A driving safety detection method based on flexible electronic skin

Abstract

The application provides a driving safety detection method based on a flexible electronic skin, which comprises the following steps: setting an upper surface conductive layer and a lower surface conductive layer on the opposite surfaces of a PVDF base to form a composite functional film, the upper and lower surface conductive layers forming a flexible capacitive sensor, and the upper and lower surface conductive layers and the PVDF base forming a flexible piezoelectric sensor; constructing a flexible pressure sensor, and then forming a flexible sensor module arranged on a steering wheel; acquiring a steering wheel control state of a driver based on the flexible capacitive sensor and the flexible pressure sensor, and acquiring an instantaneous heart rate of the driver based on the flexible piezoelectric sensor; and performing layered early warning through the steering wheel control state and the instantaneous heart rate. The composite functional film realizes one film with two uses, saves cost, and eliminates signal space-time deviation caused by position difference of the sensor; and the flexible sensor module realizes multi-dimensional and redundant detection on the off-hand state, and improves the accuracy and anti-false alarm capability of the off-hand state detection.

Description

Technical Field

[0001] This invention relates to the field of autonomous driving technology, and in particular to a driving safety detection method based on flexible electronic skin. Background Technology

[0002] With the rapid popularization of Level 2 and above autonomous driving functions, hands-on detection (HoD) and physiological signal detection have evolved from "icing on the cake" to "entry requirements." Vehicles equipped with Lane Keeping Assist (LKAS) or Traffic Jam Assist (TJA) must identify whether the driver is continuously holding the steering wheel within 3-5 seconds; otherwise, the system must issue warnings step by step and disengage longitudinal control.

[0003] Traditional detection methods are therefore facing unprecedented pressure: the torque-angle method relies on a steering column torque sensor, and when the driver only lightly touches the steering column with their fingers or wears heavy gloves, the torque signal attenuates to the noise level, making it easy for the system to misjudge as "hands off"; while the optical camera solution is intuitive, it is limited by the curved surface of the steering wheel, strong glare, dirt, and the driver's sleeves, resulting in a high false alarm rate, and requires additional lighting and viewing windows, making it difficult to meet current needs in terms of cost and installation complexity; infrared arrays are also affected by sunlight interference, and the absorption rate varies significantly with black gloves, leading to frequent false alarms in the southern summer. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a driving safety detection method based on flexible electronic skin.

[0005] To achieve the above objectives, this application provides a driving safety detection method based on flexible electronic skin, comprising the following steps: A PVDF substrate is provided, and an upper surface conductive layer and a lower surface conductive layer are formed on opposite sides of the PVDF substrate by screen printing process to form a composite functional film. The upper surface conductive layer and the lower surface conductive layer constitute a flexible capacitive sensor, and the upper surface conductive layer, the PVDF substrate and the lower surface conductive layer constitute a flexible piezoelectric sensor. A flexible pressure sensor is constructed, and a flexible sensor module is constructed on the steering wheel based on the composite functional film and the flexible pressure sensor. The sensor module is electrically connected to the control circuit inside the vehicle body. The driver's steering wheel control state is obtained based on the flexible capacitive sensor and the flexible pressure sensor. The steering wheel control state includes the grip state and the off-hand state. The driver's instantaneous heart rate is obtained based on the flexible piezoelectric sensor. Layered early warning is provided based on the steering wheel control status and the instantaneous heart rate.

[0006] Furthermore, the step of constructing the flexible pressure sensor includes: A flexible substrate layer is constructed using polydimethylsiloxane, and silver paste is applied on the flexible substrate layer to form a lower electrode layer. A microstructure mold is constructed based on a silicon wafer. After mixing a conductive material with a liquid PDMS base polymer, a first stirring process is performed to form a mixture. A PDMS crosslinking agent is added to the mixture, and a second stirring process is performed to obtain a piezoresistive slurry. The piezoresistive slurry is spin-coated onto the microstructure mold, and after vacuum drying, curing and demolding, a piezoresistive sensitive layer is obtained, which is then placed on the lower electrode layer. A silver paste is applied to the piezoresistive sensitive layer to form an upper electrode layer and a flexible pressure sensor.

