A memory alloy-driven robotic fish with online adjustment of flexible body stiffness

Abstract

The invention discloses a memory alloy-driven robot fish capable of adjusting the stiffness of a flexible body online. The robot fish utilizes a fish body connector to replace an adapted fish head and a flexible body tail fin mechanism, and has a split structural feature. The flexible body tail fin mechanism is connected to the fish body connector, and is composed of an active part, a passive part, and a tail fin. The active part utilizes the swing of a servo to realize the deflection of the flexible body tail fin, and the rotation of a motor drives a rotating rod to rotate to realize the wave motion of the flexible body, and the rotating rod selects an elastic rod with online variable stiffness. The passive part utilizes a memory alloy actuator to change the stiffness of an elastic plate of a tail shank online, and is suitable for the stiffness change in working conditions such as straight swimming and turning of the robot fish. The tail fin part simulates the tail fin skeleton structure through fin rays, and utilizes a memory alloy actuator to drive the fin rays to bend so as to control the fin surface to realize curling, bending, multi-free wave motion, and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater robots and relates to a memory alloy-driven robot fish capable of online adjusting the rigidity of a flexible body. Background Art

[0002] Bionic robot fish is a new type of underwater robot with high maneuverability, high concealment and low noise. It is widely used in underwater resource exploration, underwater equipment inspection, underwater biological observation and underwater archeology. The flexible tail fin is the main propulsion mechanism of the robot fish. The change of the stiffness of the bionic fish body can significantly improve the swimming efficiency and stability of the robot fish. Therefore, researchers hope to imitate the skeletal structure, tendons and muscles of the fish body to design a flexible body robot fish with online adjustable stiffness that takes into account both swimming speed and efficiency.

[0003] Existing research shows that the remarkable athletic performance of fish and their flexible movements are achieved by actively adjusting the stiffness of the body. Specifically, the dorsal lateral tendons and ventral lateral tendons near the keel of fish will act as antagonistic muscle drivers to adjust the stiffness of the fish body. The two protruding dorsal and ventral tendons extend backward to the tail fin. When the fish body cruises at high speed, these tendons become extremely hard, and at low speed, the tendons become relaxed and soft, and the sides of the spine also bend when the "C" is activated.

[0004] The flexible body part of the present invention simulates the muscle fibers and ligament network of a fish body, changes the stiffness of the active driving part of the flexible body by using elastic rods of different stiffnesses, and uses a memory alloy actuator to change the stiffness of the elastic plate of the tail stalk online, which is suitable for the stiffness changes in working conditions such as straight swimming and turning of the robot fish. The tail fin part simulates the tail fin skeleton structure through fin rays, and uses a memory alloy actuator to drive the fin rays to bend to control the fin surface to achieve curling, bending and multi-free fluctuation movements; in addition, a silicone skin is used to simulate the rich collagen membrane of the fish body, so that the robot fish can adapt to the flapping of bodies with different stiffnesses. Summary of the invention

[0005] In response to the problems in the technical background, the present invention provides a memory alloy-driven robotic fish with online adjustment of the stiffness of a flexible body, which utilizes the swing of a servo engine to achieve deflection of the tail fin of the flexible body, utilizes the rotation of a motor to drive a rotating rod to rotate to achieve fluctuating motion of the flexible body, utilizes a tail stalk memory alloy actuator to change the stiffness of the tail stalk, utilizes a tail fin memory alloy actuator to drive the movement of each fin ray to achieve fluctuating motion of the tail fin, and propels the movement of the robotic fish through the flapping of the pectoral fins and the tail fin of the flexible body.

