A biomimetic robotic fish with amphibious capabilities and its control method

Abstract

This invention discloses a biomimetic robotic fish with amphibious capabilities and its control method, belonging to the field of robotics technology. The robotic fish comprises an unsealed head assembly, a fully sealed body assembly, and a flexible tail assembly. Symmetrically positioned on both sides of the head assembly are dual pectoral fins controlled by independent waterproof bus servos. The body assembly integrates a microcontroller, a brushless DC motor, and a reel. In underwater maneuvering mode, the microcontroller controls the brushless DC motor to pull the flexible tail assembly through a transmission rope to provide axial thrust, while independently adjusting the fluid angle of attack of the dual pectoral fins to generate lift or sinking, achieving three-dimensional spatial maneuvering. In amphibious crawling mode, the dual pectoral fins serve as mechanical support limbs, propelling the body forward through periodic contact with the ground. This invention overcomes the limitations of traditional robotic fish that rely on water buoyancy and two-dimensional planar movement, achieving continuous operation and three-dimensional attitude control across various media environments.

Description

Technical Field

[0001] This invention relates to the field of underwater biomimetic robot technology, specifically to a biomimetic robotic fish with amphibious capabilities and its control method. Background Technology

[0002] With the increasing demand for near-shore exploration, aquatic environment monitoring, and tidal flat ecological surveys, biomimetic robotic fish have become an important research direction in the field of underwater biomimetic robots due to their advantages such as high stealth, minimal environmental disturbance, and high swimming efficiency. However, in complex and ever-changing actual operating scenarios, existing biomimetic robotic fish still have significant technical limitations in terms of amphibious adaptability, propulsion efficiency, and waterproof reliability, mainly reflected in the following aspects:

[0003] First, they lack amphibious mobility across media. Most existing biomimetic robotic fish are designed for single deep-water environments, relying entirely on buoyancy and hydrodynamics. When performing tasks such as coastline patrols, tidal flat exploration, or shallow-water operations, traditional robotic fish completely lose their mobility upon encountering extremely shallow water or becoming stranded, due to the loss of hydrodynamic support. This severely limits the breadth of their applications and their ability to operate continuously across media.

[0004] Secondly, the main propulsion system suffers from frequency and efficiency bottlenecks. Traditional multi-jointed robotic fish widely use servo motors to directly drive the tail fin's oscillation. Limited by the mechanical inertia and response speed of the reduction gears inside the servo motor, the tail fin's oscillation frequency is usually limited to a low range (typically less than 3.5Hz). When facing complex water currents or requiring instantaneous bursts of thrust, low-frequency oscillation often leads to insufficient thrust and slow swimming speed, and high-frequency forced drive can easily cause severe motor overheating and overload damage. Meanwhile, existing bionic robotic fish using rope-driven propulsion generally suffer from two major defects: first, the waterproof sealing performance at the cable threading point is insufficient, allowing water to easily flow back into the sealed cavity of the machine body through the threading holes, causing damage to internal electrical components and seriously affecting the underwater working stability and service life of the robotic fish; second, the technical pain points of low drive frequency and slow swimming speed have not yet been resolved, failing to meet the requirements of high-speed operation.

[0005] In summary, existing biomimetic robotic fish still face significant technical bottlenecks in terms of adaptability across land and water, core propulsion efficiency, and waterproof reliability. Therefore, there is an urgent need to develop a biomimetic robotic fish that combines efficient main propulsion, amphibious crawling capabilities, and highly reliable waterproof performance to meet the operational needs of complex waters and border areas. Summary of the Invention

[0006] To address the shortcomings of existing biomimetic robotic fish in terms of amphibious adaptability, main propulsion efficiency, and waterproof reliability, this invention provides a biomimetic robotic fish with amphibious capabilities and its control method.

