PACKAGING MACHINE AND METHOD FOR PACKAGING WITH STRETCH FOIL

Description

[0001] The present invention relates to a method for operating a packaging machine for wrapping packaging trays for food with a packaging film, in particular a plastic film, in which the packaging film is fed to a holding mechanism with two spaced-apart holding elements to hold the fed packaging film on two opposite sides, and subsequently a fed packaging tray is pressed against the fed packaging film by lifting it from below, and then the opposite sides of the packaging film are guided under the packaging tray. The lifting of the packaging tray is effected by a lifting device that raises a lifting table designed to receive the packaging tray from a transfer position to a packaging position, and wherein the packaging tray is transported from a loading position to the transfer position via a feed belt.The lifting table includes alignment fingers beneath its support surface. These alignment fingers are located within the conveying path of the infeed conveyor, specifically within the path of the intermediate section of the conveyor, when the lifting table is in its central position. The alignment fingers are not within the conveying path of the infeed conveyor when the lifting table is in its transfer position. During transport from the loading position to the transfer position, the packaging tray is pressed against the alignment fingers by the infeed conveyor when the lifting table is in its central position.

[0002] Furthermore, the invention relates to a packaging machine for carrying out a method according to the invention for operating a packaging machine.

[0003] Supermarkets commonly use trays for packaging food products, in which both the product and the tray are wrapped in stretch film. These trays are also generally referred to as food product trays. A packaging machine is used for this process. This machine includes a feeder for the film, a holding mechanism to secure the film at two opposite sides, and a conveyor belt that feeds the trays containing the food products to a lifting device, typically a lifting table. The lifting device then raises the tray against the stretch film, stretching the film over the tray. The stretch film is pre-tensioned, meaning it is already stretched taut.The distance between the two holding devices is increased after the stretch film is fed in and before the packaging tray containing the food product is lifted against the stretch film. This ensures that the stretch film adheres evenly and neatly to the packaging tray containing the food product. The packaging film is then guided around the packaging tray using lateral folding clamps and a rear folding clamp, and folded under the tray bottom. As the tray leaves the lifting device, the front edge of the film is also folded under the tray bottom. The stretch film is then sealed under the packaging tray, for example, using a heat plate over which the packaging tray is passed. The packaging tray containing the food product is then completely enclosed by a taut stretch film.

[0004] Such a packaging machine is known, for example, from EP 1 728 720 B1. A stretch film that can be processed by such a packaging machine is known, for example, from EP 0 687 558 A2.

[0005] EP 3 187 425 A1 also shows such a packaging machine for wrapping packaging trays for food with stretch film.

[0006] To avoid malfunctions, it is important that the packaging trays are aligned parallel to the direction of travel of the infeed conveyor, so that they reach the lifting table of the lifting device parallel to the packaging film. If the packaging trays are twisted in the horizontal plane relative to the packaging film on the lifting table, malfunctions can occur during the packaging process, or the packaging appearance, and in particular the way the folding clamps fold the packaging film under the packaging tray, will be unsatisfactory. For this reason, EP 1 728 720 B1 describes a complex mechanism that aligns the packaging tray before it reaches the lifting table.

[0007] The object of the invention is to create a method and a device that solves the problem of packaging misalignment in a simpler way than in the prior art.

[0008] This problem is solved by a method having the features of claim 1 and by a packaging machine having the features of claim 8.

[0009] The invention proposes a method for operating a packaging machine for wrapping food packaging trays with packaging film. The packaging film is fed to a holding mechanism with two spaced-apart holding elements to secure the film on two opposite sides. A packaging tray is then pressed against the film by lifting it from below. The opposite sides of the packaging film are then guided under the tray. The tray is lifted by a lifting device that raises a lifting table designed to receive the tray from a transfer position to a packaging position. The tray is transported from a loading position to the transfer position via a conveyor belt.The lifting table is held in a central position by the lifting device, while the feed belt transports the packaging tray on an intermediate piece between the loading position and the transfer position.

[0010] The lifting table includes alignment fingers below its support surface. These alignment fingers are located within the conveying path of the infeed conveyor, specifically within the conveying path of the intermediate section of the conveyor, when the lifting table is in the center position. The alignment fingers are not located within the conveying path of the infeed conveyor when the lifting table is in the transfer position.

[0011] During transport from the loading position to the transfer position, the packaging tray is pressed against the alignment fingers by the feed belt when the lifting table is in the center position.

