High-frequency oscillatory tensioning bio-inspired robotic fish capable of adjusting body stiffness distribution online

Abstract

The application provides a high-frequency swing tensioning bionic robot fish with online adjustment of body rigidity distribution. The bionic robot fish comprises a flexible spine system designed to imitate the shape of a blue marlin, which is composed of a plurality of tensioning joints of a fusion saddle-shaped tensioning structure and a one-way antagonistic parallel structure, and high-frequency swing of the fish body is realized through gear set and rope transmission. A high angular velocity variable rigidity driver is connected to each tensioning joint in the variable rigidity driving system, the rotation rigidity of each joint is controlled by online adjustment of the pre-tightening force of a specific spring, and distributed rigidity adjustment is realized. Based on the direct linear mapping relationship between the rigidity and the driving rotation angle according to the pre-tensioning variable rigidity principle, the joint rigidity is quickly adjusted, and the body rigidity distribution is quickly adjusted in a wide range. The flexible silica gel fish skin not only ensures a streamlined shape to reduce fluid resistance, but also enhances the damping interaction performance with the fluid through the good interaction of the elasticity and the tensioning structure.

Description

Technical Field

[0001] This invention proposes a high-frequency swing-tension biomimetic robotic fish with online adjustment of body stiffness distribution, which relates to the field of biomimetic robot technology. Background Technology

[0002] Underwater robotics technology, as a key project in deep-sea resource development, provides indispensable technical support in critical areas such as seabed mineral exploration, national defense security monitoring, and marine ecological research. However, traditional propeller-driven underwater vehicles generally suffer from technical bottlenecks such as insufficient propulsion efficiency and lack of maneuverability, which limits their operating range and makes it difficult to meet the actual needs of deep-sea exploration.

[0003] Body and / or caudal fin (BCF) propulsion is a common swimming mode used by many high-performance fish. BCF-type fish can adjust their swimming speed, thrust, and efficiency by controlling their stiffness. While various biomimetic robotic fish based on variable stiffness structures have emerged, most operate at frequencies between 1 and 3 Hz, lacking the ability to achieve high swimming speeds. Furthermore, current high-frequency driven variable stiffness biomimetic robotic fish only utilize the caudal fin for stiffness adjustment, lacking a high-frequency driven biomimetic robotic fish with online variable body stiffness. Summary of the Invention

[0004] In view of this, in order to fill the gaps and deficiencies in the prior art, the present invention proposes a high-frequency swing tension bionic robotic fish with online adjustment of body stiffness distribution, in order to solve the problems that have occurred in the background art.

[0005] This invention proposes a high-frequency oscillating tension biomimetic robotic fish with online adjustment of body stiffness distribution, comprising the following:

[0006] This invention proposes a high-frequency oscillating tensioned bionic robotic fish with online adjustment of body stiffness distribution. It is characterized by comprising a rigid fish head assembly, a fish body assembly, and a flexible tail fin assembly. The rigid fish head assembly includes a fish head shell, a fish head base electrical control system, and a high-frequency drive mechanism. The electrical control system includes a battery and a control board. The high-frequency drive mechanism includes a set of active and passive gears, a rope transmission device, and a drive servo motor. The fish body assembly includes a tensioned integral structure, two variable stiffness servos, and a flexible silicone fish skin. The tensioned integral structure includes two tensioned joint components arranged sequentially. The first tensioned joint component is fixedly connected to the rear of the fish head base. Adjacent joint components are connected by a set of elastic elements. Each joint component has a servo motor fixedly mounted at its front. The support frame has its front end elastically connected to the previous joint component. The tail fin assembly includes a tail fin joint and a flexible tail fin fixedly connected thereto. The tail fin joint is connected to the rigid spinal member via a torsion spring. The output end of the drive servo mounted on the fish head base is fixedly connected to the drive gear, and the driven gear is fixedly connected to the swing arm. It is driven to the fish tail through a spur gear set of the speed-increasing gear set and a rope transmission system. The rope transmission system includes a swing arm and a drive rope. The drive rope passes through each joint of the rigid spinal member in sequence and extends to the drive points on both sides of the tail fin to transmit the driving force of the high-torque servo to the tail fin. The drive rope is equipped with pulleys at the bends on the rigid spinal member to reduce frictional resistance during the swinging process.