[0007] The technical solution adopted in this invention is as follows:

[0008] A biomimetic robotic fish with amphibious capabilities includes: a head assembly, which is a non-sealed frame structure; a dual pectoral fin drive system symmetrically arranged on both sides of the head assembly, including a left waterproof bus servo, a right waterproof bus servo, and left and right pectoral fins respectively connected to the output shafts of the left and right waterproof bus servos; a body assembly connected to the rear end of the head assembly, forming a completely sealed cavity; a control and power system fixedly disposed within the sealed cavity, including a battery pack, a microcontroller, an electronic speed controller, a brushless DC motor, and a wireless communication module; the microcontroller is electrically connected to the brushless DC motor via the electronic speed controller; a flexible tail drive system including a rope traction mechanism, a transmission rope, a waterproof sleeve, and a flexible tail assembly; the rope traction mechanism includes a circular winding reel fixedly mounted on the output shaft of the brushless DC motor; the root of the flexible tail assembly is fixedly connected to the rear end of the body assembly, and its end is a free-swinging end; the waterproof sleeve covers the body assembly. The area where the component connects to the flexible tail assembly is sealed with a pressure seal to achieve waterproof isolation, preventing water from flowing back into the fish body assembly through the threading holes of the transmission rope. The transmission rope is a continuous flexible cable, with its middle section wound and fixed in the groove of the circular winding reel. Its two ends serve as the left and right drive cables, respectively, and are pre-wound tightly around the circular winding reel in opposite directions. It is symmetrically arranged along the length of the flexible tail assembly through the sealed receiving cavity and anchored to corresponding anchor points on both sides of the end of the flexible tail assembly, forming a closed-loop cable drive structure. The forward and reverse rotation of the brushless DC motor drives the circular winding reel to synchronously wind and unwind the left and right drive cables, thereby pulling the flexible tail assembly to produce planar alternating oscillation. The microcontroller is configured to coordinate and control the motion phase of the dual pectoral fin drive system and the oscillation frequency and thrust vector of the flexible tail drive system to realize multi-degree-of-freedom swimming in the underwater environment and amphibious crawling in the terrestrial environment.

[0009] Furthermore, in the underwater swimming mode, the microcontroller controls the brushless DC motor to reciprocate, and the flexible tail assembly is pulled by the transmission rope to generate axial thrust; at the same time, the deflection angles of the left and right waterproof bus servos are independently adjusted to change the hydrodynamic angle of attack of the left and right pectoral fins, and the lift or sinking force is generated by the hydrodynamic effect to realize the pitch attitude adjustment and surfacing and diving of the robotic fish.

[0010] Furthermore, in the terrestrial amphibious crawling mode, the microcontroller controls the brushless DC motor to stop or enter a low-frequency idling state, and controls the left and right waterproof bus servos to perform continuous rotational movements in the same direction or alternately, driving the left and right pectoral fins to periodically contact the ground to generate support force and forward thrust, thereby realizing the terrestrial crawling movement of the body.

[0011] Furthermore, the rope traction mechanism includes a circular winding reel, and the transmission rope includes a left drive rope and a right drive rope, which are pre-wound onto the circular winding reel in opposite directions; the flexible tail assembly is integrally molded from a flexible polymer material, which is any one of thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE), polyether block amide (PEBA), or thermoplastic copolyester (TPC), and its outer geometric contour is generated based on a logarithmic spiral parametric equation, and its end is connected to a tail fin.

[0012] The present invention proposes an amphibious collaborative control method based on the above-mentioned biomimetic robotic fish, which includes the following steps: Step S1: Obtain the target motion command and determine whether the current task environment is an underwater environment or a terrestrial environment;

[0013] Step S2: When it is determined that the environment is underwater and three-dimensional swimming needs to be performed, a differential or unidirectional deflection signal is output to the dual pectoral fin drive system to change the fluid angle of attack. At the same time, a high-frequency PWM drive signal is output to the brushless DC motor to drive the flexible tail assembly to generate axial thrust. The space maneuver is completed through the active hydrodynamic coupling of the dual systems.

