Developing device with rigid member toner limiting means

An apparatus for developing an electrostatic latent image which includes a developing agent application assembly and a limiting device for limiting the amount of the developing agent held on the surface of the developing agent application assembly. The limiting device is made of a rigid member such as a sheet glass and its one surface is brought into forced contact with the surface of the developing agent application assembly.

FIELD OF THE INVENTION 
The present invention relates to an apparatus for developing an 
electrostatic latent image into a toner image in an image-forming machine 
such as an electrostatic copying machine or a laser printer. More 
specifically, the invention is concerned with an apparatus for developing 
an electrostatic latent image, which is equipped with a driven developing 
agent application means which holds the developing agent on the surface 
thereof and carries it into a developing zone, and a limiting means which 
limits the amount of the developing agent held on the surface of the 
developing agent application means. 
DESCRIPTION OF THE PRIOR ART 
In order to develop an electrostatic latent image into a toner image in an 
image-forming machine, as is well known, there has widely been used an 
apparatus for developing an electrostatic latent image, which is equipped 
with a developing agent application means constituted by a roller or an 
endless belt that is rotated in a predetermined direction. Being rotated 
in a predetermined direction, the developing agent application means moves 
through a developing agent-holding zone, a developing agent 
amount-limiting zone and a developing zone successively. In the developing 
agent-holding zone, the developing agent supplied in a suitable manner is 
held on the surface of the developing agent application means. In the 
developing agent amount-limiting zone, the limiting means acts on the 
developing agent held on the surface of the developing agent application 
means to limit its amount to be applied to a required amount. In the 
developing zone, the developing agent is applied onto the surface of an 
electrostatic latent image carrier such as a rotary drum, which has an 
electrostatic photosensitive material on the peripheral surface thereof, 
and electrostatic latent image formed on the surface of the electrostatic 
latent image carrier is developed into a toner image. In order to 
accomplish favorable developing, it is important that the developing agent 
is held in an accurately required amount and sufficiently uniformly in the 
direction of width on the surface of the developing agent application 
means by properly limiting the amount of the developing agent held on the 
surface of the developing agent application means by using the limiting 
means. 
Japanese Patent Publication No. 16736/1988 discloses an apparatus for 
developing an electrostatic latent image equipped with a limiting means 
which is constituted by an elastic rubber member that may be a synthetic 
rubber such as urethane rubber or silicone rubber. The elastic rubber 
member constituting the developing agent limiting means has one surface 
thereof or tip edge thereof that is brought into forced contact with the 
surface of the developing agent application means to limit the amount of 
the developing agent held on the surface of the developing agent 
application means to be a considerably small amount, whereby a thin layer 
of developing agent is formed on the surface of the developing agent 
application means. 
According to the apparatus for developing an electrostatic latent image 
disclosed in Japanese Patent Publication No. 16736/1988, however, the 
limiting member constituted by an elastic rubber member arouses the 
following problems that must be solved. First, physical properties of the 
elastic rubber member considerably vary depending upon the temperature and 
humidity of the atmosphere, whereby the action of the elastic rubber 
member for limiting the developing agent varies correspondingly depending 
upon the temperature and humidity of the atmosphere. Hence, the thickness 
of the developing agent layer formed on the surface of the developing 
agent application means undergoes variations correspondingly. Second, due 
to nonuniformity in the modulus of elasticity of the elastic rubber 
itself, it becomes difficult to uniformalize the force of bringing the 
elastic rubber member into contact with the surface of the developing 
agent application means to a sufficient degree in the direction of width, 
and it therefore becomes difficult to uniformly form the thin layer of the 
developing agent on the surface of the developing agent application means 
to a sufficient degree in the direction of width. Third, the elastic 
rubber member usually has a low durability and is degraded within 
relatively short periods of time. Fourth, the elastic rubber member 
usually involves error in the properties such as in the modulus of 
elasticity and hardness, the error being made during the production. 
Therefore, it is not necessarily easy to stably produce the elastic rubber 
member having required properties. 
SUMMARY OF THE INVENTION 
A principal object of the present invention is to provide a novel and 
improved apparatus for developing an electrostatic latent image which is 
capable of forming, on the surface of a developing agent application 
means, a layer of the developing agent having a thickness limited to a 
predetermined value sufficiently precisely and being sufficiently uniform 
in the direction of width by limiting the amount of the developing agent 
held on the surface of the developing agent application means very 
properly as required, without using a limiting means made of elastic 
rubber and, hence, without arousing the above-mentioned problems that stem 
from the use of the elastic rubber member. 
Another object of the present invention is to provide a novel and improved 
apparatus for developing an electrostatic latent image which is capable of 
stably forming a thin layer of the developing agent with a thickness of, 
for example about 20 .mu.m on the surface of the developing agent 
application means in addition to accomplishing the above-mentioned 
principal object. 
It has heretofore been considered as disclosed in the above-mentioned 
Japanese Patent Publication No. 16736/1988 that when the limiting means is 
constituted by using a rigid member, the layer of the developing agent 
formed on the surface of the developing agent application means becomes 
nonuniform to a striking degree making it far from being practicable. The 
present inventors, however, have conducted diligent study and experiments 
and have discovered the unexpected fact that the developing agent held on 
the surface of the developing agent application means can be limited as 
required and can be formed into a developing agent layer as desired when 
the limiting member is constituted by using a rigid member contrary to the 
conventional technical common sense and one surface of the rigid member is 
brought into forced contact with the surface of the developing agent 
application means. 
That is, in order to accomplish the above-mentioned principal technical 
assignment, the present invention provides an apparatus for developing 
electrostatic image, which comprises: 
a driven developing agent application means which holds the developing 
agent on the surface thereof in a developing agent-holding zone and 
carries the developing agent into the developing zone to apply it onto the 
electrostatic latent image; 
and a limiting means which limits the amount of the developing agent held 
on the surface of said developing agent application means in a developing 
agent-limiting zone located between said developing agent-holding zone and 
said developing zone; wherein 
said limiting means is constituted by a rigid member of which the one 
surface is brought into forced contact with the surface of said developing 
agent application means. 
