Medical catheter structure

Abstract

The invention discloses a medical catheter structure which comprises a catheter body, the catheter body is of a hollow structure, a plurality of cutting areas extending in the circumferential direction and a plurality of connecting ribs arranged in the cutting areas are arranged on the catheter body in the axis direction of the catheter body, and the cutting areas can be strip-shaped groove or spiral groove cutting areas. The pipe body is not provided with two sections with the same distribution positions of the connecting ribs in the annular direction. The harmful bending moment effect of the guide pipe is reduced by arranging the connecting ribs in the strip-shaped groove cutting area, so that the same capacity of the axial rigidity, the torsional rigidity and the bending rigidity in any bending direction of the guide pipe is continuously and gradually changed; the spring effect of the pure spiral cutting groove guide pipe is reduced by arranging the spring eliminating ribs and the moment eliminating ribs in the spiral cutting groove cutting area.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and in particular to a medical catheter structure. Background Art

[0002] Minimally invasive interventional surgery causes less trauma, allowing many patients in poor physical condition to receive treatment, and therefore has been increasingly used. Interventional surgery cannot be done without catheters. Angiography catheters are needed to observe lesions; during treatment, guide catheters are needed to protect the blood vessels that the device must pass through. Catheter products are the main tools for establishing pathways in interventional treatments, and they have high requirements for pushability, tracking, twist control, flexibility, and anti-bending properties.

[0003] By cutting different patterns on the tube body, the catheter can have better performance to meet the clinical needs of the catheter. Currently, the most common sea wave tube cutting patterns are wavy, serrated, pure spiral cutting, and cutting groove patterns. The existing cutting structures have their own advantages in performance characteristics, design difficulty, and process efficiency, but because of the lack of material on the cross section, there are harmful bending moment effects that are not conducive to catheter delivery and distal stability. In addition, the pure spiral structure has a spring effect that does not utilize catheter tracking, passing, and pushing because its structure is similar to a spring. Summary of the invention

[0004] In order to solve the problem in the prior art that the catheter structure has poor delivery, distal stability, passability and pushing performance due to the difference in bending stiffness in different directions and the spring effect.

[0005] The present application provides a medical catheter structure, including a tube body, wherein the tube body is a hollow structure, and the tube body is provided with a plurality of cutting areas extending in a circumferential direction and a plurality of connecting ribs arranged in the cutting areas along its axial direction, and the tube body does not have two sections of the connecting ribs having the same distribution position in the circumferential direction.

[0006] Furthermore, the cutting area is a strip groove, and a plurality of the strip grooves are arranged at intervals along the axial direction of the tube body.

[0007] Furthermore, when the number n of all the connecting ribs in the same strip groove is an odd number, the connecting ribs are evenly arranged in the circumferential direction of the tube body;

[0008] When the number n of all the connecting ribs in the same strip groove is an even number, the first n / 2 connecting ribs and the last n / 2 connecting ribs are arranged clockwise or counterclockwise at an angle of 360 / n, and the angle between the n / 2th connecting rib and the n / 2+1th connecting rib is 540 / n.

[0009] Further, the angle between two adjacent connecting ribs in the same strip-shaped groove is the rib distribution angle, and the rib distribution angle is 90° to 135°.

[0010] Further, the rib helix angle of the connecting rib is 30° to 150°.

[0011] Further, the difference between the rib distribution angle and the rib helix angle is greater than or equal to 20°.

[0012] Further, the cutting area is a spiral cutting groove provided on the pipe body. A plurality of connecting ribs are provided in the spiral cutting groove. The connecting ribs include anti-spring ribs and anti-moment ribs. The anti-spring ribs and the anti-moment ribs are arranged in sequence and cyclically along the axial direction of the pipe body.

[0013] Further, the anti-spring helix angle between two adjacent anti-spring ribs is greater than or equal to 430°.

[0014] Further, the pipe body is evenly divided into four regions in the circumferential direction. Two adjacent anti-spring ribs and anti-moment ribs are respectively arranged in two adjacent regions, and all the anti-spring ribs and the anti-moment ribs are evenly distributed in the four regions of the pipe body.

