Device for gripping and releasing films for pallet wrapping machines and associated operating method

Description

[0001] The present invention concerns a film gripping and releasing device for pallet wrapping machines and the operating method thereof.

[0002] In the field of pallet wrapping machines having a turntable, one of the major criticalities occurs at the end of wrapping of a pallet, when it is necessary to cut the plastic film and hold the free edge to start wrapping the next pallet.

[0003] For some decades this operation has no longer been performed manually, but with the aid of automatic or semi-automatic machines: both carry out the winding phase autonomously, but in the semi-automatic machines the cutting of the film is performed by an operator, while the automatic machines are provided with a cutting device and a gripper which holds the film until the start of the next cycle, requiring the intervention of an operator only to replace the plastic film reel.

[0004] In known automatic machines, the movement of the gripper is operated by a pneumatic device synchronized with the times of the pallet wrapping cycle: generally, in these machines the table has a thickness ranging between 5 and 10 centimeters, so it is quite simple to insert inside the table the cables necessary to bring on board of it the electrical power supply and / or the compressed air necessary for the correct functioning of the gripper.

[0005] A known method and apparatus for stretch wrapping a load is described, for example, in US 6 269 610. This shows packaging material being gripped by a packaging material holder while the load is wrapped. The packaging material holder grasps a leading edge of the packaging material as the turntable is rotated to wrap material around the load. The turntable is provided with an actuator which engages a cog mounted on a chain, the cog drives the packaging material holder along a ramp, the jaws of the packaging material holder being actuated to open and close at predetermined points along the length of the ramp.

[0006] In the most recent pallet wrapping machines, wherein the thickness of the table is less than 3 centimeters, for example as described in patent EP 2808262 in the name of same applicant, it is however practically impossible to house inside the table itself all the connections necessary for the operation of the device that operates the movement of the gripper.

[0007] The aim of this invention is therefore to eliminate the above-mentioned disadvantages.

[0008] The invention, characterised as set out in the claims, achieves that aim by mounting on the table a fully mechanical gripper.

[0009] The main advantage obtained by means of this invention is basically the fact that a gripper of this type is not conditioned in any way by the size of the table, in particular by its thickness. Furthermore, the invention can be easily mounted also on machines that have already been made and are in operation.

[0010] Finally, since pneumatic devices are not used, all the operational problems that often arise when compressed air is used are avoided at the outset.

[0011] Further advantages and features of the invention will be more apparent in the detailed description which follows, with reference to the accompanying drawings, which show an example non-limiting embodiment, wherein: figure 1 shows the invention according to a perspective view in a use condition; figure 2 shows the invention according to a top plan view in the condition shown in figure 1; figure 3 shows the invention according to a top plan view; figure 4 shows the invention according to a front perspective view; figure 5 shows the invention according to a rear perspective view; figure 6 shows the invention according to an exploded view; figure 7 shows a detail of the invention according to a side perspective view; figure 8 shows the detail of figure 7 according to a side view.

[0012] As it can be seen from the figures, the invention relates to a film gripping and releasing device for pallet wrapping machines comprising a turntable (T) and a fixed frame (F).

[0013] The device (10) comprises a gripper (11) and movement means (12) for the gripper (11) on board the table (T) according to claim 1.

[0014] In the embodiment shown in the figures, the movement means (12) for the gripper (11) comprise a closed chain (121) provided with a pair of projections (122a, 122b) fixed to the chain (121), which are alternately intercepted by the movable contact element (21) in operating position, in such a way as to shift the gripper (11) in opposite directions along the guide (14).

[0015] In order to allow its opening and closing, as can be seen in figures 7 and 8, the gripper (11) comprises two half-grippers (11a, 11b) provided with toothed bases (110a, 110b) engaged with each other, in such a way as to make the two half-grippers (11a, 11b) rotate in opposite directions. Furthermore, at least one of the half-grippers (11a, 11b) is provided with a pin (111a) projecting laterally from the gripper.

[0016] The opening means (15) for the gripper (11) comprise a first cam (15a), suitable for intercepting the pin (111a) fixed to a first half-gripper (11a) in such a way as to make the half-gripper (11a) rotate and cause the gripper (11) to open; similarly, the closing means (16) for the gripper (11) comprise a second cam (16a), suitable for intercepting the pin (111a) in such a way as to make rotate the half-gripper (11a) to which the pin (111a) is constrained in the opposite direction and to cause the gripper (11) to close.

[0017] After closing the gripper (11), to avoid the intervention of an operator, the device (10) should be equipped with film cutting means (13) which allow the completion of the wrapping in progress and the start of the one of the next pallet. Although it is not necessary for the cutting means (13) to be fixed to the gripper (11), in the solution shown in the figures they consist of a blade (13a) fixed to one side of a half-gripper (11a; 11b) facing the pallet.

