A heat-actuated artificial muscle based prosthetic finger

Abstract

The application provides a heat-actuated artificial muscle-based artificial finger, which comprises an artificial finger framework, a first artificial muscle attached to the flexion side of the artificial finger framework, and a second artificial muscle attached to the extension side of the artificial finger framework; the first artificial muscle and the second artificial muscle are made of one-way actuated shape memory polyurethane; the artificial finger further comprises a heating mechanism for actuating the first artificial muscle and the second artificial muscle. According to specific driving and transmission parameters required by a target action of a finger, the application selects one-way actuated shape memory polyurethane as an artificial muscle material, constructs a block (hard segment and soft segment) network structure, and realizes bionic matching with a finger motion variable by regulating and controlling response temperature, orientation degree, crystallinity, modulus and micro driving force.

Description

Technical Field

[0001] This invention relates to the field of smart materials technology, and in particular to a prosthetic finger based on thermo-actuated artificial muscles. Background Technology

[0002] Currently, clinical treatment options for upper limb disabilities mainly include somatic sensory electrical stimulation, acupuncture, and motor rehabilitation, with the aim of preserving limb function to the greatest extent possible. However, for more severe conditions such as hand loss, these clinical treatments cannot provide sufficient functional improvement. Intelligent-driven prosthetic hands can reconstruct the lost motor function of the limb through hand compensation, helping patients reintegrate into society.

[0003] Most prosthetic hands use a rigid frame structure and rely on high-energy-density motors to achieve the necessary control precision, torque output, and response speed. This results in complex structures, high manufacturing costs, and the need for ongoing technical support and maintenance. Furthermore, the average adult hand weighs 400 g, while most prosthetic hands, due to their motors and transmission mechanisms, exceed this weight, sometimes reaching as high as 1200 g. Unlike a human hand, the use of a prosthetic hand places all the weight on the residual muscles rather than the bones, making it difficult for patients to wear for extended periods and easily causing discomfort and muscle fatigue.

[0004] To further improve the performance of prosthetic hands, researchers have incorporated the element of "flexibility" into the fabrication of prosthetic hands. Currently, most flexible or soft prosthetic hands rely on fluid actuators, including pneumatic and hydraulic actuation. Pneumatic actuation often uses highly elastic materials such as silicone, transmitting power through air pressure, which greatly reduces the weight of the bionic hand and provides better flexibility and adaptability. For example, the Zhu team at Shanghai Jiao Tong University proposed a soft, flexible, lightweight (292 g), and low-cost inflatable soft prosthetic hand. Its fingers are embedded with a fiber-reinforced soft structure with multiple distributed hard structural layers, which can achieve a variety of dexterous grasping gestures under air pressure [Nature Biomedical Engineering, 2021: 1-10]. Tawk et al. proposed to use negative pressure to activate a 3D-printed prosthetic hand through vacuum [In 2019 IEEE / ASME International Conference on Advanced Intelligent Mechatronics (AIM). 2019: 50-55], generating an output force of ~27 N and a large linear displacement of 9.85 mm [IEEE / ASME Transactions on Mechatronics, 2019, 24(5): 2118-2129.]. However, in general, prosthetic hands powered by gas require additional cylinders / pumps, while liquid-driven ones require the addition of a pipeline system for transportation. This not only imposes stringent requirements on sealing but also limits the driving speed and efficiency. The independent driving and transmission systems reduce the portability of the entire hand [Robotics, 2022, 11(4): 71].

[0005] Based on an artificial muscle-skeleton model, De Pascali et al. from the Italian Polytechnic University designed a 3D pneumatic artificial muscle actuator called GRACE, made of polymer pleated membrane. By connecting 18 GRACEs of different sizes, they created a bionic hand with a wrist. According to precise calculations based on the mathematical model, the fingers can contract and extend at different scales, and by combining different materials and mechanical properties, various movements can be achieved [Science Robotics, 2022, 7(68): eabn4155.]. However, this method of increasing the degree of freedom through external support structures involves more assembly parts, resulting in insufficient practicality and portability. The fundamental reason for this is the separation of drive and transmission. Summary of the Invention

