A film winding and unwinding device capable of automatically changing rolls and a control method thereof

Abstract

The film winding and unwinding device with automatic roll changing and its control method relate to the technical field of winding and unwinding of film coils, and solve the problem that the film winding roller in the prior art cannot be automatically changed. The device comprises: a bracket, an unwinding roller, a tension detection and adjustment mechanism, a guide adjustment mechanism, a pressure roller, a height adjustment mechanism and an automatic roll changing mechanism. The automatic roll changing mechanism is arranged on one side of the height adjustment roller, and the automatic roll changing mechanism comprises a turntable, a winding roller and a spare winding roller are arranged on the outer circumference of the turntable, the winding roller and the spare winding roller are respectively connected to the winding servo motor through a coupling, the upper and lower parts of the turntable are respectively provided with a thickness detection mechanism, and the rear part of the turntable is connected to the transmission shaft through a rotating connection; the automatic roll changing mechanism can complete the automatic roll changing of the winding roller and the spare winding roller according to the winding situation, has a high degree of automation, and the equipment does not need to be shut down to complete the roll changing process, thereby reducing the labor intensity of workers and improving production efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of film coil winding and unwinding, and in particular to a film winding and unwinding device capable of automatically changing rolls and a control method thereof. Background Art

[0002] The material receiving part of the coil processing production line mechanically reels the raw materials into coils. It is widely used in paper rolls, cloth rolls, plastic rolls, and metal coil processing production lines. The design is diversified according to the actual process requirements. Common ones include simple rewinders and hydraulic rewinders. Rewinders generally have strict requirements on the inner diameter, outer diameter, thickness, and width of the material.

[0003] The film winding and unwinding device of the prior art requires manual roll changing. After the winding roller reaches the winding thickness, it needs to be stopped and replaced with a new winding roller. This causes frequent shutdowns, frequent manual operations, and the thickness of the film roll is difficult to control, which is not conducive to large-scale film production operations. Summary of the Invention

[0004] In response to the problem that the film winding roller in the existing technology cannot automatically change rolls, the present invention provides a film winding and unwinding device with automatic roll changing and a control method thereof. The advantage is that the winding roller can realize automatic roll changing, thereby improving the degree of automation of the winding roller roll changing.

[0005] In the first aspect, the present invention provides a film winding and unwinding device capable of automatic roll changing, comprising: a bracket, an unwinding roller, a tension detection and adjustment mechanism, a guide adjustment mechanism, a pressure roller, a height adjustment mechanism and an automatic roll changing mechanism, wherein the bracket is provided with a fixed plate, the unwinding roller is provided on the fixed plate, the unwinding roller is connected to the unwinding servo motor through a coupling, the tension detection and adjustment mechanism is provided on the upper part of the unwinding roller to adjust the tension of the coil, the guide adjustment mechanism is provided on one side of the tension detection and adjustment roller to adjust the running state of the coil, and the pressure roller is provided with a fixed plate. It is arranged on one side of the guide adjustment roller to press the coil; the height adjustment mechanism is arranged on one side of the pressure roller to adjust the running height of the coil for easy winding; the automatic roll changing mechanism is arranged on one side of the height adjustment roller; the automatic roll changing mechanism includes a turntable; a winding roller and a spare winding roller are arranged on the outer circumference of the turntable; the winding roller and the spare winding roller are respectively connected to the winding servo motor through a coupling; the upper and lower parts of the turntable are respectively provided with thickness detection mechanisms; the rear part of the turntable is connected to the drive shaft by a rotating connection to realize the rotation of the turntable.

[0006] Furthermore, the transmission shaft is connected to the large pulley, the large pulley is connected to the small pulley through belt transmission, the small pulley is connected to the reel-changing servo motor through a coupling, the reel-changing servo motor drives the small pulley to rotate, the small pulley rotates and drives the large pulley to realize the rotation of the transmission shaft, and finally controls the rotation angle of the turntable.

[0007] Furthermore, the thickness detection mechanism includes a thickness detection cylinder and a thickness detection roller. A fixed block is provided on the telescopic rod of the thickness detection cylinder, and the thickness detection roller is provided on the fixed block. A cutter is provided on one side of the fixed block for cutting the film and measuring the thickness of the winding according to the telescopic length of the telescopic rod.