[0006] The invention provides a memory alloy driven robot fish capable of adjusting the stiffness of a flexible body online. The robot fish is characterized in that the robot fish comprises a fish head upper shell, a fish head lower shell, a left pectoral fin, a right pectoral fin, a fish body connector, and a flexible body tail fin mechanism; wherein the flexible body tail fin mechanism comprises a flexible body tail fin skin, a steering gear frame, a steering gear, a tiller, a motor frame, a motor, a rotating rod, a first joint connecting plate, a second joint connecting plate, a third joint connecting plate, a first elastic rod, a second elastic rod, a tail handle elastic plate, a first tail handle memory alloy actuator, a second tail handle memory alloy actuator, a third tail handle memory alloy actuator, a fourth tail handle memory alloy actuator, a fifth tail handle memory alloy actuator, a sixth tail handle memory alloy actuator, a first tail fin ray, a second tail fin ray, a third tail fin ray, a first tail fin memory alloy actuator, a second tail fin memory alloy actuator, a third tail fin memory alloy actuator, a fourth tail fin memory alloy actuator, a fifth tail fin memory alloy actuator, a sixth tail fin memory alloy actuator, a first flexible body pressure plate, and a second flexible body pressure plate. The upper shell of the fish head is connected to the lower shell of the fish head by rivets, and the connection gap between the two is sealed by soft glue; the left pectoral fin and the right pectoral fin are connected to the lower shell of the fish head, and the pectoral fins are connected to the fish body by bonding or bolting; the fish body connector is connected to the lower shell of the fish head, and the flexible body tail fin mechanism is connected to the fish body connector; the robot fish is propelled by flapping the pectoral fins and the flexible body tail fin.

[0007] As a further technical solution, the servo frame is connected to the fish body connecting piece, the servo is installed on the servo frame, and the tiller is installed on the output shaft of the servo; the deflection of the flexible body of the bionic robotic fish is achieved by driving the servo to control the rotation of the tiller; the fish body connecting piece is composed of an elliptical cylindrical tube, and the short axis length of the cross-sectional ellipse limits the swing angle of the servo, and the angle range is -65 degrees to 65 degrees.

[0008] As a further technical solution, one end of the motor frame is connected to the tiller handle, and the other end of the motor frame is connected to the shaft hole of the servo frame through a bearing, and the rotation of the tiller handle drives the motor frame to rotate around the servo output shaft; the motor is installed in the motor frame, one end of the rotating rod is connected to the output shaft of the motor, and the other end of the rotating rod passes through the square through hole of the first joint connecting plate and the square through hole of the second joint connecting plate respectively to be connected to the square blind hole of the third joint connecting plate; the rotating rod rotates around the motor output shaft, so that the flexible body of the robot fish swings, and the body swing amplitude depends on the curvature of the rotating rod.

[0009] As a further technical solution, one end of the first elastic rod is connected to the fish body connecting piece, and the other end of the first elastic rod passes through the circular through hole of the first joint connecting plate, the circular through hole of the second joint connecting plate in sequence, and is connected to the circular through hole of the third joint connecting plate; one end of the second elastic rod is connected to the fish body connecting piece, and the other end of the second elastic rod passes through the circular through hole of the first joint connecting plate, the circular through hole of the second joint connecting plate in sequence, and is connected to the circular through hole of the third joint connecting plate; the first elastic rod and the second elastic rod both have the same elastic modulus and are mirror-symmetrical about the center plane of the body.

[0010] As a further technical solution, the tail handle elastic plate is installed in the groove of the third joint connecting plate, the first tail handle memory alloy actuator, the second tail handle memory alloy actuator and the third tail handle memory alloy actuator are respectively fixed on the positive side of the tail handle elastic plate, the fourth tail handle memory alloy actuator, the fifth tail handle memory alloy actuator and the sixth tail handle memory alloy actuator are fixed to the reverse side of the tail handle elastic plate, and the memory alloy actuators on both sides of the tail handle elastic plate are mirror-symmetric about the tail handle elastic plate; the memory alloy wire is driven by electric current to expand and contract, so that the stiffness of the tail handle elastic plate changes online.

[0011] As a further technical solution, the first tail fin ray, the second tail fin ray and the third tail fin ray are respectively installed in the blind holes of the tail handle elastic plate; the first tail fin memory alloy actuator and the fourth tail fin memory alloy actuator are fixed to the front and back sides of the first tail fin ray; the second tail fin memory alloy actuator and the fifth tail fin memory alloy actuator are fixed to the front and back sides of the second tail fin ray; the third tail fin memory alloy actuator and the sixth tail fin memory alloy actuator are fixed to the front and back sides of the third tail fin ray; and the memory alloy actuator is driven by electric current to expand and contract, so that the fin ray is bent and deformed.

[0012] As a further technical solution, the flexible body tail fin skin is sleeved onto the fish body connector using an interference fit, and the first flexible body pressure plate and the second flexible body pressure plate are installed at the connection between the flexible body tail fin skin and the fish body connector to achieve a sealing effect.

