A multi-layer heterogeneous structure thin film switch pressure sensing system

Abstract

The application belongs to the technical field of sensors, and particularly relates to a multi-layer heterogeneous structure film switch pressure sensing system, which comprises a cover layer structure module, a gradient transition layer structure module, a force sensing layer structure module, a stress deflection modeling module, an error compensation operation module and a signal output module, the cover layer adopts rigid-flex coupling double-layer composite design; the gradient transition layer reduces stress deflection angles by setting a Young's modulus gradient transition layer; the force sensing layer adopts a graphene and polyvinylidene fluoride composite material to convert pressure signals into electric signals; the system effectively eliminates systematic positioning errors caused by stress deflection in the multi-layer heterogeneous structure by combining interlayer mechanical parameter gradientization design and stress deflection modeling compensation, and can realize uniform distribution of positioning errors in the whole sensing area.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically a multilayer heterogeneous thin-film switch pressure sensing system. Background Technology

[0002] Thin-film pressure sensors are widely used in fields such as smart touch control, human-computer interaction, robot end effector force control, and pressure measurement arrays due to their characteristics of being lightweight, flexible, and highly integrable. Spatial positioning accuracy is one of the core indicators for evaluating the performance of this type of sensor, directly determining the accuracy of multi-point pressure detection and the response quality of human-computer interaction. Existing multilayer thin-film pressure sensors generally adopt a heterogeneous structure design with composite functional layers such as a cover layer, an isolation layer, and a force-sensitive layer. Each functional layer is made of materials with different mechanical properties to undertake corresponding functions such as mechanical protection, electrical isolation, and pressure-to-electrical signal conversion.

[0003] The pressure transmission analysis of existing multilayer thin-film pressure sensors generally adopts the simplified assumption that stress is transmitted in the vertical direction, treating the force-bearing points on the sensor surface and the sensing points of the force-sensitive layer as spatially corresponding positions. The structural design stage mainly focuses on the selection of functional characteristics of each layer material, while the calibration and algorithm compensation stages correct for conventional characteristics of force-sensitive materials such as nonlinearity, temperature drift, and hysteresis, which can meet the basic pressure detection and positioning requirements in low-precision scenarios.

[0004] However, this technical approach does not fully recognize the deflection effect of interlayer stress transmission in multilayer heterogeneous structures. Due to the significant differences in Young's modulus and Poisson's ratio of the materials in each functional layer, stress will be deflected during interlayer transmission, resulting in a spatial offset between the actual pressure-sensing position of the force-sensitive layer and the force-bearing point on the sensor surface. The simplified assumptions deviate fundamentally from the actual stress transmission law. Furthermore, the structural design did not take the matching of interlayer mechanical parameters into consideration, and the calibration compensation system did not cover the systematic positioning error caused by stress deflection. This resulted in the sensor exhibiting an uneven distribution of positioning error, with the edge region having a larger positioning error than the central region. When the interlayer materials were not properly matched, the positioning error could reach hundreds of micrometers or even millimeters, affecting the application of thin-film pressure sensors in high-precision pressure measurement and human-computer interaction.

[0005] Therefore, the present invention provides a multilayer heterogeneous thin-film switch pressure sensing system. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] The technical solution adopted by the present invention to solve its technical problem is as follows: The multilayer heterogeneous thin-film switch pressure sensing system of the present invention includes a cover layer structure module, a gradient transition layer structure module, a force-sensitive layer structure module, a stress deflection modeling module, an error compensation calculation module, and a signal output module.

[0008] In the cover layer structure module, the system adopts a rigid-flexible coupled double-layer composite cover layer design. The outer layer is made of high-hardness polyimide film with a thickness of 25 to 50 micrometers, and the inner layer is made of low Young's modulus silicone rubber buffer layer with a thickness of 50 to 100 micrometers. The outer and inner layers are bonded together without bubbles through a vacuum pressing process to form an integrated cover layer structure. This cover layer structure module is oriented towards the direction of the measured pressure to provide mechanical protection and initial stress diffusion for the internal structure of the sensor.

[0009] In the gradient transition layer structure module, the system sets a Young's modulus gradient transition layer between the cover layer structure module and the force-sensitive layer structure module. This transition layer is composed of multiple layers of materials with gradient Young's modulus. The ratio of Young's modulus between adjacent material layers is controlled within the range of 1.2 to 1.5. The total thickness of the transition layer is 30 micrometers to 80 micrometers. The material selected is a polyurethane and carbon nanotube composite system. The Young's modulus of the polyurethane matrix increases linearly along the thickness direction, and the volume fraction of carbon nanotubes increases linearly along the thickness direction. This gradient transition layer structure module significantly reduces the deflection angle during stress transmission through the gradient design of interlayer mechanical parameters.

