CN114705334A

CN114705334A - Linear piezoresistive touch sensor and preparation method thereof

Info

Publication number: CN114705334A
Application number: CN202210367483.3A
Authority: CN
Inventors: 吴海彬; 林科金
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2022-04-08
Filing date: 2022-04-08
Publication date: 2022-07-05
Anticipated expiration: 2042-04-08
Also published as: CN114705334B

Abstract

The invention relates to a linear piezoresistive touch sensor and a preparation method thereof, wherein the sensor comprises at least one touch sensing unit, the touch sensing unit comprises a pressure sensing layer and a lower electrode layer, and the lower electrode layer comprises an electrode A and an electrode B which are distributed in parallel in an interdigital mode; the pressure sensing layer is composed of a PDMS bulge with a downward bulge structure and a PDMS/MWCNTs composite material covering the surface of the PDMS bulge, the upper surface of the pressure sensing layer is a plane, and at least one bulge is distributed on the lower surface of the pressure sensing layer; the bulges are of a conical structure with top fillets, and the top points of the bulges are in contact with the lower electrode layer; when the pressure sensing layer is pressed, the protrusions deform, and the contact area between the protrusions and the lower electrode layer changes linearly. The sensor has good linear response and sensitivity, and is simple in preparation process and low in manufacturing cost.

Description

Linear piezoresistive touch sensor and preparation method thereof

Technical Field

The invention belongs to the technical field of piezoresistive sensors, and particularly relates to a linear piezoresistive touch sensor and a preparation method thereof.

Background

The pressure tactile sensor can be attached to an irregular surface to sense or monitor changes in external pressure. Due to excellent pressure sensing performance and good flexibility, the material plays an important role in the aspects of electronic skin, medical diagnosis, intelligent artificial limbs, man-machine interfaces, motion behavior monitoring and the like, and becomes one of the main research hotspots of the current electronic materials and devices. The piezoresistive tactile sensor has the characteristics of simple device structure, low preparation cost, easy signal processing and the like, and is the flexible tactile sensor with the widest application range at present. A representative piezoresistive tactile sensor detects pressure by a change in contact resistance between two conductive surfaces. To improve piezoresistive tactile sensor performance, the use of microstructured conductive elastomers is the most typical approach. The microstructure mainly comprises common single microstructures such as a wavy microstructure, a pyramid microstructure, a micro-column microstructure and the like, a bionic microstructure, a foam porous microstructure and a layered multilevel microstructure.

Patent CN113670487A (application date: 2021, 07/14/2021, 11/19/2021) discloses a composite flexible piezoresistive sensor based on bionic multilevel structure, which comprises an interlocking multilevel microstructure flexible electrode with a sandwich structure and a middle PANI/PVDF composite conductive fiber membrane, wherein the PANI/PVDF composite conductive fiber membrane comprises a hydrophilic modified PVDF nanofiber membrane and a PANI nanowire layer. The preparation process of the PDMS membrane with the bionic rose petal surface microstructure comprises the following steps: cleaning rose petals in water, and drying at 40-50 ℃ for 1.5-3 hours for later use; preparing a PVA solution; the prepared PVA solution is cast on the surface of rose petals, dried for 9-11 hours at room temperature, and then the rose petals are removed to obtain a PVA film with a reverse rose petal microstructure; preparing a PDMS solution; and spin-coating the prepared PDMS solution on the PVA film with the bionic rose petal surface microstructure, curing for 22-25 hours at 50-70 ℃, dissolving for 1-3 hours in a water bath at 80-100 ℃ to remove the PVA, and thus obtaining the PDMS film with the bionic rose petal surface microstructure. The sensor has good stability and high sensitivity, but has the following problems: 1) the whole preparation process takes a long time, and the template needs to be dissolved away, so that the economic effect is poor. 2) The sensor sensitivity is high at 0-1kPa, but low at 1-5kPa, thus a small linear range is seen.

CN113237580A (application date of 2021, 05 and 19 months and publication date of 2021, 08 and 10 months) discloses MXeneThe high-sensitivity piezoresistive sensor comprises a conductive material, a flexible lower electrode layer and a flexible sensitive layer, wherein the flexible lower electrode layer is prepared by the following method: fixing the lower electrode layer mask plate on the flexible sensitive layer, then placing the flexible sensitive layer on a heating table, setting the temperature of the heating table to be 50-90 ℃, uniformly spraying MXene colloidal solution on the surface of the heating table, and removing the lower electrode layer mask plate when the linear resistance of the lower electrode layer is lower than 5 ohms per 1 cm to obtain an MXene flexible lower electrode layer; the flexible sensitive layer is prepared by adopting the following method: casting PU on the rough surface of the gauze paper by taking the sand paper as a template, and peeling the PU from the surface of the sand paper after the PU is naturally dried to obtain the flexible sensitive layer with the surface microstructure; and then placing the photosensitive layer on a heating table, and uniformly spraying MXene colloidal solution on the surface of the microstructure until the linear resistance of each 1 cm of the surface is between 5 and 30 omega, thus obtaining the MXene @ PU sensitive layer with the surface microstructure. The sensitivity of the sensor is up to 10213kPa in the range of 0.2358Pa to 5.7715kPa^-1However, the following problems also exist: 1) the sensitivity is improved, but the measurement range is smaller, so that the range of linearity is also smaller, and 2) when preparing the flexible sensitive layer and the flexible lower electrode layer, MXene solution is sprayed to have certain requirements on the line resistance and is difficult to master.

