Adjustable cutting device for plastic film

Abstract

The adjustable cutting device comprises a frame body, two sets of inner guide rollers are rotationally connected to the middle of the inner side of the frame body, outer guide rollers are rotationally connected to the two ends in the frame body, a power mechanism is fixedly installed on the back face of the frame body, and a supporting frame is fixedly installed in the middle of the top of the frame body. In the using process, an operator unscrews the hand screwing type installation screw rod, the sliding blocks are matched with the inverted-T-shaped guide rails, the distance between the cutting blades can be flexibly adjusted, the cutting blades are inserted into the limiting holes to be fixed after adjustment, the different cutting width requirements are rapidly met, and compared with a traditional mode that the whole cutter set needs to be replaced, the downtime is greatly shortened, and the working efficiency is improved. In addition, due to the arc edge design of the guide rail and the sliding block, friction is reduced, abrasion is reduced, stable sliding of the cutting knife set is guaranteed, the service life of equipment is prolonged, and the flexibility and efficiency of plastic film cutting production are remarkably improved.

Description

Technical Field

[0001] This utility model relates to the field of plastic film cutting technology, and in particular to an adjustable cutting device for plastic film. Background Technology

[0002] In the modern packaging industry, plastic film, with its excellent flexibility, moisture resistance, and cost advantages, is widely used in various packaging scenarios such as food, daily necessities, and industrial products. In the plastic film production process, the cutting and winding operation, as the final step, directly determines the width specifications and quality of the finished film, and is crucial for the standardized production of packaging products. However, existing plastic film cutting technologies are limited by the tool installation method and pressure structure design, revealing significant defects such as low efficiency and poor flexibility in actual production, as detailed below:

[0003] Currently, to ensure the stability of the cutting process, most plastic film cutting equipment uses fixed-mount cutting blades. In this installation mode, once the blade position is determined, it is difficult to adjust. When production tasks require changing the film cutting width, operators usually need to disassemble and replace the entire blade assembly. This process not only involves complex disassembly and assembly operations, which are time-consuming and labor-intensive, but may also lead to a decrease in equipment accuracy due to repeated disassembly and assembly, increasing equipment maintenance costs. For example, in production lines where packaging product specifications frequently change, frequent blade replacements can cause significant downtime, severely impacting production progress. Furthermore, the replacement of fixed blade assemblies relies on manual operation, requiring high technical skills from operators, thus increasing labor costs and the risk of errors. Simultaneously, existing cutting equipment generally lacks a stable and effective pressure application structure. During continuous cutting of plastic film, if pressure cannot be applied to the film, it is prone to displacement, wrinkles, or loosening, leading to decreased cutting accuracy and quality problems such as burrs and uneven cuts. Therefore, existing technology has certain defects and shortcomings, necessitating improved design. Utility Model Content

[0004] To address the aforementioned problems, this invention proposes an adjustable cutting device for plastic film, which can more accurately solve the problems described above.

[0005] This utility model is achieved through the following technical solution:

[0006] This utility model proposes an adjustable cutting device for plastic film, including a frame, two sets of inner guide rollers rotatably connected to the middle of the inner side of the frame, outer guide rollers rotatably connected to both ends of the inner side of the frame, a power mechanism fixedly installed on the back of the frame, a support frame fixedly installed in the middle of the top of the frame, an electric push rod fixedly installed on the top of the support frame, a cutting mechanism fixedly installed at the bottom output end of the electric push rod through the support frame, and positioning mechanisms fixedly installed on both sides of the cutting mechanism.

[0007] The cutting mechanism includes a top plate, which is fixedly installed at the bottom output end of the electric push rod. The positioning mechanism is fixedly installed at the middle of both sides of the top plate. A guide rail is fixedly installed at the bottom center of the top plate, and several sets of cutting blades are slidably connected inside the guide rail.

[0008] Furthermore, the cutting blade assembly includes a slider, which is slidably connected to the inside of the guide rail. A cutting blade is fixedly installed at the bottom of the slider, and a fixed arm is fixedly installed on the outside of the slider. A mounting screw is threaded to the outer end of the fixed arm, and the end of the mounting screw passes through the fixed arm.

