Fingerprint-imitating high-sensitivity flexible sensor capable of identifying direction and preparation method thereof

Abstract

The invention discloses a fingerprint-imitating high-sensitivity flexible sensor capable of identifying directions and a preparation method thereof, and belongs to the technical field of flexible sensors. The capacitive pressure sensor array and the CPU connected with the capacitive pressure sensor array are used for detecting the magnitude and direction of the acting force between the pre-recognition material and the fingerprint bionic texture, and the periodic surface texture information of the pre-recognition material is detected. According to the capacitive pressure sensor, the strip-shaped air gaps are formed in the dielectric layer, so that the insulativity of the capacitive pressure sensor can be improved, and the capacitive pressure sensor can recognize the direction more accurately. Meanwhile, the strip-shaped air gap can significantly enhance the deformation and pressure response of the sensor, thereby improving the sensitivity of the sensor, preventing the material from being broken, and prolonging the service life. The fingerprint bionic texture has a ridge line structure, and each fingerprint is equivalent to an amplification lever, so that the sensitivity of the sensor is further enhanced. According to the method, a new research direction is provided for restoring the perception ability of the handicapped and researching the humanoid tactile receptor applied to the humanoid robot.

Description

Technical Field

[0001] The invention belongs to the technical field of flexible sensors, and in particular relates to a fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a preparation method thereof. Background Art

[0002] With the development of science and technology, flexible sensors can be embedded inside clothing, wrapped on the surface of the skin, and monitor human movement and health status in real time. They have attracted widespread attention in the fields of wearable devices, patient rehabilitation, and medical prostheses, and have become a worldwide academic frontier and research hotspot. The receptors in human skin are not a static process that is only affected by the force on the surface of an object, but a dynamic process. In this process, when the skin slides over the surface of an object, the surface structure and softness of the object can theoretically be identified through a combination of force and vibration. However, in real life, sensors that can sense human touch need to operate within a large range of vibration and pressure, and highly sensitive detection is difficult to achieve.

[0003] In the existing technology, the research on intelligent prostheses mainly focuses on the main structure and control methods of prostheses, while there are relatively few studies on the intelligent perception ability of prostheses, which can restore the perception ability of disabled people to a certain extent. In addition, in recent years, humanoid robot technology has developed rapidly. Giving robots tactile receptors like humans to intelligently control the movement of robots will become another major breakthrough in the field of robots, which will enable robots to better serve human life and production.

[0004] The skin of fingers has a completely different texture structure from the skin of other parts of the human body - fingerprints. Most human fingerprints are elliptical or spiral-shaped, which is to ensure that some of the textures can maintain the most suitable angle for grasping no matter how the fingers slide. The existence of fingerprints can not only increase friction to facilitate grasping of objects, but also help enhance tactile perception. From a microscopic perspective, the objects that humans touch on a daily basis are not absolutely smooth, and their surfaces have their own unique textures, and the skin of fingers itself also has its own specific textures. Therefore, when a finger slides to touch an object, it is equivalent to two textured surfaces contacting and rubbing against each other. According to relevant reports, fingerprint textures have the ability to detect surface structures at a scale of hundreds of microns. When a person's finger slides on the surface of an object, it interacts with the surface structure of the object to generate a vibration signal, and each fingerprint is equivalent to an amplifying lever, which transmits the amplified vibration to the mechanical receptors under the epidermis.

[0005] Therefore, the present invention proposes a fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a preparation method thereof, which is used for highly sensitive detection of human skin receptors. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a fingerprint-like high-sensitivity flexible sensor that can identify direction and a preparation method to solve the technical problem that the flexible sensors in the prior art need to perform inductive detection of the force on the object within a large vibration and pressure range, and highly sensitive detection is difficult to achieve.

[0007] A fingerprint-like high-sensitivity flexible sensor capable of identifying direction comprises a dielectric layer, wherein the upper surface of the dielectric layer is coated with a first conductive electrode array, the lower surface of the dielectric layer is coated with a second conductive electrode array, and each conductive electrode in the first conductive electrode array and the second conductive electrode array is arranged in a pair, and the two conductive electrode plates aligned up and down form a capacitive pressure sensor, and all capacitive pressure sensors form a capacitive pressure sensor array; a first packaging layer is coated on the upper part of the dielectric layer and the first conductive electrode array; an upwardly protruding fingerprint bionic texture is provided on the upper surface of the first packaging layer; the fingerprint bionic texture has a ridge structure, and the outer surface of the fingerprint bionic texture and the outer part of the first packaging layer are coated with a second packaging layer; a third packaging layer is coated on the lower part of the dielectric layer and the second conductive electrode array; each conductive electrode in the first conductive electrode array and the second conductive electrode array is connected to a CPU through a copper wire;

[0008] In working state, the fingerprint bionic texture directly contacts the pre-identified material and generates vibration. The fingerprint bionic texture with ridge structure imitates human tactile perception. The ridge structure can amplify the vibration signal. The capacitive pressure sensor array and the connected CPU are used to detect the force between the pre-identified material and the fingerprint bionic texture, the direction of the force, and the periodic surface texture information of the pre-identified material.