The words "rigid member" used in this specification stands for a member 
having a coefficient of deflection, represented by the following relation, 
##EQU1## 
wherein l is a distance (cm) between the fixed end and a point of load, E 
is a modulus of longitudinal elasticity (kg/cm.sup.2), and 
I.sub.z is a geometrical moment of inertia, of from 0 to 0.01, which 
substantially does not undergo elastic deformation under the condition 
where it is brought into forced contact with the surface of the developing 
agent application means. 
In order to considerably decrease the thickness of the layer of the 
developing agent formed on the surface of the developing agent application 
means, it is desired to extend the rigid member in a direction opposite to 
the direction in which the surface of the developing agent application 
means moves, so that the free end of the rigid member is protruded toward 
the upstream side as viewed in a direction in which the developing agent 
application means moves. From the standpoint of the thickness of the 
developing agent layer and the charging property of the toner constituting 
the developing agent, it is desired that the rigid member has a length of 
protrusion of from 0.5 to 4.0 mm, particularly, from 1.0 to 3.5 mm, and 
more particularly, from 2.0 to 2.5 mm at the free end thereof. 
The surface precision of the layer of the developing agent formed on the 
surface of the developing agent application means is seriously affected by 
the surface roughness of the region on one surface of the rigid member 
that is brought into forced contact with the surface of the developing 
agent application means. In order to form the layer of the developing 
agent which is uniform in the direction of width, it is desired that the 
surface roughness Ra (center line average roughness specified under JIS B 
0601) of at least the above-mentioned region on one surface of the rigid 
member is 6.00 or smaller, particularly, 0.20 or smaller, and more 
particularly, 0.02 or smaller. 
A material having a sufficiently small surface roughness and yet available 
at a low cost can be typified by a sheet glass. When it is desired to 
apply a bias voltage to the limiting means, there can be used a sheet 
glass (e.g., a sheet glass placed in the market in the trade name of "Nesa 
Glass") of which one surface is coated with an electrically conducting 
film. As desired, the limiting means may be constituted by using a 
stainless steel plate of which the one surface is suitably treated. 
In order to sufficiently decrease the thickness of the developing agent 
layer formed on the surface of the developing agent application means, it 
is desired to set the line pressure (pressure per a unit length in the 
direction of width) of one surface of the rigid member to be from 10 to 80 
g/cm, particularly from 20 to 70 g/cm, and more particularly from 40 to 60 
g/cm with respect to the surface of the developing agent application 
means. 
The limiting means constituted by the rigid member is particularly 
effectively used in an apparatus for developing an electrostatic latent 
image which uses a developing agent consisting of only toner having a 
volume average grain size of 8.0 to 12.0 .mu.m. In this case, it is 
desired to constitute the developing agent application means using a solid 
synthetic rubber roller having an Asker's C hardness of from 45 to 65. In 
the developing zone, it is desired that the solid synthetic rubber roller 
is brought into forced contact with the surface of the electrostatic 
latent image carrier on which is formed an electrostatic latent image that 
is to be developed, such that the solid synthetic rubber roller is 
elastically compressed by about 0.05 to about 0.15 mm. The electrostatic 
latent image carrier may be a rotary drum which has on the peripheral 
surface thereof a suitable electrostatic photosensitive material such as 
an organic photosemiconductor. In the developing zone, it is desired to 
move the surface of the electrostatic latent image carrier in the same 
direction as the direction in which the surface of the solid rubber roller 
moves, in order to establish a relationship 1.5V1.ltoreq.V2.ltoreq.2.2V1 
between a moving speed V1 of the surface of the electrostatic latent image 
carrier and a moving speed V2 of the surface of the solid rubber roller. 
In the developing agent-holding region, it is desired to dispose a foamed 
auxiliary roller that comes into forced contact with the surface of the 
solid synthetic rubber roller, so that the auxiliary roller is elastically 
compressed by 0.15 to 0.25 mm, and to move the surface of the solid rubber 
roller in the direction opposite to the direction in which the surface of 
the auxiliary roller moves in the developing agent-holding zone, in order 
to establish a relationship 0.4V2.ltoreq.V3.ltoreq.1.8V2 between the 
moving speed V2 of the surface the solid rubber roller and a moving speed 
V3 of the surface of the foamed roller. When the speed V3 is smaller than 
the speed 0.4 V2, the toner remaining on the surface of the solid 
synthetic rubber roller after developing is scraped off in a less amount 
by the auxiliary roller, with the consequence that a toner image the same 
as the previous toner image which is a so-called character memory tends to 
appear again on the developed toner image. Conversely, when the speed V3 
becomes greater than the speed 1.8 V2, the toner is excessively acted upon 
by the surface of the solid synthetic rubber roller, whereby the toner is 
electrically charged excessively, the density of the developed toner image 
becomes too small and besides, the toner tends to be scattered around due 
to the auxiliary roller that is revolving. 
In the apparatus for developing an electrostatic latent image of the 
present invention, the one surface of the rigid member constituting the 
limiting means is brought into forced contact with the surface of the 
developing agent application means, whereby the amount of the developing 
agent held on the surface of the developing agent application means is 
suitably limited and a layer of the developing agent is formed as desired 
on the surface of the developing agent application means. As will become 
obvious from the examples appearing later, the thickness of the developing 
agent layer formed on the surface of the developing agent application 
means is set to assume a required value very precisely and becomes 
sufficiently uniform in the direction of width.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the apparatus for developing an electrostatic 
latent image constituted according to the present invention will be 
described in further detail with reference to the accompanying drawings. 
With reference to FIGS. 1 and 2, the illustrated embodiment has a drum 4 
which is mounted to rotate on a center axis 2 that extends substantially 
horizontally (perpendicularly to the surface of the paper in FIG. 1). The 
drum 2 has on the peripheral surface thereof an electrostatic 
photosensitive material such as an organic photosemiconductor, and an 
electrostatic latent image is formed on the electrostatic photosensitive 
material by a suitable method such as the so-called Carlson's process. An 
apparatus for developing an electrostatic latent image which is generally 
designated at 6 is provided to develop an electrostatic latent image into 
a toner image. 
