A method for preparing an electrothermal driven artificial muscle

Abstract

The present invention belongs to the technical field of intelligent robot materials and discloses a method for preparing an electrothermally driven artificial muscle. Method: S1. Twisting nylon fiber. When the fiber self-winds to form the first coil, twisting is immediately stopped to obtain a nylon fiber in an ultimate straight state; the nylon fiber in the ultimate straight state is wound, with the winding direction being consistent with the twisting direction; the wound nylon coil is annealed in a vacuum state to obtain an artificial muscle fiber; S2. The artificial muscle fiber is roughened, sensitized, activated, and electrolessly plated with a Ni / Cu / Sn composite metal layer. The artificial muscle fiber is annealed at 140-160°C for 40-60 minutes to obtain an electrothermally driven artificial muscle. The method of the present invention ensures that the metal layer has good bonding strength with the substrate, while enabling the artificial muscle to achieve reversible drive at a low operating voltage and exhibit good contractile performance and cyclic stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent robot materials, and in particular relates to a method for preparing an electrothermal driven artificial muscle. Background Art

[0002] With the rapid development of biomimetic technology, medical equipment, soft robots, and complex terrain surveys, traditional rigid actuators have problems such as few degrees of freedom, lack of flexibility, inability to adapt to complex environments, high manufacturing and maintenance costs, and poor safety for human-machine coexistence. Therefore, researchers urgently need to develop new types of flexible actuators.

[0003] Artificial muscles are materials or devices that change shape when exposed to external physical or chemical stimuli and return to their original shape when the stimulus is removed. They are primarily driven by pressure, electricity, heat, and chemical actuation. They are considered one of the most promising actuators due to their simple control, high energy and power density, high flexibility, and softness.

[0004] Fibrous artificial muscles have attracted considerable attention due to their advantages, including high power density, large actuation deformation, high flexibility, low hysteresis, and long life. Initially, artificial inorganic fibers such as carbon nanotubes and graphene oxide have been used, followed by polymer fibers such as nylon, polyethylene, and spandex, and finally natural polymer fibers such as spider silk, silk, and cotton. Nylon fiber, a low-cost, high-strength polymer fiber, can be twisted to a critical straight state to create a wound nylon artificial muscle by further twisting. Alternatively, the twisted nylon fiber can be wound around a mandrel of a certain diameter to create a coiled nylon artificial muscle, which is then annealed to set the shape. By twisting the nylon fiber, the internally aligned fibers are continuously stretched and tilted. Because nylon has a negative thermal expansion coefficient, rising temperature causes the stretched fibers to contract, thereby rotating the entire fiber segment. When the winding (or coiling) direction aligns with the twisting direction, the artificial muscle contracts as the temperature rises; when the twisting direction is opposite, it expands.

[0005] Nylon artificial muscles usually use electric heating, hydrothermal heating or electrochemical heating methods to change the temperature, causing the nylon actuator to produce reversible reciprocating motions such as contraction, expansion or rotation. Among them, using electric thermal drive is the most convenient method.

[0006] CN111702751A discloses a device and method for making a nylon-wound artificial muscle. The artificial muscle fibers in this invention are made by co-twisting nickel-chromium alloy wire and nylon fiber. CN115948835B discloses a process for preparing shrinkage yarn based on heat-driven artificial muscle fiber materials. This invention is made by co-twisting a metal microfilament and multiple nylon filaments. Both can achieve electrothermal drive by applying a certain voltage to both ends of the artificial muscle to generate Joule heat. However, the electrothermal metal wire cannot completely cover the surface of the nylon artificial muscle. The uneven heat distribution during the drive process may cause the artificial muscle drive strain to decrease.

[0007] CN112201744A discloses the preparation and application of an electrostrictive, helically wound artificial muscle. The invention consists of a sheath (carbon nanotube film) and an inner core (nylon fiber). Electrothermal actuation is achieved by applying a voltage to the sheath. While carbon nanotubes are excellent thermal actuation materials, possessing excellent conductivity and mechanical properties, and addressing the problem of uneven heat distribution during actuation, their high cost makes them unsuitable for large-scale commercial applications.

