Flexible capacitive pressure sensor with high stability, time delay calibration method and pressure detection method thereof

Abstract

The present application selects foamed silicone rubber as a flexible dielectric layer material in a flexible capacitive pressure sensor, obtaining a high-stability pressure sensor. Further, the thickness of the flexible dielectric layer and the hardness of the foamed silicone rubber are selected to balance high detection sensitivity and high range of the sensor. Still further, the closed-cell structure in the foamed silicone rubber is opened to improve the detection sensitivity of the sensor, and when part of the closed-cell structure in the foamed silicone rubber is opened, not only the detection sensitivity of the sensor is improved, but also the high detection range is balanced. Still further, the cells in the foamed silicone rubber are designed to be arranged in a single layer to improve controllability. Considering that the reversible deformation part of the flexible dielectric layer changes with time during creep, the present application introduces a time parameter, provides a time delay calibration method, and introduces a time parameter in actual pressure detection for dynamic pressure detection, which can further improve the stability of the sensor.

Description

Technical Field

[0001] This invention belongs to the field of flexible technology and pressure sensing technology, and specifically relates to a highly stable flexible capacitive pressure sensor, its delay calibration method and pressure detection method. Background Technology

[0002] In recent years, with the development of flexible electronics technology, pressure distribution detection in flexible bodies has become a research hotspot in various countries. Currently, various types of flexible pressure sensors have been developed, such as capacitive, piezoresistive, and piezoelectric sensors. Their principle is based on the change in electrical parameters such as resistance, capacitance, or current of conductive materials or structures under pressure, and the magnitude of pressure is detected by these changes in electrical parameters. Detection stability is a key performance indicator for flexible pressure sensors. Highly stable flexible pressure sensors have broad application prospects in flexible electronics technology, such as in smart clothing, smart homes, smart robots, and biosimulation.

[0003] Flexible capacitive pressure sensors are a commonly used type of flexible pressure sensor. They consist of a flexible top electrode, a flexible bottom electrode, and a flexible dielectric material with conductive and insulating properties located between them. They offer significant advantages such as simple structure, low power consumption, and good stability. Currently, among the companies that have commercialized high-precision pressure monitoring, Canada's Xsensor and Germany's NOVEL employ capacitive solutions. Xsensor's LX series pressure array sensors operate at temperatures from 10 to 45 degrees Celsius, providing accurate pressure distribution data and comprehensive human body pressure distribution data for seat design. Their advantages include high detection accuracy (±5%), a minimum detection accuracy of 0.1 psi, and the ability to measure lower load pressures. NOVEL's Pliance system integrates 1024 sensors, a sampling frequency up to 100 Hz, and a pressure range of 1-127 N / cm². 2 The detection accuracy is ±5%, the hysteresis is less than 3%, and it can be used for static measurement as well as for recording dynamic data.

[0004] In flexible capacitive pressure sensors, the flexible dielectric material is one of the key factors affecting its detection stability. Currently, the flexible dielectric material in flexible capacitive pressure sensors mainly uses elastic organic polymers, such as polyurethane foam and ethylene propylene diene monomer (EPDM). However, most organic polymers are prone to irreversible permanent deformation and changes in hardness (elastic modulus) after prolonged and heavy loads, severely affecting the accuracy of pressure detection values. For example, when using polyurethane foam as the flexible dielectric material, the foam structure undergoes irreversible changes and hardness changes under prolonged and / or heavy loads. When the load is removed, its structure cannot fully recover, leading to changes in deformation when a load is applied again, severely affecting the stability of the detection value. To improve the stability of the detection value, the sensor often needs to be recalibrated. To improve detection stability, polymers with higher modulus are usually used, resulting in smaller deformation under load, but this leads to a decrease in detection sensitivity, minimum detection range, and detection accuracy. Therefore, surface microstructuring or conductive doping of the dielectric material is often used to improve detection sensitivity. For example, Professor Shen Guozhen's research group at the Institute of Semiconductors, Chinese Academy of Sciences, successfully developed a flexible, transparent capacitive pressure sensor based on a silver nanowire / PDMS composite dielectric layer material, achieving a sensitivity of 0.831 kPa. -1 The research group of Professor Zhang Ting at the Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, utilized the natural microstructures on the surface of lotus leaves as biomimetic templates. By expanding these microstructures, they achieved synergistic changes in multiple parameters, including reduced electrode distance, increased contact area, and altered dielectric constant. This resulted in a flexible capacitive sensor with a sensitivity of 0.815 kPa⁻¹, a response time of 38 ms, and a response range of 0-50 N. Furthermore, it exhibits selective response to different mechanical forces such as pressure, torsion, and stretching. Meanwhile, the research group of Yong-Hoon Kim at Sungkyunkwan University in South Korea reported a capacitive ion-electron (CIT) pressure sensor array composed of a high-dielectric-constant ionogel membrane (IG membrane) and conductive fabric, achieving a sensitivity as high as 308 nF / kPa.

[0005] In addition, elastic organic polymer materials are basically viscoelastic materials. Viscoelastic materials have creep characteristics, that is, when a certain stress is applied, in addition to instantaneous strain, a reversible deformation that changes with time will also occur, causing the pressure detection value to change with time, further affecting the stability of the detection value.

[0006] Therefore, improving the stability of flexible capacitive pressure sensors, ensuring their sensitivity and detection range, and achieving large-area fabrication through the selection of flexible dielectric layer materials and structural design are key aspects of flexible pressure sensor fabrication. Summary of the Invention

[0007] In view of the above-mentioned technical status, the present invention aims to provide a highly stable flexible capacitive pressure sensor.

[0008] To achieve this technical objective, the inventors, after extensive materials research and experimentation, discovered that using foamed silicone rubber as the flexible dielectric material in a flexible capacitive pressure sensor can improve the stability of the sensor's detection values, resulting in a highly stable flexible capacitive pressure sensor.

