member 400. 
The elastic member for abutment 420 is prepared by using a sponge material 
having Asker F hardness of 50.degree., and having a penetration quantity 
of about 0.3 mm in the contact area, and the contact width between the 
discharging member 400 and the developing roller 100 in the peripheral 
direction is set to be 2 mm. 
That is to say, if the hardness of the elastic member for abutment 420 
becomes high, the contact pressure between the developing roller 100 and 
the discharging member 400 becomes high, resulting in an effect of 
mechanical peeling with respect to the residual toner 10 on the developing 
roller 100. As a result, the toner 10 scratched on the surface of the 
discharging member 400 accumulates, causing spilling and fixation of 
toner. Therefore, to obtain only the discharging effect without mechanical 
scratching effect, the adhered quantity of the toner 10 on the surface of 
the discharging member 400 was visually confirmed by changing the sponge 
hardness of the elastic member for abutment 420, and as a result, it was 
found that the adhered quantity decreased dramatically with the sponge 
hardness of not higher than 70.degree. as measured by Asker F hardness. 
To ascertain the presence or absence of the development history 
(development memory) and the effect of scratching the residual toner on 
the developing roller by the toner feed roller after the discharging, with 
the developing device according to this embodiment, the following 
experiment was conducted for evaluation. 
FIGS. 3A, 3B shows the evaluation results. 
As a test image, a manuscript in which a solid white portion and a solid 
black portion exist half-and-half in the longitudinal direction of an A3 
paper is prepared and the test image is printed for 10 sheets of paper 
continuously. At this time, since the toner on the developing roller 100 
has been consumed for every printing in the area of the solid black 
portion, and new toner 10 has been supplied by the feed roller 200, the 
particle size distribution of the toner 10 is nearly constant. In the area 
of the solid white portion, however, the toner 10 is not consumed and 
passes through the discharging member 400 to return to the feed roller 
200. At this time, if the scratching effect after discharging is low, 
toner having a small particle size which passes easily through the contact 
area between the feed roller 200 and the developing roller 100, among 
residual toner on the developing roller 100, is again transferred to the 
developing zone. Accordingly, it can be seen that as the toner particle 
size distribution in the solid white area approximates to that in the 
solid black area, larger scratching effect in the contact area of the feed 
roller 200 and the developing roller 100 is obtained. 
Therefore, after the test image was printed for 10 sheets of paper 
continuously, the toner 10 on the developing roller 100 was extracted to 
measure the toner particle size distribution in the solid white portion 
and the toner particle size distribution in the solid black portion with a 
Coulter counter. 
Then, the similar experiment was conducted using a conventional developing 
device shown in FIG. 1, for comparison of the particle size distribution. 
With the conventional developing device, a Mylar sheet was attached for 
preventing the toner from leaking from a lower part of an opening in the 
developing unit onto the front face. 
As for the bias conditions used in this study, the discharging bias Ec of 
+200 (V) and the supply bias of -200 (V) (with respect to the potential of 
the developing roller) were applied respectively to respective members. 
As shown in FIG. 3A and FIG. 3B, with the developing device of this 
embodiment (with discharging bias in FIG. 3B), the difference in the toner 
particle size distribution between the solid white portion and the solid 
black portion is small. On the other hand, with the developing device 
using a conventional Mylar sheet (without discharging bias in FIG. 3A), it 
is seen that the difference in the toner particle size distribution 
between the solid white portion and the solid black portion is large. 
Therefore, with the developing devices of this embodiment, the toner 
discharged by the discharging member 400 is scratched by the feed roller 
200 and new toner 10 is applied to the developing roller 100. Moreover, 
when the existence of the development memory was ascertained using 
respective developing devices, with the developing device of this 
embodiment having a discharging member, development memory was not caused. 
On the contrary, with the developing device using a conventional Mylar 
sheet, development memory was caused in all test images. 
The second embodiment will now be described. 
