Self-calibration capacitive displacement sensor and gap measurement method

Abstract

The invention discloses a self-calibration capacitive displacement sensor and a gap measurement method. The sensor comprises a sensor measuring head unit, a signal conversion unit and a signal processing unit. According to the invention, through the design of a four-measuring-head differential structure with a known gap, the influence of a measured material, environmental factors and installation precision on the output value of the sensor is introduced, so that the sensor only needs to be calibrated once when leaving a factory and can be directly self-calibrated in subsequent use, and the measurement precision of the sensor is improved.

Description

Technical Field

[0001] This invention relates to the field of sensors, specifically a self-calibrating capacitive displacement sensor and a gap measurement method. Background Technology

[0002] Capacitive gap measurement sensors are mainly used to measure the bonding gap of composite material skins in aircraft and high-speed vehicles, the internal gap of engines, the assembly gap during the assembly process, and the gap between arbitrary conductive film layers.

[0003] Existing capacitive gap measurement sensors are built based on a parallel plate capacitor model, and their core formula is: Where C is the capacitance, ε0 is the vacuum permittivity, and ε r denoted as the relative permittivity of the medium, A as the effective area of ​​the electrode, and d as the gap being measured.

[0004] When the displacement of the object being measured causes a change in the gap d, the capacitance C changes accordingly. By converting the capacitance change into a voltage, frequency, or digital signal through a measuring circuit, the physical quantity of the gap can be deduced.

[0005] However, existing capacitive gap measurement sensors have the following drawbacks:

[0006] 1. Material specificity

[0007] When the material being measured is changed, its dielectric properties (such as the significant difference in relative permittivity between metallic conductors and insulators) directly affect the capacitance value, causing a shift in the sensor output. For example, switching from metal to ceramic (ε... r ≈4-10) or plastic (ε r If the measurement is not recalibrated (≈2-3), the measurement error may exceed 10% of the range.

[0008] 2. Environmental sensitivity

[0009] In engineering applications, the capacitance measured by the sensor is mainly composed of the measured object C1 and air C2. However, due to changes in temperature and humidity in the engineering environment, the sensor output value will be affected.

[0010] 3. Installation accuracy dependency

[0011] The sensor requires the measured surface to be strictly parallel or centered with the electrode plate (e.g., the axis of a cylindrical surface must be aligned), otherwise nonlinear errors will be introduced. Summary of the Invention

[0012] The purpose of this invention is to provide a self-calibrating capacitive displacement sensor, including a sensor probe unit, a signal conversion unit, and a signal processing unit.

[0013] The sensor probe unit includes a first pair of sensor probes and a second pair of sensor probes arranged differentially in the thickness direction.

[0014] The first pair of sensor probes includes sensor probe I and sensor probe II, which are arranged opposite each other. Sensor probe I faces one side of the object being measured, and sensor probe II faces the other side of the object being measured.

[0015] The second pair of sensor probes includes sensor probe III and sensor probe IV, which are arranged opposite to each other. Sensor probe III faces one side of the object being measured, and sensor probe IV faces the other side of the object being measured.

[0016] Sensor probe I, sensor probe II, sensor probe III, and sensor probe IV respectively monitor capacitance signal I, capacitance signal II, capacitance signal III, and capacitance signal IV, and transmit them to the signal conversion unit.

[0017] The signal conversion unit converts the capacitance signal into a signal to be processed and transmits it to the signal processing unit.

[0018] The signal processing unit determines the gap of the object being measured based on the signal to be processed and the capacitance-gap calibration equation.

[0019] The capacitance-gap calibration equation is as follows:

[0020]

[0021] In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I, sensor probe II, sensor probe III, and sensor probe IV, respectively. ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air. ε0 is the dielectric constant of vacuum. Parameters t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring. φ1 is the cross-sectional diameter of the sensor. d1 and d3 are the straight-line distances between sensor probe I and sensor probe III and one side of the object being measured. d2 and d4 are the straight-line distances between sensor probe II and sensor probe IV and the other side of the object being measured.

[0022] Before each operation of the sensor probe, the signal processing unit acquires the dielectric constant ε associated with the object being measured. a air dielectric constant ε b Then, substitute the capacitance-gap calibration equation into the sensor to perform self-calibration of the calibration equation.

[0023] Furthermore, the sensor probe includes an outermost ring, an equipotential shielding ring, and a signal ring arranged sequentially from the outside to the inside.

[0024] There are insulating gaps between the outermost ring and the equipotential shielding ring, and between the equipotential shielding ring and the signal ring.

[0025] Furthermore, the sensor probe is manufactured using printed circuit board technology.

