Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY DRUM FOR PROCESSING SEIE~T_MATERIALS
CROSS-REFERENCES ~O RELATED PATENTS
In the United Kingdom Patent 1,579,900, issued ~anuary 28,
1981, of E. C. Korte for "Sheet Feeding and Transport,"
and assigned to the assignee of the present application,
there is shown a low inertia rotary drum for transport of
flexible sheets such as paper. The drum has two longi~
tudinal slots disposed on its surface, with each slot being
connected to internal segments by spaced ports extending
therethrough. These slots enable a vacuum to be applied to
the leading and/or trailing edge of the sheet separately. A
valving system is used to control the vacuum to these slots
independently through the internal segments. The spacing of
the slots about the circumference of the drum is dependent
on the size of the sheet to be processedO A charge corona
is disposed relative to the drum and attaches the sheet to
the drum by means of electrostatic attraction.
The drum of the aforementioned invention handles a single
size sheet and requires the use of a corona for attaching
the sheet to the drum.
.
In U.S. Patent 4,202,542, by G. B. Lammers, et al., issued
December 4, 1979, entitled "Apparatus for Handling Flexible
Sheet Material of Different Sizes," and assigned to the
assignee of the present invention, there is shown a sheet
transport device including a low inertia rotary drum for
handling various size materials. The drum has a pIurality
of sets of
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longitudinally spaced ports formed on its surface.
The ports are spaced arcuately from each other about
the surface of the drum, with one set enabling a
vacuum to be applied to the leading edge of a sheet,
while only one of the other sets of por-ts applies a
vacuum to the trailing edge of the sheet in accordance
with thç dimension of the sheet in the circumferential
direction around the drum. The sheet transport
device further controls how many of the ports of the
two sets of ports apply a vacuum in accordance with
the dimension of the paper along the length of the
drum. A rotary valve is used to control the vacuum
flow i~ accordance with the size of -the sheet.
Thus, the drum of the invention processes various
size sheets but re~lires a rotary valve for controlling
vacuum flow.
..
The present invention is an improvement of the drum
o~ the aforementioned patent and patent application
in that the drum of the apparatus of the present
invention does not require the use of a tacking
corona and/or a valve for controlling vacuum. The
drum of the present invention handles various size
sheets and can be used with the structure described
in either of the above-mentioned references.
BACKGROUND OF THE INVENTION
,
l` Field of the Invention
The present invention relates to document transport
devices; more particularly, to drum type document
transport devices wherein a sheet of flexible material
(such as paper~ is attached to the drum for transport
and f~r processing.
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2. Prior Art
The use of a rotary drum for transporting sheet-like
material is well known in the prior art. The rotary
drums are often used in printing systems. In addition
to the transport function, these drums support the
sheet-like material during the printing process.
Prior art printing systems are further fitte~d with
paper handling mechanisms which load and unload a
sheet of paper onto the drum.
A necessary component of the prior art print system
is the means used to attach the sheet onto the drum.
The prior art often used mechanical fingers for
clamping sheets onto~the drum. By way of example,
U.S. Patent 2,451,079 describes a rotary drum for
supporting a sheet in a facsimile printing system.
The drum is fitted with two linear rows of pins.
The rows of pins are spaced circumferentially and
extend outwardly from the surface of the drum. One
row of pins releasably secures the leading edge of
the sheet while the other row releasably secures the
trailing edge of the sheet. A loading plate and a
- stripper bar are positioned relative to the drum.
The loading plate loads a sheet onto the drum while
the stripper bar strips a sheet from the drum.
'
2S Although the above-described mechanical clamping
system works satisfactorily for its intended purpose,
the system tends to be relatively slow and complex.
; The slowness stems from the fact tha-t the response
time in which the mechanical system clamps and
releases a sheet is relatively long. As such, the
print drums using mechanical fingers for gripping
the sheet are used with relatively low performance
printing systems.
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For high perfor~ance printing sys~ems, 't~e ~ior art
general1y uses pneumatics and/or e~e~ros~ic means
for tacking the sheet onto the drum. Prior art
~rinting systems generally use coronas as the source
for generating the electrostatic force. An example
of a prior art pri~ting system using a combination
of pneumatics and c~rona for attaching a sheet on~o
a print drum is disclosed in the above-referenced
Korte patent application.
