Array type flexible tactile sensor, preparation method thereof and tactile sensing system

Abstract

The invention provides an array type flexible tactile sensor, a preparation method thereof and a tactile sensing system. The array type flexible tactile sensor comprises a plurality of arrayed flexible tactile sensor units, each flexible tactile sensor unit sequentially comprises a friction layer, a hydrophilic layer, an electrode layer and a substrate layer from top to bottom, and the lower surface of the friction layer is a hydrophilic surface. The hydrophilic layer is added between the friction layer and the electrode layer, good attachment of the friction layer and the electrode layer can be achieved, on the basis, the electrode layer is printed on the hydrophilic layer through a simple silk-screen printing method so as to be combined with the friction layer, a silk-screen printing plate is designed to be of an array structure, and an array touch sensor can be directly obtained; large-area batch production can be realized, and the preparation efficiency is improved. The prepared array type flexible tactile sensor can realize dynamic multi-point sensing, improve the sensing sensitivity, the working stability and the resolution ratio, and can realize self-energizing and self-driving.

Description

Technical Field

[0001] The present invention relates to the technical field of tactile sensor preparation, and particularly relates to an array-type flexible tactile sensor, a preparation method thereof, and a tactile sensing system. Background Art

[0002] Sensing technology is one of the three major pillars of current information technology. With the development of the Internet, sensing technology has obtained an unprecedented development prospect. Among them, tactile sensing technology is more widely applied. It can respond to external stimuli. Compared with traditional tactile sensors, flexible tactile sensors have good flexibility and can fit well on various complex surfaces (such as various joint parts of the human body) to better perform real-time monitoring. To achieve the application of specific functions, a huge sensor network needs to be connected to the human body or a robot. Therefore, the supply of energy is crucial. However, many power sources are rigid power sources, which are relatively large in weight and volume, and inevitably have problems such as high cost and large application limitations, and are not convenient to use in flexible sensors. In addition, the current tactile sensors have low resolution and cannot accurately identify the monitored signals.

[0003] The triboelectric nanogenerator based on the coupling effect of triboelectrification and electrostatic induction can collect bio-mechanical energy and be used as the energy source of the sensor. It can convert mechanical signals into electrical signals. It generates energy in a low-frequency and lightweight manner and has the advantages of low cost and fast response time. At present, combining triboelectric nanogeneration technology with tactile sensors to prepare flexible tactile sensors with self-driving functions, low cost, high resolution, and easy large-scale production has become a research hotspot for many scholars.

[0004] In order to improve the resolution of tactile sensors, the tactile sensors are generally designed in an array structure. There is a report disclosing an array-type triboelectric tactile sensor, which includes a plurality of arrayed triboelectric tactile sensing units. A single tactile sensing unit is composed of an insulating flexible truncated cone, a metal electrode, a flexible covering layer, a flexible intermediate layer, a flexible bottom layer, and a lead wire. The triboelectric pair composed of the insulating flexible truncated cone and the metal electrode converts deformation into an electrical signal through contact electrification and electrostatic coupling effects, realizing self-powered and highly sensitive measurement of three-dimensional contact forces including contact normal stress and slip shear force. However, the structure of a single flexible sensing unit is relatively complex, and this document does not disclose a preparation method for realizing the array structure.

[0005] A flexible tactile sensor based on triboelectrification generally includes an electrode layer and a friction layer. The electrode layer is generally composed of hydrophilic materials, while the friction layer is mostly made of hydrophobic polymers. Due to the difference in hydrophilicity and hydrophobicity, it is difficult to achieve good adhesion between the friction layer and the electrode layer, which is not conducive to the fine preparation of an array structure. Most current research focuses on setting one or more reinforcing layers at the non-friction interface between the friction layer and the electrode layer to enhance the piezoelectric signals output under the action of an external force, and less attention is paid to how to prepare an array-type flexible tactile sensor based on triboelectrification. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide an array-type flexible tactile sensor, a preparation method thereof, and a tactile sensing system. The tactile sensor has an array of sensing units, which sequentially include a friction layer, a hydrophilic layer, an electrode layer, and a substrate layer from top to bottom, and can achieve close adhesion between the friction layer and the electrode layer, facilitating the preparation of an array-type sensor, and having the advantages of high resolution, high sensitivity, and good stability.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an array-type flexible tactile sensor, including a plurality of arrayed flexible tactile sensor units. Each flexible tactile sensor unit sequentially includes a friction layer, a hydrophilic layer, an electrode layer, and a substrate layer from top to bottom;

[0009] The lower surface of the friction layer is a hydrophilic surface.

