Toner metering apparatus with pressure equalization

Metering roller (3) in the electrophotographic developer cartridge (1) is unsymmetrical along its length. As the metering roller rotates it distributes toner (11) both ways between chamber 13 and chamber 19 to maintain an equilibrium level (31) between the chambers. The unsymmetrical roller simultaneously reduces and increases the area of chamber 11, and possibly also provides a significant open path to chamber 19 across its flat surfaces (35), to inherently eliminate significant pressure build-up in chamber 13. The need for a vent between the chambers is eliminated.

TECHNICAL FIELD 
This invention relates to apparatus for metering of toner powder in which 
the pressure of a rotating metering action is equalized inherently, 
thereby avoiding the use of vents. 
BACKGROUND OF THE INVENTION 
This application is an improvement of the invention described in United 
States patent application Ser. No. 07/392,680; filed Aug. 11, 1989, now 
U.S. Pat. No. 5,012,289; titled Toner Metering Apparatus, and assigned to 
the same assignee to which this application is assigned. That apparatus 
has a rotating roller interacting with three flaps to meter toner as 
required both to and away from a developer roller chamber and a toner 
supply chamber. Air pressure created by the rotating roller is reduced by 
a vent between the two chambers. Vents, however, can become clogged. A 
device which inherently eliminates the pressure differential is more 
reliable and is potentially less expensive. 
The apparatus of the foregoing patent application is the only closely 
similar structure known, and it has a symmetrical rotating roller and 
employs venting. This invention employs a roller which is non-symmetrical 
along its length. U.S. Pat. No. 3,918,839 to Blackwell et al is of 
interest only in that it shows a non-symmetrical blade, but not used for 
toner metering. 
DISCLOSURE OF THE INVENTION 
In accordance with this invention the metering roller has a different 
configuration along its length so that at some points it would be moving 
toner one way while at other points it would provide an enlarged area in 
the chamber receiving toner. This counteracts the build-up of air pressure 
between the two chambers between which the roller operates by permitting 
air to be redistributed in a single chamber and also possibly providing a 
more open path between the chambers. More specifically, the metering 
roller is elongated and the outer configuration is unsymmetrical so as 
achieve the metering action. Half of the length of the roller is 
configured so as to be the 90 degree rotation of the other half, so that 
the metering action is about equally divided between opposite locations in 
the metering cycle during revolutions of the roller. This achieves 
inherent equalization of pressure sufficient to avoid the need for any 
vent between the two chambers.

