An underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force

Abstract

This invention discloses an underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force. The gripper's bellows assembly serves as an axial linear power source and is mounted within a rigid transmission frame, driving the extension and retraction of the rigid transmission frame via hydraulic actuation. Each adjustable-stiffness flexible tentacle acts as an end effector mounted on the rigid transmission frame, retracting inward or extending outward as the frame extends and retracts. Simultaneously, each tentacle is independently hydraulically driven to bend, generating a gradient curvature to achieve envelope gripping of underwater targets. This invention solves the problem of gripping failure or target damage caused by the lack of adjustable stiffness or inaccurate gripping force control when dealing with complex shapes and vulnerable targets in existing underwater grippers. It enables flexible envelope gripping of objects of different shapes, sizes, and hardness levels, allowing for dual adjustment of contact stiffness and gripping force. It supports various gripping modes such as light handling, pinching, gripping, and clamping, and is suitable for diverse object types and a wide range of operating scenarios.

Description

Technical Field

[0001] This invention relates to a rigid-flexible coupled gripper, which falls under the field of soft robot technology, and specifically to an underwater hydraulically driven rigid-flexible coupled gripper with adjustable stiffness and gripping force. Background Technology

[0002] The ocean covers most of the Earth's surface and contains abundant resources. In recent years, the demand for marine infrastructure construction and deep-sea exploration has been growing. Deep-sea operations are diverse, often requiring the handling of objects with different characteristics. For example, when sampling marine organisms, the gripper needs to have flexible interaction capabilities to achieve non-destructive sampling of fragile organisms; during deep-sea geological exploration, the gripper needs to provide greater gripping force and load-bearing capacity to grasp heavy objects such as rocks; when operating deep-sea equipment, the gripper may encounter small-volume, heavy metal workpieces, requiring it to apply a large gripping force with a limited contact area; underwater archaeology combines the above requirements, such as when excavating porcelain, it is necessary to adhere as closely as possible to the porcelain surface and apply a large contact force while ensuring flexible interaction to achieve a firm grip on smooth porcelain.

[0003] Currently, deep-sea operation equipment mainly uses rigid mechanical grippers, which have limited applicability and are prone to damaging fragile objects. Soft grippers suffer from insufficient grip strength and low dexterity, and pneumatic soft grippers are significantly affected by buoyancy and high pressure in the marine environment, making them unsuitable for deep-sea operations. Preparing multiple sets of equipment to meet different needs not only causes inconvenience in replacement but also occupies valuable space in marine exploration equipment. Therefore, current marine exploration requires a robotic arm end effector that can adapt to most operational scenarios, possessing a certain degree of dexterity, flexible interaction capabilities, and the ability to apply significant gripping force. Summary of the Invention

[0004] To address the problems existing in the background art, the present invention provides an underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and grip force. This invention solves the problem of grasping failure or target damage caused by the non-adjustable stiffness or inaccurate grip force control of existing underwater grippers when dealing with complex shapes and vulnerable targets.

[0005] The technical solution adopted in this invention is: The present invention relates to an underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force, comprising: The rigid transmission frame serves as the skeleton of the rigid-flexible coupling gripper and provides rigid transmission.

[0006] The bellows assembly, as an axial linear power source, is installed in a rigid transmission frame. After being hydraulically driven, it drives the extension and retraction of the rigid transmission frame through its own linear extension and retraction.

[0007] Two or more stiffness-adjustable soft tentacles, each acting as an end effector with its root end evenly spaced along the circumference on the upper part of the rigid transmission frame, retract inward or expand outward when the rigid transmission frame extends or retracts. Each stiffness-adjustable soft tentacle is also equipped with a pressure deformation zone and a stiffness adjustment zone, which are independently hydraulically driven to bend to generate a gradient change in bending curvature, so as to achieve the envelope grasping of underwater targets.

[0008] The rigid transmission frame includes a base, connecting components equal in number to the number of adjustable-rigidity soft tentacles, and a top cover. The base is a plate-like structure with a first through hole in its center. The base extends circumferentially at uniform intervals as connecting blocks perpendicular to the central plate surface, equal in number to the connecting components. Each connecting component is hinged between its respective connecting block and the top cover. The top cover is a plate-like structure with a second through hole coaxial with the first through hole in its center. The top cover and the central plate surface of the base are arranged parallel to each other at intervals. Each connecting component includes a plate-like first connecting member, a second connecting member, and a third connecting member that are sequentially and coaxially hinged together. The first connecting member is mounted on the connecting block at a distance from the connecting block. On one side away from the center of the base, one side of the second connector is hinged to the plate surface of the first connector, and the other side of the second connector is hinged to one side of the third connector. The other side of each third connector is evenly hinged to the outer periphery of the top cover along the circumferential direction. The root end of each stiffness-adjustable soft tentacle is installed on the side of its respective third connector away from the base. The bellows assembly is fitted between the two through holes of the base and the top cover. The extension and retraction of the bellows assembly causes the top cover to move away from or closer to the base, thereby causing the third connector to rotate and causing each stiffness-adjustable soft tentacle to rotate inward to retract or rotate outward to unfold in a flower shape.

[0009] The hinge axes at the hinge positions between the top cover and the three connecting parts are all parallel to the center plate of the base, i.e., they are coaxially connected.

[0010] The bellows assembly includes a lower end cap, an upper end cap, four bellows retaining rings, two bellows sealing rings, and a bellows. The bellows is fitted between the lower and upper end caps. A hollow cylindrical snap-fit ​​structure is provided at the center of the opposite side of both the lower and upper end caps. A lower end cap retaining ring snap or an upper end cap retaining ring snap is evenly spaced along the circumferential edge of the snap-fit ​​structure away from the surface of the lower or upper end cap. From the root end of each upper end cap retaining ring snap to the snap-fit ​​structure between the upper end cap surface, a first bellows retaining ring, a first bellows sealing ring, and a second bellows retaining ring are sequentially fitted and tightly pressed together. The second bellows retaining ring... One end of the bellows is pressed between itself and the upper end cover plate. From the root end of each lower end cover retaining ring buckle to the buckle structure between the lower end cover plate, a third bellows retaining ring, a second bellows sealing ring, and a fourth bellows retaining ring are sequentially fitted and tightly pressed together. The fourth bellows retaining ring presses the other end of the bellows between itself and the lower end cover plate. The opposite side edges of the lower and upper end covers are respectively connected to the side of the base and the top cover away from the center of the rigid transmission frame. The bellows passes through two through holes in the base and the top cover without contacting each other. The center of the lower end cover has a bellows injection hole that connects to the inner cavity of the bellows to allow fluid medium to be introduced to drive the bellows to expand and contract.

