Note: Descriptions are shown in the official language in which they were submitted.
CA 02416366 2002-12-16
v
S8$ET R~OYRL ie COIQV~YSNG SYSTEM
TBCHNICAI. FIELD
The invention relates to systems for handl~.ng flat sheets of
media and more particularly to a system for holding and conveying a
sheet from a stack of sheets.
HACRGRGL1ND
Plates, films and proofir~ media fax imaging systems, such as
those used in the graphic arts industry, are commonly stacked in boxes
with slid-sheet sheets interspersed between adjacent media sheets.
The slip-sheet primarily functions to protect the media surface from
damage and to prevent adjacent media sheets from adhering to each
other. The slip-sheet is particularly important where the active
emulsion of the media is either sticky or particularly sensitive to
damage.
1s In the development of media for imaging tasks,. particularly
plates for lithographic printing operations, a number of often
conflicting parameters such a print run length, exposure sensitivity,
exposure latitude and processing requirements must often be traded off
against one another to achieve best results. Some media have
20 particularly good performance in, relation to the abovementioned
parameters but suffer from extreme delicacy of the ua-exposed media
emulsion,. zn a specific case, LH-pT lithographic plates supplied by
Fuji Phote Film Co. Ltd. of Tokyo, .Tapan, have a particularly delicate
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emulsion and may be scratched even by the action of removing the slip-
sheet. However, once exposed, the emulsion is durable and the plate
has good imaging and on-press performance.
Other commonly available media may have similar problems with
delicate emulsion surfaces alChough, depending on the thickness and
particular characteristics of the emulsion, scratches may or may not
remain visible after subsequent processing. While not all media
require special attention be paid to how slip-sheets are removed the
problem has been evident in a number of media products supplied in the
graphic arts industry.
In US patent 5,655,452 to M eke et. al. a slip-sheet removal
mechanism for removing a slip-sheet from a plate xs described.
H~iefly, the removal operates by activating a peeled airflow to
initiate separation between the slip-sheet and the plate. A number of
s5 suction tubes are pivoted to above the slip-sheet and the stack of
plates moved to engage the slip-sheet and the suction cups. A ;
combination of movement of the plate stack and pivoting of the suction
cups is used to separate the slipJsheet and move it Cowards a pair of
nip rollers that complete the removal operation.
- There remains a need fnr better methods of handling slip-sheets
and there is a particular need for such a slip-sheet removal mechanism
that performs the removal without any damage to the media emulsion.
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3
S'~MARY OF TxE INV~N~'xON
In a ~ixst aspect of the present invention a method of removing a
sheet from a stack of sheets involves engaging the edge of the sheet
along a portion of xts width with a picker bar, shaping the edge of
the sheet by moving the picker bar and conveying the sheet to a new
location.
In another aspect of the present invention an apparatus for
removing a sheet from a stack has a moveable picker bar extending over
a portion of the width of the slip-sheet and has one or more
7.0 engagement structures for engaging the sheet neax an edge and shaping
the edge to increase its stiffness. ' .
For an understanding of the invention, reference wi7.l now be made
by way of example to a following detailed description in conjunction
with accompanying drawings.
HRIEF D1~SCRIpTTON O~F TH$ I7~AH1ING.3
In drawings which illustrate by way of example only preferred
embodiments of the invention;
FI~._ 1-A is an isometric view of a stack of media.with a slip-sheet on
the top media sheet sad a picker bar in place ready to remove the
slip-sheet.
FrG. 1-B is an enlargEd isometric view o~ the picker bar rotated ca
show the engagement structures on the underside.
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FIG_ 2-A to 2-E depict a series of steps in removing a slip-sheet
using the picket bar of the present invention.
FrG. 3 is a side view of an. alternate embodiment of the invention
0
using a circular section picker bar.
FIG. 4 is a perspective view of an embodiment of the invention wherein ;
an additional air-jet is used to enhance the operation of the slip-
sheet removal system.
DESCRxpTION
Throughout the following description, specific details are set
1o forth in order to provide a mare thorough understanding o~ the
invention. However, the invention may be practiced without these
particulars. In other instances well known elements have not been
shown or described in detail to avoid unnecessarily obscuring the
invention. Accordingly, the specification and the drawings are to be
regarded in an illustrative rather than a restrictive sersse.
