U.S. patent number 3,921,971 [Application Number 05/484,452] was granted by the patent office on 1975-11-25 for suction device for separating and/or transporting sheets in a sheet-handling machine.
This patent grant is currently assigned to VEB Polygraph Leipzig Kombinat fur Polygraphische Maschinen und. Invention is credited to Karl-Hans Vollrath.
United States Patent |
3,921,971 |
Vollrath |
November 25, 1975 |
Suction device for separating and/or transporting sheets in a
sheet-handling machine
Abstract
The suction device includes a pneumatic cylinder and a hollow
piston in the cylinder movable between a retracted and a
non-retracted position and comprised of axially adjacent first and
second portions, at least a part of the circumferential periphery
of each of the two portions being spaced from and out of contact
with the inner periphery of the cylinder to define therewith
respective first and second spaces. The piston unit includes a
sheet-engaging portion having a suction opening which communicates
with the ambient atmosphere and constitutes the end of the hollow
interior of the piston unit, the hollow interior communicating with
the second space via the first space. The cylinder is provided with
a suction port opening into the second space to form a path for the
flow of ambient air into the suction opening and out through the
suction port, the flow cross section of the first space being
smaller than that of the second space so that the first space
constitutes a flow restriction in such path.
Inventors: |
Vollrath; Karl-Hans (Leipzig,
DT) |
Assignee: |
VEB Polygraph Leipzig Kombinat fur
Polygraphische Maschinen und (Leipzig, DL)
|
Family
ID: |
5491843 |
Appl.
No.: |
05/484,452 |
Filed: |
June 28, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Aug 4, 1973 [JA] |
|
|
48-91668 |
|
Current U.S.
Class: |
271/103; 271/108;
294/186 |
Current CPC
Class: |
B65H
3/0883 (20130101) |
Current International
Class: |
B65H
3/08 (20060101); B65H 003/08 () |
Field of
Search: |
;271/90,103,108 |
Foreign Patent Documents
Primary Examiner: Blunk; Evon C.
Assistant Examiner: Saifer; Robert
Attorney, Agent or Firm: Striker; Michael S.
Claims
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims:
1. In a sheet-handling machine, a suction device for engaging and
then holding sheets, comprising, in combination, a pneumatic
cylinder; a hollow piston units in said cylinder movable between a
retracted and a non-retracted position and comprised of axially
adjacent first and second portion, at least a part of the
circumferential periphery of each of said portions being spaced
from and out of contact with the inner periphery of said cylinder
to define therewith respective first and second spaces, said piston
unit including a sheet-engaging portion having a suction opening
which communicates with the ambient atmosphere and constitutes the
end of the hollw interior of said piston unit, said hollow interior
communicating with said second space via said first space, said
cylinder being provided with a suction port opening into said
second space to form a path for the flow of ambient air into said
suction opening and out through said port, the flow cross section
of said first space being smaller than that of said second space so
that said first space constitutes a flow restriction in said path;
and drive means for causing said piston unit to move from retracted
to non-retracted position and then back to retracted position, in
order to cause said sheet-engaging portion to move into engagement
with a sheet located in the path of movement of the latter and then
hold said sheet by suction during the movement of said piston unit
back to said retracted position, said drive means comprising
suction-generating means connected to said port and operative for
establishing subambient pressure in said second space, whereby said
piston moves from said retracted to said non-retracted position
upon the establishment of such subambient pressure as a result of
the initial difference in pressures upstream and downstream of said
first space, and whereby said piston returns to said retracted
position due to the pressure equalization resulting when the sheet
engaged and held by said sheet-engaging portion blocks further
entrance of ambient air into said suction opening of the said
sheet-engaging portion, wherein said first portion of said piston
unit is cylindrical and constitutes a hollow piston portion and
wherein said second portion of said piston unit is cylindrical and
constitutes a hollow piston rod portion, and wherein said hollow
piston portion is spaced from and out of contact with the inner
periphery of said cylinder all around the circumferential periphery
of said hollow piston portion, whereby there is no frictional wear
of the circumferential surface of said piston portion and the
facing inner surface of said cylinder, and wherein said cylinder is
further provided with an axially extending guide portion for
guiding said piston rod portion, said guide portion having an axial
end portion facing said piston portion, and wherein said piston rod
portion is further provided with a recess constituting a suction
release passage having one end opening into the ambient atmosphere
and having another end which terminates just past said axial end
portion of said guide portion when said piston unit is in said
retracted position.