[0014] Step S3: When the environment is determined to be terrestrial and amphibious crawling is required, a continuous rotation signal is output to the dual pectoral fin drive system, using the mechanical rigidity of the pectoral fins as supporting legs to drive the body forward.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] Firstly, it endows the robotic fish with amphibious mobility. This invention overcomes the limitation of traditional biomimetic robotic fish that rely entirely on water buoyancy. By configuring the dual pectoral fin drive system as an independent actuator capable of continuous omnidirectional rotation, the pectoral fins on both sides can act as auxiliary support limbs in terrestrial or extremely shallow tidal flat environments, periodically contacting the ground to generate frictional thrust. This design overcomes the defect of traditional robotic fish losing mobility once out of water, effectively expanding the device's operating range in complex, intersecting terrains.

[0017] Secondly, it enhances the dynamic maneuverability in underwater three-dimensional space. Unlike traditional variable buoyancy chambers or center of gravity adjustment mechanisms that rely on slow ascent and descent by altering static balance, this invention utilizes waterproof bus servos to directly change the hydrodynamic angle of attack of the pectoral fins on both sides. With the flexible tail assembly providing high-speed axial propulsion, the pectoral fins, similar to underwater wing surfaces, can quickly generate positive or negative hydrodynamic lift, enabling rapid response to the aircraft's pitch attitude and flexible ascent and descent operations.

[0018] Thirdly, it overcomes the bottleneck of tail propulsion frequency, improving power efficiency. The main propulsion system of the robotic fish abandons the low-frequency direct servo motor oscillation mode and adopts a cable-driven architecture with a brushless DC motor and a circular wound wheel. This architecture utilizes the low-pass filtering effect to smoothly convert the high speed of the brushless motor into high-frequency (10Hz to 12Hz) alternating oscillation of the flexible tail component. Compared with the traditional structure, it significantly improves the Strouhal number of biomimetic swimming, thereby enhancing the propulsion force of the system.

[0019] Fourth, the system's environmental tolerance is improved through a dry-wet separation architecture. The entire unit adopts a physical isolation design between an unsealed head (wet compartment) and a completely sealed body (dry compartment). The core control circuits, power supply, and brushless motors are completely isolated within the dry compartment; while the waterproof bus servos responsible for amphibious crawling and attitude control, as well as the fully flexible tail assembly without electronic components, are directly placed in the external water environment. This design significantly reduces the number of dynamically sealed components, lowers the risk of water leakage and short circuits under high-pressure water conditions, and improves the long-term reliability of the system. Attached Figure Description

[0020] Figure 1 This is a three-dimensional view of the overall appearance of the biomimetic robotic fish provided in an embodiment of the present invention;

[0021] Figure 2 This is an exploded view of the internal structure of the biomimetic robotic fish provided in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the structure of the flexible tail assembly provided in an embodiment of the present invention;

[0023] Figure 4 This is a partial top view of the rope traction mechanism and winding method provided in an embodiment of the present invention.

[0024] Explanation of reference numerals in the attached diagram: 10-Fish head assembly; 11-Waterproof bus servo; 12-Pectoral fin; 20-Fish body assembly; 21-Sealed cavity; 22-Battery pack; 23-Microcontroller; 24-Electronic speed controller; 25-Brushless DC motor; 26-Circular reel; 27-Wireless communication module; 28-Waterproof sleeve; 30-Flexible tail assembly; 31-Tail fin; 32-End anchor point; 40-Drive rope; 41-Left drive rope; 42-Right drive rope. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] Regarding the overall architecture and cabin layout: (as follows) Figure 1 and Figure 2 As shown in the exploded view, this invention adopts a "dry and wet separation" architectural design, comprising, from front to back, a fish head assembly 10, a fish body assembly 20, and a flexible tail assembly 30. The fish head assembly 10 is a non-sealed frame or semi-open structure (wet chamber). A dual pectoral fin drive system is symmetrically installed inside, namely a left-side waterproof bus servo motor 11 and a right-side waterproof bus servo motor 11. The output shafts of the left and right waterproof bus servo motors 11 are respectively connected to the left and right pectoral fins 12. The fish body assembly 20 contains a completely waterproof sealed cavity 21 (dry chamber), which is sealed by mechanical fasteners and waterproof adhesive at the shell joint surfaces, physically isolating the aquatic environment from the core electronic components.

