Detection method of automotive trim coating layer and automotive trim coating method

Abstract

The invention relates to the field of manufacturing of automotive upholstery. The invention discloses a detection method of an automotive trim coating layer and an automotive trim coating method, and the method comprises the steps: arranging a capacitance probe with a drive and an induction electrode above a to-be-detected automotive trim coating in parallel in a suspended manner, and keeping the distance stable; the high-frequency voltage source applies an excitation signal to the driving electrode to form an alternating electric field; the induction electrode acquires a coupling signal with coating information, and the coupling signal is pre-amplified; interference with the same-frequency phase modulation reference signal is converted into high-sensitivity voltage; after data acquisition, an algorithm containing environment compensation is used for analyzing and identifying thickness uniformity and flaws. A protective coating film is detected through a non-contact capacitor, the distance is strictly controlled, and the thickness uniformity and flaws are recognized through signal processing and environment compensation. The speed of the array probe is increased, parameters can be adjusted to adapt to interior trim parts made of multiple materials, and the anti-interference design ensures stable detection. The coating film adhesive force is increased through substrate treatment, the quality is guaranteed through sputtering annealing, technological parameters are controllable, the mass production requirement is met, and both quality and efficiency are considered.

Description

Technical Field

[0001] This invention relates to the field of automotive interior parts manufacturing, and in particular to a method for detecting and coating automotive interior parts. Background Technology

[0002] The requirements for the wear resistance and aesthetics of coatings on automotive interior parts are constantly increasing, and coating quality inspection is a crucial step in ensuring performance. Traditional inspection methods, such as probe measurement and caliper comparison, are often contact-based. These methods are not only prone to scratching the delicate interior coatings, causing irreversible damage, but also require separate inspections for thickness, uniformity, and defects, making the process cumbersome and inefficient. Furthermore, these methods are sensitive to changes in temperature and humidity; environmental fluctuations can easily lead to deviations in the test data, making it difficult to meet the demands of high-precision quality control.

[0003] While existing non-contact inspection technologies can avoid damage issues, they have significant limitations. For example, optical inspection methods are easily affected by the color, transparency, and surface reflectivity of the coating layer, resulting in a significant decrease in inspection accuracy for dark or highly reflective coatings. Furthermore, they are mostly single-point inspection modes, unable to achieve rapid surface scanning of interior parts, leading to long inspection times. In addition, these technologies have weak resistance to electromagnetic interference; power frequency interference from equipment in the workshop can easily cause signal distortion, making it difficult to simultaneously acquire multi-dimensional information such as coating thickness, dielectric constant, and surface defects.

[0004] At the coating process level, traditional preparation processes also have shortcomings. In the substrate pretreatment stage, incomplete cleaning and insufficient surface activation often lead to poor adhesion between the coating layer and the substrate, resulting in peeling and cracking during use. During sputtering coating, inaccurate vacuum control or fluctuations in working gas pressure can easily introduce air impurities into the coating layer, affecting its purity and uniformity. Furthermore, post-annealing parameters often rely on experience-based settings, which can leave residual internal stress, reducing the coating's wear resistance. Additionally, the disconnect between the process and testing stages makes it impossible to adjust parameters in real time, hindering quality stability in large-scale production. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a method for detecting automotive interior coating layers and a method for automotive interior coating that enables non-contact detection.

[0006] This invention discloses a method for detecting coating layers on automotive interior surfaces, comprising the following steps:

[0007] S1: A capacitance detection probe is suspended parallel above the coating layer of the automotive interior part to be tested. The probe includes one or more driving electrodes and a sensing electrode, which together constitute a capacitance sensing unit. A stable and uniform detection distance is maintained between the probe and the surface of the coating layer.

[0008] S2: A high-frequency AC voltage source is used to apply a high-frequency excitation signal to the driving electrode, forming an alternating electric field between the probe and the coating layer;

[0009] S3: The sensing electrode collects the capacitive coupling signal generated by the alternating electric field. The amplitude and phase changes of the capacitive coupling signal carry information about the coating thickness, dielectric constant and surface defects.

[0010] S4: The acquired raw capacitance signal is first amplified by a preamplifier to form an amplified signal;

[0011] S5: Introduce a reference signal with the same frequency as the high-frequency excitation signal but with adjustable phase. Through the signal interference circuit, the amplified signal and the reference signal interfere with each other, converting the small capacitance change into a highly sensitive voltage amplitude or phase change signal.

[0012] S6: The data acquisition unit captures voltage signals in real time and analyzes signal characteristics through a preset algorithm. Based on signal offset, abrupt change or specific pattern, the thickness uniformity of the coating layer and surface defects are identified respectively.

[0013] The preset algorithm includes an environmental parameter compensation module to eliminate the interference of temperature and humidity on the detection results.

[0014] Furthermore, the capacitance detection probe is manufactured using a multilayer PCB process or a ceramic packaging process, and a grounded shielding layer is provided between the driving electrode and the sensing electrode.

[0015] The electrode surface is covered with an insulating protective layer made of alumina ceramic or polyimide, with a thickness of 10-50μm.

[0016] The overall equivalent capacitance detection range of the probe is between 0.1pF and 10pF, and the detection resolution is no less than 20fF.

[0017] Furthermore, the parallel suspension setting in S1 is achieved through a micro-nano positioning platform, which has an automatic Z-axis leveling function;

[0018] The detection spacing is controlled between 1 and 30 mm, and real-time feedback and control are achieved through a laser displacement sensor to ensure that the spacing fluctuation is less than ±0.1 mm.

[0019] Furthermore, the high-frequency AC voltage source is a sinusoidal signal source with amplitude and frequency stabilization functions, with an output frequency range of 100kHz-10MHz and a peak-to-peak voltage of 1-10V;

[0020] The phase of the reference signal is adjusted by a digital phase offsetter or an analog phase shifter, with an adjustment accuracy better than 0.1 degrees.

[0021] Furthermore, the preamplifier in S4 is a low-noise, high-input-impedance charge amplifier with a gain of 1-100 times and a bandwidth greater than 10 times the excitation signal frequency.

[0022] The signal interference circuit is a phase-sensitive detector circuit or quadrature demodulation circuit based on a multiplier, which can output a DC voltage signal that is proportional to the capacitance change.

[0023] Furthermore, the S6 uses a 24-bit high-precision ADC as the core of the data acquisition unit, with a sampling rate of no less than 10MSPS;

[0024] The pre-defined algorithm analysis specifically includes the following sub-steps:

[0025] S6.1 Signal preprocessing: The acquired voltage signal is digitally filtered. First, a moving average filter is used to suppress high-frequency noise, and then a bandpass filter is used to extract the fundamental frequency component of the signal.