[0011] The corrugated pipe assembly also includes several corrugated pipe support rings. Each corrugated pipe support ring is evenly spaced inside the corrugated pipe between the two snap-fit ​​structures. Each corrugated pipe limiting ring and each corrugated pipe support ring are arranged parallel to each other along the length of the corrugated pipe and have the same structure, and all fit against the part with the largest radius of the inner wall of the corrugated pipe.

[0012] The aforementioned stiffness-adjustable soft tentacle includes a soft finger and a finger coating. The adhesive surface of the coating on the back of the finger coating fits and covers the fingertip of the soft finger shell. The ventral surface of the finger coating serves as the fingertip of the stiffness-adjustable soft tentacle. The back of the soft finger shell is provided with a pressure deformation zone and a stiffness adjustment zone. The ventral surface of the finger coating is provided with microstructure units and anchoring patterns. The root end of the soft finger is connected to the rigid frame connection hole on the side of the third connector through a soft finger connection hole. A cavity injection hole is opened at the root of the soft finger shell. After the fluid medium is injected, it expands through the soft finger cavity inside the soft finger shell at the root end, driving the stiffness-adjustable soft tentacle to bend inward to envelop and grasp.

[0013] The soft finger cavity, starting from the root end of the soft finger shell and extending along the finger length, consists of a series of interconnected cavity connecting parts arranged axially, spaced, protruding, cuboid-like toothed cavities, and a fingertip cavity. The cavity injection holes connect to the cavity connecting parts. Each toothed cavity is divided into a pressure deformation zone and a stiffness adjustment zone, located near the cavity connecting parts and the fingertip cavity, respectively. In the pressure deformation zone, the toothed cavities alternate between higher and lower deformation driving cavities, with the lower deformation driving cavity closest to the stiffness adjustment zone. In the stiffness adjustment zone, the toothed cavities alternate between a lower first stiffness adjustment cavity, a higher second stiffness adjustment cavity, and a lower third stiffness adjustment cavity, extending from the root end to the tip. The height of the second stiffness adjustment cavity is the same as the height of the lower deformation driving cavity. The fingertip cavity does not have a bending function.

[0014] The deformation driving cavities in the pressurized deformation zone have equal widths, while the width gradients of the first stiffness adjustment cavity, the second stiffness adjustment cavity, and the third stiffness adjustment cavity in the stiffness adjustment zone decrease to generate a non-uniform curvature distribution under pressurized conditions.

[0015] The microstructural units on the ventral side of the finger coating are regular hexagonal protrusions, and the microstructural units are evenly spaced and arranged in rows, so that the microstructural units are distributed in a honeycomb grid pattern with concave anchoring textures.

[0016] It also includes a hydraulic control system and a sensor group. The sensor group is used to monitor the pressure feedback of the bellows of the bellows assembly and the soft finger cavity of the stiffness-adjustable soft tentacle in real time. The hydraulic control system adjusts the volume of the injected fluid medium in a closed loop according to the pressure feedback signal, thereby realizing the coordinated control of the opening and closing span, gripping contact stiffness and contact force of the dynamic rigid-flexible coupling gripper, so that the stiffness and gripping force of the rigid-flexible coupling gripper are adjustable.

[0017] The beneficial effects of this invention are: The underwater hydraulically driven rigid-flexible coupled gripper proposed in this invention achieves a synergistic coupling of the advantages of rigid and soft structures, significantly broadening the applicable range of grasping objects. By combining a rigid transmission frame with soft tentacles, this invention integrates the high load output and precise position control capabilities of a rigid gripper with the flexible interaction and adaptive envelope characteristics of a soft gripper. It can perform envelope-style non-destructive grasping of lightweight and fragile targets, as well as achieve stable high-load grasping of large-mass targets such as rocks and metal workpieces, enabling a single gripper to adapt to grasping objects of various sizes.

[0018] Furthermore, by adjusting both contact stiffness and gripping force, this rigid-flexible coupling system can achieve continuous modulation and target combination of arbitrary contact stiffness and contact force for gripping objects with different mechanical characteristics within a two-dimensional control space consisting of the achievable stiffness range and the achievable gripping force range.

[0019] Furthermore, unlike traditional soft fingers that achieve point contact due to constant curvature, this invention utilizes a design where the internal chambers decrease in volume from proximal to distal. This causes the finger to undergo non-uniform curvature deformation under pressure, thereby achieving enveloping surface contact with the target. This surface contact not only significantly increases the effective contact area and enveloping effect, improving grip stability, but also provides a stable physical interface for precise adjustment of contact stiffness, ensuring the effectiveness of mechanical parameter adjustments.

[0020] This invention can perform flexible envelope gripping of work objects of different shapes, sizes, and hardness according to needs, and can adjust both contact stiffness and gripping force. It can achieve different gripping modes such as light picking, pinching, holding, and clamping, and can handle a wide variety of work objects and work scenarios. Attached Figure Description

[0021] Figure 1 A front view of an underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force, provided in an embodiment of the present invention; Figure 2 This is a three-dimensional structural diagram of the rigid transmission frame and its connection with the upper and lower end caps in an embodiment of the present invention; Figure 3 This is an exploded view and an axial cross-sectional view of the bellows assembly in an embodiment of the present invention; Figure 4 This is a schematic diagram of the disassembled structure of the stiffness-adjustable soft finger in an embodiment of the present invention and its connection relationship with the rigid transmission frame. Figure 5 This is a schematic diagram of the finger coating structure in an embodiment of the present invention; Figure 6 This is a schematic diagram of the adjustable stiffness soft finger body from various perspectives in an embodiment of the present invention. From top to bottom, the views are: top view, first axial sectional view, second axial sectional view, and side view. Figure 7 This is a schematic diagram of the rigid transmission frame in its retracted state in an embodiment of the present invention; In the diagram: 1. Rigid transmission frame; 10. Base; 11. First connector; 12. Second connector; 13. Third connector; 14. Top cover; 130. Soft finger connection hole; 2. Bellows assembly; 20. Lower end cover; 21. Upper end cover; 22. Bellows limiting ring; 23. Bellows sealing ring; 24. Bellows support ring; 25. Bellows; 200. Lower end cover limiting ring buckle; 201. Bellows injection hole; 210. Upper end cover limiting ring buckle; 3. Adjustable stiffness soft tentacle; 30. Soft finger; 3 00. Rigid frame connection hole; 301. Soft finger shell; 3010. Pressure deformation zone; 3011. Stiffness adjustment zone; 302. Soft finger cavity; 3020. Cavity injection hole; 3021. Cavity connection part; 3022. Deformation driving cavity; 3023. First stiffness adjustment cavity; 3024. Second stiffness adjustment cavity; 3025. Third stiffness adjustment cavity; 3026. Fingertip cavity; 31. Finger coating; 310. Coating adhesive surface; 311. Microstructure unit; 312. Anchoring texture. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Those skilled in the art will recognize that various modifications can be made without departing from the principles of the invention, and these modifications are also considered to be within the scope of protection of the present invention.