[0026] Furthermore, the outer diameter of the shielding ring satisfies the formula (φ2-φ1) / 2=3d / 2; where d is the gap between the two capacitor plates; and φ2 is the diameter of the shielding ring.

[0027] Furthermore, the thickness difference between the first pair of sensor probes and the second pair of sensor probes is d0, and 0.5mm ≥ d0 ≥ 0.05mm.

[0028] Furthermore, the signal to be processed is a voltage, frequency, or digital signal carrying a capacitance value.

[0029] Furthermore, the sensor probe adopts a three-layer flexible encapsulation structure, including a PI polyimide insulating layer, a PDMS elastic protective layer, and a nano hydrophobic coating arranged sequentially from the inside out.

[0030] Furthermore, the signal processing unit integrates an environmental compensation module for dynamically correcting dielectric parameters;

[0031] The environmental compensation module includes a digital temperature sensor and a capacitive humidity sensor for collecting environmental temperature and humidity data.

[0032] Furthermore, it also includes an offset measurement module located at the rear of the measuring head;

[0033] The offset measurement module is used to measure the real-time angle of the sensor probe in order to correct the measurement error caused by the probe not being parallel to the measurement plane;

[0034] The offset measurement module includes an electrode pair, a conductive droplet, a sealing cap, and a substrate;

[0035] The sealing cap and the base form a closed cavity;

[0036] The electrode pairs are arranged symmetrically between the substrate and the sealing cap, thus forming a hollow channel between the two electrodes; each electrode channel is connected in series with a fixed resistor.

[0037] Conductive droplets are arranged inside a hollow pipe;

[0038] The offset measurement module determines the resistance of the conductive droplet at its location using electrodes based on the droplet's position within the hollow tube, thus pinpointing the droplet's position x. This allows the module to calculate the tilt angle of the measuring head. g is the acceleration due to gravity, μ is the dynamic viscous drag factor, and x is the position of the conductive droplet.

[0039] The steps for locating a conductive droplet include: measuring the conductivity state through the corresponding pin of each electrode to determine the current position of the droplet.

[0040] A gap measurement method using the self-calibrating capacitive displacement sensor includes the following steps:

[0041] 1) The environmental compensation module collects environmental temperature and humidity data and substitutes it into the temperature and humidity-dielectric constant offset calibration curve to obtain the dielectric constant offset value, thereby correcting ε0 in the capacitance-gap calibration equation in real time.

[0042] 2) Measure the tilt angle θ of the sensor probe using the offset measurement module, and correct the straight-line distance between the sensor probe and one side of the object being measured to obtain the corrected straight-line distance, i.e.:

[0043]

[0044] In the formula, d1 and d3 are the straight-line distances between the corrected sensor probes I and III and one side of the object being measured; d2 and d4 are the straight-line distances between the corrected sensor probes II and IV and the other side of the object being measured; d1' and d3' are the straight-line distances between the original sensor probes I and III and one side of the object being measured; d'2 and d'4 are the straight-line distances between the original sensor probes II and IV and one side of the object being measured.

[0045] 3) Use the first pair of sensor probes and the second pair of sensor probes to monitor capacitance signal I, capacitance signal II, capacitance signal III, and capacitance signal IV;

[0046] 4) Convert the capacitance signal into a signal to be processed, and substitute it into the capacitance-gap calibration equation to determine the gap of the object being measured;

[0047] The capacitance-gap calibration equation is as follows:

[0048]

[0049] In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I, sensor probe II, sensor probe III, and sensor probe IV, respectively; ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air; ε0 is the dielectric constant of vacuum; parameters t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring; φ1 is the diameter of the sensor cross-section; d1 and d3 are the straight-line distances between sensor probe I, sensor probe III and one side of the object being measured; d2 and d4 are the straight-line distances between sensor probe II, sensor probe IV and the other side of the object being measured.

[0050] The technical effect of this invention is undeniable. This invention incorporates the influence of the measured material, environmental factors, and installation accuracy on the sensor output value through a four-measuring head differential structure design with known gaps. This allows the sensor to be calibrated only once at the factory and can be directly self-calibrated in subsequent use, thereby improving its measurement accuracy. Attached Figure Description

[0051] Figure 1 Side view of a traditional capacitive sensor;

[0052] Figure 2 This is a front view of a traditional capacitive sensor.