[0010] In the force-sensitive layer structure module, the system sets up a force-sensitive functional layer, which is made of graphene and polyvinylidene fluoride composite material with a thickness of 10 micrometers to 30 micrometers. The resistance change rate of the force-sensitive functional layer has an approximately linear relationship with the pressure action, and the sensitivity coefficient is greater than or equal to 0.5 millivolts per kilopascal. Flexible printed circuit electrodes are set below the force-sensitive functional layer. The electrode pattern adopts a modified interdigital structure with a finger width of 50 micrometers to 100 micrometers and a finger spacing of 80 micrometers to 150 micrometers. The electrode material is gold-plated copper foil with a thickness of 18 micrometers to 35 micrometers. This force-sensitive layer structure module is used to convert the sensed pressure signal into an electrical signal.

[0011] The stress deflection modeling module communicates with the gradient transition layer structure module and the force-sensitive layer structure module. This module integrates an analytical model of interlayer stress transfer based on elasticity theory. The analytical model is based on the constitutive equation of the multilayer composite structure. By establishing a set of simultaneous equilibrium equations for the capping layer, gradient transition layer and force-sensitive layer, it quantitatively calculates the stress transfer path, deflection angle and the equivalent load position acting on the force-sensitive layer at any surface stress point in the multilayer structure. The stress deflection modeling module has a pre-set stress deflection parameter mapping table under different interlayer Young's modulus combinations. The dimensions of the mapping table cover the parameter space from Young's modulus ratio from 1.1 to 3.0, Poisson's ratio from 0.3 to 0.45 and layer thickness ratio from 0.5 to 2.0.

[0012] The error compensation calculation module is communicatively connected to the stress deflection modeling module and the force-sensitive layer structure module. This module receives the actual sensing position coordinates output by the force-sensitive layer structure module and the original input coordinates of the surface stress points. Based on the stress deflection parameters provided by the stress deflection modeling module, it calculates the spatial position offset vector between the surface stress points and the force-sensitive layer sensing points, and corrects the original coordinates in real time according to the offset vector. The correction algorithm adopts a back projection compensation strategy. The error compensation calculation module also integrates a positioning error distribution uniformization processing unit. This unit establishes an error adaptive coordinate mapping relationship in the entire sensing area, so that the compensated positioning error is approximately uniformly distributed throughout the entire area.

[0013] The signal output module communicates with the error compensation calculation module. This module standardizes and encapsulates the corrected coordinate data and the corresponding pressure signal. The output interface supports serial peripheral interface protocol and analog voltage output mode. The transmission rate of serial peripheral interface protocol is 10 megabits per second, and the range of analog voltage output mode is 0 to 5 volts. The pressure resolution is better than 12 bits. The signal output module integrates a digital filtering unit. The filtering algorithm adopts a finite impulse response low-pass filter with a cutoff frequency of 500 Hz.

[0014] Preferably, in the gradient transition layer structure module, the number of gradient gradient material layers is not less than 5. The Young's modulus of each layer is distributed according to a preset gradient function. The gradient function is in the form of a cosine function. The minimum value of the Young's modulus appears near the interface of the force-sensitive layer structure module, and the maximum value appears near the interface of the cover layer structure module. The increment of the Young's modulus between adjacent layers is controlled within the range of 5% to 15%.

[0015] Preferably, in the stress deflection modeling module, the interlayer stress transfer analytical model also includes a boundary effect correction submodule. This submodule is specifically used to handle stress deflection calculations in the region near the sensor edge. The boundary effect correction submodule introduces a stress concentration factor to incrementally compensate for the stress deflection angle in the edge region. The value of the stress concentration factor is negatively correlated with the distance from the surface stress point to the edge. When the distance is less than 3 times the thickness of the cover layer, the boundary correction logic is enabled.

[0016] Preferably, in the error compensation calculation module, the positioning error distribution uniformity processing unit adopts a mathematical strategy of partition interpolation to divide the full sensing area into no less than 64 uniform grid sub-regions. A local coordinate mapping function is established in each sub-region, and the mapping functions of adjacent sub-regions satisfy the first-order continuous differentiability condition at the boundary, thereby ensuring the smoothness and consistency of coordinate mapping in the full sensing area.

[0017] Preferably, in the signal output module, the finite impulse response filter of the digital filtering unit has an order of not less than 128, the filter coefficients are designed using Chebyshev window functions, the stopband attenuation is greater than or equal to 60 dB, the passband ripple is less than or equal to 0.1 dB, and the signal output module also integrates an oversampling and decimation processing unit with an oversampling factor of 8 and a decimation factor of 8 to achieve an equivalent high-resolution analog-to-digital conversion effect.

[0018] Preferably, the system of the present invention further includes a temperature drift compensation module, which is communicatively connected to the force-sensitive layer structure module and the error compensation calculation module. The temperature drift compensation module collects the temperature data of the sensor's working environment in real time, with a temperature acquisition accuracy of ±0.1 degrees Celsius. Based on a preset temperature-sensitivity coefficient correspondence table, it performs temperature compensation correction on the electrical signal output by the force-sensitive layer structure module. The temperature coverage range of the temperature-sensitivity coefficient correspondence table is from -20 degrees Celsius to 80 degrees Celsius.