[0015] Further, the offset angle between two adjacent anti-spring ribs and anti-moment ribs is the spring-moment offset angle, and the spring-moment offset angle is 80° to 100°.

[0016] The present application has the following beneficial effects:

[0017] By setting the connecting ribs in the cutting area of the strip-shaped groove in the present application, the harmful bending moment effect of the catheter is reduced, so that the axial stiffness, torsional stiffness and the same ability of the bending stiffness in any bending direction of the catheter are continuously changed; by setting the anti-spring ribs and anti-moment ribs in the cutting area of the spiral cutting groove, the spring effect of the catheter with a pure spiral cutting groove is reduced, and the change of the bending stiffness of the catheter along the axial direction in any direction is consistent. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is the cylindrical surface development view of the catheter with 2 connecting ribs in the same strip-shaped groove in Embodiment 1 of the present invention;

[0020] Figure 2 It is the cross-sectional view of the catheter with 2 connecting ribs in the same strip-shaped groove in Embodiment 1 of the present invention;

[0021] Figure 3 This is a cylindrical surface development diagram of a conduit with three connecting ribs in the same strip groove of Example 1 of the present invention;

[0022] Figure 4 is a cross-sectional view of a conduit having three connecting ribs in the same strip groove according to Example 1 of the present invention;

[0023] Figure 5 is a cylindrical surface development diagram of the medical catheter structure of Example 2 of the present invention;

[0024] Figure 6 This is the cross-sectional stress distribution diagram of the uncut hypotube and the pure spiral cut conduit when bending deformation occurs.

[0025] The corresponding reference numerals in the figures are: tube body 1, spiral cutting groove 2, strip groove 3, connecting rib 4, elastic rib 41, moment rib 42. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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 creative work are within the scope of protection of the present invention.

[0027] In the description of the present invention, it should be understood that the terms "upper", "lower", "inner", "outer", "top", "bottom", "side", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. The terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0028] In addition, in the present invention, unless otherwise clearly specified and limited, the terms "installation", "connection" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] Medical catheters can be used in a variety of interventional device products, such as microcatheters, microguidewires, balloon catheters, thrombectomy stents / coil delivery guidewires, etc. Different cutting patterns are used in different devices to meet their corresponding performance requirements. Currently, the most common tube cutting patterns are pure spiral cutting and cutting groove patterns. These two cutting structures have their own advantages in performance characteristics, design difficulty, and process efficiency, but because of the lack of material on the cross section, both have harmful bending moment effects that are not conducive to catheter delivery and distal stability. In addition, the pure spiral structure has a spring effect that does not utilize catheter tracking, passing, and pushing because its structure is similar to a spring.

[0030] The spring effect refers to when the cutting structure of the catheter is similar to a spring, such as pure spiral cutting. Under the same stiffness design, because the cutting groove exists in a complete spiral line on the tube body from beginning to end, the pure spiral cutting catheter will store more strain energy when facing deformation forms such as stretching, compression, bending, and torsion. This will cause the problem of delayed distal action or even sudden distal action when operating the catheter at the proximal end.

[0031] Harmful bending moment effect refers to the situation that under a specific cross section, there is usually a tube cross section with missing materials and poor symmetry. When facing tensile, compressive, and bending deformation, additional bending moment will be generated, causing unexpected deflection of the catheter. The essential source of this bending moment effect is that the positive stress distribution on the poorly symmetrical cross section causes uneven bending moment in a certain direction. Poor symmetry means that the cross section of the tube cannot achieve axial symmetry about any axis. In medical applications, catheters will face various bending environments, so it is necessary to reduce or eliminate harmful bending moment effects and improve the stability of catheter push.

