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Description  |
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FIELD OF THE INVENTION
The present invention is directed generally to a controllable gripper
assembly. More particularly, the present invention is directed to a
controllable gripper assembly for a sheet gripper. Most specifically, the
present invention is directed to a controllable gripper assembly for a
sheet gripper for the delivery of sheets in a printing press. The
controllable gripper assembly allows the sheet gripper to be slowed below
the speed of travel of the transport chains to which the sheet gripper
units are attached. As the individual gripper units are slowed down, the
sheet which each gripper unit is transporting is released and can be
deposited on a sheet stack against sheet stops without damage being done
to the sheets. The gripper units utilize gripper carriages which are
slidably carried by gripper plates. The gripper carriages move with
respect to the transport claims to effect a slowing of the speed of sheet
travel.
DESCRIPTION OF THE PRIOR ART
Sheet delivery devices are generally known in the art and are utilized to
transport sheets from a printing press to a sheet stacking assembly or
sheet delivery pile. In such sheet delivery devices where the sheets are
conducted by transport chains to the delivery pile by means of chains
moving at a constant speed, it is necessary to reduce the forward feed
speed of the transported sheets to be delivered. The transport speed of
the sheets has to be slowed to a speed approaching zero forward movement
at the moment the sheet is deposited on the sheet pile. If the speed of
the sheet is not reduced, the sheets are apt to be damaged and the sheet
stack may not be a well-stacked pile.
One prior art sheet delivery system is shown in East German Patent DD-WP 87
048. In this device, a sheet gripper carriage is fastened on revolving
transport chains by means of connectors. The speed reduction of the
gripper carriage is accomplished by means of the separation of the track
of the gripper carriages from the chain track. A reversing wheel, which is
disposed eccentrically in relation to the gripper carriage reversing path
and has the shape of an arc of a circle, is provided for disconnecting the
transport chain. The shaft of the reversing wheel is disposed below the
center of the gripper carriage reversing path. In this way the transport
chain with the hinge point of the connector of the gripper carriage is
separated by means of the reversing wheel which is disposed eccentrically
in relation to the gripper carriage path. In the course of this, the
transport chain travels a longer distance than the gripper carriage. This
longer distance of travel of the transport chain causes the speed of the
gripper carriage and thus the speed of the sheet being transported to be
reduced.
One limitation of the sheet delivery assembly shown in this prior art
device is that it is necessary to provide two guide paths, one for the
transport chain and the other for the gripper carriage. The slowing of the
grippers in the delivery area provided in this device is approximately 20
to 30 percent of the running speed of the machine and remains constant,
since in the reversing area the chain has only a limited opportunity to be
separated in relation to the gripper carriage, which results in the
limited difference in speed between the gripper carriage and the chain.
Since this prior art sheet delivery assembly is capable of effecting only a
limited reduction in the speed of the gripper carriages with respect to
the transport chain in the area of the sheet stack area, it is necessary
to employ additional devices to slow the speed of sheet travel. Typically,
a suction roller, or similar suction elements are employed for slowing
down the sheets of printed material. This is apt to be quite
disadvantageous in the case of the use of the sheet work method since the
printed reverse side of the sheet is apt to be damaged. Also, when the
sheet transport assembly is being used to transport printed cardboard
sheets, the high kinetic energy of the sheets may be such that the high
suction source which would be necessary to slow and stop the sheets is not
available. If the sheets cannot be adequately slowed or stopped, they will
be deposited with a high residual speed at the sheet stops. This contact
between the moving sheets and the sheet stops leads to damage of the front
edges of the sheets.
If the transported sheets are not slowed down before being released from
the sheet grippers, they may well overshoot the sheet stops. The tendency
of the sheet to overshoot the sheet stops increases with increasing
machine speed. This tendency of the sheets to overshoot the sheet stack is
attempted to be counteracted by using large amounts of blowing air to
limit sheet overshooting. A significant limitation on the use of air under
pressure is that it tends to form air pockets between the individual
sheets in the stack of sheets. This leads to a reduction in quality of the
stack formation.
A further limitation of the sheet delivery device shown in the prior art
East German Patent DD-WD-87048 is that the totality of the mass inertia
forces created because of the slowing of the gripper carriages acts on the
pulling forces on the chains. This is apt to cause wear on the chain and
the gripper carriages.
