阅读说明：本技术 一种基于3d打印模板法的三维压力传感器及其制备方法 (Three-dimensional pressure sensor based on 3D printing template method and preparation method thereof ) 是由 陈小明 王春江 邵金友 田洪淼 宋启航 牛万灏 王硕 于 2020-12-31 设计创作，主要内容包括：一种基于3D打印模板法的三维压力传感器及其制备方法,压力传感器包括可定制形状的柔性桁架,桁架由可溶性光敏树脂光固化增材制造的原型作模板,得到空心结构的石墨烯/铜复合支杆；复合支杆较小面积的外表面对称设置两对柔性基底/多层摩擦电复合材料,两对正交方向传感信号互相独立,用于输出X和Y方向压力分量的大小；面积较大外表面是复合压阻结构A,以压阻方式传感信号,用于监测结构可随形变化的Z向压力信号；基于3D打印模板法的各向异性压力传感器的制备方法用于制备上述压力传感器；本发明所提供的传感器制造工艺简单,可以自由定制并快速制造,成本低、效率高、工作灵敏,并且能在包覆感知的基础上实现三维压力信号的传感与识别。(A three-dimensional pressure sensor based on a 3D printing template method and a preparation method thereof are provided, wherein the pressure sensor comprises a flexible truss with a customizable shape, and the truss is made of a prototype manufactured by photocuring and additive manufacturing of soluble photosensitive resin as a template to obtain a graphene/copper composite support rod with a hollow structure; two pairs of flexible substrates/multilayer triboelectric composite materials are symmetrically arranged on the outer surface of the composite support rod with a smaller area, and two pairs of orthogonal direction sensing signals are mutually independent and are used for outputting the magnitude of pressure components in the X direction and the Y direction; the outer surface with larger area is a composite piezoresistive structure A which senses signals in a piezoresistive mode and is used for monitoring Z-direction pressure signals of the structure which can change along with the shape; the preparation method of the anisotropic pressure sensor based on the 3D printing template method is used for preparing the pressure sensor; the sensor provided by the invention has the advantages of simple manufacturing process, free customization, quick manufacturing, low cost, high efficiency and sensitive work, and can realize the sensing and identification of the three-dimensional pressure signal on the basis of cladding sensing.)

1. A three-dimensional pressure sensor based on a 3D printing template method is characterized by comprising a soluble truss (8), wherein the soluble truss (8) is made of a prototype manufactured by photocuring and additive manufacturing of soluble photosensitive resin, the surface of the prototype is coated with a metal film and a graphene elastic layer is grown on the surface of the prototype, and a graphene/copper hollow composite support rod (19) with a hollow structure is obtained after dissolution; two pairs, namely four outer surfaces with smaller area areas, on the periphery of the hollow composite support rod (19) are provided with an A flexible substrate (15)/a plurality of layers of friction electric sensing layers, each surface is at least provided with two electrodes for independently transmitting signals by taking a friction electric signal as a sensing principle, and two pairs of orthogonal direction sensing signals are mutually independent and are used for outputting the pressure components in the X direction and the Y direction; the upper outer surface and the lower outer surface of the hollow composite support rod (19) with larger area are a composite piezoresistive structure A which is repressed by a flexible substrate B (17)/an electrode (16)/an adhesion layer/the hollow composite support rod (19), and signals are sensed in a piezoresistive mode and are used for monitoring Z-direction pressure signals of the structure which can change along with the shape.

2. The three-dimensional pressure sensor based on the 3D printing template method is characterized in that the soluble truss (8) is a five-mode material structure with shape coating and fitting characteristics or other three-dimensional designable structures with zero Poisson's ratio.

3. The three-dimensional pressure sensor based on the 3D printing template method as claimed in claim 1, wherein the soluble photosensitive resin is an acrylic-based soluble ultraviolet light curing photosensitive resin.

4. The three-dimensional pressure sensor based on the 3D printing template method is characterized in that the wrapped metal film can be a copper film or a nickel film.

5. The three-dimensional pressure sensor based on the 3D printing template method is characterized in that the flexible substrate is made of polydimethylsiloxane PDMS or silicon rubber.

