Spiral artificial muscle and shape memory polymer synergistically driven-locked variable tail fin configuration robotic fish and self-adaptive swimming method thereof

Abstract

The invention discloses a variable tail fin configuration robotic fish cooperatively driven and locked by spiral artificial muscles and a shape memory polymer and a self-adaptive swimming method thereof. The robotic fish comprises a robotic fish main body structure, a rope-driven tail fin driving system and a compliance variable-configuration tail fin unit, the robotic fish main body structure is fixedly connected with the front end of the rope-driven tail fin driving system through a bolt, and the rear end of the rope-driven tail fin driving system is fixedly connected with the compliance variable-configuration tail fin unit through gluing; the rope-driven tail fin driving system realizes power transmission through a driving rope and a spring plate; the compliance variable-configuration tail fin unit comprises a tail fin framework, two shape locking units, two driving variable-structure units and a tail fin skin, the driving variable-structure units are spiral artificial muscles, and the shape locking units are shape memory polymers. According to the robotic fish disclosed by the invention, the explosive thrust and the cruising ability of the robotic fish are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of biomimetic robotics and underwater propulsion technology, specifically to a tail fin-modulating biomimetic robotic fish based on helical artificial muscle actuation and shape memory polymer locking, and its modification method. Background Technology

[0002] As an important development direction in the field of underwater intelligent equipment, biomimetic robots rely heavily on the performance of their core propulsion component, the biomimetic fish tail fin, which directly determines the overall propulsion efficiency, maneuverability, and energy utilization. In nature, fish can actively adjust the shape of their tail fins according to different swimming conditions to achieve both efficient cruising and explosive acceleration, exhibiting excellent flexibility and variable stiffness characteristics. However, existing biomimetic fish tail fins are mostly made of fixed structures or single flexible materials, with unadjustable shapes, making it impossible to simultaneously achieve high thrust output and high propulsion efficiency in different swimming modes.

[0003] To address this issue, existing research has attempted to improve the performance of biomimetic fish tail fins using flexible materials or adjustable stiffness structures. For example, shape memory alloys (SMAs) and dielectric elastomers (DEs) have been introduced as actuating materials to achieve limited deformation control. However, these materials generally face problems such as high energy consumption for shape retention, high actuation voltage, or limited deformation amplitude, making them difficult to stably apply in miniaturized underwater robots.

[0004] Twisted and Coiled Actuator (TCA), as a novel flexible actuation material, possesses advantages such as low-voltage actuation, large stroke, and high specific power, and has been widely used in the actuation control of biomimetic structures. Shape Memory Polymer (SMP), on the other hand, can achieve reversible transformation from compliant to rigid under temperature triggering and maintain its shape under low energy consumption conditions. If TCA and SMP can be functionally coupled, a composite actuation system with both reversible response and low-power shape-locking capability can be formed, providing a new technical approach for the morphological adaptation of biomimetic fish tail fins.

[0005] However, there is currently a lack of an integrated system that can achieve variable tail fin morphology on the same platform, and there is a lack of low-power morphology locking and intelligent control strategies specifically designed for underwater environments. Summary of the Invention

[0006] To address the issues of fixed structure and unadjustable shape in existing biomimetic fish tail fins, this invention proposes a variable-configuration tail fin system and its control method based on helical artificial muscle actuation and shape memory polymer locking. This system achieves active deformation and passive locking of the tail fin in different swimming modes through the synergistic action of TCA and SMP. The system enables explosive swimming in a large updraft mode and efficient cruising in a small updraft mode, thereby significantly improving the biomimetic fish's propulsion performance, energy utilization, and adaptability to variable underwater environments.

[0007] The technical solution adopted in this invention is as follows: I. A robotic fish with a variable tail fin configuration, synergistically driven and locked by a spiral-shaped artificial muscle and a shape memory polymer. The robotic fish of the present invention includes a main body structure, a rope-driven tail fin drive system, and an adaptive variable configuration tail fin unit; the main body structure of the robotic fish is fixedly connected to the front end of the rope-driven tail fin drive system by bolts, and the rear end of the rope-driven tail fin drive system is fixedly connected to the adaptive variable configuration tail fin unit by adhesive bonding.

