Capacitive flexible pressure sensor and preparation method and application thereof

Abstract

The application relates to the technical field of flexible sensors, and particularly discloses a capacitive flexible pressure sensor, a preparation method thereof and application. The capacitive flexible pressure sensor comprises a micro-protrusion structure and a capacitive sensor; the micro-protrusion structure is a prismatic structure formed by bonding a first hard base and an elastic film; the top of the prismatic structure is the elastic film, the inclined side surface is a composite area of the first hard base and the elastic film, and adjacent side edges of the inclined side surface are connected through the elastic film; and the capacitive sensor is fixed on each inclined side surface. The capacitive sensor provided by the application is orthogonally arranged on the side wall of the micro-protrusion structure, and based on the unique three-dimensional orthogonal layout structure, three-dimensional force signal accurate decoupling can be realized, the equipment integration, detection sensitivity and detection accuracy are considered at the same time, and the technical problems that the existing flexible electronic skin process is complex and it is difficult to consider high integration and sensitivity are solved.

Description

Technical Field

[0001] This application relates to the field of flexible sensor technology, and in particular to a capacitive flexible pressure sensor, its fabrication method, and its application.

[0002] Glossary

[0003] Polydimethylsiloxane (PDMS): A high-molecular-weight organosilicon elastomer material with excellent flexibility, biocompatibility and chemical stability. After curing, it is a transparent elastomer and is one of the most widely used substrate materials in flexible electronic devices.

[0004] Polyethylene terephthalate (PET): a thermoplastic polyester material with good mechanical strength and dimensional stability.

[0005] Pre-stretch and Release Method: A process for preparing three-dimensional curved surface structures: First, an elastic substrate is mechanically stretched and fixed along a uniaxial or biaxial direction. Then, a rigid film is attached to its surface. Finally, the stretching is released. Due to the difference in elastic modulus between the two layers and the interfacial bonding effect, the system spontaneously generates buckling deformation, forming a regular concave-convex three-dimensional structure.

[0006] Capacitive pressure sensor: A pressure-sensitive device based on the principle of a parallel-plate capacitor. When an external force is applied to the sensor, the dielectric layer undergoes compression deformation, leading to a decrease in the distance between the two plates and / or a change in the dielectric constant, thereby causing a change in the capacitance. The magnitude of the external force can be estimated by measuring the change in capacitance; the basic formula is as follows: ,in, This is the capacitance value. denoted as the relative permittivity, A as the effective area of ​​the electrode, and d as the distance between the plates.

[0007] Screen printing: a thick film printing process in which conductive paste is transferred to the surface of a substrate through a patterned area on a screen using a squeegee, and then cured to form a conductive pattern.

[0008] Carbon-Doped PDMS: A composite material formed by uniformly dispersing carbon-based conductive fillers (such as carbon nanotubes, carbon black, graphene, etc.) in a PDMS matrix.

[0009] Laser engraving is a processing technique that uses a high-energy carbon dioxide laser beam to selectively etch the surface of a material. This invention uses a laser to engrave micron-level texture structures, such as microgrooves and microcone arrays, on the surface of a carbon-containing PDMS dielectric layer. This increases the surface roughness and specific surface area of ​​the dielectric layer, reduces the effective elastic modulus, and thus achieves greater compressive deformation under low-pressure conditions, significantly improving sensitivity.

[0010] ARclear: A substrate-free optically clear adhesive double-sided tape (OCA). Its adhesive layer exhibits excellent adhesion to low surface energy PDMS silicone surfaces, achieving a strong bond without plasma treatment or primer.

[0011] Three-dimensional force sensing refers to the ability to simultaneously measure the magnitude and direction of normal and tangential forces acting on a sensor surface. In electronic skin applications, three-dimensional force sensing is a key technology for simulating human tactile functions.

[0012] Decoupling: Decoupling refers to using mathematical methods, such as matrix transformation and optimization algorithms, to separate the true components of the force in each direction from the original measurement values ​​of each sensing unit, eliminate signal crosstalk, improve measurement accuracy, and reduce the mutual interference between force signals in different directions in multidimensional force sensing.

[0013] Electronic skin (E-skin): A flexible electronic device that mimics the function of human skin, capable of sensing various physical stimuli such as pressure, temperature, humidity, and texture, and has important application prospects in fields such as robotics, prosthetics, and wearable devices. Background Technology

[0014] As robotics technology expands from industrial automation to service robots, medical rehabilitation robots, and humanoid robots, endowing robots with tactile perception capabilities has become a core research topic in this field. Compared to vision and hearing, tactile perception can directly provide physical information such as contact force, deformation, and texture, enabling robots to perform fine operations and state recognition without visual assistance. Flexible electronic skin (E-skin), as a key carrier for realizing tactile perception in robots, has received widespread attention from academia and industry in recent years. The core sensing element of flexible electronic skin is a flexible pressure sensor. Based on the sensing principle, flexible pressure sensors are mainly divided into three categories: piezoelectric, piezoresistive, and capacitive. Among them, piezoelectric sensors are sensitive to dynamic forces but difficult to measure static forces and are easily affected by environmental humidity; piezoresistive sensors are low in cost and simple in principle, but have significant temperature drift; capacitive sensors, due to their simple structure, good signal stability, low power consumption, and excellent temperature stability, have become a research hotspot in the field of flexible tactile sensing. However, the tactile perception capabilities of human skin extend far beyond the detection of normal pressure—humans can sense tangential sliding force, identify contact direction, and determine the hardness and texture of objects. This means that electronic skin must simultaneously possess the ability to sense both normal and tangential forces in three dimensions. Therefore, how to integrate multiple sensing units on a flexible, stretchable substrate to achieve accurate measurement and decoupling of three-dimensional forces is the core technological challenge currently facing flexible electronic skin.

[0015] The existing flexible electronic skin has the following defects: (1) It is difficult to achieve both high integration and sensitivity: While achieving high spatial resolution and multifunctional three-dimensional force detection, the existing three-dimensional force sensing electronic skin is limited by the inherent characteristics of dielectric layer materials and micro-texture structures. The sensitivity of a single sensing unit is low, making it difficult to detect small tactile forces, such as light touch and pre-contact sensing. High-sensitivity solutions can only detect normal pressure and do not have three-dimensional force sensing capabilities. (2) The fabrication process is complex: Three-dimensional force transmission structures are often fabricated using processes such as precision mold casting, multi-layer photolithography, and three-dimensional assembly. The process involves many steps, high equipment requirements, and low yield, which is not conducive to low-cost, large-scale production and practical application promotion. The micro-texture structure on the sensor surface requires complex processes to complete. For example, although femtosecond laser direct writing can fabricate high-precision micro-nano structures, the equipment is expensive and the processing speed is slow. Although the template method can reuse the mold, the mold itself still needs to be precisely processed and there are problems such as demolding damage. (3) In the existing flexible three-dimensional force sensors, the normal force and tangential force signals are severely coupled, and the decoupling accuracy is low. (4) No targeted optimization for application scenarios. For example, companion robots and medical rehabilitation have high requirements for the flexibility, sensitivity, tactile fineness and cost of sensors, which existing solutions cannot fully meet.

[0016] Therefore, there is an urgent need for a flexible electronic skin that is simple to manufacture, has both high integration and sensitivity, and can meet the needs of a specific application scenario. Summary of the Invention

[0017] In view of this, the purpose of this application is to provide a capacitive flexible pressure sensor, its fabrication method and application, to solve the technical problems of existing flexible electronic skin processes being complex and difficult to simultaneously achieve high integration and sensitivity.