[0019] This invention also provides a compensation method for a multilayer heterogeneous thin-film switch pressure sensing system. The method includes the following steps: acquiring the original coordinates of the force-bearing point on the sensor surface and the corresponding force-sensitive layer output signal; calculating the stress transmission path and deflection angle from the force-bearing point to the force-sensitive layer using a stress deflection modeling module based on the interlayer mechanical parameters of the multilayer composite structure; determining the spatial offset of the force-sensitive layer sensing point relative to the surface force-bearing point based on the calculated deflection angle; performing reverse correction on the original coordinates based on the offset to obtain the compensated positioning coordinates; and standardizing and outputting the compensated positioning coordinates and the pressure signal.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. By setting up a gradient transition layer structure module, a Young's modulus gradually changing transition layer is established between the cover layer and the force-sensitive layer. The Young's modulus ratio between adjacent layers is controlled within the range of 1.2 to 1.5, which effectively reduces the deflection angle during stress transmission. The stress line is transformed from a drastic broken line transmission to an approximately smooth curve transmission, weakening the impact of interlayer stress deflection effect on spatial positioning accuracy. This can solve the systematic positioning error problem caused by abrupt changes in interlayer mechanical parameters in existing technologies.

[0021] 2. By setting up a stress deflection modeling module and an error compensation calculation module, an analytical model of interlayer stress transfer based on elasticity theory was established, and a stress deflection parameter mapping table covering a wide parameter space was pre-set, enabling the system to accurately calculate the position of the corresponding force-sensitive layer sensing point for any surface stress point. The original coordinates were corrected in real time through a back projection compensation strategy, effectively eliminating the positioning offset caused by the difference in mechanical parameters between layers in multilayer heterogeneous structures.

[0022] 3. By setting up a positioning error distribution uniformity processing unit, a mathematical strategy of partition interpolation is adopted to establish an error adaptive coordinate mapping relationship in the entire sensing area, so that the compensated positioning error is nearly uniformly distributed in the entire area, eliminating the inherent defect of uneven positioning error distribution between the edge area and the center area, and significantly improving the consistency performance of the sensor in the entire sensing area.

[0023] 4. By setting up a temperature drift compensation module, ambient temperature data is collected in real time and compensation is performed according to the temperature-sensitivity coefficient correspondence table, which effectively eliminates the influence of temperature changes on the sensitivity of force-sensitive materials and further improves the positioning accuracy and stability of the system in complex working environments.

[0024] 5. The high-order finite impulse response digital filtering unit and oversampling decimation processing unit integrated in the signal output module effectively suppress the impact of electromagnetic interference and quantization noise on positioning accuracy, enabling the system to maintain high response speed while possessing excellent signal-to-noise ratio performance, providing reliable signal quality assurance for high-precision pressure positioning measurement. Attached Figure Description

[0025] The invention will now be further described with reference to the accompanying drawings.

[0026] Figure 1 This is a structural block diagram of a multilayer heterogeneous thin-film switch pressure sensing system according to the present invention; Figure 2 This is a schematic diagram of the structural framework of the gradient transition layer structure module and the force-sensitive knowledge layer structure module in this invention. Detailed Implementation

[0027] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0028] Example 1: like Figure 1 and Figure 2 As shown, this embodiment is specifically applied to a high-precision thin-film pressure sensor array system, which is deployed in intelligent touch and human-computer interaction application scenarios to achieve accurate perception and spatial positioning of multi-point pressure signals; In this embodiment, the multilayer heterogeneous thin-film switch pressure sensing system includes a cover layer structure module, a gradient transition layer structure module, a force-sensitive layer structure module, a stress deflection modeling module, an error compensation calculation module, a signal output module, and a temperature drift compensation module. The modules are connected to each other through a preset data interface and communication link to form a complete data acquisition, processing, and output closed loop.

[0029] The cover layer structure module is located on the outermost layer of the system, facing the direction of the measured pressure. The cover layer structure module adopts a rigid-flexible coupled double-layer composite cover layer design, specifically including an outer high-hardness polyimide film layer and an inner low Young's modulus silicone rubber buffer layer.

[0030] The outer high-hardness polyimide film layer has a thickness of 40 micrometers. The material is a high-temperature resistant polyimide film with a Young's modulus controlled in the range of 3000 MPa to 3500 MPa and a hardness grade of Shore D85 or higher, which can withstand friction and impact under normal operating conditions.