[0023] like Figure 1 As shown, the underwater hydraulically driven rigid-flexible coupling gripper of the present invention includes a rigid transmission frame 1, a bellows assembly 2, and two or more rigidity-adjustable soft tentacles 3. The rigid transmission frame 1 serves as the skeleton of the rigid-flexible coupling gripper and provides rigid transmission. The bellows assembly 2 is installed in the rigid transmission frame 1 as an axial linear power source. After hydraulic drive, it drives the rigid transmission frame 1 to extend and retract through its own linear extension and retraction. Each rigidity-adjustable soft tentacles 3 serves as an end effector and is installed at even intervals along the circumference on the upper part of the rigid transmission frame 1. When the rigid transmission frame 1 extends and retracts, it retracts inward or extends outward. Each rigidity-adjustable soft tentacles 3 is also provided with a pressure deformation zone 3010 and a stiffness adjustment zone 3011, which are independently hydraulically driven to bend to generate a gradient change in bending curvature in order to achieve the enveloping gripping of underwater targets.

[0024] like Figure 2As shown, the gripper uses a rigid transmission frame 1 as its core support structure. The rigid transmission frame 1 includes a base 10, a number of connecting components equal to the number of adjustable-rigidity soft tentacles 3, and a top cover 14. Specifically, there can be three sets of connecting components, corresponding to three adjustable-rigidity soft tentacles 3. The base 10 is a plate-shaped structure with a first through hole in the center. The base 10 extends circumferentially at uniform intervals as connecting blocks perpendicular to the central plate surface, equal to the number of connecting components. Each connecting component is hinged between its respective connecting block and the top cover 14. The top cover 14 is a plate-shaped structure with a second through hole coaxial with the first through hole in the center. The top cover 14 and the central plate surface of the base 10 are arranged parallel to each other at intervals. Each connecting component includes a plate-shaped first connecting member 11, a second connecting member 12, and a third connecting member 13 that are sequentially and coaxially connected in series. The first connecting member 11 is installed on the side of the connecting block away from the center of the base 10. One side of the second connecting member 12 is hinged to the first connecting member 13. On the plate surface of 1, the other side of the second connector 12 is hinged to one side of the third connector 13, and the other side of each third connector 13 is evenly hinged to the outer periphery of the top cover 14 along the circumferential direction; the root end of each stiffness adjustable soft tentacle 3 is installed on the side of its respective third connector 13 away from the base 10 through the soft finger connection hole 130; the bellows assembly 2 is fitted between the two through holes of the base 10 and the top cover 14. The bellows assembly 2 extends and retracts, causing the top cover 14 to move away from or closer to the base 10, thereby causing the third connector 13 to rotate, causing each stiffness adjustable soft tentacle 3 to rotate inward to retract or rotate outward to unfold in a flower shape. The third connector 13 rotates around the second connector 12 at a large angle, the second connector 12 rotates around the first connector 11, and the second connector 12 rotates around the first connector 11 at a small angle under the action of the third connector 13 to adapt to the overall change of the rigid transmission frame 1. The hinge axes at the hinge positions of the top cover 14 and the three connecting parts 11, 12 and 13 are all parallel to the center plate surface of the base 10, that is, they are coaxially connected.

[0025] Specifically, the base 10 serves as the chassis of the entire gripper. Its bottom plane has three sets of mounting holes for fixing the lower end cap 20 of the bellows assembly 2, and multiple vertical planes each have four mounting holes. The central axis of the base 30 is 32mm from the outer edge of the multiple vertical planes. Each set of mounting holes for the lower end cap 20 has two holes, with a 10mm spacing between the holes, and the line connecting the two holes is 19mm from the central axis of the base 30. The first connector 11 has four holes at both ends, corresponding to the four holes on the vertical plane of the base 30. The upper end has a hole for coaxial connection, with the center line of the hole 8mm from the bottom surface. The second connector 12 has holes at both ends for coaxial connection, with a 21mm distance between the center lines of the two holes. The third connector 13 has holes at both ends for coaxial connection, with a 26mm distance between the center lines of the two holes, and two flexible finger connection holes 130 on its surface, with an 18mm distance between the two holes. The top cover 14 has multiple sets of protrusions on its edge, and holes are provided at the protrusions for coaxial connection. The distance between the center line of the hole and the center line of the top cover is 21mm.

[0026] The three first connectors 11 are fastened together by bolts through holes at their bottom ends and holes on the vertical connecting block plane of the base 10. Their top ends are coaxially connected to the bottom ends of the corresponding second connectors 12. The top ends of the second connectors 12 are further coaxially connected to the bottom ends of the third connectors 13. The top ends of the multiple third connectors 13 are coaxially connected to the edge protrusions of the top cover 14.

[0027] The bellows assembly 2, serving as the drive source, is nested and installed in the central region of the rigid transmission frame 1. For example... Figure 3As shown, the bellows assembly 2 includes a lower end cap 20, an upper end cap 21, four bellows retaining rings 22, two bellows sealing rings 23, and a bellows 25. The bellows 25 is fitted between the lower end cap 20 and the upper end cap 21. A hollow cylindrical snap-fit ​​structure is provided at the center of the opposite side of both the lower end cap 20 and the upper end cap 21. A lower end cap retaining ring snap 200 or an upper end cap retaining ring snap 210 extends circumferentially at even intervals along the upper edge of the snap-fit ​​structure away from its own surface on the lower end cap 20 or upper end cap 21. From the root of each upper end cap retaining ring snap 210... A first bellows retaining ring 22, a first bellows sealing ring 23, and a second bellows retaining ring 22 are sequentially fitted and tightly pressed onto the snap-fit ​​structure between the upper end cover 21 and the upper end cover 22. The second bellows retaining ring 22 presses one end of the bellows 25 between itself and the upper end cover 21. A third bellows retaining ring 22, a second bellows sealing ring 23, and a fourth bellows retaining ring 22 are sequentially fitted and tightly pressed onto the snap-fit ​​structure between the root end of each lower end cover retaining ring snap 200 and the lower end cover 20. 22. The other end of the bellows 25 is pressed between itself and the surface of the lower end cover 20. The opposite side edges of the lower end cover 20 and the upper end cover 21 are respectively connected to the side surfaces of the base 10 and the top cover 14 away from the center of the rigid transmission frame 1. The lower end cover 20 and the upper end cover 21 have similar structures and the sealing and fastening connection methods are exactly the same. The edge design of the upper end cover 21 does not interfere with the various stiffness adjustable soft tentacles 3. The bellows 25 passes through the two through holes of the base 10 and the top cover 14 without contacting each other. The center of the lower end cover 20 is provided with a bellows injection hole that connects to the inner cavity of the bellows 25. 201, the bellows 25 is driven to extend and retract by the fluid medium. The bellows assembly 2 achieves axial extension and retraction through the injection and extraction of the internal hydraulic medium. Utilizing the quasi-incompressibility of the hydraulic medium, the axial extension and retraction of the bellows assembly 2 is precisely modulated by the hydraulic volume flow rate, thereby achieving high-precision position control of the gripping opening and closing degree. At the same time, the axial driving force generated by the bellows 25 is coupled to the stiffness-adjustable soft tentacle 3 through the rigid transmission frame 1, converting the high power density of the hydraulic drive into the powerful gripping of the end effector, which significantly improves the system's ability to control heavy-duty targets.