[0009] Foamed silicone rubber is a porous polymer material made from silicone rubber as a matrix through a foaming process. It combines the advantages of both silicone rubber and foamed materials, possessing not only light weight, good insulation, and high compressibility, but also high resilience, excellent resistance to compression deformation and creep, low permanent deformation, and low repeated fatigue. Therefore, when foamed silicone rubber is used as the flexible dielectric material in a flexible capacitive pressure sensor, compared to materials like sponge or rubber, it significantly reduces the impact of irreversible permanent deformation and hardness changes after prolonged exposure to high loads on the stability of the detection values. Furthermore, it significantly reduces the impact of creep characteristics on the stability of the detection values. Moreover, foamed silicone rubber is resistant to high and low temperatures, thus having a wide operating temperature range, stable for use from -55℃ to 200℃.

[0010] That is, the technical solution provided by the present invention is: a highly stable flexible capacitive pressure sensor, comprising a first flexible conductive layer, a second flexible conductive layer, and a flexible dielectric layer sandwiched between the first flexible conductive layer and the second flexible conductive layer; the flexible dielectric layer material is foamed silicone rubber.

[0011] The matrix of the foamed silicone rubber is not limited, including polydimethylsiloxane polymer (PDMS), etc.

[0012] The preparation method of the foamed silicone rubber is not limited, including chemical foaming and physical foaming, such as hydrosilylation foaming and supercritical CO2 foaming.

[0013] In order to balance high detection sensitivity and high detection range, the inventors have also conducted in-depth research and exploration on the following aspects of flexible dielectric layers.

[0014] (a) The thickness of the flexible dielectric layer and the hardness of the foamed silicone rubber

[0015] For flexible capacitive pressure sensors, the relationship between capacitance, dielectric constant, and thickness is as follows: ε rLet ε0 be the relative permittivity of the flexible dielectric layer, ε0 be the vacuum permittivity, S be the area of ​​the sensing unit, and d be the distance between the first and second flexible conductive layers, i.e., the initial thickness of the flexible dielectric layer. Under pressure F, the thickness of the flexible dielectric layer changes, causing a change in the capacitance of the flexible capacitive pressure sensor. When the rate of change of the flexible dielectric layer thickness is small, the sensitivity of the capacitive pressure sensor is related to the thickness of the flexible dielectric layer and the hardness (elastic modulus) of the foamed silicone rubber. For a given flexible dielectric layer material, i.e., with the same elastic modulus, a smaller initial thickness of the flexible dielectric layer results in higher sensitivity of the capacitive sensor; conversely, for the same flexible dielectric layer thickness, a lower elastic modulus results in higher sensitivity.

[0016] (II) Cell structure of foamed silicone rubber

[0017] Under normal circumstances, such as Figure 1 As shown, the foamed silicone rubber, formed internally (between the upper surface 1 and lower surface 2 of the flexible dielectric layer) through a foaming process, has a closed-cell structure 3. This type of foamed silicone rubber is called closed-cell foamed silicone rubber. When a load pressure is applied, the closed-cell foamed silicone rubber has a small deformation because the internal air cannot be expelled, which is beneficial for improving the pressure detection range of the sensor. However, on the other hand, the small deformation will lead to a small change in capacitance, which will reduce the detection sensitivity of the sensor.

[0018] To improve the pressure detection sensitivity of the sensor, the inventors, after extensive experimental research, discovered that opening up the closed-cell structure in foamed silicone rubber, i.e., as shown in... Figure 3 , 4 As shown, by changing the closed-hole structure 3 into the open-hole structure 4, the deformation is significantly increased when the same pressure is applied to the open-hole structure, thereby improving the pressure detection sensitivity.

[0019] Furthermore, in order to balance high detection range and high detection sensitivity, it is preferable to open up only some of the closed-cell structures in the foamed silicone rubber to form an open-cell structure. That is, the foamed silicone rubber contains not only open-cell structures but also closed-cell structures.

[0020] There are no restrictions on the methods for opening up the closed-cell structure in foamed silicone rubber, including physical or chemical methods.

[0021] One approach is to employ a cutting process to transform at least some of the closed-cell structures within the foamed silicone rubber into open-cell structures. For example, Figure 2 As shown, the flexible dielectric layer is cut along a direction perpendicular to its thickness to form cutting line 5. The cut flexible dielectric layer is as follows: Figure 3 As shown. Furthermore, the degree of aperture formation can be adjusted by changing the distance between the cutting line 5 and the upper or lower surface of the flexible dielectric layer.

[0022] As another implementation method, laser drilling technology is used, such as Figure 4 As shown, a laser beam is used to irradiate foamed silicone rubber, causing at least some of its closed-cell structures to be broken down to form open-cell structures. The degree of opening is controlled by one or more of the following: laser beam wavelength, pulse width, power, beam divergence angle, and focusing state. Preferably, the laser beam irradiates the foamed silicone rubber, illuminating and locating the closed-cell structures, thereby enabling laser drilling to create open-cell structures from the closed-cell structures that require opening.

[0023] Alternatively, chemical methods can be used to open closed-cell structures. The methods disclosed in the prior art for opening closed-cell structures in foamed silicone rubber can be used in this invention.

[0024] (III) Cell distribution of foamed silicone rubber

[0025] like Figure 1-4 As shown, there are several pores inside the flexible dielectric layer. These pores may be randomly distributed, and there may be multiple pores in the thickness direction of the flexible dielectric layer.

[0026] This invention has found that, as Figure 5 As shown, when the flexible dielectric layer is designed with a single cell in the thickness direction, that is, when the cells inside the flexible dielectric layer are arranged in a single layer, compared with multiple cells in the thickness direction of the flexible dielectric layer, on the one hand, the density of the silicone is reduced and the porosity is increased. Under the same load, the thickness change is increased, thereby increasing the capacitance change and improving the sensitivity. On the other hand, when the cells are arranged in a single layer, the regular arrangement of the cells can greatly improve the stability, sensitivity and controllability of the sensor and the detection range. For example, the stability, sensitivity and detection range of the sensor can be controlled by controlling one or more of the following: cell density, cell size, distance from the upper surface to the cell, and distance from the lower surface to the cell.

