U.S. patent number 3,691,375 [Application Number 05/070,512] was granted by the patent office on 1972-09-12 for charging device.
This patent grant is currently assigned to Addressograph-Multigraph Corporation. Invention is credited to Stanley A. Gawron, Kristian L. Helland.
United States Patent |
3,691,375 |
Gawron , et al. |
September 12, 1972 |
CHARGING DEVICE
Abstract
Corona discharge electrodes for applying a sensitizing charge to
a moving sheet of photoelectrostatic paper are equipped with paper
guide elements which support the sheet as it moves along a path of
travel so that the sheet is kept clear of the fine wire electrodes.
The fine wire electrodes are stretched inside an elongated housing,
one side of which is open so as to freely emit the corona
discharge. The opening is provided with laterally extending, spaced
apart guides having a narrow flat support attached to the lead
edges of the opening of the housing so that the sheets of paper may
bridge the opening without entering and at the same time leaving an
uninterrupted path for the corona discharge to reach the paper.
Inventors: |
Gawron; Stanley A. (Mount
Prospect, IL), Helland; Kristian L. (Schaumburg, IL) |
Assignee: |
Addressograph-Multigraph
Corporation (Mount Prospect, IL)
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Family
ID: |
22095723 |
Appl.
No.: |
05/070,512 |
Filed: |
September 8, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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726793 |
May 6, 1968 |
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Current U.S.
Class: |
250/325 |
Current CPC
Class: |
G03G
15/0291 (20130101) |
Current International
Class: |
G03G
15/02 (20060101); G03g 015/00 () |
Field of
Search: |
;250/49.5ZC,49.5GC,49.5TC |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Church; C. E.
Parent Case Text
This is a continuation of Ser. No. 726,793 filed May 6, 1968 and
now abandoned.
Claims
We claim:
1. A charging device for applying uniform electrostatic charges to
a photoelectrostatic copy sheet having a Gurley stiffness of
greater than 50 units and moving at a predetermined rate,
comprising:
corona discharge means including discharge electrode means and
conductive shield means comprising a pair of elongated conductive
housing units each having a U-shaped cross section and being
disposed in opposing relation with the open portions facing one
another and through said open side of which is emitted an ionic
discharge from said discharge electrode means, the legs of the U of
said housing being of a predetermined length,
dielectric guide elements formed at the free ends of the legs of
the U-shaped housing at opposite sides of the opening providing an
uninterrupted path for said discharge therebetween, said elements
providing a series of laterally extending supports transverse the
path of movement of said copy sheet which guide said moving copy
sheet along the path past said opening at a predetermined distance
from said discharge electrode means, thereby to permit said sheet
to receive a uniform, unimpeded charge from said discharge
electrode means, said guide elements extending parallel to each
other and each said element is inclined in the direction of the
movement of the sheet and spaced from each other a distance of 1/2
to 1 1/2 inches across said opening to prevent said copy sheet from
entering said opening while moving thereacross, said distance
between said guide elements being established in accordance with
the stiffness of said copy sheet and the rate of movement thereof
across said opening.
2. The device as claimed in claim 1 wherein the guide elements have
an angle of inclination relative to the horizontal which ranges
between about 0 to 1.22 radians.
3. The charging device as claimed in claim 1 wherein said discharge
electrode means comprises a plurality of corona discharge wires and
wherein said conductive shield is provided with conductive
partitions enclosing respective corona discharge wires so as to
form a plural-walled compartment.
4. The device as claimed in claim 1 wherein said guide elements
comprise a dielectric material selected from the group consisting
of polytetrafluoroethylene, polyamide, or polyvinylchloride.
