Magnetic developer conveying device

A device for conveying a magnetic developer, includes a non-magnetic sleeve for carrying the magnetic developer, a resin magnet stationarily disposed in the sleeve, the magnet being of a mixture of a resin material and a magnetic material, and extending in a direction of a length of the sleeve, the magnet having first and second magnetic field generating portions, first and second magnetic members disposed outside the sleeve extending in the direction of the length of the sleeve, wherein the first and second magnetic members are spaced apart from each other and are so disposed that a magnetic force applied to the magnet by a magnetic force between the first magnetic field generating portion and the first magnetic member reduces a resultant force to the magnetic by gravity and by a magnetic force between the second magnetic field generating portion and the second magnetic member.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to a device for conveying a magnetic 
developer, which is applicable to a recording apparatus such as a copying 
machine, a printer, a laser recording apparatus and display device. The 
device according to the present invention is most suitable to a developing 
apparatus and a cleaning device for cleaning an image bearing member for 
removing the developer therefrom. 
The most typical magnetic developer conveying device is found in a 
developing apparatus or in a cleaning device used in a recording 
apparatus. 
In such an apparatus, a structure comprising an endlessly movable sleeve of 
non-magnetic material and a magnet disposed therein for producing a 
magnetic field wherein one or both of the sleeve and the magnet are 
relatively rotated, is adopted as a means for conveying the developer for 
developing a latent image or as a means for removing the developer 
remaining on the image bearing member such as a photosensitive member. 
As for the magnet, the structure is employed wherein small pieces of 
magnets are bonded on a metal core, as disclosed in U.S. Pat. No. 
4,557,582, which has been assigned to the assignee of the present 
application. 
As for the developer, one component magnetic developer or two component 
developer which is a mixture of magnetic particles and toner particles, is 
used since then the developer carried on the non-magnetic sleeve surface 
can be controlled by the magnetic field provided by the inside magnet. The 
magnetic developers are in the form of powder and have fluidity. In order 
to achieve the desired developing or cleaning operation, it is preferable 
that the developer is formed into a layer of a regulated thickness, or 
that the developer is stably collected into a developer collecting 
container. 
As an example of regulating a thickness of a one component magnetic 
developer layer, a blade of magnetic material is used, as disclosed in 
U.S. Pat. Nos. 4,386,577, 4,391,512, 4,511,239 and 4,297,970. As an 
example of regulating the thickness of two component developer wherein the 
magnetic particles are confined within a container, there is a blade of 
magnetic material disposed downstream of a magnetic pole, as disclosed in 
U.S. Pat. Nos. 4,548,489 and 4,579,082. As for the collection of the 
developer, a magnetic member is used at the collecting portion, as 
disclosed in U.S. Pat. No. 4,563,978. In order to improve the collection, 
a proposal has been made in U.S. Ser. No. 911,765 filed on Sept. 26, 1986, 
which has been assigned to the assignee of this application. As an example 
of providing a magnetic member adjacent a blade, there are U.S. Pat. No. 
4,244,322 and U.S. Ser. No. 618,558 filed on July 8, 1984. 
Thus, it will be understood that for various purposes, a magnetic member is 
disposed adjacent or in contact to the surface of the non-magnetic sleeve. 
SUMMARY OF THE INVENTION 
Recently, in order to meet the demand for reduction of the size, weight and 
cost of the apparatus, a magnet formed integrally by a resin material and 
magnetic powder mixture, attracts attention. An example of this is 
disclosed in U.S. patent application filed on Oct. 1, 1986 which has been 
assigned to the assignee of this application claiming the Conventional 
Priorities from Japanese Patent Application Nos. 221495/1985 and 
221496/1985. In putting the magnet of this type into practical use, the 
inventors have found problems which are not known. One of the problems is 
that when the magnet of this type, that is, a so-called plastic or resin 
magnet, is employed in the developing apparatus and the cleaning device, 
insufficient development and cleaning are observed, more particularly, the 
image density of the developed image varies along the length of the 
magnet, that is, the density at the central portion is different from that 
adjacent the end areas. Another problem is the occurrence of vibration of 
the apparatus. 
