STRETCHING UNIT FOR HOLDING AND STRETCHING A TUBULAR FILM, FLOW-WRAPPING DEVICE AND METHOD FOR HOLDING AND STRETCHING A TUBULAR FILM

Abstract

A stretching unit (10) is proposed for clamping and stretching a tubular film (4) in a flow wrapping device (11). The stretching unit (10) comprises: a gripping head (14); two coupling rods (15) attached to a drive means (12); and two gripping fingers (16), each gripping finger (16) fixed to the gripping head (14) and a coupling rod (15). The gripping fingers (16) are characterized in that they move from a remote position (A) to a clamping position (C) by means of a relative linear motion between the gripping head (14) and the drive means (12) parallel to a central axis (H) of the drive means (12). Furthermore, an additional stretching unit (10), a flow wrapping device (1), and methods for clamping and stretching tubular film (4) are proposed.

Description

STRETCHING UNIT FOR HOLDING AND STRETCHING A TUBULAR FILM, FLOW-WRAPPING DEVICE AND METHOD FOR HOLDING AND STRETCHING A TUBULAR FILM Field of Invention The invention relates to improvements of a stretching unit for gripping and stretching a tubular film in a flow wrapping device, wherein the stretching unit comprises a gripping head, two coupling rods attached to a drive means, and two gripping fingers, each gripping finger attached to the gripping head and a coupling rod. The invention also relates to a flow wrapping device and a method for gripping and stretching a tubular film. Background of the Invention A common method for producing packages from a roll of film is the use of a flow wrapping device. A flow wrapping device, also called a flow wrapping machine, is a packaging machine that receives a continuous, flat sheet, for example, a film of plastic material, such as a thermoplastic, which is conveyed continuously or intermittently and moves down over a forming flange and is then molded into a real shape. Ref. 331290 tubular, i.e., in a tubular film, when wrapped around a vertical filling and molding tube of the flow wrapping device. After being wrapped around the vertical filling and molding tube, the film roll is closed lengthwise by means of a longitudinal extension seal, which is applied to the film specifically by heat-sealing the lateral / longitudinal edges of the film roll or by heat-sealing in the vicinity of these edges, thereby joining them. This is accomplished by means of so-called longitudinal sealing means. The tubular film conventionally has a rectangular, elliptical, or circular cross-sectional area. Conventionally, the tubular film is closed by means of transverse sealing, preferably in a direction perpendicular to the flow direction, i.e., transverse.In this way, individual packages are formed from continuous tubular film. A product, such as a food product, is introduced by dropping it through a filling and molding tube and into the tubular film surrounding the tube. During filling, the tubular film is open transversely at its upper end, i.e., not transversely sealed. Then, and / or simultaneously, the tubular film, along with the product, moves downward, and a transverse seal is formed over the product, creating a hermetically sealed package. As a final step, or simultaneously with the application of the top seal, the package is separated from the tubular film using cutting means.To create a straight, airtight cross seal, the tubular film must be stretched across the area to be cross-sealed before and during the cross-sealing process. Stretching units are typically used for this purpose. These units operate two gripping fingers with a first pneumatic drive to clamp the tubular film. Once the tubular film is clamped, a start signal is sent to a second pneumatic drive, which then moves the gripping fingers to stretch the clamped tubular film. However, this process is time-consuming and complicated due to the two separate movements and the need to wait until the clamping process is complete before the start signal indicates that the stretching process can begin. Brief Description of the Invention The purpose of the invention is, therefore, to provide a stretching unit, a vertical flow enveloping device, and a method, which allow a tubular film to be clamped and stretched without the need to wait until a start signal indicates that the tubular film has been clamped before stretching the film. The purpose is achieved by providing a stretching unit for gripping and stretching a tubular film in a flow-enveloping device. The stretching unit consists of a gripping head, two coupling rods attached to a drive mechanism, and two gripping fingers, each attached to the gripping head and a coupling rod. The gripping fingers move from a remote position to a gripping position by means of a relative linear motion between the gripping head and the drive mechanism, parallel to a central axis of the drive mechanism. The description with respect to this embodiment of the present invention also applies to the other embodiments of the present invention and vice versa. The objects disclosed with respect to this embodiment of the present invention may also be combined with other objects described with respect to this and / or other embodiments of the present invention and vice versa. The present invention relates to a stretching unit for gripping and stretching a tubular film (rea Lnn / zznz / E / YiAi) in a flow wrapping device, wherein the stretching unit comprises a gripping head, two coupling rods attached to a drive means, and two gripping fingers, each gripping finger attached to the gripping head and a coupling rod. A flow wrapping device receives a continuous flat sheet, for example, a film of plastic material, for example, a thermoplastic material, which is conveyed continuously or intermittently and moved down onto a forming flange and then molded into a tubular shape, i.e., into a tubular film, by being wrapped around a vertical filling and molding tube of the flow wrapping device.After being wrapped around the vertical filling and molding tube, the film roll is closed lengthwise by means of a longitudinal extension seal. This seal is applied to the film, specifically by heat-sealing the lateral / longitudinal edges of the film roll or by heat-sealing near these edges, thereby joining them together. This is accomplished using so-called longitudinal