Packing box easy-to-tear cover structure and production process thereof

Abstract

The invention relates to the technical field of packaging box easy-to-tear covers, in particular to a packaging box easy-to-tear cover structure and a production process thereof.The packaging box easy-to-tear cover structure comprises the gluing procedure, specifically, a layer of edible glue is smeared on a gluing part of the outer edge of a cylindrical cover, and after gluing is finished, the cylindrical cover is transferred to enter a punching station and then stopped; a punching machine is aligned with the punching part of the cylindrical cover to punch a circular opening; after punching is finished, the cylindrical cover is transferred into a heating and film covering station to be heated, and glue is melted; and after heating, the aluminum film is immediately adhered to the cylindrical cover to manufacture the easy-to-tear cover. A traditional technology is improved into the mode that glue is sprayed on the upper ring face of a cover opening, then the cover opening and a plastic film or an aluminum film are packaged in a heat sealing mode, and the easy-to-tear cover structure is formed. The glue consumption of the new process is about 6% of that of the traditional process, the glue consumption is greatly saved, and the glue is not coated on one surface of the plastic film or the aluminum film facing the food, so that the pollution of the glue to the food is reduced, and the health degree of the food is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of easy-tear covers for packaging boxes, and in particular to an easy-tear cover structure for a packaging box and a production process thereof. Background Art

[0002] Many packages, especially some metal cans or plastic cans, are designed to be easy to open for the convenience of people. Typical examples are various cans, but it is still troublesome to open cans, and it also requires a certain amount of strength. Therefore, there are easy-tear lids that are easier to open on the market. This easy-tear lid is generally sealed with a plastic film or aluminum film, which is glued with glue. When using it, you only need to tear the plastic film or aluminum film.

[0003] The traditional easy-tear lid sealing process generally involves first coating one side of the plastic film or aluminum film with glue, then cutting it, and then hot-melt laminating it. For some food packaging boxes, the glue used needs to be edible glue. This glue is expensive, and coating the entire surface of the plastic film or aluminum film with glue requires a large amount of edible glue, which increases the production cost.

[0004] However, in actual production, it is found that the connection between the plastic film or aluminum film and the metal can or plastic can is not connected on the entire surface, so it is not necessary to apply glue to one side of the plastic film or aluminum film. The reason why the whole surface is coated with glue is that this method is simpler, mainly to save process flow and reduce processing difficulty.

[0005] Since the middle of the easy-tear cover of the packaging can is open, the connection between the plastic film or aluminum film and the can body is only a ring belt at the edge of the outer ring, and the space is small, so it is difficult to accurately apply glue to this part. In addition, the newly applied glue has a certain fluidity, so even if the edge of the ring belt can be accurately applied, the glue is easy to flow away from the opening in the middle, which not only causes the loss of glue and affects the subsequent easy-tear cover pasting effect, but also causes waste of glue and has adverse effects on other equipment. Summary of the invention

[0006] In view of this, the purpose of the present invention is to propose an easy-to-tear cover structure for a packaging box and its production process, so as to solve the problems of the prior art of gluing one side of a plastic film or an aluminum film as a whole, resulting in a large amount of glue used, resulting in increased production costs, and difficulty in accurately gluing a narrow area and glue loss.

[0007] Based on the above purpose, the present invention provides a packaging box easy-tear cover structure, comprising a cylindrical cover, a cover edge protruding outward is provided at the upper edge of the cylindrical cover, a punching part is provided at the center of the cylindrical cover, and a glue coating part is provided at the outer edge of the punching part;

[0008] An aluminum film connected to the cylindrical cover via a glue coating portion, wherein the aluminum film is adhered to the cylindrical cover via edible glue;

[0009] The production process of the above-mentioned packaging box easy-tear cover structure:

[0010] The gluing process is used to apply a layer of edible glue on the gluing part of the outer edge of the cylindrical cover. The cylindrical cover stops and starts to rotate after entering the gluing station. The gluing head used for gluing is aligned with the gluing part on the cylindrical cover and releases the edible glue, and a circle of edible glue is evenly applied on the gluing part.