[0027] Regarding the internal integration of control and power systems: combining Figure 2 As shown, a battery pack 22, an electronic speed controller 24, a microcontroller 23 serving as the core control unit, a brushless DC motor 25, and a wireless communication module 27 are installed within the sealed cavity 21. The control cables of the left and right waterproof bus servos 11 in the non-sealed area are introduced into the sealed cavity 21 through water-permeable connectors and electrically connected to the microcontroller 23.

[0028] Regarding the flexible tail drive mechanism: such as Figure 2 and Figure 4 As shown, a circular winding reel 26 is rigidly connected to the output shaft of the brushless DC motor 25. The transmission rope 40 is a continuous high-strength cable, with its middle section wound several times around the circular winding reel 26. Its two rearward-extending ends form a left drive cable 41 and a right drive cable 42, respectively. The left drive cable 41 and the right drive cable 42 pass through the internal guide channel of the flexible tail assembly 30 and are anchored to the two end anchor points 32 near the tail fin 31. Figure 3 The flexible tail assembly 30 is integrally formed using 3D printing from thermoplastic polyurethane elastomer (such as TPU) material, and its end is connected to a tail fin 31 for propulsion. The outer geometric contour of the flexible tail assembly 30 is generated based on a logarithmic spiral parametric equation. To prevent water from flowing back through the threading holes of the transmission rope, a waterproof sleeve 28 is wrapped around the area where the flexible tail assembly 30 and the fish body assembly 20 are joined.

[0029] Regarding the multimodal cooperative control method: In this embodiment of the robotic fish, the microcontroller 23 receives external environmental commands through the wireless communication module 27 and cooperatively controls the dual pectoral fin drive system and the flexible tail drive system to achieve the following two working modes:

[0030] 1. Underwater Three-Dimensional Swimming Mode: When in an underwater environment, the microcontroller 23 outputs a high-frequency PWM signal to the electronic speed controller 24, driving the brushless DC motor 25 to reciprocate within a frequency range of 1Hz to 12Hz. The alternating rotation of the circular winding reel 26 releases and retracts the left drive cable 41 and the right drive cable 42, causing the flexible tail assembly 30 to undergo continuous bending deformation, thereby driving the tail fin 31 to generate axial propulsion. Simultaneously, to achieve three-dimensional maneuvering, the microcontroller 23 independently sends deflection signals to the left and right waterproof bus servos 11. The left and right waterproof bus servos 11 drive the left and right pectoral fins 12 to change their hydrodynamic angle of attack. When the pectoral fin 12 is at a positive angle of attack, the passing water creates a pressure difference on the upper and lower surfaces of the pectoral fin, generating upward lift and driving the robotic fish to float. When the pectoral fin 12 is at a negative angle of attack, it generates downward sinking force, driving the robotic fish to dive. By combining the differential deflection of the left and right pectoral fins 12 with the thrust vector of the tail fin, a rolling torque can be generated or pitch and yaw maneuvers with a very small radius can be achieved.

