Tail fin with variable shape and rigidity and bionic robotic fish and motion mode thereof

Abstract

The invention relates to a shape rigidity variable tail fin and a bionic robotic fish and a motion mode thereof, and belongs to the technical field of underwater robot application. The device specifically comprises a tail handle center rod (35), a tail handle side rod (36), a tail fin center rod (49) and the like. The two sides of the tail fin center rod (49) are provided with single-side composite parallelogram mechanisms; a variable-stiffness regulation and control area of the tail fin is arranged between the tail fin center rod (49) and the tail handle center rod (35), and a first sliding block (37) is arranged between the tail fin center rod (49) and the tail handle center rod (35); the sliding of the first sliding block (37) can change the coverage range of the first sliding block (37) on a variable stiffness regulation and control area on one hand, and drives the single-side composite parallelogram mechanism to generate cooperative deformation on the other hand; the shape and rigidity of the tail fin of the robotic fish are cooperatively controlled, so that the swimming speed and the propelling efficiency of the robotic fish are effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of underwater robot application technology, specifically involving a variable-stiffness tail fin and its biomimetic robotic fish and locomotion mode, which can be used as an underwater platform for ecological observation, underwater exploration, reconnaissance and other fields, and has broad application prospects. Technical Background

[0002] In marine exploration, human diving operations are constrained by environmental factors such as water flow velocity, diving depth, and water turbidity, and the harsh underwater conditions further limit the scope and efficiency of manual operations. Against this backdrop, underwater robots are gradually replacing humans, undertaking various high-risk or inaccessible underwater tasks. Through long-term natural selection, underwater organisms have evolved locomotion patterns with high propulsion efficiency and excellent maneuverability, with fish swimming mechanisms being particularly typical. Biomimetic robotic fish designed based on fish characteristics can overcome the technical limitations of traditional propulsion systems, providing a key path for building efficient and flexible underwater operation platforms, and possessing significant research value and application prospects.

[0003] Current research on high-speed, high-efficiency biomimetic robotic fish mainly focuses on their tail fins. However, isolated parameterization studies of tail fin morphology or stiffness cannot achieve multi-scenario applications and lack sufficient underwater maneuverability. Therefore, this study focuses on exploring the coupling mechanism between tail fin stiffness and morphology through coordinated active adjustment, aiming to design a tail fin with variable morphology and stiffness and its biomimetic robotic fish. This robotic fish possesses high maneuverability and is suitable for various applications. Therefore, designing a tail fin with variable morphology and stiffness and its biomimetic robotic fish has significant research and engineering value.

[0004] Zhang Shiwu et al. proposed a shape-controllable underwater biomimetic propulsion device and an area-controllable underwater biomimetic propulsion device (patent application numbers: CN201510054420.2, CN201510044965.5). These devices employ a shape-area coupling design concept, but their area adjustment relies on the active shape changes of the device body for passive control, lacking independent variable control capabilities. Furthermore, their structural design does not incorporate stiffness adjustment functionality and lacks a matching biomimetic robotic fish body structure, making it impossible to construct and verify the motion mode of the entire machine. Li Lvzhou et al. proposed a variable stiffness biomimetic robotic fish and its control method (patent application number: 202311741011.0), which adjusts the temperature of the variable stiffness material of the tail fin through a heating circuit to achieve tail fin stiffness adjustment. However, this design has significant limitations. On the one hand, the application of the heating circuit poses safety hazards; on the other hand, it can only achieve control of a single stiffness parameter and cannot actively adjust the tail fin shape, resulting in limited maneuverability of the underwater device equipped with this tail fin. Zhang Zhongqiang et al. proposed a rigid-flexible coupled biomimetic robotic fish that mimics fish swim bladder buoyancy (patent application number: 202310380817.5). It also uses temperature to change the stiffness of the tail, exhibiting the shortcomings of the aforementioned patent. In summary, the coordinating and controllable morphology and stiffness of the tail fin in robotic fish has not yet been effectively studied. Summary of the Invention

[0005] The purpose of this invention is to provide an underwater exploration platform with high swimming performance and strong environmental adaptability. By integrating the morphological control structure and stiffness control unit of the biomimetic robotic fish's tail fin, a biomimetic tail fin with synergistically controllable morphology and stiffness is constructed. Based on the coupled control characteristics of this tail fin, the propulsion efficiency and swimming speed of the robotic fish are simultaneously improved. Furthermore, this invention also provides a motion control method for a biomimetic robotic fish equipped with this synergistically controlled tail fin, further enhancing the robotic fish's environmental adaptability through the coordinated movement of the tail fin and pectoral fins.