[0026] S6.2 Feature Extraction: Calculate the amplitude and phase of the signal, or analyze its spectral characteristics through Fast Fourier Transform;

[0027] S6.3 Thickness and Uniformity Analysis: Multiple sets of capacitance values ​​are collected using a standard coating sample with a preset thickness. A calibration curve of capacitance value and coating thickness is obtained by fitting the curve. The thickness is inverted using the real-time capacitance value. The uniformity index is calculated based on the distribution of thickness values. The uniformity index is the difference between the maximum and minimum thickness values ​​in the detection area, or the ratio of the standard deviation of thickness to the average thickness.

[0028] S6.4 Defect Identification: Edge detection algorithm or wavelet transform algorithm is used to identify abrupt changes in the signal. If the signal amplitude drops sharply or the phase changes abruptly, it is determined that there is a defect in the corresponding area. The size and severity of the defect are evaluated based on the width and amplitude of the abrupt signal.

[0029] Furthermore, the capacitance detection probe can be integrated into an array probe, containing multiple sensing units arranged in an array, which can realize a one-time surface scan of the coating layer. Combined with the scanning motion control system, a two-dimensional distribution map of the coating quality of the entire interior part surface can be quickly constructed.

[0030] Furthermore, the entire detection system is integrated into an electromagnetically shielded enclosure to isolate external radio frequency interference and power frequency interference;

[0031] All critical signal lines inside the enclosure are connected using shielded coaxial cables.

[0032] The detection system also integrates temperature and humidity sensors to collect environmental parameters in real time and transmit them to the environmental parameter compensation module with a preset algorithm.

[0033] This invention discloses a method for coating automotive interior surfaces, followed by a detection method for the coating layer of automotive interior surfaces as described above, comprising the following steps:

[0034] A1 Substrate Pretreatment: The substrate of the automotive interior parts undergoes a multi-step pretreatment. First, the substrate surface is ultrasonically cleaned with a neutral detergent to remove surface oil and dust. Then, it is rinsed clean with deionized water and subsequently placed in a drying equipment for drying.

[0035] After drying, the substrate is placed in a plasma treatment chamber and the surface of the substrate is activated using inert gas plasma.

[0036] A2 Sputtering Preparation: Fix the pretreated automotive interior part substrate onto the sample holder in the magnetron sputtering vacuum chamber. Select the appropriate sputtering target according to the functional requirements of the coating layer. The target can be a metal target or a compound target.

[0037] Close the vacuum chamber and start the vacuum system to evacuate the vacuum chamber until the preset vacuum level is reached inside the vacuum chamber.

[0038] A3 sputtering coating: Inert working gas is introduced into the vacuum chamber, and the gas flow rate is adjusted to maintain the preset working pressure inside the vacuum chamber;

[0039] A preset type of power supply is applied to the sputtering target, and the sputtering power is adjusted to a preset value so that the target is sputtered under the action of electric and magnetic fields. After the target atoms or ions detach from the target surface, they are deposited on the substrate surface to form a continuous coating layer.

[0040] A4 Post-treatment: After the coating is completed, turn off the power and working gas, and wait for the vacuum chamber temperature to drop to room temperature before taking out the interior parts;

[0041] The coated interior parts are placed in an annealing furnace for annealing treatment. By controlling the annealing temperature and holding time, the residual stress inside the coating layer is removed.

[0042] A5 Coating Inspection: Inspecting the coating layer.

[0043] Furthermore, in the plasma activation treatment in A1, argon is used as the inert gas, the plasma power is controlled at 50-150W, and the treatment time is 30-120s;

[0044] In A2, the compound target is specifically a SiO2 target or an Al2O3 target, with a preset vacuum level of ≤5×10⁻. 4 Pa;

[0045] In A3, the inert working gas is argon, the gas flow rate is 20-50 sccm, the preset working gas pressure is 0.1-1 Pa, the sputtering power is 100-500 W, and the thickness of the formed coating layer is 50-500 nm.

[0046] The annealing temperature for A4 is 80-150℃, and the holding time is 30-60 minutes.

[0047] The beneficial effects of this invention are:

[0048] The detection method of this invention can capture the characteristics of the coating layer while avoiding damage. It employs a non-contact capacitive probe design, avoiding the scratching and indentation problems of traditional contact detection on the coating layer. Simultaneously, a micro-nano positioning platform and a laser displacement sensor strictly control the detection distance, laying a stable foundation for signal acquisition. A high-frequency alternating electric field amplifies subtle changes in the coating layer; combined with signal amplification and interference techniques, it can convert minute capacitance changes into a high-sensitivity voltage signal. An environmental compensation module in the preset algorithm eliminates temperature and humidity interference. Combined with high-precision data acquisition and analysis, it enables the identification of coating layer thickness uniformity and surface defects, addressing the pain point of insufficient accuracy in traditional detection methods.

[0049] The testing method boasts high efficiency and broad adaptability. An array-type probe paired with a scanning motion control system enables a single-pass surface scan of the coating layer, significantly reducing testing time compared to point-by-point inspection. It also rapidly generates a two-dimensional quality distribution map, providing a clear overview of the overall coating condition. Parameters such as the detection spacing and excitation frequency are flexibly adjustable to accommodate automotive interior parts of varying thicknesses and materials. An electromagnetic shielding box and coaxial shielded cables isolate external interference, ensuring stable test results under different operating conditions. This overcomes environmental limitations, meets diverse testing needs for automotive interior parts, and lowers the barrier to practical application.

[0050] The integrated coating method ensures high-quality coating layers that are suitable for large-scale production. The substrate undergoes ultrasonic cleaning to remove impurities, followed by plasma activation to enhance surface energy, significantly improving coating adhesion and preventing peeling. High-vacuum environment and parameter control during sputtering minimize impurity contamination, ensuring a pure and uniform coating layer. Annealing eliminates residual stress, improving the coating's wear resistance and stability. Controllable process parameters at each stage eliminate the need for complex manual intervention, ensuring consistency in mass production while matching production line rhythm, balancing coating quality and production efficiency to meet the manufacturing needs of automotive interior parts. Attached Figure Description

[0051] Figure 1 This is a flowchart illustrating a method for detecting a coating layer on automotive interior surfaces according to an embodiment of this application. Detailed Implementation

[0052] To enable those skilled in the art to better understand the present invention, the technical solutions in the specific embodiments of the present invention will be clearly and completely described below.

[0053] This invention discloses a method for detecting coating layers on automotive interior surfaces, comprising the following steps:

[0054] S1: A capacitance detection probe is suspended parallel above the coating layer of the automotive interior part to be tested. The probe includes one or more driving electrodes and a sensing electrode, which together constitute a capacitance sensing unit. A stable and uniform detection distance is maintained between the probe and the surface of the coating layer.

[0055] S2: A high-frequency AC voltage source is used to apply a high-frequency excitation signal to the driving electrode, forming an alternating electric field between the probe and the coating layer;

[0056] S3: The sensing electrode collects the capacitive coupling signal generated by the alternating electric field. The amplitude and phase changes of the capacitive coupling signal carry information about the coating thickness, dielectric constant and surface defects.