5. A device for uniformly charging a flexible photoelectrostatic
copy sheet which has a Gurley stiffness greater than 50 units and
which is moving along a predetermined path at a predetermined rate
comprising:
corona discharge means including discharge electrode means and
conductive shield means comprising a pair of elongated conductive
housing units each having a U-shaped cross section and being
disposed in opposing relation on opposite sides of said
predetermined path and through the open sides of which are emitted
from said electrode means an ionic discharge against the copy
sheet, said opening defined by laterally extending spaced apart
dielectric guide means formed at the free ends of the leg portions
of the U shaped housing said guide means being inclined in the
direction of the movement of said copy sheet which support and
guide the moving copy sheet past said opening, and being separated
from each other in the direction of movement of said copy sheet a
distance of 1/2 to 1 1/2 inches, sufficient to support said sheet
having said stiffness at a predetermined distance from said
discharge electrode means while bridging said opening without
entering therein.
6. The device as claimed in claim 5 wherein the sheet is moving at
a rate of from 10 to 30 feet per minute.
7. The device as claimed in claim 6 wherein the passing sheet moves
along a generally horizontal path and the guide means are inclined
in the direction of movement of the sheet.
8. The device as claimed in claim 7 wherein the guide means have an
angle of inclination relative to the horizontal which ranges
between about 0 to 1.22 radians.
9. A charging assembly for charging photoelectrostatic recording
sheet of a Gurley stiffness of greater than 50 units moving along a
predetermined path at a predetermined rate comprising opposing
discharge electrode means in spaced apart relation arranged so that
said path passes therebetween for applying charges of opposite
polarity to the respective surfaces of said sheet, each said
discharge electrode means including a corona discharge wire
partially surrounded by an elongated conductive shield having a
U-shaped cross section with the open side thereof extending
parallel to said wire and through which ionic discharge may flow
onto a respective surface of said sheet, and laterally extending
dielectric guide elements mounted on the free ends of the legs of
said U-shaped shield at opposing longitudinal edges of said
opening, said guide elements including flat surfaces extending from
the legs of said shield and inclined slightly toward said recording
sheet in the direction of movement thereof, the guide elements of
said respective opposing discharge electrode means being in spaced
alignment with respect to each other, the distance between said
guide elements being chosen in accordance with the stiffness of the
recording sheet being charged and the rate of movement thereof,
said distance being in the range of 1/2 to 1 1/2 inches, thereby to
guide said sheet in its movement along said path without permitting
the entrance of said sheet into said openings, said guide elements
leaving the path from said wires to said respective surfaces on
said sheet unobstructed along the longitudinal extent of said
openings for the free passage therethrough of said ionic discharges
and maintaining said recording sheet at a location so that a
uniform charge is applied to the opposite surfaces thereof.
10. A device for charging a moving flexible photoelectrostatic
recording sheet, comprising:
fixedly mounted corona discharge means partially enclosed in an
elongated conductive shield having a longitudinally extending
upwardly facing opening therein through which said discharge may
pass uninterrupted to said moving recording sheet and
air inlet ports located in said conductive shield including air
blow means to provide an air stream through said opening toward the
passing recording sheet, said air stream acting against the surface
of said photoelectrostatic sheet as it passes across said opening
to support and maintain said sheet in spaced relation from said
opening and on a predetermined path as it passes said corona
discharge means.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to corona discharge electrodes and
more specifically relates to the construction of a guide element
for supporting the photoelectrostatic member as it passes over the
charging electrode so that the member is protected against entering
the electrode proper and at the same time providing an
uninterrupted areaway through which the corona discharge may pass
from the electrode.
The construction of discharge electrodes of the type employed in
this invention generally involves a fine wire connected to a DC
power source and being enclosed in an elongated conductive housing
or shieldlike member having a longitudinally extending opening
therein through which the corona discharge is emitted. The shield
partially surrounds the wire, and as the wire generates a corona
discharge the grounded conductive shield tends to direct the ionic
emission through the opening.
In locating such a charging device in a typical copying apparatus,
the elongated housing is positioned transverse the path of the
photoelectrostatic copying sheet in order that the full width of
the sheet receives the sensitizing charge. Understandably, the
individual sheets passing over such an electrode arrangement would
on occasion find their way into the opening rather than pass over
it, becoming entangled and damaging the fine wire electrode.
