High-stretchability capacitance-piezoresistive dual-mode flexible skin-like system

Abstract

The invention discloses a capacitance-piezoresistive type dual-mode flexible skin-like system with high stretchability. According to the invention, the sponge composite sensing unit presents two different states of an insulator and a conductor under the action of pressure, dual-mode measurement of proximity sense and pressure sense is realized by adopting a single-sensing-body mechanism, and when a measured object is not contacted, the sensing unit works in a high-resistance-state dielectric state, so that capacitive proximity sense measurement can be realized; after a measured object is contacted, the sensing unit generates a percolation phenomenon under the action of pressure and is adjusted to be in a low-resistance state conductor state, piezoresistive pressure touch measurement can be realized, the sensing electrode layer adopts a snakelike island-bridge structure, the tensile deformation of a skin-like system is limited in a snakelike wire part, and on the premise that the structural flexibility and stretchability of the measurement unit are ensured, the measurement precision is improved. And the coupling response between units in the array is reduced.

Description

Technical Field

[0001] The present invention relates to a flexible skin-like system in the field of sensors, and in particular to a highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system. Background Art

[0002] Inspired by the biological mechanoreceptors of real human skin, flexible tactile sensors with high structural flexibility and stretchability can intuitively convert mechanical deformation caused by external pressure, temperature, vibration or distance changes into obtainable physical stimulation even when repeatedly bent, stretched and twisted. Therefore, they have great application potential in soft robots, electronic skins, stretchable touch displays, health monitoring, medical diagnosis and other human-computer interactions. Arrayed flexible skin-like systems containing flexible tactile sensors have good repeatability, low temperature sensitivity, low power consumption and high spatial resolution, and have gradually been applied to the reconstruction of tactile force functions of intelligent robot hands. However, the following key points and problems continue to emerge during use:

[0003] 1) Robots are faced with various safety and predictability issues when used in human-computer interaction. Only by fully perceiving the real-time changes in the external environment, especially the distance, position, shape and other information of obstacles, and avoiding unnecessary collisions, can the safety of interaction between robots and humans be guaranteed.

[0004] 2) Introducing soft materials into the preparation of dielectrics and electrode substrates has greatly improved the flexibility of the sensor body to some extent. However, since the conductive electrodes are mostly rigid metals without sufficient mechanical compliance to adapt to various mechanical deformations, most flexible skin-like systems are still limited by conformal stretchability, especially on curved surfaces. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system. The present invention utilizes the two different states of insulator and conductor presented by the sensitive unit under different pressures, and adopts the mechanism of a single sensor to realize the dual-mode measurement of proximity and pressure touch. When the object to be measured is not in contact, the sensitive unit works in a high-resistance dielectric state, which can realize capacitive proximity measurement. After contacting the object to be measured, the sensitive unit produces percolation phenomenon under the action of pressure and adjusts to a low-resistance conductor state, which can realize piezoresistive pressure touch measurement. The sensing electrode layer adopts a serpentine island-bridge structure to limit the tensile deformation of the skin-like system to the serpentine wire part. Under the premise of ensuring the flexibility and stretchability of the measurement unit structure, the coupling response between the units within the array is reduced.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] 1. A highly stretchable capacitive-piezoresistive dual-modal flexible skin-like system

[0008] The skin-like system includes a sensing unit, which includes a stacked sponge composite sensitive unit and a sensing electrode unit, wherein the surface of the sponge composite sensitive unit serves as a surface in contact with the object to be measured; when the object to be measured is not in contact with the sponge composite sensitive unit, the sponge composite sensitive unit is in an insulating state, and when the object to be measured is in contact with the sponge composite sensitive unit, the sponge composite sensitive unit is in a conductive state.