As for pneumatic sy~tems, the general scheme is to
use a segmented drum to transport the sheet. Vacuum
for attaching and/or dislodging the sheet is selec-
tively applied to-va~ious zones or segments on the
drum. The drum is referred to as being segmented
because at times during the operation of the system,
segments of the drum may or may not have vacuum
present.
U.S. Patent 3,545,746 is an e~ample of the prior art
se~mented drum. The patent describes a document
transport consisting of a hollow cylindrical transport
drum and docu~ent loading and unloading means disposed
reLative thereto. The cylindrical surface of the
drum is fitted with longitudinal and circumferential
slots. The inside o the drum is vented to atmosphere
- 25 by communicating holes. ~ static partition divide~
the interior of the drum into two pneumatically
independent compartments. By rotating the drum and
applying a vacuum to one of the compartments, a
; document can be carried around with it, to a limited
extent, determined by the size of the evacuated
compartment.
U.S. Patent 4,145j~40 is another example of the
prior art segmented type vacuum drum. The drum is
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adapted for transporting flexible sheets. The drum
is fabricated with an active suction zone or sector
for gripping the sheets. The drum consists of an
inner stationary cylindrical member and an outer
rotary Gylindrical member. The stationary member is
fitted with a suction source and a pressure source.
Both sources are displaced relative to each other
about the circumference of the stationary cylindrical
member. The suction source is vented -through a
groove to the outside surface of the inner stationary
member. Likewise, the pressure source is vented
through a recess formed on the surface of the inner
stationary member. A sector of the outer rotary
member is fitted with rows of apertures. The apertures
interconnect the inside surface of the stationary
member to the outside surface. A common duct inter- -
connects a row of apertures to the groove or the
recess. Each duct is fitted with a piston. The
piston controls the pressure (negative or positive)
to the apertures. Vacuum (negative pressure) and/or
puffs of air (positive pressure) is applied to the
sector of the drum as the outer member is rotated
rFlative to the lnner.
.
It is also well known in the prior art to use valves
as a means to control vacuum flow to the active
segment of the drum. By way of example, U.S. Patents
- 3,663,012 and 3,466,029 describes sectored vacuum
transport dxums wherein valves are used to control
vacuum to the active sector of the drum.
.
Although the use of pneumatics or a combination of
pneumatics and electrostatics is a significant
improvement over the use of mechanical gadgets for
tacking sheets onto a drum, the prior art pneumatic
document transport systems still have several dis-
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advantages. [n the first instance, the segmenteddrum design tends to be complex. The complexity
increases as the numbér of sheet sizes, which the
transport system handles, increases.
A complex valving system is generally needed in the
prior art pneuma-tic systems. The valving system is
needed to select which port receives 10w at any
particular time. The valvin~ system increases as
the sheet size, which the system handles, increases.
Another requirement for a valving system is that the
system must know the paper size to enable the supply
of vacuum to the proper ports. This requires the
intervention of an operator to make a sheet size
selection or the use of logic to detect the sheet
size. Moreover, with a valving system, one has to
use extra care in selecting the valve and in position-
ing it relativé to the drum. Both valve selection
and valve positioning are important since the response
time of the drum is directly dependent on both
variables. Due to their complexity, the prior art
pneumatic document transport system has relatively
low reliability.
Another prior art problem area is in the type of
vacuum system used. As was described previously,
the vacuum system is needed to evacuate the drum.
Stated another way, the vacuum system creates the
orce-for tacking a sheet onto the drum. The problem
in thi.s area stems from the fact that in that type
of vacuum system, there is a wide swing in the~
vacuum between load and no-load conditions on the
drum. By way of example, at no-load condition (that
is with no paper on the drum), the vacuum is relatively
low. At load condition (that is with paper on the
drum), the vacuum is substantially higher.
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The wide swing in vacuum has several undesirable
repercussions. In the first instance, there is a
large mismatch between the vacuum requirements to
attach and retain a sheet onto the drum. Generally,
a relatively high flow is required for attachment,
but a relatively low vacuum force is re~uired for
retainment. As such, there is a need to recognize
that -there is a close relationship be-tween the
vacuum system which generates the vacuum requirements
and to design the vacuum system to minimize the
mismatch.