sealing means. The tubular film conventionally has a rectangular, elliptical, or circular cross-sectional area. Typically, the tubular film is closed by transverse sealing means, preferably in a direction perpendicular to the flow direction, i.e., transverse. In this way, individual packages are formed from the continuous tubular film.A product, such as a food product, is introduced into the tubular film by dropping it through a filling and molding tube and into the tubular film surrounding the tube, over a first lower transverse seal. During filling, the tubular film is open transversely, i.e., without a transverse seal, at its upper end. Then, and / or simultaneously, the tubular film, along with the product, moves downward, and a top transverse seal is formed over the product, creating a hermetically sealed package. As a final step, or simultaneously with the application of the top seal, the package is separated from the tubular film by cutting means.To create a straight, airtight cross seal, the tubular film is stretched across the area to be cross-sealed before and during cross-sealing by a stretching unit of the flow wrap device. To grip and stretch the tubular film, the stretching unit comprises two coupling rods attached to a movement area of ​​the stretching unit, two gripping fingers, each gripping finger attached to a gripping head of the stretching unit and a coupling rod. According to the present invention, the gripping fingers move from a remote position to a clamping position by means of a relative linear motion between the gripping head and the moving means, parallel to a central axis of the moving means. Due to this motion parallel to the central axis of the moving means, the tubular film is both clamped and stretched in a single operation. The inventive stretching unit eliminates the need to separate the clamping and stretching steps and wait for a start signal, indicating that the tubular film is clamped, before stretching the film. The coupling rods are preferably arranged in a V-shape. Preferably, the coupling rods are arranged in a plane parallel to the central axis of the drive means. Preferably, the coupling rods are rotatably connected to the drive means, more preferably at a first end of the coupling rods. It is preferable that the coupling rods are connected to the drive means by means of third pivot points in the area Lnn / zznz / E / YiAi at the first end of the coupling rods. The gripping fingers are preferably connected to the coupling rods at a second end of the coupling rods, the second end being opposite the first end. Preferably, the gripping fingers are connected to the coupling rods by means of second pivot points. The gripping fingers are preferably arranged on the side of the coupling rods furthest from the gripping head.Preferably, the gripping fingers are rotatably connected to the gripping head via first pivot points. The first pivot point is preferably located at a second end of the gripping head, with the second end opposite a first end of the gripping head, wherein the first end of the gripping head is preferably located adjacent to or at least partially enclosing the means of movement. Preferably, the gripping head partially encloses the coupling rods. Preferably, the gripping head covers at least partially the top and / or bottom of the coupling rods, as well as the sides of the coupling rods furthest from the other respective coupling rod. The gripping head is preferably Y-shaped, U-shaped, or V-shaped. Another inventive or preferred embodiment of the present invention that also solves the proposed problem is a stretching unit for gripping and stretching a tubular film in a flow-enveloping device. The stretching unit comprises a gripping head, two coupling rods attached to a drive means, and two gripping fingers, each gripping finger attached to the gripping head and a coupling rod. The gripping fingers move from a remote position to a gripping position by means of a relative linear motion between the gripping head and the drive means, parallel to a central axis of the drive means. The description with respect to this embodiment of the present invention also applies to the other embodiments of the present invention and vice versa. The objects described with respect to this embodiment of the present invention may also be combined with other objects described with respect to this and / or other embodiments of the present invention and vice versa. This embodiment of the present invention relates to a stretching unit for holding and stretching a tubular film in a flow-enveloping device, the stretching unit comprising a gripping head, two coupling rods attached to a moving means, and two gripping fingers, each gripping finger attached to the gripping head and a coupling rod. According to this embodiment of the present invention, the gripping fingers are moved from a remote position to a gripping position by a rotational movement of the gripping fingers. This rotational movement enables a smooth transition between gripping and stretching. The inventive stretching unit eliminates the need to separate the gripping and stretching steps and wait for a start signal, indicating that the tubular film is gripped, before stretching the film. The coupling rods are preferably arranged in a V-shape. Preferably, the coupling rods are arranged in a plane parallel to the central axis of the drive means. Preferably, the coupling rods are rotatably connected to the drive means, more preferably at a first end of the coupling rods. It is preferable that the coupling rods are connected to the drive means by means of third pivot points at the first end of the coupling rods. The gripping fingers are preferably connected to the coupling rods at a second end of the coupling rods, the second end being opposite the first end. Preferably, the gripping fingers are connected to the coupling rods by means of second pivot points. The gripping fingers are preferably arranged on the side of the coupling rods furthest from the gripping head.Preferably, the gripping fingers are rotatably connected to the gripping head via first pivot points. The first pivot point is preferably located at a second end of the gripping head, the second end being opposite a first end of the gripping head, wherein the first end of the gripping head is preferably located