[0009] A plurality of strip air gaps are evenly distributed inside the dielectric layer, and the strip air gaps are arranged in an area outside the area directly facing the first conductive electrode array and the second conductive electrode array, so as to improve the insulation of the capacitive pressure sensor, thereby improving the sensor's recognition accuracy of direction.

[0010] Each fingerprint of the fingerprint bionic texture is equivalent to an amplifying lever, which transmits the amplified vibration to the first conductive plate array and the dielectric layer.

[0011] The fingerprint bionic texture is formed by 3D printing.

[0012] The method in which the CPU detects the magnitude of the force between the pre-identified material and the fingerprint bionic texture, the direction of the force, and detects the periodic surface texture information of the pre-identified material is as follows:

[0013] ① In the CPU, each conductive electrode plate in the first conductive electrode plate array and the second conductive electrode plate array is numbered, and the conductive electrode plates facing each other in the first conductive electrode plate array and the second conductive electrode plate array are numbered the same, and the numbering is expressed in the form of (row number, column number);

[0014] ② When the force slides over the fingerprint bionic texture above the first conductive electrode array, the vibration signal is transmitted to the first conductive electrode array, and the capacitance signal output by each individual capacitive pressure sensor is obtained through the change in the distance between the first conductive electrode array and the second conductive electrode array, which is used to characterize the magnitude of the force. The larger the capacitance value, the greater the force;

[0015] The capacitance signal calculation formula is as follows:

[0016] C=v0ε x A / d;

[0017] Where: ε0 is the dielectric constant of vacuum; ε x is the relative dielectric constant; A is the electrode plate area; d is the distance between the two plates;

[0018] ③The direction of the force is obtained:

[0019] Arrange the time when each capacitive pressure sensor in the capacitive pressure sensor array starts to output the capacitive signal in order from first to last, and then correspond to its row and column coordinates in the capacitive pressure sensor array to obtain the direction of the force acting on the fingerprint bionic texture;

[0020] ④Identify the periodic surface texture information of materials:

[0021] The frequency of the capacitance signal change of each capacitive pressure sensor in the capacitive pressure sensor array depends on the frequency of contact between the pre-identified material and the fingerprint bionic texture, and the contact frequency depends on the relative speed between the pre-identified material and the fingerprint bionic texture and the period of contact between the surface protrusions of the pre-identified material and the fingerprint bionic texture. Therefore, the periodic surface texture information of the material can be identified by the frequency of the capacitance signal change;

[0022] By performing fast Fourier transform (FFT) on the capacitance signal output by the capacitive pressure sensor, the characteristic frequency of the texture is obtained in the spectrum diagram;

[0023] At the same friction speed, as the texture spacing decreases, the characteristic frequency also increases. The position of the characteristic peak is determined by the spacing of the test texture surface. Therefore, the texture spacing can be calculated based on the characteristic frequency in the spectrum. The specific formula is:

[0024] λ = v / f;

[0025] Among them, λ is the periodic spacing of the texture, v is the relative speed of contact between the pre-identified material and the fingerprint bionic texture, and f is the characteristic frequency in the spectrum after FFT;

[0026] The periodic spacing of the texture obtained is the periodic surface texture information of the material to be identified.

[0027] A method for preparing a fingerprint-like high-sensitivity flexible sensor capable of identifying a direction, comprising the following steps, and the following steps are performed in sequence:

[0028] Step 1: prepare dielectric materials, composite conductive materials and packaging materials for later use, and measure the printing materials of fingerprint bionic textures;

[0029] Step 2: using a strip-shaped air gap forming mold and a dielectric material to cast a dielectric layer having a strip-shaped air gap in the middle;

[0030] Step 3: using an array forming mold and a composite conductive material to coat a first conductive electrode array on one side of the dielectric layer, wherein the arrangement position of the first conductive electrode array is staggered with the strip-shaped air gap;

[0031] Step 4: Connect a copper wire to the surface of each conductive electrode plate of the first conductive electrode array to serve as an electrode;

[0032] Step 5: Encapsulating the first encapsulation layer;

[0033] The upper surface of the dielectric layer and the first conductive electrode array are packaged in the first packaging layer by using a first packaging layer molding mold and packaging materials, and the proximal ends of the connection ends of the copper wires are packaged on both sides of the dielectric layer, and demolded after curing;

[0034] Step 6: Print fingerprint bionic texture;

[0035] A 3D printer is used to print the fingerprint bionic texture on a metal sheet using printing materials of the fingerprint bionic texture, and then the metal sheet is placed upside down on the upper surface of the first packaging layer, and a blade is used to separate the metal sheet and the fingerprint bionic texture;

[0036] Step 7: performing packaging of the second packaging layer;

[0037] Using the second encapsulation layer molding mold and the encapsulation material, encapsulate and solidify the fingerprint bionic texture root and the upper surface of the first encapsulation layer, and then demould;

[0038] Step 8, flip the semi-finished sensor product after demoulding in step 7 by 180 degrees, and apply the second conductive electrode plate array on the other side of the dielectric layer using the same technical means as in step 3, and align the first conductive electrode plate array and the second conductive electrode plate array one by one;

[0039] Step nine: Use the same technical means as steps four and five to connect the copper wires of the second conductive electrode array and encapsulate the dielectric layer and the copper wires to form a third encapsulation layer. After curing and demolding, the preparation of the fingerprint-like high-sensitivity flexible sensor is completed.