[0007] Furthermore, the fish head shell is a rigid structure, and the fish head shell is fixedly connected to the fish head base frame.

[0008] Furthermore, the fish body trunk is composed of at least two tension joints connected in series. Each tension joint includes two rigid spinal members, a floating ring, and several tension springs. The two rigid spinal members are connected by a rigid hinge point.

[0009] Furthermore, the tension springs are evenly distributed between the connection nodes on the rigid spinal member and the floating ring, and the preload of the tension springs is adjustable to change the rotational stiffness of the tension joint.

[0010] Furthermore, the two servos mounted on the rigid spinal rod change the preload of the tension spring by driving the disc to rotate synchronously, thereby adjusting the stiffness distribution of the fish body.

[0011] Furthermore, the floating ring adopts a circular structure, and spring connection nodes are evenly distributed on these components.

[0012] Furthermore, the supple fish skin is an integrally molded silicone structure that covers the outside of the tensioned overall structure and extends to the outside of the caudal fin joint. Its front end is sealed to the rigid fish head joint, its middle part is connected to each joint component through a fish skin buckle structure, and its rear end is fixedly connected to the caudal fin joint.

[0013] Furthermore, the tail fin is hinged to the end rigid spinal rod via a double torsion spring to improve the body's flexibility and enhance its interaction with water flow.

[0014] Furthermore, the flexible tail fin includes a rigid tail fin skeleton, the rear of which is covered with a crescent-shaped silicone tail fin. The front outer side of the rigid tail fin skeleton is provided with a mid-front section shell of the tail fin. The front end of the rigid tail fin skeleton has a screw, which is connected to the tail fin joint. A screw hole is provided on the connecting plate of the rigid spine member, and the front end of the screw is engaged with the screw hole. The tail fin joint is hinged to the rigid spine member by means of a double torsion spring, and its connection part can be regarded as a hinge point with rotational stiffness.

[0015] The present invention has the following advantages:

[0016] This invention establishes a rapid, wide-range stiffness adjustment mechanism based on pre-tensioning theory. It integrates a saddle-shaped tension structure with a unidirectional antagonistic parallel structure to construct a flexible spine, and proposes an online stiffness control method based on the principle of spring pre-tensioning.

[0017] In terms of response speed: With the high dynamic response of direct motor drive and the low computational load of linear model, the system has millisecond-level stiffness adjustment speed, which can support the robotic fish to reconstruct the stiffness distribution of the whole body in real time according to gait requirements within a single swimming cycle.

[0018] Regarding the adjustment range: By utilizing a variable stiffness mechanism to significantly alter the spring preload, a large dynamic range of stiffness distribution adjustment is achieved. The robotic fish can seamlessly switch between a "highly compliant state" to adapt to flow field disturbances and a "highly rigid state" to output high thrust, solving the problem that traditional robotic fish, due to their single stiffness, struggle to simultaneously achieve high-speed cruising and agile maneuverability.

[0019] This invention achieves high-frequency, high-efficiency oscillation drive for a flexible fish body. Addressing the bottlenecks of low drive frequency and slow swimming speed in traditional flexible robotic fish, this invention innovatively employs a composite drive scheme of "1:2 speed-increasing gear set + rope transmission." This scheme ensures high torque output while increasing the oscillation frequency to the 6Hz band, significantly improving the robotic fish's instantaneous explosive force and maximum swimming speed, enabling it to better adapt to complex underwater operating environments.

