Background of The Invention
1. Field of the Invention
[0001] The present invention relates to electrographic apparatus and to automatic means
for preventing toner dust from migrating from the developer station to other parts
of the apparatus.
2. Background of The Invention
[0002] Electrographic printer apparatus which utilize two-component toners i.e. toner plus
carrier beads
;generally operate the magnetic brush or toner applicator roll at a higher rotative
rate than those systems which employ single component toners since the quantity of
toner is much less with the two component system. All toner material consists of extremely
fine powder-like material which can become airborne. Toner particles in a two component
system are lighter in weight and non-magnetic whereas in a single component system
the toner particles are heavier and hence cannot drift as readily in air and are magnetic
so they can be held to the applicator roll by its negative field. The problem of toner
migration due to the air turbulence created by the movement of the toner-carrier particles
thus becomes a particular problem.
[0003] Brush-like seals at the edges of the rotatable photoreceptor drum tend to limit the
ambient dust to a certain degree. Still, there is sufficient migration of the toner
dust to other portions of the apparatus to produce unwanted deposits on bearings,
moving parts such as gear trains, etc., and onto the copy itself making for unreliable
and relatively dirty apparatus.
[0004] No commercially available electrostatic precipitation means has so far been economically
adapted to correct the problem.
[0005] The problem becomes especially critical in high speed printers due to the high rotational
speed of the magnetic roll carrying the so-called magnetic brush when the carrier
beads become worn hence, reducing the charge to mass ratio (Q/M). A low Q/M reduces
the attractive force between the toner particles and the carrier beads which results
in free toner particles which migrate with the air flow in the apparatus. The airborne
dust particles are thus a considerable nuisance. Summary of The Invention
[0006] As is known in the reprographic art, mixing toner material with the carrier material
(usually nonconductive beads) to form the developer generates a triboelectric charge.
The carrier beads usually have a (positive) +V
e charge while the toner particles have a (negative) -V
e charge. Some toner particles, however, are mechanically freed causing the aforementioned
dusting problem.
[0007] Electrostatic attraction and replusion are well known phenomena. Electrostatic preciptators
are used industrially to capture and remove all manner of waste products from the
stack and flue effluent.
[0008] The present invention makes use of the repulsive effect of electrostatics.
[0009] A pair of substantially similar conducting and electrostatically charged members,
albeit carrying a -
Ve (negative) charge, are arranged in spaced apart ' relation to the photoreceptor
recording drum of an electrophotographic apparatus. The charged members are disposed
across the width of the drum and adjacent to the developer station (or unit) in the
apparatus. Dielectric support members maintain the charged electrostatic elements
in close proximity (but not touching) to the drum surface. A spacing of a few ten
thousandths of an inch is sufficient to effectively seal the area adjacent the drum
and toner station against dust. Application of a negative potential to the electrostatic
charged members causes the negatively charged toner dust to be completely repelled
from the area adjacent to each electrostatic member.
[0010] More specifically, the present invention comprises a pair of conductive (e.g. copper)
elongated, thin, strips mounted to respective dielectric, molded members. The two
assemblies are positioned adjacent to but separated from the periphery of the photoreceptor
drum of an electrophotographic printer. So as to prevent the electrical field produced
by the adjacent positively charged corotron from attracting toner dust a shunt or
ground in the form of a grounded conductive member secured to the lowermost of the
two electrostatic repeller members effectively shunts or grounds the field lines from
the corotron preventing negatively charged toner from being attracted to the corotron.
[0011] This arrangement completely eliminates the toper dusting problem and keeps the area
around the photoreceptor drum clean and assuring more legible copy.
Brief Description of The Drawings
[0012]
Figure 1 is a side elevational view, partially in phantom illustrating a portion of
electrophotographic apparatus embodying the present invention;
Figure 2 is a front view (partially broken away) of a portion of the apparatus of
Figure 1;
Figure 3 is a view (partially broken away) of the electrostatic repeller member of
Figures 1 and 2, and
Figure 4 is a view (partially broken away) of the shunt means of the present invention.
Description of A Preferred Embodiment
[0013] The present invention relates to reprographic electrophotographic apparatus of the
type described and claimed in USSN 429,861 filed September 30, 1982 in the name of
Richard C. Fedder for "Toner Concentration Sensor For Electrographic Apparatus" assigned
to the same assignee as the present invention.
[0014] In dry copying apparatus in order to produce clean, clear, crisp, black printing
(copy) on white paper for example, to a line definition generally acceptable to the
eye as regular or standard printing, it is necessary to employ an extremely fine dry
powder toner material. The subject apparatus also utilizes what is characterized as
a two component developer i.e. a finely powdered toner and larger carrier beads.
[0015] Mixing the toner and carrier beads to form the so called developer generates a tribo-electric
charge. The carrier beads acquire a positive (+V
e) charge while the toner material acquires a negative (-V
e) charge. Inevitably, some toner particles remain uncharged or go free to produce
an ambient dust which migrates at random to all parts of the surrounding atmosphere
and hardware.
[0016] Physical seals cannot be placed along the cylindrical surface of the photo drum for
obvious reasons. Anything that touches the polished surface of the drum would tend
to distrub the surface charge and thus interfere with the printing.
[0017] The problem is solved by utilizing the phenomenon of attraction and replusion i.e.
like charges repel one another while unlike changes attract.
