EP0111739B1 - Method and apparatus for repeatedly removing and turning the top layer of a stack of rectangular plastic foil pieces - Google Patents

Description

The invention relates to a method for removing and turning the topmost layer of a stack of rectangular plastic film pieces, in which the topmost layer is raised in the area of one longitudinal edge by suction and pivoted by an angular range, and in which the pivoted longitudinal edge portion is gripped by a gripper device, in parallel subtracted to the stacking level in the direction of the opposite longitudinal edge and beyond and placed next to the stack with its top side down, the vertical distance between the gripper device and the stack being less than the width of the plastic film piece.

In a known method of the aforementioned type (DE-AS 23 28 007) the uppermost piece of film of a stack is grasped in the region of a longitudinal edge by a suction gripper, raised and pulled off in the direction transverse to the detected longitudinal edge of the stack until it is with its The edge area comes to rest on a gripper designed as a suction element, which pivots the sheet with the detected edge by approximately 180 ° and thereby places it around a support body provided approximately centrally above the stack. The gripper places the gripped edge area of the sheet on the opposite longitudinal edge of the stack, from where the sheet is gripped by means of a further suction pad and completely pulled off the stack in the now turned position and placed next to the stack.

In this known method, it is inevitable that the pieces of film located on the stack and also the piece of film removed in each case are charged electrostatically. The separation of the top piece of film and its removal from the stack is extremely difficult. When placing the electrostatically charged pieces of film there are further difficulties because the electrostatic charge creates adhesive forces which firmly press the sheet to be placed onto the respective base.

In another known method (DE-AS 24 52 049), the uppermost sack of a stack is detected by a lifting and lowering suction device on one longitudinal edge and raised in the direction perpendicular to the stack, the part of the sack remaining on the stack being considerably more Frictional effect is shifted on the stack. Rotating roller conveyors reach under the raised end of the sack and convey the sack that has been removed to a further conveyor.

Even with this separation of the sacks, the above-mentioned electrostatic charges result from the friction of the uppermost sack on the sack of the stack below, with the disadvantages caused thereby. It is therefore often the case that not only a single sack but also several sacks are detected during removal, which lead to a hindrance or necessary interruption of the subsequent work process.

It has also become known (DE-AS 26 31 599) to separate stacked hose pieces located in a magazine for sack or bag production, however, in deviation from the present invention, the bottom hose piece in the stack is detected and fed to a further conveyor. Drums which are moved about their longitudinal axis and with their longitudinal axes along a circular path are used to remove the lowest tube piece in the stack. These have suction cups arranged in a row in a recess of the circumferential surfaces, which grip the bottom hose section along a longitudinal edge and hold it in place during the further movement of the drums, so that the detected hose section is wound onto the circumference of the respective drum and transferred to a further conveyor. When the hose sections are removed, there is no lateral pulling off of the hose section to be removed, so that electrostatic charges are largely avoided, but this removal process requires a very complex device and requires extraordinarily high suction forces. The bottom hose section of the stack is namely pressed firmly by the stack above it against the necessary support surfaces for the edges of the stack formed by the stack shaft, so that corresponding suction forces must be exerted on the edge region in order for the hose section to be detected with its edge region lying on top of it To be able to pull off the stack.

For feeding sheets on a stack to a deposit table (DE-PS 251 342), a solution is provided in which a suction tube is swingingly held on a crank arm and in its lowest position detects the top sheet of the stack on one of its longitudinal edges and in In the course of a pivoting movement directed upwards on a circular arc, the detected longitudinal edge lifts and first moves in the direction of the opposite longitudinal edge, so that the detected arc is removed from the stack in the manner of a peeling movement at least over a considerable part of its length. The gripper passes the sheet in its uppermost position to cooperating feed rollers which convey the sheet on to the depositing table. In this known embodiment, however, the sheet is not turned over, but is transferred to the lay-up table in such a way that its top, which is on the stack, also goes up on the lay-up table points. To the extent that in this known solution the top sheet of a stack is removed from the stack by a kind of peeling movement, electrostatic charging can be avoided, but even with this known solution there is a risk that at least towards the end of the top sheet removal on the Stack slides along and causes electrostatic charges.