6. The three-dimensional pressure sensor based on the 3D printing template method is characterized in that the number of the electrodes arranged on each surface can be determined according to the mode of a channel and an acquisition circuit of a signal acquisition device.

7. The method for preparing the three-dimensional pressure sensor based on the 3D printing template method, which is based on the claim 1, comprises the following steps:

the first step, the preparation of the soluble photosensitive resin (4) based on the 3D printing template method: mixing a photoinitiator bisacylphosphorus oxide, a reaction monomer N, N-dimethylacrylamide, a comonomer methacrylic acid, a cracking agent methacrylic anhydride and a filler polyvinylpyrrolidone in a certain ratio, and uniformly dispersing to obtain a soluble photosensitive resin 9;

the soluble photosensitive resin 9 comprises the following components in parts by weight: 1-5 parts of photoinitiator bisacylphosphorus oxide, 20-30 parts of reaction monomer N, N dimethylacrylamide, 40-50 parts of comonomer methacrylic acid, 2-5 parts of cracking agent methacrylic anhydride and 5-10 parts of filler polyvinylpyrrolidone;

secondly, preparing a soluble truss (8): adjusting the ultra-high precision light curing molding equipment (4) to a working state, enabling soluble photosensitive resin (9) to flow into the resin tank (3) along the cup wall, completely immersing the light curing worktable top (7) into the liquid level of the photosensitive resin (9), generating the light curing worktable top by the computer (5), transmitting the light spot image of a corresponding lamella into the ultraviolet light generator (1) through the data bus (6), outputting the light spot image of the corresponding lamella, controlling the lifting movement of the light curing worktable top (7), controlling the resin between the light curing worktable top (7) and the leveling film (2) by layered curing through the ultraviolet light generator (1), and completing the preparation process of the soluble truss (8) according to the instruction of the computer (5);

step three, preparing the copper/graphene hollow support rod: taking the soluble truss (8) off the photocuring workbench (7), cleaning and drying the soluble truss, then putting the soluble truss into a copper film evaporation instrument, and obtaining a copper/resin composite material with a copper film coated on the surface after 1 minute; then based on an electrodeposition device, after electrifying and depositing, freezing and drying to obtain a copper film/resin composite truss (8) wrapped with a layer of reduced graphene oxide film, and cleaning and drying; preparing an alkaline aqueous solution, putting the truss (8) into the alkaline aqueous solution for etching reaction, dissolving resin to obtain a hollow support rod structure, and cleaning and drying to obtain a reduced graphene oxide/copper hollow composite support rod (19);

fourthly, preparing a piezoresistive sensing layer: a layer of metal (16) is evaporated on a flexible substrate (17) of the component B to serve as an electrode, leads are led out from the electrode and the upper surface of a truss (8) respectively, then a layer of Polydimethylsiloxane (PDMS) is arranged on the three-quarter area of the surface of the electrode to serve as an adhesion layer of the flexible substrate (17) and the prepared hollow composite support rod (19), the hollow truss is immersed in the Polydimethylsiloxane (PDMS), curing is carried out in an oven at the temperature of about 80 ℃, and the composite piezoresistive structure A of the flexible substrate (17)/the electrode (16)/the adhesion layer/the hollow composite support rod (19) is obtained after cooling to the room temperature;

fifthly, preparing a triboelectric sensing layer: arranging a plurality of layers of graphene (14) on a flexible substrate (15) A as an electrode through chemical vapor deposition or wet transfer of the graphene, and covering a triboelectric material PET (13) on the graphene (14) substrate; the triboelectric material PET (13) is used as a substrate, the triboelectric material PET (13) is provided with a plurality of layers of graphene to obtain the other electrode (12) of the triboelectric sensing layer, leads are respectively led out from the two electrodes, and then a layer of Polydimethylsiloxane (PDMS) is uniformly coated on the electrode (12) in a spin mode to obtain the triboelectric sensing layer (11).

Sixthly, preparing the anisotropic pressure sensor: and respectively adhering two pairs of surfaces with smaller areas in the composite piezoresistive structure A with a triboelectric sensing layer (11) together to form a piezoresistive/triboelectric composite pressure sensing structure with a sensing surface B and a sensing surface C, and cooling after solidification to obtain the anisotropic pressure sensor.

