Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Corona Detection Apparatus
Field of the Invention
The invention relates to apparatus for detecting
5 the presence of corona, in general, and to apparatus
for detecting the presence of corona controlling
electrostatic charges on a moving web of charge-
retaining material, in particular.
10 Description of the Prior Art
The presence of electrostatic charges on charge
re~;n-ing materials causes many problems. In photog-
raphy, for example, electrostatic charges on film
units stacked within a film cassette could cause
15 clin~ing of the film units to one another with
such intensity that proper ejection of a film
- unit from the cassette may b~ prevented if the
effects o, such charges are not controlled. Such
electrostatic charges may be controlled by control-
20 ling the charge levels on components of the film
prior to final film unit assembly.
One technique for controlling electrostatic
charges in charge-retaining materials coMprises
the establishing a corona between an electrode
25 and a reference surface spaced from said electrode
and the passing of the material through the spatial
current path produced by the corona. This technique
is widely used and is quite effective for regulating
electrostatic charges in such materials. However,
30 in order properly to employ corona in this m~nner
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for electrostatic charge control, it is necessary to
provide for a reliable source of corcna to avoid any
interruption in the eletrostatic charge controlling
process. Current practices for insuring the presence
5 of a corona employ at least two corona sources,
one source supplving charge controlling corona to
a moving web, for example,the other sourcel spaced
from the first corona source in the direction of
web movement, being maintained in a deenergized
10 state and capable of supplying the same electro-
static charge controlling corona level to the
moving web when it is energized. An operator
monitors voltmeter and current meter of the power
supply of the active corona source. ~eviations in
15 the readings of the voltmeter and/or ammeter
from a predetermined range or set of ranges are
considered to be an indication of corona-loss.
In such a situation the standby corona source is
immediately activated to continue khe process
20 of controlling the electrostatic charge on the
moving web, without interruption.
Not only is it an obvious disadvantage to
monitor a machine by an operator, but also neither
ammeter nor volmeter indications are always
25 reliable indications of corona loss. Sometimes
a particular ammeter and/or voltmeter may indicate
the presence of an active corona source when, in
fact, no corona is present. Not only does this
interrupt the charge controlling process, it is
30 also difflcult and costly to determine xeadily
which portions of the moving web have not been
properly charged, and subsequently to charge these
portions, especially in a high-volume, time-
oriented production setting.
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In accordance wlth the present invention there is pro-
vided apparatus for assuriny the availability of electrostatic
charge controlling corona for controlling the electrostatic charge
level on charge-retaining material, comprising: first and second
electrically conductive reference surfaces; a first corona source
for producing a first stream of electric charges between said
first corona source and said first reference sur-face; a second
corona source for producing a second stream of charges between
said second corona source and said second reference surface;
an electrical conductor in the path of said first stream of elec-
tric charges produced by said first corona source wherein an
electric current is produced in said conductor as a result of
a portion of the said first stream of electric charges impinging
on said electrical conductor; and means responsive to the said
conductor current in said electrical conductor for energizing
said second corona source when the magnitude of the current in
said conductor is equal to or less than a prede-termined magnitude
as a result of loss of corona from said first corona source where-
by the uninterrupted availability of corona produced elec-tric
charges for controlling the electrostatic charge level on charge-
retaining material is thereby assured for material that is ini-
tially passed be-tween said first corona source and said first
reference surface, and subsequently between said second corona
source and said second reference surface.
The invention will n()w be described in greater detail
with reference to the accompanying drawings, in which:
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Figure 1 is a schema-tic dlagram, in eleva-tion, of a
moving web being subjected to electrostatic charge controlling
corona in accordance with the prior art.
Figure 2A is a schematic diagram, in eleva-tion, of
the corona detec-tion apparatus of the present invention which
includes means for automatically providing an alternate corona
source whenever a loss of corona is detected.
F`igure 2B is a top view of a portion of the corona
source and moving web of Figure 2A, and a corona sensing conduc-
-tor positioned near the edge of the spacial current path produced
by said corona source.
Figure 3A is a schematic of a corona sensing conductor
similar to that in Figure 2A except that the conductor is posi--
tioned between -the corona source and the moving web whose charge
is being controlled.
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Fig. 3B shows a corona sensing conductor
positioned between a corona source and a moving web
whose charge is being controlled by said corona
source, that is physically supported at two points
5 rather than at one point as in Figs. 2B and 3A.