The invention has for its object to provide a method of the type described in such a way that not only an electrostatic charging of the plastic film pieces is avoided by their removal, but also a safe separation of the edges of the superimposed film pieces is achieved when the edges of the film pieces adhesive forces caused by mechanical connections or by sticking to one another or by the previous welding or cutting process are connected to one another. To solve the above problem, the method mentioned in the introduction is characterized according to the invention in that the longitudinal edge of the plastic film pieces designed as sacks or tube sections is raised by suction only in one corner region and pivoted by an angular range of approximately 90 ° and the subsequent removal of the top layer parallel to the stacking plane is carried out in such a way that a horizontal displacement of the portion of the gripped sack or tube portion remaining on the stack is avoided.

Raising the uppermost sack or hose section in the corner region of the stack is advantageous because the adhesive forces between the sacks or hose sections lying on top of each other are lowest here. The respective corner section can be gripped by about 90 ° and moved parallel to the stack surface, so that a peeling movement takes place along parallel lines parallel to the diagonal of the sack or piece of film and thereby a safe separation of the edge areas of the raised corner adjoining singular sack or hose section is favored. If necessary. Existing edge connections between the uppermost and the underlying sack or hose section are separated with this type of pulling off and thus a reliable separation of the sacks or hose sections is achieved.

When removing and turning a sack that is open on one side, it is advantageous if it is raised and pivoted in the bottom region of the longitudinal edge. As a result of the bottom seam, the stacked sacks are at a greater distance from one another in the area of the bottom longitudinal edge, so that the corners formed by the bottom edge and the longitudinal edge can be more easily grasped by the suction device than the corners in the area of the sack opening. Since the sacks are stacked on top of each other after the bottom seam has been produced, it cannot be ruled out that the still warm weld seams, particularly in the bottom area, lead to a mechanical connection between adjacent sacks. The described lifting in the corner region of the bottom of the sack and the subsequent pull-off movement result in a particularly favorable tear-off angle between the sacks which may stick together in the region of the bottom edge.

To carry out the method, the invention is based on a device which has a lifting and lowering suction device with at least one suction head and a gripper device which interacts with this suction head. This device is characterized according to the invention in that the suction head is connected via a swivel arm to an axis running approximately horizontally and inclined to the edges of the stack and is held pivotably about a further axis extending transversely thereto in the plane of the bearing surface of the suction head in such a way that for detecting the a longitudinally movable gripper device is provided for depositing the sack or tubular film section, the vertical distance from the stack being less than the length of the sack or tubular film section in the direction of movement of the gripper device, and that the stack on its end facing the deposited sack or tubular film section abuts a stop.

Since the approximately horizontal pivot axis of the suction head is inclined with respect to the edges of the stack, the dividing line runs parallel to the pivot axis over a corner of the stack when the sack is lifted off, at least until the longitudinal edge section is taken over by the gripper device. As soon as the corner of the sack or tubular film section is erected by the suction device, the gripper device can grip a longitudinal section adjacent to the corner in order to subsequently pull the sack or tubular film section from the stack. The stop arranged at the edge of the stack ensures that during the movement of the gripper device when the sack or tubular film section is removed it is not displaced relative to the stack, so that electrostatic charging phenomena are avoided. Since the vertical distance between the gripper device and the stack is less than the length of the sack or tubular film section in the pulling direction, the top of the sack is turned downwards when the sack is pulled off, which results in the sack being reversed.

The device is expediently provided with equipped with a pivotable hold-down device which can be pressed onto the stack in the region of the raised corner section after the corner section of the sack or tubular film section has been raised. The hold-down device can thus press the stack after lifting the first corner area of the uppermost sack or tubular film section, i.e. already after separation of very short longitudinal edge sections, and thus favors the removal of the sack or tubular film section even when the edges of the sacks lying one above the other are mechanically connected or outside the corner section Tubular film sections. Furthermore, it is advisable to arrange the suction head so as to be pivotable about the approximately horizontal axis along a circular arc section over an angular range of approximately 90 °. The pivoting angle of approximately 90 ° leads to the vertical erection of the corner section, so that the gripper device can grasp this corner section in a simple manner.

A particularly simple solution results. if the gripper device is arranged laterally next to the stack and is pivotably held with a gripper head above the stack in an approximately horizontal plane along a circular arc section. It is advantageous if the pivoting device consists essentially of a linkage which can be pivoted about a vertical axis and is connected to the gripper head, the drive being possible, for example, via a piston-cylinder arrangement.

It is also advantageous if the gripper device is equipped with clamping jaws which can be pivoted relative to one another. Here, the corner section raised by the suction device is held in a clamping position between the jaws until the sack is put down. To put the sack down, the jaws have to open, the time of opening essentially depends on the vertical distance between the jaws and the horizontal plane of the stack.

