A fabrication process and control method for a free-curvature biomimetic artificial muscle fan blade

Abstract

This invention discloses a fabrication process and control method for a free-curvature bionic artificial muscle fan blade, belonging to the field of bionic artificial muscle fan blade technology. It involves mixing sodium alginate, a natural polymer, with an ionic liquid to prepare a biomass gel electro-actuated membrane with high output force density and high strength at room temperature. A biomass gel conductive ink, made by blending gallium indium tin alloy with sodium alginate powder, is used as the electrode film. The resulting artificial muscle fan blade exhibits high energy conversion efficiency, low starting voltage, fast response speed, and higher structural strength at room temperature. Finally, the fan-shaped electrode is divided into several regions, which can be independently powered to control the curvature effect. This invention provides a simple fabrication process and control method for a free-curvature bionic artificial muscle fan blade, with stable structure, rapid deformation, and strong controllability, offering new ideas for the research and application of artificial muscle devices.

Description

Technical Field

[0001] This invention relates to the field of bionic artificial muscle fan blade technology, and in particular to a preparation process and control method for a free curvature bionic artificial muscle fan blade. Background Technology

[0002] When power is required from fluids, most existing drive systems employ axial-flow propellers. However, the design of these blades requires complex aerodynamic calculations, and once finalized, they have their own optimal operating speed and direction. In the actual operation of most equipment, prolonged operation at sub-optimal speeds inevitably leads to energy waste due to inefficiency. Therefore, developing a simple, practical, and freely adjustable aerodynamic fan blade capable of adapting to different speed ranges to improve the efficiency and capability of axial-flow propellers, and to support research in advancing aerial and underwater exploration, is of significant value and importance. Summary of the Invention

[0003] The purpose of this invention is to provide a preparation process and control method for a free-curvature biomimetic artificial muscle fan blade. The principle is clear, the operation is simple, and it has universal applicability. Simultaneously, it provides the optimal proportion of building materials and process parameters based on this process, thereby obtaining a biomass gel artificial muscle fan blade with high response efficiency, fast deformation rate, freely variable curvature, and self-shaping properties.

[0004] To achieve the above objectives, this invention provides a fabrication process and control method for a free-curvature biomimetic artificial muscle fan blade, comprising the following steps:

[0005] S1: Preparation of biomimetic artificial muscle fan blade electro-actuated membrane solution; Weigh 4g sodium alginate, add 200mL distilled water to a beaker, pour in sodium alginate powder to dissolve it completely, add 6mL glycerol and 4mL ionic liquid, stir until the solution presents a colorless gel-like substance without solid particles or flocculent matter; then sonicate the solution for 10min to remove bubbles, thus obtaining the biomimetic artificial muscle fan blade electro-actuated membrane solution;

[0006] S2: Preparation of biomass conductive ink for electrode film; Weigh sodium alginate powder and place it in a petri dish, inject high melting point gallium indium tin alloy into it, heat to melt the gallium indium tin alloy, stir with a glass rod to make the sodium alginate powder completely coated with gallium indium tin alloy, presenting a silver colloidal state, then transfer it to a beaker, add 50ml of distilled water and ultrasonically disperse for 30min, stir at 60℃ for 1h to obtain biomass conductive ink for artificial muscle fan blades;

[0007] S3: Prepare a self-heating actuation membrane fan blade; use a 3D printer to print the designed fan blade mold with ABS material, arrange the heating wire according to the preset shape in the mold, then pour the biomimetic artificial muscle fan blade electro-actuating solution obtained in step S1 into the mold, and dry it at 60℃ for 48 hours in a vacuum drying oven to obtain the main body of the artificial muscle fan blade.

[0008] S4: Print the driving electrode of the artificial muscle fan blade; Pour the biomass conductive ink obtained in step S2 into the slurry tank of the clay printer, place the main body of the biomass gel artificial muscle fan blade obtained in step S3 into the customized positioning mold, making its upper surface flush with the top surface of the mold; Place the mold on the base of the clay printer, print the shape of the upper surface electrode on the actuation film of the artificial muscle fan blade according to the pre-programmed sequence, and fill the contact surface for connecting the circuit at the tail of the artificial muscle, put it in the drying oven to dry, repeat 5 times to obtain the top electrode film; Then invert the blade and repeat the above steps to make the bottom electrode film.

