Resistance-type porous flexible pressure sensor and manufacturing method thereof

Abstract

The invention relates to a resistance-type porous flexible pressure sensor and a manufacturing method thereof, the whole sensor is of a sandwich structure, the bottom layer is a structural substrate, the surface layer is a contact layer, the middle layer is composed of a plurality of discrete sensing units, and each discrete sensing unit is composed of a porous structure and conductive fibers. The conductive fiber is embedded in the porous structure and is provided with a plurality of section crack structures, separated cutting grooves are formed between the adjacent discrete sensing units, and separation grooves corresponding to the cutting grooves are formed in the contact layer. The manufacturing method comprises the following steps: preparing the supporting structure by using a molding spin-coating process, performing coupling integration of the conductive fibers by using a 3D printing method, and finally completing integrated controllable and reliable manufacturing of the pressure sensor by using a high-temperature foaming stretching and laser cutting process. According to the resistive porous flexible pressure sensor, on one hand, the detection sensitivity and the detection range of the pressure sensor on pressure can be remarkably improved, and on the other hand, sensing decoupling of a contact interface can be achieved so as to be used for measuring distributed pressure.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to a resistive porous flexible pressure sensor and a manufacturing method thereof. Background Art

[0002] Compared with traditional rigid sensors, flexible sensors have attracted widespread attention from researchers in recent years due to their bendable and stretchable properties and their ability to be attached to surfaces with complex shapes. They have shown great potential application value in wearable devices, soft robots, electronic skin, and human-computer interaction.

[0003] As an important component of flexible sensors, resistive porous flexible pressure sensors have attracted much attention due to their simple structure, easy signal collection and good linearity. Their working principle is to convert external pressure stimulation into changes in the resistance of porous sensitive materials in the sensor, adjust the value of the output voltage or current signal, and realize quantitative feedback of external pressure through linear calibration. At present, the preparation methods of porous sensitive materials can be divided into two categories: one is to process conductive materials that do not have a porous structure into porous conductors by means of 3D printing, etching, etc.; the other is to attach a layer of conductive material inside or on the surface of porous structural materials by processes such as dip dyeing, screen printing, and inkjet printing to form a porous conductor. Although the first manufacturing method can significantly improve the stability and durability of the sensor, it has many disadvantages such as complex preparation process, high cost, and difficulty in large-scale production; the second step-by-step manufacturing method has a simple preparation process, low cost, and easy large-scale production, but the attached conductive material is easy to fall off during use, which seriously limits the stability and durability of the sensor. How to achieve the complementary advantages, mutual elimination of disadvantages and mutual assistance of the above two methods is a technical constraint on the leapfrog development of resistive porous flexible pressure sensors. Summary of the invention

[0004] In order to solve the difficulties of the above-mentioned prior art, the purpose of the present invention is to provide a resistive porous flexible pressure sensor, which can be manufactured in an integrated manner, has a simple preparation process and low cost, has the advantages of high sensitivity, wide detection range, good stability and durability, and can decouple the sensing signal for measuring distributed pressure.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A resistive porous flexible pressure sensor has a sandwich structure as a whole, wherein the bottom layer is a structural substrate, the surface layer is a contact layer, and the middle layer is composed of a number of discrete sensitive units; the discrete sensitive units are composed of a porous structure and conductive fibers, the conductive fibers are embedded in the porous structure and have multiple cross-sectional crack structures; separation cutting grooves are provided between adjacent discrete sensitive units, and separation grooves corresponding to the cutting grooves are provided on the contact layer.

[0006] A method for manufacturing a resistive porous flexible pressure sensor comprises the following steps: The first step is to prepare the support structure: the composite material in a fluid state is molded in the machined millimeter-scale template, and the excess composite material on the surface of the machined millimeter-scale template is removed by spin coating; then a layer of polymer is continuously filled on the surface of the machined millimeter-scale template as a structural substrate, and the composite material and the structural substrate are placed in a 50°C environment and heated for 4 hours for curing, and after demolding, a support structure with array units on the surface is obtained; The second step is the coupling integration of the conductive fibers: setting the 3D printing process parameters, using a 3D printer to print the conductive fibers and lead circuits on the surface of each unit of the support structure, the conductive fibers and lead circuits are bonded to the unit surface and kept in shape; a layer of composite material is continued to be filled on the conductive fibers and lead circuits, and then the support structure, the conductive fibers and lead circuits and the composite material that continues to be filled are pre-cured to obtain a pre-cured structure; finally, a layer of polymer is spin-coated on the surface of the pre-cured structure as a contact layer, and the pre-cured structure and the contact layer are placed at 50°C and heated for 4 hours for curing to obtain a cured self-connected structure; The third step is the integrated preparation of the resistive porous flexible pressure sensor: the cured self-connected structure obtained in the second step is foamed at high temperature, so that the composite material from the first step to the second step expands into a porous structure, and the conductive fiber is stretched to produce multiple cross-sectional crack structures; then the surface of the foamed cured self-connected structure is customized and cut by laser to obtain a resistive porous flexible pressure sensor.