It will be apparent that a need exists for a controllable gripper assembly
which will slow the delivery of sheets in a manner which overcomes the
limitations of the prior art devices. The controllable gripper assembly of
the present invention provides such a device and is a significant advance
in the art.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a controllable gripper
assembly.
Another object of the present invention is to provide a controllable
gripper assembly for a sheet gripper.
A further object of the present invention is to provide a controllable
gripper assembly for a sheet gripper for the delivery of sheets in a
printing press.
Yet another object of the present invention is to provide a controllable
gripper assembly for the slowed delivery of printed sheets to a sheet
stack.
Still a further object of the present invention is to provide a
controllable gripper assembly in which the speed of the grippers can be
varied over a wide range of speeds.
Even yet another object of the present invention is to provide a
controllable gripper assembly in which the effect of the mass inertia
forces on the transport chains is reduced.
As will be discussed in greater detail in the description of the preferred
embodiments which are set forth subsequently, the controllable gripper
assembly in accordance with the present invention utilizes a plurality of
sheet grippers which are arranged on a gripper carriage. The gripper
carriage is, in turn, slidably supported in guides that are carried by
plates which are attached to the spaced transport chains. A spring is used
to bias the carriage and to allow it to be slid in the direction opposite
to that of the direction of travel of the transport chains to thus slow
down the transport speed of the sheet held by the grippers on the
carriage. A pair of connector arms are attached to the carriage and to the
plates. These connectors are joined by a toggle joint that is caused to
move to slide the carriage in the side plates. The toggle joint is caused
to move by engagement with a curved cam track.
The controllable gripper assembly of the present invention makes it
possible to deposit sheets in a sheet stack at any speed. Further, by
varying the profile of the curved cam track, the speed of sheet deposit in
the sheet stack can be held constant over a range of machine speeds and
hence transport chain speeds.
Since the controllable gripper assembly allows the sheets to be slowed down
to nearly no forward speed, it is possible to operate the suction roller
or other similar suction source that is also used to decelerate the sheets
with very little suction force. This use of little suction force is a
particular benefit for sheet work. In addition, much less air is blown
onto the sheet stack so that the quality of the stack is improved as there
are less apt to be air pockets in the sheet stack. The use of less air
also helps eliminate the appearance of ink smears when the sheets are
deposited on the sheet stack.
The controllable gripper assembly of the present invention also eliminates
the overshooting of the sheets beyond the bottom sheet stops and their
associated shaft. In addition, the leading edges of the sheets are not
deformed when they contact the sheet stops due to the low forward speed of
the printed materials. A further benefit of the assembly is that the
effect of the mass inertia forces on the gripper carriages in the course
of their slow-down is reduced because the greater part of these forces is
equalized within the gripper units. The balance of these forces can be
compensated for by providing an equal and opposite force through the
proper structuring of the lead in and lead out portions of the curved cam
tracks. This allows the gripper carriages of two spaced gripper assemblies
to move in opposing directions at the same time.
It will thus be seen that the controllable gripper assembly of the present
invention overcomes the limitations of the prior art devices. It provides
a device which is a substantial advance in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
While the novel features of the controllable gripper assembly in accordance
with the present invention are set forth with particularity in the
appended claims, a full and complete understanding of the invention may be
had by referring to the description of the preferred embodiments, which
are presented subsequently, and as illustrated in the accompanying
drawings, in which:
FIG. 1 is a schematic view of a transport chain and guides with a
controllable gripper assembly for a sheet-fed rotary printing press in
accordance with the present invention;
FIG. 2 is a perspective view of a controllable gripper unit taken in the
encircled portion of FIG. 1;
FIG. 3 is a schematic view of a first preferred embodiment of a
controllable gripper unit in its sheet transport position;
FIG. 4 is a view similar to FIG. 3 and showing the controllable gripper
unit in its sheet slow down position;
FIG. 5 is a schematic view of a second preferred embodiment of a
controllable gripper unit of the present invention and showing the
transport chain being reversed at the sheet deposit position;
FIG. 6 is a schematic view generally similar to FIG. 5 and showing opposing
controllable gripper units; and
FIG. 7 is a schematic view of the controllable gripper assembly of the
present invention and showing an adjustable control cam curve section.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring initially to FIG. 1, there may be seen a preferred embodiment of
a controllable gripper assembly in accordance with the present invention.