[0008] The main structure of the robotic fish includes an outer shell and an internal system. The internal system is located inside the outer shell. The outer shell adopts a biomimetic design of the Bluefin tuna, and the surface of the outer shell integrates dorsal fins, pelvic fins, and movable pectoral fins. The main internal system includes a lithium battery, an electronic control system, a drive servo system, and a water pressure sensor; the discharge cable of the lithium battery is connected to the input terminal of the electronic control system, and the charging cable of the lithium battery is connected to the spring pin connector; the output terminal of the electronic control system is electrically connected to the input terminal of the drive servo system, and the output terminal of the drive servo system is connected to the rope-driven tail fin drive system; the water pressure sensor is electrically connected to the electronic control system.

[0009] The electronic control system is a three-layer stacked control circuit board structure, including a LoRa wireless communication board, a main control unit board, and a power drive board arranged sequentially from top to bottom. The circuit boards are electrically connected to each other via board-to-board connectors. The discharge cable of the lithium battery is electrically connected to the input terminal of the power drive board, and the output terminal of the power drive board is electrically connected to the input terminal of the LoRa wireless communication board via connectors. The output terminal of the LoRa wireless communication board is electrically connected to the input terminal of the main control unit board. The drive servo system includes three servos. The first servo and the second servo are arranged on both sides of the electronic control system, and the third servo is arranged at the rear of the electronic control system. The third servo is connected to the rope-driven tail fin drive system via a servo disc arranged on its output shaft. Each servo is connected to the main control unit board and the power drive board of the electronic control system, respectively. The water pressure sensor is connected to the main control unit board of the electronic control system. A fish body central pattern generator is installed on the main control unit board.

[0010] The compliant variable-configuration caudal fin unit includes a caudal fin skeleton, two lock-shaped units, two drive-variant units, and a caudal fin skin; The front part of the caudal fin skeleton is connected to the rear end of the rope-driven caudal fin drive system. The upper and lower rear ends of the caudal fin skeleton are respectively fixed to a locking unit by adhesive bonding. The two locking units are arranged symmetrically from top to bottom. Each locking unit has a drive variant unit on one side. The caudal fin skeleton, the two locking units, and the two drive variant units together constitute the internal structure of the caudal fin. The caudal fin skin covers the outside of the internal structure of the caudal fin and is connected to the rear end of the rope-driven caudal fin drive system.

[0011] The cable-driven tail fin drive system includes two spring plates, a skeleton unit, and a drive cable. The main body shell of the robotic fish is connected to the tail fin skin via two spring plates, which are respectively located at the upper and lower parts of the cable-driven tail fin drive system. The skeleton unit is located between the two spring plates and includes several skeleton discs. These skeleton discs are arranged at intervals along the axial direction of the cable-driven tail fin drive system and are connected by pins. The first skeleton disc along the swimming direction of the robotic fish is fixedly connected to the main body shell of the robotic fish, and the last skeleton disc is fixedly connected to the tail fin skin. The front end of each spring plate is fixedly connected to the first skeleton disc, and the rear end of each spring plate is fixedly connected to the last skeleton disc. The skeleton discs are provided with guide holes. One end of the drive cable is wound around the servo disc of the third servo output shaft of the drive servo system, and the other end of the drive cable passes through the guide hole and connects to the last skeleton disc of the skeleton unit.

[0012] The tail fin skeleton has a hollow section. The output cable of the power drive board in the electronic control system is led out through the guide hole and the hollow section and then connected to the lock-shaped unit.

[0013] The driving mechanism unit is a spiral artificial muscle, which is mainly made of polyamide fiber and nickel wire wound together. The driving mechanism unit generates axial contraction after being heated. The locking unit is a shape memory polymer, which is made by mixing and curing epoxy resin and amine curing agent in a mass ratio of 59:41. At 30-80℃, the locking unit transitions from stiffness to flexibility. The tail fin skin is made of flexible silicone material with a Shore hardness of 5, and the tail fin skeleton is made of acrylonitrile butadiene styrene copolymer material.

[0014] II. Adaptive Swimming Method of a Robotic Fish with a Locked Tail Fin Configuration Driven by Helical Artificial Muscles and Shape Memory Polymers The adaptive traversal method includes the following steps: S1. The robotic fish is activated and enters acceleration mode. The central mode generator of the fish generates a rhythmic signal of the first frequency, which drives the adaptive variable configuration tail fin unit to swing. At the same time, the main control unit board controls the locking unit to maintain the first state, and the adaptive variable configuration tail fin unit is in the first frontal surface shape.

