Flexible tactile sensing system with geometric strain compensation function and signal processing method thereof
By introducing asymmetric microdome units and adaptive conformal layers into a flexible tactile sensor, and combining them with signal processing methods, the problems of reference drift and sensitivity heterogeneity caused by curvature were solved, and high-precision pressure measurement on curved surfaces was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANHUA UNIV
- Filing Date
- 2026-05-29
- Publication Date
- 2026-07-24
AI Technical Summary
When flexible tactile sensors are conformally attached to curved substrates, the initial pre-strain caused by the curvature of the substrate leads to nonlinear drift of the reference resistance value and sensitivity heterogeneity, affecting the reliability and accuracy of the sensor.
A flexible adaptive conformal layer, a flexible sensing array layer, and a packaging protective layer are stacked from bottom to top. The asymmetric micro-dome unit and the flexible adaptive conformal layer with an elastic modulus lower than that of the sensing array layer are used to absorb in-plane strain. The initial resistance value is reset by signal processing and the curvature effect is eliminated by a second-order compensation model.
It significantly reduces the mechanical interference of curvature on the sensor, improves the structural stability and signal consistency of the sensor under curved surface attachment conditions, controls the pressure measurement error within ±5%, and enhances the perception accuracy and reliability of curved surface conformal tactile interaction scenarios.
Smart Images
Figure CN122448409A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of flexible electronics and intelligent sensing technology, and in particular to a flexible tactile sensing system with geometric strain compensation function and its signal processing method. Background Technology
[0002] With the rapid development of intelligent connected vehicles, flexible tactile sensors are increasingly being used in cockpit interfaces with complex geometries, such as steering wheels, center consoles, seats, and door armrests. These sensors typically need to be conformally attached to non-planar substrate surfaces to accurately perceive interactive actions such as touch and grip by the driver or passengers.
[0003] However, when flexible sensors are conformally attached to curved substrates, the curvature of the substrate causes the sensor's functional layer to deviate from its mechanical neutral axis, resulting in a non-negligible initial pre-strain within the sensor. Electrically, this pre-strain manifests as a non-linear drift in the reference resistance value; that is, the sensor outputs a non-constant resistance value that varies with curvature even when not subjected to external pressure. Furthermore, the pre-strain also causes heterogeneous evolution in the sensor's sensitivity to the same pressure at different spatial locations during subsequent stress application; that is, the sensor's sensitivity is no longer uniform and constant, but rather closely related to the curvature of its location.
[0004] The aforementioned issues of reference drift and sensitivity variation can lead to false triggering of touch interaction systems in practical applications (e.g., misinterpreting resistance changes caused by bending as pressure signals) or a significant decrease in sensing accuracy (e.g., the same pressure produces different amplitude outputs in different curvature regions), thus severely restricting the reliability and practicality of flexible tactile sensing systems in curved conformal scenarios.
[0005] Currently, some studies have attempted to reduce the effects of bending by optimizing sensor materials or adjusting structural thickness, but most of these studies only address single curvature or planar conditions, lacking a systematic and synergistic solution that can simultaneously address reference drift and sensitivity heterogeneity. Therefore, there is an urgent need for a flexible tactile sensing system that can adapt to curved surface geometry and compensate for signal distortion caused by curvature, along with corresponding signal processing methods. Summary of the Invention
[0006] The purpose of this invention is to provide a flexible tactile sensing system with geometric strain compensation function and its signal processing method, aiming to solve the problems of initial pre-strain, nonlinear drift of reference resistance and spatial heterogeneity of sensitivity caused by the curvature of the substrate when the flexible tactile sensing system is attached to a curved surface.
[0007] To achieve the above objectives, the present invention provides a flexible tactile sensing system with geometric strain compensation function, comprising: The flexible adaptive conformal layer, the flexible sensor array layer, and the encapsulation protection layer are stacked sequentially from bottom to top. The flexible sensing array layer contains several discretely distributed asymmetric microdome units; The elastic modulus of the flexible adaptive conformal layer is lower than that of the flexible sensing array layer.
[0008] Preferably, the asymmetric microdome unit has an asymmetric geometry to counteract the normal component force generated by the flexible tactile sensing system in a bent state.
[0009] Preferably, the flexible adaptive conformal layer absorbs in-plane strain induced by the curvature of the attached substrate through shear deformation.
[0010] Preferably, the flexible sensing array layer is made of a piezoresistive flexible material, and the resistance value of the flexible sensing array layer varies with the pressure and bending strain.