[0040] The strip-shaped air gap forming mold in step 2 comprises a containing box and a row of long strips that are evenly arranged and penetrate the containing box; gaps are left between the long strips and the upper top surface and the lower bottom plate of the containing box; a non-stick coating is sprayed on the inside of the containing box and the surface of the long strips of the strip-shaped air gap forming mold;

[0041] The specific method of casting in the step 2 is: pouring the dielectric material prepared in the step 1 into the strip air gap forming mold, and when the dielectric material fills the containing box, using a blade to scrape the top surface of the containing box, and then placing the mold under an ultraviolet light source for irradiation and curing, the long strip is pulled out of the containing box, and then demolded from the containing box to take out the successfully cast dielectric layer.

[0042] The array forming mold in step 3 is a rectangular cover-shaped structure, and a plurality of hollow structures arranged in an array are arranged on the surface of the upper cover, and the arrangement positions of the hollow structures are staggered with the strip-shaped air gaps of the dielectric layer;

[0043] The specific method for coating the first conductive electrode plate array in the step three is: clamping the array forming mold on the dielectric layer prepared in the step two and compacting it, staggering the hollow structure and the strip air gap, filling the hollow structure with the composite conductive material, using a blade to scrape the composite conductive material, and naturally curing it for 24 hours, removing the array forming mold, forming a conductive electrode plate at each hollow structure, and the first conductive electrode plate array is coated on the dielectric layer.

[0044] The specific method for encapsulating the first encapsulation layer in step five is as follows: the copper wires in step four are led out from the small holes opened on both sides of the encapsulation layer molding mold, the encapsulation layer molding mold is sleeved on the outer periphery of the dielectric layer, and the encapsulation material is poured onto the first conductive electrode array until the encapsulation layer molding mold is filled, and naturally cured at room temperature for 12 hours, and the encapsulation layer molding mold is removed.

[0045] Through the above design scheme, the present invention can bring the following beneficial effects:

[0046] The present invention utilizes a capacitive pressure sensor array and a connected CPU to detect the magnitude of the force between the pre-identified material and the fingerprint bionic texture, the direction from which the force comes, and detects the periodic surface texture information of the pre-identified material.

[0047] In the present invention, a strip-shaped air gap is provided in the dielectric layer, which can improve the insulation of the capacitive pressure sensor and make the fingerprint-like high-sensitivity flexible sensor more accurate in direction recognition. At the same time, the strip-shaped air gap makes it easier for the sensor to be compressed when it is subjected to pressure, thereby significantly enhancing the deformation and pressure response of the sensor, thereby improving the sensitivity of the sensor. By properly arranging the air gap structure, the external force can be absorbed and relieved, the material can be prevented from breaking, and the sensor can also show a repeatable response of thousands of cycles under bending or stretching conditions, thereby extending the service life of the sensor.

[0048] The fingerprint bionic texture has a ridge structure. The fingerprint bionic texture imitates the structure of human fingerprints. The fingerprint bionic texture is elliptical to ensure that the fingerprint bionic high-sensitivity flexible sensor can identify forces from all directions. At the same time, each fingerprint is equivalent to an amplifying lever, which transmits the amplified vibration to the first conductive plate array and the dielectric layer, further enhancing the sensitivity of the sensor.

[0049] The present invention proposes a new research direction for restoring the perception ability of disabled people and for studying human-like tactile receptors applied to humanoid robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The present invention is further described below with reference to the accompanying drawings and specific embodiments:

[0051] Figure 1 It is a structural schematic diagram of a fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a sensor in a preparation method of the present invention;

[0052] Figure 2 It is a structural schematic diagram of a fingerprint bionic texture in a high-sensitivity flexible fingerprint-like sensor capable of identifying direction and a preparation method of the present invention;

[0053] Figure 3 It is a structural schematic diagram of a strip-shaped air gap forming mold in a fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a preparation method of the present invention;

[0054] Figure 4 It is a structural schematic diagram of an array forming mold in a fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a preparation method of the present invention;

[0055] Figure 5 It is a schematic structural diagram of a packaging layer molding mold in a fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a preparation method of the present invention;

[0056] Figure 6 The present invention is a schematic diagram of the numbering of conductive electrode plates in a fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a preparation method thereof.

[0057] In the figure, 1-dielectric layer, 2-first conductive electrode plate array, 3-first packaging layer, 4-fingerprint bionic texture, 5-second packaging layer, 6-second conductive electrode plate array, 7-third packaging layer, 8-strip air gap molding mold, 9-array molding mold, 10-packaging layer molding mold, 11-strip air gap, 801-housing box, 802-row-shaped long strips. DETAILED DESCRIPTION

[0058] A fingerprint-like high-sensitivity flexible sensor capable of identifying direction and a preparation method thereof are further described below through specific embodiments.

