Skin-like multi-mode tactile sensor and preparation method thereof

Abstract

The invention discloses a skin-like multi-mode tactile sensor and a preparation method thereof, and belongs to the technical field of sensors, the sensor comprises an isolation layer lower substrate, electrodes, a sensing layer and a protection layer upper substrate from bottom to top; the lower substrate adopts a hydrogenated styrene-butadiene block copolymer (SEBS), and in the preparation process of the SEBS substrate, isopropanol can be taken away by overnight volatilization of a toluene solution, so that a porous substrate is formed, and the substrate has air permeability; the electrode uses a mixed solution of PEDOT: PSS PH1000 and DMSO, so that the conductivity of the electrode can be effectively improved; the porous structure of the sensing layer is formed by using cube sugar as a sacrifice template, and the resistance change of the sensing layer is caused by pressing deformation, so that different electric signals are formed, and the change of temperature and tiny pressure can be sensed.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to a skin-like multimodal tactile sensor and a preparation method thereof. Background Art

[0002] Skin-like multimodal tactile sensors can accurately simulate human touch and have the ability to sense temperature, vertical pressure, and sliding touch. In the medical field, they can be applied to prosthetic limbs for the disabled. By integrating them on the surface of prosthetic limbs, they can help disabled people perceive temperature, pressure, and sliding touch in a multimodal way, effectively solving the problem of single tactile sensor data perception at present. In the field of consumer electronics, they can be applied to wearable devices, combined with virtual reality and augmented reality technologies, to give users a better interactive and immersive experience through sensitive tactile feedback. In the field of intelligent robots, they can be integrated into robotic arms to help robots identify different objects by touch, and can be integrated into the robot's electronic skin to help robots perceive temperature and pressure, thereby effectively improving the robot's work efficiency and safety.

[0003] In the early stages of the development of skin-like tactile sensors, research mainly focused on bionics and materials science. By using some polymer flexible materials, some single functions of the skin were imitated; then some circuit technology was added to better record the generation and propagation of electrical signals, while developing some flexible, highly sensitive, and highly linear electronic materials; then development began to form a sensor array method, which integrates multiple sensors to measure multimodal data such as temperature and pressure, and uses artificial intelligence technology to achieve the classification, recording, processing, and feedback of tactile signals.

[0004] In the future, in terms of materials, we can develop low-cost materials with higher sensitivity, better stretchability, self-healing, better conductivity, excellent biocompatibility and low toxicity; in terms of process manufacturing, we can optimize the production process, reduce costs, improve the commercial development of sensors, and find production technologies that can be manufactured on a large scale; in functional integration, we can provide more comprehensive data detection capabilities, including sound, light, heat, force, electricity, odor, chemicals, etc., and add better artificial intelligence algorithms to enhance data collection and processing; in application, we can provide personalized services so that sensors can meet the diversified needs of the market.

[0005] Fiber optic sensors can have good sensitivity, but have low spatial resolution and are expensive; In flexible electronic devices, inorganic semiconductors exhibit high carrier mobility, but their inherent stiffness and brittleness greatly hinder their application in flexible electronic products; Piezoresistive sensors mainly detect pressure changes through changes in the resistance of the sensing material, but due to the properties of the sensing material, pressure and resistance do not change linearly; The substrates of flexible electronic products have good elasticity but are not breathable; Most tactile sensors can be called pressure sensors, mainly because they can only detect changes in pressure alone. Summary of the invention

[0007] The object of the present invention is to provide a skin-like multimodal tactile sensor and a method for preparing the same.

[0008] Based on the above purpose, the present invention adopts the following technical solutions: A method for preparing a skin-like multimodal tactile sensor, the process is as follows: (1) Dissolve SEBS particles in toluene to prepare a 50-70 mg / mL SEBS solution, then mix the SEBS solution and isopropanol in a volume ratio of 5:(1-3), apply it on the current collector, and dry it in air to obtain the substrate under the isolation layer; (2) inkjet printing electrodes on the substrate under the isolation layer, wherein the electrodes are snake-shaped interdigitated electrodes; (3) The PDMS prepolymer and curing agent are prepared in proportion to form a PDMS liquid, and then sugar cubes are immersed in the liquid, and the solution immersed in the sugar cubes is solidified to obtain a template. The solidified template is placed in water until the sugar cubes are completely dissolved, and then taken out and dried to obtain a porous template of the sensing layer. The aqueous dispersion of PEDOT:PSS PH 1000 and ethylene glycol are mixed in a volume ratio of (5-15):1 to prepare a conductive solution, and then the upper and lower surfaces of the porous template are pretreated by oxygen plasma, and then the treated porous template is immersed in the conductive solution for 0.5-2 hours, and then dried and taken out to obtain the sensing layer, which is cut to the required size; (4) The PDMS prepolymer and curing agent are prepared in proportion to form a PDMS liquid, vacuum degassing is performed, and then the degassing PDMS is evenly coated on the silicon wafer, dried, and cut to the required size as the upper substrate of the protective layer; (5) Use conductive glue to stick the sensing layer to the lower substrate of the isolation layer printed with electrodes, and then use conductive glue to encapsulate the upper substrate of the protective layer on the other side of the sensing layer.