The developing apparatus 6 is equipped with a developing housing 8 which 
has a bottom wall 10, a front side wall 12 and a rear side wall 14 (refer 
also to FIGS. 3 and 4) that stand upright from both ends of the bottom 
wall 10. Between the two side walls 12 and 14 of the developing housing 8 
are arranged a developing agent application means 16, a limiting means 18, 
a feeding means 20 and an agitator means 22. Moreover, though not 
illustrated, a toner cartridge holding the toner is disposed over the 
agitator means 22. 
The developing agent application means 16 includes a rotary shaft 24 
rotatably mounted between the two side walls 12 and 14 of the developing 
housing 8, a roller 26 fixed to the rotary shaft 24, and collar members 28 
rotatably mounted on the rotary shaft 24 on both sides of the roller 26. 
The rotary shaft 24 can be made of a suitable metallic material such as a 
stainless steel. It is desired that the roller 26 is made of a material 
which is relatively soft and is electrically conductive. A preferred 
material for forming the roller 26 can be typified by an electrically 
conducting solid rubber such as an urethane rubber. The roller 26 should 
have an Asker's C hardness of from about 45 to about 65, and should, 
further, have a volume resistivity of from about 10.sup.6 to about 
10.sup.9 .OMEGA..cm. The collar members 28 can be made of a suitable 
synthetic resin having an outer diameter which is slightly smaller than 
the outer diameter of the roller 26. The roller 26 and the collar members 
28 of the developing agent application means 16 are exposed through an 
opening formed in the developing housing 8 and face a drum 4. The 
peripheral surfaces of the collar members 28 are brought into contact with 
the peripheral surface of the drum 4, so that the roller 26 is positioned 
at a required position with respect to the drum 4. Since the outer 
diameter of the roller 26 is slightly greater than the outer diameter of 
the collar members 28, the peripheral surface of the roller 26 is brought 
into forced contact with the peripheral surface of the drum 4, and the 
peripheral surface of the roller 26 is slightly compressed resiliently in 
the forcibly contacting region. Usually, it is desired that the amount of 
compression of the roller 26 is from about 0.05 to about 0.15 mm though it 
may vary depending upon the outer diameter size of the roller 26. 
As shown in FIG. 4, the rear end of the rotary shaft 24 of the developing 
agent application means 16 rearwardly protrudes beyond the rear side wall 
14 of the developing housing 8, and an input gear 30 is fitted to the rear 
end which protrudes. The input gear 30 is coupled to an electric motor 
(not shown) via a suitable transmission means (not shown), and the rotary 
shaft 24 is continuously rotated in a direction indicated by arrow 32 in 
FIG. 1. With reference to FIG. 1, the roller 26 is continuously rotated in 
the direction indicated by arrow 32 with the rotation of the rotary shaft 
24, and the peripheral surface of the roller 26 is conveyed passing 
through a developing agent-holding zone 34, a developing agent-limiting 
zone 36 and a developing zone 38, successively. In the developing 
agent-holding zone 34 as will be described later in further detail, the 
feeding means 20 acts on the roller 26, whereby the used developing agent 
held on the peripheral surface of the roller 26 is peeled off the roller 
26 and the fresh developing agent is newly fed onto the peripheral surface 
of the roller 26. In the developing agent-limiting zone 36, the limiting 
means 18 acts on the developing agent held on the peripheral surface of 
the roller 26, whereby the developing agent held on the peripheral surface 
of the roller 26 is limited to a required amount to form a thin layer. 
Upon receiving the action of the limiting means 18, furthermore, the toner 
constituting the developing agent is frictionally charged into a 
predetermined polarity, e.g., into a positive polarity. In the developing 
zone 38, the developing agent is applied onto the electrostatic latent 
image on the electrostatic photosensitive material disposed on the 
peripheral surface of the drum 4 so that the electrostatic latent image is 
developed into a toner image. For instance, the electrostatic latent image 
has a non-image region which is charged to about +700 V and an image 
region which is charged to about +120 V, and the toner adheres onto the 
image region (so-called reversal developing). The drum 4 is continuously 
rotated in a direction indicated by arrow 40 in FIG. 1. In the developing 
zone 38, therefore, the peripheral surface of the drum 4 and the 
peripheral surface of the roller 26 of the developing agent application 
means 16 move in the same direction. A moving speed V2 of the peripheral 
surface of the roller 26 is set to be slightly greater than a moving speed 
V1 of the peripheral surface of the drum 4, preferably in a relationship 
of 1.5 V1.ltoreq.V2.ltoreq.2.2 V1. In this case, the developing agent is 
sufficiently carried by the roller 26 to the developing zone 38, the toner 
that has once adhered to the non-image portion of the electrostatic latent 
image is properly peeled off by the scraping action of the peripheral 
surface of the roller 26 on the peripheral surface of the drum 4 and, 
thus, there can be obtained a good toner image having a properly developed 
density without fogging. Desirably, the developing agent consists of toner 
only having a volume average grain size (vol. 50%: the volume of the toner 
smaller than the volume average grain size is the same as the volume of 
the toner larger than the volume average grain size) of from 8.0 to 12.0 
.mu.m and a volume resistivity of eighth power of ten or greater. 
With further reference to FIGS. 1 and 2, the limiting means 18 includes a 
rotary shaft 42 which is rotatably mounted between the two side walls 12 
and 14 of the developing housing 8. A support member 46 is fitted via a 
connection bracket 44 to the rotary shaft 42 that can be constituted by a 
stainless steel rod. The connection bracket 44 and the support member 46 
can be made of a suitable metal plate such as a stainless steel or 
aluminum plate. The support member 46 has an L-shape in cross section, and 
a rigid member 48 is fastened to the inside surface of the support member 
by a suitable method such as screws. As clearly diagramed in FIG. 3, the 
front end of the rotary shaft 42 protrudes forward beyond the front side 
wall 12 of the developing housing 8, and a coupling member 50 is fitted to 
the protruded front end thereof. On the other hand, an L-shaped bracket 52 
is fastened to the front surface of the front side wall 12 of the 
developing housing 8, and a threaded hole is formed in the support portion 
of the bracket 52. A threaded rod 54 is screwed into the threaded hole of 
the bracket 52, and a lock nut 56 is screwed to the threaded rod 54. A 
tension spring 58 is extended between an end portion of the threaded rod 
54 and a free end of the coupling member 50. The tension spring 58 
resiliently urges the rotary shaft 42 in the clockwise direction in FIG. 