[0053] Figure 3 Design for sensor self-calibration structure;

[0054] Figure 4 Self-calibration of sensor calibration curve;

[0055] Figure 5 This is a schematic diagram of the offset measurement module;

[0056] Figure 6 A schematic diagram of the positioning of a conductive droplet;

[0057] Among them, sensor probe I1, sensor probe II2, sensor probe III3, sensor probe IV4, outermost ring 5, equipotential shielding ring 6, signal ring 7, and insulation gap 8. Detailed Implementation

[0058] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0059] Example 1:

[0060] See Figures 1 to 6 A self-calibrating capacitive displacement sensor includes a sensor probe unit, a signal conversion unit, and a signal processing unit.

[0061] The sensor probe unit includes a first pair of sensor probes and a second pair of sensor probes arranged differentially in the thickness direction.

[0062] The first pair of sensor probes includes sensor probe I1 and sensor probe II2 arranged opposite to each other. Sensor probe I1 faces one side of the object being measured, and sensor probe II2 faces the other side of the object being measured.

[0063] The second pair of sensor probes includes sensor probe III3 and sensor probe IV4 arranged opposite to each other. Sensor probe III3 faces one side of the object being measured, and sensor probe IV4 faces the other side of the object being measured.

[0064] The sensor probes I1, II2, III3, and IV4 respectively monitor capacitance signals I, II, III, and IV, and transmit them to the signal conversion unit.

[0065] The signal conversion unit converts the capacitance signal into a signal to be processed and transmits it to the signal processing unit.

[0066] The signal processing unit determines the gap of the object being measured based on the signal to be processed and the capacitance-gap calibration equation.

[0067] The capacitance-gap calibration equation is as follows:

[0068]

[0069] In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I1, sensor probe II2, sensor probe III3, and sensor probe IV4, respectively. ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air. ε0 is the dielectric constant of vacuum. Parameters

[0070] t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring. φ1 is the cross-sectional diameter of the sensor. d1 and d3 are the straight-line distances between sensor probe I1, sensor probe III3 and one side of the object being measured. d2 and d4 are the straight-line distances between sensor probe II2, sensor probe IV4 and the other side of the object being measured.

[0071] Before each operation of the sensor probe, the signal processing unit acquires the dielectric constant ε associated with the object being measured. a air dielectric constant ε b Then, substitute the capacitance-gap calibration equation into the sensor to perform self-calibration of the calibration equation.

[0072] The sensor probe includes, from the outside to the inside, an outermost ring 5, an equipotential shielding ring 6, and a signal ring 7.

[0073] Among them, there are insulating gaps 8 between the outermost ring 5 and the equipotential shielding ring 6, and between the equipotential shielding ring 6 and the signal ring 7.

[0074] The sensor probe is manufactured using printed circuit board technology.

[0075] The outer diameter of the shielding ring satisfies the formula (φ2-φ1) / 2=3d / 2; where d is the gap between the two capacitor plates; and φ2 is the diameter of the shielding ring.

[0076] The thickness difference between the first pair of sensor probes and the second pair of sensor probes is d0, and 0.5mm ≥ d0 ≥ 0.05mm.

[0077] The signal to be processed is a voltage, frequency, or digital signal carrying a capacitance value.

[0078] The sensor probe adopts a three-layer flexible encapsulation structure, including a PI polyimide insulating layer, a PDMS elastic protective layer, and a nano hydrophobic coating arranged sequentially from the inside out.

[0079] The signal processing unit integrates an environmental compensation module for dynamically correcting dielectric parameters.

[0080] The environmental compensation module includes a digital temperature sensor and a capacitive humidity sensor for collecting environmental temperature and humidity data.

[0081] The sensor also includes an offset measurement module located at the rear of the measuring head;

[0082] The offset measurement module is used to measure the real-time angle of the sensor probe in order to correct the measurement error caused by the probe not being parallel to the measurement plane;

[0083] The offset measurement module includes an electrode pair, a conductive droplet, a sealing cap, and a substrate;

[0084] The sealing cap and the base form a closed cavity;

[0085] The electrode pairs are arranged symmetrically between the substrate and the sealing cap, thus forming a hollow channel between the two electrodes; each electrode channel is connected in series with a fixed resistor.

[0086] Conductive droplets are arranged inside a hollow pipe;

[0087] The offset measurement module determines the resistance of the conductive droplet at its location using electrodes based on the droplet's position within the hollow tube, thus pinpointing the droplet's position x. This allows the module to calculate the tilt angle of the measuring head. g is the acceleration due to gravity, μ is the dynamic viscous drag factor, and x is the position of the conductive droplet.

[0088] The steps for locating a conductive droplet include: measuring the conductivity state through the corresponding pin of each electrode to determine the current position of the droplet.