A transport chain, generally at 1, travels about a path and transfers
printed sheets from a suitable printing unit (not shown) to a sheet stack,
generally at 13. It will be understood that the transport chain 1 shown in
FIG. 1 is typically one of a pair of similar spaced transport chains 1, as
seen in FIG. 2.
The transport chain 1 is conducted over a suitable chain wheel 2 and a
chain reversing wheel 3. A plurality of chain guides, which are not
specifically shown, are placed along the paths of chain travel. A
plurality of controllable gripper units 4 are secured to the transport
chain 1 at selected distances. It will be understood that each gripper
unit 4 extends between the two spaced transport chains 1, as may be seen
generally in FIG. 2 and further that the chain wheels 2 and the chain
reversing wheels 3 for the two transport chains operate in p irs and are
connected by suitable shafts which are not specifically shown.
Again referring to FIG. 1, each controllable gripper unit 4 has a plurality
of generally conventional sheet grippers 7. In the gripper unit shown in
FIG. 1, the unit is about to engage the chain reversing wheel 3 and the
transport chain 2 is moving in the direction indicated by arrow A. The
gripper unit 4 moves into engagement with a curved control cam 9 that is
engaged by a roller lever 8 which releases the gripper 7 so that a sheet
11 will be released and will be deposited against the sheet stops 1 on the
sheet stack 13.
Referring now primarily to FIGS. 2 and 3 there may be seen a first
preferred embodiment of a controllable gripper unit, generally at 4, in
accordance with the present invention. FIG. 2 is a perspective view and
shows the gripper unit 4 extending between the two spaced elongated
transport chains 1. Each gripper unit 4 utilizes a pair of spaced gripper
plates 14 with one such plate being secured to each of the transport
chains 1 by spaced bearing bolts 16. Each plate 14 has a pair of guides 17
which are disposed longitudinally on the inner surface of the plate and
extend generally parallel to the transport chains 1. The plates 14 are
hingedly connected to the chains 17 so that they can move as the chains 1
go around the chain wheel 2 and the chain reversing wheel 3.
A gripper carriage 18 is slidably carried between the two spaced plates 14
and slides in the guides 17. The gripper carriage 18 carries a plurality
of sheet grippers which are all identified by reference numeral 7. These
grippers include gripper striking faces 19, gripper levers 21, a roller
lever 8 and the gripper shaft 22. It will be understood that the gripper
roller lever 8 is usable to open and close the grippers in a generally
known manner by engagement with a suitable cam plate or the like. A
tension spring 25 is disposed between a hinge pin 23 on the plate 14 and a
hinge pin 24 on the slidable carriage 18. A first free arm end of a toggle
lever 26 is connected to the hinge 23 while a second free arm end of the
toggle lever 26 is secured to the slidable carriage 8. The two arms of the
toggle lever 26 join at a hinge joint where they are connected to a curve
roller 27.
As may be seen by comparing FIGS. 3 and 4, in which FIG. 3 shows the
gripper unit 4 in a sheet transport position and FIG. 4 shows the gripper
unit 4 in a sheet release position, the toggle lever 26 is operable by
engagement of the curve roller 27 with a contoured gripper opening curve
cam 28, as may be seen in FIG. 5, and the gripper carriage 18 is slid in
the guides 17 in the direction indicated by arrow B against the force of
the tension spring 25 and opposite to the direction of movement of the
transport chains 1. The angle of the toggle lever 26 has increased form a
value of x seen in FIG. 3 to a larger value y, as seen in FIG. 4. This
movement of the gripper carriage 18 in a direction opposite to the
direction of movement of the transport chains 1 has the effect of stopping
the forward speed of the sheet 11 so that when it is released by movement
of the roller lever 8, it will fall onto the sheet stack 13 and will abut
the sheet stops 12 with a minimal forward speed.