This invention is described in relation to a novel slip-sheet
removal system that is able to remove a sJ.i~p-sheet from a media '
~ai~hout damaging the delicate emulsion. The method of removal of the
present invention specifically avoids causing relative movement
2o between the slip-sheet and the media emulsion. While of particular
application in removing slip-sheet from a stack of media in a graphic
arts imaging system, the method and apparatus of the present invention
may be useful in handling any type of media particularly where the
CA 02416366 2002-12-16
media, is delicate and susceptible tv damage. The term "media should
be read to include all manner of media used in imaging and printing
operations,
Slips-sheets are commonly flimsy sheet$ of paper but may also be
plasticised yr other specially treated sheets depending on the media
in use. In particular, lithographic plates are typically shipped in
boxes of 25 or more plates with thin paper slip-sheets interspersed
between plates. rn an automatic plate handling system the stack of
plates are commonly placed in an access position from which they are
loaded onto the imaging engine by some manner c~ automated handler.
the slip-sheets represent a problem for automatic media handling in
that they must be removed prior to imaging. the removal is often
complicated by electrostatic attraction between the sheet and the
media surfaces. Because the slip-sheet is in intimate contact with
the surface of the media a removal mechanism should also allow for the
ingress of air undex the slip-sheet as it is removed. The slip-sheet
removal mechanism has the task of reliably separating the sheet from .
the plate and removing it to a location where it can be disposed of.
It has been ob9erved by the inventors o~ the present invention that
emulsion damage may ocCUr during slip-sheet removal whenever the edges
are dxagged or the material is bunched up andtor creased. During the
slip-sheet removal process, the shearing action between the slip~sheeG
and the plate becomes localized to these creased areas and scuffing ox
scratching may occur. Further, it has been determined that if the i
a
slip-sheet can be engaged without forming creases so that it remains
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in a flat sheet, and the engaged sheet can be lifted avray from the
media in substantially this condition scuffing may be completely
avoided,
One possible solution is to engage the edge of the slip-sheet
with an extended picker bar, either with a plurality of suction cup$
or a vacuum groove distributed aver substantially the entire length of
the sheet. While this solution has been found to work adequately
there are some problems. Firstly, imaging systems typically
accommodate a wide variety of media sixes and the bar v~rould have to be
the full width of the largest media used. For smaller media sizes the '
bar overlaps the edges causSng problems with vacuum escapement whexe ,
there is no slip-sheet material to engage. This problem can be
addressed by providing zoned vacuum delivery albeit at higher cyst and
complexity. Secondly, the length of the bar for 'Very Large Format j
(VLF) size imaging devices becomes almost unmanageable and overly
expensive since it must be made sufficiently rigid so as not to deform
during actuation. .
Azl embodiment of the presenC invention is shown in rtLi. 1-A, A
stack of media with slip-sheet interspersed 8 are shown in as access
2o position. The autoloder device is not shown except for the slip-sheet
removal components for sake of clarity_ The top media sheet 14 (shown
in cutaway view) in the stack a is covered by a slip-sheet la. A
picker bar 11. is shown. in position to engage the slip-sheet is at one '
4
edge. 4Jhile in an automatic system the stack may comprise a plurality ,'~
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cf media sheets, a manually loaded system may only have one media
sheet in an access position.
One possible embodiment of picker bar 11 is shown in F=ti. 1-a.