[0006] To address the problems of complex mechanical structure, heavy weight, and insufficient biomimetic movement of current prosthetic hands, this invention provides a prosthetic finger based on thermo-actuated artificial muscles. The mechanical control is shifted from electric drive to structural and material design. Through the combination and design of thermo-actuated materials and the prosthetic finger skeleton structure, the "drive-transmission" fusion of the prosthetic finger is achieved, while reproducing the biomimetic movement of the human hand. In addition, the invention also achieves the goals of structural simplification and weight reduction.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a prosthetic finger based on thermally actuated artificial muscles, comprising a prosthetic finger skeleton, a first artificial muscle attached to the flexion side of the prosthetic finger skeleton, and a second artificial muscle attached to the extension side of the prosthetic finger skeleton; the first artificial muscle and the second artificial muscle are made of unidirectional actuated shape memory polyurethane; the prosthetic finger also includes a heating mechanism for actuating the first artificial muscle and the second artificial muscle.

[0009] In a preferred embodiment, the prosthetic finger skeleton includes a metacarpal bone, a proximal phalanx, a middle phalanx, and a distal phalanx connected in sequence; the first artificial muscle is attached sequentially through the flexion side of the metacarpal bone, the flexion side of the proximal phalanx, the flexion side of the middle phalanx, and the flexion side of the distal phalanx; the second artificial muscle is attached to the extension side of the metacarpal bone; the heating mechanism is an electrothermal film, including a first electrothermal film attached to the end of the flexion side of the metacarpal bone near the proximal phalanx, a second electrothermal film attached to the end of the extension side of the metacarpal bone away from the proximal phalanx, a third and a fourth electrothermal film attached to both ends of the flexion side of the proximal phalanx, a fifth electrothermal film attached to the flexion side of the middle phalanx, and a sixth electrothermal film attached to the flexion side of the distal phalanx.

[0010] In a preferred embodiment, the soft segment of the unidirectional actuated shape memory polyurethane is polycaprolactone diol, and the hard segment is a polycondensation product of diisocyanate and 1,4-butanediol.

[0011] Preferably, the diisocyanate is diphenylmethyl diisocyanate (MDI).

[0012] Preferably, the mass of the hard segment is 35% to 45% of the mass of the unidirectional actuated shape memory polyurethane.

[0013] Preferably, the preparation method of the unidirectional actuated shape memory polyurethane includes the following steps:

[0014] (1) Polycaprolactone diol and diisocyanate were prepolymerized at 80~100℃;

[0015] (2) After adding 1,4-butanediol, continue the reaction at 80~100℃;

[0016] Preferably, the molar ratio of the total number of hydroxyl groups in the 1,4-butanediol and polycaprolactone diol to the isocyanate group in the diisocyanate is 1:1 to 1.2;

[0017] Preferably, the molecular weight of the polycaprolactone polyol is 3000~5000 g / mol;

[0018] Preferably, in step (1), the reaction time for the prepolymerization is 2-3 h;

[0019] Preferably, in step (2), the duration of the continued reaction is 0.5 to 5 minutes.

[0020] In the technical solution of the present invention, the unidirectional actuated shape memory polyurethane has thermal response actuation, the thermal response actuation temperature is determined by the "crystallization-melting" transition temperature of the soft segment, and the thermal actuation work capacity is determined by the change in enthalpy of crystal melting during the thermal actuation process.

[0021] In a preferred embodiment, the unidirectional actuation shape memory polyurethane used to prepare the first artificial muscle undergoes pre-stretching strain and shape fixation.

[0022] Preferably, the pre-stretch strain is the crystallization-melting temperature T. m The tensile strain is reduced to ≥100%; the shape is fixed below the "crystallization-melting" temperature T. m Fixed shape.

[0023] In a preferred embodiment, the extensor sides of the metacarpal, proximal phalanx, middle phalanx, and distal phalanx are connected in sequence by an extensor tendon rope; a first positioning pulley and a second positioning pulley are sequentially arranged along the inner edge of the metacarpal towards the proximal phalanx; one end of the extensor tendon rope is offset around the first positioning pulley and the second positioning pulley and fixed to the second artificial muscle.

[0024] In a preferred embodiment, it also includes two symmetrically distributed joint-connected tendon cords on both sides of the pseudophalanx; a rotation center is provided at the connection points of the metacarpal-proximal phalanx, proximal phalanx-middle phalanx, and middle phalanx-distal phalanx, and the two symmetrical joint-connected tendon cords are sequentially connected to the metacarpals and each phalanx through the rotation center.

