A bionic fish structure with foldable and variable stiffness adjustment

Abstract

The application discloses a bionic fish structure with foldable and variable rigidity adjustment functions, and belongs to the technical field of bionic fish structures. In order to solve the problems of high energy loss rate, slow swimming speed, poor stability at high speed, and the fact that a large amount of space cannot be left in the fish head for bearing, the application comprises a fish head unit, a fish body unit and a foldable tail fin, the fish head unit and the foldable tail fin are arranged at two ends of the fish body unit respectively, the fish body unit comprises an outer skeleton, a foldable dorsal fin unit, a fish body swing unit and a fish tail variable rigidity adjustment assembly, the foldable dorsal fin unit, the fish body swing unit and the fish tail variable rigidity adjustment assembly are arranged in the outer skeleton, one end of the fish body swing unit is detachably connected with the fish head unit, the other end of the fish body swing unit extends out of the tail end of the outer skeleton and is detachably connected with the foldable tail fin, the foldable dorsal fin unit is located above the fish body swing unit, the top of the foldable dorsal fin unit penetrates through the outer skeleton and extends above the outer skeleton, and the fish tail variable rigidity adjustment assembly is located above the fish body swing unit and in the inner part of the outer skeleton. The application is used as a bionic fish structure for underwater detection.

Description

Technical Field

[0001] This invention belongs to the field of biomimetic fish structure technology, specifically relating to a biomimetic fish structure that is both foldable and has adjustable stiffness. Background Technology

[0002] Bionic fish are a new type of surface and underwater exploration robot that mimics the shape and movement characteristics of fish. Compared with traditional underwater exploration equipment, bionic fish abandon propeller propulsion, overcoming the drawbacks of high noise, low efficiency, and high energy consumption associated with propeller propulsion. With the gradual development of technology, higher demands are being placed on the performance of existing bionic fish. Current bionic fish only imitate the movement patterns of fish, with their dorsal and caudal fins fixed during operation. This results in significant resistance when attempting high-speed swimming in water, limiting the swimming speed of the bionic fish. Furthermore, the power sources for body swaying and the power sources controlling caudal fin deformation are independent, leading to energy waste and mechanical errors, affecting the reliability and stability of the bionic fish at high speeds. Existing bionic fish also lack the ability to incorporate caudal fin deformation and variable stiffness, thus limiting their swimming speed and environmental adaptability. Therefore, developing a bionic fish structure capable of high-speed underwater swimming with high stability is highly practical. Summary of the Invention

[0003] To address the problems of high energy loss, slow swimming speed, poor stability during high-speed swimming, and insufficient space inside the head of existing bionic fish, this invention provides a bionic fish structure that is both foldable and adjustable in stiffness.

[0004] A biomimetic fish structure that combines foldability and variable stiffness adjustment includes a fish head unit, a fish body unit, and a foldable tail fin. The fish head unit and the foldable tail fin are respectively located at both ends of the fish body unit, and both the fish head unit and the foldable tail fin are detachably connected to the fish body unit.

[0005] The fish head unit includes a fish head shell, an electronic speed controller, a swing motor, a swing housing, a receiver, a power supply, a motor bracket, and a gear reducer. The motor bracket is located at the opening of the fish head shell, and the fish head shell is detachably connected to the motor bracket. The swing housing is located inside the fish head shell, and the swing housing is detachably connected to the motor bracket. Both the swing motor and the gear reducer are installed in the swing housing, and the power output shaft of the swing motor is connected to the power input end of the gear reducer. The power output shaft of the gear reducer passes through the motor bracket and extends into the fish body unit. The electronic speed controller is fixed on the motor bracket and connected to the swing motor via wiring. The receiver and the power supply are both located below the swing housing, and the power supply is fixedly connected to the motor bracket. The power output end of the power supply is connected to the electronic speed controller via a wire. The receiver is fixed on the power supply and connected to the electronic speed controller via a wire.

[0006] The fish body unit includes an outer skeleton, a foldable dorsal fin unit, and a fish body swaying unit. The front end of the outer skeleton is connected to the fish head shell through a motor bracket. The foldable dorsal fin unit and the fish body swaying unit are both located in the outer skeleton. One end of the fish body swaying unit is detachably connected to the motor bracket. The power input part of the fish body swaying unit is connected to the power output shaft of the gear reducer. The other end of the fish body swaying unit extends out of the tail end of the outer skeleton and is detachably connected to the foldable tail fin. The foldable dorsal fin unit is located above the fish body swaying unit and is detachably connected to the motor bracket. The top of the foldable dorsal fin unit passes through the outer skeleton and extends to the top of the outer skeleton.

[0007] Furthermore, the fish head unit also includes two foldable pectoral fin units, which are symmetrically arranged on both sides of the fish head unit, and the power end of each foldable pectoral fin unit passes through the fish head shell and is mounted on the motor bracket.

[0008] Furthermore, the motor bracket is provided with two connecting hole plates, which are symmetrically arranged on both sides of the swing housing, and one end of each connecting hole plate is fixedly connected to the side of the motor bracket facing the fish head housing.

[0009] Furthermore, the foldable pectoral fin unit includes a first pectoral fin segment, a pectoral fin folding motor, a second pectoral fin segment, a pectoral fin rolling connecting rod, and a pectoral fin rolling motor. The pectoral fin rolling motor is located on the side of the connecting plate facing the swing housing, and the housing of the pectoral fin rolling motor is fixedly connected to the connecting plate. One end of the pectoral fin rolling connecting rod passes through the connecting plate and is connected to the motor output shaft of the pectoral fin rolling motor. The other end of the pectoral fin rolling connecting rod extends to the outside of the fish head shell and is fixedly connected to the second pectoral fin segment. The first pectoral fin segment is located on the second pectoral fin segment. The fin segment away from the fish head shell is hinged to the second pectoral fin segment via a hinge arm. The pectoral fin folding motor is located between the first and second pectoral fin segments, and the housing of the pectoral fin folding motor is fixedly connected to the second pectoral fin segment. The power output shaft of the pectoral fin folding motor is connected to the first pectoral fin segment. The pectoral fin folding motor acts as a power source to drive the first pectoral fin segment to fold relative to the second pectoral fin segment. The pectoral fin rolling motor acts as a power source to drive the pectoral fin structure formed by the first and second pectoral fin segments to roll relative to the fish head shell.