[0008] CN116276939A discloses a fast-response thermally driven spirally wound artificial muscle. CN116533226A discloses a method for preparing an electrically driven artificial muscle. To achieve good electrothermal drive performance and reduce the cost of electrothermal artificial muscles, both methods employ silver and platinum coatings, respectively, as the electrothermal drive layer. However, both are precious metals, making them unsuitable for large-scale industrial production. Summary of the Invention

[0009] To overcome the shortcomings and deficiencies of the prior art, the present invention provides a method for preparing an electrothermally driven artificial muscle. The artificial muscle prepared using this method can achieve reversible actuation at a low operating voltage and exhibits excellent contractile performance and cyclic stability. This method also reduces the cost of preparing nylon artificial muscles.

[0010] The purpose of the present invention is achieved through the following technical solutions.

[0011] A method for preparing an electrothermal driven artificial muscle comprises the following steps:

[0012] S1. Twisting a nylon fiber. When the fiber self-winds to form the first coil, the twisting is stopped immediately to obtain a nylon fiber in an ultimate straight state; winding the nylon fiber in the ultimate straight state, with the winding direction being consistent with the twisting direction; annealing the wound nylon coil in a vacuum state to obtain an artificial muscle fiber;

[0013] S2. roughening, sensitizing, and activating the artificial muscle fibers to obtain processed artificial muscle fibers;

[0014] S3, electrolessly plating a Ni / Cu / Sn composite metal layer on the treated artificial muscle fibers;

[0015] S4. Annealing the artificial muscle fiber coated with the composite metal layer at 140-160° C. for 40-60 min to obtain an electrothermally driven artificial muscle.

[0016] The specific steps of step S3 are:

[0017] S3-1: The treated artificial muscle fibers are subjected to electroless nickel plating; the electroless nickel plating solution comprises: NiSO4·6H2O 26-30 g / L, NaH2PO2·H2O 22-28 g / L, C6H5Na3O7·3H2O (sodium citrate) 25-40 g / L, CH4N2S (thiourea) 1-2 g / L, CH3COONa 11-14 g / L, and a pH value of 4.8-5.0; the electroless nickel plating treatment conditions are 85-90°C for 4-6 min;

[0018] S3-2: The artificial muscle fibers after electroless Ni plating were electrolessly plated with Cu; the electroless Cu plating solution was: CuSO4·5H2O 10-19 g / L, NiSO4 9-15 g / L, NaH2PO2·2H2O 75-80 g, C6H5Na3O7·3H2O (sodium citrate) 30-35 g / L, H3BO3 35-40 g / L, Na2EDTA 10-15 g / L; the electroless Cu plating conditions were 50-65°C for 5-10 min;

[0019] S3-3: The artificial muscle fibers after electroless Ni / Cu plating are electrolessly plated with Sn. The electroless Sn plating solution is: SnSO4 30-35g / L, H2SO4 42-48ml / L, CH4N2S (thiourea) 45-55g / L, NaH2PO2·2H2O 70-75g / L, EDTA 1g / L; the conditions for electroless Sn plating are electroless plating at 35-40°C for 1-10min.

[0020] Winding the nylon fiber in the ultimate straight state means winding the fiber into a curled state under a load without breaking the fiber; specifically, winding the nylon fiber in the ultimate straight state means winding the fiber to a critical twist under a load.

[0021] Winding involves attaching a load to one end of a nylon fiber in a critical straight line state, securing the other end of the fiber to a winding device, and then securing the winding device to a horizontal motor. The motor is then activated, winding the fiber around the device in the same direction as the twisting direction. After winding is complete, the other end of the fiber is secured to the device. For example, if the load is 500-1000g, the critical twist is 382 turns / meter when the load is 500g.

[0022] Annealing conditions in step S1: The annealing temperature is higher than the maximum driving temperature of the artificial muscle fiber and lower than its melting point. Specifically, the annealing conditions in step S1 are annealing at 180° C. for 85 to 95 minutes under vacuum.