[0012] In one embodiment, the alignment fingers for the packaging tray form a straight stop that runs orthogonally to the transport direction of the conveyor belt, and the packaging tray is pressed against the alignment fingers by the transport movement of the feed belt.

[0013] In one embodiment, the feed belt has a coefficient of friction such that the packaging tray is transported on the feed belt in the transport direction when the feed belt moves in the conveying direction, and the packaging tray slides on the feed belt when the packaging tray touches the alignment fingers and the feed belt moves in the transport direction.

[0014] In one embodiment, the lifting table is lowered from the central position to the transfer position by the lifting device after the packaging tray has been bumped against the alignment fingers.

[0015] In one embodiment, the lifting device lowers the lifting table from the central position to the transfer position in a shorter time than the feed belt transports the packaging tray from an upper edge of the alignment fingers to a front edge of the lifting table.

[0016] In one embodiment, the time at which the packaging tray contacts the alignment fingers is determined by a timer that starts when the packaging tray is transferred from a weighing belt to the infeed belt. In another embodiment, the time at which the packaging tray contacts the alignment fingers is determined by a sensor located near or on the alignment fingers.

[0017] In one embodiment, the lifting table is raised from the transfer position to the packaging position by the lifting device after the packaging tray has been moved to the transfer position on the lifting table by the feed belt.

[0018] The invention proposes a packaging machine for wrapping food packaging trays with a packaging film. The packaging machine is particularly suitable for carrying out the method according to the invention. The packaging machine comprises a feeding device for supplying the packaging film, a holding mechanism with two spaced-apart holding elements to hold the supplied packaging film on two opposite sides, the distance between the two holding elements being adjustable, and a feed belt for supplying the packaging trays from a loading position to a transfer position. The packaging machine includes a lifting device for moving the supplied packaging tray from the transfer position to a packaging position on a lifting table by lifting it from below and pressing it against the supplied packaging film.The packaging machine includes an operating mode in which the lifting table is held in a central position by the lifting device, while the feed belt transports the packaging tray on an intermediate piece between the loading position and the transfer position.

[0019] The lifting table includes alignment fingers below its support surface. These alignment fingers are located within the conveying path of the infeed conveyor, specifically within the conveying path of the intermediate section of the conveyor, when the lifting table is in the center position. The alignment fingers are not located within the conveying path of the infeed conveyor when the lifting table is in the transfer position.

[0020] During transport from the loading position to the transfer position, the packaging tray is pressed against the alignment fingers by the feed belt when the lifting table is in the center position.

[0021] In one embodiment, the lifting table consists of a base plate on which several rod-shaped supports are mounted. Tiltable heads are attached to the upper sides of the supports. These heads form a support surface for the packaging tray on the lifting table. L-shaped, downward-facing alignment fingers are attached to the base plate; these form a stop in the path of the infeed conveyor when the lifting table is in its central position.

[0022] In one embodiment, the feed belt is designed as a belt made of several parallel belts running in the transport direction, each belt being guided around a deflection roller located at the rear in the transport direction, and in particular the rear deflection rollers intersecting the base of the lifting table in the horizontal plane.

[0023] In one embodiment, the alignment fingers are arranged between the belts when the lifting table is in the center position.

[0024] In one embodiment, the base plate includes recesses so that the base plate can be moved through the conveying plane formed by the belts. In particular, the belts of the feed belt move through the recesses when the base plate moves vertically.

[0025] Some embodiments of the invention are shown by way of example in the drawings and described below. They show: Fig. 1 Packaging machine in schematic representation, Fig. 2 Section of the packaging machine with feed belt and lifting table, Fig. 3a and b Lifting table in a transfer position and in a middle position.

[0026] Fig. 1 Figure 1 shows a schematic representation of a packaging machine 1. The upper part of the figure shows a schematic top view and the lower part of the figure shows a side view of the packaging machine 1.

[0027] Packaging machine 1 comprises a film dispenser 217, a film feeder 216, a

[0028] The film transport device 214 and a film cutting device 215 arranged between the film feed device 216 and the film transport device 214. A roll of packaging film K, in particular a plastic film, can be inserted into the film dispenser 217 and held there by a film holder or roll holder. By means of the film feed device 216, an unwound end of the packaging film K can then be transferred to the film transport device 214.

[0029] The film transport device 214 has two parallel, spaced-apart belt conveyors 201 and 202 to convey the supplied packaging film K along two opposite sides in a transport direction X until the leading edge of the packaging film K reaches the front end of the film transport direction 214 (as viewed in the transport direction X). At this point, the film transport stops, and the packaging film K is cut from the remaining film roll by the film cutting device 215. Furthermore, the belt conveyors 201 and 202 are designed to clamp the cut packaging film K along the two opposite sides. For this purpose, lifting actuators (not shown) of a type generally known from the prior art can be provided.