[0009] Furthermore, the conductive solution in step (3) is doped with carbon nanofibers, gold nanoparticles or silver nanoparticles, and the preparation process is: ultrasonically dispersing the carbon nanofibers, gold nanoparticles or silver nanoparticles in ethanol to obtain an ethanol solution of the dopant, adding DMSO to Clevios PEDOT:PSS PH1000 to obtain a DMSO mixed solution of PEDOT:PSS, and mixing the ethanol solution of the dopant and the DMSO mixed solution of PEDOT:PSS in a volume ratio of (1-4):(4-1) to obtain a doped conductive solution, wherein the concentration of the dopant in the ethanol solution of the dopant is 1-5wt%, and the concentration of DMSO in the DMSO mixed solution of PEDOT:PSS is 1-5wt%.

[0010] Furthermore, it also includes a humidity inspection layer. Polypyrrole is added to methanol and stirred to obtain a solution with a polypyrrole concentration of 10~50 wt%. The solution is spin-coated on a substrate and dried to obtain a humidity inspection layer of 0.05~0.3 mm; the humidity inspection layer is encapsulated between the sensing layer and the protective layer on the substrate.

[0011] Furthermore, in step (2), the inkjet printing ink is prepared by mixing 75 wt% to 85 wt% of an aqueous dispersion of PEDOT:PSS PH1000, 5 wt% to 15 wt% of dimethyl sulfoxide, and 5 wt% to 15 wt% of anhydrous ethanol.

[0012] Furthermore, in step (2), the printing speed is 1-20 mm / s.

[0013] Furthermore, the pretreatment in step (3) refers to pretreatment at 50-70 W for 50-70 s.

[0014] Furthermore, the thickness of the substrate under the isolation layer is 0.1-0.5 mm, the thickness of the electrode is 0.1-10 mm; the thickness of the sensing layer is 1-3 mm, and the thickness of the substrate on the protective layer is 0.1-0.3 mm.

[0015] During the preparation of the SEBS substrate, the volatilization of the toluene solution will take away the isopropanol, thus forming a porous substrate, which makes the substrate breathable; the electrode uses a mixed solution of PEDOT:PSS PH1000 and DMSO, which can effectively increase the conductivity of the electrode; the porous structure of the sensing layer is formed by using sugar cubes as sacrificial templates, and the resistance of the sensing layer changes through pressing and deformation, thereby forming different electrical signals, and can sense changes in temperature and subtle pressure. Inkjet printing technology can significantly reduce manufacturing costs and achieve high-precision electrode printing.

[0016] The present invention combines data processing technology with a classification algorithm of machine learning, can effectively distinguish the perception of different objects, perform rapid perception, and improve the efficiency and accuracy of data processing.

[0017] In summary, the present invention has the following advantages: 1. Structural innovation: the sensing layer adopts a multi-layer composite porous structure plus a three-dimensional structure, which can increase the sensitivity while performing multi-modal data perception of temperature, pressure and force in the sliding direction.

[0018] 2. Manufacturing process, using inkjet printing to reduce production costs and improve production efficiency.

[0019] 3. Data processing, using intelligent data processing algorithms, enhances real-time detection and feedback of electrical signals, improves detection accuracy, and adds classification algorithms to help sensors better detect data.

