Note: Descriptions are shown in the official language in which they were submitted.
2126877
BACKGROUND OF THE INVENTION
The present invention relates to moving and transporting
stacks of paper and similar materials, and more particularly
to the deliberate use of electrostatic charges to pin sheets
of paper together in a stack which can then be easily
transported and stored.
Electrostatic forces Oll webs or sheets of paper often
interfere with the operation of paper converting machinery.
These charges are of opposing polarity so that one side of the
continuous web is of positive polarity while the other side is
of negative polarity. This causes the web to be attracted to
machinery components or to adjacent webs (in case of multiple
web processing with webs being unwound from several mill
rolls, or when a single web is slit into ribbons which are
then superimposed in the processing machine for further
processing). Once sheeted, the webs are then stacked onto
skids up to about six or seven feet high. The skid loads are
then transported by fork-lifts to a temporary storage area or
moved directly to the next processing machine such as a
destacker and cartonizing machine manufactured and sold by
Involvo, 33 Brook Street, West Hartford, Connecticut.
In order to prevent machine jam-ups due to sheets
clinging together from the time they are cut from the endless
web until they are stacked at the delivery end of the sheeter,
great care is taken to avoid or eliminate electro-static
charges between the paper layers. This facilitates the flow
of the, cut sheets into the delivery stack at the sheeter. As
the endless web (ribbons) advances from the unwind roll
through pull roller systems before and after the printing
stations and throuyh the printing stations, it comes in
contact with metal rollers or metal cylinders on one side and
rubber or plastic covered rollers or cylinders on the other.
Typical examples are: (1) driven steel pull rollers on one
side of the web and rubber or plastic covered nipper wheels
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(or nipper rollers) on the other; (2) rubber covered
impression cylinder on one side of the web and a metal gravure
cylinder on the other (in gravure presses); and (3) rubber
covered blanket cylinder on one side and steel impression
cylinder on the other side (in web offset presses). While
passing through the nips of such cylinders or rollers of
different materials on each side of the web, the electrostatic
charges on the paper surfaces are altered and may add to or
subtract from the already existing electrostatic charge on
that side of the paper and thereby cause an imbalance that
interferes with the high speed operation of the paper
processing machine.
The prior art teaches the use of static eliminators to
neutralize the electrostatic charges on both sides of the webs
to reduce or eliminate jam-ups and other interference with the
free flow of the still endless paper webs (or ribbons). The
simplest method of prior art is the use of metal tinsel
connected to ground and with the free ends of the tinsel
touching the moving web.
Other prior art methods for eliminating undesired
electrostatic charges from moving webs of paper and similar
materials include the use of the nuclear static eliminators,
air ionizing devices or static eliminator rods. These devices
are commercially available and will effectively neutralize the
static charges on a moving web or sheet of paper and thus
eliminate the undesired clinging together of webs or sheets
and their undesired attraction to machinery components or to
each other. Eliminating these electrostatic charges causes
the sheets to repel each other in a manner similar to that of
magnetic poles having like charges. In addition to this, a
boundary layer of air remains between several of the uppermost
sheets on the stack, such that these sheets slide easily
around when the stack is moved such as during transport by
fork-lifts. The boundary layer of air is squeezed out between
the lower layers when the weight of the sheets accumulated on
top exceeds the repelling force from the like charges between
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the layers of paper plus the force required to move the
boundary layer of air. Normal friction then prevents the
lower sheets in the stack from sliding, while the upper sheets
still are free to slide around.
When the skid loads of paper are moved, the uppermost
sheets have a tendency to slide off, fall down to the floor
where they are spoiled. This is particularly severe when
handling sheets having the so-called "Kromekote"* surfaces
which are very smooth (very low coefficient of friction) and
contain chemicals having a very high dielectric constant (such
as the titanates). "Kromekote" sheets (coated on both sides)
and having a thickness of .008 to .010 inches and a sheet size
of about 23 x 35 inches sell for approximately one US dollar
($1.00) per sheet wholesale so that the loss of a few sheets
from each stack at the paper processing plant could be
substantial.