8. The method for preparing the three-dimensional pressure sensor based on the 3D printing template method according to claim 7, wherein the metal layer sputtered in the third step is copper or nickel.

9. The method for preparing a three-dimensional pressure sensor based on a 3D printing template method according to claim 7, wherein the alkaline aqueous solution for chemically corroding the hollow rod in the third step is sodium hydroxide or potassium hydroxide aqueous solution, and the concentration of the sodium hydroxide or potassium hydroxide aqueous solution is 0.1-2 mol/L.

10. The method for preparing a three-dimensional pressure sensor based on the 3D printing template method according to claim 7, wherein the specific parameters of the electric deposition in the third step are voltage of 10-36V, current density of 0.5-5A/dm2, and electric time of 0.1-2 hours;

in the third step, the temperature of freeze drying is-120 to-70 ℃, and the freeze drying time is 2 to 4 hours;

in the third step, the multilayer reduced graphene oxide obtained by electrodeposition is washed and dried, deionized water is adopted for washing in the washing process, and then the multilayer reduced graphene oxide is dried at room temperature;

in the fourth step, the metal 16 is nickel Ni, copper Cu or chromium Cr.

Technical Field

The invention relates to the technical field of additive manufacturing processes and sensors, in particular to a three-dimensional pressure sensor based on a 3D printing template method and a preparation method thereof.

Background

With the rapid development of the flexible electronic field and the popularization of the internet of things technology, wearable electronic devices capable of monitoring physical signals of human physiological indexes (such as heartbeat, pulse, movement period, blood pressure and the like) and labor production states (such as main shaft jumping, robot movement state perception and the like) are gradually applied to social life, the obtained information is used for quantitative acquisition of human health conditions and detection of service type mechanical states, a processing mode of relevant physical signals is quantified, a vital role is played for establishing a bidirectional information channel of a human/machine control interface, and the rapid manufacturing of a relevant functional flexible sensing device becomes a research hotspot in recent years.

The pressure sensor which is widely researched and applied in the traditional sense is still made of inorganic materials (such as silicon, copper, ZnO and the like), so that the pressure sensor has the limitations of single pressure sensing direction, single sensing dimension and low functional integration, and once tensile deformation or external signal interference is generated, the pressure sensor cannot play a good shape reshaping capacity, and also fails due to structural fatigue of sensor hardware, so that data cannot be accurately acquired.

In recent years, the wearable flexible pressure sensor researched and developed overcomes the defects of a rigid device to a certain extent, and has better shape fitting capacity and deformation range. The flexible pressure sensors in the prior art are mainly classified into the following types:

1. strain gauge piezoresistive sensing: the method comprises the steps of preparing films with various structures by using inorganic materials, fixing the films on a substrate of a sensing object body through rigid coating, converting the deformation of the substrate into the change of film resistance under the signal transmission of at least two electrodes, converting the change into the fluctuation of current in a circuit to obtain a strain sensor with the function of sensing the shape change of the substrate, and reversibly synthesizing the pressure applied to the body through the superposition of a plurality of sensing units.

2. Multidimensional piezoresistive sensing: the method is characterized in that PDMS is used as a flexible substrate, a multi-scale and porous one-dimensional lead, a two-dimensional film and a three-dimensional sponge block are prepared by designing the structure and the synthesis mode of graphene and Carbon Nano Tubes (CNT), a sensing unit is further packaged in an array and a lamination mode by micro-structure design and micro-contact design, piezoresistive sensors with different sensitivities and sensing ranges are generated, and load sizes of different forms are detected according to different deformation.

3. Coupled sensing of multiple sensing modes: modules such as piezoresistance, piezoelectricity, triboelectricity and capacitance sensing are coupled into a sensor by utilizing different structural designs to form a closed-loop signal monitoring system, and the system has research space in the fields of new energy pressure sensing devices, electronic skins, micro-drivers, micro-actuators and the like.