So far, the prior art has failed to recognize and
address the interrelation between the vacuum require-
ments (at the drum) and the design of the vacuum
system.
.
In addition, the high vacuum tends to damage a sheet
on the drum. More important, in some types of
application, such as ink jet printing, the high
vacuum is totally unacceptable. The reason is that
the high vacuum sucks the ink through the paper.
The prior art attempts to solve the problem by using
a relief valve to reduce the pressure at the drum.
Needless to say, the use of the relief valve tends
to complicate the system and increase cost.
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25 ~ SUMMAR~ OF THE INVENTION
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An object of this invention is to provide a more
eficient sheet handling apparatus than was heretofore
designed.
.
.
Another object of the present invention is to provide
a nonsegmented drum for handling various size sheets.
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Still another object is to provide a vacuum drum
with a relatively uniform vacuum between load and
no~load conditions.
.
The present invention accomplishes the fore~oing by
generating variable flow zones on the surface of the
drum during loading and variable vacuum force zones
on the surface of the drum durin~ the period of time
when the sheet is retained on said drum. The vacuum
force and flow zones are highest at predetermined
zones; particularly, in the zones whereat the leading
and trailing edge of the sheet attaches to the drum.
The vaGuum and flow are generated by slots and
communicating ports disposed on the surface of the
drum. By varying the sizes of the slots and the
number and/or size of holes, the variable vacuum
force and flo~ zones are created.
`
The present sheet handling apparatus includes a low
inertia rotary drum which supports variable size
~`sheets of paper. Th~ drum is journaled at its
opposite ends for rotation. A plurality of spaced
elongated slots are fabricated on the cylindrical
surface of the drum. The slots are placed along the
longitudinal and circumferential dimensions of the
drum.~ The slots, along the longitudinal dimension
of the drum, are configured to~support three sizes
of sheets.~ The slots around the circumference of
the drum are configured into a leading edge slot and
a plurality of trailing edge slots. The leading
edge slot supports the leading edge of all sized
sheets, whi~le each trailing edge slot supports the
trailing edge of a different sized sheet. The
spacings between the leading edge slots and the
trailing edge slots are dictated by the size of -the
sheets. A high flow, low vacuum blower is coupled
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to the drum. Communicating ports or holes are
fabricated in the slots. The holes communicate the
vacuum to the surface of the drum.
In one feature of the invention, one or more arcuate
slots are disposed in the circumferential dimension
of the drum. One or more pick-off fingers coact
with the slots to strip a shéet from said drum.
In another feature of the invention, the population
and/or si~e of the holes are greatest in the leading
and trailing edge slots.
In yet another feature of the invention, an elongated
load guide is disposed relative to the surface of
the drum. The guide forces a sheet to conform -to
the surface of the drum~
The foregoing and other features and advantages of
the invention will be apparent from the following
more particular description of the preferred embodiment
of the invention, as illustrated in the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
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FIG. l is a schematic view of the document handling
.
apparatus ~according to the teaching of the present
invention.
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FIG. 2 shows a schematic of the print drum.
.
FIG. 3 shows a cross-sectional view of the print
drum.
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FIG. ~ shows a cross-sectional view of the document
handling apparatus.
FIG. 5 is a schematic view of the vacuum drum unfolded.
The view is helpful in understanding the layout of
the slots and communicating ports on the surface of
the drum.
FIG. 6 is a graph showing the characteristics of
various vacuum systems. The graph is helpful in
understanding the design of an efficient vacuum
system.
DETAILED ~ESCRIPTION OF THE PREFERRED EMBODIMENT
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As is used in the specification, the word "pump"
means a type of air compressor characterized as a
high pressure, low mass flow rate device usually of
the positive displacement type.
.
As is used in the specification, the word "blower"
means a type of air compressor characterized as a
high mass flow rate device usually of the nonpositive
displacement (dynamic) type.
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Although the present invention can be used in any
environment wherein flexible sheet-like materials
are transported,~the invention is well suited for
use in a printing environment, and as such, will be
described accordingly. However, this should not be
construed~as a limitation on~the scope of the presenb
nvention since it is within the skill of the art to
adap~ the invention for use in other environments
without departing from the scope and spirit of the
pr-fient invenelon .