[0009] The sensing electrode unit includes a first sensing electrode layer and a second sensing electrode layer which are stacked, the first sensing electrode layer is in close contact with the sponge composite sensitive unit, the first sensing electrode layer includes a first sensing electrode, a second sensing electrode and a longitudinal serpentine wire, the first sensing electrode and the second sensing electrode are both spiral-shaped, the spiral-shaped first sensing electrode and the spiral-shaped second sensing electrode are arranged at intervals to form a mosquito-repellent-coil-shaped electrode assembly, the first sensing electrode layer is provided with N×N mosquito-repellent-coil-shaped electrode assemblies arranged in an array, the first sensing electrodes in two mosquito-repellent-coil-shaped electrode assemblies adjacent in the longitudinal direction are connected by the longitudinal serpentine wire to form a longitudinal sensing unit; the second sensing electrode layer includes a transverse serpentine wire, the second sensing electrodes in two mosquito-repellent-coil-shaped electrode assemblies adjacent in the transverse direction are connected by the transverse serpentine wire to form a transverse sensing unit.

[0010] The sponge composite sensitive unit is also covered with a TPU packaging film.

[0011] The sponge composite sensitive unit is a composite material prepared by using polydimethylsiloxane as a flexible substrate and conductive carbon black particles as fillers. The composite material is a sponge-like porous structure with a pore size of μm level. Perfluorotributylamine is used as a sacrificial solution during the preparation process.

[0012] The preparation method of the sponge composite sensitive unit comprises the following steps:

[0013] Firstly, the base gel and the curing agent are mixed to obtain a polydimethylsiloxane pre-solution, and then perfluorotributylamine is dispersed in the polydimethylsiloxane pre-solution and stirred for 5 minutes to prepare a PDMS-C12F27 emulsion; then, the conductive carbon black particles are added to the PDMS-C12F27 emulsion and stirred thoroughly, and then poured into a mold and placed in a vacuum dryer for degassing; thereafter, the mixture is cured in a vacuum drying oven, and the cured composite material is ultrasonically cleaned, and finally dried to remove moisture to obtain a sponge composite sensitive unit.

[0014] 2. A method for perceiving proximity and pressure touch

[0015] The sensing method adopts the highly stretchable capacitive-piezoresistive dual-modal flexible skin-like system, and the sensing method includes:

[0016] When the measured object is not in contact with the skin-like system, the sensor capacitance change of the mosquito coil-shaped electrode assembly in the activated state is measured, and compared with the calibrated sensor capacitance change-distance curve to calculate the distance between the measured object and the skin-like system;

[0017] The object under test contacts the surface of the skin-like system, and the change in the sensor resistance of the mosquito-repellent coil-shaped electrode assembly in the activated state is measured and compared with the sensor resistance change-normal pressure curve to calculate the normal pressure of the object under test.

[0018] The present invention has the following beneficial effects:

[0019] 1) According to the percolation effect of conductive composite materials under load, the differential response of sensitive units in different load areas can be used to work in both capacitive and piezoresistive measurement states, realizing a distributed robot proximity and pressure tactile dual-modal intelligent perception reconstruction method based on the principle of single-body tactile sensing, which is crucial to further improve the accuracy and safety of human-computer interaction.

[0020] 2) Introducing the serpentine island bridge structure into the preparation of metal sensing electrodes can reduce the coupling response between units within the array while ensuring the improvement of the flexibility and stretchability of the sensor, thereby ensuring accurate pressure mapping. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is an exploded view of the sensor structure of the present invention.

[0022] Figure 2 It is a schematic diagram of the structure of the first sensing electrode layer of the present invention.

[0023] Figure 3 It is a schematic diagram of the structure of the second sensing electrode layer of the present invention.

[0024] Figure 4 It is a schematic diagram of the structure of the first sensing electrode and the second sensing electrode in the sensing unit of the present invention.

[0025] Figure 5 It is a schematic diagram of the capacitive proximity measurement principle of the sensor of the present invention.

[0026] Figure 6 It is a schematic diagram of the equivalent dielectric constant measured by the proximity sensor of the present invention.

[0027] Figure 7 It is a schematic diagram of the piezoresistive tactile pressure measurement principle of the sensor of the present invention.