[0059] Example:

[0060] like Figure 1 As shown, a fingerprint-like high-sensitivity flexible sensor capable of identifying direction comprises a dielectric layer 1, wherein a plurality of strip-shaped air gaps 11 are evenly distributed inside the dielectric layer 1; the upper surface of the dielectric layer 1 is coated with a first conductive electrode plate array 2; the upper side of the first conductive electrode plate array 2 is coated with a first packaging layer 3; the upper surface of the first packaging layer 3 has a fingerprint bionic texture 4 printed by 3D printing technology; the upper surface of the first packaging layer 3 and the root of the fingerprint bionic texture 4 are coated with a second packaging layer 5; the lower surface of the dielectric layer 1 is coated with a second conductive electrode plate array 6; the lower side of the second conductive electrode plate array 6 is coated with a third packaging layer 7.

[0061] The plane where the strip air gap 11 is located is parallel to the plane where the first conductive electrode array 2 is located. The strip air gap 11 is set in a partial area other than the area directly facing the first conductive electrode array 2 and the second conductive electrode array 6, which can improve the insulation of the capacitive pressure sensor and make the fingerprint-like high-sensitivity flexible sensor more accurate in direction recognition. At the same time, the strip air gap 11 makes it easier for the sensor to be compressed when it is subjected to pressure, thereby significantly enhancing the deformation and pressure response of the sensor, thereby improving the sensitivity of the sensor. By properly arranging the air gap structure, it can absorb and relieve external forces, prevent material rupture, and make the sensor show thousands of cycles of repeatable response under bending or stretching conditions, thereby extending the service life of the sensor.

[0062] like Figure 2 As shown, the fingerprint bionic texture 4 imitates the structure of human fingerprints and is elliptical, so as to ensure that the fingerprint bionic high-sensitivity flexible sensor can identify forces from all directions. At the same time, each fingerprint is equivalent to an amplifying lever, which transmits the amplified vibration to the first conductive plate array 2 and the dielectric layer 1.

[0063] In order to further improve the sensitivity of the sensor, a plurality of capacitor plates facing each other are distributed on the upper and lower surfaces of the dielectric layer 1, which respectively constitute the first conductive plate array 2 and the second conductive plate array 6. When the sensor interacts with the object to be identified, the fingerprint bionic texture 4 directly interacts with the contact material, and the first conductive plate array 2 and the second conductive plate array 6 are combined to form a soft capacitive pressure sensor array, which is combined with the fingerprint bionic texture 4 with a ridge structure, so that the sensor has the ability to detect pressure and vibration within the working range of human tactile perception.

[0064] The fingerprint bionic texture 4 is formed by 3D printing.

[0065] The strip air gap 11 is formed by a strip air gap forming mold 8, which is composed of a relatively slidable accommodation box 801 and a row of long strips 802; the first conductive electrode plate array 2 and the second conductive electrode plate array 6 are formed by an array forming mold 9; the first encapsulation layer 3 and the second encapsulation layer 5 are formed by an array forming mold 10. The strip air gap forming mold 8, the array forming mold 9 and the array forming mold 10 of this embodiment are all completed by 3D printing.

[0066] The first encapsulation layer 3 and the third encapsulation layer 7 protect the conductive electrode array, and the first encapsulation layer 3 and the dielectric layer 1 and the third encapsulation layer 7 and the dielectric layer 1 are tightly combined to increase the mechanical strength of the fingerprint-like high-sensitivity flexible sensor. The second encapsulation layer 5 protects the fingerprint bionic texture 4 to prevent the fingerprint bionic texture 4 from falling off the surface of the first encapsulation layer 3 due to external force.

[0067] A method for preparing a fingerprint-like high-sensitivity flexible sensor capable of identifying direction comprises the following steps, and the following steps are performed in sequence:

[0068] Step 1: Prepare dielectric materials, composite conductive materials and packaging materials for use:

[0069] ① The dielectric layer 1 of this embodiment is prepared by using a composite material of EBECRYL8413 and a diluent EBECRYL114. EBECRYL8413 is a high-performance epoxy resin curing agent, while EBECRYL114 is a diluent. These two materials can be mixed together to make the dielectric layer 1 of the capacitive pressure sensor. The composite material of EBECRYL8413 and EBECRYL114 as the dielectric layer 1 can provide excellent electrical properties and mechanical stability. The high-performance epoxy resin curing agent of EBECRYL8413 can provide good insulation properties, while the addition of a diluent (such as EBECRYL 114) can adjust the viscosity of the resin, making it easier to apply and flow, which helps to improve the leveling and uniformity of the coating, and also improves the flexibility of the coating. In addition, this composite material can also optimize the performance of the dielectric layer 1 by adjusting the proportion of EBECRYL114 to meet the needs of different applications. For example, reducing the proportion of EBECRYL114 can increase the mechanical strength and heat resistance of the dielectric layer 1.

[0070] The specific preparation method of the dielectric layer 1 is:

[0071] Step a, respectively weighing with a high-precision balance, mixing EBECRYL8413 and diluent EBECRYL114 in a ratio of 1:1, and then stirring for 10 minutes. Through experimental verification, the larger the ratio of EBECRYL8413 and diluent EBECRYL114, the worse the elasticity and the lower the viscosity, and the smaller the ratio, the better the elasticity, but the viscosity increases. Therefore, this embodiment adopts a ratio of 1:1 to achieve the best viscoelasticity and the best performance as the dielectric layer 1;

[0072] Step b: In order to prevent the obtained elastomer from having too high a hardness, a photoinitiator is added at a ratio of 1.5% in this embodiment and stirred for 5 minutes;

[0073] Step c, heating the stirred mixture in a water bath at 60°C for 10 min;

[0074] Step d, vacuum to remove bubbles, the pressure is as low as about 900Pa, the seal does not need to be too tight, and the valve pressure is dynamically adjusted according to the degree of bubble removal, until there is no large amount of bubbles overflowing and no surface film is formed;

[0075] Step e: store the liquid from which bubbles have been removed away from light and wait for use when molding.