Additionally, when the skid loads of paper stacks are
automatically destacked on the INVOLVO* destacker, the
uppermost sheets of the individual reams being destacked again
slide around and cause undesirable trouble until the reams are
cartonized. This occurs because the weight has been removed
and the charges of like polarity again want to levitate the
upper sheets. The faster the machine runs, the more
disturbance there is. This then limits the production speed
of the machine to well below the rated mechanical speed.
*Kromekote and INVOLVO are trademarks.
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2126877
SUMMARY OF THE INVENTION
The present invention is designed to overcome the above
noted limitations that are attendant in the "prior art" and
toward this end it contemplates the provision of a novel
method and apparatus for deliberately inducing electrostatic
charges of opposite polarities into stacks of sheets of paper
in order to hold them together during transport.
An object of this invention is the deliberate application
of an electrostatic charge having a polarity opposite to the
charge existing in the pile (or stack) to neutralize the
repelling force between the uppermost layers, allowing their
weight to push out the entrapped layers of air and thereby to
cause intimate contact between the sheets of paper so that the
normal coefficient of friction is restored and the undesired
slippage eliminated.
Another object is to provide a method and apparatus which
induces electrostatic charges of opposite polarity in
individual stacks of paper being destacked from skid loads of
paper for cartonizing.
It is a further object to provide such a method which can
be easily practiced using automated machinery.
Still another object is to provide such an apparatus
which may be readily and economically fabricated and will
enjoy a long life and operation.
It has now been found that the foregoing and related
objects can be readily attained in an apparatus using
electrostatic charges to temporarily hold sheets of paper in
assembly which assembles a skid load stack of sheets of paper
with each sheet having an electrostatic charge introduced
thereon which tends to repel the sheet from adjacent sheets in
the skid load stack. In addition, as the skid load stack is
assembled, a layer of air is introduced between adjacent
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2126877
sheets whereby the electrostatic forces and layers of air
cause adjacent sheets to slide relative to one another if the
skid load stack is moved. By introducing an opposite
electrostatic charge into at least an upper portion of the
skid load stack, the opposite electrostatic charge having an
opposite polarity to the electrostatic charge introduced
during the assembly step, the sheets in the upper portion of
the skid load stack are caused to attract to one another
thereby decreasing the tendency of the sheets in the upper
portion to slide relative to one another if the skid load
stack is moved.
During further processing, predetermined numbers of
sheets from the skid load are separated to form individual
stacks of sheets. An electrostatic charge of opposite
polarity to the existing electrostatic cllarge in the lower
portion sheets is introduced thereby causing the sheets in the
individual stacks to attract to one another thereby decreasing
the tendency of the sheets to repel one another. The
individual stacks can then be moved for further processing.
Desirably, to introduce the opposite electrostatic
charge, an electrostatic charging device is provided adjacent
a path along which the individual stacks of sheets pass. The
electrostatic charging device can be moved relative to the
individual stacks by a computer controller to optimize the
distance between the electrostatic charging device and the top
of the individual stacks.
The invention will be fully understood when reference is
made to the following detailed description taken in
conjunction with the accompanying drawings.
2126877
BRIEF DESCRIPTION OF rr~E DRAWINGS
Figure 1 is a schematic side elevational view of the
delivery end of a paper converting machine in which sheets are
cut from an endless web and stacked in a pile delivery or
other stack forming devicei
Figure 2 is a schematic side elevational view of the
electrostatic charge inducing method of the present invention
being practiced on a skid load of paper produced by the
machine of Figure l;
Figure 3 is a schematic top elevational view of a
destacker installation modified in accordance with the present
invention to induce electrostatic charges of opposite polarity
to individual stacks of paper being separated from a skid load
of paper; and
Figure 4 is a schernatic side elevational view of the
destacking station of the destacker installation of Figure 3.