[0011] The present invention also provides a signal processing method for a flexible tactile sensing system with geometric strain compensation function, applied to the aforementioned flexible tactile sensing system with geometric strain compensation function, comprising the following steps: S1. Obtain the radius of curvature at the attachment location of the flexible tactile sensing system. ; S2. Based on the preset electromechanical mapping function, calculate the current radius of curvature. The initial resistance value below And set the initial resistance value as electrical zero; S3. Based on the real-time measured change in resistance. With the initial resistance value The contact pressure signal was obtained by using a compensation model. .
[0012] Preferably, the initial resistance value in step S2 Calculate according to the following formula: ; in, This is the reference resistance for a flexible tactile sensing system under strain-free conditions. For strain gauge factor, The distance of the asymmetric microdome unit from the neutral axis. Let be the radius of curvature.
[0013] Preferably, the compensation model in step S3 is a second-order compensation model: ; in, and For the radius of curvature calibrated through preliminary experiments The characteristic function of .
[0014] Preferably, contact pressure signal This is obtained by performing an inverse function operation on the second-order compensation model, so that different radii of curvature... Under the same pressure input The output corresponds to the same resistance change.
[0015] Therefore, the present invention employs the above-mentioned flexible tactile sensing system with geometric strain compensation function and its signal processing method, which has the following beneficial effects: (1) By setting a flexible adaptive conformal layer with an elastic modulus lower than that of the flexible sensing array layer, the in-plane strain induced by the curvature of the substrate is absorbed by its shear deformation, and the normal component force under bending state is offset by the asymmetric micro dome unit. From the perspective of physical structure, the mechanical interference of curvature on the sensing layer is significantly reduced, and the structural stability and signal consistency of the sensor under curved surface attachment conditions are improved.
[0016] (2) By obtaining the radius of curvature of the attachment position, the initial resistance value under the current curvature is reset to the electrical zero based on the electromechanical mapping function, and the second-order compensation model related to curvature is used to solve the resistance change measured in real time. This effectively eliminates the reference resistance drift and piezoresistive nonlinear response caused by curvature, so that the same pressure outputs a consistent signal under different curvature backgrounds.
[0017] (3) By combining the geometric strain compensation of the physical structure with the back-end signal processing algorithm, the pressure measurement error under the surface attachment condition can be controlled within ±5% (0-5 kPa pressure range), which is significantly better than the ±30% error when uncompensated. This effectively avoids the false triggering of the interactive system and improves the perception accuracy and reliability of surface conformal tactile interaction scenarios such as smart cockpits and wearable devices.
[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the flexible tactile sensing system with geometric strain compensation function of the present invention; Figure 2 This is an analytical diagram of the deformation of the asymmetric microdome unit in the flexible sensing array layer of this invention under the conformal state of the curved surface; Figure 3 This is a baseline drift curve of the initial resistance under different curvatures in an embodiment of the present invention; Figure 4 These are comparison diagrams of signal waveforms before and after compensation in an embodiment of the present invention: (a) uncompensated signal waveform, (b) compensated signal waveform; Figure 5This is a flowchart of the signal processing method for the flexible tactile sensing system with geometric strain compensation function of the present invention.
[0020] Figure Labels 1. Encapsulation and protection layer; 2. Flexible sensor array layer; 3. Flexible adaptive conformal layer; 21. Asymmetric microdome unit. Detailed Implementation
[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.
[0022] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.
[0023] Example 1 I. System Structure like Figure 1 As shown, this embodiment provides a flexible tactile sensing system with geometric strain compensation function. The system's stacked structure, from bottom to top, includes: a flexible adaptive conformal layer 3, a flexible sensing array layer 2, and an encapsulation protection layer 1.
[0024] The flexible adaptive conformal layer 3 is made of a flexible polymer material with a low elastic modulus (such as Ecoflex, PDMS, etc.), with a thickness of 0.2 mm to 0.5 mm, and is used to attach to the surface of a substrate with a curved topography (such as a car steering wheel, center console, etc.). The elastic modulus of the flexible adaptive conformal layer 3 is designed to be lower than that of the flexible sensing array layer 2, so that when the system as a whole bends, it mainly absorbs the in-plane strain induced by the curvature of the substrate through shear deformation, reducing the pre-strain transmitted to the sensing array layer.
[0025] The flexible sensing array layer 2 is composed of a piezoresistive flexible material (such as PDMS or hydrogel doped with conductive fillers), whose resistance varies with the applied pressure and bending strain. This layer contains multiple discretely distributed asymmetric microdome units 21, each with an asymmetric geometry in a cross-section perpendicular to the stacking direction. This asymmetric shape, through a pre-defined structural gradient, can counteract the normal force generated by the sensor under bending conditions, thereby reducing the interference of curvature on sensing sensitivity.