[0028] like Figure 2 and Figure 3 As shown, the lower end cap 20 of the bellows assembly is fastened to the base 10, while the upper end cap 21 is fastened to the top cap 14. The bellows assembly 2 is driven to extend and contract axially by injecting and extracting liquid. The bellows injection hole 201 provided in the center of the lower end cap 20 is used for injecting and extracting liquid.

[0029] The bellows assembly 2 also includes several bellows support rings 24, specifically two. Each bellows support ring 24 is evenly spaced inside the bellows 25 between the two snap-fit ​​structures to prevent radial collapse of the bellows 25 when liquid is extracted. Each bellows limiting ring 22 and each bellows support ring 24 are arranged parallel to each other along the length of the bellows 25 and have the same structure, all fitting against the point of maximum radius of the inner wall of the bellows 25. The materials of the lower end cap 20, upper end cap 21, bellows limiting ring 22, and bellows support ring 24 are elastic, and the material of the bellows sealing ring 23 has considerable elasticity.

[0030] The outer diameter of the bellows limiting ring 22 is equal to the maximum inner diameter of the bellows 25, and the inner diameter is equal to the outer diameter of the columnar part of the lower end cap 20; the outer wall contour of the bellows sealing ring 23 is grooved, which fits completely with the protrusion of the inner wall of the bellows, and the inner diameter of the bellows sealing ring 23 is slightly smaller than the outer diameter of the columnar part of the lower end cap 20; a bellows limiting ring 22 is embedded in two adjacent grooves near the port of the bellows 25, and a bellows sealing ring 23 is embedded between the two bellows limiting rings 22. The lower end cap 20 is connected to the bellows 25 by a mechanical compression sealing structure. The sealing structure includes two bellows limiting rings 22 located in the groove of the inner wall of the bellows 25, and a bellows sealing ring 23 sandwiched between the two bellows limiting rings 22. The outer wall deformation of the bellows sealing ring 23 is interference-fitted with the protrusion of the inner wall of the bellows 25. Multiple limiting ring buckles 200 and 210 are provided on the periphery of the columnar part of the lower end cap 20. The top of the limiting ring buckles 200 and 210 is a guide slope, and the bottom is an outwardly extending locking plane. The axial distance between the locking plane and the base plane of the lower end cap 20 is slightly less than the total thickness of the two bellows limiting rings 22, the uncompressed bellows sealing ring 23, and the wall of the bellows 25. During assembly, the lower end cap 20 is embedded into the center of the bellows retaining ring 22 by the radial elastic deformation of the retaining ring clips 200 and 210. The holding force of the locking plane causes the two bellows retaining rings 22 to exert axial compression on the bellows sealing ring 23, thereby generating radial compensating stress and achieving a highly reliable seal on the inner wall of the bellows 25. The distance from the bottom surface of the retaining ring clips 200 and 210 to the upper surface of their corresponding end caps 20 and 21 is slightly less than the sum of the thicknesses of the two bellows retaining rings 22, the uncompressed bellows sealing ring 23, and the bellows 25.

[0031] like Figure 1 and Figure 7As shown, the bellows assembly 2 serves as the driving core of the underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force provided in this embodiment. Under the drive of the bellows assembly 2, the rigid transmission frame 1 drives multiple flexible tentacles 3 with adjustable stiffness to rotate inward to tighten or rotate outward to open in a flower shape. When liquid is injected into the bellows assembly 2, the bellows 25 extends, pushing the upper end cap 21 and causing the top cap 14, which is fastened to it, to move upward, thereby causing multiple third connectors 13 to rotate outward around the second connector 12, thereby causing multiple stiffness-adjustable soft tentacles 3 to open outward; when liquid is extracted from the bellows assembly 2, the bellows 25 shortens, pulling the upper end cap 21 and causing the top cap 14, which is fastened to it, to move downward, thereby causing multiple third connectors 13 to rotate inward around the second connector 12, thereby causing multiple stiffness-adjustable soft tentacles 3 to tighten inward; during the opening and tightening movements, the second connector 12 rotates around the first connector 11 at a small angle under the action of the third connector 13 to adapt to the overall change of the rigid transmission frame 1.

[0032] like Figure 1 , Figure 4 and Figure 6 As shown, the stiffness-adjustable soft tentacle 3 includes a soft finger 30 made of flexible elastic material and a finger coating 31. The coating adhesive surface 310 on the back of the finger coating 31 is shaped and covers the fingertip surface of the soft finger shell 301 of the soft finger 30. The ventral surface of the finger coating 31 serves as the fingertip surface of the stiffness-adjustable soft tentacle 3. The finger coating 31 covers the inside and all sides of the soft finger shell 301. The back of the soft finger shell 301 is provided with a pressure deformation area 3010 and a stiffness adjustment area 3011. The ventral surface of the finger coating 31 is provided with microstructure units 311 and anchoring patterns 312. The root end of the soft finger 30 is connected to the soft finger... The connecting hole 130 and the rigid frame connecting hole 300 on the side of the third connector 13 are connected in a mating manner; a cavity injection hole 3020 is opened at the root of the soft finger shell 301. After the fluid medium is injected, it expands through the soft finger cavity 302 inside the soft finger shell 301 at the root end, driving the stiffness adjustable soft tentacle 3 to bend inward to envelop and grasp. The stiffness adjustable soft tentacle 3 uses the pre-tension force generated by the hydraulic medium on the soft finger cavity 302 to counteract the deformation tendency caused by the external load; by increasing the volume of injected liquid, the circumferential stress of the soft finger shell 301 is increased, thereby improving the anti-distortion stiffness of the soft finger 30 in the spatial dimension.