[0020] It possesses excellent biomimetic flexibility and fluid interaction performance. Through the synergistic design of the tensioned integral structure and the one-piece molded silicone fish skin, the biomimetic characteristics of the fish body—"externally flexible and internally variable stiffness"—are achieved. The flexible fish skin not only ensures a streamlined shape to reduce fluid resistance, but also utilizes its own elasticity to form a damping system with the tensioned skeleton, effectively enhancing the passive interaction performance of the robotic fish with the surrounding water flow and improving energy utilization efficiency. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall external structure of an embodiment of the present invention;

[0022] Figure 2 This is a side view of the overall internal structure of an embodiment of the present invention;

[0023] Figure 3 This is a top view of the overall internal structure of an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of the internal structure of the fish head component in an embodiment of the present invention;

[0025] Figure 5 This is a schematic diagram of the connection structure of the tension joint component in an embodiment of the present invention;

[0026] Figure 6 This is a schematic diagram of the tail fin assembly in an embodiment of the present invention.

[0027] In the diagram: 1. Rigid fish head shell; 2. Fish head frame; 3. Flexible silicone fish skin; 4. Crescent-shaped silicone tail fin; 5. Variable stiffness servo; 6. First tension joint; 7. Second variable stiffness servo; 8. Second tension joint; 9. Tail fin joint; 10. Variable stiffness spring; 11. Gear set; 12. Swing arm; 13. Drive rope; 14. Floating ring; 15. Tension spring; 16. Rigid spine member three; 17. Disc; 18. Rigid spine member two; 19. Rigid spine member; 20. Drive servo; 21. Pulley; 22. Battery; 23. Ordinary bolt; 24. Servo bracket; 25. Variable stiffness non-elastic rope; 26. Connecting spring; 27. Double torsion spring; 28. Screw; 29. ​​Buckle; 30. Control panel. Detailed Implementation

[0028] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0029] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0031] like Figures 1 to 6 As shown, this invention proposes a high-frequency swing-tension biomimetic robotic fish with online adjustment of body stiffness distribution, comprising the following:

[0032] like Figure 1 As shown, this embodiment provides a tensioned bionic robotic fish, including a rigid fish head assembly, a fish body assembly, and a flexible tail fin assembly. The rigid fish head assembly includes a fish head shell 1, an electrical control system, and a high-frequency drive mechanism. The electrical control system includes a battery 22 and a control board 30. The high-frequency drive mechanism includes a set of active and passive gear sets 11, a rope transmission device, and a drive servo motor 20. The fish body assembly includes a tensioned integral structure, two variable stiffness servos 5 and 7, and a flexible silicone fish skin 3. The tensioned integral structure includes two tensioned joint components arranged sequentially front to back. The first tensioned joint component 6 is fixedly connected to the rear of the fish head base 2. Adjacent joint components are connected by a set of elastic elements 15. A servo motor bracket 24 is fixedly installed at the front of each joint component. The tail fin assembly is elastically connected to the previous joint component; the tail fin assembly includes a tail fin joint 9 and a crescent-shaped silicone tail fin 4 fixedly connected to it, and the tail fin joint is connected to the rigid spinal member by a double torsion spring 27; the output end of the drive servo 20 mounted on the fish head base 2 is fixedly connected to the active gear, and the passive gear is fixedly connected to the swing arm 12, and is driven to the fish tail through a spur gear set with a 1:2 transmission ratio and a rope transmission system; the rope transmission system includes the swing arm 12 and the drive rope 13, the drive rope passes through each joint of the rigid spinal member in sequence and extends to the drive points on both sides of the tail fin to transmit the driving force of the high torque servo to the tail fin, and the drive rope is provided with a pulley 21 at the bend of the rigid spinal member to reduce the frictional resistance during the swinging process.

[0033] The drive servo motor is fixed to the fish head base frame via a servo motor bracket and ordinary bolts. The high-frequency oscillation of the robotic fish is achieved by the drive servo motor 20 through the combination of the active and passive gear set 11 and the rope transmission device. Specifically, the active gear is fixed to the drive servo motor 20 mounted on the rigid spine rod 1 via a servo disc, and meshes with the passive gear also mounted on the spine rod 1. The passive gear is fixed to the swing arm 12, and the meshing transmission of the gear set allows the swing arm 12 to swing left and right. One end of the drive rope 13 is connected to the swing arm of the passive gear, and the other end is guided by a fixed pulley, passes through various joints, and extends to the caudal fin joint 9, achieving efficient drive of the caudal fin 4. Pulleys 21 are provided at the turning positions on the rigid spine rod to reduce friction loss during rope transmission and ensure transmission efficiency and caudal fin 4 response speed. The transmission ratio of the active and passive gears is 1:2, allowing the swing arm 12 to obtain a large swing angle, while the drive servo motor 20 only needs to rotate a small angle, thereby achieving a high oscillation frequency. The drive system enables the tail fin to swing at a maximum frequency of 6 Hz, which significantly improves the swing speed and propulsion efficiency compared to the traditional servo direct drive method, and breaks through the technical bottleneck of limited swimming speed caused by low drive frequency.