[0032] The harmful bending moment effect is further explained by analyzing the stress of uncut hypotubes, pure spiral cut hypotubes, and cut groove pattern hypotubes during bending deformation. Figure 6 As shown in (a), when the bending moment M is applied to the two ends of the uncut hypotube to cause bending deformation, because the cross section of the uncut hypotube is axisymmetric about any axis passing through the center of the circle, the resultant bending moment of the normal stress on the cross section to Y is 0, that is, no additional harmful bending moment effect is generated. Figure 6 As shown in (b), when the two ends of the pure spiral cutting catheter are bent and deformed by the bending moment M, such as the smiley face bending with X as the neutral layer, the cross-sectional stress distribution is the same as above. However, due to the pure spiral cutting, there is a notch feature in the cross section, and the stress disappears here. Therefore, in the Y-axis direction perpendicular to the current neutral axis X, the positive stress on the cross section is no longer zero, and an additional harmful bending moment effect will be generated, which will cause the pure spiral cutting sea wave tube to bend along the Y-axis, which is manifested as an uncontrolled and random swing at the distal end of the catheter.

[0033] The cross-sectional shape of the cut-groove patterned corrugated tube also has material deficiencies, and the missing areas are related to the number and width of the ribs in the cut grooves. However, since axial symmetry about any axis passing through the center of the circle cannot be achieved for the cross-section, harmful bending moment effects similar to those of the purely helically cut corrugated tube will inevitably occur.

[0034] Embodiment 1

[0035] In view of the problems such as harmful bending moment effects and spring effects existing in existing medical catheters, Embodiment 1 of the present application provides a medical catheter structure, as Figures 1-4 shown, including a tube body 1. The tube body 1 is a hollow structure. Along the axial direction of the tube body 1, there are a plurality of cutting areas extending circumferentially and a plurality of connecting ribs 4 arranged in the cutting areas. There are no two sections on the tube body 1 where the distribution positions of the connecting ribs 4 in the circumferential direction are the same.

[0036] Specifically, the cutting area is a strip-shaped groove 3, and a plurality of strip-shaped grooves 3 are arranged at intervals along the axial direction of the tube body 1. At least two connecting ribs 4 are arranged in each strip-shaped groove 3, and all the connecting ribs 4 are arranged helically along the axial direction of the tube body 1.

[0037] Specifically, in some embodiments, when aiming to reduce the difference in bending stiffness in different directions of the same cross-section, the distribution of the connecting ribs 4 in the same strip-shaped groove should be such that the most unfavorable bending directions of different ribs, that is, the directions with the largest moment of inertia of the ribs, are evenly distributed on the circumference. When the number n of all the connecting ribs 4 in the same strip-shaped groove 3 is odd, the connecting ribs 4 are evenly arranged in the circumferential direction of the tube body 1, that is, all the connecting ribs are arranged in sequence clockwise or counterclockwise at an angle of 360 / n. When the number n of all the connecting ribs 4 in the same strip-shaped groove 3 is even, the first n / 2 connecting ribs 4 and the last n / 2 connecting ribs 4 are arranged in sequence clockwise or counterclockwise at an angle of 360 / n, and the angle between the n / 2-th connecting rib 4 and the (n / 2 + 1)-th connecting rib 4 is 540 / n. The number of the connecting ribs 4 can be determined according to the required bending stiffness and torsional stiffness of the catheter. A smaller number of connecting ribs can make the catheter more flexible, and a larger number of connecting ribs can make the catheter more rigid. In some embodiments, the number of the connecting ribs can generally be set to 2 to 4.

