A method for manufacturing a large-strain artificial muscle using super twisting

Abstract

The application relates to a manufacturing method of a large-strain artificial muscle by using super twisting, which comprises the following steps: infiltrating carbon nanotube fibers into composite organic silicone rubber, and then preparing super-helix structure composite artificial muscle yarn by using a twisting method, so that the carbon nanotube artificial muscle yarn fiber with the super-helix structure prepared by the method can provide a larger stroke and reversible driving, and has a wide application prospect in bionic robots, electric heating rehabilitation gloves, wearable devices and the like. Compared with a pneumatic, magnetic heating, electrochemical and other driving modes, the electric heating driving mode has inherent advantages such as wide application, simple energy acquisition, and the driving mode is widely applied in daily life, energy sources are simple to obtain, and additional equipment is not needed.

Description

TECHNICAL FIELD

[0001] The application relates to a manufacturing method of a large-strain artificial muscle by using super twisting, and is suitable for the technical fields of intelligent fabrics, flexible rehabilitation gloves and bionic robots. BACKGROUND

[0002] The artificial muscle is a flexible driver imitating natural muscles. The artificial muscle can generate stretching, bending, twisting and their combinations under external stimulation conditions (such as temperature, current, humidity, ions, light and magnetic field). The artificial muscle is a new type of bionic flexible driver, is similar to biological muscles, has the advantages of large contraction stress, high power density and high energy conversion efficiency, and has a wide application prospect in the fields of soft robots, flexible exoskeletons, intelligent fabrics, sensors and biological medical treatment.

[0003] At present, the intelligent materials that can be used as artificial muscles include shape memory alloys, electroactive polymers, carbon nanotube fibers, nylon wires, graphene fibers, natural fibers and polyethylene fibers. The carbon nanotube fiber is one of various macroscopic assemblies of carbon nanotubes (CNT), inherits the excellent electrical conductivity, thermal conductivity, mechanical strength and other characteristics of carbon nanotubes, and is the material with the highest specific strength among the known materials. The carbon nanotube artificial muscle yarn made of the carbon nanotube fiber has the advantages of large strength, fast response speed, good cycle performance and low working voltage. It is found through research that the fiber made of pure carbon nanotubes has good electrical conductivity, thermal conductivity and anisotropy, and expands when heated, but the strain of the artificial muscle yarn made of pure carbon nanotube is only 1%, and the practical application value is not large.

[0004] The driving modes of carbon nanotube artificial muscle yarns are various, such as electrochemical driving, pneumatic driving and light driving, etc. For the electrochemical driving of the carbon nanotube artificial muscle yarn, mainly in the electrolyte or gel electrolyte, the carbon nanotube artificial muscle yarn is used as the working electrode, and after the voltage is applied, the solvated ions in the electrolyte / quality re-enter the micro-nano channels between the carbon nanotube fiber bundles, causing the material to deform macroscopically, so that the driving of the carbon nanotube artificial muscle yarn can be controlled by changing the voltage. Although the electrochemical driving has the advantages of low voltage, easy control, high energy density and no thermal effect, it needs to use electrolyte, but there is no effective packaging method at present, and the application scene is limited. For the pneumatic driving of the carbon nanotube artificial muscle yarn, mainly the pneumatic carbon nanotube artificial muscle yarn is driven by the uneven volume expansion caused by the gas embedded cavity to cause deformation, which has the characteristics of fast driving, large contraction stroke, programmable, etc., but they need a pressure pump, which is not convenient to carry and use. For the light driving of the carbon nanotube artificial muscle yarn, due to the relatively small shrinkage strain and slow response, its use is limited. For the electrothermal driving of the carbon nanotube artificial muscle yarn, it is favored by many researchers due to its advantages of clean and non-polluting, easy to obtain, easy to control and simple to make. SUMMARY

[0005] The purpose of the present application is to provide a method for making large-strain artificial muscle by super twisting, which improves the output strain and cycle stability of the carbon nanotube artificial muscle yarn under electrothermal driving.