[0009] Furthermore, the mounting screw is a hand-tightening screw, and the guide rail has limit holes arranged linearly at equal intervals on the side near the fixed arm. The end of the mounting screw is inserted into the limit hole. The cross-sectional shape of the internal cavity of the guide rail is convex, and the side shape of the slider is also convex. The outer surface corners of the slider and the guide rail are rounded.

[0010] Furthermore, support legs are fixedly installed at the four corners of the bottom of the frame, and bottom support frames are fixedly installed at the bottom of the support legs.

[0011] Furthermore, the positioning mechanism includes side arms, which are fixedly installed on the middle of both sides of the top plate. A base plate is fixedly installed on the top outer end of the side arms. Telescopic springs are fixedly installed at equal intervals in a linear arrangement on the bottom of the base plate. A base is fixedly installed on the bottom of the telescopic springs. The side of the base is U-shaped. A positioning roller is rotatably connected inside the base. The positioning roller is arranged on the outside of two sets of inner guide rollers.

[0012] Furthermore, a support rod is fixedly installed on the top of the base, the end of the support rod penetrates through the base plate, and the support rod and the base plate are slidably connected.

[0013] Furthermore, the power mechanism includes side seats and worm gears. The side seats are fixedly installed at both ends of the back of the frame. A worm is rotatably connected to the inner side of the side seats. There are four worm gears, which are rotatably connected to the two sides and the middle of the back of the frame, respectively. The two outer worm gears are fixedly connected to the back of the outer guide roller, and the two inner worm gears are fixedly connected to the back of the inner guide roller. A drive motor is fixedly installed on the outer side of one side seat, and the output end of the drive motor is fixedly connected to one end of the worm.

[0014] The beneficial effects of this utility model are:

[0015] 1. This device achieves stable conveying and positioning of plastic film through the coordinated operation of the power mechanism, positioning mechanism and roller group. The drive motor drives the worm gear and worm wheel to rotate the outer guide roller and inner guide roller to convey the film. The electric push rod drives the positioning roller to move down, forming a squeezing force with the outer guide roller and inner guide roller to fix the film. The telescopic spring of the positioning mechanism continuously applies pressure, and the support rod assists in stabilization to prevent film displacement and wrinkles. This design ensures that the film is conveyed flat. In conjunction with the cutting blade group, it effectively avoids problems such as rough edges and uneven cuts during cutting, improves the product qualification rate, and ensures that the cutting operation is efficient and accurate.

[0016] 2. This device adopts an adjustable cutting blade assembly design, which can improve its cutting flexibility and adaptability. During use, the operator can loosen the hand-tightening installation screw and flexibly adjust the cutting blade spacing by using the cooperation of the slider and the convex guide rail. After adjustment, it can be inserted into the limiting hole for fixation, quickly adapting to different cutting width requirements. Compared with the traditional method of replacing the entire blade assembly, it significantly reduces downtime, and is especially suitable for production lines with varying packaging specifications. In addition, the rounded corner design of the guide rail and slider reduces friction and wear, ensures stable sliding of the cutting blade assembly, extends the service life of the equipment, and significantly improves the flexibility and efficiency of plastic film cutting production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0018] Figure 2 This is a schematic diagram of the rear view structure of this utility model;

[0019] Figure 3 This is a front view schematic diagram of the cutting mechanism and positioning mechanism of this utility model;

[0020] Figure 4 This is a rear view schematic diagram of the cutting mechanism and positioning mechanism of this utility model;

[0021] Figure 5 This utility model Figure 4 A magnified structural diagram at point A.

[0022] In the diagram: 1. Frame; 2. Inner guide roller; 3. Outer guide roller; 4. Support frame; 5. Electric push rod; 6. Power mechanism; 61. Side seat; 62. Worm gear; 63. Worm wheel; 64. Drive motor; 7. Cutting mechanism; 71. Top plate; 72. Guide rail; 73. Cutting blade assembly; 731. Slider; 732. Cutting blade; 733. Fixed arm; 734. Mounting screw; 735. Limiting hole; 8. Positioning mechanism; 81. Side arm; 82. Base plate; 83. Telescopic spring; 84. Base; 85. Positioning roller; 86. Support rod; 9. Support leg; 10. Support frame. Detailed Implementation

[0023] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0024] Example 1

[0025] An adjustable cutting device for plastic film includes a frame 1, two sets of inner guide rollers 2 are rotatably connected to the middle of the inner side of the frame 1, outer guide rollers 3 are rotatably connected to both ends of the inner side of the frame 1, a power mechanism 6 is fixedly installed on the back of the frame 1, a support frame 4 is fixedly installed in the middle of the top of the frame 1, an electric push rod 5 is fixedly installed on the top of the support frame 4, a cutting mechanism 7 is fixedly installed at the bottom output end of the electric push rod 5 through the support frame 10, and positioning mechanisms 8 are fixedly installed on both sides of the cutting mechanism 7.