1, whereby one surface, i.e., inside surface of the rigid member 48 is 
brought into forced contact with the peripheral surface of the roller 26 
of the developing agent application means 16. The contacting force of the 
rigid member 48 with respect to the peripheral surface of the roller 26 
can be suitably adjusted by changing the position at which the threaded 
rod 54 is fixed to the bracket 52. 
It is desired that the rigid member 48 is constituted by a plate-like 
member of which at least the one surface (i.e., surface forcibly contacted 
to the peripheral surface of the roller 26) extends in the direction of 
width (direction perpendicular to the surface of the paper in FIG. 1) 
along the peripheral surface of the roller 26. As will be understood from 
the description appearing later, it is desired that the region on one 
surface of the rigid member 48 that is at least brought into forced 
contact with the peripheral surface of the roller 26 has a sufficiently 
small surface roughness i.e., the center line average roughness, Ra, 
stipulated under JIS B 0601, is 6.00 or smaller, particularly, 0.20 or 
smaller, and more particularly, 0.02 or smaller. When the surface 
roughness on one surface of the rigid member 48 becomes excessive, the 
surface of the thin developing agent layer on the peripheral surface of 
the roller 26 of the developing agent application means 16 is not 
sufficiently flattened and tends to become nonuniform. A sheet glass 
placed in the market can be favorably used as a rigid material for forming 
the rigid member 48 because it is available at a relatively low cost yet 
maintaining the surface roughness very small. An electrically conducting 
film may be applied onto one surface of the sheet glass when it is desired 
to apply a required voltage to the rigid member 48 to control the electric 
charging property of the toner. As the sheet glass having an electrically 
conducting film applied onto one surface thereof, there can be favorably 
used a sheet glass that has been placed in the market in the trade name of 
"Nesa Glass". The rigid member 48 can be constituted by using a suitable 
metal plate such as a stainless steel instead of using the sheet glass. As 
required, the one surface of the metal plate constituting the rigid member 
48 may be suitably treated in order to sufficiently decrease the surface 
roughness on one surface of the metal plate. If desired, the rigid member 
48 may be constituted by using a laminate of a sheet glass and a metal 
plate, and the one surface that comes into forced contact with the roller 
26 of the developing agent application means 16 may be defined by the 
exposed surface of the sheet glass. 
The contacting force of the rigid member 48 with respect to the peripheral 
surface of the roller 26 of the developing agent application means 16 can 
be suitably set depending upon the thickness of the developing agent layer 
that is formed on the peripheral surface of the roller 26. The thickness 
of the developing agent layer decreases with an increase in the contacting 
force. As the contacting force becomes too great, on the other hand, the 
roller 26 tends to be prevented from smoothly rotating. In the developing 
mode of the illustrated embodiment, the developing agent layer formed on 
the peripheral surface of the roller 26 usually have a thickness of 15 to 
40 .mu.m and, particularly preferably , about 20 .mu.m. In order to form 
the developing agent layer having such a thickness, the rigid member 48 is 
preferably brought into forced contact with the peripheral surface of the 
roller 26 at a line pressure (pressure per a unit length in the direction 
of width) of from 10 to 80 g/cm, more preferably from 20 to 70 g/cm, and 
particularly preferably from 40 to 60 g/cm. 
It is desired that the free end of the rigid member 48 is slightly 
protruded toward the upstream side beyond a portion where the rigid member 
48 is brought into forced contact with the roller 26 as viewed in a 
direction in which the roller 26 moves. The length of protrusion of the 
free end of the rigid member 48 (i.e., the length from the contacting 
center of the roller 26 and the rigid member 48 to the free end of the 
rigid member 48) PL should, generally, be from 0.5 to 4.0 mm, preferably 
from 0.8 to 3.5 mm, and more preferably from 1.0 to 2.0 mm. As will be 
referred to later, when the length of protrusion PL becomes too short or 
substantially zero, the limiting action of the rigid member 48 becomes 
excessive and it becomes difficult to obtain a suitable developing agent 
layer. When the length of protrusion becomes too long, the thickness of 
the formed developing agent layer tends to become too great and the amount 
of charge of the toner tends to become too small. 