[0018] To achieve the above technical objectives, this application provides a capacitive flexible pressure sensor, including a micro-protrusion structure and a capacitive sensor;

[0019] The micro-protrusion structure is a truncated pyramid structure formed by bonding a first rigid substrate and an elastic film; the top of the truncated pyramid structure is an elastic film, the inclined side is a composite area of ​​the first rigid substrate and the elastic film, and the adjacent sides of the inclined side are connected by the elastic film; a capacitive sensor is fixed on each inclined side.

[0020] Furthermore, the capacitive sensor includes a second rigid substrate, an upper electrode, a carbon-containing dielectric layer, a lower electrode, and a third rigid substrate arranged sequentially.

[0021] The carbon dielectric layer consists of two independent carbon thin films arranged at intervals, and the relatively mating surfaces of the carbon thin films are provided with microtexture structures.

[0022] Furthermore, the microtexture structure is a microgroove array, a microcone array, or a micropyramid array.

[0023] Furthermore, the surface of the capacitive flexible pressure sensor is covered with a flexible encapsulation layer.

[0024] This application provides a method for fabricating a capacitive flexible pressure sensor, comprising the following steps:

[0025] Step S1: Prepare a first rigid substrate and an elastic film. The elastic modulus of the first rigid substrate is less than that of the elastic film. Process the first rigid substrate to obtain a fixed frame with a preset through hole. Step S2: Stretch the elastic film to put it in a stretched state. Bond the fixed frame to the stretched elastic film, and the bonding area forms a rigid constraint area.

[0026] Step S3: Fix the capacitive sensor to the surface of the rigid constraint area;

[0027] Step S4: Release the tension of the elastic membrane to allow it to retract. The rigid constraint area buckles and deforms as the elastic membrane retracts, forming a micro-protrusion structure, thus obtaining a capacitive flexible pressure sensor.

[0028] Furthermore, it also includes a packaging step: pouring a flexible adhesive onto the surface of the capacitive flexible pressure sensor, which, after curing, forms a flexible encapsulation layer covering the capacitive flexible pressure sensor.

[0029] This application provides a capacitive flexible pressure testing system, including a capacitive flexible pressure sensor, a conductive lead-out circuit assembly, a capacitance acquisition and signal processing module, and a three-dimensional force decoupling calculation module;

[0030] Capacitive flexible pressure sensors are used to sense the deformation differences at different locations under normal and tangential forces, generating differentiated multi-channel capacitive signals.

[0031] The conductive lead-out circuit assembly is electrically connected to the capacitive flexible pressure sensor to transmit the capacitive signal generated by the capacitive flexible pressure sensor to the capacitance acquisition and signal processing module.

[0032] The capacitance acquisition and signal processing module is used to acquire and summarize multiple capacitance signals in real time.

[0033] The three-dimensional force decoupling calculation module is used to receive capacitance signals, perform three-dimensional force decoupling calculations, and output the three-dimensional force components corresponding to the normal and tangential directions.

[0034] Furthermore, the capacitance acquisition and signal processing module includes a PCAP01 capacitance detection chip and an STM32F1 microcontroller;

[0035] The PCAP01 capacitance detection chip is used to independently acquire real-time capacitance signals from capacitance sensors; the STM32F1 microcontroller is electrically connected to the PCAP01 capacitance detection chip and is used to summarize, organize, and transmit the capacitance signals.

[0036] Furthermore, in the three-dimensional force decoupling calculation module, the relationship between the capacitance change and the force on the capacitive flexible pressure sensor is as follows:

[0037] ;

[0038] Where S is the sensitivity matrix. This represents the change in capacitance of the nth channel caused by a unit force in the j-th direction; Fx, Fy, and Fz are the components of the three-dimensional force; ΔC1~ΔC n These represent the capacitance changes corresponding to the 1st to the nth capacitance sensors, respectively.

[0039] The solution obtained using the pseudo-inverse method is: ;in, Let be the decoupling matrix, ΔC be the capacitance change vector, and F be the three-dimensional force vector.

[0040] Furthermore, in the three-dimensional force decoupling calculation module, the decoupling calculation process is as follows:

[0041] Step S1: Apply known normal force Fz, tangential force Fx, and tangential force Fy sequentially to the capacitive flexible pressure sensor;

[0042] Step S2: Record the capacitance change of the multi-channel capacitive sensor under each applied force;

[0043] Step S3: Use gradient descent or Adam optimization algorithm to iteratively solve the sensitivity matrix S to obtain the optimal estimate of the sensitivity matrix;

[0044] Step S4: Calculate the corresponding decoupling matrix D based on the optimal estimate, and pre-store the decoupling matrix D in the STM32F1 microcontroller;

[0045] In step S5, during the actual detection process, the STM32F1 microcontroller performs matrix operations on the real-time collected capacitance change and the decoupling matrix D to calculate and output the estimated values ​​of the three-dimensional force components Fx, Fy, and Fz in real time.

[0046] This application provides a robotic electronic skin, including a capacitive flexible pressure sensor or a capacitive flexible pressure testing system.

[0047] In summary, this application provides a capacitive flexible pressure sensor, including a micro-protrusion structure and a capacitive sensor. The micro-protrusion structure is a truncated pyramid structure formed by bonding a first rigid substrate and an elastic film. The top of the truncated pyramid structure is the elastic film, and the inclined side is a composite region of the first rigid substrate and the elastic film, with adjacent sides of the inclined side connected by the elastic film. A capacitive sensor is fixed on each inclined side. The capacitive sensor provided in this application is orthogonally arranged in the orientation of the micro-protrusion structure. Based on this unique three-dimensional orthogonal layout structure, precise decoupling of three-dimensional force signals can be achieved, balancing device integration, detection sensitivity, and detection accuracy.

[0048] Compared with existing technologies, the capacitive flexible pressure sensor provided in this application can simultaneously achieve precise decoupling of three-dimensional force signals, taking into account the device integration, detection sensitivity and detection accuracy. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 A schematic diagram of the microtexture structure prepared by the laser engraving and laser cutting processes provided in Example 1;

[0051] Figure 2 A schematic diagram of the fabrication process and structure of the capacitive sensor provided in Example 2;

[0052] Figure 3 A process flow diagram for fabricating the capacitive flexible pressure sensor provided in Example 1;

[0053] Figure 4 A physical rendering of the capacitive flexible pressure sensor provided in Example 1;

[0054] Figure 5 This is a schematic diagram of the overall structure of the capacitive flexible pressure sensor provided in Example 2;

[0055] Figure 6 The capacitance measurement circuit diagram provided in Example 5;

[0056] Figure 7 This is a schematic diagram of the real-time data acquisition and force calculation visualization interface of the capacitive flexible pressure testing system provided in Example 6;

[0057] Figure 8 The distribution of data points showing the rate of change of capacitance value of the sensor when no pressure is applied during measurement using the capacitive flexible pressure testing system provided in Example 6;

[0058] Figure 9 This is a schematic diagram comparing the deviation between the PCAP measured value and the actual value during measurement using the capacitive flexible pressure testing system provided in Example 6.

[0059] Figure 10 The graph shows the sensitivity comparison curves of capacitive flexible pressure sensors; where A is the sensitivity curve of the capacitive flexible pressure sensor provided in Comparative Example 1, and B is the sensitivity curve of the capacitive flexible pressure sensor provided in Example 2. Detailed Implementation

[0060] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments in this application specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application.

[0061] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0062] Unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0063] The raw materials used in this invention are not particularly restricted in their source; they can be purchased on the market or prepared using conventional methods known to those skilled in the art.