[0010] Furthermore, the foldable dorsal fin unit includes a flexible rope, a pulley, a pulley support, a motor connecting plate, a rope winding mechanism, a rope winding motor, and a dorsal fin. The rope winding motor is located above the fish body swaying unit and is detachably connected to the motor bracket via the motor connecting plate. The rope winding mechanism is mounted on the power output shaft of the rope winding motor. One end of the flexible rope is wound around the rope winding motor. The rope winding motor serves as a power source to drive the rope winding mechanism to perform rope winding and unwinding actions. The pulley support is located on the motor bracket and is detachably connected to the motor bracket. The pulley is located on the pulley support and is rotatably connected to the pulley support. The dorsal fin is located on the outer top of the outer frame, and the bottom of the dorsal fin is fixedly connected to the outer top of the outer frame. The other end of the flexible rope is tensioned by the pulley and then inserted and fixed to the dorsal fin. As the rope winding mechanism drives the flexible rope to perform winding and unwinding actions, the dorsal fin folds and unfolds synchronously relative to the outer frame.

[0011] Furthermore, a rope winding motor mounting base is fixedly connected to the upper part of the side of the motor bracket facing the outer frame. The rope winding motor mounting base is provided with a pulley support bracket, and the rope winding motor mounting base and the pulley support bracket are integrally formed. The rope winding motor is mounted on the rope winding motor mounting base and is detachably connected to the rope winding motor mounting base through a motor connecting plate. The pulley support is mounted on the pulley support bracket and is detachably connected to the pulley support bracket.

[0012] Furthermore, the fish body swinging unit includes a coupling, a sleeve, a drive wheel, a mechanical flexible shaft, a tailstock, two elastic beams, two slide rails, and a sliding unit. The drive wheel is inclinedly mounted on one end of the sleeve and is fixedly connected to the sleeve. The coupling is fixedly connected inside the sleeve. The power output shaft of the gear reducer is connected to one end of the coupling. The mechanical flexible shaft extends through the drive wheel into the sleeve and is connected to the other end of the coupling inside the sleeve. The other end of the mechanical flexible shaft is inserted into the tailstock and hinged to the tailstock through a hinge sleeve. Two slide rail supports are symmetrically arranged on the side of the motor bracket facing the fish body unit. One end of each slide rail support is fixedly connected to the motor bracket. Each slide rail is correspondingly mounted on one slide rail support and is detachably connected to the slide rail support. Each sliding unit is correspondingly mounted on one slide rail and is slidably connected to the slide rail. Two elastic beams are symmetrically arranged on both sides of the mechanical flexible shaft. One end of each elastic beam is detachably connected to the tailstock, and the other end of each elastic beam is detachably connected to the sliding unit.

[0013] The sliding unit includes an omnidirectional wheel, an elastic beam mounting bracket, a movable slider, and an energy storage spring. The movable slider is set on the slide rail and is slidably connected to the slide rail. The elastic beam mounting bracket is fixedly connected to the movable slider. The other end of each elastic beam is detachably connected to the corresponding elastic beam mounting bracket. An extension plate is provided on the side of the elastic beam mounting bracket near the sleeve. The omnidirectional wheel is mounted on the extension plate through a wheel frame and is in close contact with the side of the drive wheel near the fish head unit. The energy storage spring is set between the elastic beam mounting bracket and the motor bracket. One end of the energy storage spring is fixedly connected to the elastic beam mounting bracket, and the other end of the energy storage spring is fixedly connected to the motor bracket.

[0014] Furthermore, the tailstock is equipped with a fishtail folding drive assembly, the power input end of which is connected to the other end of the mechanical flexible shaft, and the power output end of which is connected to the folding fishtail.

[0015] The fishtail folding drive assembly includes a first bevel gear shaft, a driving bevel gear, a second bevel gear shaft, a first drive shaft, a torsion spring, a second drive shaft, two driving bevel gears with missing teeth, and two driven gears. The first and second bevel gear shafts are coaxially aligned within the tailstock, with the smooth shaft portions of both shafts inserted into the inner wall of the tailstock and rotatably connected to it via bearings. The driving bevel gear is positioned between the first and second bevel gear shafts, meshing with both the bevel teeth of the first and second bevel gear shafts. The driving bevel gear is mounted on the other end of a mechanical flexible shaft. One driving bevel gear with missing teeth is mounted on the smooth shaft of the first bevel gear shaft and rotates synchronously with it. The other driving bevel gear with missing teeth is mounted on the smooth shaft of the second bevel gear shaft. The optical shaft rotates synchronously with the No. 2 bevel gear shaft. The No. 1 and No. 2 drive shafts are coaxially opposite each other in the tail section. One end of the No. 1 drive shaft and one end of the No. 2 drive shaft are inserted into the inner wall of the tail section and rotatably connected to the tail section through bearings. The No. 1 drive shaft is located on the side of the No. 1 bevel gear shaft away from the fish head unit, and the No. 2 drive shaft is located on the side of the No. 2 bevel gear shaft away from the fish head unit. Two driven gears are respectively mounted on the No. 1 drive shaft and the No. 2 drive shaft, and each driven gear is meshed with a driving gear with missing teeth. The foldable tail fin is installed between the No. 1 drive shaft and the No. 2 drive shaft. The outermost foldable plates on both sides are respectively mounted on the No. 1 drive shaft and the No. 2 drive shaft. The torsion spring is installed at the foldable tail fin folding center shaft, and the two ends of the torsion spring are embedded in the outermost foldable plates on both sides of the foldable tail fin.

[0016] Furthermore, the deployable tail fin includes a conjoined airbag fan and two deployable plates. The two deployable plates are respectively mounted on a first drive shaft and a second drive shaft, and each deployable plate rotates synchronously with the first drive shaft or the second drive shaft it is located on. The conjoined airbag fan is positioned between the two deployable plates, and both ends of the conjoined airbag fan are fixedly connected to the inner sidewall of one of the deployable plates.

[0017] Furthermore, the fish body unit also includes a tail stiffness adjustment assembly, which comprises an elastic air chamber, a crank slider, a crank connecting rod, a crank motor, a crank motor bracket, an air outlet pipe, an electric air pump, and an air inlet pipe. The elastic air chamber is attached to the inner top of the outer frame and has a partition that divides its interior into a buoyancy chamber and a variable stiffness chamber. The electric air pump is located between the elastic air chamber and the tail fin and is fixedly connected to the tail fin. The air inlet pipe is located between the electric air pump and the elastic air chamber. One end of the air intake pipe is connected to the outlet of the electric air pump, and the other end of the air intake pipe is connected to the buoyancy chamber. The crank motor bracket is fixedly connected to the tailstock. The crank motor is mounted on the crank motor bracket. One end of the crank connecting rod is fitted onto the power output shaft of the crank motor. The other end of the crank connecting rod is hinged to the crank slider. The crank slider is set in the variable stiffness chamber and is slidably connected to the inner wall of the variable stiffness chamber. The air outlet pipe is set between the integrated airbag fan surface and the elastic air chamber. One end of the air outlet pipe is connected to the variable stiffness chamber, and the other end of the air outlet pipe is connected to the integrated airbag fan surface.

