Sensor for monitoring fatigue driving

Abstract

The invention discloses a sensor for monitoring fatigue driving, and relates to the technical field of sensors, a piezoelectric layer in the sensor for monitoring fatigue driving is of an imitated dragonfly wing profile structure of a negative Poisson's ratio structure, the Young modulus and rigidity are reduced by the structure, and when the piezoelectric layer is stretched or compressed, the piezoelectric layer can be prevented from being damaged. When the dragonfly-imitating wing profile is stressed, unique deformation of expansion or contraction can be generated in the direction perpendicular to the stress direction, so that the strain response capacity of the structure is effectively improved, tiny strain near the eye circumference can be monitored, the flexible dragonfly-imitating wing profile structure is matched with the eye circumference curved surface, the stress of the whole structure is dispersed, and local strain is reduced; the situation that the monitoring stability of the sensor is reduced due to tensile fatigue is avoided, the detection sensitivity of eye actions is improved, and then the monitoring accuracy of fatigue driving is improved.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a sensor for monitoring fatigued driving. Background Technology

[0002] Traffic accidents caused by fatigued driving are common. When fatigued, drivers may experience physical discomfort such as blurred vision, back pain, stiff movements, and swollen hands and feet. They may also experience poor concentration, slow reaction time, impaired thinking, mental distraction, anxiety, and irritability, impacting their mental health. In severe cases, they may lose control of the vehicle, leading to injury or even death.

[0003] In existing technologies, there are methods for detecting eye movements using flexible strain sensors. However, existing flexible strain sensors have simple structures (such as planar thin films), high Young's modulus, and high rigidity, resulting in poor facial fit, low long-term wearing comfort, and low sensitivity in detecting eye movements, making it difficult to achieve accurate fatigue driving monitoring. Summary of the Invention

[0004] Therefore, it is necessary to provide a sensor for monitoring fatigue driving in response to the above-mentioned technical problems.

[0005] The present invention adopts the following technical solution: This invention provides a sensor for monitoring fatigued driving, comprising: a flexible strain sensor unit; the flexible strain sensor unit includes: a piezoelectric layer with electrodes, the piezoelectric layer having a dragonfly-wing-shaped profile structure with a negative Poisson's ratio; the piezoelectric layer expands in the direction perpendicular to the force when stretched, and contracts in the direction perpendicular to the force when compressed; the electrodes are used to extract the current generated by the piezoelectric layer under the piezoelectric effect of external force.

[0006] The above-mentioned at least one technical solution adopted in this invention can achieve the following beneficial effects: The piezoelectric layer in the sensor for monitoring driver fatigue of this invention is a dragonfly-wing-shaped profile structure with a negative Poisson's ratio. This structure reduces Young's modulus and rigidity, and when subjected to tension or compression, it will produce unique deformation of expansion or contraction perpendicular to the direction of force, thereby effectively improving the strain response capability of the structure. It can detect small strains near the eyes, and the flexible dragonfly-wing-shaped profile structure is adapted to the curved surface of the eye. The stress dispersion of the entire structure reduces local strain, avoids the reduction of sensor monitoring stability due to tensile fatigue, improves the detection sensitivity of eye movements, and thus improves the accuracy of monitoring driver fatigue. Attached Figure Description

[0007] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0008] Figure 1 A schematic diagram of a flexible strain sensor unit provided by the present invention; Figure 2 A schematic diagram of a sensor array structure provided by the present invention; Figure 3 A schematic diagram of a sensor for monitoring fatigue driving provided by the present invention; Figure 4 This invention provides a schematic diagram of eye movement detection. Figure 5 A schematic diagram of the output voltage for blinking motion provided by the present invention; Figure 6 This is a schematic diagram illustrating the working principle of a sensor provided by the present invention. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0010] Currently, methods for monitoring fatigued driving include those based on physiological signals such as electroencephalogram (EEG) and electrocardiogram (ECG). These methods involve complex equipment and inconvenient electrode placement, which can affect the driver's normal driving. Other methods are based on driving behaviors such as steering wheel operation, lane keeping, and braking and acceleration. These methods are greatly affected by factors such as driving habits, road conditions, and vehicle type. Still others are based on vehicle speed and trajectory. However, these methods alone cannot accurately determine fatigue and are prone to misjudgment. They need to be used in conjunction with other parameters and monitoring methods.