2. In a sheet-handling machine, a suction device for engaging and
then holding sheets, comprising, in combination, a pneumatic
cylinder; a hollow piston unit in said cylinder movable between a
retracted and a non-retracted position and comprised of axially
adjacent first and second portions, at least a part of the
circumferential periphery of each of said portions being spaced
from and out of contact with the inner periphery of said cylinder
to define therewith respective first and second spaces, said piston
unit including a sheet-engaging portion having a suction opening
which communicates with the ambient atmosphere and constitutes the
end of the hollow interior of said piston unit, said hollow
interior communicating with said second space via said first space,
said cylinder being provided with a suction port opening into said
second space to form a path for the flow of ambient air into said
suction opening and out through said port, the flow cross section
of said first space being smaller than that of said second space so
that said first space constitutes a flow restriction in said path;
and drive means for causing said piston unit to move from retracted
to non-retracted position and then back to retracted position, in
order to cause said sheet-engaging portion to move into engagement
with a sheet located in the path of movement of the latter and then
hold said sheet by suction during the movement of said piston unit
back to said retracted position, said drive means comprising
suction-generating means connected to said port and operative when
activated for establishing subambient pressure in said second
space, whereby said piston unit moves from said retracted to said
non-retracted position upon the establishment of such subambient
pressure as a result of the initial difference in pressures
upstream and downstream of said first space, and whereby said
piston unit returns to said retracted position due to the pressure
equalization resulting when the sheet engaged and held by said
sheet-engaging portion blocks further entrance of ambient air into
said suction opening of said sheet-engaging portion, the hollow
interior of said piston unit and the part of the hollow interior of
said cylinder external to said piston unit together forming when
said suction opening is blocked by a sheet and said piston unit is
in the retracted position a closed chamber sealed off from the
ambient atmosphere to such an extent that the subambient pressure
established in such a chamber by said suction-generating means
maintains said piston unit in the retracted position indefinitely
until said suction-generating means is deactivated.
3. In a sheet-handling machine as defined in claim 2, wherein said
first space is annular and wherein said second space is
annular.
4. In a sheet-handling machine as defined in claim 2, wherein said
first and second portions of said piston unit are cylindrical and
coaxial, with the diameter of said first portion being larger than
the diameter of said second portion, and wherein said first and
second spaces are both annular.
5. In a sheet-handling machine as defined in claim 2, wherein at
least one of said first and second portions of said piston unit is
spaced from and out of contact with the inner periphery of said
cylinder all around the circumferential periphery of said at least
one of said portions.
6. In a sheet-handling machine as defined in claim 2, wherein at
least said first portion of said piston unit is spaced from and out
of contact with the inner periphery of said cylinder all around the
circumferential periphery of said first portion.
7. In a sheet-handling machine as defined in claim 2, wherein at
least said second portion of said piston unit is spaced from and
out of contact with the inner periphery of said cylinder all around
the circumferential periphery of said second portion.
8. In a sheet-handling machine as defined in claim 2, wherein said
first space constitutes the only flow restriction in said path.
9. In a sheet-handling machine as defined in claim 2, wherein said
cylinder is further provided with a suction release opening having
a flow cross-sectional area so related to that of said second space
and to the magnitude of said subambient pressure in said chamber
that when a sheet engaged and held by said sheet-engaging portion
blocks off said suction opening the loss of suction inside said
hollow piston unit is insufficient to result in termination of the
holding action, but so related to the volume of said second space
that upon deactivation of said suction-generating means ambient air
entering said suction release passage can quickly destroy the
subambient pressure in said second space.
10. In a sheet-handling machine as defined in claim 2, wherein said
first portion of said piston unit is cylindrical and constitutes a
hollow piston portion and wherein said second portion of said
piston unit is cylindrical and constitutes a hollow piston rod
portion, and wherein said hollow piston portion is spaced from said
out of contact with the inner periphery of said cylinder all around
the circumferential periphery of said hollow piston portion,
whereby there is no frictional wear of the circumferential surface
of said piston portion and the facing inner surface of said
cylinder, and wherein said cylinder is further provided with an
axially extending guide portion for guiding said piston rod
portion, said guide portion having an axial end portion facing said
piston portion, and wherein said piston rod portion is further
provided with a recess constituting a suction release passage
having one end opening into the ambient atmosphere and having
another end which terminates just past said axial end portions of
said guide portion when said piston unit is in said retracted
position.