[0018] The beneficial effects of this application compared to the prior art are:

[0019] 1. This application proposes a biomimetic fish structure that combines foldability and adjustable stiffness. Based on the foldable, fan-shaped tail structure, which can close and open at different swing positions, a novel biomimetic robotic fish tail fin propulsion mechanism is proposed. When the tail swings to the midpoint, it closes, forming a streamlined structure that reduces water flow resistance. When the tail swings to its extreme positions on both sides, it opens, increasing the force-bearing area and generating greater propulsion. Through this closing and opening mechanism of the tail, resistance is effectively reduced and propulsion is increased, thereby improving the swimming efficiency of the biomimetic robotic fish.

[0020] 2. This application proposes a biomimetic fish structure that combines foldability and adjustable stiffness. The foldable dorsal fin design effectively prevents rolling and improves turning performance. The retracted dorsal fin helps reduce water resistance during swimming, increasing the speed and efficiency of the robotic fish. Simultaneously, the foldable pectoral fin design of this invention also reduces swimming resistance and improves swimming efficiency.

[0021] 3. This application proposes a biomimetic fish structure that combines folding and flexible extension with adjustable stiffness. A tilted rotating disk is driven by a motor that swings the fish's head, alternately compressing springs on both sides of the fish body to achieve swaying. Simultaneously, a mechanical flexible shaft transmits the drive to the tail, where a bevel gear set changes the drive direction. Incomplete and complete gears control the opening and closing of the tail. The tail is open under the action of a torsion spring; when the incomplete and complete gears mesh, the tail closes. This is an underactuated method, allowing the tail fin's folding and extension to be adapted to the drive mechanism.

[0022] 4. This application proposes a biomimetic fish structure that combines foldability and variable stiffness adjustment. It utilizes a dual-chamber air chamber structure, with one chamber for stiffness adjustment and the other for buoyancy adjustment. By controlling the injection or release of gas, the stiffness of the fish tail can be altered. This variable stiffness tail can optimize propulsion and improve the energy efficiency of the robotic fish. The tail fin can change shape through the foldable structure and its stiffness through the air chamber structure, improving the biomimetic fish's environmental adaptability. Furthermore, buoyancy adjustment compensation can be achieved by regulating the gas flow into and out of the buoyancy adjustment chamber. Attached Figure Description

[0023] Figure 1 This is a three-dimensional structural diagram of the biomimetic fish structure described in this application;

[0024] Figure 2 This is a front view schematic diagram of the biomimetic fish structure described in this application;

[0025] Figure 3 This is a schematic diagram of the internal structure of the fish body in the biomimetic fish structure described in this application;

[0026] Figure 4 This is a schematic diagram of the fish head unit in the biomimetic fish structure described in this application;

[0027] Figure 5 This is a schematic diagram of the foldable pectoral fin unit in the biomimetic fish structure described in this application;

[0028] Figure 6 This is a schematic diagram of the motor support structure in the bionic fish structure described in this application;

[0029] Figure 7 This is a schematic diagram of the foldable dorsal fin unit in the biomimetic fish structure described in this application;

[0030] Figure 8 This is a schematic diagram of the fish body swaying unit in the bionic fish structure described in this application;

[0031] Figure 9 This is a front view schematic diagram of the caudal peduncle in the biomimetic fish structure described in this application;

[0032] Figure 10 for Figure 9 Sectional view along the middle AA direction:

[0033] Figure 11 This is a schematic diagram of the tail folding drive component in the bionic fish structure described in this application;

[0034] Figure 12 This is a schematic diagram of the foldable tail fin in the biomimetic fish structure described in this application;

[0035] Figure 13 This is a schematic diagram of the tail stiffness adjustment component in the biomimetic fish structure described in this application;

[0036] Figure 14 This is a schematic diagram of the interior of the elastic air chamber in the biomimetic fish structure described in this application;

[0037] The diagram shows: 1. Fish head unit; 1-1. Electronic speed controller; 1-2. Oscillating motor; 1-3. Oscillating housing; 1-4. Receiver; 1-5. Power supply; 1-6. Motor bracket; 1-7. Connecting plate; 2. Fish body unit; 3. Foldable tail fin; 4. Pectoral fin section 1; 5. Pectoral fin folding motor; 6. Pectoral fin section 2; 7. Pectoral fin rolling connecting rod; 8. Pectoral fin rolling motor; 9. Slide rail bracket; 10. Flexible rope; 11. Pulley; 12. Pulley support; 13. Motor connecting plate; 14. Rope winding mechanism; 15. Rope winding motor; 16. Dorsal fin; 17. Gear reducer; 18. Coupling; 19. Sleeve; 20. Drive wheel. 21. Disc, 22. Mechanical flexible shaft, 23. Elastic beam, 24. Slide rail, 25. Omnidirectional wheel, 26. Elastic beam mounting bracket, 27. Moving slider, 28. Energy storage spring, 29. Tailstock, 30. No. 1 bevel gear shaft, 31. Drive bevel gear, 32. No. 2 bevel gear shaft, 33. No. 1 transmission shaft, 34. Torsion spring, 35. Driven gear, 36. No. 2 transmission shaft, 37. Elastic air chamber, 38. Buoyancy chamber, 39. Variable stiffness chamber, 40. Crank slider, 41. Crank connecting rod, 42. Crank motor, 43. Crank motor bracket, 44. Air outlet pipe, 45. Electric air pump, and 46. Air inlet pipe. Detailed Implementation

[0038] Specific implementation method one: Combining Figures 1 to 14 This embodiment describes a biomimetic fish structure that combines foldability and adjustable stiffness. The biomimetic fish structure includes a fish head unit 1, a fish body unit 2, and a foldable tail fin 3. The fish head unit 1 and the foldable tail fin 3 are respectively disposed at both ends of the fish body unit 2, and both the fish head unit 1 and the foldable tail fin 3 are detachably connected to the fish body unit 2.