[0007] In the first step to the second step, the composite material is obtained by mixing the polymer and the foaming agent in a mass ratio of 100:5-10, and fully stirring for 10 hours by a small stirrer; the foaming agent is selected from sodium bicarbonate or ammonium bicarbonate or azoisobutyronitrile or benzenesulfonylhydrazide.

[0008] In the second step, the 3D printer is a fused deposition modeling or ink direct writing printer; the conductive fiber and lead circuit materials are selected to be conductive polymers with a viscosity coefficient of 300-500 Pa·s.

[0009] In the second step, the pre-curing process parameters are heating at 50° C. for 5 minutes.

[0010] In the second step, the thickness of the contact layer is on the scale of hundreds of microns.

[0011] The polymers involved in the first step and the second step are both made of the same material, silicone rubber or polyurethane.

[0012] In the third step, the high temperature foaming process parameters are heating at 60-110° C. for 1-5 minutes.

[0013] The beneficial effects of the present invention are: The present invention proposes a resistive porous flexible pressure sensor and a manufacturing method thereof. On the one hand, the resistive porous flexible pressure sensor can utilize the excellent pressure-induced deformability of the high-porosity porous structure to drive the opening and closing changes of the cross-sectional crack structure in the conductive fiber, so that the number of conductive pathways changes suddenly, thereby significantly improving the pressure sensor's detection sensitivity and detection range to pressure. On the other hand, since each discrete sensitive unit in the middle layer is subjected to independent / unaffected forces, the sensing decoupling of the contact interface can be achieved for the measurement of distributed pressure. Secondly, the low-cost, high-efficiency multi-structure, multi-material foaming and stretching manufacturing process can realize the integrated, controllable and reliable manufacturing of the resistive porous flexible pressure sensor, thereby significantly improving its stability and fatigue service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of the resistive porous flexible pressure sensor of the present invention.

[0015] Figure 2 It is a schematic diagram of the resistance change of each discrete sensitive unit when the resistive porous flexible pressure sensor of the present invention contacts the target surface and is subjected to distributed pressure.

[0016] Figure 3 It is a schematic diagram of the present invention after molding the filled composite material in the machined millimeter scale template.

[0017] Figure 4 It is a structural schematic diagram of the support structure of the present invention.

[0018] Figure 5 It is a schematic diagram of 3D printing conductive fibers and lead circuits on the surface of a support structure according to the present invention.

[0019] Figure 6 This is a schematic diagram of the present invention of continuing to fill the surface of the support structure with composite material to cover the conductive fibers and lead circuits.

[0020] Figure 7 It is a schematic structural diagram of the cured self-connecting structure of the present invention.

[0021] Figure 8 It is a schematic diagram of the high temperature foaming method of the present invention to generate a porous structure and to promote the introduction of conductive fibers into a cross-sectional crack structure.

[0022] Fig. 9 Schematic diagram of the laser cutting process of the present invention.

[0023] Figure: 1. Structural substrate; 2. Contact layer; 3. Porous structure; 4. Conductive fibers; 5. Cross-sectional crack structure; 6. Target surface; 7. Machined millimeter-scale template; 8. Composite material; 9. 3D printer; 10. Laser; 11. Cutting groove. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0025] Reference Figure 1 A resistive porous flexible pressure sensor has a sandwich structure as a whole. The bottom layer is a structural substrate 1, the surface layer is a contact layer 2, and the middle layer is composed of a number of discrete sensitive units; the discrete sensitive units are composed of a porous structure 3 and a conductive fiber 4, the conductive fiber 4 is embedded in the porous structure 3 and has a plurality of cross-sectional crack structures 5; a separation cutting groove 11 is provided between adjacent discrete sensitive units, and a separation groove corresponding to the cutting groove 11 is opened on the contact layer 2.