[0076] ② The composite conductive material of this embodiment selects PEDOT:PSS / graphene composite material. As a new type of conductive material, PEDOT:PSS / graphene composite material has excellent conductivity: PEDOT:PSS itself has good conductivity, and the introduction of graphene can further improve the conductivity of the material. The main characteristics of the sensor of PEDOT:PSS and graphene composite materials in terms of sensitivity are its high sensitivity and fast response time. This material can detect very small pressure changes, and has a fast response speed, and can give accurate measurement results in a short time. In addition, its high conductivity also helps to increase the signal transmission speed, thereby improving the overall sensing efficiency. The doping amount of 12% by mass fraction selected in this embodiment makes the sensitivity of the capacitive pressure sensor reach the optimal state at this time.

[0077] The composite conductive material is prepared by a solution blending method, as follows:

[0078] Step a, using a precision electronic balance to weigh an appropriate amount of PEDOT:PSS;

[0079] Step b, weighing graphene according to a doping concentration of 12%, adding the weighed graphene into anhydrous ethanol, ultrasonically dispersing for 60 minutes, dispersing the graphene in anhydrous ethanol by using a high-frequency oscillator, and then shrinking the graphene to maintain the conductivity of the flexible wire while improving the density and conductivity of the graphene in the composite conductive material.

[0080] Step c, adding to PEDOT:PSS and stirring for 30 minutes, and ultrasonically dispersing for 10 minutes;

[0081] Step d, heating the mixed conductive polymer to volatilize the anhydrous ethanol part of the mixed material, so that the prepared composite material has the viscosity of scraping, the heating temperature is 40 ° C, the heating time is 10 minutes, the heating time is too short, the anhydrous ethanol is not fully volatilized, the heating time is too long, the material will appear dry and peeling phenomenon, so the heating time is determined by the volatilization of anhydrous ethanol in the mixed material.

[0082] ③ Preparation of packaging materials of this embodiment:

[0083] Since polydimethylsiloxane has good optical and chemical properties, and has the advantages of low price, simple processing, good stretchability, and excellent toughness, this embodiment selects this material as the flexible substrate material, and the specific preparation process is as follows:

[0084] Step a, fully mixing polydimethylsiloxane and diluent in a mass percentage of 10:1 and stirring for 10 minutes;

[0085] Step b: Pour the mixture into a culture dish with a diameter of 60 mm, and then vacuum to remove bubbles, with the pressure as low as about 900

[0086] Pa, the seal does not need to be too tight. The valve pressure can be adjusted dynamically according to the degree of bubble removal until no large amount of bubbles overflow.

[0087] ④ The fingerprint bionic texture 4 of this embodiment adopts the finished polylactic acid material purchased from the market. The polylactic acid material has good tensile strength and ductility, good fluidity, can be easily printed with various complex patterns, and has high hardness after printing. When the fingerprint texture made of polylactic acid rubs against the surface of an object, the vibration signal generated is stronger, which is more conducive to the output of the capacitance signal of the capacitive pressure sensor.

[0088] Step 2: Prepare dielectric layer 1:

[0089] Evenly spray the OKS 571 Teflon non-stick coating inside the receiving box of the strip air gap forming mold 8 and the surface of the row-shaped strips, adjust the relative position between the receiving box and the row-shaped strips of the strip air gap forming mold 8, so that the row-shaped strips penetrate the receiving box, so as to form the strip air gap 11; after the coating is dry, slowly pour the previously prepared EBECRYL8413 and EBECRYL114 dielectric layer 1 materials into the strip air gap forming mold 8, and when the natural flow is no longer carried out, use a blade to scrape and apply evenly, and then put the mold under a UV light source for irradiation and curing. After 5 minutes, slowly pull the row-shaped strips of the strip air gap forming mold 8 out of the receiving box, demould and remove the dielectric layer 1 from the receiving box, and cut off the irregular and uneven thickness parts around;

[0090] Step 3: Prepare the first conductive electrode array 2:

[0091] The prepared array forming mold 9 is clamped on the dielectric layer 1 prepared in step 2 and compacted, and the prepared PEDOT:PSS / graphene composite material is slowly poured in. When the natural flow is no longer carried out, a blade is used for scraping and coating, and the coating is evenly applied. The matrix forming mold is removed after natural curing for 24 hours.

