CN115969295B - A rigidity adjustment mechanism for composite insertion portion of endoscope and endoscope - Google Patents

Abstract

The invention is applicable to the technical field of endoscopes, and provides a rigidity adjusting mechanism of a composite insertion part of an endoscope and the endoscope, comprising: a sheath, a distal tube section of the sheath configured to have a first bending stiffness and a second bending stiffness, respectively, in at least a first direction and a second direction; wherein the first direction and the second direction are radial directions of the distal tube segment; an insertion tube comprising an active bending section formed at a distal end of the insertion tube; the insertion Guan Rong is arranged in the sheath tube, the active bending section is accommodated in the accommodating space of the distal tube section, and the active bending section can be rotatably arranged relative to the distal tube section; the rotating angle between the sheath tube and the insertion tube is switched by rotating the proximal end of the sheath tube or the proximal end of the insertion tube, so that the distal end of the insertion portion after the sheath tube and the insertion tube are matched and installed can be switched in soft and hard, the insertion portion is conveniently inserted into a target area in a human body and then is controllably bent, and the damage of a doctor to human tissues in the operation process is reduced.

Description

A rigidity adjustment mechanism for composite insertion portion of endoscope and endoscope

Technical Field

The invention belongs to the technical field of endoscopes and relates to a rigidity adjustment mechanism of an endoscope composite insertion part and an endoscope.

Background Art

An endoscope is a device that detects the body cavity environment by inserting an insertion portion with at least lighting and photographing functions into the natural channel of the human body or the opening of the surgical area. By operating a handle located outside the human body, the bending angle of the active bending section located at the front end of the endoscope insertion portion is adjusted, thereby deflecting it in a predetermined direction, helping people obtain observations with a larger visual angle range.

Among them, when entering the human body through a natural cavity, it is usually necessary to use an endoscope with a flexible insertion portion, and the active bending section at the distal end of the insertion portion is controllably bent so that the lighting unit and the image processing unit can be introduced into the curved cavity of the human body; however, in the scenario of introducing the endoscope into the human body through an opening in the surgical area, an endoscope with a rigid insertion portion is currently used for operation. The disadvantage is that the distal end of the insertion portion cannot be turned autonomously, and the viewing angle of the surgical field can only be adjusted by rotating the rigid insertion portion, which limits the doctor's operating field of view and makes it difficult to perform surgical operations on the surgical area within a larger range; and if the rigid insertion portion is forcibly rotated, it is easy to tear human tissue, thereby increasing trauma to the patient.

Summary of the invention

The object of the present invention is to provide a stiffness adjustment mechanism for a composite insertion portion of an endoscope, comprising:

A sheath tube, wherein the distal tube section of the sheath tube is configured to have a first bending stiffness and a second bending stiffness in at least a first direction and a second direction, respectively; wherein the first direction and the second direction are radial directions of the distal tube section;

An insertion tube, the insertion tube comprising an active bending section, the active bending section being formed at the distal end of the insertion tube; the insertion tube is accommodated in the sheath tube, the active bending section is accommodated in the accommodation space of the distal tube section, and the active bending section can be rotatably arranged relative to the distal tube section;

The first bending stiffness satisfies the following condition: the distal tube segment cannot bend when subjected to a force from a first direction; the second bending stiffness satisfies the following condition: when the active bending segment bends toward the second direction, the distal tube segment can be passively bent.

Preferably, the distal tube section comprises:

An outer tube, an inner tube and connecting ribs, wherein the outer tube is sleeved on the outside of the inner tube, and the outer tube and the inner tube are connected and fixed by connecting ribs, the connecting ribs are arranged along the axial direction of the distal tube section, and the connecting ribs define a suction channel between the outer tube and the inner tube.

Preferably, the proximal end of the inner tube terminates near the proximal end of the active bending section.

Preferably, at least one of the outer tube and the inner tube comprises:

A ridge and a rib, wherein the ridge and the rib are distributed along the axial direction of the distal tube segment, and the rib is distributed on one side of the ridge along the circumferential direction of the distal tube segment;

The ridge has the first bending stiffness in the first direction, and the rib has the second bending stiffness in the second direction.

Preferably, the rib is provided with grooves distributed radially along the distal tube segment;

Alternatively, the average wall thickness of the ribs is smaller than the wall thickness of the ridges.

Preferably, the spine and the ribs are integrally formed by double-material injection molding; wherein the ribs are made of a material with a first elastic modulus, and the spine is made of a material with a second elastic modulus; wherein the first elastic modulus is smaller than the second elastic modulus.