[0039] The fish head unit 1 includes a fish head shell, an electronic speed controller 1-1, a swing motor 1-2, a swing housing 1-3, a receiver 1-4, a power supply 1-5, a motor bracket 1-6, and a gear reducer 17. The motor bracket 1-6 is located at the opening of the fish head shell, and the fish head shell is detachably connected to the motor bracket 1-6. The swing housing 1-3 is located inside the fish head shell, and the swing housing 1-3 is detachably connected to the motor bracket 1-6. The swing motor 1-2 and the gear reducer 17 are both installed in the swing housing 1-3, and the power output shaft of the swing motor 1-2 is connected to the gear reducer. The power input end of gearbox 17 is connected, the power output shaft of gearbox 17 passes through motor bracket 1-6 and extends into fish body unit 2, electronic speed controller 1-1 is fixed on motor bracket 1-6 and connected to swing motor 1-2, receiver 1-4 and power supply 1-5 are both located below swing housing 1-3, and power supply 1-5 is fixedly connected to motor bracket 1-6, and the power output end of power supply 1-5 is connected to electronic speed controller 1-1 through wire, receiver 1-4 is fixed on power supply 1-5 and connected to electronic speed controller 1-1 by wire, for receiving signals;

[0040] The fish body unit 2 includes an outer skeleton, a foldable dorsal fin unit, and a fish body swaying unit. The first end of the outer skeleton is connected to the fish head shell through a motor bracket 1-6. The foldable dorsal fin unit and the fish body swaying unit are both located in the outer skeleton. One end of the fish body swaying unit is detachably connected to the motor bracket 1-6. The power input part of the fish body swaying unit is connected to the power output shaft of the gear reducer 17. The other end of the fish body swaying unit extends out of the tail end of the outer skeleton and is detachably connected to the foldable tail fin 3. The foldable dorsal fin unit is located above the fish body swaying unit and is detachably connected to the motor bracket 1-6. The top of the foldable dorsal fin unit passes through the outer skeleton and extends to the top of the outer skeleton.

[0041] In this embodiment, the fish head unit 1 mainly includes a control module for controlling the movement of the fish body, some motors and power supply. This application effectively improves the load-bearing capacity of the fish head unit 1 through the large-capacity design of the fish head shape. The outer skeleton in the fish body unit 2 is a hollow multi-segment structure, which is used to cooperate with the swaying action of the fish body when working. The foldable dorsal fin unit and foldable tail fin 3 connected to the fish body can adjust their own shape and structure when the bionic fish is working, which is conducive to improving the swimming speed and swimming stability of the bionic fish.

[0042] Specific Implementation Method Two: Combining Figures 1 to 14 This embodiment differs from Specific Embodiment 1 in that the fish head unit 1 further includes two foldable pectoral fin units. These two foldable pectoral fin units are symmetrically arranged on both sides of the fish head unit 1, and the power end of each foldable pectoral fin unit passes through the fish head shell and is mounted on the motor bracket 1-6. Other components and connections are the same as in Specific Embodiment 1.

[0043] Specific implementation method three: Combining Figures 1 to 14 This embodiment differs from Specific Embodiment Two in that the motor bracket 1-6 is provided with two connecting plate 1-7. The two connecting plate 1-7 are symmetrically arranged on both sides of the swing housing 1-3, and one end of each connecting plate 1-7 is fixedly connected to the side of the motor bracket 1-6 facing the fish head shell. Other components and connection methods are the same as in Specific Embodiment Two.

[0044] Specific implementation method four: Combination Figures 1 to 14 This embodiment differs from Specific Embodiment Three in that the foldable pectoral fin unit includes a first pectoral fin segment 4, a pectoral fin folding motor 5, a second pectoral fin segment 6, a pectoral fin rolling connecting rod 7, and a pectoral fin rolling motor 8. The pectoral fin rolling motor 8 is located on the side of the connecting plate 1-7 facing the swing housing 1-3, and the housing of the pectoral fin rolling motor 8 is fixedly connected to the connecting plate 1-7. One end of the pectoral fin rolling connecting rod 7 passes through the connecting plate 1-7 and is connected to the motor output shaft of the pectoral fin rolling motor 8. The other end of the pectoral fin rolling connecting rod 7 extends to the outside of the fish head shell and is fixed to the second pectoral fin segment 6. The pectoral fin segment 4 is located on the side of the pectoral fin segment 6 away from the fish head shell and is hinged to the pectoral fin segment 6 via a hinge arm. A pectoral fin folding / spreading motor 5 is located between the pectoral fin segments 4 and 6, and its housing is fixedly connected to the pectoral fin segment 6. The power output shaft of the pectoral fin folding / spreading motor 5 is connected to the pectoral fin segment 4. The pectoral fin folding / spreading motor 5 acts as a power source to drive the pectoral fin segment 4 to fold / spread relative to the pectoral fin segment 6. A pectoral fin rolling motor 8 acts as a power source to drive the pectoral fin structure formed by the pectoral fin segments 4 and 6 to roll relative to the fish head shell. Other components and connections are the same as in specific embodiment three.

[0045] Referring to the descriptions of specific embodiments two to four, the foldable pectoral fin unit in this embodiment is divided into two parts, with the two pectoral fin sections connected in a hinge-like manner. Driven by the pectoral fin folding motor 5, the first pectoral fin segment 4 can swing relative to the second pectoral fin segment 6. Simultaneously, driven by the pectoral fin rolling motor 8, the overall structure formed by the first pectoral fin segment 4 and the second pectoral fin segment 6 can roll relative to the fish head shell. Through the coordination between the folding and rolling actions of the foldable pectoral fin unit, the bionic fish can more comprehensively adapt to the movement of water flow. Adjusting the shape of the pectoral fin according to changes in water flow can help reduce the swimming resistance of the bionic fish and improve its swimming speed and stability in the water.

[0046] Specific Implementation Method Five: Combining Figures 1 to 14This embodiment differs from specific embodiment four in that the foldable dorsal fin unit includes a flexible rope 10, a pulley 11, a pulley support 12, a motor connecting plate 13, a rope winding mechanism 14, a rope winding motor 15, and a dorsal fin 16. The rope winding motor 15 is positioned above the fish body swaying unit and is detachably connected to the motor brackets 1-6 via the motor connecting plate 13. The rope winding mechanism 14 is mounted on the power output shaft of the rope winding motor 15. One end of the flexible rope 10 is wound around the rope winding motor 15, and the rope winding motor 15 serves as a power source to drive the rope winding mechanism. The mechanism performs rope winding and unwinding actions. A pulley support 12 is mounted on the motor bracket 1-6 and detachably connected to it. A pulley 11 is mounted on the pulley support 12 and rotatably connected to it. A dorsal fin 16 is mounted on the outer top of the outer frame, and its bottom is fixedly connected to the outer top of the outer frame. The other end of the flexible rope 10 is tensioned by the pulley 11 and then threaded and fixed onto the dorsal fin 16. As the rope winding mechanism 14 drives the flexible rope 10 to wind and unwind, the dorsal fin 16 folds and unfolds synchronously relative to the outer frame. Other components and connections are the same as in specific embodiment four.

[0047] Specific Implementation Method Six: Combination Figures 1 to 14 This embodiment differs from specific embodiment five in that a rope winding motor mounting base is fixedly connected to the upper part of the side of the motor bracket 1-6 facing the outer frame. The rope winding motor mounting base is equipped with a pulley support bracket, and the rope winding motor mounting base and the pulley support bracket are integrally formed. The rope winding motor 15 is mounted on the rope winding motor mounting base and detachably connected to it via a motor connecting plate 13. The pulley support 12 is mounted on the pulley support bracket and detachably connected to it. Other components and connection methods are the same as in specific embodiment five.

