Flexible driving reducing device with corrugated pipe sealing structure

Abstract

The invention discloses a flexible driving reducing device with a corrugated pipe sealing structure. The flexible driving reducing device comprises a driving unit, a transmission assembly, a reducing assembly and a sealing assembly. The transmission assembly is connected with the driving unit, the tail end of the transmission assembly is sleeved with the reducing assembly, and the transmission assembly is wrapped with the sealing assembly. The device mainly solves the problem that a transmission part is rusted and blocked due to sealing failure of an existing mechanical expansion mechanism in a liquid environment (such as a human bladder and an industrial liquid filling pipeline), and meanwhile solves the technical problem that a rigid transmission structure cannot adapt to a bent channel for operation.

Description

Technical Field

[0001] This invention relates to the field of mechanical transmission and minimally invasive interventional devices, and in particular to a flexible drive variable diameter device with a bellows sealing structure. Background Technology

[0002] In interventional procedures in urology and gastroenterology, as well as in-situ maintenance of long-distance industrial pipelines, it is often necessary to deliver the working device through narrow, winding channels to the target location and perform radial expansion to complete tasks such as support, retrieval, or pipe wall repair. Current conventional technologies are mainly divided into two categories: fluid-driven and mechanically driven. While fluid-driven devices (such as balloon catheters) offer good flexibility, they rely on flexible force application and are prone to uneven expansion when faced with irregular pipe deformations. Furthermore, the expansion process inevitably completely blocks the fluid passage, making long-term operation impossible. Mechanically driven devices (such as metal expanders), while possessing high rigidity and shape retention capabilities, traditional designs often rely on rigid linkages or direct shaft transmissions, making them difficult to adapt to physiological bends or industrial U-shaped bends. Forced advancement can easily cause mechanical damage to the inner wall of the channel.

[0003] More critically, the aforementioned existing devices exhibit significant sealing and protection deficiencies in liquid-filled conditions (such as the urine environment inside a human bladder or industrial pipelines filled with sewage). Traditional mechanical reducing mechanisms typically contain precision components such as lead screws, hinges, or sliding pairs. If directly exposed to liquids or environments containing impurities, they are highly susceptible to lubrication failure and corrosion due to media intrusion. Furthermore, the crystallization of salts in bodily fluids or the deposition of particulate matter in sewage can cause mechanical jamming, preventing the device from retracting properly and posing serious safety hazards.

[0004] To address corrosion and jamming issues, existing technologies attempt to seal the mechanism by adding an elastic shield or bellows to the outside. However, during contraction and expansion, the axial length or internal volume of a radially variable diameter mechanism typically changes drastically. If a fully enclosed structure is used, the change in internal volume leads to rapid fluctuations in internal air pressure, resulting in significant pneumatic resistance or a piston effect. This pressure resistance not only increases the load on the drive system but, in extreme cases, can cause the seals to collapse or burst due to excessive internal and external pressure differences, leading to complete protection failure. Currently, the industry lacks a variable diameter operating device that can adapt to large-angle bending transmission, achieve reliable dynamic sealing in liquid or impurity environments, and effectively balance internal air pressure. Summary of the Invention

[0005] Purpose of the invention: In view of the shortcomings and defects of the prior art, the present invention provides a flexible drive diameter changing device with a bellows sealing structure. This device mainly solves the problem of corrosion and jamming of transmission components caused by sealing failure of existing mechanical expansion mechanisms in liquid environments (such as human bladders and industrial liquid filling pipes). At the same time, it solves the technical problem that rigid transmission structures cannot adapt to curved channels for operation.

[0006] Technical solution: The present invention provides a flexible drive diameter changing device with a bellows sealing structure, characterized in that it includes a drive unit, a transmission component, a diameter changing component, and a sealing component; the transmission component is connected to the drive unit, the diameter changing component is sleeved on the end of the transmission component, and the sealing component is wrapped around the outside of the transmission component.