64~00
Referring to the drawings, and particularly to FIGS.
1 and 4, there is shown a document handling system
10 according to the teaching of the present invention.
For brevity cf description, common elements in the
figures will be identified by common numerals.
Also, conventional elements such as support frame,
mechanical coupling, bearings, etc. are omitted from
the drawings. It is believed that the omitted
elements can be easily suppli.ed ~y an artisan having
ordinary skill in the mechanical art, and the omission
further simplifies the description of the invention
shown in the drawings and described hereinafter.
The document handling system 10 includes a low
inertia rotary drum 12. The drum includes a cylindri-
cal shell 14 with end members 16 and 18 fixedly
attached to opposite en~s of tha cylindrical shell.
A tubular member 20 is securely fastened into end
- member 16. As will be described subsequently, the
tubular memker 20 conveys negative pressure to the
interior of drum 12. As is shown more clearly in
FIG. 2, a shaft 22 is attached to end members 18. A
pair of conventional bearings and mechanical couplings
(not shown) are coupled to shaft 22 and tube 20,
respectively. The bearing is securely attached to
the machine frame (not shown). A drive motor (not
shown) is coupled to shaft 22. The drum is therefore
journaled for rotation in the bearings (not shown)
and is driven by the motor (not shown) in a direction
shown by arrow 24. A vacuum plenum 26 is coupled to
tubular member 20. A blower 28 is coupled to the
plenum through tube 30. As will be described
hereinafter, the interior of drum 12 is evacuated by
the blower. A seal member 32 is positioned about
; tube 20 and prevents escape of negative pressure to
the atmosphere~ In the preferred embodiment of this
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invention, the blower is a low vacuum, high volume
flow blower.
Still referring to FIG. l, a loading s-tation 32 and
an unloading station 34 are positioned relative to
the surface of the rotatiny drum. The function of
the loading station 32 is to load flexible sheet-
like material such as paper sheets, in seriatim from
a stack 36 of sheets loaded in support tray 38. The
topmost sheet in the pile is fed along guide channel
40 where the leading edge of the sheet is first
attached to a predetermined zone on the cylindrical
surface of the drum. Downstream from the loading
zone, in the direction of drum rotation, an arcuate
elongated guide member 42 is mounted relative to the
cylindrical surface of the drum. The function of
the guide member is to force a sheet to conform to
the surface of drum 12. The ~uide member has a
length substantially e~uivalent to the length of the
drum and runs in a direction parallel to the axis of
rotation of said drum. In thé preferred embodiment
of this invention, the spaces between the cylindrical
surface of the drum and the inner surface of the
guide member is approximately 0.05 centimeters. As
is shown in FIG. l, a paper sheet 44 is securely
attached to the cylindrical surface of the drum.
; The sheet on the drum is processed by~a processing
station (not shown) which is positioned relative to
the drum and between the loading and unloading
stations. The processing station may be an ink jet
head which writes readable characters on the paper
as said paper is transported through the processing
station. After processing, the sheet 44 and other
sheets similarly situated are stripped from the drum
` ~y a plurality of stripping fingers ~6. As is shown
more cl-arly in FIG. 2, the~e strlpping ~lngers are
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lowered to coact with a plurallty of circumferential
slots 48 fabricated in.the circumferential dimension
of the drum; The detached sheets travel over the
top surface of guide member 50 and into output tray
52.
. An operator can then remove the processed sheet from
the output tray. It should be noted that altho~ugh a
plurality of circumferential slots and a plurality
of mechanical fingers are used to detach the shèet
from the drum, in a preferred embodiment of this
invention, only a single slot and a single detach
finger is used. It is therefore obvious that any
number of slots and associated fingers can be used
to detach the processed sheet from the surface of .
the drum.