[0023] The twisting refers to connecting one end of the nylon fiber to a vertical motor and hanging a weight on the other end so that it does not rotate with the motor to prevent the nylon fiber from untwisting during the twisting process; starting the motor to twist the nylon fiber, and when the fiber self-winds to form the first coil, the twisting is immediately stopped to obtain a nylon fiber in a critical straight state.

[0024] Specifically, the ends of a nylon fiber are attached to two paper clips, the top of which is connected to a motor, and a weight is hung from the bottom. A steel wire is passed through the bottom paper clip to prevent the nylon fiber from untwisting during the twisting process. The motor is turned on to twist the nylon fiber in one direction. When the fiber self-winds to form the first coil, the twisting is stopped immediately, resulting in a nylon fiber in a critically straight state.

[0025] The roughening in step S2 refers to roughening the artificial muscle fibers in a roughening solution: the formula of the roughening solution is H2SO4 10% to 18% (volume), CH3COOH 20% to 30% (volume); the roughening treatment conditions are: roughening at 20 to 40°C for 10 to 30 seconds;

[0026] The sensitization refers to sensitizing the roughened fiber in a sensitizing solution; the sensitizing solution is a stannous chloride solution with a pH value of 0.5 to 1.5 and a concentration of 10 to 15 g / L; the sensitization treatment condition is to place the roughened fiber in the sensitizing solution for 5 to 15 minutes;

[0027] The activation treatment refers to activating the sensitized fiber in an activation solution having a pH value of 0.8 to 1.2 and a concentration of 0.1 to 0.2 g / L palladium chloride solution. The activation treatment condition is to treat the sensitized fiber in the activation solution for 3 to 6 minutes.

[0028] After sensitization and activation, the fiber is washed with water.

[0029] Before roughening, the artificial muscle fibers were degreased and cleaned, that is, the fibers were immersed in ethanol for 10-20 minutes at room temperature, taken out and rinsed with water, and dried naturally.

[0030] The present invention uses an acid solution to roughen the surface of nylon fibers, providing mechanical anchoring sites for the metal coating and improving the adhesion of the metal coating on its surface; and uses annealing treatment to release the internal stress of the composite coating, preventing the coating from cracking and peeling during the cyclic driving process, which leads to reduced driving performance.

[0031] The present invention utilizes the surface metal composite coating to generate Joule heating, drives muscle fibers to generate greater strain with a lower voltage, and has better cycle stability.

[0032] The coating method of the present invention not only makes the bonding between the metal layer and the substrate strong, but also enables the artificial muscle to have good electrical conductivity, contractility and electrothermal drive properties.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] 1. The present invention winds nylon fibers in a critical linear state onto a core rod of a certain diameter, increases the distance between coils, and obtains an artificial muscle with reversible cyclic strain, large driving stroke, and high strength after annealing and shaping.

[0035] 2. After the fiber surface is roughened, a physical anchoring site is provided for the metal composite coating, which greatly improves the bonding strength between the coating and the substrate.

[0036] 3. The use of metal Ni / Cu / Sn composite coating ensures good bonding strength of the coating while reducing the resistivity from 850Ω / m to 130Ω / m, greatly improving the conductivity and electrothermal drive performance of the electrothermal nylon artificial muscle.

[0037] 4. The nylon artificial muscle prepared above was annealed at a temperature of 140-160°C for 40 minutes to release the internal stress in the metal coating and prevent cracking and peeling during the cyclic driving process. After 400 cycle tests, the performance did not decrease significantly, showing excellent cyclic stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 These are scanning electron microscope images of the surface coating of the electrothermal nylon artificial muscle in Example 1 before and after annealing treatment; (a) before annealing treatment, (b) after annealing treatment;

[0039] Figure 2 is the change in resistivity of electrothermal nylon artificial muscles plated with Ni, Ni / Cu, and Ni / Cu / Sn;