[0028] In the figure: 1. sponge composite sensitive unit, 2. sensing electrode unit, 3. TPU packaging film, 4. first sensing electrode layer, 5. second sensing electrode layer, 6. first sensing electrode, 7. longitudinal serpentine wire, 8. electrical contact point, 9. measured object, 10. equivalent sensing resistor, 11. second sensing electrode, 12. transverse serpentine wire. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] The present invention proposes a highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system. The skin-like system includes a sensing unit, and the sensing unit includes a stacked sponge composite sensitive unit 1 and a sensing electrode unit 2. The surface of the sponge composite sensitive unit 1 serves as the surface in contact with the object 9 to be measured; when the object 9 to be measured is not in contact with the sponge composite sensitive unit 1, the sponge composite sensitive unit 1 is in a high-resistance insulator state, and when the object 9 to be measured is in contact with the sponge composite sensitive unit 1, the sponge composite sensitive unit 1 is in a conductor state. The present invention utilizes the two different states of the sensitive unit 1, namely, an insulator and a conductor, under different pressures, and adopts a single sensor mechanism to achieve dual-mode measurement of proximity and pressure touch.

[0031] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the sensing electrode unit 2 is a double-layered flexible printed circuit board, specifically including a first sensing electrode layer 4 and a second sensing electrode layer 5 arranged in a stacked manner. The first sensing electrode layer 4 is in close contact with the sponge composite sensitive unit 1. The first sensing electrode layer 4 includes a first sensing electrode 6, a second sensing electrode 11 and a longitudinal serpentine wire 7. The first sensing electrode 6 and the second sensing electrode 11 are both spiral-shaped. The arrangement of the sensing electrodes in a spiral pattern can effectively enhance the edge effect of the capacitor electric field, thereby improving the proximity measurement sensitivity. The spiral first sensing electrode 6 and the spiral second sensing electrode 11 are arranged at intervals to form a mosquito coil-shaped electrode assembly, and the first sensing electrode 6 in each mosquito coil-shaped electrode assembly is denoted as S x , the second sensing electrode 11 is denoted as S yAnd form a group of sensing electrode pairs. The first sensing electrode layer 4 is provided with N×N mosquito coil-shaped electrode assemblies arranged in the form of an array. The first sensing electrodes 6 in the two adjacent mosquito coil-shaped electrode assemblies are connected by a longitudinal serpentine wire 7 to form a longitudinal sensing unit. The longitudinal sensing unit is an island-bridge structure with the first sensing electrode 6 as an island and the longitudinal serpentine wire 7 as a bridge; the second sensing electrode layer 5 includes a transverse serpentine wire 12. The second sensing electrodes 11 in the two adjacent mosquito coil-shaped electrode assemblies are connected to the transverse serpentine wire 12 through an electrical contact point 8 to form a transverse sensing unit. The transverse sensing unit is an island-bridge structure with the second sensing electrode 11 as an island and the transverse serpentine wire 12 as a bridge. The design of the island bridge structure limits the tensile deformation of the skin-like system to the serpentine wire part, and reduces the coupling response between the units in the array while ensuring the flexibility and stretchability of the measurement unit structure. The number of longitudinal sensing units and transverse sensing units is N. Figure 1 and Figure 2 In the embodiment, the mosquito coil-shaped electrode assembly of the sensing electrode unit 2 is 3×3. The three transverse serpentine wires 12 are respectively denoted as T j1 , T j2 and T j3 , the three longitudinal serpentine conductors 7 are respectively denoted as T i1 , T i2 and T i3 When the longitudinal and transverse serpentine wires (7 and 12) connecting the two first sensing electrodes 6 and the second sensing electrodes 11 in the same sensing unit are activated at the same time, the actual value of the sensing capacitance or sensing resistance in the sensing unit can be measured. The three longitudinal serpentine wires 7 and the three transverse serpentine wires 12 are activated in sequence, and the sensing capacitance or sensing resistance in the 3×3 sensing units can be measured in real time by scanning the circuit.

[0032] The sponge composite sensitive unit 1 is a composite material prepared with polydimethylsiloxane (PDMS) as a flexible substrate and conductive carbon black particles (CB) as a filler. The composite material is a sponge-like porous structure with a pore size of μm level. Perfluorotributylamine (C12F27) is used as a sacrificial solution during the preparation process.

