Development station having apertured thin film for controlling the flow of developer material

A development station conveys developer material from a sump to a magnetic brush for development of latent images on a photoconductor. The developer material flows through a slot adjacent the magnetic brush. A thin film having a plurality of apertures is positioned adjacent the slot. The film is movable to align the apertures with the slot so that developer material can pass through the slot to the brush. Movement of the film perforations out of alignment with the slot shuts off the flow of developer material to the magnetic brush.

BACKGROUND OF THE INVENTION 
U.S. Pat. No. 4,553,829, issued Nov. 19, 1985 in the name of J. Bares, and 
entitled "Metering Blade for Use in a Development System" discloses a 
magnetic brush development station wherein developer material from a sump 
is provided to a magnetic brush for development of latent images on a 
photoconductor. A metering blade engageable with the brush has a plurality 
of apertures arranged in rows through which the developer material must 
pass as it travels from the sump to the magnetic brush for development of 
latent images. The size of the apertures controls the thickness of the 
layer of developer material advanced to the latent image. A similar 
disclosure appears in U.S. Pat. No. 4,523,833, issued June 18, 1985 in the 
name of T. B. Jones, and entitled "Developer Roller Metering Blade." In 
the Jones patent electrodes are connected to a voltage source and to the 
blade to regulate the quantity of developer material that passes through 
the apertures in the blade, thereby controlling the thickness of the layer 
of developer material on the magnetic brush. Column 6, lines 64-68 of the 
Jones patent suggests that adjustment of the intensity of the electrical 
field to a suitable level will prevent developer material from passing 
through the apertures so that an on/off type of control can be achieved. 
Apparatus of the type disclosed in the patents identified above require a 
metering blade to be held tightly in engagement with the outer surface of 
the magnetic brush. If the shell of the brush rotates, substantial wear 
can occur. Even if the shell is stationary there is a critical adjustment 
of the blade against the shell in order to maintain the required control 
of developer material. If the material leaks under the blade contamination 
can result and complete shutoff of material will not be achieved. 
Moreover, the apparatus shown in both of such patents allows developer 
material to be in contact with the magnetic brush at all times, thus 
increasing the torque required to drive the magnetic brush even when no 
flow of developer material is desired. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide accurate 
metering and, when desired, complete shutoff of developer material to a 
magnetic brush without using a blade resting against the magnetic brush, 
thereby avoiding the need for critical adjustment of the blade, reducing 
the torque applied to the magnetic brush and decreasing contamination 
caused by material leaking past the blade. Other objects of the invention 
are to provide an improved developer metering and shutoff apparatus which 
is self sealing, which increases developer life and decreases torque 
requirements by being able to shut off developer flow to the magnetic 
brush, and which improves the life of the wiper blade typically provided 
for scraping developer material from the magnetic brush after such 
material passes through a development zone. 
The present invention relates to electrographic apparatus having a 
development station with a magnetic brush for applying developer material 
to a photoconductor. Means are provided for feeding developer material to 
the magnetic brush, and an opening is defined between the magnetic brush 
and the feeding means through which developer material passes as it is 
conveyed to the brush. The improvement of the invention comprises means 
for controlling flow of developer material from the feeding means to the 
magnetic brush through the opening. The controlling means comprises a 
member having a plurality of apertures through which developer material 
can flow. The controlling means also comprises means for moving the 
apertured member between a first position wherein the apertures are 
aligned with the opening so that developer material from the feeding means 
can pass through the apertures and be delivered to the magnetic brush and 
a second position wherein the apertures are displaced from the opening to 
block the flow of developer material from the feeding means to the opening 
.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1 of the drawings, a development station of an 
electrographic apparatus is generally designated 10 and comprises a 
housing 12 that defines a sump 14 for receiving developer material. A 
photoconductor 16 travels across the upper portion of the housing 12 and 
contains on its lower surface one or more latent electrostatic images that 
are developed by developer material from sump 14. The developed images can 
be transferred to a copy sheet and fused thereto in a known manner or 
fused onto the photoconductor itself. 