[0064] This application provides a capacitive flexible pressure sensor, including a micro-protrusion structure and a capacitive sensor;

[0065] The micro-protrusion structure is a truncated pyramid structure formed by bonding a first rigid substrate and an elastic film; the top of the truncated pyramid structure is an elastic film, the inclined side is a composite area of ​​the first rigid substrate and the elastic film, and the adjacent sides of the inclined side are connected by the elastic film; a capacitive sensor is fixed on each inclined side.

[0066] It should be noted that the edges divide the sidewalls of the micro-protrusion structure into multiple independent inclined surfaces, each corresponding to a stress-bearing region. Each stress-bearing region is independently equipped with a capacitive sensor. This differential layout can achieve partial decoupling of normal and tangential forces at the physical level: the capacitive sensors are orthogonally arranged on the inclined surfaces of the micro-protrusion structure. When the capacitive flexible pressure sensor is subjected to a normal force, the capacitive sensor is uniformly compressed; when the capacitive flexible pressure sensor is subjected to a tangential force, the micro-protrusion structure tilts, the capacitive sensor on the side of the applied force is compressed, and the capacitance increases, while the capacitive sensor on the opposite side is stretched or decompressed, and the capacitance decreases. The changes in capacitive sensors on adjacent sides are small. Through this differentiated response mode, three-dimensional force decoupling can be achieved, and three-dimensional forces can be distinguished.

[0067] In some embodiments, the micro-protrusion structure is a bottomless frustum structure, or a frustum structure with a bottom made of an elastic material.

[0068] It should be noted that the bottomless or flexible bottom micro-protrusion structure, combined with the elastic membrane connecting the inclined side, can provide sufficient deformation space for the micro-protrusion structure, especially its inclined side, under stress.

[0069] In some embodiments, the frustum structure can be a triangular frustum, a quadrangular frustum, a pentagonal frustum, or other frustum structures with more edges. The number of capacitive sensors varies with the frustum structure and the number of inclined surfaces.

[0070] In some preferred embodiments, the elastic modulus of the elastic film is about 1 to 3 MPa, and the elastic modulus of the first rigid substrate is 2 to 4 GPa.

[0071] It should be noted that, according to the principle of minimum potential energy structure, the out-of-plane bending deformation energy of an elastic film with a thickness much smaller than the planar feature size is much smaller than its in-plane compressive deformation energy. Therefore, when the elastic film undergoes significant elastic contraction, while the first rigid substrate hardly contracts, the interfacial bonding force between the two causes stress concentration in the elastic film at the edge of the first rigid substrate, leading to local buckling and upward arching to form a micro-protrusion structure. This micro-protrusion structure provides an ideal mechanical transmission platform for three-dimensional force sensing.

[0072] In some embodiments, the capacitive sensor includes a second rigid substrate, an upper electrode, a carbon-containing dielectric layer, a lower electrode, and a third rigid substrate arranged sequentially; the carbon-containing dielectric layer is composed of two independent carbon-containing thin films arranged at intervals, and the relatively mating surfaces of the carbon-containing thin films are provided with microtexture structures.

[0073] In some embodiments, the upper electrode and the lower electrode are prepared using conductive carbon black or graphite composite slurry.

[0074] In some embodiments, the carbon-containing dielectric layer is a PDMS dielectric layer doped with carbon-based conductive filler, and the carbon doping ratio in the carbon-containing dielectric layer is [missing information]. .

[0075] Carbon-based conductive fillers include at least one of carbon nanotubes, multilayer carbon nanotubes, carbon black, graphene, reduced graphene oxide, or metal nanoparticles (such as Ag nanoparticles). The PDMS dielectric layer is obtained by mixing PDMS prepolymer and PDMS curing agent at a mass ratio of 10 to 15:1 and then curing.

[0076] It should be noted that by introducing carbon-based conductive fillers into the PDMS matrix, the overall dielectric constant of the dielectric layer can be effectively improved, and a significant piezocapacitive effect can be induced, thereby achieving enhanced sensitivity based on material modification and providing an electrical performance basis for the detection of weak low-voltage signals by the sensor.

[0077] In some embodiments, microtexture structures are prepared using laser engraving, photolithography, cutting, template method, or chemical etching. The microtexture structures can be geometric shapes such as microgroove arrays, microcone arrays, micropyramid arrays, microhemispherical arrays, and microcylindrical arrays. The microtexture structures can also be biomimetic textures, such as micropapillary structure arrays on the surface of lotus leaves or microstructure arrays of rose petals. The geometric structure and parameters of the microtexture structures in this application can be flexibly designed according to the target sensitivity range.

[0078] In some preferred embodiments, a Trotec Q400 laser cutting machine is used, and the process parameters for the laser engraving process are as follows: processing power of 5% to 20% power output, scanning speed of 200 to 500 mm / s; surface texture depth of the micro-textured structure is 20 to 80 μm, and texture spacing is 40 to 200 μm.

[0079] It should be noted that by constructing micro-texture structures such as micro-grooves and micro-cones on the surface of the dielectric layer, the equivalent elastic modulus can be reduced, the effective contact area can be increased, and the sensitivity of the sensor in the low-pressure region can be significantly improved.

[0080] Furthermore, by employing a dual synergistic enhancement strategy of carbon filler doping modification and surface laser microtexturing, the low-pressure detection sensitivity of the sensor can be simultaneously improved from both electrical and mechanical perspectives. On the one hand, carbon-based conductive filler doping can increase the dielectric constant of the PDMS dielectric layer, enabling the sensor to generate a larger capacitance change response under the same deformation, thus strengthening the electrical sensing capability. On the other hand, by constructing a regular microtexture structure on the surface of the carbon-containing PDMS dielectric layer, the overall equivalent elastic modulus of the dielectric layer can be effectively reduced, allowing the dielectric layer to undergo significant compressive deformation under small pressure. This simultaneously increases the effective contact area of ​​the electrode, further amplifying the capacitance signal in the low-pressure range and solving the defects of traditional planar PDMS dielectric layers, such as excessive hardness, small low-pressure deformation, and insufficient sensitivity.

[0081] In some embodiments, the surface of the capacitive flexible pressure sensor is covered with a flexible encapsulation layer, the thickness of which is 8-10 mm.

[0082] This application provides a method for fabricating a capacitive flexible pressure sensor, comprising the following steps:

[0083] Step S1: Prepare a first rigid substrate and an elastic film. The elastic modulus of the first rigid substrate is less than that of the elastic film. Process the first rigid substrate to obtain a fixed frame with a preset through hole.

[0084] Step S2: The elastic film is stretched to put it in a stretched state, and the fixed frame is bonded to the stretched elastic film. The bonded area forms a rigid constraint area.

[0085] Step S3: Fix the capacitive sensor to the surface of the rigid constraint area;

[0086] Step S4: Release the tension of the elastic membrane to allow it to retract. The rigid constraint area buckles and deforms as the elastic membrane retracts, forming a micro-protrusion structure, thus obtaining a capacitive flexible pressure sensor.

[0087] It should be noted that this application uses a pre-stretching and release one-time molding process to prepare capacitive flexible pressure sensors, which completely eliminates the complex processes such as multi-layer stacking, three-dimensional assembly, and precision micro-nano processing that traditional sensors rely on. This effectively simplifies the preparation process, reduces the processing accuracy requirements, improves the product yield, and enables low-cost, large-scale batch preparation of sensors.

[0088] It should also be noted that the outline shape of the preset through hole opened on the annular fixed frame can be designed to match the target frustum structure; for example, when the frustum structure is a quadrangular frustum, the shape of the preset through hole is set to a rectangle.