[0030] The film transport device 214 is designed such that the distance between the two belt conveyors 201 and 202 is adjustable. To adjust the mutual distance, the first belt conveyor 201 or the second belt conveyor 202, or both belt conveyors 201 and 202 simultaneously, can be moved transversely to the film transport direction X, in particular by means of a motor drive which is controlled by a control unit of the packaging machine 1.

[0031] Furthermore, the packaging machine 1 has a feed conveyor 102 via which packaging trays P, containing food products and to be wrapped with packaging film K, can be fed to a lifting table 105 of the packaging machine 1. The feed conveyor 102 consists of several parallel belts that engage with the lifting table. The lifting table 105 is designed to transport each packaging tray P upwards to the packaging film K held in the film transport device 214, such that the packaging tray P is pressed against the packaging film K from below, so that the packaging film K automatically wraps around the packaging tray P during the lifting process. This upper position of the lifting table 105 is the packaging position. The lower position of the lifting table 105, in which the packaging tray P is conveyed onto the lifting table 105 by means of the feed conveyor 102, is the transfer position.

[0032] A weighing belt is located upstream of the feed belt 102. 101 with an integrated scale that can determine the weight of the packaging tray P and the food product. This is generally optional for packaging machines 1 and is used for packaging machines 1 that are suitable for labeling a packaging tray P with a label indicating the weight of the packaging tray P and the food product it contains. A printer connected to the scale 101 can then print a label indicating the weight of the filled packaging tray P. The labeling device takes the label from the printer and applies it to the packaged packaging tray P.

[0033] The packaging tray P is placed by an operator onto the weighing conveyor 101, or, in the case of a packaging machine 1 without a weighing conveyor 101, onto the front part of the infeed conveyor 102. This is the loading position of the packaging machine. A camera 103 is provided in the infeed area of ​​the packaging machine, i.e., in the infeed area of ​​the infeed conveyor 102 or on the weighing conveyor 101, which can be used to recognize different tray types. The packaging process is adjusted by the control unit according to the recognized packaging tray P. A light barrier 104 can also be used to detect when a packaging tray is moved by the infeed conveyor 102 against the alignment finger located on the lifting table 105. The lifting table is referred to below in relation to Fig. 2 , 3a and 3b described.

[0034] To further wrap the packaging trays P, after lifting the packaging tray P, the packaging film K is guided downwards around the packaging tray P using lateral folding clamps 108a and 108b and a rear folding clamp 110, and folded under the packaging tray P or its base. The packaging tray P is then pushed out of the film packing area onto a sealing plate 107 using a pusher 109, which also folds the front end of the packaging film K under the packaging tray P. The sealing plate 107 is heated to a temperature at which the ends of the packaging film K folded under the packaging tray P are welded or sealed together.

[0035] Finally, the packaged packaging tray P can be filled with a container in the Fig. 1 The labelling device (not shown) is provided with a label which includes, among other things, the weight determined by the scale 101 and is then transported out of the packaging machine via a transverse conveyor belt 106.

[0036] A stretchable plastic film, also known as a stretch film, can be used as packaging film. This packaging film is thermoplastic and can be sealed or welded at high temperatures. The thickness of the packaging film is typically between 10 µm and 60 µm.

[0037] Fig. 2 Figure 1 shows a packaging machine 1 in a front view. A front opening forms a guide channel, at the entrance of which the weighing belt 101 is located. Following the weighing belt 101 is the infeed belt 102. The infeed belt 102 is designed as a belt conveyor with four parallel belts. The belts of the infeed belt form a horizontal plane on which the packaging tray P rests with its underside. The infeed belt 102, i.e., the belts of the infeed belt 102, lead to a lifting table 105. The lifting table 105 is in Fig. 3a and 3bThe lifting table 105 is shown in more detail below and consists of several rod-shaped supports, each with a tilting head attached to its upper surface. These heads form a support surface for the packaging tray. In the transfer position of the lifting table 105, the belts of the feed conveyor guide the components into the spaces between the rod-shaped supports. The horizontal plane formed by the belts of the feed conveyor is positioned slightly above the horizontal plane formed by the heads. This allows a packaging tray P to be transported onto the lifting table 105 via the belts of the feed conveyor. When the lifting table 105 is raised, the heads push the packaging tray P upwards, and it is removed from the feed conveyor 102.