212687~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning first to Figure 1, therein illustrated is the
delivery end of a paper converting machine generally indicated
by the numeral 10. As a printed perforated, punched or
otherwise processed endless web or ribbon of paper 12 moves
toward the delivery end of the paper converting machine 10, it
usually passes through a rotary sheeter section generally
indicated by the numeral 14 where sheets are cut from the
endless web 12 and moved through high speed and low speed
conveyor belt sections, respectively indicated by the numerals
16 and 18, into a pile delivery or other stack forming device
20 fo~ further in-line or off-line processing.
The rotary sheeter section 14 includes a rotary cutting
knife device 22 upstream from a pair of nipper rollers 24, the
upper of which is mounted for swinging movement as indicated
by arrow 26. At the instant the rotary cutting knife 22
severs a sheet 28 from the leading end of the continuous web
12, web tension downstream of the continuous web 12 is lost
and the nipper rollers 24 just upstream of the rotary cutter
knife device 22 push the leading end of the web 12 beyond the
rotary cutter knife device 22 and into the high speed belt
section 16 with its upper and lower belts 30 and 32. The
upper and lower belts 30 and 32 are staggered across the web
12 so that they can be adjusted to make contact with the
leading end of the web 12 and pull it forward. The surface
speed of these belts is considerably higher than the speed of
the moving web 12 for several reasons. First, the belts 30
and 32 pull the web 12 taught to allow cutting under tension.
Secondly, they quickly move the cut sheet 28 away from the
endless web 12 as soon as the rotary cutter knife device 22
has severed it from the continuous web 12. Finally, they
create a space 34 between successive cut sheets so as to
facilitate overlapping (shingling) of cut sheets as indicated
by numeral 36 in the slow speed belt section 18 further
downstream. Since the high speed belts 30 and 32 have rubber
or plastic surfaces which rub on the slower speed leading end
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2126877
of the continuous web 12 until the sheets have been cut and
accelerated to the higher belt speed, electrostatic charges of
the same negative polarity 38 are being generated on both
sides of the just cut sheet 28.
As the spaced apart sheets 28 coming from the high speed
belt section 16 move into the low speed belt section 18, the
low speed belts rub on both sides of the sheets to cause them
to slow down, and the sheets partially slide over each other
as shown by numeral 36. This increases the electrostatic
forces 38 of negative polarity on both sides of the sheets.
Since the charge on the lower side of the upper sheet is of
the same polarity as the charge on the top side of the next
lower sheet, the sheets are being repelled by the
electrostatic forces and a thin layer of air is permitted to
stay between the sheets. No effort is made to remove the
electrostatic forces of same polarity because they facilitate
the sliding of the sheets over each other as they form a pile
or a stack in the stacking device 20. The stack can form a
skid load 40 up to about six feet (6') high. Often air blasts
from a compressor 44 are deliberately introduced to enhance
the floating of the sheets into the pile or stack. When the
pile or stack builds up sufficiently, the weight of the upper
sheets in the pile or stack overcomes the repelling force from
the electrostatic charges of equal polarity and will push out
some of the air entrapped between the lower sheets; however,
the electrostatic forces remain in the accumulated pile or
stack and cause problems when the skid load 40 is moved to an
off-line, automatic destacking and cartonizing machine (Fig.
3) where reams of sheets are destacked from the skid load 40
and cartonized.
Depending upon moisture content, surface coatings and
basis weight of the paper as well as the intensity of the
electrostatic forces between the sheets, the weight of the
upper 1/8" to 2" thick layers of sheets is often insufficient
to overcome the repelling electrostatic forces existing
between the upper sheets so that the boundary layers of air
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21268~7
between the upper sheets are not pushed out. When the skid
load 40 of paper is removed from the stacking device 20 to
storage or further processing in the destacker/cartonizing
machine, the upper sheets float around, get displaced, or even
fall off. This results in costly damage and inefficiency.
To neutralize the repelling force between the uppermost
sheets of the skid load 40 before it is moved, an
electrostatic emitting device 46, with its power pack 48, as
shown in Figure 2 is used to neutralize the repelling forces
by deliberately applying an electrostatic charge 49 having a
polarity opposite to the charge existing in the skid load 40.