[0089] A gap measurement method using the self-calibrating capacitive displacement sensor includes the following steps:

[0090] 1) The environmental compensation module collects environmental temperature and humidity data and substitutes it into the temperature and humidity-dielectric constant offset calibration curve to obtain the dielectric constant offset value, thereby correcting ε0 in the capacitance-gap calibration equation in real time.

[0091] 2) Measure the tilt angle θ of the sensor probe using the offset measurement module, and correct the straight-line distance between the sensor probe and one side of the object being measured to obtain the corrected straight-line distance, i.e.:

[0092]

[0093] In the formula, d1 and d3 are the straight-line distances between the corrected sensor probes I and III and one side of the object being measured; d2 and d4 are the straight-line distances between the corrected sensor probes II and IV and the other side of the object being measured; d1' and d3' are the straight-line distances between the original sensor probes I and III and one side of the object being measured; d'2 and d'4 are the straight-line distances between the original sensor probes II and IV and one side of the object being measured.

[0094] 3) Use the first pair of sensor probes and the second pair of sensor probes to monitor capacitance signal I, capacitance signal II, capacitance signal III, and capacitance signal IV;

[0095] 4) Convert the capacitance signal into a signal to be processed, and substitute it into the capacitance-gap calibration equation to determine the gap of the object being measured;

[0096] The capacitance-gap calibration equation is as follows:

[0097]

[0098] In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I, sensor probe II, sensor probe III, and sensor probe IV, respectively; ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air; ε0 is the dielectric constant of vacuum; parameters t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring; φ1 is the diameter of the sensor cross-section; d1 and d3 are the straight-line distances between sensor probe I, sensor probe III and one side of the object being measured; d2 and d4 are the straight-line distances between sensor probe II, sensor probe IV and the other side of the object being measured.

[0099] Example 2:

[0100] A self-calibrating capacitive displacement sensor includes a sensor probe unit, a signal conversion unit, and a signal processing unit.

[0101] The sensor probe unit includes a first pair of sensor probes and a second pair of sensor probes arranged differentially in the thickness direction.

[0102] The first pair of sensor probes includes sensor probe I1 and sensor probe II2 arranged opposite to each other. Sensor probe I1 faces one side of the object being measured, and sensor probe II2 faces the other side of the object being measured.

[0103] The second pair of sensor probes includes sensor probe III3 and sensor probe IV4 arranged opposite to each other. Sensor probe III3 faces one side of the object being measured, and sensor probe IV4 faces the other side of the object being measured.

[0104] The sensor probes I1, II2, III3, and IV4 respectively monitor capacitance signals I, II, III, and IV, and transmit them to the signal conversion unit.

[0105] The signal conversion unit converts the capacitance signal into a signal to be processed and transmits it to the signal processing unit.

[0106] The signal processing unit determines the gap of the object being measured based on the signal to be processed and the capacitance-gap calibration equation.

[0107] The capacitance-gap calibration equation is as follows:

[0108]

[0109] In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I1, sensor probe II2, sensor probe III3, and sensor probe IV4, respectively. ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air. ε0 is the dielectric constant of vacuum. Parameters

[0110] t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring. φ1 is the cross-sectional diameter of the sensor. d1 and d3 are the straight-line distances between sensor probe I1, sensor probe III3 and one side of the object being measured. d2 and d4 are the straight-line distances between sensor probe II2, sensor probe IV4 and the other side of the object being measured.

[0111] Before each operation of the sensor probe, the signal processing unit acquires the dielectric constant ε associated with the object being measured. a air dielectric constant ε b Then, substitute the capacitance-gap calibration equation into the sensor to perform self-calibration of the calibration equation.

[0112] Example 3:

[0113] A self-calibrating capacitive displacement sensor, with the same technical content as Embodiment 2, further comprising, from the outside to the inside, an outermost ring 5, an equipotential shielding ring 6, and a signal ring 7.

[0114] Among them, there are insulating gaps 8 between the outermost ring 5 and the equipotential shielding ring 6, and between the equipotential shielding ring 6 and the signal ring 7.

[0115] Example 4:

[0116] A self-calibrating capacitive displacement sensor, with the same technical content as any one of embodiments 2-3, further wherein the sensor probe is fabricated using printed circuit board technology.

[0117] Example 5:

[0118] A self-calibrating capacitive displacement sensor, with the same technical content as any one of embodiments 2-4, further wherein the outer diameter of the shielding ring satisfies the formula (φ2-φ1) / 2=3d / 2; where d is the gap between the two capacitor plates; and φ2 is the diameter of the shielding ring.