[0006] The aforementioned biomimetic robotic fish tail fin with variable morphological stiffness is characterized by: comprising a caudal peduncle and a tail fin skeleton; wherein the caudal peduncle consists of a thick central rod and two thin lateral rods; wherein the central rod is located in the middle of the front of the two lateral rods and is relatively fixed; wherein the tail fin skeleton includes a central rod, the front of which extends into the middle of the rear of the two lateral rods and is relatively fixed; wherein the upper and lower sides of the central rod are each composed of several connecting rods forming a single-sided composite parallelogram mechanism; wherein the single-sided composite parallelogram mechanism is composed of N consecutively connected parallelogram units, where N is an integer from 1 to 5. The four sides of each parallelogram unit are named A, B, C, and D, respectively, where sides A and C are parallel to the central rod. The first unit's side A corresponds to the central rod segment, and subsequent units are stacked sequentially, with the side A of the next unit being the segment of the connecting rod containing the side C of the previous unit. All units' sides B are located on the same connecting rod, achieving linkage between different segments. Each link is hinged with rivets, and auxiliary links are added to optimize hydrodynamic performance. A gap is reserved between the central link of the caudal fin and the central link of the caudal shank, which is the variable stiffness control area of ​​the caudal fin. The first slider covers this area and is driven to slide via a traction line, which simultaneously deforms the link mechanism to adjust the caudal fin shape. By changing the coverage area of ​​the variable stiffness region, the stiffness of the caudal fin is dynamically adjusted, achieving coordinated control of shape and stiffness. The entire outer surface is covered with an elastic sleeve, and the opening is sealed and fixed to the drive housing.

[0007] The aforementioned biomimetic robotic fish with variable shape and stiffness tail fin is characterized by: comprising a fish body and a tail fin swinging mechanism; wherein the fish body includes a fish body, a center of gravity adjustment device, a pectoral fin rotation device, and a counterweight chamber; wherein the center of gravity adjustment device is installed in the bottom area of ​​the fish body; wherein a counterweight plate is installed in the counterweight chamber; wherein the pectoral fin rotation device is installed on both sides of the upper side of the fish body; wherein the dorsal fin is located on the uppermost side of the robotic fish; the aforementioned fish body also includes a tail fin shape and stiffness drive mechanism, which consists of a servo motor, a servo motor disc, a winch, and a traction line in sequence; wherein one end of the traction line is fixed to the winch. The other end is fixed to the slider of the caudal fin skeleton; the caudal fin swing mechanism is connected to the fish body at one end and to the caudal peduncle at the other end, and is composed of a caudal fin swing drive assembly and a caudal fin swing assembly; the caudal fin swing drive assembly is installed at the rear of the fish body and is composed of a motor, a transmission sleeve, and an L-shaped eccentric wheel in sequence; the caudal fin swing assembly includes a swing housing and a swing guide slide; the swing guide slide is fixed in the swing housing by bearings and retaining rings; the swing guide slide is provided with a groove along the axial direction; the L-shaped eccentric wheel cooperates with the groove to convert the rotational motion output by the motor into the reciprocating swing motion of the swing housing.

[0008] The aforementioned variable-rigidity tail fin and its biomimetic robotic fish and locomotion mechanism are characterized by the following processes: (I) Caudal fin morphology and stiffness change process: In the initial state, the caudal fin is crescent-shaped, that is, the first slider covers the stiffness change area. At this time, the stiffness of the caudal fin is relatively large, forming a high-stiffness crescent-shaped caudal fin. When the traction line pulls the first slider forward, the subsequent linkage mechanism follows, the caudal fin becomes a fan-shaped surface, and at the same time, the stiffness change area covered by the slider is exposed, the stiffness of the caudal fin decreases, forming a low-stiffness fan-shaped caudal fin.

[0009] (II) The movement process of a biomimetic robotic fish with variable tail fin shape and stiffness: Mode 1, Fast and Efficient Forward Movement: In the initial state, the tail fin is a high-rigidity crescent-shaped tail fin. At this time, setting the swimming speed of the robotic fish to the high-frequency range can efficiently achieve high speed.

[0010] Mode 2: When the tail fin becomes a low-stiffness fan-shaped tail fin, the robotic fish sets its swimming speed to a low frequency, enabling it to efficiently complete various other movement modes. Movement Mode 2-1: Coordinated Turning of Yaw and Forward Motion from Pectoral Fins and Tail Fins: When starting a turn, the low-stiffness fan-shaped tail fin swings back and forth periodically at an angle of ±30°, outputting forward thrust through hydrodynamic action; simultaneously triggering differential attitude control of the pectoral fins, the inner pectoral fin deflects to a vertical plane orthogonal to the incoming current to form significant lateral resistance, while the outer pectoral fin maintains a parallel posture to the fish body. The difference in resistance on both sides forms a clockwise turning torque on the fish's central axis, driving the head to turn.