[0007] The transmission assembly includes a flexible transmission shaft and a lead screw transmission pair. The rotational power generated by the drive unit is transmitted to the lead screw transmission pair through the flexible transmission shaft. The lead screw transmission pair converts the received rotational motion into linear reciprocating motion along the axial direction and drives the variable diameter assembly to undergo elastic deformation through push-pull action, thereby realizing radial expansion or contraction.

[0008] The transmission assembly adopts a coaxial composite structure of spindle and sheath. The flexible transmission shaft includes a flexible transmission shaft spindle located at the center and a stationary sheath surrounding it. The stationary sheath is the flexible transmission shaft sheath. The flexible transmission shaft spindle connects the drive unit and the lead screw shaft, transmitting rotational power. The two ends of the flexible transmission shaft sheath are respectively fixed to the housing of the drive unit and the stationary end of the lead screw transmission pair (such as the front bearing seat), using the torsional stiffness of the flexible transmission shaft sheath to provide anti-rotation support for the end mechanism. An annular ventilation gap is maintained between the flexible transmission shaft spindle and the flexible transmission shaft sheath. The far end of the gap is connected to the sealed cavity and the internal air guide channel on the front bearing seat, and the near end of the gap extends to the drive unit located in a non-liquid environment (external or liquid-free area) and communicates with the outside atmosphere. The inner wall of the flexible transmission shaft sheath or the outer wall of the flexible transmission shaft spindle is provided with a spiral air guide groove or a braided mesh structure to ensure that the ventilation gap will not be completely closed when the flexible transmission shaft spindle undergoes a large-angle bend, ensuring unobstructed airflow.

[0009] The sealed cavity employs a remote gap breathing method. When the pressure inside the cavity fluctuates due to the compression or elongation of the bellows, the gas directly exchanges with the outside atmosphere through the annular ventilation gap inside the flexible transmission shaft. No additional ventilation duct is required. The breathing function is achieved by utilizing the structural gap of the transmission component itself, which balances the air pressure and ensures complete isolation between the internal and external liquid working environments of the device.

[0010] The lead screw drive pair converts the received rotational motion into linear reciprocating motion along the axial direction. The diameter-changing component also serves as an anti-rotation constraint mechanism. The diameter-changing component has torsional stiffness. The two ends of the diameter-changing component are respectively connected to the ball nut assembly and the stationary component at the far end of the lead screw shaft, which restricts the ball nut assembly from rotating with the lead screw shaft, thereby ensuring the effective conversion of rotational motion into linear motion.

[0011] The sealing component is an axially expandable bellows structure. The bellows is sleeved outside the lead screw drive pair. One end of the bellows is sealed to the relatively stationary end of the lead screw drive pair (such as the front bearing seat), and the other end is sealed to the linear motion output end of the lead screw drive pair (such as the ball nut). The bellows extends or compresses as the ball nut moves, forming a dynamic sealed cavity that completely isolates the working section of the precision lead screw from the external environment.

[0012] The transmission assembly adopts a segmented flexible connection structure. The flexible transmission shaft is located between the drive unit and the lead screw transmission pair. The input end of the flexible transmission shaft is connected to the drive unit through a coupling, and the output end of the flexible transmission shaft is connected to the input end of the lead screw transmission pair through a rigid sleeve adapter. The rigid sleeve adapter has an axial mounting hole inside. The distal end of the flexible transmission shaft spindle and the proximal end of the lead screw shaft are respectively inserted into the mounting hole and fixed by lateral set screws, pins, or mechanical pressing to ensure that the rotational power can be transmitted from the flexible shaft to the lead screw shaft without gaps.

[0013] The variable diameter component is a mesh-woven structure or a cage-like structure composed of multiple elastic strips; it is made of nickel-titanium alloy shape memory metal or high-strength spring steel. When applied in the medical field (such as bladder expansion), the variable diameter component is made of nickel-titanium alloy shape memory metal, utilizing its superelasticity and biocompatibility to provide gentle and constant support during expansion, avoiding damage to biological tissue. When applied in the industrial field (such as pipe support), the variable diameter component is made of high-strength spring steel to provide greater mechanical support stiffness.