[0031] 2. Terrestrial Amphibious Reptile Mode: When the robotic fish is in a shallow or land-based environment, the microcontroller 23 controls the brushless DC motor 25 to stop operating (or to idle at an extremely low frequency to coordinate with the body's twisting motion and reduce system power consumption). At this time, the motion control is switched to the dual pectoral fin drive system. The microcontroller 23 sends mode switching and control commands to the left and right waterproof bus servos 11, switching them from a position closed-loop control mode to a speed closed-loop continuous rotation mode. The waterproof bus servos 11 output continuous unidirectional rotation or large-angle periodic reciprocating oscillation. The left and right pectoral fins 12 serve as mechanical support limbs, periodically contacting the ground during rotation / oscillation. Utilizing the mechanical structural rigidity of the pectoral fins 12 and the friction with the ground as supporting reaction forces, the body is directly driven to crawl forward on the terrestrial base. This mode breaks through the limitation of traditional robotic fish relying entirely on hydrodynamic propulsion. Based on the above-mentioned underwater and land crawling modes, the specific implementation of the present invention fully verifies the reliability of the dry-wet separation architecture, as well as the high propulsion efficiency and three-dimensional maneuverability advantages brought about by the coordinated control of brushless cable drive and bus servo motor.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A biomimetic robotic fish with amphibious capabilities, characterized in that, It includes a fish head assembly (10), a dual pectoral fin drive system, a fish body assembly (20), a control and power system, and a flexible tail drive system; The fish head assembly (10) is a non-sealed frame structure; The dual pectoral fin drive system is symmetrically arranged on both sides of the fish head assembly (10), including a left waterproof bus servo (11), a right waterproof bus servo (11), and a left pectoral fin (12) connected to the output shaft of the left waterproof bus servo and a right pectoral fin (12) connected to the output shaft of the right waterproof bus servo; the left waterproof bus servo (11) and the right waterproof bus servo (11) can independently control the pitch angle adjustment and circumferential rotation of the corresponding pectoral fins, realizing independent dual-degree-of-freedom drive; The front end of the fish body assembly (20) is sealed to the rear end of the fish head assembly (10), and a sealed receiving cavity (21) is formed inside it; the rear end wall of the sealed receiving cavity (21) is provided with an output port for the transmission rope (40) to pass through, and a waterproof dynamic sealing assembly is fixedly installed at the output port. The control and power system is fixedly installed in the sealed cavity (21) and includes a battery pack (22), a microcontroller (23), an electronic speed controller (24), a brushless DC motor (25), and a wireless communication module (27); the microcontroller (23) is electrically connected to the brushless DC motor (25) via the electronic speed controller (24); the flexible tail drive system includes a rope traction mechanism, a transmission rope (40), a waterproof sleeve (28), and a flexible tail assembly (30); The rope traction mechanism includes a circular winding wheel (26) fixedly mounted on the output shaft of the brushless DC motor (25); The base of the flexible tail assembly (30) is fixedly connected to the rear end of the fish body assembly (20), and its end is a free swinging end; The waterproof sleeve (28) is wrapped around the outside of the joint area between the fish body component (20) and the flexible tail component (30). The waterproof sleeve (28) achieves waterproof isolation by compression and sealing, and is used to prevent water from flowing back into the fish body component (20) along the threading hole of the transmission rope (40). The transmission rope (40) is a continuous flexible rope, the middle of which is wound and fixed in the groove of the circular winding wheel (26), and its two ends serve as the left drive rope (41) and the right drive rope (42) respectively. The left drive rope (41) and the right drive rope (42) are pre-wound tightly on the circular winding wheel (26) in opposite directions. After passing through the waterproof dynamic sealing assembly and exiting the sealing cavity (21), they are symmetrically arranged along the length direction of the flexible tail assembly (30) and anchored to the corresponding anchor points on both sides of the end of the flexible tail assembly (30) to form a closed-loop cable drive structure. The forward and reverse rotation of the brushless DC motor (25) drives the circular winding wheel (26) to simultaneously wind and unwind the left drive cable (41) and the right drive cable (42), thereby pulling the flexible tail assembly (30) to generate planar alternating oscillation. The microcontroller (23) is configured to: achieve multi-degree-of-freedom swimming of the robotic fish in the underwater environment and amphibious crawling in the terrestrial environment by coordinating the motion phase of the dual pectoral fin drive system with the swing frequency and thrust vector of the flexible tail drive system.

2. The biomimetic robotic fish with amphibious capabilities according to claim 1, characterized in that, In the swimming mode of the underwater environment, the microcontroller (23) controls the brushless DC motor (25) to reciprocate through the electronic speed controller (24), and pulls the flexible tail assembly (30) to swing at high frequency through the transmission rope (40) to generate axial propulsion. At the same time, the deflection angles of the left waterproof bus servo (11) and the right waterproof bus servo (11) are independently adjusted, and the fluid angle of attack of the left pectoral fin (12) and the right pectoral fin (12) are synchronously adjusted to realize the pitch attitude adjustment and surfacing and diving of the robot fish, or the difference in fluid angle of attack between the two is differentially adjusted to realize the turning maneuver of the robot fish.