[0119] Example 6:

[0120] A self-calibrating capacitive displacement sensor, with the same technical content as any one of embodiments 2-5, further wherein the thickness difference between the first pair of sensor probes and the second pair of sensor probes is d0, and 0.5mm≥d0≥0.05mm.

[0121] Example 7:

[0122] A self-calibrating capacitive displacement sensor, with the same technical content as any one of embodiments 2-6, further wherein the signal to be processed is a voltage, frequency or digital signal carrying a capacitance value.

[0123] Example 8:

[0124] A self-calibrating capacitive displacement sensor, with the same technical content as any one of embodiments 2-7, further wherein the sensor probe adopts a three-layer flexible encapsulation structure, including a PI polyimide insulating layer, a PDMS elastic protective layer, and a nano hydrophobic coating arranged sequentially from the inside to the outside.

[0125] Specifically, the sensor probe adopts a three-layer flexible encapsulation structure, from the inside out: a 0.1mm thick PI polyimide insulating layer, a 0.05mm thick PDMS elastic protective layer, and an outer layer of nano-hydrophobic coating (such as fluorinated polysiloxane) to achieve a composite encapsulation that is insulating, moisture-proof, and fatigue-resistant.

[0126] Example 9:

[0127] A self-calibrating capacitive displacement sensor, with the same technical content as any one of embodiments 2-8, further comprising an environmental compensation module for dynamically correcting dielectric parameters integrated within the signal processing unit;

[0128] The environmental compensation module includes a digital temperature sensor and a capacitive humidity sensor for collecting environmental temperature and humidity data.

[0129] The environmental compensation module achieves dynamic correction of dielectric parameters through the following steps: 1) Collect ambient temperature and humidity data before startup; 2) Obtain the temperature and humidity-dielectric constant offset calibration curve by looking up a table; 3) Correct εr in the capacitance-gap formula in real time; 4) Calculate the gap value after dynamic compensation.

[0130] Example 10:

[0131] A self-calibrating capacitive displacement sensor, with the same technical content as any one of embodiments 2-9, further includes an offset measurement module located at the rear of the measuring head;

[0132] The offset measurement module is used to measure the real-time angle of the sensor probe in order to correct the measurement error caused by the probe not being parallel to the measurement plane;

[0133] The offset measurement module includes an electrode pair, a conductive droplet, a sealing cap, and a substrate;

[0134] The sealing cap and the base form a closed cavity;

[0135] The electrode pairs are arranged symmetrically between the substrate and the sealing cap, thus forming a hollow channel between the two electrodes; each electrode channel is connected in series with a fixed resistor.

[0136] Conductive droplets are arranged inside a hollow pipe;

[0137] The offset measurement module determines the resistance of the conductive droplet at its location using electrodes based on the droplet's position within the hollow tube, thus pinpointing the droplet's position x. This allows the module to calculate the tilt angle of the measuring head. g is the acceleration due to gravity, μ is the dynamic viscous drag factor, and x is the position of the conductive droplet.

[0138] The steps for locating a conductive droplet include: measuring the conductivity state through the corresponding pin of each electrode to determine the current position of the droplet.

[0139] Specifically, in the sensor structure, each electrode channel is connected in series with a fixed resistor (e.g., R1–R7), and the corresponding pin of each electrode can measure its conductivity state. When a conductive droplet covers an electrode pair, it creates a closed circuit between the electrodes, forming a voltage distribution with a specific resistance value. The system determines the current position of the droplet by reading the voltage or conductivity state on different channels.

[0140] Assuming the length of the conductive droplet covers 1–2 electrode pairs, the center of the droplet can be located by comparing the resistance changes of multiple electrode pairs due to changes in conductivity. Alternatively, it can be designed as a segmented voltage reading; once a channel is conductive, it indicates that the droplet covers that location.

[0141] Calculation of tilt angle:

[0142] Assume the length of the droplet rolling channel is L, the center electrode is at position x = 0, the leftward direction is negative and the rightward direction is positive, the current droplet position is x, and the channel height is h.

[0143] If a droplet rolls to one side due to tilting, its position x and tilt angle θ approximately satisfy the following formula.

[0144]

[0145] Where g is the acceleration due to gravity and μ is the dynamic viscous drag factor, and the droplet velocity is stable, we can obtain:

[0146]

[0147] Example 11:

[0148] A gap measurement method for a self-calibrating capacitive displacement sensor according to any one of embodiments 1-10 includes the following steps:

[0149] 1) The environmental compensation module collects environmental temperature and humidity data and substitutes it into the temperature and humidity-dielectric constant offset calibration curve to obtain the dielectric constant offset value, thereby correcting ε0 in the capacitance-gap calibration equation in real time.