Preferably, the connecting rib and the ridge are located in the same radial direction of the active bending section.

Preferably, the proximal end of the sheath tube comprises a connecting portion, and the connecting portion is rotatably sealedly connected to the proximal end of the insertion tube.

Preferably, the distal tube section includes an outer tube and a protrusion, wherein the protrusion extends along the axial direction of the outer tube; the root of the protrusion is fixed to the inner wall surface of the outer tube, and the end of the protrusion protruding along the radial direction of the outer tube is a free end; and the free ends of the plurality of protrusions jointly define the accommodating space, and the accommodating space is used to install the active bending section.

An endoscope comprises the above-mentioned stiffness adjustment mechanism of the composite insertion part of the endoscope.

Beneficial effects:

In the present invention, the rotation angle between the sheath and the insertion tube is switched by rotating the proximal end of the sheath or the proximal end of the insertion tube, and then the distal end of the insertion portion after the sheath and the insertion tube are installed in coordination can be switched between soft and hard, which facilitates the insertion portion to be inserted into the target area in the human body and then bend in a controllable manner, effectively reducing the damage to human tissue caused by the doctor during the operation and reducing the number of holes opened by the doctor in the human body.

In the present invention, the active bending section and the distal tube section are rotationally sealed, so that the active bending section and the distal tube section of the sheath tube have better fit, preventing the active bending section from being unable to make the distal tube section bend synchronously and at the same angle during the bending operation due to the clearance between the fitting parts of the active bending section and the distal tube section.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG1 is a schematic diagram of a sheath structure provided by an embodiment of the present invention;

2 is a schematic diagram of the structure of an endoscope provided by an embodiment of the present invention and a schematic diagram of a partially enlarged structure of an active bending section A at the distal end of the insertion tube;

3 is a schematic diagram of the assembly structure of the tube sheath and the insertion tube, and a partially enlarged structural diagram of the distal tube segment B of the sheath provided in an embodiment of the present invention;

4 is a partial enlarged schematic diagram of a G region in an assembled state of a sheath and an insertion tube provided by an embodiment of the present invention;

FIG5 is a schematic diagram of a three-dimensional structure of a sheath provided in an embodiment of the present invention;

FIG6 is a schematic diagram of the internal structure of the sheath provided in an embodiment of the present invention;

7 is a schematic diagram of a projection structure of a sheath along the axial direction provided by an embodiment of the present invention;

FIG8 is a schematic diagram of a sheath structure provided by another embodiment of the present invention;

9 is a schematic diagram of the assembly structure of the sheath and the insertion tube provided by another embodiment of the present invention;

10 is a schematic diagram of a first structure in which the pivot axis of the sheath is orthogonal to the bending axis of the active bending section provided by an embodiment of the present invention;

11 is a schematic diagram of a second structure in which the pivot axis of the sheath is orthogonal to the bending axis of the active bending section provided by an embodiment of the present invention;

12 is a schematic diagram of a first structure in which the pivot axis of the sheath is coplanar with the bending axis of the active bending section provided by an embodiment of the present invention;

13 is a schematic diagram of a second structure in which the pivot axis of the sheath is coplanar with the bending axis of the active bending section provided by an embodiment of the present invention;

FIG. 14 is a schematic diagram showing the structure of the sheath suction function demonstration provided in an embodiment of the present invention.

10. Handle; 11. Rotating part; 12. Insertion tube; 13. Active bending section; 131. Snake bone joint; 132. Riveted part; 14. Injection channel; 20. Sheath; 21. Proximal tube section; 22. Distal tube section; 22a. Accommodating space; 22b. Suction channel; 221. Rib; 221a. Groove; 222. Ridge; 223. Connecting rib; 223a. Protrusion; 224. Inner tube; 224a. Annular space; 225. Outer tube; 23. Suction nozzle; 24. Connecting part.

DETAILED DESCRIPTION

The following description provides many different embodiments or examples for implementing different features of the present invention. The components and arrangements described in the following specific examples are only used to simplify the present invention and are only used as examples, not to limit the present invention.

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than 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 work belong to the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

In the present invention, unless otherwise clearly specified and limited, a first feature being above or below a second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through another feature between them. Moreover, a first feature being above, above, and above a second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being below, below, and below a second feature includes the first feature being directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

In addition, in the present invention, "proximal end" and "distal end" refer to the far and near positions of the structure relative to human operation in the use environment, so as to facilitate the description of the positional relationship between components and facilitate understanding; for the same component, "proximal end" and "distal end" are the relative positional relationship of the component, not absolute; therefore, it should be understood from the perspective of realizing the principles of the present invention, and should not deviate from the essence of the present invention.

