A shape memory alloy control based amphibious variable stiffness fin

Abstract

This invention relates to an amphibious variable stiffness fin controlled by shape memory alloy, comprising: a pectoral fin root mounting base, a rotatable coaxial center, a fixed boundary main fan bone, an intermediate driven fan bone, a driving boundary main fan bone, a flexible film, an arc-shaped groove, a cylindrical slider, a first baffle, and a second baffle. The fixed boundary main fan bone is fixed to the rotatable coaxial center, and the driving boundary main fan bone rotates around the rotatable coaxial center. The intermediate driven fan bone is located between the fixed boundary main fan bone and the driving boundary main fan bone, and is mounted on the pectoral fin root mounting base via the rotatable coaxial center. The arc-shaped groove is mounted on the pectoral fin root mounting base with the coaxial center as its center. The root driving part of the driving boundary main fan bone is rigidly connected to the cylindrical slider. The first baffle and the second baffle are located on both sides of the arc-shaped groove. Compared with the prior art, this invention has the advantages of simple control logic and better adaptability to water-land transition conditions.

Description

Technical Field

[0001] This invention relates to the fields of biomimetic robots, underwater robots and amphibious robots, and in particular to an amphibious variable stiffness fin controlled by shape memory alloy. Background Technology

[0002] This invention relates to the fields of biomimetic robots, underwater robots, and amphibious robots, and particularly to a fan-shaped variable stiffness pectoral fin for an amphibious robotic fish and its control method. Specifically, it relates to a fin structure and control method that utilizes a fan-shaped fan bone, a flexible film driven unfolding structure, and a root arc-shaped sliding groove station switching mechanism to achieve switching between unfolded, semi-unfolded, and folded states.

[0003] The background technology should describe its current state and shortcomings. For inventions involving devices or structures, a written description can be provided, along with accompanying drawings, briefly introducing its working principle and detailing its disadvantages. If a patent search has been conducted, please cite relevant literature and its detailed sources.

[0004] With the development of underwater robots, biomimetic robotic fish, and amphibious robots, fish fin structures are not only responsible for underwater propulsion, attitude adjustment, and steering, but are also gradually being endowed with functions such as support, paddling, and rocking in transitional water-land environments. Therefore, whether the pectoral fins can achieve stiffness adjustment and configuration switching under different working conditions has become an important technical issue for improving the environmental adaptability of amphibious robotic fish.

[0005] Most existing fish fin structures are of fixed stiffness, with their fin surface area and skeletal structure remaining largely unchanged during operation. While such structures can meet basic paddling requirements in purely underwater propulsion scenarios, in environments transitioning between shore, shallow waters, mudflats, and land, the fixed large fin surface area leads to increased drag and significant bottom interference. Conversely, the fixed folding structure cannot provide sufficient effective area in the water, making it difficult to simultaneously meet the dual functional requirements of underwater propulsion and land support.

[0006] To address the aforementioned issues, some existing solutions employ servo motors, electric motors, hydraulic actuators, or shape memory alloy drive devices, in conjunction with linkages, locking components, or synchronous deployment mechanisms, to control the folding and unfolding of the fins. However, these existing solutions generally suffer from the following drawbacks: The root mechanism is complex and difficult to miniaturize. Especially when the space at the base of the pectoral fin is limited, using multi-link, locking claw, synchronous deployment mechanism or gear transmission mechanism can easily lead to structural crowding, which is not conducive to the compact integration of the two pectoral fins.

[0007] Continuous angle servo control requires high precision. Some solutions rely on a single actuator to precisely control the unfolding angle of multiple fan ribs, which is quite difficult to control and requires high levels of waterproof sealing, motor feedback, and transmission accuracy in underwater environments.

[0008] The semi-spreading transition mode is unclear. Existing folded fin structures mostly emphasize the two terminal states of "fully spread" and "fully folded", while paying insufficient attention to the intermediate mode of "partially spread and partially folded" which is suitable for amphibious transitional environments, making it difficult to achieve stable three-state switching.

[0009] Traditional claw-type positioning mechanisms have high timing requirements. If a claw slot-type positioning method is used, intermediate stations often rely on instantaneous locking, which is easily affected by drive response speed, material thermal hysteresis, and impact rebound, thus affecting the reliability of mode switching.

[0010] The synchronization control mechanism for the middle fan ribs is complex. For fan-shaped fins, the middle fan ribs typically rely on a flexible membrane and the geometric relationship between adjacent fan ribs to unfold passively. Forcing a complex synchronization mechanism would not only increase manufacturing difficulty but also easily diminish the simplicity of the fan-shaped structure itself.

[0011] Therefore, there is a need for an amphibious variable stiffness pectoral fin structure and its control method that has a clearer structure, a more compact root mechanism, and is suitable for switching between deployed, semi-deployed and folded states in a discrete workstation manner.

[0012] The invention disclosed in CN118877168A is a shape memory alloy-driven biomimetic pectoral fin mechanism with fin-body fusion. Its features include: a fish body, pectoral fin skin, pectoral fin base, wire guide holes, a shape memory alloy actuator assembly for the fin rays, a fin ray assembly, a shape memory alloy spring assembly, and a fin root assembly. The fish body is a partial portion of the fish shell, used only to illustrate the connection method between the pectoral fin and the fish body. The pectoral fin base is installed into a groove on the fish body, the fin roots are all installed into the shaft holes of the pectoral fin base, the fin rays are all bonded to their respective fin roots, the shape memory alloy actuators are bonded to the corresponding fin ray surfaces, the shape memory alloy springs are connected to the corresponding fin roots, and the pectoral fin skin is connected to the pectoral fin base. This invention uses shape memory alloy actuators and shape memory alloy springs to drive the fin rays to bend, thereby controlling the rigid-flexible coupling of the fin surface to achieve movements such as retraction, abduction, curling, bending, and multi-free undulation. The pectoral fin base is connected to a groove on the surface of the fish body, eliminating the seam between the pectoral fin root and the fish body, thus exhibiting fin-body fusion characteristics and increasing the thrust of the pectoral fin. However, the device provided by this scheme only emphasizes the design at both ends and cannot meet the actual needs of amphibious transition conditions. Summary of the Invention

[0013] The purpose of this invention is to overcome the defects of the prior art by providing an amphibious variable stiffness fin based on shape memory alloy control, so as to solve the problems in the prior art where the fin structure is difficult to balance underwater propulsion and land support, the root mode switching mechanism is complex, the intermediate mode is unstable, and the continuous angle control is difficult.