The picker bar shown generally at 14 comprises a rigid angled frame
with a plurality of compliant suction cups 18 on the face for engaging
the slip-sheet. Vacuum is supplied to the suction cup9 18 via a
number of vacuum lines 6. The suction cups 10 engage the slip-sheet
when a vacuum source (not shown) is connected to the end of line 5,
Advantageously a plurality of small diameter suction cups are used
30 which reduces the possibility of the slip-sheet being deformed uxlder
the cups and thus forming creases that may scuff the emulsion. it was
experimentally determined that suction cups purchased from Anvar Corp
of Hudson MA, model QFA7 part number 2.700004, with a face diameter of
around 7 mm worked particularly well. Suction cups. 18 may be made
from a compliant matex-ial or simply suction holes formed directly in
the frame. The vacuum may be applied directly or indirectly by using
Bernoulli effect holes. Alternatively, a longitudinal vacuum groove
may be formed in the frame a to distribute the vacuum over a larger
area. Mechanical fingers may also be used to pick and hold the slip-
2o sheet, but for extremely delicate media there will be a higher risk of
scuffing the emulsion. " -
As can be seen in g=Ci. 1-A the picker bar only engages the
central area of one edge of the slip-Sheet. The method of operation
of the picker bar will be further explained with reference to FxG. aA~
2E. For sake of clarity the actuator mechanisms for moving the bar
CA 02416366 2002-12-16
towards the slip-sheet and for rotating it into engagement with the
slip-sheet are not shown in the drawing figures since such mechanisms
are well known zn the art. Referring now to FTG. Z-A, initial
engagement with the slip-sheet is with the heel 16 of the picker bar
s frame. At this stage, the suction cups 18 are still oriented away
from slip-sheet la. It may be necessary to add a compliant padding to
the heel 16 of frame 14 to ensure that it does not scuff the plate l0
through the slip-sheet 13. The rear of the heel can also be curved to
reduce scuffing, and the padding may e~ctend around the curved portions
to of frame 14 as well. In the drawing figures, the gaQ betureen the
slip-sheet 12 and the media 10 is exaggeraCed for clarity but in
reality, the slip-sheet 12 rests on the plate.
In F=6. a-g the auction cups Z8 pn bar 14 are rotated in a
direction shown by arrow 19 into engagement with slip-sheet la
1S whereafter a vacuum source knot shown) i.s connected to auction cups 18
to secure the slip-sheet to the picker bar. The vacuum may be
generated using any known convenient means and shay be applied by
electrically activating a vacuum source or by opening a
electromechanical valve or a combination of both. The vacuum may be
20 applied before the suction cups engage the slip-sheet but applying it
after the cups are in contact is preferred. Referring now to ~za. 2-
C, once the slip-shEet 18 is held by the suction cups lc the picker
bar is rotated back in the direction shown by arxow a0. This rotation
causes the slip-sheet to lift off the plate 10 while simultaneously
25 curling the edge. The curling of the s7.ip-sheet edge, shown in
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perspective view in FZO. 2-n, offers a substantive advantage ever
simply lifting the slip-sheet 1Z directly off the plate. Firstly, any
attempt to lift the slip-sheet directly from the position shown in
FxG. ~-s will likely cause the sheet to bunch and crease when the
portion held by the picker bar 14 is pulled. The outer edges (shown
at a1 in BIG. 2Ts) may still adhere to the media ~a until the
electrostatic forces are broken and air ingress releases the slip-
sheet. Under thecQ conditions, creases may form and the media
emulsion may be scuffed. Secondly, the force needed to peel the slip-
to sheet away in a curling motion is legs than that required for direct
lifting. In essence, introducing the curl compensates for the fact
that picker bar i4 does not extend over the entire width of the slip-
sheet 1Z by forming an at least partially rigid edge befoxe lifting
it. It also provides an edge, along which the attractive forces are
at least partially reduced thus facilitating further partial or
complete peeling allowing eventual complete removal of the sheet
without introducing creasing or bunching. The amount of curl may be
90°as shown ox greater; larger curl typically providing a
progressively stiffer edge. On the other hand, a curl of less than 90°
msy also be acceptable depending on the width and materials of the
slip-sheet and the media.
Once the stiffened edge is Formed, the slip-sheet may be peeled
off the plate as shown in FI6. a~~ by one of or a combination of
mvveu~ent in the dizections shown by arrows Z4 and ~6. The cuxled edge
prevents the outer edges from falling back arid scuffing the media
CA 02416366 2002-12-16
emulsion_ As the slip-sheet is peeled back, an edgs 28 continues to
propagate allowing the electrostatic and other forces to be broken
along the width of the slip-sheet, thus avoiding creasing or bunching.
The slip-sheet thus at Least partially removed may be passed on to a
5 disposal mechanism such as the slip-sheet compactor described in
commonly assigned US provisional patent application 60/393657 by
Williams.