[0010] Preferably, the lower surface of the friction layer is a hydrophilic surface modified with a surfactant.

[0011] Preferably, the surfactant is selected from any one or more of sodium dodecyl sulfate, sodium diisobutyl sulfosuccinate, decyl trimethyl ammonium chloride, or sodium dodecyl benzene sulfonate.

[0012] Preferably, the friction layer is selected from any one or more of perfluoroethylene propylene copolymer, polytetrafluoroethylene, polydimethylsiloxane, polyethylene, polyoxyethylene, polystyrene, polypropylene, polyvinyl chloride, or polyvinylidene chloride.

[0013] Preferably, the hydrophilic layer is selected from any one or more of polyvinyl alcohol, polyimide, or polyurethane.

[0014] Preferably, the electrode layer is selected from any one of graphene, modified graphene, modified graphene biocomposite, carbon nanotube, modified carbon nanotube, modified carbon nanotube biocomposite, or PEDOT:PSS.

[0015] Further preferably, the electrode layer is a carboxylated multi-walled carbon nanotube / chitosan composite material.

[0016] Preferably, the base layer is selected from any one of polyurethane, polyimide, polyethylene terephthalate or polydimethylsiloxane.

[0017] In a second aspect, the present invention also provides a method for preparing the above-mentioned array-type flexible tactile sensor, comprising the following steps:

[0018] (1) After hydrophilically modifying the friction layer, a hydrophilic layer is prepared on its surface;

[0019] (2) The electrode layer is coated on the surface of the hydrophilic layer by a screen printing method;

[0020] Among them, the screen printing plate used in the screen printing method has an array structure;

[0021] (3) The base layer is combined with the electrode layer to obtain the array-type flexible tactile sensor.

[0022] Preferably, the hydrophilic modification is specifically: after subjecting the friction layer to oxygen plasma treatment, it is further treated with a surfactant.

[0023] Preferably, the radio frequency power of the oxygen plasma treatment is 100-130 W, the time is 30-60 s, and the oxygen flow rate is 120-160 sccm.

[0024] In a third aspect, the present invention also provides a tactile sensing system, comprising the array-type flexible tactile sensor involved in the above technical solution.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] (1) The present invention provides an array-type flexible tactile sensor, comprising a plurality of arrayed flexible tactile sensor units. The flexible tactile sensor unit sequentially includes a friction layer, a hydrophilic layer, an electrode layer and a base layer from top to bottom. By hydrophilically modifying the friction layer and then covering a hydrophilic layer on its surface, good fitting between the friction layer and the electrode layer is achieved;

[0027] (2) On the basis that the friction layer and the electrode layer can be well fitted, the present invention can print the electrode layer on the hydrophilic layer by a simple screen printing method, thereby combining with the friction layer, and designing the screen printing plate into an array structure, and an arrayed tactile sensor can be directly obtained, which is beneficial to realizing large-area batch production and improving the preparation efficiency;

[0028] (3) The array - type flexible tactile sensor provided by the present invention can achieve dynamic multi - point sensing, improve the conversion efficiency, sensing sensitivity, working stability and resolution of the sensor for converting bio - energy into electrical energy, can achieve self - power supply and self - driving, does not require external power supply, and the selection of the flexible substrate makes the sensor have good wearability. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the screen - printing method;

[0030] Figure 2 It is a schematic structural diagram of the array - type flexible tactile sensor;

[0031] Figure 3 It is a design diagram of the array - type structure;

[0032] Figure 4 It is a sensitivity test curve graph of the array - type flexible tactile sensor;

[0033] Figure 5 It is a stability test result graph of the array - type flexible tactile sensor;

[0034] Figure 6 It is a micro - nano structure image (5 cm) formed after the nanofiber membrane in Example 2 is treated with sandpaper;

[0035] Figure 7 SEM image of the nanofiber membrane in Example 2. Detailed Embodiments

[0036] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0037] Aiming at the problems of the complex structure of the flexible tactile sensor in the prior art and the difficulty in preparing a sensor with an array - type structure, the present invention provides an array - type flexible tactile sensor, which includes a plurality of arrayed flexible tactile sensor units. Each flexible tactile sensor unit sequentially includes a friction layer, a hydrophilic layer, an electrode layer and a base layer from top to bottom.

