Developer housing

A development system for developing latent magnetic images with magnetic toner comprises a developer housing having an upper chamber communicating through a selectively variable opening with a lower chamber, the lower chamber defining the development zone and being provided with peripheral edge seals. In operation, magnetic toner is gravity fed through the selectively variable opening to the lower chamber, filling the lower chamber to provide flood contact development of the latent magnetic image residing on a magnetizable member which is moved in a direction counter to that of gravity flow. Optional baffles are preferably included in the developer housing and above the development zone to prevent machine contamination by toner powder cloud during high speed development.

BACKGROUND OF THE INVENTION 
This invention relates to magnetic imaging; and, more particularly, to 
development apparatus for applying magnetic toner to latent magnetic 
images. 
Latent magnetic images on magnetizable imaging members are typically 
developed by deposition of magnetic developer material commonly referred 
to as magnetic toner onto the magnetizable imaging member. The developing 
material is attracted to the magnetizable member by magnetic fields 
constituting the latent magnetic image. 
However, in developing latent magnetic images on a magnetizable member it 
is necessary to introduce the developing material within a very short 
distance from the latent magnetic image, typically within about 10 microns 
of the image, due to the short range nature of the magnetic forces 
associated with the latent magnetic image. Accordingly, flood contact 
development of latent magnetic images is generally preferred as a 
technique which will insure that the magnetic toner material is introduced 
within the short distance from a latent magnetic image to allow full, 
dense development. 
PRIOR ART STATEMENT 
Flood contact development for xerographic development is shown in U.S. Pat. 
Nos. 3,685,488 (FIGS. 1, 2 and 3), U.S. Pat. No. 3,380,437 (FIGS. 1-3); 
3,393,663 (FIG. 2); 3,547,660 (FIGS. 1, 2 and 4); 3,641,977 (FIGS. 1-4) 
and in 3,682,137 (FIGS. 1 and 2). Descriptive portions of the 
aforementioned patents corresponding to the figures describe the 
xerographic developer behavior and operation of the apparatus. Flood 
contact development of latent magnetic images with magnetic toner is 
disclosed in U.S. Pat. No. 2,943,908 (FIG. 2). All of the aforementioned 
patents are deemed relevant only to the extent of showing flood, contact 
development of a latent image with toner material; except for 
aforementioned U.S. Pat. No. 3,685,488 (FIG. 2) illustrating a "Y" shaped 
relationship between toner hopper and toner development zone for 
continuous flow xerographic development. 
However, the magnetic forces associated with latent magnetic images are 
much weaker than the electrostatic forces associated with latent 
electrostatic images utilized in xerography. Accordingly, for high speed, 
cyclical magnetic imaging it is essential to the production of good 
quality images having high contrast that the development zone, and thus 
the length of time in which the latent magnetic image is in contact with 
the magnetic toner, be selectively variable to accommodate variations in 
magnetic field strengths of various magnetic recording materials. 
Furthermore, with single component magnetic toner, in contrast to two 
component xerographic developer comprising carrier and toner, it is not 
necessary to have continuous or intermittent developer motion to maintain 
the triboelectric relationship between the toner and carrier. 
Thus, it is desirable to have a compact tank development system for 
developing latent magnetic images which is capable of providing a 
selectively variable development zone, which has magnetic toner storage 
capacity for automatically replenishing toner depleted from the 
development zone in a simplified manner, which prevents continuous flow of 
toner out through the bottom of the development zone and which is capable 
of maintaining intimate contact between magnetic toner and the imaging 
member bearing the latent magnetic image throughout the entire development 
zone. 
SUMMARY OF THE INVENTION 
Objects of this invention, therefore, are to provide the aforementioned 
functions and advantages in a novel, compact tank development system for 
developing latent magnetic images with magnetic toner. 
The aforementioned objects and advantages and others are realized in 
accordance with the practice of the present invention by a tank 
development system comprising a developer housing having therein a "Y" 
shaped relation between an upper toner supply chamber which communicates 
through a selectively variable opening with a lower development zone; the 
developer housing having side and bottom edge seals for low friction, 
conformable engagement with a magnetizable imaging member. For use in high 
speed magnetic development, the tank development system is provided with 
baffles above the development zone to entrap airborne toner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is seen an embodiment of the present 
invention particularly preferred for development of latent magnetic images 
residing on magnetic webs or tape. The tank development apparatus in FIG. 
1 comprises a housing 1 having an opening 30 in the uppermost wall covered 
by a sliding member 31 retained by flanges 2 and 3. Walls 9 and 4 of 
housing 1 define a toner storage or supply chamber communicating with a 
development zone A through an opening 8. Metering plate 5 is moveable into 
and out of opening 8 by movement of retention member 7 along slot 6 in 
wall 4. The developer housing is made of non-magnetic materials such as 
stainless steel to minimize interference with the latent magnetic image 
which is undergoing development and to minimize interference with the 
flowing properties of magnetic material deposited in the toner storage 
chamber. 
Wall 20 of housing 1 is shaped to conform to a predetermined path of travel 
of the magnetizable imaging member which is to be latently magnetically 
imaged and developed. Wall 20 may comprise a portion of either wall 9, or 
of wall 4, or may be a separate wall member of the developer housing. 