[0034] In this embodiment, the tensioned integral structure includes two tensioning joint components 6 and 8.

[0035] The tension joint component includes two rigid spinal rods, a floating ring, and several tension springs. The rigid spinal rods are interconnected through rigid hinge points. The floating ring 14 has a circular structure and is evenly distributed with spring connection nodes, which can be connected by springs 15. The variable stiffness springs 10 are evenly distributed on the outer ring connection nodes of the rigid spinal rods and the floating ring 14, forming a composite structure of a saddle-shaped tension structure and an antagonistic parallel mechanism. By adjusting the preload of the variable stiffness springs 10, the joint rotation stiffness can be effectively changed, thereby achieving dynamic adjustment of the flexible distribution of the fish body.

[0036] In this embodiment, a compact, embedded variable stiffness actuator is designed. The mechanism mainly consists of a variable stiffness servo motor 5 mounted on a rigid spinal member, a drive disk 17, a variable stiffness inelastic rope 25, and variable stiffness springs 10. The variable stiffness servo motor 5 serves as the core actuator, with its output shaft fixedly connected to the drive disk 17. The specific adjustment process is as follows: when increased body stiffness is required, the variable stiffness servo motor 5 drives the drive disk 17 to rotate, causing the drive disk 17 to wind around the variable stiffness inelastic rope 25, thereby simultaneously stretching the multiple variable stiffness springs 10 connected between the floating ring 14 and the rigid spinal member. The increased spring elongation significantly enhances the internal preload, requiring the tensioned joint to overcome a larger restoring torque during rotational deformation, thus macroscopically manifesting as an increase in joint stiffness. Conversely, rotating the servo motor in the opposite direction reduces stiffness. This mechanism cleverly utilizes the internal space of the tensioned structure, achieving stiffness adjustment without increasing the robot's external dimensions.

[0037] The flexible tail fin includes a rigid tail fin skeleton, the rear of which is covered with a crescent-shaped silicone tail fin 4. A mid-front section shell of the tail fin is provided on the outer side of the front part of the rigid tail fin skeleton. The front end of the rigid tail fin skeleton has a bolt, which is connected to the tail fin joint. A screw hole is provided on the connecting plate of the rigid spinal member 3. The front end of the screw 28 is engaged with the screw hole. The tail fin joint 9 is hinged to the rigid spinal member 3 by means of a double torsion spring 27. The connection part can be regarded as a hinge point with rotational stiffness. The tail fin joint 9 and the rigid spinal member 3 are connected by the double torsion spring 27.

[0038] In this embodiment, the fish head shell 1 is a rigid structure, and the fish head shell 1 is fixedly connected to the fish head base frame 2. The flexible fish skin 3 is silicone fish skin, which covers the tensioned overall structure and the outer side of the tail fin joint. Its front end is connected to the fish head shell 1, its middle part is connected to each joint component through fish skin buckles 29, and its rear end is connected to the flexible tail fin 4.

[0039] In addition to the above, the present invention also has related embodiments, including the following:

[0040] This invention proposes a high-frequency swinging tension bionic robotic fish with online adjustment of body stiffness distribution, comprising three parts: a rigid fish head assembly, a fish body trunk assembly, and a flexible tail fin assembly.