[0026] During the specific implementation process, the porous structure 3 with high porosity has excellent pressure-induced deformability. During the compression process, it can drive the cross-sectional crack structure 5 in the conductive fiber 4 to open and close (i.e., microcrack mechanism), so that the number of conductive paths changes suddenly, which significantly improves the pressure sensor's detection sensitivity and detection range to pressure; secondly, since each discrete sensitive unit in the middle layer is subjected to independent / unaffected forces, the sensing decoupling of the contact interface can be achieved: when the pressure sensor contacts the target surface 6 (the target surface 6 is an inclined plane) and is subjected to distributed pressure, the discrete sensitive unit subjected to greater pressure will deform more and the resistance change will be more obvious, refer to Figure 2 , that is |ΔR1|>|ΔR2|>|ΔR3|>|ΔR4|>|ΔR5|.

[0027] A method for manufacturing a resistive porous flexible pressure sensor comprises the following steps: The first step is to prepare the support structure: refer to Figure 3 , a composite material 8 in a fluid state is molded in a machined millimeter-scale template 7 that has been treated with low surface energy, and the excess composite material 8 on the surface of the machined millimeter-scale template 7 is removed by a spin coating process; the spin coating process parameters are a low speed of 1000 rpm for 10 seconds and a high speed of 5000 rpm for 50 seconds; then a layer of polymer with a thickness of millimeters is continuously filled on the surface of the machined millimeter-scale template 7 as a structural substrate 1, the composite material 8 and the structural substrate 1 are placed in a 50°C environment and heated for 4 hours to achieve curing, and a support structure with array units on the surface is obtained after demolding, such as Figure 4 As shown; Preferably, the composite material 8 is obtained by mixing the polymer and the foaming agent in a mass ratio of 100:5-10 and stirring them for 10 hours in a small stirrer; the foaming agent is a material that is easy to obtain, has a large gas emission and a starting decomposition temperature greater than 50° C., such as sodium bicarbonate or ammonium bicarbonate or azoisobutyronitrile or benzenesulfonylhydrazide; The second step is the coupling integration of conductive fibers: Figure 5 , set 3D printing process parameters, use fused deposition modeling or ink direct writing type 3D printer 9 to print conductive fibers 4 and lead circuits on each unit surface on the support structure. Since the conductive fibers 4 and lead circuits just printed are sticky, they can adhere to the unit surface and maintain their shape; then continue to fill a layer of composite material 8 with a thickness of millimeters on the conductive fibers 4 and the lead circuits to cover the conductive fibers 4 and the lead circuits, place them in a 50°C environment and heat for 5 minutes for pre-curing treatment to achieve structural shaping, and obtain a pre-cured structure, such as Figure 6 As shown; then set the spin coating parameters, spin coat a layer of polymer on the surface of the pre-cured structure as the contact layer 2, place it in a 50°C environment and heat it for 4 hours to achieve the curing self-connection between the pre-cured structure and the contact layer 2, and obtain a cured self-connection structure, such as Figure 7 As shown; Preferably, the thickness of the contact layer 2 is in the order of hundreds of micrometers to enhance the pressure-induced deformability of the resistive porous flexible pressure sensor; Preferably, the conductive fiber 4 and the lead circuit material are selected from TangoBlackPlus FLX980 conductive polymer or Eel conductive TPU fiber or PDMS / CNTs composite material and the viscosity coefficient is 300-500 Pa·s; Preferably, the polymers involved in the first step and the second step are made of the same material, silicone rubber or polyurethane; The third step is the integrated preparation of the resistive porous flexible pressure sensor: the cured self-connected structure obtained in the second step is placed in a 60-110°C environment and heated for 1-5 minutes for high-temperature foaming. During this process, the foaming agent will decompose into gas, causing the composite material 8 from the first step to the second step to expand into a porous structure 3. At the same time, the tensile stress generated during the foaming process causes the conductive fiber 4 to produce a cross-sectional crack structure 5, introducing a microcrack sensing effect, such as Figure 8 As shown; then set the laser cutting process parameters, use the laser 10 to perform customized cutting on the surface of the solidified self-connected structure after foaming, and realize the integrated controllable and reliable manufacturing of the resistive porous flexible pressure sensor, such as Fig. 9 shown.