[0011] Mode 2-2: Descent and Ascent Process The diagonal diving and surfacing motion works as follows: For diving, the center of gravity adjustment device shifts the center of gravity forward, causing the robotic fish's head to droop; the pectoral fin rotation devices on both sides cause the pectoral fin plates to tilt downward, generating a downward force through the water flow difference; then, the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to swim forward and downward, ultimately completing the diving motion; For surfacing, the center of gravity adjustment device shifts the center of gravity backward, causing the robotic fish's head to tilt upward; the pectoral fin rotation devices on both sides cause the pectoral fin plates to tilt upward, generating an upward force through the water flow difference; then, the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to swim forward and upward, ultimately completing the diving and surfacing motion. The spiral diving and surfacing motion involves several mechanisms. For diving, the center of gravity adjustment device shifts the center of gravity forward, causing the robotic fish's head to droop continuously. Simultaneously, a pectoral fin rotation device on one side causes the fin to tilt downwards, while the other side remains parallel to the water flow. Then, the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to turn and ultimately complete the spiral diving motion. For surfacing, the center of gravity adjustment device shifts the center of gravity backwards, causing the robotic fish's head to tilt upwards. Simultaneously, a pectoral fin rotation device on one side causes the fin to tilt upwards, while the other side remains parallel to the water flow. Then, the tail fin swings back and forth, causing the robot to turn and ultimately complete the spiral surfacing motion. Motion Mode 3, Water-Air Crossing Medium: Before the robotic fish crosses the medium, while in the water, the center of gravity adjustment device shifts the center of gravity backward, causing the robotic fish's head to tilt upward. At the same time, the pectoral fin rotation device causes the pectoral fins on both sides to tilt upward, generating an upward force through the water flow difference. Then, the crescent-shaped high-rigidity tail fin swings back and forth, causing the robotic fish to swim forward and upward, generating a rapid diagonal upward straight motion. The robotic fish obtains maximum diagonal upward speed, causing it to rush out of the water diagonally. When the robot crosses the medium, that is, from underwater to air, the center of gravity adjustment device shifts the center of gravity forward, causing the robotic fish's head to droop. The pectoral fin rotation device causes the pectoral fins on both sides to tilt downward, and the tail fin stops swinging, allowing it to fall into the water with less resistance.

[0012] The aforementioned pectoral fin rotation device mainly includes pectoral fin plates, a connecting bracket, a servo arm, a rotating shaft, and a pectoral fin servo motor. One end of the rotating shaft is fixedly connected to the servo motor output shaft, and the other end is rigidly connected to the servo arm. The servo arm is bolted into the groove of the connecting bracket. The pectoral fin plates mate with two optical shafts on the connecting bracket and are secured with bolts. When the servo motor rotates, power is transmitted sequentially through the rotating shaft to the servo arm, which in turn drives the connecting bracket to rotate synchronously, ultimately driving the pectoral fin plates to complete the rotation. In this device, the servo motor is internally fixed within the fish's body cavity, and its exposed parts are coated with waterproof adhesive to isolate water and prevent water from entering the fish's body cavity. O-rings are embedded inside the rotating shaft to form a sealed structure to prevent water from entering the servo motor. This pectoral fin rotation device has the technical advantages of simple structure, convenient assembly, and high operational reliability. The aforementioned center of gravity adjustment device mainly includes a center of gravity adjustment motor, a second slider, a nut, a linear bearing, a guide shaft, a lead screw, and a counterweight box. The nut and linear bearing are installed in the second slider. The second slider is mounted on the guide shaft via the linear bearing. The lead screw is connected to the output shaft of the center of gravity adjustment motor, and the lead screw and the nut in the second slider form a lead screw-nut pair. The counterweight box is fixed to the second slider. A lead weight is placed in the counterweight box and fixed to the second slider with 3M adhesive. Using the lead screw-nut pair, when the center of gravity adjustment motor rotates, it drives the second slider to move, which in turn drives the counterweight box and the lead weight to move, ultimately achieving center of gravity adjustment. Two guide shafts and a lead screw pass through the second slider and are fixed inside the fish body, preventing the second slider and the counterweight box from moving left, right, up, or down, thus improving the stability of the center of gravity adjustment device. The center of gravity adjustment device has a simple structure, is easy to install, and has high reliability in center of gravity adjustment. Compared with the prior art, the present invention has the following advantages: 1. In this invention, a novel caudal fin with a linkage mechanism as the frame is proposed, which innovatively realizes the coordinated dynamic control of the caudal fin shape and stiffness, and realizes the adaptive switching of the caudal fin shape and stiffness in different frequency bands according to swimming needs, effectively improving the swimming speed and efficiency of the robotic fish in water. 2. In this invention, a composite biomimetic robotic fish combining pectoral fins and caudal fins is proposed. The change in the posture of the pectoral fins and the change in the shape and stiffness of the caudal fins are combined to effectively simulate the movement of fish, improve the maneuverability of the robotic fish in water, provide more movement modes for the robot platform, and the robotic fish has strong survivability and environmental adaptability. 3. In this invention, the robotic fish can perform multiple movement modes underwater and can also leap out of the water, making it applicable to a wider range of scenarios. The robotic fish uses multiple sensors, which can coordinate the robot's movement to restore it to normal when the robot experiences abnormal problems such as yaw, tilt, drooping or pitching. Attached Figure Description