[0014] The objective of this invention can be achieved through the following technical solutions: An amphibious variable stiffness fin controlled by shape memory alloy, comprising: The components include: a pectoral fin root mounting base, a rotatable coaxial center, a fixed boundary main fan rib, an intermediate driven fan rib, an intermediate driven fan rib, an intermediate driven fan rib, a driving boundary main fan rib, a flexible film, an arc-shaped slide groove, a cylindrical slider, a first baffle, and a second baffle. The fixed boundary main fan bone is fixed on the rotatable connection coaxial center, and the driving boundary main fan bone rotates around the rotatable connection coaxial center; the intermediate driven fan bone, the intermediate driven fan bone and the intermediate driven fan bone are located between the fixed boundary main fan bone and the driving boundary main fan bone, and are respectively installed on the pectoral fin root mounting seat through the rotatable connection coaxial center; The flexible film is connected to the fixed boundary main fan bone, the intermediate driven fan bone, the intermediate driven fan bone, the intermediate driven fan bone, and the driving boundary main fan bone, respectively; the arc-shaped slide is mounted on the pectoral fin root mounting seat with the rotatable connection coaxial center as the center; the cylindrical slider is located in the arc-shaped slide; the root driving part of the driving boundary main fan bone is rigidly connected to the cylindrical slider; the first baffle and the second baffle are located on both sides of the arc-shaped slide.

[0015] Furthermore, a first shape memory alloy drive component, a second shape memory alloy drive component, a third shape memory alloy drive component, and a fourth shape memory alloy drive component are also installed on the pectoral fin root mounting base; the first shape memory alloy drive component and the second shape memory alloy drive component are respectively connected to the two ends of the arc-shaped slide groove; the third shape memory alloy drive component and the fourth shape memory alloy drive component are located on both sides of the arc-shaped slide groove.

[0016] Furthermore, the arc-shaped slide is sequentially equipped with a first shape memory alloy drive component, a flexible push plate, a first baffle, a third shape memory alloy drive component, a second baffle, a fourth shape memory alloy drive component, a flexible push plate, and a second shape memory alloy drive component from one end to the other.

[0017] Furthermore, the arc-shaped chute is also provided with an unfolded station, a semi-unfolded station, and a folded station; the unfolded station is located between the flexible push plate and the first baffle; the semi-unfolded station is located in the middle of the arc-shaped chute; and the folded station is located between the fourth shape memory alloy drive and the flexible push plate.

[0018] Furthermore, the first shape memory alloy driving component and the second shape memory alloy driving component respectively contact the lower region of the cylindrical slider through a flexible push plate, and are used to push the cylindrical slider along the tangential direction of the arc-shaped groove.

[0019] Furthermore, the third shape memory alloy driver is used to control the first baffle; the fourth shape memory alloy driver controls the second baffle; The areas where the first and second baffles contact the cylindrical slider are complementary curved surface structures.

[0020] Furthermore, when the cylindrical slider is in the semi-expanded position, the distance between each fan bone along the fixed boundary main fan bone to the driving boundary main fan bone gradually decreases, presenting a gradual transition state of partial unfolding and partial folding.

[0021] Furthermore, the cylindrical slider is vertically positioned within the arc-shaped groove; the bottom of the cylindrical slider contacts the bottom surface of the arc-shaped groove and slides along the groove, while the cylindrical slider body does not roll.

[0022] Furthermore, the first and second baffles move up and down in a direction perpendicular to the movement path of the cylindrical slider, which is used to selectively block or allow the cylindrical slider to pass.

[0023] Furthermore, the first and second baffles are in the blocking position when not excited, and descend to the release position when the corresponding third or fourth shape memory alloy driver is excited.

[0024] Compared with the prior art, the present invention has the following advantages: (1) The present invention sets a first baffle and a second baffle on both sides of the arc-shaped slide, and restricts the work station area by releasing and blocking the cylindrical slider through the baffle. The movement range of the slider is thus divided into multiple work station areas. The boundary of each area is determined by the open or closed state of the baffle. The slider stops stably after it comes into contact with the baffle, without relying on instantaneous locking action. For example, when the pectoral fin needs to switch from a fully deployed state to a semi-folded state, the first baffle descends and releases under the drive of the shape memory alloy, releasing the obstruction to the cylindrical slider; the cylindrical slider, rigidly connected to the root of the main fan bone of the drive boundary, moves along the folding direction to the semi-deployed position, while the first baffle resumes its obstruction, keeping the cylindrical slider in the semi-deployed position; when the pectoral fin needs to switch from a semi-folded state to a folded state, the second baffle descends and releases, releasing the obstruction to the cylindrical slider; the cylindrical slider moves along the folding direction to the folded position, while the second baffle resumes its obstruction, keeping the cylindrical slider in the folded position; during the movement of the cylindrical slider, the main fan bone of the drive boundary contracts inward around the coaxial center of the rotatable connection, and through the tension of the flexible film and the geometric constraints between adjacent fan bones, it sequentially drives the intermediate driven fan bones to contract step by step; This completely eliminates the high sensitivity of traditional locking mechanisms to drive response speed, thermal hysteresis time of shape memory alloy materials, and impact rebound, so that there will be no uncertain state of locking failure or semi-locking during mode switching. The switching is smoother, and the ability to resist water flow impact and ground reaction force interference is stronger, which significantly improves the working reliability in amphibious environments.

