Device for the insertion of an auxiliary mandrel into a PTFE inner tube

Abstract

The utility model provides a kind of device that assists mandrel to be worn into PTFE inner layer pipe, including vacuum clamping mechanism and conveying mechanism, vacuum clamping mechanism includes two first clamping units and vacuum pump, and the vacuum suction force generated by first clamping unit is adsorbed on the inner wall of first clamping unit by vacuum pump, and two first clamping units respectively adsorb the both ends of PTFE inner layer pipe;Conveying mechanism is close to one of two first clamping units, and two first clamping units are linearly distributed on the conveying path of conveying mechanism, and conveying mechanism includes first drive motor, first conveying caterpillar and second conveying caterpillar, and first drive motor is used to drive first conveying caterpillar rotation, and second conveying caterpillar is matched with first conveying caterpillar to jointly drive mandrel to move towards the direction of first clamping unit and promote mandrel to be worn into PTFE inner layer pipe.

Description

Technical Field

[0001] This utility model relates to the field of medical catheter technology, and in particular to a device for assisting the insertion of a mandrel into a PTFE inner tube. Background Technology

[0002] Currently, medical catheters generally have a three-layer structure. PTFE has extremely low lubricity, so it is widely used in the inner layer of medical catheters.

[0003] In existing technologies, the manufacturing process of medical catheters generally involves first fitting a PTFE inner tube onto a mandrel, followed by subsequent processing. However, because the PTFE inner tube is typically quite thin, workers must be careful and slow when fitting it onto the mandrel. This not only results in long manual operation times and low efficiency, but also increases the risk of damaging the PTFE inner tube due to uneven or excessive pushing force, leading to product defects and affecting product quality. Utility Model Content

[0004] The purpose of this invention is to provide a device for assisting the insertion of a mandrel into a PTFE inner tube, aiming to solve or at least partially solve the shortcomings of the aforementioned background technology. It uses a conveyor belt to semi-automatically and continuously and stably insert the mandrel into the PTFE inner tube, thereby achieving the PTFE inner tube being fitted onto the mandrel. This not only significantly reduces manual operation and improves production efficiency, but also reduces defects such as damage to the PTFE inner tube caused by uneven pushing or excessive pushing force due to manual operation, thus improving the product qualification rate.

[0005] This utility model provides a device for assisting the insertion of a mandrel into a PTFE inner tube, including a vacuum clamping mechanism and a conveying mechanism. The vacuum clamping mechanism includes two first clamping units and a vacuum pump. The first clamping units use the vacuum suction generated by the vacuum pump to adsorb the PTFE inner tube onto the inner wall of the first clamping unit. The two first clamping units respectively adsorb and fix both ends of the PTFE inner tube. The conveying mechanism is located close to one of the two first clamping units, and the two first clamping units are linearly distributed on the conveying path of the conveying mechanism. The conveying mechanism includes a first drive motor, a first conveying track, and a second conveying track. The first drive motor is used to drive the first conveying track to rotate. The second conveying track cooperates with the first conveying track to jointly drive the mandrel towards the first clamping unit and push the mandrel into the PTFE inner tube.

[0006] Optionally, each first clamping unit consists of two symmetrically arranged first vacuum suction claws. The cross-section of the first vacuum suction claw is arc-shaped and the centers of the cross-sections of the two first vacuum suction claws are the same. The two first vacuum suction claws cooperate to clamp the PTFE inner tube. When the two first vacuum suction claws clamp the PTFE inner tube, the inner wall of the first vacuum suction claw abuts against the outer wall of the PTFE inner tube.

[0007] Optionally, the inner diameter d1 of the first clamping unit is greater than or equal to the outer diameter D1 of the PTFE inner tube.

[0008] Optionally, the distance L between the first conveyor track and the second conveyor track is less than or equal to the outer diameter D2 of the mandrel.

[0009] Optionally, the first conveyor track and the second conveyor track are arranged in parallel.