To protect against this occurrence and still maintain a sufficient
opening in the electrode through which the ionic discharge might
pass, the opening in the conductive shield in prior construction
was protected with fine diameter monofilament lines, usually nylon
or teflon, stretched in an obliquely arranged lacing with respect
to the path of the sheet. In this manner, the lacing of
monofilament lines across the opening provided a support and guide
structure for the sheet so that the sheet did not become entangled
in the wire.
Such a construction was not without disadvantages since the plastic
lacings tended to deteriorate in the ozone atmosphere generated in
the vicinity of the electrode, becoming fragile and breaking. The
unnoticed presence of a snapped lacing created the precise hazard
to be avoided, namely creating an obstacle course for the paper.
This required a frequent servicing problem necessitating
replacement of the broken lacings, as well as broken wire
electrodes.
An even greater disadvantage in this type of a paper support guide
was the interference presented by the lacings to the ionic
discharge preventing the sheet from receiving a uniform
electrostatic charge. Areas on the member will be charged well
below the saturation level, and upon exposure to originals having
indicia of low contrast value, these areas will become discharged
giving the appearance of no image. The ability to lay down a
uniform charge is very important to obtaining quality copies.
Hence, it is desirable in the construction of such corona discharge
electrodes to provide a reliable, and easy to maintain charging
apparatus.
BRIEF DESCRIPTION OF INVENTION
The present invention involves a corona discharge electrode in
which the use of lacings of monofilament material across the
opening to the electrode has been eliminated. One of its important
advantages is that the same degree of protection against the
photoelectrostatic copy sheet becoming entangled in the corona wire
is provided without any obstruction whatsoever to the path of the
discharge emitted by the corona wire. Since the opening across the
charging device is unobstructed, nothing interfers with the corona
discharge and the sheet is uniformly charged.
However, the present invention provides further advantages in that
the support or guide construction is extremely sturdy so that it
obviates the need for frequent replacement in order to maintain the
charging device operative. In the preferred embodiment of this
invention, there is provided an elongated conductive shield or
housing which encloses a fine wire supported on suitable insulators
along the longitudinal direction of the housing. The enclosures
around the wire are complete, save for one side, for the purpose of
providing an exitway for the corona discharge.
In the usual application a pair of such electrodes are disposed in
opposing relation transverse the direction of travel of the
photoelectrostatic member. The photoelectrostatic member is
required to pass between the oppositely facing openings of the
electrodes receiving an electrostatic charge on each surface. The
electrodes are respectively connected to the positive and negative
terminals of a high potential source. The first corona discharge
device connected to the negative terminal of a high voltage supply
is adapted to apply a negative voltage to the wire electrode.
Similarly, the second corona discharge device is connected to the
positive terminal of a high voltage supply and is adapted to apply
positive voltage to the corona wire. Thus, one surface of the
photoelectrostatic member is exposed to a corona discharge of one
polarity and the opposite surface is exposed to a corona discharge
of the opposite polarity. The high voltage applied to the first
corona discharge device results in a production of a negative
corona discharge which in turn generates a discharge of negative
ions directed to the photoconductive surface providing the
sensitizing charge. In general practice the photoelectrostatic
member will have one surface coated with a photoconductive layer,
such as for example zinc oxide in a resin binder. Such a
photoconductive layer is charged negatively.
It will be appreciated that, as the sheet moves between the two
corona electrodes, it is necessary that it be supported along a
predetermined path out of contact with the electrode wires so that
a uniform charge can be deposited thereon. To accomplish this the
instant invention provides a guide element extending upward from
the edge of the opening of the housing or shield so that it
presents a support over which the photoelectrostatic member can
slide. The support itself is a rigid, narrow slatlike configuration
which presents a flat surface extending longitudinally along the
opening guiding the sheet as it moves transversely over the
opening. A second such guide support is affixed to the adjacent
parallel edge so as to intercept the sheet as it advances across
the opening to provide sufficient support over a short span of the
sheet so that it cannot flex and enter the opening.