[0038] In the present invention, the lower surface of the friction layer is a hydrophilic surface. Preferably, a surface hydrophilic modification treatment method is used to perform hydrophilic modification on the friction layer. For example, methods such as plasma treatment, ultraviolet ozone treatment, layer-by-layer self-assembly, sol-gel method, dynamic coating modification, silanization, and graft copolymerization can be selected. In the present invention, the lower surface of the friction layer is preferably a hydrophilic surface modified by a surfactant, and more preferably a hydrophilic surface treated by oxygen plasma treatment and surfactant treatment in sequence. After the oxygen plasma treatment, an oxide layer is formed on the surface of the friction layer, and then the surfactant treatment is continued. The surfactant is amphiphilic, so that the lipophilic interface in the surfactant contacts the oxide layer, and the hydrophilic interface is exposed on the side away from the oxide layer, thus making the surface of the friction layer a hydrophilic surface. The surfactant includes any one or more of sodium dodecyl sulfate (SDS), sodium diisobutyl sulfosuccinate, decyl trimethyl ammonium chloride, or sodium dodecyl benzene sulfonate.

[0039] The above-mentioned array-type flexible tactile sensor can be attached to an object for monitoring the usage situation of the object. For example, the base layer of the tactile sensor can be attached to a mouse to monitor usage situations such as the click frequency when a human uses the mouse. The working principle is as follows: When the skin (finger) contacts the surface friction layer, charge generation occurs due to contact between the skin and the PDMS layer, and charges will accumulate on the surface. The surface of the friction layer is negatively charged, and the surface of the skin is positively charged. At this time, the device as a whole shows electrical neutrality. When the skin separates from the surface of the friction layer, in order to balance the negative charges accumulated on the surface of the friction layer, electrons transfer from the electrode layer to the ground, and the electrode layer gradually becomes positively charged with the same number of charges as the friction layer. When the skin approaches and contacts the friction layer again, electrons flow back from the ground to the electrode layer.

[0040] The above-mentioned array-type flexible tactile sensor provided by the present invention can be directly attached to the human skin for monitoring human health information. For example, the array-type tactile sensor can be attached to the human neck (where the friction layer contacts the skin). During the twisting of the human neck, induction signals are generated to detect the degree of change in neck movement. Similarly, it can also be attached to the wrists and ankles of the human body. The working principle is the same as the above content.

[0041] The tactile sensor provided by the present invention includes a plurality of arrayed flexible tactile sensor units, which sequentially include a friction layer, a hydrophilic layer, an electrode layer, and a base layer from top to bottom. After performing hydrophilic modification on the friction layer and then covering a hydrophilic layer on its surface, the friction layer can be well attached to the electrode layer, which is beneficial for preparing an array structure to achieve dynamic multi-point sensing, improve the conversion efficiency of the sensor to convert bio-mechanical energy into electrical energy, sensing sensitivity, working stability, and resolution, and can achieve self-power supply and self-driving without the supply of an external power source. Moreover, the selection of the flexible substrate makes the sensor have good wearability.

[0042] The present invention also provides a method for preparing the array-type flexible tactile sensor involved in the above technical solution, including the following steps:

[0043] (1) After the friction layer is subjected to hydrophilic modification treatment, a hydrophilic layer is prepared on its surface;

[0044] (2) The electrode layer is coated on the surface of the hydrophilic layer by using a screen printing method;

[0045] Among them, the screen printing plate used in the screen printing method has an array structure;

[0046] (3) The base layer and the electrode layer are combined to obtain the array-type flexible tactile sensor.

[0047] According to the present invention, first, the friction layer is subjected to hydrophilic modification treatment, and then a hydrophilic layer is prepared on its surface. In the present invention, the friction layer is selected from any one or more of perfluoroethylene propylene copolymer, polytetrafluoroethylene, polydimethylsiloxane, polyethylene, polyoxyethylene, polystyrene, polypropylene, polyvinyl chloride or polyvinylidene chloride. After the surface functional modification of the above materials, they can also be used as the friction layer materials. The friction layer can be directly purchased or prepared according to the conventional preparation methods well-known to those skilled in the art. For example, it can be prepared by a spin coating method or an electrospinning method. The spin coating method preferably includes a low-speed stage (or static drop coating) and a high-speed stage. The rotation speed in the low-speed stage is 800-1000 r / min, the time is 25-40 s, the rotation speed in the high-speed stage is 3000-5000 r / min, and the time is about 1 min. The electrospinning method can produce polymer filaments with a nanoscale diameter as the friction layer. The obtained friction layer has a high specific surface area and porosity, which can increase the air permeability of the friction layer and the interaction area between the friction layer and the object to be detected, and is expected to greatly improve the performance of the sensor.