[0041] The high-frequency drive system consists of the following components: the output end of the drive servo 20 mounted on the fish head frame 2 is fixedly connected to the active gear, and the passive gear is fixedly connected to the swing arm 12. It is driven to the fish tail through a spur gear set 11 with a 1:2 transmission ratio and a rope transmission system. The rope transmission system includes the swing arm 12 and the drive rope 13. The drive rope 13 passes through each joint of the rigid spine member and extends to the two drive points on both sides of the crescent-shaped silicone tail fin 4 to transmit the driving force of the high-torque servo to the crescent-shaped silicone tail fin 4. The drive rope 13 is equipped with a pulley 21 at the bend of the rigid spine member to reduce friction loss during the rope transmission process and ensure transmission efficiency and response speed of the crescent-shaped silicone tail fin 4.

[0042] Furthermore, the variable stiffness tensioned spine system consists of multiple series-connected tensioning joint mechanisms. This invention successfully designed and implemented a compact variable stiffness joint mechanism based on the pre-tensioning principle. The tensioning joint mechanism includes two rigid spinal members, a floating ring 14, and several tension springs. The rigid spinal members are interconnected through rigid hinge points. The floating ring 14 has a circular structure and evenly distributed spring connection nodes, allowing for connection via springs. The tension springs are evenly distributed on the outer ring connection nodes of the rigid spinal members and the floating ring 14, forming a composite structure of a saddle-shaped tensioning structure and an antagonistic parallel mechanism. By using a variable stiffness servo motor 5 mounted on the spine to drive the disk to rotate, the connecting springs 26 or elastic ropes are extended or retracted. By changing the preload of specific springs, the rotational stiffness of each joint can be changed, thereby dynamically adjusting the transmission characteristics and frequency of the fish's body waves, enabling the robotic fish to achieve a balance of rigidity and flexibility under different swimming conditions.

[0043] Furthermore, based on the principle of pre-tensioned variable stiffness, this invention constructs an explicit mapping model between the joint driving angle and the output stiffness. In a tensioned integral structure, the rotational stiffness of the joint depends not only on the spring's elastic coefficient but also on the pre-tension of the elastic element at its equilibrium position. This invention changes the static equilibrium length of the spring through an adjustment mechanism, thereby altering its internal tension. According to the tensioned structure mechanics model, the equivalent rotational stiffness of the joint... Adjustment angle with drive They exhibit a linear positive correlation, and their mathematical model can be expressed as:

[0044] ;

[0045] In the formula, The stiffness gain coefficient is a structure-related factor, mainly determined by the spring stiffness coefficient, joint geometry, and attachment point location. This represents the initial rotational stiffness of the system. Let be the rotation angle of the variable stiffness servo 5. This theoretical model shows that the rotation angle of the servo can be controlled linearly. This allows for control of joint stiffness. The direct linear control of stiffness, without the need for complex nonlinear inverse calculations, provides a solid theoretical support for the accurate prediction and control of stiffness.

[0046] Furthermore, thanks to the aforementioned principles, this invention successfully enhances the dynamic performance of stiffness adjustment by integrating a dedicated servo motor with high angular velocity as the actuator. This means that the robotic fish can dynamically reconstruct its overall stiffness distribution pattern in real time within a single swimming cycle, based on the needs of the swimming task. This rapid stiffness reconstruction capability allows the robotic fish to instantly switch between the uniform stiffness distribution required for efficient cruising and the non-uniform stiffness distribution required for rapid maneuvering, providing a core guarantee for achieving transient maneuvering, efficient propulsion, and dynamic swimming mode switching, significantly improving its dynamic performance and environmental adaptability in complex underwater environments. Moreover, the stiffness variation range is limited by the maximum rotation angle of the actuator (…). The stiffness coefficient (μ) and the mechanical properties of the robotic fish are jointly determined. Through design and selection, the system can achieve a wide range of adjustments from a near-flexible initial state to a high stiffness several times greater. This allows the robotic fish's body to switch between two distinctly different mechanical states of "extreme compliance" and "high rigidity" to adapt to various mission requirements, from efficient cruising to explosive acceleration.