[0048] In conjunction with the descriptions of specific embodiments five and six, both the rope winding motor 15 and the rope winding mechanism 14 are disposed in the rope winding motor mounting base and connected to the rope winding motor mounting base through the motor connecting plate 13. The motor connecting plate 13 is used to protect the rope winding motor 15 and the rope winding mechanism 14, so that the rope winding motor 15 and the rope winding mechanism 14 can be located in the chamber formed between the rope winding motor mounting base and the motor connecting plate 13, thereby preventing the rope winding motor 15 and the rope winding mechanism 14 from being affected by the underwater working environment.

[0049] The foldable dorsal fin is a key inventive feature of this application, effectively preventing rollover and improving turning performance. The retracted dorsal fin helps reduce water resistance during swimming, increasing the speed and efficiency of the robotic fish. Simultaneously, the foldable pectoral fin design of this invention also reduces swimming resistance and improves swimming efficiency.

[0050] Specific implementation method seven: Combining Figures 1 to 14This embodiment differs from specific embodiment six in that the fish body oscillation unit includes a coupling 18, a sleeve 19, a drive wheel 20, a mechanical flexible shaft 21, a tailstock 28, two elastic beams 22, two slide rails 23, and a sliding unit. The drive wheel 20 is inclinedly disposed on one end of the sleeve 19 and is fixedly connected to the sleeve 19. The coupling 18 is fixedly connected inside the sleeve 19. One end of the coupling 18 is connected to the power output shaft of the gear reducer 17. One end of the mechanical flexible shaft 21 passes through the drive wheel 20, extends into the sleeve 19, and is connected to the other end of the coupling 18. The other end of the mechanical flexible shaft 21 is inserted into... The tail fin 28 is hinged to the tail fin 28 via a hinge sleeve. Two slide rail brackets 9 are symmetrically arranged on the side of the motor bracket 1-6 facing the fish body unit. One end of each slide rail bracket 9 is fixedly connected to the motor bracket 1-6. Each slide rail 23 is correspondingly arranged on one slide rail bracket 9, and each slide rail 23 is detachably connected to the slide rail bracket 9. Each sliding unit is correspondingly arranged on one slide rail 23, and each sliding unit is slidably connected to the slide rail 23. Two elastic beams 22 are symmetrically arranged on both sides of the mechanical flexible shaft 21. One end of each elastic beam 22 is detachably connected to the tail fin 28, and the other end of each elastic beam 22 is detachably connected to the sliding unit.

[0051] The sliding unit includes an omnidirectional wheel 24, an elastic beam mounting support 25, a movable slider 26, and an energy storage spring 27. The movable slider 26 is mounted on the slide rail 23 and is slidably connected to the slide rail 23. The elastic beam mounting support 25 is fixedly connected to the movable slider 26. The other end of each elastic beam 22 is detachably connected to the corresponding elastic beam mounting support 25. The elastic beam mounting support 25 has an extension plate on the side near the sleeve 19. The omnidirectional wheel 24 is mounted on the extension plate via a wheel frame and is in close contact with the side of the drive wheel 20 near the fish head unit 1. The energy storage spring 27 is located between the elastic beam mounting support 25 and the motor bracket 1-6. One end of the energy storage spring 27 is fixedly connected to the elastic beam mounting support 25, and the other end of the energy storage spring 27 is fixedly connected to the motor bracket 1-6. Other components and connection methods are the same as in specific embodiment six.

[0052] The fish body swaying unit provided in this embodiment drives an inclined drive wheel 20 via a fish head swaying motor, alternately compressing the energy storage springs 27 on both sides of the fish body to achieve swaying. Simultaneously, a mechanical flexible shaft 21 transmits the drive to the fish tail, where a bevel gear set changes the drive direction, and incomplete and complete gears control the opening and closing of the tail. The tail is open under the action of a torsion spring; when the incomplete and complete gears mesh, the tail closes. This is an underactuated method, allowing the tail fin to fold and extend in accordance with the drive mechanism.

[0053] The fish body swaying unit in this application also has the advantage of using a single power source to drive the fish body swaying and the fish tail swaying, thus avoiding working errors when two power sources work together, which would affect the synchronization of the fish body swaying and the fish tail swaying. This solution can improve energy efficiency.

[0054] Specific implementation method eight: Combination Figures 1 to 14 This embodiment differs from specific embodiment seven in that the tail shank 28 is provided with a fish tail folding drive assembly, the power input end of the fish tail folding drive assembly is connected to the other end of the mechanical flexible shaft 21, and the power output end of the fish tail folding drive assembly is connected to the folding fish tail 3.

[0055] The fishtail folding drive assembly includes a first bevel gear shaft 29, a driving bevel gear 31, a second bevel gear shaft 32, a first transmission shaft 33, a torsion spring 34, a second transmission shaft 36, two driving toothed gears 30, and two driven gears 35. The first bevel gear shaft 29 and the second bevel gear shaft 32 are coaxially arranged opposite each other in the tailstock 28, and the optical shaft portions of both the first bevel gear shaft 29 and the second bevel gear shaft 32 are inserted into the inner wall of the tailstock 28 and rotate with the tailstock 28 through bearings. The drive bevel gear 31 is positioned between the first bevel gear shaft 29 and the second bevel gear shaft 32, and the drive bevel gear 31 is meshed with both the bevel gear portion of the first bevel gear shaft 29 and the bevel gear portion of the second bevel gear shaft 32. The drive bevel gear 31 is mounted on the other end of the mechanical flexible shaft 21. One drive bevel gear 30 with missing teeth is mounted on the smooth shaft portion of the first bevel gear shaft 29 and rotates synchronously with the first bevel gear shaft 29. The other drive bevel gear 30 with missing teeth is mounted on the second bevel gear shaft 22. The axle 32 rotates synchronously with the second bevel gear shaft 32 on its optical shaft portion. The first drive shaft 33 and the second drive shaft 36 are coaxially and oppositely disposed in the tailstock 28, with one end of the first drive shaft 33 and one end of the second drive shaft 36 inserted into the inner wall of the tailstock 28 and rotatably connected to the tailstock 28 via bearings. The first drive shaft 33 is disposed on the side of the first bevel gear shaft 29 away from the fish head unit 1, and the second drive shaft 36 is disposed on the side of the second bevel gear shaft 32 away from the fish head unit 1. On one side, two driven gears 35 are respectively mounted on the first drive shaft 33 and the second drive shaft 36, and each driven gear 35 is meshed with a driving gear 30 with missing teeth. The foldable tail fin 3 is installed between the first drive shaft 33 and the second drive shaft 36. The outermost folding plates on both sides are respectively mounted on the first drive shaft 33 and the second drive shaft 36. A torsion spring 34 is installed at the folding center axis of the foldable tail fin, and the two ends of the torsion spring are embedded in the outermost folding plates on both sides of the foldable tail fin. Other components and connection methods are the same as in specific embodiment seven.