By analyzing the application scenarios of rigid endoscopes in the prior art, it can be concluded that the reason for not using an endoscope with a flexible insertion portion is that the endoscope with a flexible insertion portion will be compressed and bent by human tissue during the process of intervening in human tissue due to the low bending stiffness of the active bending section, making it difficult for doctors to accurately and quickly insert the insertion portion into the target area in the human body. Therefore, after long-term research by the inventor, the drawbacks of the above-mentioned rigid insertion endoscope have been solved. The specific solution is as follows:

The present invention provides a stiffness adjustment mechanism for a composite insertion portion of an endoscope, comprising:

The sheath 20, as shown in Figures 1 to 3, can be detachably or fixedly mounted on the outer periphery of the insertion portion of the endoscope, so that the sheath 20 is sleeved on the outer side of the insertion portion; the distal tube section 22 of the sheath 20 is configured to have a first bending stiffness and a second bending stiffness in at least a first direction and a second direction, respectively; wherein the first direction and the second direction are radial directions of the distal tube section 22; specifically, in the schematic structural diagram of Figure 1, it can be understood that the first direction is the positive direction of the Z axis or the negative direction of the Z axis; the second direction is the positive direction of the X axis or the negative direction of the X axis. In addition, the proximal tube section 21 of the sheath 20 is a smooth and rigid tube body, so that the sheath 20 maintains a rigid shape during the insertion process and is easy to insert; the proximal tube section 21 of the sheath 20 terminates at the front end of the handle 10, as described in Figure 3.

Furthermore, the mechanical property of the distal segment 22 of the sheath 20 is manifested in that, when the forces F2 and F1 act in the positive direction of the X-axis or in the reverse direction of the X-axis respectively, the distal segment 22 of the sheath 20 can be bent, presenting the bending direction or state shown by the dotted line in Figure 1; however, when an external force acts in the positive direction of the Z-axis or in the reverse direction of the Z-axis, the distal segment 22 of the sheath 20 cannot be bent; this characteristic enables the distal segment 22 of the sheath 20 to be bent or restricted from bending when the bending direction of the active bending segment 13 of the endoscope insertion tube 12 is adapted to the first direction or the second direction respectively; the mechanical property exhibited by the distal segment 22 of the sheath 20 is related to its structure or material, which will be described in detail in the subsequent text.

Insertion tube 12, please refer to FIG. 2, the insertion tube 12 includes an active bending section 13, and the active bending section 13 is formed at the distal end of the insertion tube 12; the active bending section 13 shown in FIG. 2 includes: a snake bone joint 131 and a rivet 132, the snake bone joints 131 are riveted in series in sequence through the rivet 132, so that the snake bone joints 131 can rotate about the pivot axis q formed by the rivet 132 under the traction force of the traction rope, so that the active bending section 13 can bend, and the bending direction is as shown in the E1 and E2 directions in FIG. 2, wherein the traction rope is distributed on both sides of the pivot axis q along the axial direction.

Please refer to Figures 3 to 5, the insertion tube 12 is accommodated in the sheath tube 20, the active bending segment 13 is accommodated in the accommodating space 22a of the distal tube segment 22, and the active bending segment 13 can be rotatably arranged relative to the distal tube segment 22. In an optional embodiment, the active bending segment 13 and the distal tube segment 22 are rotationally sealed, so that the active bending segment 13 and the distal tube segment 22 of the sheath tube 20 have better fit, preventing the active bending segment 13 from being unable to make the distal tube segment 22 bend synchronously and at the same angle during the bending operation due to the clearance between the fitting parts of the active bending segment 13 and the distal tube segment 22.

The first bending stiffness of the distal tube segment 22 of the sheath tube 20 in the first direction (Z axis) and the second bending stiffness in the second direction (X axis) are specifically as follows: the first bending stiffness satisfies the following conditions: the distal tube segment 22 cannot bend when subjected to a force from the first direction (Z axis); the second bending stiffness satisfies the following conditions: when the active bending segment 13 bends toward the second direction (X axis), the distal tube segment 22 can be passively bent.