[0089] In some embodiments, the method further includes an encapsulation step: pouring a flexible adhesive onto the surface of the capacitive flexible pressure sensor, and curing it to form a flexible encapsulation layer covering the capacitive flexible pressure sensor.

[0090] This application provides a capacitive flexible pressure testing system, including a capacitive flexible pressure sensor, a conductive lead-out circuit assembly, a capacitance acquisition and signal processing module, and a three-dimensional force decoupling calculation module;

[0091] Capacitive flexible pressure sensors are used to sense the deformation differences at different locations under normal and tangential forces, generating differentiated multi-channel capacitive signals.

[0092] The conductive lead-out circuit assembly is electrically connected to the capacitive flexible pressure sensor to transmit the capacitive signal generated by the capacitive flexible pressure sensor to the capacitance acquisition and signal processing module.

[0093] The capacitance acquisition and signal processing module is used to acquire and summarize multiple capacitance signals in real time.

[0094] The three-dimensional force decoupling calculation module is used to receive capacitance signals, perform three-dimensional force decoupling calculations, and output the three-dimensional force components corresponding to the normal and tangential directions.

[0095] In some embodiments, the capacitance acquisition and signal processing module is equipped with a dedicated capacitance-to-digital converter chip. The selected capacitance-to-digital converter chip can be any one of the following: ADI series AD7745, AD7746, TI series FDC1004, FDC2214, and PCAP01.

[0096] In some specific embodiments, the capacitance acquisition and signal processing module includes a PCAP01 capacitance detection chip and an STM32F1 microcontroller; the PCAP01 capacitance detection chip is used to independently acquire the real-time capacitance signal of the capacitance sensor; the STM32F1 microcontroller is electrically connected to the PCAP01 capacitance detection chip and is used to summarize, organize and transmit the capacitance signal.

[0097] It should be noted that the three-dimensional force decoupling operation, a linear method, has low computational cost and good real-time performance, making it more suitable for embedded STM32F1 microcontrollers.

[0098] In some embodiments, the relationship between the capacitance change and the force on the capacitive flexible pressure sensor in the three-dimensional force decoupling calculation module is as follows:

[0099] ;

[0100] Where S is the sensitivity matrix. This represents the change in capacitance of the nth channel caused by a unit force in the j-th direction; Fx, Fy, and Fz are the components of the three-dimensional force; ΔC1~ΔC n These represent the capacitance changes corresponding to the 1st to the nth capacitance sensors, with each capacitance sensor corresponding to one capacitance channel;

[0101] The solution obtained using the pseudo-inverse method is: ;in, The decoupling matrix is ​​denoted by ΔC, which is the capacitance change vector, consisting of the capacitance changes ΔC1 to ΔC of the 1st to nth capacitance sensors. n Arranged in channel order, it forms the input data for the algorithm; F is a three-dimensional force vector, containing orthogonal three-dimensional components Fx, Fy, and Fz, which is the force result output by the algorithm.

[0102] Furthermore, in the three-dimensional force decoupling calculation module, the decoupling calculation process is as follows:

[0103] Step S1: Apply known normal force Fz, tangential force Fx, and tangential force Fy sequentially to the capacitive flexible pressure sensor;

[0104] Step S2: Record the capacitance change of the multi-channel capacitive sensor under each applied force;

[0105] Step S3: Use gradient descent or Adam optimization algorithm to iteratively solve the sensitivity matrix S to obtain the optimal estimate of the sensitivity matrix;

[0106] Step S4: Calculate the corresponding decoupling matrix D based on the optimal estimate, and pre-store the decoupling matrix D in the STM32F1 microcontroller;

[0107] In step S5, during the actual detection process, the STM32F1 microcontroller performs matrix operations on the real-time collected capacitance change and the decoupling matrix D to calculate and output the estimated values ​​of the three-dimensional force components Fx, Fy, and Fz in real time.

[0108] It should be noted that this invention orthogonally arranges capacitive sensors on the oblique side of a three-dimensional micro-protrusion structure. This allows each sensor to exhibit regular and differentiated capacitive response characteristics under external forces in different directions (Fx, Fy, Fz), thus weakening force signal coupling interference at the physical structure level. Based on this, matrix iterative optimization is performed using gradient descent and Adam optimization algorithms to establish a precise mathematical mapping relationship between the four-channel capacitive signals and the three-dimensional force components. This enables accurate differentiation and high-precision decoupling of multi-dimensional force signals in complex flexible stress scenarios, significantly reducing multi-dimensional force decoupling errors.

[0109] As an alternative implementation, in addition to the linear method based on three-dimensional force decoupling calculation, machine learning methods such as neural networks and support vector machines can also be used to establish a nonlinear capacitance-force mapping model to handle a wider range of nonlinear responses and hysteresis effects.

[0110] This application provides a robotic electronic skin, including a capacitive flexible pressure sensor or a capacitive flexible pressure testing system.

[0111] It should be noted that the capacitive flexible pressure sensor or capacitive flexible pressure testing system combines structural simplicity, low-pressure high sensitivity, high-precision decoupling of three-dimensional force, and large-area array integration capability. It effectively solves the industry pain point that traditional robot electronic skin cannot simultaneously achieve both integration and sensing sensitivity. It is suitable for a wide range of scenarios, especially for application fields with stringent requirements for flexible fit, fine tactile perception accuracy, and multi-dimensional force detection stability, such as companion service robots, medical rehabilitation robots, and robot dexterous hands.

[0112] The applicant further provides the following specific embodiments to describe the present invention. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0113] Preparation Example 1

[0114] This preparation example provides a method for preparing a carbon-containing PDMS dielectric layer, including the following steps:

[0115] Step S1, Preparation of carbon-containing PDMS film: Carbon-based conductive filler Ketjen Black EC600JD is incorporated into PDMS prepolymer at a ratio of 1 wt%. The carbon-based conductive filler is uniformly dispersed in PDMS prepolymer using ultrasonic dispersion or mechanical stirring to form a stable composite slurry. PDMS curing agent is added to the composite slurry and mixed evenly, wherein the mass ratio of PDMS prepolymer to PDMS curing agent is 15:1. Subsequently, a carbon-containing PDMS wet film with a thickness of 200 μm is formed on the surface of the target substrate using an automatic film forming machine. After curing, a carbon-containing PDMS film is obtained. In this preparation example, the carbon-containing PDMS wet film can also be directly coated on the side of the PET substrate printed with carbon electrodes to eliminate the subsequent assembly process with the carbon electrode substrate.

[0116] Step S2, Laser Engraving of Microtexture Structures: Using a Trotec Q400 laser engraving machine, a CO2 laser is used to texture one side of the carbon-containing PDMS film. The processing power is set to 5%–20% power output, and the scanning speed is 200–500 mm / s. Various target microtexture structures, such as microgroove arrays, microcone arrays, or micropyramid arrays, are formed on one side of the PDMS film. The surface texture depth is 20–80 μm, and the texture spacing is 40–200 μm. In this preparation example, a cutting process can be used instead of the laser engraving process, such as… Figure 1 The microstructure morphology diagram shown; Figure 1 In the figure, A represents the microtexture structure obtained through laser engraving. Figure 1 In section B, the micro-textured structure is formed using a cutting process. From... Figure 1 As can be seen, both processing methods can produce microtexture structures with complete outlines and clear morphology.

[0117] Step S3, Preparation of carbon-containing PDMS dielectric layer: Two sets of carbon-containing PDMS films with microtextured structures on their surfaces are arranged opposite each other with the side having the microtextured structure.

[0118] In this preparation example, the laser engraving process parameters, microtexture structure pattern type, and geometric dimensions can all be optimized, adapted, and adjusted according to the target detection sensitivity of the sensor.