[0014] The geometry of the variable diameter assembly is adjusted by the linear displacement of the lead screw drive pair.

[0015] Retraction action (used for entering or exiting the channel): The drive unit drives the lead screw to rotate, causing the ball nut assembly to move towards the flexible drive shaft, i.e., the proximal end; this action increases the distance between the ball nut assembly and the lead screw head, thereby applying axial tension to the variable diameter assembly; under the action of tension, the variable diameter assembly is axially elongated, and its radial dimension is reduced accordingly until it reaches the minimum outer diameter contraction state, which facilitates the device to pass through narrow cavities;

[0016] Expansion action (for fixed-point support or operation): The drive unit drives the lead screw to rotate in the opposite direction, causing the ball nut assembly to move away from the flexible drive shaft, i.e., to the far end; this action reduces the distance between the ball nut assembly and the lead screw head, thereby applying axial thrust or releasing tension to the variable diameter assembly; under axial compression, the mesh structure of the variable diameter assembly bulges outward and deforms, and its radial dimension increases accordingly until it reaches the preset expansion state, achieving effective fitting and support of the target cavity.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0018] This invention, by incorporating a follow-up bellows sealing assembly, completely solves the protection problem of mechanical transmission mechanisms in liquid environments. The bellows expands and contracts synchronously with the axial movement of the ball nut, forming a dynamically sealed chamber that completely physically isolates the precision lead screw drive pair from the external working environment (such as urine in a human bladder or oil and cutting fluid in industrial pipelines). This design effectively avoids problems such as lead screw corrosion, lubricant loss, and mechanical jamming caused by liquid infiltration, significantly improving the reliability and service life of the device under harsh operating conditions.

[0019] This invention employs a drive system combining a flexible drive shaft and a ball screw pair, balancing path adaptability with motion control precision. The flexible drive shaft design breaks the limitations of traditional rigid direct connections, allowing the device to flexibly traverse curved human urethras or complex industrial pipelines to reach the work point. The ball screw pair at the end converts rotational motion into high-precision linear reciprocating motion. Compared to pneumatic inflation or hydraulic drives, this invention enables precise quantitative control of the expansion diameter of the variable-diameter component. In particular, when using a trapezoidal screw drive pair with self-locking characteristics, the device can maintain its supporting form for an extended period even when the power source is cut off, effectively avoiding the risk of accidental retraction due to motor power failure or control malfunction, further ensuring operational safety.

[0020] This invention utilizes a variable-diameter component made of nickel-titanium alloy or highly elastic material to achieve flexible fit and effective support for the target cavity. Particularly for medical rehabilitation scenarios, the preferred nickel-titanium alloy material leverages its shape memory effect and superelasticity, allowing the stent to exhibit a natural expansion tendency in its normally open state. In the contracted state, the stent is stretched by moving the nut towards the flexible shaft, allowing it to smoothly enter the narrow channel. This combined mechanism of mechanical contraction and elastic expansion ensures both gentle force during expansion (without damaging biological tissue) and smooth retraction.

[0021] The flexible drive variable diameter device with a bellows sealing structure proposed in this invention fills the application gap of precision mechanical expansion equipment in the field of liquid sealing. This technical solution, through modular design, resolves the contradiction between sealing performance and flexible transmission in existing technologies. It can not only serve as a high-end medical device for bladder balloon therapy, but also be widely applied to fields such as petrochemical pipeline inspection and foreign object retrieval in confined spaces in aerospace, greatly improving the versatility and environmental adaptability of existing expansion support equipment, and possessing significant economic benefits and promotional value. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention;

[0023] Figure 2 This is a schematic diagram of the structure of the present invention in a contracted state;

[0024] Figure 3 This is a schematic diagram of the structure of the present invention in its expanded (working) state;

[0025] Figure 4 This is a schematic diagram of the cross-sectional structure of the present invention in its expanded (working) state;

[0026] Figure 5 for Figure 4 A schematic diagram of the local structure at point C;