[0018] Viewing Figure 1 of the drawings, the present invention is seen to include a rotatable
photoreceptor drum 10 having a photoconductive surface 12 for receiving a visual image
of information or data thereon. Below, and slightly to the left, (off center) is one
of two corotrons 14. (The other corotron to the right of the first is not shown since
it forms no part of this invention). Immediately to the left and above the corotron
14, secured as by bolts 16 to the extrusion hardware frame 18, is an L-shaped glass
filled nylon lower bar member 20. Member 20 is arranged to extend (from side to side)
across the drum 10 in very close but noncontacting proximity thereto. Adjacent to
but above and separated from the lower bar member 20 is an upper L-shaped glass filled
nylon bar member 22. Each bar member 20 and 22 is provided with a elongated fairly
wide channel or groove 24 extending from end to end of the respective member. One
end of each member 20 and 22 is provided with a substantially rectangular aperture
26, which will be explained shortly. An opposite integral portion of each bar member
20 and 22 is provided with a plurality of attachment holes 28 arranged in spaced apart
relation on a thickened or raised land portion 30. The latter portion 30 extends from
end to end of each bar strengthening element for retaining the attachment bolts 16.
The two mounting-support members 20 and 22 are otherwise identical in cross section,
only their physical orientation is different. The upper member 22 is angled as seen
in Figure 1 so as to take advantage of the available hardware to which it is physically
attached. The lower member 20 is likewise situated to enable its attachment to available
hardware structure. Since no corotron is used above the member 22 there is no need
for a second shunt (to be described shortly) as is used with the lower member 22.
[0019] An elongated, relatively thin, conductive copper strip 32, one end of which is provided
with an integral bent tang 34, Figure 2 including an attachement hole 36, is seated
in the longitudinal groove or channel 24 in respective members 20 and 22. The bent
tang 34 is received within the rectangular aperture 26. The physical mounting arrangement
of the two members 20 and 22 is such that the flat planar facing portion of each copper
strip 32 is generally oriented toward the surface of drum 10 with the strip 32 of
lower member 20 being substantially parallel to the drum surface. As seen in Figure
1 the two (upper and lower) electrostatic repelling devices 20 and 22 are disposed
relative to a magnetic brush development roller member 38 mounted in close but non
contacting proximity to drum 10. The outer shell 39 of member 38 rotates past a plurality
of internally disposed fixed magnets (not shown) to carry developer 40 (toner plus
carrier) from a source (not shown) upwardly by the rotatable magnet member 38 into
surface contact with drum 10 as members 10 and 38 are rotated during machine operation.
At the interface between the member 38 and drum 10 the lines of force due to the internal
magnet arrangement of member 38 and the electrostatic charge on drum 10 causes the
developer 40 to assume a longitudinal ridge, land or magnetic brush 42 between the
periphery of member 38 and drum 10 parallel to the axis of rotation of member 38.
The shell of member 38 carries a B+ potential charge of approximately 300 volts. The
drum 10 is provided with a B+ potential of 750-800 volts. The two electrostatic repeller
devices are each provided with a negative potential of approximately - 1200 volts
over leads 44 from a source (not shown).
[0020] A corotron 14, disposed below and to the right of roll 38 is maintained at a B+ potential
of 4500 to 6000 volts over lead 48, from a source (not shown).
[0021] Because of the high voltage applied to corotron 14 the field lines generated by this
element spread outwardly therefrom and into the area adjacent to the magnetic brush
42. Ordinarily, this would result in the negatively charged toner developer being
attracted away from the brush area to the corotron 14. However, the present invention
utilizes a shunt member 46, e.g. a copper strip, bent out of the main plane into a
v-shape as seen in Figure 1. Attachment notches 48 are provided along its length so
as to secure member 46 to the lower member 20 as by bolts 16. Shunt member 46 is coextensive
with lower repeller member 32 attached as shown to the frame 18 which is at ground
potential.
[0022] In operation, with the electrical potentials_, applied to respective members as stated
hereinbefore the toner developer dust generated during operation of the withindescribed
apparatus is confined to the area between the drum 10 and members 20 and 22 and the
brush generating member 38. No toner is permitted to escape into the ambient or surrounding
atmosphere.
[0023] This structural arrangement effectively directs or shunts the lines of force from
corotron 14 to ground thus preventing any ambient toner dust from spreading.outwardly
away from the brush area 42 overcoming the dusting problem.
[0024] An additional benefit derived from this structural combination is that the optical
density of the print is enhanced by the concentration of toner adjacent the printing
area on drum 10.
1. Electrostatic toner dust repeller apparatus for an electrophotographic printing
device in which the rotation of a magnetic toner applicator brush roller generates
a particular atmosphere of toner dust comprising:
a first electrostatic toner repelling means,
a second electrostatic toner repelling means,
said first and second repelling means being arranged on opposite sides of said toner
applicator brush roller and adjacent to the peripheral surface of a photoreceptor
drum,
means for applying an electrical potential to each of said repelling means said potential
being opposite in polarity to the polarity of said toner effective to repel said toner
from the area immediately adjacent to said repelling means and to concentrate said
toner at said magnetic toner applicator roller adjacent to the peripheral surface
of said drum.
2. The invention in accordance with Claim 1 further including means for shunting and
grounding the electric field from a charging corotron disposed adjacent to one of
said electrostatic repeller means.
3. The invention in accordance with Claim 2 wherein said shunt means comprises an
elongated conductive plate-like member having means grounding said members to the
frame of said apparatus.
4. The invention in accordance with Claim 1 wherein said shunt means comprises a substantially
v-shaped, thin, flat planar copper member bent to accommodate the radial curvature
of said receptor drum.
5. The invention in accordance with Claim 1 wherein each of said first and second
electrostatic repeller means comprises a thin, flat, planar copper member, each one
of which is supported longitudinally within a groove of a respective dielectric member.
6. The invention in accordance with Claim 5 wherein said dielectric members are substantially
identical in configuration.