Electrographic development apparatus having coordinated gate mechanism and wiper

A development station for electrographic apparatus has a magnetic brush which receives developer material from a sump and applies it to a latent image on a photoconductor. A metering slot for the developer material is provided adjacent the magnetic brush. A gate mechanism controls flow of developer material through the slot by moving between an open position adjacent the metering slot to allow developer material to pass through the slot and a closed position to block flow of developer material through the slot. A wiper blade removes excess developer material from the brush after the image has been developed. The wiper blade is movable into and out of engagement with the magnetic brush and is coupled to the gate mechanism so that when the gate is closed the wiper blade is out of engagement with the brush.

BACKGROUND OF THE INVENTION 
This invention relates to a development station for an electrographic 
apparatus having a magnetic brush for developing an electrostatic image 
wherein flow of developer material to the brush and removal of material 
from the brush are controlled together for starting and stopping 
development of the images. 
In electrographic development apparatus there is a recognized need to be 
able to create a layer of development particles on a magnetic brush 
quickly in order to develop an image and to shut off the flow of 
development material to the brush when development of images is not 
desired. For example, U.S. Pat. No. 3,579,139, issued Apr. 20, 1971, 
discloses a developer unit having devices which control the developing 
action of the unit so that the action can be switched on or off rapidly. 
The developer unit has two brushes, and a gate adjacent one of the brushes 
is mounted for movement into and out of engagement with the brush to 
control the flow of developer material to the one brush. The second brush 
of the developer unit has a magnet which is rotated to interrupt flow of 
developer material over the second brush. The magnet and the gate are 
controlled by the machine programming system and can be simultaneously 
operated by the programming system. A mechanism for controlling formation 
of bristles on the brush is needed not only for applying black toner but 
also in color copiers where toners of two or more colors are provided to a 
photoconductor, and it is important to be able to rapidly start and stop 
any one of several development stations with accuracy to avoid overlapping 
of the different toners on the photoconductor. 
It is also known to provide a wiper blade for scraping developer material 
from a magnetic brush after the developer material has passed through the 
development zone. Such a wiper blade can return toner-depleted developer 
material to a sump for replenishment of toner before the developer 
material is again provided to the development zone. Such wiper blades tend 
to have a short useful life due to constant engagement of the blade with 
the magnetic brush. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide electrographic 
development apparatus with improved gating of the flow of developer 
material to a magnetic brush, and to coordinate the gating action with 
operation of a wiper blade which removes developer material from the 
magnetic brush. 
In accordance with the present invention an electrographic development 
station has a magnetic brush for applying developer material to a latent 
electrostatic image on a photoconductor to develop the image. The station 
has a metering slot adjacent the magnetic brush, and means are provided 
for feeding developer material to the slot so that the material can be 
provided to the brush for use in developing the image. A wiper blade 
removes excess developer material from the brush after the image has been 
developed. The improvement of the invention includes a gate mechanism 
which is mounted for movement between an open position adjacent the 
metering slot so that developer material can pass through the slot and a 
closed position wherein the gate mechanism blocks the developer material 
through the slot. Means are provided for moving the wiper blade into and 
out of engagement with the magnetic brush. Means are provided for coupling 
the wiper blade and the gate mechanism together for coordinated movement 
so that the wiper blade is in engagement with the magnetic brush when the 
gate mechanism is in its open position, and the wiper blade is out of 
engagement with the magnetic brush when the gate mechanism is in its 
closed position.

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 
then 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 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 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. The thickness of the 
layer of the developer material on the shell is controlled by a metering 
skive 44 located adjacent but spaced from the outer surface of the shell 
24 and between the feeding means 36 and the photoconductor 16. 
The 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. 
Referring now to FIGS. 1-3 of the drawings, a wiper block 50 is provided 
between the magnetic brush 16 and the ribbon blender 26. The block is 
mounted for pivotal movement about a pivot 52. Along the left side of the 
block there is provided a wiper blade 54 which extends substantially the 
full length of the magnetic brush 18. Normally the wiper blade is in 
contact with the shell 24 of the magnetic brush to scrape developer 
material from the shell, as shown by arrow 56, and return such material to 
the sump for mixing with other developer material in the sump. 
