CN111256884A - Flexible sensor capable of identifying pressure and shear force - Google Patents

Flexible sensor capable of identifying pressure and shear force Download PDF

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CN111256884A
CN111256884A CN202010114649.1A CN202010114649A CN111256884A CN 111256884 A CN111256884 A CN 111256884A CN 202010114649 A CN202010114649 A CN 202010114649A CN 111256884 A CN111256884 A CN 111256884A
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strain
shear
grid
pressure
shear strain
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CN111256884B (en
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冯雪
刘亚风
马寅佶
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Tsinghua University
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Tsinghua University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/18—Measuring force or stress, in general using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/16—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force
    • G01L5/161—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force using variations in ohmic resistance
    • G01L5/162—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force using variations in ohmic resistance of piezoresistors

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  • Force Measurement Appropriate To Specific Purposes (AREA)

Abstract

A flexible sensor capable of identifying pressure and shear force comprises a signal sensitive layer and a micro-structural layer. The signal sensitive layer comprises a strain gate; the strain gate comprises a compressive strain gate (2) and a plurality of shear strain gates (1). The flexible sensor comprises at least two groups of shear strain grids (1), wherein the two shear strain grids (1) in the same group are located on two sides of the pressure strain grid (2) along the radial direction of the circumference. The microstructure layer comprises a pressure strain grid combination part (4) and a shear strain grid combination part (5); the microstructure (7) of the pressure strain grid combination part (4) covers the metal line segment of the pressure strain grid (2) in the radial direction of the circumference, the microstructure (7) of the shear strain grid combination part (5) is provided with a part which exceeds the metal line segment of the corresponding shear strain grid (1) in the radial direction, and the combination body formed by the shear strain grid combination parts (5) and the corresponding shear strain grids (1) is symmetrical about the circle center of the circumference.

Description

Flexible sensor capable of identifying pressure and shear force
Technical Field
The invention relates to the technical field of sensors, in particular to a flexible sensor capable of identifying pressure and shear force.
Background
With the development of scientific technology and the improvement of the living standard of people, wearable equipment for medical treatment and health receives more and more attention of people. Stress or strain sensors have wide applications in the fields of health detection, smart screens, human-computer interaction, electronic skins, and the like. In recent years, various flexible stress/strain sensors suitable for wearable devices, such as a strain sensor based on biocellulose, a silver nanowire sensor, a graphene flexible sensor, and the like, have been developed.
For future intelligent wearable equipment, the development trend is to simulate human skin to realize detection of complex mechanical signals, and most of the existing flexible sensors can only sense compressive stress or compressive strain and cannot detect shear stress and distinguish the direction of the shear stress.
Disclosure of Invention
The present invention has been made in view of the state of the art described above. The invention aims to provide a flexible sensor capable of identifying pressure and shearing force, wherein the flexible sensor can identify the pressure and the magnitude and direction of the shearing force.
Providing a flexible sensor capable of identifying pressure and shearing force, which comprises a substrate, a signal sensitive layer and a micro-structural layer, wherein the signal sensitive layer comprises a strain gate and is laminated on the upper surface of the substrate;
the flexible sensor comprises a flexible sensor and a plurality of shear strain grids, wherein the flexible sensor comprises at least two groups of shear strain grids, and the two shear strain grids in the same group are positioned on two sides of the pressure strain grids along the radial direction of the circumference;
the microstructure layer comprises a plurality of microstructures, and the microstructure layer comprises a pressure strain grid combination part and a shear strain grid combination part;
the microstructure of the compressive strain grid combination part covers the metal line segment of the compressive strain grid in the radial direction of the circumference, the microstructure of the shear strain grid combination part is provided with a part which exceeds the metal line segment of the corresponding shear strain grid in the radial direction of the circumference, and a combination formed by the plurality of shear strain grid combination parts and the corresponding shear strain grids is symmetrical about the center of the circumference.
In at least one embodiment, the flexible sensor further comprises a conductive network that leads out both ends of the compressive strain grids and each of the shear strain grids for forming a conductive loop.
In at least one embodiment, the conductive network includes a connecting wire connecting each of the shear and compressive strain grids together and a conductive wire for forming an electrical circuit between the strain grids and an external electrical device.