[0150] 2) Measure the tilt angle θ of the sensor probe using the offset measurement module, and correct the straight-line distance between the sensor probe and one side of the object being measured to obtain the corrected straight-line distance, i.e.:

[0151]

[0152] In the formula, d1 and d3 are the straight-line distances between the corrected sensor probe I and sensor probe III and one side of the object being measured; d2 and d4 are the straight-line distances between the corrected sensor probe II and sensor probe IV and the other side of the object being measured; d1' and d3' are the straight-line distances between the original sensor probe I and sensor probe III and one side of the object being measured; d'2 and d'4 are the straight-line distances between the original sensor probe II and sensor probe IV and one side of the object being measured; and L is the length of the conductive droplet rolling channel.

[0153] 3) Use the first pair of sensor probes and the second pair of sensor probes to monitor capacitance signal I, capacitance signal II, capacitance signal III, and capacitance signal IV;

[0154] 4) Convert the capacitance signal into a signal to be processed, and substitute it into the capacitance-gap calibration equation to determine the gap of the object being measured;

[0155] The capacitance-gap calibration equation is as follows:

[0156]

[0157] In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I, sensor probe II, sensor probe III, and sensor probe IV, respectively; ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air; ε0 is the dielectric constant of vacuum; parameters t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring; φ1 is the diameter of the sensor cross-section; d1 and d3 are the straight-line distances between sensor probe I, sensor probe III and one side of the object being measured; d2 and d4 are the straight-line distances between sensor probe II, sensor probe IV and the other side of the object being measured.

[0158] Example 12:

[0159] A self-calibrating capacitive displacement sensor, the details of which are as follows:

[0160] In the process of measuring the gap between the mold and the substrate using a capacitive sensor, the sensor probe has a significant impact on the resolution and accuracy of the entire measurement system. In particular, because the sensor probe needs to penetrate deep into the tiny gap between the skin and the mold, and ideally without affecting the original gap size, an ultra-thin sensor probe design is required. Traditional sensor probe diagrams, as shown in Figures 1 and 2, consist of a signal ring, an equipotential shielding ring, an outermost ring, and the insulating gaps between them. The capacitance of an ideal parallel-plate capacitor can be calculated using a formula, but the edge effect of the capacitor plates is a crucial issue that cannot be ignored in sensor probe design. To consider the impact of the edge effect on the capacitive sensor, it is first necessary to know the capacitance generated by the edge effect. The additional capacitance generated by the capacitor plates can be expressed as:

[0161]

[0162] In the formula, ε0 is the vacuum permittivity; ε rLet be the dielectric constant of the medium between the plates; r be the radius of the capacitor plates; h be the thickness of the capacitor plates; and d be the gap between the two plates. From Equation 2, it is known that the larger the plate radius, the smaller the ratio of the additional capacitance to the ideal capacitance. The edge effect of the capacitive sensor has a significant impact on the output linearity of the sensor. In a sensor system, the sensor probe is its sensitive element, directly affecting the performance of the entire system. Generally, the sensor probe is made circular, and its end face and the measured object form the two plates of a capacitor with a capacitance of C. x Considering the above analysis of edge effects, an equipotential shielding ring of a certain width should be added around the sensor end face. At the same time, considering the measurement requirements in practical applications, an outermost ring connected to the ground should be designed on the outer layer.

[0163] Let the diameter of the sensor end face be r1, the diameter of the shielding ring be r2, the diameter of the outermost ring be r3, the gap width between the outer edge of the sensor end face and the inner edge of the shielding ring be t, the gap width between the outer edge of the shielding ring and the inner edge of the outermost ring be T, and the thickness of the sensor probe be h. An ideal capacitor can be modeled as a Gaussian hollow cylinder in vacuum, with the plane intercepted by the perpendicular intersection of two infinitely large, parallel, opposite-sign, and equal-density charge planes serving as the plates. The capacitance of this ideal capacitor is:

[0164]

[0165] in The output of the operational amplifier amplitude modulation circuit is:

[0166]

[0167] From the model of an ideal capacitor, we know that the gap between the outer edge of the sensor end face and the inner edge of the equipotential shielding ring is equal to the wall thickness of the Gaussian surface. However, in a real sensor, the gap cannot be zero. Since the electric field between the sensor plates is symmetrical, and the sensor probe has a thickness of h and a certain flux, the potential at the gap can be expressed as:

[0168]