The invention is explained in more detail below on the basis of an exemplary embodiment shown schematically in the drawing.

• Fig. 1 die Draufsicht auf eine erfindungsgemäße Vorrichtung,
• Fig. 2 einen Schnitt durch die Vorrichtung längs der Linie A-A gemäß Fig. i,
• Fig. 3 eine Seitenansicht des Greifers gemäß Fig. 1,
• Fig. 4 eine Seitenansicht des Stapels mit einem vom Saugkopf angehobenen Eckabschnitt eines Sackes,
• Fig. 5 eine Seitenansicht gemäß Fig. 4 nach Erfassen des Eckabschnittes durch eine Greifereinrichtung und
• Fig. 6 eine weitere Seitenansicht gemäß Fig. 4 und 5, wobei das Abziehen eines Sackes in verschiedenen Arbeitsstellungen der Greifereinrichtung dargestellt ist.

Show it:

• 1 is a top view of a device according to the invention,
• 2 shows a section through the device along the line AA according to FIG. I,
• 3 shows a side view of the gripper according to FIG. 1,
• 4 shows a side view of the stack with a corner portion of a sack raised by the suction head,
• Fig. 5 is a side view of FIG. 4 after gripping the corner section by a gripper device and
• 6 shows a further side view according to FIGS. 4 and 5, the removal of a sack being shown in different working positions of the gripper device.

The device shown in FIG. 1 is used to remove a sack i which is open on one side from a stack of sacks of this type, designated overall by 2. In a first step, a suction device 3 with a suction head 4, which is connected to a swivel axis 8 via a linkage 5, serves to remove the uppermost sack of the stack 2. By means of a piston cylinder device 7, the suction head 4 can be pivoted through an angular range of approximately 90 ° into a vertical plane inclined with respect to the side edges of the stack. In the position pivoted through 90 °, the suction head and the linkage are shown in dashed lines and identified by 4a and 5a. Furthermore, the suction head 4 with its linkage 5 can be pivoted about an axis 8a by means of a further piston-cylinder arrangement 8, as can be seen in particular from FIG. 2. Thus, the suction head 4 can be pivoted to the side after lifting the corner portion of the bag i and suck the corner portion of the next bag after moving back again.

1 also shows a gripper device 9, the gripper head 10 of which is equipped with clamping jaws 11 and 12 which can be pivoted relative to one another. The gripper head 10 is connected via rods 13 and 14 to a stationary frame 15. The gripper head 10 with its jaws 11 and 12 can be pivoted about a vertical axis 16 fixed to the frame along an arc section in the direction of the double arrows 17 and 18. A piston-cylinder arrangement 19 serves as the swivel drive, which is connected on the one hand to the frame 15 and on the other hand to the rod 13.

The open position of the jaws 11, 12 is designated in Fig.1 with 11 a and 12a. FIG. 3 also shows the swivel head 10 in its two working positions, the clamping position of the clamping jaws 11, 12 being shown with solid lines and the open position with dashed lines and being designated by 11 a and 12 a. The clamping jaws 11 and 12 are expediently actuated via a piston-cylinder arrangement with the interposition of a pivoting lever.

A pivotable hold-down device 20 is provided for holding the stack 2 after the corner section of the bag 1 has been lifted off and raised, which can be actuated via a piston-cylinder arrangement 21.

The function of the device according to FIGS. 1 to 3 is explained below with reference to FIGS. 4 to 6. To lift the top sack 1 from the

Stack 2, the sack 1 is gripped at its corner section 1 by the suction head 4. In this working position, the suction head 4 is shown in dashed lines. By swiveling the suction head 4 in the direction of arrow 22, the suction head arrives in the position denoted by 4a. In this position, the corner section 1a and the subsequent longitudinal edge section approximately perpendicular to the stack 2, so that the sack 1 can be gripped by the gripper head 10 at a longitudinal edge section adjacent to the corner section 1a. For this purpose, the clamping jaws of the gripper head 10 fold out of their opening position designated 11a and 12a into their clamping position designated 11 and 12, as can be seen from FIG. 5.