[0018] The operating method of the film gripping and releasing device (10) above-described therefore comprises the following steps: initially, and for about a couple of rotations of the rotating table (T), the film is clamped by the gripper (11) while the film is wrapped around the pallet, also covering the gripper (11) to ensure that the wrapping begins correctly; then, the pallet makes a first stop when the device (10) is in front of the fixed frame (F). At this time, as it can be seen in figures 1 and 2, the movable contact element (21) comes out of a seat (21a) on the frame (F) in such a way as to intercept the first projection (122a) fixed to the chain (121), holding the first projection (122a) blocked while the table (T) resumes its rotation; blocking the projection (122a) causes the chain (121) to slide in the opposite direction to that of rotation, and the consequent dragging of the gripper (11) along the guide (14) in such a way that the gripper (11) opens and releases the film. This occurs as a result of the fact that the gripper (11), fixed to the chain (121), on its path along the guide (14) comes across the first cam (15a) that intercepts the pin (111a) fixed to the first half-gripper (11a), causing its rotation, and the consequent opening of the gripper (11) which in this way releases the film.

[0019] Due to the circular shape of the table (T), after about one eighth of a turn, the contact element (21) no longer interferes with the first projection (122a) when the gripper (11) in the open position has reached its end stop along the guide (14); the movable contact element (21) retracts into its seat (21a) before the completion of the first rotation of the table (T) and the pallet wrapping continues until, once the wrapping operation is complete, the pallet stops again in front of the fixed frame (F). The movable contact element (21) comes out again from its seat (21a) and intercepts the second projection (122b), positioned on a branch of the chain (121) opposite to the one on which it is positioned the first projection (121a), holding the second projection (122b) blocked during the table (T) restart. Therefore, the sliding of the chain (121) in the opposite direction to that of rotation causes the gripper (11) to be dragged backwards along the guide (14) in such a way that the gripper (11) closes and again clamps the film, cutting the film at the pallet side by means of the blade (13a) and holding the film from the frame (F) side to start the wrapping of the next pallet. The closing of the gripper (11) is caused by the fact that, at the beginning of its backward stroke along the guide (14), the pin (111a) is intercepted by the second cam (16a) which causes a rotation in the opposite direction with respect to the previous one of the first half-gripper (11a) and the consequent closing of the gripper (11).

Claims

1. Film gripping and releasing device for pallet wrapping machines which comprise a turntable (T) and a fixed frame (F), characterised in that said device comprises a gripper (11) and movement means (12) for the gripper (11) on board the table (T), and a movable contact element (21) constrained to the frame (F), the contact element being suitable for going from a retracted home position to an operating position projecting from the frame (F), wherein the movement means (12) for the gripper (11) comprise a closed chain (121) provided with a pair of projections (122a,122b) fixed to the chain (121), which are suitable for being alternately intercepted by the movable contact element (21) in the operating position, in such a way as to shift the gripper (11) in opposite directions along a guide (14), on said guide (14) there being opening means (15) and closing means (16) for the gripper (11) which are suitable for making the gripper (11) go from a closed position in which it clamps the film to an open position in which it releases the film, and vice versa.

2. Device according to claim 1, characterised in that the gripper (11) comprises two half-grippers (11a,11b) provided with toothed bases (110a,110b) engaged with each other, in such a way as to make the two half-grippers (11a,11b) rotate in opposite directions.

3. Device according to claim 2, characterised in that the opening means (15) for the gripper (11) comprise a first cam (15a), suitable for intercepting a pin (111a) fixed to a first half-gripper (11a) in such a way as to make said half-gripper (11a) rotate and to cause the gripper (11) to open.

4. Device according to claim 2 or 3, characterised in that the closing means (16) for the gripper (11) comprise a second cam (16a), suitable for intercepting the pin (111a) in such a way as to make the half-gripper (11a) to which the pin (111a) is constrained rotate and to cause the gripper (11) to close.

5. Device according to claim 1 or 2, characterised in that it comprises film cutting means (13).

6. Device according to claim 5, characterised in that the film cutting means (13) comprise a blade (13a) fixed to a half-gripper (11a; 11b).

7. Operating method of a film gripping and releasing device for pallet wrapping machines according to any one of the preceding claims, characterised in that it comprises the following steps: - clamping of the film by the gripper (11) during the initial wrapping step; - when the pallet makes its first stop, extraction of the movable contact element (21) in such a way that the movable contact element (21) intercepts the first projection (122a), holding the first projection (122a) blocked during the start of table (T) rotation; - sliding of the chain (121) in the opposite direction to that of rotation, and dragging of the gripper (11) along the guide (14) in such a way that the gripper (11) opens and releases the film; - retraction of the movable contact element (21) before completion of the first revolution of the table (T); - when the pallet makes its second stop, again extraction of the movable contact element (21) in such a way that the movable contact element (21) intercepts the second projection (122b), holding the second projection (122b) blocked during the table (T) restart; - sliding of the chain (121) in the opposite direction to that of rotation, and dragging of the gripper (11) backwards along the guide (14) in such a way that the gripper (11) closes and again clamps the film for wrapping the next pallet.

8. Method according to claim 7, characterised in that it comprises a final step of cutting the film, in which the film is freed on the pallet side and retained on the frame (F) side for the next wrapping operation.