[0025] In a preferred embodiment, a timing control mechanism is also included; the timing control mechanism outputs a signal to control the heating mechanism to heat the first artificial muscle and the second artificial muscle; in the technical solution of the present invention, by controlling the heating sequence of artificial muscles in different regions, the artificial muscles on the extension and flexion sides of each region can be coordinated to actuate, thereby driving the bionic movement of the prosthetic finger.

[0026] The above technical solution has the following advantages or beneficial effects:

[0027] This invention selects unidirectional actuation shape memory polyurethane as the artificial muscle material based on the specific driving and transmission parameters required for the target finger movement. A segmented (hard and soft) network structure is constructed, and by controlling the response temperature, orientation, crystallinity, modulus, and microscopic driving force, a biomimetic match is achieved with the finger's movement variables. The thickness, length, and other dimensions of the artificial muscle can be calculated based on modeling according to the force or response speed required for the prosthetic finger's movement.

[0028] This invention places artificial muscles on the flexion and / or extension sides of the metacarpals and finger joints to form human-like antagonistic tissues. When heated, the artificial muscles on the flexion side contract; when cooled, the finger movement is fixed; and when reheated, the artificial muscles on the extension side contract, causing the entire finger to extend. The prosthetic finger designed in this invention can guide the extension and contraction of the artificial muscles in a restrictive manner, so that the two can be effectively integrated to achieve the target movement.

[0029] This invention uses a timing control mechanism to heat artificial muscles in different areas, achieving biomimetic motion mimicry in the prosthetic hand. It boasts high biomimicry and integration, a compact structure, simple control, and fast response, making it suitable for infant prosthetic hands where space is limited and weight is critical. The actuation threshold is low, requiring only 2V for operation, resulting in low energy consumption. Furthermore, it simplifies the structure and reduces weight. Attached Figure Description

[0030] The invention, its features, shape, and advantages will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings. Like reference numerals denote like parts throughout the drawings. The drawings are not intentionally drawn to scale; the focus is on illustrating the spirit of the invention.

[0031] Figure 1 This is a schematic diagram of the overall structure of the prosthetic finger based on thermo-actuated artificial muscle in Embodiment 2 of the present invention.

[0032] Figure 2 This is a full cross-sectional schematic diagram of the prosthetic finger based on thermo-actuated artificial muscle in Embodiment 2 of the present invention.

[0033] Figure 3 This is a graph showing the tensile stress-strain test results of unidirectional shape memory polyurethane with different hard segment contents in Embodiment 1 of the present invention.

[0034] Figure 4 These are performance test diagrams of unidirectional shape memory polyurethane before and after stretching in Embodiment 1 of the present invention.

[0035] Figure 5 This is a characterization diagram of the contractile actuation capability of the artificial muscle in Embodiment 1 of the present invention.

[0036] Figure 6This is an infrared image of the spur finger during the actuation process in Embodiment 2 of the present invention. Detailed Implementation

[0037] 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 a part of the embodiments of the present invention, and not all of them. Therefore, the detailed description of the embodiments of the present 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 present invention without inventive effort are within the protection scope of the present invention.

[0038] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0041] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0042] Example 1: Synthetic Artificial Muscle

[0043] This embodiment uses unidirectional actuation of shape memory polyurethane (T... m-SMPU) is used as a material for synthesizing artificial muscles. The raw materials and dosages are shown in Tables 1 and 2.

[0044] Table 1

[0045]

[0046] Taking S2 as an example, the specific synthesis steps are as follows: Weigh PCL, MDI, and BDO and heat them in a vacuum oven at 105℃ for 2 hours to dry the moisture; add 30 g of PCL and 17.5 g of MDI to a three-necked flask and carry out the prepolymerization reaction in an oil bath at 85℃, stirring for 2 hours (260 rpm) while removing bubbles under vacuum; add 5.85 g of BDO dropwise, react for 2 minutes, and the product is T. m -SMPU; the product was poured onto a polytetrafluoroethylene plate and dried in an oven at 85°C for 16 h; 4 g of the dried sample was dissolved in 33.4 g of N,N-dimethylformamide (DMF) and magnetically stirred at 65°C for 2 h; the mixture was poured into a polytetrafluoroethylene mold for film formation, and then dried in an oven at 80°C for 8 h to remove the solvent, thus obtaining unidirectional actuated shape memory polyurethane (T... m -SMPU) artificial muscle film sample (thickness 0.12 mm, crystallization-melting temperature T) m (The temperature range is 38~50℃).