[0013] Figure 1 This is a three-dimensional view of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 2 This is an exploded view of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 3 This is a three-dimensional diagram of the body of the biomimetic robotic fish with variable tail fin shape and stiffness as described in this invention. Figure 4 This is an exploded view of the body of the biomimetic robotic fish with variable tail fin shape and stiffness as described in this invention. Figure 5 This is an exploded view of the pectoral fin swinging structure of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 6 This is an exploded view of the center of gravity adjustment structure of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 7 This is a three-dimensional diagram of the tail fin drive structure of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 8 This is an exploded view of the tail fin drive structure of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 9 This is a three-dimensional diagram of the tail fin linkage structure of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 10 This is an exploded view of the tail fin linkage structure of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 11 This is a three-dimensional diagram of the high-rigidity crescent-shaped linkage mechanism of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 12 This is a three-dimensional diagram of the low-stiffness sector linkage mechanism of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 13This is a schematic diagram of the crescent-shaped tail of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention moving in a high-frequency state. Figure 14 This is a schematic diagram of the fan-shaped tail of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention moving in a low-frequency state. Figure 15 This is a schematic diagram of the pectoral and caudal fins working together to make a right turn in the biomimetic robotic fish with variable tail fin shape and stiffness as described in this invention. Figure 16 This is a schematic diagram of the pectoral and caudal fins working together to make a left turn in the biomimetic robotic fish with variable tail fin shape and stiffness as described in this invention. Figure 17 This is a schematic diagram of the diving of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 18 This is a schematic diagram of the floating of the biomimetic robotic fish with variable tail fin shape and stiffness as described in this invention. Figure 19 This is a cross-media schematic diagram of the biomimetic robotic fish with variable tail fin shape and stiffness described in this invention. Figure 1-19 Name of the winning designation: A. Fish body; B. Tail fin oscillation structure; C. Tail fin linkage structure; 1. Switch; 2. Fish body cover; 3. Winch; 4. Servo disc; 5. Servo; 6. Battery; 7. Center of gravity adjustment device; 8. Fish body; 9. Pectoral fin rotation device; 10. Counterweight compartment; 11. L-shaped eccentric wheel; 12. Transmission sleeve; 13. Motor; 14. Traction line; 15. Rubber hose; 16. Dorsal fin; 17. Aviation connector; 18. Pectoral fin plate; 19. Connecting bracket; 20. Servo arm; 21. Rotary shaft; 22. Pectoral fin servo; 23. Center of gravity adjustment motor; 24. Sliding block; 25. Nut; 26. Linear bearing. 27 Second slider, 28 Optical axis, 29 Counterweight box, 30 Hole retaining ring, 31 Bearing, 32 Swing guide slide, 33 Swing housing, 34 Pagoda spring, 35 Tail handle center rod, 36 Tail handle side rod, 37 First slider, 38 Pull rod, 39 Connecting rod one, 40 Connecting rod two, 41 Connecting rod three, 42 Connecting rod four, 43 Connecting rod five, 44 Connecting rod six, 45 Connecting rod seven, 46 Connecting rod eight, 47 Connecting rod nine, 48 Connecting rod ten, 49 Tail fin center rod, 50 Elastic sleeve. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Combination Figure 1-19The purpose of this invention is to provide a tail fin with controllable shape and stiffness, and its biomimetic robotic fish movement mechanism. The invention is characterized by comprising a fish body A, a tail fin swinging structure B, and a tail fin connecting rod structure C. The fish body A and the tail fin swinging structure B, as well as the tail fin swinging structure B and the tail fin connecting rod structure C, are all fixed with screws. The robotic fish adopts a modular design, with each component, including the fish body A, the tail fin drive structure B, and the tail fin connecting rod structure C, being an independent module. This allows for independent experimentation or rapid replacement in case of damage, facilitating robot maintenance, improving efficiency, and making it more suitable as an underwater research platform.

[0015] Combination Figure 3-4 This embodiment describes the body A of a biomimetic robotic fish with variable tail fin shape and stiffness. It mainly includes a switch 1, a fish body cover 2, a winch 3, a servo motor 4, a servo motor 5, a battery 6, a center of gravity adjustment device 7, a fish body 8, a pectoral fin rotation device 9, a counterweight chamber 10, an L-shaped eccentric wheel 11, a transmission sleeve 12, a motor 13, a traction cable 14, a hose 15, a dorsal fin 16, and an aviation connector 17. The center of gravity adjustment device 7 is installed at the bottom of the fish body 8 to lower the center of gravity and adjust the robotic fish's center of gravity. The counterweight is placed in the counterweight chamber 10 for easy weight adjustment of the robotic fish. The pectoral fin rotation device 9 is installed on both sides of the upper side of the fish body 8 to achieve various movement modes of the robotic fish. The motor 13, transmission sleeve 12, and L-shaped eccentric wheel 11 are installed at the rear of the fish body 8, forming the drive device of the robotic fish. The servo motor 5, along with the servo motor disc 4, winch 3, traction line 14, and hose 15, forms the wire-driven tail fin linkage mechanism C of the robotic fish, which is mounted on the upper side of the fish body 8. The dorsal fin 17 is located on the top side of the robotic fish and is connected to the fish body cover 2 by screws, which can effectively reduce water resistance.