[0008] Furthermore, the central angle of the arc formed between the winding roller and the spare winding roller is set to 90°, that is, the winding roller and the spare winding roller are arranged at an interval of 90° on the outer circumference of the turntable, which facilitates the rotation of the turntable when changing the roll.

[0009] Furthermore, the height adjustment mechanism includes a height adjustment cylinder and a pair of rollers. A slider is provided on the telescopic rod of the height adjustment cylinder. The slider is provided in a slide groove of the fixed plate. The pair of rollers is fixed on the slider. The slider slides in the slide groove to drive the pair of rollers to move and adjust the height of the coil between the pair of rollers.

[0010] Furthermore, the pressure roller includes an upper pressure roller and a lower pressure roller, which are respectively connected to an upper slider and a lower slider, and the upper slider and the lower slider are arranged in a groove of the fixed profile in a sliding connection manner. The upper slider is connected to the top of the groove of the fixed profile through a spring, and a screw is provided at the lower part of the lower slider. The position of the lower pressure roller is adjusted by the screw, thereby changing the stretching length of the spring. The elastic force of the upper pressure roller stretched by the spring changes. The pressure generated by the upper pressure roller on the film can be described as F=mg-kx. The pressure roller can press the two coils together, which is conducive to winding, prevents bubbles between the coils during the winding process, and improves the winding quality.

[0011] Furthermore, the guide adjustment mechanism includes two upper and lower guide rollers, a telescopic rod, a fixed seat, a connecting plate, and a screw. The fixed seat is connected to the fixed plate, and the connecting plate is arranged on the fixed seat. The fixed seat is provided with a rotating shaft, one end of the rotating shaft is provided with a knob, and the other end of the rotating shaft is fixedly connected to the telescopic rod. The telescopic rod is connected to the guide roller via a screw. By rotating the rotating shaft knob on the fixed seat, the position of the guide roller can be adjusted arbitrarily with the length of the telescopic rod as the radius. By changing the length of the telescopic rod, the guide roller can be moved to any position in space. The axial movement of the guide roller can be achieved by rotating the screw. The arbitrary adjustment of the guide roller is conducive to the control of the tension during the winding process and facilitates the change of position. The axial movement of the guide roller can achieve preliminary deviation correction of the coiled material.

[0012] Furthermore, the tension detection and adjustment mechanism includes two tension guide rollers and a tension detection roller. The tension detection roller is arranged on the upper part of the two tension guide rollers. The coil passes around the tension detection roller through the tension guide roller, converting the coil tension into pressure on the tension detection roller. The tension detection roller is equipped with a pressure sensor, which converts the force into an electrical signal. The speed of the rewinding and unwinding servo motor is controlled by the controller to achieve tension control.

[0013] Furthermore, the unwinding roller comprises an upper unwinding roller and a lower unwinding roller, which unwind the two coils at the same time to finally synthesize the composite coil.

[0014] In a second aspect, the present invention provides a method for controlling a film winding and unwinding device capable of automatic roll change, comprising the following steps:

[0015] 1) The coil is placed on the unwinding roller. The coil passes through the tension detection and adjustment mechanism, the guide adjustment mechanism, the pressure roller and the height adjustment mechanism in sequence, and finally reaches the winding roller;

[0016] 2) The thickness detection mechanism on the upper part of the turntable detects the winding thickness of the winding roller, and the height adjustment mechanism adjusts the winding height of the coil to make the winding height consistent with the height of the coil on the winding roller. The coil diameter of the winding roller gradually increases until the diameter of the winding roller reaches the target value, and the upper thickness detection mechanism stops working;

[0017] 3) The turntable rotates a certain angle through the transmission shaft, causing the winding roller to rotate to the bottom of the turntable. At the same time, the height adjustment mechanism moves to the top, and the spare winding roller rotates to the thickness detection mechanism position at the bottom of the turntable. At this time, the coil is arranged in a straight line between the height adjustment mechanism, the spare winding roller, and the winding roller. The thickness detection mechanism at the bottom works and expands and contracts. The spare winding roller presses the coil, and the tool of the thickness detection mechanism cuts the coil. The winding servo motor of the spare winding roller starts working, completing one roll changing process.