In at least one embodiment, the pressure strain gate generates a change in resistance Δ R when the flexible sensor is subjected to a pressure1And identifying the pressure F applied to the flexible sensor according to the formula (1-1), the formula (1-2) and the formula (1-3)P：
ΔR1＝K1ε1(1-1)；
Figure BDA0002391105150000021
Figure BDA0002391105150000022
Wherein E is1Elastic modulus, K, of the microstructure of the compressive strain gate1Is the strain sensitivity coefficient, ε, of the compressive strain gauge1Is the compressive strain of the compressive strain gate, σ is the compressive stress of the compressive strain gate, d1A width of the microstructure that is a compressive strain gate;
when the flexible sensor is subjected to shearing force, the same group of shear strain grids are subjected to a shear force component FτAlong the shear force component FτThe shear strain grids positioned in the front and the rear directions of the shear strain grids generate resistance changes delta R respectively21And Δ R22The flexible sensor is according to formula (2-1) and formula (2)-2), formula (2-3), formula (3-1), formula (3-2) and formula (3-3) identify the shear force component Fτ：
For the component force F along the shearing forceτThe shear strain grid with the direction of (a):
ΔR21＝K21ε21(2-1)；
Figure BDA0002391105150000031
Figure BDA0002391105150000032
for the component force F along the shearing forceτThe shear strain grid of which the direction is located behind:
ΔR22＝K22ε22(3-1)；
Figure BDA0002391105150000033
Figure BDA0002391105150000034
wherein E is21And E22Modulus of elasticity, K, of the microstructure of the corresponding shear strain grid21And K22For the corresponding strain sensitivity coefficient, epsilon, of the shear strain grid21And ε22For corresponding compressive strain, σ, of the shear strain grid21And σ22Compressive stress for the corresponding shear strain grid, η21And η22For the positional offset of the microstructure of the respective shear strain grid and the metal line section of the respective shear strain grid, L21And L22Height of the microstructure of the corresponding shear strain grid, d21And d22A width of the microstructure that is the corresponding shear strain gate;
the shear force applied to the flexible sensor passes through the stations of different groupsThe shear force component F identified by the shear force strain gridτSynthesized according to the quadrilateral rule.
In at least one embodiment, the flexible sensor comprises two sets of the shear strain grids arranged orthogonally.
In at least one embodiment, the shear strain grid includes a plurality of arc-shaped metal wire segments arranged at intervals along the radial direction and connected into a whole, and the lengths of the metal wire segments arranged in sequence from outside to inside along the radial direction are gradually reduced, so that the shear strain grid is in a fan shape.
In at least one embodiment, the microstructures of the shear strain grid joint are columns and are arranged in a plurality of arcs concentric with the shear strain grid, or the microstructures of the shear strain grid joint are in the shape of arcs concentric with the shear strain grid,
and a plurality of microstructures are arranged on each metal line segment of the shear strain grid at intervals.
In at least one embodiment, the shear strain grating is integrally formed by bending the metal wire in a serpentine shape multiple times.
In at least one embodiment, the metal wire segments of the compressive strain gate are located on a plurality of concentric circular tracks and the compressive strain gate is disc-shaped.
In at least one embodiment, the microstructure of the compressive strain grating bond is a cylinder and is arranged in a plurality of rings concentric with the compressive strain grating, or the microstructure of the compressive strain grating bond is in the shape of a ring concentric with the compressive strain grating,
and arranging a plurality of microstructures on each metal wire section of the compressive strain gate at intervals.
In at least one embodiment, the microstructure of the compressive strain grid joint covers the metal wire segment of the compressive strain grid exactly or with a portion beyond the metal wire segment of the compressive strain grid in a radial direction of the circumference.
In at least one embodiment, the compressive strain grating comprises a plurality of semicircular metal wire segments distributed on both sides of a diameter of the circumference to form two compressive strain grating parts connected at the center of the circumference.
In at least one embodiment, the microstructure layer further includes a flexible substrate, the plurality of microstructures are supported on the flexible substrate, the microstructures are cantilever structures, and fixed ends of the microstructures are disposed on the flexible substrate.
The following beneficial effects can be obtained through the technical scheme:
when the flexible sensor is subjected to shearing force, the microstructures are bent, and the bending directions of the microstructures covering the shearing force strain grid joint parts of the two shearing force strain grids of each group are opposite, so that the resistance changes of the two shearing force strain grids of each group are different, and the shearing force component force applied to each group of shearing force strain grids can be obtained according to a formula. And then according to a parallelogram rule, synthesizing the shearing force components acting along the arrangement directions of the shearing force strain grids of different groups, so that the flexible sensor can measure the shearing force (including the magnitude and the direction of the shearing force) in any direction.
