Conveying device for conveying products

Abstract

The invention relates to a conveying device (1) for conveying products (e.g. food products), the conveying device comprising: a planar motor drive system for conveying the products contactlessly over a planar conveying surface; and a sheet-like cover (12) on the conveying surface of the planar motor drive system, wherein the cover (12) separates the planar motor drive system from the products and protects the planar motor drive system from contamination by the products. According to the invention, the cover (12) is an elastic cover film (12).

Description

[0001] DESCRIPTION

[0002] Conveyor system for conveying products

[0003] Technical field of the invention

[0004] The invention relates to a conveying device for conveying products (e.g., food products). Furthermore, the invention relates to the novel use of an elastic cover film for covering a conveying surface of a planar motor drive system in such a conveying device.

[0005] Background of the invention

[0006] In food processing plants for processing food products (e.g. cheese, sausage, meat), the food products are usually transported by conveyor belts along a processing line between different processing stations, where the food products are, for example, scanned, weighed, cut, formatted, buffered and packaged.

[0007] In a more recent development (e.g., DE 10 2021 105 105 Al), a conveying system with a planar motor drive is used instead of conveyor belts to transport the food products. For example, the planar motor drive system marketed by the German company Beckhoff Automation GmbH under the product name XPianar™ can be used. In this system, the products to be conveyed are placed on a conveying carrier, which, according to the relevant technical terminology, is also referred to as a "mover" or "shuttle." The conveying carrier with the food products arranged on it (e.g., stacks of cheese slices) is then moved by the planar motor drive system without contact across a flat conveying surface, with the conveying path of the carrier on the surface being freely programmable.To prevent contamination of the planar motor drive system and its internal components, it is also known to separate the conveying surface of the planar motor drive system from the products by means of a cover. The aforementioned company, Beckhoff Automation GmbH, offers a rigid stainless steel plate with a thickness of 0.5 mm for this purpose, which is mounted on the conveying surface of the planar motor drive system. However, this known technical solution for covering the conveying surface of the planar motor drive system has several disadvantages, which are briefly described below.

[0008] A disadvantage of the well-known method of covering the conveying surface with a stainless steel plate is its insufficient flexibility under temperature fluctuations and local heat sources in the machine components of the planar motor drive system. This leads to unevenness and waviness in the stainless steel plate. In extreme cases, this thermally induced unevenness or waviness can even result in material-abrasive sliding contact between the underside of the conveying carrier ("mover") and the unevenness on the top of the stainless steel plate, which must be prevented.

[0009] Another disadvantage of the thermally induced unevenness of the stainless steel plate is that depressions form on the top surface of the stainless steel plate, which leads to additional effort when cleaning the stainless steel plate.

[0010] Furthermore, the stainless steel plate offers limited serviceability for replacing defective components. For example, the planar motor drive system typically consists of several rectangular tiles that can be individually replaced in case of a malfunction, but this is made more difficult by the stainless steel plate.

[0011] Finally, stainless steel plates are only of limited use in applications with higher hygiene requirements, such as in the production of food products or pharmaceuticals.

[0012] Description of the invention

[0013] The invention is therefore based on the objective of creating a correspondingly improved conveying device that avoids the aforementioned disadvantages as far as possible.

[0014] This problem is solved by a conveying device according to the invention and the main claim.

[0015] The conveying device according to the invention is generally suitable for conveying products. Preferably, however, the conveying device according to the invention is designed to convey food products, such as stacks of cheese slices or sausage slices. However, the invention is not limited to food products with regard to the products to be conveyed, but is also suitable, for example, for conveying pharmaceutical products, to name just one further example. The term "products" used within the scope of the invention is therefore not limited to the examples mentioned above. Furthermore, the principle of a cover film according to the invention can also be implemented when using the conveying device within a packaging machine.

[0016] In accordance with the prior art described above, the conveying device according to the invention also features a planar motor drive system for conveying the products contactlessly on a flat conveying surface. For example, this could be the planar motor drive system marketed by the German company Beckhoff Automation GmbH under the product name XPianar™. Alternatively, the planar motor drive system could be the system marketed by the German company Bosch Rexroth AG under the product name ctrIX FLOW6D®. However, the invention is not limited to these specific types of planar motor drive systems, but can also be implemented with other types of planar motor drive systems.