[0048] After the friction layer is prepared, it is preferably subjected to hydrophilic modification treatment first. The methods for surface hydrophilic modification treatment can include plasma treatment, ultraviolet ozone treatment, layer-by-layer self-assembly, sol-gel method, dynamic coating modification, silanization, graft copolymerization, and the like. The present invention preferably uses a surfactant to treat the friction layer to change its surface energy to make it hydrophilic. However, when using a single surfactant to treat the friction layer, as the reaction time prolongs, part of the surfactant will penetrate into the interior of the friction layer, thereby reducing the flexibility of the friction layer and making it prone to fracture, which is not conducive to the practical application of the sensor. Therefore, the present invention further adopts a superimposed hydrophilic modification treatment method combining oxygen plasma treatment and surfactant treatment to prevent the surfactant from penetrating into the interior of the friction layer by pre-constructing an oxide layer on the surface of the friction layer. In the present invention, the hydrophilic modification is specifically as follows: after the friction layer is subjected to oxygen plasma treatment, it is then treated with a surfactant. The oxygen plasma treatment can be carried out using a conventional oxygen plasma instrument. The radio frequency power of the oxygen plasma treatment is 100-130 W, the time is 30-60 s, and the oxygen flow rate is 120-160 sccm. After the oxygen plasma treatment is completed, the treated friction layer is directly immersed in the surfactant solution, then taken out, rinsed and dried to obtain a hydrophilic friction layer. The selection of the surfactant is as described in the above technical solution and will not be elaborated here one by one. The soaking time is 20-40 s. When rinsing, deionized water is used, and then the friction layer is dried with nitrogen gas.

[0049] It should be noted that in order to further increase the specific surface area of the friction layer to improve the sensing performance, plasma etching or simple sandpaper treatment can be used to treat the surface of the friction layer so that the surface of the friction layer in contact with the external object or skin has a micro-nano structure.

[0050] After obtaining the hydrophilic friction layer, a hydrophilic layer is constructed on the surface of the friction layer. The hydrophilic layer is selected from any one or more of polyvinyl alcohol, polyimide, or polyurethane, and is preferably polyvinyl alcohol (PVA). The preparation of the PVA can be carried out according to the conventional method. The present invention preferably heats the aqueous solution of PVA at 90-95 °C for 2-4 h, and then adds glutaraldehyde (GA) and a small amount of dilute acid to promote crosslinking to obtain a GA-crosslinked PVA solution. Then, referring to the spin coating method in the above technical solution, the GA-crosslinked PVA solution is spin-coated on the hydrophilic friction layer to obtain a hydrophilic layer-friction layer; or the electrospinning method is used to form a film of the GA-crosslinked PVA solution on the hydrophilic friction layer to obtain a hydrophilic layer-friction layer material.

[0051] It should be noted that the main function of the hydrophilic layer is to form a hydrophilic surface on the surface of the friction layer, which is superimposed and synergistic with the above-mentioned plasma treatment and surfactant treatment. The purpose is to enable the electrode layer to achieve a clear printed array structure on the friction layer. At the same time, the hydrophilic layer is selected as a polymer. While the generator is working, it can also form a polar distribution of charges, relatively increasing the output.

[0052] After obtaining the hydrophilic layer-friction layer material, first prepare the electrode layer raw material, and then use the screen printing method to coat the electrode layer raw material on the surface of the hydrophilic layer. The electrode layer is selected from any one of graphene, modified graphene, modified graphene biocomposite material, carbon nanotube, modified carbon nanotube, modified carbon nanotube biocomposite material or PEDOT:PSS. Among them, carbon nanotubes can be divided into single-walled carbon nanotubes and multi-walled carbon nanotubes according to the difference in the number of layers. Single-walled carbon nanotubes have better electrical conductivity than multi-walled carbon nanotubes, but the preparation cost of multi-walled carbon nanotubes is lower. Appropriate electrode materials can be selected according to the performance requirements and cost requirements of the device. In the present invention, considering from the cost perspective while meeting the electrical conductivity requirements, multi-walled carbon nanotubes are selected. However, due to the large specific surface area and aspect ratio of carbon nanotubes, adjacent carbon nanotubes will agglomerate due to relatively strong van der Waals forces, which is not conducive to subsequent printing. Therefore, effective dispersion of carbon nanotubes is very important. In the present invention, multi-walled carbon nanotubes are preferentially carboxylated, and then chitosan with good biocompatibility is used for electrostatic adsorption with carboxylated multi-walled carbon nanotubes, and finally a well-dispersed carboxylated multi-walled carbon nanotube / chitosan composite material is obtained as the electrode layer raw material.