[0092] Step 4: Connect a conductive copper wire to the surface of each conductive electrode plate of the first conductive electrode plate array 2 to serve as an electrode;

[0093] Step 5: Prepare the first encapsulation layer 3:

[0094] Align the inner wall of the prepared array forming mold 10 with the four sides of the dielectric layer 1 prepared in step 2, and lead the conductive copper wires connected from the surface of each conductive electrode plate in step 4 out of the small holes opened on both sides of the array forming mold 10. After the array forming mold 10 is placed, slowly pour a certain volume of polydimethylsiloxane packaging material on the first conductive electrode plate array 2, and naturally cure it at room temperature for 12 hours. Use a thin blade to gently remove the array forming mold 10 and remove the surrounding irregular parts;

[0095] Step 6: Print fingerprint bionic texture 4:

[0096] A thin metal sheet is laid on the molding platform of the 3D printer, and the fingerprint bionic texture 4 is printed on the metal sheet using polylactic acid material. After the fingerprint bionic texture 4 is printed, the printed fingerprint bionic texture 4 and the metal sheet are placed upside down on the surface of the first packaging layer 3, and the metal sheet and the fingerprint bionic texture 4 are separated by a thin blade and the metal sheet is removed;

[0097] Step 7: preparing the second encapsulation layer 5:

[0098] Place the inner wall of the prepared array forming mold 10 in contact with the four sides of the first encapsulation layer 3 prepared in step 5, slowly pour a certain volume of polydimethylsiloxane encapsulation material on the first encapsulation layer 3 prepared in step 5, and naturally cure it at room temperature for 12 hours. Use a thin blade to gently remove the array forming mold 10 and remove the surrounding irregular parts;

[0099] Step 8: Flip the material cured in step 7 by 180 degrees, and prepare a second conductive electrode array 6 on the other side of the dielectric layer 1 having the fingerprint bionic texture 4, the preparation method being the same as step 3.

[0100] Step 9: Connect a conductive copper wire to the surface of each conductive electrode plate of the second conductive electrode plate array 6 to be used as an electrode;

[0101] Step 10, align the inner wall of the prepared array molding mold 10 with the four sides of the dielectric layer 1, lead the conductive copper wires connected in step 9 out of the small holes opened on both sides of the array molding mold 10, slowly pour a certain amount of polydimethylsiloxane packaging material on the second conductive electrode array 6, and naturally cure it at room temperature for 48 hours. Use a thin blade to gently remove the array molding mold 10 and remove the surrounding irregular parts to complete the preparation of the fingerprint-like high-sensitivity flexible sensor.

[0102] A detection method for a fingerprint-like high-sensitivity flexible sensor capable of identifying direction is as follows:

[0103] Each conductive plate in the first conductive plate array 2 and the second conductive plate array 6 is numbered. The conductive plates facing each other in the first conductive plate array 2 and the second conductive plate array 6 are numbered the same. The numbering is expressed in the form of (row number, column number), that is, each pair of conductive plates in the first conductive plate array 2 and the second conductive plate array 6 is numbered (1, 1), (1, 2) ... (8, 5), such as Figure 6 shown.

[0104] When a force slides over the fingerprint bionic texture 4 above the conductive plate array, a vibration signal will be generated, and the fingerprint bionic texture 4 is equivalent to an amplifying lever, which transmits the amplified vibration to the conductive plate array. The size and direction information of the action can be obtained by outputting a capacitance signal through each individual capacitive pressure sensor in the conductive plate array.

[0105] ① Detect the magnitude of the force:

[0106] When a force acts on the fingerprint bionic texture 4 on the capacitive pressure sensor array square composed of the first conductive electrode array 2 and the second conductive electrode array 6, the distance between the corresponding conductive electrodes in the first conductive electrode array 2 and the second conductive electrode array 6 will change accordingly. According to the capacitance calculation formula:

[0107] C=ε0ε x A / d

[0108] Where: ε0 is the dielectric constant of vacuum; ε x is the relative dielectric constant; A is the area of ​​the electrode plate; d is the distance between the two plates. The greater the force acting on the sensor, the smaller the distance between the two conductive plates facing each other, so the capacitance output by the sensor is greater. Therefore, the magnitude of the force can be judged by the size of the capacitance signal output by the sensor.

[0109] ②Detect the direction of the force:

[0110] When the force slides over the capacitive sensor, the capacitive sensor is subjected to pressure, and the distance between the two conductive plates changes, and then the corresponding capacitive signal is output. Therefore, we can observe the time sequence of the individual capacitive sensors in the capacitive sensor array composed of the first conductive plate array 2 and the second conductive plate array 6 starting to output the capacitive signal, arrange the capacitive sensors with capacitive signal output in the order of the output capacitive signal time, and then correspond to their row and column coordinates in the sensor array, and then we can know the direction of the force on the fingerprint bionic texture 4 sliding over the fingerprint high-sensitivity flexible sensor.

[0111] ③Identify the periodic surface texture information of materials:

[0112] The frequency of the change of the capacitance signal of a single capacitance sensor in the capacitance sensor array composed of the first conductive electrode array 2 and the second conductive electrode array 6 depends on the frequency of contact with the fingerprint bionic texture 4. This depends on the relative speed of the scanned object and the period of contact between the protrusions on the surface of the object and the fingerprint bionic texture 4. Therefore, the periodic surface texture information of the material can be identified by the frequency of the change of the capacitance signal.