[0025] (2) The semi-expanded state defined in this invention is not a simple uniformly reduced fan shape, but a gradually transitional shape with the side of the main fan bone near the fixed boundary being more expanded and the side of the main fan bone near the driving boundary being more contracted. The effective expanded area is about half of the fully expanded state according to actual measurements. This asymmetrical gradual configuration is more in line with the actual needs of amphibious transition conditions than the uniformly reduced fan shape: the fixed side retains a larger expanded area to maintain a certain hydrodynamic propulsion efficiency or land surface support stability, while the driving side is significantly contracted to reduce the scraping resistance with the ground, vegetation or gravel when moving on the land surface. At the same time, the reduction in the overall projected area also reduces the lateral impact torque of the water flow, making the attitude of the robotic fish easier to control in shallow water or wave environments. This is an advantage that traditional two-end design cannot provide.

[0026] (3) The present invention adopts a fixed boundary main fan bone and a driving boundary main fan bone to form a folding fan-shaped boundary frame. The intermediate driven fan bone does not have an independent driving mechanism. Instead, it achieves driven unfolding or retraction through a flexible film and the geometric constraint relationship between adjacent fan bones. When the driving boundary main fan bone stops at different discrete work position angles, the entire fin surface presents three stable forms: fully unfolded, half-unfolded, and fully folded. This allows the same pectoral fin to adapt to various amphibious operation scenarios such as efficient propulsion in water, crawling in the water-land transition zone or shallow water propulsion, and passing through narrow environments or low-resistance retraction and carrying without replacement. At the same time, it retains the inherent simplicity, lightweight and low friction characteristics of the folding fan structure, avoiding the complexity and reliability problems caused by designing a separate driving and locking mechanism for each intermediate fan bone.

[0027] (4) In this invention, an arc-shaped groove is set on the mounting seat at the root of the pectoral fin with the rotatable coaxial center as the center. The cylindrical slider is placed in the groove and rigidly connected to the root driving part of the main fan bone of the driving boundary. Since the center of the arc-shaped groove coincides with the rotation center of the fan bone, the working position of the slider in the groove directly and uniquely corresponds to the angular position of the main fan bone of the driving boundary. This driving design avoids the dead point, singular position or nonlinear transmission ratio problems that are unavoidable when converting linear motion into angular motion in the traditional scheme. The angular definition is intuitive and the mechanical repeatability positioning accuracy is high, without the need for complex kinematic calibration. At the same time, the groove itself has a dual function of guiding and limiting the slider, providing a reliable mechanical basis for discrete working position control. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of an amphibious robotic fish in its initial state (deployed state) based on shape memory alloy-controlled amphibious variable stiffness fins, provided in an embodiment of the present invention. Figure 2 This is a front view of the overall structure of an amphibious robotic fish with amphibious variable stiffness fins controlled by shape memory alloy, provided in an embodiment of the present invention. Figure 3This is a left view of the overall structure of an amphibious robotic fish with fins controlled by shape memory alloy, provided in an embodiment of the present invention. Figure 4 This is a top view of the overall structure of an amphibious robotic fish with amphibious variable stiffness fins controlled by shape memory alloy, provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the structure of a single pectoral fin of an amphibious variable stiffness fin controlled by shape memory alloy in a semi-spreading state, provided in an embodiment of the present invention. Figure 6 This is a schematic diagram of the structure of a single pectoral fin of an amphibious variable stiffness fin controlled by shape memory alloy in a folded state, provided in an embodiment of the present invention. Figure 7 This is a main flowchart of a modal switching control method for amphibious variable stiffness fins based on shape memory alloy control provided in an embodiment of the present invention; Figure 8 This is a sub-flowchart of a mode switching of an amphibious variable stiffness fin controlled by shape memory alloy, provided in an embodiment of the present invention. Figure 9 This is a flowchart of a three-modal kinematic control method for amphibious variable stiffness fins based on shape memory alloys, provided in an embodiment of the present invention.

[0029] The reference numerals in the attached figures can preferably be defined as follows: 1-Pectoral fin root mounting base; 2-Rotatably connected coaxial center; 3-B1 Fixed boundary main fan rib; 4-B2 Intermediate driven fan rib; 5-B3 Intermediate driven fan rib; 6-B4 Intermediate driven fan rib; 7-B5 Driving boundary main fan rib; 8-Flexible film; 9-Arc-shaped groove; 10-Cylindrical slider; 11-First baffle; 12-Second baffle; 13-First shape memory alloy driving component (unfolding direction); 14-Second shape memory alloy driving component (folding direction). 15-Third shape memory alloy drive component (first baffle); 16-Fourth shape memory alloy drive component (second baffle); 17-Flexible small push plate; 18-Expanded state station P1; 19-Semi-expanded state station P2; 20-Folded state station P3; 16-Fourth shape memory alloy drive component (second baffle); 17-Flexible small push plate; 18-Expanded state station P1; 19-Semi-expanded state station P2; 20-Folded state station P3. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0032] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0033] Example 1 like Figure 1 As shown, this embodiment provides an amphibious variable stiffness fin controlled by shape memory alloy, comprising: 1. Pectoral fin root mounting base; 2. Rotatably connected coaxial center; 3. Fixed boundary main fan bone; 4. Intermediate driven fan bone; 5. Intermediate driven fan bone; 6. Drive boundary main fan bone; 7. Flexible film; 8. Arc-shaped slide groove; 9. Cylindrical slider; 10. First baffle; 11. Second baffle; 12. The fixed boundary main fan bone 3 is fixed on the rotatable connecting coaxial center 2, and the driving boundary main fan bone 7 rotates around the rotatable connecting coaxial center 2; the intermediate driven fan bone 4, intermediate driven fan bone 5 and intermediate driven fan bone 6 are located between the fixed boundary main fan bone 3 and the driving boundary main fan bone 7, and are respectively installed on the pectoral fin root mounting seat 1 through the rotatable connecting coaxial center 2. The flexible film 8 is connected to the fixed boundary main fan rib 3, the intermediate driven fan rib 4, the intermediate driven fan rib 5, the intermediate driven fan rib 6 and the driving boundary main fan rib 7 respectively; the arc-shaped slide 9 is installed on the pectoral fin root mounting seat 1 with the rotatable connection coaxial center 2 as the center; the cylindrical slider 10 is located in the arc-shaped slide 9; the root driving part of the driving boundary main fan rib 7 is rigidly connected to the cylindrical slider 10; the first baffle 11 and the second baffle 12 are located on both sides of the arc-shaped slide 9.