[0027] When the pores inside the flexible dielectric layer are arranged in a single layer, the thickness of the flexible dielectric layer is preferably controlled at 0.6mm-1.5mm, and more preferably at 0.8mm-1.2mm.

[0028] Preferably, the distance from the upper surface to each bubble is 0.01mm-0.2mm.

[0029] Preferably, the distance from the lower surface to each bubble is 0.01mm-0.2mm.

[0030] Preferably, the size of each pore is 0.4-1.0 mm along the thickness direction of the flexible dielectric layer, more preferably 0.5-0.8 mm.

[0031] Preferably, the size of each pore is 0.2-1.0 mm along the direction perpendicular to the thickness of the flexible dielectric layer, more preferably 0.4-0.8 mm.

[0032] Preferably, during the production of foamed silicone rubber, the single-layer arrangement of cells is obtained by adjusting the formula and / or controlling the temperature during the foaming process.

[0033] Taking into account (I), after extensive experimental exploration, the inventors discovered that selecting foamed silicone rubber with a Shore A hardness (tested according to the national standard GB / T 531.1-2008) of 10-40 Shore A as the flexible dielectric layer, and controlling the thickness of the flexible dielectric layer to 0.6mm-2.0mm, can ensure high detection stability while also taking into account high detection range and high detection sensitivity.

[0034] Furthermore, considering both (I) and (II), foamed silicone rubber with a Shore A hardness of 10-40 Shore A is selected as the flexible dielectric layer. The thickness of the flexible dielectric layer is controlled between 0.6mm and 2.0mm, and the closed-cell structure is changed to an open-cell structure. The stress of the foamed silicone rubber under 25% compression deformation can reach 30-62kPa, which can further improve the detection sensitivity. When both open-cell and closed-cell structures exist in the foamed silicone rubber, both high detection range and high detection sensitivity can be achieved.

[0035] Furthermore, considering both (I) and (III), foamed silicone rubber with a Shore A hardness of 10-40 Shore A was selected as the flexible dielectric layer, and the thickness of the flexible dielectric layer was controlled between 0.6mm and 2.0mm. Figure 5 As shown, when the flexible dielectric layer has a single pore along its thickness direction, that is, when the pores inside the flexible dielectric layer are arranged in a single layer, it can not only further improve the detection sensitivity, but also improve the stability, detection sensitivity and controllability of the detection range.

[0036] Furthermore, considering (I), (II), and (III) comprehensively, foamed silicone rubber with a Shore A hardness of 10-40 Shore A is selected as the flexible dielectric layer. The thickness of the flexible dielectric layer is controlled between 0.6mm and 2.0mm. The pores inside the flexible dielectric layer are arranged in a single layer, and, as... Figure 7 , 9 As shown in Figures 10 and 11, when the flexible dielectric layer has an open-hole structure, the detection sensitivity can be further improved, and it is also beneficial to improve the detection stability, sensitivity, and controllability of the detection range. Preferably, as shown in Figures 10 and 11... Figure 9 , 11 As shown, when foamed silicone rubber contains not only open-cell structures but also closed-cell structures, it can achieve both high detection range and high detection sensitivity.

[0037] This invention considers the materials used in flexible capacitive pressure sensors, selecting foamed silicone rubber as the flexible dielectric layer material. Due to its high compressibility, high resilience, excellent resistance to compression deformation and creep, low permanent deformation, and low repeated fatigue, foamed silicone rubber significantly improves the stability of flexible capacitive pressure sensors. This solves the problem of unstable pressure readings caused by irreversible permanent deformation and hardness changes in existing flexible dielectric layers, which are prone to occur after prolonged exposure to heavy loads. Furthermore, this invention deeply considers the thickness of the flexible dielectric layer, the hardness of the foamed silicone rubber, its pore structure, and pore distribution. By selecting the appropriate thickness and hardness of the foamed silicone rubber, designing the pore structure, and controlling the pore distribution, it not only improves high stability but also achieves high detection range and high detection sensitivity, while enhancing performance controllability. Therefore, it significantly improves the overall performance of flexible capacitive pressure sensors and has broad application prospects.

[0038] Furthermore, this invention also considers the creep characteristics of the flexible dielectric layer, aiming to solve the problem of unstable sensor pressure detection values ​​caused by the reversible deformation portion that changes over time during the creep of the flexible dielectric layer, while maintaining the sensor's shape and structure. This further improves the detection stability of the flexible capacitive pressure sensor of this invention. To this end, the inventors also provide a calibration method for the flexible capacitive pressure sensor, introducing a time parameter, referred to as delay calibration, which specifically includes the following steps:

[0039] Pressure is applied to the flexible capacitive pressure sensor, and the pressure values ​​are the calibrated reference pressure values, denoted as P1, P2...P K K is an integer greater than or equal to 1, and is applied for a certain time T at each reference pressure value, and the pressure is measured at the reference pressure value P. x Under pressure loading, the capacitance value C output by the flexible capacitive pressure sensor 基准压力 The curve showing the change with loading time t is called the delay calibration curve, denoted as C. 基准压力 (P x ,t), 0≤t≤T, x are 1, 2, 3...K respectively.