[0031] The outer and inner layers are bonded together without bubbles using a vacuum pressing process. The thickness of the bonding layer is controlled within the range of 5 to 10 micrometers to ensure a stable integrated cover structure between the two layers. The inner layer, a low Young's modulus silicone rubber buffer layer, has a thickness of 80 micrometers. The silicone rubber matrix is ​​an addition-type room temperature vulcanizing silicone rubber with a Young's modulus controlled within the range of 0.5 MPa to 1.0 MPa and an elongation at break greater than 400%, which can effectively absorb the impact energy transmitted from the high-hardness outer layer.

[0032] The overall thickness of the cover layer structure module is 120 micrometers to 135 micrometers. This module is located on the outermost side of the sensor and is used to provide mechanical protection for the internal structure of the sensor. It also diffuses the external pressure acting on the sensor surface in the initial stage, so that the concentrated load acting on the cover layer is distributed into a relatively uniform load and then transferred to the lower layer.

[0033] The gradient transition layer structure module is set between the cover layer structure module and the force-sensitive layer structure module to realize the gradient transition of mechanical parameters between layers. The gradient transition layer structure module is composed of multiple layers of materials with gradient-changing Young's modulus, and the ratio of Young's modulus between adjacent material layers is controlled within the range of 1.2 to 1.5.

[0034] The total thickness of the gradient transition layer structure module is selected as 55 micrometers. It is composed of 6 layers of polyurethane and carbon nanotube composite materials with different Young's moduli stacked sequentially. The Young's modulus of the polyurethane matrix of each layer increases linearly along the thickness direction. The Young's modulus of the first polyurethane matrix is ​​5 MPa, and the Young's modulus of the sixth polyurethane matrix is ​​25 MPa.

[0035] The volume fraction of carbon nanotubes also increases linearly along the thickness direction, with the first layer of carbon nanotubes having a volume fraction of 1% and the sixth layer having a volume fraction of 5%.

[0036] The Young's modulus ratio between each layer is precisely controlled within the range of 1.25 to 1.35, and the increment of Young's modulus between adjacent layers is 12%. The gradient function is a cosine function. The minimum value of Young's modulus occurs near the interface of the force-sensitive layer structural module, and the maximum value occurs near the interface of the cover layer structural module.

[0037] The gradient transition layer structure module transforms the stress transmission process from a drastic broken line to an approximately smooth curve through the gradient design of interlayer mechanical parameters, significantly reducing the deflection angle during stress transmission.

[0038] The force-sensitive layer structure module is located below the gradient transition layer structure module and is used to convert the sensed pressure signal into an electrical signal. The force-sensitive layer structure module includes a force-sensitive functional layer and flexible printed circuit electrodes.

[0039] The force-sensitive functional layer is composed of graphene and polyvinylidene fluoride composite material with a thickness of 20 micrometers and a graphene volume fraction of 2%. The resistance change rate of the force-sensitive functional layer is approximately linearly related to the pressure, and the sensitivity coefficient is 0.65 millivolts per kilopascal. The resistance value of the force-sensitive functional layer decreases linearly with increasing pressure.

[0040] Flexible printed circuit electrodes are set below the force-sensitive functional layer. The electrode pattern adopts an improved interdigital structure with a finger width of 80 micrometers and a finger spacing of 120 micrometers. The total number of interdigital electrodes is 48 pairs.

[0041] The electrode material is gold-plated copper foil with a thickness of 25 micrometers and a gold plating layer thickness of 0.5 micrometers, ensuring that the electrode has good conductivity and corrosion resistance. The flexible printed circuit electrode is electrically connected to the subsequent signal processing circuit through flexible connection lines with a line width of 50 micrometers and a line spacing of 50 micrometers.

[0042] The stress deflection modeling module communicates with the gradient transition layer structure module and the force-sensitive layer structure module. The stress deflection modeling module integrates an analytical model of interlayer stress transfer based on elasticity theory. This analytical model uses the constitutive equations of multilayer composite structures as its mathematical foundation and performs calculations by establishing a system of simultaneous equilibrium equations for the overlying layer, gradient transition layer, and force-sensitive layer.

[0043] The analytical model treats the capping layer, gradient transition layer, and force-sensitive layer as three elastic bodies. Each layer has its own Young's modulus, Poisson's ratio, and thickness parameters. The analytical model establishes a set of equilibrium equations for the three-layer structure, constrained by the stress tensor continuity condition and the displacement compatibility condition. By solving this set of equations, the stress field distribution at any surface stress point within the multi-layer structure can be obtained.

[0044] Based on the stress field distribution results, the analytical model further calculates the stress line transmission path and deflection angle, and determines the position of the equivalent load acting on the force-sensitive layer. The stress deflection modeling module also has a pre-set stress deflection parameter mapping table. The dimensions of this mapping table cover the parameter space from Young's modulus ratio from 1.1 to 3.0, Poisson's ratio from 0.3 to 0.45, and layer thickness ratio from 0.5 to 2.0, containing more than 10,000 sets of calibration data points. Each set of data in the mapping table includes the stress deflection angle, stress amplification factor, and equivalent load offset distance under specific mechanical parameter combinations.