[0013] As a further technical solution, a robotic fish is provided, comprising the above-mentioned robotic fish driven by a memory alloy and capable of online adjusting the stiffness of a flexible body.

[0014] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention.

[0015] The beneficial effects of the present invention are:

[0016] The bionic robot fish divides the fish body and the flexible body tail fin mechanism into two parts through a fish body connector. The fish head and the flexible body tail fin mechanism can be replaced at will, and it has the characteristics and functions of a split design.

[0017] The flexible body part changes the stiffness of the active driving part of the flexible body by using elastic rods with different stiffness; the stiffness of the elastic plate of the tail stalk is changed online by using a memory alloy actuator, which is suitable for the stiffness changes in working conditions such as straight swimming and turning of the robot fish.

[0018] The tail fin part simulates the tail fin skeleton structure through fin rays, and uses memory alloy actuators to drive the fin rays to bend to control the fin surface to achieve curling, bending, and multi-free fluctuation movements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the three-dimensional structure of a robotic fish with skin that is driven by a memory alloy and has the ability to online adjust the stiffness of a flexible body according to an embodiment of the present invention.

[0020] Figure 2 This is a top view of a robotic fish with skin that is driven by a memory alloy and has an online adjustment of the stiffness of a flexible body according to an embodiment of the present invention.

[0021] Figure 3 for Figure 1 A schematic diagram of the three-dimensional structure of a flexible body / tail fin without skin of a memory alloy-driven robotic fish with online adjustment of flexible body stiffness is shown.

[0022] Figure 4 for Figure 3 A front view of a flexible body / tail fin without skin of a memory alloy-driven robotic fish with online adjustment of flexible body stiffness is shown.

[0023] Figure 5 for Figure 3 A left view of a flexible body / tail fin without skin of a memory alloy-driven robotic fish with online adjustment of flexible body stiffness is shown.

[0024] Figure 6 for Figure 3 A top view of the flexible body / tail fin without skin of a memory alloy-driven robotic fish with online adjustment of flexible body stiffness is shown.

[0025] Figure 7 for Figure 3 A rear view of a flexible body / tail fin without skin of a memory alloy-driven robotic fish with online adjustment of flexible body stiffness is shown.

[0026] Figure 8 for Figure 5A cross-sectional view of a memory alloy-driven robotic fish with online adjustment of flexible body stiffness along the AA section line is shown.

[0027] Fig. 9 for Figure 6 A cross-sectional view of a memory alloy-driven robotic fish with online adjustment of flexible body stiffness along the BB section line is shown.

[0028] Figure numerals: fish head upper shell 1, fish head lower shell 2, fish body connecting piece 3, flexible body tail fin mechanism 4, right pectoral fin 6, left pectoral fin 7, servo 8, tiller 9, servo frame 10, motor frame 11, tail handle elastic plate 13, rotating rod 17, motor 19, flexible body tail fin skin 401, first flexible body pressure plate 501, second flexible body pressure plate 502, first joint connecting plate 1201, second joint connecting plate 1202, third joint connecting plate 1203, first tail fin memory alloy actuator 1401, second tail fin memory alloy actuator 1402, third tail fin memory alloy actuator 1 403, fourth tail fin memory alloy actuator 1404, fifth tail fin memory alloy actuator 1405, sixth tail fin memory alloy actuator 1406, first tail fin ray 1501, second tail fin ray 1502, third tail fin ray 1503, first tail handle memory alloy actuator 1601, second tail handle memory alloy actuator 1602, third tail handle memory alloy actuator 1603, fourth tail handle memory alloy actuator 1604, fifth tail handle memory alloy actuator 1605, sixth tail handle memory alloy actuator 1606, first elastic rod 1801, second elastic rod 1802. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be understood that the present invention uses the terms "first", "second", etc. to describe various information, but these information should not be limited to these terms, and these terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, "first" information may also be referred to as "second" information, and similarly, "second" information may also be referred to as "first" information.