BEST MODE FOR CARRYING OUT THE INVENTION 
As described in the foregoing application, the invention in the preferred 
embodiment resides in a replaceable cartridge 1 used with an 
electrophotographic printing device. FIG. 1 is identical to FIG. 4 of that 
application except for the reference numerals being different, the venting 
structure being eliminated, and the metering roller 3 being unsymmetrical, 
as shown in detail in FIG. 2a and FIG. 2b. Also, the sectioning of FIG. 1 
should be understood as being outward of the middle of roller 3. 
Photoconductor drum 5 is also contained in cartridge 1, and the mechanisms 
shown in FIG. 1 interact with drum 5 to apply toner to it. Cartridge 1 
includes a developer roller 7 which rotates in the direction of arrow 9 to 
carry toner 11 from the developer roller chamber 13 past the doctor blade 
14 into contact with the photoconductor drum 5. The toner adder roller 15 
rotates in the same direction as the developer roller 7. 
Toner 11 comprises a blend of styrene-acrylic resin, wax, carbon black, 
silicon carbide, Aerosil and a charge control agent. The toner has a 
nominal particle size of 11 microns. Toner is supplied to the developer 
roller chamber 13 from a supply chamber 19 through the action of toner 
metering roller 3. During operation a paddle 21 constantly rotates within 
the supply chamber 19 to insure that toner 11 does not agglomerate and is 
in the vicinity of the toner metering roller 3. The toner metering roller 
3 cooperates with three flaps 23, 25, and 27, which extend continuously 
along the operative length of metering roller 3 and press against roller 
3, to meter the toner 11 from the supply chamber 19 and to effect removal 
of excess toner 11 from the developer roller chamber 13 back to the supply 
chamber 19. Scraper fingers 29, which are positioned at regular intervals 
along the operative length of metering roller 3, act to clean the surface 
of the toner metering roller 3 to insure that the toner is dislodged 
therefrom. The flaps 23 and 25 and the fingers 29 are made of a thin 
flexible plastic material. Flap 27, which has the largest deflection, 
tends to take on a permanent set when plastic, and is of resilient metal 
to maintain its form, with the tip rounded to reduce frictional binding. 
For clarity in FIG. 1 flaps 23, 25 and 27 and fingers 29 are shown only as 
they press against the forward, sectioned part of roller 3. 
The cartridge 1 is sealed so that toner 11 remains within the cartridge 1 
until consumed by the action of developer roller 7 carrying the toner 11 
to the drum 5. Unused toner on the developer roller 7 is returned to the 
developer roller chamber 13 upon continued rotation of the developer 
roller 7. 
As described in the foregoing patent application, when the amount of toner 
supplied to the developer roller chamber 13 reaches an equilibrium level 
31, it is necessary to maintain this equilibrium level without appreciably 
adding further amounts of toner to the developer roller chamber 13. In 
order to accomplish this, the toner metering roller 3 acts to remove toner 
11 from the developer roller chamber 13 after the toner 11 reaches the 
equilibrium level. This is achieved by the interaction of the metering 
roller surface with the flaps 23, 25 and 27. 
As shown in FIG. 2a and FIG. 2b, metering roller 3 has opposing raised 
faces 33 connected by opposing flat surfaces 35. In accordance with this 
invention, this configuration of faces 33 and flat surfaces 35 is 
positioned 90 degrees different from one another on two sides of roller 3, 
so that the half of roller 3 on one side of its longitudinal middle has 
the raised faces 33 offset 90 degrees from the raised faces 33 of the 
other half. 
During operation, the opposing raised faces 33 necessarily move toward the 
chambers 13 and 19 simultaneously, thereby tending to sweep surrounding 
air primarily from supply chamber 19 to developer roller chamber 13. In 
accordance with this invention, however, as the raised faces 33 of one 
longitudinal side of roller 3 extend into the chambers 13 and 19, the flat 
surfaces 35 of the other half of the longitudinal side of roller 3 extend 
between the chambers 13 and 19. This dissipates any pumping action by the 
roller 3 between chambers 13 and 19 to eliminate significant pressure 
build-up between chamber 13 and 19. 
During operation of the device disclosed in the foregoing patent 
application, rotation of the flattened roller 3 along with the sealing 
against roller 3 of the flaps 23, 25 and 27 creates a varying volume in 
developer chamber 13. Without venting, this volume change creates 
unacceptably large air pressure variation in chamber 13. Venting couples 
the small space in developer chamber 13 to the relatively large air space 
in toner chamber 19. The volume change in chamber 19 being a smaller 
percentage of the available volume for the affected air mass than that of 
chamber 13, the resultant pressure variation is substantially reduced by 
venting to chamber 19. In accordance with this invention, roller 3 causes 
a volume reduction on one side of chamber 13 at the same time it creates 
an expanded volume on the other side of chamber 13. Air is believed to 
shuttle back and forth from one side of chamber 13 to the other without 
any appreciable pressure rise, although air may also pass to chamber 19 in 
the direction of the flat surfaces of roller 3. 
The need for a permanent vent between chambers 13 and 19 is eliminated. 
Specifically, a small, tangible cost reduction is realized by the 
elimination of a tape cover used in the vent path to minimize toner flow 
through the vent path. More importantly, the potential of the vent 
becoming clogged is eliminated since no vent is employed. 
It will be recognized that the metering roller 3 may take various surface 
configurations or be divided into more than two differently oriented 
sections, and that some venting may also be used as a supplement, all 
within the spirit and scope of this invention. Accordingly, patent 
coverage should be in accordance with such scope with particular reference 
to the following claims.