[0040] Figure 3 The contraction performance of the electrothermal nylon artificial muscle in Example 1 at different voltages with a load of 50 g (a) and 100 g (b);

[0041] Figure 4 The electrothermal nylon artificial muscle in Example 1 was subjected to a cyclic stability test under a load of 50 g;

[0042] Figure 5 This is a thermal imaging image of the electrothermal nylon artificial muscle in Example 1 when driven under a load of 100 g. DETAILED DESCRIPTION

[0043] The present invention will be described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0044] Example 1

[0045] 1. Preparation of nylon artificial muscle:

[0046] 1) Twisting of nylon fiber: A section of nylon fiber with a diameter of 0.77 mm was attached to two paper clips at each end. One end of the fiber served as the top and was connected to a motor. A 500 g weight was suspended from the other end of the fiber. A steel wire was passed through the bottom paper clip to prevent the nylon fiber from untwisting during twisting. The motor was started to twist the nylon fiber in a clockwise direction (with the twist direction being S). Twisting was stopped immediately when the fiber self-wound to form the first coil, resulting in a nylon fiber in a critical straight state.

[0047] 2) Mandrel Winding: While maintaining the weight of one end of the nylon fiber obtained in the extreme straight state in the above steps, thread the end of the fiber connected to the motor through a butterfly buckle to secure the twisted fiber firmly to a mandrel with a diameter of 1.5 mm. The mandrel is fixed to a horizontal motor, which is started to drive the fiber to be wound clockwise (in the same direction as the twisting) around the mandrel (the critical twist is 382 turns / meter). After winding, the other end of the fiber is fixed to the mandrel.

[0048] 3) Annealing: The nylon coil fixed to the mandrel was placed in a vacuum drying oven and annealed at 180°C (a temperature higher than the maximum actuation temperature of the artificial muscle and lower than its melting point) for 90 minutes. The sample was then naturally cooled at room temperature and the mandrel was removed, completing the preparation of the artificial muscle fiber.

[0049] 2. Pretreatment process

[0050] 1) Fiber surface degreasing and cleaning: Soak the nylon fiber in ethanol for 15 minutes at room temperature, then remove it and rinse it with deionized water and let it dry naturally;

[0051] 2) Fiber surface roughening treatment: The roughening solution is mainly composed of H2SO4 15% (volume concentration) and CH3COOH 25% (volume concentration), and the roughening process is carried out at 35°C for 20 seconds;

[0052] 3) Sensitization and activation treatment: A stannous chloride solution with a pH of 1 and a concentration of 15 g / L was prepared as a sensitizing solution. The roughened nylon fiber was placed in the sensitizing solution and magnetically stirred for 15 minutes. After sensitization, the fiber was removed and rinsed three times with deionized water. A palladium chloride solution with a pH of 1 and a concentration of 0.15 g / L was prepared as an activation solution. The sensitized nylon fiber was placed in the activation solution and magnetically stirred for 6 minutes. The fiber was then rinsed three times with deionized water to ensure stable palladium particles deposited on the surface.

[0053] 3. Preparation of metal conductive composite coating:

[0054] 1) The activated nylon artificial muscle fibers were electrolessly plated with nickel. The formula and process conditions for the electroless nickel-phosphorus alloy plating were as follows: NiSO4·6H2O 28 g / L, NaH2PO2·H2O 24 g / L, C6H5Na3O7·3H2O 27 g / L, CH4N2S (thiourea) 1.3 g / L, CH3COONa 12 g / L, pH 4.9 (adjusted with aqueous ammonia); the plating was carried out at 90°C for 4 min.