[0007] Furthermore, the step of constructing a flexible sensor module mounted on the steering wheel based on the composite functional film and the flexible pressure sensor includes: The flexible pressure sensor is disposed on one side of the composite functional film to form a composite structure; The composite structure is encapsulated and cured using a flexible encapsulation material to form a flexible sensor module; The flexible sensor module is attached to the steering wheel using pressure-sensitive adhesive.

[0008] Furthermore, the control circuit includes a microcontroller, a capacitance measurement unit, and an internal capacitor. The step of acquiring the driver's steering wheel control state based on the flexible capacitance sensor and the flexible pressure sensor, wherein the steering wheel control state includes a gripping state and a hands-off state, includes: The connection between the capacitance measurement unit and the flexible capacitance sensor is disconnected by the microcontroller, so that the capacitance measurement unit can detect the charging and discharging time of the internal capacitor to obtain a reference duration; The microcontroller connects the capacitance measurement unit to the flexible capacitance sensor, so that the flexible capacitance sensor and the internal capacitor form a parallel circuit. The capacitance measurement unit detects the charging and discharging time of the parallel circuit to obtain the detection duration. The duration difference is obtained based on the detection duration and the reference duration. The driver's grip pressure is obtained through the flexible pressure sensor, the grip pressure is compared with a pressure threshold, and the duration difference is compared with a duration threshold. If the duration difference is greater than the duration threshold and the grip pressure is greater than the pressure threshold, then the driver is determined to be in a gripping state. If the duration difference is less than the duration threshold and / or the grip pressure is less than the pressure threshold, then the driver is determined to be in a hands-free state.

[0009] Furthermore, the control circuit also includes a charge amplifier and an amplification and filtering circuit. The flexible pressure sensor is electrically connected to the microcontroller through the charge amplifier and the amplification and filtering circuit. The step of obtaining the driver's grip pressure through the flexible pressure sensor includes: The pressure charge of the flexible pressure sensor is obtained through the charge amplifier, and the pressure charge is converted into an output voltage. The output voltage is conditioned by the amplification and filtering circuit to obtain an analog voltage, which is then transmitted to the microcontroller to convert the analog voltage into grip pressure.

[0010] Furthermore, the step of acquiring the driver's instantaneous heart rate based on the flexible piezoelectric sensor includes: The flexible piezoelectric sensor acquires the pulsation signal of the radial artery in the driver's hand, converts the pulsation signal into a charge signal, and then converts the charge signal into an initial voltage signal through a charge amplifier. The initial voltage signal is filtered and motion artifacts are corrected to obtain the final voltage signal; The time interval between two adjacent peaks is obtained from the final voltage signal using a peak detection algorithm, and the instantaneous heart rate is obtained through the time interval.

[0011] Furthermore, the step of providing tiered early warning based on the steering wheel control state and the instantaneous heart rate includes: The instantaneous heart rate is compared with the safe heart rate range; Determine whether the steering wheel control state is in the off-hand state. If the steering wheel control state is in the off-hand state, obtain the off-hand duration and compare the off-hand duration with the off-hand threshold. If the instantaneous heart rate exceeds the safe heart rate range or the time spent away from the hand exceeds the time spent away from the hand threshold, a level one warning will be triggered. If the instantaneous heart rate exceeds the safe heart rate range and the time spent away from the hand exceeds the time spent away from the hand threshold, a level two warning is triggered.

[0012] Furthermore, the hand-off threshold is 15 seconds, and the safe heart rate range is 50 beats / min to 120 beats / min.

[0013] Furthermore, after the step of triggering a secondary alarm if the instantaneous heart rate exceeds the safe heart rate range and the time spent away from the hand exceeds the time spent away from the hand threshold, the method further includes: Two instantaneous heart rates at a preset time interval are selected as the baseline heart rates. The heart rate change value is obtained through the two baseline heart rates. The heart rate change value is compared with the mutation threshold. If the heart rate change value is greater than the mutation threshold, a level three warning is triggered.

[0014] Furthermore, the preset time interval is 3 seconds, and the mutation threshold is 20 times / min.