[0038] In some other embodiments, when aiming to reduce the harmful bending moment effect of the defect cross-section, the distribution of the connecting ribs 4 in the same strip-shaped groove should minimize the additional bending moment effect in any direction of the cross-section. Specifically, the pipe body 1 is evenly divided into four regions in the circumferential direction, and two adjacent connecting ribs 4 in the same strip-shaped groove 3 are arranged in two adjacent regions, and all the connecting ribs 4 are evenly distributed in the four regions of the pipe body 1. That is, a rectangular coordinate system in any direction is established on the cross-section of the pipe body 1, and all the connecting ribs should fall into adjacent quadrants with the highest probability and the number of connecting ribs in each quadrant should be minimized. Optionally, the distribution angle between the connecting ribs with opposite or the same direction of stress on the cross-section of the pipe body is most likely to be between 90° and 180°. Specifically, the included angle between two adjacent connecting ribs 4 in the same strip-shaped groove 3 is the rib distribution angle α, and the rib distribution angle α is 90° to 135°. Preferably, when the number n of the connecting ribs 4 is 2, the rib distribution angle α is 90°; when n = 3, the rib distribution angle α > 90°, preferably 120°; when n = 4, the rib distribution angle α is 90°. Exemplarily, as Figure 1 and 2 show the possible distribution of the connecting ribs 4 on the cross-section of the pipe body at the strip-shaped groove when the number of the connecting ribs 4 in the same strip-shaped groove is 2; as Figure 3 and 4 show the possible distribution of the connecting ribs 4 on the cross-section of the pipe body at the strip-shaped groove when the number of the connecting ribs 4 in the same strip-shaped groove is 3.

[0039] Based on the two principles of reducing the difference in bending stiffness in different directions of the same cross-section and reducing the harmful bending moment effect of the defect cross-section, the distribution angle between adjacent connecting ribs under different numbers of connecting ribs can be determined in this embodiment.

[0040] Specifically, in some embodiments, the rib helix angle β of the connecting ribs 4 is 30° to 150°. Specifically, in some embodiments, the difference between the rib distribution angle and the rib helix angle is greater than or equal to 20°. All the connecting ribs 4 in this embodiment are helically arranged along the axial direction of the pipe body 1, and the offset angle between the connecting ribs in two adjacent strip-shaped grooves is the rib helix angle β. The purpose of setting the rib helix angle β is to evenly distribute the asymmetric defects on each strip-shaped groove cross-section along the circumference in the axial direction. On the one hand, it ensures that the conduit can exhibit the same stiffness characteristics in any direction, and on the other hand, it can offset the harmful bending moment effect that is difficult to completely eliminate in each cross-section through a proper rib helix angle design.

[0041] Design principle of the rib helix angle β in this embodiment: (1) To avoid slow change in the most difficult bending direction of the catheter along the axial direction (where the moment of inertia of the corresponding cross-section is the largest), resulting in differences in bending stiffness in different directions, the rib helix angle β is 30° to 150°. (2) Based on the number of slot rows of the strip-shaped groove 3 on the tube body, so that there are no two sections on the tube body 1 where the distribution positions of the connecting ribs 4 are the same in the circumferential direction, that is, all the connecting ribs 4 are evenly distributed in the circumferential direction, and the exact value of the rib helix angle β is calculated. (3) Ensure that the most difficult bending direction changes rapidly in the axial direction, that is, the distribution of the same or approximate most difficult bending direction in the axial direction is not concentrated. Based on the principle that all the connecting ribs 4 are evenly distributed in the circumferential direction, the rib helix angle β should be 90° ± 20 degrees. (4) The difference between the size of the rib helix angle β and the rib distribution angle α is greater than or equal to 20°, so that the distribution of the same or approximate most difficult bending direction in the axial direction is not concentrated. (5) To avoid the connecting ribs 4 on the slot row from having a cyclic distribution in the circumferential direction of the tube body, causing the catheter to have an uneven dominant bending direction, the rib helix angle β and similar angles cannot be divisible by 360° and its integer multiples.

[0042] In this embodiment, the length L1 of the strip-shaped groove cutting area on the tube body 1, or the number of slot rows in the strip-shaped groove cutting area, can be determined according to the design requirements of the catheter.

[0043] In this embodiment, by setting the connecting ribs in the strip-shaped groove cutting area, the harmful bending moment effect of the catheter is reduced, so that the axial stiffness, torsional stiffness and the same ability of the bending stiffness in any bending direction of the catheter change continuously, that is, the cross-sectional characteristics of the catheter change continuously in any direction.