adjacent to or at least partially enclosing the means of movement. Preferably, the gripping head partially encloses the coupling rods. Preferably, the gripping head covers at least partially the top and / or bottom of the coupling rods, as well as the sides of the coupling rods that are opposite each other. The gripping head is preferably Y-shaped, U-shaped, or V-shaped. Preferably, the coupling rods and / or gripping fingers and / or gripping head and / or the Lnn / zznz / E / YiAi moving means are made of metal or plastic. According to a preferred embodiment of the invention, each gripping finger, preferably at one of its end sections, is attached to the gripping head by a first pivot point, and each gripping finger is attached to the coupling rods by a second pivot point. The relative linear motion between the gripping head and the drive means results in a rotational movement of the gripping fingers about the first pivot point and, therefore, a transition from the remote position to the gripping or return position. Preferably, each coupling rod is attached to the drive means by a third pivot point. According to a preferred embodiment of the invention, the moving means is connected to a first actuating means, the first actuating means being preferably a pneumatic cylinder. Alternatively, the first actuating means is an electric motor, preferably a linear motor. According to a preferred embodiment of the invention, the gripping head is connected to a second drive means, the second drive means being preferably an electric motor, more preferably a linear motor, and even more preferably a linear servomotor. Compared to, for example, pneumatic cylinders, a linear motor allows for extremely precise control of the stretching force. The position of the gripping head driven by the linear motor, preferably a linear servomotor, is always known without the need for an additional sensor. Furthermore, the linear motor allows for the application of high forces and prevents slippage. Since the linear motor can be precisely controlled, the stretching force can be adjusted to the material properties of the tubular film and / or different bag shapes. With the linear motor, tearing of the tubular film can be avoided. Preferably, the drive means is a powered rod. Preferably, the gripping head is connected to the second drive means by means of an additional drive means. The additional drive means is preferably a tube. The tube is preferably arranged parallel to the drive means and at least partially coaxial with it. This allows for advantageous power transmission from the second drive means to the gripping head, while minimizing installation space and allowing for relatively free choice of the location of the second drive means. The additional drive means is preferably made of a metal and / or a synthetic material. According to a preferred embodiment of the invention, movement of the moving means along its central axis is limited by a mechanical stop. Preferably, movement of the moving means toward the tubular film is also limited by the mechanical stop. Preferably, the movement is limited to restrict the rotation of the gripping fingers to the intermediate position. This advantageously limits the movement of the moving means, thereby preventing malfunctions and / or damage to the stretching unit due to, for example, impacts from the gripping fingers. Preferably, the position of the mechanical stop is adjustable in a direction parallel to the central axis of the moving means. Preferably, the position of the mechanical stop is adjusted according to the size and / or shape of the tubular film and / or the packages. The problem of the invention is also achieved by providing a flow enclosure device. The description with respect to this embodiment of the present invention also applies to the other embodiments of the present invention and vice versa. The objects described with respect to this embodiment of the present invention may also be combined with other objects described with respect to this and / or other embodiments of the present invention and vice versa. This embodiment of the present invention relates to a flow wrapping device. A flow wrapping device receives a continuous flat sheet, for example, a film of plastic material, for example, a thermoplastic material, which is continuously or intermittently conveyed and moves down onto a forming flange and then molded into a tubular shape, i.e., a tubular film, by being wrapped around a vertical filling and molding tube of the flow wrapping device. After being wrapped around the vertical filling and molding tube, the film roll is closed lengthwise by means of a longitudinal stretch seal, which is applied to the film, especially by heat sealing the lateral / longitudinal edges of the film roll or by heat sealing in the vicinity of these edges, thereby joining them together.This is accomplished by means of what are known as longitudinal sealing means. The tubular film conventionally has a rectangular, elliptical, or circular cross-sectional area. The tubular film is conventionally closed by transverse sealing means, preferably in a direction perpendicular to the flow direction, i.e., transverse. This defines individual packages from the continuous tubular film. A product, such as a food product, is introduced into the tubular film by dropping it through a filling and molding tube and into the tubular film surrounding the tube, over a first lower transverse seal. During filling, the upper end of the tubular film is open in the transverse direction, i.e., without a transverse seal.Next, and / or simultaneously, the tubular film, along with its product, is moved downwards, and a top cross seal is formed over the product, thereby producing a hermetically sealed package. As a final step, or simultaneously with the application of the top seal, the package is separated from the tubular film by cutting means. To create a straight, hermetic cross seal, the tubular film is stretched along the cross-sectional area to be cross-sealed before and during the cross-sealing process by a stretching unit of the flow wrap device. To grip and stretch the tubular film, the stretching unit comprises two coupling rods attached to a movement means of the stretching unit, and two gripping fingers, each gripping finger attached to a gripping head of the