[0053] Then, use the screen printing method to print the electrode layer raw material on the surface of the hydrophilic layer to obtain the electrode layer-hydrophilic layer-friction layer material. The screen printing method can be operated according to the technical means well-known to those skilled in the art. Among them, the electrode layer raw material is used as conductive ink, the screen printing plate has an array structure, and the substrate is the hydrophilic layer-friction layer. The schematic diagram of the screen printing method is as Figure 1 shown. When printing, pour the conductive ink at one end of the screen printing plate, apply a certain pressure to the ink part on the screen printing plate with a squeegee, and at the same time move uniformly towards the other end of the screen printing plate. The ink is extruded from the array mesh holes to the substrate by the squeegee during the movement, and the electrode layer can be printed on the surface of the hydrophilic layer. The printing plate surface in the screen printing method is soft and has a certain elasticity, which is not only suitable for printing on soft items such as paper and cloth, but also suitable for printing on hard items. The printed ink layer is thick and has strong covering power. Through the screen printing method, the design of the electrode layer pattern shape can be realized, and the preparation of the array electrode layer can be achieved, laying a foundation for realizing multi-function and high performance.

[0054] After obtaining the electrode layer-hydrophilic layer-friction layer material, the present invention preferably uses a base layer for encapsulation and bearing to obtain an array-type tactile sensor with a base layer-electrode layer-hydrophilic layer-friction layer structure. The base layer is selected from high molecular polymer materials such as polyurethane, polyimide, polyethylene terephthalate, or polydimethylsiloxane. It can be spin-coated on the surface of the electrode layer to form a film by spin coating, or electrospun on the surface of the electrode layer to form a film by electrospinning. If the base layer is a finished product directly purchased from the market, the base layer and the electrode layer can also be combined by hot pressing.

[0055] In the preparation method of the above-mentioned array-type flexible tactile sensor provided by the present invention, after the friction layer is subjected to hydrophilic modification treatment and then a hydrophilic layer is continuously covered on its surface, the friction layer and the electrode layer are well adhered. On this basis, the electrode layer can be directly printed on the hydrophilic layer by a simple screen printing method, so as to be combined with the friction layer, and the screen printing plate is designed into an array structure, and an array-structured sensor can be directly obtained, which is conducive to realizing large-area batch production and improving the preparation efficiency.

[0056] The present invention also provides a tactile sensing system, which includes the array-type flexible tactile sensor prepared by the above technical solution, and may also include a signal acquisition module, a control module, and a power supply module.

[0057] Among them, the array-type flexible tactile sensor is used to sense the external force acting on it and output a pressure electrical signal corresponding to the external force;

[0058] The signal acquisition module is connected to the array-type flexible tactile sensor and is used to collect and process the pressure electrical signal output by the array-type flexible tactile sensor;

[0059] The adjustment module is connected to the signal acquisition module and is used to adjust the external force acting on the array-type flexible tactile sensor according to the pressure electrical signal output by the signal acquisition module;

[0060] The power supply module is connected to the signal acquisition module and is used to supply power to the signal acquisition module.

[0061] To further illustrate the present invention, the following detailed description is provided through the following examples. The experimental raw materials used in the following examples of the present invention can be purchased from the market or prepared according to the conventional preparation methods well-known to those skilled in the art. Among them, chitosan was purchased from Macklin Biochemical Technology Co., Ltd., with a degree of deacetylation of 90%, MW = 200000; carboxylated multi-walled carbon nanotubes and multi-walled carbon nanotubes were both purchased from Aladdin Biochemical Technology Co., Ltd., with a purity > 98%, tube diameter: 5 - 15 nm, tube length: 10 - 30 μm; PDMS prepolymer and curing agent were purchased from Dow Corning Co., Ltd., model 184.