The inventors have made considerable investigations to find the cause of 
those problems and have determined that the magnetic field provided by the 
magnet (inside magnetic field generating means) varies significantly in 
the operating portion for the development or cleaning. It has further been 
determined that there is a portion wherein the variation is large and a 
portion wherein the variation is small, as a result of further 
investigation about the operating portions. 
The inventors have finally found that the resin magnet itself is bent or 
flexed to a certain extent and concluded that the bending is caused by the 
magnetic member disposed around the non-magnetic sleeve as described 
above. The present invention is based on the new finding of the problems 
and causes of the problems, which are significant in practically using a 
magnet of this type. 
The problems are not known and are recognized for the first time by the 
inventors. 
According to the inventors' analysis, the bending, deflection or 
deformation of the magnet is caused by the magnetic force produced between 
the outside magnetic member and the inside resin magnet, more 
particularly, the resin magnet is attracted toward the magnetic member by 
the magnetic force so that the resin magnet itself deforms. 
It is, therefore, an object of the present invention to provide a magnetic 
developer conveying device wherein the deformation of the magnet is 
effectively prevented, so as to allow the desirable developing or cleaning 
operation or the like. 
According to an embodiment of the present invention, the deforming magnetic 
force is reduced by a balancing magnetic member or members. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a developing apparatus incorporating a 
magnetic developer conveying device according to an embodiment of the 
present invention. The developing apparatus comprises a sleeve 4 of 
non-magnetic material having a surface which is closely opposed to an 
unshown latent image bearing member in the form of a drum to develop the 
latent image thereon. A magnet roll 5 is disposed inside the non-magnetic 
sleeve 4 coaxially with the sleeve 4 in the manner that a uniform 
clearance is maintained between the inside surface of the non-magnetic 
sleeve 4 and the magnet roll 5. The magnet roll 5 is fixed to a frame of 
the apparatus at both longitudinal ends thereof. The magnet roll 5 
functions as a means for producing a magnetic field. The magnet roll 5 in 
this embodiment is made by dispersing ferrite in nylon resin and properly 
directing magnetic poles. The present invention is particularly suitable 
to the magnet roll which has been integrally formed by the resin. The 
magnet roll 5 and the non-magnetic sleeve 4 are relatively rotatable about 
the common axis. 
At a left upper portion of the non-magnetic sleeve 4 in this Figure, a 
blade 3 of a magnetic material is provided which has a free end spaced 
from the outer surface of the non-magnetic sleeve 4 with a predetermined 
clearance. The magnetic blade 3 functions as means for regulating a 
thickness of a developer layer formed on the sleeve 4 surface and extends 
along the sleeve and the magnet roll including the central portion 
thereof. A magnetic attraction force produced between the magnetic blade 3 
and the magnet roll 5 is effective to attract an excess amount of the 
developer from the developer deposited on the non-magnetic sleeve 4 by the 
magnet roll 5, so that a proper amount of the developer is carried on the 
sleeve 4 to a developing station where the sleeve 4 is opposed to the 
latent image bearing member. 
Adjacent the bottom of the non-magnetic sleeve 4, that is, at a position 
radially opposite to the magnetic blade 3, a correction or balancing 
magnetic member 8 is mounted to the bottom of the opening of the container 
of a plastic or resin material for containing the developer 2. The 
correcting magnetic member 8 has a width which is larger than the width of 
the magnetic pole (N) which is opposed to the bottom of the opening. The 
correcting magnetic member 8 extends along the length of the sleeve and 
the roll including the central portions thereof. By the provision of the 
correcting member 8, the forces applied to the magnetic roll 5, namely, 
the attraction force M between the magnetic blade 3 and the magnet roll 5, 
the gravity G to the magnet roll 5 and the attraction force M1 between the 
correcting member 8 and the magnet roll 5, are substantially balanced as 
shown in FIG. 2, since the resultant vector R is substantially zero. The 
correcting member 8 has a surface of magnetic material positioned away 
from the blade 3 by about 180 degrees with respect to the axis of the 
sleeve 4. 