stretching unit and a coupling rod. According to the present embodiment of the invention, the flow wrapping device comprises an inventive stretching unit. The inventive stretching unit eliminates the need to separate the clamping and stretching steps and wait for a start signal, indicating that the tubular film is clamped, before stretching the tubular film. Preferably, the stretching unit is movably connected to the flow wrapping device. Preferably, the stretching unit is movable along the transport direction of the tubular film. This enables continuous operation of the flow wrapping device, i.e., film material is continuously conveyed into the flow wrapping device instead of intermittently. For this purpose, the stretching unit, as well as the transverse sealing means, preferably move parallel to the tubular film during clamping, stretching, and transverse sealing. Preferably, the cross-sealing means are mounted on a cross-sealing support. Preferably, the cross-sealing support is movable along and against the transport direction of the tubular film. Preferably, the stretching unit is connected to the cross-sealing support. Preferably, the cross-sealing support moves with a motion similar to that of a circulating elevator along and against the transport direction of the tubular film, wherein clamping, stretching, and cross-sealing are performed during a movement along the transport direction of the tubular film. The problem of the invention is also solved by providing a method for clamping and stretching a tubular film in a flow-enveloping device using a stretching unit, preferably a stretching unit according to the present invention, by moving two gripping fingers of the stretching unit from an initial position to a clamping position. In a first step, a moving means of the stretching unit moves relative to a gripping head of the stretching unit in a first direction, preferably towards the tubular film. By doing so, the gripping fingers move from the remote position to an intermediate position. In a second step, the gripping head moves relative to the moving means in a second direction, which is opposite to the first direction. By doing so, the gripping fingers move from the intermediate position to the clamping position.This is how the tubular film is held. The tubular film is stretched by an additional movement of the gripping head in the second direction. The description with respect to this embodiment of the present invention also applies to the other embodiments of the present invention and vice versa. The objects disclosed with respect to this embodiment of the present invention may also be combined with other objects described with respect to this and / or other embodiments of the present invention and vice versa. This embodiment of the present invention relates to a method for clamping and stretching a tubular film in a flow wrapping device. A flow wrapping device receives a continuous flat sheet, for example, a film of plastic material, for example, a thermoplastic material, which is continuously or intermittently conveyed and moved down onto a forming flange and then molded into a tubular shape, i.e., into a tubular film, by being wrapped around a vertical filling and molding tube of the flow wrapping device. After being wrapped around the vertical filling and molding tube, the film roll is closed lengthwise by means of a longitudinal stretch seal, which is applied to the film, especially by heat sealing the lateral / longitudinal edges of the film roll or by heat sealing in the vicinity of these edges, thereby joining them.This is accomplished by means of what are called longitudinal sealing means. The tubular film conventionally has a rectangular, elliptical, or circular cross-sectional area. The tubular film is conventionally closed by transverse sealing means, preferably in a direction perpendicular to the flow direction, i.e., transversely. In this way, individual packages are defined from the continuous tubular film. A product, such as a food product, is introduced into the tubular film by dropping it through a filling and molding tube and into the tubular film surrounding the filling and molding tube and over a first lower transverse seal. During filling, the tubular film is open in the transverse direction at its upper end, i.e., it has no transverse seal.Next, and / or simultaneously, the tubular film, along with its product, is moved downwards, and a top cross seal is formed over the product, thereby creating a hermetically sealed package. As a final step, or simultaneously with the application of the top seal, the package is separated from the tubular film by cutting means. To create a straight, hermetic cross seal, the tubular film is stretched along the area to be cross-sealed before and during the cross-sealing process using a stretching unit of the flow wrap device. To grip and stretch the tubular film, the stretching unit comprises two coupling rods attached to a movement means of the stretching unit, two gripping fingers, each gripping finger attached to a gripping head of the stretching unit and to a coupling rod. According to the present invention, in a first step, a moving means of the stretching unit moves relative to a gripping head of the stretching unit in a first direction, preferably towards the tubular film. By doing so, the gripping fingers move from the remote position to an intermediate position. In a second step, the gripping head moves relative to the moving means in a second direction, which is opposite to the first direction. By doing so, the gripping fingers move from the intermediate position to the clamping position, gripping the tubular film. The tubular film is stretched by a further movement of the gripping head in the second direction. Due to the movement in the second direction, the tubular film is gripped and stretched in a single working operation.The inventive method eliminates the need to separate the clamping and stretching steps and wait for a start signal, indicating that the tubular film is clamped, before stretching the tubular film. Preferably, the second direction is arranged parallel to the central axis of the drive means. Preferably, the stretching unit releases the tubular film when the tubular film is transversely sealed. Preferably, to release the tubular film, in a third step, the moving