[0062] Example 1

[0063] This example provides an array - type flexible tactile sensor. Its structural schematic diagram is as shown in Figure 2 and it successively includes a friction layer, a hydrophilic layer, an electrode layer, and a substrate layer from top to bottom. The specific preparation method is as follows:

[0064] (1) At room temperature, chitosan powder is dissolved in a 1wt% acetic acid solution at a concentration of 1% (w / v), and during the process, it is continuously stirred with a glass rod in a beaker until completely dissolved to obtain a protonated chitosan solution dissolved in acetic acid;

[0065] (2) Take 200mg of carboxylated multi - walled carbon nanotubes, 100mg of cetyltrimethylammonium bromide, and 10mL of the acetic acid solution of chitosan and mix them in a beaker. Place it on a magnetic stirrer for mechanical stirring (500r / min, 15min), and then perform ultrasonic dispersion in a cell crusher to make the carboxylated multi - walled carbon nanotubes and chitosan evenly dispersed in the solution. Then, heat it in an open - mouth manner on a hot plate at 60℃ to evaporate most of the water until the solution becomes viscous, obtaining a carboxylated multi - walled carbon nanotube / chitosan composite material, that is, the electrode layer material;

[0066] (3) Mix the PDMS prepolymer and the curing agent in a ratio of 10:1, stir well, and evacuate to remove air bubbles (30min) to obtain a PDMS solution;

[0067] Prepare a glass plate, wipe the surface of the glass plate with alcohol to ensure that its surface has no impurities and dust. Install a spin coater and a vacuum pump, turn on the vacuum pump, place the glass plate at the center of the substrate, adsorb it firmly, and rotate it evenly. The spin - coating process is divided into two gradient stages. The first stage is low - speed rotation. During the low - speed rotation stage, drop the PDMS solution, and it must be dropped exactly at the center of the substrate. The second stage is high - speed rotation. Accelerate to the final spin - coating speed to form a coating with the correct thickness. Among them, the low - speed rotation speed is 900r / min, the time is 30s, the high - speed rotation speed is 4000r / min, the time is 1min, and it is dried at 80℃ for 20min to finally form a PDMS layer, that is, the friction layer;

[0068] (4) Treat the PDMS layer with a PLASMACLEANER instrument (radio - frequency power is 120W, oxygen flow rate is 150sccm) for 40s, then immerse the treated PDMS layer in a 0.5wt% SDS solution for 30s, rinse it with deionized water for 30s, and finally dry it with nitrogen to obtain a hydrophilic PDMS layer;

[0069] Take 4 g of PVA particles and 40 g of water in a 50 mL round-bottom flask, swell in cold water, stir well, then place in an oil bath and heat to dissolve at 90 °C for 2 h. Then add 5 mL of 10 wt% GA (glutaraldehyde) and 500 μL of dilute hydrochloric acid to obtain a GA-crosslinked PVA solution, which is the hydrophilic layer material;

[0070] Referring to the spin-coating method in step (3), spin-coat the GA-crosslinked PVA solution on the hydrophilic PDMS layer to obtain a hydrophilic layer-PDMS layer;

[0071] (5) Use the screen printing method to print the electrode layer material obtained in step (2) on the surface of the hydrophilic layer in the hydrophilic layer-PDMS layer obtained in step (4), then place it in an oven and dry at 60 °C for 10 min, and fix the copper enameled wire to the end of the electrode layer material with conductive silver paste;

[0072] Among them, the screen printing plate has Figure 3 the array structure shown.

[0073] (6) Take 15 mL of PDMS solution, dry it at 80 °C to obtain a PDMS film, which is the base layer. Use the hot pressing method to combine the base layer with the electrode layer material printed on the surface of the hydrophilic layer to finally prepare an array-type flexible tactile sensor.

[0074] For the obtained array-type flexible tactile sensor, use a linear motor to test its sensitivity and stability. The test results are as shown in Figure 4 and Figure 5 shown. Figure 4 is the sensitivity test curve graph of the array-type flexible tactile sensor, Figure 5 is the stability test result graph of the array-type flexible tactile sensor. As can be seen from Figure 4 , under a small external force, this tactile sensor has excellent response sensitivity. As can be seen from Figure 5 , after about 1000 cycles of testing, the peak value of the output current does not change significantly, indicating that this tactile sensor has excellent working stability.