[0018] 4) Similarly, when the thickness detection mechanism at the bottom detects that the winding diameter of the spare winding roller reaches the target value, the thickness detection mechanism at the bottom stops working, and the turntable rotates a certain angle through the transmission shaft to rotate the spare winding roller to the upper end of the turntable. At the same time, the height adjustment mechanism moves to the lower end, and the winding roller rotates to the thickness detection mechanism position on the upper part of the turntable. At this time, the coil is arranged in a straight line between the height adjustment mechanism, the winding roller, and the spare winding roller. The upper thickness detection mechanism works, the thickness detection mechanism extends and retracts, the winding roller presses the coil, the tool of the thickness detection mechanism cuts the coil, and the winding servo motor of the winding roller starts working, and the roll changing process is started again.

[0019] The beneficial effects of the present invention are that the automatic roll changing mechanism can automatically change the rolls between the winding roller and the spare winding roller according to the winding situation, with a high degree of automation. The equipment does not need to be shut down to complete the roll changing process, which reduces the labor intensity of workers and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 It is a structural schematic diagram of the present invention.

[0022] Figure 2 It is a structural diagram of the automatic roll changing mechanism.

[0023] Figure 3 It is a side structural schematic diagram of the present invention.

[0024] Figure 4 It is a structural diagram of the pressure roller.

[0025] Figure 5 It is a structural diagram of the guide adjustment mechanism.

[0026] Figure 6 This is a schematic diagram of the structure when the roll is changed for the first time.

[0027] Figure 7 It is a structural diagram when changing the roll for the second time.

[0028] In the figure, 1, bracket, 2, lower unwinding roller, 3, fixed plate, 4, upper unwinding roller, 5, tension guide roller, 6, upper tension detection roller, 7, lower tension detection roller, 8, guide adjustment mechanism, 9, pressure roller, 10, height adjustment mechanism, 11, automatic roll changing mechanism, 12, small pulley, 13, turntable, 14, winding roller, 15, spare winding roller, 16, thickness detection mechanism, 17, transmission shaft, 18, large pulley, 19, thickness detection cylinder, 20, thickness detection roller, 21, cutter, 22, height adjustment cylinder, 23, pair of rollers, 24, slide, 25, upper pressure roller, 26, lower pressure roller, 27, groove, 28, lead screw, 29, spring, 30, guide roller, 31, telescopic rod, 32, fixed seat, 33, connecting plate, 34, screw, 35, rotating shaft. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0030] A film winding and unwinding device capable of automatic roll changing comprises: a bracket 1, an upper unwinding roller 4, a lower unwinding roller 2, an upper tension detection roller 6, a tension guide roller 5, a lower tension detection roller 7, a guide adjustment mechanism 8, a pressure roller 9, a height adjustment mechanism 10 and an automatic roll changing mechanism 11, wherein a fixed plate 3 is provided on the bracket 1, the upper unwinding roller 4 and the lower unwinding roller 2 are respectively provided on the fixed plate 3, the upper unwinding roller 4 and the lower unwinding roller 2 are respectively connected to the unwinding servo motor through a coupling, the tension guide roller 5 is respectively provided on the upper part of the upper unwinding roller 4 and the lower unwinding roller 2, the lower tension detection roller 7 and the upper tension detection roller 6 are respectively provided on the tension guide roller 5 At the upper part, the coil passes through the tension guide roller 5 and bypasses the tension detection roller, converting the coil tension into pressure on the tension detection roller. The tension detection roller is equipped with a pressure sensor to convert the force into an electrical signal. The controller controls the speed of the rewinding and unwinding servo motor to achieve tension control and adjust the tension of the coil; the guide adjustment mechanism 8 is arranged on the right side of the guide roller 5 to adjust the running state of the coil, the pressure roller 9 is arranged on the right side of the guide adjustment roller 8 to press the coil, the height adjustment mechanism 10 is arranged on the right side of the pressure roller 9 to adjust the running height of the coil for easy rewinding, and the automatic roll changing mechanism 11 is arranged on the right side of the height adjustment roller 10 to automatically The roll changing mechanism 11 includes a turntable 13, on the outer circumference of which a winding roller 14 and a spare winding roller 15 are provided. The central angle of the arc length formed between the winding roller 14 and the spare winding roller 15 is set to 90°, that is, the winding roller 14 and the spare winding roller 15 are arranged at a 90° interval on the outer circumference of the turntable 13, which makes it convenient to rotate the turntable 13 when changing the roll. The winding roller 14 and the spare winding roller 15 are respectively connected to the winding servo motor through a coupling. The upper and lower parts of the turntable 13 are respectively provided with a thickness detection mechanism 16, which includes a thickness detection cylinder 19 and a thickness detection roller 20. The extension of the thickness detection cylinder 19 A fixed block is provided on the retraction rod, and a thickness detection roller 20 is provided on the fixed block. A cutter 21 is provided on one side of the fixed block for cutting the film and measuring the thickness of the winding according to the telescopic length of the telescopic rod; the rear part of the turntable 13 is connected to the transmission shaft 17 by a rotation connection, the transmission shaft 17 is connected to the large pulley 18, the large pulley 18 is connected to the small pulley 12 by a belt drive, and the small pulley 12 is connected to the roll-changing servo motor through a coupling, and the roll-changing servo motor drives the small pulley 12 to rotate, and the small pulley 12 rotates and drives the large pulley 18 to realize the rotation of the transmission shaft 17, and finally controls the rotation angle of the turntable 13.