[0045] When the system performs actual calculations, the stress deflection modeling module first performs a two-dimensional interpolation lookup in the mapping table based on the current combination of interlayer mechanical parameters to obtain the corresponding stress deflection parameters, and then corrects the calculation results by combining the analytical model.

[0046] The stress deflection modeling module also includes a boundary effect correction submodule, which is specifically designed to handle stress deflection calculations in areas near the sensor edge. The boundary effect correction submodule introduces a stress concentration factor to incrementally compensate for the stress deflection angle in the edge region. The value of the stress concentration factor is negatively correlated with the distance from the stress point on the surface to the edge. When the distance is less than 3 times the thickness of the overlay layer, i.e., 360 micrometers, the boundary correction logic is enabled, and the boundary correction amount is calculated according to the reciprocal of the stress concentration factor.

[0047] The error compensation calculation module is communicatively connected to the stress deflection modeling module and the force-sensitive layer structure module. The error compensation calculation module receives the actual sensing position coordinates output by the force-sensitive layer structure module and the original input coordinates of the surface stress point. Based on the stress deflection parameters provided by the stress deflection modeling module, it calculates the spatial position offset vector between the surface stress point and the force-sensitive layer sensing point, and corrects the original coordinates in real time according to the offset vector.

[0048] The correction algorithm adopts a back projection compensation strategy. After obtaining the coordinates of the force-sensitive layer sensing point and the stress deflection parameters, the error compensation calculation module calculates the back projection vector based on the deflection angle and offset distance, and translates the coordinates of the force-sensitive layer sensing point along the direction of the back projection vector to obtain the compensated coordinates of the surface stress point.

[0049] The error compensation calculation module also integrates a positioning error distribution uniformity processing unit. This unit establishes an error-adaptive coordinate mapping relationship in the entire sensing area, so that the compensated positioning error is nearly uniformly distributed throughout the entire area.

[0050] The positioning error distribution homogenization processing unit employs a partitioned interpolation mathematical strategy, dividing the entire sensing area into 64 uniform grid sub-regions, each measuring 15 mm by 15 mm. A local coordinate mapping function is established within each sub-region, using a bivariate cubic polynomial form containing 16 undetermined coefficients.

[0051] The mapping functions of adjacent sub-regions satisfy the condition of first-order continuous differentiability at the boundary, that is, the function values ​​are the same and the first-order partial derivatives are continuous at the common boundary. By establishing the above continuous partition mapping relationship within the entire sensing area, the positioning error distribution homogenization processing unit eliminates the inherent defect of uneven positioning error distribution between the edge region and the center region.

[0052] The signal output module communicates with the error compensation calculation module. The signal output module standardizes and encapsulates the corrected coordinate data and corresponding pressure signal. The output interface supports both serial peripheral interface protocol and analog voltage output mode. The serial peripheral interface protocol is configured with a transmission rate of 10 megabits per second, using full-duplex communication mode. The data frame format includes four fields: frame header, data length, data content, and check bit. The analog voltage output mode has a range of 0 to 5 volts, with a pressure resolution better than 12 bits, meaning the pressure measurement accuracy reaches 1 / 4096 of the full scale.

[0053] The signal output module integrates a digital filtering unit. The filtering algorithm uses a finite impulse response low-pass filter. The filter is designed as a 128th order filter with Chebyshev window function coefficients. The stopband attenuation is 65 dB, the passband ripple is 0.05 dB, and the cutoff frequency is 500 Hz.

[0054] The signal output module also integrates oversampling and decimation processing units, with an oversampling factor of 8 and a decimation factor of 8. Through the cascaded processing of oversampling and decimation, an equivalent high-resolution analog-to-digital conversion effect is achieved, effectively reducing the impact of quantization noise on measurement accuracy.

[0055] The temperature drift compensation module is communicatively connected to the force-sensitive layer structure module and the error compensation calculation module. The temperature drift compensation module acquires real-time temperature data of the sensor's operating environment, with a temperature acquisition accuracy of ±0.1 degrees Celsius.

[0056] The temperature acquisition unit uses a platinum resistance temperature sensor with a temperature measurement range of -40 degrees Celsius to 120 degrees Celsius and a temperature sensitivity of 0.385 ohms per degree Celsius. The temperature drift compensation module performs temperature compensation correction on the electrical signal output by the force-sensitive layer structure module according to the preset temperature-sensitivity coefficient correspondence table.

[0057] The temperature-sensitivity coefficient correspondence table covers a temperature range from -20 degrees Celsius to 80 degrees Celsius, and contains 101 calibration data points. The interval between adjacent calibration temperatures is 1 degree Celsius. Each calibration data point records the sensitivity coefficient correction value of the force-sensitive functional layer under a specific temperature condition. The sensitivity coefficient correction value shows a linear decreasing trend as the temperature increases.