[0119] This preparation example adopts a dual sensitivity enhancement strategy of "carbon material doping and surface microtexturing structure" to enhance the sensitivity of the carbon-containing PDMS dielectric layer, as follows: (1) Dielectric constant enhancement effect: By doping carbon conductive filler into the PDMS insulating matrix, a large number of conductive filler-insulating matrix microcapacitor interfaces can be constructed inside the matrix. According to the Maxwell-Wagner interface polarization theory, under the action of electric field, the heterogeneous interface will undergo charge accumulation and polarization, which effectively improves the overall equivalent dielectric constant of the composite material. Experimental verification shows that the carbon-containing PDMS dielectric layer prepared by this scheme can reach a piezocapacitive sensitivity factor of 70, which greatly improves the basic sensing response capability of the capacitive sensor. (2) Piezocapacitive response effect: Under the action of external pressure load, the carbon-containing PDMS dielectric layer undergoes elastic compression deformation, and the spacing and distribution state of the internal carbon conductive filler change accordingly, so that the dielectric constant changes with the pressure magnitude, generating additional capacitance signal, which further improves the pressure sensing sensitivity and response accuracy of the capacitive sensor. (3) The microtexture structure changes the dielectric layer from a continuous medium to a porous / columnar structure, and the equivalent elastic modulus is significantly reduced. Under the same external force, the microtextured structured dielectric layer generates greater compressive strain, thereby increasing the relative change in capacitance. (2) In the low-pressure region, the tips of the microtextured structure preferentially contact and deform; as the pressure increases, the main body of the microtextured structure gradually participates in compression. The above multi-level deformation mechanism extends the linear response range of the sensor.

[0120] Preparation Example 2

[0121] See Figure 2 This example provides a method for fabricating a capacitive sensor, comprising the following steps:

[0122] Step S1: Prepare the PDMS substrate and the carbon-containing PDMS dielectric layer:

[0123] PDMS substrate preparation: PDMS prepolymer and PDMS curing agent are mixed evenly at a mass ratio of 10:1, and then a PDMS wet film is formed by automatic film forming machine. After curing treatment, the PDMS substrate is obtained.

[0124] Preparation of carbon-containing PDMS dielectric layer: The carbon-containing PDMS dielectric layer was prepared using the method provided in Preparation Example 1. The specific preparation parameters are as follows: the mass ratio of PDMS prepolymer to PDMS curing agent is 15:1; a Trotec Q400 laser cutting machine was used with a processing power of 15% power output and a scanning speed of 350 mm / s; the target microtexture structure is a microgroove array with a surface texture depth of 50 μm and a texture spacing of 120 μm.

[0125] Step S2, screen printing to prepare carbon electrodes:

[0126] Screen printing stencil preparation: A custom-made screen printing stencil is fabricated based on the electrode design parameters of the capacitance sensor. The capacitance sensor employs a double-layer electrode structure, consisting of an upper electrode and a lower electrode. The electrode pattern is designed as an interdigitated structure or a rectangular planar structure. The electrode dimensions match the dimensions of the rigid constraint area, ensuring that the electrodes can completely conform to the inclined side of the micro-protrusion structure, and multiple sets of electrodes are evenly distributed and rotated along the Z-axis. The effective electrode area is controlled within the range of 2mm×2mm to 8mm×8mm, and the screen is selected with a mesh size of 200-300 mesh to ensure the accuracy and uniformity of the carbon paste printing pattern.

[0127] Carbon electrode preparation: Conductive carbon black was selected as the electrode material. The patterns of the upper and lower electrodes were printed on a 10μm thick PET substrate using a screen printing plate. After printing, the PET substrate was placed in a 60℃ constant temperature oven for 60 minutes to cure, resulting in a PET substrate with carbon electrodes printed on its surface, i.e., a PET substrate with the upper electrode and the lower electrode printed on its surface.

[0128] Step S3, Assembly and Packaging:

[0129] Assembly: Place the PET substrate with the upper electrode and the PET substrate with the lower electrode printed on the surface onto the PDMS substrate, with the sides with the printed electrodes facing each other; attach the carbon-containing PDMS dielectric layer between the upper and lower electrodes to assemble a complete capacitive sensor.

[0130] Encapsulation: The PDMS prepolymer and PDMS curing agent are mixed uniformly at a mass ratio of 15:1 and poured onto the surface of the capacitive sensor.

[0131] In this fabrication example, the core function of the encapsulation process is to isolate the carbon electrode from environmental moisture and dust, preventing it from being eroded and failing due to dust. Therefore, the capacitive sensor can be individually encapsulated first, or the capacitive sensor can be assembled to the target mounting location and then encapsulated together.

[0132] The structure of the capacitive sensor obtained in this preparation example is as follows: Figure 2 As shown in Part 3 of the document:

[0133] The capacitive sensor comprises a PDMS substrate, a PET substrate, a lower electrode, a carbon-containing dielectric layer, an upper electrode, and the PET substrate arranged sequentially; wherein, the PET substrate is a rigid substrate;

[0134] The carbon-containing dielectric layer consists of two independent carbon-containing thin films arranged at intervals, and the relatively mating surfaces of the carbon-containing thin films are provided with a micro-texture structure in the form of a micro-groove array.

[0135] Example 1

[0136] See Figure 3This embodiment provides a method for fabricating a capacitive flexible pressure sensor, including the following steps:

[0137] Step S1, Preparation of PDMS substrate and annular fixation frame:

[0138] PDMS substrate preparation: PDMS prepolymer and PDMS curing agent were mixed uniformly at a mass ratio of 10:1 to obtain a prepolymer solution; the prepolymer solution was subjected to vacuum degassing treatment, and the prepolymer solution was coated onto a flat PET substrate with a thickness of 100μm, a length and width of 297mm*210mm, and a temperature resistance of 150℃ using an automatic film forming machine until a wet film with a thickness of 300μm was formed; the PET substrate covered with the wet film was placed under 80℃ for heat curing for 1 hour, and then the PET substrate was peeled off to obtain an elastic film with a thickness of approximately 270μm. The elastic film was cut into round pieces with a diameter of 90mm for later use.

[0139] Preparation of the ring-shaped fixing frame: ARclear brand PET substrate with a thickness of 100μm was selected, and the PET substrate was processed by laser cutting to obtain a ring-shaped fixing frame with matrix-shaped through holes.

[0140] Step S2, Pre-stretching and fixing the elastic film: Fix the elastic film on the stretching device and stretch it evenly in the radial direction of the elastic film until its diameter is 130% of the original diameter of the elastic film. Then use a clamp to fix it and keep it in a stretched state.

[0141] Step S3, bonding the elastic film and the annular fixing frame: using ARclear double-sided tape, the 50μm thick annular fixing frame is bonded to the surface of the elastic film in a stretched state, and the bonding area forms a rigid constraint zone.

[0142] Step S4, Capacitive Sensor Bonding: Take 4 sets of unencapsulated capacitive sensors prepared in Preparation Example 2, align them precisely with the rigid constraint region, and then bond them to the elastic film surface of the rigid constraint region with ARclear double-sided adhesive, so that the 4 sets of capacitive sensors form an array of capacitive sensing units arranged orthogonally.

[0143] Step S5, forming a micro-protrusion structure: The stretching device is slowly released, and the elastic film undergoes radial contraction due to its own elastic restoring force; due to the limiting effect of the rigid constraint area, the bonding area cannot contract synchronously, and the elastic film undergoes compression buckling deformation at the rigid constraint boundary to form a micro-protrusion structure.