Turning now to FIG. 4 is a cross-section of the
schematic shown in FIG. 1. As was stated previously,
elements in this schematic which are common with
elements previously identified in FIG. 1 are identified
by the same numerals. As was described previous~ly,
the sheets (not shown) are fed in seriatim from
support tray 38 along guide channel 40 and onto the
cylindrical surface of drum 12. Loading of the
sheet is assisted by elongated guide member ~2. A
,
pair o feed rollers 50 and 52, respectively, are
disposed within the feed path of the.sheet. The
guide rollers are mounted so that a relatively small
opening separates the rollers. The opening is
: ~ sufficiently small to allow free passage of a sheet
therebetween. Feed roller 50 is coupled through a
:~: mechanical linkage 54 to solenoid 56. The solenoid
is connected by conductor 58 to controller 60. As
will be described subsequently, when a control
sig~al is outFutted on conductor 58, ~he solenoid
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pivots roller 50 to clamp a sheet positioned between
rollers 50 and 52, respectively. The sheet is
subsequently fed onto the surface of the drum.
- A paper gate 62 is pivotally mounted in the paper
path and downstream from feed rollers S0 and 52,
respectively. The paper gate is coupled through a
machanical linkage 64 to a solenoid 66. The solenoid
is coupled by conductor 68 into controller 60. In
operation, a sheet of paper (not shown) is fed from
the top of a paper stack in bin 38 by a feed mechani6m
(not shown). By way of example, a-paper ~eed mechanism
referred to as a shingler and described in U.S. Patents
4,113,245 and 4,175,741 may be the paper feed means. The
paper passes through the opening between feed rollers
50 and 52 and the leading edge is stopped by paper
gate 6~ Enabling signals are outputted on conductors
58 and 68, respectively. The signal on conductor 68
activates solenoid 66. As a result of the actuation,
the gate 62 is pivoted from the leading edge of the
sheet. S~milarly, the signal on conductor 58 acti~ates
solenoid 56 Solenoid 56 then forces feed roller 50
to lower, thereby forcing contact of the sheet with
both rollers. The roller 50 is then rotated by a
rotatlng means (not shown) in a counterclockwise
direction, thereby feeding the sheet onto the cylindri-
- - cal surface of drum 12 synchronized in position and
surface velocity with the drum. Generally, the drum
610ws down during loading, speeds up~during processing
and again slows down when a sheet is to be removed
therefrom. Stated another way, paper is delivered
to the drum at a first velocity. Paper is processed
on the drum at a second ~elocity. Usually the
second velocity is hlgher than the first.
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Still referring to FIG. 4, pick-off fingers 46 are
fabricated with an upper sloping surface and are
substantially cone-shaped with the bottom surface of
the cone having concave surface for coacting with-
the circumference of the drum. The pick-off fingers
are fixedly coupled to shaft 70. Shaft 70 is coupled
through mechanical linkage 72 to solenoid 74.
Conductor 76 connects the solenoid to controller 60.
In operation, a control signal is outputted on
conductor 76 from controller 60. ~he signal activates
solenoid 74 and the shaft 70 is rotated in a counter-
clockwise direction so that the pick-off fingers are
lowered into slots 48. Of course, if a single slot
and pick-off finger is used, then the pick-off
finger is lowered in the single slot. As such, a
sheet which is on the drum rides along the upper
incline surface of pick-off finger 48 over guide
member 50 and into tray 52. It should be noted, at
this point, that several other types of loading
Z0 devices may be used without departing from the scope
of the present invention. By way of example, the
loading mechanism described in accordance with the
above cross-referenced Korte application may be the
loading mechanism. Similarly, other types of unloading
mechanisms can be used to unload a sheet from the
drum.
.
As was stated previously, the means which are used
to attach a sheet onto the drum is vacuum. As is
shown in FIGS. 2, 3 and 5, a plurality of slots and
holes are used for controllin~ and communicating the
vacuum to the surface of drum 12. In FIG. 2, the
drum is shown in its normal (that is unrolled) form.
In FIG. 3, a cross-section of the drum of FIG. 2 is
shown. In FIG. 5, the drum is shown i.n an unrolled
form. In the unrolled representation form, the drum
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occupies a flat rectangular area. It is believed
that the showing in FIG. 5 will highlight the slots
and communicating portostructure. The structure
enables variable force vacuum zones to be present on
the cylindrical surface of the drum. No valving or
other prior art segmenting are needed to establish
the variable force vacuum zones on the drum. As
before, common elements in the figures will be
identified by common numerals. As can be seen in
the drawings, the drum is fitted with a longitudinal
scribe line 74 and a circumferential scribe line 76.