[0033] The preparation method of the sponge composite sensitive unit 1 comprises the following steps:

[0034] First, a base gel and a curing agent are mixed in a ratio of 20:1 to obtain a polydimethylsiloxane (PDMS) pre-solution, and then perfluorotributylamine (C12F27) is dispersed in the polydimethylsiloxane (PDMS) pre-solution at a concentration ratio of 40 vol%, and the mixture is stirred at 2000 rpm for 5 minutes to prepare a stable PDMS-C12F27 emulsion; then, conductive carbon black particles are added to the PDMS-C12F27 emulsion at a weight percentage of 1.5% and stirred thoroughly, and then cast into an aluminum alloy mold and placed in a vacuum dryer for a degassing process at 30°C for 30 minutes; then, the mixture is cured in a vacuum drying oven at 80°C for two hours, and the cured composite material is placed in deionized water for ultrasonic cleaning for 6 hours, and finally dried at 60°C for 1 hour to remove moisture to obtain a sponge composite sensitive unit 1.

[0035] A TPU (Thermoplastic urethanes) packaging film 3 is also attached to the sponge composite sensitive unit 1 .

[0036] The present invention also proposes a method for sensing proximity and pressure touch, the sensing method adopts a highly stretchable capacitive-piezoresistive dual-modal flexible skin-like system, and the sensing method includes:

[0037] When the object 8 under test is not in contact with the skin-like system and gradually approaches the skin-like system, the sponge composite sensitive unit 1 is not subjected to external pressure and presents a high-resistance insulator form. Therefore, the object 8 under test, the sponge composite sensitive unit 1 and the air can be regarded as dielectrics with different dielectric constants. As the distance of the object 8 under test approaches, the equivalent dielectric constant changes, and causes the sensing capacitance to change. The sensing capacitance change of the mosquito-repellent coil-shaped electrode assembly in the activated state is measured and compared with the calibrated sensing capacitance change-distance curve to calculate the distance between the object 8 under test and the skin-like system; the activation state of the mosquito-repellent coil-shaped electrode assembly is scanned line by line.

[0038] The object 8 to be measured contacts the surface of the skin-like system (i.e., the TPU packaging film 3). At this time, under the action of the external load, the conductive particles inside or on the surface of the sensitive unit 1 move, causing the conduction path to be rearranged, and the high-resistance effect of the microresistor gradually weakens, and percolation occurs at a specific threshold value, which is manifested as a sharp decrease in conductivity. The potential drop inside the conductive composite material can be ignored, and the sensitive unit 1 is adjusted to a conductor state, which is equivalent to a sensing resistor. The sensing resistor is connected in series with the first sensing electrode 6 and the second sensing electrode 11 to form a conductive path. Therefore, when the object 8 to be measured contacts the surface of the sensor, a pressure tactile force is generated on the contact surface, causing the sponge composite sensitive unit 1 to deform, and the sensing resistor also changes. The change in the sensing resistance of the mosquito coil-shaped electrode assembly in the activated state is measured, and compared with the sensing resistance change-normal pressure curve, the normal pressure of the object 8 to be measured is calculated, and the measurement of piezoresistive pressure tactile sensation is realized.

[0039] The specific principles are as follows:

[0040] like Figure 5 and Figure 6 As shown, when the measured object 9 gradually approaches the sensor, the sponge composite sensitive unit 1 is not subjected to external pressure and presents a high-resistance insulator form. Therefore, the measured object 9, the sponge composite sensitive unit 1 and the air can be regarded as dielectrics with different dielectric constants, and the size of the sensing capacitor is determined by the common equivalent dielectric constant of the measured object 8, the sponge composite sensitive unit 1 and the air.

[0041] The sensing electrodes in the sensing unit are arranged in a centrally symmetrical spiral pattern. To accurately calculate the size of the sensing capacitance, the first sensing electrode 6 and the second sensing electrode 11 in each mosquito coil-shaped electrode assembly are equivalent to two coplanar electrodes with a width of w and a length of l. The calculation formula of the length l is shown in formula (1):

[0042]

[0043] Where n is the number of turns of the helix, D is the outer diameter, and d is the inner diameter.