The pxesent invention is not limited to hand3.ing slip-sheet
material but may also be employed to handle any flimsy media using a
1o picker bar that is shorter than the width of the media. In
particular. graphic arts film and colour proofing media commor~ly
comprise an emulsion on a thin sheet of palyestsr that may suffer
either emulsion damage or creasing during handling. The loading of a
flimsy media that has delicate emulsion may prohibit engaging the.
is emulsion side or sliding the emulsion over Che back of another sheet.
If the media sheets are stacked emulsion side down the pickax bar may
engage the rear surface of the sheet and peel it back so that there is
substantial3.y less slippage betweers adjacent sheets. The picker bar
may be used in a fully automatic system where the sheet is picked from
a pluKality of sheets in a stack or it may be used in a semi-automatic
position where a single sheet is placed in an-access position to be
auxomatieally loaded into the imaging device. Likewise, the same
picker bar may be used to convey the sheet from the imaging device on ;
completion o~ imaging. '
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Tn an alternative embodiment, the picker bar may be constructed .
uszng a circular section shown in x~I6. 3. The circular section picker
bar 30 allows the edge of slip-sheet la to be curled to form an edge
in the shape of a partial tube and xnay be advantageous since a curled
tube's stiffness will be consistent in more directions than other
shapes. Furthermore the circular section bar may be made from common
bar or tube stack whereas the angled bar shown in the drawing figures
may have to be custom fabrieaCed.
Actuators suitable for placing the picker bar on the sheet and
rotating to engage the suction cups are well known. Pneumatic .
actuators, motors, stepper motors or servvrnotors may be used.
Typically, the actuation functions reguired include a translation tv
place the pzcker bar on the slip~sheet and an actuation to rotate the
bar into engagement. The Potation may be supplied by a separate s
z5 actuator or the bar may simply be allowed to roll ~o bring the suction
cups into engagement. The rotation of the picker bar may also be
synchronized to the forward and backward movement of the picker bar to
eliminate the possibility o,f the slip-sheet being slid forward over
the media emulsion when the bar is rotated to engage the auction cups
as shown in FIG. ~-8. IF the shearing friction between the slip-sheet
and the media emulsion or other sheets in the ~star.~s is 3.ow, this may
be addresser) by actively rotating the picker bar when engaging the '
engagement structures rather than just. allowing it to roll forward.
On the other hand, if the shearing friction is consistent and the
slip-sheet does rzot slide easily a separate actuator may be
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eliminated. Alternatively, the bar & suction cups may be lowered
directly into engagement without the requirement of a further
rotation.
In another embodiment shown in F=G. 4, one or more air jets d0
may be prozrided to assist in introducing the curl, should a kink 42
form in the edge of the slip-sheet. The air jet 40 may be blown along
the slip-sheet ZZ to snap the edge into the desired shape. The
direction of the air jet 40 is only one example of many possibilities,
including multiple air jet directions at the same time, or sequenced .
to air jets. Air jet ~0 may be mounted on picker bar 14 or may be
separately mounted.
Once the curl is formed in the edge of the sheet and a
propagating edge is established (as described in relation to item ~8
of 1~IG. 2-E), the sheer may be remo~red in either direction. The sheet
1,s may be folded over itself and removed in a direction towards tho .
opposite edge o~ the stack from the edge that was e~ng~aged.
Alternatively, the sheet may be slid off in a direction away from the
stack, Lead by the curxed edge.
I
While the shape for stiffening the front edge of the slip--sheet l
l
2o has'been described as a "curl~ in this descriptioirl, it may be any of a
variety of sha~ges including but not limited to a 'V" shape, sine wave'
shags. Furthermore, the shape may or may not include a creasing of '
the edge to increase stiffness. Such creasing would not be a problem
if performed once the slip-sheet if lifted away from the media. ~'he
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curl described herein has the advantage of being easy to create and
has a low chance of scuffing the media. Accordingly, the term "curl°
is used herein to describe any shape that is given to the edge of the
slip-sheet or media with the intent of stiffening.
s As will be apparent to those skilled in the art in the light of
the foregoing disclosure, many alterations acrd modifications are
possible in the practice of this invention without departing from the
spirit or scope thereof.