[0015] S2. When the main control unit board receives the cruise command, the main control unit board controls the locking unit to change to the second state, then powers on the drive variable configuration unit and causes it to retract, and drives the adaptive variable configuration tail fin unit to switch from the first frontal surface form to the second frontal surface form, and then locks the second frontal surface form. Specifically, it consists of the following three sub-steps: S21. When the main control unit board receives the cruise command, the main control unit board heats the lock-type unit to make it switch to a compliant state. S22. Subsequently, the drive variable configuration unit is energized and heated, causing it to contract and drive the compliant variable configuration tail fin unit to switch from the first frontal surface shape to the second frontal surface shape. S23, then stop heating the drive variable configuration unit and let it cool down. Finally, the compliant variable configuration tail fin unit locks the second frontal surface shape, and then stop supplying power to the drive variable configuration unit.

[0016] S3. Subsequently, the central mode generator of the fish body switches to a second frequency rhythm signal to drive the adaptive variable configuration caudal fin unit to swing.

[0017] S4. When the main control unit board receives the acceleration command again, the cruise mode is deactivated. The main control unit board controls the locking unit to change state again, drives the adaptive variable configuration tail fin unit to return to the first frontal surface shape and lock it. At the same time, the fish body central mode generator switches back to the first frequency rhythm signal. Specifically, it consists of the following two sub-steps: S41. When the main control unit board receives the acceleration command again, the cruise mode is deactivated. The main control unit board heats the lock-shaped unit to make it compliant. The shape memory effect of the lock-shaped unit drives the compliant variable configuration tail fin unit to restore the first frontal surface shape. S42, then stop driving the variable configuration unit and cool it down. Finally, the adaptive variable configuration tail fin unit locks the first frontal surface morphology, while the fish body central mode generator switches back to the first frequency rhythm signal.

[0018] The innovation of this invention lies in the adoption of an adaptive variable-configuration tail fin unit. This unit is an intelligent tail fin system capable of autonomously changing its configuration under multiple operating conditions, achieving active adjustment of the tail fin's shape and long-term locking without power consumption. This invention combines the reversible deformation characteristics of the TCA (Transverse Coel-Anatomical Rectifier) ​​with the power-free shape-locking characteristics of the SMP (Self-Modulating Medium-Range) system, endowing the variable-configuration tail fin with the ability to switch operating modes on the same platform: it can achieve high-efficiency oscillation on a small updraft surface and also convert to high-thrust oscillation on a large updraft surface. This system effectively solves the inherent limitation of existing biomimetic fish tail fins, which, due to their fixed shape, cannot simultaneously achieve both acceleration and efficient cruising, thus significantly improving the explosive thrust and cruising capability of the robotic fish.

[0019] The beneficial effects of this invention are: Compared to existing biomimetic fish tail fin structures, this invention constructs an intelligent tail fin system capable of autonomously changing its configuration under multiple operating conditions, based on a synergistic driving and locking mechanism of helical polymer artificial muscle (TCA) and shape memory polymer (SMP). This achieves active adjustment of the tail fin's shape and long-term locking without power consumption. On the same platform, this system implements a large tail fin upwind surface for acceleration and a small tail fin upwind surface for efficient cruising, effectively solving the problems of low energy efficiency and poor adaptability to operating conditions caused by the fixed shape of traditional biomimetic fish tail fins. This significantly improves the overall performance of the robotic fish in terms of propulsion efficiency, acceleration performance, attitude stability, and overall endurance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of a variable tail fin configuration robotic fish that is synergistically driven and locked by a spiral artificial muscle and a shape memory polymer according to the present invention. Figure 2 This is a top view of the internal structure of the robotic fish of the present invention; Figure 3 This is a schematic diagram illustrating the switching of the variable tail fin of the present invention between the large and small frontal surfaces. Figure 4 This is a flowchart of the method for controlling the tail fin configuration of fish according to the present invention; Figure 5 The thrust curves at 1Hz represent the different swing amplitudes of the fish tail fin before and after the tail fin configuration change according to the present invention.

[0021] Among them: 100, main structure of the robotic fish; 110, lithium battery; 120, electronic control system; 130, drive servo system; 140, water pressure sensor; 200, rope-driven tail fin drive system; 210, spring plate; 220, drive rope; 230, skeleton disc; 300, compliant variable configuration tail fin unit; 310, tail fin skeleton; 320, lock-shaped unit; 330, drive variable configuration unit; 340, tail fin skin. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 and Figure 2 As shown, the robotic fish of the present invention includes a main body structure 100, a rope-driven tail fin drive system 200, and an adaptive variable configuration tail fin unit 300; the main body structure 100 and the front end of the rope-driven tail fin drive system 200 are fixedly connected by bolts, and the rear end of the rope-driven tail fin drive system 200 and the adaptive variable configuration tail fin unit 300 are fixedly connected by adhesive bonding.