head moves relative to the drive means in the first direction and thus moves the gripping fingers from the clamping position to the intermediate position. Preferably, the drive means is fixed in its position during the third step. Preferably, the third step follows the second step.Preferably, in a fourth step, the moving means moves relative to the gripping head (rea Lnn / zznz / E / YiAi) in the second direction, thereby moving the gripping fingers from the intermediate position to the remote position. Preferably, the fourth step follows the third step. Another inventive or preferred embodiment of the present invention, which also solves the problem described herein, is a method for clamping and stretching a tubular film in a flow-enveloping device using a stretching unit, preferably a stretching unit according to the present invention, by moving two gripping fingers of the stretching unit from a remote position to a clamping position. In a first step, the gripping fingers are rotated in a gripping plane orthogonal to a transport direction of the tubular film toward each other from the remote position to an intermediate position. In a second step, the gripping fingers are rotated in the gripping plane toward each other from the intermediate position to the clamping position. The tubular film is clamped between the gripping fingers. The gripping fingers move linearly in the gripping plane to stretch the clamped tubular film. The description with respect to this embodiment of the present invention also applies to the other embodiments of the present invention and vice versa. The objects disclosed with respect to this embodiment of the present invention can also be combined with other objects described with respect to this and / or other embodiments of the present invention and vice versa. This embodiment of the present invention relates to a method for clamping and stretching a tubular film in a flow wrapping device. A flow wrapping device receives a continuous flat sheet, for example, a film of plastic material, for example, a thermoplastic material, which is continuously or intermittently conveyed and moves down onto a forming flange and then molded into a tubular shape, i.e., a tubular film, by being wrapped around a vertical filling and molding tube of the flow wrapping device. After being wrapped around the vertical filling and molding tube, the film roll is closed lengthwise by means of a longitudinal stretch seal, which is applied to the film, especially by heat-sealing the lateral / longitudinal edges of the film roll or by heat-sealing in the vicinity of these edges, thereby joining them together.This is accomplished by means of what are called longitudinal sealing means. The tubular film conventionally has a rectangular, elliptical, or circular cross-sectional area. The tubular film is conventionally closed by transverse sealing means, preferably in a direction perpendicular to the flow direction, i.e., transversely. In this way, individual packages are defined from the continuous tubular film. A product, such as a food product, is introduced into the tubular film by dropping it through a filling and molding tube and into the tubular film surrounding the filling and molding tube and over a first lower transverse seal. During filling, the tubular film is open transversely, i.e., without a transverse seal at its upper end.Next, and / or simultaneously, the tubular film, along with its product, moves downward along a conveying direction, and a top cross seal is then formed over the product, creating a hermetically sealed package. As a final step, or simultaneously with the application of the top seal, the package is separated from the tubular film by cutting means. To create a straight, hermetic cross seal, the tubular film is stretched along the area to be cross-sealed before and during the cross-sealing process using a stretching unit of the flow wrap device.To hold and stretch the Lnn / zznz / E / YiAi tubular film, the stretching unit comprises two coupling rods attached to a movement means of the stretching unit, two gripping fingers, each gripping finger attached to a gripping head of the stretching unit and a coupling rod. According to the present invention, in a first step, the gripping fingers are rotated in a gripping plane orthogonal to a transport direction of the tubular film toward each other from the remote position to an intermediate position. In a second step, the gripping fingers are rotated in the gripping plane toward each other from the intermediate position to the clamping position, in which the tubular film is clamped between the gripping fingers. The gripping fingers then move linearly in the gripping plane to stretch the clamped tubular film. Due to the rotational movement of the gripping fingers, a smooth transition between clamping and stretching is enabled. The inventive method eliminates the need to separate the clamping and stretching steps and wait for a start signal, indicating that the tubular film is clamped, before stretching the tubular film.Preferably, the stretching unit releases the tubular film when the tubular film is transversely sealed. Preferably, to release the tubular film, in a third step, the gripping fingers are rotated in the gripping plane away from each other from the clamping position to the intermediate position, in which the tubular film is released. Preferably, the gripping fingers move linearly in the gripping plane opposite to the linear movement of the gripping fingers in the first step. Preferably, the gripping fingers are rotated away from each other from the intermediate position to the remote position in a fourth step. Preferably, the third step follows the second step. Preferably, the fourth step follows the third step. Preferably, the tubular film is not held between the gripping fingers in the remote and intermediate positions. This advantageously allows the tubular film to pass through the stretching unit without risk of damage. According to a preferred embodiment of the invention, rotation of the gripping fingers in the gripping plane and extension are caused by relative movement between the gripping head and the moving means parallel to a central axis of the moving means. Preferably, the relative movement between the gripping head and the moving means parallel to a central axis of