[0011] Punching process: after the gluing process is completed, the cylindrical cover is transported to the punching station and stops, and the punching machine is aligned with the punching part of the cylindrical cover to punch out a circular opening;

[0012] Heating process: after the punching process is completed, the cylindrical cover is transferred to the heating and laminating station for heating to melt the edible glue;

[0013] In the laminating process, after the cylindrical cover is heated at the heating laminating station, the aluminum film is immediately pasted onto the cylindrical cover to form an easy-tear cover, and then the easy-tear cover is transported and removed, waiting for the edible glue to cool before inspection and bagging.

[0014] Furthermore, it comprises a pedestal, on which a gluing station, a punching station and a heating and laminating station are arranged in sequence from front to back;

[0015] The gluing station is provided with a lifting platform, on which a gluing head and a connecting ring are fixedly connected, the outer diameter of the connecting ring is the same as the diameter of the punching part, and the gluing head is located outside the connecting ring.

[0016] Furthermore, a plurality of equally spaced air jets are provided at the bottom of the connecting ring, and an air pipe is connected to the upper end of the connecting ring, one end of the air pipe is connected to the air jets, and the other end is connected to an external air pump, and a glue pipe is connected to the upper end of the glue coating head, and the other end of the glue pipe is connected to an external glue barrel.

[0017] Furthermore, a turntable is provided at the bottom of the lifting platform, the turntable is rotatably connected to the base, and a magnetic ring is fixedly connected to the upper surface of the turntable. A motor for driving the turntable to rotate is also provided in the base.

[0018] Furthermore, a baffle is provided on the pedestal, the baffle is located at the rear side of the turntable, and the baffle is slidably connected to the pedestal, and a cylinder for driving the baffle to slide up and down is also provided in the pedestal.

[0019] Furthermore, a screw rod is rotatably connected to the pedestal, the lifting platform is threadedly connected to the screw rod, and a motor for driving the screw rod to rotate is also arranged in the pedestal.

[0020] Furthermore, a folding sheet is fixedly connected to the upper surface of the aluminum film.

[0021] Furthermore, the pedestal is provided with two side slides, the inner side of the side slides is provided with a slide groove, and the cover edge on the cylindrical cover is located in the slide groove and is slidably connected thereto.

[0022] Furthermore, a conductive sheet is provided at the bottom of the slide slot, and a plurality of electromagnets arranged at equal distances are fixedly connected to the top of the slide slot.

[0023] Furthermore, a DC power supply is provided in the pedestal, the positive and negative electrodes of the DC power supply are respectively connected to the conductive sheets in the two slide slots, and the electromagnets are sequentially connected in parallel to the conductive sheets.

[0024] The beneficial effects of the present invention are as follows: 1. The traditional method of coating one side of the plastic film or aluminum film with glue and then cutting and hot-melting is improved to spraying glue on the upper ring surface of the cover and then heat-sealing with the plastic film or aluminum film to form an easy-to-tear cover structure. The glue usage of the new process is about 6% of that of the traditional process, which greatly saves the glue usage, and the side of the plastic film or aluminum film facing the food is not coated with glue, which reduces the contamination of glue to the food and improves the health of the food.

[0025] 2. The production equipment is designed with a side slide that cooperates with the cylindrical cover, so that the cover edge of the cylindrical cover can be located exactly in the slide groove on the inner side of the side slide and slide in it to ensure the accuracy of the position of the cylindrical cover. The slide groove is equipped with a conductive sheet and an electromagnet. The cylindrical cover cooperates with the conductive sheets on both sides to form a closed loop, and then the electromagnet in the forward direction of the cylindrical cover is energized. The electromagnet generates magnetic force and can attract the cylindrical cover to slide forward. The electromagnet on the rear side of the cylindrical cover will automatically cut off the power after leaving, ensuring smooth transportation during the production of the cylindrical cover and no impact on processing.