[0016] Combination Figure 5 This embodiment describes a pectoral fin rotation device 9 for a biomimetic robotic fish with variable tail fin shape and stiffness. It mainly includes a pectoral fin plate 18, a connecting bracket 19, a servo arm 20, a rotating shaft 21, and a pectoral fin servo 22. One end of the rotating shaft 21 is rigidly fixed to the output shaft of the pectoral fin servo 22, and the other end is fixedly connected to the servo arm 20. The servo arm 20 is detachably mounted in a pre-set groove on the connecting bracket 19 using bolts, ensuring a stable structure after assembly. The pectoral fin plate 18 and two optical axes on the connecting bracket 19 are fitted together and fastened with bolts to ensure reliable connection. When the pectoral fin servo 22 is activated and outputs rotational power, the power is sequentially transmitted to the servo arm 20 via the rotating shaft 21, thereby driving the connecting bracket 19, which is fixedly connected to the servo arm 20, to rotate synchronously. Ultimately, this drives the pectoral fin plate 18 to complete a rotational movement at a preset angle, achieving pectoral fin attitude control.

[0017] Combination Figure 6This embodiment describes a center-of-gravity adjustment device 7 for a biomimetic robotic fish with variable tail fin shape and stiffness. It mainly includes a center-of-gravity adjustment motor 23, a slider baffle 24, a nut 25, linear bearings 26, a second slider 27, an optical axis 28, and a counterweight box 29. The center-of-gravity adjustment motor 23 is glued to the slider baffle 24; the nut 25 and two linear bearings 26 are installed in the second slider 27; the second slider 27 is installed on the optical axis 28 via linear bearings 44; a lead screw is connected to the output shaft of the center-of-gravity adjustment motor 23, and the lead screw and the nut 25 in the second slider 27 form a lead screw-nut pair; a lead block is placed on the counterweight box 29 and fixed to the second slider 27; when the center-of-gravity adjustment motor 23 rotates, it drives the second slider 27 to move, which in turn drives the counterweight box 29 and the lead block to move, ultimately achieving center-of-gravity adjustment.

[0018] Combination Figure 7-8 This embodiment describes the tail fin drive structure B of a biomimetic robotic fish with variable tail fin shape and stiffness. It mainly includes a retaining ring 30, a bearing 31, a swing guide slide 32, a swing housing 33, and a pagoda spring 34. The swing guide slide 32 is fixed to a pre-set mounting position inside the swing housing 33 by the retaining ring 30. The bearing 31 is mounted on the corresponding mounting surface of the swing guide slide 32. The swing guide slide 32, the retaining ring 30, and the bearing 31 are assembled together inside the swing housing 33 to form an integrated transmission assembly. This assembly can convert the rotational motion output by the motor 13 into the reciprocating swing motion of the swing housing 33, providing the power basis for the biomimetic swing of the tail fin. The pagoda spring 34 is internally installed inside the swing housing 33, with one end positioned and fixed by a pre-set groove on the protrusion inside the swing housing 33, ensuring assembly stability.

[0019] Combination Figure 9-10This embodiment describes the tail fin linkage structure C of a biomimetic robotic fish with variable tail fin shape and stiffness. It mainly includes a traction line 14, a central tail peduncle 35, side tail peduncle rods 36, a first slider 37, a pull rod 38, connecting rod one 39, connecting rod two 40, connecting rod three 41, connecting rod four 42, connecting rod five 43, connecting rod six 44, connecting rod seven 45, connecting rod eight 46, connecting rod nine 47, connecting rod ten 48, the central tail fin rod 49, and a rubber sleeve 50. Two thin side tail peduncle rods 36 and one thick central tail peduncle rod 35 are glued together to form the tail peduncle, which is embedded in the drive housing 33 and detachably secured with bolts. A single-sided composite parallelogram mechanism is configured on each of the upper and lower sides of the central tail fin rod 49. This mechanism is composed of N continuously connected parallelogram units, where N is an integer from 1 to 5, providing structural support for tail fin shape transformation. Each parallelogram unit is named A, B, C, and D, with sides A and C parallel to the caudal fin center rod 49. In this mechanism, the A side of the first unit corresponds to a pre-defined segment on the caudal fin center rod 49; subsequent units are stacked on the outside of the previous unit, and the A side of the next unit is a pre-defined segment on the link to which the C side of the previous unit belongs; the B sides of all parallelogram units are consecutive adjacent segments on the same link, achieving multi-unit linkage and coordination. Taking N as 3 as an example, link 1 39 is the D side of the first unit, link 2 40 is the C side of the first unit and part of its segment is the A side of the second unit, and different segments of link 6 44 are the B sides of the three parallelogram units; similarly, link 3 41 is the D side of the second parallelogram, link 7 45 is its C side and part of its segment is the A side of the third parallelogram, link 4 42 is the D side of the third parallelogram, and link 5 43 is its C side. To optimize the hydrodynamic effect of the underwater oscillation of the tail fin, connecting rods 46 and 48 can be added to the blank area of ​​the parallelogram unit. All connecting rods are riveted as rotating pairs. The tail fin center rod 49 is fixed to the middle position of the two tail shank side rods 36 by rivets. The reserved gap formed between the tail shank center rod 35 and the tail fin center rod 49 is the variable stiffness control area of ​​the tail fin, providing a structural basis for stiffness adjustment. The first slider 37 is riveted to the upper and lower pull rods 38 and covers the variable stiffness area. The traction line 14 is fixed to the first slider 37 with strong adhesive. When the traction line 14 pulls the first slider 37 to slide along the preset trajectory, it can simultaneously drive the linkage mechanism to deform to adjust the tail fin shape. By changing the coverage of the variable stiffness area, the tail fin stiffness can be dynamically adjusted to achieve coordinated control of shape and stiffness. The rubber sleeve 50 covers the multi-link mechanism, and the open end is fixed to the oscillation shell 33 with glue and waterproof glue to achieve underwater sealing.