Specifically, in an optional embodiment, the distal tube section 22 of the sheath tube 20 includes:

The outer tube 225, the inner tube 224 and the connecting rib 223 are shown in conjunction with FIGS. 5 and 6. The outer tube 225 is sleeved on the outer side of the inner tube 224, and the outer tube 225 and the inner tube 224 are connected and fixed by the connecting rib 223. The connecting rib 223 is arranged along the axial direction of the distal tube section 22, and the connecting rib 223 defines a suction channel 22b between the outer tube 225 and the inner tube 224. The annular space 224a surrounded by the inner tube 224 forms the installation area of the active bending section 13 of the endoscope; the proximal end of the inner tube 224 terminates near the proximal end of the active bending section 13.

In an optional embodiment, the connecting ribs 223 may be circumferentially distributed in the area between the outer tube 225 and the inner tube 224 to improve the support between the outer tube 225 and the inner tube 224. The number of the connecting ribs 223 is not limited. As a preferred solution, please continue to combine with Figures 1, 3 and 5, any one of the outer tube 225 and the inner tube 224 includes:

The ridge 222 and the rib 221 are distributed along the axial direction of the distal tube segment 22, and the rib 221 is distributed on one side of the ridge 222 along the circumferential direction of the distal tube segment 22; in the structures shown in Figures 1, 3 and 5, the ridge 222 and the rib 221 are both arranged on the outer tube 225, and in other embodiments, the ridge 222 and the rib 221 can be arranged on the inner tube 224, or on both the outer tube 225 and the inner tube 224.

Regarding the ridge 222 , please refer to FIG. 1 . The ridge 222 has the first bending stiffness in the first direction (Z axis), and the rib 221 has the second bending stiffness in the second direction (X axis). Specifically, in the foregoing, the second bending stiffness in the second direction (X-axis) is manifested as follows: in the positive direction of the X-axis or the reverse direction of the X-axis, under the action of F2 and F1 respectively, the distal tube segment 22 of the sheath tube 20 can be bent. The reason for the bending is that the ridge 222 has a low bending stiffness in this direction. Specifically, in an optional embodiment, the thickness of the ridge 222 along the Z-axis direction may be greater than the thickness along the X-direction, so that the ridge 222 is not easily bent in the Z-axis direction; in an optional embodiment, the rib 221 may also be provided with grooves 221a radially distributed along the distal tube segment 22, and by providing the grooves 221a, the mechanical strength of the ridge 222 on both sides of the radial direction is reduced; or, in other optional embodiments, the average wall thickness of the rib 221 is less than the wall thickness of the ridge 222, that is, the rib 221 is a thin-walled setting, and its basic principle is the same as that of providing a thin-walled rib. The groove 221a is similar, that is, the mechanical strength is reduced by reducing the amount of material used; but it should be noted that, as a preference, the groove direction of the groove 221a is located in the plane formed by the X-axis and the Z-axis, please continue to refer to Figure 1, so that when the active bending section 13 bends toward the second direction (X-axis), the distal tube section 22 is driven to passively bend, and the recessed space of the groove 221a is compressed during the bending process, and the material of the rib 221 is not forced to be squeezed; in addition, in the implementation scheme of providing the groove 221a on the outer surface of the outer tube 225, in order to improve the smoothness of the surface of the distal tube section 22 of the sheath tube 20 without affecting the tissue sinking into the recessed space of the groove 221a during the process of the sheath tube 20 being intervened in the human body, and the impact on the intervention process, a skin can be laid on the outer surface of the distal tube section 22 of the sheath tube 20 to cover the recessed space of the groove 221a.

In order to make the distal tube section 22 of the sheath tube 20 have the first bending stiffness in the first direction, and the rib 221 have the second bending stiffness in the second direction, the following embodiments may also be adopted, specifically, the ridge 222 and the rib 221 are formed by a double-material injection molding process; wherein the rib 221 is made of a material with a first elastic modulus, and the ridge 222 is made of a material with a second elastic modulus; wherein the first elastic modulus is smaller than the second elastic modulus.

In order to improve the bending strength of the distal tube section 22 of the sheath tube 20 in the first direction (Z axis), the connecting rib 223 and the ridge 222 may be located in the same radial direction of the active bending section 13. Specifically, referring to FIG. 7 , the projection of the connecting rib 223 in the direction of the central axis of the sheath tube 20 has a dimension L2 in the X-axis direction that is smaller than the dimension L1 in the Z-axis direction. Therefore, the bending stiffness of the connecting rib 223 in the second direction (X axis) is smaller than the bending stiffness in the first direction (Z axis), and it should be noted that, in a specific optional embodiment, the bending stiffness of the distal tube section 22 of the sheath tube 20 in the first direction and the second direction is mainly provided by the connecting rib 223.