[0011] Existing flexible strain sensors employ simple structures (such as planar thin films) without incorporating biomimetic structures or special mechanical designs. Typically, planar thin-film polyvinylidene difluoride (PVDF) piezoelectric films have a Young's modulus of 3.57 GPa, are highly rigid, and are not easily deformed, making them unsuitable for deformation detection.

[0012] Therefore, this invention proposes a patterned design for the sensing structure of PVDF thin films, reducing Young's modulus and rigidity while achieving sensitive detection of deformation (such as strain caused by blinking or eye movement). Existing flexible strain sensors used for monitoring fatigued driving often have poor fit (the sensors are relatively thick), resulting in low comfort during long-term wear and susceptibility to measurement errors due to stress concentration. Existing sensors also lack stability, and tensile fatigue reduces sensor lifespan.

[0013] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0014] In one or more embodiments of the present invention, a sensor for monitoring fatigued driving is provided, comprising: a flexible strain sensor unit.

[0015] Figure 1 This is a schematic diagram of a flexible strain sensor unit according to the present invention. As can be seen, the present invention provides a flexible strain sensor unit with a negative Poisson's ratio structure and a dragonfly-like wing profile. The flexible strain sensor unit mainly includes a piezoelectric layer with electrodes, which has a negative Poisson's ratio, mimicking the contour of a dragonfly wing. Through this unique structural design, the sensor's sensitivity to weak strain signals from the human body is improved, enabling real-time and accurate monitoring of driver fatigue and preventing traffic accidents.

[0016] Figure 1 The left side of the image shows a schematic diagram of a dragonfly wing. Based on the outline of a dragonfly wing, this invention proposes a novel biomimetic unit structure, namely... Figure 1 The right side of the middle section is shown. r 1 = 0.5mm~1mm r 2 = 0.5mm~2mm t / 2 = 0.3mm~0.8mm, x =1.12mm. When subjected to tension or compression, this structure will produce a unique deformation of contraction or expansion perpendicular to the direction of force, thereby effectively improving the structure's strain response capability.

[0017] In order to enable the sensor to detect minute strains near the eyelids, in one or more embodiments of the present invention, the sensor for monitoring fatigue driving may include multiple arrayed flexible strain sensor units, and each flexible strain sensor unit is connected by a piezoelectric layer of a circular structure, forming an overall negative Poisson's ratio structure network; the circular structure includes a circular outline of a preset size and long strips symmetrically arranged at both ends of the circular outline.

[0018] By forming an array structure based on a unit cell structure, the mechanical properties and strain transfer efficiency of the sensor are further enhanced. For example... Figure 2 As shown, Figure 2This is a schematic diagram of a sensor array structure according to the present invention.

[0019] This design solves the problem of stress concentration in traditional structures, thereby improving measurement accuracy. It also allows the sensor to better fit the human body, improving comfort. Furthermore, this structure reduces local strain in the sensor, preventing sensor stability from being reduced due to tensile fatigue.

[0020] The present invention also provides a fabrication process for a sensor for monitoring fatigue driving. The sensor is fabricated using micro-nano technology, with a device size of 10mm×8mm×0.1mm and a weight of 50mg as an example.

[0021] (1) Preparation for cutting piezoelectric film: Cut the PVDF piezoelectric film with 30nm~90nm thick Cu / Ni electrodes on both sides into 3cm×2cm films for later use. In order to avoid the PVDF piezoelectric film from failing to process due to wrinkles and misalignment, the PVDF film needs to be attached to the UV film temporary substrate.

[0022] (2) Functional layer cutting: Multiple array-distributed flexible strain sensor units can be obtained by patterning and integrally cutting a rectangular piezoelectric film using a laser cutting machine. Specifically, a laser cutting machine can be used to pattern the PVDF piezoelectric film. The cutting speed can be 50~100mm / s, the cutting frequency can be 50kHz, and the pulse width is 19ns, ensuring the integrity and smoothness of the PVDF piezoelectric film edge.

[0023] (3) Temporary substrate debonding: Irradiate the cut PVDF piezoelectric film with UV substrate with a UV lamp for 2 minutes. It should be noted that in order to control the surface temperature of the PVDF piezoelectric film, the debonding process should be carried out intermittently. After 30 seconds under the UV lamp, the PVDF piezoelectric film should be cooled in the air for 1 minute before the next UV irradiation. After repeating this operation several times, the surface adhesiveness of the UV film will be lost. Manually remove the excess part, leaving only the dragonfly wing structure.