The development station 10 has a magnetic brush 18 for applying developer 
material to the images on photoconductor 16. The brush illustrated 
comprises a core 20 having a plurality of magnets 22 spaced around the 
core, and a cylindrical, non magnetic shell 24 that surrounds the core 20. 
The core and/or shell can be fixed or rotatable, as known in the art. As 
illustrated in the drawings, the core 20 is rotatable in a clockwise 
direction, and the shell rotates in a counterclockwise direction to 
thereby feed developer material in a counterclockwise direction to the 
photoconductor. 
Developer material in sump 14 can be mixed, agitated and triboelectrically 
sheared by means of a ribbon blender generally designated 26. Blender 26 
comprises a shaft 28 that is rotatable about its axis and has a plurality 
of rods 30 projecting therefrom. The rods carry inner and outer helical 
ribbons 32, 34. The pitch of the ribbon 32 is opposite from ribbon 34 so 
that when the shaft 28 is driven in a counterclockwise direction as shown 
in FIG. 1, ribbon 32 tends to drive developer material in one direction 
through the sump 14 while ribbon 34 tends to drive the material in the 
opposite direction. 
Material from sump 14 is moved by the ribbon blender not only axially in 
the sump but also radially outwardly so that some of the material is 
provided to a feeding means generally shown at 36. Feeding means 36 
includes a shaft 38 that is rotated in a clockwise direction and carries 
two or more plates 40. The plates support a plurality of vanes 42 that 
pick up developer material from the ribbon blender 26 and bring such 
material into close proximity with the shell 24 of the magnetic brush 18. 
At that point the magnets 22 of the core 20 attract the developer material 
to the shell so that it can be delivered to the photoconductor 16 by the 
magnetic brush. 
The electrographic apparatus described hereinbefore is disclosed in more 
detail in European Patent Office Publication No. 160,830, published Nov. 
13, 1985, which is based on U.S. patent application Ser. No. 597,323, 
filed Apr. 6, 1984. Reference is made to that publication for a more 
complete description of the apparatus. 
Control means generally designated 50 is provided for regulating the flow 
of developer material from the feeding means 36 to the magnetic brush 18. 
As best shown in FIGS. 2 and 3, the control means 50 comprises an elongate 
block 52 that is beneath the lower right portion of the magnetic brush. 
Thus block 52 is located between the magnetic brush and the sump and also 
between the magnetic brush and the feeding means 36. Block 52 can be 
connected to or supported from the housing 14 in a suitable manner. In the 
central portion of the block 52 there is an elongate, generally 
rectangular feed slot 54 that is substantially aligned with the portions 
of the feed means 36 and magnetic brush 18 that are closest to each other. 
Preferably the slot 54 extends substantially the full length of the 
magnetic brush 18 and is closely adjacent the feeding means 36. Slot 54 
comprises a metering slot through which material can pass from the feeding 
means 36 to the magnetic brush as explained in more detail later. A 
curved, generally cylindrical surface 56 is provided on block 52 on both 
sides of the slot 54. The particular curvature shown in the drawings has 
its center at or near the axis of rotation of the magnetic brush 18. This 
location of the center of curvature can be varied, of course. 
Movement of developer material through metering slot 54 is controlled by a 
thin, compliant film 60 that is stretched across the surface 56 and slot 
54. Film 60 is attached at its ends to reels or shafts 62, 64, each of 
which are rotatable in two opposite directions so that the film can be 
wound onto or unwound from each of the shafts. Shafts 62, 64 are located 
with respect to surface 56 so that an intermediate portion of the film 
extends along and is urged against surface 56. As best shown in FIG. 4, a 
plurality of spaced and aligned apertures 66 are provided in this 
intermediate portion of the film. The apertures preferably are spaced from 
each other along the width of the film 60 and aligned in a row. Preferably 
the perforations are provided throughout substantially the entire length 
of the slot 54. 