[0038] Fig. 3a shows the lifting table 105 of the packaging machine 1 in the transfer position, that is, in the lower position. Fig. 3b Figure 1 shows the lifting table 105 of the packaging machine 1 in the center position, that is, in the position in which the packaging tray P is pressed against the alignment fingers by the feed conveyor 102 when the packaging tray is moved on the feed conveyor along an intermediate section between the loading position and the transfer position. The center position and the packaging position differ only slightly. It is only necessary to ensure that, in the center position, the upper edge of the heads does not touch the packaging film K already in the holding devices.

[0039] The lifting table 105, i.e., the lifting device, consists of a support 301 connected to a frame of the packaging machine 1. It includes a motor 302 to which a lifting mechanism 303 is connected. The lifting mechanism moves rods 311, which are attached to the support 301 by means of a sliding bearing 312, in a vertical direction. A base plate 304 of the lifting table 105 is located on the rods 311. The base plate includes four forward-facing recesses 310 into which the belts of the feed conveyor 102 can engage. Several rod-shaped supports 305 are attached to the base plate 304 and project vertically upwards from the base plate 304. Tiltable heads 306 are arranged at the upper end of the rod-shaped supports 305. The tilting heads 306 form a horizontal plane 308 on which the packaging tray lies when it is moved upwards in a vertical direction by the lifting mechanism.The heads 306 are tiltable and tip over upon contact with the folding jaws so as not to impede the movement of the folding jaws. L-shaped, downward-pointing alignment fingers 309 are attached to the base plate. The alignment fingers 309 form a stop in the transport direction, which is oriented orthogonally to the transport direction.

[0040] The belts of the feed conveyor 102 form a schematically indicated horizontal plane 307, which is slightly higher in the vertical direction than the plane 308 formed by the heads 306 when the lifting table 105 is in the transfer position ( Fig. 3a ). When the lifting table 105 is in the central position, the belts of the feed conveyor 102 form a schematically indicated horizontal plane 307 through which the alignment fingers 309 project in a vertical direction ( Fig. 3bThe alignment fingers thus form a stop that is orthogonal to the transport direction of the feed belt. A packaging tray being transported on the feed belt 102 in the transport direction therefore abuts the vertical plane formed by the alignment fingers 309. Because the alignment fingers form a plane orthogonal to the plane 307 of the feed belt 102, the packaging tray is aligned perpendicular to the transport direction by the alignment fingers 309.

[0041] The functions of various elements shown in the drawings, including the function blocks, can be implemented by dedicated hardware or by generic hardware capable of executing software in conjunction with the appropriate software. If the functions are provided by a processor, they can be provided by a single dedicated processor, a single shared processor, or multiple generic processors, which may themselves be shared. The functions can be provided, without limitation, by a digital signal processor (DSP), network processor, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), read-only memory (ROM) with stored software, random-access memory (RAM), and non-volatile memory.

Claims

1. Method for operating a packaging machine (1) for wrapping packaging trays (P) for food with a packaging film (K), in which the packaging film (K) is fed to a holding mechanism (214), having two holding means (201, 202) spaced apart from one another, in order for the fed packaging film (K) to be held on two mutually opposite sides, and then a fed packaging tray (P) is pressed against the fed packaging film (K) from below by being raised, and then the mutually opposite sides of the packaging film (K) are passed below the packaging tray (P), wherein the raising of the packaging tray (P) is carried out by a raising device, which raises a lifting table (105), configured for receiving the packaging tray (P), from a transfer position into a packaging position, and wherein the packaging tray (P) is transported via a feed belt (102) from a loading position to the transfer position, characterized in that the lifting table (105) is held in a middle position by the raising device while the feed belt (102) transports the packaging tray (P) on an intermediate section between the loading position and the transfer position, wherein the lifting table (105) comprises alignment fingers below the bearing surface of the lifting table (105), wherein the alignment fingers (309) are situated in the conveying path of the feed belt (102), in particular in the conveying path of the intermediate section of the feed belt (102), when the lifting table (105) is arranged in the middle position, and the alignment fingers (309) are not situated in the conveying path of the feed belt (102) when the lifting table (105) is in the transfer position, and wherein the packaging tray (P) is pressed against the alignment fingers (309) during the transport from the loading position to the transfer position by the feed belt (102) when the lifting table (105) is in the middle position.