[0034] Specifically, The pectoral fin root mounting base 1 is also equipped with a first shape memory alloy drive component 13, a second shape memory alloy drive component 14, a third shape memory alloy drive component 15, and a fourth shape memory alloy drive component 16; the first shape memory alloy drive component 13 and the second shape memory alloy drive component 14 are respectively connected to the two ends of the arc-shaped slide groove 9; the third shape memory alloy drive component 15 and the fourth shape memory alloy drive component 16 are located on both sides of the arc-shaped slide groove 9.

[0035] Specifically, The arc-shaped slide 9 is sequentially equipped with a first shape memory alloy drive component 13, a flexible push plate 17, a first baffle 11, a third shape memory alloy drive component 15, a second baffle 12, a fourth shape memory alloy drive component 16, a flexible push plate 17, and a second shape memory alloy drive component 14 from one end to the other.

[0036] Specifically, The arc-shaped chute 9 is also provided with an unfolded station 18, a semi-unfolded station 19, and a folded station 20; the unfolded station 18 is located between the flexible push plate 17 and the first baffle 11; the semi-unfolded station 19 is located in the middle of the arc-shaped chute 9; and the folded station 20 is located between the fourth shape memory alloy drive component 16 and the flexible push plate 17.

[0037] Specifically, like Figures 1 to 6 As shown, the pectoral fins of the present invention are located on both sides of the amphibious robotic fish, with their roots mounted on the pectoral fin root mounting base 1. The pectoral fins adopt a fan-shaped rib structure with a total of five ribs. Among them, the B1 fixed boundary main rib 3 is fixed near the rotatable connecting coaxial center 2, the B5 driving boundary main rib 7 can rotate around the rotatable connecting coaxial center 2, the B2 intermediate driven rib 4, the B3 intermediate driven rib 5, and the B4 intermediate driven rib 6 are located between the B1 fixed boundary main rib 3 and the B5 driving boundary main rib 7, and a flexible membrane 8 connects adjacent ribs.

[0038] Preferably, the non-film structural components of the present invention, such as the pectoral fin root mounting base 1, B1 fixed boundary main fan rib 3, B2 intermediate driven fan rib 4, B3 intermediate driven fan rib 5, B4 intermediate driven fan rib 6, B5 driving boundary main fan rib 7, first baffle 11, second baffle 12, flexible push plate 17, and cylindrical sleeve for accommodating the driving components, are preferably integrally formed or assembled after being formed separately using 3D printing material. Considering the overall structural strength, fatigue performance, wear resistance, and manufacturing consistency, the 3D printing material is preferably PA12 nylon material to balance the stiffness requirements during repeated opening and closing of the pectoral fin and the durability in amphibious environments.

[0039] Specifically, The principles behind pectoral fin deployment include: like Figures 1 to 4As shown, in the unfolded state, the B5 driving boundary main fan bone 7 is positioned relatively far from the B1 fixed boundary main fan bone 3, and the flexible membrane 8 is stretched out between the fan bones, thus forming a larger effective fin surface. The intermediate driven fan bones 4, 5, and 6 are not actively driven by a complex synchronization mechanism, but rather gradually unfold by relying mainly on the tension transmission of the flexible membrane 8 and the geometric relationship between adjacent fan bones, thereby maintaining the simplicity of the folding fan-shaped fin structure.

[0040] Preferably, the flexible film 8 is made of high-toughness thermoplastic polyurethane film (TPU) to ensure flexibility, tear resistance, and flexural strength during repeated folding, flapping, and contact with the ground by the pectoral fins. Compared to ordinary brittle film materials, TPU film is more suitable as a flexible connecting layer between the ribs of the fan-shaped fin, thereby maintaining a stable film transition between the unfolded, semi-unfolded, and folded states.

[0041] The principle of the root mode switching mechanism includes: An arc-shaped groove 9 is provided at the base of the pectoral fin, and the arc-shaped groove 9 is arranged with the coaxial center 2 of rotatable connection as the center. The cylindrical slider 10 is vertically arranged in the arc-shaped groove 9, the bottom of the cylindrical slider 10 contacts the bottom surface of the arc-shaped groove 9 and slides along the arc-shaped groove, and the cylindrical slider 10 body does not roll.

[0042] The cylindrical slider 10 is integrally formed with or rigidly connected to the root driving part of the main fan bone 7 of the B5 driving boundary. Therefore, the position of the cylindrical slider 10 in the arc-shaped groove 9 directly corresponds to the angular position of the main fan bone 7 of the B5 driving boundary. In other words, when the cylindrical slider 10 moves along the arc-shaped groove 9, the main fan bone 7 of the B5 driving boundary simultaneously rotates around the rotatable coaxial center 2, thereby driving the entire pectoral fin to open and close.

[0043] The arc-shaped slide 9 is equipped with an unfolded station P118, a semi-unfolded station P219, and a folded station P320. When the cylindrical slider 10 reaches different stations, B5 drives the boundary main fan bone 7 to the corresponding unfolded, semi-unfolded, or folded position.

[0044] The baffle control principle includes: A first baffle 11 is provided between the unfolded station P118 and the semi-unfolded station P219, and a second baffle 12 is provided between the semi-unfolded station P219 and the folded station P320. The first baffle 11 and the second baffle 12 move up and down in a direction perpendicular to the movement path of the cylindrical slider 10, and are used to selectively block or release the cylindrical slider 10.

[0045] Preferably, the first baffle 11 and the second baffle 12 are in the blocking position when not excited, and descend to the releasing position when the corresponding third shape memory alloy drive 15 or fourth shape memory alloy drive 16 is excited. The area where the baffle contacts the cylindrical slider 10 is preferably provided with a complementary curved surface structure to improve blocking stability and reduce the risk of jamming.

[0046] The driving principle includes: The unfolding direction is driven by a first shape memory alloy drive member 13, and the folding direction is driven by a second shape memory alloy drive member 14. The first shape memory alloy drive member 13 and the second shape memory alloy drive member 14 respectively contact the lower region of the cylindrical slider 10 through a flexible push plate 17, and are used to push the cylindrical slider 10 along the tangential direction of the arc-shaped slide groove 9.