[0031] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, inside, outside, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0032] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, assembling, and matching should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0033] Please refer to the attached Figure 1-Figure 9 The present invention discloses a memory alloy-driven robot fish with online adjustment of the stiffness of a flexible body. The robot fish utilizes the swing of a servo engine to realize the deflection of a tail fin of a flexible body, utilizes the rotation of a motor to drive the rotation of a rotating rod to realize the wave motion of a flexible body, utilizes the stiffness of a tail stalk memory alloy actuator to change the stiffness of a tail stalk, utilizes the tail fin memory alloy actuator to drive the movement of each fin ray, and realizes the wave motion of a tail fin. The robot fish is characterized in that: an upper shell 1 of a fish head is connected to a lower shell 2 of a fish head by rivets, and a connection gap between the two is sealed by soft glue; a left pectoral fin 7 and a right pectoral fin 6 are connected to the lower shell 2 of a fish head, and the connection between the pectoral fin and the fish body can be achieved by bonding or bolting, and the present invention does not impose specific restrictions; a fish body connector 3 is connected to the lower shell 2 of a fish head by bolts, and a servo engine frame 10 in a tail fin mechanism 4 of a flexible body is connected to the fish body connector 3 by bolts; the robot fish is propelled by the coordinated flapping of the pectoral fins and the tail fin of a flexible body, and the wave motion of the online variable stiffness flexible body and tail fin ray ray can generate greater propulsion force, thereby improving the swimming efficiency of the robot fish.

[0034] The servo 8 is installed to the servo frame 10 by bolts, the tiller 9 is fixed to the output shaft of the servo 8 by bolts, one end of the motor frame 11 is connected to the tiller 9 by bolts, and the other end of the motor frame 11 is connected to the shaft hole of the servo frame 10 by a bearing. The rotation of the tiller 9 is driven by energizing the servo 8, thereby driving the motor frame 11 to rotate around the output shaft of the servo 8, thereby realizing the overall deflection of the flexible body of the bionic robot fish. The positioning shaft hole of the servo frame 10 solves the problem of unstable single-axis output of the servo; the fish body connector 3 is composed of an elliptical cylindrical tube, and the minor axis length of the cross-sectional ellipse limits the swing angle of the servo 8, and the angle range is -65 degrees to 65 degrees.

[0035] The motor 19 is installed in the motor frame 11 by bolts, one end of the rotating rod 17 is connected to the output shaft of the motor, and the other end of the rotating rod 17 passes through the square through hole of the first joint connecting plate 1201 and the square through hole of the second joint connecting plate 1202 to be connected to the square blind hole of the third joint connecting plate 1203; the rotating rod 17 rotates around the output shaft of the motor 19, so that the flexible body of the robot fish flaps, and the flapping amplitude of the body depends on the curvature of the rotating rod 17; the rotating rod 17 is made of memory alloy material, and the curvature of the rod can be changed by inputting current.

[0036] One end of the first elastic rod 1701 is connected to the blind hole of the fish body connector 3 by bonding, and the other end of the first elastic rod 1701 passes through the circular through hole of the first joint connecting plate 1201 and the circular through hole of the second joint connecting plate 1202 in sequence to be connected to the circular through hole of the third joint connecting plate 1203; one end of the second elastic rod 1702 is connected to the blind hole of the fish body connector 3 by bonding, and the other end of the second elastic rod 1702 passes through the circular through hole of the first joint connecting plate 1201 and the circular through hole of the second joint connecting plate 1202 in sequence to be connected to the circular through hole of the third joint connecting plate 1203, wherein both It is connected to the circular through holes of the first joint connecting plate 1201, the second joint connecting plate 1202 and the third joint connecting plate 1203 by bonding. The distance between the three is determined by the fluctuation curve of the fish body in principle. In the mechanism, it is bonded to the first elastic rod 1701, the second elastic rod 1702 is fixed, and the inner groove of the flexible body skin 401 is determined to ensure stable movement; the first elastic rod 1701 and the second elastic rod 1702 are both composed of superelastic wire of memory alloy with the same elastic modulus, and are mirror-symmetrical about the center plane of the body in the installation position, so that the flexible body has the bionics of fish tendons, thereby improving propulsion efficiency and performance.