[0009] S5: Replace the biomass conductive ink with a biomimetic artificial muscle fan blade electro-actuating membrane solution, and use a clay printer to fill the gap between the electrode membranes with the actuation membrane solution to ensure the integrity of the fan blade; finally, wrap the obtained biomimetic artificial muscle fan blade with a polyvinyl chloride film, and put it into a vacuum sealing machine for sealing to obtain a biomimetic artificial muscle fan blade with a combination of rigidity and flexibility and self-adjusting curvature.

[0010] Preferably, in step S1, the sodium alginate is dissolved in distilled water under the following conditions: water bath heating at 60°C and stirring at a constant speed of 800 r / min.

[0011] Preferably, in step S2, 2g of sodium alginate powder and 2mL of liquid gallium indium tin alloy are mixed with the sodium alginate powder, and the mixture is heated in a water bath to maintain the temperature at 55°C, so that the sodium alginate powder is completely coated by the gallium indium tin alloy.

[0012] A control method for a free-curvature bionic artificial muscle fan blade involves numbering the eight electrodes connected to the root of the fan blade electrode membrane as 1-8. Electrodes 1 and 8, 2 and 7, and 3 and 6 are paired up to form the electrode energizing area, where the required voltage and direction must be applied according to the programming. Electrodes 4 and 5 are the heating wire energizing area, which can be connected to the positive and negative terminals of the power supply.

[0013] Preferably, when heating the fan blades, the entire fan blade is heated to soften the electrode film and actuation film before performing any deformation strategies, and regions 4 and 5 are connected to the positive and negative terminals of the power supply.

[0014] Preferably, the outer fan blades are controlled to curl: when the fan blades need to be concave downwards, area 1 is connected to the positive terminal of the power supply and area 8 is connected to the negative terminal of the power supply; when the fan blades need to be convex upwards, area 1 is connected to the negative terminal of the power supply and area 8 is connected to the positive terminal of the power supply.

[0015] Preferably, the middle fan blades are controlled to curl: when the middle fan blades need to be concave downwards, area 2 is connected to the positive terminal of the power supply and area 7 is connected to the negative terminal of the power supply; when the fan blades need to be convex upwards, area 1 is connected to the negative terminal of the power supply and area 8 is connected to the positive terminal of the power supply.

[0016] Preferably, the inner fan blades are controlled to curl: when the inner side of the fan blades is concave downwards, region 3 is connected to the positive terminal of the power supply and region 6 is connected to the power supply; when the inner side of the fan blades is convex upwards, region 3 is connected to the negative terminal of the power supply and region 6 is connected to the positive terminal of the power supply.

[0017] Therefore, the present invention employs a fabrication process and control method for a free-curvature biomimetic artificial muscle fan blade with the above-described structure, the advantages of which are:

[0018] First, the addition of an ionic liquid with a large molecular weight difference between cations and anions enables the bionic artificial muscle to achieve higher output force density and longer lifespan. Simultaneously, compared to traditional viscoelastic bionic artificial muscle materials, the high melting point of [EM Im][BF4] gives the bionic artificial muscle higher structural strength at room temperature. High-melting-point gallium indium tin alloy replaces carbon nanotubes in the bionic artificial muscle electrode membrane. Compared to traditional electrode membranes, liquid metal has higher conductivity and liquid fluidity at high temperatures, significantly reducing the viscoelastic forces that the bionic artificial muscle needs to overcome during output, resulting in higher energy conversion efficiency. Furthermore, its solidification characteristics at room temperature, combined with [EM Im][BF4], enable the artificial muscle to cool and solidify after reaching a specific shape, thus avoiding the reduction in lifespan caused by prolonged work.