Regarding the distal tube segment 22 of the sheath tube 20, the following implementation mode can also be adopted, please refer to Figures 8 and 9, the distal tube segment 22 includes an outer tube 225 and a protrusion 223a, the protrusion 223a extends along the axial direction of the outer tube 225; the root of the protrusion 223a is fixed to the inner wall surface of the outer tube 225, and the end of the protrusion 223a protruding along the radial direction of the outer tube 225 is a free end; and the free ends of the plurality of protrusions 223a jointly define the accommodating space 22a, and the accommodating space 22a is used to install the active bending segment 13.

Please refer to the attached drawings 10 to 14. In the present invention, the sheath tube 20 is installed into the insertion tube 12 of the endoscope along the axial direction, so that the active bending section 13 is accommodated in the distal tube section 22 of the sheath tube 20, and the proximal end of the sheath tube 20 includes a connecting portion 24, and the connecting portion 24 is rotatably sealed and connected to the proximal end of the insertion tube 12. In particular, as shown in FIG10, the pivot axis q of the active bending section 13 and the pivot axis p of the sheath tube 20 that can be bent along the second direction are orthogonally arranged, wherein the pivot axis q is not only one shown in FIG10, but can be understood as a set of pivot axes of multiple snake bone joints 131, as shown in FIG11; similarly, the pivot axis p is not only one shown in FIG10, but a set of pivot axes distributed along the length direction of the spine 222. In the state shown in FIG. 10 , the insertion portion composed of the sheath tube 20 and the endoscope insertion tube 12 cannot be bent as a whole. The reason is that the bending stiffness of the distal tube section 22 of the sheath tube 20 in the first direction (Z axis) and the second direction (X axis) is different; specifically, the distal tube section 22 can only be bent in the second direction (X axis) with the pivot axis p as the rotation axis, but cannot be bent in the first direction (Z axis); however, the active bending section 13 of the endoscope insertion tube 12 can only be rotated and bent with the pivot axis q as the pivot center. When an angle exists between a plane formed by the pivot axis q of the plurality of pivot axes 13 and a plane formed by the pivot axis p of the distal tube segment 22 of the sheath tube 20, the active bending segment 13 and the distal tube segment 22 of the sheath tube 20 restrain each other, so that the insertion portion as a whole obtains better rigidity and cannot be bent. Therefore, when the pivot axis q and the pivot axis p are in a non-coplanar condition, the insertion portion can be smoothly inserted into the human body. Figures 10 and 11 show that the pivot axis q and the pivot axis p are in an orthogonal state, which is a preferred solution for achieving the non-bendability of the insertion portion.

Please refer to Figures 12 and 13 , the pivot axis q of the active bending section 13 and the pivot axis p of the distal tube section 22 are coplanarly arranged, that is, the operator can actively control the active bending section 13 to bend in a preset direction, thereby driving the distal tube section 22 to bend in a second direction, thereby realizing the bending operation after the insertion portion intervenes in the human tissue.

It should be noted that the sheath 20 and the insertion tube 12 are coaxially arranged and can rotate relative to each other. Specifically, a rotating portion 11 is arranged at the rear end of the insertion tube 12. Rotating the rotating portion 11 can drive the insertion tube 12 to rotate. Therefore, the operator can switch the rotation angle between Figure 10 and Figure 12 by rotating the proximal end of the sheath 20 or the proximal end of the insertion tube 12, and then realize that the distal end of the insertion portion after the sheath 20 and the insertion tube 12 are installed in coordination can achieve soft and hard switching, which is convenient for inserting the insertion portion into the target area in the human body and then performing controllable bending, effectively reducing the damage to human tissue during operation by the doctor and reducing the number of holes opened by the doctor in the human body.

Please refer to Figure 14. The sheath tube 20 of the present invention has a suction channel 22b opened along the axial direction between the outer tube 225 and the inner tube 224. The suction channel 22b is connected to the suction nozzle 23 located at the rear end of the sheath tube 20. For example, when stone cleaning is required, liquid can be injected into the stone area from the injection channel 14 in the endoscope insertion tube 12 so that the stone and the liquid form a mixture, and then suction is performed through a negative pressure suction mechanism connected to the suction nozzle 23. The mixture of the stone and the liquid is extracted from the suction channel 22b through the L suction path by the suction action of the negative pressure suction mechanism.