[0027] Figure 6 for Figure 4 A schematic diagram of the local structure at point D;

[0028] Figure 7 for Figure 4 A schematic diagram of the local structure at point B;

[0029] Figure 8 for Figure 7 A schematic diagram of the partial structure at point A;

[0030] Figure 9 This is a schematic diagram of the internal structure of the transmission assembly of the present invention;

[0031] Figure 10 for Figure 9 A schematic diagram of the AA cross-sectional structure;

[0032] Figure 11 for Figure 10 A schematic diagram of the structure at point E;

[0033] In the figure, 1 is the drive unit; 2 is the coupling; 3 is the flexible transmission shaft mandrel; 4 is the rigid sleeve adapter; 5 is the front bearing housing; 6 is the bellows; 7 is the ball nut assembly; 8 is the diameter reducing assembly; 9 is the lead screw shaft; 10 is the push rod; 11 is the rear bearing housing; 12 is the internal air guide channel; and 13 is the flexible transmission shaft sleeve. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Example:

[0036] like Figure 1 , Figure 2 , Figure 3 The flexible drive variable diameter device with a bellows sealing structure in this embodiment mainly consists of three parts: a power input module, a flexible transmission module, and an end effector module.

[0037] The power source for the power and flexible transmission system comes from the drive unit 1 (preferably a micro stepper motor or servo motor in this embodiment), which provides precise rotation angle control. The motor output shaft of the drive unit 1 is connected to the proximal end of the flexible transmission shaft spindle 3 via a coupling 2.

[0038] The flexible drive shaft mandrel 3 is located at the center, with its proximal end connected to the motor output shaft via coupling 2, and its distal end rigidly connected to the lead screw shaft 9 through the central hole of the rigid sleeve adapter 4. This flexible drive shaft mandrel 3 is responsible for transmitting the rotational torque of the motor to the lead screw.

[0039] The flexible drive shaft sleeve 13 is coaxially wrapped around the outside of the flexible drive shaft spindle 3. Its proximal end is fixedly connected to the stationary housing of the drive unit 1, and its distal end is airtightly fixedly connected to the rear end face of the front bearing housing 5. This flexible drive shaft sleeve 13 not only serves a protective function, but also acts as a mechanical "foundation". It uses its own torsional stiffness to restrict the rotation of the front bearing housing 5 with the spindle, thereby ensuring that the ball nut assembly 7 at the end can move linearly relative to the stationary bearing housing.

[0040] The distal end of the flexible drive shaft spindle 3 is rigidly connected to the input end of the lead screw shaft 9 via a rigid sleeve connector 4. The rigid sleeve connector 4 is an axially hollow structure, with its two ends respectively fitted onto the ends of the flexible drive shaft spindle 3 and the lead screw shaft 9; this connector is locked with radial set screws or mechanical interference fit to ensure that slippage does not occur under high torque transmission.

[0041] This embodiment innovatively constructs a "remote gap breathing circuit" by utilizing the internal structure of the above-mentioned composite transmission component to solve the problem of air pressure fluctuation in the sealed cavity caused by the bellows seal.

[0042] During assembly, a flexible drive shaft sleeve 13 with an inner diameter slightly larger than the outer diameter of the flexible drive shaft spindle 3 is selected, so that a continuous annular ventilation gap is naturally formed between the inner wall of the sleeve and the outer wall of the spindle.

[0043] like Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 An internal air passage 12 is provided inside the front bearing housing 5. One end of the passage opens into the sealed cavity formed by the bellows 6 and the lead screw shaft 9, and the other end is directly connected to the annular air gap inside the flexible drive shaft sleeve 13.

[0044] When the device contracts, causing the bellows 6 to be compressed, the air pressure inside the sealed cavity increases instantaneously. The high-pressure gas enters directly into the annular ventilation gap of the flexible drive shaft through the internal air guide channel 12, and is rapidly discharged backward along this gap to the drive unit 1 located in a non-liquid environment (external or liquid-free zone). Conversely, when the bellows 6 extends, the air in the non-liquid environment flows back along the same path to compensate.