[0019] Secondly, compared to traditional fan blades made of metal or plastic, using biomimetic artificial muscles as fan blades will give them greater flexibility. Traditional fan blades, due to their fixed shape, have fixed energy efficiency and wind pressure-speed curves, making them suitable only for specific applications and resulting in significant energy loss when reverse thrust is required. In contrast, biomimetic artificial muscle fan blades can freely change their curvature and achieve a flipping effect. This design allows propellers using biomimetic artificial muscles to adapt to different speed ranges while maintaining optimal energy efficiency curves, and can achieve efficient propulsion in both forward and reverse directions.

[0020] Third, a partitioned electrode design is adopted, and the electrodes are constructed using 3D printing additive manufacturing. The repeated casting process ensures good adhesion between the interfaces, giving the artificial muscle fan blade excellent integrity and allowing for customization of the electrode shape according to needs. This provides the biomimetic artificial muscle fan blade with more surface curvature options, which is helpful for fluid dynamics research, expands the choices for energy-saving propulsion, and provides new ideas for the future development of artificial muscles.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the artificial muscle fan blade of the present invention.

[0023] Figure 2 This is an enlarged view of the electrified area at the bottom of the artificial muscle fan blade of the present invention.

[0024] Figure 3 This is a schematic diagram of the assembled artificial muscle fan blades of the present invention.

[0025] Figure 4 This invention relates to the division of the energized region in the electric drive control strategy for the artificial muscle fan blades.

[0026] Figure 5 This is a schematic diagram of the electrical control of the heating behavior of the artificial muscle fan blades in this invention.

[0027] Figure 6 This is a schematic diagram of the outer blade bending electric control strategy of the artificial muscle fan blade electric drive control strategy of the present invention.

[0028] Figure 7 This is a schematic diagram of the middle part of the electric drive control strategy for the artificial muscle fan blades of the present invention, which is the electric control strategy for bending the fan blades.

[0029] Figure 8 This is a schematic diagram of the inner fan blade bending electric control strategy of the artificial muscle fan blade electric drive control strategy of the present invention.

[0030] Figure labels: 1. Main body of artificial muscle fan blade; 2. Electrode membrane; 3. Electro-actuated membrane solution of bionic artificial muscle fan blade. Detailed Implementation

[0031] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0033] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0034] Example 1

[0035] The fabrication of a free-curvature biomimetic artificial muscle fan blade can be mainly divided into the following stages: preparing a biomass gel artificial muscle fan blade actuation membrane solution, preparing biomass gel conductive ink, constructing a biomass gel artificial muscle fan blade mold to prepare the actuation membrane and pre-embed heating wires, printing biomass gel artificial muscle electrodes, repairing the biomass gel artificial muscle fan blade, and encapsulating it. Utilizing 3D printing stacking technology, the device exhibits high integrity, greater customization freedom, and significantly reduced operational difficulty.

[0036] Preparation of biomass gel artificial muscle fan blade actuation membrane solution

[0037] Measure 200 mL of distilled water into a 200 mL beaker and place it in a water bath magnetic stirrer. Set the temperature to 60°C and stir continuously. Once the temperature inside the beaker reaches 60°C, weigh 4 g of sodium alginate using an analytical balance. Then, increase the speed of the magnetic stirrer to create a vortex on the surface of the liquid in the beaker. At this point, quickly add a small amount of the weighed sodium alginate powder along the beaker wall to disperse it evenly and prevent clumping. After all the sodium alginate has been added, adjust the speed of the magnetic stirrer to 800 rpm and stir continuously for 1 hour. The solution will then become a colorless gel with no solid particles or flocculent matter. Next, place the beaker in an ultrasonic cleaner for about 10 minutes to remove air bubbles, thus obtaining the biomass gel biomimetic artificial muscle fan blade actuator membrane solution 3.