The monitoring object of the flexible pressure sensor is often discrete pressure data, the signal feedback of pressure direction and vector characteristics is lacked, vector pressure signals presented as three-dimensional physical quantity in practice are not matched, a physical body of a signal source presents the sensing characteristic of forced deformation, and a contact surface is easy to damage under long-term work; meanwhile, the manufacturing process is often limited by the shape and structure of the designed sensor, most of the manufacturing processes of the existing pressure sensing devices are based on single-layer circuit structures and multi-layer sandwich structures and adopt methods such as photoetching, imprinting, etching, laminating and the like, so that the sensing of multi-dimensional pressure signals (size and direction) is realized in a mode of overlapping a plurality of single-dimensional pressure sensors, the process is complex, the efficiency is low, the manufacturing cost is increased, the application range and the application field of the pressure sensors are influenced, and the measurement range and the interaction result are limited.

Therefore, how to enable the flexible pressure sensor to have the capability of sensing anisotropic pressure signals, overcome the structure non-customizability of a microstructure manufacturing link, increase the coupling types of multi-mode sensing, and realize the pressure sensor with good shape covering capability and high sensitivity becomes a problem worthy of research.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a three-dimensional pressure sensor based on a 3D printing template method and a preparation method thereof, the sensor with three-dimensional anisotropic pressure sensing is realized by a customizable structure through the 3D printing template method, and on the basis of overcoming the defects of the conventional pressure sensor, the invention provides a method for preparing the sensor so as to realize the accuracy and reliability of vector pressure signal sensing.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a three-dimensional pressure sensor based on a 3D printing template method comprises a soluble truss 8, wherein the truss 8 takes a prototype manufactured by photocuring and additive manufacturing of soluble photosensitive resin as a template, the surface of the template is coated with a metal film and a graphene elastic layer is grown on the surface of the template, and a graphene/copper hollow composite support rod 19 with a hollow structure is obtained after dissolution; the A flexible substrate 15/multilayer friction electric sensing layers are arranged on two pairs of four outer surfaces with smaller areas on the periphery of the hollow composite support rod 19, at least two electrodes for independently transmitting signals are arranged on each surface by taking friction electric signals as a sensing principle, and two pairs of orthogonal direction sensing signals are independent to each other and used for outputting the pressure components in the X direction and the Y direction; the upper and lower outer surfaces of the hollow composite strut 19 with larger area are a composite piezoresistive structure A which is formed by repressing a flexible substrate 17, an electrode 16, an adhesive layer and the hollow composite strut 19 in a mode of piezoresistance, and signals are sensed and used for monitoring Z-direction pressure signals of the structure which can change along with the shape.

The truss 8 is a five-mode material structure with shape coating and fitting characteristics or other three-dimensional designable structures with zero Poisson's ratio.

The soluble photosensitive resin is acrylic-based soluble ultraviolet light curing photosensitive resin.

The wrapped metal film can adopt a copper film or a nickel film.

The flexible substrate is made of polydimethylsiloxane PDMS or silicon rubber.

The number of the electrodes arranged on each surface can be determined according to the mode of a signal acquisition device channel and an acquisition circuit.

The preparation method of the three-dimensional pressure sensor based on the 3D printing template method comprises the following steps:

step one, preparing a soluble photosensitive resin 4 based on a 3D printing template method: mixing a photoinitiator bisacylphosphorus oxide, a reaction monomer N, N-dimethylacrylamide, a comonomer methacrylic acid, a cracking agent methacrylic anhydride and a filler polyvinylpyrrolidone in a certain ratio, and uniformly dispersing to obtain a soluble photosensitive resin 9;

the soluble photosensitive resin 9 comprises the following components in parts by weight: 1-5 parts of photoinitiator bisacylphosphorus oxide, 20-30 parts of reaction monomer N, N dimethylacrylamide, 40-50 parts of comonomer methacrylic acid, 2-5 parts of cracking agent methacrylic anhydride and 5-10 parts of filler polyvinylpyrrolidone;

second step, preparation of soluble truss 8: adjusting the ultrahigh-precision photocuring forming equipment 4 to be in a working state, enabling soluble photosensitive resin 9 to flow into the resin tank 3 along the cup wall, completely immersing the photocuring worktable 7 into the liquid surface of the soluble photosensitive resin 9, generating the light spot image by the computer 5, transmitting the light spot image to the ultraviolet generator 1 by the data bus 6 to output a corresponding lamella, controlling the lifting movement of the photocuring worktable 7, controlling the resin between the photocuring worktable 7 and the leveling film 2 by using the ultraviolet generator 1 for layered curing, and completing the preparation process of the soluble truss 8 according to the instruction of the computer 5;