[0169] Analysis of the above formula shows that the larger the gap value h / t, the smaller the potential at the midpoint of the gap. When h ≥ 5t, the potential at the midpoint of the gap is close to zero; further increasing h / t will not significantly improve the sensor's performance. A cylindrical capacitor is formed between the probe signal loop and the outer shielding ring. Its capacitance can be obtained through conformal mapping:

[0170]

[0171] From the above formula, we can know the capacitance value C. pThe thickness of the probe is linearly related to the probe thickness h, and h should not be too large. In this project, the probe design uses printed circuit board (PCB) technology, and its thickness depends on the thickness of the pads on the flexible PCB, which is determined by the manufacturing process. Therefore, the size of the gap t needs to be minimized. Adding equipotential shielding rings can effectively suppress the influence of edge effects. When the outer diameter of the shielding ring satisfies the formula (φ2-φ) / 2=3d / 2, the electric field of the sensor signal loop is basically unaffected by edge effects. Therefore, the outer diameter of the shielding ring should be selected according to this formula. Furthermore, to reduce the power dissipation of the shielding ring and ensure the integrity of its end-face electric field lines, the gap T between the outer edge of the shielding ring and the inner edge of the outermost ring should be as large as possible.

[0172] The following are the key innovative aspects of the sensor:

[0173] Because the sensor's output value is affected by material specificity, environmental sensitivity, and installation accuracy dependence during measurement, the sensor needs to be calibrated before each measurement, which significantly impacts the sensor's measurement efficiency. Furthermore, in some measurement scenarios, it is difficult to obtain actual material samples for calibration; therefore, a self-calibration structure design for the sensor is necessary. This paper proposes a self-calibration structure design for the sensor, incorporating thickness-direction differential measurements, such as... Figure 3 As shown. Figure 3 In this configuration, the sensors are attached to two planes, creating a fixed height difference d0 between them.

[0174] Assuming there are two pairs of capacitive sensors at the same location with a thickness difference of d0, the dielectric loss caused by the composite material is normalized to the dielectric constant ε. a In this context, the dielectric constant of air is ε. b Then we can list the following system of equations:

[0175]

[0176] The equations can be used to solve for ε, which is material-related. a ε related to air environment b The environmental and material parameters, along with the current gap values ​​d1 and d2, are input into the sensor output value calculation model to perform self-calibration of the sensor's calibration curve. Figure 4 As shown. The sensor can be fabricated using printed circuit board (PCB) technology, and can be layered according to this design principle in both rigid PCB and flexible PCB systems.

Claims

1. A self-calibrating capacitive displacement sensor, characterized in that, It includes a sensor probe unit, a signal conversion unit, and the signal processing unit; The sensor probe unit includes a first pair of sensor probes and a second pair of sensor probes differentially arranged in the thickness direction; The first pair of sensor probes includes sensor probe I (1) and sensor probe II (2) arranged opposite to each other; sensor probe I (1) faces one side of the object being measured, and sensor probe II (2) faces the other side of the object being measured. The second pair of sensor probes includes sensor probe III (3) and sensor probe IV (4) arranged opposite to each other; sensor probe III (3) faces one side of the object being measured, and sensor probe IV (4) faces the other side of the object being measured. The sensor probe I (1), sensor probe II (2), sensor probe III (3), and sensor probe IV (4) respectively monitor capacitance signal I, capacitance signal II, capacitance signal III, and capacitance signal IV, and transmit them to the signal conversion unit; The signal conversion unit converts the capacitance signal into a signal to be processed and transmits it to the signal processing unit; The signal processing unit determines the gap of the object under test based on the signal to be processed and the capacitance-gap calibration equation. The capacitance-gap calibration equation is as follows: In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I (1), sensor probe II (2), sensor probe III (3), and sensor probe IV (4); ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air; ε0 is the dielectric constant of vacuum; parameters t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring; φ1 is the diameter of the sensor cross section; d1 and d3 are the straight-line distances between sensor probe I (1) and sensor probe III (3) and one side of the object being measured; d2 and d4 are the straight-line distances between sensor probe II (2) and sensor probe IV (4) and the other side of the object being measured. Before each operation of the sensor probe, the signal processing unit acquires the dielectric constant ε associated with the object being measured. a air dielectric constant ε b Then, substitute the capacitance-gap calibration equation into the sensor to perform self-calibration of the calibration equation.

2. The self-calibrating capacitive displacement sensor according to claim 1, characterized in that, The sensor probe includes an outermost ring (5), an equipotential shielding ring (6), and a signal ring (7) arranged sequentially from the outside to the inside; Among them, there are insulating gaps (8) between the outermost ring (5) and the equipotential shielding ring (6), and between the equipotential shielding ring (6) and the signal ring (7).