[0047] Preferably, the first shape memory alloy drive component 13, the second shape memory alloy drive component 14, the third shape memory alloy drive component 15, and the fourth shape memory alloy drive component 16 can all adopt shape memory alloy spring structures and are respectively installed in corresponding cylindrical sleeves. The cylindrical sleeves are preferably filled with a low specific heat capacity liquid to improve the heating response speed during energization and to improve the uniformity of heat transfer around the spring. Considering cost, availability, electrical insulation, and low specific heat capacity, the low specific heat capacity liquid is preferably mineral oil, and further preferably industrial white mineral oil or transformer mineral oil. A conductive heating layer or a resistance heating element is provided on the outer wall of the cylindrical sleeve. By energizing the sleeve, the sleeve and the liquid inside are heated, thereby causing the corresponding shape memory alloy spring to contract due to heat and output driving force.

[0048] Since the cylindrical slider 10 in this invention directly corresponds to the corner position of the main fan bone 7 of the B5 driving boundary, the first shape memory alloy driving member 13 and the second shape memory alloy driving member 14 actually correspond to the pectoral fin's unfolding direction driving and folding direction driving, respectively.

[0049] The formation principles of the three modes include: 1. Expanded state like Figures 1 to 4 As shown, when the cylindrical slider 10 is in the unfolded position P118, the B5 driving boundary main fan bone 7 is in a larger unfolding angle position, the flexible film 8 is basically in the unfolded state, and the pectoral fin forms the maximum effective fin surface.

[0050] 2. Semi-expanded state like Figure 5As shown, when the cylindrical slider 10 is in the semi-expanded state position P219, the main fan rib 7 of the B5 driving boundary retracts at a certain angle towards the main fan rib 3 of the B1 fixed boundary. Since the intermediate driven fan ribs 4, 5, and 6 mainly rely on the flexible membrane 8 for drive, the semi-expanded state is not a fan shape where all fan ribs are uniformly reduced, but rather forms a gradual configuration where the side closer to B1 is more expanded and the side closer to B5 is more contracted. In this configuration, the flexible membrane 8 still forms a more obvious working fin surface on the fixed side, while it partially folds on the driving side, thus making the effective unfolded area about half of the unfolded state.

[0051] 3. Folded state like Figure 6 As shown, when the cylindrical slider 10 is in the folded position P320, the main fan bone 7 of the B5 driving boundary obviously converges towards the main fan bone 3 of the B1 fixed boundary, and the intermediate driven fan bones 4, 5, and 6 follow layer by layer. Most of the flexible film 8 is folded, and the entire pectoral fin forms a compact folded bundle structure.

[0052] like Figure 7 As shown, this embodiment also provides a mode switching control method for amphibious variable stiffness fins based on shape memory alloy control, including: The preferred control method of the present invention is to use only binary control of "heating / not heating" for each shape memory alloy drive component.

[0053] like Figure 8 As shown, the process of switching from the unfolded state to the semi-unfolded state is as follows: First, the third shape memory alloy drive component 15 is heated to lower the first baffle 11 for release; then the second shape memory alloy drive component 14 is heated to move the cylindrical slider 10 along the arc-shaped slide 9 in the folding direction to the semi-unfolded state station P219; after the first baffle 11 resumes blocking, the cylindrical slider 10 stops at P2.

[0054] Switching from the semi-expanded state to the folded state: Heating the fourth shape memory alloy drive 16 causes the second baffle 12 to descend and release; then heating the second shape memory alloy drive 14 causes the cylindrical slider 10 to move to the folded state station P320; after the second baffle 12 resumes blocking, the cylindrical slider 10 stays at P3.

[0055] Switching from folded state to semi-expanded state: Heating the fourth shape memory alloy drive 16 to allow the second baffle 12 to pass; then heating the first shape memory alloy drive 13 to move the cylindrical slider 10 in the unfolding direction to the semi-expanded state station P219; after the second baffle 12 resumes blocking, the cylindrical slider 10 stays at P2.

[0056] Switching from the semi-unfolded state to the unfolded state: Heating the third shape memory alloy drive 15 to allow the first baffle 11 to pass; then heating the first shape memory alloy drive 13 to move the cylindrical slider 10 in the unfolding direction to the unfolded state station P118; after the first baffle 11 resumes blocking, the cylindrical slider 10 stays at P1.

[0057] Through the above structure and control method, the present invention achieves stable switching of the pectoral fin between the deployed, semi-deployed and folded states without relying on complex continuous servo control.

[0058] Example 2 This embodiment provides a kinematic analysis and control method for three-modal fish fins, including: To further illustrate the motion patterns and control methods of the pectoral fin in the three modes of unfolded, semi-unfolded, and folded states of this invention, a kinematic model based on a combination of root position switching and intra-modal periodic flapping is established. The pectoral fin of this invention adopts a fan-shaped rib structure, with an arc-shaped groove at the root. A cylindrical slider slides along the arc-shaped groove and is directly associated with the driving part at the root of the main fan rib of the driving boundary, thus ensuring that the position of the cylindrical slider directly corresponds to the angular position of the main fan rib of the driving boundary. Based on this structural feature, the pectoral fin motion can be divided into two parts: configuration switching motion and intra-modal periodic motion.

[0059] 1. Configurational Kinematics Let the radius of the arc-shaped groove be R, the displacement of the cylindrical slider along the arc length of the arc-shaped groove be s, and the rotation angle of the driving boundary main fan bone B5 be θ5, then we have: θ5 = θ 5，0 + s / R Where, θ 5，0 The initial angular position is shown. Since the cylindrical slider is directly connected to the main fan bone of the driving boundary, the position change of the cylindrical slider can be directly mapped to the angular displacement change of the main fan bone of the driving boundary, thereby driving the entire folding fan-shaped fin to complete the opening and closing configuration change. This direct mapping relationship between "slider position and main fan bone angular displacement" is different from traditional multi-link or locking claw positioning mechanisms and is more suitable for discrete mode switching of miniaturized amphibious pectoral fins.