The numerical data of this embodiment will now be described. Each of the 
magnetic poles shown in FIG. 1 of the magnet roll 5 provides 650.+-.80 
Gausses. The outer diameter of the magnet roll 5 is 18 mm; the weight 
thereof is 180 g. The magnetic blade 3 is directed to the N pole of the 
magnet roll 5 with a clearance of 2.2 mm from the surface of the sleeve 4. 
The distance from the correcting member 8 to the magnet is about 2.8 mm. 
Under those conditions, the maximum deformation of the magnet roll 5 is 
not more than 0.05 mm. With such a deformation, the variation in the 
magnetic field at the developing station is not more than 10 Gausses. When 
the correcting member 8 is removed from the structure of this embodiment, 
the deformation is 0.15 mm, and the variation in the magnetic field is 60 
Gausses. Thus, it has been confirmed that significant improvement is 
provided by the correcting member 8. 
The correcting member 8 is further effective to reinforce the container 6 
of a resin material. The correcting member 8 is disposed opposed to the 
bottom clearance of the container 6. 
The developer is a magnetic developer and may be one component magnetic 
toner or two component developer containing magnetic particles. 
FIG. 3 illustrates a second embodiment of the present invention, wherein 
two correcting magnetic members 81 and 82 are employed, as contrasted to 
the first embodiment. In this embodiment, the distances l1 and l2 between 
the non-magnetic sleeve 4 and the correcting members 81 and 82, are set to 
be larger than the distance L between the magnetic blade 3 and the 
non-magnetic sleeve 4. However, it is preferable that the distances l1 and 
l2 are not more than 3 mm in order to provide sufficient magnetic 
attraction. Due to the distance relations, the correcting magnetic members 
81 and 82 function only as a means for preventing the deformation or 
deflection of the magnet roll 5 but do not have the function of regulating 
the developer. 
Where a plurality of the correcting magnetic members are used, as in this 
embodiment, the influence, to the intended function, of the errors in the 
dimensions and positions of those members, is reduced, so that the 
reduction of the resultant force R is stabilized, reaching zero. 
The numerical data of this embodiment will now be described. The material 
of the stationary magnet roll 5 is the same as in the first embodiment, 
and each of the magnetic poles provides 600.+-.50 Gausses. The magnet roll 
5 has an outer diameter of 12 mm. The distance L=0.25 mm; l1 is 1.0 mm; 
and l2 is 0.5 mm. Under those conditions, the maximum deformation of the 
magnet roll 5 is 0.07 mm; and the magnetic field variation in the 
developing position is 20 Gausses. When the correcting magnetic members 
are removed from the structure of this embodiment, the deformation has 
been found to be 0.25 mm with the magnetic field variation of 80 Gausses. 
Thus, it has been confirmed that the significant improvement has been 
achieved. 
The advantage of reinforcing the container is also provided in this 
embodiment. 
As will be understood, the single correcting member of the first embodiment 
corresponds to a structure where the plural correcting members of the 
second embodiment are connected integrally, and therefore, the correcting 
function is preferably stabilized. 
As described above, according to the present invention, the correcting 
member is disposed so as to balance the magnetic forces and the gravity 
applied to the magnet roll, thus greatly reducing the resultant force. 
Therefore, the deflection of the resin magnet is significantly reduced, 
and therefore, the vibration or non-uniform density of the image produced 
by the deformation is remarkably decreased. Thus, the performance of the 
developing device and the cleaning device is significantly improved. 
As an additional advantage, the correcting member is effective to reinforce 
the developer container. 