[0047] Table 2

[0048]

[0049] In Table 2, the hard segment content = (m MDI +m BDO ) / (m MDI +m BDO +m PCL-diol ).

[0050] The T synthesized in this embodiment m The tensile stress-strain results for SMPU are shown below. Figure 3 As shown in the figure, the artificial muscle film sample with a hard segment content of 40 wt% exhibited the highest elongation at break (1126%) and an elastic modulus of 2.33 MPa. This is because the cross-linking degree of the system was optimal at this formulation. Therefore, the sample with a hard segment content of 40 wt% in S2 was used for subsequent experiments.

[0051] Sample S2 was stretched to 100% strain at 50℃, and then fixed at 15℃. The 2D-XRD test results before and after stretching are shown in the figure. Figure 4 The figure shows the changes in crystallinity and orientation of the samples before and after stretching, reflecting the microstructural evolution caused by external force. Figure 4Figure a in the image is the 2D-XRD pattern before stretching. Figure 4 Image b in the image is the stretched 2D-XRD pattern. Figure 4 Figure c in the diagram shows the equatorial integral before stretching. Figure 4 The d-plot in the image shows the equatorial integral after stretching. From... Figure 4 As can be seen from the figure, the crystal plane of the sample before stretching exhibits a uniform diffraction ring pattern (Figure a). After stretching, the two-dimensional diffraction signal is concentrated and enhanced in the equatorial direction, proving that the strain-induced crystal morphology has changed (Figure b). From the integral results of the two-dimensional diffraction signal, it can be seen that the integral in the equatorial direction before stretching (Figure c) shows a significant increase in overall crystallinity after stretching. From the azimuth integral of the (110) crystal plane (Figure d), it can be obtained that the crystal has been oriented in the stretching direction. Therefore, the T prepared in this embodiment m During the stretching process, the oriented crystals of SMPU undergo a melting phase transition, releasing the mechanical energy stored during the stretching process, which in turn performs work and generates thermal actuation.

[0052] Sample S2 was cut into a thin film sample with a length of 7 cm, a width of 6 mm, and a thickness of 0.12 mm. It was stretched at 50°C and fixed at 15°C, resulting in a length of 13.5 cm. After being subjected to thermal stimulation (i.e., at a temperature higher than T),... m It can lift heavy objects by contraction. Specifically, as shown... Figure 5 As shown, the S2 thin film sample (mass 0.065 g), after being heated to a temperature above 50°C, was able to lift an object 810 times its own weight (mass 50.0 g) by approximately 6 cm within 4 seconds, indicating that the material possesses excellent work and driving capabilities, with a work density of 461 J / kg. -1 The power density is 115 W kg. -1 .

[0053] Example 2: Prosthetic finger based on thermo-actuated artificial muscle

[0054] In this embodiment, sample S2 from Example 1 is used as the artificial muscle material to prepare a prosthetic finger, such as... Figure 1-2 As shown, the details are as follows:

[0055] The prosthetic finger based on thermally actuated artificial muscles in this embodiment includes a prosthetic finger skeleton, a first artificial muscle 01 attached to the flexion side of the prosthetic finger skeleton, and a second artificial muscle 02 attached to the extension side of the prosthetic finger skeleton; the first artificial muscle and the second artificial muscle are made from the S2 sample in Example 1; the prosthetic finger also includes a heating mechanism for actuating the first artificial muscle and the second artificial muscle.

[0056] Furthermore, the prosthetic finger skeleton includes a metacarpal bone 10, a proximal phalanx 20, a middle phalanx 30, and a distal phalanx 40 connected in sequence; a first artificial muscle 01 is attached sequentially through and attached to the flexion side of the metacarpal bone 10, the flexion side of the proximal phalanx 20, the flexion side of the middle phalanx 30, and the flexion side of the distal phalanx 40; a second artificial muscle 02 is attached to the extension side of the metacarpal bone 10; the heating mechanism is an electric heating film, including a first electric heating film 11 attached to the flexion side of the metacarpal bone near the proximal phalanx, a second electric heating film 12 attached to the extension side of the metacarpal bone away from the proximal phalanx, a third electric heating film 21 and a fourth electric heating film 22 attached to both ends of the flexion side of the proximal phalanx, a fifth electric heating film 31 attached to the flexion side of the middle phalanx, and a sixth electric heating film 41 attached to the flexion side of the distal phalanx.