[0017] The conveying device according to the invention, in accordance with the prior art described above, has a flat cover on the conveying surface of the planar motor drive system, wherein the cover separates the planar motor drive system from the products to be conveyed and protects it from contamination by the products. Therefore, when cleaning the planar motor drive system, only the top surface of the flat cover needs to be cleaned, whereas the internal machine parts of the planar motor drive system are protected from contamination during operation and therefore do not need to be cleaned.

[0018] The invention is characterized by the fact that the cover is not a stainless steel plate, but an elastic cover film. This makes it possible to stretch the cover film elastically over the conveying surface of the planar motor drive system. The elastic tensioning of the cover film over the conveying surface allows for compensation of temperature fluctuations and the corresponding differences in thermal expansion of the cover film on the one hand and the surrounding frame on the other, so that the cover film always lies smoothly on the conveying surface and does not form any waves or unevenness. The elastic tensioning of the cover film on the conveying surface of the planar motor drive system thus prevents material-abrasive sliding contact between the underside of the conveying carrier ("mover") and the cover film.

[0019] Furthermore, the elastic tensioning of the cover film on the conveying surface of the planar motor drive system also prevents the disruptive trough formation on the surface of the cover that occurs with the state of the art, thereby reducing the effort required for the maintenance of the conveying equipment.

[0020] In a preferred embodiment of the invention, the conveying surface of the planar motor drive system is rectangular and has two opposite narrow sides and two opposite long sides. The long sides are preferably longer than the narrow sides, but it is also possible for the conveying surface to be square, in which case the long sides and the narrow sides are of equal length.

[0021] Firstly, the cover film is elastically spring-fixed to the opposite narrow sides of the conveying surface in order to elastically tension the cover film between the opposite narrow sides of the conveying surface.

[0022] Secondly, the cover film is also elastically spring-fixed to the opposite longitudinal sides of the conveying surface in order to elastically tension the cover film between the opposite longitudinal sides of the conveying surface.

[0023] The cover film is therefore preferably elastically tensioned both longitudinally (i.e., parallel to the long sides of the conveying surface) and transversely (i.e., parallel to the short sides of the conveying surface). This is advantageous because elastic tensioning in only one direction could lead to an undesirable sagging of the cover film, meaning the cover film would then taper in the middle with respect to the tension direction and would no longer be rectangular.

[0024] The elastic fixation of the cover film to the opposite narrow sides of the conveying surface is preferably achieved by a clamping strip on each side, aligned parallel to the respective narrow side of the conveying surface. The cover film is clamped in the opposing clamping strips, preferably across its entire width. This is advantageous because the clamping force for tensioning the cover film is thus distributed evenly across its entire width and introduced into the cover film. The actual elastic tension between the opposite narrow sides of the conveying surface is achieved by at least one first spring element that engages the respective clamping strip. This spring element can be, for example, an expansion bolt or a spring (e.g., a coil spring) that engages the respective clamping strip.In the preferred embodiment of the invention, four helical springs are provided which engage the associated clamping strip to tension the cover film, wherein the four helical springs are arranged equidistantly distributed over the length of the clamping strips.

[0025] For mechanically tensioning the cover film between the opposite narrow sides of the conveying surface of the planar motor drive system, a shaped piece is preferably arranged on each of the opposite narrow sides of the conveying surface. This shaped piece has a quarter-circle cross-section, thus forming a rounded guide surface over which the cover film is guided. For example, the rounded guide surface can have a radius of curvature of at least 2 mm, 5 mm, 1 cm, 2 cm, or 5 cm to prevent the cover film from kinking when guided over the rounded guide surface. On the inner side of each shaped piece, the rounded conveying surface preferably runs horizontally, while on the outer side of each shaped piece, the rounded conveying surface preferably runs vertically downwards. The shaped pieces thus convert a force from the first spring element (e.g.,The tension force (extending from the coil spring and directed vertically downwards) is converted into a horizontally directed tension force on the cover film.

[0026] The mechanical tensioning of the elastic cover film between the opposing longitudinal sides of the conveying surface of the planar motor drive system is preferably achieved differently by means of at least one clamping element for clamping the cover film to the opposing longitudinal sides of the conveying surface. Preferably, several clamping elements are provided, which are distributed along the longitudinal sides of the conveying surface, preferably equidistantly. In the preferred embodiment of the invention, four such clamping elements are provided on each longitudinal side of the conveying surface. The cover film is clamped at several separate force application points in the opposing clamping elements.In contrast to mechanical tensioning at the narrow sides of the conveying surface, the force is not applied evenly across the entire width of the cover film, but only at the separate force application points on the clamping pieces. The actual clamping force is applied by at least one second spring element (e.g., a coil spring) acting on each of the clamping pieces. This second spring element (e.g., a coil spring) preferably acts in a vertical direction, with the clamping pieces converting the vertically oriented clamping force of the second spring element into a horizontally oriented clamping force on the cover film.