[0026] The encapsulation protective layer 1 is an insulating flexible film (e.g., polyimide or PET) with a thickness of approximately 0.05 mm to 0.1 mm, used to protect the sensing array layer from the influence of the external environment (moisture, dust, mechanical scratches).
[0027] II. Bending Deformation and Baseline Drift Figure 2 The deformation analysis of the asymmetric microdome element 21 under conformal curved surface conditions is shown. When the system is attached to a convex substrate, the bottom of the asymmetric microdome element 21 is subjected to tensile strain (…). The top is subjected to compressive strain ( The neutral axis is located at a certain height within the element. According to the bending theory in mechanics of materials, the distance from the neutral axis is... The strain produced by the position is: ; in, Let be the radius of curvature. For Figure 2 In the case of a convex surface, the strain at the bottom (y>0) is tensile (ε+), and the strain at the top (y<0) is compressive (ε-).
[0028] In this embodiment, the asymmetric microdome unit 21 is used to adjust its geometry so that, within the target curvature range, the sensitive area of the asymmetric microdome unit 21 is as close as possible to the neutral axis, thereby reducing the pre-strain.
[0029] Even with optimized design, residual pre-strain can still cause the reference resistance value to drift. For example... Figure 3 As shown, the horizontal axis represents curvature. (Unit: mm) -1 The relationship between the radius of curvature R and the curvature R is as follows: The vertical axis represents the initial resistance value. (Unit: Ω). Experimental data shows that as curvature increases (i.e., radius of curvature decreases), the initial resistance value exhibits a non-linear upward trend. If this baseline drift is not compensated for, it will lead to serious errors in subsequent pressure measurements.
[0030] III. Signal Processing Methods The core of this invention lies in eliminating the influence of curvature on pressure signals through back-end algorithms. Figure 5 A flowchart of the signal processing method is shown. The following explanation uses a specific application scenario: Assume this flexible tactile sensing system is attached to the 3 o'clock position of a car steering wheel (radius of curvature). =50mm), used to detect the driver's hand grip pressure.
[0031] Step S1: Obtain the radius of curvature.
[0032] During the system power-on initialization phase, the microcontroller unit (MCU) reads the preset attachment position curvature radius. This value can be calibrated during production using 3D scanning and stored in the MCU's non-volatile memory. In this embodiment, =50 mm.
[0033] Step S2: Reset the electrical zero point.
[0034] The MCU calculates the initial resistance value at the current curvature based on the pre-stored electromechanical mapping function. This mapping function is based on the formulas of mechanics of materials: ; in, =100Ω, which is the reference resistance value of the flexible tactile sensing system in a strain-free (planar) state; =2.0, which is the strain specification factor for the piezoresistive material; =0.5mm, which is the distance of the asymmetric microdome unit 21 from the neutral axis; =50mm, which is the radius of curvature.
[0035] Substituting, we get: =100×(1+2.0×500.5)=100×(1+0.02)=102Ω.
[0036] The MCU sets this 102 Ω as the current electrical zero. In other words, in subsequent measurements, only resistance values exceeding 102 Ω are considered to be caused by external pressure.
[0037] Step S3: Use a compensation model to calculate the pressure.
[0038] During system operation, the MCU reads the current resistance value of the sensor array in real time at a sampling rate of 100 Hz. And calculate the change in resistance. It should be noted that when there is no pressure, =0; when pressure is applied. >0.
[0039] This embodiment uses a second-order compensation model to describe the contact pressure signal. Relationship with relative resistance change: ; in, and It is a value pre-calibrated experimentally regarding the radius of curvature. The characteristic function of . For =50mm, obtained after calibration =0.02kPa -1 , =0.001kPa -2 .
[0040] Substitute the known values into: =102Ω, For real-time measured values (e.g., measured values) =2.04Ω), then: ; Solve the quadratic equation in one variable, taking positive real solutions: ≈0.954kPa.
[0041] This yields the contact pressure signal. ≈0.954 kPa. If an uncompensated traditional linear model is used ( ,in If the sensitivity is constant, then approximately 1.2 kPa is obtained, with an error of approximately 25%. The compensation method in this embodiment effectively eliminates the nonlinear error caused by curvature.
[0042] Step S4: Output pressure signal.
[0043] The MCU will solve the result The value is sent to the vehicle's interactive host via the CAN / LIN bus to trigger the corresponding interactive function (for example, when the pressure exceeds 1 kPa, it is judged as "grip the steering wheel").
[0044] IV. Preliminary Experiment Calibration Method In order to obtain and The characteristic function can be calibrated using the following experiments before implementation: Multiple samples of flexible tactile sensing systems with identical structures were fabricated.