[0047] Furthermore, the flexible silicone fish skin 3 is a crescent-shaped silicone fish skin. It covers the outer side of the tensioned overall structure and the caudal fin joint 9, with its front end connecting to the fish head shell. Eight fixing buckles 29 in the middle are used to bind it to the internal rigid spinal member via cable ties, and its rear end connects to the flexible caudal fin. This design ensures a streamlined shape to reduce fluid resistance, while also leveraging its own elasticity and the tensioned structure to enhance its damping interaction with the fluid.

[0048] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

[0049] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-frequency oscillating tension biomimetic robotic fish with online adjustment of body stiffness distribution, characterized in that, The fish includes a rigid fish head assembly, a fish body assembly, and a flexible tail fin assembly. The rigid fish head assembly comprises a fish head shell, a fish head base electrical control system, and a high-frequency drive mechanism. The electrical control system includes a battery and a control board. The high-frequency drive mechanism includes a set of active and passive gears, a rope transmission device, and a drive servo motor. The fish body assembly includes a tensioned integral structure, two variable stiffness servos, and flexible silicone fish skin. The tensioned integral structure includes two tensioned joint components arranged sequentially. The first tensioned joint component is fixedly connected to the rear of the fish head base. Adjacent joint components are connected by a set of elastic elements. A servo motor bracket is fixedly installed at the front of each joint component. The front of the servo motor bracket is connected to the previous joint component. The tail fin assembly is elastically connected; the tail fin assembly includes a tail fin joint and a flexible tail fin fixedly connected thereto, and the tail fin joint is connected to the rigid spinal member by a torsion spring; the output end of the drive servo mounted on the fish head base is fixedly connected to the drive gear, and the driven gear is fixedly connected to the swing arm, and is driven to the fish tail by the spur gear set of the speed-increasing gear set and the rope transmission system; the rope transmission system includes a swing arm and a drive rope, the drive rope passes through each joint of the rigid spinal member in sequence and extends to the drive points on both sides of the tail fin to transmit the driving force of the high torque servo to the tail fin, and the drive rope is provided with pulleys at the bends on the rigid spinal member to reduce the frictional resistance during the swinging process.

2. The high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 1, characterized in that, The fish head shell is a rigid structure and is fixedly connected to the fish head base frame.

3. The high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 1, characterized in that, The fish's body trunk is composed of at least two tension joints connected in series. Each tension joint includes two rigid spinal members, a floating ring, and several tension springs. The two rigid spinal members are connected by a rigid hinge point.

4. The high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 3, characterized in that, The tension springs are evenly distributed between the connection nodes on the rigid spinal member and the floating ring. The preload of the tension springs is adjustable to change the rotational stiffness of the tension joint.

5. The high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 3, characterized in that, The two servo motors mounted on the rigid spinal rod change the preload of the tension spring by driving the disc to rotate synchronously, thereby adjusting the stiffness distribution of the fish body.

6. The high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 3, characterized in that, The floating ring uses a circular structure, and spring connection nodes are evenly distributed on these components.

7. The high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 1, characterized in that, The soft fish skin is a one-piece molded silicone structure that covers the outside of the tensioned overall structure and extends to the outside of the caudal fin joint. Its front end is sealed to the rigid fish head joint, its middle part is connected to each joint component through the fish skin buckle structure, and its rear end is fixed to the caudal fin joint.

8. The high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 1, characterized in that, The tail fin is hinged to the end rigid spindle via double torsion springs to improve the body's flexibility and enhance its interaction with water flow.

9. A high-frequency oscillating tension bionic robotic fish with online adjustment of body stiffness distribution according to claim 1, characterized in that, The flexible tail fin includes a rigid tail fin skeleton, the rear of which is covered with a crescent-shaped silicone tail fin. The front outer side of the rigid tail fin skeleton is provided with a mid-front section shell of the tail fin. The front end of the rigid tail fin skeleton has a screw, which is connected to the tail fin joint. A screw hole is opened on the connecting plate of the rigid spine member, and the front end of the screw is connected to the screw hole. The tail fin joint is hinged to the rigid spine member by means of a double torsion spring, and its connection part can be regarded as a hinge point with rotational stiffness.

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