With reference to FIGS. 1 and 2, the feeding means 20 includes a rotary 
shaft 60 that is rotatably mounted between the two side walls 12 and 14 of 
the developing housing 8, and an auxiliary roller 62 fitted to the rotary 
shaft 60. It is desired that the auxiliary roller 62 is constituted by a 
foamed material such as foamed silicone or foamed urethane. The auxiliary 
roller 62 is brought into forced contact with the roller 26 of the 
developing agent application means 16. It is desired that the foamed 
material forming the auxiliary roller 62 has a hardness (e.g., Asker's C 
hardness of about 35) which is considerably smaller than the hardness of 
the roller 26, and that when the auxiliary roller 62 is brought into 
contact with the roller 26, the auxiliary roller 62 is elastically 
compressed by about 0.15 to 0.25 mm in the region of forced contact. The 
agitator means 22 includes a rotary shaft 64 rotatably mounted between the 
two side walls 12 and 14 of the developing housing 8 and an agitator 
member 66 fitted to the rotary shaft 64. The agitator member 66 has 
radially protruded portions that protrude in the radial direction from 
both ends of the rotary shaft 64 and a main portion that extends between 
the radially protruded portions in parallel with the rotary shaft 64. As 
clearly shown in FIG. 4, both the rear end of the rotary shaft 60 of the 
feeding means 20 and the rear end of the rotary shaft 64 of the agitator 
means 22 rearwardly protrude beyond the rear side wall 14 of the 
developing housing 8, and input gears 68 and 70 are fitted to these 
protruded rear ends, respectively. The input gear 68 and the input gear 70 
are in mesh with each other. A rearwardly extending short shaft 72 is 
fitted to the rear side wall 14 of the developing housing 8, and a 
transmission gear 74 is fitted to the short shaft 72. The input gear 68 is 
engaged with the transmission gear 74 which is engaged with the input gear 
30 fitted to the rotary shaft 24 of the developing agent application means 
16. When the rotary shaft 24 and roller 26 of the developing agent 
application means 16 are rotated in a direction of arrow 32 in FIG. 1, the 
rotary shaft 60 and auxiliary roller 62 of the feeding means 20 are 
rotated in a direction indicated by arrow 76 in FIG. 1, and the rotary 
shaft 64 and agitator member 66 of the agitator means 22 are rotated in a 
direction indicated by arrow 78 in FIG. 1. The agitator member 66 of the 
agitator means 22 rotating in the direction of arrow 78 works to agitate 
the toner or developing agent that flows down from a toner cartridge (not 
shown) disposed at an upper position as well as the developing agent 
peeled off the roller 26 of the developing agent application means 16 due 
to the action of the feeding means 20. The auxiliary roller 62 of the 
feeding means 20 rotating in the direction of arrow 76 holds the 
developing agent agitated by the agitator means 66 on the peripheral 
surface thereof, and feeds the developing agent onto the peripheral 
surface of the roller 26 on the downstream side, as viewed in a direction 
in which the roller 26 rotates, of the portion where the auxiliary roller 
62 is forcibly contacting to the roller 26 of the developing agent 
application means 16. Then, after the developing operation through the 
developing zone 38, the auxiliary roller 62 scrapes off the developing 
agent remaining on the peripheral surface of the roller 26 on the upstream 
side, as viewed in a direction in which the roller 26 rotates, of the 
portion where the auxiliary roller 62 is forcibly contacted to them roller 
26. As indicated by arrows 32 and 76 in FIG. 1, the roller 26 and the 
auxiliary roller 62 rotate in the opposite directions relative to each 
other at the portion where they are forcibly contacted to each other. From 
the results of extensive experiments conducted by the present inventors, 
it is desired that a relationship 0.75 V2.ltoreq.V3.ltoreq.0.85 V2 is 
established between a moving speed V2 of the peripheral surface of the 
roller 26 and a moving speed V3 of the peripheral surface of the auxiliary 
roller 62. 
Described below are various examples comparative example of the present 
invention. 
[EXAMPLE 1] 
A developing apparatus constituted as shown in FIGS. 1 to 4 was prepared 
and operated. The roller of the developing agent application means in the 
developing apparatus was made of a solid urethane rubber, and possessed an 
Asker's C hardness of 55, an outer diameter of 20.00 mm and a length of 
234.00 mm in the direction of the axial thereof. The collar members of the 
developing agent application means were made of a polyacetal resin, and 
possessed an outer diameter of 19.90 mm. By bringing the peripheral 
surfaces of the collar members into contact with the peripheral surface of 
the drum, therefore, the roller was elastically compressed by 0.10 mm in 
the developing zone. The auxiliary roller of the feeding means was made of 
foamed silicone (closed-cellular type), and possessed an Asker's C 
hardness of 35, an outer diameter of 12.00 mm and a length of 215.50 mm in 
the direction of axis thereof. The number of revolutions of the roller of 
the developing agent application means was 80.1 rpm, the number of 
revolutions of the auxiliary roller of the feeding means was 110.5 rpm 
and, hence, a relationship 0.828 V2=V3 was established between a moving 
speed V2 of the peripheral surface of the roller of the developing agent 
application means and a moving speed V3 of the peripheral surface of the 
auxiliary roller of the feeding means. 
The rigid member of the limiting means was made of a soda quartz glass 
(Nesa Glass) having a thin electrically conductive tin oxide thin film 
applied onto the surface thereof that comes into forced contact with the 
roller of the developing agent application means, and possessed a 
thickness of 1.2 mm and a length of 214.5 mm in the lengthwise direction. 
The line pressure of the rigid member against the peripheral surface of 
the roller of the developing agent application means was 46.38 g/cm. The 
length PL of protrusion PL (FIG. 1) of the free end of the rigid member 
was 3.0 mm. The surface roughness Ra on the surface of the rigid member 
forcibly contacted to the roller was 0.01 as measured by using a surface 
roughness-measuring instrument that is placed in the market by Tokyo 
Seimitsu Co. in the trade name of "Handysurf E-30A". The coefficient of 
deflection of the rigid member was 1.18.times.10.sup.-6. 
The developing agent used was a one-component type developing agent 
consisting of only toner having a volume average grain size (vol. 50%) of 
10.52 .mu.m and a bulk density, as stipulated under JIS K5010, of 0.303 
g/cm.sup.2. An organic photosemiconductor (organic photosemiconductor of a 
model disclosed in Japanese Laid-Open Patent Publication No. 295853/1992) 
was disposed on the peripheral surface of the drum on which will be formed 
an electrostatic latent image that is to be developed by the developing 
apparatus, and the drum possessed the outer diameter of 40.00 mm. The 
number of revolutions of the drum was 22.9 rpm and, hence, a relationship 
was 1.747 V1=V2 between a moving speed V1 of the peripheral surface of the 
drum and a moving speed V2 of the peripheral surface of the roller of the 
developing agent application means. A bias voltage of +350 V was applied 
to the rotary shaft made of a stainless steel of the developing agent 
application means, a bias voltage of +50 V was applied to the rotary shaft 
made of a stainless steel of the feeding means, and a bias voltage of +350 
V was applied to the thin electrically conducting tin oxide film applied 
onto one surface of the rigid member of the limiting means. 