[0038] Preparation of electrode membrane biomass gel conductive ink

[0039] Weigh 2g of sodium alginate powder and place it in an evaporating dish. Simultaneously, heat an appropriate amount of gallium indium tin alloy solid in a beaker at 55°C in a water bath until it is completely melted. Then, use a medical syringe to measure 2mL of liquid gallium indium tin alloy and inject it into the evaporating dish. Place the evaporating dish on an iron stand and use an alcohol lamp to maintain the molten state of the gallium indium tin alloy. Then, stir the mixture of sodium alginate powder and gallium indium tin alloy with a glass rod until the sodium alginate powder is completely coated with gallium indium tin alloy. Transfer the resulting silvery gel to a beaker, add 50mL of distilled water, heat in a water bath to 60°C, and then transfer to an ultrasonic cell disruptor. After ultrasonic treatment for 30 minutes, the electrode membrane biomass gel conductive ink is obtained.

[0040] Constructing a biomass gel artificial muscle fan blade mold to prepare an actuator membrane and pre-embed heating wires

[0041] In 3D modeling software, a mold with the desired fan blade shape and a wall height of 15mm is drawn. A scale is drawn on the inner wall 10mm from the bottom, and a support with a height of 0.5mm is drawn inside according to the required pre-embedded resistance wire trajectory. The mold is printed using ABS material. The resistance wire is then placed on the support, and the biomass gel biomimetic artificial muscle fan blade actuation membrane solution obtained in step one is poured into it until it reaches the scale. The mold is then placed in a vacuum drying oven and dried at 60℃ for 48 hours to obtain the main body of the biomass gel artificial muscle fan blade.

[0042] Printed biomass gel artificial muscle driving electrodes

[0043] The biomass gel conductive ink obtained in step two is poured into the extrusion can of the clay printer, and the can is kept warm. A mold is designed based on the biomass gel artificial muscle fan blade to the moving membrane obtained in step three, ensuring the top of the mold is flush with the surface of the moving membrane for optimal printing results. This mold is fixed to the printing plate of the clay printer, and its Z-axis is readjusted. The clay printer is then started to print the biomass gel conductive ink in the pre-designed electrode shape, resulting in electrode film 2. After printing, the fan blade and mold are transferred to a vacuum drying oven and dried at 60°C for 6 hours. After drying, this process is repeated four times to obtain an electrode of sufficient thickness to ensure adequate conductivity and toughness. After printing one side of the electrode, the biomass gel artificial muscle fan blade is flipped over, and the above operation is repeated to create the other side of the electrode.

[0044] Repairing and encapsulating the fan blades of biomass gel artificial muscle

[0045] The biomass gel conductive ink in the clay printer was replaced with a biomimetic artificial muscle fan blade electro-actuating membrane solution 3. The actuation membrane solution was then injected into the gap between the electrode films 2 using the same clay printer. Finally, the solution was dried until the surface was flush to ensure the integrity of the fan blade and extend its lifespan. The resulting biomimetic artificial muscle fan blade was then wrapped in a polyvinyl chloride film and sealed in a vacuum sealing machine to obtain a flexible and self-adjusting curvature biomimetic artificial muscle fan blade.

[0046] The reagents used in the above steps include: sodium alginate (analytical grade, 90%), glycerol (≥99%), ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EM Im][BF4], analytical grade, 99%), liquid metal (indium tin alloy, melting point 47℃), and heating wire (Φ0.5mm). Other auxiliary experimental tools include: beaker (200mL), analytical balance, spatula, qualitative filter paper (Φ15cm), magnetic stirrer, glass rod, pipette, ultrasonic cell disruptor, mortar and pestle, 3D printer, clay printer, vacuum drying oven, and vacuum sealing machine.

[0047] Example 2

[0048] Control method of free curvature bionic artificial muscle fan blade: The eight electrodes connected to the root of the electrode membrane of each fan blade are numbered 1-8 respectively. The electrodes 1 and 8, 2 and 7, and 3 and 6 are paired up to form the electrode energizing area, which needs to be applied with the required voltage and direction according to the program; the electrodes 4 and 5 are the heating wire energizing area, which can be connected to the positive and negative terminals of the power supply.

[0049] When heating the fan blades, before implementing any deformation strategies, heat the entire fan blade to soften the electrode film and actuation film, and then connect regions 4 and 5 to the positive and negative terminals of the power supply.