[0027] It has already been mentioned above that the second spring element for the mechanical preloading of the clamping pieces is preferably a helical spring. However, the invention is not limited to helical springs with regard to the type of second spring element.

[0028] The preceding description of the elastic tensioning of the cover film on the conveying surface of the planar motor drive system shows that the tensioning between the opposite narrow sides of the conveying surface differs from the tensioning between the opposite long sides of the conveying surface. When tensioning between the opposite narrow sides of the conveying surface, the tensioning force is preferably distributed evenly across the entire width of the cover film and introduced into the film. In contrast, when elastically tensioning the cover film between the opposite long sides of the conveying surface, the tensioning force is preferably introduced only at the separate force application points located at the clamping elements.

[0029] A preferred embodiment of the conveying device according to the invention has been described above, in which clamping is carried out by means of the clamping pieces on the longitudinal sides of the conveying surface, while clamping is carried out by means of the clamping strips on the narrow sides of the conveying surface. However, a reverse arrangement is also possible within the scope of the invention, in which clamping is carried out by means of the clamping pieces on the narrow sides of the conveying surface, while clamping is carried out by means of the clamping strips on the longitudinal sides of the conveying surface.

[0030] Furthermore, it should be mentioned that the conveying surface of the planar motor drive system is preferably surrounded by a circumferential sealing frame, with the cover film sealingly abutting the circumferential sealing frame.

[0031] Generally speaking, the cover film is preferably very thin to minimize the attenuation of the magnetic field generated by the planar motor drive system. Therefore, the thickness of the cover film is preferably no more than 1 mm, 0.5 mm, 0.25 mm, or 0.15 mm. The cover film is preferably so thin that the magnetic field generated by the planar motor drive system is attenuated by less than 10%, 5%, 2%, or even less than 1%. However, the cover film should preferably have a thickness of at least 0.15 mm. Furthermore, the cover film is preferably made of plastic or stainless steel, for example, a chromium-nickel alloy such as an iron-chromium-nickel-molybdenum alloy (e.g., X2CrNiMol7-12-2). Firstly, this choice of material for the cover film is advantageous because the magnetic field of the planar motor drive system is only slightly weakened by the cover film.On the other hand, this choice of material also offers the advantage that the cover film hardly corrodes and is easy to clean.

[0032] Furthermore, it should be mentioned that the conveying surface is preferably surrounded by a support frame, which can be made, for example, of aluminum or an aluminum alloy. The support frame and the cover film are preferably made of materials with different coefficients of thermal expansion, namely, for example, aluminum for the support frame and stainless steel for the cover film. This means that the support frame and the cover film expand to different degrees in response to the temperature fluctuations that occur during operation. The cover film is elastically tensioned within the support frame, with this elastic tension compensating for the different thermal expansion rates of the materials of the support frame and the cover film.

[0033] Furthermore, it should be noted that the conveying surface of the planar motor drive system is preferably composed of several rectangular tiles, as is also the case in the prior art described above. However, in the conveying device according to the invention, the individual tiles of the planar motor drive system can preferably be replaced from below without first removing the cover film. It should also be noted that the individual tiles of the planar motor drive system do not necessarily have to be rectangular. Rather, the conveying surface of the planar motor drive system can also be composed of tiles of other shapes.

[0034] The products to be conveyed are preferably arranged on a conveying carrier ("mover") which, together with the product to be conveyed (e.g., a stack of sausage slices), is movable without contact above the conveying surface, particularly at a suspension height of 1 mm to 5 mm above the conveying surface. Furthermore, it should generally be noted that the conveying carrier preferably has a load-bearing capacity of at least 100 g, 200 g, 500 g, 1 kg, or at least 2 kg.

[0035] Finally, the invention also claims protection for the novel use of an elastic cover film for covering a conveying surface of a planar motor drive system in a conveying device for conveying products (e.g. food products), wherein the cover film is preferably stretched elastically over the conveying surface of the planar motor drive system.

[0036] Other advantageous embodiments of the invention are characterized in the dependent claims or are explained in more detail below together with the description of the preferred embodiment of the invention with reference to the figures.