In an environment of a temperature of 20.degree. C. and a humidity of 65%, 
the roller of the developing agent application means, the auxiliary roller 
of the feeding means and the agitator means were stopped after every 
rotation for 6 seconds, in order to measure the thickness of the 
developing agent layer held on the peripheral surface of the roller of the 
developing agent application means, amount of electric charge and amount 
of the filled developing agent between the developing agent-limiting zone 
and the developing zone. The thickness of the developing agent layer was 
measured by an ordinary microscopic measuring method (in which thickness 
of the developing agent layer was measured based upon a difference between 
when the microscope was focused on the peripheral surface of the roller 
and when the microscope was focused on the peripheral surface of the 
developing agent layer). The amount of the electric charge of the 
developing agent was calculated in terms of the amount of electric charge 
per gram of toner (.mu.c/g) by sucking the toner from the peripheral 
surface of the roller with an ordinary noncontact-type instrument for 
measuring the amount of electric charge of the toner (of a model shown in 
FIG. 8 of Japanese Patent Application No. 261482/1992), and dividing the 
value measured using a potentiometer by the weight of the toner. The 
amount of the filled developing agent was calculated in terms of the 
weight of the toner per square centimeter (g/cm.sup.2) on the peripheral 
surface of the roller by dividing the amount of the toner sucked using the 
above measuring instrument by the area of suction on the peripheral 
surface of the roller. As for the thickness of the developing agent layer, 
the thickness of the developing agent layer was measured at four places at 
a spaced distance in the lengthwise direction of the roller of the 
developing agent application means, and the measurement was taken two 
times (the roller of the developing agent application means, the auxiliary 
roller of the feeding means and the agitator means were rotated for 6 
seconds and were stopped to take the measurement of the first time and 
then, the roller of the developing agent application means, the auxiliary 
roller of the feeding means and the agitator means were rotated again for 
6 seconds and were stopped to take the measurement of the second time) in 
order to calculate an average value of measurement and a maximum 
difference among the measured values. The amount of electric charge and 
the amount of the filled developing agent were measured by sucking the 
toner at a central portion in the lengthwise direction of the roller of 
the developing agent application means and repeating such measurement 
eight times (measurement was repeated eight times by rotating the roller 
of the developing agent application means, the auxiliary roller of the 
feeding means and the agitator means for 6 seconds each time and stopping 
them), in order to calculate an average value of measurement and a maximum 
difference among the measured values. The calculated average value of 
layer thickness, maximum difference thereof, average value of the amount 
of electric charge, maximum difference thereof, average value of the 
amount of the filled developing agent and maximum difference thereof are 
as shown in Table 1. 
Then the organic photosemiconductor material disposed on the peripheral 
surface of the drum was electrically charged uniformly and was then 
selectively irradiated with a laser beam in order to form an electrostatic 
latent image having a non-image region of +700 V and an image region of 
+120 V on the organic photosemiconductor. The electrostatic latent image 
included a plural number of image regions (so-called solid-black regions) 
each having a size of 30.times.30 mm. The electrostatic latent image was 
developed into a toner image (reversal developing) by using the above 
developing apparatus, and the toner image was transferred onto a common 
paper. In transferring the toner image, the surface of the common paper 
was brought into intimate contact with the peripheral surface of the drum 
and a discharge voltage of -5500 V was applied to a corona discharger 
disposed on the back surface side of the common paper. The toner image 
transferred onto the common paper was fixed using an ordinary fixing 
device that includes a heated roller and a pushing roller, and, then, the 
density ID of the image region and the density FD of the non-image region 
were measured by using a reflection densitometer placed in the market by 
Tokyo Denshoku Co. in the trade name of "TC-6DS". The results are as shown 
in Table 1 below. 
[EXAMPLE 2] 
The toner image was transferred onto a common paper and then fixed under 
the same conditions as in the above-mentioned Example 1 with the exception 
of changing the bias voltage applied to the rotary shaft of the developing 
agent application means. Then, the density ID of the image region and the 
density FD of the non-image region were measured. The results are as shown 
in FIGS. 5 and 6. 
EXAMPLE 3] 
By using the same developing apparatus as that of the above-mentioned 
Example 1, the layer thickness and the amount of electric charge of the 
developing agent held on the peripheral surface of the roller of the 
developing agent application means were measured under the same conditions 
as those of the above-mentioned Example 1 with the exception of changing 
the length of protrusion PL of the free end of the rigid member of the 
developing agent application means in the environment of a temperature of 
20.degree. C. and a humidity of 50%. The results are as shown in FIGS. 7 
and 8. 
[EXAMPLE 4] 
By using the same developing apparatus as that of the above-mentioned 
Example 1, the layer thickness and the amount of electric charge of the 
developing agent held on the peripheral surface of the roller of the 
developing agent application means were measured under the same conditions 
as those of the above-mentioned Example 1 with the exception of changing 
the line pressure of the rigid member with respect to the peripheral 
surface of the roller of the developing agent application means in the 
environment of a temperature of 20.degree. C. and a humidity of 50%. The 
results are as shown in FIGS. 9 and 10. 
[EXAMPLE 5] 
By using the same developing apparatus as that of the above-mentioned 
Example 1, the layer thickness, the amount of electric charge and the 
amount of the filled developing agent held on the peripheral surface of 
the roller of the developing agent application means were measured under 
the same conditions as those of the above-mentioned Example 1 with the 
exception of using, as a rigid member, a soda quartz glass having no 
electrically conducting film on one surface thereof and without applying a 
bias voltage to the rigid member of the developing agent application 
means. Further, the toner image was transferred onto a common paper and 
fixed, and then, the density ID of the image region and the density FD of 
the non-image density on the common paper were measured. The surface of 
the rigid member forcibly contacted to the peripheral surface of the 
roller exhibited a roughness Ra of 0.01, and the coefficient of deflection 
of the rigid member was 1.18.times.10.sup.-6. The measurement results were 
as shown in Table 1 below. 
[EXAMPLE 6] 
By using the same developing apparatus as that of the above-mentioned 
Example 1, the layer thickness, the amount of electric charge and the 
amount of the filled developing agent held on the peripheral surface of 
the roller of the developing agent application means were measured under 
the same conditions as those of the above-mentioned Example 1 with the 
exception of using, as a rigid member, a stainless steel plate having a 
thickness of 3.0 mm of which the surface has been specially treated to 
exhibit a considerably small roughness and which has been placed in the 
market in the trade name of "Stavax". Further, the toner image was 
transferred onto a common paper and fixed, and then, the density ID of the 
image region and the density FD of the non-image density on the common 
paper were measured. The surface of the rigid member placed forcibly into 
contact with the peripheral surface of the roller exhibited a coarseness 
Ra of 0.06, and the coefficient of deflection of the rigid member was 
2.63.times.10.sup.-8. The measurement results were as shown in Table 1 
below. 