[0144] Step S6, Encapsulation and Protection: PDMS prepolymer and PDMS curing agent are uniformly mixed at a mass ratio of 15:1 and poured onto the surface of the micro-protrusion structure to which the capacitive sensor is bonded. After curing, an electronic skin encapsulation layer with a thickness of 8mm to 10mm is formed, ultimately yielding a capacitive flexible pressure sensor, as shown in Figure 4. This electronic skin not only fixes the overall three-dimensional structure of the sensor and isolates it from the erosion and damage of the electrodes and dielectric layer by environmental humidity and dust, but also ensures accurate transmission of external forces without affecting the sensor's force transmission sensitivity and detection accuracy.

[0145] In this embodiment, the elastic modulus of the elastic film is approximately 1–3 MPa, which is much smaller than the elastic modulus of the PET substrate (approximately 2–4 GPa). Therefore, based on the principle of minimum potential energy structure, this embodiment utilizes the principle that an elastic film with a thickness much smaller than the planar feature size has a much smaller out-of-plane bending deformation energy than its in-plane compressive deformation energy. It is known that when the tension is released, the elastic film undergoes significant elastic contraction, while the PET substrate hardly contracts. The interfacial bonding force between the two causes stress concentration in the elastic film at the edge of the PET substrate, leading to local buckling. The rigidly constrained area arches upward to form a convex structure, while the non-rigidly constrained area forms a downward concave transition zone. This concave-convex structure provides an ideal mechanical transmission platform for three-dimensional force sensing.

[0146] Example 2

[0147] like Figure 5 As shown, this embodiment provides a capacitive flexible pressure sensor, which is prepared using the preparation method provided in Embodiment 1.

[0148] The capacitive flexible pressure sensor includes an annular fixing frame, an elastic film, and a capacitive sensor that are sequentially bonded together. The annular fixing frame is made of PET material and serves as the first rigid substrate. The bonding area between the annular fixing frame and the elastic film constitutes a rigid constraint area, while the area where only the elastic film is set at the through hole of the annular fixing frame is a non-rigid constraint area.

[0149] A rigid constraint area, consisting of a ring-shaped fixed frame and an elastic membrane, bulges upward to form a micro-protrusion structure, specifically a bottomless frustum configuration. The top of the micro-protrusion structure is a planar elastic membrane without rigid constraints. The sidewalls of the micro-protrusion structure are divided into four inclined surfaces by four inclined edges. These four inclined surfaces are rigid constraint areas used to bond capacitive sensors. Each inclined surface corresponds to a stress-bearing region. By utilizing the changes in the capacitive sensors in different stress-bearing regions, preliminary decoupling of forces can be achieved, distinguishing forces from different directions. The rigid constraint areas are interconnected through a contracted elastic membrane. The bottomless micro-protrusion structure, combined with the elastic membrane connecting the rigid constraint areas, provides ample deformation space for the micro-protrusion structure, especially its inclined side surfaces, under stress.

[0150] The capacitive sensors are bonded and fixed to the surface of an elastic thin film in a rigid constraint region, and are orthogonally distributed. The capacitive sensor includes a PET substrate with an upper electrode printed on it and a PET substrate with a lower electrode printed on it, and a carbon-containing PDMS dielectric layer is disposed between the upper and lower carbon electrodes.

[0151] In this embodiment, the height of the micro-protrusion structure can be dynamically controlled by adjusting the film pre-stretch ratio and the PET frame thickness, and the controllable range of protrusion height is 1μm to 6μm.

[0152] The capacitive flexible pressure sensor provided in this embodiment achieves partial decoupling of normal and tangential forces at the physical level through a differential layout: four capacitive sensors are orthogonally arranged at the four positions of the micro-protrusion structure. When the capacitive flexible pressure sensor is subjected to a normal force, the four capacitive sensors are uniformly compressed; when the capacitive flexible pressure sensor is subjected to a tangential force, the micro-protrusion structure tilts, the capacitive sensor on the side of the applied force is compressed and its capacitance increases, while the capacitive sensor on the opposite side is stretched or decompressed and its capacitance decreases. The changes in capacitive sensors on adjacent sides are small. This differentiated response mode can distinguish three-dimensional forces.

[0153] Example 3

[0154] This embodiment provides a capacitive flexible pressure testing system, including the capacitive flexible pressure sensor of Embodiment 2, a conductive lead-out circuit assembly, a capacitance acquisition and signal processing module, and a three-dimensional force decoupling calculation module;

[0155] The capacitive flexible pressure sensor comprises a micro-protrusion structure and a capacitive sensor array. The array consists of four independent capacitive sensors, each positioned on one of the four oblique sides of the frustum-shaped micro-protrusion structure, numbered C1, C2, C3, and C4 respectively. These sensors synchronously sense deformation changes at different locations on the substrate, generating differentiated capacitive signal responses. When an external three-dimensional force is applied to the surface of the capacitive flexible pressure sensor, it drives the micro-protrusion structure to undergo non-uniform, differentiated deformation. This deformation is synchronously transmitted to each capacitive sensing unit, relying on the differential characteristics of the four sensing signals to construct the physical structural basis for three-dimensional force decoupling.

[0156] The conductive lead-out circuit assembly consists of conductive wiring extending from the upper and lower electrodes of each capacitance sensor and metal pads, used to achieve electrical conduction between the sensing array and the back-end acquisition chip, and to stably transmit the four capacitance signals to the signal input channel of the PCAP01 capacitance detection chip.

[0157] The capacitance acquisition and signal processing module includes a PCAP01 high-precision capacitance detection chip and an STM32F1 microcontroller. The PCAP01 capacitance measurement chip is the detection unit, which, together with the STM32F1 microcontroller, forms a hardware circuit. The PCAP01 chip is responsible for acquiring the capacitance signals of each sensing unit, and the STM32F1 microcontroller completes the data aggregation and transmission.

[0158] The three-dimensional force decoupling calculation module performs three-dimensional force decoupling calculations on the transmitted data and outputs accurate three-dimensional force components Fx, Fy, and Fz.

[0159] Example 4

[0160] The capacitive flexible pressure sensor of the present invention can achieve partial decoupling of normal force and tangential force. In order to further reduce signal coupling and improve measurement accuracy, this embodiment provides a three-dimensional force decoupling algorithm based on the decoupling matrix.

[0161] Based on the working principle of the capacitive flexible pressure sensor, the relationship between the capacitance change ΔC and the applied force F is shown in the following equation:

[0162] ;

[0163] That is, ΔC = S × F, where S is the sensitivity matrix, and S nj This represents the change in capacitance of the nth channel caused by a unit force in the j-th direction.

[0164] Since matrix S is usually not a square matrix (4×3), it needs to be solved using the pseudo-inverse method: ;in, This is a 3×4 decoupling matrix, where ΔC is the capacitance change vector, representing the capacitance changes ΔC1 to ΔC of the 1st to nth capacitance sensors. n The input data is arranged in the order of the channels; F is the three-dimensional force vector, which includes orthogonal three-dimensional components Fx, Fy, and Fz, and is the force result output by the solution.

[0165] Therefore, the method for calibrating the decoupling matrix is ​​as follows:

[0166] Step S1: Apply known normal force Fz, tangential force Fx, and tangential force Fy to the capacitive flexible pressure sensor using a precision force loading device.

[0167] Step S2: Record the capacitance changes of the four channels under different force values, and denote them as ΔC1, ΔC2, ΔC3, and ΔC4, respectively.