[0010] Optionally, the vacuum clamping mechanism further includes at least one second clamping unit disposed between the two first clamping units.

[0011] Optionally, each second clamping unit consists of two symmetrically arranged second vacuum suction claws. The cross-section of the second vacuum suction claw is arc-shaped and the centers of the cross-sections of the two second vacuum suction claws are the same. The two second vacuum suction claws cooperate to clamp the PTFE inner tube. When the two second vacuum suction claws clamp the PTFE inner tube, the inner wall of the second vacuum suction claw abuts against the outer wall of the PTFE inner tube.

[0012] Optionally, the inner diameter d2 of the second clamping unit is greater than or equal to the outer diameter D1 of the PTFE inner tube.

[0013] Optionally, the conveying mechanism further includes a second drive motor for driving the second conveyor track to rotate.

[0014] Optionally, the first drive motor and the second drive motor have the same rotation speed and opposite rotation directions.

[0015] This utility model provides a device for assisting the insertion of a mandrel into a PTFE inner tube. Through the cooperation of a first clamping unit and a vacuum pump, the vacuum suction generated by the vacuum pump causes the first clamping unit to adhere to the outer wall of the PTFE inner tube, thereby clamping and fixing both ends of the PTFE inner tube to keep it straight, so that the mandrel can be smoothly inserted. Through the cooperation of a first drive motor, a first conveyor belt, and a second conveyor belt, the mandrel is clamped between the first and second conveyor belts. The first drive motor drives the first conveyor belt to rotate, which in turn drives the second conveyor belt to rotate and the mandrel to move along the PTFE inner tube, so that the mandrel can be inserted into the PTFE inner tube at a uniform speed and slowly. In existing technologies, it takes approximately 5-10 minutes to manually insert a single mandrel into the PTFE inner tube, with a product qualification rate of 80%. This invention significantly reduces manual operation time while simultaneously improving the product qualification rate, taking only about 1 minute to insert a single mandrel into the PTFE inner tube, achieving a 100% product qualification rate. Therefore, this invention not only significantly reduces manual operation and improves production efficiency but also reduces defects such as damage to the PTFE inner tube caused by uneven pushing or excessive pushing force during manual operation, thus further improving the product qualification rate. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this utility model and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of an auxiliary mandrel inserted into a PTFE inner tube according to Embodiment 1 of this utility model.

[0018] Figure 2 for Figure 1 A magnified diagram of point A in the middle.

[0019] Figure 3 for Figure 1 A magnified diagram of point B in the middle.

[0020] Figure 4 for Figure 1 A schematic diagram of the first clamping unit is shown.

[0021] Figure 5 for Figure 4 The first clamping unit shown is a cross-sectional view.

[0022] Figure 6This is a schematic diagram of an auxiliary mandrel inserted into a PTFE inner tube according to Embodiment 2 of this utility model.

[0023] Figure 7 for Figure 6 A magnified diagram of point C.

[0024] Figure 8 for Figure 6 A schematic diagram of the second clamping unit is shown.

[0025] Figure 9 for Figure 8 The cross-sectional view of the second clamping unit shown.

[0026] Figure 10 This is a schematic diagram of an auxiliary mandrel inserted into a PTFE inner tube according to Embodiment 3 of this utility model.

[0027] The attached diagram lists the components represented by each number as follows: 10. Vacuum clamping mechanism; 11. First clamping unit; 111. First vacuum suction claw; 112. First adsorption hole; 12. Second clamping unit; 121. Second vacuum suction claw; 122. Second adsorption hole; 20. Conveying mechanism; 21. First conveyor belt; 22. Second conveyor belt; 23. First drive motor; 24. Second drive motor; 100. PTFE inner tube; 200. Mandrel. Detailed Implementation

[0028] The specific embodiments of this utility model will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, of the embodiments of this utility model. Based on the description of this utility model, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this utility model.

[0029] Unless otherwise explicitly specified and limited, the terms "setup," "installation," and "connection" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of these terms based on the specific circumstances.