[0058] When performing temperature compensation, the temperature drift compensation module first performs linear interpolation in the temperature-sensitivity coefficient correspondence table based on the real-time collected temperature value to obtain the sensitivity coefficient correction value corresponding to the current temperature. Then, it multiplies the correction value by the original electrical signal to obtain the temperature-compensated electrical signal output.

[0059] The system workflow is as follows: When the measured pressure is applied to any position on the sensor surface, the system starts a complete data acquisition, processing and output process. First, the cover layer structure module bears the external pressure. The high-hardness polyimide film layer disperses and diffuses the concentrated pressure and then transfers it to the low Young's modulus silicone rubber buffer layer. The silicone rubber buffer layer further absorbs the impact energy and makes the pressure distribution tend to be uniform.

[0060] The diffused pressure is transmitted to the gradient transition layer structural module through the adhesive interface between the capping layer and the gradient transition layer. The six layers of polyurethane and carbon nanotube composite material in the gradient transition layer structural module transmit the pressure sequentially along the thickness direction. Since the Young's modulus of each layer of material is distributed in a gradient increase, the stress line gradually becomes smooth and deflected during the interlayer transmission of pressure. The deflection angle is significantly smaller than that of the interlayer interface in the traditional non-gradient design. After the pressure is transmitted to the force-sensitive layer structural module, it acts on the surface of the force-sensitive functional layer, causing the resistance value of the graphene and polyvinylidene fluoride composite material to change.

[0061] The flexible printed circuit electrode detects the resistance change of the force-sensitive functional layer in real time and converts the resistance change into a corresponding voltage signal. The improved interdigitated structure design of the electrode increases the effective contact area between the force-sensitive functional layer and the electrode, thereby improving the sensitivity and uniformity of signal acquisition.

[0062] The voltage signal output by the force-sensitive layer structure module is synchronously transmitted to the stress deflection modeling module and the temperature drift compensation module along with the original coordinate data. The temperature drift compensation module performs lookup and interpolation calculations in the temperature-sensitivity coefficient correspondence table based on the real-time collected ambient temperature value to obtain the sensitivity coefficient correction value under the current temperature conditions.

[0063] The temperature drift compensation module multiplies the original voltage signal by the sensitivity coefficient correction value to obtain the temperature-compensated voltage signal. The compensated voltage signal reflects the actual pressure after eliminating the influence of temperature factors.

[0064] Meanwhile, the stress deflection modeling module calculates the stress transmission path and deflection angle corresponding to the current surface stress point by solving a set of equilibrium equations based on the interlayer mechanical parameters of the cover layer, gradient transition layer and force-sensitive layer. The stress deflection modeling module first determines whether the surface stress point is located in the effective sensing area of ​​the sensor. When the stress point is located in the effective sensing area, the stress deflection analytical calculation is triggered.

[0065] When the stress point is close to the sensor edge and the distance from the edge is less than 360 micrometers, the stress deflection modeling module simultaneously activates the boundary effect correction submodule, which incrementally compensates for the deflection angle by introducing a stress concentration factor.

[0066] The stress deflection modeling module determines the spatial offset of the force-sensitive layer sensing point relative to the surface stress point based on the calculated deflection angle and stress deflection parameter mapping table.

[0067] The error compensation calculation module receives the actual perceived position coordinates output by the force-sensitive layer structure module and the spatial position offset provided by the stress deflection modeling module.

[0068] The error compensation calculation module performs back projection compensation calculation on the original coordinates based on the offset vector. The specific steps include: calculating the direction component and magnitude component of the back projection vector based on the deflection angle, superimposing the back projection vector onto the coordinates of the sensing point of the force-sensitive layer to obtain the initial compensation coordinates of the surface force point, and then entering the positioning error distribution homogenization processing unit for secondary correction.

[0069] The positioning error distribution uniformity processing unit first determines the grid sub-region number to which it belongs based on the initial compensation coordinates, and then calls the local coordinate mapping function of the sub-region to perform coordinate transformation.

[0070] The local coordinate mapping function adopts a bivariate cubic polynomial form for nonlinear mapping. The mapping function of adjacent sub-regions is guaranteed to be first-order continuous and differentiable at the boundary, ensuring the smoothness and consistency of coordinate mapping within the entire sensing area.

[0071] After partitioned interpolation correction, the output is uniformized and compensated positioning coordinates.

[0072] The signal output module receives the compensated positioning coordinates output by the error compensation calculation module and the pressure signal output by the temperature drift compensation module.

[0073] The signal output module first standardizes and encapsulates the compensated positioning coordinates and pressure signal, organizing the data content according to a predefined data frame format. The standardized and encapsulated data can be transmitted through two output modes.

[0074] In serial peripheral interface output mode, data frames are sent to the external master device through the serial peripheral interface protocol at a transmission rate of 10 megabits per second.