[EXAMPLE 7] 
By using the same developing apparatus as that of the above-mentioned 
Example 2, the toner image was transferred onto a common paper under the 
same conditions as those of the above-mentioned Example 2 with the 
exception of using, as a rigid member, a stainless steel plate having a 
thickness of 3.0 mm of which the surface has been specially treated to 
exhibit a considerably small roughness and which has been placed in the 
market in the trade name of "Stavax". Then, the density ID of the image 
region and the density FD of the non-image region on the common paper were 
measured. The results were as shown in FIGS. 11 and 12. 
[EXAMPLE 8 ] 
By using the same developing apparatus as that of the above-mentioned 
Example 1, the layer thickness, the amount of electric charge and the 
amount of the filled developing agent held on the peripheral surface of 
the roller of the developing agent application means were measured under 
the same conditions as those of the above-mentioned Example 1 with the 
exception of using an ordinary stainless steel plate as a rigid member. 
Further, the toner image was transferred onto a common paper and fixed, 
and then, the density ID of the image region and the density FD of the 
non-image density on the common paper were measured. The surface of the 
rigid member placed forcibly into contact with the peripheral surface of 
the roller exhibited a roughness Ra of 0.18, and the coefficient of 
deflection of the rigid member was 4.38.times.10.sup.-7. The measurement 
results were as shown in Table 1 below. 
[EXAMPLE 9] 
By using the same developing apparatus as that of the above-mentioned 
Example 1, the layer thickness, the amount of electric charge and the 
amount of the filled developing agent held on the peripheral surface of 
the roller of the developing agent application means were measured under 
the same conditions as those of the above-mentioned Example 1 with the 
exception of using, as a rigid member, a stainless steel plate having a 
relatively large surface roughness. Further, the toner image was 
transferred onto a common paper and fixed, and then, the density ID of the 
image region and the density FD of the non-image density on the common 
paper were measured. The surface of the rigid member placed forcibly into 
contact with the peripheral surface of the roller exhibited a roughness Ra 
of 3.32, and the coefficient of deflection of the rigid member was 
4.38.times.10.sup.-7. The measurement results were as shown in Table 1 
below. [Comparative Example ] 
By using the same developing apparatus as that of the above-mentioned 
Example 1, the layer thickness, the amount of electric charge and the 
amount of the filled developing agent held on the peripheral surface of 
the roller of the developing agent application means were measured under 
the same conditions as those of the above-mentioned Example 1 with the 
exception of using, as the limiting means, a stainless steel plate having 
a coefficient of deflection of 3.00.times.10.sup.-2, i.e. a non-rigid 
member and having a thickness of 0.1 mm. Further, the toner image was 
transferred onto a common paper and fixed, and the density ID of the image 
region and the density FD of the non-image density were measured. The 
surface of the rigid member placed forcibly into contact with the 
peripheral surface of the roller exhibited a roughness Ra of 0.30. The 
measurement results were as shown in Table 1 below. 
TABLE 1 
__________________________________________________________________________ 
Amount of Amount of the 
Thickness of 
electric charge 
filled developing 
Density 
Density 
Surface Coefficient 
layer (.mu.m) 
(.mu.c/g) agent (mg/cm.sup.2) 
ID of 
FD of 
roughness of Average 
Max Average 
Max Average 
Max image 
non-image 
(Ra) deflection 
value 
difference 
value 
difference 
value 
difference 
region 
region 
__________________________________________________________________________ 
Example 1 
0.01 1.18 .times. 10.sup.-6 
29.8 7.8 16.03 
3.7 9.31 0.8 1.399 
0.001 
Example 5 
0.01 1.18 .times. 10.sup.-6 
30.4 7.9 16.01 
3.2 9.20 0.7 1,396 
0.001 
Example 6 
0.06 2.63 .times. 10.sup.-8 
33.0 8.0 15.46 
2.5 10.97 
2.7 1.400 
0.001 
Example 8 
0.18 4.38 .times. 10.sup.-7 
32.5 9.6 13.21 
4.8 12.32 
2.9 1.408 
0.005 
Example 9 
3.32 4.38 .times. 10.sup.-7 
35.4 12.2 13.40 
6.2 7.13 3.6 1.402 
0.008 
Compara- 
0.30 3.00 .times. 10.sup.-2 
31.0 15.3 14.03 
8.0 11.50 
5.5 1.400 
0.012 
tive 
Example 
__________________________________________________________________________ 
It is understood from a consideration of the measurement results shown in 
Table 1 that when the limiting member is the rigid member, the maximum 
differences among the measured values in any of the layer thickness of the 
developing agent, the amount of electric charge thereof and the amount of 
the filled developing agent are decreased in comparison with the results 
obtained when the limiting member is a non-rigid member, and that the 
developing agent layer has a sufficiently uniform thickness in the 
direction of width on the roller of the developing agent application 
means. Further, it is recognized from the measurement results that there 
is no significant difference among the densities ID of the image region, 
but when the limiting member is made of a non-rigid member, the density FD 
of the non-image region becomes relatively great. When the density FD of 
the non-image region exceeds 0.01, generally, so-called fogging that can 
be perceived with the naked eyes is produced. Further, it is recognized 
that as the surface roughness of the limiting member is smaller, the 
uniformity in the axial direction of the roller of the developing agent 
layer formed on the roller of the developing agent application means is 
improved and the density FD of the non-image region is also decreased. 
[EXAMPLE 10] 
Using the same developing apparatus as that of the above-mentioned Example 
1, the developing, the transferring and the fixing were carried out 
continuously ten thousand times under the same conditions as those of the 
above-mentioned Example 1 (i.e., in the environment of a temperature of 
20.degree. C. and a humidity of 65%). Then, the amount of electric charge 
of the layer of the developing agent held on the peripheral surface of the 
roller of the developing agent application means and the density ID of the 
image region and the density FD of the non-image region of the toner image 
fixed on a common paper were measured in the initial state (prior to the 
continuous operations) and after ten thousand operations (after the 
continuous operations). The results are as shown in Table 2 below. 