[0037] Brief description of the drawings

[0038] Figure 1 shows a perspective view of a conveying device according to the invention with a planar motor drive system and a cover film for covering the conveying surface of the planar motor drive system.

[0039] Figure 2 shows a perspective view of the conveying device from Figure 1, with the cover film removed.

[0040] Figure 3 shows an enlarged detail view of detail Y from Figure 2.

[0041] Figure 4 shows a detailed view of the cover film with two clamping strips.

[0042] Figure 5 shows a perspective view of the planar motor drive system without the cover film.

[0043] Figure 6 shows an enlarged perspective view of detail X from Figure 5.

[0044] Figure 7 shows a side view of a conveying material carrier (“mover”) of the conveying device according to the invention.

[0045] Detailed description of the drawings

[0046] The following describes an embodiment of a conveying device 1 according to the invention, as illustrated in the drawings, which serves to convey food products, such as stacks of sausage slices or cheese slices. The conveying device according to the invention partially corresponds to the known conveying device already mentioned at the outset, as described in patent application DE 102021105105 Al. To avoid repetition, reference is therefore made to this patent application.

[0047] The conveyor device 1 according to the invention comprises a planar motor drive system 2, which is shown in particular in Figures 2 and 5. The planar motor drive system 2 is a system known per se, which is marketed by the German company Beckhoff Automation GmbH under the product name XPianar™.

[0048] On its upper surface, the planar motor drive system 2 has a flat and horizontally oriented conveying surface 3, which is composed of numerous square tiles 4. A conveying carrier 5 can be conveyed contactlessly on the conveying surface 3. The conveying carrier 5 is also commonly referred to as a "mover" or "shuttle" and is shown individually in Figure 7. The conveying carrier 5 has numerous matrix-like pins 6 on its upper surface, which project vertically upwards and form a loading surface for receiving a food product 7 with their upper end faces. The food product 7 is shown only schematically here. The food product 7 could, for example, be a stack of sausage slices or cheese slices.The conveying surface 3 of the planar motor drive system 2 is rectangular with two opposite long sides 8, 9 and two opposite short sides 10, 11.

[0049] The conveying surface 3 of the planar motor drive system 2 is covered on its upper side by an elastic cover film 12, which prevents contamination of the planar motor drive system 2 by the food products 7. The elastic cover film 12 is elastically tensioned in a support frame 13 between both the opposite longitudinal sides 8, 9 of the conveying surface 3 and between the opposite narrow sides 10, 11 of the conveying surface 3. The elastic tensioning of the cover film 12 in the support frame 13 is advantageous because the cover film 12 and the support frame 13 are made of different materials and therefore have different coefficients of thermal expansion. The support frame 13 is made of aluminum, while the cover film 12 is made of the stainless steel X2CrNiMol7-12-2. Therefore, when heated during operation, the cover film 12 expands differently than the support frame 13 due to thermal expansion.The elastic tensioning of the cover film 12 in the support frame 13 ensures that, despite these differing thermal expansions, the cover film 12 always lies flat on the upper surface of the conveying surface 3. This prevents unevenness in the cover film 12 from causing abrasive contact between the underside of the conveying carriers 5 and the upper surface of the cover film 12. Furthermore, the elastic tensioning of the cover film 12 also prevents the formation of a trough on the upper surface of the cover film 12, which is problematic in prior art designs, thus minimizing cleaning requirements.

[0050] The elastic tensioning of the cover film 12 in the opposite narrow sides 10, 11 of the conveying surface 3 will now be described.

[0051] On the opposite narrow sides 10, 11 of the conveying surface 3 are shaped pieces 14, 15, which form a quarter circle in cross-section, as can be seen particularly clearly in the detailed view in Figure 3. The shaped pieces 14 thus form a rounded guide surface for the cover film 12, preventing the cover film 12 from kinking. The cover film 12 is therefore guided over the rounded guide surface formed by the two shaped pieces 14, 15 on the opposite narrow sides 10, 11 of the conveying surface 3. To prevent the cover film 12 from kinking, the guide surface of the shaped pieces 14, 15 each has a radius of curvature of R = 5 mm. On the outer sides of the guide pieces 14, 15, the guide surface is oriented vertically, while on their inner sides, the guide surface of the shaped pieces 14, 15 is oriented horizontally.