The weight of the uppermost sheets then pushes out the
entrapped layers of air whereby intimate contact between the
sheets is achieved allowing the normal friction therebetween
to prevent undesired slippage.
The electrostatic emitting device 46 is a charging bar
made by SIMC0*, 2257 N. Penn Road, Hatfield, PA 19440 and
described in U.S. Patent No. 3,735,198. It provides up to
25,000 volts, 8mA. The depth of penetration varies depending
upon the strength of the applied charge, the moisture content
of the paper (conductivity), and the distance between the
electrostatic emitting device 46 and ground (earth). After
the application of the charge, the skid load 40 of paper can
then be moved for further processing without the upper sheets
25 sliding around or falling off. Since the deliberate
application of electrostatic force penetrates only a short
distance into the top of the pile, it does not neutralize the
electrostatic force of opposite polarity further down in the
pile.
Turning now to Figure 3, therein is illustrated a
destacking and cartonizing installation generally indicated by
numeral 50 and modified in accordance with the present
invention. The installation 50 is manufactured and sold by
Involvo, 33 Brook Street, West Hartford, Connecticut. The
*SIMC0 is a trademark.
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2126877
skid load of pape.r 40 is placed onto an infeed conveyor 52 of
the installation 5 and 15 automatically, advanced to the
destacker 54. At the destacker 54 as shown in Figure 4, the
total height of the skid load 40 is automatically sensed by a
proximity switch 56 and the ream thicknesses of the proper
sheet count are then computer calculated by a computer
controller 58 in a well known manner. The computer controller
58 is a conventional microprocessor of the type generally
found as original equipment in the Involvo destacking and
cartonizing machine 50 which is programmed to perform the
functions of the present inventioll. The computer controller
58 causes a lifting platform 60 holding the skid load 40 to be
elevated as indicated by arrows 62 allowiny reams 64 of the
proper count to be automatically destacked and moved onto a
conveyor belt 66 by a pusher 67. As the ream 64 is pushed off
the skid load 40, the electrostatic charges 69 of equal
polarity (still existing between the sheets of paper in the
lower portion of the skid load 40 being destacked) reduce the
friction between sheets allowing them to slide around under
the slightest external force. To eliminate this problem, an
electrostatic emitting device 68 is mounted at the beginning
of the conveyor 66 emitting electrostatic charges 71 of
positive polarity and moves automatically up or down as
indicated by arrow 71 in accordance with a computer generated
signal from the controller 58 corresponding to the height of
the ream of paper 64 that is being passed underneath the
electrostatic emitting device 68.
The electrostatic emitting device 68 is identical to the
electrostatic emitting device 46 shown in Figure 2 and has
emitter points spaced 1/2 to 2 inches apart and positioned
above the conveyor belt 66 close to the nearest edge of the
skid load 40 in such a way that the ream 64 being destacked
passes below the electrostatic emitting device 68. The tips
of the emitter points are desirably no more than three inches
above the top surface of the ream. The distance between the
emitter tips and the top of the ream 64 is adjusted
autom~tically as indicated by arrow 73 by the controller 58 to
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2126877
account for the thickness of the ream power pack 72 so as to
keep this distance at a minimum for maximum efficiency. The
actual movement indicated by arrow 73 can be accomplished by a
servomotor or pneumatic cylinder with a position controller
(not shown). Both, the voltage applied to the electrostatic
emitting device 68 and the gap distance between the ream of
paper 64 and the bottom of the electrostatic emitting device
68 can be adjusted by the machine operator to control the
static charges that hold the ream together. A metal support
plate 70, over which the conveyor belt 66 moves, is connected
to ground potential (earth) to maximize static charging by the
electrostatic emitting device 68. A power pack 72 is
connected to the existing house power line 74 (usually 120 or
220 Volts AC) and provides an adjustable (up to 25,000 Volts,
8 mA) voltage of positive polarity to the emitter points on
the electrostatic emitting device 68. For optimum results,
the air gap between top of ream 64 and bottom of the
electrostatic emitting device 68 is between 1/2" and 1";
although acceptable results can also be achieved with somewhat
greater air gaps provided the ream 64 being destacked is
thinner and/or the operating voltage of the electrostatic
emitting device 68 is increased. Typically, one can work with
a voltage of 16,000 Volts when the gap is about 1" and the
ream thickness is about 6", or when the gap is about 4" and
the ream thickness is only 4". A 6" thick ream would require
approximately 20,000 Volts when the gap is increased to about
4" and approximately 24,000 Volts when the air gap is
increased to about 7". The computer controller can be used to
automatically adjust both the gap and the voltage to achieve
optimum results.