Patent CN112213004B (application date is 2021, 10, 12 days, published as 2022, 02, 08 days) discloses a large-response-range, high-sensitivity tactile sensor based on gradient elastic modulus, which comprises an encapsulation layer, a flexible substrate/electrode, and a gradient pore structure pressure sensing layer, wherein the flexible substrate/electrode is made by evaporating an ITO film on a flexible substrate, the gradient pore structure pressure sensing layer is made of a gradient pore structure polymer material and a conductive material, the gradient pore structure polymer material is prepared by a steam method, the preparation temperature is 120-, and (3) after the gradient hole structure pressure sensing layer is subjected to oxygen plasma treatment, pressing the gradient hole structure pressure sensing layer between the upper flexible substrate/electrode and the lower flexible substrate/electrode, and packaging by adopting PDMS. The sensor always keeps the capability of high sensitivity and quick response time in a large response range. But the following problems are simultaneously existed: 1) not single linear but piecewise linear in a large range, 2) strict requirements on preparation process.

Therefore, there is a need for a method for manufacturing a piezoresistive tactile sensor, which requires a simple manufacturing process and ensures that the sensor maintains good linearity and sensitivity over a wide range.

Disclosure of Invention

The invention aims to provide a linear piezoresistive tactile sensor and a preparation method thereof.

In order to achieve the purpose, the invention adopts the technical scheme that: a linear piezoresistive tactile sensor comprises at least one tactile sensing unit, wherein the tactile sensing unit comprises a pressure sensing layer and a lower electrode layer, and the lower electrode layer comprises electrodes A and electrodes B which are distributed in an interdigital mode in parallel; the pressure sensing layer is composed of a PDMS bulge with a downward bulge structure and a PDMS/MWCNTs composite material covering the surface of the PDMS bulge, the upper surface of the pressure sensing layer is a plane, and at least one bulge is distributed on the lower surface of the pressure sensing layer; the bulges are of a conical structure with top fillets, and the top points of the bulges are in contact with the lower electrode layer; when the pressure sensing layer is pressed, the protrusions deform, and the contact area between the protrusions and the lower electrode layer changes linearly.

Furthermore, the PDMS/MWCNTs composite material is prepared by doping 6-10% of MWCNTs conductive particles into PMDS.

Further, the lower electrode layer is prepared by printing the electrode A and the electrode B on the flexible substrate in a screen printing mode.

Further, the flexible substrate is PET or PI.

Furthermore, the protrusion degree of the protrusions is micrometer-scale, the ratio of the radius of the top fillet to the radius of the conical base is greater than 1:10, and the height of the protrusions is smaller than 1 mm.

The invention also provides a preparation method of the linear piezoresistive tactile sensor, which comprises the following steps:

step 1, coating single-component room temperature vulcanized silicone rubber in a resin mold comprising a plurality of conical-structure bulges with top fillets for curing at normal temperature, and stripping the cured silicone rubber from the resin mold to obtain a silicone rubber mold;

step 2, adding PDMS into a solvent, and magnetically stirring for 1 h; adding MWCNTs conductive particles into a solvent, and dispersing for 1h by using an ultrasonic disperser;

step 3, mixing the two solutions obtained in the step 2, and dispersing for 15min by using an ultrasonic disperser; placing the dispersed solution on a heating platform, heating at a constant temperature of 70 ℃ until the solvent is completely volatilized, then adding a PDMS curing agent, and stirring for 15min to obtain a PDMS/MWCNTs composite material;

step 4, mixing PDMS with set mass and PDMS curing agent, stirring for 15min, placing in a vacuum drying oven for vacuum treatment for 30min until bubbles are completely eliminated to obtain PDMS reagent;

step 5, coating the PDMS/MWCNTs composite material obtained in the step 3 on the silicon rubber mold, coating the PDMS reagent obtained in the step 4, then placing the silicon rubber mold into a vacuum drying oven for vacuum treatment for 20min, and heating the silicon rubber mold at a constant temperature of 80 ℃ for 2h for curing to obtain a pressure sensing layer;

and 6, peeling the obtained pressure sensing layer from the silicon rubber mold, placing the pressure sensing layer on the lower electrode layer, and connecting the pressure sensing layer and the lower electrode layer together to obtain the linear piezoresistive tactile sensor.