Description
BACKGROUND OF THE INVENTION
The invention relates to a sheet-separating and/or
sheet-transporting suction device of the type conventionally used
in sheet-handling machinery, such as in printing machines, copying
machines, and the like.
A variety of such sheet-separating and/or sheet-transporting
suction devices of this type is already known, especially for
removing sheets from a stack of sheets, and for then feeding the
successively removed sheets onto a conveyor which transports the
sheets into a printing machine, or the like. These sheet-separating
and/or sheet-transporting suction devices are synchronized with the
operations of the associated sheet-handling machine and are
pneumatically controlled by the synchronized application and
removal of operating suction. This timed application and removal of
operating suction is for example customarily synchronized with the
movement of a holding arrangement on which one or more of such
suction devices are mounted; for example, the suction devices
engage the top sheet of a stack and the holding arrangement moves
along a predetermined path to a location above a conveyor belt,
whereupon the operating suction is removed and the sheet falls onto
the conveyor belt, the holding arrangement then performing a return
movement back to the stack for the engagement of the next
sheet.
It is disclosed in a variety of publications (among them West
German published Pat. application 2,132,434) to provide the suction
devices in a fixed housing, and in particular in such a manner that
the suction devices are mounted on pistons which can be raised and
lowered, the pistons being returned to their upper starting
positions by biasing springs when the operating suction is
removed.
Another such sheet-separating and -feeding suction device for
pneumatic sheet-handling machinery is also disclosed in West German
petty Pat. 7,022,786. In this construction, likewise, a compression
spring holds a piston in the upper position thereof, the piston
carrying the sheet-engaging suction nozzle; between the suction
chamber for the movement of the piston into the operating position,
i.e., for the downward movement of the piston into contact with the
stack of sheets, and the suction chamber for the upwards movement
of the piston upon closing off of the suction nozzle of the suction
device by the actual sheet which is to be removed from the stack
and/or transported or fed, there is formed a flow restriction
passage so configurated that in the vicinity of the piston a bore
is arranged in the piston rod. In order to avoid a jamming of the
piston with this latter construction, as well as with all the known
constructions, the surface portions of the piston and those of the
inner wall of the cylinder which contact each other during relative
sliding movement therebetween must be of high quality material and
manufactured in a very precise manner, with narrow tolerances. Each
of the known designs includes at least two working or
sliding-contact surfaces, placing high demands upon the precision
of the shape and mounting of the relatively movable parts; the
necessarily narrow tolerances require a relatively complicated
method of construction which is not advantageous from the
manufacturer's point of view.
SUMMARY OF THE INVENTION
One object of the invention is to provide a sheet-separating and/or
sheet-feeding or -transporting suction device which avoids the
disadvantages of the prior-art devices.
Another object of the invention is to provide such a suction device
which does not depart altogether from the basic structure of the
prior-art devices, but which is different in respects which permit
the manufacture of the suction device in an uncomplicated manner,
in which relatively large tolerances are permissible, and which
lends itself readily to the formation of the suction device from
plastic. In particular, it is considered very important to be able
to design a suction device of the type in question which operates
on the pressure-difference principle of the prior-art devices, but
which can be made of plastic material in a simple manufacturing
process, and which after being manufactured and installed requires
virtually no maintenance.
These objects, and others which will become more understandable
from the following description of a preferred embodiment of the
invention, can be set, according to one advantageous concept of the
invention, by providing a sheet-separating and/or
sheet-transporting or feeding suction device in which the
flow-restricting passage hitherto provided in the form of a bore in
the piston rod is replaced by a flow-restricting passage in the
form of an annular clearance between the piston and the surrounding
cylinder, with the piston rod of the piston being guided for
sliding movement in a simple elongated piston rod guide member. It
is advantageous to furthermore provide adjacent to the piston rod,
in the region of the suction inlet of the suction device, and in
particular in the region of the elongated piston rod guide member,
at least one suction-release passage extending in direction
parallel to the elongated piston rod, the suction release passage
terminating just above the upper edge of the piston rod guide
member, when the piston is in the upper (retracted) position
thereof.