2. Method for operating a packaging machine (1) according to Claim 1, characterized in that the alignment fingers (309) for the packaging tray (P) form a straight stop which extends orthogonally to the transport direction of the conveyor belt, and the packaging tray (P) is pressed against the alignment fingers (309) by way of the transport movement of the feed belt (102).

3. Method for operating a packaging machine (1) according to Claim 1 or 2, characterized in that the feed belt (102) has a coefficient of friction such that the packaging tray (P) is transported on the feed belt (102) in the transport direction when the feed belt (102) moves in the conveying direction and the packaging tray (P) slides on the feed belt (102) when the packaging tray (P) abuts against the alignment fingers (309) and the feed belt (102) at the same time moves in the transport direction.

4. Method for operating a packaging machine (1) according to one of Claims 1 to 3, characterized in that the lifting table (105) is lowered from the middle position into the transfer position by the raising device after the packaging tray (P) has come into abutment with the alignment fingers (309).

5. Method for operating a packaging machine (1) according to Claim 4, characterized in that the time taken for the raising device to lower the lifting table (105) from the middle position into the transfer position is shorter than the time taken for the feed belt (102) to transport the packaging tray (P) from a top edge of the alignment fingers (309) to a front edge of the lifting table (105).

6. Method for operating a packaging machine (1) according to Claim 4 or 5, characterized in that the time at which the packaging tray (P) abuts against the alignment fingers (309) is determined by the running-down of a timer that is started when the packaging tray (P) is transferred from a weighing belt (101) to the feed belt (102), or is determined by a sensor in the vicinity of the alignment fingers (309) or at the alignment fingers (309).

7. Method for operating a packaging machine (1) according to one of Claims 1 to 6, characterized in that the lifting table (105) is raised from the transfer position into the packaging position by the raising device after the packaging tray (P) has been moved onto the lifting table (105) and into the transfer position by the feed belt (102).

8. Packaging machine for wrapping packaging trays (P) for food with a packaging film (K), in particular for carrying out the method according to one of the preceding claims, having a feed device (216) for feeding the packaging film (K), having a holding mechanism (214), which has two holding means (201, 202) spaced apart from one another, in order for the fed packaging film (K) to be held on two mutually opposite sides, wherein the distance of the two holding means (201, 202) from one another is adjustable, having a feed belt (102) for feeding the packaging trays (P) from a loading position to a transfer position, and having a raising device in order for the fed packaging tray (P) to be moved from the transfer position into a packaging position, and to be pressed against the fed packaging film (K), on a lifting table (105) from below by being raised, characterized in that the packaging machine (1) has an operating mode in which the lifting table (105) is held in a middle position by the raising device while the feed belt (102) transports the packaging tray (P) on an intermediate section between the loading position and the transfer position, wherein the lifting table (105) comprises alignment fingers (309) below the bearing surface of the lifting table (105), wherein the alignment fingers (309) are situated in the conveying path of the feed belt (102), in particular in the conveying path of the intermediate section of the feed belt (102), when the lifting table (105) is arranged in the middle position, and the alignment fingers (309) are not situated in the conveying path of the feed belt (102) when the lifting table (105) is in the transfer position, and in that the packaging tray (P) is pressed against the alignment fingers (309) during the transport from the loading position to the transfer position by the feed belt (102) when the lifting table (105) is in the middle position.

9. Packaging machine for wrapping packaging trays (P) according to Claim 8, characterized in that the lifting table (105) consists of a base plate (304) to which there are attached multiple rod-shaped holders (305) to whose top sides in particular tiltable heads (306) are attached, wherein the heads (306) form a bearing surface of the lifting table (105) for the packaging tray (P), and wherein L-shaped and downwardly oriented alignment fingers (309) are attached to the base plate (304) and form a stop in the transport path of the feed belt (102) when the lifting table (105) is in the middle position.

10. Packaging machine for wrapping packaging trays (P) according to Claim 8 or 9, characterized in that the feed belt (102) is in the form of a belt made up of multiple straps extending in parallel in the transport direction, wherein each strap is guided around a deflection roller which is at the rear in the transport direction, and wherein in particular the rear deflection rollers, in the horizontal plane, overlap the base surface of the lifting table (105).

11. Packaging machine for wrapping packaging trays (P) according to Claim 10, characterized in that the alignment fingers (309) are arranged between the straps when the lifting table (105) is in the middle position.

12. Packaging machine for wrapping packaging trays (P) according to Claim 10 or 11, where dependent on Claim 9, characterized in that the base plate (304) comprises recesses (310) such that the base plate (304) is movable through the conveying plane formed by the straps.