The scribe lines are the alignment line~ on the
drum. Generally, the leading edge 78 (FIG. l) of
the sheet is aligned relative to or parallel with
scribe line 74. Drum rotation is in the direction
shown by arrow 80. The lengthwise dimension of the
sheet is usually aligned with the longitudinal
scribe line. Similarly, the widthwise direction of
the sheet is usually aligned with circumferential
scribe line 76. It should be noted that the alignment
of the sheet may be reversed without departing from
the scope of the present invention.
Still referring to FIGS. 2, 3 and 5, the entire
cylindrical surface of the drum has a plurality of
- 25 elongated slots fabricated thereon. The function of
the slots is to allow the vacuum to be effective
over a wide area of paper. -The sLots are arranged
in linear rows and in spaced relation along the
longitudinal axis and the circumferential axis of
the drum. For ease of description, the slots are
numbered in ascending order in the direction opposite
to that of the drum. By way of example, slot 86 is
identified as the leading edge slot. This slot
generates the vacuum force which attaches the leading
35 edge of the sheet to the drum. Slots 88-102 are the
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intermedia-te slots and function to attach the center
part of the sheet onto the drum. Slots 104 and 106
are the trailing edge slots. The function of these
slots is to at-tach the trailing edge of a sheet onto
the drum. Additionally, the width (size) of the
slots vary. More particularly, -the leading edge
slots 86 are wider than the intermediate slots 88
102. Similarly, the trailing edge slots 104 and 106
are wider than the intermediate slots. This enables
a slightly higher vacuum force to be present at the
trailing edge of the sheet.
Still referring to FIGS. 2, 3 and 5, the slots are
conigured in spaced linear rows along the longitudinal
and the circumferential dimension of the drum.
Also, the slots are configured into groups or sets,
both in the longitudinal dimension and the circumfer-
ential dimension of the drum. Each set or group is
adapted for supporting a different size sheet. By
way of example, the first group of slots (identified
20 by numbers 108 and 118) extends along the longitudinal
dimension o the drum and is positioned between
scribe line 76 and dotted line llO. The first group
o~ slots also extend in the circumferential dimension
of the-drum and are bound by scribe line 74 and
~trailing edge slot 106. The first group of slots
support a first size sheet, say 8-1/2" x 11" sized
sheet.
.
Likewise the second set of slots (identified by
~ numerals 112 and 116) are bound in the circumferential
dimension of the drum by scribe line 74 and trailing
edge slot 104. In the longitudinal dimension, the
second set is bound by dotted line 109 and scribe
.
line 76. The second group of slots support a second
size of sheet, say the international paper A4. Ihe
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size of the A~ paper is approxima-tely 210 x 297 mm
or 8-1/4" x 11.7".
Finally the third set of slots (identi~ied by numerals
114 and 118) support a third size of sheets, say, 8-
1/2" x 14" sized sheet.
The third set of slots are bound along the lon~i-tudinal
dimension by dotted line 111 and scribe line 75 and
in the circumferential direction by scribe line 74
and trailing edge slot 106. Although FIG. 5 shows
that the drum is able to support three different
sizes of sheets, this should not be construed as a
limitation on the scope of the present invention.
Since it is within the skill of the art to design
the drum's surface so that more than or fewer than
three sizes of sheéts can be supported. In other
words, the slots can be configured to support variable
size sheets.
As is evident from the above description, the circum-
ferential dimension of the drum supports sheets
having a specific width (say 8-1/2"). Likewise, the
distance identified as 116 supports sheets having
second width such as the so-called A-4 paper. The
A 4 paper is the designation given to an inter-
~ nationally sized paper. Of course, any other config-
; 25 uration can be designed for supporting other types
of sheets without departing from the scope of the
present invention.
A plurality of circumferential slots 113 are disposed
around the circumference of the drum. The detach
finger coacts with the ci~rcumferential slots to
remove a sheet from the drum. Although a plurality
of slots are shown in FIG. 5, in one embodiment of
the present ~nven~ion only a single slot is used.