[0015] Compared with existing technologies, the beneficial effects of this invention are as follows: By constructing the upper and lower conductive layers on the PVDF substrate to form the composite functional film, a dual-purpose film is achieved, realizing hardware integration at the material level. This significantly reduces the types of materials, layered structures, and assembly processes required by traditional discrete designs, significantly reducing the overall cost, volume, and weight of the system, and improving production consistency and reliability. The flexible capacitive sensor and the flexible piezoelectric sensor share the same physical carrier (PVDF substrate), and they completely overlap in space, fundamentally eliminating signal spatiotemporal deviations caused by sensor position differences. The flexible capacitive sensor, the flexible pressure sensor, and the flexible piezoelectric sensor have high conformity to the steering wheel surface and good air permeability. Through the interaction between the three and the driver's hands, the driver's driving state is analyzed, effectively reducing the false alarm rate caused by environmental interference and significantly improving detection efficiency. The system ensures high reliability and accuracy. The flexible capacitive sensor, flexible pressure sensor, and flexible piezoelectric sensor are integrated into the steering wheel, with concealed wiring. The overall system structure is compact and highly integrated, without altering the original steering wheel structure, making it easy to modify and apply to different vehicle models, and possessing good versatility. The combination of the composite functional film and the flexible pressure sensor effectively suppresses common interference factors such as temperature changes, humidity, vehicle vibration, slight hand movements, or wearing gloves, significantly reducing the risk of false alarms and missed alarms caused by the environmental influences of a single sensor. This achieves multi-dimensional, redundant detection of the hands-off state, improving the accuracy, robustness, and anti-false alarm capability of hands-off state detection. The flexible sensor module not only monitors driving behavior compliance but also assesses the driver's real-time physiological load and sudden health risks, enabling a more intelligent and comprehensive assessment of driving risks, achieving early warning of potential dangers and multi-layered safety protection. Attached Figure Description

[0016] Figure 1 This is a flowchart of a driving safety detection method based on flexible electronic skin in an embodiment of the present invention; Figure 2This is a schematic diagram of the partial connection structure between the flexible pressure sensor, the composite functional film, and the control circuit in the driving safety detection method based on flexible electronic skin in an embodiment of the present invention. Figure 3 This is a schematic diagram of the flexible sensor module in the driving safety detection method based on flexible electronic skin in an embodiment of the present invention; Figure 4 This is a diagram showing the working state of the flexible capacitive sensor in the driving safety detection method based on flexible electronic skin in an embodiment of the present invention. Figure 5 This is a diagram showing the working state of the flexible piezoelectric sensor in the driving safety detection method based on flexible electronic skin in an embodiment of the present invention. Figure 6 This is a schematic diagram of the installation structure of the flexible sensor module on the steering wheel in the driving safety detection method based on flexible electronic skin in an embodiment of the present invention; The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0017] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0018] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] Please see Figures 1 to 5 The present invention provides a driving safety detection method based on flexible electronic skin, comprising the following steps: S10: Provide a PVDF substrate, and form a composite functional film by screen printing on two opposite sides of the PVDF substrate with an upper surface conductive layer and a lower surface conductive layer. The upper surface conductive layer and the lower surface conductive layer constitute a flexible capacitive sensor, and the upper surface conductive layer, the PVDF substrate and the lower surface conductive layer constitute a flexible piezoelectric sensor. Understandably, the flexible capacitive sensor detects the steering wheel control state based on proximity capacitance. In some embodiments, the upper or lower conductive layer can be directly grounded to form the flexible capacitive sensor as a single electrode. In this embodiment, both the upper and lower conductive layers are silver paste layers.

[0021] S20: Construct a flexible pressure sensor. Based on the composite functional film and the flexible pressure sensor, construct a flexible sensor module installed on the steering wheel. The sensor module is electrically connected to the control circuit inside the vehicle body. In this embodiment, the control circuit includes a microcontroller, a capacitance measurement unit, an internal capacitor, a charge amplifier, and an amplification and filtering circuit.