The contact depth of the toner feed roller 200 and the developing roller 
100, and the feed capability and removal capability of the toner feed 
roller 200 will be described. With regard to the feed capability of the 
toner feed roller 200 when the physical property value of the sponge was 
quite the same and the contact depth was different, an experiment was 
conducted in a manner described below. 
Using a developing device 1 having the same construction as in the first 
embodiment, the developing device was stopped after the developing roller 
100 conducted development of solid black on the photosensitive material 
(OPC drum) 51 for two rounds, and the quantity of toner adhered on the 
photosensitive material 51 was measured for every round. 
In this case, the following method was used for measurement of the adhered 
quantity. 
The toner on the photosensitive material 51 is peeled off from the 
photosensitive material 51 by using a suction device (not shown) having a 
nozzle. The nozzle of the suction device is provided with a filter for 
gathering the sucked toner, and the sucked toner can be received in the 
nozzle. 
Therefore, the peeled quantity of toner can be obtained by subtracting the 
weight of the nozzle before sucking the toner from the weight of the 
nozzle after suction. 
Furthermore, the toner quantity per unit area can be obtained by measuring 
the peeled area on the developing roller. As experiment conditions, supply 
bias of -700 (V), discharging bias of -500 (V) (the same potential as the 
developing roller), and developing bias of -500 () were used, and the 
toner feed roller 200 is a sponge roller comprising an electroconductive 
urethane sponge material having a cell density of 80/in., resistance of 
10.sup.5 (.OMEGA.), and sponge hardness of 68.degree. as measured by Asker 
F hardness. 
The experiment result is shown in FIG. 4. 
As seen from FIG. 4, it is necessary to set the contact depth between the 
developing roller 100 and the feed roller 200 to be 0.5 mm or more in 
order to secure the followability of toner feed. 
Furthermore, the removal capability of the toner feed roller 200 in the 
case where the physical property value of the sponge is quite the same and 
only the contact depth is different will be evaluated in the following 
experiment. 
In this case, as in the first embodiment, the evaluation is performed 
according to the difference in the particle size distribution of the toner 
on the developing roller 100. In addition, to confirm the toner removal 
capability of only the feed roller 200, the evaluation was performed 
without applying discharging bias. The experiment results are shown in 
FIG. 5A and FIG. 5B. 
As shown in FIG. 5A, with the contact depth of 0.5 mm, the toner particle 
size distribution largely differs in the solid black portion and in the 
solid white portion, while as shown in FIG. 5B, with the contact depth of 
1 mm, the difference in the toner particle size distribution is improved. 
Therefore, it can be understood that the contact depth must be deep to 
peel off the toner on the developing roller only by the feed roller 200. 
Then by changing the foamed cell density from 50/in. to 180/in. for 
detailed evaluation, it was found that followability of the solid black 
density can be secured without development history and good results were 
obtained, at the foamed cell density of from 80/in. to 140/in. and with 
the contact depth with the developing roller of from 0.5 to 1 mm. 
The third embodiment will now be described. 
The developing device used in the third embodiment has the same 
construction as in the first embodiment, and as the discharging member 
400, an antistatic film "Bayfol AS-A" having a thickness of 0.2 mm 
produced by Bayer AG in Germany was used. To the toner feed roller 200, 
supply bias voltage Et of -200 (V) (with respect to the developing roller) 
was impressed, and to the discharging member 400, discharging bias voltage 
Ec of from 0 to +300 (V) (with respect to the developing roller) was 
impressed, thereby the existence of development memory was examined. 
Moreover, to examine the effect of scratching the residual toner on the 
developing roller 100 after being discharged by means of the toner feed 
roller 200, the following experiment was conducted for evaluation. 