In the first preferred embodiment of the controllable gripper unit 4 shown
in FIGS. 2 and 3, the carriage 18 slides in the direction B against the
force of the tension spring 25. In the second preferred embodiment shown
in FIG. 5, the gripper carriage 18, as it moves in the direction B is
opposed by a compression spring 32. In this situation the compression
spring 32 is fastened to the gripper carriage 18 at hinge point 24 and to
the plate 14 at an attachment point 33. It would be possible in both of
the first and second preferred embodiments to substitute other devices for
the tension spring 25 or the compression spring 32. For example, gas
springs or a leg spring could be used. If a leg spring were utilized, it
would be positioned at the joint of the toggle lever 26 opposite the curve
roller 27 and would engage the two arms of the toggle lever 26. It would
also be possible to use a torsion bar which would be positioned in hollow
transverse tie bars between the plates 14.
As the controllable gripper unit depicted in FIG. 5 passes around the
transport chain reversing wheel and its curve roller 27 engages the
control curve cam 28, the gripper carriage 18 first slides in the
direction indicated by arrow B, and after the gripper unit has moved
around the control curve cam 28, the carriage 18 again moves in the
direction A. Only a small portion of the mass inertia forces arising
during the shifting of the carriage 18 and its subsequent acceleration
acts on the tensile load in the transport chains 1 and thus induces a
torque load on the machine. The major part of these forces is equalized
inside the gripper unit 4.
These mass inertia forces may be reduced even further by utilizing an
arrangement of gripper units 4 and a control curve cam 29, as shown in
FIG. 6. The curve control cam 29 is shaped in such a way that at the time
the lower gripper unit 4 enters the curve and places the curve roller 27
in the curve lead-in 31, the gripper unit 4' which, looking in the
transport direction A, has preceded it, engages the curve lead-out 31'
with its curve roller 27' at the same time. The shapes of the curve
lead-in 31 and lead-out 31' for the gripper units 4, 4' assure that the
still remaining portion of the mass inertia forces acting on the transport
chains I are equalized by the oppositely acting mass inertia forces of the
gripper units 4, 4' in that the carriage 18' of the gripper unit 4'
experiences acceleration at the start of its movement through the curve 29
in the curve lead-out 31', while the carriage 18 of the gripper unit 4
experiences deceleration at the start of its movement through the curve 29
in the curve lead-in 31. In this case the curve 29 with the curve lead-in
31 and lead-out 31' is embodied in such a way that the curve rollers 27,
27' of the gripper units 4, 4' pass the respective curve lead-in 31 and
lead-out 31' at the same time.
In the embodiment of the controllable gripper assembly depicted in FIG. 7,
there is shown an adjustable control curve cam 28 for use with the chain
reversing wheel 3 end of the assembly. In this depiction, the details of
the controllable gripper unit 4 have been left out for the sake of
simplicity. The control curve cam 28 is connected by a hinge joint to an
adjustable cam element 34. This cam element 34 is adjustable by a control
element 35 which may be a servo motor or other device that can be operated
mechanically, pneumatically, hydraulically, or in a similar manner. An
adjusting spindle could be provided as the control element 35 so that it
could be adjusted manually. It is possible to operate the control element
35 independently of the machine speed via the machine control.
In the embodiment depicted in FIG. 7, the transport chains 1 move in the
direction depicted by the arrow A. The controllable gripper unit 4 moves
into the area of the adjustable curve element 34 and the curve roller 27
is actuated in the toggle joint 26 in such a way that the angle between
the connectors of the toggle lever 26 changes from a value x to a value y,
as shown in FIGS. 3 and 4. The gripper carriage 19 moves in the guides 17
in the direction of the arrow B; i.e. opposite to the transport direction
A. By means of this relative movement, the carriage 18 is slowed down in
relation to the chain revolution speed. The grippers 7 then open and the
sheet 11 is placed on the sheet stack 13. By changing the position of the
curve element 34, a depositing speed of almost zero in relation to the
chain revolution speed is possible. Displacing the curve element 34 in the
direction of the arrow C in FIG. 7 increases the retardation of the
carriage 18, In this way, the slow-down of the carriage 18 can be adjusted
as a function of the machine speed. Thus the same sheet deposit speeds can
be achieved for different machine speeds.
While preferred embodiments of a controllable gripper assembly in
accordance with the present invention is set forth fully and completely
hereinabove, it will be apparent to one of skill in the art that a number
of changes in, for example the type of transport chains used, the type of
chain wheel and chain reversing wheel, the number of gripper units and the
like may be made without departing from the true spirit and scope of the
present invention which is accordingly to be limited only by the following
claims.
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