[0022] Specifically, step S20 includes: S210: A flexible substrate layer is constructed using polydimethylsiloxane, and silver paste is applied on the flexible substrate layer to form a lower electrode layer on the flexible substrate layer; S220: Based on the construction of a microstructure mold on a silicon wafer, a conductive material is mixed with a liquid PDMS base polymer and then subjected to a first stirring process to form a mixture. A PDMS crosslinking agent is added to the mixture and a second stirring process is performed to obtain a piezoresistive slurry. S230: The piezoresistive slurry is spin-coated onto the microstructure mold, and after vacuum drying, curing and demolding, a piezoresistive sensitive layer is obtained, and the piezoresistive sensitive layer is disposed on the lower electrode layer. S240: Silver paste is applied to the piezoresistive sensitive layer to form an upper electrode layer and a flexible pressure sensor. S250: The flexible pressure sensor is disposed on one side of the composite functional film to form a composite structure; S260: The composite structure is encapsulated and cured using a flexible encapsulation material to form a flexible sensor module; In this embodiment, the flexible encapsulation material is uncured PDMS, and preferably, the thickness of the flexible sensor module is 0.5mm to 1mm.

[0023] S270: The flexible sensor module is attached to the steering wheel using pressure-sensitive adhesive; In some embodiments, the flexible sensor module is directly integrated with the steering wheel cover using a one-time molding process, and then installed on the steering wheel. The lead wires (positive, negative, and signal wires) of the flexible sensor module are concealed along the inside of the steering wheel spokes and connected to the control circuitry inside the vehicle body.

[0024] S30: The driver's steering wheel control state is obtained based on the flexible capacitive sensor and the flexible pressure sensor. The steering wheel control state includes the grip state and the off-hand state. The driver's instantaneous heart rate is obtained based on the flexible piezoelectric sensor. Step S30 includes: S310: The connection between the capacitance measurement unit and the flexible capacitance sensor is disconnected by the microcontroller, so that the capacitance measurement unit can detect the charging and discharging time of the internal capacitor to obtain a reference duration; In this embodiment, several charging and discharging times can be obtained, and the reference duration is obtained based on the average of these charging and discharging times. This method eliminates the influence of changes in ambient temperature and humidity on the accuracy of capacitance measurement, improving the accuracy of steering wheel control state recognition. Understandably, the microcontroller implements on / off control through a multiplexer switch.

[0025] S320: The microcontroller connects the capacitance measurement unit to the flexible capacitance sensor, so that the flexible capacitance sensor and the internal capacitor form a parallel circuit. The capacitance measurement unit detects the charging and discharging time of the parallel circuit to obtain the detection duration. When the driver grips the steering wheel, the driver, acting as a good conductor, forms a parallel capacitor structure with the flexible capacitive sensor, causing a change in the overall capacitance value of the flexible capacitive sensor. Understandably, the flexible capacitive sensor and the capacitance measurement unit are connected via a flexible circuit.

[0026] S330: Obtain the duration difference based on the detection duration and the reference duration; Compared to directly identifying the steering wheel control state through changes in capacitance, by acquiring the reference duration and the detection duration, the minute capacitance changes introduced by the human hand (using the picometer method) can be amplified into significant changes in charging and discharging time. This avoids misidentification of the steering wheel control state caused by capacitance effects from ambient temperature, humidity, etc., and improves detection accuracy.

[0027] S340: The driver's grip pressure is obtained through the flexible pressure sensor, the grip pressure is compared with a pressure threshold, and the duration difference is compared with a duration threshold; Specifically, the pressure charge of the flexible pressure sensor is obtained through the charge amplifier, and the pressure charge is converted into an output voltage; When the driver's hands grip the steering wheel, pressure is applied to the flexible pressure sensor. According to the linear relationship of the piezoelectric effect, a pressure charge proportional to the applied pressure is generated inside the flexible pressure sensor. When this charge is injected into the feedback capacitor inside the charge amplifier, the charge amplifier generates the output voltage based on the ratio between the pressure charge and the capacitance value of the feedback capacitor.

[0028] The output voltage is conditioned by the amplification and filtering circuit to obtain an analog voltage, which is then transmitted to the microcontroller to convert the analog voltage into grip pressure. After acquiring the output voltage, its signal may still be weak. Therefore, the signal-to-noise ratio of the output voltage is improved through the amplification and filtering circuit to obtain the analog voltage. After reading the analog voltage, the microcontroller converts it into a digital value, and then converts the digital value into a gripping pressure according to a preset calibration curve. When the flexible pressure sensor is not assembled, a preset pressure is applied to it by a pressure device to generate a corresponding preset digital value. The preset calibration curve is constructed based on the preset pressure and the preset digital value.