[0044] The height of the highest point of the measured object 9 from the first sensing electrode 6 and the second sensing electrode 11 is defined as h 1 The height of the lowest point of the measured object 9 (the distance between the measured object 9 and the sensor) from the first sensing electrode 6 to the second sensing electrode 11 is h 2 , the thickness of sensitive unit 1 is h 3 , then as the distance of the measured object 9 approaches, h 1 and h 2 The height will be adjusted accordingly, and the equivalent dielectric constant ε eff Changes occur, as shown in formula (2):

[0045]

[0046] Among them, ε obj is the dielectric constant of the object 9, ε air is the dielectric constant of air, ε com is the dielectric constant of the sponge composite sensitive unit 1, ε i is the i-th equivalent dielectric constant, and other related parameters have the following relationship:

[0047]

[0048] is the complete elliptic integral of the first kind, k = k i , k 0 ', k i ', k 0 , k i and k i ' is the first and second equivalent elliptic modulus, and the two initial modulus parameters k 0 , k 0 ' can be calculated based on the structural parameters of the electrodes on the same surface:

[0049]

[0050] Among them, h i (i=1, 2, 3) is the thickness of the layered structure, w and a represent the width of the first sensing electrode 6 and the second sensing electrode 11 and half of the distance between the first sensing electrode 6 and the second sensing electrode 11 , respectively.

[0051] Therefore, under the premise of knowing the dielectric constant of the measured object 9, the relationship between the relative change of the sensing capacitance and the distance can be obtained:

[0052]

[0053] At this point, we only need to pay attention to the sensor capacitor C s The change of the measured object 9 is the distance from the sensor. 2 By using the functional relationship of , capacitive proximity measurement can be realized.

[0054] The sponge composite sensitive unit 1 uses carbon black particles as a conductive filler, and combined with the graded sponge structure, two basic micro-nano structures appear, including a conductive path and a separated electrode plate, which can basically be equivalent to a micro-resistor and a micro-capacitor. When the object to be measured contacts the surface of the skin-like system, the sensitive unit 1 is subjected to the external load, and the movement of the conductive particles inside or on the surface causes the conduction path to be rearranged, the high-resistance effect of the micro-resistor gradually weakens, and percolation occurs at a specific threshold and manifests as a sharp decrease in conductivity. The potential drop inside the conductive composite material can be ignored, and the sensitive unit 1 is adjusted to a conductor state, which is equivalent to a sensing resistor 10. The sensing resistor 10 is connected in series with the two first sensing electrodes 6 and the second sensing electrode 11 to form a conductive path, such as Figure 7 Therefore, when the object 9 contacts the sensor surface, the contact surface generates a pressure tactile force, causing the sponge composite sensitive unit 1 to deform, and at the same time, the resistance value R of the sensing resistor 10 increases. s The resistance value of the sensing resistor 10 R s The proportional relationship between the change in and the normal pressure can realize the measurement of piezoresistive pressure tactile sensation.

[0055]

[0056] Among them, R s is the sensing resistance of the sponge composite sensitive unit 1, R 0 is the measured initial resistance, is the porosity ratio of the composite material, and κ is the compression deformation.

[0057] The present invention is based on the percolation effect of conductive composite materials under load, and utilizes the differential responses of sensitive units in different load areas. It can work in capacitive and piezoresistive measurement states, and realizes a dynamic reconstruction strategy and proximity recognition detection method of distributed robot pressure tactile perception based on the principle of single tactile sensing. When not in contact with the object to be measured, the sensitive unit works in a high-resistance dielectric state, and capacitive proximity measurement can be realized. After contacting the object to be measured, the sensitive unit produces percolation under the action of pressure and is adjusted to a low-resistance conductor state, and piezoresistive pressure tactile measurement can be realized. Compared with traditional flexible dielectric materials, the sensing electrode layer adopts a serpentine island-bridge structure, which limits the tensile deformation of the skin-like system to the serpentine wire part. Under the premise of ensuring the flexibility and stretchability of the measurement unit structure, the coupling response between units in the array is reduced, and the high sensitivity of flexible proximity and three-dimensional pressure tactile measurement is guaranteed.