[0075] Example 2

[0076] This example provides an array-type flexible tactile sensor, the schematic structural diagram of which is as shown in Figure 2 shown, and successively includes a friction layer, a hydrophilic layer, an electrode layer and a base layer from top to bottom; the specific preparation method is as follows:

[0077] (1) Perform ultrasonic dispersion on a 20% mass fraction PEDOT / PSS solution for 30 min to ensure good dispersion of the solution without deposition;

[0078] (2) Preparation of the hydrophilic layer on the base layer: Mix acetic anhydride and DMF in a ratio of 1:1, and then mix it with the polyamic acid solution in a mass ratio of 100:35. Stir evenly in an environment below 0 °C, and use the spin coating method to coat the base PU film, including the low-speed stage (or static dropwise coating) and the high-speed stage of spin coating. The rotation speed in the low-speed stage is 800 - 1000 r / min, the time is 25 - 40 s, the rotation speed in the high-speed stage is 5000 - 7000 r / min, and the time is about 1 min. Then put it into ovens at 120 °C and 300 °C successively, and after dehydration and curing, a polyurethane-polyimide layer is obtained;

[0079] (3) Apply the dispersed PEDOT / PSS electrode material on one side of the electrode pattern of the screen printing plate. The screen printing squeegee prints the PEDOT / PSS electrode material on the base, and then put it into a drying oven for drying. Fix the copper enameled wire at the end of the electrode material with conductive silver paste;

[0080] (4) Preparation of the friction layer: Preparation of a PU solution with a mass fraction of 18%: PU particles + DMF + acetone. Through the electrospinning method, the electrospinning parameters (voltage, receiving distance, feeding speed) are 20 kV, 20 cm, and 0.5 mL / h respectively. Use a 20-gauge needle to prepare a nanofiber membrane with a micro-nano structure on the sandpaper;

[0081] Combine the prepared PU nanofiber membrane / PU film with the electrode material screen-printed on the base layer by the hot pressing method.

[0082] Among them Figure 6 is the micro-nano structure image (5 cm) formed after the nanofiber membrane is treated with sandpaper, Figure 7 SEM image of the nanofiber membrane.

[0083] Example 3

[0084] This example provides an array-type flexible tactile sensor, and its structural schematic diagram is as Figure 2 shown, which successively includes a friction layer, a hydrophilic layer, an electrode layer, and a base layer from top to bottom; the specific preparation method is as follows:

[0085] (1) Preparation of the base layer: Place the PET film in an ultrasonic cleaner filled with deionized water for cleaning, with the ultrasonic power of 80 W and the ultrasonic time of 10 min. Then pour out the deionized water, add acetone to the ultrasonic cleaner, and place the PET film in acetone for ultrasonic cleaning for 10 min. Finally, take out the film and put it into a constant temperature oven for drying;

[0086] (2) Preparation of a hydrophilic layer on the base layer: The PET film was treated with a PLASMACLEANER instrument (radio frequency power of 120 W and oxygen flow rate of 150 sccm) for 40 s, then the treated PET film was immersed in a 1 wt% sodium dodecylbenzenesulfonate solution for 30 s, rinsed with deionized water for 30 s, and finally dried with nitrogen to obtain a hydrophilic PET layer;

[0087] 4 g of PVA particles and 40 g of water were placed in a 50 mL round-bottom flask, swollen in cold water, and after sufficient stirring, placed in an oil bath and heated to dissolve at 90 °C for 2 h. Then, 5 mL of 10 wt% GA (glutaraldehyde) and 500 μL of dilute hydrochloric acid were added to obtain a GA-crosslinked PVA solution, which is the hydrophilic layer material;

[0088] The speed of low-speed rotation was 900 r / min and the time was 30 s, the speed of high-speed rotation was 4000 r / min and the time was 1 min, and it was dried at 80 °C for 20 min to finally form a hydrophilic layer. The GA-crosslinked PVA solution was spin-coated on the hydrophilic PET film to obtain a hydrophilic layer-PET layer;

[0089] (3) Preparation of the electrode layer: Weigh 1 g of chitosan powder and dissolve it in 19 g of deionized water to form a viscous liquid by heating. Weigh a certain amount of conductive filler PEDOT:PSS, solvent ethylene glycol, and binder chitosan using an electronic balance respectively;

[0090] Place a certain amount of conductive filler, solvent, and binder in a beaker and stir with a heatable magnetic stirrer at a heating temperature of 40 - 60 °C for 1 h to obtain an ink material;