[0052] Furthermore, it should be mentioned that the cover film 12 is clamped at opposite narrow sides 10, 11 in clamping strips 16, 17, uniformly across the entire width of each clamping strip 16, 17. The clamping strips 16, 17 serve to introduce the elastic tension force into the cover film 12. Clamping the cover film 12 along the entire length of the clamping strips 16, 17 has the advantage that the elastic tension force is applied uniformly across the entire width of the cover film 12 at the narrow sides 10, 11 of the conveying surface 3, so that the cover film 12 is evenly tensioned at the narrow sides 10, 11 of the conveying surface 3.

[0053] The clamping strips 16, 17 are each held in a yoke 18, as can be seen particularly in Figure 3. The yoke 18 is in turn pulled downwards by several coil springs 19. The coil springs 19 thus generate a vertically oriented clamping force on the yoke 18 and therefore also on the clamping strip 17. This vertically oriented clamping force is then converted by the curved guide surface of the molded parts 14, 15 into a horizontally oriented clamping force, which acts on the cover film 12 and elastically clamps it between the opposite narrow sides 10, 11 of the conveying surface 3. The elastic clamping of the cover film 12 between the opposite long sides 8, 9 of the conveying surface 3 will now be described.

[0054] Four clamping pieces 20 on each side serve this purpose, clamping the cover film 12 laterally at several spatially separated force application points. A helical spring 21 acts on each of the individual clamping pieces 20, the helical springs 21 being oriented substantially vertically, as can be seen particularly in Figure 6. The helical springs 21 are each anchored at their lower end in an abutment 22. The clamping pieces 20 convert the substantially vertically oriented tension force of the helical springs 21 into a horizontally oriented tension force, which acts on the cover film 12 and elastically tensions it between the opposite longitudinal sides 8, 9.

[0055] The cover film 3 is thus stretched in two directions: firstly in the longitudinal direction (i.e., between the opposite narrow sides 10, 11) and secondly in the transverse direction (i.e., between the opposite long sides 8, 9). The tension between the opposite long sides 8, 9 prevents the tension between the opposite narrow sides 10, 11 from forming a waist in the cover film 12, i.e., an undesirable narrowing of the cover film 12 between the opposite narrow sides 10, 11.

[0056] Furthermore, it should be mentioned that the support frame 13 also forms a circumferential sealing surface 23 on the inside, against which the cover film 12 rests in a sealing manner. This seal prevents the ingress of liquid into the lower area where electronic components are housed. For the sake of simplicity, the sealing frame 23 is shown in the drawing only as a dashed line to facilitate understanding.

[0057] Furthermore, it should be mentioned that the individual tiles 4 of the planar motor drive system 2 can be replaced individually. The replacement of the individual tiles 4 of the planar motor drive system 2 is possible from below. This is advantageous because it eliminates the need to remove the cover film 12 to replace one of the tiles 4.

[0058] The invention is not limited to the preferred embodiment described above. Rather, the invention also includes variants and modifications that likewise make use of the inventive concept and therefore fall within the scope of protection. In particular, the invention also claims protection for the subject matter and the features of the dependent claims independently of the respective referenced claims and, in particular, also without the features of the main claim. The invention thus comprises various aspects of the invention that enjoy independent protection.

[0059] Advantages of the invention

[0060] The invention offers several advantages, which are briefly summarized below. One advantage is that, due to its elastic tension over the conveying surface, the elastic cover film compensates for differing thermal expansions of the conveying surface of the planar motor drive system on the one hand and the support frame for the cover film on the other, so that the cover film always lies flat on the conveying surface. This prevents disruptive trough formation on the upper surface of the cover film. It also prevents material-abrasive sliding contact between the underside of the conveying carriers and the upper surface of the cover film.

[0061] • In contrast to the known cover in the form of a stainless steel plate, the cover film according to the invention shields the magnetic field of the planar motor drive system less strongly.

[0062] • The conveying device according to the invention is particularly service-friendly, since the individual tiles of the planar motor drive system can be replaced without prior dismantling of the cover film.

[0063] • The conveying device according to the invention is particularly suitable for use in areas with high hygiene requirements, such as food processing.