[0026] The cutting mechanism 7 includes a top plate 71, which is fixedly installed at the bottom output end of the electric push rod 5. A positioning mechanism 8 is fixedly installed on both sides of the top plate 71. A guide rail 72 is fixedly installed at the bottom center of the top plate 71. Several sets of cutting blades 73 are slidably connected inside the guide rail 72. When this adjustable plastic film cutting device is working, the drive motor 64 in the power mechanism 6 on the back of the frame 1 starts, driving the worm gear 62 to rotate. The worm gear 62 meshes with the worm wheel 63, thereby causing the outer guide rollers 3 at both ends and the two sets of inner guide rollers 2 in the middle of the inner side of the frame 1 to rotate synchronously, achieving stable conveying of the plastic film. When the cutting width needs to be adjusted, the operator loosens the hand screws on the cutting blade sets 73. The mounting screw 734 is used to adjust the position of the cutting blade 732 on the guide rail 72 by sliding the slider 731 and the guide rail 72. After the adjustment is in place, the screw is tightened and its end is inserted into the limiting hole 735 for fixation. Then, the electric push rod 5 on the top of the support frame 4 extends, driving the top plate 71 and the cutting mechanism 7 connected to the bottom output end to move down, so that the cutting blade assembly 73 cuts the film. During the cutting process, the positioning mechanisms 8 on both sides of the top plate 71 play a role, and the telescopic spring 83 provides elastic pressure to keep the positioning roller 85 in contact with the film. The support rod 86 slides in the substrate 82 to ensure the stability of the positioning roller 85, prevent film displacement and wrinkles, and ensure that the cutting work is completed accurately and efficiently.

[0027] Combination Figures 3-5As shown, the cutting blade assembly 73 includes a slider 731, which is slidably connected to the inside of the guide rail 72. A cutting blade 732 is fixedly installed at the bottom of the slider 731, and a fixed arm 733 is fixedly installed on the outside of the slider 731. A mounting screw 734 is threaded to the outer end of the fixed arm 733. The end of the mounting screw 734 passes through the fixed arm 733 and is a hand-tightening screw. Limiting holes 735 are linearly arranged at equal intervals on the side of the guide rail 72 near the fixed arm 733. The end of the mounting screw 734 is inserted into the limiting hole 735. The cross-sectional shape of the internal cavity of the guide rail 72 is convex. The side shape of the slider 731 is also convex. The corners of the outer surfaces of the slider 731 and the guide rail 72 are rounded. Support legs 9 are fixedly installed at the four corners of the bottom of the frame 1, and a bottom support frame 10 is fixedly installed at the bottom of the support legs 9.

[0028] In the above-described embodiments of this application, during the application of this device, when the cutting blade assembly 73 is working, if it is necessary to adjust the cutting width of the plastic film, the operator can quickly adjust it by hand-tightening the mounting screw 734. After loosening the screw, because the slider 731 and the guide rail 72 adopt a convex cross-section, the convex structure design allows the slider 731 to slide stably and flexibly inside the guide rail 72. The operator can accurately adjust the position of the cutting blade 732 according to actual needs. After adjustment, the mounting screw 734 is tightened so that its end is inserted. The guide rail 72 has equally spaced limiting holes 735 on its side, which firmly fix the slider 731 and the cutting blade 732, ensuring that the blade will not shift during the cutting process. At the same time, the rounded corners of the outer surface of the slider 731 and the guide rail 72 prevent injury to the human body during operation and adjustment. The support legs 9 at the four corners of the bottom of the frame 1 and the bottom support frame 10 provide stable support for the entire cutting device, enhance the stability of the equipment during operation, and prevent the cutting accuracy from being affected by shaking. This allows the cutting blade assembly 73 to complete the film cutting task efficiently and reliably.

