Magnetic brush developing device

A magnetic brush developing device comprising a developing roller including a cylindrical stationary magnet and a sleeve rotatably mounted around the magnet, the developing roller being disposed adjacent the surface of a latent image bearing member, the cylindrical magnet having a developing magnetic pole facing the surface of the latent image forming member and transporting magnetic poles respectively disposed above and below the developing magnetic pole in adjacent relation thereto, the transporting magnetic poles being narrower in width than and having an opposite polarity to the developing magnetic pole.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a magnetic brush developing device, and more 
particularly to a magnetic brush developing device for use in an 
electrophotographic reproducing machine. 
2. Discussion of the Prior Art 
Magnetic brush developing devices are disclosed in U.S. Pat. Nos. 2,786,439 
and 2,786,440 issued to C. J. Young in 1957. A magnetic brush developing 
device is very effective for reproducing continuous tone images, and 
because of this, the device is increasingly used in electrophotographic 
reproducing machines or the like. 
Generally in magnetic brush development, a developer consisting of an iron 
powder carrier and toner is formed into brush-like burs by means of a 
developing roller consisting of a stationary magnet and a sleeve rotating 
around the stationary magnet so that the brush-like burs may slidingly 
pass over the surface of an electrostatic latent image bearing member 
thereby developing the electrostatic latent image into a visual image. 
Transportation of the developer is effected by the sleeve rotating about 
the magnet and hence the transportability of the developer is largely 
dependent upon the magnetic field produced by the magnet used. 
The magnet used in the prior art is of a rectangular cross-section as shown 
in FIG. 1, a sleeve 2 being rotatably mounted around the rectangular 
magnet. A transporting magnet 3 delivers the developer to the succeeding 
magnet 1. 
Because the rectangular cross-sectional shape magnet 1 has magnetic poles 
in the right and reverse sides thereof, flux density A in the vertical 
direction with respect to the developing magnetic pole (as shown by 
phantom line A) is high, while flux density B in the direction tangential 
to the magnetic pole (as shown by phantom line B) is low. Since flux 
density B in the tangential direction contributes to transportion of the 
developer, the transportability of the magnetic pole in the conventional 
device has been extremely low, and hence the permissible range of flow 
rate of developer has been extremely limited. For this reason, if an 
increase in the amount of developer to be transported is needed for 
increasing the developing speed, the magnetic pole in the conventional 
device will fail to transport the required amount of developer properly, 
with the resulting accumulation of developer in the supply side of 
developing roller, the accumulated developer being eventually spilt off 
from the roller to the outside of the developing device. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide an improved 
magnetic brush developing device for transporting developer. 
Other objects and advantages of this invention will be apparent from a 
reading of the following specification and claims taken with the drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 2, there is diagrammatically illustrated a magnetic brush 
developing device 10 in accordance with the invention. A casing 11 has an 
open portion 13 facing a latent image bearing member 12, opening 13 
covering the entire length in the axial direction of the latent image 
bearing member 12. Disposed in casing 11 are a developing roller 14 and a 
developer transporting roller 15 which are disposed in vertically 
contiguous relation with respect to each other; a toner feeding unit 16; a 
developer scraping baffle 17 facing developing roller 14; and a developer 
reservoir 18. 
The developing roller 14 consists of a stationary cylindrical magnet 19 
having plural magnetic poles, and a sleeve 20 rotatably mounted around the 
cylindrical magnet 19. The plurality of magnetic poles of cylindrical 
magnet 19 includes a developing magnetic pole 21 having a width large 
enough to effect development and upper and lower transporting magnetic 
poles 22 and 23 respectively disposed upwardly and downwardly of 
developing magnetic pole 21 in adjacent relation thereto. Upper and lower 
transporting magnetic poles 22 and 23 contribute to transportation of the 
developer. Respective transporting magnetic poles 22 and 23 are narrower 
in width than the developing magnetic pole 21. Disposed adjacent to 
transporting magnetic pole 23 and near to transporting roller 15 is an 
auxiliary magnetic pole 24, which smoothes the delivery of developer from 
transporting roller 15 to developing roller 14. 
The magnetic poles of cylindrical magnet 19 are so arranged around the 
outer periphery of cylinder that their polarities may alternate with 
respect to each other. Thus, developing magnetic pole 21 may be a North 
pole while transporting magnetic poles 22 and 23 may be South poles while 
auxiliary transporting magnetic pole 24 would be a North pole. 
The feeding of developer to developing roller 14 is effected by 
transporting roller 15, which also has a cylindrical magnet 25 as in 
developing roller 14. The cylindrical magnet 25 has a magnetic pole 26 
disposed adjacent to and in facing relation to auxiliary transporting 
magnetic pole 24 of developing roller 14, the polarity of pole 26 being 
opposite to that of auxiliary magnetic pole 24. Magnetic poles 27 and 28 
are disposed in facing relation to the developer transporting path and 
substantially apart from one another, the spacing between poles 26, 27 and 
28 being preferably substantially equal with magnetic poles 27 and 28 
being of opposite polarity with respect to each other. A cylindrical 
sleeve 29 is rotatably mounted around cylindrical magnet 25. 
In operation of the magnetic brush developing device thus described, the 
developer from developer reservoir 18 is transported upwardly with the aid 
of cylindrical magnet 25 and cylindrical sleeve 29 of transporting roller 
15 and then delivered to auxiliary transporting magnetic pole 24 of 
developing roller 14. The developer fed to developing roller 14 is 
transported to developing magnetic pole 21 by means of transporting 
magnetic pole 23 of cylindrical magnet 19 through rotation of sleeve 20. 
The developer is now formed into brush-like burs due to the magnetic field 
of developing magnetic pole 21, so that the burs of developer slidingly 
pass over the surface of the latent image bearing member 12 whereby 
development is achieved. 
After completion of development, the developing agent, whose toner is 
reduced, is transported upwardly by means of transporting magnetic pole 22 
towards developer scraping member 17 whereby the developer is scraped off 
of the surface of developing roller 14. The developer thus scraped off 
drops downwards joining with toner fed from the toner feeding unit 16 and 
is received by developing agent reservoir 18 to be uniformly mixed with 
the newly added toner. 
In the magnetic brush developing device according to the present invention, 
transporting magnetic poles 22 and 23 of cylindrical magnet 19 are 
disposed adjacent developing magnetic pole 21 so that flux density B' in 
the direction tangential to developing magnetic pole 21 is large, as shown 
in FIG. 3, as compared to that of the rectangular magnet used in the prior 
art. This improves the transportability of developing magnetic pole 21 for 
the developer. Dotted line A' in FIG. 3 represents a flux density in the 
direction perpendicular to the developing magnetic pole 21. 
Because transportation of the developer is greatly improved, the 
permissible range of developer flow rate is increased. Increased developer 
flow rate permits increased developing speed without risk of leakage of 
the developer to the outside of the developing device. 
Furthermore, even if a gap variation between latent image bearing member 12 
and developing roller 14 arises, the stream of developer is maintained in 
a normal condition without the developer being leaked to the outside of 
the device, and thus an image of high quality will be reproduced.