the moving means causes relative movement of the first rotary joints and the second rotary joints, by which rotation of the gripping fingers is produced. Preferably, the gripping head is moved by an electric motor, a linear motor, or more preferably a linear servomotor. Preferably, the moving mechanism is driven by a pneumatic cylinder. With a linear motor, the stretching action can be controlled with extreme precision. The position of the gripping head, driven by a linear motor (preferably a linear servo motor), is always known without the need for an additional sensor. Furthermore, the linear motor allows for the application of high forces and prevents slippage. Because the linear motor can be precisely controlled, the stretching force can be adjusted to the properties of the tubular film material and / or different bag shapes. The linear motor also prevents tearing of the tubular film. Preferably, the driving force of the electric motor and / or linear motor and / or linear servomotor is controlled according to the material properties and / or the geometry of the tubular film. This makes it advantageous to adapt the stretching force to an optimal level, ensuring that the tubular film is stretched correctly and preventing it from tearing. Preferably, in the second step, the movement of the gripping head in the second direction is limited, specifically by a specific path setting of the electric motor and / or linear motor and / or linear servomotor. This prevents the tubular film from tearing. The position of the gripping head is preferably determined by the status of the electric motor and / or linear motor and / or linear servomotor. Preferably, the path setting is adapted to the material properties and / or the geometry of the tubular film. Preferably, during the second step, the movement of the gripping head is limited, and more preferably, the movement of the gripping head is limited in the second direction. Preferably, the movement is limited by a maximum force / torque setting of the electric motor and / or linear motor and / or linear servomotor. As soon as this maximum setting is reached, the movement stops. Other details, features, and advantages of the present invention are described by the figures and by the following description of preferred embodiments based on the figures. The figures only illustrate exemplary embodiments of the present invention, which do not restrict the essential idea of ​​the invention. Brief Description of the Figures Figure 1 schematically illustrates a flow enclosure device in accordance with a preferred embodiment of the present invention. Figures 2A-2C schematically illustrate a gripping unit according to a preferred embodiment of the present invention and a method according to a preferred embodiment of the present invention. Figure 3 schematically illustrates a gripping unit in accordance with a preferred embodiment of the present invention. Detailed Description of the Invention In the different figures, the same parts are always provided with the same reference symbols and are therefore generally named or mentioned only once. In Figure 1, the flow wrapping device 1 according to the invention is shown schematically. A flow wrapping device 1 is a packaging machine that forms a roll of flat film 4 into a tubular film 4, which is conveyed along a filling and molding tube 2. The two ends of this tubular film 4 are joined by sealing them with a longitudinal sealing means 5. Subsequently, the item to be packaged is filled into the tubular film 4, and a transverse seal is applied to the tubular film 4 to close the package. Simultaneously or after applying the transverse seal, the finished packages 7 are separated by cutting the tubular film 4. The flow wrapping device 1 comprises a frame / box 8, in which a forming flange 3, a filling and molding tube 2, longitudinal sealing means 5, and transverse sealing means 6 are provided.The flow-enveloping device 1 may comprise gas-forming means to form the bottom and / or top portion of each package. A roll of film 4, especially a weldable plastic film 4, is supplied from a reel 9, which continuously or intermittently supplies the flat film 4 to a forming flange 3, which forms the film roll 4 into a more or less tubular shape around a filling and molding tube 2. In the context of the present invention, a tubular shape of the packages 7 or of the film 4 means any cross-sectional shape, including a circular or other shape, and especially a rectangular or generally polygonal shape. Longitudinal sealing means 5, provided downstream of the forming flange 3, seal together the edges of the tubular film 4. After sealing, the bottom of the package 7 can be formed by a special bottom-forming means, for example, gas-forming means.Finally, transverse seals are applied, preferably extending perpendicular to the flow direction of the tubular film 4, specifically by means of transverse sealing means 6. These transverse sealing means 6 apply to the package 7 not only an upper / second transverse seal that closes the top of the package 7, but also advantageously provide, preferably simultaneously, a lower / first transverse seal that defines the bottom of the subsequent package 7. The produced packages 7 are separated from one another by a cutting means 6, which is preferably incorporated into the transverse sealing means 6. Between the application of the lower and upper transverse seals to each package 7, the package 7 is filled with the product.Before the cross seal is applied, the package 7 / tubular film 4 is clamped and stretched by an area Lnn / zznz / E / YiAi stretching unit 10. Stretching the tubular film 4 allows the tubular film 4 to be laid flat in the transverse sealing means 6, which is crucial for a straight and airtight transverse seal. Figures 2A-2C schematically illustrate a gripping unit 10 according to a preferred embodiment of the present invention and a method according to a preferred embodiment of the present invention. Figure 2A illustrates the gripping unit 10 in a remote position A. The preferably rubber-coated and / or textured gripping surfaces 17 of the gripping fingers 16 are not in contact with each other and provide sufficient space to place a tubular film 4 between the gripping surfaces 17 and transport the tubular film 4 in a transport direction T. When the tubular