[0168] Step S3: Based on multiple sets of calibration data, use the gradient descent method or the Adam optimization algorithm to solve for the optimal estimate of the sensitivity matrix S;

[0169] Step S4, calculate the decoupling matrix The data is stored in the STM32F1 microcontroller. In actual testing, the STM32F1 microcontroller multiplies the real-time acquired ΔC vector by the decoupling matrix D to obtain the estimated values ​​of the three-dimensional force components Fx, Fy, and Fz.

[0170] To further improve decoupling accuracy, auxiliary algorithms such as temperature compensation and hysteresis compensation can be combined, and some filtering algorithms can also be used to improve the monitoring signal-to-noise ratio of the applied force sequence.

[0171] Example 5

[0172] See Figure 6 This embodiment provides a capacitance measurement circuit, including a PCAP01 capacitance measurement chip unit, a power management unit, and an external signal interface unit, for acquiring capacitance values ​​from multiple capacitance sensors and communicating with an STM32F1 microcontroller.

[0173] The power management unit uses the XC6206P332MR low-dropout linear regulator chip U2 to convert 5V input to 3.3V system power, providing stable operating power for the PCAP01 measurement chip, communication interface, and sensor acquisition channel. Input side: Pin 3, VIN, is connected to an external VCC-5V power supply, with parallel filter capacitors C1 (10μF) and C2 (100nF) connected to GND to suppress input power ripple and high-frequency interference. Output side: Pin 2, VOUT, outputs a stable 3.3V voltage, with parallel filter capacitors C3 (10μF) and C4 (100nF) to optimize output voltage smoothness. Power indicator circuit: The VOUT output terminal is connected in series with a current-limiting resistor R4 and an LED1, then grounded. LED1 is constantly lit when powered on, and pin 1, VSS, is grounded.

[0174] The PCAP01 capacitance measurement chip unit is used for high-precision sampling of multi-channel sensing capacitance, and is equipped with complete power supply filtering, reference voltage regulation, sampling buffer, and SPI communication peripheral circuitry. The VDD pin is connected to VCC-3V3, with parallel power supply filter capacitors C7 (4.7μF) and C11 (100nF). The PT2REF reference pin is synchronously connected to VCC-3V3, with a filter capacitor C8 (100nF) to provide a stable voltage for the chip. The GND and EP ground pins are directly connected to the system common ground to reduce analog signal noise. The VPP_OTP pin is pulled down to GND via R3 (470kΩ) to configure the chip's factory default OTP register operating mode. The BUFFCAP array pins (PC0~PC5) are externally connected to ground with parallel buffer capacitors C6 (4.7μF) and C14 (100nF) to amplify weak sensing capacitance signals and improve the detection signal-to-noise ratio. The PCAP01AD analog output pin is grounded with a filter capacitor C9 (33nF) to suppress analog sampling noise. A composite filter capacitor, C13 (4.7μF) and C12 (100nF), is connected in parallel to the BUFFCAP, TXOUT, OXIN, and OXOUT pins to stabilize the operating point of the internal charge amplification circuit. The MOSI, SSN, SCK, and MISO pins output four SPI signals (PCAP-MOSI, PCAP-SSN, PCAP-SCK, PCAP-MISO) for transmitting capacitance sampling data to the STM32F1 microcontroller. The INTN interrupt pin outputs a level signal for the STM32F1 microcontroller to receive the chip's sampling completion interrupt notification. The MOSI_EN pin is enabled by the main controller's output level for SPI communication. The chip reserves four differential capacitance acquisition channels: IN0_A / IN0_B, IN1_A / IN1_B, IN2_A / IN2_B, and IN3_A / IN3_B, corresponding to the four capacitance sensors C1 to C4 in Example 3, enabling synchronous detection of four channels of capacitance.

[0175] The external signal interface unit features multiple PZ254V series 2.54mm pitch pin headers for modular plug-and-play connections of sensor input, main control communication, and external power supply. Sensor capacitor input sockets H5, H6, H7, and H8: four dual-channel sockets corresponding to the four differential acquisition channels IN0 to IN3. The common pin of each socket is connected to GND for connecting the upper and lower electrode leads of the flexible capacitive sensor, connecting the four sensing capacitors to the PCAP01 chip's detection channel. A C0 (C15) compensation capacitor pad is reserved for connecting an external reference compensation capacitor C0_gnd as needed to eliminate parasitic capacitance detection errors. SPI communication socket H4: a four-wire socket with PCAP-MOSI, PCAP-SSN, PCAP-SCK, and PCAP-MISO signals respectively, directly connected to the STM32 main control MCU's SPI peripheral pins for bidirectional transmission of sampled data. Power input socket H1: a dual-power supply socket, connecting to both an external VCC-5V input power supply and the chip's operating VCC-3V3 power supply. Multi-functional expansion socket H2: A multi-pin reserved socket, including GND common ground and spare IO expansion pins. The external 5V power supply is regulated by U2 to generate a stable 3.3V voltage, which powers the PCAP01 chip and all interfaces. The four differential capacitance signals of the flexible three-dimensional force sensor are connected to the IN0-IN3 acquisition channels of PCAP01 through sockets H5-H8. After the PCAP01 performs charge amplification and capacitance analog-to-digital conversion internally, the four capacitance values ​​are uploaded to the STM32F1 microcontroller through the SPI bus of socket H4. After receiving the capacitance signals, the microcontroller forwards them to the three-dimensional force decoupling calculation module, which combines the three-dimensional force decoupling algorithm to complete the analytical calculation of the three-dimensional force.

[0176] Example 6

[0177] This embodiment provides a capacitive flexible pressure testing system, including the capacitive flexible pressure sensor of Embodiment 2, a conductive lead-out circuit assembly, a capacitance acquisition and signal processing module, and a three-dimensional force decoupling calculation module;

[0178] The capacitive flexible pressure sensor comprises a micro-protrusion structure and a capacitive sensor array. The array consists of four independent capacitive sensors, each positioned on one of the four oblique sides of the frustum-shaped micro-protrusion structure, numbered C1, C2, C3, and C4 respectively. These sensors synchronously sense deformation changes at different locations on the substrate, generating differentiated capacitive signal responses. When an external three-dimensional force is applied to the surface of the capacitive flexible pressure sensor, it drives the micro-protrusion structure to undergo non-uniform, differentiated deformation. This deformation is synchronously transmitted to each capacitive sensing unit, relying on the differential characteristics of the four sensing signals to construct the physical structural basis for three-dimensional force decoupling.

[0179] The conductive lead-out circuit assembly consists of conductive wiring extending from the upper and lower electrodes of each capacitance sensor and metal pads, used to achieve electrical conduction between the sensing array and the back-end acquisition chip, and to stably transmit the four capacitance signals to the signal input channel of the PCAP01 capacitance detection chip.

[0180] The capacitance acquisition and signal processing module includes a PCAP01 high-precision capacitance detection chip and an STM32F1 microcontroller. Specifically, the capacitance measurement circuit of Example 5 is used for data processing.

[0181] The three-dimensional force decoupling calculation module uses the three-dimensional force decoupling algorithm of Example 4 for secondary decoupling.

[0182] Figure 7 This is a schematic diagram of the visualization interface for real-time data acquisition and force calculation of a capacitive flexible pressure testing system. The upper left corner shows the layout of the four sensing units and the corresponding force values. The size of the blue circle in the upper right corner of the interface represents the magnitude of the Z-axis force component, and the red vector arrows represent the force components in the X and Y planes. The lower part of the interface displays the real-time capacitance values ​​acquired by the four channels.