[0029] Example 2

[0030] Combination Figures 1-4As shown, the positioning mechanism 8 includes side arms 81, which are fixedly installed on the middle of both sides of the top plate 71. A base plate 82 is fixedly installed on the outer top of the side arms 81. Telescopic springs 83 are fixedly installed at equal intervals in a linear arrangement on the bottom of the base plate 82. A base 84 is fixedly installed on the bottom of the telescopic springs 83. The side of the base 84 is U-shaped. A positioning roller 85 is rotatably connected inside the base 84. The positioning roller 85 is arranged on the outer side of the two sets of inner guide rollers 2. A support rod 86 is fixedly installed on the top of the base 84. The end of the support rod 86 passes through the base plate 82. The support rod 86 and the base plate 82 are connected. 2. Sliding connection. The power mechanism 6 includes a side seat 61 and a worm gear 63. The side seat 61 is fixedly installed at both ends of the back of the frame 1. A worm 62 is rotatably connected to the inner side of the side seat 61. There are four worm gears 63. The four worm gears 63 are rotatably connected to the two sides and the middle of the back of the frame 1, respectively. The front of the two outer worm gears 63 is fixedly connected to the back of the outer guide roller 3, and the front of the two inner worm gears 63 is fixedly connected to the back of the inner guide roller 2. A drive motor 64 is fixedly installed on the outer side of one side seat 61. The output end of the drive motor 64 is fixedly connected to one end of the worm 62.

[0031] In the above-described embodiments of this application, during the operation of this device, the power mechanism 6 and the positioning mechanism 8 work together. The drive motor 64 starts and drives the worm gear 62 to rotate. Through the meshing of the worm gear 62 with the four worm wheels 63, the outer worm wheel 63 drives the outer guide roller 3 and the inner worm wheel 63 drives the inner guide roller 2 to rotate synchronously, thereby achieving stable conveying of the plastic film. At the same time, the electric push rod 5 pushes the top plate 71 down, and the side arm 81 moves down synchronously with the top plate 71. The telescopic spring 83 at the bottom of the base plate 82 is compressed, generating elastic pressure and transmitting it to the U-shaped base 84, causing the base 82 to rotate. The positioning roller 85 inside the 4 is closely attached to the film surface outside the two sets of inner guide rollers 2. During the film conveying process, the positioning roller 85 rotates synchronously with the film, and the support rod 86 slides in the substrate 82 to ensure that the base 84 moves vertically and prevent the positioning roller 85 from shifting. The elastic design of the telescopic spring 83 enables the positioning roller 85 to adapt to changes in film thickness and always maintain stable pressure, effectively preventing the film from shifting or wrinkling during the cutting process. The power mechanism 6 provides continuous conveying power, and the positioning mechanism 8, through elastic pressure and guide limit, jointly ensures the stability of the film during cutting and improves cutting accuracy and quality.

[0032] The working principle and advantages of this utility model are as follows: When the device is in operation, the drive motor 64 is started, which drives the worm gear 62 to rotate. The worm gear 62 meshes with the worm wheel 63, causing the outer guide roller 3 and the inner guide roller 2 to rotate. At this time, the plastic film is placed on the inner guide roller 2 and the outer guide roller 3, and the electric push rod 5 is started to extend and drive the positioning roller 85 at the bottom to move down. The outer guide roller 3 and the inner guide roller 2 form a squeezing force with the positioning roller 85 to stably position the film. At this time, the power mechanism 6 is started to realize the conveying of the plastic film. According to the required cutting width, the operator can loosen the hand-tightening mounting screw 734 of the cutting blade assembly 73, slide the slider 731 on the guide rail 72 to adjust the position of the cutting blade 732, and tighten the screw after adjustment, inserting its end into the limiting hole 735 for fixation, quickly completing the cutting width adjustment. The electric push rod 5 pushes the top plate 71 and the cutting blade assembly 73. The film is cut by moving downwards. During the cutting process, the telescopic spring 83 of the positioning mechanism 8 provides elastic pressure, ensuring that the positioning roller 85 always adheres to the film. The support rod 86 slides within the substrate 82, ensuring the stability of the positioning roller 85 and preventing film displacement and wrinkles. The convex fit and rounded corner design of the guide rail 72 and the slider 731 ensure smooth and stable sliding of the cutting blade assembly 73, reducing wobbling. The support leg 9 and the bottom support frame 10 enhance the stability of the equipment. This device, through the adjustable cutting blade assembly 73 design, avoids the cumbersome operation of changing blade assemblies in traditional equipment, saving time and labor costs and improving production flexibility. The elastic pressure structure of the positioning mechanism 8 ensures the flatness of the film, improves cutting accuracy, and reduces problems such as burrs and uneven cuts. The stable equipment structure and smooth sliding of the cutting blade assembly 73 extend the service life of the blades, ensure continuous production, and effectively improve production efficiency and product quality.