[0033] The soft finger cavity 302, extending from the root end of the soft finger shell 301 along the finger length direction, consists of a series of interconnected cavity connecting portions 3021, spaced-apart rectangular toothed cavities, and a fingertip cavity 3026 arranged axially. A cavity injection hole 3020 connects to the cavity connecting portions 3021. Each toothed cavity is divided into a pressure deformation zone 3010 and a stiffness adjustment zone 3011. The pressure deformation zone 3010 and the stiffness adjustment zone 3011 are located on opposite sides of the cavity connecting portions 3021 and the fingertip cavity 3026, respectively. The length of the pressure deformation zone 3010 is greater than the length of the stiffness adjustment zone 3011. The toothed cavities in the pressure deformation zone 3010 are alternately arranged with higher deformation driving cavities 3022 and lower deformation driving cavities 3022. The higher deformation driving cavities 3022 have a uniform height, while the lower ones have a uniform height. The variable-drive cavities 3022 have a consistent height and are used to drive finger bending and provide gripping force. The one closest to the stiffness adjustment zone 3011 is a lower deformation-drive cavity 3022. The toothed cavities in the stiffness adjustment zone 3011 are arranged alternately from root to tip as a lower first stiffness adjustment cavity 3023, a higher second stiffness adjustment cavity 3024, and a lower third stiffness adjustment cavity 3025, so that the soft finger 30 produces a gradient bending curvature when bending. The height of the second stiffness adjustment cavity 3024 is the same as the height of the lower deformation-drive cavity 3022, and the height of the first stiffness adjustment cavity 3023 and the third stiffness adjustment cavity 3025 is the same. The fingertip cavity 3026 is close to the back of the soft finger shell 301 and parallel to the finger length direction. The fingertip cavity 3026 does not have a bending function.

[0034] The deformation driving cavities 3022 in the pressure deformation zone 3010 have uniform widths, while the widths of the first stiffness adjustment cavities 3023, the second stiffness adjustment cavity 3024, and the third stiffness adjustment cavity 3025 in the stiffness adjustment zone 3011 decrease in a gradient manner. This creates a non-uniform curvature distribution under pressure. The design principle is to compensate for deformation stress through gradient distribution, causing the deformation curvature to gradually decrease from the proximal end to the distal end, until the curvature at the fingertip approaches zero. This non-uniform curvature deformation design overcomes the fingertip point contact defect caused by the "uniform curvature bending" of traditional soft fingers, achieving envelope surface contact during the grasping process. Thus, while adjusting stiffness, it limits curvature to ensure surface contact with the grasping object, significantly improving the stability and contact area of ​​the grasp.

[0035] The microstructure units 311 on the ventral side of the finger coating 31 are regular hexagonal protrusions. Each microstructure unit 311 is evenly spaced and arranged in rows, so that the concave anchoring textures 312 distributed in a honeycomb grid pattern between each microstructure unit 311 can discharge the liquid film on the contact surface or anchor the tiny protrusions on the surface of the target to be grasped during underwater grasping operations, thereby improving the grasping adhesion.

[0036] The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force provided in this embodiment is designed with a three-finger structure, corresponding to three sets of connecting parts. The third connecting part 13 in each set is fastened to a flexible tentacles with adjustable stiffness 3.

[0037] like Figure 3 As shown, the lower end cap 20, upper end cap 21, bellows limiting ring 22, and bellows support ring 24 in the bellows assembly 2 are all 3D printed from materials with a certain elastic deformation capability, such as TPU; the bellows sealing ring 23 is made of rubber and has a good sealing effect; the bellows 25 is a common plastic bellows.

[0038] To address the high-pressure underwater environment and the liquid injection / extraction requirements of the bellows assembly 2 during gripper operation, this embodiment features a highly reliable mechanical compression sealing structure. Taking the sealing and fastening connection between the lower end cap 20 and the bellows 25 as an example: The lower end cap 20 includes a base plane at the bottommost end, a hollow columnar portion above the base plane with an outer diameter of 20mm, and several lower end cap retaining ring buckles 200 arranged at equal angles above the hollow columnar portion. The top of the lower end cap retaining ring buckle 200 is a guide slope with an inclination of about 18.4 degrees, and the bottom is an outwardly extending locking plane with an outward extension distance of 2mm. The distance between the locking plane and the lower base plane is 8mm, which is slightly less than the total thickness of the two retaining rings, the uncompressed sealing ring, and the corrugated pipe wall.

[0039] Relying on the elasticity of the bellows retaining ring 22 itself, a bellows retaining ring 22 is respectively provided in two consecutive grooves on the inner wall of the bellows 25 near the lower end. The thickness of the bellows retaining ring 22 is 2mm. The inner diameter of the bellows retaining ring 22 is equal to the outer diameter of the hollow cylindrical part of the lower end cap, and the outer diameter is 28.5mm. A bellows sealing ring 23 is provided at the protrusion on the inner wall of the bellows between the two bellows retaining rings 22. The thickness of the bellows sealing ring 23 is 4mm. The outer side of the bellows sealing ring 23 is a dovetail groove, which is interference-fitted with the protrusion on the inner wall of the bellows (the diameter of the protrusion on the inner wall of the bellows in the uncompressed state is 23.5mm, which is slightly smaller than the diameter of the narrowest part of the dovetail groove on the outer side of the bellows sealing ring 23 in the uncompressed state, which is 23.9mm). The inner diameter of the bellows sealing ring 23 is 19.8mm, which is slightly smaller than the outer diameter of the hollow cylindrical part of the lower end cap.

[0040] During assembly, push the lower end cap 20 into the bellows retaining ring 22. The guide slope at the top of the lower end cap retaining ring buckle 200 first contacts the bellows retaining ring 22. The guide slope converts the axial pushing force into radial pressure, thereby squeezing and tilting the lower end cap retaining ring buckle 200, which has a certain elastic deformation capacity, radially inward, so that the lower end cap 20 can be pushed into the bellows retaining ring 22. Continue to push the lower end cap 20 inward and clamp the two bellows retaining rings 22 by hand to compress the bellows sealing ring 23, reducing its axial thickness, until the distance between the locking plane of the lower end cap and the base plane is greater than the total thickness of the two retaining rings, the one compressed sealing ring, and the one bellows wall. The lower end cap retaining ring buckle 200 then pops outward radially, and you can release your hands.