[0113] Fourier transform is a method of converting a time domain signal to a frequency domain signal. It decomposes a signal into multiple signals composed of sine waves of different frequencies, so as to more clearly display the frequency domain characteristics of the signal. Therefore, in this embodiment, the capacitance signal output by the capacitance sensor is subjected to a fast Fourier transform FFT, and the characteristic frequency of the texture is obtained in the spectrum diagram. Under the same friction speed, as the texture spacing decreases, the characteristic frequency also increases. The position of the characteristic peak is determined by the spacing of the test texture surface. Therefore, the texture spacing can be calculated based on the characteristic frequency in the spectrum diagram. The formula is as follows:

[0114] λ = v / f;

[0115] Among them, λ is the periodic spacing of the texture, v is the relative speed of contact between the pre-identified material and the fingerprint bionic texture, and f is the characteristic frequency in the spectrum diagram after FFT. The periodic spacing of the texture can be calculated, which is the periodic surface texture information of the material to be identified.

Claims

1. A fingerprint-like high-sensitivity flexible sensor capable of identifying direction, characterized by: The invention comprises a dielectric layer (1), wherein the upper surface of the dielectric layer (1) is coated with a first conductive electrode array (2), the lower surface of the dielectric layer (1) is coated with a second conductive electrode array (6), and the conductive electrode arrays in the first conductive electrode array (2) and the second conductive electrode array (6) are arranged in a pair one above the other, the two conductive electrode arrays aligned one above the other form a capacitive pressure sensor, and all the capacitive pressure sensors form a capacitive pressure sensor array; the dielectric layer (1) and the upper part of the first conductive electrode array (2) are coated with a second conductive electrode array (6). A packaging layer (3); the upper surface of the first packaging layer (3) is provided with a fingerprint bionic texture (4) protruding upward; the fingerprint bionic texture (4) has a ridge structure, and the outer surface of the fingerprint bionic texture (4) and the outside of the first packaging layer (3) are coated with a second packaging layer (5); a third packaging layer (7) is coated on the lower part of the dielectric layer (1) and the second conductive electrode array (6); each conductive electrode of the first conductive electrode array (2) and the second conductive electrode array (6) is connected to a CPU via a copper wire; In a working state, the fingerprint bionic texture (4) directly contacts the pre-identified material and generates vibrations. The fingerprint bionic texture (4) with a ridge structure simulates human tactile perception. The ridge structure can amplify the vibration signal. The capacitive pressure sensor array and the connected CPU are used to detect the magnitude of the force between the pre-identified material and the fingerprint bionic texture (4) and the direction of the force, and the periodic surface texture information of the pre-identified material is detected.

2. The fingerprint-like high-sensitivity flexible sensor capable of identifying direction according to claim 1 is characterized in that: A plurality of strip-shaped air gaps (11) are evenly distributed inside the dielectric layer (1), and the strip-shaped air gaps (11) are arranged in an area outside the area directly facing the first conductive electrode array (2) and the second conductive electrode array (6), so as to improve the insulation of the capacitive pressure sensor, thereby improving the sensor's recognition accuracy of direction.

3. The fingerprint-like high-sensitivity flexible sensor capable of identifying direction according to claim 1 is characterized in that: Each fingerprint of the fingerprint bionic texture (4) is equivalent to an amplifying lever, which transmits the amplified vibration to the first conductive electrode plate array (2) and the dielectric layer (1).

4. The fingerprint-like high-sensitivity flexible sensor capable of identifying direction according to claim 1 is characterized in that: The fingerprint bionic texture (4) is formed by 3D printing.

5. The fingerprint-like high-sensitivity flexible sensor capable of identifying direction according to claim 1 is characterized in that: The method in which the CPU detects the magnitude of the force between the pre-identified material and the fingerprint bionic texture (4), the direction from which the force comes, and detects the periodic surface texture information of the pre-identified material is as follows: ① In the CPU, each conductive electrode plate in the first conductive electrode plate array (2) and the second conductive electrode plate array (6) is numbered, and the conductive electrode plates facing each other in the first conductive electrode plate array (2) and the second conductive electrode plate array (6) have the same number, and the numbering format is (row number, column number); ② When the force slides over the fingerprint bionic texture (4) above the first conductive electrode array (2), a vibration signal is transmitted to the first conductive electrode array (2), and a capacitance signal output by each individual capacitive pressure sensor is obtained through the change in the distance between the first conductive electrode array (2) and the second conductive electrode array (6), which is used to characterize the magnitude of the force. The larger the capacitance value, the greater the force; The capacitance signal calculation formula is as follows: C=ε0ε x A / d; Where: ε0 is the dielectric constant of vacuum; ε x is the relative dielectric constant; A is the electrode plate area; d is the distance between the two plates; ③The direction of the force is obtained: Arrange the time when each capacitive pressure sensor in the capacitive pressure sensor array starts to output a capacitive signal in order from first to last, and then correspond the row and column coordinates of each capacitive pressure sensor in the capacitive pressure sensor array to obtain the direction of the force acting on the fingerprint bionic texture (4); ④Identify the periodic surface texture information of materials: The frequency of the capacitance signal change of each capacitive pressure sensor in the capacitive pressure sensor array depends on the frequency of contact between the pre-identified material and the fingerprint bionic texture (4), and the contact frequency depends on the relative speed between the pre-identified material and the fingerprint bionic texture (4) and the period of contact between the surface protrusions of the pre-identified material and the fingerprint bionic texture (4). Therefore, the periodic surface texture information of the material can be identified by the frequency of the capacitance signal change; By performing fast Fourier transform (FFT) on the capacitance signal output by the capacitive pressure sensor, the characteristic frequency of the texture is obtained in the spectrum diagram; At the same friction speed, as the texture spacing decreases, the characteristic frequency also increases. The position of the characteristic peak is determined by the spacing of the test texture surface. Therefore, the texture spacing can be calculated based on the characteristic frequency in the spectrum. The specific formula is: λ = v / f; Among them, λ is the periodic spacing of the texture, v is the relative speed of contact between the pre-identified material and the fingerprint bionic texture, and f is the characteristic frequency in the spectrum after FFT; The periodic spacing of the texture obtained is the periodic surface texture information of the material to be identified.