[0024] like Figure 1 As shown, the main structure 100 of the robotic fish includes an outer shell and an internal system. The internal system is located inside the outer shell. The outer shell adopts a biomimetic design of the bluefin tuna. The surface of the outer shell integrates dorsal fins, pelvic fins and movable pectoral fins, which can simulate the swimming posture of real fish. The main internal system includes a lithium battery 110, an electronic control system 120, a drive servo system 130, and a water pressure sensor 140. The lithium battery 110 is located at the head of the main body structure 100 of the robotic fish. The discharge cable of the lithium battery 110 is connected to the input terminal of the electronic control system 120, and the charging cable of the lithium battery 110 is connected to a pogopin connector. The pogopin is used to connect to an external power source, which charges the robotic fish when connected. The output terminal of the electronic control system 120 is electrically connected to the input terminal of the drive servo system 130, and the output terminal of the drive servo system 130 is connected to the rope-driven tail fin drive system 200. The water pressure sensor 140 is electrically connected to the electronic control system 120 and is located at the rear of the main body structure 100 of the robotic fish. It is used to achieve constant-depth swimming. The water pressure sensor 140 senses the underwater pressure in real time and, in conjunction with the pectoral fin pitch adjustment, achieves constant-depth swimming control of the robotic fish.

[0025] The electronic control system 120 has a three-layer stacked control circuit board structure. The electronic control system 120 includes, from top to bottom, a LoRa wireless communication board, a main control unit board, and a power drive board. The circuit boards are electrically connected to each other via board-to-board connectors and reliably fixed to the fish body with bolts. The discharge cable of the lithium battery 110 is electrically connected to the input terminal of the power drive board. The output terminal of the power drive board is electrically connected to the input terminal of the LoRa wireless communication board via connectors. The output terminal of the LoRa wireless communication board is electrically connected to the input terminal of the main control unit board to supply power to the LoRa wireless communication board and the main control unit board. The drive servo system 130 includes three independent servos, each with an output torque of 12. kg·cm, respectively used to control the pitching motion of the pectoral fin and the reciprocating oscillation of the caudal fin. The electronic control system 120 has a first servo motor and a second servo motor arranged on both sides, with the two servo motors located inside the dorsal fin of the main body structure 100 of the robotic fish. A third servo motor is located at the rear of the electronic control system 120 and is connected to the rope-driven caudal fin drive system 200 via a servo disc located on its output shaft. Inside the ventral fin of the main body structure 100 of the robotic fish, each servo motor is connected to the main control unit board and power drive board of the electronic control system 120. The water pressure sensor 140 is connected to the main control unit board of the electronic control system 120. A fish central pattern generator (CPG) is installed on the main control unit board to generate rhythmic signals to control the periodic oscillation of the compliant variable configuration caudal fin unit 300. The lithium battery 110 has a capacity of 1800 mAh.

[0026] The adaptive variable configuration caudal fin unit 300 includes a caudal fin skeleton 310, two lock-shaped units 320, two drive variable configuration units 330, and a caudal fin skin 340; The front part of the caudal fin skeleton 310 is connected to the rear end of the rope-driven caudal fin drive system 200. The upper and lower rear ends of the caudal fin skeleton 310 are respectively fixedly connected to a locking unit 320 by adhesive bonding. The two locking units 320 are arranged symmetrically from top to bottom. Each locking unit 320 has a drive variant unit 330 on one side. The caudal fin skeleton 310, the two locking units 320 and the two drive variant units 330 together constitute the internal structure of the caudal fin. The caudal fin skin 340 covers the outside of the internal structure of the caudal fin and is connected to the rear end of the rope-driven caudal fin drive system 200.