The present invention also provides an endoscope, comprising the above-mentioned stiffness adjustment mechanism of the composite insertion portion of the endoscope.

It should be noted that the endoscope in the embodiment of the present application can be a bronchoscope, a pyeloscope, an esophagoscope, a gastroscope, a colonoscope, an otoscope, a rhinoscope, a stomatoscope, a laryngoscope, a colposcope, a laparoscope, an arthroscope, etc. The embodiment of the present application does not specifically limit the type of the endoscope.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A stiffness adjustment mechanism for a composite insertion portion of an endoscope, characterized by comprising: A sheath tube (20), wherein a distal tube section (22) of the sheath tube (20) is configured to have a first bending stiffness and a second bending stiffness in at least a first direction and a second direction, respectively; wherein the first direction and the second direction are radial directions of the distal tube section (22); An insertion tube (12), the insertion tube (12) comprising an active bending section (13), the active bending section (13) being formed at the distal end of the insertion tube (12); the insertion tube (12) being accommodated in the sheath tube (20), the active bending section (13) being accommodated in an accommodation space (22a) of the distal tube section (22), and the active bending section (13) being rotatable relative to the distal tube section (22); The first bending stiffness satisfies the following condition: the distal tube section (22) cannot bend when subjected to a force from a first direction; and the second bending stiffness satisfies the following condition: when the active bending section (13) bends in the second direction, the distal tube section (22) can be passively bent. 2. The stiffness adjustment mechanism of the composite insertion portion of an endoscope according to claim 1, characterized in that the distal tube section (22) comprises: An outer tube (225), an inner tube (224) and a connecting rib (223), wherein the outer tube (225) is sleeved on the outer side of the inner tube (224), and the outer tube (225) and the inner tube (224) are connected and fixed via the connecting rib (223), the connecting rib (223) being arranged along the axial direction of the distal tube section (22), and the connecting rib (223) defining a suction channel (22b) between the outer tube (225) and the inner tube (224). 3. A stiffness adjustment mechanism for an endoscope composite insertion portion according to claim 2, characterized in that the proximal end of the inner tube (224) terminates near the proximal end of the active bending section (13). 4. The stiffness adjustment mechanism of the composite insertion portion of an endoscope according to claim 3, characterized in that at least one of the outer tube (225) and the inner tube (224) comprises: A ridge (222) and a rib (221), wherein the ridge (222) and the rib (221) are distributed along the axial direction of the distal tube segment (22), and the rib (221) is distributed on one side of the ridge (222) along the circumferential direction of the distal tube segment (22); The ridge (222) has the first bending stiffness in the first direction, and the rib (221) has the second bending stiffness in the second direction. 5. The rigidity adjustment mechanism of the composite insertion portion of an endoscope according to claim 4, characterized in that: the rib (221) is provided with grooves (221a) distributed along the radial direction of the distal tube section (22); Alternatively, the average wall thickness of the rib (221) is smaller than the wall thickness of the ridge (222). 6. The rigidity adjustment mechanism of the composite insertion portion of an endoscope according to claim 4, characterized in that: The ridge (222) and the rib (221) are integrally formed by double-material injection molding; wherein the rib (221) is made of a material with a first elastic modulus, and the ridge (222) is made of a material with a second elastic modulus; wherein the first elastic modulus is smaller than the second elastic modulus. 7. A stiffness adjustment mechanism for an endoscope composite insertion portion according to claim 4, characterized in that the connecting rib (223) and the ridge (222) are located in the same radial direction of the active bending section (13). 8. A stiffness adjustment mechanism for an endoscope composite insertion portion according to claim 1, characterized in that the proximal end of the sheath tube (20) comprises a connecting portion (24), and the connecting portion (24) is rotationally sealedly connected to the proximal end of the insertion tube (12). 9. According to the stiffness adjustment mechanism of the composite insertion portion of an endoscope as described in claim 1, it is characterized in that: the distal tube section (22) includes an outer tube (225) and a protrusion (223a), and the protrusion (223a) extends along the axial direction of the outer tube (225); the root of the protrusion (223a) is fixed to the inner wall surface of the outer tube (225), and the end of the protrusion (223a) protruding along the radial direction of the outer tube (225) is a free end; and the free ends of the plurality of protrusions (223a) jointly define the accommodating space (22a), and the accommodating space (22a) is used to install the active bending section (13). 10. An endoscope, comprising a stiffness adjustment mechanism of an endoscope composite insertion portion according to any one of claims 1 to 9.