[0045] This design not only eliminates air resistance caused by the "piston effect," but more importantly, the vent is always located at the drive end, away from the working fluid. This physical isolation ensures that external fluids such as urine and cutting fluid cannot be drawn into the bellows cavity, achieving true full sealing and long-term protection.

[0046] Variable diameter assembly 8 (e.g.) Figure 1 The mesh support (cage-like structure) is fitted onto the outermost layer of the device. Its distal end is fixedly connected to the push rod 10 located at the top of the lead screw shaft 9. The push rod 10 is installed at the end of the lead screw shaft 9 via a miniature bearing or retaining ring structure, so that the push rod 10 is fixed in axial position relative to the lead screw shaft 9 but can rotate relative to it (i.e., when the lead screw rotates, the push rod 10 does not rotate with it). The variable diameter assembly 8 is made of a metal material (such as nickel-titanium alloy) with a certain torsional stiffness. Since the distal end of the variable diameter assembly 8 is restricted from rotation by the push rod assembly 10, its proximal end applies a circumferential constraint torque to the ball nut assembly 7, which plays a role in preventing rotation and guiding. When the drive unit 1 drives the lead screw shaft 9 to rotate, the ball nut assembly 7 can only move axially due to the circumferential tension of the variable diameter assembly 8, thereby pushing the variable diameter assembly 8 to expand or contract.

[0047] Its proximal end is fixedly connected to a movable ball nut assembly 7. By changing the relative distance between the ball nut assembly 7 and the fixed push rod 10, the variable diameter assembly 8 is forced to undergo elastic buckling deformation.

[0048] The screw drive pair is preferably a ball screw pair to improve transmission efficiency by utilizing its low friction characteristics. However, this embodiment is not limited to this. In embodiments targeting minimally invasive interventions (such as extremely fine diameter tubes) or single-use applications, the screw drive pair can also be a trapezoidal screw pair (sliding screw pair) or a planetary roller screw pair. Compared to ball screws, trapezoidal screw pairs have the following significant advantages: 1. Easy miniaturization: No need for a circulating ball structure, the nut size can be greatly reduced, making it easy to integrate into micro-catheters with a diameter of less than 3mm; 2. Self-locking function: Utilizing the large helix angle friction of the trapezoidal thread, self-locking is achieved when power is cut off. When the drive unit 1 stops outputting torque, even if the diameter-changing component 8 applies a retraction reaction force, the nut can remain in its current position, thereby preventing the stent from collapsing unexpectedly and significantly improving the safety during the operation; 3. Low cost: Suitable for mass production of disposable medical consumables.

[0049] This embodiment elaborates on the operating logic of the device in the "normally open state", such as Figure 2 (Contraction) and Figure 3 (Expanded) as shown.

[0050] Initial / Expansion State ( Figure 3 The variable diameter assembly 8 designed in this device has shape memory characteristics (normally open type). When there is no external force intervention or the nut is in its natural position, the variable diameter assembly 8 bulges outward by its own elasticity to form a spherical or ellipsoidal support body with the largest radial diameter (Dmax). At this time, the ball nut assembly 7 is located at the far end of the lead screw (close to the rear bearing housing 11), and the two are relatively close, so the variable diameter assembly is in a relaxed or slightly compressed state.

[0051] contraction process ( Figure 2 When the device needs to enter a narrow passage (such as through the urethra into the bladder), the operator activates the drive unit 1: the motor drives the lead screw 9 to rotate, driving the ball nut assembly 7 forward (i.e., towards the flexible transmission shaft spindle 3). As the nut advances, the distance between the ball nut assembly 7 and the rear bearing seat 11 increases. The two ends of the reducing assembly 8 are subjected to strong axial tension, forcing the mesh structure to stretch and lengthen. According to geometry, axial elongation inevitably leads to radial contraction. When the nut reaches its limit position, the reducing assembly 8 is close to or near the surface of the transmission assembly, and the outer diameter reaches its minimum (Dmin), at which point the device can smoothly pass through the narrow orifice.