Drawings
FIG. 1 is a schematic view of a body portion of a pressure and shear force identifiable flexible sensor of the present invention.
FIG. 2 is a general schematic view of a strain gage of a flexible sensor and a close-up view thereof.
Fig. 3 is a general schematic view of a microstructure layer of a flexible sensor and a partially enlarged view thereof.
Fig. 4 is a schematic view of a first embodiment of a microstructure in combination with a metal line segment of a compressive strain gate, showing that the width of the microstructure is greater than the width of the metal line segment of the compressive strain gate.
Fig. 5 is a schematic view of a second embodiment of a microstructure in combination with a metal line segment of a compressive strain gate, showing that the width of the microstructure is equal to the width of the metal line segment of the compressive strain gate.
FIG. 6 is a schematic diagram of a first embodiment of a combination of metal line segments and microstructures of two shear strain grids of the same set.
FIG. 7 is a schematic diagram of a second embodiment of a combination of metal line segments and microstructures of two shear strain grids of the same set.
Description of reference numerals:
the structure comprises 1 shear strain grid, 11 metal line segments of the shear strain grid, 2 pressure strain grid, 21 metal line segments of the pressure strain grid, 3 conductive network, 31 connecting lines, 32 conducting wires, 33 outgoing lines, 4 pressure strain grid combination parts, 5 shear strain grid combination parts, 6 substrates and 7 microstructures.
Detailed Description
Exemplary embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the detailed description is intended only to teach one skilled in the art how to practice the invention, and is not intended to be exhaustive or to limit the scope of the invention.
As shown in fig. 1, 2 and 3, the present disclosure provides a flexible sensor that can recognize a pressure applied perpendicular to a paper surface and a shear force applied parallel to the paper surface. The flexible sensor is a wafer, and the main body of the flexible sensor comprises a substrate 6, a signal sensitive layer and a micro-structural layer which are laminated and combined. The side of the substrate 6 that is used to bond the signal sensitive layer and the microstructure layer is defined below as the "upper" side, and the opposite side is the "lower" side.
The signal sensitive layer is laminated on the upper surface of the substrate 6, and the microstructure layer is laminated on the upper surface of the signal sensitive layer. The substrate 6 may be made of, for example, a flexible material, and may be, for example, a polymer film. The signal sensitive layer can convert force signals into electric signals, and the micro-structural layer can be a high polymer film which comprises a plurality of micro-structures 7 and is of a human body fingerprint imitating structure.
The signal sensitive layer comprises a strain grid comprising a compressive strain grid 2 and a plurality (e.g. four) shear strain grids 1 and a conductive network 3. The shear strain grids 1 are arranged along the circumferential direction, and the pressure strain grids 2 are positioned at the circle center of the circumference. Specifically, the compressive strain grids 2 may be disk-shaped, and each shear strain grid 1 may be sector-shaped concentric with the compressive strain grid 2.
The circumference enclosed by the shear strain grids 1 and the compressive strain grid 2 have the same radial direction, circumferential direction and circle center, and the circumference enclosed by the shear strain grids 1 and the compressive strain grid 2 are referred to as the radial direction, the circumferential direction and the circle center. The "width" of the microstructure 7 referred to herein is the dimension of the microstructure 7 in the radial direction.
The shear strain grids 1 are arranged in pairs, and the signal sensitive layer comprises at least two groups of shear strain grids 1. In each group of shear strain grids 1, the arrangement direction of the two shear strain grids 1 passes through the center of the pressure strain grid 2, for example, the radial direction of the pressure strain grid 2, and the two shear strain grids 1 are symmetrical about the center of the pressure strain grid 2.
It should be understood that in the embodiment where the compressive strain grating 2 does not have a center, the two shear strain gratings 1 are arranged through the center of the compressive strain grating 2.
The compressive strain grid 2 and the shear strain grid 1 both comprise a plurality of metal line segments which are arranged at intervals along the radial direction and extend along the circumferential direction. The shear strain grid 1 comprises a plurality of arc-shaped metal line sections 11 which are arranged at intervals along the radial direction, the arc-shaped metal line sections 11 are connected end to form a snake shape, and the lengths of the metal line sections 11 which are sequentially arranged along the radial direction from outside to inside are gradually reduced, so that the shear strain grid 1 is in a fan shape as a whole.