[0057] S4: The acquired raw capacitance signal is first amplified by a preamplifier to form an amplified signal;

[0058] S5: Introduce a reference signal with the same frequency as the high-frequency excitation signal but with adjustable phase. Through the signal interference circuit, the amplified signal and the reference signal interfere with each other, converting the small capacitance change into a highly sensitive voltage amplitude or phase change signal.

[0059] S6: The data acquisition unit captures voltage signals in real time and analyzes signal characteristics through a preset algorithm. Based on signal offset, abrupt change or specific pattern, the thickness uniformity of the coating layer and surface defects are identified respectively.

[0060] The preset algorithm includes an environmental parameter compensation module to eliminate the interference of temperature and humidity on the detection results.

[0061] S1: Setting up and controlling the spacing of the capacitance detection probe. Determine the placement of the automotive interior component to be tested, ensuring the coating surface is flat and without significant tilt. The capacitance detection probe is then deployed above the coating. The probe structure includes one or more driving electrodes for emitting an electric field and a sensing electrode for receiving coupled signals. Both are fixed by an insulating bracket, forming a closed capacitance sensing unit. To achieve non-contact detection, a precision mechanical bracket or micro-positioning device is used to keep the probe parallel to the coating surface and suspended in mid-air. In practice, a level can be used to calibrate the parallelism between the probe plane and the coating surface, ensuring the angle between them does not exceed 0.1°. Simultaneously, the detection spacing must be strictly controlled. A laser rangefinder sensor monitors the distance between the probe and the coating in real time, and a servo motor fine-tunes the probe height to stabilize the spacing within a preset range with minimal fluctuations, avoiding interference with the capacitance signal due to spacing changes.

[0062] The non-contact design avoids physical damage to the coating layer such as scratches and indentations caused by traditional contact detection, making it especially suitable for detecting coatings in automotive interiors; the stable and uniform spacing provides consistent spatial conditions for subsequent electric field coupling, reducing signal errors caused by distance fluctuations and laying the foundation for detection accuracy.

[0063] S2: A high-frequency excitation signal is applied to form an alternating electric field. A high-frequency AC voltage source, such as a sine wave signal generator, is selected. Its output signal must have stable amplitude and frequency characteristics to ensure stable electric field strength. The output terminal of the voltage source is electrically connected to the driving electrode of the probe. A high-frequency excitation signal is applied to the driving electrode through a wire. The frequency can be selected according to the thickness of the coating layer, usually 100kHz-10MHz. When the high-frequency signal passes through the driving electrode, an alternating electromagnetic field is generated around the electrode. The electromagnetic field penetrates the air gap and acts on the coating layer below. Since the coating layer is dielectric or has a certain degree of conductivity, the electromagnetic field will form induced charges inside the coating layer and couple with the interior substrate. Finally, a closed alternating electric field loop is formed between the driving electrode, the coating layer, and the substrate. The distribution of the electric field is directly affected by the physical properties of the coating layer.

[0064] Compared to DC electric fields, alternating electric fields make it easier to collect dynamic signals through induction electrodes, facilitating subsequent circuit amplification and processing of the signals. At the same time, they avoid the charge accumulation problem under DC electric fields and reduce signal drift.

[0065] S3: The principle of capacitive coupling signal acquisition and information carrying: The sensing electrode is connected to the signal acquisition circuit through a shielded wire. When an alternating electric field acts on the coating layer, changes in the coating layer's thickness, dielectric constant, or surface condition will alter the coupling strength of the electric field. If the coating layer thickens, the thickness of the medium through which the electric field passes increases, the capacitance decreases, and the amplitude of the coupled signal acquired by the sensing electrode decreases. An increase in the dielectric constant increases capacitive coupling, leading to an increase in signal amplitude. If there are defects such as scratches or bubbles on the surface, the discontinuity of the medium at the defect location will cause abrupt changes in the electric field distribution, resulting in a phase jump in the signal. The sensing electrode converts these electric field changes into electrical signals, i.e., capacitive coupling signals. The magnitude of the signal directly reflects the change in capacitance, while the phase shift reflects the change in the electric field propagation path. Both carry information about the coating layer's thickness, dielectric constant, and surface defects.

[0066] A single-path signal acquisition method can simultaneously obtain multiple coating layer parameters, such as thickness, dielectric constant, and defects, without the need for multiple tests, thus improving detection efficiency. The dual characteristics of signal amplitude and phase provide redundant information for subsequent analysis. Even if one feature is interfered with, it can still be judged through another feature, thereby improving the anti-interference capability of the detection.

[0067] S4: Amplification of the original capacitance signal. The original capacitance signal output from the sensing electrode is connected to a preamplifier, preferably a low-noise, high-input-impedance type, such as a charge amplifier. Since the original signal is typically small and susceptible to environmental electromagnetic interference, the amplifier uses internal circuitry, such as an operational amplifier, to amplify the signal amplitude by a preset factor, such as 1-100 times, converting it into a larger amplified signal. Simultaneously, the amplifier's high input impedance reduces absorption of the original signal, preventing signal attenuation; the low-noise design suppresses noise generated by the circuit itself, ensuring that the amplified signal retains the subtle characteristics of the original signal, such as minor amplitude fluctuations or phase shifts.

[0068] Amplifying weak signals to a level that subsequent circuits can stably recognize solves the problem that the original signals are difficult to process due to their low amplitude; low-noise amplification ensures that the effective information in the signal is not drowned out by noise, providing a high-quality signal source for subsequent analysis.

[0069] S5: The conversion between reference signal interference and minute capacitance changes begins with a signal generator producing a reference signal with the same frequency as the high-frequency excitation signal in S2. The phase of this reference signal can be adjusted using a digital phase shifter, with an adjustment accuracy within 0.1 degrees. Then, the amplified signal output from S4 and the reference signal are simultaneously input into a signal interference circuit, such as a phase-sensitive detector circuit based on a multiplier. When the two signals are at the same frequency, interference occurs. If the amplified signal experiences a minute phase shift due to capacitance changes, the interference will output a DC voltage signal proportional to the phase shift. Conversely, if the amplitude of the amplified signal changes slightly, the interference will output a voltage signal proportional to the amplitude change. In this way, the originally difficult-to-identify minute capacitance changes are transformed into intuitive and easily measurable voltage amplitude or phase change signals.

[0070] By utilizing the interference effect, minute capacitance changes are converted into significant voltage / phase changes, improving detection sensitivity by 1-2 orders of magnitude. This allows for the capture of micron-level surface defects or height variations in the coating layer. The adjustable phase function of the reference signal can compensate for the inherent phase difference of the system through calibration, ensuring optimal interference effect and improving the accuracy of signal conversion.