[0040] When this flexible capacitive pressure sensor is used for pressure detection under actual load, the detection method also incorporates pressure loading time, which is called a dynamic detection method, including the following steps:

[0041] (1) Real-time detection of the capacitance value C output by the flexible capacitive pressure sensor during the loading time Ty. Ty ;

[0042] (2) Using loading time and capacitance value as comparison parameters, C Ty By comparing with the delay calibration curve, a set of close calibration capacitance values ​​C were obtained.基准压力 ;

[0043] That is, first, the loading time is compared to find the time closest to Ty, which is Tm. Then, the calibration capacitor value C at time Tm is selected from the delay calibration curve. 基准压力 (P x (Tm); then compare the capacitance value and set C Ty With C 基准压力 (P x Compare with Tm to obtain C Ty Located in C 基准压力 (P z Tm) and C 基准压力 (P z+1 The reference pressure P is a set of calibrated capacitance values ​​that are close to Tm. z P z+1 The rated capacitance value C is below 基准压力 (P z Tm) and C 基准压力 (P z+1 (Tm), z = 1, 2, 3... or K-1;

[0044] (3) Using linear interpolation, for C Ty With C 基准压力 (P z Tm), C 基准压力 (P z+1 Interpolation calculations are performed on Tm to obtain the loading time T. y The load pressure value F(t) within the range, 0≤t≤T y .

[0045] The pressure application device is not limited. It can be a positioning and transmission component including a working platform and a pressure head testing component, as disclosed in patent document CN101281073A; it can also be a device including an air pump, an inflation valve, and a sealed cavity, in which a flexible capacitive pressure sensor is placed in the sealed cavity, the air pump is used to inflate the sealed cavity, and the gas pressure in the cavity is adjusted by the inflation valve, such as the calibration device disclosed in patent document CN201610077262.7; it can also be an airbag device, such as the airbag device disclosed in CN106525332 A.

[0046] The loading time T y The output capacitance value can be used as a reference. If the load is lost, the output capacitance value returns to its initial value, and the load loading time T... y Then the value is reset to zero, and the timer restarts when the load is applied again.

[0047] In step (3), the linear interpolation method can be based on the loading time T. y and the output capacitance value CTy As a bivariate bilinear interpolation, it can also be selected to be related to the loading time T. y Linear interpolation is performed on the closest calibration value. The loading time T is... y It is not limited to the specified time T. When T y When the value is greater than T, extrapolation can be used or the calibration value at time T can be used.

[0048] The above describes the delay calibration and dynamic pressure detection process for a single pressure sensor. When several of the aforementioned flexible capacitive pressure sensor arrays are arranged to form a pressure array sensor, the entire pressure array sensor is pressurized. Through microcomputer control and row / column scanning, the pressure data of each pressure sensor is calculated. The delay calibration and dynamic pressure detection of each pressure sensor are then performed using the method described above. Therefore, the delay calibration and dynamic pressure detection method of this invention can also be applied to pressure array sensors. In one implementation, the first flexible conductive layer consists of M parallel conductive strips with spacing between adjacent strips; the second flexible conductive layer consists of N parallel conductive strips with spacing between adjacent strips, where M≥1 and N≥1; the conductive strips of the first and second flexible conductive layers form M×N intersections, each intersection connected by the flexible dielectric layer, and each intersection constitutes a sensing unit, forming an M×N pressure array sensor.

[0049] Compared with the prior art, the delay calibration method provided by the present invention has the following beneficial effects:

[0050] (1) For flexible capacitive pressure sensors, the elastic creep of flexible capacitive pressure sensors is considered in the output calibration. The time parameter is introduced, which effectively solves the output error caused by elastic creep and further improves the detection stability of the sensor.

[0051] (2) After calibrating the output of the flexible capacitive pressure sensor using the delay calibration method of the present invention, a time parameter is also introduced in the actual load pressure detection. The capacitance value output after the load is loaded for a certain time is detected. The loading time and the output capacitance value are used as comparison parameters and compared with the delay calibration of the sensor to obtain a set of close calibration values. Then, the actual load pressure value is obtained by using the linear interpolation method.

[0052] (3) The calibration method and dynamic detection method of the present invention are simple and easy to operate, and have good application prospects in the production and use of flexible capacitive pressure sensors. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the cross-sectional structure of the flexible dielectric layer made of closed-cell foamed silicone rubber according to the present invention.

[0054] Figure 2 yes Figure 1 A schematic diagram of the cross-sectional structure of closed-cell foamed silicone rubber through a cutting process to create open-cell structures.

[0055] Figure 3 This is the scripture Figure 2 A schematic diagram of the cross-sectional structure after the hole is opened by the cutting process.

[0056] Figure 4 yes Figure 1 A schematic diagram of the cross-sectional structure of closed-cell foamed silicone rubber after it has been opened by laser pore-opening process.

[0057] Figure 5 This is a cross-sectional schematic diagram of the flexible dielectric layer made of closed-cell foamed silicone rubber of the present invention when the foam cells are arranged in a single layer.

[0058] Figure 6 yes Figure 5 A schematic diagram of the cross-sectional structure of closed-cell foamed silicone rubber through a cutting process to create open-cell structures.

[0059] Figure 7 This is the scripture Figure 6 A schematic diagram of the cross-sectional structure after the hole is opened by the cutting process.

[0060] Figure 8 yes Figure 5 A schematic diagram of the cross-sectional structure of closed-cell foamed silicone rubber through a cutting process to create open-cell structures.

[0061] Figure 9 This is the scripture Figure 8 A schematic diagram of the cross-sectional structure after the hole is opened by the cutting process.

[0062] Figure 10 yes Figure 5 A schematic diagram of the cross-sectional structure of closed-cell foamed silicone rubber after it has been opened by laser pore-opening process.

[0063] Figure 11 yes Figure 5 A schematic diagram of the cross-sectional structure of closed-cell foamed silicone rubber after partial opening of pores by laser opening process.

[0064] Figure 12 This is a schematic diagram of the cross-sectional structure of the flexible capacitive pressure sensor in Embodiment 1 of the present invention.

[0065] Figure 13 This is a schematic diagram of the cross-sectional structure of the flexible capacitive pressure sensor in Embodiment 2 of the present invention.

[0066] Figure 14 This is a cross-sectional view of the flexible dielectric layer in Embodiments 1-2 of the present invention, perpendicular to the thickness direction.

[0067] Figure 15 This is a cross-sectional view of the flexible dielectric layer in the thickness direction in Embodiment 2 of the present invention.