One advantage of this new construction is that the sheet-separating
and/or -transporting and/or -feeding suction device is inherently
of low mass and suitable for manufacture from plastic. In addition,
compared to known suction devices of this general type, the
arrangement of the suction release passage mentioned above has the
advantage that when the suction-generating device is turned off,
the suction within the suction device almost immediately
terminates, so that the sheet being held by such suction force
almost immediately drops; on the other hand, when the
suction-generating device is on, the existence of the suction
release passage does not detract from the reliability with which
the sheet is held by the suction nozzle of the device. As a result,
the operating cycle of the sheet-separating and/or
sheet-transporting or feeding device can be gone through repeatedly
with the very high precision and at very high speed.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself, however, both as to its construction and its
method of operation, together with additional object and advantages
thereof, will be best understood from the following description of
specific embodiments when read in connection with the accompanying
drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a cross-sectional view through a preferred embodiment of
the invention;
FIG. 2 is a view of a portion of the structure shown in FIG. 1,
viewed as indicated by the arrow line II-II of FIG. 1; and
FIG. 3 is a section taken on line III-III of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference numeral 1 designates the cylinder of the
sheet-transporting and/or -separating device. Arranged inside the
cylinder 1 is a piston 2 integral with a piston rod 3. The piston
rod 3 and the piston 2 are provided with an internal suction
conduit 3a. The piston rod 3 is slidable in a relatively long
piston rod guide member 4. Arranged intermediate the piston 2 and
the piston rod guide member 4 is a compression spring 5 which
exerts upon the piston 2 a force tending to urge the latter to the
uppermost, retracted position, shown in FIG. 1. The piston rod 3 is
provided with a longitudinally extending recess 6 which together
with the adjoining surface portions of the piston rod guide member
4 forms a suction release passage. This suction release passage 6
extends from the sheet-engaging suction nozzle 8 up into the
cylinder 1 and terminates shortly past the upper edge 7 of the
piston rod guide member 4. Instead of employing a single such
suction release passage 6, it would also be possible to provide a
plurality of such suction release passages, but with the combined
flow cross-sections of all of the passages equalling the flow
cross-section of the suction release passage used when only a
single such passage is employed. The sheet-engaging suction nozzle
8 is arranged at the lower end of the piston rod 3 and is held in
place by the radially compressive force of the surrounding elastic
members, which for example are made of elastically resilient
plastic; this manner of assembly makes for easy removal of the
suction nozzle 8 and replacement by another such nozzle, when this
is necessary.
The piston rod guide member 4 is secured to the cylinder 1 by means
of one or more mounting screws 9, for which purpose the cylinder 1
is provided with one or more mounting collars 10. One such collar
10 (such as the one depicted in FIG. 1) can be made considerably
longer than otherwise necessary, so as to form a mounting sleeve,
and serve for the securing of the entire suction device to a
(non-illustrated) supporting framework of a sheet transporting
arrangement, or the like. For the sake of fast and reliable
assembly of the piston rod guide member 4 with the other parts of
the structure, the member 4 has embedded therein one or more
radially outwardly projecting pins 11. As shown particularly
clearly in FIG. 2, the radially outwardly projecting pins 11 can be
introduced into L-shaped slots 12 in the lower portion of the
peripheral wall of the cylinder 1 to form with such L-shaped slots
12 bayonet-type connections.
The upper end of the cylinder 1 is provided on its inner surface
with a plurality of abutment members 13 which serve to establish an
upper end position for the piston 2 against the upwards pushing
force of the compression spring 5.
The operating suction connector port 14 is so arranged on the lower
part of the cylinder 1 that the piston 2 can be drawn by the force
of suction down to the level of the upper edge 7 of the piston rod
guide member 4.
Between the outer periphery of the piston 2 and the inner periphery
of the cylinder 1 there is defined an annular clearance 15 the flow
cross-sectional area of which is substantially smaller than the
flow cross-sectional area of the space surrounding the piston rod
3a.