[0031] The height adjustment mechanism 10 includes a height adjustment cylinder 22 and a pair of rollers 23. A slider is provided on the telescopic rod of the height adjustment cylinder 22. The slider is set in a slide groove 24 of the fixed plate. The pair of rollers 23 are fixed on the slider. The slider slides in the slide groove 24, driving the pair of rollers 23 to move and adjust the height of the coil between the pair of rollers 23.

[0032] The pressure roller 9 includes an upper pressure roller 25 and a lower pressure roller 26, which are connected to an upper slider and a lower slider respectively. The upper slider and the lower slider are arranged in a groove 27 of the fixed profile in a sliding connection. The upper slider is connected to the top of the groove 27 of the fixed profile through a spring 29. A screw 28 is provided at the lower part of the lower slider. The position of the lower pressure roller 26 is adjusted by the screw 28, thereby changing the stretching length of the spring 29. The elastic force of the spring 29 stretching the upper pressure roller 25 changes. The pressure exerted by the upper pressure roller 25 on the film can be described as F=mg-kx, where mg is the gravity of the upper pressure roller 25. The pressure roller can press the two coils together, which is conducive to winding, prevents bubbles between the coils during the winding process, and improves the winding quality.

[0033] The guide adjustment mechanism 8 includes two upper and lower guide rollers 30, a telescopic rod 31, a fixed base 32, a connecting plate 33, and a screw 34. The fixed base 32 is connected to the fixed plate, and the connecting plate 33 is mounted on the fixed base 32. The fixed base 32 is provided with a rotating shaft 35. One end of the rotating shaft 35 is provided with a knob, and the other end of the rotating shaft 35 is fixedly connected to the telescopic rod 31. The telescopic rod 31 is connected to the guide roller 30 via a screw 34. By rotating the knob of the rotating shaft 35 on the fixed base 32, the guide roller 30 can be adjusted to any position within the radius of the telescopic rod 31. By changing the length of the telescopic rod 31, the guide roller 30 can be moved to any position in space. The guide roller 30 can be moved axially by rotating the screw 34. The arbitrary adjustment of the guide roller 30 facilitates tension control during the winding process and facilitates position changes. The axial movement of the guide roller 30 can achieve preliminary deviation correction of the coiled material.