A metering slot 60 for developer material flowing to the magnetic brush is 
defined by the skive 44 and the wiper block 50. The width of the metering 
slot is exaggerated in the drawings to better illustrate the slot and 
related structures. Flow of material through slot 60 is controlled by a 
gate mechanism 62. The gate mechanism comprises an abutment 64 located 
along the edge of skive 44 and extending substantially the full length of 
the magnetic brush 18. 
The gate mechanism also includes a gate 66 that is slideably mounted on the 
block 50 by one or more bolts 68 that are mounted on the block and extend 
through elongate slots 70 in the gate. This mounting of the gate on the 
block 50 allows it to be moved between an open position shown in FIG. 2 
and a closed position shown in FIG. 3. When the gate mechanism is in the 
open position developer material can flow along the path shown by arrow 72 
between the end of the gate 66 and the abutment 64 and thus flow through 
the metering slot 60 and be provided to the magnetic brush 18. On the 
other hand, when the gate is moved to its closed position shown in FIG. 3 
the end of the gate 66 contacts the abutment 64 and thus effectively 
blocks the flow of developer material through the metering slot to the 
magnetic brush, thereby cutting off the flow of developer material to the 
photoconductor 16. At that point any further developer material advanced 
by the feed means 36 will travel along the path shown by arrow 74 in FIG. 
3 leading toward the sump 14. 
During initial movement of the gate 66 from its FIG. 2 toward its FIG. 3 
position the gate moves relative to wiper block 50 due to the elongate 
slot 70. After that initial movement the end of the slot strikes the 
mounting bolt 68 to cause pivotal movement of the wiper block 50 about the 
axis of pivot 52. This effects movement of the wiper blade 54 from its 
FIG. 2 to its FIG. 3 position and thereby disengages the wiper blade from 
the outer surface of shell 24. Thus the wiper blade is coupled to the gate 
so that the movement of the gate and blade are coordinated to ensure that 
the wiper blade is in engagement with the shell when the gate mechanism is 
open and to ensure separation of the wiper blade from the shell when the 
gate mechanism is closed. 
Movement of the gate mechanism 62 and block 50 can be accomplished in any 
suitable manner. For example, a solenoid 76 can be provided and connected 
to the gate 66 as shown diagrammatically at 78. 
A modification of the invention is illustrated in FIG. 4 of the drawings. 
In FIG. 4 the same reference numerals have been used to indicate the same 
or similar parts. In this embodiment the gating mechanism for controlling 
the flow of developer material through the metering slot 60 is provided by 
a tapered end portion 80 of a metering skive 82. The tip end 84 of end 
portion 80 normally is positioned in closely spaced relation to the gate 
66 attached to the metering block 50. In this embodiment a gate 81 is 
rigidly secured to the block 50 by mounting bolts 83. 
Skive 82 is mounted for pivotal movement about the axis of a pivot 86 so 
that the tip 84 can be moved from its solid to its dotted line positions. 
When in the solid line position the skive 82 allows developer material to 
flow through the metering slot 60 to the magnetic brush 18 and skive 82 
defines the thickness of the layer of developer material on the brush. 
When the skive is pivoted to bring the tip 84 to its dotted line position, 
the tip engages the outer surface of the shell 24 of the magnetic brush to 
close the metering slot to the flow of developer material and scrape any 
developer material from the brush. This pivotal movement can be affected 
by any suitable means, such as by a rotary solenoid shown at 88 which is 
connected directly to the pivot 86 and is effective, when energized, to 
swing the skive between the positions illustrated. 