[0006] The technical scheme adopted by the present application is as follows: a method for manufacturing a large-strain artificial muscle by using super twisting, comprising the following steps: S1: winding a carbon nanotube film into a cylindrical shape, then connecting one end of the carbon nanotube film to a motor, applying a weight to the other end, connecting the weight end with a long strip-shaped object, clamping the long strip-shaped object with the object to ensure that the lower end does not rotate with the motor, and twisting the carbon nanotube film into a state of just forming a fiber at a specified speed of the motor, then taking out the carbon nanotube fiber, cutting off the parts twisted poorly at both ends, and then using a paper clip to knot and fix again; S2: immersing the carbon nanotube fiber in the step S1 in a diluted silica gel solution, taking out the carbon nanotube fiber vertically after a specified time of soaking, and performing drying treatment; S3: re-connecting one end of the carbon nanotube fiber solidified in the step S2 to the motor, applying a weight to the other end, connecting the weight end with a long strip-shaped object, clamping the long strip-shaped object with the object to ensure that the lower end does not rotate with the motor, rotating the motor at a specified speed until the carbon nanotube fiber solidified is twisted into a carbon nanotube artificial muscle yarn of super helical structure, and immediately powering off the motor; and S4: taking out the carbon nanotube artificial muscle yarn of super helical structure in the step S3, hanging the yarn on an iron stand, knotting copper wires on the paper clips at both ends as conductive wires for power supply, connecting the copper wires at both ends with a direct current stabilized power supply, and training the carbon nanotube artificial muscle yarn of super helical structure in performance by applying a voltage.

[0007] In the above scheme, in the step S1, the preparation method of the carbon nanotube film in a cylindrical shape is as follows: vertically arranging carbon nanotube arrays in a mold, drawing out a carbon nanotube film with more than 6 layers, and winding the carbon nanotube film into a cylindrical shape through the mold, wherein the total width of the carbon nanotube film is greater than 200 mm.

[0008] In the above scheme, in the step S1, the preparation method of the carbon nanotube vertical array is as follows: preparing by a chemical vapor deposition method (CVD), first, using methane as a carbon source, ferrocene and thiophene vapor as a catalyst and a growth promoter respectively, and passing the above gaseous raw materials into a reactor with helium as a carrier gas, and performing the synthesis process of the carbon nanotube at a temperature of more than 700 DEG C, ensuring that the reaction is performed in a hydrogen atmosphere, and finally obtaining a multi-walled carbon nanotube vertical array.

[0009] In the above scheme, in the step S2, the preparation method of the silica gel solution is as follows: configuring a silica gel solution according to a specified proportion with a silica gel base and a curing agent, then diluting with an organic solvent, and performing degassing treatment after dilution.

[0010] In the above scheme, in the step S2, the drying process is as follows: placing the fiber into a vacuum drying box for rapid solidification after taking out, or naturally air-drying solidification at room temperature.

[0011] In the above scheme, in step S3, the specific process of forming the superhelix structure carbon nanotube artificial muscle yarn is that: in the process of motor rotation, the solidified carbon nanotube fiber is first twisted into a helix structure, then the motor is continuously controlled at the same speed to continue twisting, until the fiber length becomes shorter and the diameter becomes larger, indicating that a superhelix structure has appeared, and until the fiber is completely formed into a superhelix structure carbon nanotube artificial muscle yarn.

[0012] In the above scheme, in step S4, the specific process of training the performance of the superhelix structure carbon nanotube artificial muscle yarn is that: a weight is hung at the lower end of the superhelix structure carbon nanotube artificial muscle yarn, and the helical joint of the carbon nanotube artificial muscle yarn is pulled apart. When training, a pulse of 1 Hz, a duty cycle of 50%, and a voltage of 3 V is used to test whether it can conduct electricity, and after it is observed that it can conduct electricity, the voltage is increased by 2 V each time, and after each voltage is added, the voltage is used to continue training for ten seconds under the same conditions as before, and the voltage is gradually increased until smoke appears, and the power is immediately turned off. With a voltage of 3-4 V lower than the voltage when the smoke appears, continue to train until the contraction performance of the carbon nanotube artificial muscle yarn tends to be stable, and subsequent training is carried out with a current of 0.05 A lower than the current in the case of smoke. The cyclic stability of the trained carbon nanotube artificial muscle yarn reaches an optimal state.

[0013] The present application also protects a large-strain carbon nanotube artificial muscle yarn formed by the above manufacturing method.

[0014] The present application has the following advantages: (1) The superhelix structure carbon nanotube artificial muscle yarn fiber improved by the method can provide a larger stroke and reversible drive, and has a wide application prospect in bionic robots, electric heating rehabilitation gloves, wearable devices, etc. (2) Compared with pneumatic, magnetic heating, electrochemical and other driving methods, electric heating driving has inherent advantages such as wide application, simple energy acquisition, and its driving method is widely used in daily life, and the energy source is easy to obtain without the need for additional equipment. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 . Process diagram of superhelix structure carbon nanotube artificial muscle yarn.

[0016] Figure 2 . SEM diagram of carbon nanotube artificial muscle yarn.