[0029] S350: If the duration difference is greater than the duration threshold and the grip pressure is greater than the pressure threshold, then the driver is determined to be in a gripping state; if the duration difference is less than the duration threshold and / or the grip pressure is less than the pressure threshold, then the driver is determined to be in a hands-free state. S360: The driver's radial artery pulsation signal is acquired through the flexible piezoelectric sensor, and the pulsation signal is converted into a charge signal. The charge signal is then converted into an initial voltage signal through a charge amplifier. When the driver holds the steering wheel, the pulse in their hand generates periodic pressure on the flexible piezoelectric sensor. According to the piezoelectric effect, polarization occurs inside, generating a charge signal proportional to the rate of pressure change. The charge is converted into voltage by the charge amplifier and amplified to a processable level to form the initial voltage signal.

[0030] S370: Filter and correct motion artifacts on the initial voltage signal to obtain the final voltage signal; In this embodiment, the filtering process includes high-pass filtering and low-pass filtering. The high-pass filtering removes the baseline drift of the extremely low-frequency signal caused by static hand pressure, temperature drift, etc., and the low-pass filtering removes interference such as high-frequency muscle noise and circuit noise that are much higher than the heart rate frequency. This ensures that the main components of the initial voltage signal after filtering are related to the heart rate, but motion interference still exists.

[0031] Acceleration data along three axes is simultaneously acquired at a high sampling rate using a triaxial MEMS accelerometer to obtain an acceleration vector. A least mean square adaptive filtering algorithm is employed, using the acceleration vector as a noise reference input and the initial voltage signal as the desired response. The adaptive filter filters the acceleration vector through a set of variable weights to generate an estimated motion noise vector. The error signal between the motion noise vector and the initial voltage signal is obtained; this error signal is the final voltage signal. Understandably, the variable weights are iteratively updated based on the error signal. After the algorithm converges, the estimated motion noise vector is no longer mixed with motion noise in the initial voltage signal, thus eliminating motion interference and improving the accuracy of subsequent instantaneous heart rate acquisition. Understandably, the control circuit also includes a filtering unit and a correction unit. The flexible piezoelectric sensor is connected to the microcontroller through the filtering unit and the correction unit, and the microcontroller acquires the instantaneous heart rate.

[0032] S380: Obtain the time interval between two adjacent peaks from the final voltage signal using a peak detection algorithm, and obtain the instantaneous heart rate through the time interval; Understandably, instantaneous heart rate = 60 / time interval.

[0033] S40: Layered warning is provided based on the steering wheel control status and the instantaneous heart rate; Understandably, the control circuit also includes an early warning module, which is electrically connected to the microcontroller to implement corresponding early warning control based on the output signal of the microcontroller.

[0034] Specifically, step 40 includes: S410: Compare the instantaneous heart rate with the safe heart rate range; In this embodiment, the safe heart rate range is 50 beats / min to 120 beats / min.

[0035] S420: Determine whether the steering wheel control state is in the off-hand state. If the steering wheel control state is in the off-hand state, obtain the off-hand duration and compare the off-hand duration with the off-hand threshold. In this embodiment, the hand-off threshold is 15 seconds.

[0036] S430: If the instantaneous heart rate exceeds the safe heart rate range or the time spent away from the hand exceeds the time spent away from the hand threshold, a level one warning is triggered; In this embodiment, the first-level warning is a dashboard icon prompt.

[0037] S440: If the instantaneous heart rate exceeds the safe heart rate range and the time spent away from the hand exceeds the time spent away from the hand threshold, a level two warning is triggered; In this embodiment, the secondary warning is a central control prompt tone played.

[0038] Preferably, step S40 further includes: S450: Select two instantaneous heart rates at a preset time interval as the reference heart rate, obtain the heart rate change value through the two reference heart rates, compare the heart rate change value with the mutation threshold, and if the heart rate change value is greater than the mutation threshold, trigger a level three warning. In this embodiment, the preset time interval is 3 seconds, and the mutation threshold is 20 times / min. Understandably, the instantaneous heart rate when the steering wheel is in the off-hand state and the instantaneous heart rate 3 seconds prior to this state are selected as the baseline heart rate. By setting the preset time interval, a low-pass filtering effect is introduced, canceling out brief pulses during the difference calculation, thus identifying continuous and stable heart rate changes, improving the specificity of the detection, and reducing false alarms.