[0026] 3. A turntable is set at the gluing station, and a magnetic ring is set on the upper surface of the turntable. After the cylindrical cover is blocked and positioned by the baffle, the turntable can rotate with the cylindrical cover, and cooperate with the fixed gluing head to accurately apply a layer of edible glue on the gluing part of the cylindrical cover. In addition, a connecting ring with the same diameter as the punching part is set, and a number of equidistantly arranged air jets are provided at the bottom of the connecting ring. When the gluing head is applying glue, the air jets are spraying at the same time, which avoids the glue from flowing from the outer gluing part to the middle punching part during gluing, reduces the waste of glue and avoids adverse effects on other equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a schematic diagram of the overall structural principle of the production device of the present invention.

[0029] Figure 2 It is a front view of the production device of the present invention.

[0030] Figure 3 It is a schematic diagram of the structure of the turntable part in the production device of the present invention.

[0031] Figure 4 It is a schematic structural diagram of the lifting platform part in the production device of the present invention.

[0032] Figure 5 for Figure 1 Enlarged view of part A.

[0033] Figure 6 It is a schematic diagram of the electrical connection principle between the conductive sheet and the electromagnet in the production device of the present invention.

[0034] Figure 7 It is a schematic diagram of the structural principle of the cylindrical cover in the product of the present invention.

[0035] Figure 8 It is a schematic diagram of the overall structure of the easy-tear cover in the product of the present invention.

[0036] The markings in the figure are:

[0037] 01. Cylindrical cover, 02. Cover edge, 03. Gluing unit, 04. Punching unit, 05. Aluminum film, 06. Folding sheet, 101. Base, 102. Side slide, 103. Slide, 104. Turntable, 105. Magnetic ring, 106. Lifting platform, 107. Screw, 108. Gluing head, 109. Connecting ring, 110. Glue pipe, 111. Air pipe, 112. Punching machine, 113. Baffle, 114. Air jet, 115. Conductive sheet, 116. Electromagnet, 117. DC power supply. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0039] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0040] A first aspect of the present invention, as Figure 1 , Figure 2 , Figure 7 and Figure 8 As shown, since the traditional easy-tear cover sealing process generally first applies glue to one side of the plastic film or aluminum film as a whole, then cuts it, and then performs hot melt lamination, for some food packaging boxes, the glue used needs to be edible glue. The price of this glue is high, and if the glue is applied to the entire surface of the plastic film or aluminum film, the amount of edible glue used will be relatively large, which leads to an increase in production costs. Therefore, the packaging box easy-tear cover structure of the present invention includes a cylindrical cover 01, and a cover edge 02 protruding outward is also provided at the upper edge of the cylindrical cover 01, a punching portion 04 is provided at the center of the cylindrical cover 01, and a glue coating portion 03 is provided at the outer edge of the punching portion 04. An aluminum film 05 connected to the cylindrical cover 01 through the glue coating portion 03, the aluminum film 05 is pasted on the cylindrical cover 01 through edible glue, and a folding sheet 06 is also fixedly connected to the upper surface of the aluminum film 05. In addition, the process is improved to first spray glue on the upper ring surface of the cover, and then heat-seal it with a plastic film or an aluminum film to form an easy-to-tear cover structure.

[0041] Specifically, it includes a gluing process, a punching process, a heating process and a laminating process. The gluing process is used to apply a layer of edible glue on the gluing part 03 of the outer edge of the cylindrical cover 01. The cylindrical cover 01 stops and starts to rotate after entering the gluing station. The gluing head 108 used for gluing is aligned with the gluing part 03 on the cylindrical cover 01 and releases the edible glue, and a circle of edible glue is evenly applied on the gluing part 03. After the gluing process is completed, the cylindrical cover 01 is transported to the punching station and stops. The punching machine 112 is aligned with the punching part 04 of the cylindrical cover 01 to punch out a circular opening. After the punching process is completed, the cylindrical cover 01 is transported to the heating laminating station for heating to melt the edible glue. After heating the cylindrical cover 01 at the heating laminating station, the aluminum film 05 is immediately pasted to the cylindrical cover 01 to make an easy-tear cover, and then the easy-tear cover is transported and removed, and the edible glue is waited for to cool before being inspected and bagged.