[0071] S6: Signal Acquisition, Algorithm Analysis, and Environmental Compensation. This data acquisition unit, based on a 24-bit high-precision ADC, captures the voltage signal output from S5 in real time. The sampling rate must be no less than 10 MSPS to ensure complete recording of the signal's dynamic changes. The acquired signal is fed into a preset algorithm for analysis: The first step is signal preprocessing, such as moving average filtering and bandpass filtering, to remove high-frequency noise and power frequency interference; the second step is feature extraction, calculating the signal's amplitude, phase, or spectral characteristics; the third step is thickness and uniformity analysis, comparing the real-time signal characteristics to the coating thickness by comparing with the calibration curve of a standard sample, and calculating the thickness difference within the detection area, such as the difference between the maximum and minimum values, to assess uniformity; the fourth step is defect identification, capturing abrupt changes in the signal through edge detection or wavelet transform, and judging the size and severity of defects based on the amplitude and duration of the abrupt changes. Meanwhile, the environmental parameter compensation module in the algorithm receives data from temperature and humidity sensors in real time. Based on historical experimental data and experience, such as adjusting the thickness value by -0.01μm for every 1°C increase in temperature, a compensation model for temperature, humidity, and signal drift is established. For example, a linear or polynomial fitting relationship can be used to correct the detection results in real time, eliminating the influence of environmental changes on the results. The combination of high-precision data acquisition and algorithm analysis enables quantitative detection of coating thickness uniformity and surface defects. The detection results can be quantified into specific values, such as thickness error ±0.1μm and defect size 0.5mm. The environmental parameter compensation module solves the signal drift problem caused by temperature and humidity changes, ensuring stable accuracy in different environments and improving the practicality and reliability of the method.

[0072] As one implementation method, the capacitance detection probe is manufactured using a multilayer PCB process or a ceramic packaging process, with a grounding shielding layer between the driving electrode and the sensing electrode; the electrode surface is covered with an insulating protective layer, which is made of alumina ceramic or polyimide and has a thickness of 10-50μm; the overall equivalent capacitance detection range of the probe is between 0.1pF and 10pF, and the detection resolution is not less than 20fF.

[0073] The capacitance detection probe is manufactured using either a multilayer PCB process or a ceramic packaging process. In the multilayer PCB process, driving and sensing electrodes are formed by photolithography and etching copper foil layer by layer. Each layer is isolated by an insulating dielectric layer. A copper foil area is reserved between the driving and sensing electrodes as a grounding shield, which is thickened by electroplating and then connected to the system ground. In the ceramic packaging process, a ceramic substrate is prepared by tape casting or dry pressing. Electrode patterns are formed using screen printing of silver or copper paste. A grounding shield is printed between the two electrodes and sintered to ensure insulation between the shield and the electrodes and precise positioning. The grounding shield blocks direct electric field coupling between the driving and sensing electrodes, preventing crosstalk between electrodes from interfering with the detection signal, and also isolates electromagnetic noise from the external environment.

[0074] The insulating protective layer on the electrode surface is formed through sputtering, coating, or sintering processes. If alumina ceramic is used, a thin film is deposited on the electrode surface using magnetron sputtering, controlling the sputtering power and time to achieve a thickness of 10-50 μm, followed by high-temperature annealing to increase density. If polyimide is used, liquid polyimide resin is coated and cured in a constant-temperature oven at stepped temperatures, such as pre-curing at 80℃, medium curing at 150℃, and complete curing at 200℃, to form a uniform film. The 10-50 μm thickness effectively protects the electrode from wear without excessively increasing the electric field penetration path.

[0075] The electrode surface is covered with an insulating protective layer made of alumina ceramic or polyimide, with a thickness of 10-50 μm. Since the thickness of the protective layer is much smaller than the detection spacing, its influence on capacitance measurement has been eliminated as a fixed offset during the initial calibration of the system.

[0076] As one implementation method, the parallel suspension setting in S1 is achieved through a micro-nano positioning platform, which has an automatic Z-axis leveling function; the detection spacing is controlled at 1-30mm, and real-time feedback and control are performed through a laser displacement sensor to ensure that the spacing fluctuation is less than ±0.1mm.

[0077] The parallel suspension setting of the capacitance detection probe in S1 is achieved through a micro-nano positioning platform. The Z-axis automatic leveling function of this platform is completed collaboratively by multiple sets of precision drive units and tilt detection components. Three Z-axis drive modules, such as piezoelectric ceramic actuators or high-precision servo motors, are installed at the bottom of the platform in a triangular arrangement. Each drive module can independently achieve nanometer-level displacement adjustment. At the same time, a micro tilt sensor is integrated into the platform's bearing surface to detect the tilt angle between the probe plane and the surface of the coating layer of the automotive interior part being tested in real time. When the tilt sensor detects that the parallelism between the two exceeds a preset threshold, such as 0.1°, the platform control system calculates the adjustment amount of each drive module based on the tilt direction and angle. For example, if the probe front end is detected to be too low, the front drive module is slightly raised, while the rear drive module remains unchanged or slightly lowered until the tilt sensor reports that the parallelism meets the requirements, thus completing the automatic leveling.

[0078] The detection spacing is controlled through a closed-loop control system formed by a laser displacement sensor and a micro-nano positioning platform. The laser displacement sensor is fixed to the side of the probe, and its emitted laser beam is perpendicularly pointed to the surface of the coating layer. By measuring the time difference between the laser's emission and reflection back to the sensor, the actual distance between the probe and the coating layer surface is calculated in real time. The sensor transmits the distance data to the platform controller in the form of an electrical signal. The controller compares the actual distance with the preset detection spacing: if the actual distance is greater than the set value, the controller drives the Z-axis module to move the probe downwards; if the actual distance is less than the set value, it drives the probe upwards. The response time of the entire adjustment process is controlled at the millisecond level, ensuring that the spacing fluctuation is always less than ±0.1mm.

[0079] The Z-axis automatic leveling function avoids probe tilting caused by slight tilting of the automotive interior parts surface or uneven platform placement, ensuring uniform spacing between the probe area and the coating layer, and eliminating local capacitance signal deviation caused by tilting. The real-time feedback and closed-loop control of the laser displacement sensor maintain the stability of the detection spacing with extremely high precision, solving the spacing drift problem caused by vibration and temperature deformation in traditional mechanical positioning, and providing a reliable spatial reference for stable acquisition of capacitance signals. The adjustable spacing range of 1-30mm can adapt to automotive interior coating layers of different thicknesses and materials, improving the versatility of the detection method.

[0080] As one implementation method, the high-frequency AC voltage source is a sine wave signal source with amplitude and frequency stabilization functions, with an output frequency range of 100kHz-10MHz and a peak-to-peak voltage of 1-10V; the phase of the reference signal is adjusted by a digital phase offsetter or an analog phase shifter circuit, with an adjustment accuracy better than 0.1 degrees.

[0081] The high-frequency AC voltage source employs a sinusoidal signal source with amplitude and frequency stabilization functions, consisting of a high-precision crystal oscillator, a phase-locked loop (PLL) circuit, and an automatic gain control module. The crystal oscillator provides a reference frequency signal, which is divided or multiplied by the PLL circuit to generate an adjustable output frequency within the range of 100kHz-10MHz. The target frequency can be set via a knob or digital interface, with frequency stability controlled within ±1ppm. The automatic gain control module monitors the amplitude of the output signal in real time. When the amplitude deviates from the set value due to load changes or power fluctuations, the module adjusts the gain of its internal amplifier to stabilize the peak-to-peak output voltage within 1-10V, ensuring that the amplitude and frequency of the high-frequency excitation signal applied to the drive electrodes remain stable.