[0068] Figure 16 This is a schematic diagram of applying pressure to a flexible capacitive pressure sensor using an airbag device.

[0069] Figure 17 These are curves showing the relationship between the displacement and the load size of the flexible capacitive pressure sensor in Embodiments 1 and 2 of the present invention.

[0070] Figure 18 These are curves showing the relationship between the capacitance change and the load size of the flexible capacitive pressure sensor in Embodiments 1 and 2 of the present invention.

[0071] Figure 19 This is a schematic diagram of the cross-sectional structure of the flexible capacitive pressure sensor in Embodiment 3 of the present invention.

[0072] Figure 20 This is a schematic diagram of the cross-sectional structure of the flexible capacitive pressure sensor in Embodiment 4 of the present invention.

[0073] Figure 21 This is a cross-sectional view of the flexible dielectric layer in Embodiments 3-4 of the present invention, perpendicular to the thickness direction.

[0074] Figure 22 This is a cross-sectional view of the flexible dielectric layer in the thickness direction in Embodiment 3 of the present invention.

[0075] Figure 23 These are curves showing the relationship between the displacement and the load size of the flexible capacitive pressure sensor in Embodiments 3 and 4 of the present invention.

[0076] Figure 24 These are curves showing the relationship between the capacitance change and the load size of the flexible capacitive pressure sensor in Embodiments 3 and 4 of the present invention.

[0077] Figure 25 This is a schematic diagram of the cross-sectional structure of the flexible capacitive pressure sensor in Embodiment 5 of the present invention.

[0078] Figure 26 This is a cross-sectional view of the flexible dielectric layer in the thickness direction in Embodiment 5 of the present invention.

[0079] Figure 27 This is the curve showing the change of the output value of the flexible capacitive pressure sensor with time t within a 12-hour loading range of the calibrated reference air pressure in Embodiment 8 of the present invention.

[0080] Figure 28 It is the instantaneous calibration value of the flexible capacitive pressure sensor under the calibration reference air pressure loading condition in Embodiment 9 of the present invention.

[0081] Figure 29 These are the force value versus time curves measured in Embodiments 8 and 9 of this invention.

[0082] Appendix Figure 1-11 The reference numerals in the figures are: 1-upper surface of the flexible dielectric layer; 2-lower surface of the flexible dielectric layer; 3-closed-hole structure; 4-open-hole structure; 5-cutting line.

[0083] Appendix Figure 12 , 13 The reference numerals in the figures 19, 20, and 25 are: flexible dielectric layer 10, flexible first conductive layer 21, flexible second conductive layer 22, first encapsulation layer 31, and second encapsulation layer 32.

[0084] Appendix Figure 16 The reference numerals in the figures are: flexible capacitive pressure sensor 100, flat plate 200, and airbag device 300. Detailed Implementation

[0085] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0086] Example 1:

[0087] In this embodiment, as Figure 12 As shown, the flexible capacitive pressure sensor includes a first encapsulation layer 31, a second encapsulation layer 32, a flexible first conductive layer 21, a flexible second conductive layer 22, and a flexible dielectric layer 10 sandwiched between the flexible first conductive layer 21 and the flexible second conductive layer 22.

[0088] The first encapsulation layer 31 and the second encapsulation layer 32 are made of polyester taffeta or polyester fabric containing spandex, and are used to encapsulate the flexible capacitive pressure sensor.

[0089] The first flexible conductive layer 21 is made of carbon nanotube conductive cloth, and the second flexible conductive layer 22 is also made of carbon nanotube conductive cloth. The first flexible conductive layer 21 and the second flexible conductive layer 22 are respectively connected to the capacitive sensing circuit board via wires.

[0090] The flexible dielectric layer 10 is made of foamed silicone rubber based on PDMS, with a Shore A hardness of 30 and a thickness of 1.0 mm.

[0091] Example 2:

[0092] In this embodiment, the flexible capacitive pressure sensor structure is basically the same as that in Embodiment 1. The difference is that in this embodiment, the following is used: Figure 6 , 7The cutting process shown involves cutting the upper and lower surfaces of the flexible dielectric layer along a cutting direction perpendicular to the thickness of the flexible dielectric layer. The first cutting line is 0.1 mm from the upper surface 1 of the flexible dielectric layer, and the second cutting line is 0.1 mm from the lower surface, thus cutting some closed-hole structures in the flexible dielectric layer into open-hole structures.

[0093] Figure 14 This is a view of the flexible dielectric layer in Examples 1 and 2 perpendicular to its thickness direction, showing that a number of pores are distributed inside the flexible dielectric layer, and the size of each pore in the direction perpendicular to the thickness of the flexible dielectric layer is in the range of 0.1-0.3 mm.

[0094] The flexible dielectric layer in Examples 1 and 2 has advantages such as good insulation, high compressibility, high resilience, excellent resistance to compressive deformation, low permanent deformation, and low repeated fatigue, and can be used stably in the range of -55℃ to 200℃.

[0095] Figure 15 This is a view of the flexible dielectric layer 10 along the thickness direction in Embodiment 2, showing that after cutting, some of the bubbles on the upper and lower surfaces of the flexible dielectric layer are open-cell structures, while the bubbles in the remaining parts of the upper and lower surfaces are closed-cell structures.

[0096] The same load was applied to the flexible capacitive pressure sensors of Examples 1 and 2, such as... Figure 16 As shown, the load acts perpendicularly on the first encapsulation layer 31, and the relationship curve between the sensor's displacement and the load magnitude is as follows. Figure 17 As shown, the curve relating the sensor's capacitance change to the load size is as follows: Figure 18 As shown, under the same load conditions, the displacement of the flexible dielectric layer with a partially open structure in Example 2 is higher than that of the flexible dielectric layer with a closed structure in Example 1, which leads to an increase in capacitance change and thus improves the sensitivity of the sensor.

[0097] Example 3:

[0098] In this embodiment, the flexible capacitive pressure sensor structure is basically the same as that in Embodiment 1, except that, as shown in... Figure 19 As shown, the pores inside the flexible dielectric layer are arranged in a single layer.