[0030] The terms “upper,” “lower,” “left,” “right,” “front,” “back,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of description and simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0031] The terms “first,” “second,” “third,” etc., are used merely to distinguish elements with similar attributes, not to indicate or imply relative importance or a specific order.

[0032] The terms “include,” “comprising,” or any other variation thereof are intended to cover non-exclusive inclusion, which includes not only the elements listed but also other elements not expressly listed.

[0033] Example 1: Please see Figures 1-5 A device for assisting the insertion of a mandrel into a PTFE inner tube includes a vacuum clamping mechanism 10 and a conveying mechanism 20.

[0034] The vacuum clamping mechanism 10 includes two first clamping units 11 and a vacuum pump (not shown). The first clamping unit 11 uses the vacuum suction force generated by the vacuum pump to adsorb the PTFE inner tube 100 onto the inner wall of the first clamping unit 11. The two first clamping units 11 respectively adsorb and fix the two ends of the PTFE inner tube 100.

[0035] The conveying mechanism 20 is positioned close to one of the two first clamping units 11, and the two first clamping units 11 are arranged in a straight line on the conveying path of the conveying mechanism 20. The conveying mechanism 20 includes a first drive motor 23, a first conveying track 21, and a second conveying track 22. The first drive motor 23 is used to drive the first conveying track 21 to rotate. The second conveying track 22 cooperates with the first conveying track 21 to jointly drive the mandrel 200 to move toward the first clamping unit 11 and push the mandrel 200 into the PTFE inner tube 100.

[0036] As described above, the present invention provides an auxiliary device for inserting a mandrel into a PTFE inner tube. Through the cooperation of the first clamping unit 11 and the vacuum pump, the vacuum suction generated by the vacuum pump causes the first clamping unit 11 to adhere to the outer wall of the PTFE inner tube 100, thereby fixing both ends of the PTFE inner tube 100 and keeping it straight so that the mandrel 200 can be smoothly inserted. Through the cooperation of the first drive motor 23, the first conveyor belt 21, and the second conveyor belt 22, the mandrel 200 is clamped between the first conveyor belt 21 and the second conveyor belt 22. The first drive motor 23 drives the first conveyor belt 21 to rotate, and the first conveyor belt 21 simultaneously drives the second conveyor belt 22 to rotate and the mandrel 200 to move towards the PTFE inner tube 100, so that the mandrel 200 is inserted into the PTFE inner tube 100 at a uniform speed and slowly. In the existing technology, it takes about 5-10 minutes to manually insert a single mandrel 200 into the PTFE inner tube 100, and the product qualification rate is 80%. However, this utility model can significantly reduce the time of manual operation and improve the product qualification rate. It takes about 1 minute to insert a single mandrel 200 into the PTFE inner tube 100, and the product qualification rate is 100%. Therefore, this utility model can not only significantly reduce manual operation and improve production efficiency, but also reduce defects such as damage to the PTFE inner tube 100 caused by uneven pushing or excessive pushing force during manual operation, and improve the product qualification rate.

[0037] Furthermore, each first clamping unit 11 consists of two symmetrically arranged first vacuum suction claws 111. The cross-section of the first vacuum suction claw 111 is arc-shaped and the centers of the cross-sections of the two first vacuum suction claws 111 are the same. The two first vacuum suction claws 111 cooperate to clamp the PTFE inner tube 100. When the two first vacuum suction claws 111 clamp the PTFE inner tube 100, the inner wall of the first vacuum suction claw 111 abuts against the outer wall of the PTFE inner tube 100, so that the first clamping unit 11 clamps and adsorbs and fixes the two ends of the PTFE inner tube 100. Moreover, the suction force of the first clamping unit 11 can keep the tube openings at both ends of the PTFE inner tube 100 in a maximum open state so that the mandrel 200 can be smoothly inserted.