[0057] Furthermore, the unidirectional actuation shape memory polyurethane used to prepare the first artificial muscle 01 is subjected to tensile strain to 100% at 50°C and low-temperature fixation at 15°C. In this embodiment, the first artificial muscle on the flexion side is pre-stretched and its shape is fixed, while the second artificial muscle 02 is not pre-stretched and its shape is fixed. This ensures that the second artificial muscle 02 can undergo tensile strain and complete flexion during the bending actuation of the prosthetic finger.

[0058] Furthermore, the extension sides of the metacarpal 10, proximal phalanx 20, middle phalanx 30, and distal phalanx 40 are connected in sequence by an extension tendon rope 03; a first positioning pulley 13 and a second positioning pulley 14 are arranged in sequence along the inner edge of the metacarpal towards the proximal phalanx 20; one end of the extension tendon rope 03 is offset around the first positioning pulley 13 and the second positioning pulley 14 and fixed to the second artificial muscle 02.

[0059] Furthermore, the prosthetic finger also includes two symmetrically distributed joint-connected tendon cords 04 on both sides of the prosthetic finger skeleton; a rotation center is provided at the connection points of metacarpal bone 10-proximal phalanx 20, proximal phalanx 20-middle phalanx 30, and middle phalanx 30-distal phalanx 40, and the two symmetrically distributed joint-connected tendon cords 04 are connected to the metacarpal bone 10 and each phalanx in sequence through the rotation center.

[0060] Furthermore, the artificial finger also includes a timing control mechanism; the timing control mechanism outputs a signal to control the heating mechanism to heat the first artificial muscle 01 and the second artificial muscle 02.

[0061] The actuation process of the spur finger in this embodiment is as follows:

[0062] When the prosthetic finger needs to flex, the timing control mechanism outputs signals to heat the first and second electrothermal films 11 and 12 within the metacarpal bone 10, the third and fourth electrothermal films 21 and 22 within the proximal phalanx 20, the fifth electrothermal film 31 within the middle phalanx 30, and the sixth electrothermal film 41 within the distal phalanx 40 according to the grasping requirements. To achieve biomimetic flexion, the temperature of the electrothermal films on the flexion side needs to be controlled to be higher than that on the extension side. For example, the first, third, and fourth electrothermal films on the flexion side... 22. The fifth and sixth heating films 31 and 41 heat up to increase the temperature. The first artificial muscle 01 on the flexion side begins to contract under thermal stimulation exceeding 38°C, exhibiting thermal contraction actuation during the continuous heating up to 50°C. Simultaneously, the heating process of the second heating film 12 on the extension side is slower than that of the heating film on the flexion side. During the temperature rise to 45°C, the soft segment crystals of the second artificial muscle 02 on the extension side melt and exhibit thermal passive stretching actuation along with the flexion movement of the first artificial muscle 01. In the above process, the thermally contraction-actuated first artificial muscle 01 pulls each phalanx to begin flexion around its respective center of rotation, with each joint flexing at the same angular velocity, achieving biomimetic movement. Furthermore, this flexion transmits force to the second artificial muscle 02 on the extension side through the extension tendon tract 03, meaning the second artificial muscle 02 passively stretches and lengthens to compensate for the contraction stroke of the first artificial muscle 01 during flexion. In this embodiment, the prosthetic finger can also finely control the flexion of each phalanx at different angular velocities by adjusting the heating rate or heating sequence of the heating film on the flexion side, so as to adapt to the gripping of objects of different shapes.