Fig. 3C is the same as Fig. 3B except that
the corona sensing conductor is positioned near
the edge of the spacial current path produced by
the corona source.
10 Description of the Preferred Embodiments
In Figure 1, numeral 10 indicates corona-type
electrostatic charge controlling apparatus for
controlling charges on a moving web of charge-
retaining material constructed in accordance with
15 the teachings of the prior art.
Web support or backing rollers 12 and 14 are
cylindrically shaped~ are electrically conductive
and are mounted for rotation about axes 16 and 18,
respectively. ~rive means (not shown) move a
20 charge-retaining web 20 in the direction of arrow
22 over backing rollers 12 and 14. As the web 20
is moving the rollers 12 and 14 rotate about axes
16 and 13, respectively, as a result of the fric
tional engagement of the surace of web 20 with
25 the surface of the rollers 12 and 14~
The input of a primary high voltage power
supply 24 is connected to a relatively low voltage
source (not shown) at terminal 26 through a path
28. The high voltage output of the power supply
30 ~4 is connected to a corona electrode 30 ~lrough
a path 32. Normally several corona sources are
employed per web charging station, but one corona
source only has been shown. Power supply 24 is
energized by the manual act~ation of a switch 34,
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and the level of the voltage at corona source
or electrode 30 is manually adjusted to the desired
corona voltage level by knob 36.
Similarly, the input of an alternate high
5 voltage power supply 38 is connected to a rela-
tively low power source (not shown) at terminal
40 through path 42. The high voltage output of
said alternate power supply 38 is connected to
alternate corona source elec~rode 44 through
lO path 46. Alternate power supply 38 is energized
by the manual actuation of switch 48, and the level
of the voltage at alternate corona source or elec-
trode 44 is manually set to the desired corona
voltage level by a knob 50.
~en the power supply 2a is energized by
actuating the switch 34 a high voltage is produced
at its output; this produces a corona at corona
source 30 and a current or stream of electric
charges 51 between said corona source 30 and
20 grounded backing roller 12. The desired corona
level is controlled by rotating knob 36 while
monitoring voltmeter 52 and/or ammeter 54.
Alternatively, the corona levels can be deter-
mined empirically by measuring the charge le~els
25 on charge-retaining materials after said materials
have been subjected to the electric charges 51.
When web 20 is passed between electrode 30 and
grounded backing roller 12 through current 51
ha~ing a predetermined magnitude, the desired
30 electrostatic charge level will be produced on
said web 20.
Web 20 is moved between corona source or
electrode 44 and grounded backing roller 14 after
moving between electrode 30 and backing roller 12.
35 While corona current is present between corona
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source or electrode 30 and roller 12 no electro-
static charge-controlling corona is present
between alternate source 44 and backing roller 14.
An operator monitors meters 52, 54 to insure a
5 predetermined range of values. If the meter read-
ings deviate from the predetermined range, it is
assumed that the corona source has failed. When
this happens the operator energizes alternate
power supply 38 by actuating power control swltch
10 48 to its ON position. When power supply 38 is
energized corona source 44 produces a corona
current or a stream of electric charges 56 e~ual to
current 51 produced by electrode 30; the desired
corona level produced by electrode 44 is established
lS by the rotation of knob 50 and the monitoring of
meters 58 and 60 on alternate power supply 38. If
alternate power supply 38 is energi~ed promptly
after loss of corona occurs at electrode 30,
there is no interruption in the level of charge
20 on moving web 20 as long as the web 20 moves
between corona source 44 and backing roller 14
after it moves between corona source 30 and backing
roller 12. A problem with the prior art charge
controlling apparatus of Fig. l is that the corona-
25 loss indication provided by meters 52, 54 on powersupply 24 are not consistently accurate. In many
instances a meter reading will be well within a
predetermined range of values indicating the pres-
ence of charge-controlling corona when, in fact,
30 a corona is not present. The apparatus of the
present invention avoids any interruption of charge
controlling corona by consistently indicating its
presence or lack thereof.