In other embodiments, the shear strain grid 1 may further include a plurality of linear metal line segments 11 arranged at intervals along the radial direction, and the plurality of linear metal line segments 11 are connected end to form a serpentine shape.
The shear strain gate 1 may be integrally formed by bending the metal wire in a serpentine shape a plurality of times. Thus, the shear strain grid 1 is smoother and more convenient to bond with the microstructure layer. Of course, the form of the shear strain grid 1 is not limited thereto.
Of course, in other embodiments, the shear strain grid 1 may be formed by connecting a plurality of metal wires in a serpentine shape.
The compressive strain gate 2 comprises a plurality of semicircular metal wire segments 21, and the plurality of semicircular metal wire segments 21 are distributed on two sides of one diameter of the compressive strain gate 2 so as to form two compressive strain gate parts. In each compressive strain gate part, a plurality of metal wire segments 21 are connected end to form a snake shape, and the two compressive strain gate parts are connected at the center of the compressive strain gate 2. The two partial semicircular wire sections of the compressive strain gauge are substantially symmetrical with respect to the above-mentioned diameter, so that the wire sections 21 of the compressive strain gauge 2 are mainly located on a plurality of circular tracks.
In other embodiments, the metal line segment 21 of the compressive strain gate 2 may be located on a spiral trajectory centered at the center of the compressive strain gate 2.
The conductive network 3 comprises a connection line 31, a plurality of (e.g. six) wires 32 and a plurality of outgoing lines 33. The connecting line 31 may have a circular arc shape, and the connecting line 31 connects the shear strain gauge 1 and the compressive strain gauge 2 together. The connecting lines 31 may connect the radially innermost side of each shear strain grid 1 and the radially outermost side of the compressive strain grid 2. The bond wires 31 and 32 form an electrical loop between the strain gauge and an external electrical device. The wires 32 are connected to the connection wires 31, the respective shear strain grids 1 and the compressive strain grids 2. The lead-out line 33 is used to connect the lead wire 32 with an external electric device to transmit an electric signal.
Specifically, the radially outermost metal line segment 21 of one compressive strain gauge part is connected to one lead 32, and the radially outermost metal line segment 21 of the other compressive strain gauge part is connected to a connection line 31, and the connection line 31 is connected to one lead 32. The radially innermost metal wire segment 11 of each shear strain grid 1 is connected to a connecting wire 31, and the radially outermost metal wire segment 11 of each shear strain grid 1 is connected to a conducting wire 32.
In this way, the conductive network 3 outputs the force information (in the form of electrical signals) collected by the shear strain gauge 1 and the compressive strain gauge 2, respectively.
The microstructure layer comprises a plurality of microstructures 7 and a flexible substrate, and the plurality of microstructures 7 and the flexible substrate can be formed into a whole through a casting process. The microstructure 7 is a cantilever structure, and the fixed end of the microstructure is arranged on the flexible substrate. Microstructures 7 typically have a size of 5 microns to 500 microns with a plurality of microstructures 7 dispersed within the microstructure layer. Both the microstructures 7 and the flexible substrate may be formed of a flexible material. The microstructures 7 are, for example, pillars, and specifically, may be cubic pillars or cylinders.
The microstructure layer comprises a plurality of microstructures 7 with a cantilever structure, can realize local stress concentration and imitate a fingerprint structure of a palm of a person, so that the flexible sensor has high sensitivity.
In other embodiments, the microstructure 7 may also be an elongated sheet, such as an arc-shaped or semicircular sheet, and the microstructure layer includes a plurality of radially spaced sheets, and the sheet still forms a "cantilever" structure with one end of the sheet disposed on the flexible substrate as a fixed end.
The microstructure layer comprises a pressure strain grid combination part 4 and a shear strain grid combination part 5, the pressure strain grid combination part 4 covers the upper surface of the pressure strain grid 2, and the shear strain grid combination part 5 can comprise a plurality of split parts so as to respectively cover the upper surface of the shear strain grid 1 in a one-to-one correspondence mode.
The compressive strain gate joint 4 may have the same shape as the compressive strain gate 2, for example, a disk shape. The microstructures 7 of the compressive strain gate combination part 4 can be arranged into a plurality of rings concentric with the compressive strain gate 2, and the rings formed by the microstructures 7 of the compressive strain gate combination part 4 can cover the metal wire segments 21 of the compressive strain gate 2 on the circular track in a one-to-one correspondence manner. A plurality of microstructures 7 spaced apart along the extending direction of the metal line segment 21 may be provided corresponding to each metal line segment 21.