[0050] Controlling the outer fan blade curling: When the fan blade needs to be concave downwards, area 1 is connected to the positive power supply and area 8 is connected to the negative power supply; when the fan blade needs to be convex upwards, area 1 is connected to the negative power supply and area 8 is connected to the positive power supply.

[0051] Controlling the curling of the middle fan blades: When the middle fan blades need to be concave downwards, connect area 2 to the positive terminal of the power supply and area 7 to the negative terminal of the power supply; when the fan blades need to be convex upwards, connect area 1 to the negative terminal of the power supply and area 8 to the positive terminal of the power supply.

[0052] Controlling the curling of the inner fan blades: When the inner side of the fan blades is concave downwards, region 3 is connected to the positive terminal of the power supply and region 6 is connected to the power supply; when the inner side of the fan blades is convex upwards, region 3 is connected to the negative terminal of the power supply and region 6 is connected to the positive terminal of the power supply.

[0053] Therefore, this invention employs a fabrication process and control method for a free-curvature bionic artificial muscle fan blade with the aforementioned structure. An ionic liquid with a large molecular weight difference between cations and anions is added, enabling the bionic artificial muscle to achieve higher output force density and longer service life. Simultaneously, compared to traditional viscoelastic bionic artificial muscle materials, the high melting point of [EMIm][BF4] endows the bionic artificial muscle with higher structural strength at room temperature. A high-melting-point gallium indium tin alloy is added to the bionic artificial muscle electrode film to replace carbon nanotubes. Compared to traditional electrode films, liquid metal has higher conductivity and liquid fluidity at high temperatures, significantly reducing the viscoelastic force that the bionic artificial muscle needs to overcome during output, resulting in higher energy conversion efficiency. Its solidification characteristics at room temperature, combined with [EMIm][BF4], enable the artificial muscle to cool and solidify after reaching a specific shape, thus avoiding a reduction in lifespan caused by prolonged work. Compared to traditional metal or plastic fan blades, using bionic artificial muscle as the fan blade will provide greater flexibility. Traditional fan blades, due to their fixed shape, have fixed energy efficiency and wind pressure-speed curves, making them suitable only for specific applications and resulting in significant energy loss when reverse thrust is required. In contrast, bionic artificial muscle fan blades can freely change their curvature and achieve a flipping effect. This design allows propellers using bionic artificial muscles to adapt to different speed ranges while maintaining optimal energy efficiency curves, and to achieve efficient propulsion in both forward and reverse directions. Employing a partitioned electrode design and using 3D printing additive manufacturing for electrode construction, along with a repeated casting process, ensures good adhesion between interfaces, giving the artificial muscle fan blade excellent integrity and allowing for free customization of electrode shapes. This provides bionic artificial muscle fan blades with more surface curvature options, contributing to fluid dynamics research, expanding the choices for energy-saving propellers, and providing new ideas for the future development of artificial muscles.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A manufacturing process for a free-curvature biomimetic artificial muscle fan blade, characterized in that: Includes the following steps: S1: Preparation of biomimetic artificial muscle fan blade electro-actuated membrane solution; Weigh 4g sodium alginate, add 200mL distilled water to a beaker, pour in sodium alginate powder to dissolve it completely, add 6mL glycerol and 4mL ionic liquid, stir until the solution presents a colorless gel-like substance without solid particles or flocculent matter; then sonicate the solution for 10min to remove bubbles, thus obtaining the biomimetic artificial muscle fan blade electro-actuated membrane solution; S2: Preparation of biomass conductive ink for electrode film; Weigh sodium alginate powder and place it in a petri dish, inject high melting point gallium indium tin alloy into it, heat to melt the gallium indium tin alloy, stir with a glass rod to make the sodium alginate powder completely coated with gallium indium tin alloy, presenting a silver colloidal state, then transfer it to a beaker, add 50ml of distilled water and ultrasonically disperse for 30min, stir at 60℃ for 1h to obtain biomass conductive ink for artificial muscle fan blades; S3: Prepare a self-heating actuation membrane fan blade; use a 3D printer to print the designed fan blade mold with ABS material, arrange the heating wire according to the preset shape in the mold, then pour the biomimetic artificial muscle fan blade electro-actuated membrane solution obtained in step S1 into the mold, and dry it at 60℃ for 48 hours in a vacuum drying oven to obtain the main body of the artificial muscle fan blade. S4: Print the driving electrode of the artificial muscle fan blade; Pour the biomass conductive ink obtained in step S2 into the slurry tank of the clay printer, place the main body of the biomass gel artificial muscle fan blade obtained in step S3 into the customized positioning mold, making its upper surface flush with the top surface of the mold; Place the mold on the base of the clay printer, print the shape of the upper surface electrode on the artificial muscle fan blade actuation film according to the pre-programmed pattern, put it in the drying oven to dry, repeat 5 times to obtain the top electrode film; Then invert the fan blade and repeat the above steps to make the bottom electrode film; S5: Replace the biomass conductive ink with a biomimetic artificial muscle fan blade electro-actuated membrane solution, and use a clay printer to fill the gap between the electrode membranes with the electro-actuated membrane solution to ensure the integrity of the fan blade; finally, wrap the obtained biomimetic artificial muscle fan blade with a polyvinyl chloride film, and put it into a vacuum sealing machine for sealing to obtain a biomimetic artificial muscle fan blade with a combination of rigidity and flexibility and self-adjusting curvature.