step three, preparing the copper/graphene hollow support rod: taking the soluble truss 8 off the photocuring workbench 7, cleaning and drying, then putting the soluble truss into a copper film evaporation instrument, and obtaining a copper/resin composite material with the surface coated with a layer of copper film after 1 minute; then based on an electrodeposition device, carrying out power-on deposition, freezing and drying to obtain a copper film/resin composite truss 8 wrapped with a layer of reduced graphene oxide film, and cleaning and drying; preparing an alkaline aqueous solution, placing the truss 8 into the alkaline aqueous solution for etching reaction, dissolving resin to obtain a hollow support rod structure, and cleaning and drying to obtain a reduced graphene oxide/copper hollow composite support rod 19;

fourthly, preparing a piezoresistive sensing layer: a layer of metal 16 is evaporated on the flexible substrate 17B to serve as an electrode, leads are respectively led out from the electrode and the upper surface of the truss 8, then a layer of polydimethylsiloxane PDMS is arranged on the three-quarter area of the surface of the electrode to serve as an adhesion layer of the flexible substrate 17B and the prepared hollow composite support rod 19, the hollow truss is immersed in the Polydimethylsiloxane (PDMS), the PDMS is solidified in an oven at the temperature of about 80 ℃, and the composite piezoresistive structure A of the flexible substrate 17/the electrode 16/the adhesion layer/the hollow composite support rod 19 is obtained after the PDMS is cooled to the room temperature;

fifthly, preparing a triboelectric sensing layer: arranging a plurality of layers of graphene 14 on the A flexible substrate 15 as electrodes through chemical vapor deposition or wet transfer of graphene, and covering a triboelectric material PET13 on the graphene 14 substrate; the triboelectric material PET13 is used as a substrate, multiple layers of graphene are arranged on the triboelectric material PET13 to obtain the other electrode 12 of the triboelectric sensing layer, leads are respectively led out from the two electrodes, and then a layer of Polydimethylsiloxane (PDMS) is uniformly spin-coated on the electrode 12 to obtain the triboelectric sensing layer 11.

Sixthly, preparing the anisotropic pressure sensor: and respectively adhering two pairs of surfaces with smaller areas in the composite piezoresistive structure A with the triboelectric sensing layer 11 together to form a piezoresistive/triboelectric composite pressure sensing structure with a sensing surface B and a sensing surface C, and cooling after solidification to obtain the anisotropic pressure sensor.

The metal layer sputtered in the third step is made of copper or nickel.

And in the third step, the alkaline aqueous solution for chemically corroding the hollow rod piece is sodium hydroxide or potassium hydroxide aqueous solution, and the concentration of the alkaline aqueous solution is 0.1-2 mol/L.

The specific parameters of the electrification deposition in the third step are that the voltage is 10-36V, the current density is 0.5-5A/dm2, and the electrification time is 0.1-2 hours.

In the third step, the temperature of freeze drying is-120 to-70 ℃, and the freeze drying time is 2 to 4 hours.

In the fourth step, the metal 16 is nickel Ni, copper Cu or chromium Cr.

And in the third step, the multilayer reduced graphene oxide obtained by electrodeposition is washed and dried, and is washed by deionized water in the washing process and then dried at room temperature.

The anisotropic pressure sensor based on the soluble resin and the preparation method thereof can enable the anisotropic pressure sensor to have the characteristics of customizability, flexibility, good stretching and compression of a sensing surface structure, and through the structural design of five-mode materials, when the structure is under the action of the pressure of a main sensing surface, the pressure sensor can sense the magnitude of a received piezoresistive signal and can also sense the magnitudes of component forces in three orthogonal directions through sensing surfaces which do not interfere with signal output mutually, so that the direction of a resultant force is synthesized, a mapping model of the compression direction and the compression magnitude is established, and the sensing of any three-dimensional vector pressure signal is realized.