The wiper blade 54 can be moved from a position in engagement with the 
outer surface of shell 24 to a position spaced therefrom by a similar 
rotary solenoid 90 connected to the pivot 52 for the metering block 50 so 
that when the solenoid is energized it swings the metering block in a 
counterclockwise direction to move the blade 54 away from the shell. Both 
solenoids 88 and 90 can be controlled from the logic and control unit LCU 
of the electrographic apparatus so that their movements and operation are 
coordinated. The solenoids can be energized simultaneously, or if desired, 
solenoid 88 can be energized to shut off the flow of material through the 
metering slot 60 a brief period of time before the wiper blade 54 is 
disengaged from the sleeve 24. This allows the wiper blade to scrape 
developer material from the shell that was on the shell before the 
metering slot was closed by the tip 84 of the skive. 
During operation of either of the embodiments of the invention, the ribbon 
blender 26 is effective to circulate and mix developer material in sump 
14, triboelectrically charge it and provide such material to the feed 
means 36. The feed means 36 picks up the developer material and delivers 
it to the metering slot 60. When the metering slot is open, as shown in 
FIG. 2 and in solid lines in FIG. 4, the magnets 22 of the magnetic brush 
attract the developer material through the slot to allow its 
transportation to the photoconductor 16 for developing of electrostatic 
images thereon. The thickness of developer material on the magnetic brush 
is governed by the metering skives 44 and 82. After the developer material 
passes to the left side of the magnetic brush and past the development 
zone between the magnetic brush and the photoconductor, the developer 
material remaining on the magnetic brush is removed by the wiper blade 54 
which allows it to return to the sump for mixing with other material 
therein. Additional fresh toner can be provided to the sump in a 
conventional manner. 
When it is desired to shut off the flow of developer material to the 
magnetic brush, the gate mechanism of FIGS. 1-3 is energized by solenoid 
76 which affects movement of the gate 66 toward the skive 44. After some 
movement of the gate, the left end of slot 70 will engage the mounting 
bolt 68 to effect pivotal movement of the wiper block 50 and thus separate 
the wiper blade 54 from the magnetic brush just as the gate 66 comes into 
contact with the abutment 64 to shut off the metering slot. At this time 
the parts are in the position illustrated in FIG. 3 and developer material 
brought toward the metering slot by the feed means 36 will travel along 
the path shown by the arrow 74 and be returned to the sump. 
In a similar manner, when solenoids 88 and 90 of FIG. 4 are energized the 
skive 82 swings to its dotted line position so that its tip end engages 
the sleeve 24 of the magnetic brush to close the gate and shut off the 
flow of developer material to the brush. Simultaneously, or after a slight 
delay, solenoid 90 swings the metering block 50 about pivot 52 to bring 
the wiper blade 54 to its dotted line position. 
There are a number of advantages resulting from the invention. Developer 
material ages during use, and developer aging is decreased by stopping the 
flow of the developer material to the magnetic brush during periods when 
images are not to be developed. Secondly, this termination of flow of 
developer material around the magnetic brush also decreases contamination 
by the development station of adjacent areas due to dusting that occurs by 
circulation of the developer material. Another advantage is that the wiper 
blades have a tendency to age quickly due to their constant contact with 
the shell of the magnetic brush. By separating the wiper blade from the 
shell during periods of non use, the life of the wiper blade can be 
increased. 
In some instances color copies are produced in electrographic apparatus 
having two or more developer stations. In such stations it is important to 
make certain that toner materials of one color are provided to the 
photoconductor at any given time or, alternatively, that other developer 
apparatus for another color toner is separated from the photoconductor 
while toner of one color is being provided to the photoconductor. By 
gating the development station to its closed position utilizing the 
mechanisms of the present invention, there is no longer a need to move the 
entire toning station relative to the photoconductor, as typically 
occurred with prior art apparatus. 
Another advantage of the invention is that it reduces the torque required 
for operation of the development station. More specifically, transport of 
development material around the magnetic brush requires a certain amount 
of torque. By shutting off the flow of material around the development 
station during periods of non use, the torque requirements are reduced. 
This is important in electrographic apparatus because such apparatus have 
fairly highpower requirements and the power requirements can constitute a 
limitation on addition of other apparatus. Moreover, the application of 
torque is accompanied by the generation of heat and possibly eddy currents 
which adversely affect the operation of the apparatus. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but 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.