[0082] Phase adjustment of the reference signal is achieved through a digital phase shifter or an analog phase-shifting circuit. When using a digital phase shifter, a reference frequency signal from a high-frequency AC voltage source is used as input. An FPGA or dedicated digital signal processing chip samples the signal and calculates the phase delay. Each delay step corresponds to a fixed phase increment. The user can set the target phase through the control system, and the chip outputs a reference signal with the corresponding phase shift. When using an analog phase-shifting circuit, a precision RC network or a variable phase shifter chip is used to adjust the resistance or capacitance values ​​in the circuit to change the signal's phase hysteresis. This is monitored in real-time by a phase meter, and phase adjustment is achieved through a fine-tuning knob. Both methods employ calibration procedures to ensure an adjustment accuracy better than 0.1 degrees.

[0083] A stable amplitude and frequency sinusoidal signal source provides a stable excitation basis for the alternating electric field, avoiding changes in the reference signal of capacitive coupling caused by frequency drift or amplitude fluctuation, and ensuring the comparability of signals at different detection periods or different detection points; the frequency range of 100kHz-10MHz can be adapted to automotive interior coating layers of different thicknesses, and the voltage range of 1-10V can adjust the electric field strength according to the dielectric constant of the coating layer, enhancing detection adaptability; the high-precision phase adjustment of the reference signal can cancel the inherent phase difference of the system, ensuring that it is in the best coupling state with the amplified signal during interference, maximizing the conversion sensitivity of small capacitance changes, and improving detection accuracy.

[0084] In one implementation, the preamplifier used in S4 is a low-noise, high-input-impedance charge amplifier. It is implemented using an amplification circuit based on a high-precision operational amplifier. The gain range is set from 1 to 100 times through feedback capacitors and resistor networks. Users can flexibly adjust the gain value using a digital potentiometer or jumper cap according to the signal strength. The input stage of the charge amplifier uses JFET or CMOS technology to ensure an input impedance higher than 1GΩ, effectively reducing the signal source load effect. Simultaneously, it integrates low-noise designs, such as using metal film resistors and polypropylene capacitors, to reduce the equivalent input noise to the microvolt level. The amplifier's bandwidth is achieved through optimized circuit layout and the selection of high-speed operational amplifiers, ensuring that the bandwidth is greater than 10 times the excitation signal frequency. For example, when the excitation frequency is 10MHz, the amplifier bandwidth needs to exceed 100MHz to fully preserve the high-frequency components of the signal.

[0085] The signal interference circuit is implemented using a phase-sensitive detector circuit or a quadrature demodulation circuit based on a multiplier. For the phase-sensitive detector circuit, the core is an analog multiplier chip, such as the AD630. The amplified signal output from S4 and the reference signal are simultaneously input into the multiplier. The multiplication operation generates an output containing sum and difference frequency components. High-frequency components are then filtered out by a low-pass filter, ultimately outputting a DC voltage signal proportional to the capacitance change. If a quadrature demodulation circuit is used, two quadrature reference signals are generated by a local oscillator and mixed with the amplified signal respectively. After processing by an integrator, in-phase and quadrature components are obtained. Amplitude and phase information are extracted through vector operations and converted into a DC voltage output. The reference signal and the excitation signal are strictly in sync, and the phase can be adjusted by a digital phase offset to ensure optimal interference effect.

[0086] A high-input-impedance charge amplifier amplifies the weak raw capacitance signal to a processable range while minimizing signal attenuation and noise introduction, providing a clear and stable signal source for subsequent circuits. Its wide bandwidth design ensures distortion-free transmission of high-frequency excitation signals, avoiding signal distortion. The signal interference circuit converts minute capacitance changes into a highly sensitive DC voltage signal through interference, significantly improving detection resolution and enabling the system to identify capacitance changes on the order of 20 fF, corresponding to micron-level thickness differences or surface defects in the coating layer.

[0087] As one implementation method, S6 uses a 24-bit high-precision ADC as the core of the data acquisition unit, which directly or through a high-speed sample-and-hold circuit samples the amplified signal output by the preamplifier, with a sampling rate of not less than 10MSPS.

[0088] The default algorithm runs on embedded DSPs, FPGAs, or industrial-grade multi-core processors. The default algorithm analysis specifically includes the following sub-steps:

[0089] S6.1 Signal preprocessing: The acquired voltage signal is digitally filtered. First, a moving average filter is used to suppress high-frequency noise, and then a bandpass filter is used to extract the fundamental frequency component of the signal.

[0090] S6.2 Feature Extraction: Calculate the amplitude and phase of the signal, or analyze its spectral characteristics through Fast Fourier Transform;

[0091] S6.3 Thickness and Uniformity Analysis: Multiple sets of capacitance values ​​are collected using a standard coating sample with a preset thickness. A calibration curve of capacitance value and coating thickness is obtained by fitting the curve. The thickness is inverted using the real-time capacitance value. The uniformity index is calculated based on the distribution of thickness values. The uniformity index is the difference between the maximum and minimum thickness values ​​in the detection area, or the ratio of the standard deviation of thickness to the average thickness.

[0092] S6.4 Defect Identification: Edge detection algorithm or wavelet transform algorithm is used to identify abrupt changes in the signal. If the signal amplitude drops sharply or the phase changes abruptly, it is determined that there is a defect in the corresponding area. The size and severity of the defect are evaluated based on the width and amplitude of the abrupt signal.

[0093] The data acquisition unit in S6 employs a 24-bit high-precision ADC chip. This chip utilizes oversampling and digital filtering techniques to increase the sampling rate to at least 10 MSPS, meaning it can acquire 100,000 data points per second. The analog input of the ADC is connected to the output of the signal interference circuit in S5 via an anti-aliasing filter, ensuring that the analog signal is not distorted during digitization. The acquired digital voltage signal is transmitted in real-time to the embedded processor or host computer via SPI or a parallel interface, providing a complete data stream for subsequent pre-defined algorithm analysis.

[0094] The analysis of the preset algorithm is implemented through embedded software or a host computer program, and specifically includes four sub-steps. In the S6.1 signal preprocessing, the acquired voltage signal is first subjected to a moving average filter, using a fixed-length data window, for example, containing 100 sampling points, and the arithmetic mean of the data within the window is calculated to smooth high-frequency random noise. Subsequently, a digital bandpass filter is applied, with its passband center frequency set to the fundamental frequency of the excitation signal, and the passband width adjusted according to the signal characteristics, effectively extracting the fundamental frequency component of the signal and suppressing harmonic interference and power frequency noise.