Further, the resin mold is manufactured by 3D printing.

Compared with the prior art, the invention has the following beneficial effects: the utility model provides a linear piezoresistive tactile sensor and preparation method thereof compares in the lower linear detection scope of traditional sensor, and this sensor passes through the protruding structural design of the circular cone structure of band top fillet, can guarantee that the sensor has good linear response and good sensitivity in great measuring range, is applicable to the pressure signal detection of throat pronunciation, finger bending and other positions. In addition, the sensor has the advantages of simple preparation process, low manufacturing cost and low requirement on the operating environment, and is suitable for mass production.

Drawings

FIG. 1 is a schematic diagram of a linear piezoresistive tactile sensor according to an embodiment of the invention;

FIG. 2 is a functional diagram of a linear piezoresistive tactile sensor according to an embodiment of the present invention;

FIG. 3 is a schematic view of a bump in a different configuration in an embodiment of the invention;

FIG. 4 is a graph of contact area versus pressure for different protrusions of the structure according to an embodiment of the present invention;

FIG. 5 is a schematic flow chart of the preparation of a silicone rubber mold in the embodiment of the invention;

FIG. 6 is a schematic flow chart of the preparation of the pressure sensing layer in the embodiment of the present invention;

FIG. 7 is a schematic flow chart illustrating the preparation of the lower electrode layer in the embodiment of the present invention;

FIG. 8 is a schematic diagram of a sensor array consisting of 9 sensor units according to an embodiment of the present invention;

FIG. 9 is a graph showing the results of a linear piezoresistive tactile sensor detecting external pressure in an embodiment of the present invention;

in the figure: 1-a pressure sensing layer; 2-a lower electrode layer; 3-PDMS protrusions with top rounded cone structures; 4-PDMS/MWCNTs composite material covering the projections; 5-electrode B; 6-PET film; 7-electrode A; 8-resin mold with top round angle cone structure projection; 9-silicone rubber in molding; 10, manufacturing a silicon rubber mold with a pressure sensing layer with a top rounded-corner conical structure protrusion; 11-PDMS/MWCNTs composite material; 12-PDMS reagent; 13-a pressure sensing layer with a top rounded-corner conical structure bulge; 14-silver paste coating for printing; 15-printing the completed lower electrode layer; 16-screen printed PET film substrate; 17-a sensing unit; 18-FPC board; 19-row extraction electrodes; 20-row extraction electrodes; 21-row extraction electrodes; 22-column extraction electrodes; 23-column extraction electrodes; 24-column extraction electrodes.

Detailed Description

The invention is further explained below with reference to the drawings and the embodiments.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

Fig. 1 is a schematic structural diagram of a resistive tactile sensor unit according to this embodiment, and fig. 2 is a schematic operational diagram of the resistive tactile sensor according to this embodiment. As shown in fig. 1-2, the piezoresistive tactile sensor unit is composed of a pressure sensing layer 1 composed of PDMS bumps 3 with rounded cones at the top and PDMS/MWCNTs composite 4 coated on the bumps, and a lower electrode layer 2 composed of electrode a7 and electrode B5 formed by screen printing silver paste paint on a PET film 6. When the pressure perception layer is pressed, the protrusions generate elastic deformation to be compressed, the contact area of the PDMS/MWCNTs composite material covering the protrusions and the lower electrode layer is changed, the resistance value is changed, the current value flowing through the pressure perception layer is changed, and the pressure of the pressure perception layer can be known through measuring the current value change.

As shown in fig. 3-4, the piezoresistive sensor proposed in this embodiment is based on the contact piezoresistive effect, the variation of the relative current is proportional to the contact area a, as long as the contact area a and the external acting force are also in a linear relationship, the variation of the current value and the external acting force are in a linear relationship, and the PDMS material is simulated by using finite element analysis, it can be found that the linear response of the contact area of the structure with the ratio of the vertex angle radius to the cone radius of 1:10 to the acting force is the best, and the linearity is deteriorated as the vertex angle radius is increased. Therefore, the protrusion is finally selected to be a structure with the ratio of the radius of the top fillet to the radius of the cone of 1:10 and the radius of the cone of 0.8 mm.

As shown in fig. 5 to 7, the present embodiment provides a linear piezoresistive tactile sensor, which is prepared by the following steps:

firstly, uniformly coating the silicon rubber on a 3D printing resin mold 8 which is made by printing in advance, curing at normal temperature, and slowly stripping the silicon rubber from the resin mold by using tweezers to obtain a silicon rubber mold 10.