[0060] The arc-shaped chute is equipped with an unfolded station P1, a semi-unfolded station P2, and a folded station P3, which correspond to: θ5 = θ P1 θ5 = θ P2 θ5 = θ P3 , and θ P1 > θ P2 > θ P3 Among them, the unfolded state corresponds to the maximum unfolding angle, the semi-unfolded state corresponds to the intermediate unfolding angle, and the folded state corresponds to the minimum unfolding angle. The intermediate driven fan ribs B2, B3, and B4 achieve driven rotation through flexible film tension transmission and geometric constraints of adjacent fan ribs. Their rotation angles can be expressed as continuous functions of the rotation angle θ5 of the driving boundary main fan rib, i.e.: θ i = f i (θ5), i = 2, 3, 4 This creates a kinematic relationship in which the boundary actively drives the unfolding of the intermediate fan-shaped structure.

[0061] 2. Intramodal periodic kinematics After the discrete modes are determined, the pectoral fin can perform periodic oscillations around its fin root to achieve underwater propulsion, water-land transition support, or low-drag recovery. Let the principal oscillation angle of the pectoral fin be φ. m (t), the pitch angle of the chord is β m (t), then the periodic motion in the m-th mode can be expressed as: φ m (t) = A m sin(2πf m t + φ m ) β m (t) = B m sin(2πf m t + φ m + Δ m ) Among them, A m f is the oscillation amplitude in the m-th mode. m φ is the oscillation frequency. m As the initial phase, B m Δ is the pitch amplitude in the chord direction. m This refers to the pitch phase difference. By coupling the modal configuration with the flapping parameters, the pectoral fins can be configured to correspond to different propulsion, support, and drag reduction objectives under different media environments.

[0062] 3. Kinematic analysis and control of the unfolded state When the cylindrical slider is in the deployed position P1, the main fan bone of the driving boundary B5 is at a large deployment angle, the flexible membrane is basically fully deployed, and the pectoral fin forms its maximum effective fin surface. This mode is mainly used for underwater propulsion and attitude control. In the deployed state: θ5 = θ P1 φ1(t) = A1 sin(2πf1t + φ1) β1(t) = B1 sin(2πf1t + φ1 + Δ1) Preferably, a larger swing amplitude A1 and a larger effective fin surface are taken in the unfolded state to obtain a higher propulsion force; the pitch phase difference Δ1 is preferably controlled within a range conducive to forming stable flapping propulsion. The unfolded state is suitable for performing high-efficiency cruising, accelerating propulsion, and steering assist control.

[0063] 4. Kinematic Analysis and Control of the Semi-unfolded State When the cylindrical slider is at the semi-unfolded state station P2, the driving boundary main fan bone B5 is driven to fold towards the fixed boundary main fan bone B1 by a certain angle. Since the intermediate driven fan bones are mainly driven to unfold by the tension of the flexible film and the geometric relationship with adjacent fan bones, the semi-unfolded state is not a sector formed by uniformly reducing each fan bone, but a gradually changing configuration with "more unfolded on the fixed side and more folded on the driving side". In this mode, the working fin surface on the fixed side of the pectoral fin remains relatively obvious, while the driving side is partially folded, so that the pectoral fin can reduce the overall resistance and ground interference while retaining certain propulsion and support capabilities, and is more suitable for the water-land transition working condition.

[0064] θ5 = θ P2 θ1 > θ2 > θ3 > θ4 > θ5 Among them, θ1 corresponds to the larger unfolding angle on the side of the fixed boundary main fan bone, and θ5 corresponds to the smaller unfolding angle of the driving boundary main fan bone. This relationship reflects the gradually changing unfolding characteristics of the semi-unfolded state and is one of the important characteristics that distinguish this invention from the uniform intermediate unfolded state. The within-mode periodic motion of the semi-unfolded state can be expressed as: φ2(t) = A2 sin(2πf2t + φ2) β2(t) = B2 sin(2πf2t + φ2 + Δ2) A3 < A2 < A1 To highlight its water-land transition adaptability, the semi-unfolded state preferably adopts segmented control of the support phase - recovery phase. Let a motion cycle be T, where 0 ≤ t < λT is the support phase, λT ≤ t < T is the recovery phase, and 0.5 < λ < 0.8. Then within the support phase: φ2s(t) = A2s [1 - cos(πt / (λT))] It is used to maintain a larger contact area and a slower sliding speed to obtain propulsion force or support force; within the recovery phase: φ2r(t) = φ 2，1 - v r (t - λT), and vr > vs This indicates that the velocity during the recovery phase is greater than the velocity during the support phase, in order to reduce water resistance or ground interference during the swinging process. Therefore, the semi-unfolded state is not simply a geometric intermediate position, but an independent functional mode that takes into account propulsion, support, drag reduction, and stability. Its control objectives can be summarized as follows: J2 = w1F prop + w2F sup - w3D - w4M dist Among them, F prop To advance the component, F sup D is the support component, and M is the resistance component. dist For the unfavorable disturbance torque, w1 to w4 are weighting coefficients. This objective function shows that the semi-expanded state seeks an optimal compromise between propulsion, support, low drag, and stability, rather than simply maximizing propulsion.

[0065] 5. Kinematic analysis and control of folded states When the cylindrical slider is in the folded state position P3, the driving boundary main fan bone B5 clearly converges towards the fixed boundary main fan bone B1, with the intermediate driven fan bones following layer by layer. Most of the flexible membrane folds, and the entire pectoral fin forms a compact, folded bundle structure. This mode is mainly used for low-drag convergence, obstacle avoidance, and land-based auxiliary support. In the folded state: θ5 = θ P3 φ3(t) = A3sin(2πf3t + φ3) β3(t) ≈ 0 A3 represents the minimum value among the three modes, indicating that the folded mode primarily performs low-amplitude oscillations, compact recovery, or ground point contact support actions, rather than pursuing large-area fin flapping propulsion. This mode is suitable for reducing drag, minimizing interference, and improving environmental passability.