[EXAMPLE 11] 
Continuous ten thousand operations of the developing, the transferring and 
the fixing were carried out under the same conditions as those of the 
above-mentioned Example 10 with the exception of using, as the rigid 
member, an ordinary stainless steel plate used in the above-mentioned 
Example 8. Then, the amount of electric charge of the layer of the 
developing agent held on the peripheral surface of the roller of the 
developing agent application means and the density ID of the image region 
and the density FD of the non-image region of the toner image fixed on a 
common paper were measured in the initial state (prior to the continuous 
operations) and after ten thousand operations (after the continuous 
operations). The results are as shown in Table 2 below. 
[EXAMPLE 12] 
Using the same developing apparatus as that of the above-mentioned Example 
1, the developing, the transferring and the fixing were carried out 
continuously two thousand times under the same conditions as those of the 
above-mentioned Example 1 with the excepting that the developing apparatus 
was allowed to stand in an environment of a low temperature and a low 
humidity, i.e. at a temperature of 10.degree. C. and a humidity of 45% for 
12 hours, and thereafter the operations were carried out in the aforesaid 
environment. Then, the density ID of the image region and the density FD 
of the non-image region of the toner image fixed on a common paper were 
measured in the initial state (prior to the continuous operations) and 
after two thousand operations (after the continuous operations). The 
results are as shown in Table 3 below. 
[EXAMPLE 13] 
Continuous two thousand operations of the developing, the transferring and 
the fixing were carried out under the same conditions as those of the 
above-mentioned Example 12 with the exception of using, as the rigid 
member, an ordinary stainless steel plate used in the above-mentioned 
Example 8. Then, the density ID of the image region and the density FD of 
the non-image region of the toner image fixed on a common paper were 
measured in the initial state (prior to the continuous operations) and 
after two thousand operations (after the continuous operations). The 
results are as shown in Table 3 below. 
[EXAMPLE 14] 
Using the same developing apparatus as that of the above-mentioned Example 
1, the developing, the transferring and the fixing were carried out 
continuously two thousand times under the same conditions as those of the 
above-mentioned Example 1 with the exception that the developing apparatus 
was allowed to stand in an environment of a high temperature and a high 
humidity, i.e. at a temperature of 35.degree. C. and a humidity of 85% for 
12 hours, and thereafter the operations were carried out in the aforesaid 
environment. Then, the density ID of the image region and the density FD 
of the non-image region of the toner image fixed on a common paper were 
measured in the initial state (prior to the continuous operations) and 
after two thousand operations (after the continuous operations). The 
results are as shown in Table 3 below. 
[EXAMPLE 15] 
Continuous two thousand operations of the developing, the transferring and 
the fixing were carried out under the same conditions as those of the 
above-mentioned Example 14 with the exception of using, as the rigid 
member, an ordinary stainless steel plate used in the above-mentioned 
Example 8. Then, the density ID of the image region and the density FD of 
the non-image region of the toner image fixed on a common paper were 
measured in the initial state (prior to the continuous operations) and 
after two thousand operations (after the continuous operations). The 
results are as shown in Table 3 below. 
TABLE 2 
__________________________________________________________________________ 
Amount of electric 
Density ID of 
Density FD of 
Surface Coefficient 
charge (.mu.c/g) 
image region 
non-image region 
roughness of Initial 
After Initial 
After Initial 
After 
(Ra) deflection 
state 
10,000 times 
state 
10,000 times 
state 
10,000 times 
__________________________________________________________________________ 
Example 
0.01 1.18 .times. 10.sup.-6 
16.03 
15.74 1.399 
1.388 0.001 
0.000 
10 
Example 
0.18 4.38 .times. 10.sup.-7 
13.21 
10.91 1.408 
1.409 0.001 
0.003 
11 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Density ID of 
Density FD of 
Surface Coefficient image region 
non-image region 
roughness of Initial 
After Initial 
After 
(Ra) deflection 
Environment 
state 
2,000 times 
state 
2,000 times 
__________________________________________________________________________ 
Example 
0.01 1.18 .times. 10.sup.-6 
Low temperature, 
1.375 
1.382 0.002 
0.002 
12 low humidity 
Example 
0.18 4.38 .times. 10.sup.-7 
Low temperature, 
1.373 
1.389 0.003 
0.00 
13 low humidity 
Example 
0.01 1.18 .times. 10.sup.-6 
High temperature, 
1.400 
1.373 0.003 
0.001 
14 high humidity 
Example 
0.18 4.38 .times. 10.sup.-7 
High temperature, 
1.171 
1.357 0.010 
0.002 
15 high humidity 
__________________________________________________________________________ 
It is recognized from the measurement results in Table 2 that there is no 
significant difference among the densities ID of the image region in an 
ordinary environment, but the density FD of the non-image region after 
continuous operations in the case where the rigid member is made of an 
ordinary stainless steel are somewhat greater than those in the case where 
the rigid member is made of a soda quartz glass (Nesa Glass) having an 
electrically conductive tin oxide thin film applied onto the surface 
thereof. However, the density FD value, 0.003, of the non-image region 
after the ten thousand operations is a practically acceptable value, and 
no fogging that is undesirable in practical use is produced. 
Furthermore, it is recognized from the consideration of the measurement 
results shown in Table 3 that when the rigid member is made of ordinary 
stainless steel, the density FD of the non-image region becomes relatively 
high immediately after having been allowed to stand in the 
high-temperature and high-humidity environment and hence, so-called 
fogging tends to be formed, while when the rigid member is made of a soda 
quartz glass (Nesa Glass) having an electrically conductive tin oxide thin 
film applied onto the surface thereof, there can be obtained a 
sufficiently stable and good toner image even upon such a change in the 
environment. 
In the apparatus for developing an electrostatic latent image according to 
the present invention, the amount of the developing agent held on the 
surface of the developing agent application means is limited to become 
very uniform and very stable in the direction of width as desired owing to 
the action of the limiting means that includes the rigid member. The rigid 
member of the limiting means is produced at a sufficiently low cost and 
can be stably used for extended periods of time. 
Though a preferred embodiment of the present invention was described above 
in detail with reference to the accompanying drawings, it should be noted 
that the invention is in no way limited to the above embodiment only but 
can be varied or modified in a variety of other ways without departing 
from the scope of the invention.