Note: Descriptions are shown in the official language in which they were submitted.
CA 02286952 1999-10-18
Apparatus for Moving Stackable Bag Packs, in
particular Plastic Bags with Bottom Folds
The present invention relates to a device for moving
stackable packs of bags, in particular, plastic bags with bottom
folds, with a pin stack conveyor that incorporates a movable pin-
stack chain with stack pins that moves incrementally and a
removal station that incorporates a robot with a gripper formed
in the manner of pincers.
DE 38 34 115 Cl makes general reference to the use of a
robot in order to automate the removal process in a removal
station. However, this known device proceeds from the idea that
the individual plastic bag are retained in a bag stack by using
wire clips. Details as to how the robot is to be used for the
removal of the plastic bags are not provided in this document;
rather it is stated very generally that the use of a robot has
not as yet been pursued for reasons of complexity and cost.
In the case of stack removal, it is also generally
known that the use of wire clips to keep the individual plastic
bags in the bag stack should be avoided. Rather, the individual
plastic bags are blocked to form a bag stack right in the pin-
stack conveyor, this being done in that the plastic bags are
welded together by pressure and heat, at specific places, for
example in an area that is delimited by a line of perforations.
It is true that in this way it is possible to achieve a
significant simplification during the production of the plastic
bags, since removal of the bags that from the pin stack conveyor
can be managed much better and, in addition, it is much simpler
to pack the plastic bags ire cartons or the like. Even so, the
operator must ensure the quality of the blocked bag pack and
prepare it for packaging, for example in a cartons. This
preparation for packaging in a carton entails particular
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difficulties, especially in the case of plastic bags with bottom
folds. This is so because the plastic bags that lie one on top
of the other in the stack tend to fan out in the folded bottom
area and are thus thicker at that point than in the flat head
area. Depending on the type of and size of the bags involved,
the bottom area will tend to break out if the bag pack is put in
a horizontal or nearly horizontal position. For this reason,
even if a robot-controlled mufti-function hand is used, the
operator will have his hands full ensuring that uniform packs of
bags are formed. Frequently, this can be done only if the
production speed is reduced so that the person responsible for
removing can keep up with the preparation of the packs.
It is the objectives of the present invention to create
an apparatus of the type described in the introduction hereto,
for transporting stackable packs of bags, in particular plastic
bags with bottom folds, with which the removal and transfer of
bag stacks from a pin stack conveyor to a packaging station is
made even simpler and more rapid by appropriate automation.
According to the present invention, this objective has
bean achieved in that in the area of the removal station the pin-
stack conveyor incorporates a pivot plate that moves the bag pack
that is ready for removal from a position in which it is
essentially suspended from the stack pins into an essentially
horizontal position and the gripper hand incorporates two
clamping devices that are positioned so as to be diagonally
opposite each other and grip the bag pack on both sides, as well
as a pressure element that acts essentially on the middle of the
bag pack and which can be adjusted for height. The means
according to the present invention provide a comparatively simple
solution to prevent the undesirable break-out of the bottom fold
area of the plastic bag. In particular, this is achieved in
that the bag pack that is suspended in the pin-stack conveyor is
moved by the pivot plate into an essentially horizontal position,
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from which the bag pack that is being acted upon by the pressure
element or a hold-down element connected thereto can be gripped
by the gripper hand and held on the opposing sides by the
clamping devices, so that movement of the pressure element
relative to the bag pack causes the pack to be bent, thereby
ensuring that the bottom fold area can no longer break out. By
means of a robot that supports the gripper hand and by its
transport movements, once the outer clamping devices have been
released downward movement of the pressure element can deposit
the bag pack in a waiting carton or the like, when the pressure
element forming a V-bend can deposit the bag pack from the
releasing clamping devices on to the bottom of the carton or on
to a pack that is already in place in said carton. The gripper
hand does not simply allow the a pack to drop; rather, the pack
is optimally positioned on the last bag pack to have been
deposited in the carton.
In another development of the present invention, the
pressure element is formed by a bending bar that essentially
extends in the longitudinal direction of the bag pack.
The bending bar or a supporting rail that holds this is
secured to a first carrier plate by an adjusting cylinder that
can be adjusted for height, the first carrier plate being
connected either directly or indirectly to a boom arm of the
robot.
The first supporting plate and a second supporting
plate that is interleaved with this accommodate guide bars for
supporting arms that are supported therein so as to be
adjustable, the holding brackets of the clamping devices being
connected in pairs to the free ends of these that face towards
one side. The holding brackets can be moved by hydraulic
cylinders to the dimensions of the particular bag packs that are
to be transported.
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A preferred embodiment of the present invention will be
described in greater detai-~ below on the basis of the drawings
appended hereto. These drawings show the following:
Figure l: a plan view of a part of a bag-making machine with a
pin-stack conveyor, including a robot with a gripper
hand as well as an associated removal station;
Figure 2: a side view of the pin stack conveyor with a part of
the gripper hand, at enlarged scale;
Figure 3: a partial cross section through the gripper hand in an
open position;
Figure 4: an associated view of the gripper hand;
Figure 5: a diagrammatic side view of the gripper;
Figure 6: a cross section view corresponding to Figure 3,
although in a position gripping a bag pack;
Figure 7: a view corresponding to Figure 6, in a position wherein
the bag pack is released.