2. The fabrication process of a free-curvature biomimetic artificial muscle fan blade according to claim 1, characterized in that: In step S1, the sodium alginate is dissolved in distilled water under the following conditions: water bath heating at 60°C and stirring at a constant speed of 800 r / min.

3. The manufacturing process of a free-curvature biomimetic artificial muscle fan blade according to claim 2, characterized in that: In step S2, 2g of sodium alginate powder and 2mL of liquid gallium indium tin alloy are mixed with sodium alginate powder and heated in a water bath at 55°C to completely coat the sodium alginate powder with gallium indium tin alloy.

4. A method for controlling the blades of a free-curvature biomimetic artificial muscle, characterized in that, The free curvature bionic artificial muscle fan blade prepared by the preparation process of the free curvature bionic artificial muscle fan blade according to any one of claims 1-3 is controlled as follows: the 8 electrodes connected to the root of the fan blade electrode film are numbered 1-8 respectively. The electrodes 1 and 8, 2 and 7, and 3 and 6 are paired up to form the electrode energizing area, and the required voltage and direction need to be applied according to the programming; the electrodes 4 and 5 are the heating wire energizing area, which can be connected to the positive and negative terminals of the power supply.

5. The method for controlling the free-curvature bionic artificial muscle fan blade according to claim 4, characterized in that: When heating the fan blades, before implementing any deformation strategies, heat the entire fan blade to soften the electrode film and actuation film, and then connect regions 4 and 5 to the positive and negative terminals of the power supply.

6. The method for controlling the free-curvature bionic artificial muscle fan blade according to claim 5, characterized in that: Controlling the outer fan blade curling: When the fan blade needs to be concave downwards, area 1 is connected to the positive power supply and area 8 is connected to the negative power supply; when the fan blade needs to be convex upwards, area 1 is connected to the negative power supply and area 8 is connected to the positive power supply.

7. The method for controlling the free-curvature bionic artificial muscle fan blade according to claim 6, characterized in that: Controlling the curling of the middle fan blades: When the middle fan blades need to be concave downwards, connect area 2 to the positive terminal of the power supply and area 7 to the negative terminal of the power supply; when the fan blades need to be convex upwards, connect area 1 to the negative terminal of the power supply and area 8 to the positive terminal of the power supply.

8. The method for controlling a free-curvature bionic artificial muscle fan blade according to claim 7, characterized in that: Controlling the curling of the inner fan blades: When the inner side of the fan blades is concave downwards, region 3 is connected to the positive terminal of the power supply and region 6 is connected to the negative terminal of the power supply; when the inner side of the fan blades is convex upwards, region 3 is connected to the negative terminal of the power supply and region 6 is connected to the positive terminal of the power supply.

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