[0066] 6. Trimodal Hybrid Motion Control In summary, the pectoral fin system of this invention belongs to a hybrid motion system of "discrete configuration switching + continuous flapping within a mode". Let the system state be x, the input be u, and the mode set be m∈{P1, P2, P3}, then it can be expressed as: = f m (x, u), m∈{P1, P2, P3} m + = Γ(m, σ ij ) The switching between the unfolded and semi-unfolded states is controlled by the first baffle, while the switching between the semi-unfolded and folded states is controlled by the second baffle. The unfolding and folding directions are driven by corresponding shape memory alloy actuators. Mode switching and intra-mode motion control can be achieved by performing binary control (heating / non-heating) on ​​each shape memory alloy actuator. Compared with existing continuous servo control methods, this control method has the advantages of compact structure, simple control logic, and clear support for transition modes.

[0067] like Figure 9 As shown, the three-modal fin kinematic control method of the present invention includes the following steps: starting, initializing system parameters, reading environment and task status, determining the current working condition type, selecting the target mode, performing mode switching, performing periodic motion control under the corresponding mode, real-time monitoring of status, and determining whether it is necessary to switch modes again.

[0068] This invention mainly solves the following technical problems: A fan-shaped pectoral fin structure suitable for amphibious robotic fish is provided, which allows the same pectoral fin to switch between an extended state, a semi-extended state, and a folded state; A root station switching mechanism based on an arc-shaped slide groove and a cylindrical slider is provided, which enables the angular position of the main fan bone of the drive boundary to be directly defined by a discrete station method. A mode switching mechanism for controlling the release and obstruction of workstations using a lifting baffle is provided to avoid the timing sensitivity problem caused by the instantaneous locking method of traditional locking claws; A simplified execution system is provided that utilizes shape memory alloy driving components to achieve unfolding direction driving, folding direction driving, and baffle release control, so that the control mode can be switched between three modes simply by heating / not heating. A semi-expanded configuration is provided, which allows the pectoral fins to present a gradual transition state of "more expanded towards the fixed side and more contracted towards the driving side" when in the middle position, so that the effective expansion area is about half of the expanded state, which meets the needs of the water-land transition working condition.

[0069] The beneficial effects of this invention include: It adopts a folding fan-shaped rib structure, which is suitable for the amphibious variable stiffness requirements.

[0070] This invention uses a fixed boundary main fan bone and a driving boundary main fan bone to form a folding fan-shaped boundary frame. The middle fan bone unfolds passively through a flexible film and the relationship between adjacent fan bones, so that the pectoral fin can form a large area of ​​unfolded fin surface, or it can be folded into a more compact folded configuration.

[0071] The driving boundary main fan bone rotation angle is directly defined by using arc-shaped slide grooves and cylindrical sliders.

[0072] The cylindrical slider is directly connected to the drive unit at the root of the main fan bone of the drive boundary, so that the working position of the slider in the arc-shaped groove directly corresponds to the corner position of the main fan bone of the drive boundary, avoiding the dead point or singular position problem in the linear-corner conversion mechanism.

[0073] The baffle-type station control avoids the problem of instantaneous locking of traditional claw-type locks.

[0074] This invention uses a first baffle and a second baffle to control the release and obstruction between workstations, and restricts the slider position by the workstation interval, without relying on the instantaneous capture of the locking claw slot, thus improving the reliability of mode switching.

[0075] The control logic is simple.

[0076] In this invention, the unfolding direction, folding direction, and two baffles are each controlled by an independent shape memory alloy drive. The control method only requires two states, "heating" and "not heating," to complete the three-state switching, thus reducing the control complexity.

[0077] In addition, the use of a heating sleeve-type shape memory alloy spring drive structure filled with a low specific heat capacity liquid can improve the consistency of thermal response while ensuring drive compactness; the non-film structure of the fin is manufactured by 3D printing of PA12 nylon, and the flexible film 8 is made of TPU film, which is conducive to taking into account the requirements of strength, toughness, flexural resistance and rapid prototype manufacturing.

[0078] The semi-deployed state is more suitable for amphibious transition conditions.

[0079] The semi-spread state is not a uniformly shrinking fan shape, but a gradual configuration where the fixed side is more spread out and the driving side is more contracted. This allows the pectoral fins to retain a certain spread area while increasing the overall degree of contraction, making it more suitable for transitional environments between water and land.

[0080] The root structure is compact, making it suitable for miniaturized layouts.

[0081] This invention eliminates the complex multi-stage synchronous deployment mechanism and the claw-type locking mechanism. The root structure consists of an arc-shaped slide groove, a cylindrical slider, a baffle, and a small number of driving components, which facilitates miniaturization and integration.

[0082] The key technical points that this invention needs to protect include: A fan-shaped amphibious variable stiffness pectoral fin structure includes a pectoral fin root mounting seat 1, a rotatable coaxial center 2, a fixed boundary main fan bone 3, a driving boundary main fan bone 7, intermediate driven fan bones 4, 5, and 6, and a flexible membrane 8, thereby forming a three-state fin structure that can be unfolded, semi-unfolded, and folded. An arc-shaped slide groove 9 is provided with a rotatable coaxial center 2 as the center, and a cylindrical slider 10 slides along the arc-shaped slide groove 9, wherein the cylindrical slider 10 is directly associated with the driving part at the root of the driving boundary main fan bone 7, so that the position of the slider directly corresponds to the corner of the driving boundary main fan bone 7. A mode switching mechanism with lifting baffles set between the nine stations of an arc-shaped chute, wherein the first baffle 11 and the second baffle 12 respectively control the release and blocking between the unfolded station P118 and the semi-unfolded station P219, and between the semi-unfolded station P219 and the folded station P320. A baffle control method in which the baffle is in the blocking position by default and descends to release the passage after being excited by the corresponding shape memory alloy driving component, wherein the third shape memory alloy driving component 15 controls the first baffle 11 and the fourth shape memory alloy driving component 16 controls the second baffle 12. A method for achieving three-mode switching of pectoral fins by means of the coordinated action of a first shape memory alloy drive 13, a second shape memory alloy drive 14, and baffle release drive 15 and 16, using only heating / non-heating control; One definition of a semi-expanded state is that the semi-expanded state is a gradual transitional state of partial expansion and partial folding, which is "more expanded on the side of the main fan bone 3 near the fixed boundary and more contracted on the side of the main fan bone 7 near the driving boundary", rather than a uniformly angularly shrinking state. A preferred structural configuration is provided whereby a cylindrical slider 10 is complementaryly limited by baffles 11 and 12, and a driving component acts on the lower part of the cylindrical slider 10 via a flexible push plate 17.