In other embodiments, the shape of the microstructure 7 of the compressive strain grating bonding part 4 may be a ring shape concentric with the compressive strain grating 2, i.e. the microstructure 7 is a ring-shaped body.
In other embodiments, the shape of the compressive strain gate bonding part 4 may be other shapes capable of covering the compressive strain gate 2.
As shown in fig. 4 and 5, the microstructure 7 of the compressive strain gate bonding portion 4 may just cover the metal line segment 21 of the compressive strain gate 2, or have a portion radially beyond the metal line segment 21 of the compressive strain gate 2, for example, the radial dimension (width) of the microstructure 7 may be greater than or equal to the width of the metal line segment 21 of the compressive strain gate 2. When pressure is applied to the compressive strain grid joint 4, the pressure can be completely collected and transferred to the compressive strain grid 2.
The shear strain grid joint 5 may have the same shape as the shear strain grid 1, for example, a sector shape, and the shear strain grid joint 5 may cover the shear strain grid 1 entirely in the circumferential direction. The microstructures 7 of the shear strain grid joint part 5 can be arranged into a plurality of arcs concentric with the shear strain grid 1, and the lengths of the arcs arranged in sequence from outside to inside along the radial direction are gradually reduced. The arcs formed by the microstructures 7 of the shear strain grid joint part 5 can cover the metal wire sections 11 of the shear strain grid 1 in a one-to-one correspondence mode. A plurality of microstructures 7 spaced apart along the extending direction of the metal line segment 11 may be provided corresponding to each metal line segment 11.
In other embodiments, the shape of the microstructure 7 of the shear strain grid joint 5 may be an arc concentric with the shear strain grid 1, i.e. the microstructure 7 is an arc-shaped body.
In other embodiments, the shape of the shear strain grid joint 5 may be other shapes that can cover the shear strain grid 1.
The microstructures 7 of the shear strain grid joints 5 have portions that radially exceed the metal line segments 11 of the corresponding shear strain grid 1, i.e., the microstructures 7 of the shear strain grid joints 5 radially overlap the metal line segments 11 of the shear strain grid 1 and exceed the metal line segments 11, or are radially offset from the metal line segments 11 of the shear strain grid 1. For the same shear strain grid 1, the parts of the microstructures 7 of the shear strain grid joints 5 beyond the metal line segments 11 of the corresponding shear strain grid 1 are the same. The combination of the shear strain grid joints 5 and the corresponding shear strain grids 1 is symmetrical about the center of the pressure strain grid 2.
As shown in fig. 6, in one embodiment, the microstructures 7 of the shear strain grid joint 5 may radially cover the metal line segment 11 of the shear strain grid 1 and radially outwardly exceed the metal line segment 11, i.e. the radially inner edge of the microstructures 7 of the shear strain grid joint 5 is aligned with the radially inner edge of the metal line segment 11 of the shear strain grid 1, and the radially outer edge of the microstructures 7 of the shear strain grid joint 5 exceeds the radially outer edge of the metal line segment 11 of the shear strain grid 1.
In other embodiments, the microstructures 7 of the shear strain grid joint 5 may also radially cover the metal line segment 11 of the shear strain grid 1 and radially inwardly beyond the metal line segment 11.
As shown in fig. 7, in another embodiment, the microstructures 7 of the shear strain grid joint 5 may be offset radially inward from the metal line segments 11 of the shear strain grid 1, i.e. the radially inner edge of the microstructures 7 of the shear strain grid joint 5 exceeds the radially inner edge of the metal line segments 11 of the shear strain grid 1, and the radially outer edge of the metal line segments 11 of the shear strain grid 1 exceeds the radially outer edge of the microstructures 7 of the shear strain grid joint 5.
In other embodiments, the microstructures 7 of the shear strain grid joint 5 may be staggered radially outward from the metal wire segments 11 of the shear strain grid 1.
When the flexible sensor is subjected to a shearing force, the microstructures 7 are bent, and the bending directions of the microstructures 7 covering the shearing force strain grid joint parts 5 of the two shearing force strain grids 1 in each group are opposite, so that the resistance changes of the two shearing force strain grids 1 in each group are different, and the shearing force component force (detailed below) applied to each group of the shearing force strain grids 1 can be obtained according to a formula. And then according to the parallelogram rule, the shearing force components acting along the arrangement directions of the shearing force strain grids 1 of different groups are synthesized, so that the flexible sensor can measure the shearing force (including the magnitude and the direction of the shearing force) in any direction.