[0099] Example 4:

[0100] In this embodiment, the structure of the flexible capacitive pressure sensor is basically the same as that in Embodiment 3, except that, as shown in... Figure 20 As shown, the pores inside the flexible dielectric layer have an open-cell structure. Figure 10As shown, a laser-driven aperture technology is used, in which a laser beam is used to irradiate a flexible dielectric layer. By controlling one or more of the laser wavelength, pulse width, beam divergence angle, and focusing state, the aperture is created, and the closed-hole structure inside the flexible dielectric layer is broken down to form an open-hole structure.

[0101] Figure 21 This is a view of the flexible dielectric layer in Examples 3 and 4 perpendicular to its thickness direction, showing that a number of pores are distributed inside the flexible dielectric layer, and the size of each pore in the direction perpendicular to the thickness of the flexible dielectric layer is in the range of 0.2-0.6 mm.

[0102] Figure 22 This is a cross-sectional view of the flexible dielectric layer 10 in Example 3 along its thickness direction, showing that the pores inside the flexible dielectric layer are arranged in a single layer. The size of the pores in the thickness direction of the flexible dielectric layer is in the range of 0.9-0.95mm. The distance from the upper surface of the flexible dielectric layer to each pore is 0.01mm-0.05mm, and the distance from the lower surface to each pore is 0.01mm-0.05mm.

[0103] This flexible dielectric block has advantages such as good insulation, high compressibility, high resilience, excellent resistance to compressive deformation, low permanent deformation, and low repeated fatigue. It can be used stably in the range of -55℃ to 200℃.

[0104] The same load was applied to the flexible capacitive pressure sensors of Examples 3 and 4, such as... Figure 16 As shown, the load acts perpendicularly on the first encapsulation layer 31, and the relationship curve between the sensor's displacement and the load magnitude is as follows. Figure 23 As shown, the curve relating the sensor's capacitance change to the load size is as follows: Figure 24 As shown, under the same load conditions, the displacement of the flexible dielectric layer with an open structure in Example 4 is higher than that of the flexible dielectric layer with a closed structure in Example 3, which leads to an increase in capacitance change and thus improves the sensitivity of the sensor.

[0105] The maximum range, stress under 25% compressive deformation, and capacitance change of the samples in Examples 1-4 were tested using a universal tensile testing machine (Shin Sansei, model C65.102) and an impedance analyzer (Hioki, model IM3536). The results are shown in the table below.

[0106] Dielectric layer thickness 1.0mm 0.8mm 1.0mm 1.0mm Compressive stress, 25% 62kPa 30kPa 50kPa 35kPa Sensor area D30mm D30mm D30mm D30mm Maximum range 70kPa 40kPa 50kPa 45kPa Capacitance change (100N) 4pF 13pF 12pF 20pF

[0107] Example 5:

[0108] In this embodiment, the structure of the flexible capacitive pressure sensor is basically the same as that in Embodiment 3, except that, as shown in... Figure 6 , 7The cutting process shown involves cutting the upper surface of the flexible dielectric layer along a cutting direction perpendicular to the thickness of the flexible dielectric layer. The cutting line is 0.1 mm away from the upper surface of the flexible dielectric layer, thus transforming the closed-hole structure in the flexible dielectric layer into an open-hole structure. A schematic diagram of the sensor structure after cutting is shown below. Figure 25 As shown.

[0109] Figure 26 This is a cross-sectional view of the flexible dielectric layer 10 in Example 4 along its thickness direction, showing that the pores inside the flexible dielectric layer are arranged in a single layer, and each pore is an open structure.

[0110] Example 6:

[0111] In this embodiment, the flexible capacitive pressure sensor structure is basically the same as that in Embodiment 5. The difference is that in this embodiment, the pores inside the flexible dielectric layer are arranged in a single layer. The size of the pores in the thickness direction of the flexible dielectric layer is in the range of 0.6-0.9mm. The distance from the upper surface of the flexible dielectric layer to each pore is 0.05mm-0.2mm, and the distance from the lower surface to each pore is 0.05mm-0.2mm. The upper surface of the flexible dielectric layer is cut along the cutting direction perpendicular to the thickness of the flexible dielectric layer. The distance from the cutting line to the upper surface of the flexible dielectric layer is 0.2mm, so that some closed-cell structures in the flexible dielectric layer are cut into open-cell structures.

[0112] Example 7:

[0113] In this embodiment, the flexible capacitive pressure sensor structure is basically the same as that in Embodiment 4. The difference is that a laser-drilled hole process is used, and a beam of light is used to irradiate the flexible dielectric layer to locate the closed hole structure within it. Figure 11 As shown, laser drilling is used to transform a closed-hole structure into an open-hole structure that requires opening.

[0114] Example 8:

[0115] In this embodiment, the flexible capacitive pressure sensor has the same structure as in Embodiment 1.

[0116] In practical applications, flexible capacitive pressure sensors require calibration. To address the issue of unstable pressure readings caused by the reversible deformation of the flexible dielectric layer over time during creep, this embodiment introduces a time parameter and provides a time-delay calibration method, as detailed below.

[0117] like Figure 16 As shown, the area of ​​the flexible capacitive pressure sensor 100 is S0. The flexible capacitive pressure sensor 100 is laid flat on the plate 200, and the air pressure P is uniformly applied to the entire flexible capacitive pressure sensor 100 by the airbag device 300 whose size is adapted to the flexible capacitive pressure sensor 100.

[0118] The range of this flexible capacitive pressure sensor is 0-70 kPa, and the time-delay calibration method is as follows:

[0119] (1) Determination of the reference pressure for calibration

[0120] Based on the sensor's range, 10 pressure values ​​were selected as calibration reference pressure values, denoted as P1, P2...P 10 , P1=0kpa, P2=(70kpa-0kpa) / 9, P3=(70kpa-0kpa)×2 / 9, P3=(70kpa-0kpa)×3 / 6,…P 10 =70 kPa.