[0039] In this embodiment, the three-level warning system consists of a central control alert sound and steering wheel vibration. Furthermore, steering wheel vibration is achieved through a linear resonance mechanism installed inside the steering wheel.

[0040] By constructing the upper and lower conductive layers on the PVDF substrate to form the composite functional film, a dual-purpose film is achieved, realizing hardware integration at the material level. This significantly reduces the types of materials, layered structures, and assembly processes required by traditional discrete designs, substantially reducing the overall system cost, volume, and weight, while improving production consistency and reliability. The flexible capacitive sensor and the flexible piezoelectric sensor share the same physical carrier (PVDF substrate), and they completely overlap in space, fundamentally eliminating signal spatiotemporal deviations caused by sensor position differences. The flexible capacitive sensor, the flexible pressure sensor, and the flexible piezoelectric sensor have high conformity to the steering wheel surface and good air permeability. Through the interaction between the three and the driver's hands, the driver's driving state is analyzed, effectively reducing the false alarm rate caused by environmental interference and significantly improving the reliability and accuracy of detection. The flexible capacitive sensor, flexible pressure sensor, and flexible piezoelectric sensor are integrated into the steering wheel, with concealed wiring. The overall system structure is compact and highly integrated, without altering the original steering wheel structure, making it easy to modify and apply to different vehicle models and possessing good versatility. The combination of the composite functional film and the flexible pressure sensor effectively suppresses common interference factors such as temperature changes, humidity effects, vehicle vibration, slight hand movements, or wearing gloves, significantly reducing the risk of false alarms and missed alarms caused by the environmental influences of a single sensor. It achieves multi-dimensional and redundant detection of the hands-off state, improving the accuracy, robustness, and anti-false alarm capability of hands-off state detection. The flexible sensor module not only monitors driving behavior compliance but also assesses the driver's real-time physiological load and sudden health risks, enabling a more intelligent and comprehensive assessment of driving risks, achieving early warning of potential dangers and multi-layered safety protection.

[0041] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A driving safety detection method based on flexible electronic skin, characterized in that, Includes the following steps: A PVDF substrate is provided, and an upper surface conductive layer and a lower surface conductive layer are formed on opposite sides of the PVDF substrate by screen printing process to form a composite functional film. The upper surface conductive layer and the lower surface conductive layer constitute a flexible capacitive sensor, and the upper surface conductive layer, the PVDF substrate and the lower surface conductive layer constitute a flexible piezoelectric sensor. A flexible pressure sensor is constructed, and a flexible sensor module is constructed on the steering wheel based on the composite functional film and the flexible pressure sensor. The sensor module is electrically connected to the control circuit inside the vehicle body. The driver's steering wheel control state is obtained based on the flexible capacitive sensor and the flexible pressure sensor. The steering wheel control state includes the grip state and the off-hand state. The driver's instantaneous heart rate is obtained based on the flexible piezoelectric sensor. Layered early warning is provided based on the steering wheel control status and the instantaneous heart rate.

2. The driving safety detection method based on flexible electronic skin according to claim 1, characterized in that, The steps for constructing the flexible pressure sensor include: A flexible substrate layer is constructed using polydimethylsiloxane, and silver paste is applied on the flexible substrate layer to form a lower electrode layer. A microstructure mold is constructed based on a silicon wafer. After mixing a conductive material with a liquid PDMS base polymer, a first stirring process is performed to form a mixture. A PDMS crosslinking agent is added to the mixture, and a second stirring process is performed to obtain a piezoresistive slurry. The piezoresistive slurry is spin-coated onto the microstructure mold, and after vacuum drying, curing and demolding, a piezoresistive sensitive layer is obtained, which is then placed on the lower electrode layer. A silver paste is applied to the piezoresistive sensitive layer to form an upper electrode layer and a flexible pressure sensor.

3. The driving safety detection method based on flexible electronic skin according to claim 1, characterized in that, The steps of constructing a flexible sensor module on the steering wheel based on the composite functional film and the flexible pressure sensor include: The flexible pressure sensor is disposed on one side of the composite functional film to form a composite structure; The composite structure is encapsulated and cured using a flexible encapsulation material to form a flexible sensor module; The flexible sensor module is attached to the steering wheel using pressure-sensitive adhesive.