[0024] (4) Electrode lead assembly: Use 10 mm × 3 mm Cu tape as the electrode lead of the sensor, and use PI tape to stably connect the electrode to the test signal acquisition circuit. In order to prevent the lead from short-circuiting due to brief contact during the stretching process, the connecting wires of the top electrode and the bottom electrode can be staggered.

[0025] (5) Encapsulation: The PDMS solution is obtained by fully mixing the prepolymer and crosslinking agent at a mass mixing ratio of 10:1, 20:1 or 5:1, and then the prepared PDMS solution is slowly poured onto the sensor for encapsulation. Figure 3 This is a schematic diagram of a sensor used to monitor driver fatigue, as described in this invention.

[0026] In practical applications, this sensor for monitoring driver fatigue can be attached to the periorbital area to detect strain changes caused by blinking. When the user blinks, the piezoelectric layer deforms under the external force caused by blinking, generating a current that is conducted through the electrodes. The periorbital area can include at least one of the upper eyelid, lower eyelid, and temple, bending with the movement of the periorbital muscles. In the d31 operating mode, the piezoelectric layer generates polarized charges, and the output voltage varies with the degree of bending (positive charge is generated when stretched, and negative charge is generated when recovering).

[0027] Therefore, the aforementioned flexible strain sensor can be connected to the eye-tracking signal receiving circuit via a shielded wire. For example... Figure 4 As shown, Figure 4 This is a schematic diagram of an eye movement detection method according to the present invention. The eye movement signal receiving circuit includes a charge-to-voltage module and a voltage amplification module. The PVDF sensor detects the strain changes caused by blinking and converts them into electrical signals. Then, the obtained eye movement signals are bandpass filtered and amplified by the charge-to-voltage module and the voltage amplification module. The signals are then converted from analog to digital by an ADC at a sufficient sampling rate (e.g., 200Hz) to obtain digital signals. Next, the eye movement signal processing module needs to analyze these digital signals to determine the timing and duration of each blink, and then calculate the blink frequency. The blink frequency is the number of times the driver blinks per minute, and the eye closure duration is the time it takes for the driver's upper eyelid to open from the beginning of closure.

[0028] The eye-tracking signal processing module determines the blink frequency and eye closure duration of eye-tracking signals measured using a PVDF flexible strain sensor based on a time window function. The time window function divides the continuous signal into different time windows for analysis within each window. The preset time window size is selected as the duration of a single blink (0.2s~0.3s). The module determines the peak (high threshold) and trough (low threshold) of the signal within the time window starting from the collected blink signals over a preset time period (which can be randomly selected), and calculates the difference between them as the preset maximum amplitude change threshold. If the maximum amplitude change value of the time window is less than the threshold, the time window is moved to the next time point by a sliding step (e.g., 0.03 seconds). If the maximum amplitude change value of the time window is greater than the threshold, the blink count is incremented, and the module moves to the next node by the time window size, until the preset time period ends. The blink frequency is obtained by dividing the blink count over the preset time period by the time period. Furthermore, the eye-tracking signal processing module can calculate the blink peak and eye closure duration based on signal sampling within the time window. According to the Nyquist theorem, if the upper limit of the blinking frequency is 15Hz (corresponding to a period of approximately 66ms), the sampling rate should be ≥30Hz. Using a sampling rate of 100Hz~200Hz ensures detailed capture (such as the speed of eye closing). The peak of the signal within the time window is obtained through sampling, along with the time point t from the baseline (near 0) to the peak. start and the time point t from the peak back to the baseline end The duration of closing the eyes is t. end ~t start In a healthy adult who is awake and relaxed, the duration of a single eye closure is usually 0.1s to 0.4s. If the duration of eye closure sampled within the time window is less than 0.4s, it is considered a normal blink, the blink count is incremented by one, and the duration of eye closure is recorded. If the duration of eye closure sampled within the time window is greater than 0.4s, it can be considered a sign of fatigue.