[0020] Combination Figure 11-19 This embodiment describes a method for the coordinated movement of a biomimetic robotic fish with variable tail fin shape and stiffness, including the following processes: The process of caudal fin morphological and stiffness-variable motion: combined with Figure 11-12This embodiment describes a method for moving the caudal fin with different shapes and stiffnesses, including the following process: In the initial state, the tail fin is crescent-shaped, and the first slider 37 covers the variable stiffness area. At this time, the stiffness of the tail fin is relatively large, forming a high-stiffness crescent-shaped tail fin. When the servo motor 5 rotates counterclockwise, it drives the winch 3 to pull the traction line 14. The first slider 37 moves forward passively, and the subsequent linkage mechanism follows. The tail fin becomes a fan-shaped surface. At the same time, the variable stiffness area covered by the first slider 37 is exposed, and the stiffness of the tail fin decreases, forming a low-stiffness fan-shaped tail fin.

[0021] The movement process of a biomimetic robotic fish with variable tail fin shape and stiffness: Combination Figure 13-14 This embodiment is the first motion mode of a biomimetic robotic fish with variable tail fin shape and stiffness, which is a fast and efficient forward motion. When in the initial state, the tail fin is a crescent shape with high stiffness. At this time, the robotic fish can set the swimming speed in the high frequency range and can efficiently obtain high speed. When the servo motor 5 rotates, the tail fin becomes a fan shape with low stiffness. At this time, the robotic fish can set the swimming speed in the low frequency range and can efficiently complete multiple motion modes. Combination Figure 15-16 This embodiment demonstrates motion mode two-1, where the yaw generated by the pectoral fin and the forward motion generated by the caudal fin work together for a turn: For a right turn: combining... Figure 15 As shown, during a turn, the low-stiffness fan-shaped tail fin periodically swings back and forth at an angle of ±30°, generating forward thrust through hydrodynamic action. Simultaneously, differential attitude control of the pectoral fins is triggered; the right pectoral fin deflects to a vertical plane perpendicular to the incoming current to create significant lateral drag, while the left pectoral fin maintains a parallel posture to the fish's body. The difference in drag between the two sides creates a clockwise turning torque on the fish's central axis, driving the head to turn. For left turns, combined with... Figure 16 As shown, when starting to turn, the low-stiffness fan-shaped tail fin swings back and forth periodically at an angle of ±30°, outputting forward thrust through hydrodynamic action; simultaneously triggering differential attitude control of the pectoral fins, the left pectoral fin deflects to a vertical plane orthogonal to the incoming current to form significant lateral resistance, while the right pectoral fin maintains a parallel posture with the fish body. The difference in resistance on both sides forms a counterclockwise turning torque on the fish body's central axis, driving the head to deflect.

[0022] Combination Figure 17-18 This embodiment describes the diving and surfacing movements of a biomimetic robotic fish with variable tail fin shape and stiffness in motion mode two-2. In this motion mode, the tail fin drive structure B, combined with the center of gravity adjustment device 7 and the pectoral fin rotation device 9, provides the following two motion methods: Inclined Diving and Ascending Motion: In this motion mode, for the diving motion, the center of gravity adjustment motor 23 rotates to move the counterweight box 29 forward, thereby causing the head of the robotic fish to droop. The pectoral fin servos 22 on both sides rotate, causing the pectoral fin plates to tilt downward. A downward force is generated through the water flow difference. Then, the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to swim forward and downward, finally completing the diving motion. For the ascending motion, the center of gravity adjustment motor 22 rotates to move the counterweight box 29 backward, thereby causing the head of the robotic fish to tilt upward. The pectoral fin servos 22 on both sides rotate, causing the pectoral fin plates 18 to tilt upward. An upward force is generated through the water flow difference. Then, the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to swim forward and upward, finally completing the diving and ascending motion. Spiral Diving and Ascending Motion: In this motion mode, for the diving motion, the center of gravity adjustment motor 23 rotates, causing the counterweight box 29 to move forward, which in turn causes the head of the robotic fish to continuously droop. At the same time, one side of the pectoral fin servo motor 22 rotates, one side of the pectoral fin plate 18 tilts downward, while the other side remains unchanged and parallel to the water flow. Then, the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to turn, and finally completes the diving motion; the left pectoral fin tilting downward is a counterclockwise spiral diving motion; the right pectoral fin tilting downward is a clockwise spiral diving motion. For the ascending motion, the center of gravity adjustment motor 23 rotates, causing the counterweight box 29 to move backward, which in turn causes the head of the robotic fish to tilt upward. At the same time, one side of the pectoral fin servo motor 22 rotates, one side of the pectoral fin plate 18 tilts upward, while the other side remains unchanged and parallel to the water flow. Then, the tail fin swings back and forth, causing the robot to turn, and finally completes the ascending motion; the left pectoral fin tilting upward is a counterclockwise spiral ascending motion; the right pectoral fin tilting upward is a clockwise spiral ascending motion.