[0095] In feature extraction in S6.2, for the preprocessed signal, the amplitude is obtained by calculating the difference between the maximum and minimum values ​​of the signal within one period, or the phase is analyzed by comparing it with a reference signal through zero-crossing detection. Simultaneously, a Fast Fourier Transform can be used to convert the time-domain signal to the frequency domain, analyzing its main peak amplitude, harmonic components, and other characteristics in the spectrum, thereby comprehensively characterizing the signal features.

[0096] In the S6.3 thickness and uniformity analysis, a calibration curve must first be established through a calibration procedure. Using a series of standard coating samples with known thicknesses, voltage signals derived from the corresponding capacitance values ​​are collected under fixed testing conditions. The least squares method is used to fit multiple sets of data into capacitance-thickness or voltage-thickness curves and store them. In actual testing, the real-time acquired voltage values ​​are substituted into this calibration curve, and the coating thickness value is directly obtained through interpolation. By statistically analyzing the thickness values ​​at all measurement points within the testing area, the difference between the maximum and minimum values ​​is calculated as one uniformity indicator, or the ratio of the standard deviation of all thickness values ​​to their average value is calculated as another uniformity indicator, thereby quantitatively assessing the consistency of the coating thickness distribution. The material, substrate type, dielectric constant, and other parameters of the standard coating samples must be consistent with those of the part under test.

[0097] Any signal variation deviating from the normal pattern is identified as an abnormality in the coating layer, encompassing surface defects such as scratches, bubbles, and uneven thickness affecting functionality. In S6.4 defect identification, edge detection algorithms, such as the Canny operator, are used to find sharp drops in signal amplitude by calculating the first derivative of the signal; or wavelet transform algorithms are used to perform multi-resolution analysis of the signal by selecting appropriate wavelet basis functions to identify singular abrupt changes at specific scales. When the algorithm detects a sharp drop in signal amplitude exceeding a preset threshold, or a phase jump exceeding a preset angle, it determines that a surface defect exists in the corresponding detection area. By analyzing the width and duration of the abrupt signal, combined with the scanning speed, the longitudinal dimension of the defect can be calculated; by analyzing the amplitude of the abrupt signal, the severity of the physical property changes caused by the defect can be assessed.

[0098] A high-precision ADC ensures the complete and accurate digitization of the original voltage signal, laying a reliable data foundation for subsequent analysis. The pre-defined algorithm, through systematic digital filtering, feature extraction, calibration inversion, and defect identification steps, transforms the original voltage signal into intuitive thickness values, uniformity indicators, and defect information, achieving automated and quantitative comprehensive evaluation of the coating quality. This not only improves detection efficiency and objectivity but also effectively detects micron-sized surface defects by identifying and quantifying signal abrupt changes, significantly enhancing the overall performance and practical value of the detection method.

[0099] In one implementation, the capacitance detection probe is integrated into an array probe. This is achieved by fabricating multiple identical capacitance sensing units on a shared substrate using photolithography or printing processes. These sensing units are arranged in a regular M-row × N-column array. Each independent sensing unit contains one or more driving electrodes and a sensing electrode, with a structure identical to that of a single probe. The row lines of all driving electrodes and the column lines of the sensing electrodes are connected to a dedicated multiplexed switch array circuit. Under the command of the control unit's logic signals, this circuit sequentially or in a specific mode rapidly selects different rows and columns of sensing units, causing them to take turns operating. This effectively achieves a one-time surface scan of the coating layer in a rectangular area below the probe, rather than the traditional single-point scanning. The array control circuit employs a time-division driving strategy, applying an excitation signal to only one driving electrode at a time, while the remaining adjacent driving electrodes are grounded or placed in a high-impedance state. To achieve complete detection of the entire interior trim surface, this array probe is mounted on a scanning motion control system. This system typically includes linear modules in both the X and Y axes, driven by servo or stepper motors, and equipped with a linear scale or encoder for position feedback. The control unit coordinates the circuit scanning of the probe array with the displacement of the motion system. After the array probe completes a surface scan of a position, the motion system moves it by a step distance, which is usually less than or equal to the array's own scanning width, thus ensuring seamless connection between adjacent scan areas and ultimately covering the entire surface of the interior trim part under test.

[0100] All data collected by the array probes, including the position coordinates of each sensing unit and the corresponding capacitance inversion thickness or defect signals, are uniformly sent to the host computer software. The software algorithm performs two-dimensional interpolation and smoothing based on these data points, ultimately generating an intuitive two-dimensional distribution map of the coating quality across the entire interior trim surface. This distribution map can be presented in the form of a thickness contour map, a uniformity color block map, or a defect marker map.

[0101] By combining an array probe with scanning motion, the detection mode is upgraded from inefficient single-point measurement to efficient surface scanning measurement, greatly improving the overall inspection efficiency of large-sized automotive interior parts. Acquiring massive amounts of data points across the entire surface at once comprehensively and without omission reflects the quality status of the coating layer, particularly clearly showing the macroscopic trend of thickness variations and the distribution of local defects. This provides unprecedentedly detailed data support for production process improvement and quality control, significantly enhancing the practical value and automation level of this inspection method. Normal thickness variations manifest as a gentle gradient, spatially continuous; while defects appear as isolated, sharp-edged anomalies or areas. Historical experience can be built through multiple inspections, allowing for the determination of whether a defect is due to uneven thickness. The array probe uses signal processing algorithms to suppress crosstalk, such as time-division multiplexing or spatial filtering.

[0102] In one implementation, the entire testing system is integrated into a specially designed electromagnetically shielded enclosure. This enclosure is constructed of galvanized steel or aluminum alloy, forming a continuous conductive cavity. All seams between the enclosure panels are filled with beryllium copper finger springs to ensure continuous electrical connections. The enclosure door uses double-layered shielded glass as an observation window, with its wire mesh maintaining good contact with the door frame. All cable inlets and outlets on the enclosure are equipped with RF filter connectors, and the power supply inlet is fitted with an AC power filter to block external radio frequency interference and power frequency interference from entering the enclosure.

[0103] Key signal lines inside the enclosure, including high-frequency excitation signal transmission lines, induction electrode signal lines, and reference signal lines, are all connected using coaxial shielded cables. The outer braided shielding layer of these cables is connected to the enclosure ground plane at both ends via metal BNC or SMA connectors, achieving a 360-degree circumference connection and forming a complete Faraday cage structure. The signal ground wire is reliably connected to the enclosure ground plane at a single point, avoiding the formation of ground loops.

[0104] The detection system also integrates digital temperature and humidity sensors, typically installed inside the enclosure near the capacitive sensing probe, but avoiding direct contact with the excitation source to prevent self-heating. The temperature sensor can be a PT100 or an integrated chip such as the DS18B20, while the humidity sensor can be a capacitive polymer thin-film sensor. The sensors connect to the main control unit via digital interfaces such as I2C or a single-bus interface, acquiring environmental parameter data in real time and transmitting it to the environmental parameter compensation module with a preset algorithm.