[0055] 2) The nylon artificial muscle fibers after electroless Ni plating were electrolessly plated with Cu. The electroless Cu plating formula and process conditions were as follows: CuSO4·5H2O 17g / L, NiSO4 10g / L, NaH2PO2·2H2O 76g, C6H5Na3O7·3H2O (sodium citrate) 34g / L, H3BO3 36g / L, Na2EDTA 12g / L; electroless plating at 60°C for 6min;

[0056] 3) After electroless Ni / Cu plating, the nylon artificial muscle fibers were electrolessly plated with Sn. The electroless Sn plating formula and process conditions were as follows: SnSO₄ 32 g / L, H₂SO₄ 44 ml / L, CH₄N₂S 48 g / L, NaH₂PO₂·2H₂O 73 g / L, and EDTA 1 g / L. The plating was performed at 40°C for 2 min, followed by three rinses with deionized water and air drying.

[0057] 4) After natural drying, place it at 150°C for 45 minutes for annealing.

[0058] Comparison of the SEM images of the coating state after 50 cycles of electrothermal nylon artificial muscle actuation before and after annealing treatment, as shown in Figure 2. Figure 1 shown. Figure 1 (a) The coating of the nylon artificial muscle before annealing showed obvious peeling after actuation. Figure 1 (b) The phenomenon is significantly improved after annealing.

[0059] Figure 2 The resistivity changes of electrothermal nylon artificial muscles coated with Ni, Ni / Cu, and Ni / Cu / Sn are shown. The use of a Ni / Cu / Sn composite coating ensures good adhesion and reduces the resistivity from 850Ω / m to 30Ω / m, significantly improving its electrothermal drive performance.

[0060] Performance testing:

[0061] (1) The electrothermal nylon artificial muscle provided by the present invention can provide a large driving force at a low driving voltage. A certain voltage is applied to both ends of the artificial muscle prepared in Example 1 using a DC power supply, and the contraction length change of the artificial muscle is recorded using a laser displacement sensor. When a load of fixed mass is hung on one end, the length of the composite nylon artificial muscle contracts as the voltage increases. The results are as follows. Figure 3 shown.

[0062] Figure 3 Figure 1 shows the contractile performance of the electrothermal nylon artificial muscle in Example 1 under loads of 50g (a) and 100g (b) at different voltages. The relationship between the actuation deformation and applied voltage is shown for the nylon artificial muscle under loads of 50g and 100g, respectively. Increasing the applied voltage increases the actuation range of the artificial muscle, with the maximum strain exceeding 40%.

[0063] (2) Cycle life is an important criterion for measuring the performance of artificial muscles. In the present invention, the parameters in the cycle test are: external applied load of 0.98MPa, input voltage of 9V, square wave voltage of 0.014Hz frequency, duty cycle of 50%, and cycle stability test. The performance test results of the artificial muscle prepared in Example 1 are as follows: Figure 4 After 400 cycles, the performance did not show a downward trend, showing good cycle stability.

[0064] (3) A voltage of 15 V was applied under a load of 100 g, and the temperature rise process of the artificial muscle prepared in Example 1 was observed using a thermal imaging camera. Figure 5 This is a thermal imaging image of the electrothermal nylon artificial muscle in Example 1 when driven under a load of 100g. Figure 5 It can be seen that under this voltage, contraction strain can be generated rapidly, the contraction strain rate exceeds 40%, and the surface temperature is uniform, achieving uniform heating of the surface of the nylon artificial muscle.