[0045] The samples were attached to molds with different radii of curvature (e.g., =∞ (plane), 100mm, 50mm, 25mm, 10mm).
[0046] For each radius of curvature, a series of known pressures (e.g., 0, 0.5, 1.0, 1.5, 2.0 kPa) are applied, and the corresponding resistance changes are recorded. .
[0047] Calculate under various pressures Using quadratic polynomial fitting, the curvature under this curvature is obtained and .
[0048] Will and For the radius of curvature respectively (or curvature) By fitting the function, we obtain the function. and It can usually be expressed in polynomial form. , .
[0049] The fitted coefficients are stored in the MCU's lookup table or calculation formula.
[0050] V. Application Examples Taking a car steering wheel as an example, the flexible tactile sensing system of this invention is attached to the inner side of the steering wheel rim (radius of curvature approximately 45mm-60mm). When the driver holds the steering wheel, multiple asymmetric micro-dome units 21 in the sensor array detect the pressure distribution at different locations. The initial resistance value of each unit... Each unit's grip force is calculated and reset independently based on its actual curvature at its location. The MCU processes the signals from each unit in parallel and ultimately outputs a grip force distribution map of the entire hand to determine whether the driver's driving posture is safe.
[0051] Experimental results show that, within the pressure range of 0-5 kPa, after compensation using this method, the pressure measurement error under different radii of curvature is less than ±5%, while the maximum error without compensation can reach ±30%. Figure 4 The signal waveforms before and after compensation were compared: the top image shows the uncompensated signal, where the baseline drifts (the curve fluctuates up and down) and the amplitude changes with the curvature; the bottom image shows the compensated signal, where the baseline is stable and the response amplitude is basically the same under the same pressure.
[0052] Therefore, this invention employs the aforementioned flexible tactile sensing system and its signal processing method with geometric strain compensation function. Through the geometric structure of the asymmetric microdome unit and the modulus matching of the flexible adaptive conformal layer, it effectively absorbs in-plane strain and cancels the normal component force, reducing the mechanical interference of curvature on the sensing layer. Based on this, by combining a reference resistance reset based on the radius of curvature and a second-order compensation model, it eliminates baseline drift and piezoresistive nonlinear response caused by curvature.
[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.
Claims
1. A flexible tactile sensing system with geometric strain compensation function, characterized in that, include: The flexible adaptive conformal layer, the flexible sensor array layer, and the encapsulation protection layer are stacked sequentially from bottom to top. The flexible sensing array layer contains several discretely distributed asymmetric microdome units; The elastic modulus of the flexible adaptive conformal layer is lower than that of the flexible sensing array layer.
2. The flexible tactile sensing system with geometric strain compensation function according to claim 1, characterized in that, The asymmetric microdome unit has an asymmetric geometry to counteract the normal force generated by the flexible tactile sensing system when it is bent.
3. The flexible tactile sensing system with geometric strain compensation function according to claim 1, characterized in that, The flexible adaptive conformal layer absorbs in-plane strain induced by the curvature of the attached substrate through shear deformation.
4. The flexible tactile sensing system with geometric strain compensation function according to claim 1, characterized in that, The flexible sensing array layer is made of piezoresistive flexible material, and the resistance value of the flexible sensing array layer changes with the pressure and bending strain.
5. A signal processing method for a flexible tactile sensing system with geometric strain compensation function, applied to the flexible tactile sensing system with geometric strain compensation function as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Obtain the radius of curvature at the attachment location of the flexible tactile sensing system. ; S2. Based on the preset electromechanical mapping function, calculate the current radius of curvature. The initial resistance value below And set the initial resistance value as electrical zero; S3. Based on the real-time measured change in resistance. With the initial resistance value The contact pressure signal was obtained by using a compensation model. .
6. The signal processing method for the flexible tactile sensing system with geometric strain compensation function according to claim 5, characterized in that, Initial resistance value in step S2 Calculate according to the following formula: ； in, This is the reference resistance for a flexible tactile sensing system under strain-free conditions. For strain gauge factor, The distance of the asymmetric microdome unit from the neutral axis. Let be the radius of curvature.
7. The signal processing method for the flexible tactile sensing system with geometric strain compensation function according to claim 6, characterized in that, The compensation model in step S3 is a second-order compensation model: ； in, and For the radius of curvature calibrated through preliminary experiments The characteristic function of .
8. The signal processing method for the flexible tactile sensing system with geometric strain compensation function according to claim 7, characterized in that, Contact pressure signal This is obtained by performing an inverse function operation on the second-order compensation model, so that different radii of curvature... Under the same pressure input The output corresponds to the same resistance change.