Directing this electrostatic force 71 of positive
polarity toward the top of the ream of paper 64 being
destacked and against the grounded plate 70 below the conveyor
belt 66 balances the negative electrostatic charge existing
between the layers of paper (described above) and thereby
eliminates the pre-existing repelling force, and the positive
charge 71 being applied from the electrostatic emitting device
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~t2687~
68 through the ream of paper 64 toward the grounding plate
actually causes the individual layers of paper to attract each
other and to temporarily bond the sheets together. This
electrostatic bonding force will diminish with time until the
deliberately induced excessive charges are again at their
natural neutral level. The time to again reach this natural
level varies from somewhat less than one hour to several days
but is of more than sufficient duration to hold the reams or
stacks of paper together during the processing and packaging
operations.
Referring again to Figure 3, after the conveyor 66, the
reams of paper 64 then flow into a squaring station 76, on
through inspection stations at numerals 78 through 88 and into
a cartonizing machine 90 where a bottom carton is formed
around the ream and so is a top lid. Once the skid load 40 is
emptied, an empty skid removal device 92 removes the empty
skid from the destacker 54.
Typically, reams of 500 sheets, each up to .012" thick
(total of 6" thick pack) can retain the electrostatic holding
effect long enough to process the ream through the entire
machine until the finished and sealed cartons are palletized.
The holding charge does diminish with time so that the sheets
will no longer cling together when the printer receives the
cartons of paper for further processing.
Although the above specifically describes the intentional
use of electrostatic charges to eliminate undesired sliding
around of the uppermost sheets of paper on skid loads being
destacked into reams for cartonizing, the method of this
invention can be also used to eliminate problems with the
upper sheets of paper sliding around on thinner stacks or
packs of paper that are automatically moved from the batch
counter delivery end of a sheeter for other types of further
processing. Typical applications are on machines that
automatically produce and package products such as loose leaf
filler sheets, spiral bound notebooks, steno pads, memo pads,
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8 7 7
and the like. In each such case, the paper is unwound fromone or more mill rolls, printed, perforated or otherwise
improved and then cut into sheets which are collected in
batches of predetermined count and then finished in-line. The
in-line finishing operations may consist of punching file
holes, applying front and back cover sheets, spiral binding or
padding, wrapping and/or cartonizing. As the stacks or packs
are being formed and batched, the same electrostatic charges
of negative polarity described above are on both sides of each
sheet in the stack or pack. As the collated sets, packs,
stacks, or reams are automatically pushed from the collecting
tray toward the finishing end of the processing line, the
individual sheets want to slide around because the entrapped
air and the electrostatic forces of equal polarity do not
allow intimate contact and friction between those layers of
paper. Deliberately forcing an electrostatic charge of
positive polarity by the method of this invention into the
negatively charged sheets of paper will temporarily hold the
individual packages of sheets together during the finishing
operations and permit increased production speeds by
eliminating disturbances from the undesired sliding around of
sheets.
Thus, it can be seen from the foregoing specification and
attached drawings that the method and apparatus of the present
invention provides a unique means for causing intimate contact
between adjacent sheets of paper in a stack thereby
eliminating undesirable slippage.
The preferred embodiment described above admirably
achieves the objects of the invention; however, it will be
appreciated that the departures can be made by those skilled
in the art without departing from the spirit and scope of the
invention which is limited only by the following claims.