[0105] The electromagnetic shielding enclosure effectively isolates the high-sensitivity capacitance detection system from interference from the complex external electromagnetic environment, ensuring the stability of microvolt-level signal acquisition. The use of coaxial shielded cables throughout the internal circuitry minimizes crosstalk and radiation loss during signal transmission, guaranteeing the integrity of high-frequency signals. Integrated temperature and humidity sensors, along with real-time environmental parameter acquisition and compensation, directly address the issues of dielectric constant drift and circuit parameter variations caused by temperature and humidity changes. This significantly improves the long-term stability and measurement accuracy of the detection system under different operating environments, resulting in highly reliable and repeatable test results.

[0106] This invention discloses a method for preparing a coating layer for automotive interior parts using magnetron sputtering technology, which includes the following steps:

[0107] A1 Substrate Pretreatment: The automotive interior parts substrate undergoes a multi-step pretreatment process. First, the substrate surface is ultrasonically cleaned with a neutral detergent to remove surface oil and dust. Then, it is rinsed with deionized water and placed in a drying equipment for drying. After drying, the substrate is placed in a plasma treatment chamber and activated with inert gas plasma to increase the substrate surface energy and enhance the adhesion between the subsequent coating layer and the substrate.

[0108] A2 Sputtering Preparation: Fix the pretreated automotive interior part substrate onto the sample holder in the magnetron sputtering vacuum chamber. Select the appropriate sputtering target according to the functional requirements of the coating layer. The target can be a metal target or a compound target. Close the vacuum chamber and start the vacuum system to evacuate the vacuum chamber until the preset vacuum level is reached inside the vacuum chamber.

[0109] A3 sputtering coating: Inert working gas is introduced into the vacuum chamber, and the gas flow rate is adjusted to maintain the vacuum chamber at the preset working pressure; a preset type of power supply, DC power supply or RF power supply, is applied to the sputtering target, and the sputtering power is adjusted to the preset value so that the target is sputtered under the action of electric field and magnetic field. After the target atoms or ions detach from the target surface, they are deposited on the substrate surface to form a continuous coating layer.

[0110] The type of power supply should be selected based on the conductivity of the sputtering target: If a metal target, such as an aluminum target or a copper target, is selected, a DC power supply should be applied because of the excellent conductivity of the target material to avoid the accumulation of charge on the target surface; if a compound target is selected, an RF power supply should be applied because the target material is an insulating or semi-insulating material, and the charge accumulation on the target surface should be eliminated by the periodic reversal of the RF electric field.

[0111] A4 Post-treatment: After the coating is completed, turn off the power and working gas. After the vacuum chamber temperature drops to room temperature, take out the interior parts. Put the coated interior parts into the annealing furnace for annealing treatment. By controlling the annealing temperature and holding time, the residual stress inside the coating layer is removed, and the stability and wear resistance of the coating layer are improved.

[0112] A5 Coating Inspection: The coating layer is inspected using the inspection methods for automotive interior coating layers.

[0113] This invention utilizes a four-step process—substrate pretreatment, sputtering preparation, sputtering coating, and post-treatment—to deposit a high-quality coating layer on the surface of automotive interior parts substrates through the synergistic effect of the electric and magnetic fields in magnetron sputtering technology. By controlling the process at each stage, the adhesion, continuity, and stability of the coating layer are ensured.

[0114] The first step is substrate pretreatment. The substrate is first ultrasonically cleaned with a neutral cleaning agent, using the vibration of the ultrasound to remove surface oil and dust. Then, residual cleaning agent is rinsed off with deionized water, and the substrate is dried before entering the plasma treatment chamber. Inert gas plasma acts on the substrate surface, breaking the inert chemical bonds and increasing the surface energy. This creates conditions for a tight bond between the subsequent coating layer and the substrate, avoiding the risk of coating peeling.

[0115] The second step is sputtering preparation. The pretreated substrate is fixed on the sample holder in the vacuum chamber, and a metal target or a compound target is selected according to the function of the coating layer. Then, the vacuum is evacuated to the preset vacuum level. The purpose is to remove air impurities in the vacuum chamber and prevent impurities from being mixed into the coating layer during the sputtering process, which would affect the coating quality.

[0116] The third step is sputtering deposition. An inert working gas is introduced into the vacuum chamber and a preset pressure is maintained. The inert gas can provide the ion environment required for sputtering and will not react with the target or substrate. A DC or RF power supply is applied to the target. Under the action of the electric field, the inert gas is ionized to generate ions. The ions are accelerated by the electric field and bombard the target. At the same time, the magnetic field constrains the trajectory of the ions, enhances the bombardment efficiency, and causes the target atoms or ions to detach from the surface, and finally deposit a continuous coating layer on the substrate surface.

[0117] The fourth step is post-processing. After the coating is completed, the workpiece is removed after the vacuum chamber has cooled to room temperature to avoid deformation of the substrate or coating layer caused by high temperature removal. Then, the temperature and holding time are controlled by the annealing furnace to make the atomic arrangement inside the coating layer more stable, eliminate the residual stress generated during the sputtering process, and prevent the coating layer from cracking or wearing during subsequent use.

[0118] The coating layer prepared by this method exhibits strong adhesion and is not easily detached. Ultrasonic cleaning during substrate pretreatment removes surface impurities, while plasma activation enhances surface energy, allowing the target atoms to bond more tightly to the substrate. This solves the problem of easy peeling in traditional coating layers, making it suitable for the long-term use requirements of automotive interior parts. The coating layer exhibits stable quality and high purity. The high-vacuum environment during sputtering preparation reduces impurity contamination, and the coordinated control of electric and magnetic fields during sputtering ensures uniform target deposition, resulting in a continuous, gap-free coating layer that meets the stringent standards for appearance and performance of automotive interior parts. Depending on the function, metal or compound targets can be selected, and different power supply types can be used to prepare coating layers with different properties such as wear resistance and decorative properties. Simultaneously, annealing treatment improves the stability and wear resistance of the coating layer, extending the service life of interior parts. The process parameters for each step are controllable, and the rhythm of pretreatment, sputtering, and post-treatment can be matched to the production line speed, requiring no complex manual intervention. This ensures both consistency and efficiency in mass production, making it suitable for the large-scale manufacturing of automotive interior parts.

[0119] In one implementation method, plasma activation treatment in A1 uses argon as an inert gas, with plasma power controlled at 50-150W and treatment time at 30-120s.

[0120] In A2, the compound target is specifically a SiO2 target or an Al2O3 target, with a preset vacuum level of ≤5×10⁻. 4 Pa;

[0121] In A3, the inert working gas is argon, the gas flow rate is 20-50 sccm, the preset working gas pressure is 0.1-1 Pa, the sputtering power is 100-500 W, and the thickness of the formed coating layer is 50-500 nm.

[0122] The annealing temperature in A4 is 80-150℃, and the holding time is 30-60min.