[0056] Specific Implementation Method Nine: Combining Figures 1 to 14This embodiment differs from specific embodiment eight in that the deployable tail fin 3 includes a connected airbag fan and two deployable plates. The two deployable plates are respectively mounted on a first drive shaft 33 and a second drive shaft 36, and each deployable plate rotates synchronously with its corresponding drive shaft 33 or drive shaft 36. The connected airbag fan is positioned between the two deployable plates, and both ends of the connected airbag fan are fixedly connected to the inner wall of one of the deployable plates. Other components and connections are the same as in specific embodiment eight.

[0057] Specific Implementation Method Ten: Combining Figures 1 to 14 This embodiment differs from specific embodiment nine in that the fish body unit 2 also includes a tail stiffness adjustment component. This component includes an elastic air chamber 37, a crank slider 40, a crank connecting rod 41, a crank motor 42, a crank motor bracket 43, an air outlet pipe 44, an electric air pump 45, and an air inlet pipe 46. The elastic air chamber 37 is attached to the inner top of the outer frame. A partition divides the interior of the elastic air chamber 37 into two chambers: a buoyancy chamber 38 and a variable stiffness chamber 39. The electric air pump 45 is positioned between the elastic air chamber 37 and the tailstock 28, and is fixedly connected to the tailstock 28. The air inlet pipe 46 is located between the electric air pump 45 and the elastic air chamber 37. Between the air chambers 37, one end of the air inlet pipe 46 is connected to the air outlet of the electric air pump 45, and the other end of the air inlet pipe 46 is connected to the buoyancy chamber 38. The crank motor bracket 43 is fixedly connected to the tailstock 28. The crank motor 42 is mounted on the crank motor bracket 43. One end of the crank connecting rod 41 is fitted onto the power output shaft of the crank motor 42, and the other end of the crank connecting rod 41 is hinged to the crank slider 40. The crank slider 40 is disposed in the variable stiffness chamber 39 and slidably connected to the inner wall of the variable stiffness chamber 39. The air outlet pipe 44 is disposed between the integrated airbag fan surface and the elastic air chamber 37, and one end of the air outlet pipe 44 is connected to the variable stiffness chamber 39, while the other end of the air outlet pipe 44 is connected to the integrated airbag fan surface. Other components and connections are the same as in specific embodiment nine.

[0058] Referring to the descriptions in Specific Embodiments 8 to 10, in this embodiment, the elastic air chamber 37 with a dual-chamber design includes a variable stiffness chamber 39. By controlling the injection or release of gas, the stiffness of the fishtail 3 is altered. Increasing the gas pressure increases the stiffness of the fishtail 3, providing greater thrust and higher propulsion efficiency; decreasing the gas pressure decreases the stiffness of the fishtail 3, making it more flexible and enabling more agile movement and greater maneuverability. This variable stiffness fishtail improves the energy efficiency of the robotic fish. The other chamber is a buoyancy chamber 38. By adjusting the gas flow in and out of the buoyancy chamber 38, buoyancy adjustment compensation can be performed, changing the buoyancy of the robotic fish. Increasing the gas expands the buoyancy chamber 38, increasing the buoyancy of the robotic fish; decreasing the gas contracts the buoyancy chamber 38, decreasing the buoyancy.

[0059] The present invention has been disclosed above with preferred embodiments, but it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed structure and technical content to create equivalent embodiments without departing from the scope of the present invention. However, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

[0060] Working principle

[0061] This application provides a biomimetic fish structure that combines foldability and adjustable stiffness. During operation, the structure can adapt the shape of its fins to changes in the aquatic environment. The specific working process is as follows:

[0062] When the remote control for the electronic speed controller is turned on and the throttle lever is pushed, the correctly connected swing motor is started. Power is transmitted through the gear reducer to the coupling, which in turn drives the sleeve and drive wheel to rotate. The drive wheel, via a universal wheel and a flexible beam mounting bracket, alternately compresses the springs on both sides, causing the fish to swing left and right. Simultaneously, the other end of the coupling connects to a mechanical flexible shaft, transferring power to the fish tail's drive bevel gear. The drive bevel gear meshes with bevel gears one and two, causing their shafts to rotate in opposite directions while maintaining the same rotational speed, equal to the mechanical flexible shaft's speed. Power is then transmitted to the drive toothed gear, and then to the driven gear. The toothed gear has half the total number of teeth missing. This design ensures that within one cycle, when the fish swings to the left or right, the drive and driven gears disengage, allowing the fish tail to unfold under the action of the torsion spring. When the fish swings to the center position, the drive and driven gears mesh again, allowing the fish tail to fold up under the action of opposing forces on both sides.

[0063] The pectoral fin folding motor and pectoral fin rolling motor are driven independently, and the fin folding or unfolding is controlled according to the working needs and usage scenarios of the bionic fish.

[0064] The retractable dorsal fin is independently driven by a winding motor. When the winding motor is turned on, the rigid frame of the retractable dorsal fin rests against the fish's back, meaning the dorsal fin is in a folded state. When the winding motor is turned off, the retractable dorsal fin remains in an extended state under the support of elastic materials.

[0065] The variable stiffness chamber within the elastic gas cavity is filled with gas. When the crank motor starts, it drives the crank-connecting rod to rotate, pushing the crank slider and propelling the gas into the integrated airbag fan-shaped structure that can fold out the fish tail. When the crank-connecting rod rotates to the other side, the gas in the integrated airbag fan-shaped structure is extracted. Therefore, by adjusting the position of the gas, the air pressure in the fish tail can be changed, thereby altering the tail's stiffness. This allows the robotic fish to move flexibly in different underwater environments, maintaining high stiffness when high thrust is needed and reducing stiffness when agile turning is required. Simultaneously, the electric air pump controls the expansion of the buoyancy chamber when gas is injected, increasing the robotic fish's buoyancy. Conversely, the pump controls the contraction of the buoyancy chamber when gas is extracted, decreasing the robotic fish's buoyancy. This gas buoyancy chamber function enables the robotic fish to autonomously adjust its depth, laying the foundation for future research.