[0017] Figure 3 . Cyclic stability test performance diagram of CNT@Mold MaxTM25 superhelix structure artificial muscle yarn under a frequency of 2 Hz, a voltage of 13 V, and a load of 8.965 g.

[0018] Figure 4. The corresponding strain-time graph of CNT@Mold Max™25 super coiled structure artificial muscle yarn at 15 V, 11.2 MPa, 0.2 Hz.

[0019] Figure 5 . The driving strain performance comparison chart of super coiled structure and common coiled structure with composite silica gel at different frequencies. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described in more detail below with reference to the accompanying drawings.

[0021] The present application provides a method for manufacturing large-strain artificial muscle using super twisting, and the manufacturing process is shown in FIG. 1. Figure 1 The specific steps are as follows.

[0022] Step one: prepare spinnable carbon nanotube array by existing chemical vapor deposition method (CVD). First, use methane as carbon source, ferrocene and thiophene vapor as catalyst and growth promoter respectively. Pass the above gaseous raw materials into the reactor with helium as carrier gas. The synthesis process of carbon nanotube is carried out at high temperature (above 700℃), and the reaction is carried out in hydrogen atmosphere, so that multi-walled carbon nanotube array can be prepared.

[0023] Step two: use a mold to pull out a carbon nanotube film with a total width of more than 200 mm from the vertical array of carbon nanotubes, with several layers (more than 6 layers for better strength). The two ends of the pulled film are respectively stuck on the double-sided adhesive of the mold, and the double-sided adhesive is used again to stick on the two ends of the pulled film. Two paper clips are stuck on the double-sided adhesive. Roll the paper clips to make the carbon nanotube film form a roll structure. Take the roll-shaped film off the mold, fix one end of the film on the motor shaft with a paper clip, and hang a 4g weight on the other end to make it naturally sag. The weight is used to ensure that the carbon nanotube film is straightened. The hanging weight end uses a long strip object (such as a ribbon) to block the paper clip to ensure that the lower end of the film does not rotate with the rotation of the motor shaft. Use an Arduino development board to control the motor to rotate at a speed of 200 rpm in one direction. When the roll-shaped film becomes a fiber state, immediately turn off the motor. Take off the fiber, cut off the two ends that are not treated, and then tie knots on the two ends of the twisted fiber with paper clips.

[0024] Step three: prepare a silica gel solution. Any silica gel with a large thermal expansion coefficient can be used in this patent. The silica gel used in this example is Mold Max TM 25, Mold Max TM25 is a condensation type silicone rubber, purchased from Smooth-On, USA. The base and curing agent are configured in a mass ratio of 20:1, and the diluent is diluted in a mass ratio of 1:3. In this embodiment, n-hexane is used as the diluent. After the silicone rubber and the diluent are mixed, a magnetic stirrer is added and the mixture is stirred evenly using a magnetic stirrer. The magnetic stirrer is then removed and the mixture is degassed in a vacuum device for 5 minutes.

[0025] Step four: The treated silicone rubber is poured into a special mold, and the fiber with the re-knotted fiber in step two is fully immersed in the silicone rubber. The fiber is immersed for 5-8 seconds and then taken out vertically from the solution surface, so that the silicone rubber coating on the surface of the fiber is more uniform and there are no uneven points in the form of droplets. If there are uneven points, the fiber is fully immersed again and then taken out vertically. After the fiber is taken out, it is placed in a vacuum drying oven and treated at 60°C for 2 hours to achieve rapid curing. The fiber can also be naturally air-dried and cured at room temperature for 8 hours to achieve the same curing effect.

[0026] The carbon nanotube film has many pores inside and on the surface of the fiber. The use of silicone rubber for immersion can allow the silicone rubber to enter the interior of the carbon nanotube fiber and fully combine with the fiber, thereby forming a silicone rubber composite carbon nanotube fiber. The incorporation of a certain amount of silicone rubber into the carbon nanotube fiber can significantly increase the thermal expansion coefficient of the artificial muscle composite fiber. When the temperature rises, the spiral nodes of the yarn will expand radially, causing the artificial muscle yarn to contract axially.

[0027] Step four: The cured silicone rubber composite carbon nanotube fiber is placed back on the twisting device for twisting. One end is fixed to the motor shaft with a paperclip, and the other end is suspended with a 4 g weight to allow it to hang naturally. The weight is used to ensure that the carbon nanotube film is straightened. The end with the weight uses a long object (such as a cable tie) to hold the paperclip, ensuring that the lower end of the film does not rotate with the motor shaft. An Arduino development board is used to control the motor to rotate at a speed of 200 rpm in one direction. During the formation of the spiral winding structure, the diameter of the fiber will slightly increase and the length will decrease. When the spiral structure is completely formed, the twisting continues, and during the process of ordinary spiral to super-spiral structure, the diameter of the fiber will significantly increase and the length will decrease rapidly. After the super-spiral structure is completely formed (as shown in Figure 2 The motor is immediately disconnected to prevent the fiber from breaking due to excessive cutting force.