[0063] When the prosthetic finger in a heat-induced flexed state needs to extend, the timing control mechanism outputs a signal to heat the second heating film 12 (in the flexed state, the second artificial muscle 02 is in a passively stretched state) to raise its temperature to 50°C. The second artificial muscle 02 exhibits heat contraction actuation under thermal stimulation. Simultaneously, the timing control mechanism outputs a signal to stop heating the first heating film 11, third heating film 21, fourth heating film 22, fifth heating film 31, and sixth heating film 41 on the flexed side, causing their temperatures to drop. As the temperature of the first artificial muscle 01 on the flexed side decreases from 50°C to 38°C, it exhibits heat passive stretching actuation along with the contraction of the second artificial muscle 02. That is, while the second artificial muscle 02 is heat-contracted, it pulls the stretching tendon rope 03, causing each phalanx to rotate counterclockwise around its respective center of rotation, exhibiting an extension movement; and the first artificial muscle 01 on the flexed side is stretched and lengthened by these phalanxes until the prosthetic finger returns to a fully extended state.

[0064] Weighing the artificial muscle and prosthetic finger in this embodiment reveals that the total weight of the first and second artificial muscles of a single prosthetic finger is less than 0.1 g, and the weight of a single prosthetic finger is only 6 g. Infrared imaging of the prosthetic finger during actuation in this embodiment is shown below. Figure 6As shown, the electrothermal film in this embodiment can satisfy the thermal stimulation of 38°C under a 2V voltage, thereby achieving the bending actuation of the prosthetic finger.

[0065] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A thermo-actuated artificial muscle based prosthetic finger, characterized by, The prosthetic finger includes a prosthetic finger skeleton, a first artificial muscle attached to the flexion side of the prosthetic finger skeleton, and a second artificial muscle attached to the extension side of the prosthetic finger skeleton; the first artificial muscle and the second artificial muscle are made of one-way actuation shape memory polyurethane; the prosthetic finger further includes a heating mechanism for actuation of the first artificial muscle and the second artificial muscle; the first artificial muscle is pre-stretched and shape-fixed, and the second artificial muscle is not pre-stretched and shape-fixed. The prosthetic finger skeleton includes metacarpal, proximal phalanx, middle phalanx and distal phalanx connected in sequence; the first artificial muscle penetrates and is attached to the flexion side of the metacarpal, the flexion side of the proximal phalanx, the flexion side of the middle phalanx and the flexion side of the distal phalanx in sequence; the second artificial muscle is attached to the extension side of the metacarpal; the heating mechanism is an electrothermal film, including a first electrothermal film attached to one end of the flexion side of the metacarpal close to the proximal phalanx, a second electrothermal film attached to one end of the extension side of the metacarpal away from the proximal phalanx, a third electrothermal film and a fourth electrothermal film attached to both ends of the flexion side of the proximal phalanx, a fifth electrothermal film attached to the flexion side of the middle phalanx, and a sixth electrothermal film attached to the flexion side of the distal phalanx. The extension sides of the metacarpal, the proximal phalanx, the middle phalanx and the distal phalanx are connected in sequence by an extension tendon; the metacarpal is provided with a first positioning pulley and a second positioning pulley in sequence along the direction towards the proximal phalanx; one end of the extension tendon is misaligned around the first positioning pulley and the second positioning pulley and is fixed to the second artificial muscle.

2. The artificial finger according to claim 1, characterized in that The soft segment of the one-way actuation shape memory polyurethane is polycaprolactone diol, and the hard segment is the polycondensation product of diisocyanate and 1,4-butanediol.

3. The artificial finger according to claim 2, characterized in that The diisocyanate is diphenylmethyl diisocyanate.

4. The artificial finger according to claim 2, characterized in that The mass of the hard segment is 35% to 45% of the mass of the one-way actuation shape memory polyurethane.

5. The artificial finger according to claim 2, characterized in that The preparation method of the one-way actuation shape memory polyurethane includes the following steps: (1) pre-polymerization of polycaprolactone diol and diisocyanate at 80 to 100°C; (2) continue to react at 80 to 100°C after adding 1,4-butanediol.

6. The artificial finger according to claim 1, characterized in that It also includes two symmetrical joint series tendons distributed on both sides of the prosthetic finger skeleton; the connection positions of the metacarpal-proximal phalanx, the proximal phalanx-middle phalanx and the middle phalanx-distal phalanx are provided with rotation centers, and the two symmetrical joint series tendons are connected to the metacarpal and the phalanges in sequence through the rotation centers.

7. The artificial finger according to claim 1, characterized in that It also includes a time sequence control mechanism; the output signal of the time sequence control mechanism is used to control the heating of the first artificial muscle and the second artificial muscle by the heating mechanism.

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