[0044] Embodiment 2

[0045] Embodiment 2 of the present application provides a medical catheter structure, as Figure 5 shown, including a tube body 1. The tube body 1 is a hollow structure. Along the axial direction of the tube body 1, there are a plurality of cutting areas extending circumferentially and a plurality of connecting ribs 4 arranged in the cutting areas. There are no two sections on the tube body 1 where the distribution positions of the connecting ribs 4 are the same in the circumferential direction.

[0046] Specifically, the cutting area is a spiral cutting groove 2 provided on the tube body 1. A plurality of connecting ribs 4 are provided in the spiral cutting groove 2. The connecting ribs 4 include an elastic damping rib 41 and a moment damping rib 42. The elastic damping rib 41 and the moment damping rib 42 are arranged in sequence and cyclically along the axial direction of the tube body 1. In this embodiment, by providing the elastic damping rib 41 and the moment damping rib 42 in the spiral cutting groove, its spring effect and harmful bending moment effect are reduced.

[0047] Specifically, the anti-bounce helix angle γ between two adjacent anti-bounce ribs 41 is greater than or equal to 430°. This is the design principle of the anti-bounce helix angle γ in this embodiment. (1) According to the section moment of inertia formula, to ensure that the bending stiffness of the catheter exhibits approximately the same bending characteristics in different bending directions, the anti-bounce helix angle γ between two adjacent anti-bounce ribs 41 is around 90° + 360° * n, where n is a positive integer. Optionally, the anti-bounce helix angle γ is greater than or equal to 430°. To better destroy the spring effect without overly affecting the stiffness of the catheter, the anti-bounce helix angle γ between two adjacent anti-bounce ribs 41 is preferably 450°, which is the reference helix angle. (2) To avoid the advantages and disadvantages of the catheter's bending direction caused by mass concentration, the connecting ribs 4 should be non-periodically and evenly distributed in the circumferential direction of the pipe body 1, that is, there are no two sections on the pipe body 1 where the distribution positions of the connecting ribs 4 are the same. Therefore, based on the reference helix angle, the number of connecting ribs 4 can be initially determined according to the number of helical cutting grooves 2 on the pipe body 1, so that all the connecting ribs 4 are non-periodically and evenly distributed in the circumferential direction of the pipe body 1. The specific value of the anti-bounce helix angle γ can be accurately determined. Further, with the anti-bounce helix angle γ as the center and a range of ±10°, the final helix angle is determined. The difference between the size of the final helix angle and the anti-bounce helix angle γ in this embodiment is within a certain range to avoid too large a difference between the calculated number of connecting ribs 4 and the initial setting. (3) To avoid the periodic cyclic distribution of the connecting ribs 4 in the circumferential direction of the pipe body due to processing errors, etc., resulting in an uneven dominant bending direction and affecting the performance of the catheter, the anti-bounce helix angle γ and its approximate angles are not divisible by 360 degrees and its integer multiples.

[0048] The harmful bending moment effect refers to the asymmetry caused by the lack of cross-sectional material, which in turn leads to the bending moment imbalance of the cross-sectional stress in certain directions. The anti-bounce helix angle introduced to reduce the spring effect will exacerbate the harmful bending moment effect because it destroys the self-cancellation of the harmful bending moment within the pure helix structure period. Therefore, by introducing the anti-bending moment helix angle, the harmful bending moment effect generated by only setting the anti-bounce helix angle can be offset. The design principle of the anti-bending moment helix angle δ in this embodiment is the same as that of the anti-bounce helix angle.

[0049] Specifically, the offset angle between adjacent bullet-eliminating ribs 41 and moment-eliminating ribs 42 is the bullet-moment offset angle θ, and the bullet-moment offset angle θ is 80° to 100°. The setting of the bullet-moment offset angle θ can eliminate the harmful bending moment effect caused by the setting of connecting ribs. The design principle of the bullet-moment offset angle θ is as follows: (1) The theoretical principle is that the distribution of bullet-eliminating ribs and moment-eliminating ribs within the same spiral period should minimize the additional bending moment effect in any direction of the cross-section, that is, the bending moment effects of bullet-eliminating ribs and moment-eliminating ribs cancel each other out. (2) The pipe body 1 is evenly divided into four regions in the circumferential direction, and adjacent bullet-eliminating ribs 41 and moment-eliminating ribs 42 are respectively arranged in adjacent regions, and all bullet-eliminating ribs 41 and moment-eliminating ribs 42 are evenly distributed in the four regions of the pipe body 1. That is, a rectangular coordinate system in any direction is established on the cross-section of the pipe body, then the two connecting ribs 4 are most likely to fall in adjacent quadrants and minimize the number of ribs in each quadrant. (3) In some embodiments, preferably, the bullet-moment offset angle θ is 90°.