[0028] Super twisting of carbon nanotube fiber can increase the twist of the fiber and reduce the length of the yarn. With the increase of twist, the strain of the yarn will also be greater and greater, because in the twisting process, with the increase of twist, the length of the yarn is constantly shortened, so its space can be stretched is getting bigger and bigger. Super twisting is great for increasing the space gain.

[0029] Step five: after taking down the super twisted carbon nanotube artificial muscle yarn, hang it on the iron stand, and tie a knot on the two ends of the paper clip with copper wire as the conductor for power supply. Use a DC stabilized power supply to connect the two ends of the copper wire to apply a low voltage square wave first, train its stability, and gradually increase the voltage to train the muscle until the muscle contraction performance is stable. Specifically, hang a slightly heavier object than the twisted one at the lower end of the artificial muscle, pull apart the spiral joints of the artificial muscle, and train it first using a 1 Hz, 50% duty cycle, 3 V pulse to test its ability to conduct electricity. After observing that the artificial muscle can conduct electricity, increase the voltage by 2 V, and after each voltage increase, train the muscle for ten seconds at the same conditions as before. Gradually increase the voltage until the muscle smokes, immediately turn off the power, and continue to train at a voltage that is 3-4 V lower than the smoking voltage until the muscle's contraction performance tends to be stable. Subsequent training is carried out at a current that is 0.05 A lower than the current at the time of smoking. The trained muscle has better cycle stability performance, as shown in Figure 3 .

[0030] Step six: hang the weight used for training on the super twisted carbon nanotube artificial muscle yarn in a sealed space to apply voltage for stress-strain testing to prevent external airflow from blowing the muscle and interfering with the test results. Use a displacement sensor and Labview software to test the time and displacement, and then obtain the strain-time relationship graph.

[0031] The preparation mechanism of the electro-thermal driving type super-twisted carbon nanotube artificial muscle yarn prepared by the application is as follows: silica gel, as a typical flexible driving material, has a large thermal expansion coefficient, and thus has a strong gain for improving the strain of the super-helical winding type fiber artificial muscle. In addition to the selected material having a large thermal expansion coefficient, the driving performance mainly depends on factors such as the twist density, moment of inertia and applied stress of the composite yarn. In particular, the higher the twist density has a greater impact on the output strain. The super-helical winding structure makes the super-helical winding artificial muscle yarn have a larger twist than the ordinary helical winding artificial muscle, which is the key to improving the strain performance of the carbon nanotube fiber artificial muscle. Because the axial length change of the artificial muscle fiber is proportional to the twist. After the silica gel is compounded with the carbon nanotube fiber, the super-helical winding artificial muscle is formed by over-twisting. Then, a voltage is applied to both ends of the artificial muscle, the carbon nanotube yarn is used as a heat source, and then Joule heat is generated. With the change of temperature, the super-helical winding composite fiber artificial muscle produces a larger expansion in the radial direction, and the radial expansion of the yarn causes the super-helical winding structure to shrink in the axial direction. When the applied voltage is removed, the temperature of the artificial muscle yarn gradually decreases, and then the initial state is restored, and the cycle stability is good, as shown in the accompanying drawings. Figure 3 The whole driving process achieves the purposes of large strain, electro-thermal driving, no pollution and environmental protection. Here, we compare the output strain under different twisting degrees, that is, the output strain of the ordinary helical winding structure formed by ordinary twisting and the over-helical structure formed by super-twisting. As shown in the accompanying drawings, Figure 4 and Figure 5 The maximum output strain can reach 45%.

[0032] The super-helical structure large-strain carbon nanotube artificial muscle yarn proposed in the application has the characteristics of large strain and fast response. The design method and performance test operation of the carbon nanotube fiber composite yarn artificial muscle driven by electro-thermal driving are simple and convenient, economical and environmental protection, high mechanical strength, and have high stability. When a stress of about 10 MPa is applied, the contraction strain of the super-helical structure large-strain carbon nanotube artificial muscle yarn can reach 45%. Due to the improvement of the strain, it has shown great application prospects in the fields of soft actuators, bionic manipulators and rehabilitation gloves.