[0023] Combination Figure 19 In this embodiment, the three-mode water-air-crossing motion is as follows: Before the robot crosses the medium, that is, while in the water, the center of gravity adjustment motor 23 rotates to move the counterweight box 29 backward, thereby causing the robot fish's head to tilt upward. At the same time, the pectoral fins on both sides tilt upward, generating an upward force through the water flow difference. Then, the crescent-shaped high-rigidity tail fin swings back and forth, causing the robot to swim forward and upward, generating a rapid diagonal upward straight motion. The robot obtains the maximum diagonal upward speed, causing it to rush out of the water diagonally. When the robot crosses the medium, that is, from underwater to air, the center of gravity adjustment motor 23 rotates to move the counterweight box 29 forward, thereby causing the robot fish's head to drop. The pectoral fin servos 22 on both sides rotate, causing the pectoral fin plates to tilt downward, and the tail fin stops swinging, allowing it to fall into the water with less resistance.

Claims

1. A biomimetic robotic fish tail fin with variable shape stiffness, characterized in that: Including the caudal peduncle and caudal fin skeleton; The aforementioned tailstock consists of a tailstock center rod (35) and two tailstock side rods (36); wherein the tailstock center rod (35) is located in the middle of the front part of the two tailstock side rods (36) and is relatively fixed; The aforementioned caudal fin skeleton includes a central rod (49) of the caudal fin, the front part of which extends into the middle of the rear of two caudal peduncle lateral rods (36) and is relatively fixed; the upper and lower sides of the central rod (49) are respectively composed of several connecting rods forming a single-sided compound parallelogram mechanism; the specific structure of the single-sided compound parallelogram mechanism is as follows: it is composed of N parallelogram mechanisms connected in sequence, and the four sides of a single parallelogram are successively called side A, side B, side C, and side D, where side A and side C are connected to the central rod of the caudal fin. The core rod (49) is parallel; the A side of the first parallelogram mechanism in the single-sided compound parallelogram mechanism is a segment on the tail fin center rod (49); the next parallelogram mechanism is located outside the previous parallelogram mechanism, and the A side of the next parallelogram mechanism is a segment on the connecting rod where the C side of the previous parallelogram mechanism is located, and the B side of the next parallelogram mechanism and the B side of the previous parallelogram mechanism are adjacent segments on the same connecting rod; the above N is a natural number between 1 and 5; A gap is reserved between the caudal fin center rod (49) and the caudal peduncle center rod (35), which is the caudal fin's variable stiffness control area. A first slider (37) is set in this area. The first slider (37) can slide on the caudal peduncle center rod (35). The first slider (37) is connected to the traction line (14). When the traction line (14) is subjected to traction force, it can drive the first slider (37) to slide along the caudal peduncle center rod (35). The first slider (37) is also connected to the connecting rod where the D side of the first parallelogram mechanism of the single-sided compound parallelogram mechanism is located through the pull rod (38). The sliding of the first slider (37) can change its coverage of the variable stiffness control area on the one hand, and drive the single-sided compound parallelogram mechanism to undergo coordinated deformation on the other hand. It can realize the coordinated control of shape and stiffness. An elastic sleeve (50) is installed on the outside of the caudal peduncle and caudal fin skeleton.

2. A robotic fish having the biomimetic robotic fish tail fin with variable morphological stiffness as described in claim 1, characterized in that: It also includes the fish body (A) and the tail fin swinging mechanism (B); The aforementioned fish body (A) includes a fish body (8), a center of gravity adjustment device (7), a pectoral fin rotation device (9), and a counterweight chamber (10); wherein the center of gravity adjustment device (7) is installed in the bottom area of ​​the fish body (8); a counterweight plate is installed in the counterweight chamber (10); the pectoral fin rotation device (9) is installed on both sides of the upper side of the fish body (8); and the dorsal fin (17) is located on the uppermost side of the robotic fish. The fish body part (A) also includes a tail fin shape stiffness drive mechanism, which consists of a servo motor (5), a servo motor disk (4), a winch (3), and a traction line (14) in sequence; one end of the traction line (14) is fixed to the winch (3), and the other end is fixed to the first slider (37) of the tail fin skeleton; The tail fin swing mechanism (B) is connected to the fish body (8) at one end and to the tail peduncle at the other end. It consists of a tail fin swing drive assembly and a tail fin swing assembly. The tail fin swing drive assembly is installed behind the fish body (8) and consists of a motor (13), a transmission sleeve (12), and an L-shaped eccentric wheel (11) in sequence. The tail fin swing assembly includes a swing housing (33) and a swing guide slide (32). The swing guide slide (32) is fixed in the drive housing (33) at both ends by bearings (31) and retaining rings (30) for hole positioning. The swing guide slide (32) is provided with a groove along the axial direction. The L-shaped eccentric wheel (11) cooperates with the groove to convert the rotational motion output by the motor (13) into the reciprocating swing motion of the swing housing (33).