[0027] The rope-driven tail fin drive system 200 includes two spring plates 210, a skeleton unit 230, and a drive rope 220. The outer shell of the robotic fish main structure 100 and the tail fin skin 340 are connected by two spring plates 210. The spring plates are arranged on the central axis of the robotic fish. The front end of each spring plate 210 is connected to the rear end of the outer shell of the robotic fish main structure 100, and the rear end of each spring plate 210 is connected to the front end of the tail fin skin 340 of the compliant variable configuration tail fin unit 300. The two spring plates 210 are respectively set at the upper and lower parts of the rope-driven tail fin drive system 200. The skeleton unit 230 is set between the two spring plates 210. The skeleton unit 230 provides overall structural support for the system, ensuring the stability and transmission efficiency of the tail fin drive system during operation. Unit 230 includes several skeleton discs, which are spaced apart along the axial direction of the rope-driven tail fin drive system 200. The skeleton discs are connected by pins. The first skeleton disc along the swimming direction of the robotic fish is fixedly connected to the outer shell of the main body structure 100 of the robotic fish, and the last skeleton disc is fixedly connected to the tail fin skin 340. The front end of each spring plate 210 is fixedly connected to the first skeleton disc, and the rear end of each spring plate 210 is fixedly connected to the last skeleton disc. The middle skeleton disc is provided with a groove for the spring plate 210 to pass through. The skeleton disc 230 is provided with a guide hole. One end of the drive rope 220 is wound around the servo disc of the third servo output shaft of the drive servo system 130, and the other end of the drive rope 220 passes through the guide hole and is connected to the last skeleton disc of the skeleton unit 230.

[0028] The drive rope 220 serves as a power transmission component, converting the rotational motion of the servo system 130 into the oscillating motion of the tail fin. The frame disc 230 provides overall structural support for the system, ensuring the stability and transmission efficiency of the tail fin drive system during operation.

[0029] The tail fin skeleton 310 has a hollow section. The output cable of the power drive board in the electronic control system 120 is led out through the guide hole and the hollow section and connected to the lock-shaped unit 320.

[0030] The drive unit 330 is a spiral artificial muscle (TCA). The spiral artificial muscle (TCA) is mainly made of polyamide fiber (nylon 66 polymer fiber) wound with nickel wire. The diameter of the nickel wire is 0.15mm. When the drive unit 330 is heated, it generates axial contraction, thereby outputting tensile force to drive the tail fin to achieve active shape adjustment. The locking unit 320 is a shape memory polymer (SMP). The shape memory polymer (SMP) is made by mixing and curing epoxy resin (Epon-828) and amine curing agent (Jeffamine D-400) in a mass ratio of 59:41. At 30-80℃, the locking unit 320 transitions from high rigidity to flexibility, thereby realizing the locking and unlocking of the tail fin shape. The caudal fin skin 340 is made of flexible silicone material with a Shore hardness of 5, which further enhances the flexibility of the caudal fin and optimizes its hydrodynamic performance. The caudal fin skeleton 310 is made of 3D printed acrylonitrile butadiene styrene copolymer (ABS) material to provide the overall structural strength of the caudal fin.

[0031] In practical implementation, the control and sensing unit uses an STM32 series microcontroller as its core. It precisely adjusts the input voltages of the TCA and SMP via a PWM strategy to achieve coordinated control of the entire process of "driving-deformation-locking-cooling". The system integrates a K-type thermocouple for temperature acquisition, an INA226 module for power detection, and an SX1278 LoRa communication unit for remote command interaction and data transmission with the host computer.

[0032] like Figure 3 As shown, the adaptive swimming method of a robotic fish with a variable tail fin configuration, which is synergistically driven and locked by helical artificial muscles and shape memory polymers, includes the following steps: S1. The robotic fish is activated and enters acceleration mode. The Central Pattern Generator (CPG) generates a rhythmic signal of the first frequency. The rhythmic signal of the first frequency is received by the compliant variable configuration tail fin unit 300 and drives the compliant variable configuration tail fin unit 300 to swing. At the same time, the main control unit board controls the locking unit 320 to maintain the first state of low temperature and high rigidity, and drives the variable configuration unit 330 to be in a de-energized state. The compliant variable configuration tail fin unit 300 is in the first frontal surface form to achieve high-efficiency propulsion.

[0033] S2. When the main control unit board receives the cruise command, the main control unit board controls the locking unit 320 to change to the second state, and then powers on the drive variable configuration unit 330 to make it retract, and drives the adaptive variable configuration tail fin unit 300 to switch from the first frontal surface form to the second frontal surface form, and then locks the second frontal surface form. Specifically, it consists of the following three sub-steps: S21. When the main control unit board receives the cruise command, the main control unit board heats the lock-type unit 320 to make it switch to a compliant state. S22. Subsequently, the drive variable configuration unit 330 is energized and heated, causing it to contract and drive the compliant variable configuration tail fin unit 300 to switch from the first frontal surface shape to the second frontal surface shape. S23, then stop heating the drive variable configuration unit 330 and cool it to a low temperature and high stiffness state. Finally, the compliant variable configuration tail fin unit 300 locks the second frontal surface shape, and then stop supplying power to the drive variable configuration unit 330.