Resilient seal forming means 11 may comprise any resilient, including 
deformable material. Typical suitable materials include, Teflon, a 
trademark for DuPont tetrafluoroethylene fluorocarbon resins; soft rubber 
and polyvinyl chloride foam. Seal forming means 11 is affixed to walls 9 
and 20 at least along the predetermined path of travel of the magnetizable 
imaging member which is to be developed. Resilient seal forming means 11 
is affixed to walls 20 and 9 on the sides thereof opposite the toner 
supply chamber as can best be seen from viewing FIG. 2. Resilient seal 
forming means 11 is affixed along the edges of walls 20 and 9 and along 
the bottom of wall 20. As depicted in FIGS. 1 and 2 a low friction 
material is applied to the surface of resilient seal forming means 11 as 
surface 13. Low friction surface 13 comprises a material which has a 
coefficient of friction less than that of the material of resilient seal 
forming means 11. Teflon provides an entirely satisfactory low friction 
layer 13 which can be adhered to or bonded to 11. Low friction surface 13 
is utilized to minimize damage to the magnetizable imaging member by 
decreasing the sliding friction. Resilient means 11 and surface 13 can be 
fabricated into a single member such as a flexible Teflon member and 
molded plastics with low friction surfaces can also be used. 
The embodiments depicted in FIGS. 1 and 2 are particularly suited for 
magnetic development of latent magnetic images because magnetic imaging 
systems are capable of being run at high speeds such as 100 inches or 
greater and the magnetic developer material comprises only toner and not 
the relatively heavier carrier typically found in xerographic development. 
The combination of high speeds and small, light weight magnetic toner 
particles typically produces powder clouds of airborne toner which cause 
contamination of the machine and a general increase in the amount of 
undesired toner residing on background areas of finished hard copy. When 
the present invention is to be employed in high speed magnetic printing 
engines, it is particularly preferred to remove the airborne toner prior 
to its departure from the vicinity of the developing apparatus. As shown 
in FIGS. 1 and 2, this can be conveniently achieved in the present 
invention by locating baffles 10 above the development zone and adapting 
of baffles 10 to direct toner back into the toner supply chamber. While 
several baffle locations and designs can be employed in a perfectly 
satisfactory manner, FIG. 1 depicts baffles 10 extending through slots in 
wall 9. Airborne toner is diverted by baffles 10 from a region between the 
magnetizable imaging member, deformable seal forming means 11, and wall 9 
through slots in wall 9 and back into the toner supply chamber. To 
minimize the formation of powder clouds of airborne toner, baffles 12 are 
mounted on wall 20 on the side of wall 20 facing the magnetizable imaging 
member. Baffles 12 may take any effective shape and it has been found that 
simple bars (shown in FIG. 2) having a height which precludes contact with 
the surface of the magnetizable imaging member when layer 13 is in 
engagement therewith will perform satisfactorily in reducing the formation 
of powder clouds of airborne toner. 
As toner is poured through opening 30 into the toner supply chamber, it 
passes through opening 8 into the space defined by the magnetizable 
imaging member in contact with layer 13, deformable seal forming means 11 
and the top of opening 8. Metering plate 5 can be adjusted so that the 
magnetic toner replenishment rate from the magnetic toner supply chamber 
into the development zone just equals the depletion of magnetic toner from 
the development zone. The height of the developer zone is automatically 
maintained by toner in the supply chamber. While FIG. 1 shows plate 5 
operatively connected to wall 4 to thus act as a metering plate, plate 5 
could be operatively connected to wall 9 to act as a development zone 
adjustment plate by effectively extending the terminal portion of wall 9 
(top most portion of opening 8) selectively and variably closer to or 
further away from wall 20. Since the primary height of the development 
zone is determined by the uppermost portion of opening 8, the height of 
the developer zone A can be effectively controlled to compensate for the 
magnetic field strength emanating from the latent magnetic image on the 
magnetizable imaging member. This is depicted in FIG. 5, wherein like 
numerals refer to like components of FIG. 1. In FIG. 5, it can be seen how 
developer zone height adjusting plate 5' defines an opening 8' which is 
different than opening 8 depicted in FIG. 1. In FIG. 5, the developer zone 
height will correspond to the uppermost portion of opening 8'. 
FIG. 3 schematically illustrates the employment of the embodiment of FIGS. 
1 and 2 or FIG. 5 to develop a latent magnetic image residing on a 
magnetic web or magnetic tape 14. The predetermined portion of the path of 
travel taken by magnetic tape 14 selected for the developer station (i.e., 
that portion of the path of travel of tape 14 along which the developer 
zone A is to be located) in an arcuate path about roller 15. The path of 
travel of tape 14 as depicted in FIG. 3, comes into the developer zone 
from the left, is routed about roller 15, against a backing member 16, and 
diverted onto other process stations by idler rollers 17 and 18. Tape 14 
can be utilized in the form of an endless loop or can be utilized in 
association with supply and takeup reels. The significant point to be 
noted in FIG. 3 is that the wall portion of the developer housing which 
extends below the toner supply chamber and enters into defining the 
developer zone is made very small and performs in an entirely satisfactory 
manner. Yet, the amount of toner present in the toner supply toner of the 
tank development system of the present invention is many times greater 
than that contained in the development zone, allowing automatic 
replenishment of toner in the development zone and the development of 
numerous latent magnetic images. 
FIG. 4 schematically illustrates the utilization of another embodiment of 
the present invention in connection with magnetically developing a latent 
magnetic image which resides on a magnetizable imaging member formed along 
or wrapped around a drum surface. Magnetizable imaging member 17 is formed 
along or wrapped around the surface of drum 16 in FIG. 4. Developer 
housing 1 is essentially the same as that depicted in FIGS. 1-3 and 5 but 
shows a longer wall portion 20' as an illustration of permissible 
variations in accordance with the spirit of the present invention which 
allow the creation of a developer zone around any predetermined portion of 
a path of travel of a magnetizable imaging member. 
Other modifications and variations will become apparent to those skilled in 
the art upon a reading of the present disclosure. These are intended to be 
within the scope of the present invention.