film 4 is disposed between the gripping surfaces 17 of the gripping fingers 16, a first drive means (see Figure 3) moves the drive means 12 in a first direction DI along the central axis H of the drive means 12 relative to the gripping head 14. The drive means 12 is provided here as a driven rod.The first means of actuation is provided here as a pneumatic Lnn / zznz / E / YiAi cylinder. Here, the gripping head 14 partially encloses the coupling rods 15, which are rotatably connected to the movement means 12. The gripping fingers 16 are rotatably connected to the gripping head 14 at the first pivot points 18 and rotatably connected to the coupling rods 15 at the second pivot points 19. Due to the relative motion between the coupling rods 15 and the gripping head 14, the gripping fingers 16 rotate about the first pivot points 18 in a gripping plane G from the remote position A to the intermediate position B. Figure 2B shows the gripping fingers 16 already rotated in the gripping plane G due to the movement of the moving means 12 relative to the gripping head 14 in the first direction DI to the intermediate position B. The gripping surfaces 17 have moved towards each other, but are still separated, so that the tubular film 4 is not held between the gripping fingers 16, but preferably in the immediate vicinity of the tubular film 4. The position of the stretching unit 10 shown here is the intermediate position B. In this position, the moving means 12 has preferably reached a mechanical stop (not shown here, see Figure 3), which prevents further movement of the moving means 12 in the first direction DI. After the gripping fingers have reached the intermediate position B, the gripping head 14 moves in the second direction D2, which is opposite but parallel to the first direction DI, by means of a second drive means (see Figure 3). The second drive means is preferably a linear motor, preferably a servomotor, and is connected to the gripping head 14 by means of an additional drive means 3. The additional drive means 3 is a tube that is arranged parallel to the central axis H of the drive means 12 and preferably coaxial to the means 12, more preferably so that it partially encloses the drive means 12. The movement of the gripping head 14 in the second direction D2 relative to the movement means 12 causes the gripping fingers 16 to rotate further until the tubular film 4 is held between the gripping surfaces 17, as shown in Figure 2C. Figure 2C shows the stretching unit 10 in clamping position C. The tubular film 4 is held between the gripping fingers 16. To stretch the held tubular film 4, the gripping head Lnn / zznz / E / YiAi moves further in the second direction D2. Overall, this results in a smooth clamping and stretching process of the tubular film 4, leading to a significant increase in efficiency. Furthermore, since the first and second drive means produce forces that are relatively antiparallel to each other, the gripping unit 10 operates with balanced forces, advantageously extending its service life. Preferably, the tubular film 4 is released when the tubular film 4 is transversely sealed, i.e., when the transverse sealing means (see Figure 1) is attached to the tubular film 4 for transverse sealing. Preferably, to release the tubular film 4, the gripping head 14 is moved in the first direction DI by the second drive means. Preferably, the movement means 12 is fixed in its position, such that the movement of the gripping head 14 is relative to the drive means 12. Preferably, the first drive means is used to fix the movement means 12 in its position. Here, the movement of the gripping head 14 in the first direction DI relative to the movement means 12 causes the gripping fingers 16 to rotate away from each other. Preferably, the stretching unit 10 moves from the clamping position C to the intermediate position B.Preferably, the movement means 12 move in the second direction D2 relative to the gripping head 14, leading to an additional rotation of the gripping fingers 16, moving them further apart. This preferably moves the stretching unit from the intermediate position B to the remote position A. Figure 3 schematically illustrates a gripping unit 10 according to a preferred embodiment of the present invention. In this illustration, the first actuating means 21 and the second actuating means 20 are shown. Here, the first actuating means 21 is a pneumatic cylinder and the second actuating means 20 is an electric linear servomotor. This has the advantage that the gripping and stretching movement can be carried out very quickly, powerfully, and precisely. In contrast to actuating the gripping unit 10 solely with pneumatic cylinders, it is not necessary to install any separate additional sensor to detect the spatial position of the gripping fingers 16. On the left and in the center of the gripping unit 10, the clamping devices for securing the gripping unit 10 in a flow-enveloping device are visible (see Figure 1). Figure 3 further shows the mechanical stop 22.The mechanical stop 22 limits the movement of the moving means 12 towards the tubular film. Here, the mechanical stop 22 consists of two flanges. When the moving means 12 moves along its central axis, one flange of the mechanical stop 22 moves. The other flange of the mechanical stop 22 is fixed. The movement of the moving means 12 is limited by the contact of the two flanges. Preferably, the position of the mechanical stop 22 can be adjusted to adapt the stretching unit 10 to different sizes and geometries of the tubular film. Reference symbols Flow envelope device Filling and molding tube Forming flange Film / tubular film Longitudinal sealing medium Transverse sealing medium and / or cutting medium Package / Bag Frame / Box Reel area Lnn / zznz / E / YiAi Grip unit Means of movement Additional means of movement Grip head Tie rod Grip finger Grip surface First pivot point Second pivot point Second means of actuation First means of actuation Mechanical stop Remote Position B Intermediate position C Clamping position DI First direction D2 Second direction G Grip plane H Central axis T Transport Directorate It is hereby stated that, as of this date, the best method known to the applicant to implement the aforementioned invention is the one that is clear from the present description of the invention.