To examine the effect of scratching the residual toner with the toner feed 
roller 200, a manuscript in which a solid white portion and a solid black 
portion exist half-and-half in the longitudinal direction of an A3 paper 
is prepared and the test image is printed for 10 sheets of paper 
continuously. At this time, since the toner on the developing roller 100 
has been consumed for every printing in the area of the solid black 
portion, and new toner 10 has been supplied by the feed roller 200, the 
particle size distribution of the toner 10 is nearly constant. In the area 
of the solid white portion, however, the toner 10 is not consumed and 
passes through the discharging member 400 to return to the feed roller 
200. At this time, if the scratching effect after discharging is low, a 
toner having a small particle size which passes easily through the contact 
area between the feed roller 200 and the developing roller 100, among 
residual toner on the developing roller 100, is again transferred to the 
developing zone. 
Accordingly, it can be considered that as the toner particle size 
distribution in the solid white area approximates to that in the solid 
black area, the larger the scratching effect in the contact area of the 
feed roller 200 and the developing roller 100 is obtained. 
Therefore, after the test image was printed for 10 sheets of paper 
continuously, the toner 10 on the developing roller 100 was gathered to 
measure the toner particle size distribution in the solid white portion 
and the toner particle size distribution in the solid black portion by 
means of a particle size distribution measuring device (Coulter Multisizer 
II). FIG. 6 shows the result of calculation of the toner removal rate by 
applying the discharging bias. 
In this case, the toner removal rate was calculated according to the 
following formula, using a peak value of the toner particle size 
distribution in the solid black portion and a peak value of the toner 
particle size distribution in the solid white portion: 
##EQU1## 
According to FIG. 6, it can be seen that as the impressed voltage of the 
discharging bias increases, the toner removal rate increases. Therefore, 
it was found that by applying a discharging bias to the discharging member 
400, the effect of removing the residual toner on the developing roller 
100 with the feed roller 200 was improved. 
The fourth embodiment will now be described. 
The developing device 1 used in the fourth embodiment has the same 
construction as in the first embodiment, and as the toner feed roller, an 
elastic foamed body having a cell density of 80/in. was used, and 
evaluation was performed by setting the contact depth with the developing 
roller to be 1 mm. In addition, as the discharging member, an antistatic 
film "Bayfol AS-A" having a thickness of 0.2 mm produced by Bayer AG in 
Germany was used. To the toner feed roller 200, supply bias voltage Et of 
from 0 to -400 (V) (with respect to the developing roller) was impressed, 
and to the discharging member, discharging bias voltage Ec of from 0 to 
+300 (V) (with respect to the developing roller) was impressed, thereby 
the followability of solid black density and the occurrence of development 
memory under the conditions for applying each supply bias and discharging 
bias was evaluated. 
In this case, the toner supply followability was evaluated by preparing a 
solid black image, printing the solid black portion on an A3 paper, and 
determinating the resulting fluctuation in the optical density. 
For an evaluation of a development memory, a test pattern for confirming a 
development memory, which has a checker pattern in a beginning portion to 
write the image, and thereafter has an image density of halftone, was 
prepared. This checker pattern is a square with each side 15 mm long, in 
which a white portion and a black portion exist alternately. Upon starting 
printing, checker patterns in three lines were printed, thereafter 
halftone image having an average optical density of 0.4 (measurement value 
with Machbeth RD918) was printed, thereby development history was 
confirmed and evaluated. 
Actually, the developing device of this embodiment was incorporated into a 
laser printer, and a solid black manuscript or a test pattern for 
confirming a development memory was printed on an A3 paper using the laser 
printer. 
FIG. 7 shows a result of existence of development memory and the 
followability of solid black density due to the supply bias and 
discharging bias. As shown in FIG. 7, when the supply bias is 0 (V), that 
is, the same potential as that of the developing roller, the followability 
of the solid black density cannot be obtained. In addition, when the 
discharging bias is 0 (V), that is, the same potential as that of the 
developing roller, discharging effect cannot be obtained, and under a 
condition that the supply bias of from 0 to -400 (V) is applied, 
development memory cannot be removed. From a level of discharging bias of 
+100 (V) or higher, removal of the development memory becomes possible. 