[0029] This invention also provides an embodiment in which a fabricated flexible sensor is attached near the driver's eyelids, and the electrical signals output by the sensor are acquired in real time through an eye movement signal receiving circuit. Based on the weak signals monitored from the eyelids, the current blinking duration and blinking frequency of the monitored subject are determined. Figure 5 As shown, Figure 5 This is a schematic diagram of the output voltage for a blinking motion in this invention. Substituting the values ​​into the signal-to-noise ratio formula, the signal-to-noise ratio (SNR) is calculated to be ≥35dB.

[0030] In one or more embodiments of the present invention, the location of the electrodes is not specifically limited. After the piezoelectric layer is obtained according to the method provided by the present invention, the electrodes can be set as needed. Figure 6 This is a schematic diagram illustrating the working principle of a sensor in this invention. Figure 6The "V" in the middle circle indicates voltage measurement. Indicates that external forces are acting upon it. i Indicates the direction of current.

[0031] The piezoelectric layer in the sensor for monitoring driver fatigue of this invention is a dragonfly-wing-shaped profile structure with a negative Poisson's ratio. This structure reduces Young's modulus and rigidity, and when subjected to tension or compression, it will produce unique deformation of expansion or contraction perpendicular to the direction of force, thereby effectively improving the strain response capability of the structure. It can detect small strains near the eyes, and the flexible dragonfly-wing-shaped profile structure is adapted to the curved surface of the eye. The stress dispersion of the entire structure reduces local strain, avoids the reduction of sensor monitoring stability due to tensile fatigue, improves the detection sensitivity of eye movements, and thus improves the accuracy of monitoring driver fatigue.

[0032] Specifically, at least one of the above-mentioned technical solutions adopted in this invention can achieve the following beneficial effects: High sensitivity: The dragonfly wing-like structure (negative Poisson's ratio structure) makes the sensor significantly responsive to micro-strain caused by eyelid movement, with a peak-to-peak voltage of approximately 200mV for the upper eyelid and a signal-to-noise ratio ≥35dB. Figure 5 ).

[0033] High fit: The thin and flexible structure and circular connection design adapt to the curvature of the eye area, providing better comfort than traditional rigid sensors.

[0034] High stability: The stress dispersion design reduces local strain and prevents the sensor from losing stability due to tensile fatigue.

[0035] Low cost: No complex calibration is required; it can be directly applied to the skin, and the cost is much lower than that of computer eye-tracking systems.

[0036] It should also be noted that the terms "comprising," "including," or any other variations thereof in this invention are intended to cover non-exclusive inclusion, that is, in addition to the elements listed in this invention, other elements not expressly listed may also be included.

[0037] The various embodiments in this invention are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0038] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A sensor for monitoring driver fatigue, characterized in that, include: Flexible strain sensor unit; The flexible strain sensor unit includes: a piezoelectric layer with electrodes, wherein the piezoelectric layer has a dragonfly wing-shaped profile structure with a negative Poisson's ratio. The piezoelectric layer expands in the direction perpendicular to the force when stretched, and contracts in the direction perpendicular to the force when compressed; the electrode is used to extract the current generated by the piezoelectric layer under the piezoelectric effect of external force.

2. The sensor for monitoring fatigued driving as described in claim 1, characterized in that, It includes multiple arrayed flexible strain sensor units, each connected by a piezoelectric layer of a circular structure, forming an overall negative Poisson's ratio network; the circular structure includes a circular outline of a preset size and long strips symmetrically arranged at both ends of the circular outline.

3. The sensor for monitoring fatigued driving as described in claim 2, characterized in that, Multiple arrayed flexible strain sensor units are obtained by patterning and integrally cutting a rectangular piezoelectric film using a laser cutting machine; the laser cutting machine has a cutting speed of 50~100mm / s, a cutting frequency of 50kHz, and a pulse width of 19ns.

4. The sensor for monitoring fatigued driving as described in claim 1, characterized in that, The piezoelectric layer is a polyvinylidene fluoride piezoelectric layer.

5. The sensor for monitoring fatigued driving as described in claim 1, characterized in that, The electrode is a Cu / Ni electrode.

6. The sensor for monitoring fatigued driving as described in any one of claims 1 to 5, characterized in that, The sensor is applied around the eye; the area around the eye includes at least one of the upper eyelid, lower eyelid, and temple.

7. The sensor for monitoring fatigued driving as described in claim 6, characterized in that, The sensor is used to detect strain changes caused by blinking. When the user blinks, the piezoelectric layer deforms under the external force caused by blinking, generating current and which is then discharged through the electrode.

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