[0034] In a second aspect, the present invention provides a method for controlling a film winding and unwinding device capable of automatic roll change, comprising the following steps:

[0035] 1) Two different coils are placed on the upper unwinding roller 4 and the lower unwinding roller 2 respectively. The coils pass through the guide roller 5, the upper tension detection roller 6, the lower tension detection roller 7, the guide adjustment mechanism 8, the pressure roller 9 and the counter roller 23 in sequence, and finally reach the winding roller 14;

[0036] 2) The thickness detection mechanism 16 on the upper part of the turntable 13 detects the winding thickness of the winding roller 14. The height adjustment cylinder 22 adjusts the height of the roller 23 by telescoping to keep the winding height of the coil level with the height of the coil on the winding roller 14. The diameter of the coil on the winding roller 14 gradually increases until the diameter of the winding roller 14 reaches the target value. The upper thickness detection mechanism 16 stops working.

[0037] 3) The turntable 13 rotates 90° counterclockwise through the transmission shaft 17, causing the winding roller 14 to rotate to the bottom of the turntable 13, while the counter roller 23 moves to the top, and the spare winding roller 15 rotates to the position of the thickness detection mechanism 16 at the bottom of the turntable 13. At this time, Figure 6 As shown, the coil is arranged in a straight line between the counter roller 23, the spare winding roller 15, and the winding roller 14. The thickness detection mechanism 16 at the bottom is working, and the thickness detection cylinder 19 is extended and retracted, controlling the thickness detection roller 20 and the spare winding roller 15 to press the coil. The cutter 21 cuts the coil, and the winding servo motor of the spare winding roller 15 starts working, completing a coil changing process.

[0038] 4) Similarly, when the thickness detection mechanism 16 at the bottom detects that the winding diameter of the spare winding roller 15 reaches the target value, the thickness detection mechanism 16 at the bottom stops working, and the turntable 13 rotates 90° clockwise through the transmission shaft 17, so that the spare winding roller 15 rotates to the upper end of the turntable 13, and at the same time, the roller 23 moves to the lower end, and the winding roller 14 rotates to the thickness detection mechanism position above the turntable 13. At this time, Figure 7 As shown, the coil is arranged in a straight line between the pair of rollers 23, the winding roller 14, and the spare winding roller 15. The upper thickness detection mechanism 16 works, the thickness detection cylinder 19 extends and retracts, and controls the thickness detection roller 20 and the winding roller 14 to press the coil, the cutter 21 cuts the coil, and the winding servo motor of the winding roller 14 starts working, and the coil changing process is started again.

[0039] Although the present invention has been described in detail with reference to the accompanying drawings and in conjunction with preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, persons of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be easily conceived by persons skilled in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention.