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Turning now to Fig. 2, the numeral 62 generally
lndicates corona-type apparatus for controlling
electrostatic charges on a moving web. Web support
or backing rollers 64 and 66 are electrically
5 conductive and are mounted for rotation about
axes 68 and 70, respectlvely. Drive means (not
shown) are provided to move a web 72 in the
direction of arrow 74. As the web 72 is moving,
rollers 64 and 66 rotate as a result of the fric-
10 tional engagement with ~he surface of web 72.
A high voltage power supply 76 is connectedto a voltage source (not shown) at terminal 78
through path 80. The output of the power supply
76 is connected to electrode 82 through path 84.
15 Power supply 76 is energized by the actuation of
switch 86, and the voltage level at corona source
or electrode 82 is set by a knob 88. Similarlyt
an alternate high voltage power supply 90 is con-
nected to a power source (not shown~ at terminal
20 92 through path 94. The output of the alternate
power supply 90 is connected to alterna~e corona
electrode 96 ~hrough path 98~ The alternate
power supply 90 is energized by a switch 100,
and the voltage level at alternate corona electrode
25 96 is set by a knob 102.
The alternate high voltage power supply-90
may also be energized by switch means 104. When
a predetermined current i5 produced in conductor
106 by impinging current or stream of electric
30 charges 108, switching mPans 104 has no effect
on the energization of alternate power supply 90.
~Iowever, if the current level in conductor 106
drops below a predetermined level (normally to zero),
current amplifier 110 coupled to the conductor 106
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generates a signal. This signal is routed to switch
means 104 through path 112 causing the switch means
104 to energlze power supply 90 through an alternate
energization path internal of the power supply.
The power supply 76 is energized by actuating
switch 86 to produce a high voltage, a corona at
electrode 82 and a current or streami of electric
charges 108 between the corona source 82 and grounded
backing roller 64. The desired corona level is
10 established by the knob 88 while monitoring volt-
meter 114 and/or ammeter 116. When the web 72
passes between electrode 82 and grounded backing
roller 64 through the current 108, ~he desired
electrostatic charge level is produced on the web
15 72.
When the power supply 90 is energized, corona
electrode 96 produces a corona current or stream of
electric charges 118 equal to the current 108;
the desired corona level produced by electrode
20 96 having previously been established by the moni-
toring of voltmeter 120 and ammeter 122 on alternate
power supply 90.
The web 72 is moved between the corona elec~
trode 96 and the grounded backing roller 66 after
25 it has moved through electrode 82 and backing roller
64. As lony as a corona curxent is present between
the electrode 82 and the roller 64 no current flows
between the alternate corona source 96 and the
ba~king roller 56. The presence of a corona between
30 the electrode 82 and the roller 64 is detected hy
the conductor 106 positioned in the stream of elec-
tric charges 108. If the charges 108 impinging on
~- the conductor 106 drop below a predetermined lével,
the current amplifier 110 causes the switch means
35 104 to energize power supply 90. Alternate power-
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supply 90 is energized as soon as the loss of corona
current 108 is detected and, therefore, no interrup-
tion in the charge level on moving web 72 occurs
as long as the moving web 72 moves between the corona
5 source 96 and the backing roller 66 aft:er it has
moved between the corona source 82 and the backing
roller 64.
A corona sensing conductor such as conductor
1~6 may take many forms and may be mounted many
10 different ways. In Fig. 2B, for example, the end
of current sensing conductor 106 is positioned near
the edge of stream of electric charges 108 and does
not interfere witX electric charges or ions moving
between corona source 82 and web 72. In Fig. 3A,
15 the end of cuxrent sensing conductor 124 is posi-
tioned in the stream of electric charges 126 be-
tween corona electrode 128 and moving web 130
where it intereres slightly with electric charges
moving toward said web 130.
In Figs. 3B and 3C a current sensing conduc~or
is shown tautly mounted between a pair of insula-
tive support members. In Fig. 3B conductor 132
extends between support members 134A and 134B.
Conductor 132 passes through the path of electric
25 charges 136 moving between corona source 138 and
moving web 140. In Fig. 3C conductor 142 extends
between support members 144A and 144B, and passes
through stream of electric charges 146. In Fig.
3B there is a slight interference with electric
30 charges moving between corona source 138 and web
140. However, in Fig. 3C there is no interference
with electric charges moving between corona source
148 and moving web 150.
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It will be apparent to those skilled in the art
from the foregoing description of my invention that
various improvements and modifications may be made
without departin~ from its true scope.