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Still referring to FIGS. 2, 3 and 5, a plurality of
communicating ports 120 are fabricated in the cylindri-
cal surface of the drum. The communicating ports,
sometimes called holes, interconnect the interior of
the ~rum to the cylindrical surface. The function
o these holes is to supply vacuum from the interior
of the drum to the external surface. The population
and/or size of these holes are such that variable
flow zones are generated on the cylindrical surface
of the drum. As is shown in the figures, a relatively
high number (population) and/or size of holes are
shown in the leading edge slot 86. As such, a
relatively high flow which attaches the leading edge
of the sheet-is experienced in this zone. Similarly,
a relatively high number and/or size of holes are
disposed in leading edge slots 104 and 106, respect
ively. As such a relatively high flow for attaching
the trailing edge of the sheets is experienced in
the trailing zone.
The population of holes in the intermediate slots
88-102 are scanty and therefore a relatively low
flow zone is positioned between these rows. Stated
another way, there are fewer holes in the intermediate
slots than there are in the leading edge slot and/or
the trailing edge slots. Although not shown in FIG.
5, in a preferred embodiment of the present invention,
the population and/or size of holes in the trailing
edge slots are greater than those in the leading
edge slots. This creates a hlgher flow (attraction)
~one at the trailing edge of the sheets than at the
leading edge.
It should be noted that the leading and trailing
edge zones OIl the drum are the most criti~cal areas
for attachment and retainment of a sheet. For
~ .
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attachment of the shee-t's leading and trailing
edges, hi~h flow is re~uired which is provided by a
large port flow area (i.e., number of holes and/or
size). For retainment of the sheet's leading and
trailing edges, a certain vacuum force is required
which is provided by wide slots. Zones interior to
the leading and trailing edge zones have lower flow
and vacuum force re~uirements for attachment and
retainment. These zones only need a low flow and a
low vacuum force which are provided by smaller port
flow areas and narrower slots respectively. The
type of vacuum system used in the present invention
interacts with these slot widths and port flow areas
to satisfy the different zone attachment and retainment
re~uirements. This is done more effectively at both
load and no-load conditions.
Although the showing in FIGS. 2, 3 and 5 shows a
particular combination of slots and holes for a
particular desi~n, these should not limit the scope
of the present invention. It should be understood
that the number of holes, the number of slots, the
sizes o the holes and the sizes of the slots can be
amended by one having ordinary skill in this art
without departing from the scope of the present
invention. By way o example, the following table
shows a listing of hole size, slot size, etc. for a
typical drum. However, it should be understood that
it is within the skill of the art to change these
numbers without departing from the scope of the
present in enti~n.
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21
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u~ ~r ~r ~r ~r ~P ~r ~r ~r ~r ~r ~r
t~ r~ ~ r 1- r~
u~ . . . . . . . . . .
NNNNNNNNNNN
~r r r ~r 'r 'r ~ ~r ~r ~r ~r ~r
~DlD~D~D~D~D~D
~ .
1~ Ll.l (~) . . . . . . . . . . .
~D~D~D~D~D~D~D~D~D~D
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Z~N~,~r ~ ~r ~r ~r ~r ~ ~r
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r~ I` ~` 1` 1` r~ 1`` 1` 1` 1` 1`
NNNNN~NNNNN
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Z, O O O 0, 0 0 0 0 O, O O
: H ~,~
Z ~ W N
: ~ ~ Z
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Pl: U~ N N N N N N N N N N N
Z; Z
N O ~n U'l 1~ N O O ~\
~0 : ~1 ~1 ~I N N N t~
H
U'l O O O O O' O O O Ul U'l
N Lll 111 11~ U') Ul U1 Lf~ 11~ N N
N ~ i ~i ~i ~I N N
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r-l r-l r-l r-l r~l r-l N N
r-l r-l r ~ r~ l rl r~ ~1 ~) ~)
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N O ~ 111 rl r~ l r-lr l r-l rl r-l Ll~ 117
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f~ N
~ 111 ~I r l r~ ~Ir-l r~ l r-l 11~ Ul
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23
Table 1 gives the details for the slots. The table
should be read in conjunction with FIG. 5. The rows
in the -table and figure are numbered 86 through 106.