[0020] 4. The porous structure of the substrate solves the problem of air permeability of electronic skin BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the sensor of the present invention; Figure 2 is a SEM image of the substrate under the isolation layer obtained in Example 1; Figure 3 is the inkjet-printed electrode pattern obtained in Example 1; Figure 4 is a SEM image of the porous sensing layer prepared in Example 1; Figure 5 is a pressure variation diagram of the sensor obtained in Example 1; Figure 6 is a temperature variation diagram of the sensor obtained in Example 1; Figure 7 is a thermal map detected by the sensor array prepared in Example 1; Figure 8 is a pressure variation diagram of the sensor obtained in Example 2; Fig. 9 is a graph showing changes in pressure, temperature and humidity of the sensor obtained in Example 3; Fig.10 It is the influence of the thickness and speed of inkjet printing during electrode preparation on the sensor. DETAILED DESCRIPTION

[0022] Example 1 A method for preparing a skin-like multimodal tactile sensor, the process is as follows: (1) Preparation of the substrate under the isolation layer: First, 900 mg of SEBS (hydrogenated styrene-butadiene block copolymer) particles with a particle size of 2 mm were dissolved in 15 mL of toluene to prepare a 60 mg / mL SEBS solution. Then, the 60 mg / mL SEBS solution and isopropanol were mixed in a volume ratio of 5:2, coated on aluminum foil, and dried at room temperature and ventilation for 48 hours to obtain the substrate under the isolation layer. The pore structure is as follows: Figure 2 As shown, the thickness of the lower substrate is 0.2 mm, the porosity reaches 50%, the pore size is about 0.02 mm, and the density is 30 ppi.

[0023] (2) Preparation of electrode layer: The electrode was printed on the substrate under the isolation layer by inkjet printing. The inkjet printing ink was a mixture of 80wt% PEDOT:PSS PH1000 aqueous dispersion (purchased from Clevios PH1000 of Heraeus), 10wt% dimethyl sulfoxide (DMSO), and 10wt% anhydrous ethanol. The printing speed was 1mm / s, and the printed electrode thickness was 0.1mm. The pattern was as follows: Figure 3 As shown, the use of snake-shaped interdigitated electrodes effectively ensures the stretchability and conductivity of the electrode. The electrode is printed on the lower substrate, and the resistance is measured using a multimeter to be about 5k ohms. Through repeated stretching, it is found that the electrode resistance basically does not change, the conductivity is still good, and the resistance is maintained at about 5k ohms.

[0024] (3) Porous sensing layer: The flexible material polydimethylsiloxane (PDMS) was used. First, 25 mL of PDMS liquid was prepared using a PDMS prepolymer and a matching curing agent in a ratio of 10:1. Then, 6 pieces of commercially available Taikoo edible sugar cubes were immersed in the liquid and immersed in a vacuum environment so that the sugar cubes were fully immersed. After immersion for two hours, the template was placed in a drying oven and dried at 80°C for 3 hours or at room temperature overnight to solidify the solution immersed in the sugar cubes. The solidified template was then placed in water for 1 hour until the sugar cubes were completely dissolved. The porous sponge structure template of the sensing layer was taken out and then placed in a drying oven for 2 hours to remove excess water. Next, a conductive solution was prepared by mixing the purchased Clevios PEDOT:PSS PH 1000 aqueous dispersion with ethylene glycol in a volume ratio of 10:1 to form a conductive solution. The upper and lower surfaces of the porous sponge structure template were then pretreated with oxygen plasma, i.e., at 60 W in a plasma cleaner for 60 min. s, and then immerse the treated porous sponge structure template in the conductive solution. After immersion for 1 hour, place it in an oven at 80°C for about 2 hours, then take it out to obtain the porous conductive sensing layer, and then cut it to obtain a porous sensing layer with a thickness of 2 mm, a length of 5 mm, and a width of 5 mm. The SEM image of the porous sensing layer is shown in Figure 4As shown in the figure, it can be seen that there are a large number of porous structures. By continuously pressing, the contact area inside the sensing layer can be increased, thereby increasing the conductive path and reducing the resistance of the sensing layer. Therefore, the external pressure signal can be converted into a resistance signal for detection.

[0025] (4) Preparation of the upper substrate of the protective layer: First, use the PDMS prepolymer and curing agent in a ratio of 10:1 to prepare 25 mL of PDMS liquid, then vacuum treat to extract bubbles, and then evenly apply the treated PDMS on the silicon wafer. Use a coating machine with a speed of 500 r / min for 18 s. Finally, dry the spin-coated PDMS at 80°C for 1 hour and cut it into a size of 8 mm long, 8 mm wide, and 150 mm thick as the upper substrate of the protective layer.

[0026] (5) Packaging: Use epoxy conductive glue (purchased from Suzhou Xinwei High-tech Materials Co., Ltd.) to make the sensing layer stick to the lower substrate of the isolation layer of the printed electrode. Finally, use epoxy conductive glue to encapsulate the upper substrate of the protective layer on the other side of the sensing layer to obtain the product.