In the circumstance that several electrodes are aligned side by
side, a series of such guide supports would be provided so that the
natural stiffness of short spans of the sheet will be sufficient to
bridge the gap between said guide supports.
It has been found advantageous to incline the surface of the guide
elements in the direction of the movement of the sheet relative to
the horizontal in the range between 0 and 1.22 radians. This serves
to guide the sheet upwards and away from the opening as it tends to
flex downward by virtue of its own weight.
The gap between the guide supports must be sufficiently narrow in
order to enable the sheet to move across the opening without
entering therein and becoming entangled with the corona wire. A
relationship has been worked out relating the stiffness of the
sheet as measured on a conventional paper stiffness tester. It was
found that to span a gap of 1 1/2 inches it would require a Gurley
stiffness value measured in the machine direction of at least 50
units.
Another factor which affects the ability of the sheet to be
sustained in a given path is the rate at which it moves past the
guide supports. Moving at a rate of at least 10 feet per minute, a
photoelectrostatic member having the aforementioned minimum
stiffness would easily bridge the gap of 1 1/2 inches between the
guide elements. In practice the speeds encountered in copiers can
range anywhere from 10 to 30 feet per minute, the distance between
the guide elements range between about 1/2 to 1 1/2 inches,
preferably nine-sixteenths to 1 inch, and the stiffness of the
sheet is usually greater than 50 units. If a sheet has a lesser
stiffness value than 50 units, it may be necessary to decrease the
distance between the guide elements and vary the speed.
While it has been proposed heretofore to locate multiple strands of
corona wire in a single shield, it has been found advantageous to
separate the individual wires by the conductive partition so as to
provide a support for the guide element. The presence of the
intervening conductive wall between the individual wires tend to
give a greater efficiency of emission of the discharge by providing
a more complete conductive shield around each wire. By comparison
to the practice of having multiple wires inside one shield, the
ionic discharge from the several wires tend to interfere with one
another. In the present circumstance the ionic discharge is further
controlled by the presence of the added conductive surface. As the
electrodes, having the guide elements disposed as aforedescribed,
are oppositely disposed transverse the path of the
photoelectrostatic member, there is provided a series of converging
throat portions through which the photoelectrostatic member must
pass as it is moved between the charging electrodes. At its widest
portion the throat may range from one-half inch to three-quarters
inch wide, gradually narrowing to an opening of about one-eighth to
three-eighths inch.
As the sheet is charged it is important to avoid contact with a
conductive material since this would cause the charge to leak off.
To avoid this problem, the guide elements are covered with a
dielectric material so that the charge deposited on the sheet is
not dissipated as it makes contact with the guide elements. Any
dielectric material may be employed having a resistivity greater
that 10.sup.10 ohm-centimeters. Such materials as
polytetrafluoroethylene, polyamide or polyvinylchloride have been
found to give excellent results. The requirement of a dielectric
material has given rise to another advantage such as when using a
material such as polytetrafluoroethylene or a polyamide type
plastic in that they provide almost a frictionless contact over
which the paper can easily slide.
In another embodiment of this invention the photoelectrostatic
member may have a Gurley stiffness less than 50 units, that is, it
may be a soft and flimsy sheet. Understandably, such a sheet will
tend to respond more easily to gravitational forces and fall into
the opening between the guide elements of the lower electrode. To
support the sheet out of contact with the corona wire, the guide
construction as described above is employed, and additionally there
is provided a gentle stream of air to support the sheet along a
predetermined path between the two electrodes. To accomplish this,
the conductive shield is provided with air ports connected to a
blower which sends a stream of air directed against the bottom
surface of the photoconductive member providing a platform of air
as it moves over the guide members past the opposing discharging
electrodes.
It is the general object of this invention to provide an improved
corona discharge electrode that uniformly charges a
photoelectrostatic recording member as it is supported out of
contact from the source of corona discharge by keeping open and
uninterrupted the path of discharge to the photoelectrostatic
member.
It is another object of this invention to provide an improved
corona discharge electrode in which the discharge wire is partially
surrounded by a conductive shield having an uninterrupted opening
through which the corona discharge may pass.