[0042] The new process uses about 6% of the glue used in the traditional process, which greatly saves glue. The side of the plastic film or aluminum film facing the food is not coated with glue, which reduces glue contamination to food and improves the health of the food.

[0043] A second aspect of the present invention, as Figure 1 , Figure 3 , Figure 4 and Figure 7 As shown, since the middle of the easy-tear cover of the packaging can body is open, the connection between the plastic film or aluminum film and the can body is only a revolving belt at the edge of the outer ring, and the space is small, so it is difficult to accurately apply glue to this part. Moreover, the newly applied glue has a certain fluidity, so even if the edge of the revolving belt can be accurately coated with glue, the glue is easy to stay from the opening in the middle, which not only causes the loss of glue to affect the subsequent easy-tear cover pasting effect, but also the lost glue will cause waste, and it will also have an adverse effect on other equipment. Therefore, in view of the new process, the production equipment of the present invention includes a base 101, and the base 101 is sequentially provided with a gluing station, a punching station and a heating and laminating station from front to back.

[0044] The key point is that a lifting platform 106 is provided on the gluing station, and a gluing head 108 and a connecting ring 109 are fixedly connected to the lifting platform 106. The outer diameter of the connecting ring 109 is the same as the diameter of the punching part 04, and the gluing head 108 is located outside the connecting ring 109. The bottom of the connecting ring 109 is provided with a plurality of equally spaced jets 114, and the upper end of the connecting ring 109 is also connected to an air supply pipe 111, one end of the air supply pipe 111 is connected to the jets 114, and the other end is connected to an external air pump, and the upper end of the gluing head 108 is also connected to a glue supply pipe 110, and the other end of the glue supply pipe 110 is connected to an external glue barrel. The base 101 is also rotatably connected to a screw 107, and the lifting platform 106 is threadedly connected to the screw 107, and the base 101 is also provided with a motor for driving the screw 107 to rotate.

[0045] In addition, a turntable 104 is provided at the bottom of the lifting platform 106, and the turntable 104 is rotatably connected to the base 101, and a magnetic ring 105 is fixedly connected to the upper surface of the turntable 104, and a motor for driving the turntable 104 to rotate is also provided in the base 101. A baffle 113 is also provided on the base 101, and the baffle 113 is located at the rear side of the turntable 104, and the baffle 113 is slidably connected to the base 101, and a cylinder for driving the baffle 113 to slide up and down is also provided in the base 101.

[0046] A turntable 104 is provided at the gluing station, and a magnetic ring 105 is provided on the upper surface of the turntable 104. After the cylindrical cover 01 is blocked and positioned by the baffle 113, the turntable 104 can rotate with the cylindrical cover 01, and cooperate with the fixed gluing head 108 to accurately apply a layer of edible glue on the gluing part 03 of the cylindrical cover 01. In addition, a connecting ring 109 with the same diameter as the punching part 04 is provided, and a plurality of air jets 114 arranged equidistantly are provided at the bottom of the connecting ring 109. When the gluing head 108 is applying glue, the air jets 114 are simultaneously spraying, which prevents the glue from flowing from the outer gluing part 03 to the middle punching part 04 during gluing, reduces the waste of glue and avoids adverse effects on other equipment.

[0047] A third aspect of the present invention is as follows Figure 1 , Figure 5 , Figure 6 and Figure 7As shown, in order to enable the cylindrical cover 01 to be smoothly and orderly transferred between various stations on the platform 101, two side slides 102 are also provided on the platform 101, and a slide groove 103 is provided on the inner side of the side slide 102. The cover edge 02 on the cylindrical cover 01 is located in the slide groove 103 and is slidably connected thereto. A conductive sheet 115 is provided at the bottom of the slide groove 103, and a plurality of electromagnets 116 arranged equidistantly are fixedly connected to the top of the slide groove 103. A DC power supply 117 is also provided in the platform 101, and the positive and negative poles of the DC power supply 117 are respectively connected to the conductive sheets 115 in the two slide grooves 103, and the electromagnets 116 are sequentially connected in parallel to the conductive sheets 115.