[0027] Figure 5 This is the pressure change diagram of the sensor made in Example 1, with the loading pressure on the left and the unloading pressure on the right. Both show the response under pressures of 10kPa, 40kPa, 50kPa, 60kPa, and 70kPa, and convert the pressure signal into the resistance change of the sensor, and the fast response and fast release time only takes 60ms.

[0028] Figure 6 This is a temperature variation diagram of the sensor obtained in Example 1. Figure 6 The figure shows the change in resistance of the sensor from 30°C to 70°C as the temperature increases, and draws a fitting curve of the resistance change rate. It can be clearly seen that the sensor can produce a linear resistance change as the temperature increases. The small figure gives the measured self-resistance of the sensor at the corresponding temperature.

[0029] Figure 7 For the thermal map detected by the sensor array in Example 1, a 3×3 two-dimensional array is made, with a total of 9 sensor units, each of which can detect and transmit data. During the detection process, first, each sensor unit will respond to the change of physical quantity within its detection range and convert it into an electrical signal, which is then transmitted to the multiplexer through the electrode. The multiplexer will obtain the detection signals of all sensor units, and then amplify the signal through the signal amplifier for subsequent signal processing, and then convert the analog signal into a digital signal through the analog-to-digital converter and transmit it to the computer. Finally, the computer obtains the digital signal and visualizes the digital signal data to better observe the detected signal. Figure 7The heat map shown is the result of visualization. Through the heat map distribution, red indicates high pressure, blue indicates pressure close to zero, and the value is the corresponding resistance change rate. It can be clearly detected that this is an I-shaped object. At the same time, five kinds of objects were pressed and recognized, that is, the five objects were placed vertically at the center of the sensor array, and then the sensor data corresponding to the five objects were recorded respectively, and then classified and trained through convolutional neural networks. After training, the five objects were pressed and tested respectively. Each object was tested 100 times, and the accuracy was calculated. The accuracy of the detection is shown in Table 1.

[0030] Table 1 thing apple banana Water cup sponge egg Accuracy 92% 95% 90% 98% 96% Example 2 Nanocomposite material technology is used to mix nanomaterials (gold nanoparticles, silver nanoparticles) or nanofibers (carbon nanofibers) into sensing materials to improve the mechanical properties, conductivity and durability of the sensor.

[0031] First, the carbon nanotubes were dispersed in anhydrous ethanol at a concentration of 2 wt %, and ultrasonic treatment was performed for 30 minutes to ensure uniform dispersion. Then, 3 wt % DMSO was added to Clevios PEDOT:PSS PH1000 as a surfactant and stirred for 30 minutes to mix it evenly. The ethanol solution of carbon nanotubes and the DMSO mixed solution of PEDOT:PSS were gradually mixed in a ratio of 1:4, 2:3, 3:2, and 4:1, and stirred in a high-speed stirrer for 30 minutes to ensure that the solution was uniform. At the same time, the DMSO mixed solution of PEDOT:PSS and the ethanol solution of carbon nanotubes were used as controls. Then, each solution was used to make the sensing layer. The other implementation steps were the same as in Example 1, except that the PEDOT:PSS solution soaked in Example 1 was replaced with a newly prepared PEDOT:PSS solution with nanoparticles added. Figure 8 As shown by Figure 8 It can be seen that after adding nanoparticles, the sensing layer maintains a low resistance of 820 ohms under a low pressure of 200 Pa. It can be seen that the addition of nanoparticles effectively improves the conductivity of the sensing layer.

[0032] Example 3 Multifunctional integration technology integrates multiple functions of a single sensor into one sensor (pressure, temperature, humidity, etc.), thereby increasing the application range of the sensor. This embodiment adds a humidity detection layer. First, add polypyrrole (PPy) to methanol with a polypyrrole concentration of 20 wt%, stir until completely dissolved, then invert the solution on a silicon wafer and spin coat at 500 r / min for 15 seconds, then dry at 80°C for 1 hour to obtain a 0.1 mm thin film, which is encapsulated between the sensing layer and the protective layer substrate for humidity detection. Others are the same as in Example 1. Fig. 9 As shown, measured changes in pressure, temperature, and humidity can all cause changes in the sensor's voltage.