3. The biomimetic robotic fish with amphibious capabilities according to claim 1, characterized in that, In the amphibious crawling mode in the terrestrial environment, the microcontroller (23) controls the brushless DC motor (25) to stop output or reduce the oscillation output frequency through the electronic speed controller (24), so that the flexible tail assembly (30) remains stationary or oscillates slightly; at the same time, it controls the left waterproof bus servo (11) and the right waterproof bus servo (11) to rotate in the same direction or alternately, driving the left pectoral fin (12) and the right pectoral fin (12) to periodically contact the ground to generate support force and forward thrust, so as to realize the land crawling of the robotic fish.

4. The biomimetic robotic fish with amphibious capabilities according to claim 1, characterized in that, The outer geometric contour of the flexible tail assembly (30) is generated based on the logarithmic spiral parametric equation; the left drive cable (41) and the right drive cable (42) of the transmission rope (40) are anchored to the corresponding anchor points at the end of the flexible tail assembly (30) with a preset preload force to ensure the transmission accuracy and response speed of the cable drive structure.

5. The biomimetic robotic fish with amphibious capabilities according to any one of claims 1 to 4, characterized in that, The flexible tail assembly (30) is integrally molded from a flexible polymer material, which is any one of the following four types: (1) Thermoplastic polyurethane (TPU) with a Shore A hardness of 75A-95A is integrally processed using FDM (Fused Deposition Modeling) process; (2) Thermoplastic elastomer (TPE) with a Shore A hardness of 50A-80A is integrally processed using FDM (Fused Deposition Modeling) process; (3) Polyether block amide PEBA is integrally formed by SLS selective laser sintering or FDM fused deposition modeling. (4) Thermoplastic copolyester (TPC) with Shore A hardness of 30A-70A is integrally processed by FDM melt deposition molding process.

6. The biomimetic robotic fish with amphibious capabilities according to any one of claims 1 to 5, characterized in that, The waterproof sleeve (28) is integrally formed by casting silicone material through a mold. The Shore A hardness of the silicone is 10A-50A.

7. A collaborative control method for a biomimetic robotic fish with amphibious capabilities, characterized in that, The method is implemented based on the biomimetic robotic fish with amphibious capabilities as described in any one of claims 1 to 6, and includes the following steps: Step S1: The microcontroller (23) obtains the target motion command sent by the host computer and determines whether the working environment corresponding to the current task is an underwater environment or a land environment; Step S2: When it is determined that the environment is underwater and three-dimensional swimming is required, the microcontroller (23) analyzes the target motion command and outputs a unidirectional deflection signal to the dual pectoral fin drive system to synchronously adjust the fluid angle of attack of the left pectoral fin (12) and the right pectoral fin (12), or outputs a differential deflection signal to adjust the angle of attack difference between the left and right pectoral fins; at the same time, it outputs a high-frequency PWM control signal to the electronic speed controller (24) to control the brushless DC motor (25) to reciprocate, and then pulls the flexible tail assembly (30) through the transmission rope to generate axial propulsion alternating oscillation; through the hydrodynamic coupling of the dual pectoral fin drive system and the flexible tail drive system, the underwater space maneuver of the robotic fish is completed; Step S3: When it is determined that the environment is terrestrial and amphibious crawling is required, the microcontroller (23) controls the brushless DC motor (25) to stop output or reduce the output frequency, so that the flexible tail assembly (30) remains stationary or swings slightly; at the same time, it outputs a continuous rotation signal to the dual pectoral fin drive system, using the structural rigidity of the left pectoral fin (12) and the right pectoral fin (12) as supporting feet, and drives the body forward through periodic actions of synchronous rotation in the same direction or alternating rotation.

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