It is a further object of this invention to provide a corona
discharge electrode employing an air stream for supporting the
photoelectrostatic member out of contact from the discharge
wires.
It is a specific object to provide an improved corona discharge
electrode which more efficiently utilizes the available ionic
discharge produced by the corona source.
DESCRIPTION OF THE DRAWINGS
Several embodiments of this invention have been illustrated
diagrammatically in the accompanying drawings, but it is to be
expressly understood that said drawings are for purposes of
illustration only and are not to be taken as a definition of the
limits of the invention, reference being had to the appended claims
for this purpose. In the drawings,
FIG. 1 is a cross-sectional view of the preferred embodiment of
this invention;
FIG. 2 is a plan view taken along line 2--2 of FIG. 1;
FIG. 3 is a cross-sectional view of another embodiment of this
invention using an air stream to hold the photoelectrostatic member
away from the charging electrode.
Referring now to the drawings, FIGS. 1 and 2 illustrate the
preferred embodiment of this invention in which there is shown a
corona charging assembly identified by the general reference
numeral 10. The charging assembly 10 is comprised of an upper
charging electrode 12 and a lower charging electrode 14 which are
disposed in opposing relationship to one another forming a pathway
as indicated by the arrow 16. The photoelectrostatic member 20 is
fed along the pathway 16 being advanced by a set of nipping rollers
22, which moves the member between the upper and lower electrodes
12 and 14, respectively. The photoelectrostatic member, for
example, may be a zinc oxide type coated paper. As the
photoelectrostatic member 20 exist the assembly it is received by a
set of nipping rollers 24 which advances the sheet to the next
station in the copying apparatus.
It should be pointed out that the upper and lower electrodes are
identical with the exception that they are connected to oppositely
poled voltage supplies. Accordingly, the description of the upper
electrode will be fully applicable to the lower electrode. The
source of corona discharge is a fine wire 26 (FIG. 2) which is
stretched between insulating binding posts 28, 30 and 32, 34. The
wire electrode 26 is enclosed in a compartmented housing or
conductive shield 36 so that each set of binding posts having
stretched therebetween the corona wire is fully shielded by the
wall sections 38, 40 and 42 so as to form the compartments 44 and
46. Each compartment holds a single wire and has an opening therein
indicated by numeral 50 and 52.
It will be appreciated at this point that the photoelectrostatic
member 20 as it passes between the two electrodes 12 and 14 must be
protected from making contact with the conductive wall sections of
the conductive shield 36 or otherwise the sensitizing charge being
applied by the corona wire 26 will be dissipated. In accordance
with one of the features of this invention there is provided the
support members 38a, 40a and 42a integrally formed on the ends of
the wall sections 38, 40 and 42, respectively, providing a surface
over which the photoelectrostatic member 20 may slide and be
supported bridging the openings 50 and 52 without entering the
compartments 44 or 46 and thereby becoming entangled or ensnared
with the corona wire 26.
It will be observed that each of the support elements 38a, 40a and
42a provide a flat face portion which tends to support a narrow
transverse segment of the advancing photoelectrostatic member 20.
As shown in FIG. 2, the face portions extend laterally along the
length of the housing so as to form a continuous transverse support
for the member 20 on either side of the openings 50 and 52.
The support members or guide elements 38a, 40a and 42a are covered
with a dielectric material 54 so as to form an insulating cover
over the conductive shield protecting the photoelectrostatic member
from making contact with metal. As described earlier, the
dielectric material may be any one of a number of plastic materials
which also offer the advantage of decreasing the coefficient of
friction between the paper and the support member so that it easily
slides over the surface.