[0058] Finally, it should be noted that the above embodiments and explanations are only used to illustrate the technical solution of the present invention rather than to limit it. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope disclosed in the technical solution of the present invention, which should be included in the scope of protection of the claims of the present invention.

Claims

1. A highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system, characterized in that: The invention comprises a sensing unit, wherein the sensing unit comprises a sponge composite sensitive unit (1) and a sensing electrode unit (2) arranged in a stacked manner, wherein the surface of the sponge composite sensitive unit (1) serves as a surface in contact with a measured object (9); when the measured object (9) is not in contact with the sponge composite sensitive unit (1), the sponge composite sensitive unit (1) is in an insulating state, and when the measured object (9) is in contact with the sponge composite sensitive unit (1), the sponge composite sensitive unit (1) is in a conductive state.

2. A highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system according to claim 1, characterized in that: The sensing electrode unit (2) comprises a first sensing electrode layer (4) and a second sensing electrode layer (5) which are stacked, the first sensing electrode layer (4) being in close contact with the sponge composite sensing unit (1), the first sensing electrode layer (4) comprising a first sensing electrode (6), a second sensing electrode (11) and a longitudinal serpentine wire (7), the first sensing electrode (6) and the second sensing electrode (11) both being spiral-shaped, the spiral-shaped first sensing electrode (6) and the spiral-shaped second sensing electrode (11) being arranged at intervals to form a mosquito coil-shaped electrode assembly, the first sensing electrode layer (4) being provided with N×N mosquito coil-shaped electrode assemblies arranged in an array, the first sensing electrodes (6) in two mosquito coil-shaped electrode assemblies adjacent to each other in the longitudinal direction being connected by the longitudinal serpentine wire (7) to form a longitudinal sensing unit; the second sensing electrode layer (5) comprising a transverse serpentine wire (12), the second sensing electrodes (11) in two mosquito coil-shaped electrode assemblies adjacent to each other in the transverse direction being connected by the transverse serpentine wire (12) to form a transverse sensing unit.

3. The highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system according to claim 1, characterized in that: The sponge composite sensitive unit (1) is also adhered with a TPU packaging film (3).

4. The highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system according to claim 1, characterized in that: The sponge composite sensitive unit (1) is a composite material prepared by using polydimethylsiloxane as a flexible substrate and conductive carbon black particles as a filler. The composite material is a sponge-like porous structure with a pore size of μm level. During the preparation process, perfluorotributylamine is used as a sacrificial solution.

5. The highly stretchable capacitive-piezoresistive dual-mode flexible skin-like system according to claim 1, characterized in that: The preparation method of the sponge composite sensitive unit (1) comprises the following steps: First, a base gel and a curing agent are mixed to obtain a polydimethylsiloxane pre-solution, and then perfluorotributylamine is dispersed in the polydimethylsiloxane pre-solution and stirred for 5 minutes to prepare a PDMS-C12F27 emulsion; then, conductive carbon black particles are added to the PDMS-C12F27 emulsion and stirred for mixing, and then poured into a mold and placed in a vacuum dryer for degassing; then the mixture is cured in a vacuum drying oven, and then the cured composite material is ultrasonically cleaned, and finally dried to remove moisture to obtain a sponge composite sensitive unit (1).

6. A method for sensing proximity and pressure touch, characterized in that: The sensing method adopts the highly stretchable capacitive-piezoresistive dual-modal flexible skin-like system according to claim 1, and the sensing method comprises: When the measured object (8) is not in contact with the skin-like system, the sensor capacitance change of the mosquito coil-shaped electrode assembly in the activated state is measured, and compared with the calibrated sensor capacitance change-distance curve to calculate the distance between the measured object (8) and the skin-like system; The object to be measured (8) contacts the surface of the skin-like system, and the change in the sensing resistance of the mosquito coil-shaped electrode assembly in an activated state is measured and compared with the sensing resistance change-normal pressure curve to calculate and obtain the normal pressure of the object to be measured (8).

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