[0048] The production equipment is designed with a side slide 102 that cooperates with the cylindrical cover 01, so that the cover edge 02 of the cylindrical cover 01 can be exactly located in the slide groove 103 on the inner side of the side slide 102, and slide connected therein to ensure the accurate position of the cylindrical cover 01. The slide groove 103 is provided with a conductive sheet 115 and an electromagnet 116. The cylindrical cover 01 cooperates with the conductive sheets 115 on both sides to form a closed loop, and then the electromagnet 116 in the forward direction of the cylindrical cover 01 is energized. The electromagnet 116 generates magnetic force when it is energized, and then it can attract the cylindrical cover 01 to slide forward. The electromagnet 116 on the rear side of the cylindrical cover 01 will automatically cut off the power after leaving, ensuring that the cylindrical cover 01 is smoothly transported during the production process and is not affected during processing.

[0049] In summary, the present invention improves the traditional method of coating one side of the plastic film or aluminum film with glue as a whole, and then cutting and hot-melting and laminating it, by first spraying glue on the upper ring surface of the cover, and then heat-sealing it with the plastic film or aluminum film to form an easy-to-tear cover structure. The amount of glue used in the new process is about 6% of that in the traditional process, which greatly saves the amount of glue used, and the side of the plastic film or aluminum film facing the food is not coated with glue, which reduces the contamination of the food by glue and improves the health of the food. The production equipment is designed with a side slide 102 that cooperates with the cylindrical cover 01, so that the cover edge 02 of the cylindrical cover 01 can be exactly located in the slide groove 103 on the inner side of the side slide 102, and is slidably connected therein to ensure the accurate position of the cylindrical cover 01. The slide 103 is provided with a conductive sheet 115 and an electromagnet 116. The cylindrical cover 01 cooperates with the conductive sheets 115 on both sides to form a closed loop, and then the electromagnet 116 in the forward direction of the cylindrical cover 01 is energized. The electromagnet 116 generates magnetic force and can attract the cylindrical cover 01 to slide forward. The electromagnet 116 on the rear side of the cylindrical cover 01 will automatically cut off the power after leaving, ensuring that the cylindrical cover 01 is smoothly transported during production and is not affected during processing. A turntable 104 is set on the gluing station, and a magnetic ring 105 is set on the upper surface of the turntable 104. After the cylindrical cover 01 is blocked and positioned by the baffle 113, the turntable 104 can rotate with the cylindrical cover 01, and cooperate with the fixed gluing head 108 to accurately apply a layer of edible glue on the gluing part 03 of the cylindrical cover 01. In addition, a connecting ring 109 with the same diameter as the punching part 04 is set, and a plurality of equidistantly arranged air jets 114 are provided at the bottom of the connecting ring 109. When the glue coating head 108 is coating glue, the air jet 114 is jetting at the same time, which prevents the glue from flowing from the outer glue coating part 03 to the middle punching part 04 during coating glue, thereby reducing the waste of glue and avoiding adverse effects on other equipment.

[0050] It should be understood by those skilled in the art that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention, including the claims, is limited to these examples; within the context of the present invention, the technical features in the above embodiments or in different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0051] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A packaging box easy-tear cover structure, comprising a cylindrical cover (01), wherein an outwardly protruding cover edge (02) is provided at the upper edge of the cylindrical cover (01), characterized in that: A punching portion (04) is provided at the center of the cylindrical cover (01), and a glue coating portion (03) is provided at the outer edge of the punching portion (04); An aluminum film (05) is connected to the cylindrical cover (01) via a glue coating portion (03); the aluminum film (05) is adhered to the cylindrical cover (01) via edible glue; a folding sheet (06) is also fixedly connected to the upper surface of the aluminum film (05).