[0038] In this embodiment, the cross-section of the first vacuum suction claw 111 is semi-circular, and the cross-section of the first clamping unit 11 is circular. When the two first vacuum suction claws 111 clamp the PTFE inner tube 100, the two first vacuum suction claws 111 surround the circumference of the PTFE inner tube 100, making the fixation of the two ends of the PTFE inner tube 100 by the first clamping unit 11 more stable.

[0039] More specifically, the inner wall of the first vacuum gripper 111 is provided with at least one first adsorption hole 112, which is connected to a vacuum pump, enabling the first vacuum gripper 111 to clamp and adsorb the PTFE inner tube 100. In this embodiment, the inner wall of the first vacuum gripper 111 is provided with two first adsorption holes 112, and the vacuum degree generated by the first vacuum gripper 111 during operation is -30 Pa.

[0040] Furthermore, the inner diameter d1 of the first clamping unit 11 is greater than or equal to the outer diameter D1 of the PTFE inner tube 100. This setting ensures that the PTFE inner tube 100 can be inserted into the first clamping unit 11 and avoids the first vacuum suction claw 111 from squeezing the PTFE inner tube 100, which would cause the mandrel 200 to damage the PTFE inner tube 100 during the insertion process.

[0041] Furthermore, the distance L between the first conveyor belt 21 and the second conveyor belt 22 is less than or equal to the outer diameter D2 of the mandrel 200. This arrangement ensures that the first conveyor belt 21 and the second conveyor belt 22 clamp the mandrel 200, so that the first conveyor belt 21 can simultaneously drive the second conveyor belt 22 to rotate and the mandrel 200 to move towards the PTFE inner tube 100, thereby realizing that the mandrel 200 enters the PTFE inner tube 100 at a uniform speed and slowly.

[0042] Furthermore, the first conveyor track 21 and the second conveyor track 22 are arranged in parallel, which makes the process of the conveyor mechanism 20 pushing the spindle 200 more stable and uniform.

[0043] The working process of the device for inserting the auxiliary mandrel into the PTFE inner tube provided in this embodiment: (1) The operator inserts both ends of the PTFE inner tube 100 into the two first clamping units 11 respectively to complete the initial clamping of the PTFE inner tube 100; then, the vacuum pump is started, the first vacuum suction claw 111 generates vacuum suction and adsorbs the PTFE inner tube 100 to complete the fixation of the PTFE inner tube 100.

[0044] (2) The operator places the mandrel 200 between the first conveyor belt 21 and the second conveyor belt 22, so that the first conveyor belt 21 and the second conveyor belt 22 clamp the mandrel 200; then, the first drive motor 23 is started, and the first conveyor belt 21 and the second conveyor belt 22 rotate synchronously and drive the mandrel 200 to approach the PTFE inner tube 100.

[0045] (3) The mandrel 200 is gradually inserted into the PTFE inner tube 100 until the mandrel 200 is completely inserted into the PTFE inner tube 100. The operator then turns off the vacuum pump and the first drive motor 23, and the work is completed.

[0046] Example 2: A device for inserting an auxiliary mandrel into a PTFE inner tube, the structure of which is similar to that of the device for inserting an auxiliary mandrel into a PTFE inner tube in Example 1, the difference being: Please see Figures 6-9 The vacuum clamping mechanism 10 also includes at least one second clamping unit 12, which is disposed between two first clamping units 11, and the first clamping units 11 and the second clamping unit 12 are linearly distributed on the conveying path of the conveying mechanism 20. The second clamping unit 12 can support the middle section of the PTFE inner tube 100, keeping it straight so that the mandrel 200 can be smoothly inserted, while preventing the mandrel 200 from damaging the PTFE inner tube 100.

[0047] Furthermore, each second clamping unit 12 consists of two symmetrically arranged second vacuum suction claws 121. The cross-section of the second vacuum suction claws 121 is arc-shaped and the centers of the cross-sections of the two second vacuum suction claws 121 are the same. The two second vacuum suction claws 121 cooperate to clamp the PTFE inner tube 100. When the two second vacuum suction claws 121 clamp the PTFE inner tube 100, the inner wall of the second vacuum suction claws 121 abuts against the outer wall of the PTFE inner tube 100, so that the second clamping unit 12 clamps and adsorbs and fixes the middle section of the PTFE inner tube 100. Moreover, the suction force of the second clamping unit 12 can keep the middle section of the PTFE inner tube 100 in a maximally open state so that the mandrel 200 can be smoothly inserted.