Meanwhile, the invention also provides a preparation process of the sensor based on the 3D printing template method, which increases the designable thresholds of the shape and the function and reduces the limit of the process to the structure. The invention is particularly suitable for the situation that the direction of force needs to be detected in wearable equipment in a complex environment, can completely coat the contact surface of the sensed pressure body, reduces the risk that the contact surface is damaged due to the complex shape of a sensed object, has high precision and reliability, and has wide application prospect in the fields of flexible sensing and multi-dimensional pressure sensing.

Drawings

Fig. 1 is a schematic diagram of a 3D printing template method-based photocuring additive manufacturing process according to an embodiment of the present invention.

Fig. 2 is a schematic view of a photo-curing additive manufacturing exposure surface of a photosensitive resin according to an embodiment of the invention.

Fig. 3 is a schematic diagram of a soluble truss obtained by photocuring based on a 3D printing template method in an embodiment of the present invention.

Fig. 4 is a schematic view of an apparatus for electrodeposition reduction of graphene oxide in an embodiment of the present invention.

Fig. 5 is a schematic diagram of the preparation and dissolution of the coated graphene/copper to obtain the hollow truss according to the embodiment of the invention.

FIG. 6 is a schematic diagram of a sandwich triboelectric structure and resulting triboelectric sensor layer made according to an embodiment of the present invention.

FIG. 7 is a schematic view of an embodiment of the present invention adhering a triboelectric sensing layer to a hollow truss.

FIG. 8 is a schematic illustration of bonding a flexible truss to piezoresistive and triboelectric sensing surfaces in an embodiment of the invention.

Fig. 9 is a cross-sectional view of a sensor of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the drawings and examples.

Referring to fig. 9, a three-dimensional pressure sensor based on a 3D printing template method includes a soluble truss 8, the soluble truss 8 is made of a prototype manufactured by photocuring and additive manufacturing of soluble photosensitive resin, a metal film is wrapped on the surface of the template, a graphene elastic layer is grown on the surface of the template, and a graphene/copper hollow composite support rod 19 with a hollow structure is obtained after melting; the A flexible substrate 15/multilayer friction electric sensing layers are arranged on two pairs of four outer surfaces with smaller areas on the periphery of the hollow composite support rod 19, at least two electrodes for independently transmitting signals are arranged on each surface by taking friction electric signals as a sensing principle, and two pairs of orthogonal direction sensing signals are independent to each other and used for outputting the pressure components in the X direction and the Y direction; the upper and lower outer surfaces of the hollow composite strut 19 with larger area are a composite piezoresistive structure A which is formed by repressing a flexible substrate 17, an electrode 16, an adhesive layer and the hollow composite strut 19 in a mode of piezoresistance, and signals are sensed and used for monitoring Z-direction pressure signals of the structure which can change along with the shape. Because the sensor structurally has mechanical anisotropy, the component force signals in three directions can be synthesized and the vector characteristic of the anisotropic pressure signal can be sensed.

The three-dimensional pressure sensor based on the 3D printing template method and the preparation method thereof comprise the following steps:

the first step, the material selection and preparation of the soluble photosensitive resin 4 based on the 3D printing template method: the invention provides a soluble photosensitive resin, which is formed rapidly by the following components through free radical polymerization under ultraviolet curing. Uniformly mixing a photoinitiator bisacylphosphorus oxide, a reaction monomer N, N-dimethylacrylamide, a comonomer methacrylic acid, a cracking agent methacrylic anhydride and a filler polyvinylpyrrolidone according to a certain mass fraction ratio, and uniformly dispersing under magnetic stirring to obtain the soluble photosensitive resin 9.

The material preparation of the soluble photosensitive resin in the first step comprises the following steps: 25 parts of reaction monomer N, N-dimethylacrylamide, 45 parts of comonomer methacrylic acid and 5 parts of cracking agent methacrylic anhydride are selected to be mixed under the heating of an oil bath at 50 ℃, and then 9 parts of polyvinylpyrrolidone and 3 parts of photoinitiator bisacylphosphorus oxide are gradually and respectively added to be uniformly dispersed.