Claims

Having described the invention as above, the following claims are claimed as property:

1. Stretching unit for holding and stretching a tubular film in a flow wrapping device, comprising: - a gripping head; - two coupling rods attached to a moving means; - two gripping fingers, each gripping finger attached to the gripping head and a coupling rod; characterized in that the gripping fingers move from a remote position to a clamping position by means of a relative linear movement between the gripping head and the moving means parallel to a central axis of the moving means.

2. A stretching unit according to claim 1 or the preamble of claim 1, characterized in that the gripping fingers are moved from a remote position to a gripping position by a rotational movement of the gripping fingers.

3. A stretching unit according to any of the preceding claims, characterized in that each gripping finger is attached to the gripping head by a first pivot point and each gripping finger is attached to the coupling rods by a second pivot point, wherein a relative linear movement between the gripping head and the movement means results in a rotational movement of the gripping fingers.

4. Stretching unit according to any of the preceding claims, characterized in that the movement means is attached to a first drive means, wherein the first drive means is preferably a pneumatic cylinder.

5. Stretching unit according to any of the preceding claims, characterized in that the gripping head is connected to a second drive means, wherein the second drive means is preferably an electric motor, more preferably a linear motor, and even more preferably a linear servomotor.

6. A stretching unit according to any of the preceding claims, characterized in that the drive means is provided as a driven rod and / or in which the gripping head is attached to the second drive means by way of an additional drive means, wherein the additional drive means is preferably a tube, the tube preferably being arranged parallel to the drive means and at least partially coaxial with the drive means.

7. Stretching unit according to any of the preceding claims, characterized in that a movement of the movement means along the central axis thereof is limited by a mechanical stop.

8. Flow wrapping device, characterized in that it comprises a stretching unit in accordance with any of the preceding claims.

9. A method for clamping and stretching a tubular film in a flow-enveloping device using a stretching unit, preferably according to any of the preceding claims, characterized in that: - in a first step, a moving means of the stretching unit moves relative to a gripping head of the stretching unit in a first direction, preferably towards the tubular film, and thereby moves the gripping fingers from the remote position to an intermediate position; - in a second step, the gripping head moves relative to the moving means in a second direction, which is opposite to the first direction, and thereby moves the gripping fingers from the intermediate position to the clamping position and thereby clamps the tubular film; wherein the tubular film is stretched by a further movement of the gripping head in the second direction.

10. A method for clamping and stretching a tubular film in a flow wrapping device using a stretching unit, preferably according to any one of claims 1 to 8, characterized in that: in a first step, the gripping fingers are rotated in a gripping plane orthogonal to a transport direction of the tubular film relative to each other from the remote position to an intermediate position; in a second step, the gripping fingers are rotated in the gripping plane relative to each other from the intermediate position to the clamping position, wherein the tubular film is clamped between the gripping fingers, the gripping fingers being moved linearly in the gripping plane to stretch the clamped tubular film.

11. Method according to claim 9 or 10, characterized in that the tubular film is not held between the gripping fingers in the remote and intermediate positions.

12. Method according to any of claims 9 to 11, characterized in that a rotation of the gripping fingers in the gripping plane and the stretching is caused by a relative movement between the gripping head and the movement means parallel to a central axis of the movement means.

13. Method according to any of claims 9 to 12, characterized in that the gripping head is moved by an electric motor, a linear motor, more preferably a linear servomotor and / or in which the means of movement is moved by a pneumatic cylinder.

14. Method according to claim 13, characterized in that the driving force of the electric motor and / or linear motor and / or linear servomotor is controlled based on material properties and / or a tubular film geometry.

15. Method according to any of claims 9 to 14, characterized in that the second step the movement of the gripping head in the second direction is limited, wherein the movement of the gripping head in the second direction is preferably limited by an adjustment of the path of the electric motor and / or the linear motor and / or the linear servomotor.

16. Method in accordance with any of claims 9 to 14, characterized in that the second step limits the movement of the gripping head.

17. Method according to claim 16, characterized in that the movement of the gripping head is limited in the second direction.

18. Method in accordance with any of claims 16 or 17, characterized in that the movement is limited by a maximum driving force / torque adjustment of the electric motor and / or linear motor and / or linear servomotor.

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