[0028] On the one hand, the resistive porous flexible pressure sensor of the present invention can utilize the excellent pressure-induced deformability of the high-porosity porous structure to drive the opening and closing changes of the cross-sectional crack structure in the conductive fiber, so that the number of conductive pathways changes suddenly, significantly improving the pressure sensor's detection sensitivity and detection range to pressure; on the other hand, since each discrete sensitive unit in the middle layer is subjected to independent / mutually independent forces, the sensing decoupling of the contact interface can be achieved for the measurement of distributed pressure; secondly, the low-cost, high-efficiency multi-structure, multi-material foaming and stretching manufacturing process can realize the integrated, controllable and reliable manufacturing of the resistive porous flexible pressure sensor, significantly improving its stability and fatigue service life.

Claims

1. A resistive porous flexible pressure sensor, characterized in that: The overall structure is a sandwich structure, wherein the bottom layer is a structural substrate (1), the surface layer is a contact layer (2), and the middle layer is composed of a plurality of discrete sensitive units; the discrete sensitive units are composed of a porous structure (3) and conductive fibers (4), the conductive fibers (4) are embedded in the porous structure (3) and have a plurality of cross-sectional crack structures (5); separating cutting grooves (11) are provided between adjacent discrete sensitive units, and a separating groove corresponding to the cutting grooves (11) is provided on the contact layer (2).

2. A method for manufacturing a resistive porous flexible pressure sensor, characterized in that: The following steps are involved: The first step is to prepare the support structure: a composite material (8) in a fluid state is molded into a machined millimeter-scale template (7), and the excess composite material (8) on the surface of the machined millimeter-scale template (7) is removed by a spin coating process; a layer of polymer is then filled on the surface of the machined millimeter-scale template (7) as a structural substrate (1), and the composite material (8) and the structural substrate (1) are placed in a 50° C. environment and heated for 4 hours for curing, and after demolding, a support structure with array units on the surface is obtained; The second step is the coupling integration of the conductive fibers: setting the 3D printing process parameters, using a 3D printer (9) to print the conductive fibers (4) and the lead circuit on the surface of each unit on the support structure, the conductive fibers (4) and the lead circuit are bonded to the unit surface and kept in shape; a layer of composite material (8) is continuously filled on the conductive fibers (4) and the lead circuit, and then the support structure, the conductive fibers (4) and the lead circuit and the composite material (8) that are continuously filled are pre-cured to obtain a pre-cured structure; finally, a layer of polymer is spin-coated on the surface of the pre-cured structure as a contact layer (2), and the pre-cured structure and the contact layer (2) are heated at 50° C. for 4 hours for curing to obtain a cured self-connected structure; The third step is the integrated preparation of the resistive porous flexible pressure sensor: the cured self-connecting structure obtained in the second step is subjected to high-temperature foaming, so that the composite material (8) from the first step to the second step expands into a porous structure (3), and the conductive fiber (4) is stretched to produce multiple cross-sectional crack structures (5); then, the surface of the foamed cured self-connecting structure is customized and cut using a laser (10) to obtain a resistive porous flexible pressure sensor.

3. The method for manufacturing a resistive porous flexible pressure sensor according to claim 2, characterized in that: In the first step to the second step, the composite material (8) is obtained by mixing the polymer and the foaming agent in a mass ratio of 100:5-10 and stirring them for 10 hours in a small stirrer; the foaming agent is selected from sodium bicarbonate or ammonium bicarbonate or azoisobutyronitrile or benzenesulfonylhydrazide.

4. The method for manufacturing a resistive porous flexible pressure sensor according to claim 2, characterized in that: In the second step, the 3D printer (9) is a fused deposition modeling or ink direct writing printer; the conductive fiber (4) and the lead circuit material are selected to be a conductive polymer with a viscosity coefficient of 300-500 Pa·s.

5. The method for manufacturing a resistive porous flexible pressure sensor according to claim 2, characterized in that: In the second step, the pre-curing process parameters are heating at 50° C. for 5 minutes.

6. The method for manufacturing a resistive porous flexible pressure sensor according to claim 2, characterized in that: In the second step, the thickness of the contact layer (2) is on the scale of hundreds of micrometers.

7. The method for manufacturing a resistive porous flexible pressure sensor according to claim 2, characterized in that: The polymers involved in the first step and the second step are both made of the same material, silicone rubber or polyurethane.

8. The method for manufacturing a resistive porous flexible pressure sensor according to claim 2, characterized in that: In the third step, the high temperature foaming process parameters are heating at 60-110° C. for 1-5 minutes.

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