The pressure strain grid 2 can generate resistance change under the action of pressure, and the pressure F borne by the flexible sensor can be obtained according to the relationship between the resistance change and the pressure strain, the pressure stress and the pressureP。
Resistance change versus compressive strain: Δ R1＝K1ε1(1-1)；
Relationship of compressive strain to compressive stress:
Figure BDA0002391105150000101
relationship of compressive stress to pressure:
Figure BDA0002391105150000102
wherein E is1Modulus of elasticity, K, of microstructure 7 to cover the compressive strain gate 21Is the strain sensitivity coefficient, epsilon, of the compressive strain gage 21For compressive strain, σ is compressive stress, Δ R1For the change in resistance of the compressive strain gate 2, d1The width of the microstructure 7 of the compressively strained gate 2.
Resistance change Δ R1Can be measured to obtain the elastic modulus E1Strain sensitivity coefficient K1The pressure stress sigma of the pressure strain grid 2 can be obtained by combining the formulas (1-1) and (1-2) and substituting the sigma into the formula (1-3), namely the pressure on the flexible sensor can be obtained.
Preferably, the two sets of shear strain grids 1 may be arranged orthogonally along the X-axis and the Y-axis, i.e. the straight lines on which the two sets of shear strain grids 1 lie are orthogonal to each other.
The method for calculating the shear force component received by the group of shear strain grids 1 is described below by taking the group of shear strain grids 1 arranged on the X axis as an example, and the method for calculating the shear force component received by the group of shear strain grids 1 arranged on the Y axis is the same.
In a group of shear strain grids 1 arranged on an X axis, two shear strain grids 1 are respectively positioned on two sides of an origin of the X axis. Assuming that the shearing force borne by the flexible sensor is a shearing force component F on the X axisτThe two shear strain grids 1 of the set are subjected to asymmetric (different) compressive stresses σ in the positive direction of the X-axis21And σ22。
Along shear force component FτIs located forward (X-axis positive direction), i.e. the shear strain grid 1 located in the X-axis positive direction is subjected to a compressive stress σ21Comprises the following steps:
Figure BDA0002391105150000111
along shear force component FτIs in the rear direction, i.e. in the negative X-axis direction, the shear strain grid 1 is subjected to a compressive stress σ22Comprises the following steps:
Figure BDA0002391105150000112
wherein, η21And η22The position of the microstructure 7 of the corresponding shear strain grid 1 is deviated from the position of the metal line segment 11 of the corresponding shear strain grid 1, namely the distance m between the radial center line h of the microstructure 7 and the radial center line t of the metal line segment 11 of the shear strain grid 1; fpIs the pressure to which the flexible sensor is subjected, L21And L22Height of microstructure 7 of corresponding shear strain grid 1, d21And d22The width of the microstructure 7 of the corresponding shear strain gate 1.
Compressive stress σ experienced by a set of shear strain grids 1 in a known X-axis21And σ22On the premise of (1), the shearing force component F borne by a group of shearing force strain grids 1 on the X axis can be determined according to the formulas (2-3) and (3-3)τ. Shear force component F applied to different groups of shear strain grids 1τAnd synthesizing the shearing force borne by the flexible sensor according to the parallelogram rule.
The pressure F to which the flexible sensor is subjected can also be determined again according to equations (2-3) and (3-3)pWhen F is determined by the formulae (2-3) and (3-3)pWith F determined by the formula (1-3)pWhen different, the accurate F can be obtained by taking the average valuep。
How to obtain the compressive stress sigma to which the shear strain gage 1 is subjected is described below21And σ22。
The shear strain grid 1 can generate resistance change under the action of force, and corresponding stress can be obtained according to the relationship between the resistance change and strain and stress.
For component F along shearing forceτIn the direction of the shear strain grid 1:
resistance change versus compressive strain: Δ R21＝K21ε21(2-1)；
Relationship of compressive strain to compressive stress:
Figure BDA0002391105150000121
for the component force F along the shearing forceτThe direction of (1) is located at the rear:
resistance change versus compressive strain: Δ R22＝K22ε22(3-1)；
Relationship of compressive strain to compressive stress:
Figure BDA0002391105150000122
wherein E is21And E22Modulus of elasticity, K, of microstructure 7 for corresponding shear strain grid 121And K22Is expressed as the strain sensitivity coefficient, epsilon, of the corresponding shear strain grid 121And ε22Is the compressive strain of the corresponding shear strain grid 1.