[0033] When this adjustable plastic film cutting device is in operation, the drive motor 64 in the power mechanism 6 drives the worm gear 62 to rotate, which in turn drives the worm wheel 63, causing the outer guide roller 3 and the inner guide roller 2 to work together to complete the smooth conveying of the plastic film. During the conveying process, the film will pass through the adjusted cutting blade 732, at which point the cutting blade 732 can be stably cut and separated in multiple groups. When it is necessary to adjust the film cutting width, the operator can directly loosen the hand-tightening mounting screw 734 of the cutting blade assembly 73. Since the slider 731 and the guide rail 72 adopt a convex cross section, they can slide flexibly on the guide rail 72 for precise adjustment. After adjusting the spacing of the cutting blades 732, the screw is inserted into the limiting hole 735 for fixation, allowing for quick adaptation to different specifications. Compared to the traditional method of replacing the entire blade assembly, this significantly shortens preparation time. During cutting, the electric push rod 5 pushes the cutting mechanism 7 down, and the positioning mechanism 8 plays a crucial role. The telescopic spring 83 provides continuous elastic pressure, ensuring that the positioning roller 85 fits tightly against the film. The support rod 86 slides within the substrate 82, providing guidance and limiting effects, effectively preventing film displacement and wrinkles, ensuring cutting accuracy, and reducing scrap rate. Simultaneously, the rounded corner design of the guide rail 72 and slider 731 reduces friction and wear. To ensure stable sliding of the cutting blade assembly 73 and extend the service life of the equipment, this device is equipped with corresponding unwinding and rewinding devices on both sides of its frame 1. One end of the unwinding device releases the film, which is then driven by the power mechanism 6 to be conveyed on the frame 1. The rewinding device on the other side can rewind the cut film. The unwinding and rewinding devices are existing technologies and will not be described in detail here. It can be seen that the application of this device can effectively improve the flexibility and efficiency of plastic film production and cutting. The adjustable cutting blade assembly 73 completely changes the limitations of the traditional fixed blade assembly, and can quickly respond to changes without disassembling or replacing the blade assembly. To meet different cutting width requirements, this equipment is especially suitable for production lines where packaging product specifications change frequently, greatly reducing downtime and improving production continuity. In terms of quality assurance, the elastic pressure design of the positioning mechanism 8 can effectively solve the cutting quality problem caused by uneven force on the film, making the cut neat and burr-free, and improving the product qualification rate. In addition, the optimized design of the equipment structure, such as the convex guide rail 72 and slider 731, stable support legs 9 and bottom support frame 10, enhances the overall stability and durability of the equipment, reduces maintenance costs, and meets the needs of the modern packaging industry for efficient, precise and continuous cutting of plastic films.

[0034] The main structural components and electronic components of this adjustable plastic film cutting device are rationally designed. The frame 1 is welded from 4-6mm thick Q235B steel plate, with dimensions of 2000mm×1200mm×1500mm. It is equipped with support legs 9 with a diameter of 50-80mm and a height of 0-100mm, and a 10mm thick rust-proof bottom support frame 10 to ensure stability. The outer guide roller 3 and inner guide roller 2 are 800-1200mm long and 60-80mm in diameter, made of 45# steel with chrome plating, and have a circular runout tolerance of ≤0.05mm to ensure smooth film transport. The carbide blades of the cutting blade assembly 73 are 0.8-1.2mm thick with a cutting edge angle of 15°-20°. The gap between the convex guide rail 72 and the slider 731 is 0.02- The 0.05mm limit hole 735 has a spacing of 20-50mm, facilitating adjustment and precise cutting. The positioning roller 85 has a diameter of 40-60mm and is covered with a polyurethane elastic layer with a Shore hardness of A80-90. It is paired with a telescopic spring 83 with an elastic coefficient of 5-10N / mm and a compression stroke of 20-30mm, and a stainless steel 304 support rod 86 with a diameter of 8-10mm to achieve stable clamping. In terms of electronic components, the Y132M-4 three-phase asynchronous motor is driven by a 380V industrial power supply and a frequency converter. The DT50 electric push rod 5, Siemens S7-1200 series PLC, and WLCA12-2N limit sensor are all powered by 24V DC converted from the internal switching power supply, working together to achieve automated and precise control.

