Sensor probe, eddy current sensor and method of measuring thereof

Abstract

The application provides a sensor probe, an eddy current sensor and a measurement method thereof. The sensor probe comprises a columnar framework, a detection coil, a reference coil, a cable and a reference object. The detection coil and the reference coil are arranged in the columnar framework and are led out through the cable. The reference object is arranged on the side of the reference coil away from the detection coil, and a preset distance is provided between the reference object and the reference coil. The detection coil and the reference coil are PCB coils. The detection coil is used to generate an eddy current effect with an external measured object. The reference coil is used to generate an eddy current effect with the reference object. The material of the measured object is the same as that of the reference object. The sensor probe, the eddy current sensor and the measurement method thereof provided by the application solve the problem that the existing eddy current sensor cannot achieve nanometer resolution under a 3mm range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a sensor probe, an eddy current sensor and a measurement method thereof. BACKGROUND

[0002] The eddy current sensor is a sensor based on electromagnetic induction principle, which has the characteristics of good long-term working reliability, high sensitivity, strong anti-interference ability, fast response speed and no influence of oil and water medium, and is widely used in real-time monitoring of shaft displacement, shaft vibration and shaft speed of large-scale rotating machinery in industrial production and scientific research.

[0003] With the continuous development of science and technology, the eddy current sensor gradually catches up with the capacitive displacement sensor in terms of resolution and measurement accuracy, and the eddy current sensor is simpler to install and use, and has lower cost compared with the laser displacement sensor, which makes it the main choice in many complex working conditions.

[0004] However, although the eddy current sensor has reached micron-level resolution in terms of measurement accuracy, it is still a great challenge for those skilled in the art to achieve nanometer-level resolution, especially under 3mm range, due to the existence of temperature drift and nonlinearity problems. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a sensor probe, an eddy current sensor and a measurement method thereof, which can solve the problem that the existing eddy current sensor cannot achieve nanometer-level resolution under 3mm range.

[0006] To achieve the above-mentioned purposes and other related purposes, the present application provides a sensor probe, which comprises a columnar framework, a detection coil, a reference coil, a cable and a reference object.

[0007] The detection coil and the reference coil are arranged in the columnar framework and led out through the cable, and the reference object is arranged on the side of the reference coil away from the detection coil and has a predetermined distance from the reference coil; wherein the detection coil and the reference coil are PCB coils, the detection coil is used to generate eddy current effect with an external measured object, the reference coil is used to generate eddy current effect with the reference object, and the measured object and the reference object are made of the same material.

[0008] Optionally, the sensor probe further comprises a shielding object arranged in the columnar framework and located between the detection coil and the reference coil.

[0009] Optionally, the detection coil and the reference coil have equal coil diameters, and the distance between the detection coil and the reference coil is greater than 5 times the coil diameter.

[0010] Optionally, the reference object is arranged in the columnar framework in a fixed or detachable manner.

[0011] Optionally, the preset distance between the reference object and the reference coil is less than or equal to 0.3 mm.

[0012] Optionally, the columnar framework is made of aluminum metal, and the columnar framework is filled with sealant.

[0013] The application further provides an eddy current sensor, which comprises the sensor probe and the preamplifier as described above, and the sensor probe is connected to the preamplifier through a cable; wherein the preamplifier comprises a signal providing circuit and a signal processing circuit.

[0014] The signal providing circuit is configured to provide a first excitation signal, a second excitation signal, a detection signal and a reference signal, wherein the first excitation signal and the second excitation signal have a phase difference of 90°.

[0015] The signal processing circuit is connected to the signal providing circuit, and is configured to perform quadrature demodulation on a difference signal of the detection signal and the reference signal according to the first excitation signal and the second excitation signal to obtain an output voltage signal.

[0016] Optionally, the signal providing circuit comprises a first signal source module, a second signal source module, a power amplification module, a first resistor and a second resistor.

[0017] The first signal source module is configured to provide the first excitation signal.

[0018] The second signal source module is configured to provide the second excitation signal.

[0019] The power amplification module is connected to the first signal source module, and is configured to perform power amplification on the first excitation signal.

[0020] The first end of the first resistor is connected to the power amplification module, and the second end is connected to the detection coil in the sensor probe and outputs the detection signal.

[0021] The first end of the second resistor is connected to the power amplification module, and the second end is connected to the reference coil in the sensor probe and outputs the reference signal.

[0022] Optionally, the signal processing circuit comprises a differential amplification module, a phase-sensitive detection module and a processor module.