[0052] During the release / re-expansion process, once the device reaches the target location (e.g., inside the bladder): the motor rotates in the opposite direction, driving the ball nut assembly 7 to move backward (i.e., away from the flexible drive shaft spindle 3). The axial tension is gradually released, and the variable diameter assembly 8, under the combined action of its own elastic restoring force and the nut thrust, rapidly retracts and shortens, bulging outward. The device returns to its original position. Figure 3The expanded state shown provides flexible support to the inner wall of the cavity or allows for dilation treatment.

[0053] In this embodiment, the device serves as a disposable or reusable bladder dilator.

[0054] The variable diameter component 8 is woven from nickel-titanium alloy wire and undergoes heat setting treatment to ensure that its austenitic phase transformation end temperature is lower than the human body temperature (e.g., 25℃-35℃), guaranteeing that the device remains in a highly elastic state after implantation. The corrugated tube 6 is made of medical-grade silicone or TPU material, which has excellent biocompatibility and resistance to urine corrosion.

[0055] The bellows sealing structure effectively prevents crystalline salts in urine from entering the threaded gap of the lead screw, thus avoiding instrument jamming. At the same time, the flexible support of the nickel-titanium alloy prevents mechanical compression damage to the bladder mucosa.

[0056] In this embodiment, the device serves as a pipe inner wall support or a foreign object gripper.

[0057] The reducing assembly 8 is replaced with high-strength 65Mn spring steel or stainless steel spring steel to provide stronger radial support stiffness and meet the heavy-duty requirements of industrial pipelines. The bellows 6 is made of stainless steel or oil-resistant fluororubber to resist industrial cutting fluids or high-temperature environments.

[0058] By adding barbs or magnetic modules to the mesh of the reducing assembly 8, the device can also clean or grab foreign objects in the pipe while expanding.

[0059] 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 within the protection scope of the present invention.

Claims

1. A flexible drive expansion device having a bellows seal structure, characterized by: Including drive unit (1), transmission assembly, variable diameter assembly (8) and sealing assembly; The transmission assembly is connected with the drive unit (1), the variable diameter assembly (8) is sleeved at the end of the transmission assembly, and the sealing assembly is wrapped outside the transmission assembly.

2. The flexible drive expansion device having a bellows seal structure according to claim 1, characterized by: The transmission assembly includes a flexible transmission shaft and a screw transmission pair, and the rotary power generated by the drive unit (1) is transmitted to the screw transmission pair through the flexible transmission shaft, the screw transmission pair converts the received rotary motion into linear reciprocating motion along the axial direction, and drives the variable diameter assembly (8) to elastically deform through the push-pull action, so that the radial expansion or contraction is realized.

3. The flexible drive expansion device having a bellows seal structure according to claim 2, characterized by: The transmission assembly adopts a core shaft-sheath coaxial composite structure, the flexible transmission shaft includes a flexible transmission shaft core shaft (3) located at the center and a static sheath wrapped outside, and the static sheath is a flexible transmission shaft sheath (13); The flexible transmission shaft core shaft (3) is connected with the drive unit (1) and the screw shaft (9) and transmits rotary power; The two ends of the flexible transmission shaft sheath (13) are fixed on the shell of the drive unit (1) and the static end of the screw transmission pair respectively, and the anti-torsional stiffness of the flexible transmission shaft sheath (13) is used to provide anti-rotation support for the end mechanism; There is an annular ventilation gap between the flexible transmission shaft core shaft (3) and the flexible transmission shaft sheath (13), the far end of the gap is communicated with the internal air guide channel (12) on the closed containing cavity and the front bearing seat (5), and the near end of the gap extends to the drive unit (1) located in a non-liquid environment and is communicated with the atmosphere; The inner wall of the flexible transmission shaft sheath (13) or the outer wall of the flexible transmission shaft core shaft (3) is provided with a spiral air guide groove or adopts a woven mesh tube structure, so that when the flexible transmission shaft core shaft (3) is bent at a large angle, the ventilation gap is not completely closed, and the air passage is ensured to be unobstructed.