One of the shafts, such as shaft 64, is connected to a motor M so that the 
shaft can be driven to move the film 60 along surface 56 from its FIG. 2 
to its FIG. 3 position and thereby move the apertures 66 from a position 
aligned with the slot 54, as shown in FIG. 2, to a position wherein the 
apertures are offset from slot 54, as shown in FIG. 3. Return movement of 
the film can be effected by another motor connected to shaft 62, or by a 
spring which urges shaft 62 in a counterclockwise direction. 
In operation, when developer material is to be provided to magnetic brush 
18 for developing latent images on the photoconductor, film 60 is moved to 
its position shown in FIG. 2. Operation of the ribbon blender 26 and the 
feeding means 36 brings a supply of developer material into the area 
between the feeding means and the adjacent portion of the magnetic brush 
18. At this time the magnets 22 of the magnetic brush attract the 
developer material toward the magnetic brush, thereby causing some of the 
material to flow along the path shown by arrow 70 in FIG. 2 through the 
apertures 66 and the metering slot 54. The material thus attracted to the 
magnetic brush is advanced by the brush to the developing zone between the 
brush and the photoconductor. The thickness of the layer of material 
deposited on the magnetic brush is governed by the size and number of 
apertures 66 and an edge 72 of the block 52, which acts as a metering 
skive. After the developer material on the magnetic brush passes the 
development zone, it is scraped from the outer surface of the magnetic 
brush by a wiper 74 secured to the left edge of block 52 and engageable 
with the outer surface of the magnetic brush. 
When it is desired to shut off the flow of developer material to the 
magnetic brush, motor M is energized to rotate shaft 64 in a clockwise 
direction and thereby move the aperture 66 of film 60 from the position 
aligned with slot 54, as shown in FIGS. 2 and 4, to the position shown in 
FIG. 3 wherein the apertures are offset from the slot 54, thereby shutting 
off the flow of developer material through the slot to the magnetic brush. 
At this time a tight seal is formed across the width of the slot 54 by the 
film 60. More specifically, the magnets 22 of the magnetic brush continue 
to attract developer material from feeding means 36 toward the magnetic 
brush. This material is urged against the thin compliant film 60, causing 
it to be forced tightly against the periphery of the slot 54. In addition, 
the film is held tightly against surface 56 due to the location of shafts 
62, 64 relative to that surface. This seal not only assures complete 
shutoff of the flow of developer material through the slot, but also helps 
assure undesirable leaking of developer material from inside the housing 
12 to the exterior of the housing through the slot or from around the 
magnetic brush. Thus contamination is decreased, copy quality is increased 
and service calls are decreased. 
A number of advantages result from the apparatus for shutting off flow of 
developer material to the magnetic brush. First of all, less torque is 
required to drive the magnetic brush when the flow of developer material 
to the brush has been shut off. This not only reduces torque requirements 
but also reduces power requirements and heat generated by operation of the 
development station. Moreover, the life of the developer material is 
increased by limiting its exposure to the magnetic brush. Another 
advantage is that the metering skive provided by edge 72 need not be 
critical, as with some prior devices, since the number and size of the 
apertures 66 largely provide the critical metering of the developer 
material to the magnetic brush. In addition, the life of wiper 74 is 
prolonged because it is not required to constantly remove developer 
material from the magnetic brush. 
Another advantage of the invention is that very little movement of the film 
is required to start or stop the flow of developer material to the 
magnetic brush. This is important, especially in color copiers where a 
series of development stations are provided and they need to be cycled on 
and off at precisely the right time in the machine cycle for development 
of the latent images on the photoconductor. 
Another advantage of the apparatus of the invention is that the size of the 
metering apertures can be readily changed, as desired, in order to provide 
different operating conditions. In this regard, it will be understood that 
more than one row of metering apertures can be provided in the film 60 and 
spaced from each other so that one or the other row of perforations can be 
aligned with the slot 54 by rotating the shafts 62, 64. This simple 
adjustment could be provided by the machine operator or by the logic and 
control apparatus of the machine without the need for a skilled service 
person. 
While the invention has been described in connection with a preferred 
embodiment thereof, it will be understood that variations and 
modifications can be effected within the spirit and scope of the invention 
as described hereinabove and as defined in the appended claims.