[0075] In analog voltage output mode, the compensated positioning coordinates are converted into two analog voltage signals and output to the external data acquisition device. The range of the analog voltage signals is 0 to 5 volts, and the corresponding coordinate range is the spatial position of the sensor's effective sensing area.

[0076] The analog voltage signal has a resolution of 12 bits, while the pressure signal has a resolution better than 12 bits. Meanwhile, the signal output module integrates a finite impulse response low-pass filter to filter the original digital signal, and the 128th-order Chebyshev window effectively suppresses high-frequency noise and electromagnetic interference.

[0077] The signal output module also performs oversampling and decimation processing. The oversampling unit repeatedly samples the filtered signal at a rate 8 times that of the original sampling rate, and the decimation unit downsamples the oversampled signal by 8 times and takes the average value to achieve an equivalent high-resolution analog-to-digital conversion effect.

[0078] Example 2: This embodiment shares the same basic architecture and workflow as Embodiment 1. The main difference lies in the adaptive adjustment of the specific parameter configuration of the gradient transition layer structure module and the parameter mapping table coverage of the stress deflection modeling module to meet the differentiated needs of different application scenarios.

[0079] In the gradient transition layer structure module, this embodiment adjusts the number of stacked layers to 8 and the total thickness to 70 micrometers.

[0080] The Young's modulus distribution of the 8-layer polyurethane-carbon nanotube composite material was controlled by a gradient function in the form of a cosine function.

[0081] The Young's modulus of the first layer is 3 MPa, and that of the eighth layer is 35 MPa. The increase in Young's modulus between adjacent layers is controlled within the range of 8% to 10%. The gradient function in the form of a cosine function ensures that the Young's modulus exhibits a smooth transition near the interface of the capping layer and near the interface of the force-sensitive layer, effectively avoiding abrupt changes in the mechanical properties of the interlayer interfaces.

[0082] The minimum value of Young's modulus appears at the interface of the eighth layer near the force-sensitive layer structure module, and the maximum value appears at the interface of the first layer near the cover layer structure module.

[0083] The volume fraction of carbon nanotubes also follows a cosine function distribution along the thickness direction, with the first layer having a volume fraction of 0.5% and the eighth layer having a volume fraction of 6%. The addition of carbon nanotubes effectively improves the electrical conductivity and mechanical uniformity of the composite system.

[0084] The total thickness of the gradient transition layer structure module is increased to 70 micrometers, which allows for more smooth deflection space during stress transmission and further reduces the interlayer stress deflection angle.

[0085] In the stress deflection modeling module, this embodiment expands the preset stress deflection parameter mapping table, increasing the covered parameter space to include Young's modulus ratios from 1.1 to 4.0, Poisson's ratios from 0.25 to 0.48, and layer thickness ratios from 0.3 to 3.0. The expanded mapping table contains over 25,000 sets of calibration data points, enabling it to handle a wider range of material parameter combinations.

[0086] The analytical model employs an improved numerical iterative algorithm when solving the simultaneous equilibrium equations, increasing the iterative convergence accuracy to 1 × 10⁻⁶, effectively enhancing the accuracy and stability of the calculation results.

[0087] In the signal output module, this embodiment increases the order of the finite impulse response filter to 256, increases the stopband attenuation of the Chebyshev window function of the filter coefficients to 75 dB, and reduces the passband ripple to 0.02 dB.

[0088] Higher filter order and steeper stopband attenuation characteristics enable digital filtering units to more effectively suppress high-frequency interference signals, providing more reliable signal quality assurance for high-precision pressure positioning measurements.

[0089] This embodiment is applicable to high-end application scenarios with higher requirements for interlayer mechanical parameter matching and more stringent requirements for spatial positioning accuracy, such as precision force control robot end-effector sensing and pressure detection of high-end medical equipment.

[0090] Example 3: This embodiment has the same basic architecture and workflow as Embodiment 1. The main difference is that some functional modules of the system adopt a simplified design scheme to adapt to the needs of cost-sensitive application scenarios.

[0091] In the gradient transition layer structure module, this embodiment simplifies the number of layers to 5, reducing the total thickness to 40 micrometers. The Young's modulus distribution of the 5-layer polyurethane-carbon nanotube composite material adopts a linear increasing distribution rather than a cosine function distribution. The Young's modulus of the first layer is 8 MPa, the Young's modulus of the fifth layer is 20 MPa, and the increase in Young's modulus between adjacent layers is controlled within the range of 10% to 15%.

[0092] The Young's modulus ratio between adjacent material layers is controlled within the range of 1.25 to 1.40. The simplified gradient transition layer structure module maintains the basic function of smooth interlayer stress transfer while reducing manufacturing complexity and material costs.

[0093] In the force-sensitive layer structure module, this embodiment adjusts the thickness of the force-sensitive functional layer to 15 micrometers and the sensitivity coefficient to 0.55 millivolts per kilopascal.