Claims

1. A control method for a film unwinding and rewinding device capable of automatic roll changing, comprising a film unwinding and rewinding device, wherein the film unwinding and rewinding device comprises a bracket, an unwinding roller, a tension detection and adjustment mechanism, a guide adjustment mechanism, a pressure roller, a height adjustment mechanism and an automatic roll changing mechanism; the bracket is provided with a fixed plate, the unwinding roller is provided on the fixed plate, the unwinding roller is connected to the unwinding servo motor through a coupling, the tension detection and adjustment mechanism is provided on the upper part of the unwinding roller; the guide adjustment mechanism is provided on one side of the tension detection and adjustment roller to adjust the running state of the roll; the pressure roller is provided on one side of the guide adjustment roller to press the roll; the height adjustment mechanism is provided on the upper part of the unwinding roller It is placed on one side of the pressure roller to adjust the running height of the coil; the automatic roll changing mechanism is arranged on one side of the height adjusting roller; the automatic roll changing mechanism includes a turntable, a winding roller and a spare winding roller are arranged on the outer circumference of the turntable, the winding roller and the spare winding roller are respectively connected to the winding servo motor through a coupling, the upper and lower parts of the turntable are respectively provided with a thickness detection mechanism, and the rear part of the turntable is connected to the transmission shaft by a rotating connection; the thickness detection mechanism includes a thickness detection cylinder and a thickness detection roller, a fixed block is provided on the telescopic rod of the thickness detection cylinder, the thickness detection roller is arranged on the fixed block, and a cutter is provided on one side of the fixed block; it is characterized in that The following steps are involved: 1) The coil is placed on the unwinding roller. The coil passes through the tension detection and adjustment mechanism, the guide adjustment mechanism, the pressure roller and the height adjustment mechanism in sequence, and finally reaches the winding roller. 2) The thickness detection mechanism on the upper part of the turntable detects the winding thickness of the winding roller. The height adjustment mechanism adjusts the winding height of the coil to make the winding height consistent with the height of the coil on the winding roller. The coil diameter of the winding roller gradually increases until the diameter of the winding roller reaches the target value. The upper thickness detection mechanism stops working. 3) The turntable rotates a certain angle through the transmission shaft, causing the winding roller to rotate to the bottom of the turntable. At the same time, the height adjustment mechanism moves to the top, and the standby winding roller rotates to the thickness detection mechanism position at the bottom of the turntable. At this time, the coil is arranged in a straight line between the height adjustment mechanism, the standby winding roller, and the winding roller. The thickness detection mechanism at the bottom works and expands and contracts. The standby winding roller presses the coil, and the tool of the thickness detection mechanism cuts the coil. The winding servo motor of the standby winding roller starts working, completing one roll changing process. 4) When the thickness detection mechanism at the lower part detects that the winding diameter of the spare winding roller reaches the target value, the thickness detection mechanism at the lower part stops working, and the turntable rotates a certain angle through the transmission shaft to rotate the spare winding roller to the upper end of the turntable. At the same time, the height adjustment mechanism moves to the lower end, and the winding roller rotates to the position of the thickness detection mechanism at the upper part of the turntable. At this time, the coil is arranged in a straight line between the height adjustment mechanism, the winding roller, and the spare winding roller. The thickness detection mechanism at the upper part works, the thickness detection mechanism extends and retracts, the winding roller presses the coil, the tool of the thickness detection mechanism cuts the coil, and the winding servo motor of the winding roller starts working, and the coil changing process begins again.

2. The control method of a film winding and unwinding device capable of automatic roll change according to claim 1, characterized in that: The transmission shaft is connected to the large pulley, the large pulley is connected to the small pulley through a belt transmission, and the small pulley is connected to the roll-changing servo motor through a coupling.

3. A control method for a film winding and unwinding device capable of automatic roll change according to claim 1 or 2, characterized in that: The center angle of the arc length formed between the winding roller and the spare winding roller is set to 90°.

4. The control method of a film winding and unwinding device capable of automatic roll change according to claim 3, characterized in that: The height adjustment mechanism includes a height adjustment cylinder and a pair of rollers. A slider is provided on the telescopic rod of the height adjustment cylinder. The slider is set in a sliding groove of the fixed plate, and the pair of rollers is fixed on the slider.

5. The control method of the film winding and unwinding device capable of automatic roll change according to claim 4, characterized in that: The pressure roller includes an upper pressure roller and a lower pressure roller, which are respectively connected to an upper slider and a lower slider. The upper slider and the lower slider are arranged in the groove of the fixed profile in a sliding connection manner. The upper slider is connected to the top of the fixed profile groove through a spring, and a screw is provided at the lower part of the lower slider.

6. The control method of the film winding and unwinding device capable of automatic roll change according to claim 5, characterized in that: The tension detection and adjustment mechanism comprises two tension guide rollers and a tension detection roller. The tension detection roller is arranged on the upper part of the two tension guide rollers, and the tension detection roller is provided with a pressure sensor.

7. The control method of the film winding and unwinding device capable of automatic roll change according to claim 6, characterized in that: The guide adjustment mechanism includes two upper and lower guide rollers, a telescopic rod, a fixed seat, a connecting plate and a screw. The fixed seat is connected to the fixed plate, and the connecting plate is arranged on the fixed seat. A rotating shaft is provided on the fixed seat. A knob is provided at one end of the rotating shaft, and the other end of the rotating shaft is fixedly connected to the telescopic rod. The telescopic rod is connected to the guide roller through a screw.

8. The control method of the film winding and unwinding device capable of automatic roll change according to claim 7, characterized in that: The unwinding roller comprises an upper unwinding roller and a lower unwinding roller.

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