And step two, preparing a soluble scaffold: as shown in fig. 1, preparation of the soluble truss 8: adjusting the ultrahigh-precision photocuring forming equipment 4 to be in a working state, enabling the soluble photosensitive resin 9 to flow into the resin tank 3 along the cup wall, completely immersing the photocuring worktable 7 into the liquid surface of the soluble photosensitive resin 9, generating the light spot image by the computer 5, transmitting the light spot image to the ultraviolet light generator 1 by the data bus 6 to output a corresponding lamella, controlling the lifting movement of the photocuring worktable 7, controlling the resin between the photocuring worktable 7 and the leveling film 2 by using the ultraviolet light generator 1 for layered curing, and completing the preparation process of the soluble truss 8 according to the instruction of the computer 5.

In the second step, in the process of pouring the soluble photosensitive resin into the resin tank 3, the removal of air bubbles in the resin needs to be considered, and the steps of standing, variable speed centrifugation, suction filtration and the like are included;

optionally, according to the type characteristics of the operating equipment, bubble-free photosensitive resin is poured in, the upper liquid level of the photosensitive resin 9 is ensured to be flush with the leveling film 2, the forming focal length of the light curing equipment 4 is adjusted, and the optimal exposure distance is met.

Optionally, the adhering operation of the leveling film 2 and the resin tank 3 can also generate bubbles, the leveling film is firstly immersed into the resin from one end, and the angle between the leveling film and the liquid level of the resin is slowly reduced, so that no bubbles appear in the resin; meanwhile, the workbench 2 can be lifted in advance, and bubbles around the workbench cannot flow into the resin gap in the lifting process.

In the photocuring additive manufacturing process, namely in the second step, the printing layer thickness is designed according to the truss structure, and according to the principle that the more complicated the structure layer thickness is divided into smaller layers, the printing layer thickness of the truss structure part is basically controlled to be 0.05-0.1 mm, the exposure time is set to be 2s, the illumination intensity is set to be 25Lux, meanwhile, a printing support layer needs to be added, the exposure time of the support layer is controlled to be 4s, and the exposure intensity is set to be 30Lux, so that the smooth separation of the soluble truss 8 from the workbench 7 and the forming precision of the truss structure are ensured.

Step three, preparing the copper/graphene hollow support rod: taking the soluble truss 8 off the light curing workbench 7, cleaning and drying; then putting the component into a copper film evaporation instrument, and obtaining a copper film 21 with a surface coated with a layer of 10 microns after 1 minute to obtain the copper/resin composite truss shown in figure 5; then preparing an electrodeposition device as shown in fig. 4, performing electrodeposition, freeze-drying to obtain a graphene oxide layer 20, and then cleaning and drying the component; preparing an alkaline aqueous solution, putting the soluble truss 8 into the solution for chemical reaction, dissolving resin to obtain a hollow support rod structure, and cleaning and drying to obtain a reduced graphene oxide/copper hollow support rod 19;

in the third step, the graphene oxide layer 20 is obtained by freeze drying after electrodeposition, and the electrodeposition comprises the following steps: mixing a graphene oxide solution of 3mg/mL with a hydrogen chloride aqueous solution of 0.1mL/L, taking a platinum plate as a counter electrode, placing a copper/resin composite truss at the other end of the electrode, depositing for 5 minutes at a voltage of 30V to obtain a composite truss coated with a layer of graphene, cleaning the truss, and freeze-drying to obtain the copper film/resin composite truss coated with a layer of reduced graphene oxide film.

The freeze drying process during the synthesis of the reduced graphene oxide comprises the following steps:

the method comprises the steps of firstly, gently cleaning reduced graphene oxide hydrogel obtained through electrodeposition with a large amount of deionized water, then placing the cleaned reduced graphene oxide hydrogel in an oven at 90 ℃ for 6 hours with 0.1mol/L ascorbic acid, placing the synthesized sample in an environment at minus 80 ℃ for freeze drying for 24 hours, and finally drying the sample in a vacuum oven to obtain a freeze-dried reduced graphene oxide coating.

And in the third step, 1mol/L sodium hydroxide or potassium hydroxide aqueous solution is adopted as an alkaline aqueous solution corrosive agent for chemically corroding the hollow rod piece, and the solution is slowly stirred by a glass rod in the corrosion process until the hollow support rod is formed, and then the truss is cleaned and dried.