[0037] The tail handle elastic plate 13 is installed in the square groove of the third joint connecting plate 1203 by bonding. The first tail handle memory alloy actuator 1601, the second tail handle memory alloy actuator 1602 and the third tail handle memory alloy actuator 1603 are respectively fixed on the front side of the tail handle elastic plate 13 by bonding. The fourth tail handle memory alloy actuator 1604, the fifth tail handle memory alloy actuator 1605 and the sixth tail handle memory alloy actuator 1606 are fixed to the back side of the tail handle elastic plate 13 by bonding. The memory alloy actuators on the front and back sides of the tail handle elastic plate 13 are mirror-symmetric about the tail handle elastic plate 13. The tail handle elastic plate 13 is made of elastic thermoplastic polyurethane rubber material. The memory alloy wire is driven by electric current to expand and contract, so that the stiffness of the tail handle elastic plate 13 changes online. The number of memory alloy actuators arranged on one side of the tail handle elastic plate 13 is not limited to 3. The number and distance of the arranged memory alloy actuators determine the stiffness change range of the tail handle elastic plate 13.

[0038] The first tail fin ray 1501, the second tail fin ray 1502 and the third tail fin ray 1503 are respectively installed in the blind hole of the tail handle elastic plate 13 by bonding, wherein the angle between the three depends on the size of the tail fin, or is determined according to the study of the main tail fin ray; the first tail fin memory alloy actuator 1401 and the fourth tail fin memory alloy actuator 1404 are respectively fixed to the front and back sides of the first tail fin ray 1501 by bonding; the second tail fin memory alloy actuator 1402 and the fifth tail fin memory alloy actuator 1405 are respectively fixed to the front and back sides of the first tail fin ray 1501 by bonding; They are respectively fixed to the front and back sides of the second tail fin fin 1502; the third tail fin memory alloy actuator 1403 and the sixth tail fin memory alloy actuator 1406 are respectively fixed to the front and back sides of the third tail fin fin 1503 by bonding; the fin rays are all made of elastic thermoplastic polyurethane rubber material, and the memory alloy wire in the memory alloy actuator is driven by electric current to expand and contract, thereby controlling the bending movement of each fin ray to simulate the spanwise fluctuation of the tail fin surface, and by inputting different currents to each memory alloy wire, the different curvatures of the fin rays are controlled to simulate the chordwise fluctuation of the tail fin surface.

[0039] The flexible body tail fin skin 401 is put on the fish body connecting piece 3 by interference fit, and the first flexible body pressure plate 501 and the second flexible body pressure plate 502 fix the flexible body tail fin skin 401 to the fish body connecting piece 3 by bolts to achieve a sealing effect; the flexible body tail fin skin 401 is cast with silicone rubber material and has a certain elasticity, so that the flapping of the mechanism and the tail fin rays can tear the skin to move.

[0040] Through the above-mentioned mechanism and method, the present invention has a split design feature and function of the bionic robot fish, and the fish body connector can be used to arbitrarily replace a more suitable fish head and flexible body tail fin mechanism; the flexible body part changes the stiffness of the active driving part of the flexible body by using elastic rods with different stiffnesses, and uses a memory alloy actuator to change the stiffness of the tail handle elastic plate online, which is suitable for the stiffness changes in the robot fish's straight swimming, turning and other working conditions; the tail fin part simulates the tail fin skeleton structure through fin rays, and uses a memory alloy actuator to drive the fin rays to bend to control the fin surface to achieve curling, bending and multiple free fluctuations and other movements; the body stiffness of fish is time-varying during different swimming behaviors, and the present invention designs a memory alloy-driven robot fish that can adjust the flexible body stiffness online.