Claims

1. A method for preparing an electrothermal driven artificial muscle, characterized in that: The following steps are involved: S1. Twisting a nylon fiber. When the fiber self-winds to form the first coil, the twisting is stopped immediately to obtain a nylon fiber in an ultimate straight state; winding the nylon fiber in the ultimate straight state, with the winding direction being consistent with the twisting direction; annealing the wound nylon coil in a vacuum state to obtain an artificial muscle fiber; S2. performing roughening, sensitization, and activation treatments on the artificial muscle fibers to obtain treated artificial muscle fibers; S3, electrolessly plating a Ni / Cu / Sn composite metal layer on the treated artificial muscle fibers; S4, annealing the artificial muscle fiber coated with the composite metal layer at 140-160° C. for 40-60 min to obtain an electrothermally driven artificial muscle; The specific steps of step S3 are: S3-1: The treated artificial muscle fibers are subjected to electroless nickel plating; the electroless nickel plating solution comprises: NiSO4·6H2O 26-30 g / L, NaH2PO2·H2O 22-28 g / L, C6H5Na3O7·3H2O 25-40 g / L, CH4N2S 1-2 g / L, CH3COONa 11-14 g / L, and a pH value of 4.8-5.0; the electroless nickel plating treatment conditions are 85-90°C for 4-6 min; S3-2: The artificial muscle fibers after electroless Ni plating were electrolessly plated with Cu. The electroless Cu plating solution was: CuSO4·5H2O 10-19 g / L, NiSO4 9-15 g / L, NaH2PO2·2H2O 75-80 g / L, C6H5Na3O7·3H2O 30-35 g / L, H3BO3 35-40 g / L, Na2EDTA 10-15 g / L. The electroless Cu plating conditions were 50-65°C for 5-10 min. S3-3: The artificial muscle fibers after electroless Ni / Cu plating were electrolessly plated with Sn. The electroless Sn plating solution was: SnSO4 30-35g / L, H2SO4 42-48ml / L, CH4N2S 45-55g / L, NaH2PO2·2H2O 70-75g / L, EDTA 1g / L; the electroless Sn plating conditions were 35-40°C for 1-10 min.

2. The method for preparing the electrothermal driven artificial muscle according to claim 1, characterized in that: The step S1 of winding the nylon fiber in the ultimate straight state means winding the fiber into a curled state under load without breaking the fiber; Annealing molding conditions in step S1: the annealing temperature is higher than the maximum driving temperature of the artificial muscle fiber and lower than its melting point.

3. The method for preparing the electrothermal driven artificial muscle according to claim 2, characterized in that: The annealing molding condition in step S1 is annealing treatment at 180° C. for 85 to 95 minutes under vacuum.

4. The method for preparing the electrothermal driven artificial muscle according to claim 1, characterized in that: The roughening in step S2 refers to roughening the artificial muscle fibers in a roughening solution: the formula of the roughening solution is 10% to 18% by volume of H2SO4 and 20% to 30% by volume of CH3COOH; the roughening treatment conditions are: roughening at 20 to 40°C for 10 to 30 seconds; The sensitization refers to sensitizing the roughened fiber in a sensitizing solution; the sensitizing solution is a stannous chloride solution with a pH value of 0.5 to 1.5 and a concentration of 10 to 15 g / L; the sensitization treatment condition is to place the roughened fiber in the sensitizing solution for 5 to 15 minutes; The activation treatment refers to activating the sensitized fiber in an activation solution, wherein the activation solution has a pH value of 0.8-1.2 and a concentration of 0.1-0.2 g / L palladium chloride solution; The activation treatment conditions are to treat the sensitized fiber in the activation solution for 3 to 6 minutes; After sensitization and activation, the fiber is washed with water.

5. The method for preparing the electrothermal driven artificial muscle according to claim 1, characterized in that: Before roughening, the artificial muscle fibers were degreased and cleaned, that is, the fibers were immersed in ethanol for 10-20 minutes at room temperature, taken out and rinsed with water, and dried naturally.

6. The method for preparing the electrothermal driven artificial muscle according to claim 1, characterized in that: The winding refers to fixing a load on one end of the nylon fiber in the extreme straight state, fixing the other end of the fiber on a winding device, fixing the winding device on a horizontal motor, starting the motor, driving the fiber to be wound on the winding device in the same direction as the twisting direction, removing the load after the winding is completed, and fixing the end of the fiber without the load on the winding device.

7. The method for preparing the electrothermal driven artificial muscle according to claim 1, characterized in that: The twisting process involves connecting one end of the nylon fiber to a vertical motor and hanging a weight on the other end so that it does not rotate with the motor, thereby preventing the nylon fiber from untwisting during the twisting process. The motor is started to twist the nylon fiber. When the fiber self-winds to form the first coil, the twisting is stopped immediately to obtain the nylon fiber in the critical limit straight state.

8. An electrothermal driven artificial muscle obtained by the preparation method according to any one of claims 1 to 7.

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