[0094] The finger width of the flexible printed circuit electrode was adjusted to 70 micrometers, and the finger spacing was adjusted to 100 micrometers. The ratio of finger width to finger spacing was kept within an optimized range of approximately 0.7, ensuring the uniformity and sensitivity of signal acquisition.

[0095] In the signal output module, this embodiment reduces the order of the finite impulse response filter to 64th order, the Chebyshev window function stopband attenuation of the filter coefficients to 55 dB, and the passband ripple to 0.1 dB. The oversampling factor is reduced to 4 times, and the decimation factor is reduced to 4.

[0096] The simplified digital filtering and oversampling decimation processing unit meets basic noise suppression requirements while reducing the computational load and chip resource consumption of subsequent data processing units.

[0097] In the stress deflection modeling module, this embodiment simplifies the preset stress deflection parameter mapping table. The dimensions of the mapping table cover the parameter space with Young's modulus ratio ranging from 1.1 to 2.5, Poisson's ratio ranging from 0.30 to 0.42, and layer thickness ratio ranging from 0.5 to 1.8.

[0098] The simplified mapping table contains approximately 5,000 sets of calibration data points, reducing storage space requirements and table lookup time.

[0099] This embodiment is applicable to large-scale consumer electronics applications with high cost control requirements and relatively low requirements for spatial positioning accuracy, such as pressure touch control in smart wearable devices and pressure sensing in smart home devices.

[0100] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multilayer heterogeneous thin-film switch pressure sensing system, characterized in that, The system includes: The original coordinates of the force points on the sensor surface and the corresponding output signal of the force-sensitive layer are obtained. When the force points on the surface are located in the effective sensing area of ​​the sensor, stress deflection modeling is triggered. Based on the interlayer mechanical parameters of the capping layer, the Young's modulus gradient transition layer and the force-sensitive functional layer, the stress transmission path and deflection angle of any stress point in the multilayer structure are calculated by the stress deflection analytical model. The spatial offset of the force-sensitive layer sensing point relative to the surface force point is determined based on the calculated deflection angle. The original coordinates are then back-projected and compensated based on the offset to obtain the compensated positioning coordinates. Output the compensated positioning coordinates and pressure signals; And a positioning error distribution uniformity processing unit, which uses a partition interpolation strategy to divide the full sensing area into multiple uniform grid sub-regions in the compensation action, establishes a local coordinate mapping function in each sub-region, and the mapping functions of adjacent sub-regions satisfy the first-order continuous differentiable condition at the boundary. And a stress deflection parameter mapping table, in which the corresponding deflection parameter is determined in the calculation action according to the stress deflection parameter mapping table under different interlayer Young's modulus combinations.

2. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 1, characterized in that, The stress deflection analytical model calculates the stress transmission path, deflection angle, and equivalent load location by establishing a set of simultaneous equilibrium equations for the overlying layer, gradient transition layer, and force-sensitive layer.

3. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 1, characterized in that, In the compensation action, the spatial position offset vector between the surface stress point and the force-sensitive layer sensing point is calculated based on the stress deflection parameter, and the original coordinates are corrected in real time according to the offset vector.

4. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 1, characterized in that, In the compensation action, a mathematical strategy of partition interpolation is used to divide the entire sensing area into no fewer than 64 uniform grid sub-regions. Establish a local coordinate mapping function within each sub-region, and ensure that the mapping functions of adjacent sub-regions satisfy the first-order continuous differentiability condition at the boundary.

5. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 1, characterized in that, In the modeling triggering process, the stacking of gradient transition layers controls stress transfer. The gradient transition layer is composed of multiple layers of materials with gradient-varying Young's modulus, and the ratio of Young's modulus between adjacent material layers is within a preset range.

6. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 5, characterized in that, In the layered structure, the Young's modulus distribution is controlled by a gradient function in the form of a cosine function, and the increment of Young's modulus between adjacent layers is within a preset range.

7. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 1, characterized in that, In the calculation process, the deflection parameters are determined based on the parameter space covered by a preset stress deflection parameter mapping table; The dimensions of the mapping table cover the ranges of Young's modulus ratio, Poisson's ratio, and layer thickness ratio.

8. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 1, characterized in that, In the output action, the corrected coordinate data and the corresponding pressure signal are standardized and encapsulated.

9. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 8, characterized in that, Finite impulse response digital filtering is applied to the coordinate data and pressure signal in the standardized package.

10. The multilayer heterogeneous thin-film switch pressure sensing system according to claim 1, characterized in that, The system is also communicatively connected to the force-sensitive layer structure module and the error compensation calculation module. Before the compensation action, temperature data of the sensor's working environment is collected, and the output signal of the force-sensitive layer is corrected by temperature compensation according to the preset temperature-sensitivity coefficient correspondence table.

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