Secondly, adding PDMS into IPA, magnetically stirring for 1h, adding MWCNTs into IPA, dispersing for 1h through an ultrasonic disperser, mixing the two dispersions, dispersing for 15min through the ultrasonic disperser, placing the dispersed solution on a heating platform, heating at a constant temperature of 70 ℃ until the IPA solution is completely volatilized, and adding a PDMS curing agent to obtain the PDMS/MWCNTs composite material 11. And then, mixing PDMS with a certain mass and a PDMS curing agent, manually stirring for 15min, and then placing the mixture into a vacuum drying oven for vacuum treatment for 30min to eliminate bubbles, thereby obtaining the PDMS reagent 12. And uniformly coating the PDMS/MWCNTs composite material on a silicon rubber mold, coating a PDMS reagent, putting the silicon rubber mold into a vacuum drying oven, performing vacuum treatment for 20min, heating the silicon rubber mold at a constant temperature of 80 ℃ for 2h for curing, and peeling the silicon rubber mold by using tweezers to obtain the pressure sensing layer 13.

And then, selecting a silver paste coating 14 to perform screen printing on the PET film substrate 16, and putting the PET film substrate into a vacuum drying oven to heat at a constant temperature of 60 ℃ for 1 hour to solidify a silver paste material, so that the lower electrode layer 15 can be prepared.

Finally, the pressure sensing layer 13 is placed on the lower electrode layer 15, and the piezoresistive tactile sensor unit is manufactured.

As shown in fig. 8, the linear piezoresistive tactile sensor unit proposed in this embodiment may include at least 2 tactile sensor units 17 to form a sensor array, where all the sensor units of the sensor array have the same lower electrode layer; the electrodes A of the lower electrode layers of all the sensor units of the sensor array are connected in the order of columns and led out as

column detection electrodes

22, 23, 24; the electrodes B of the lower electrode layers of all the sensing units of the sensor array are connected in line sequence, and

detection electrodes

19, 20 and 21 are led out; the lower electrode layer 18 thereof is made of a flexible printed circuit.

As shown in FIG. 9, the proposed linearity of the present embodimentThe piezoresistive sensor proves that the sensor is in the middle and low pressure range (<100 kPa) and the sensitivity is 0.211kPa^-1。

Compared with the prior art, the linear piezoresistive tactile sensor provided by the embodiment has the following beneficial effects:

1. the manufacturing process is simple, the process for manufacturing the pressure sensing layer is simple, the used mold is made of a mature and reliable 3D printing technology, the lower electrode layer is obtained by a reliable screen printing technology, the manufacturing process is very simple, and the cost is low.

2. The piezoresistive tactile sensor has good linearity, and the change of the relative current and the external pressure are in a linear relationship when the change of the external acting force and the change of the contact area are obtained through finite element simulation analysis, so that the piezoresistive tactile sensor has good linearity.

3. The measuring range is great, and the pressure perception layer of this embodiment has 64 conical bulge structures that have a top fillet, and protruding height is 0.8mm, has very big compressibility, has improved the measuring range of sensor to a certain extent.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. The linear piezoresistive touch sensor is characterized by comprising at least one touch sensing unit, wherein the touch sensing unit comprises a pressure sensing layer and a lower electrode layer, and the lower electrode layer comprises electrodes A and electrodes B which are distributed in an interdigital mode in parallel; the pressure sensing layer is composed of a PDMS bulge with a downward bulge structure and a PDMS/MWCNTs composite material covering the surface of the PDMS bulge, the upper surface of the pressure sensing layer is a plane, and at least one bulge is distributed on the lower surface of the pressure sensing layer; the bulges are of a conical structure with top fillets, and the top points of the bulges are in contact with the lower electrode layer; when the pressure sensing layer is pressed, the protrusions deform, and the contact area between the protrusions and the lower electrode layer changes linearly.

2. The linear piezoresistive tactile sensor according to claim 1, wherein said PDMS/MWCNTs composite material is prepared by PMDS incorporating 6% to 10% of MWCNTs conductive particles.

3. The linear piezoresistive touch sensor according to claim 1, wherein the lower electrode layer is formed by printing the electrode a and the electrode B on a flexible substrate by means of screen printing.

4. The linear piezoresistive tactile sensor according to claim 3, wherein the flexible substrate is PET or PI.

5. The linear piezoresistive touch sensor according to claim 1, wherein the protrusion is in the order of microns, the ratio of the radius of the apex fillet to the radius of the conical base is greater than 1:10, and the height of the protrusion is less than 1 mm.

6. A method of making a linear piezoresistive touch sensor according to any of the claims 1-5, comprising the steps of:

step 1, coating single-component room-temperature vulcanized silicone rubber in a resin mold comprising a plurality of conical-structure bulges with top fillets for normal-temperature curing, and stripping the cured silicone rubber from the resin mold to obtain a silicone rubber mold;

7. The method of manufacturing a linear piezoresistive tactile sensor according to any of the claims 6, wherein the resin mould is made by 3D printing.