Particularly, the present invention is advantageous in view of the fact 
that, in order to meet the recent demand for reduction of size, weight and 
cost, a more flexible magnet roll is used, such as a magnet roll produced 
through a process wherein it is integrally formed without core metal from 
the mixture of magnetic powder and binder resin and then the magnetic 
particles are property directed and magnetized. This is because the 
problems solved by the present invention is a significant cause of 
insufficient development or insufficient cleaning. By the present 
invention, such a magnet roll becomes practically usable, and therefore, 
inexpensive, small and light apparatus as a whole can be provided with 
stabilized developing and cleaning operations. 
According to the inventors' investigations, the deformation or deflection 
of the magnet roll is significantly large when the diameter of the resin 
magnet roll is not more than 20 mm. In that case, the variation in the 
magnetic field (magnetic flux density) in a certain region exceeds 100 
Gausses, which prevents reduction of the apparatus size. When the present 
invention is used, the maximum deformation occurring in the middle of the 
length of the magnet roll can be reduced to not more than 0.1 mm; and the 
variation in the magnetic flux density is not more than 40 Gausses, even 
to the extent of not more than 20 Gausses. Therefore, a small diameter 
resin magnet roll is practically usable without inconvenience. 
It is preferable that the reduced resultant force R is directed so that the 
resin magnet is pushed toward the portion where the development or 
cleaning operation is performed, since then the tolerance of the amount of 
deformation is wider than when the force R is directed otherwise. The 
force R effective to push the magnet toward the acting area can 
accommodate the possible errors resulting from variations in the 
manufacturing, and therefore, it is particularly advantageous in the case 
of mass-production. As shown in FIG. 1 it is preferable that the 
correcting member 8 has a surface substantially along the circumference of 
the non-magnetic sleeve 4, and the width is preferably not less than 7 mm. 
The position where the correcting member is mounted is not particularly 
limited, if the resultant force is reduced and if the resin magnet is 
stabilized. For example, the correcting member of the magnetic material 
may be a part of the container. Furthermore, plural correcting members may 
be distributed in the circumferential direction, and in this case, the 
resultant force is stably reduced substantially to zero. 
The correcting member of the magnetic material is employed in order to 
reduce the resultant force vector applied to the magnetic field generating 
means, and is not intended to limit or regulate the thickness of the 
developer layer on the non-magnetic sleeve. Therefore, the distance 
between the correcting member and the non-magnetic sleeve is preferably 
larger than the distance between the developer regulating member and the 
non-magnetic sleeve. 
The correcting member may be a magnet, and it may be fixed to the part of 
the container of a resin material, and in this case, the correcting member 
is effective to reinforce the container. 
Most often, the correcting member is disposed radially opposite to the 
developer layer regulating member. It is preferable that at least one of 
the correcting members or a part of the correcting member is disposed in 
the clearance formed between the non-magnetic sleeve and the bottom of the 
container, since then the developer in the container is prevented from 
leaking out through this clearance. The correcting member of the magnetic 
material may be a magnet. 
The shape of the latent image bearing member is not limited, but may be a 
drum, belt or sheet. 
The resin material constituting the resin magnet is preferably polyamide 
resin (nylon) when it is integrally formed with its shaft, and other 
examples of the resin material are synthetic resin, rubber or a mixture of 
two or more resin materials. More particularly, usable resin materials are 
rigid polyvinyl-chloride resin, polystyrene resin, polypropylene resin, 
styrene-acrylonitrile resin, ABS resin, polyacetal resin, polycarbonate 
resin, polyphenylene resin, polysulfone resin and the like. 
Furthermore, it has been found that when the resultant force applied to the 
resin magnet roller (the vector sum of the gravity and the magnetic 
attraction forces applied thereto) is larger than 413 g (uniformly 
distributed load), the situation is similar to those shown in FIGS. 5 and 
7, with the result of significant deformation of the roll. When the 
magnetic correcting member as described above is added, it has been 
confirmed that there is no practical problem if the resultant force is not 
more than 400 g (uniformly distributed load). Further investigation by the 
inventors have determined that when the resultant force is not more than 
100 g (uniformly distributed load), the deformation is satisfactorily 
reduced even under the condition of relatively high temperature and 
humidity, and it is durable to the change of ambient conditions when, for 
example, the machine is transported. Further, when the resultant force is 
not more than 100 g, the clearance between the developer carrying sleeve 4 
and the resin roll 5 can be decreased, whereby the magnetic flux density 
at the surface of the developer carrying surface 4 can be increased, and 
therefore, the diameter of the roll (4, 5) can be reduced. 