After the sack 1 has been gripped by the clamping jaws 11 and 12, the suction head 4, which can be pivoted in two planes, is moved back to its starting position laterally next to the stack, as shown in broken lines in FIG. 2. During the return movement of the suction head 4, the sack 1 is pulled off the stack 2 by the gripper head 10 in the manner of a peeling movement in the direction of the arrows 23 and 24. At the edge of the stack 2, a stop 26 is provided so that the portion of the bag 1 still resting on the stack 2 during the pulling-off is not displaced horizontally. In addition, since the distance between the gripper head 10 and the stack 2 is chosen to be less than the length of the sack 1, the sack 1 is folded over when it is removed from the stack 2, so that it comes to lie with its original top down. After the sack 1 has been completely removed from the stack 2, the sack 1 is deposited next to the stack 2 by the further movement of the gripper head 10 in the direction of the arrow 25. In this stage of the method, the clamping jaws 11 and 12 open, so that the clamped section of the bag 1 also falls onto a storage surface 27.

The storage surface 27 can be a conveyor device that transports the bag 1 to a filling device for filling the bag. The position of the gripper head 10 in the discharge position 10a is also shown in FIG. 1. After the sack 1 has been ejected, that is to say after the clamping jaws 11 and 12 have been opened, the gripper head 10 is pivoted back to the left into its starting position in the illustration according to FIG. 6. This pivoting range is also shown in FIG. 1 by the lines marked with the double arrows 17 and 18.

In the pull-off process described above, all areas of the sack 1 are lifted approximately vertically to the sacks underneath, and a horizontal displacement of the sack 1 on the stack 2 is avoided. In this way, there is no longer any electrostatic charge. which make it difficult or impossible to remove individual bags. By gripping the bag with the suction head 4 at its corner section, any mechanical connections that may be present in the

Edge areas of adjacent stacked sacks of the stack 2 are easily torn open during the pulling-off process, so that this also enables reliable separation of the sacks.

Claims (7)

1. A method of removing and turning over the current top layer of a pile (2) of rectangular plastics sheet articles (1) wherein the current top layer is lifted in the region of a longitudinal edge by suction and swung horizontally through an angular range, and wherein the swung portion of longitudinal edge is grasped by a gripper device (9), withdrawn parallel to the plane of the pile in the direction of the opposite longitudinal edge and beyond, and deposited, face downwards, beside the pile (2), the vertical distance of the gripper device (9) from the pile being shorter than the width of the plastics sheet article, characterised in that the longitudinal edge of the plastics sheet articles (1), which are constructed in the form of bags or lengths of hose, is only lifted by suction in one corner region and swung horizontally over an angular range of about 90° and the subsequent withdrawal of the top layer parallel to the plane of the pile is carried out so that a horizontal displacement of the portion of the grasped bag or length of hose remaining on the pile (2) is avoided.

2. A method as claimed in Claim 1, characterised in that when bags open at one side are removed and turned over, these are lifted and swung in the bottom region of the longitudinal edge.

3. An apparatus for carrying out the method as claimed in Claim 1 or 2, which comprises a suction device able to be raised and lowered and having at least one suction head, and a gripper device cooperating with this suction head, characterised in that the suction head (4) is connected, through a swivel arm (5), to a substantially horizontal pin (6) extending inclined to the edges of the pile (2) and is held for swinging in the plane of the contact surface of the suction head about a further pin (8a) extending transversely to the first, that in order to grasp the portion of longitudinal edge lifted by the suction head (4) and to deposit the bag (1) or length of tubular sheet, a gripper device (9) is provided which is movable horizontally and the vertical distance of which from the pile (2) is shorter than the dimension of the bag (1) or length of tubular sheet in the direction of movement of the gripper device and that the pile bears against a stop (26) at its end face adjacent to the deposited bag (1) or length of tubular sheet.

4. An apparatus as claimed in Claim 3, characterised by a pivotable holding-down means (20) which can be pressed onto the pile (2) in the region of the lifted corner portion after the corner portion (1a) of the bag (1) or length of tubular sheet has been lifted.

5. An apparatus as claimed in any of the preceding Claims, characterised in that the suction head (4) can be swung about the pin (6) along a portion of an arc over an angular range (22) of about 90°.

6. An apparatus as claimed in any of the preceding Claims, characterised in that the gripper device (9) is disposed laterally beside the pile (2) and is held with a gripper head (10) pivotable above the pile (2) in a substantially horizontal plane along a portion of an arc.

7. An apparatus as claimed in any of the preceding Claims, characterised in that the gripper device (9) is equipped with clamping jaws (11, 12) which can be pivoted towards one another.

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