[0123] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for detecting a coated layer of an automotive interior, characterized by, The method comprises the following steps: S1: A capacitive detection probe is arranged in parallel above the coating layer of the automobile interior part to be detected, the probe comprising one or more driving electrodes and a sensing electrode, which together form a capacitive sensing unit; the probe and the surface of the coating layer maintain a stable and uniform detection distance; S2: A high-frequency alternating voltage source is used to apply a high-frequency excitation signal to the driving electrode, forming an alternating electric field between the probe and the coating layer; S3: The sensing electrode collects a capacitive coupling signal generated due to the action of the alternating electric field; the amplitude and phase changes of the capacitive coupling signal carry information about the thickness, dielectric constant and surface flaws of the coating layer; S4: The original capacitive signal collected is first amplified by a preamplifier to form an amplified signal; S5: A reference signal with the same frequency as the high-frequency excitation signal but with adjustable phase is introduced, and the amplified signal and the reference signal are interfered with each other through a signal interference circuit, so that the small capacitive change is converted into a high-sensitivity voltage amplitude or phase change signal; S6: A data acquisition unit is used to capture the voltage signal in real time, and a preset algorithm is used to analyze the signal characteristics; according to the signal offset, sudden change or specific pattern, the thickness uniformity state and surface flaw condition of the coating layer are identified respectively; The preset algorithm includes an environmental parameter compensation module for eliminating the interference of temperature and humidity on the detection result.

2. The method according to claim 1, characterized in that: The capacitive detection probe is manufactured by using a multi-layer PCB process or a ceramic packaging process, and a grounding shielding layer is arranged between the driving electrode and the sensing electrode; The electrode surface is covered with an insulating protective layer made of aluminum oxide ceramic or polyimide, and the thickness is 10-50 μm; The overall equivalent capacitance detection range of the probe is between 0.1 pF and 10 pF, and the detection resolution is not less than 20 fF.

3. The method according to claim 1, characterized in that: The parallel suspension in S1 is realized by using a micro-nano positioning platform, which has a Z-direction automatic leveling function; The detection distance is controlled to be 1-30 mm, and a laser displacement sensor is used for real-time feedback and control to ensure that the distance fluctuation is less than ±0.1 mm.

4. The method according to claim 1, characterized in that: The high-frequency alternating voltage source is a sine wave signal source with stable amplitude and frequency, and the output frequency range is 100 kHz-10 MHz, and the voltage peak-peak value is 1-10 V; The phase of the reference signal is adjusted by a digital phase shifter or an analog phase shift circuit, and the adjustment accuracy is better than 0.1 degree.

5. The method according to claim 1, characterized in that: The preamplifier in S4 is a low-noise, high-input-impedance charge amplifier, and the gain is 1-100 times, and the bandwidth is more than 10 times the frequency of the excitation signal; The signal interference circuit is a phase-sensitive detection circuit or a quadrature demodulation circuit based on a multiplier, which can output a direct current voltage signal proportional to the capacitive change.

6. The method according to claim 1, characterized in that: The 24-bit high-precision ADC is used as the core of the data acquisition unit in S6, and the sampling rate is not less than 10 MSPS; The preset algorithm analysis specifically includes the following sub-steps: S6.1 Signal preprocessing: the collected voltage signal is digitally filtered, first a moving average filter is used to suppress high-frequency noise, and then a band-pass filter is used to extract the signal fundamental component; S6.2 Feature extraction: calculate the amplitude and phase of the signal, or analyze its frequency spectrum characteristics through fast Fourier transform; S6.3 Thickness and uniformity analysis: collect multiple sets of capacitance values through a standard plated film sample plate with a preset thickness, fit to obtain a calibration curve of capacitance value and film thickness, and then invert the thickness from the real-time capacitance value; calculate the uniformity index according to the distribution of the thickness value, which is the difference between the maximum and minimum thickness in the detection area, or the ratio of the thickness standard deviation to the average thickness; S6.4 Defect identification: use edge detection algorithm or wavelet transform algorithm to identify the abrupt change point in the signal, if the signal amplitude decreases sharply or the phase jumps, it is determined that there is a defect in the corresponding area, and the size and severity of the defect are evaluated according to the width and amplitude of the abrupt signal.

7. The detection method of the automotive interior coating layer according to claim 1, characterized in that: The capacitance detection probe can be integrated into an array probe, which includes multiple sensing units arranged in an array, capable of realizing one-time surface scanning of the coating layer, and combined with a scanning motion control system, a two-dimensional distribution map of the coating quality of the entire interior surface can be quickly constructed.

8. The detection method of the automotive interior coating layer according to claim 1, characterized in that: The entire detection system is integrated in an electromagnetic shielding box to isolate external radio frequency interference and power frequency interference; The key signal lines inside the box are connected by coaxial shielded cables; The detection system also integrates temperature and humidity sensors to collect real-time environmental parameters and transmit them to the environmental parameter compensation module of the preset algorithm.

9. A coating method for automotive interior, characterized in that the detection method of any one of the coating layers for automotive interior according to claims 1 to 8 is used after the coating. The steps include: A1 Base pretreatment: multiple pretreatments are performed on the automotive interior base, first a neutral cleaning agent is used to ultrasonically clean the surface of the base to remove surface oil and dust, then deionized water is used to rinse it clean, and then it is placed in a drying device for drying treatment; After drying, the base is placed in a plasma treatment chamber, and an inert gas plasma is used to activate the surface of the base; A2 Sputtering preparation: the pretreated automotive interior base is fixed on the sample holder in the magnetron sputtering vacuum chamber, and the corresponding sputtering target material is selected according to the functional requirements of the coating layer, which can be a metal target or a compound target; Close the vacuum chamber and start the vacuum system to vacuum the vacuum chamber until the internal pressure reaches the preset vacuum degree; A3 Sputtering coating: inert working gas is introduced into the vacuum chamber, and the gas flow is adjusted to maintain the internal pressure of the vacuum chamber at the preset working pressure; A preset type of power supply is applied to the sputtering target, and the sputtering power is adjusted to the preset value, so that the target material is sputtered under the action of electric field and magnetic field, and the target atoms or ions are separated from the surface of the target material and deposited on the surface of the base to form a continuous coating layer. A4 post-processing: after the coating is completed, the power supply and working gas are turned off, and the interior trim part is taken out after the vacuum chamber temperature drops to room temperature; The coated interior trim part is placed in an annealing furnace for annealing treatment, and the residual stress in the coating layer is removed by controlling the annealing temperature and holding time; A5 coating detection: the coating layer is detected.

10. The automotive interior coating method according to claim 9, wherein: A1 plasma activation treatment, using argon as inert gas, plasma power control is 50-150W, processing time is 30-120s; The target of the compound in A2 is specifically SiO2 target or Al2O3 target, and the preset vacuum degree is ≤5×10⁻ 4 Pa; A3 inert working gas is argon, gas flow is 20-50sccm, preset working gas pressure is 0.1-1Pa, sputtering power is 100-500W, and the formed coating layer thickness is 50-500nm; A4 annealing temperature is 80-150℃, holding time is 30-60min.

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