[0035] Of course, there may be other implementations of this utility model. Based on this implementation, other implementations obtained by those skilled in the art without any creative effort are all within the scope of protection of this utility model.

Claims

1. An adjustable cutting device for plastic film, characterized in that, The frame includes a frame (1), with two sets of inner guide rollers (2) rotatably connected to the middle of the inner side of the frame (1), and outer guide rollers (3) rotatably connected to both ends of the frame (1). A power mechanism (6) is fixedly installed on the back of the frame (1), and a support frame (4) is fixedly installed in the middle of the top of the frame (1). An electric push rod (5) is fixedly installed on the top of the support frame (4), and a cutting mechanism (7) is fixedly installed at the bottom output end of the electric push rod (5) through the support frame (10). A positioning mechanism (8) is fixedly installed on both sides of the cutting mechanism (7). The cutting mechanism (7) includes a top plate (71), which is fixedly installed at the bottom output end of the electric push rod (5). The positioning mechanism (8) is fixedly installed at the middle of both sides of the top plate (71). A guide rail (72) is fixedly installed at the bottom middle of the top plate (71). Several sets of cutting blades (73) are slidably connected inside the guide rail (72).

2. The adjustable cutting device for plastic film according to claim 1, characterized in that, The cutting blade assembly (73) includes a slider (731), which is slidably connected to the inside of the guide rail (72). A cutting blade (732) is fixedly installed at the bottom of the slider (731), and a fixing arm (733) is fixedly installed on the outside of the slider (731). A mounting screw (734) is threadedly connected to the outer end of the fixing arm (733), and the end of the mounting screw (734) passes through the fixing arm (733).

3. The adjustable cutting device for plastic film according to claim 2, characterized in that, The mounting screw (734) is a hand-tightening screw. The guide rail (72) has limit holes (735) arranged linearly at equal intervals on one side near the fixed arm (733). The end of the mounting screw (734) is inserted into the limit hole (735). The cross-sectional shape of the internal cavity of the guide rail (72) is convex. The side shape of the slider (731) is also convex. The corners of the outer surfaces of the slider (731) and the guide rail (72) are rounded.

4. The adjustable cutting device for plastic film according to claim 1, characterized in that, Support legs (9) are fixedly installed at the four corners of the bottom of the frame (1), and a bottom support frame (10) is fixedly installed at the bottom of the support legs (9).

5. The adjustable cutting device for plastic film according to claim 1, characterized in that, The positioning mechanism (8) includes a side arm (81), which is fixedly installed on the middle of both sides of the top plate (71). A base plate (82) is fixedly installed on the outer top of the side arm (81). Telescopic springs (83) are fixedly installed at equal intervals in a linear arrangement on the bottom of the base plate (82). A base (84) is fixedly installed on the bottom of the telescopic springs (83). The side of the base (84) is U-shaped. A positioning roller (85) is rotatably connected inside the base (84). The positioning roller (85) is arranged on the outside of the two sets of inner guide rollers (2).

6. The adjustable cutting device for plastic film according to claim 5, characterized in that, A support rod (86) is fixedly installed on the top of the base (84), and the end of the support rod (86) penetrates the base plate (82). The support rod (86) and the base plate (82) are slidably connected.

7. The adjustable cutting device for plastic film according to claim 1, characterized in that, The power mechanism (6) includes a side seat (61) and a worm gear (63). The side seat (61) is fixedly installed on both ends of the back of the frame (1). A worm (62) is rotatably connected to the inner side of the side seat (61). There are four worm gears (63). The four worm gears (63) are rotatably connected to the two sides and the middle of the back of the frame (1). The two worm gears (63) on the outer side are fixedly connected to the back of the outer guide roller (3) on the front. The two worm gears (63) on the inner side are fixedly connected to the back of the inner guide roller (2) on the front. A drive motor (64) is fixedly installed on the outer side of one side seat (61). The output end of the drive motor (64) is fixedly connected to one end of the worm (62).

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