4. The driving safety detection method based on flexible electronic skin according to claim 1, characterized in that, The control circuit includes a microcontroller, a capacitance measurement unit, and an internal capacitor. The step of acquiring the driver's steering wheel control state based on the flexible capacitance sensor and the flexible pressure sensor, wherein the steering wheel control state includes a gripping state and a hands-off state, includes: The connection between the capacitance measurement unit and the flexible capacitance sensor is disconnected by the microcontroller, so that the capacitance measurement unit can detect the charging and discharging time of the internal capacitor to obtain a reference duration; The microcontroller connects the capacitance measurement unit to the flexible capacitance sensor, so that the flexible capacitance sensor and the internal capacitor form a parallel circuit. The capacitance measurement unit detects the charging and discharging time of the parallel circuit to obtain the detection duration. The duration difference is obtained based on the detection duration and the reference duration. The driver's grip pressure is obtained through the flexible pressure sensor, the grip pressure is compared with a pressure threshold, and the duration difference is compared with a duration threshold. If the duration difference is greater than the duration threshold and the grip pressure is greater than the pressure threshold, then the driver is determined to be in a gripping state. If the duration difference is less than the duration threshold and / or the grip pressure is less than the pressure threshold, then the driver is determined to be in a hands-free state.

5. The driving safety detection method based on flexible electronic skin according to claim 4, characterized in that, The control circuit further includes a charge amplifier and an amplification and filtering circuit. The flexible pressure sensor is electrically connected to the microcontroller through the charge amplifier and the amplification and filtering circuit. The step of obtaining the driver's grip pressure through the flexible pressure sensor includes: The pressure charge of the flexible pressure sensor is obtained through the charge amplifier, and the pressure charge is converted into an output voltage. The output voltage is conditioned by the amplification and filtering circuit to obtain an analog voltage, which is then transmitted to the microcontroller to convert the analog voltage into grip pressure.

6. The driving safety detection method based on flexible electronic skin according to claim 1, characterized in that, The step of acquiring the driver's instantaneous heart rate based on the flexible piezoelectric sensor includes: The flexible piezoelectric sensor acquires the pulsation signal of the radial artery in the driver's hand, converts the pulsation signal into a charge signal, and then converts the charge signal into an initial voltage signal through a charge amplifier. The initial voltage signal is filtered and motion artifacts are corrected to obtain the final voltage signal; The time interval between two adjacent peaks is obtained from the final voltage signal using a peak detection algorithm, and the instantaneous heart rate is obtained through the time interval.

7. The driving safety detection method based on flexible electronic skin according to claim 1, characterized in that, The step of providing tiered early warning based on the steering wheel control state and the instantaneous heart rate includes: The instantaneous heart rate is compared with the safe heart rate range; Determine whether the steering wheel control state is in the off-hand state. If the steering wheel control state is in the off-hand state, obtain the off-hand duration and compare the off-hand duration with the off-hand threshold. If the instantaneous heart rate exceeds the safe heart rate range or the time spent away from the hand exceeds the time spent away from the hand threshold, a level one warning will be triggered. If the instantaneous heart rate exceeds the safe heart rate range and the time spent away from the hand exceeds the time spent away from the hand threshold, a level two warning is triggered.

8. The driving safety detection method based on flexible electronic skin according to claim 7, characterized in that, The hand-off threshold is 15 seconds, and the safe heart rate range is 50 beats / min to 120 beats / min.

9. The driving safety detection method based on flexible electronic skin according to claim 7, characterized in that, After the step of triggering a level two alarm if the instantaneous heart rate exceeds the safe heart rate range and the time spent away from the hand exceeds the time spent away from the hand threshold, the method further includes: Two instantaneous heart rates at a preset time interval are selected as the baseline heart rates. The heart rate change value is obtained through the two baseline heart rates. The heart rate change value is compared with the mutation threshold. If the heart rate change value is greater than the mutation threshold, a level three warning is triggered.

10. The driving safety detection method based on flexible electronic skin according to claim 9, characterized in that, The preset time interval is 3 seconds, and the mutation threshold is 20 times / min.

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