[0083] A kinematic control method for fish fins that combines discrete workstation configuration switching with continuous flapping within a mode, wherein the cylindrical slider 10 switches between the unfolded workstation P118, the semi-unfolded workstation P219 and the folded workstation P320 to define the discrete angular position of the driving boundary main fan bone 7, while the pectoral fin performs continuous periodic oscillation in the corresponding mode.

[0084] A phased control method for a semi-deployed state, wherein the semi-deployed state adopts segmented control of support phase and recovery phase, the support phase is used to improve propulsion or support force, and the recovery phase is used to reduce gyration resistance and ground interference, so as to adapt to the water-land transition condition.

[0085] A kinematic definition of the semi-spreading state based on a gradient configuration, wherein the semi-spreading state satisfies the condition that the degree of spread along the span decreases monotonically from the fixed side to the driving side, thereby reducing the overall drag of the pectoral fin while retaining an effective working fin surface.

[0086] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A shape memory alloy control based amphibious variable stiffness fin, characterized in that, include: Pectoral fin root mounting base (1), rotatable coaxial center (2), fixed boundary main fan bone (3), intermediate driven fan bone (4), intermediate driven fan bone (5), intermediate driven fan bone (6), driving boundary main fan bone (7), flexible film (8), arc-shaped slide (9), cylindrical slider (10), first baffle (11) and second baffle (12); The fixed boundary main fan bone (3) is fixed on the rotatable connection coaxial center (2), and the driving boundary main fan bone (7) rotates around the rotatable connection coaxial center (2); the intermediate driven fan bone (4), intermediate driven fan bone (5) and intermediate driven fan bone (6) are located between the fixed boundary main fan bone (3) and the driving boundary main fan bone (7), and are respectively installed on the pectoral fin root mounting seat (1) through the rotatable connection coaxial center (2); The flexible film (8) is connected to the fixed boundary main fan bone (3), the intermediate driven fan bone (4), the intermediate driven fan bone (5), the intermediate driven fan bone (6) and the driving boundary main fan bone (7) respectively; the arc-shaped slide groove (9) is installed on the pectoral fin root mounting seat (1) with the rotatable connection coaxial center (2) as the center; the cylindrical slider (10) is located in the arc-shaped slide groove (9); the root driving part of the driving boundary main fan bone (7) is rigidly connected to the cylindrical slider (10); the first baffle (11) and the second baffle (12) are located on both sides of the arc-shaped slide groove (9).

2. The shape memory alloy based controlled variable stiffness amphibious fish fin of claim 1, wherein, The pectoral fin root mounting base (1) is also equipped with a first shape memory alloy drive (13), a second shape memory alloy drive (14), a third shape memory alloy drive (15), and a fourth shape memory alloy drive (16); the first shape memory alloy drive (13) and the second shape memory alloy drive (14) are respectively connected to the two ends of the arc-shaped slide (9); the third shape memory alloy drive (15) and the fourth shape memory alloy drive (16) are located on both sides of the arc-shaped slide (9).

3. The amphibious variable stiffness fin based on shape memory alloy control according to claim 2, characterized in that, The arc-shaped slide (9) is sequentially equipped with a first shape memory alloy drive (13), a flexible push plate (17), a first baffle (11), a third shape memory alloy drive (15), a second baffle (12), a fourth shape memory alloy drive (16), a flexible push plate (17), and a second shape memory alloy drive (14) from one end to the other.

4. The amphibious variable stiffness fin based on shape memory alloy control according to claim 3, characterized in that, The arc-shaped chute (9) is also provided with an unfolded station (18), a semi-unfolded station (19), and a folded station (20); the unfolded station (18) is located between the flexible push plate (17) and the first baffle (11); the semi-unfolded station (19) is located in the middle of the arc-shaped chute (9); and the folded station (20) is located between the fourth shape memory alloy drive component (16) and the flexible push plate (17).

5. The amphibious variable stiffness fin based on shape memory alloy control according to claim 2, characterized in that, The first shape memory alloy drive (13) and the second shape memory alloy drive (14) respectively contact the lower region of the cylindrical slider (10) through the flexible push plate (17) to push the cylindrical slider (10) along the tangential direction of the arc-shaped groove (9).

6. The amphibious variable stiffness fin based on shape memory alloy control according to claim 2, characterized in that, The third shape memory alloy drive (15) is used to control the first baffle (11); the fourth shape memory alloy drive (16) controls the second baffle (12). The areas where the first baffle (11) and the second baffle (12) contact the cylindrical slider (10) are complementary curved surface structures.

7. The amphibious variable stiffness fin based on shape memory alloy control according to claim 1, characterized in that, When the cylindrical slider (10) is in the semi-expanded position (19), the distance between each fan bone gradually decreases along the fixed boundary main fan bone (3) to the driving boundary main fan bone (7), presenting a gradual transition state of partial unfolding and partial folding.

8. The amphibious variable stiffness fin based on shape memory alloy control according to claim 1, characterized in that, The cylindrical slider (10) is vertically arranged in the arc-shaped groove (9); the bottom of the cylindrical slider (10) contacts the bottom surface of the arc-shaped groove (9) and slides along the arc groove, and the cylindrical slider (10) body does not roll.

9. The amphibious variable stiffness fin based on shape memory alloy control according to claim 1, characterized in that, The first baffle (11) and the second baffle (12) move up and down in a direction perpendicular to the movement path of the cylindrical slider (10) to selectively block or allow the cylindrical slider (10) to pass.

10. An amphibious variable stiffness fin based on shape memory alloy control according to claim 9, characterized in that, The first baffle (11) and the second baffle (12) are in the blocking position when not excited, and descend to the release position when the corresponding third shape memory alloy drive (15) or fourth shape memory alloy drive (16) is excited.

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