[0033] Example 4 Inkjet printing technology improves the parameters of inkjet printing and effectively increases the sensitivity and repeatability of the sensor. By changing the printing thickness and printing speed, a better conductive electrode printing method can be found. Some comparison results are shown below. Fig.10 As shown in the figure, increasing the printing thickness can reduce the generation of resistance. This application found 120 microns as the most suitable printing thickness, which can ensure that the electrode has high conductivity. At the same time, as the printing speed increases, the printing accuracy decreases. This application found a printing speed of 10mm / s to achieve better printing quality.

[0034] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a skin-like multimodal tactile sensor, characterized in that: The process is as follows: (1) Dissolve SEBS particles in toluene to prepare a 50-70 mg / mL SEBS solution, then mix the SEBS solution and isopropanol in a volume ratio of 5:(1-3), apply it on the current collector, and dry it in air to obtain the substrate under the isolation layer; (2) inkjet printing electrodes on the substrate below the isolation layer, wherein the electrodes are snake-shaped interdigitated electrodes; (3) The PDMS prepolymer and curing agent are prepared in proportion to form a PDMS liquid, and then sugar cubes are immersed in the liquid, and the solution immersed in the sugar cubes is solidified to obtain a template. The solidified template is placed in water until the sugar cubes are completely dissolved, and then taken out and dried to obtain a porous template of the sensing layer. The aqueous dispersion of PEDOT:PSS PH 1000 and ethylene glycol are mixed in a volume ratio of (5-15):1 to prepare a conductive solution, and then the upper and lower surfaces of the porous template are pretreated by oxygen plasma, and then the treated porous template is immersed in the conductive solution for 0.5-2 hours, and then dried and taken out to obtain the sensing layer, which is cut to the required size; (4) The PDMS prepolymer and curing agent are prepared in proportion to form a PDMS liquid, vacuum degassing is performed, and then the degassing PDMS is evenly coated on the silicon wafer, dried, and cut to the required size as the upper substrate of the protective layer; (5) Use conductive glue to stick the sensing layer to the lower substrate of the isolation layer printed with electrodes, and then use conductive glue to encapsulate the upper substrate of the protective layer on the other side of the sensing layer.

2. The method for preparing the skin-like multimodal tactile sensor according to claim 1, characterized in that: The conductive solution in step (3) is doped with carbon nanofibers, gold nanoparticles or silver nanoparticles, and the preparation process is: ultrasonically dispersing carbon nanofibers, gold nanoparticles or silver nanoparticles in ethanol to obtain an ethanol solution of the dopant, adding DMSO to Clevios PEDOT:PSSPH1000 to obtain a DMSO mixed solution of PEDOT:PSS, and mixing the ethanol solution of the dopant and the DMSO mixed solution of PEDOT:PSS in a volume ratio of (1-4):(4-1) to obtain a doped conductive solution, wherein the concentration of the dopant in the ethanol solution of the dopant is 1-5wt%, and the concentration of DMSO in the DMSO mixed solution of PEDOT:PSS is 1-5wt%.

3. The method for preparing the skin-like multimodal tactile sensor according to claim 1, characterized in that: It also includes a humidity inspection layer. Polypyrrole is added to methanol and stirred to obtain a solution with a polypyrrole concentration of 10-50 wt%. The solution is spin-coated on a substrate and dried to obtain a humidity inspection layer of 0.05-0.3 mm; the humidity inspection layer is encapsulated between the sensing layer and the protective layer on the substrate.

4. The method for preparing the skin-like multimodal tactile sensor according to claim 1, characterized in that: In step (2), the inkjet printing ink is prepared by mixing 75 wt% to 85 wt% of an aqueous dispersion of PEDOT:PSS PH1000, 5 wt% to 15 wt% of dimethyl sulfoxide, and 5 wt% to 15 wt% of anhydrous ethanol.

5. The method for preparing the skin-like multimodal tactile sensor according to claim 1, characterized in that: In step (2), the printing speed is 1~20mm / s.

6. The method for preparing the skin-like multimodal tactile sensor according to claim 1, characterized in that: The pretreatment in step (3) refers to pretreatment at 50 to 70 W for 50 to 70 s.

7. The skin-like multimodal tactile sensor prepared by the preparation method according to any one of claims 1 to 6, wherein the thickness of the substrate under the isolation layer is 0.1-0.5 mm, the thickness of the electrode is 0.1-10 mm; the thickness of the sensing layer is 1-3 mm, and the thickness of the substrate above the protective layer is 0.1-0.3 mm.

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