[0064] Reference symbol list

[0065] 1 funding facility

[0066] 2 Planar motor drive system of the conveyor system

[0067] 3 Conveyor area of ​​the planar motor drive system

[0068] 4 tiles of the conveying surface of the planar motor drive system

[0069] 5 conveying carriers (“mover”)

[0070] 6 pins on the top of the conveyor carrier

[0071] 7 Food product 8, 9 Long sides of the conveying surface

[0072] 10, 11 Narrow sides of the conveying surface

[0073] 12 Cover film for covering the conveying area

[0074] 13 support frames

[0075] 14, 15 Fittings on the narrow sides of the conveying surface with rounded guide surface 16, 17 Clamping strips on the narrow sides of the conveying surface for clamping the cover film 18 Yoke on the narrow sides of the conveying surface for tensioning the clamping strips

[0076] 19 coil springs for tensioning the clamping strips using the yoke

[0077] 20 clamping pieces on the opposite long sides of the conveyor surface for clamping the cover film.

[0078] 21 coil springs for mechanically pre-tensioning the clamping pieces

[0079] 22 Abutments for the coil springs for mechanical preloading of the clamping pieces 23 Sealing surface

[0080] R Radius of curvature of the guide surface of the molded parts

Claims

REQUIREMENTS 1. Conveying device (1) for conveying products (7), in particular for conveying food products (7), with a) a planar motor drive system (2) for contactless conveying of the products (7) on a flat conveying surface (3), and b) a flat cover (12) on the conveying surface (3) of the planar motor drive system (2), wherein the cover separates the planar motor drive system (2) from the products (7) and protects it from contamination by the products (7), characterized by c) that the cover (12) is an elastic cover film (12).

2. Conveying device (1) according to claim 1, characterized in that the cover film (12) is elastically stretched over the conveying surface (3) of the planar motor drive system (2).

3. Conveying device (1) according to one of the preceding claims, characterized in that a) the conveying surface (3) is rectangular with two opposite narrow sides (10, 11) and two opposite long sides (8, 9), wherein the long sides (8, 9) are preferably longer than the narrow sides (10, 11), b) that the cover film (12) is elastically spring-fixed to the opposite narrow sides (10, 11) of the conveying surface (3) in order to elastically tension the cover film (12) between the opposite narrow sides (10, 11) of the conveying surface (3), and / or c) that the cover film (12) is elastically spring-fixed to the opposite longitudinal sides (8, 9) of the conveying surface (3) in order to elastically tension the cover film (12) between the opposite longitudinal sides (8, 9) of the conveying surface (3).

4. Conveying device according to claim 3, characterized in that, a) that a clamping strip (16, 17) is arranged on each of the opposite narrow sides (10, 11) of the conveying surface (3), wherein the two clamping strips (16, 17) are aligned parallel to the narrow sides (10, 11) of the conveying surface (3), b) that the cover film (12) is clamped in the opposing clamping strips (16, 17), preferably over the entire width of the cover film (12) in the clamping strips (16, 17), c) that the opposing clamping strips (16, 17) are mechanically pre-tensioned by at least one first spring element (19) in order to elastically stretch the cover film (12) between the opposing narrow sides (10, 11) over the conveying surface (3).

5. Conveying device (1) according to claim 4, characterized in that the at least one first spring element (19) for mechanical pretensioning of the opposing clamping strips (16, 17) is an expansion screw or a spring (19), in particular a coil spring (19).

6. Conveying device (1) according to one of claims 3 to 5, characterized in that a) the cover film (12) is guided over a molded piece (14, 15) on the opposite narrow sides (10, 11), b) that the shaped pieces (14, 15) each form a rounded guide surface over which the cover film (12) is guided, c) that the rounded guide surface preferably has a radius of curvature (R) of at least 2 mm, 5 mm, 1 cm, 2 cm or 5 cm in order to prevent the cover film (12) from buckling when guided over the guide surface. d) that the shaped pieces (14, 15) preferably each form a quarter circle in cross-section, so that the guide surface is oriented horizontally on the inside and vertically downwards on the outside with respect to the conveying surface (3), so that a vertical clamping force of the first spring element (19) is converted into a horizontal clamping force on the cover film (12).

7. Conveying device (1) according to one of the preceding claims, characterized in that a) at least one clamping piece (20) is arranged on each of the opposite longitudinal sides (8, 9) of the conveying surface (3), b) that the cover film (12) is clamped in the opposing clamping pieces (20), and c) that the opposing clamping pieces (20) are mechanically pre-tensioned by a second spring element (21) in order to elastically stretch the cover film (12) between the opposing longitudinal sides (8, 9) over the conveying surface (3).