[0050] The length L2 or the number of spirals of the spiral cutting section of the pipe body 1 in this embodiment can be determined according to the design requirements of the catheter and is not subject to mandatory requirements.

[0051] In this embodiment, through the setting of bullet-eliminating ribs and moment-eliminating ribs in the cutting area of the spiral cutting groove, the spring effect of the pure spiral cutting groove catheter is reduced, and the change in the flexural rigidity of the catheter in any direction along the axis is consistent.

[0052] The above-disclosed are only the preferred exemplary embodiments of the present invention. Of course, the scope of rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A medical catheter structure, characterized in that, It includes a tube body (1), the tube body (1) is of a hollow structure, and a plurality of cutting areas extending circumferentially and a plurality of connecting ribs (4) arranged in the cutting areas are provided on the tube body (1) along its axial direction. There are no two sections on the tube body (1) where the connecting ribs (4) are distributed at the same position in the circumferential direction.

2. The medical catheter structure according to claim 1, characterized in that, The cutting area is a strip-shaped groove (3), and a plurality of the strip-shaped grooves (3) are arranged at intervals along the axial direction of the tube body (1).

3. The medical catheter structure according to claim 2, characterized in that, When the number n of all the connecting ribs (4) in the same strip-shaped groove (3) is odd, the connecting ribs (4) are evenly arranged in the circumferential direction of the tube body (1); When the number n of all the connecting ribs (4) in the same strip-shaped groove (3) is even, the first n / 2 connecting ribs (4) and the last n / 2 connecting ribs (4) are sequentially arranged at an angle of 360 / n in the clockwise or counterclockwise direction, and the angle between the n / 2-th connecting rib (4) and the (n / 2 + 1)-th connecting rib (4) is 540 / n.

4. The medical catheter structure according to claim 2, characterized in that, The included angle between two adjacent connecting ribs (4) in the same strip-shaped groove (3) is the rib distribution angle, and the rib distribution angle is 90° to 135°.

5. The medical catheter structure according to claim 4, characterized in that, The rib helix angle of the connecting rib (4) is 30° to 150°.

6. The medical catheter structure according to claim 5, characterized in that, The difference between the rib distribution angle and the rib helix angle is greater than or equal to 20°.

7. The medical catheter structure according to claim 1, characterized in that, The cutting area is a spiral cutting groove (2) provided on the tube body (1), and a plurality of the connecting ribs (4) are arranged in the spiral cutting groove (2). The connecting rib (4) includes an anti-elastic rib (41) and an anti-moment rib (42), and the anti-elastic rib (41) and the anti-moment rib (42) are sequentially arranged in a cycle along the axial direction of the tube body (1).

8. The medical catheter structure according to claim 7, characterized in that, The anti-elastic helix angle between two adjacent anti-elastic ribs (41) is greater than or equal to 430°.

9. The medical catheter structure according to claim 7, characterized in that, The tube body (1) is evenly divided into four regions in the circumferential direction, and two adjacent anti-elastic ribs (41) and anti-moment ribs (42) are respectively arranged in two adjacent regions, and all the anti-elastic ribs (41) and the anti-moment ribs (42) are evenly distributed in the four regions of the tube body (1).

10. The medical catheter structure according to claim 9, characterized in that, The offset angle between two adjacent anti-elastic ribs (41) and the anti-moment ribs (42) is the anti-elastic and anti-moment offset angle, and the anti-elastic and anti-moment offset angle is 80° to 100°.

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