[0121] (2) Delay calibration

[0122] An air pressure P is applied to the entire flexible capacitive pressure sensor 100 using an airbag device 300, and the loading time of this air pressure P is T = 12 hours. The air pressure values ​​controlled by the air pressure P are P1, P2...P1 in step (1). 10 The change in the output value C of the flexible capacitive pressure sensor 10 with time t within the time range of 0-12 hours is detected and denoted as C. 基准压力 (P x ,t), 0≤t≤T, x=1,2,3……or10, to obtain as Figure 27 The curve shown represents the change.

[0123] The time-delay calibrated flexible capacitive pressure sensor is used for pressure detection under actual load, including the measurement of characteristic parameter values ​​of the time-delay output and pressure conversion. The specific steps are as follows:

[0124] (3) Measurement of characteristic parameter values ​​of delayed output

[0125] An actual load was applied to the flexible capacitive pressure sensor, and the load T was tested and recorded. y The output capacitance value C under time conditions Ty ;

[0126] (4) Using the output capacitance value and loading time as comparison parameters, the capacitance value C Ty Compare the time delay calibration curve obtained in step (2). For example, first compare the loading time and find that the time closest to Ty is Tm. Then, select the calibration C at time Tm from the time delay calibration curve of the flexible capacitive pressure sensor. 基准压力 (P x (Tm), then compare the capacitance value, and C Ty With this calibration C 基准压力 (P x Compare with Tm to obtain C Ty Located in C基准压力 (P z Tm) and C 基准压力 (P z+1 The calibration values ​​between Tm and P, i.e., close to each other, are the pressure values ​​and the reference air pressure P. z P z+1 The capacitance value is given by z = 1, 2, 3... or 10;

[0127] (5) Using linear interpolation, for C Ty The obtained calibration value C 基准压力 (P z Tm), C 基准压力 (P z+1 Interpolation calculations were performed on Tm to obtain the load pressure value F(t) under Ty as follows:

[0128]

[0129] Where Cx is between C 基准压力 (Pz+1, Tm) - C 基准压力 The capacitance values ​​between (Pz, Tm).

[0130] Example 9:

[0131] This embodiment is a comparative embodiment of embodiment 8.

[0132] In this embodiment, the flexible capacitive pressure sensor has the same structure as the sensor in Embodiment 8. The difference is that in this embodiment, the calibration method for the flexible capacitive pressure sensor is instantaneous calibration, as detailed below:

[0133] (1) Determination of the reference pressure for calibration

[0134] Same as step (1) in Example 8

[0135] (2) Real-time calibration

[0136] like Figure 16 As shown, the airbag device 300 applies air pressure P to the entire flexible capacitive pressure sensor 10, and controls the air pressure values ​​of P to be P1, P2...P1 in step (1). 10 The detection was performed at a pressure value of P. x The instantaneous output capacitance value under pressure is C. 基准压力 (P x (x = 1, 2, ..., 10). Then the instantaneous calibration of this flexible capacitive pressure sensor under the calibration reference pressure is as follows: Figure 28 As shown.

[0137] The calibrated flexible capacitive pressure sensor is used for pressure detection under actual load, including the measurement of characteristic parameter values ​​of delayed output and pressure conversion, specifically including the following steps:

[0138] (3) Measurement of characteristic parameter values ​​of delayed output

[0139] An actual load was applied to the flexible array pressure sensor, and the load T was tested and recorded using a circuit testing module. y The output capacitance value C under time conditions Ty ;

[0140] (4) Using the output capacitance value as a comparison parameter, the capacitance value C Ty The instantaneous calibration C of the detection unit obtained in step (2) 基准压力 (P x By comparison, a set of calibration values ​​that are close to each other was obtained, C. 基准压力 (P z )、C 基准压力 (P z+1 ), z = 1, 2, 3... or 10; using linear interpolation methods, for C Ty With the obtained set of calibration values ​​C Pz C -Pz+1 Interpolation calculations were performed to obtain the load pressure value F(t) under Ty as follows:

[0141]

[0142] Where Cx is the capacitance value between C reference pressure (Pz+1) and C reference pressure (Pz).

[0143] Following the calibration methods shown in Examples 8 and 9, loads of 10N, 20N, 30N, and 40N were applied to the flexible capacitive pressure sensor for 1.5 hours, 1.5 hours, 1.5 hours, and 1.5 hours, respectively. The force-time curves measured using the detection methods in Examples 6 and 7 are shown below. Figure 29 As shown, compared with Example 9, the stability of the force value was significantly improved after using the delay calibration in Example 8.

[0144] Examples 10-15:

[0145] In Examples 10-15, the flexible capacitive pressure sensor structures are the same as those in Examples 2-7.

[0146] In Examples 10-15, the calibration method for the flexible capacitive pressure sensor is the same as that in Example 8, which is the time-delay calibration method.

[0147] In Examples 10-15, the detection method of the flexible capacitive pressure sensor is the same as that in Example 8, which is a dynamic detection method.

[0148] Examples 16-22:

[0149] In Examples 16-22, the flexible capacitive pressure sensor structures are the same as those in Examples 1-7, except that: the flexible first conductive layer 21 consists of 4 parallel conductive strips with spacing between adjacent conductive strips; the flexible second conductive layer 22 consists of 6 parallel conductive strips with spacing between adjacent conductive strips; the conductive strips of the first flexible conductive layer 21 and the conductive strips of the second flexible conductive layer 22 form 4×6 vertical intersections, each vertical intersection is connected by a flexible dielectric layer, and each intersection is a sensing unit, for a total of 24 sensing units, thus obtaining a pressure array sensor.

[0150] The pressure array sensor is pressurized using an airbag. The pressure data of each pressure sensing unit is calculated by microcomputer control and row and column scanning. The method in Examples 8 and 9 is used to perform time delay calibration and dynamic pressure detection on each pressure sensing unit.