[0034] S3. Subsequently, the fish central mode generator (CPG) switches to a second frequency rhythm signal. The rhythm signal is received by the compliant variable configuration caudal fin unit 300 and drives the compliant variable configuration caudal fin unit 300 to swing, so as to improve propulsion efficiency.

[0035] S4. When the main control unit board receives the acceleration command, it cancels the cruise mode and controls the locking unit 320 to change state again, driving the adaptive variable configuration tail fin unit 300 to return to the first frontal surface shape and lock it. At the same time, the fish body central mode generator (CPG) switches back to the first frequency rhythm signal.

[0036] Specifically, it consists of the following two sub-steps: S41. After the cruise requirement is released, the main control unit board heats the lock-shaped unit 320 to make it compliant, and uses the shape memory effect of the lock-shaped unit 320 to drive the compliant variable configuration tail fin unit 300 to restore the first frontal surface shape. S42, then stop driving the variable configuration unit 330 and cool it to a low temperature and high stiffness state. Finally, the adaptive variable configuration tail fin unit 300 locks the first frontal surface shape, and at the same time the fish body central mode generator (CPG) switches back to the first frequency rhythm signal.

[0037] The first frontal surface morphology is the large frontal surface morphology, which is the fully extended morphology of the compliant variable configuration tail fin unit 300. During the acceleration phase, the lock-shaped unit 320 achieves an axial contraction rate of 15%, which reduces the frontal surface area of ​​the tail fin of the compliant variable configuration tail fin unit 300 by about 25%, switching to the second frontal surface morphology, which is the small frontal surface morphology.

[0038] The large frontal surface effectively reduces the drag of the tail fin in the water, allowing it to swing efficiently. Its larger frontal area allows for more interaction with the water during swinging, effectively squeezing and pushing the surrounding water flow, which is then instantly converted into a powerful burst of thrust, precisely meeting the propulsion needs of the robotic fish for instantaneous acceleration and rapid start-up. During the cruising phase, it switches to a small frontal surface. Its smaller frontal area significantly reduces the impact and frictional resistance of the water flow on the tail fin, reducing energy consumption during continuous swimming. At the same time, it allows the water to flow more smoothly over the fin surface, greatly improving propulsion efficiency and thus significantly enhancing the robotic fish's cruising ability and endurance.

[0039] The switching between the two working modes is achieved through the coordinated control of the TCA drive unit and the SMP locking unit, enabling the robotic fish to autonomously adapt to different working conditions according to actual swimming needs, and possessing the dual advantages of high mobility and high energy efficiency.

[0040] like Figure 3The diagram illustrates the working principle of the caudal fin switching between the large and small upstream face. Initially, the caudal fin is in the large upstream face configuration. The configuration switch is achieved by coordinating the temperature control of the SMP locking unit 320 and the TCA-driven deformation unit 330. When the SMP locking unit is heated and becomes compliant, the caudal fin skeleton can deform freely. At this time, the TCA-driven deformation unit, after being heated, contracts axially, driving the caudal fin to change from the large upstream face configuration to the small upstream face configuration. After reaching the target configuration, the SMP locking unit cools and returns to rigidity, locking the caudal fin configuration. The TCA-driven unit is then de-energized, and the system maintains the small upstream face state with zero power consumption. Through this control process, the system achieves a complete switch from the large upstream face to the small upstream face configuration and maintains the target configuration without external energy input.

[0041] like Figure 4 The diagram illustrates a flowchart of the fish tail fin configuration control method of the present invention. When the tail fin is in a large updraft state, if it needs to switch to a small updraft state, the control system first activates the SMP locking unit 320 and monitors its temperature in real time via thermocouples. When the SMP reaches its glass transition temperature and softens, the control system immediately activates the TCA driving configuration unit 330, driving the tail fin skeleton to bend and deform, gradually adjusting to a small updraft shape. After the tail fin reaches the target shape, the control system stops activating the locking unit, allowing it to cool, solidify, and lock the shape; then it stops activating the driving configuration unit. At this time, the tail fin remains in a small updraft state under the locking effect of the SMP, requiring no additional energy input. When it is necessary to restore the large updraft state, the control system reactivates the locking unit 320, using the shape memory effect of the SMP to drive the tail fin to automatically restore to the initial large updraft shape, completing a full configuration switching cycle.