Referring again to FIG. 1, it will be seen that each of the support
members 38a, 40a and 42a are formed at a slight incline in the
direction of movement of the photoelectrostatic member along the
path 16. Considering the path 16 as a horizontal plane, the angle
at which the support member is positioned with respect to the
horizontal may range between 0 and 1.22 radians, preferably between
0.35 and 0.8 radians. By positioning each of the support members in
this manner there is formed between the corresponding support
members of the lower electrode 14 a funnel type guide element
having a rather wide entryway 56 which narrows down to an exitway
58. This arrangement tends to guide the sheet more accurately along
the particular path and any tendency of the sheet to deviate from
the horizontal will find it engaging one of the surfaces of the
support members tending to redirect it towards the path of movement
along the arrow 16. It will be observed that the support members
leave the openings 50 and 52 clear and unobstructed so that the
discharge from the wire 26 can act upon the photoelectrostatic
member uninterrupted. This assures uniform charging of the member
20.
As described earlier, the spacing between the guide elements 38a,
40a and 42a is a function of the stiffness and speed of the member
20. For example, a conventional zinc oxide/resin binder
photoelectrostatic copy paper generally has a Gurley stiffness
measured in the machine direction greater than 50 units. If such a
sheet is moved between the electrode 12 and 14 at a speed which
ranges about 10 to 20 feet per minute, the distance between the
guide elements can range between about 1/2 to 1 1/2 inches,
preferably nine-sixteenth to 1 inch. The stiffness of the sheet
holds it on the path defined by the arrow 16 and the support
members on the lower electrode 14 tend to support the sheet against
the force of gravity guiding it along the path so that it is
uniformly charged.
It will be observed that each of the wire electrodes 26 are
enclosed by the conductive shield 36 and in particular, the
compartments 44 and 46 are separated by the wall section 40. This
arrangement provides a shielding effect on three sides for each
compartment so that the ionic discharge from each wire does not
interfere with the next adjacent wire permitting a more efficient
utilization of the ionic discharge from the wires through their
respective openings 50 and 52.
Referring to FIG. 3, there is illustrated another embodiment of the
invention showing the oppositely disposed electrodes 60 and 61 in
spaced apart relation providing a path 63 therebetween for the
passage of a photoelectrostatic member 20. This embodiment is
particularly suited to handle sheets that are rather flimsy having
a Gurley stiffness measurement of less than 50 units. The lower
portion of the assembly is constructed in a manner similar to
either one of the electrodes described in conjunction with FIG. 1.
The corona wire electrode 62 is fixed at each end to a binding post
identified as 64 and 66, only one post being shown of each pair.
The wire is enclosed in a housing or conductive shield 68 having a
series of upright walls 70, 72 and 74 so as to form separate
compartments 76 and 78 for each electrode. Affixed to the edge
portion of each of the walls is a support member 70a, 72a and 74a
which support the member advanced through the assembly by the
infeed roller set 80 and the outfeed roller set 82.
The support members 70a, 72a and 74a are similar in construction to
the support members described in connection with FIG. 1. Due to the
flimsy character of the sheet it will tend to deviate from the path
which is equidistant from the electrodes and to keep it supported
out of contact with the electrodes air-blow means are employed to
urge the sheet along a straight path. The bottom wall portion 84 of
the housing 68 is provided with air inlet ports 86 through which is
forced air from a centrifugal type blower 88 connected to said
ports by a suitable conduit 90. The air enters through the ports
86, passes through compartments 76, 78 and thence through the
openings 92 and 94 formed between the upright walls 70, 72 and 74.
The use of a gentle stream of air to retain the photoelectrostatic
member along its path of movement as it passes through the charging
assembly renders less critical the shape, size, and spacing between
the support members. While in the previous embodiment the general
shape and spacing between the support members was of importance,
the use of a positive air stream requires only that a generally
flat surface be provided which could be parallel to the direction
of the sheet. The use of an air stream, therefore, provides another
technique for controlling the photoelectrostatic member in a manner
which permits an uninterrupted and unobstructive path for the ionic
discharge emitted by the corona wire to the photoconductive surface
on the sheet.
While the invention has been specifically described and illustrated
with respect to certain embodiments, it is to be understood that
the invention is not restricted to these embodiments and that
reference should be had to the appended claims for a definition of
the limits of the invention.
* * * * *