[0151] The embodiments described above provide a detailed explanation of the technical solution of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A highly stable flexible capacitive pressure sensor, comprising a first flexible conductive layer, a second flexible conductive layer, and a flexible dielectric layer sandwiched between the first flexible conductive layer and the second flexible conductive layer; characterized in that: The flexible dielectric layer material is foamed silicone rubber, and the foamed silicone rubber contains a single layer of cells arranged in a single layer. The flexible dielectric layer is cut along a direction perpendicular to its thickness, so that at least part of the closed-cell structure inside the foamed silicone rubber is opened up to become an open-cell structure. Alternatively, a laser drilling process can be used to break through at least part of the closed-cell structure inside the foamed silicone rubber, turning it into an open-cell structure.

2. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: Foamed silicone rubber is a polydimethylsiloxane polymer.

3. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: The Shore A hardness of the foamed silicone rubber is 10-40 Shore A; the thickness of the flexible dielectric layer is 0.6mm-2.0mm.

4. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: After opening, the stress of foamed silicone rubber under 25% compression deformation is 30-62 kPa.

5. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: The degree of aperture formation can be adjusted by changing the distance from the cutting line to the upper or lower surface of the flexible dielectric layer.

6. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: The degree of aperture formation can be controlled by adjusting one or more of the following: laser wavelength, pulse width, beam divergence angle, and focusing state.

7. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: Laser drilling is performed on foamed silicone rubber by irradiating it with a light beam, which can locate the closed-cell structure within it. The closed-cell structure that needs to be opened is then drilled with a laser.

8. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: The thickness of the flexible dielectric layer is controlled between 0.6 mm and 1.5 mm.

9. The highly stable flexible capacitive pressure sensor as described in claim 8, characterized in that: The thickness of the flexible dielectric layer is 0.8mm-1.2mm.

10. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: The distance from the upper surface of the flexible dielectric layer to the pores is 0.01mm-0.2mm.

11. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: The distance from the lower surface of the flexible dielectric layer to each pore is 0.01mm-0.2mm.

12. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: Along the thickness direction of the flexible dielectric layer, the size of each pore is 0.4-1.0 mm.

13. The highly stable flexible capacitive pressure sensor as described in claim 12, characterized in that: Each bubble has a size of 0.5-0.8mm.

14. The highly stable flexible capacitive pressure sensor as described in claim 1, characterized in that: Along the direction perpendicular to the thickness of the flexible dielectric layer, the size of each bubble is 0.2-1.0 mm.

15. The highly stable flexible capacitive pressure sensor as described in claim 14, characterized in that: Each bubble has a size of 0.4-0.8 mm.

16. A time-delay calibration method using the highly stable flexible capacitive pressure sensor according to any one of claims 1 to 15, characterized in that: The steps include the following: Pressure is applied to the flexible capacitive pressure sensor, and the pressure values ​​are the calibrated reference pressure values, denoted as P1, P2...P K K is an integer greater than or equal to 1, and is applied for a certain time T at each reference pressure value, and the pressure is measured at the reference pressure value P. x Under pressure loading, the capacitance value C output by the flexible capacitive pressure sensor 基准压力 The curve showing the change with loading time t is called the delay calibration curve, denoted as C. 基准压力 (P) x ,t), 0≤t≤T, x are 1, 2, 3...K respectively.

17. A method for pressure detection using the time delay calibration method according to claim 16, characterized in that: The steps include the following: (1) Real-time detection of the capacitance value C output by the flexible capacitive pressure sensor when the loading time is Ty. Ty ; (2) Using loading time and capacitance value as comparison parameters, C Ty By comparing with the delay calibration curve, a set of close calibration capacitance values ​​C were obtained. 基准压力 (P) z Tm) and C 基准压力 (P) z+1 (Tm), z = 1, 2, 3... or K-1; That is, first, the loading time is compared to find the time closest to Ty, which is Tm. Then, the calibration capacitor value C at time Tm is selected from the delay calibration curve. 基准压力 (P) x (Tm); then compare the capacitance value, and C Ty With C 基准压力 (P) x Compare with Tm to obtain C Ty Located in C 基准压力 (P) z Tm) and C 基准压力 (P) z+1 The reference pressure P is a set of calibrated capacitance values ​​that are close to Tm. z P z+1 The rated capacitance value C is below 基准压力 (P) z Tm) and C 基准压力 (P) z+1 (Tm), z = 1, 2, 3... or K-1; (3) Using linear interpolation, for C Ty With C 基准压力 (P) z Tm), C 基准压力 (P) z+1 Interpolation calculations are performed on Tm to obtain the loading time T. y The load pressure value F(t) within the range, 0≤t≤T y .

18. The pressure detection method as described in claim 17, characterized in that: In step (3), the linear interpolation method uses the loading time T y and the output characteristic parameter value C Ty Perform bilinear interpolation as a bivariate, or select a value related to the loading time T. y Linear interpolation is performed on the closest calibration value.

19. A flexible capacitive pressure array sensor, characterized in that: The highly stable flexible capacitive pressure sensor described in any one of claims 1 to 15 is used; the first flexible conductive layer is composed of M parallel conductive strips, and there is a gap between adjacent conductive strips; The second flexible conductive layer consists of N parallel conductive strips, with a spacing between adjacent conductive strips, M≥1 and N≥1; the conductive strips of the first flexible conductive layer and the conductive strips of the second flexible conductive layer form M×N intersections, each intersection is connected through the flexible dielectric layer, and each intersection is a sensing unit, forming an M×N pressure array sensor.

20. The pressure detection method of the flexible capacitive pressure array sensor as described in claim 19, characterized in that: The pressure array sensor is pressurized as a whole, and the pressure data of each pressure sensing unit is calculated by microcomputer control and row and column scanning. The delay calibration method described in claim 16 is used to perform delay calibration on each pressure sensing unit, and the pressure detection method described in claim 17 is used to perform pressure detection on each pressure sensing unit.

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