Resistance change Δ R21And Δ R22Can be measured to obtain the elastic modulus E21And E22Strain sensitivity coefficient K21And K22Depending on the material.
When the materials of the two shear strain grids 1 are the same, the strain sensitivity coefficient K21And K22Are equal. When the materials of the microstructures 7 corresponding to the two shear strain grids 1 are the same, the elastic modulus E21And E22Are equal. When the shapes of the microstructures 7 corresponding to the two shear strain grids 1 are the same, L21And L22Equal, d21And d22Are equal.
The use of the flexible sensor is described by taking the example of detecting the stress on the surface of the skin.
The skin in the area of the adhesive is first cleaned and then the flexible sensor is applied to the skin surface, after which an external load is applied to the flexible sensor. The applied load is first applied to the microstructured layer and creates a stress concentration in the microstructured layer that transfers the force to the signal sensitive layer. The signal sensitive layer generates strain under the action of external force to generate resistance change, so that shearing force and pressure are measured, and the display is displayed.
The flexible sensor has the characteristics of low cost, high sensitivity, good repeatability and capability of identifying the pressure stress and the shear stress, can identify the magnitude and the direction of the shear stress, and has a good application prospect in the fields of biological health detection, human-computer interaction, electronic skin and the like, and the micro-structural layer simulates the fingerprint of a human palm so as to help the flexible sensor to identify the stresses in different directions and different types.
It should be understood that the flexible material may be PDMS (polydimethylsiloxane) or the like.
It should be understood that the above embodiments are only exemplary and are not intended to limit the present invention. Various modifications and alterations of the above-described embodiments may be made by those skilled in the art in light of the teachings of the present invention without departing from the scope thereof.

Claims (13)

1. A flexible sensor capable of identifying pressure and shear force comprises a substrate (6), and is characterized by further comprising a signal sensitive layer and a microstructure layer, wherein the signal sensitive layer comprises a strain gate and is laminated on the upper surface of the substrate (6);
the strain grids comprise a plurality of shear strain grids (1) arranged along the circumferential direction and pressure strain grids (2) located in the centers of the shear strain grids (1), each shear strain grid (1) and each pressure strain grid (2) are provided with a plurality of metal line segments which are connected end to form a snake shape, the shear strain grids (1) are arranged in pairs, the flexible sensor comprises at least two groups of shear strain grids (1), and two shear strain grids (1) in the same group are located on two sides of each pressure strain grid (2) along the radial direction of the circumference;
the microstructure layer comprises a plurality of microstructures (7), and the microstructure layer comprises a pressure strain grid combination part (4) and a shear strain grid combination part (5);
the microstructure (7) of the compressive strain grid combination part (4) covers the metal line segment of the compressive strain grid (2) in the radial direction of the circumference, the microstructure (7) of the shear strain grid combination part (5) is provided with a part exceeding the metal line segment of the corresponding shear strain grid (1) in the radial direction of the circumference, and a combination formed by the shear strain grid combination parts (5) and the corresponding shear strain grids (1) is symmetrical about the center of the circumference.
2. The flexible pressure and shear force identifiable sensor according to claim 1, further comprising a conductive network (3), wherein the conductive network (3) leads out both ends of the pressure strain grid (2) and each shear strain grid (1) for forming a conductive loop.
3. A flexible sensor capable of identifying pressure and shear force according to claim 2, wherein the conductive network (3) comprises a connection line (31) and a lead (32), the connection line (31) connects each shear strain grid (1) and the pressure strain grid (2) together, and the connection line (31) and the lead (32) are used for forming an electrical circuit between the strain grids and an external electrical device.