Claims

1. A biomimetic fish structure that combines foldability and adjustable stiffness, characterized in that: The biomimetic fish structure includes a fish head unit (1), a fish body unit (2), and a foldable tail fin (3). The fish head unit (1) and the foldable tail fin (3) are respectively located at both ends of the fish body unit (2), and the fish head unit (1) and the foldable tail fin (3) are detachably connected to the fish body unit (2). The fish head unit (1) includes a fish head shell, an electronic speed controller (1-1), a swing motor (1-2), a swing housing (1-3), a receiver (1-4), a power supply (1-5), a motor bracket (1-6), and a gear reducer (17). The motor bracket (1-6) is located at the opening of the fish head shell, and the fish head shell is detachably connected to the motor bracket (1-6). The swing housing (1-3) is located inside the fish head shell, and the swing housing (1-3) is detachably connected to the motor bracket (1-6). The swing motor (1-2) and the gear reducer (17) are both installed in the swing housing (1-3), and the power output shaft of the swing motor (1-2) is connected to the gear reducer (17). The power input end of the gear reducer (17) is connected to the power output shaft of the gear reducer (17), which passes through the motor bracket (1-6) and extends into the fish body unit (2). The electronic speed controller (1-1) is fixed on the motor bracket (1-6) and connected to the swing motor (1-2) by wiring. The receiver (1-4) and the power supply (1-5) are both located below the swing housing (1-3). The power supply (1-5) is fixedly connected to the motor bracket (1-6), and the power output end of the power supply (1-5) is connected to the power input end of the electronic speed controller (1-1) by wire. The receiver (1-4) is fixed on the power supply (1-5) and connected to the electronic speed controller (1-1) by wire to receive signals. The fish body unit (2) includes an outer skeleton, a foldable dorsal fin unit and a fish body swinging unit. The first end of the outer skeleton is connected to the fish head shell through a motor bracket (1-6). The foldable dorsal fin unit and the fish body swinging unit are both located in the outer skeleton. One end of the fish body swinging unit is detachably connected to the motor bracket (1-6). The power input part of the fish body swinging unit is connected to the power output shaft of the gear reducer (17). The other end of the fish body swinging unit extends out of the tail end of the outer skeleton and is detachably connected to the foldable tail fin (3). The foldable dorsal fin unit is located above the fish body swinging unit and is detachably connected to the motor bracket (1-6). The top of the foldable dorsal fin unit passes through the outer skeleton and extends to the top of the outer skeleton. The fish body oscillation unit includes a coupling (18), a sleeve (19), a drive wheel (20), a mechanical flexible shaft (21), a tail rail (28), two elastic beams (22), two slide rails (23), and a sliding unit. The drive wheel (20) is inclinedly mounted on one end of the sleeve (19), and the drive wheel (20) is fixedly connected to the sleeve (19). The coupling (18) is fixedly connected inside the sleeve (19). One end of the coupling (18) is connected to the power output shaft of the gear reducer (17). One end of the mechanical flexible shaft (21) passes through the drive wheel (20) and extends into the sleeve (19) and is connected to the coupling (18). The other end of the mechanical flexible shaft (21) is inserted into the tail rail (28) and hinged. The sleeve is hinged to the tailstock (28). Two slide rail brackets (9) are symmetrically provided on the side of the motor bracket (1-6) facing the fish body unit. One end of each slide rail bracket (9) is fixedly connected to the motor bracket (1-6). Each slide rail (23) is correspondingly set on one slide rail bracket (9). Each slide rail (23) is detachably connected to the slide rail bracket (9). Each sliding unit is correspondingly set on one slide rail (23). Each sliding unit is slidably connected to the slide rail (23). Two elastic beams (22) are symmetrically set on both sides of the mechanical flexible shaft (21). One end of each elastic beam (22) is detachably connected to the tailstock (28). The other end of each elastic beam (22) is detachably connected to the sliding unit. The tail (28) is provided with a fish tail folding drive assembly. The power input end of the fish tail folding drive assembly is connected to the other end of the mechanical flexible shaft (21), and the power output end of the fish tail folding drive assembly is connected to the folding fish tail (3). The fishtail folding drive assembly includes a first bevel gear shaft (29), a driving bevel gear (31), a second bevel gear shaft (32), a first drive shaft (33), a torsion spring (34), a second drive shaft (36), two driving toothed gears (30), and two driven gears (35). The first bevel gear shaft (29) and the second bevel gear shaft (32) are coaxially arranged opposite each other in the tailstock (28), and the optical shaft portions of the first bevel gear shaft (29) and the second bevel gear shaft (32) are both inserted into the inner wall of the tailstock (28) and rotate with the tailstock (28) through bearings. The connection is made such that the active bevel gear (31) is positioned between the first bevel gear shaft (29) and the second bevel gear shaft (32), and the active bevel gear (31) meshes with both the bevel teeth of the first bevel gear shaft (29) and the bevel teeth of the second bevel gear shaft (32). The active bevel gear (31) is mounted on the other end of the mechanical flexible shaft (21). One active toothed gear (30) is mounted on the smooth shaft of the first bevel gear shaft (29) and rotates synchronously with the first bevel gear shaft (29). The other active toothed gear (30) is mounted on the smooth shaft of the second bevel gear shaft (32). The shaft rotates synchronously with the second bevel gear shaft (32). The first drive shaft (33) and the second drive shaft (36) are coaxially opposite each other in the tailstock (28), and one end of the first drive shaft (33) and one end of the second drive shaft (36) are inserted into the inner wall of the tailstock (28) and rotatably connected to the tailstock (28) through bearings. The first drive shaft (33) is located on the side of the first bevel gear shaft (29) away from the fish head unit (1), and the second drive shaft (36) is located on the side of the second bevel gear shaft (32) away from the fish head unit (1). The two driven gears ( 35) respectively mounted on the first drive shaft (33) and the second drive shaft (36), and each driven gear (35) meshes with a driving gear (30) with a toothed tooth. The foldable tail fin (3) is installed between the first drive shaft (33) and the second drive shaft (36). The outermost folding plates on both sides of the foldable tail fin (3) are respectively mounted on the first drive shaft (33) and the second drive shaft (36). The torsion spring (34) is installed at the folding center axis of the foldable tail fin (3). The two ends of the torsion spring (34) are embedded in the outermost folding plates on both sides of the foldable tail fin (3).

2. The biomimetic fish structure with both foldability and adjustable stiffness according to claim 1, characterized in that: The fish head unit (1) also includes two foldable pectoral fin units. The two foldable pectoral fin units are symmetrically arranged on both sides of the fish head unit (1), and the power end of each foldable pectoral fin unit passes through the fish head shell and is mounted on the motor bracket (1-6).

3. The biomimetic fish structure with both foldability and adjustable stiffness according to claim 1, characterized in that: The motor bracket (1-6) is provided with two connecting hole plates (1-7). The two connecting hole plates (1-7) are symmetrically arranged on both sides of the swing housing (1-3), and one end of each connecting hole plate (1-7) is fixedly connected to the side of the motor bracket (1-6) facing the fish head shell.