8. Conveying device (1) according to claim 7, characterized in that, a) that several clamping pieces (20) are arranged on each of the opposite longitudinal sides (8, 9) of the conveying surface (3), b) that the clamping pieces (20) are arranged distributed along the longitudinal sides (8, 9) of the conveying surface (3), in particular equidistantly, c) the cover film (12) is clamped at several separate force application points in the opposing clamping pieces (20), and d) that the opposing clamping pieces (20) are mechanically pre-tensioned by a second spring element (21) in order to elastically stretch the cover film (12) between the opposing longitudinal sides (8, 9) over the conveying surface (3), e) that the second spring element (21) preferably acts in a vertical direction and the clamping pieces (20) convert the vertical clamping force of the second spring element (21) into a horizontal clamping force on the cover film (12).

9. Conveying device (1) according to claim 7 or 8, characterized in that the second spring element (21) for mechanical preloading of the at least one clamping piece (20) is a helical spring (21).

10. Conveying device (1) according to one of the preceding claims, characterized in that a) the cover film (12) is elastically tensioned between the opposite narrow sides (10, 11) of the conveying surface (3) by a first spring force, wherein the first spring force acts on the cover film (12) uniformly distributed over the entire length of the narrow sides (10, 11) of the conveying surface (3), in particular via the clamping strips (16, 17), and / or b) that the cover film (12) is elastically tensioned between the opposite longitudinal sides (8, 9) of the conveying surface (3) by a second spring force, wherein the second spring force does not act on the cover film (12) distributed over the entire length of the longitudinal sides (8, 9) of the conveying surface (3), but only at several separate force application points, in particular at the clamping pieces (20).

11. Conveying device (1) according to one of the preceding claims, characterized in that a) the conveying surface (3) is surrounded by a circumferential sealing frame (23), and b) the cover film (12) is in a sealing position against the circumferential sealing frame (23).

12. Conveying device (1) according to one of the preceding claims, characterized in that a) the cover film (12) has a thickness of at most 1 mm, 0.5 mm, 0.25 mm or 0.15 mm, and / or b) that the cover film (12) has a thickness of at least 0.15 mm, and / or c) that the cover film (12) is made of plastic or stainless steel, in particular of a chromium-nickel alloy, in particular of an iron-chromium-nickel-molybdenum alloy, in particular of X2CrNiMol7-12-2, and / or d) that the cover film (12) has a flatness that is more accurate than 0.5 mm, 0.25 mm or 0.1 mm.

13. Conveying device (1) according to one of the preceding claims, characterized in that a) the conveying surface (3) is surrounded by a support frame (13), in particular made of aluminium or an aluminium alloy, b) that the support frame (13) and the cover film (12) are made of materials with different coefficients of thermal expansion, and c) that the cover film (12) is elastically tensioned in the support frame (13), wherein the tensioning of the cover film (12) compensates for the different coefficients of thermal expansion of the materials of the support frame (13) and the cover film (12).

14. Conveyor device (1) according to one of the preceding claims, characterized in that a) the conveying surface (3) of the planar motor drive system (2) is composed of several rectangular tiles (4), and b) that the individual tiles (4) of the planar motor drive system (2) are preferably replaceable from below without removing the cover film (12), and c) that the conveying surface (3) of the planar motor drive system (2) is preferably rectangular.

15. Conveyor device (1) according to one of the preceding claims, characterized in that a) the planar motor drive system (2) operates electromagnetically, and / or b) that the planar motor drive system (2) has at least one conveying carrier (5) for receiving the product (7) to be conveyed, wherein the conveying carrier (5) with the product (7) to be conveyed is movable without contact above the conveying surface (3), in particular at a floating height of 1 mm to 5 mm above the conveying surface (3), and / or c) that the conveying carrier (5) has a load-bearing capacity of at least 100 g, 200 g, 500 g, 1 kg or at least 2 kg, and / or d) that the planar motor drive system (2) for contactless conveying of the products (7) generates a magnetic field and the cover film (12) reduces the magnetic field by less than 10%, 5%, 2% or 1%.

16. Use of an elastic cover film (12) for covering a conveying surface (3) of a planar motor drive system (2) in a conveying device (1) for conveying products (7), in particular for conveying food products (7), wherein the cover film (12) is preferably stretched elastically over the conveying surface (3) of the planar motor drive system (2), in particular between opposite narrow sides (10, 11) of the conveying surface (3) and between opposite longitudinal sides (8, 9) of the conveying surface (3).

Images