4. Flexible sensor capable of identifying pressure and shear force according to claim 1, characterized in that the pressure strain grid (2) generates a change in resistance Δ R when the flexible sensor is subjected to pressure1And identifying the pressure F applied to the flexible sensor according to the formula (1-1), the formula (1-2) and the formula (1-3)P：
ΔR1＝K1ε1(1-1)；
Figure FDA0002391105140000021
Figure FDA0002391105140000022
Wherein E is1Is the elastic modulus, K, of the microstructure (7) of the compressive strain gate (2)1Is the strain sensitivity coefficient, epsilon, of the pressure strain grid (2)1Is the compressive strain of the compressive strain gauge (2), σ is the compressive stress of the compressive strain gauge (2), d1The width of the microstructure (7) being a compressive strain gate (2);
when the flexible sensor is subjected to shear force, the same group of shear strain grids (1) is subjected to shear force component FτAlong the shear force component FτThe shear strain grids (1) positioned in the front and the rear directions respectively generate resistance changes delta R21And Δ R22The flexible sensor identifies the shear force component F according to formula (2-1), formula (2-2), formula (2-3), formula (3-1), formula (3-2), and formula (3-3)τ：
For the component force F along the shearing forceτThe shear strain grid (1) being located forward:
ΔR21＝K21ε21(2-1)；
Figure FDA0002391105140000023
Figure FDA0002391105140000024
for the component force F along the shearing forceτThe shear strain grid (1) with a direction behind:
ΔR22＝K22ε22(3-1)；
Figure FDA0002391105140000031
Figure FDA0002391105140000032
wherein E is21And E22The modulus of elasticity, K, of the microstructure (7) of the corresponding shear strain grid (1)21And K22For the corresponding strain sensitivity coefficient, epsilon, of the shear strain grid (1)21And ε22For corresponding compressive strain, σ, of the shear strain grid (1)21And σ22For the corresponding compressive stress of the shear strain grid (1), η21And η22Is as followsThe microstructure of the shear strain grid (1) is offset from the position of the corresponding metal line segment of the shear strain grid (1), L21And L22Is the height of the microstructure (7) of the corresponding shear strain grid (1), d21And d22Is the width of the microstructure (7) of the respective shear strain gate (1);
the shearing force borne by the flexible sensor is the shearing force component F identified by the shearing force strain grids (1) of different groupsτSynthesized according to the quadrilateral rule.
5. The identifiable pressure and shear flexible sensor according to any of claims 1-4, characterized in that the flexible sensor comprises two sets of the shear strain grids (1), the two sets of the shear strain grids (1) being arranged orthogonally.
6. The flexible pressure and shear force sensor as claimed in any one of claims 1 to 4, wherein the shear strain grid (1) comprises a plurality of arc-shaped metal wire segments arranged at intervals along the radial direction and connected into a whole, and the lengths of the metal wire segments arranged in sequence from the outside to the inside along the radial direction are gradually reduced so that the shear strain grid (1) is in a fan shape.
7. Flexible sensor capable of identifying pressure and shear force according to claim 6, characterized in that the microstructures (7) of the shear strain grid connection (5) are cylinders and are arranged in a plurality of arcs concentric with the shear strain grid (1), or the microstructures (7) of the shear strain grid connection (5) are in the shape of arcs concentric with the shear strain grid (1),
a plurality of microstructures (7) are arranged on each metal wire section of the shear strain grid (1) at intervals.
8. Flexible sensor of the kind that can identify pressure and shear forces according to any of claims 1-4, characterized in that the shear strain grid (1) is integrally formed by bending a metal wire multiple times in a serpentine shape.
9. Flexible sensor of identifiable pressure and shear force according to one of claims 1-4, characterized in that the metal wire sections of the pressure-strain grid (2) are located on a plurality of concentric circular tracks and the pressure-strain grid (2) is disc-shaped.
10. The pressure and shear identifiable flexible sensor according to claim 9, characterized in that the microstructures (7) of the compressive strain grating bond (4) are cylinders and are arranged in a plurality of rings concentric with the compressive strain grating (2), or the microstructures (7) of the compressive strain grating bond (4) are ring-shaped concentric with the compressive strain grating (2),
a plurality of microstructures (7) are arranged on each metal wire section of the compressive strain gate (2) at intervals.
11. Flexible sensor capable of identifying pressure and shear forces according to any of claims 1 to 4, characterized in that the microstructure (7) of the compressive strain gate bonding (4) covers the metal wire section of the compressive strain gate (2) exactly in the radial direction of the circumference or has a portion beyond the metal wire section of the compressive strain gate (2).
12. Flexible sensor of the kind that can identify pressure and shear forces according to any of claims 1-4, characterized in that the pressure-strain grid (2) comprises a plurality of semicircular wire segments distributed on both sides of one diameter of the circumference so as to form two pressure-strain grid parts that are connected at the center of the circumference.
13. The flexible pressure and shear force sensor of any one of claims 1 to 4, wherein the microstructure layer further comprises a flexible substrate, the plurality of microstructures (7) are carried on the flexible substrate, the microstructures (7) are cantilever structures and fixed ends thereof are provided on the flexible substrate.
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