[0091] Weigh multi-walled carbon nanotubes with mass fractions of 10%, 15%, and 20% and a dispersant (mass ratio 2:1) respectively using an electronic balance. Then add the multi-walled carbon nanotubes and the dispersant to the ink binder and disperse them ultrasonically for 15 min, and then continue to heat and stir evenly with a magnetic stirrer to obtain a conductive ink;

[0092] (4) Preparation of the friction layer: Weigh chitosan (CS) and polyethylene oxide (PEO) in a mass ratio of 1:1. After mixing, transfer them to a reagent bottle and add a 1% acetic acid solution by mass to obtain a CS / PEO mixed solution with a mass fraction of 4%. Transfer the mixed solution to a syringe for electrospinning. The electrospinning parameters (voltage, receiving distance, and feeding speed) are 20 kV, 20 cm, and 0.5 mL / h respectively. Use a 20-gauge needle to electrospin and prepare a CS / PEO nanofiber membrane. Immerse the CS / PEO nanofiber membrane in deionized water at room temperature for two days to remove the water-soluble PEO, and change the deionized water every four hours. Prepare a mixed solution of 1 mol / L sodium carbonate and sodium hydroxide (1:1, w / w). Immerse the CS nanofiber membrane after removing PEO in the mixed solution to neutralize the protonated amino groups on chitosan, and rinse with deionized water until the pH shows neutral. After taking out the fiber membrane, place it in a vacuum drying oven and dry it for 48 h;

[0093] Screen-print the conductive inks with different mass fractions of carbon nanotubes on the hydrophilic layer-PET layer respectively, and use a hot pressing method to combine the prepared CS / PEO nanofiber membrane with the electrode material screen-printed on the base layer to obtain the tactile sensor.

[0094] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An array-type flexible tactile sensor, characterized in that, it includes a plurality of arrayed flexible tactile sensor units, and the flexible tactile sensor units sequentially include a friction layer, a hydrophilic layer, an electrode layer, and a base layer from top to bottom; the lower surface of the friction layer is a hydrophilic surface.

2. The array-type flexible tactile sensor according to claim 1, characterized in that, the lower surface of the friction layer is a hydrophilic surface modified by a surfactant.

3. The array-type flexible tactile sensor according to claim 2, characterized in that, the surfactant is selected from any one or more of sodium dodecyl sulfate, sodium diisobutyl sulfosuccinate, decyl trimethyl ammonium chloride, or sodium dodecyl benzene sulfonate.

4. The array-type flexible tactile sensor according to claim 1, characterized in that, the friction layer is selected from any one or more of perfluoroethylene propylene copolymer, polytetrafluoroethylene, polydimethylsiloxane, polyethylene, polyoxyethylene, polystyrene, polypropylene, polyvinyl chloride, or polyvinylidene chloride; the hydrophilic layer is selected from any one or more of polyvinyl alcohol, polyimide, or polyurethane.

5. The array-type flexible tactile sensor according to claim 1, characterized in that, the electrode layer is selected from any one of graphene, modified graphene, modified graphene biocomposite, carbon nanotubes, modified carbon nanotubes, modified carbon nanotube biocomposite, or PEDOT:PSS; the base layer is selected from any one of polyurethane, polyimide, polyethylene terephthalate, or polydimethylsiloxane.

6. The array-type flexible tactile sensor according to claim 5, characterized in that, the electrode layer is a carboxylated multi-walled carbon nanotube / chitosan composite material.

7. The preparation method of the array-type flexible tactile sensor according to any one of claims 1 to 6, characterized in that, it includes the following steps: (1) After hydrophilically modifying the friction layer, a hydrophilic layer is prepared on its surface; (2) The electrode layer is coated on the surface of the hydrophilic layer by a screen printing method; wherein, the screen printing plate used in the screen printing method has an array structure; (3) The base layer is combined with the electrode layer to obtain the array-type flexible tactile sensor.

8. The preparation method according to claim 7, characterized in that, the hydrophilic modification is specifically: after subjecting the friction layer to oxygen plasma treatment, it is further treated with a surfactant.

9. The preparation method according to claim 7, characterized in that, the radio frequency power of the oxygen plasma treatment is 100 - 130 W, the time is 30 - 60 s, and the oxygen flow rate is 120 - 160 sccm.

10. A tactile sensing system, characterized in that, it includes the array-type flexible tactile sensor according to any one of claims 1 to 6 or the array-type flexible tactile sensor prepared by the preparation method according to any one of claims 7 to 9.

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