[0042] like Figure 5 The figure shows a comparison of thrust curves for the fish's tail fin at a 1 Hz oscillation frequency, corresponding to three oscillation amplitudes of 28°, 70°, and 112°. As can be seen from the figure, the overall thrust level is relatively high in the large upstream face state before deformation. After the morphological switching is completed through the coordinated action of the lock-shaped unit and the driving deformation unit, the upstream face decreases. Under the same frequency and amplitude conditions, the instantaneous peak thrust and average thrust decrease to varying degrees in each operating condition, and the greater the oscillation amplitude, the more significant the thrust difference.

Claims

1. A robotic fish with a variable tail fin configuration, characterized by: a spiral-shaped artificial muscle and a shape memory polymer working together to drive and lock the tail fin, wherein: The system includes a main body structure (100) of a robotic fish, a rope-driven tail fin drive system (200) and an adaptive variable configuration tail fin unit (300); the main body structure (100) of the robotic fish is fixedly connected to the front end of the rope-driven tail fin drive system (200) by bolts, and the rear end of the rope-driven tail fin drive system (200) is fixedly connected to the adaptive variable configuration tail fin unit (300) by adhesive bonding.

2. The spiral-shaped artificial muscle and shape memory polymer synergistically driven-locked variable tail fin robotic fish according to claim 1, characterized in that: The main structure (100) of the robotic fish includes an outer shell and an internal system. The internal system is located inside the outer shell. The outer shell adopts a biomimetic shape design of the bluefin tuna. The surface of the outer shell is integrated with a dorsal fin, pelvic fin, and movable pectoral fin. The main internal system includes a lithium battery (110), an electronic control system (120), a drive servo system (130), and a water pressure sensor (140); the discharge cable of the lithium battery (110) is connected to the input terminal of the electronic control system (120), and the charging cable of the lithium battery (110) is connected to a spring pin connector; the output terminal of the electronic control system (120) is electrically connected to the input terminal of the drive servo system (130), and the output terminal of the drive servo system (130) is connected to the rope-driven tail fin drive system (200); the water pressure sensor (140) is electrically connected to the electronic control system (120).

3. The variable tail fin configuration robotic fish according to claim 2, characterized in that: The electronic control system (120) is a three-layer stacked control circuit board structure, including a LoRa wireless communication board, a main control unit board, and a power drive board arranged sequentially from top to bottom. The circuit boards are electrically connected to each other via board-to-board connectors. The discharge cable of the lithium battery (110) is electrically connected to the input terminal of the power drive board. The output terminal of the power drive board is electrically connected to the input terminal of the LoRa wireless communication board via connectors. The output terminal of the LoRa wireless communication board is electrically connected to the input terminal of the main control unit board. The drive servo system... (130) includes three servo motors. The first servo motor and the second servo motor are respectively arranged on both sides of the electronic control system (120). The third servo motor is arranged at the rear of the electronic control system (120). The third servo motor is connected to the rope-driven tail fin drive system (200) through the servo disk arranged on its output shaft. Each servo motor is connected to the main control unit board and the power drive board of the electronic control system (120). The water pressure sensor (140) is connected to the main control unit board of the electronic control system (120). The fish body central mode generator is installed on the main control unit board.

4. The variable tail fin configuration robotic fish according to claim 1, characterized in that: The compliant variable configuration caudal fin unit (300) includes a caudal fin skeleton (310), two lock-shaped units (320), two drive variable configuration units (330), and a caudal fin skin (340). The front part of the caudal fin skeleton (310) is connected to the rear end of the rope-driven caudal fin drive system (200). The upper and lower rear ends of the caudal fin skeleton (310) are respectively fixedly connected to one of the locking units (320) by adhesive bonding. The two locking units (320) are arranged symmetrically from top to bottom. Each locking unit (320) has a drive variant unit (330) on one side. The caudal fin skeleton (310), the two locking units (320) and the two drive variant units (330) together constitute the internal structure of the caudal fin. The caudal fin skin (340) covers the outside of the internal structure of the caudal fin. The caudal fin skin (340) is connected to the rear end of the rope-driven caudal fin drive system (200).