[0183] Figure 8 The distribution of data points showing the rate of change of capacitance value of the sensor when no pressure is applied during measurement using the capacitive flexible pressure testing system provided in Example 6; Figure 9 This is a schematic diagram comparing the deviation between the PCAP measured value and the actual value during measurement using the capacitive flexible pressure testing system provided in Example 6; the first column of data C in the figure represents the nominal value of the standard capacitor C0, and the second column PCAP represents the capacitance value C_ measured by the PCAP01 chip. PCAP ; Third column C_ delta For (C_ PCAP -C0), the absolute value is taken in subsequent calculations; the fourth column is the calculation of the capacitance change rate C_ delta / C0 represents the magnitude of the deviation of the capacitance change rate.

[0184] In the actual test conditions of this embodiment, the measurement error mainly comes from two types: (1) noise of the capacitance detection circuit: such as Figure 8 As shown, the peak-to-peak value of the capacitance change rate ΔC / C0 under no pressure loading is less than 0.03; substituting this fluctuation into the sensitivity curve, the force measurement error introduced by circuit noise is calculated to be less than 0.0654N; (2) Inherent deviation of PCAP chip capacitance measurement: The sensitivity calibration and actual acquisition of this scheme both use the PCAP01 chip, and the capacitance value measured by this chip has a systematic deviation from the real standard capacitance. Figure 9 It can be seen that the deviation of the chip's measured capacitance from the standard capacitance is about 5.13%, which corresponds to a system fluctuation deviation of 0.0513 for the capacitance change rate ΔC / C0. The force measurement error introduced by this can reach up to 0.1118N.

[0185] Comparative Example 1

[0186] This comparative example provides a capacitive flexible pressure sensor, which differs from Example 2 in that: neither the upper nor lower surfaces of the carbon-containing PDMS dielectric layer have microtexture structures, and the dielectric layer as a whole has a smooth planar structure.

[0187] The pressure sensing performance of the capacitive flexible pressure sensor with microtextured structure prepared in Example 2 and the smooth planar capacitive flexible pressure sensor prepared in this comparative example were compared and tested. The test results are as follows. Figure 10 As shown.

[0188] Within the pressure testing range of 0.1 kPa to 20 kPa, the sensitivity of the sensor with a smooth dielectric layer and no microtexture structure is: .

[0189] Example 2, employing a surface-textured structured carbon PDMS dielectric layer, has a sensor sensitivity of [missing information]. , Compared to a smooth planar structure, the introduction of microtexture structures on the dielectric layer surface can improve the detection sensitivity of the sensing unit by approximately 1.6 times.

[0190] The above are merely preferred embodiments of this application and are not intended to limit the present invention. Although this application has been described in detail with reference to examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A capacitive flexible pressure sensor, characterized in that, Including micro-protrusion structures and capacitive sensors; The micro-protrusion structure is a frustum structure formed by bonding a first rigid substrate and an elastic film; the top of the frustum structure is an elastic film, the inclined side is a composite area of ​​the first rigid substrate and the elastic film, and the adjacent sides of the inclined side are connected by the elastic film; the capacitive sensor is fixed on each of the inclined sides.

2. The capacitive flexible pressure sensor according to claim 1, characterized in that, The capacitive sensor includes a second rigid substrate, an upper electrode, a carbon-containing dielectric layer, a lower electrode, and a third rigid substrate arranged sequentially. The carbon-containing dielectric layer is composed of two independent carbon-containing thin films arranged at intervals, and the relatively mating surfaces of the carbon-containing thin films are provided with micro-texture structures.

3. The capacitive flexible pressure sensor according to claim 1, characterized in that, The surface of the capacitive flexible pressure sensor is covered with a flexible encapsulation layer.

4. A method for manufacturing a capacitive flexible pressure sensor according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1: Prepare a first rigid substrate and an elastic film, wherein the elastic modulus of the first rigid substrate is less than that of the elastic film; process the first rigid substrate to obtain a fixing frame with a preset through hole. Step S2: The elastic film is stretched to put it in a stretched state, and the fixed frame is bonded to the stretched elastic film, forming a rigid constraint area in the bonding area. Step S3: Fix the capacitive sensor to the surface of the rigid constraint area; Step S4: Release the tension of the elastic film to allow it to retract. The rigid constraint area undergoes buckling deformation as the elastic film retracts, forming a micro-protrusion structure, thus obtaining a capacitive flexible pressure sensor.

5. The method for fabricating a capacitive flexible pressure sensor according to claim 4, characterized in that, It also includes a packaging step: pouring a flexible adhesive onto the surface of the capacitive flexible pressure sensor, which, after curing, forms a flexible encapsulation layer covering the capacitive flexible pressure sensor.

6. A capacitive flexible pressure testing system, characterized in that, Includes the capacitive flexible pressure sensor, conductive lead-out circuit assembly, capacitance acquisition and signal processing module, and three-dimensional force decoupling calculation module as described in any one of claims 1 to 3; The capacitive flexible pressure sensor is used to sense the deformation differences at different positions under normal and tangential forces, and generate differentiated multi-channel capacitive signals. The conductive lead-out line assembly is electrically connected to the capacitive flexible pressure sensor and is used to transmit the capacitive signal generated by the capacitive flexible pressure sensor to the capacitance acquisition and signal processing module. The capacitance acquisition and signal processing module is used to acquire and aggregate multiple capacitance signals in real time. The three-dimensional force decoupling calculation module is used to receive the capacitance signal, perform three-dimensional force decoupling calculation, and output the three-dimensional force components corresponding to the normal and tangential directions.

7. The capacitive flexible pressure testing system according to claim 6, characterized in that, The capacitance acquisition and signal processing module includes a PCAP01 capacitance detection chip and an STM32F1 microcontroller. The PCAP01 capacitance detection chip is used to independently acquire real-time capacitance signals from capacitance sensors; the STM32F1 microcontroller is electrically connected to the PCAP01 capacitance detection chip and is used to summarize, organize, and transmit capacitance signals.

8. The capacitive flexible pressure testing system according to claim 6, characterized in that, In the three-dimensional force decoupling calculation module, the relationship between the capacitance change and the force on the capacitive flexible pressure sensor is as follows: ； Where S is the sensitivity matrix. This represents the change in capacitance of the nth channel caused by a unit force in the j-th direction; Fx, Fy, and Fz are the components of the three-dimensional force; ΔC1~ΔC n These represent the capacitance changes corresponding to the 1st to the nth capacitance sensors, respectively. The solution obtained using the pseudo-inverse method is: ;in, Let be the decoupling matrix, ΔC be the capacitance change vector, and F be the three-dimensional force vector.

9. The capacitive flexible pressure testing system according to claim 8, characterized in that, In the three-dimensional force decoupling calculation module, the decoupling calculation process is as follows: Step S1: Apply known normal force Fz, tangential force Fx, and tangential force Fy sequentially to the capacitive flexible pressure sensor; Step S2: Record the capacitance change of the multi-channel capacitive sensor under each applied force; Step S3: Use gradient descent or Adam optimization algorithm to iteratively solve the sensitivity matrix S to obtain the optimal estimate of the sensitivity matrix; Step S4: Calculate the corresponding decoupling matrix D based on the optimal estimate, and pre-store the decoupling matrix D in the STM32F1 microcontroller; In step S5, during the actual detection process, the STM32F1 microcontroller performs matrix operations on the real-time collected capacitance change and the decoupling matrix D to calculate and output the estimated values ​​of the three-dimensional force components Fx, Fy, and Fz in real time.

10. A robotic electronic skin, characterized in that, It includes the capacitive flexible pressure sensor according to any one of claims 1 to 3, or the capacitive flexible pressure sensor obtained by the preparation method according to any one of claims 4 to 5, or the capacitive flexible pressure testing system according to any one of claims 6 to 9.

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