4. The flexible drive expansion device having a bellows seal structure according to claim 3, characterized by: The closed containing cavity adopts a remote gap breathing method, when the bellows (6) is compressed or elongated to cause pressure fluctuation in the cavity, the gas is directly exchanged between the closed cavity and the atmosphere through the annular ventilation gap in the flexible transmission shaft; Without adding an additional ventilation pipe, the breathing function is realized by using the structural gap of the transmission assembly, which balances the air pressure and ensures that the internal and external liquid working environments of the device are completely isolated.

5. The flexible drive expansion device with bellows seal structure of claim 2, wherein: The screw transmission pair converts the received rotary motion into linear reciprocating motion along the axial direction, the variable diameter assembly (8) serves as an anti-rotation restraint mechanism, the variable diameter assembly (8) has torsional stiffness, and the two ends of the variable diameter assembly (8) are connected with the ball nut assembly (7) and the static assembly at the far end of the screw shaft (9) respectively, so that the ball nut assembly (7) is limited to rotate with the screw shaft (9), thereby ensuring the effective conversion of rotary motion to linear motion.

6. The flexible drive expansion device with bellows seal structure of claim 2, wherein: The sealing assembly is an axially extendable bellows structure; The bellows (6) is sleeved outside the screw transmission pair, one end of the bellows (6) is sealingly connected with the relatively static end of the screw transmission pair, and the other end is sealingly connected with the linear motion output end of the screw transmission pair; The bellows (6) is elongated or compressed with the movement of the ball nut, forming a dynamic closed containing cavity, which completely isolates the working section of the precision screw and the external environment.

7. The flexible drive expansion device with bellows seal structure of claim 2, wherein: The transmission assembly adopts a segmented flexible connection structure, the flexible transmission shaft is located between the driving unit (1) and the screw transmission pair, the input end of the flexible transmission shaft is connected with the driving unit (1) through the shaft coupling (2), and the output end of the flexible transmission shaft is connected with the input end of the screw transmission pair through the rigid sleeve adapter (4); the rigid sleeve adapter (4) is internally provided with an axial mounting hole, the distal end of the flexible transmission shaft shaft (3) and the proximal end of the screw shaft (9) are respectively inserted into the mounting hole, and are fixed through the lateral set screw, the pin or the mechanical pressure connection mode, so that the rotary power can be transmitted from the flexible shaft to the screw shaft (9) without clearance.

8. The flexible drive expansion device with bellows seal structure of claim 1, wherein: The variable diameter assembly (8) is a net-like woven structure or a cage-like structure composed of a plurality of elastic strips; the variable diameter assembly (8) is made of a nickel-titanium alloy shape memory metal or a high-strength spring steel.

9. The flexible drive expansion device with bellows seal structure of claim 2, wherein: The linear displacement of the screw transmission pair is used to adjust the geometric shape of the variable diameter assembly (8).

10. The flexible drive variable diameter device having a bellows seal structure of any of claims 1-9, wherein: Contraction action: the driving unit (1) drives the screw to rotate, drives the ball nut assembly (7) to move towards the flexible transmission shaft, that is, the proximal end; this action increases the distance between the ball nut assembly (7) and the screw head end, thereby applying an axial tension to the variable diameter assembly (8); under the action of the tension, the variable diameter assembly (8) is axially elongated, and the radial dimension thereof is reduced, until the contraction state of the minimum outer diameter is reached, so as to facilitate the device to pass through the narrow cavity; Expansion action: the driving unit (1) drives the screw to rotate reversely, drives the ball nut assembly (7) to move away from the flexible transmission shaft, that is, the distal end; this action reduces the distance between the ball nut assembly (7) and the screw head end, thereby applying an axial thrust or releasing the tension to the variable diameter assembly; under the action of the axial compression, the net-like structure of the variable diameter assembly (8) is deformed outward, the radial dimension thereof is increased, until the preset expansion state is reached, so as to realize the effective fitting and support to the target cavity.

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