2. A production process for an easy-tear cover structure of a packaging box, used for producing the easy-tear cover structure of a packaging box according to claim 1, characterized in that: The steps include: The gluing process is used to apply a layer of edible glue on the gluing portion (03) at the outer edge of the cylindrical cover (01). The cylindrical cover (01) stops and starts to rotate after entering the gluing station of the production equipment. The gluing head (108) used for gluing in the production equipment is aligned with the gluing portion (03) on the cylindrical cover (01) and releases the edible glue, and evenly applies a circle of edible glue on the gluing portion (03); Punching process: after the gluing process is completed, the cylindrical cover (01) is transported to the punching station in the production equipment and stops, and the punching machine (112) is aligned with the punching part (04) of the cylindrical cover (01) to punch out a circular opening; A heating process, after the punching process is completed, the cylindrical cover (01) is transferred to a heating and laminating station in the production equipment for heating to melt the edible glue; In the laminating process, after the cylindrical cover (01) is heated at the heating laminating station, the aluminum film (05) is immediately pasted onto the cylindrical cover (01) to form an easy-tear cover, and then the easy-tear cover is transported and removed, and the edible glue is waited to cool before being inspected and bagged.

3. The production process of the easy-tear cover structure of a packaging box according to claim 2, characterized in that: The production equipment comprises a base (101), and the gluing station, the punching station and the heating and laminating station are arranged on the base (101) in sequence from front to back; The gluing station is provided with a lifting platform (106), and a gluing head (108) and a connecting ring (109) are fixedly connected to the lifting platform (106). The outer diameter of the connecting ring (109) is the same as the diameter of the punching part (04), and the gluing head (108) is located outside the connecting ring (109).

4. The production process of the easy-tear cover structure of a packaging box according to claim 3, characterized in that: The bottom of the connecting ring (109) is provided with a plurality of equidistantly arranged air jets (114); the upper end of the connecting ring (109) is also connected to an air supply pipe (111); one end of the air supply pipe (111) is connected to the air jets (114); and the other end is connected to an external air pump; the upper end of the glue coating head (108) is also connected to a glue supply pipe (110); and the other end of the glue supply pipe (110) is connected to an external glue barrel.

5. The production process of the easy-tear cover structure of a packaging box according to claim 3, characterized in that: A turntable (104) is also provided at the bottom of the lifting platform (106). The turntable (104) is rotatably connected to the base (101), and a magnetic ring (105) is fixedly connected to the upper surface of the turntable (104). A motor for driving the turntable (104) to rotate is also provided inside the base (101).

6. The production process of the easy-tear cover structure of a packaging box according to claim 5, characterized in that: The pedestal (101) is also provided with a baffle (113), the baffle (113) is located at the rear side of the turntable (104), and the baffle (113) is slidably connected to the pedestal (101), and a cylinder for driving the baffle (113) to slide up and down is also provided in the pedestal (101).

7. The production process of the easy-tear cover structure of a packaging box according to claim 3, characterized in that: The base (101) is also rotatably connected to a screw rod (107), the lifting platform (106) is threadedly connected to the screw rod (107), and a motor for driving the screw rod (107) to rotate is also provided in the base (101).

8. The production process of the easy-tear cover structure of a packaging box according to claim 3, characterized in that: The base (101) is also provided with two side slides (102), the inner side of the side slides (102) is provided with a slide groove (103), and the cover edge (02) on the cylindrical cover (01) is located in the slide groove (103) and is slidably connected thereto.

9. The production process of the easy-tear cover structure of a packaging box according to claim 8, characterized in that: A conductive sheet (115) is provided at the bottom of the slide groove (103), and a plurality of electromagnets (116) arranged at equal distances are fixedly connected to the top of the slide groove (103).

10. The production process of the easy-tear cover structure of a packaging box according to claim 9, characterized in that: A direct current power source (117) is also provided in the pedestal (101), and the positive and negative electrodes of the direct current power source (117) are respectively connected to the conductive sheets (115) in the two slide slots (103), and the electromagnets (116) are sequentially connected in parallel to the conductive sheets (115).

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