[0041] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A memory alloy driven robotic fish capable of online adjusting the stiffness of a flexible body, characterized in that: The invention comprises an upper shell of a fish head, a lower shell of a fish head, a left pectoral fin, a right pectoral fin, a fish body connector, and a flexible body tail fin mechanism; wherein the flexible body tail fin mechanism comprises a flexible body tail fin skin, a steering gear frame, a steering gear, a tiller, a motor frame, a motor, a rotating rod, a first joint connecting plate, a second joint connecting plate, a third joint connecting plate, a first elastic rod, a second elastic rod, a tail handle elastic plate, a first tail handle memory alloy actuator, a second tail handle memory alloy actuator, a third tail handle memory alloy actuator, a fourth tail handle memory alloy actuator, a fifth tail handle memory alloy actuator, a sixth tail handle memory alloy actuator, a first tail fin ray, a second tail fin ray, a third tail fin ray, a first tail fin memory alloy actuator, a second tail fin memory alloy actuator, a third tail fin memory alloy actuator, a fourth tail fin memory alloy actuator, a fifth tail fin memory alloy actuator, a sixth tail fin memory alloy actuator, a first flexible body pressure plate, and a second flexible body pressure plate. The upper shell of the fish head is connected to the lower shell of the fish head by rivets, and a connection gap between the two is sealed by soft glue; the left pectoral fin and the right pectoral fin are connected to the lower shell of the fish head, and the pectoral fin is connected to the fish body by bonding or bolting; the fish body connector is connected to the lower shell of the fish head, and the flexible body tail fin mechanism is connected to the fish body connector; the pectoral fin and the flexible body tail fin mechanism are flapped to propel the robot fish to move; The steering gear frame is connected to the fish body connecting piece, the steering gear is installed on the steering gear frame, and the tiller is installed on the output shaft of the steering gear; the steering gear is driven to control the tiller to rotate, so as to realize the deflection of the flexible body of the bionic robotic fish; the fish body connecting piece is composed of an elliptical cylindrical tube, and the minor axis length of the cross-section ellipse limits the swing angle of the steering gear, and the angle range is -65 degrees to 65 degrees; One end of the motor frame is connected to the tiller handle, and the other end of the motor frame is connected to the shaft hole of the servo frame through a bearing, and the rotation of the tiller handle drives the motor frame to rotate around the servo output shaft; the motor is installed in the motor frame, one end of the rotating rod is connected to the output shaft of the motor, and the other end of the rotating rod passes through the square through hole of the first joint connecting plate and the square through hole of the second joint connecting plate respectively to be connected to the square blind hole of the third joint connecting plate; the rotating rod rotates around the motor output shaft, so that the flexible body of the robot fish flaps, and the flapping amplitude of the body depends on the curvature of the rotating rod.

2. The memory alloy driven robotic fish capable of online adjusting the stiffness of a flexible body according to claim 1, characterized in that: One end of the first elastic rod is connected to the fish body connecting piece, and the other end of the first elastic rod passes through the circular through hole of the first joint connecting plate and the circular through hole of the second joint connecting plate in sequence to be connected to the circular through hole of the third joint connecting plate; one end of the second elastic rod is connected to the fish body connecting piece, and the other end of the second elastic rod passes through the circular through hole of the first joint connecting plate and the circular through hole of the second joint connecting plate in sequence to be connected to the circular through hole of the third joint connecting plate; the first elastic rod and the second elastic rod have the same elastic modulus and are mirror-symmetrical about the center plane of the body.

3. The memory alloy driven robotic fish capable of online adjusting the stiffness of a flexible body according to claim 1, characterized in that: The tail handle elastic plate is installed in the groove of the third joint connecting plate, the first tail handle memory alloy actuator, the second tail handle memory alloy actuator and the third tail handle memory alloy actuator are respectively fixed on the positive side of the tail handle elastic plate, the fourth tail handle memory alloy actuator, the fifth tail handle memory alloy actuator and the sixth tail handle memory alloy actuator are fixed to the reverse side of the tail handle elastic plate, and the memory alloy actuators on both sides of the tail handle elastic plate are mirror-symmetric about the tail handle elastic plate; the memory alloy wire is driven by electric current to expand and contract, so that the stiffness of the tail handle elastic plate changes online.

4. The memory alloy driven robotic fish capable of online adjusting the stiffness of a flexible body according to claim 3, characterized in that: The first tail fin ray, the second tail fin ray and the third tail fin ray are respectively installed in the blind holes of the tail handle elastic plate; the first tail fin memory alloy actuator and the fourth tail fin memory alloy actuator are respectively fixed to the front and back sides of the first tail fin ray; the second tail fin memory alloy actuator and the fifth tail fin memory alloy actuator are respectively fixed to the front and back sides of the second tail fin ray; the third tail fin memory alloy actuator and the sixth tail fin memory alloy actuator are respectively fixed to the front and back sides of the third tail fin ray; and the memory alloy actuator is driven by electric current to expand and contract, so that the fin ray is bent and deformed.

5. The memory alloy driven robotic fish capable of online adjusting the stiffness of a flexible body according to claim 1, characterized in that: The flexible body tail fin skin is put on the fish body connecting piece by interference fit, and the first flexible body pressure plate and the second flexible body pressure plate are installed at the connection between the flexible body tail fin skin and the fish body connecting piece to achieve a sealing effect.

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