Figure 1 is a diagrammatic view of a bag-making machine
1 that is configured and equipped to manufacture plastic bags,
for example plastic bags with a bottom fold. To this end, a
plastic foil web of thermoplastic material is wound off a supply
roll in a winding stand (not shown herein); this web can be
formed as a tubular foil web. Within the bag-making machine 1,
the tubular foil web is guided by means of drive rollers and
tension rollers (not shown herein). Two suspension holes are
made in the plastic foil web by means of devices (not shown
herein) and individual bags can be separated off from the tubular
foil web by means of a transverse-cut welding device (not shown
herein). Finally, these bags are moved to the pin-stack
conveyor 2 by means of a pin-stack chain 3 that moves
incrementally. Once on the pin stack conveyor, plastic bags
that are collected continuously can be formed into bag packs in
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the manner known per se. To this end, the pin-stack conveyor
has stack pins 4 on the pin stack chain 3 that are arranged in
pairs, and as can be seen from Figure 2, the bag pack 5 is hung
on these by way of the suspension openings in the bags, when it
then hangs down essentially freely. The bags collected into
packs are blocked with each other in the pin-stack conveyor in
the manner known per se.
Once a blocked bag stack 5 has been formed on the pin
stack chain 3, the finished bag stack is removed at the end of
the pin-stack conveyor 3 with the help of a robot 6 that is
arranged at the end of the pin-stack conveyor 2, and which has a
gripper hand 8 that is mounted on a boom 7. The function of the
robot or the gripper 8 is described in greater detail below.
A freely moving, rotatable roller 9 is provided at the
removal station of the pin stack conveyor 2 in order to improve
guidance of the bag stack 5; this roller 9 keeps the bag stack 5
a short distance away from a pivot plate 11 that is supported so
as to be rotatable about an essentially horizontal axis 12 at the
upper end of the pin-stack conveyor 2. With the aid of this
pivot plate 11, the bag pack 5 can be moved from the suspended
position indicated in Figure 2 by the broken lines into an
essentially horizontal position that is indicated in Figure 2 by
broken lines. An adjusting cylinder 13 is used to pivot the
pivot plate, and this is articulated so as to be able to pivot on
an arm 14 of the supporting frame 15 at point 16. Figure 2 also
shows a part of the gripper hand in order to indicate the
position from which the gripper hand 8 grasps the bag pack 5 that
is lying essentially horizontally in a manner described in
greater detail below and then guides it to a removal station 18
in the direction indicated by the arrow 17, where there is an
empty carton 19 that can accommodate a plurality of bag packs 5.
As can be seen from Figure 3 and Figure 4, the gripper
hand 8 has carrier plates 20, 21 that are interleaved and which
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can move each other along a longitudinal guide 23; one of these
is secured to the boom 7 of the robot 6. Just below the
underside of the carrier plate 20 there is a pressure element 22
in the form of a bending bar that is supported on a supporting
rail 22'. The level of the bending bar 22 can be adjusted for
height by way of an adjusting cylinder 24 for purposes that will
be described in greater detail below. Guide rails 25, 26 that
are offset relative to each other are arranged on the carrier
plate 20, 21; these are arranged in pairs towards one or the
other side. The guide rails serve to accommodate supporting
arms 27, 28 that are installed in them so as to be movable and on
which diametrically opposed retaining brackets 29, 31 are guided.
A piston-cylinder unit 32, 33 is provided in order to move each
retaining bracket 29, 31 into a position that accommodates the
bag pack 5 and into a release position; one piston-cylinder unit
is secured to supporting plate 22 and the other is secured to the
other supporting plate 21. The retaining brackets 31 have a
lower arm 34, 35 and an upper arm 36, 37. Clamping cylinders 38,
39 are secured to each of the upper arms 36, 37, and the piston
rods 41, 42 of these incorporate clamping pieces 43, 44.
Figure 3 and Figure 4 show the gripper hand 8 with its
clamping devices 30 extended in order to accommodate a bag pack
5, whilst Figure 5 and Figure 6 show it in the release position.
The device according to the present invention operates
as follows:
The gripper hand receiving position is shown in Figure
3, i.e., the retaining brackets 29 and 31 have been moved
outward. The pivot plate 11 of the pin stack conveyor is now
pivoted upward by the adjusting cylinder 13, so that the bag pack
5 moves from the position in which it is hanging essentially
freely downward into the position shown in Figure 2, which is
essentially horizontal; this can also be seen in Figure 3.
Then, each retaining bracket 29, 31 is moved inward by its
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associated cylinder-piston units 32, 33 so that the bag pack is
accommodated by the lower arms 34, 35 of the retaining bracket
29, 31. In the retracted position, in conjunction with the
pressure element 22, it can be ensured that the bottom fold area
cannot break out to the inside. If necessary, the bag pack can
be bent slightly by the bending bar 22 that runs obliquely upward
to the bottom fold area of the bag pack; this is shown in Figure
6. The bags or the bag pack, respectively, are held on both sides
by the clamping cylinders 38, 39 or by way of the clamping pieces
43, 44 that are located on the piston rods 41, 42, so that the
bag pack is centered in its position. The bag pack that is
clamped in this way is brought into a removal position in the
area of the packaging station 18 with the aid of the robot 6;
this is done in such a way that t:he gripper hand is situated
above a carton 19 that is to be filled and, if necessary, it
moves into this. As soon as the correct position has been
reached, the clamping cylinders 38, 39 move upward, the retaining
bracket 29, 31 remaining in the same position, and the pressure
element or the bending bar 22 is so extended that the pack is
bent into a V-shape when it is laid into the carton as is shown
in Figure 7. This ensures that the thicker or fanned-out fold
bottom areas cannot break-out and that, on the other hand, the
bag pack can be laid into a waiting carton 19. In the meantime,
the pivot plate 11 has once again been pivoted back into its
starting position, in which it faces essentially downward.
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