[0041] At this time, due to the clamping force of the locking plane and the base plane, the bellows sealing ring 23 is in an axially compressed state; since the inner diameter of the bellows sealing ring 23 is slightly smaller than the outer diameter of the hollow columnar part, the outer dovetail groove is interference-fitted with the protrusion of the inner wall of the bellows, and at the same time, the axial compression of the sealing ring generates compensating stress in the radial direction, the bellows sealing ring 23 is also in a radially compressed state, thereby achieving a sealed and tight connection between the lower end cover 20 and the bellows 25.

[0042] like Figure 3 As shown, the upper end cover 21 and the lower end cover 20 have similar structures. Several upper end cover limiting ring buckles 210 are arranged at equal angles, and the sealing and fastening connection methods are exactly the same.

[0043] Several corrugated pipe support rings 24 are sparsely arranged on the inner wall of the middle section of the corrugated pipe 25. The thickness is 1.2 mm, the inner diameter is 20 mm, and the outer diameter is 28.5 mm. They serve as supports to prevent the corrugated pipe 25 from radially collapsing and losing its function when liquid is extracted from it.

[0044] like Figure 4 As shown, multiple stiffness-adjustable soft tentacles 3 are respectively fastened to the third connector 13 of the rigid transmission frame 1. The stiffness-adjustable soft tentacles 3 include soft fingers 30 and a finger coating 31 covering their outer sides. The finger coating 31 serves as the execution interface for direct contact with the target object and is made of a flexible elastic material, such as silicone; and a special surface morphology is designed to address the slippage problem caused by water film or biological mucus on the surface of underwater objects.

[0045] like Figure 5As shown, the grasping surface array of the finger coating 31 comprises several raised hexagonal microstructural units 311, each hexagon having a perimeter of 9 mm. Recessed anchoring patterns 312, 0.4 mm wide and 1 mm deep, are provided between adjacent microstructural units 311, distributed in a honeycomb grid pattern between the hexagonal protrusions. During underwater grasping operations, these tiny microstructural units 311 can utilize high local pressure to expel water film or viscous biofilm from the target object's surface through the recessed anchoring patterns 312. When dealing with irregularly shaped rocks or textured marine organisms, the anchoring patterns 312 can anchor the tiny protrusions on the target object's surface, generating physical interlocking force and improving the grasping effect.

[0046] The basic principle of stiffness adjustment of the adjustable soft tentacle 3 is to use the pre-tension force generated by the injected liquid on the chamber to counteract the deformation tendency caused by external load; by increasing the volume of injected liquid, the circumferential stress of the soft finger shell 301 can be increased, thereby improving the anti-distortion stiffness of the adjustable soft tentacle 3 in the spatial dimension.

[0047] In existing soft gripper technologies, the driving cavities inside the soft fingers typically employ a repetitive unit design, meaning that all cavities distributed along the finger axis maintain complete uniformity in geometric dimensions, cross-sectional shape, and wall thickness. While this homogeneous structural design simplifies the manufacturing process, it presents significant mechanical limitations in actual gripping operations. Because the internal cavities are repetitive units, when a pressure medium is injected into the cavities, each segment of the finger exhibits uniform curvature deformation. During gripping, the finger with uniform curvature deformation often appears as an arc. When facing a target object with a flat or highly curved surface, the finger can only contact the object through its fingertip. This contact mode results in an extremely small contact area, making it difficult to implement a stable, enveloping grip on the object; simultaneously, the extremely small contact area makes it difficult to provide a stable physical interface for adjusting contact stiffness.

[0048] To overcome the above defects, this embodiment adopts an axial gradient cavity design inside the soft finger 30: The soft finger cavity 302 is composed of multiple axially connected chambers, which are arranged sequentially from the base of the finger to the tip: cavity injection hole 3020, cavity connection part 3021, deformation driving cavity 3022, first stiffness adjustment cavity 3023, second stiffness adjustment cavity 3024, third stiffness adjustment cavity 3025, and fingertip cavity 3026. The deformation-driven cavity 3023 is composed of multiple sub-cavities of equal width and varying heights, with a width of 24 mm and alternating heights of 20 mm and 15 mm, used to drive finger bending and provide a certain gripping force. The widths of the first stiffness adjustment cavity 3023, the second stiffness adjustment cavity 3024, and the third stiffness adjustment cavity 3025 decrease in a gradient manner, being 20 mm, 16 mm, and 12 mm respectively, and the cavity volume shows a decreasing trend, thus corresponding to a gradual decrease in curvature during bending. The fingertip cavity 3026 is a thin-film cavity with a width of 8 mm and a thickness of 2 mm. It does not have bending ability but can be filled with more liquid and enhance the stiffness of the fingertip.

[0049] The soft finger shell 301 is made of integrated soft rubber printing. The deformable part is a thin film structure made of a material with a certain degree of elasticity, with a thickness of 2mm and a Shore hardness of 40. The part at the root that is fastened to the third connecting bolt has a Shore hardness of 75. The soft finger shell 301 includes a pressure deformation zone 3010 and a stiffness adjustment zone 3011. The pressure deformation zone 3010 corresponds in position to the internal deformation driving cavity 3022; the stiffness adjustment zone 3011 corresponds in position to the internal stiffness adjustment cavities 3023, 3024, and 3025 at various levels.

[0050] Liquid medium is injected into the cavity 302 of the soft finger through the injection hole 3020. Due to the incompressibility of the liquid, the pressure deformation zone 3010 produces constant curvature deformation under pressure. The volume of the cavity inside the stiffness adjustment zone 3011 decreases gradually from the proximal end to the distal end, and the deformation curvature gradually decreases from the proximal end to the distal end, until the curvature at the fingertip approaches zero.

[0051] The function of the pressure deformation zone 3010 is as follows: when grasping a larger target object, it drives the fingers to bend inward to envelop the target object; when grasping a smaller target object, it drives the stiffness adjustment zone 3011 to tilt inward to grasp the target. The function of the stiffness adjustment zone 3011 is as follows: when grasping a larger target object, it provides a certain degree of curvature to grip the target; when grasping a smaller target object, it limits the curvature to ensure surface contact with the grasped object, significantly improving the stability and contact area of ​​the grasp, while providing a stable physical interaction interface for contact stiffness adjustment.

[0052] The axial gradient cavity design used in this embodiment can generate non-uniform curvature deformation in the stiffness adjustment zone 3011 at the end of the soft finger 30, thereby overcoming the defect of fingertip point contact caused by the uniform curvature bending of traditional soft fingers. While ensuring surface contact with the target and thus improving grasping stability, it provides a stable physical interaction interface for contact stiffness adjustment.