5. A variable tail fin configuration robotic fish with a helical artificial muscle and shape memory polymer synergistically driven and locked, as described in claim 2 or 4, characterized in that: The rope-driven tail fin drive system (200) includes two spring plates (210), a skeleton unit (230), and a drive rope (220). The outer shell of the main body structure (100) of the robotic fish and the tail fin skin (340) are connected by the two spring plates (210). The two spring plates (210) are respectively set at the upper and lower parts of the rope-driven tail fin drive system (200). The skeleton unit (230) is set between the two spring plates (210). The skeleton unit (230) includes a plurality of skeleton discs. The plurality of skeleton discs are arranged at intervals along the axial direction of the rope-driven tail fin drive system (200). The skeleton discs are connected by pins. The first skeleton disc along the direction of the robotic fish's swimming is fixedly connected to the outer shell of the main structure (100) of the robotic fish, and the last skeleton disc is fixedly connected to the tail fin skin (340). The front end of each spring plate (210) is fixedly connected to the first skeleton disc, and the rear end of each spring plate (210) is fixedly connected to the last skeleton disc. The skeleton disc (230) is provided with a guide hole. One end of the drive rope (220) is wound around the rudder disc of the third rudder output shaft of the drive servo system (130), and the other end of the drive rope (220) passes through the guide hole and is connected to the last skeleton disc of the skeleton unit (230).

6. The spiral-shaped artificial muscle and shape memory polymer synergistically driven-locked variable tail fin robotic fish according to claim 5, characterized in that: The tail fin skeleton (310) has a hollow part. The output cable of the power drive board in the electronic control system (120) is led out through the guide hole and the hollow part in sequence and connected to the lock-shaped unit (320).

7. The spiral-shaped artificial muscle and shape memory polymer synergistically driven-locked variable tail fin robotic fish according to claim 4, characterized in that: The drive-modulation unit (330) is a spiral artificial muscle, which is mainly made of polyamide fiber and nickel wire wound together. The drive-modulation unit (330) generates axial contraction after being heated. The locking unit (320) is a shape memory polymer, which is made by mixing and curing epoxy resin and amine curing agent at a mass ratio of 59:

41. At 30-80℃, the locking unit (320) transitions from stiffness to flexibility. The caudal fin skin (340) is made of flexible silicone material with a Shore hardness of 5, and the caudal fin skeleton (310) is made of acrylonitrile butadiene styrene copolymer material.

8. An adaptive swimming method for a variable tail fin configuration robotic fish synergistically driven and locked by a spiral artificial muscle and a shape memory polymer as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Start the robotic fish into acceleration mode. The central mode generator of the fish body generates a rhythmic signal of the first frequency, which drives the compliant variable configuration tail fin unit (300) to swing. At the same time, the main control unit board controls the locking unit (320) to maintain the first state, and the compliant variable configuration tail fin unit (300) is in the first frontal surface shape. S2. When the main control unit board receives the cruise command, the main control unit board controls the locking unit (320) to change to the second state, and then powers on the drive variable configuration unit (330) and causes it to retract, driving the adaptive variable configuration tail fin unit (300) to switch from the first frontal surface form to the second frontal surface form, and then locks the second frontal surface form; S3. Subsequently, the fish body central mode generator switches to a second frequency rhythm signal to drive the compliant variable configuration tail fin unit (300) to swing. S4. When the main control unit board receives the acceleration command again, it cancels the cruise mode. The main control unit board controls the locking unit (320) to change state again, drives the adaptive variable configuration tail fin unit (300) to return to the first frontal surface shape and lock it. At the same time, the fish body central mode generator switches back to the rhythm signal of the first frequency.

9. The adaptive swimming method according to claim 8, characterized in that: Step S2 specifically involves: S21. When the main control unit board receives the cruise command, the main control unit board heats the lock-shaped unit (320) to make it compliant. S22. Subsequently, the drive variable configuration unit (330) is electrically heated to cause it to contract and drive the compliant variable configuration tail fin unit (300) to switch from the first frontal surface shape to the second frontal surface shape. S23, then stop heating the drive variant unit (330) and cool it down, finally the compliant variable configuration tail fin unit (300) locks the second frontal surface shape, and then stop power supply to the drive variant unit (330).

10. The adaptive navigation method according to claim 8, characterized in that: Step S4 specifically involves: S41. When the main control unit board receives the acceleration command again, the cruise mode is deactivated. The main control unit board heats the lock-shaped unit (320) to make it compliant. The shape memory effect of the lock-shaped unit (320) drives the compliant variable configuration tail fin unit (300) to restore the first frontal surface shape. S42, then stop driving the variable configuration unit (330) and cool it down. Finally, the adaptive variable configuration tail fin unit (300) locks the first frontal surface morphology, while the fish body central mode generator switches back to the rhythm signal of the first frequency.

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