Alternatively, the washing and drying method used in the second and third steps includes: the test piece was immersed in an ethanol solution and washed for 20 seconds, and placed in deionized water for ultrasonic treatment for 1 minute, followed by drying at room temperature.

Fourthly, preparing a piezoresistive sensing layer: a layer of metal 16 is evaporated on the flexible substrate 17B to serve as an electrode, leads are respectively led out from the electrode and the upper surface of the truss 8, then a layer of Polydimethylsiloxane (PDMS) is arranged on the three-quarter area of the surface of the electrode to serve as an adhesive layer of the flexible substrate 17 and the prepared hollow truss 8, the hollow truss 8 is immersed in the PDMS, the PDMS is solidified in an oven at the temperature of about 80 ℃, and the composite piezoresistive structure A of the flexible substrate 17/the electrode 16/the adhesive layer/the truss 8 is obtained after the PDMS is cooled to the room temperature;

fifthly, preparing a triboelectric sensing layer: taking the triboelectric sensing layer on one side as an example, a graphene electrode grown on a copper film is obtained by a chemical vapor deposition process of graphene, heating to 1000 ℃ and holding for 2 hours under a pressure of 80 mTorr and a hydrogen protective atmosphere of 8mL/min, then heating to the same temperature and holding for 1 hour under a pressure of 1.6 Torr and a methane atmosphere of 20mL/min, and finally introducing 8mL/min of hydrogen into a CVD tube until cooling to room temperature (25 ℃). Then, by a wet transfer process, arranging a plurality of layers of graphene 14 on a flexible substrate 15 as electrodes, covering a triboelectric material PET13 on the graphene 14 substrate, then, by using a PET layer as a substrate by the same process, arranging a plurality of layers of graphene on a triboelectric material PET13 to obtain another electrode 12 of the triboelectric sensing layer, respectively leading out leads on the two electrodes, then, uniformly spin-coating a layer of Polydimethylsiloxane (PDMS) on the electrode 12, and obtaining the triboelectric sensing layer 11 with higher charge density after surface treatment. And obtaining two symmetrical triboelectric sensing layers B and C by adopting the same process.

Alternatively, the top surface treatment of Polydimethylsiloxane (PDMS) was carried out by a process of oxygen plasma bombardment for 120 seconds followed by fluorine functionalization for 30 seconds at 100W power and SF6 surface fluorination, resulting in a triboelectric sensor layer 11 with a higher surface charge density.

The preparation method of the graphene electrodes 12 and 14 used in the fifth step includes the following steps:

alternatively, the deposition rate of the graphene electrode layer is one layer every 15 minutes, and 4 layers of graphene are selected as the material for the electrodes 12 and 14 in the examples provided by the present invention.

Optionally, the process for preparing the electrodes 12 and 14 in the triboelectric structure by graphene wet transfer adopted in the fifth step includes the following steps: taking the electrode 12 as an example, firstly, uniformly spin-coating a layer of PMMA on graphene with a copper film as a substrate, placing PMMA/graphene/copper foil with a corresponding area size in etching liquid according to the preparation area of the electrode, transferring the etched PMMA/graphene into deionized water for cleaning by using a PET substrate after etching is completed, then placing the cleaned PMMA in acetone to remove PMMA, cleaning and drying after removing is completed to obtain the corresponding graphene electrode 12 and the PET layer 13 as the substrate.

Optionally, the etching solution is 20g/L ammonium persulfate solution or 8mol/L dilute nitric acid solution.

Sixthly, preparing the anisotropic pressure sensor: two pairs of surfaces with smaller area in the composite piezoresistive structure a are respectively adhered to the triboelectric sensing layer 11 by using an acrylic-based adhesive, as shown in fig. 7, a hollow strut 22 without deposited graphene is arranged on the triboelectric sensing layer 11 and is in contact with the upper surface of Polydimethylsiloxane (PDMS) after surface treatment to form a piezoresistive/triboelectric composite pressure sensing structure with sensing surfaces B and C, the piezoresistive/triboelectric composite pressure sensing structure is placed in an oven to be cured for 20 minutes at about 80 ℃, and after cooling, the pressure sensor with anisotropy is obtained, as shown in fig. 8.