The columns in the table represent various character-
istics of the slots. Counting from left to right,column 1 gives detail for the width of the slots.
Column 2 represents slot's displacement in the
circumferential (CIR) and longitudinal dimension o~
the drum. The circumferen-tial displacement is
measured in degrees beginning at the scribe line 74.
The longitudinal displacement is measured in other
linear units beginning from scribe line 76. Segment
(SEG) 1 is the first segment next to the scribe line
76. SEG 2 is next to 1 and so on. Column 3 represents
the linear measurement for each segment.
Table 2 gives the details for the communicating
ports. In this table, column 1 gives the diameter - ~ -
for the communicating ports. Total population gives ~.
the total number of communicatiny ports per row.
The other coltlmns give the number of communicating
ports per segment.
Referring now to FIG. 6 is a graph showing the
relationship between the traditional vacuum pump
(used in evacuating vacuum system of the prior art)
and a blower suitable for use in the present invention.
This graph is helpful in understanding the fluctuation
in vacuum experienced on the surface of the rotary
drum. It is also helpful in understandiny the
problem previously described relative to the evacuating
vacuum systems of the prior art. In FIG. 6, vacuum
pressure in pound per square inches (PSI) is plot-ted
along the ordinate of the graph. Similarly, the
flow in cubic foot per minute (CFM) is plotted along
the ~bsciaea of the graph. Curve 120 represents
,
. ~ '
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~ :~ 64900
24
the characteristics operating curve for a 0.9
horsepower (HP) blower. Similarly, curve 122 repre-
sents the operating characteristics curve for a 1.0
horsepower (HP) vacuum pump. As is seen from the
graph, the vacuum pump operating characteristic
curve to a substantial extent, parallels the ordinate
of the graph. Stated another way, the pump has a
relatively low flow with a relatively high vacuum.
The characteris-tic curve of the blower, however, has
a relatively high flow with relatively low vacuum.
Data for the characteristic curves o the blower and
vacuum pump of similar power, are obtained from the
respective manufacturers. Curve 124 represents the
characteristic curve of the drum with no paper
attached. This curve was plotted or a typical drum
having a specific layout of slots and holes. Curve
126 represents the characteristic curve or a drum
having one sized type of paper attached thereto.
The operating point o the system occurs at the
intersection where the vacuum pump characteristics
curve and the blower characteristics curve intersects
the no-load and load drum characteristics curve,
respectively. As can be seen rom the igure, at
point 3 the drum's no-load paper characteristics
curve intersects the blower curve. By running a
horizontal line rom this point to the ordinate of
- the graph, the~effective vacuum which is present in
the drum7s slots is determined. Likewise, point 4
indicates the operating point for the drum with
paper on when a blower is used. Again, a horizontal
line drawn from this point to the ordinate of the
graph shows the effective pressure in the slot of
the drum. As can be seen from the tWo pressures,
the effective pressure between no-load and load
conditions is substantially constant. This shows
that for op=imum ope-ati~n a vacuum system lncluding
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.' ~ .
~ ~ ~490~
a blower having a rela-tively high flow with relatively
low vacuum is very desirable.
Using a simllar analysis, it can be shown that
intersecting point 1 and intersecting point 2 identify
the respective operating point of the drum when a
prior art vacuum pump is used to evacuate the drum.
It is also seen that there is a wide swing between
the vacuum experienced in the drum between no-load
and load condition. This is an undesirable condition
and as such, the traditional vacuum pump is not
suitable for use in the evacuating system of the
paper transport system unless the drum is segmented
and a vacuum relief mechanism is used.
The advantages associated with the document transported
of the present invention, may be summarized as
follows:-
The system is simple and low cost, which provideshlgh reliability and fast response.
,
The system requires no valving or internal segmentation
for controlling the vacuum in the drum. The population
and/or size of the holes control the flow and provide
the source of vacuum to the slots when coverad.
'
Another advantage of the present invention is that
it enables different size sheets of flexible material
to be handlad by a nonsegmented vacuum drum.
'. - : ' ,
While the invention has beèn particularly shown and
described with re~erence to a preerred embodiment
thereof, it will be understood by those skilled in
the art that various changes in form and details may
be made therein without departing from the spirit
and scope of tb~ present in ention.
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