The present invention covers any combination of the above described 
structures. 
Referring to FIGS. 5 and 6, the description will be made as to the reasons 
why the problems solved by the present invention have not been significant 
and have not been noted. Also, reference will be made to FIGS. 7 and 8 
which illustrate the structure not using the present invention. 
FIG. 5 is a sectional view of a developing apparatus of a conventional 
type. A sleeve 4 of non-magnetic material is disposed closely to a latent 
image bearing member 1 in the form of a drum. A stationary magnet roll 51 
is disposed inside the sleeve 4 with a predetermined clearance and 
coaxially with the sleeve 4. The sleeve 4 and the magnet roll 51 are 
relatively rotatable. In the example of FIG. 5, the magnets 5 mounted on a 
reinforcing core metal are stationary, while the sleeve 4 rotates in the 
direction indicated by an arrow B. The magnetic developer (toner) 2 is 
attracted by the magnetic force by the magnet roll 5 and is deposited on 
the outer surface of the sleeve 4. The developer 2 is carried on the 
sleeve 4 rotating in the direction of the arrow B to the developing 
station where the latent image on the latent image bearing member is 
developed while the latent image bearing member is rotating in the 
direction of an arrow A. 
In order to regulate the thickness of the layer of the developer on the 
sleeve 4, a blade 3 of magnetic material (developer regulating member) is 
disposed outside sleeve 4 with its end spaced from the outer surface of 
the sleeve by a predetermined clearance. Therefore, developer exceeding 
the predetermined amount is magnetically attracted and removed from the 
sleeve 4 by the magnetic blade 3, so that the predetermined thickness of 
the layer is maintained. 
The developing apparatus further includes a stirring means 7 for stirring 
the developer 2 within the container 6. 
As shown in FIG. 6, in the conventional apparatus, the resultant force R of 
gravity G applied to the magnet roll 51 and the magnetic attraction force 
between the magnetic blade 3 and the magnet roll 51, is fairly large. 
However, the magnet roll includes a rigid metal material so that no 
substantial influence results from the resultant force R. Therefore, in 
the conventional apparatus, the problems themselves on which the inventors 
focus, have not been recognized. 
FIG. 7 illustrates a structure which is similar to FIGS. 1 and 3 structures 
but without the correcting magnetic members 8, 81 and 82, the resultant 
force applied to the resin magnet 5 which is the vector sum of the gravity 
force G and the magnetic attraction force between the magnetic blade 3 and 
the magnetic pole N in the vicinity thereof, is large enough to deform the 
stationary resin magnet even to such an extent that the position of the 
magnetic pole S at the developing station is changed with the result of 
disturbance to the developing operation. FIG. 8 illustrates the resultant 
force R in the structure of FIG. 7. It will be understood that the problem 
arises in the structure of FIG. 7. 
The present invention is most suitable to such a device wherein the 
magnetic developer is applied and carried thereon over the entire surface 
of the non-magnetic sleeve. However, the present invention is applicable 
to the case where two component developer is contained in the container, 
and only the toner particles are conveyed to the developing position. In 
such a case, the possible disturbance to the conveyance of the developer 
and the state of developer application can be prevented. In the foregoing 
description, the magnet 5 has four magnetic poles, but this is not 
limiting, and the present invention is applicable to the case where only 
the developing magnetic pole and the developer layer regulating pole are 
of resin magnet. 
While the invention has been described with reference to the structures 
disclosed herein, it is not confined to the details set forth and this 
application is intended to cover such modifications or changes as may come 
within the purposes of the improvements or the scope of the following 
claims.