However, at the time of applying supply bias of -50 (V), the supply 
capability decreased and the image density of solid black slightly 
decreased. While changing voltage for applying supply bias and discharging 
bias, the above-mentioned image for evaluation was output to obtain a 
range where excellent images can be obtained, and it was found that good 
images could be obtained if the following conditions were satisfied: 
EQU .vertline.Vc.vertline.-50.ltoreq..vertline.Vt.vertline..ltoreq..vertline.Vc 
.vertline.+100 (V). 
The fifth embodiment will now be described. 
FIG. 8 is a detailed perspective view of the developing roller 100 and the 
discharging member 400. The entire toner on the developing roller 100 can 
be discharged by designing the widthwise length Wc of the discharging 
member 400 to be slightly longer than the width of toner transfer area Wt 
on the developing roller 100. 
As described above, according to the invention of the first gist, since an 
elastic member is provided on a surface opposite to the abutting surface 
of the discharging member and the developing roller, in a contact area of 
the discharging member and the developing roller, it becomes possible to 
enlarge the contact area thereof without increasing the contact pressure 
between the developing roller and the discharging member due to the 
abutment of the discharging member with the developing roller. Moreover, 
the time when the residual toner on the developing roller comes in contact 
with the discharging member becomes long to enhance the effect of 
discharging the toner, and the scratching effect of the toner with the 
feed roller is also improved, hence an image without causing any 
development history can be obtained. 
According to the invention of the second gist, by setting the hardness of 
the elastic member to be not higher than 70.degree. measured by Asker F 
hardness, an effect to enlarge the area contacting with the developing 
roller can be easily obtained. 
According to the invention of the third gist, by defining a range of the 
foamed cell density of the feed roller, deterioration of the feed 
capability, such as blocking of toner can be prevented. Moreover, by 
limiting the contact depth, increase of torque for driving the feed roller 
is suppressed, and stable supply of toner and removal capability can be 
maintained even after the lapse of time. 
According to the invention of the fourth gist, by satisfying the toner 
removal condition and the toner feed condition of the feed member, an 
image without density unevenness and development history can be obtained. 
According to the invention of the fifth gist, by using an electroconductive 
sponge material for the feed member and impressing bias voltage of the 
same polarity as the toner charging characteristic to the feed member, 
toner can be supplied stably and sufficiently, and stable followability of 
density can be obtained even for images with large consumption of toner, 
such as solid black portions and the like. 
According to the invention of the sixth gist, by using the impressed 
voltages of the supply bias and the discharging bias in the respective 
ranges defined in the present invention, the residual toner on the 
developing roller can be satisfactorily discharged and further, toner can 
be stably supplied due to the supply bias. As a result, development 
history is not caused and density followability is also secured. 
According to the invention of the seventh gist, by using a thin-plate 
electroconductive material for the discharging member, a discharging bias 
having a polarity opposite to the charging polarity of the toner can be 
applied at the contact area of the developing roller and the discharging 
member, and therefore, electric adherence of the developing roller and the 
residual toner adhered on the surface of the developing roller can be 
reduced. 
According to the invention of the eighth gist, by using a thin plate 
material comprising polycarbonate, polybutyl terephthalate and carbon for 
the discharging member, the wear resistance of the discharging member is 
improved, thereby there is obtained an effect that deterioration of the 
discharging capability is not caused, even if it is used for a long period 
of time. 
According to the invention of the ninth gist, by bringing the discharging 
member into contact with the developing roller, the discharging member 
being longer than the toner adhering area on the developing roller in the 
axial direction of the developing roller, the entire toner on the 
developing roller passes through the contact area of the discharging 
member and the developing roller, hence there is an effect that the entire 
toner on the developing roller can be discharged after passing through the 
developing zone.