6. A method for preparing a fingerprint-like high-sensitivity flexible sensor capable of identifying a direction, wherein the method comprises: The process includes the following steps, which are performed in sequence: Step 1: prepare dielectric materials, composite conductive materials and packaging materials for later use, and measure the printing materials of fingerprint bionic texture (4); Step 2: using a strip-shaped air gap forming mold and a dielectric material to cast a dielectric layer (1) having a strip-shaped air gap (11) in the middle; Step 3: using an array forming mold and a composite conductive material to coat a first conductive electrode array (2) on one side of the dielectric layer (1), wherein the arrangement position of the first conductive electrode array (2) is staggered with the strip-shaped air gap (11); Step 4: Connect a copper wire to the surface of each conductive electrode plate of the first conductive electrode plate array (2) to serve as an electrode; Step 5: Encapsulating the first encapsulation layer (3); The upper surface of the dielectric layer (1) and the first conductive electrode array (2) are packaged with the first packaging layer (3) using a first packaging layer molding mold and packaging materials, and the proximal ends of the connection ends of the copper wires are packaged on both sides of the dielectric layer (1), and demoulding is performed after curing; Step 6: Printing fingerprint bionic texture (4); A 3D printer is used to print the fingerprint bionic texture (4) on a metal sheet using printing materials of the fingerprint bionic texture (4), and the metal sheet is then placed upside down on the upper surface of the first packaging layer (3), and a blade is used to separate the metal sheet and the fingerprint bionic texture (4); Step 7: Encapsulating the second encapsulation layer (5); Using the second encapsulation layer molding mold and the encapsulation material, the root of the fingerprint bionic texture (4) and the upper surface of the first encapsulation layer (3) are encapsulated and cured, and then demoulded; Step 8, flip the semi-finished sensor product after demoulding in step 7 by 180 degrees, and apply the second conductive electrode plate array (6) on the other side of the dielectric layer (1) using the same technical means as in step 3, and align the first conductive electrode plate array (2) and the second conductive electrode plate array (6) one by one; Step nine: using the same technical means as steps four and five in sequence, the copper wires of the second conductive electrode array (6) are connected and the dielectric layer (1) and the copper wires are packaged to form a third packaging layer (7). After curing and demoulding, the preparation of the fingerprint-like high-sensitivity flexible sensor is completed.

7. The method for preparing a direction-recognizable fingerprint-like high-sensitivity flexible sensor according to claim 6 is characterized by: The strip-shaped air gap forming mold in step 2 comprises a containing box and a row of long strips that are evenly arranged and penetrate the containing box; gaps are left between the long strips and the upper top surface and the lower bottom plate of the containing box; a non-stick coating is sprayed on the inside of the containing box and the surface of the long strips of the strip-shaped air gap forming mold; The specific method of casting in step 2 is as follows: casting the dielectric material prepared in step 1 into the strip-shaped air gap forming mold, and when the dielectric material fills the containing box, using a blade to scrape the top surface of the containing box, and then placing the mold under an ultraviolet light source for irradiation and curing, the long strip is pulled out of the containing box, and then demoulding from the containing box to take out the successfully cast dielectric layer (1).

8. The method for preparing a direction-recognizable fingerprint-like high-sensitivity flexible sensor according to claim 6 is characterized by: The array forming mold in step 3 is a rectangular cover-shaped structure, and a plurality of hollow structures arranged in an array are arranged on the surface of the upper cover, and the arrangement positions of the hollow structures are staggered with the strip-shaped air gaps (11) of the dielectric layer (1); The specific method for coating the first conductive electrode array (2) in step 3 is as follows: the array forming mold is clamped on the dielectric layer (1) prepared in step 2 and compacted, the hollow structure and the strip air gap (11) are arranged staggered, the composite conductive material is filled into the hollow structure, the composite conductive material is scraped with a blade, and naturally cured for 24 hours, the array forming mold is removed, and a conductive electrode is formed at each hollow structure, and the first conductive electrode array (2) is coated on the dielectric layer (1).

9. The method for preparing a direction-recognizable fingerprint-like high-sensitivity flexible sensor according to claim 6, characterized in that: The specific method for encapsulating the first encapsulation layer (3) in step five is as follows: the copper wires in step four are led out from the small holes opened on both sides of the encapsulation layer molding mold, the encapsulation layer molding mold is sleeved on the outer periphery of the dielectric layer (1), and the encapsulation material is poured onto the first conductive electrode array (2) until the encapsulation layer molding mold is filled, and the encapsulation layer molding mold is naturally cured at room temperature for 12 hours, and the encapsulation layer molding mold is removed.

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