[0048] In this embodiment, the cross-section of the second vacuum suction claw 121 is semi-circular, and the cross-section of the second clamping unit 12 is circular. When the two second vacuum suction claws 121 clamp the PTFE inner tube 100, the two second vacuum suction claws 121 surround the circumference of the PTFE inner tube 100, making the fixation of the two ends of the PTFE inner tube 100 by the second clamping unit 12 more stable.

[0049] More specifically, the inner wall of the second vacuum gripper 121 is provided with at least one second adsorption hole 122, which is connected to a vacuum pump, so that the second vacuum gripper 121 can clamp and adsorb the PTFE inner tube 100. In this embodiment, the inner wall of the second vacuum gripper 121 is provided with two second adsorption holes 122.

[0050] Furthermore, the inner diameter d2 of the second clamping unit 12 is greater than or equal to the outer diameter D1 of the PTFE inner tube 100. This setting ensures that the PTFE inner tube 100 can be inserted into the second clamping unit 12 and avoids the second vacuum suction claw 121 from squeezing the PTFE inner tube 100, which would cause the mandrel 200 to damage the PTFE inner tube 100 during the insertion process.

[0051] The working process of the device for inserting the auxiliary mandrel into the PTFE inner tube provided in this embodiment: (1) The operator inserts the PTFE inner tube 100 into the first clamping unit 11 and the second clamping unit 12 to complete the initial clamping of the PTFE inner tube 100; then, the vacuum pump is started, the first vacuum suction claw 111 generates vacuum suction and adsorbs the two ends of the PTFE inner tube 100, and the second vacuum suction claw 121 generates vacuum suction and adsorbs the middle section of the PTFE inner tube 100 to complete the fixation of the PTFE inner tube 100.

[0052] (2) The operator places the mandrel 200 between the first conveyor belt 21 and the second conveyor belt 22, so that the first conveyor belt 21 and the second conveyor belt 22 clamp the mandrel 200; then, the first drive motor 23 is started, and the first conveyor belt 21 and the second conveyor belt 22 rotate synchronously and drive the mandrel 200 to approach the PTFE inner tube 100.

[0053] (3) The mandrel 200 is gradually inserted into the PTFE inner tube 100 until the mandrel 200 is completely inserted into the PTFE inner tube 100. The operator then turns off the vacuum pump and the first drive motor 23, and the work is completed.

[0054] Example 3: A device for inserting an auxiliary mandrel into a PTFE inner tube, the structure of which is similar to that of the device for inserting an auxiliary mandrel into a PTFE inner tube in Embodiment 1, the difference being: Please see Figure 10 The conveying mechanism 20 also includes a second drive motor 24, which drives the second conveyor belt 22 to rotate. This arrangement not only makes the movement of the mandrel 200 smoother and more uniform, but also allows the first conveyor belt 21 and the second conveyor belt 22 to rotate simultaneously and independently. This is a redundant design; if one of the first drive motor 23 or the second drive motor 24 fails, the other can take over the operation, still maintaining the normal operation of the device and enhancing the fault tolerance of the device for the auxiliary mandrel to penetrate the PTFE inner tube.

[0055] Furthermore, the first drive motor 23 and the second drive motor 24 have the same rotation speed and opposite rotation directions, thereby enabling the first conveyor track 21 and the second conveyor track 22 to jointly drive the spindle 200 to move toward the PTFE inner tube 100.

[0056] The working process of the device for inserting the auxiliary mandrel into the PTFE inner tube provided in this embodiment: (1) The operator inserts both ends of the PTFE inner tube 100 into the two first clamping units 11 respectively to complete the initial clamping of the PTFE inner tube 100; then, the vacuum pump is started, the first vacuum suction claw 111 generates vacuum suction and adsorbs the PTFE inner tube 100 to complete the fixation of the PTFE inner tube 100.