Claims

1. A method for fabricating large-strain artificial muscles using super-twisting, characterized in that, Includes the following steps: S1: Roll the carbon nanotube film into a cylindrical shape, then connect one end to a motor and apply a weight to the other end. Connect a long strip to the end of the weight and hold the strip in place to ensure that the lower end does not rotate with the motor. Control the motor to twist the carbon nanotube film at a specified speed until it forms fibers. Remove the carbon nanotube fibers, cut off the poorly twisted parts at both ends, and then re-tie them with paperclips. S2: Immerse the carbon nanotube fibers from step S1 in a diluted silica gel solution. After immersion for a specified time, remove the carbon nanotube fibers vertically and dry them. S3: Reconnect one end of the solidified carbon nanotube fiber from step S2 to the motor, apply a weight to the other end, connect the weight end with a long strip object, and use the object to hold the long strip object in place to ensure that the lower end does not rotate with the motor. Control the motor to rotate at a specified speed until the solidified carbon nanotube fiber is completely twisted into a super-spiral structure carbon nanotube artificial muscle yarn, and immediately disconnect the power to the motor. S4: Remove the superspiral carbon nanotube artificial muscle yarn from step S3 and suspend it on an iron stand. Tie copper wires to the paperclips at both ends to act as conductors for power transmission. Connect the copper wires at both ends to a DC regulated power supply and apply voltage to train the performance of the superspiral carbon nanotube artificial muscle yarn.

2. The method for fabricating large-strain artificial muscles using super-twisting according to claim 1, characterized in that, In step S1, the preparation method of the cylindrical carbon nanotube film is as follows: carbon nanotubes are vertically arrayed and placed in a mold, and more than 6 layers of carbon nanotube film are pulled out. The total width of the carbon nanotube film is greater than 200 mm, and the carbon nanotube film is rolled into a cylindrical shape through the mold.

3. The method for fabricating large-strain artificial muscles using super-twisting according to claim 2, characterized in that, In step S1, the preparation method of the vertical array of carbon nanotubes is as follows: it is prepared by chemical vapor deposition. First, methane is used as the carbon source, ferrocene and thiophene vapor are used as catalyst and growth promoter, respectively, and helium is used as the carrier gas to introduce the above gaseous raw materials into the reactor. The synthesis process of carbon nanotubes is carried out at a temperature above 700°C, and the reaction is carried out in a hydrogen atmosphere. Finally, a vertical array of multi-walled carbon nanotubes is prepared.

4. The method for fabricating large-strain artificial muscles using super-twisting according to claim 1, characterized in that, In step S2, the method for preparing the silicone solution is as follows: the silicone matrix and the curing agent are prepared into a silicone solution according to a specified ratio, and then diluted with an organic solvent, followed by degassing treatment.

5. The method for fabricating large-strain artificial muscles using super-twisting according to claim 1, characterized in that, In step S2, the drying process is as follows: after the fiber is taken out, it is placed in a vacuum drying oven for rapid curing, or it is left to air dry and cure naturally at room temperature.

6. The method for fabricating a large-strain artificial muscle using super-twisting according to claim 1, characterized in that, In step S3, the specific process of forming the superhelical carbon nanotube artificial muscle yarn is as follows: during the rotation of the motor, the solidified carbon nanotube fibers are first twisted into a spiral structure, and then the motor is controlled to continue twisting at the same speed until the fiber length becomes shorter and the speed increases, and the diameter becomes significantly larger, indicating that a superhelical structure has appeared, until the fibers completely form a superhelical carbon nanotube artificial muscle yarn.

7. The method for fabricating large-strain artificial muscles using super-twisting according to claim 1, characterized in that, In step S4, the specific process of performance training of the superspiral carbon nanotube artificial muscle yarn is as follows: a weight is suspended at the lower end of the superspiral carbon nanotube artificial muscle yarn, and the spiral joint of the carbon nanotube artificial muscle yarn is pulled apart. During training, a 1 Hz pulse with a 50% duty cycle and a 3 V pulse is used to test whether it can conduct electricity. After observing that it can conduct electricity, the voltage is increased in increments of 2 V. After each voltage increase, the same voltage is used and the same conditions are described above, and training is continued for more than ten seconds. The voltage is gradually increased until smoke appears. The power is immediately cut off, and training is continued at a voltage 3-4 V lower than the voltage when smoke appears, until the contractile performance of the carbon nanotube artificial muscle yarn tends to stabilize. Subsequent training is carried out with a current 0.05 A lower than the current when smoke appears. After training, the cyclic stability performance of the carbon nanotube artificial muscle yarn reaches the optimal state.

8. A high-strain carbon nanotube artificial muscle yarn formed by the manufacturing method as described in claim 1.

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