3. The self-calibrating capacitive displacement sensor according to claim 1, characterized in that, The sensor probe is manufactured using printed circuit board technology.

4. A self-calibrating capacitive displacement sensor according to claim 1, characterized in that, The outer diameter of the shielding ring satisfies the formula (φ2-φ1) / 2=3d / 2; where d is the gap between the two capacitor plates; and φ2 is the diameter of the shielding ring.

5. A self-calibrating capacitive displacement sensor according to claim 1, characterized in that, The thickness difference between the first pair of sensor probes and the second pair of sensor probes is d0, and 0.5mm ≥ d0 ≥ 0.05mm.

6. A self-calibrating capacitive displacement sensor according to claim 1, characterized in that, The signal to be processed is a voltage, frequency, or digital signal carrying a capacitance value.

7. A self-calibrating capacitive displacement sensor according to claim 1, characterized in that, The sensor probe adopts a three-layer flexible encapsulation structure, including a PI polyimide insulating layer, a PDMS elastic protective layer, and a nano hydrophobic coating arranged sequentially from the inside out.

8. A self-calibrating capacitive displacement sensor according to claim 1, characterized in that, The signal processing unit integrates an environmental compensation module for dynamically correcting dielectric parameters. The environmental compensation module includes a digital temperature sensor and a capacitive humidity sensor for collecting environmental temperature and humidity data.

9. A self-calibrating capacitive displacement sensor according to claim 1, characterized in that, It also includes an offset measurement module located at the rear of the measuring head; The offset measurement module is used to measure the real-time angle of the sensor probe in order to correct the measurement error caused by the probe not being parallel to the measurement plane; The offset measurement module includes an electrode pair, a conductive droplet, a sealing cap, and a substrate; The sealing cap and the base form a closed cavity; The electrode pairs are arranged symmetrically between the substrate and the sealing cap, thus forming a hollow channel between the two electrodes; each electrode channel is connected in series with a fixed resistor. Conductive droplets are arranged inside a hollow pipe; The offset measurement module determines the resistance of the conductive droplet at its location using electrodes based on the droplet's position within the hollow tube, thus pinpointing the droplet's position x. This allows the module to calculate the tilt angle of the measuring head. g is the acceleration due to gravity, μ is the dynamic viscous drag factor, and x is the position of the conductive droplet. The steps for locating a conductive droplet include: measuring the conductivity state through the corresponding pin of each electrode to determine the current position of the droplet.

10. A gap measurement method using a self-calibrating capacitive displacement sensor according to any one of claims 1-9, characterized in that, Includes the following steps: 1) The environmental compensation module collects environmental temperature and humidity data and substitutes it into the temperature and humidity-dielectric constant offset calibration curve to obtain the dielectric constant offset value, thereby correcting ε0 in the capacitance-gap calibration equation in real time. 2) Measure the tilt angle θ of the sensor probe using the offset measurement module, and correct the straight-line distance between the sensor probe and one side of the object being measured to obtain the corrected straight-line distance, i.e.: In the formula, d1 and d3 are the straight-line distances between the corrected sensor probe I (1) and sensor probe III (3) and one side of the object being measured; d2 and d4 are the straight-line distances between the corrected sensor probe II (2) and sensor probe IV (4) and the other side of the object being measured; d′1 and d′3 are the straight-line distances between the original sensor probe I (1) and sensor probe III (3) and one side of the object being measured; d′2 and d′4 are the straight-line distances between the original sensor probe II (2) and sensor probe IV (4) and one side of the object being measured; L is the length of the conductive droplet rolling channel. 3) Use the first pair of sensor probes and the second pair of sensor probes to monitor capacitance signal I, capacitance signal II, capacitance signal III, and capacitance signal IV; 4) Convert the capacitance signal into a signal to be processed, and substitute it into the capacitance-gap calibration equation to determine the gap of the object being measured; The capacitance-gap calibration equation is as follows: In the formula, C1, C2, C3, and C4 are the capacitance values ​​monitored by sensor probe I (1), sensor probe II (2), sensor probe III (3), and sensor probe IV (4); ε a ε is the dielectric constant associated with the object being measured. b ε0 is the dielectric constant of air; ε0 is the dielectric constant of vacuum. Parameter t is the gap width between the outer edge of the sensor probe end face and the inner edge of the shielding ring; φ1 is the diameter of the sensor cross section; d1 and d3 are the straight-line distances between sensor probe I (1) and sensor probe III (3) and one side of the object being measured; d2 and d4 are the straight-line distances between sensor probe II (2) and sensor probe IV (4) and the other side of the object being measured.

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