[0057] (2) The operator places the mandrel 200 between the first conveyor belt 21 and the second conveyor belt 22, so that the first conveyor belt 21 and the second conveyor belt 22 clamp the mandrel 200; then, the first drive motor 23 and the second drive motor 24 are started, and the first conveyor belt 21 and the second conveyor belt 22 rotate synchronously and drive the mandrel 200 to approach the PTFE inner tube 100.

[0058] (3) The mandrel 200 is gradually inserted into the PTFE inner tube 100 until the mandrel 200 is completely inserted into the PTFE inner tube 100. The operator then turns off the vacuum pump, the first drive motor 23, and the second drive motor 24, and the work is completed.

[0059] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.

Claims

1. A device for assisting the insertion of a mandrel into a PTFE inner tube, characterized in that, include: The vacuum clamping mechanism (10) includes two first clamping units (11) and a vacuum pump. The first clamping unit (11) uses the vacuum suction generated by the vacuum pump to adsorb the PTFE inner tube (100) onto the inner wall of the first clamping unit (11). The two first clamping units (11) respectively adsorb and fix the two ends of the PTFE inner tube (100). The conveying mechanism (20) is located near one of the two first clamping units (11), and the two first clamping units (11) are arranged in a straight line on the conveying path of the conveying mechanism (20). The conveying mechanism (20) includes a first drive motor (23), a first conveying track (21) and a second conveying track (22). The first drive motor (23) is used to drive the first conveying track (21) to rotate. The second conveying track (22) cooperates with the first conveying track (21) to jointly drive the mandrel (200) to move toward the first clamping unit (11) and push the mandrel (200) into the PTFE inner tube (100).

2. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 1, characterized in that, Each of the first clamping units (11) consists of two symmetrically arranged first vacuum suction claws (111). The cross-section of the first vacuum suction claw (111) is arc-shaped and the center of the cross-section of the two first vacuum suction claws (111) is the same. The two first vacuum suction claws (111) cooperate to clamp the PTFE inner tube (100). When the two first vacuum suction claws (111) clamp the PTFE inner tube (100), the inner wall of the first vacuum suction claw (111) abuts against the outer wall of the PTFE inner tube (100).

3. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 2, characterized in that, The inner diameter d1 of the first clamping unit (11) is greater than or equal to the outer diameter D1 of the PTFE inner tube (100).

4. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 1, characterized in that, The distance L between the first conveyor track (21) and the second conveyor track (22) is less than or equal to the outer diameter D2 of the mandrel (200).

5. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 1, characterized in that, The first conveyor track (21) is arranged in parallel with the second conveyor track (22).

6. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 1, characterized in that, The vacuum clamping mechanism (10) further includes at least one second clamping unit (12), which is disposed between two first clamping units (11).

7. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 6, characterized in that, Each of the second clamping units (12) consists of two symmetrically arranged second vacuum suction claws (121). The cross-section of the second vacuum suction claw (121) is arc-shaped and the center of the cross-section of the two second vacuum suction claws (121) is the same. The two second vacuum suction claws (121) cooperate to clamp the PTFE inner tube (100). When the two second vacuum suction claws (121) clamp the PTFE inner tube (100), the inner wall of the second vacuum suction claw (121) abuts against the outer wall of the PTFE inner tube (100).

8. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 7, characterized in that, The inner diameter d2 of the second clamping unit (12) is greater than or equal to the outer diameter D1 of the PTFE inner tube (100).

9. The device for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 1, characterized in that, The conveying mechanism (20) further includes a second drive motor (24), which is used to drive the second conveyor track (22) to rotate.

10. The apparatus for inserting an auxiliary mandrel into a PTFE inner tube as described in claim 9, characterized in that, The first drive motor (23) and the second drive motor (24) have the same rotation speed and opposite rotation directions.

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