In the event that use is to be made of a suction nozzle 8 having a
geometrical form requiring a definite radial guidance (of the
piston 2 and accordingly of the suction nozzle 8), then one can
provide on the inner wall of the cylinder 1 a radially inwardly
recessed depression 17 likewise extending in direction parallel to
the elongation of the cylinder 1; such an arrangement prevents the
piston 2 from turning when performing its strokes.
The structure depicted in FIGS. 1-3 operates as follows:
A suction-generating device connected to the operating suction
connector port 14 is turned on, thereby establishing suction inside
the cylinder 1. Air accordingly flows into the suction nozzle 8
through the suction passage 3a, radially outwards over the upper
rim of piston 2, axially downwards through the annular clearance
15, axially downwards through the annular space surrounding the
piston rod 3, and out through the operating suction connector port
14. Also, air is initially drawn in through the suction release
passage 6 and flows out through the suction connector port 14.
Because the flow cross-sectional area of the annular clearance 15
is much smaller than that of the annular space surrounding the
piston rod 3, and much smaller than that of the operating suction
connector port 14, a greater volume of air flows out through
operating suction connector port 14 than can flow axially downwards
through the small annular clearance 15. Accordingly, the pressure
below the piston rod 2 is markedly lower than the pressure above
the piston rod 2, and the piston rod 2 is therefore drawn
downwards. When the sheet-engaging surface portion of the suction
nozzle 8 contacts the uppermost sheet on the stack 18, the flow of
ambient air into the suction nozzle 8 evidently terminates. As a
result, the difference between the pressures above and below the
piston 2 decreases towards zero. As a result there is no longer a
net suction force difference greater than the biasing force of
compression spring 5, and therefore the piston 2 is pushed upwards
by the spring 5 towards the fully retracted position of FIG. 1.
Meanwhile, the sheet engaged by the suction nozzle 8 is still
firmly held by the suction nozzle, and accordingly is lifted as the
piston 2 moves upwards to its retracted position. When the piston 2
reaches the uppermost position thereof, shown in FIG. 1, the
suction release passage 6 becomes unblocked, and ambient air begins
to flow through passage 6 into the interior of cylinder 1 and out
through port 14; this flow of air, however, is relatively small.
When it is desired that the sheet held by suction nozzle 8 be
dropped, the suction-generating device connected to port 14 is
turned off. Ambient air enters into the cylinder 1 through the
suction release passage 6. The subambient pressure inside cylinder
1 very quickly rises to ambient pressure, and the sheet drops down
from suction nozzle 8. It will be understood that meanwhile, the
entire suction device shown in FIG. 1 has, for example, been
translated rightwards, to a position directly above the illustrated
conveyor belt, so that when the sheet thusly drops it will drop
onto the conveyor belt and, for example, be fed into a copying
machine, or the like. The means for holding and moving the
illustrated suction device are per se conventional; for example,
the suction device could conceivably be mounted as shown in the
drawing on a guide track and driven by a (non-illustrated) drive
chain back and forth between the stack and the conveyor belt. The
flow cross-sectional area of the suction release passage 6 is so
small, compared to that of port 14, that, even when passage 6 is
fully unblocked, the sheet held by nozzle 8 will not be released
until the operating suction applied to port 14 is removed. On the
other hand, the flow cross-sectional area of the passage 6 is
sufficiently great, compared to the volume of cylinder 1 and taking
into account the maximum suction developed, that when the suction
applied to port 14 is removed the sheet held by nozzle 8 drops
virtually immediately. When no suction is applied to the port 14,
the compression spring 5 of course maintains the piston 2 in the
uppermost, fully retracted position thereof.
It will be understood that each of the elements described above, or
two or more together, may also find a useful application in other
types of constructions differing from the types described
above.
While the invention has been illustrated and described as embodied
in a suction device for the separating and/or transporting and/or
feeding of sheets, it is not intended to be limited to the details
shown, since various modifications and structural changes may be
made without departing in any way from the spirit of the present
invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can by applying current
knowledge readily adapt it for various applications without
omitting features that, from the standpoint of the prior art,
fairly constitute essential characteristics of the generic or
specific aspects of this invention and, therefore, such adaptations
should and are intended to be comprehended within the meaning and
range of equivalence of the following claims.
* * * * *