3. The robotic fish according to claim 2, characterized in that: The aforementioned pectoral fin rotation device (9) consists of a pectoral fin servo (22), a rotating shaft (21), a servo arm (20), a connecting bracket (19), and a pectoral fin plate (18) in sequence; one end of the rotating shaft (21) is rigidly fixed to the output shaft of the pectoral fin servo (22), and the other end is fixedly connected to the servo arm (20); the connecting bracket (19) is fixedly connected to the servo arm (20); and the pectoral fin plate (18) is fixedly connected to the bracket (19).

4. The robotic fish according to claim 2, characterized in that: The aforementioned center of gravity adjustment device (7) includes a center of gravity adjustment motor (23), a lead screw connected to the output shaft of the center of gravity adjustment motor (23); it also includes a second slider (27), and a nut (25) installed in the slider; wherein the nut (25) and the lead screw cooperate to form a lead screw and nut pair; The slider is also equipped with a linear bearing (26) and is mounted on the optical axis (28) via a linear bearing (44), allowing it to slide on the axis. A counterweight box (29) is installed on the second slider (27) mentioned above.

5. The working method of the robotic fish according to claim 2, characterized in that... The process includes the following: (1) The process of caudal fin morphological and stiffness-changing motion: In the initial state, the tail fin is crescent-shaped, that is, the first slider (37) covers the variable stiffness area. At this time, the stiffness of the tail fin is relatively large, forming a high-stiffness crescent-shaped tail fin. When the traction line (14) pulls the first slider (37) forward, the subsequent linkage mechanism follows, the tail fin becomes a fan-shaped surface, and at the same time, the variable stiffness area covered by the first slider (37) is exposed, the stiffness of the tail fin decreases, forming a low-stiffness fan-shaped tail fin. (2) The movement process of the biomimetic robotic fish with variable tail fin shape and stiffness: Mode 1, Fast and Efficient Forward Movement: In the initial state, the tail fin is a high-rigidity crescent-shaped tail fin. At this time, the robotic fish sets its swimming speed to the high-frequency range, which can efficiently obtain high speed. Mode 2: When the tail fin becomes a low-stiffness fan-shaped tail fin, the robotic fish sets its swimming speed to a low frequency, enabling it to efficiently complete various other movement modes. Mode 2-1: Coordinated turning by yaw generated by the pectoral fin and forward motion generated by the caudal fin: When starting a turn, the low-stiffness fan-shaped caudal fin swings back and forth periodically at an angle of ±30°, outputting forward thrust through hydrodynamic action; Synchronous triggering of differential posture control of pectoral fins: the inner pectoral fin deflects to a vertical plane orthogonal to the incoming flow to form significant lateral resistance, while the outer pectoral fin maintains a parallel posture with the fish body. The difference in resistance on both sides forms a clockwise turning torque on the fish body's central axis, driving the head to deflect. Mode 2-2: Descent and Ascent Processes For the downward and upward movement, the center of gravity adjustment device (7) moves the center of gravity forward, causing the head of the robotic fish to droop; the pectoral fin rotation device (9) on both sides makes the pectoral fin plates tilt downward, generating a downward force through the water flow difference; then the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to swim forward and downward, and finally completes the downward movement; for the upward movement, the center of gravity adjustment device (7) moves the center of gravity backward, causing the head of the robotic fish to tilt upward; the pectoral fin rotation device (9) on both sides makes the pectoral fin plates tilt upward, generating an upward force through the water flow difference; then the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to swim forward and upward, and finally completes the downward and upward movement. The spiral diving and surfacing motion is as follows: For the diving motion, the center of gravity adjustment device (7) moves the center of gravity forward, which causes the head of the robot fish to droop continuously. At the same time, the pectoral fin rotation device (9) on one side makes the pectoral fin plate on that side tilt downward, while the other side remains unchanged and parallel to the water flow. Then, the low-stiffness fan-shaped tail fin swings back and forth, causing the robot to turn and finally complete the spiral diving motion. For the surfacing motion, the center of gravity adjustment device (7) moves the center of gravity backward, which causes the head of the robot fish to tilt upward. At the same time, the pectoral fin rotation device (9) on one side makes the pectoral fin plate on that side tilt upward, while the other side remains unchanged and parallel to the water flow. Then, the tail fin swings back and forth, causing the robot to turn and finally complete the spiral surfacing motion. Mode 3, Water-Air Transition Medium: Before the robotic fish crosses the medium, that is, when it is in the water, the center of gravity adjustment device (7) moves the center of gravity backward, thereby causing the head of the robotic fish to tilt upward. At the same time, the pectoral fin rotation device (9) makes the pectoral fins on both sides tilt upward, generating an upward force through the difference in water flow. Then, the crescent-shaped high-rigidity tail fin swings back and forth, causing the robotic fish to swim forward and upward, generating a fast, diagonally upward and forward straight motion. The robotic fish obtains the maximum diagonally upward speed, causing it to rush out of the water at an angle. When the robot crosses the medium, that is, when it changes from underwater to air, the center of gravity adjustment device (7) moves the center of gravity forward, thereby causing the head of the robotic fish to droop. The pectoral fin rotation device (9) makes the pectoral fins on both sides tilt downward, and the tail fin stops swinging, falling into the water with less resistance.

Images