[0053] The rigid-flexible coupling gripper also includes a hydraulic control system and a sensor group. The sensor group is used to monitor the pressure feedback of the bellows 25 of the bellows assembly 2 and the soft finger cavity 302 of the stiffness adjustable soft tentacle 3 in real time. The hydraulic control system performs closed-loop adjustment of the volume of the injected fluid medium according to the pressure feedback signal, thereby realizing the coordinated programmed control of the opening and closing span, gripping contact stiffness and contact force of the rigid-flexible coupling gripper, so that the stiffness and gripping force of the rigid-flexible coupling gripper are adjustable.

[0054] Combining a hydraulic control system and a sensor array, the working method of the underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force provided in this embodiment is as follows: A rigid transmission frame driven by bellows assembly 2 couples with a stiffness-adjustable soft tentacle 3. The stiffness-adjustable soft tentacle 3 provides contact stiffness adjustment and basic gripping force, while the rigid transmission frame 1 driven by bellows assembly 2 provides additional gripping force to the stiffness-adjustable soft tentacle 3. The operation achieves a synergistic coupling of the advantages of rigid and soft structures, integrating the high load output and precise position control capabilities of the rigid gripper with the flexible interaction and adaptive envelope characteristics of the soft gripper. This enables both envelope-style non-destructive gripping of lightweight and fragile targets and stable high-load gripping of large-mass targets such as rocks and metal workpieces, giving the single gripper the ability to adapt to gripping objects of various sizes.

[0055] During grasping, firstly, the axial extension and retraction of the bellows 25 adjusts the tension of the soft finger 30, combined with the slight pressure deformation of the soft finger 30, to perform preliminary pre-envelope of the grasping target. At this time, the soft finger 30 is in a low-stiffness and soft state.

[0056] After completing the pre-envelope of the target object, the required contact force and contact stiffness during grasping are determined based on the target object's physical properties such as hardness, fragility, mass, and specific operational requirements, thereby executing the corresponding grasping operation: Low-stiffness, low-grip grasping: The retracting bellows 25 causes the low-stiffness soft finger 30 to retract inward. The pressure feedback in the soft finger cavity 302 is monitored. When a significant fluctuation in internal pressure occurs, it indicates contact with the target object, and the retraction of the bellows assembly 2 stops. At this point, the low-stiffness, low-tension, adjustable-stiffness soft tentacle 3 makes slight contact with the target object, achieving low-stiffness, low-grip grasping. This mode is suitable for grasping extremely fragile marine organisms, such as jellyfish, sponges, and corals, or for collecting samples of fragile underwater sediments and organic remains from underwater archaeology.

[0057] Low-stiffness, high-grip grasping: The bellows assembly 25 retracts while monitoring pressure feedback from the soft finger cavities 302. Once a significant pressure fluctuation occurs and contact with the object being grasped is established, the bellows assembly 2 continues to retract to provide additional gripping force. At this point, three low-stiffness, adjustable-stiffness soft tentacles 3, driven by the bellows assembly 2, firmly grip the target object, achieving low-stiffness, high-grip grasping. This mode is suitable for grasping fragile and heavy objects, such as porcelain that has been submerged underwater for a long time, as well as heavy organisms like crabs and fish.

[0058] High-rigidity, low-grip gripping: A liquid medium is injected into the soft fingers 30 to increase tension and achieve high anti-distortion stiffness. Then, the bellows 25 is contracted, and the pressure feedback within the bellows 25 is monitored. When a significant pressure fluctuation occurs, it indicates contact with the target object, and contraction of 25 stops. At this point, the three highly tensioned, adjustable-rigidity soft tentacles 3 clamp onto the target object, achieving high-rigidity, low-grip gripping. This mode is suitable for gripping objects with a certain degree of hardness and mass but a small volume, such as bolts or other small, high-hardness workpieces. When using low-rigidity, low-grip gripping for these items, the flexibility of the adjustable-rigidity soft tentacles 3 makes it difficult to apply sufficient gripping force within a limited contact area. In high-rigidity, high-grip gripping, when clamping such targets, the ends of the three fingers eventually misalign due to the large inward contraction force provided by the bellows assembly 2, resulting in poor gripping performance.

[0059] High-rigidity, high-grip gripping: After achieving low-rigidity, low-grip gripping, the bellows 25 is simultaneously retracted, and liquid is injected into the soft finger cavity 302. At this time, the three highly tensioned, rigidity-adjustable soft tentacles 3 firmly grip the target, achieving high-rigidity, high-grip gripping. This gripping mode belongs to the heavy-duty mode of this embodiment and is suitable for gripping large-mass metal workpieces, rock samples, etc., or operating rotary valves during underwater operations.

[0060] By utilizing the incompressibility of liquids and precisely adjusting the volume of the liquid medium within the bellows assembly 2 and the stiffness-adjustable soft tentacle 3, this embodiment can achieve high-precision control of contact force and contact stiffness during grasping. Furthermore, by decoupling the control of contact stiffness and contact force during the grasping process, this embodiment can achieve continuous modulation and target combination of arbitrary contact stiffness and contact force within a two-dimensional envelope space formed by the achievable stiffness range and the achievable gripping force range.

[0061] When working conditions permit, the contact and envelope conditions can be judged directly by visual inspection, without relying on pressure feedback.

[0062] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. An underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force, characterized in that, include: The rigid transmission frame (1) serves as the skeleton of the rigid-flexible coupling gripper and provides rigid transmission. The bellows assembly (2) is installed in the rigid transmission frame (1) as an axial linear power source. After being hydraulically driven, it drives the rigid transmission frame (1) to extend and retract through its own linear extension and retraction. Two or more stiffness-adjustable soft tentacles (3) are installed on the upper part of the rigid transmission frame (1) with their roots evenly spaced along the circumference as end effectors. They retract inward or expand outward when the rigid transmission frame (1) extends or retracts. Each stiffness-adjustable soft tentacle (3) is also provided with a pressure deformation zone (3010) and a stiffness adjustment zone (3011), which are independently hydraulically driven to bend to generate a gradient-changing bending curvature in order to achieve the enveloping grasp of underwater targets.

2. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 1, characterized in that: The rigid transmission frame (1) includes a base (10), a number of connecting components equal to the number of stiffness-adjustable soft tentacles (3), and a top cover (14). The base (10) is a plate-shaped structure with a first through hole in the center. The base (10) extends circumferentially at uniform intervals as connecting blocks perpendicular to the center plate surface. Each connecting component is hinged between its respective connecting block and the top cover (14). The top cover (14) is a plate-shaped structure with a second through hole in the center, coaxial with the first through hole. The top cover (14) and the center plate surface of the base (10) are arranged parallel to each other at intervals. Each connecting component includes a first connecting member (11), a second connecting member (12), and a third connecting member (13) that are hinged in series. The first connecting member (11) is installed on the connecting block away from the center of the base (10). On one side, one side of the second connector (12) is hinged to the plate surface of the first connector (11), and the other side of the second connector (12) is hinged to one side of the third connector (13). The other side of each third connector (13) is evenly hinged to the outer periphery of the top cover (14) along the circumferential direction. The root end of each stiffness adjustable soft tentacle (3) is installed on the side of its respective third connector (13) away from the base (10). The bellows assembly (2) is fitted between the two through holes of the base (10) and the top cover (14). The bellows assembly (2) extends and retracts, causing the top cover (14) to move away from or closer to the base (10), thereby causing the third connector (13) to rotate and causing each stiffness adjustable soft tentacle (3) to retract or expand.

3. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 2, characterized in that: The hinge axes at the hinge positions of the top cover (14) and the three connecting parts (11, 12, 13) are all parallel to the center plate surface of the base (10).

4. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 2, characterized in that: The bellows assembly (2) includes a lower end cap (20), an upper end cap (21), four bellows retaining rings (22), two bellows sealing rings (23), and a bellows (25). The bellows (25) is fitted between the lower end cap (20) and the upper end cap (21). A hollow cylindrical snap-fit ​​structure is provided at the center of the opposite side of both the lower end cap (20) and the upper end cap (21). The snap-fit ​​structure is located away from the lower end cap (20) or the upper end cap (21). 21) One end of the plate surface is provided with a lower end cover limiting ring buckle (200) or an upper end cover limiting ring buckle (210) extending evenly along the circumferential direction; from the root end of each upper end cover limiting ring buckle (210) to the buckle structure between the upper end cover (21) plate surface, a first bellows limiting ring (22), a first bellows sealing ring (23) and a second bellows limiting ring (22) are sequentially fitted and tightly pressed together. The second bellows limiting ring (22) will hold the bellows One end of the tube (25) is pressed between itself and the upper end cover (21) plate. From the root end of each lower end cover limiting ring buckle (200) to the buckle structure between the lower end cover (20) plate, a third bellows limiting ring (22), a second bellows sealing ring (23), and a fourth bellows limiting ring (22) are sequentially fitted and tightly pressed together. The fourth bellows limiting ring (22) presses the other end of the bellows (25) between itself and the lower end cover (20) plate. Between the surfaces; the side edges of the lower end cap (20) and the upper end cap (21) facing each other are respectively connected to the side surface of the base (10) and the top cover (14) away from the center of the rigid transmission frame (1), the bellows (25) passes through the two through holes of the base (10) and the top cover (14) without contacting each other; the center of the lower end cap (20) is provided with a bellows injection hole (201) that connects to the inner cavity of the bellows (25) so as to introduce fluid medium to drive the bellows (25) to expand and contract.

5. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 4, characterized in that: The corrugated pipe assembly (2) further includes several corrugated pipe support rings (24). Each corrugated pipe support ring (24) is evenly spaced inside the corrugated pipe (25) between the two snap-fit ​​structures. Each corrugated pipe limiting ring (22) and each corrugated pipe support ring (24) are arranged parallel to each other along the length direction of the corrugated pipe (25) and are all in contact with the maximum radius of the inner wall of the corrugated pipe (25).

6. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 2, characterized in that: The aforementioned stiffness-adjustable soft tentacle (3) includes a soft finger (30) and a finger cover (31). The adhesive surface (310) on the back of the finger cover (31) covers the fingertip of the soft finger shell (301) of the soft finger (30). The ventral surface of the finger cover (31) serves as the fingertip of the stiffness-adjustable soft tentacle (3). The back of the soft finger shell (301) is provided with a pressure deformation area (3010) and a stiffness adjustment area (3011). The ventral surface of the finger covering (31) is provided with microstructure units (311) and anchoring patterns (312); the root end of the soft finger (30) and the side of the third connector (13) are connected in a matching manner; the root of the soft finger shell (301) is provided with a cavity injection hole (3020), after the fluid medium is injected, it expands through the soft finger cavity (302) inside the soft finger shell (301) at the root end, driving the stiffness adjustable soft tentacle (3) to bend inward to envelop and grasp.

7. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 6, characterized in that: The soft finger cavity (302) consists of a connected cavity connecting portion (3021), spaced-apart toothed cavities, and a fingertip cavity (3026) sequentially from the root end of the soft finger shell (301) along the finger length direction. A cavity injection hole (3020) connects to the cavity connecting portion (3021). Each toothed cavity is divided into a pressure deformation zone (3010) and a stiffness adjustment zone (3011). The pressure deformation zone (3010) and the stiffness adjustment zone (3011) are located on the side closest to the cavity connecting portion (3021) and the fingertip cavity (3026), respectively. Each toothed cavity in the pressure deformation zone (3010) is relatively high. The deformation-driven cavity (3022) and the lower deformation-driven cavity (3022) are arranged alternately, with the lower deformation-driven cavity (3022) being closest to the stiffness adjustment zone (3011). The tooth-shaped cavities in the stiffness adjustment zone (3011) are arranged alternately from the root end to the end end as the lower first stiffness adjustment cavity (3023), the higher second stiffness adjustment cavity (3024), and the lower third stiffness adjustment cavity (3025). The height of the second stiffness adjustment cavity (3024) is the same as the height of the lower deformation-driven cavity (3022). The fingertip cavity (3026) does not have a bending function.

8. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 7, characterized in that: The deformation driving cavities (3022) of the pressurized deformation zone (3010) have equal widths, while the width gradients of the first stiffness adjustment cavity (3023), the second stiffness adjustment cavity (3024), and the third stiffness adjustment cavity (3025) of the stiffness adjustment zone (3011) decrease to produce a non-uniform curvature distribution under pressurized conditions.

9. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 6, characterized in that: The microstructure unit (311) on the ventral side of the finger covering (31) is a regular hexagonal protrusion. Each microstructure unit (311) is evenly spaced and arranged in rows, so that each microstructure unit (311) has a concave anchoring pattern (312) distributed in a honeycomb grid.

10. The underwater hydraulically driven rigid-flexible coupling gripper with adjustable stiffness and gripping force according to claim 1, characterized in that: It also includes a hydraulic control system and a sensor group. The sensor group is used to monitor the pressure feedback of the bellows assembly (2) and the stiffness adjustable soft tentacle (3) in real time. The hydraulic control system adjusts the volume of the injected fluid medium in a closed loop according to the pressure feedback signal, thereby realizing the coordinated control of the opening and closing span, gripping contact stiffness and contact force of the dynamic rigid-flexible coupling gripper, so that the stiffness gripping force of the rigid-flexible coupling gripper is adjustable.

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