4. The biomimetic fish structure with both foldability and adjustable stiffness according to claim 3, characterized in that: The foldable pectoral fin unit includes a first pectoral fin segment (4), a pectoral fin folding motor (5), a second pectoral fin segment (6), a pectoral fin rolling connecting rod (7), and a pectoral fin rolling motor (8). The pectoral fin rolling motor (8) is located on the side of the connecting plate (1-7) facing the swing housing (1-3), and the housing of the pectoral fin rolling motor (8) is fixedly connected to the connecting plate (1-7). One end of the pectoral fin rolling connecting rod (7) passes through the connecting plate (1-7) and is connected to the motor output shaft of the pectoral fin rolling motor (8). The other end of the pectoral fin rolling connecting rod (7) extends to the outside of the fish head shell and is fixedly connected to the second pectoral fin segment (6). The first pectoral fin segment (4) is located on the side of the connecting plate (1-7) facing the swing housing (1-3), and the housing of the pectoral fin rolling motor (8) is fixedly connected to the connecting plate (1-7). The second pectoral fin segment (6) is hinged to the second pectoral fin segment (6) on the side away from the fish head shell through a hinge arm. The pectoral fin folding motor (5) is located between the first pectoral fin segment (4) and the second pectoral fin segment (6), and the housing of the pectoral fin folding motor (5) is fixedly connected to the second pectoral fin segment (6). The power output shaft of the pectoral fin folding motor (5) is connected to the first pectoral fin segment (4). The pectoral fin folding motor (5) acts as a power source to drive the first pectoral fin segment (4) to fold relative to the second pectoral fin segment (6). The pectoral fin rolling motor (8) acts as a power source to drive the pectoral fin structure composed of the first pectoral fin segment (4) and the second pectoral fin segment (6) to roll relative to the fish head shell.

5. The biomimetic fish structure with both foldability and adjustable stiffness according to claim 4, characterized in that: The foldable dorsal fin unit includes a flexible rope (10), a pulley (11), a pulley support (12), a motor connecting plate (13), a rope winding mechanism (14), a rope winding motor (15), and a dorsal fin (16). The rope winding motor (15) is located above the fish body swaying unit and is detachably connected to the motor bracket (1-6) via the motor connecting plate (13). The rope winding mechanism (14) is mounted on the power output shaft of the rope winding motor (15). One end of the flexible rope (10) is wound around the rope winding motor (15). The rope winding motor (15) serves as a power source to drive the rope winding mechanism to perform rope winding and unwinding actions. The wheel support (12) is mounted on the motor bracket (1-6) and is detachably connected to the motor bracket (1-6). The pulley (11) is mounted on the pulley support (12) and is rotatably connected to the pulley support (12). The dorsal fin (16) is mounted on the outer top of the outer frame, and the bottom of the dorsal fin (16) is fixedly connected to the outer top of the outer frame. The other end of the flexible rope (10) is tensioned by the pulley (11) and inserted and fixed on the dorsal fin (16). With the rope winding mechanism (14) driving the flexible rope (10) to perform winding and unwinding actions, the dorsal fin (16) performs folding and unfolding actions synchronously with respect to the outer frame.

6. The biomimetic fish structure with both foldability and adjustable stiffness according to claim 5, characterized in that: A rope-winding motor mounting base is fixedly connected to the upper part of the side of the motor bracket (1-6) facing the outer frame. The rope-winding motor mounting base is provided with a pulley support bracket, and the rope-winding motor mounting base and the pulley support bracket are integrally formed. The rope-winding motor (15) is set on the rope-winding motor mounting base and is detachably connected to the rope-winding motor mounting base through the motor connecting plate (13). The pulley support (12) is set on the pulley support bracket and is detachably connected to the pulley support bracket.

7. A biomimetic fish structure with both foldability and adjustable stiffness according to claim 6, characterized in that: The sliding unit includes an omnidirectional wheel (24), an elastic beam mounting bracket (25), a movable slider (26), and an energy storage spring (27). The movable slider (26) is set on the slide rail (23) and is slidably connected to the slide rail (23). The elastic beam mounting bracket (25) is fixedly connected to the movable slider (26). The other end of each elastic beam (22) is detachably connected to the corresponding elastic beam mounting bracket (25). The side of the elastic beam mounting bracket (25) near the sleeve (19) is provided with an extension plate. The omnidirectional wheel (24) is mounted on the extension plate through a wheel frame. The omnidirectional wheel (24) is in close contact with the side of the drive wheel disc (20) near the fish head unit (1). The energy storage spring (27) is set between the elastic beam mounting bracket (25) and the motor bracket (1-6). One end of the energy storage spring (27) is fixedly connected to the elastic beam mounting bracket (25), and the other end of the energy storage spring (27) is fixedly connected to the motor bracket (1-6).

8. The biomimetic fish structure with both foldability and adjustable stiffness according to claim 5, characterized in that: The foldable tail fin (3) includes a connected airbag fan and two foldable plates. The two foldable plates are respectively mounted on the first drive shaft (33) and the second drive shaft (36), and each foldable plate rotates synchronously with the first drive shaft (33) or the second drive shaft (36) it is located on. The connected airbag fan is set between the two foldable plates, and the two ends of the connected airbag fan are respectively fixedly connected to the inner side wall of one of the foldable plates.

9. A biomimetic fish structure with both foldability and adjustable stiffness according to claim 8, characterized in that: The fish body unit (2) also includes a tail stiffness adjustment component, which includes an elastic air chamber (37), a crank slider (40), a crank connecting rod (41), a crank motor (42), a crank motor bracket (43), an air outlet pipe (44), an electric air pump (45), and an air inlet pipe (46). The elastic air chamber (37) is attached to the inner top of the outer frame. The elastic air chamber (37) is equipped with a partition, which divides the interior of the elastic air chamber (37) into two cavities: a buoyancy cavity (38) and a variable stiffness cavity (39). The electric air pump (45) is located between the elastic air chamber (37) and the tail fin (28), and the electric air pump (45) is fixedly connected to the tail fin (28). The air inlet pipe (46) is located between the electric air pump (45) and the elastic air chamber (37), and the air inlet pipe is connected to the tail fin (28). One end of the inlet pipe (46) is connected to the outlet of the electric air pump (45), and the other end of the inlet pipe (46) is connected to the buoyancy chamber (38). The crank motor bracket (43) is fixedly connected to the tailstock 28. The crank motor (42) is mounted on the crank motor bracket (43). One end of the crank connecting rod (41) is fitted on the power output shaft of the crank motor (42). The other end of the crank connecting rod (41) is hinged to the crank slider (40). The crank slider (40) is set in the variable stiffness chamber (39) and is slidably connected to the inner wall of the variable stiffness chamber (39). The outlet pipe (44) is set between the integrated airbag fan surface and the elastic air chamber (37). One end of the outlet pipe (44) is connected to the variable stiffness chamber (39), and the other end of the outlet pipe (44) is connected to the integrated airbag fan surface.

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