[0023] The differential amplification module is connected with the signal providing circuit, and is used for differentially amplifying the detection signal and the reference signal to obtain the difference signal;

[0024] The phase-sensitive detection module is connected with the signal providing circuit and the differential amplification module, and is used for performing phase-sensitive detection on the difference signal according to the first excitation signal to obtain a real part voltage signal, and performing phase-sensitive detection on the difference signal according to the second excitation signal to obtain an imaginary part voltage signal;

[0025] The processor module is connected with the phase-sensitive detection module, and is used for obtaining the output voltage signal according to the real part voltage signal and the imaginary part voltage signal, and obtaining the displacement of the measured object according to the output voltage signal.

[0026] Optionally, the phase-sensitive detection module comprises a first phase-sensitive detection branch and a second phase-sensitive detection branch, both of which have the same structure and comprise a multiplication unit, an amplification unit and a filtering unit.

[0027] The multiplication unit is connected with the signal providing circuit and the differential amplification module, and is used for performing logical multiplication operation on the difference signal and the first excitation signal or the second excitation signal to obtain a product signal;

[0028] The amplification unit is connected with the multiplication unit, and is used for differentially amplifying the product signal and a direct current modulation signal to obtain a product amplification signal;

[0029] The filtering unit is connected with the amplification unit, and is used for filtering out high-frequency components in the product amplification signal to obtain the real part voltage signal or the imaginary part voltage signal.

[0030] The present application further provides a measurement method of the eddy current sensor, and the measurement method comprises:

[0031] A group of excitation signals with a phase difference of 90° are provided, including a first excitation signal and a second excitation signal;

[0032] The first excitation signal is applied to the detection coil and the reference coil, so that the detection coil and the reference coil generate a detection signal and a reference signal based on the eddy current effect;

[0033] The difference signal of the detection signal and the reference signal is quadrature demodulated according to the first excitation signal and the second excitation signal to obtain an output voltage signal;

[0034] The displacement of the measured object is obtained according to the output voltage signal.

[0035] Optionally, the method for obtaining the output voltage signal comprises: performing phase-sensitive detection on the difference signal according to the first excitation signal and the second excitation signal respectively to obtain a real part voltage signal and an imaginary part voltage signal, and obtaining the output voltage signal according to the formula obtaining the output voltage signal; wherein U is the output voltage signal, Q is the real part voltage signal, and I m is the imaginary part voltage signal.

[0036] Optionally, the output voltage signal and the displacement amount are in a linear relationship, satisfying the formula U=kX+b, wherein U is the output voltage signal, X is the displacement amount, and k and b are characteristic parameters.

[0037] Optionally, the method for determining the values of the characteristic parameters k and b comprises: performing data acquisition on the measured object by the displacement measuring device and the eddy current sensor to obtain a plurality of sets of displacement amounts and corresponding output voltage signals; and determining the values of the characteristic parameters k and b by data fitting on the plurality of sets of displacement amounts and output voltage signals.

[0038] As described above, the sensor probe, the eddy current sensor and the measurement method thereof according to the present application symmetrically design the detection coil and the reference coil on the columnar skeleton, so that the two coils are subjected to almost the same temperature influence, and thus the influence of temperature drift can be eliminated by the difference between the measurement values of the two coils, i.e., the measurement error of the sensor caused by temperature change is eliminated, the measurement precision, i.e., the resolution, of the sensor is improved; at the same time, the non-linear error of the sensor can be eliminated by orthogonal demodulation processing of the detection signal and the reference signal by a set of excitation signals with a 90° phase difference, and the accuracy and reliability of the sensor are improved; the eddy current sensor according to the present application solves the problems of temperature drift and non-linearity, and can achieve a nanometer-level resolution in a 3mm range. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 A structure schematic diagram of the sensor probe in Example 1 is shown.

[0040] Figure 2 A structure schematic diagram of the sensor probe in Example 1 is shown. Figure 1 A structure schematic diagram of the sensor probe in Example 1 is shown.

[0041] Figure 3 A structure schematic diagram of the sensor probe in Example 1 is shown.

[0042] Figure 4 A structure schematic diagram of the sensor probe in Example 1 is shown. Figure 1 or Figure 2 An equivalent circuit diagram of the sensor probe in application is shown.

[0043] Figure 5 A structure schematic diagram of the preamplifier of the eddy current sensor in Example 2 is shown.

[0044] Figure 6 A structure diagram of an experimental platform based on an eddy current sensor is shown.

[0045] Figure 7 A diagram showing the output linearity of the eddy current sensor in the experimental platform is shown.

[0046] Figure 8 A diagram showing the go-repeatability of the eddy current sensor in the experimental platform is shown.

[0047] Figure 9 A diagram showing the return-repeatability of the eddy current sensor in the experimental platform is shown.

[0048] Figure 10 A diagram showing the effective value resolution of the eddy current sensor in the experimental platform is shown.

[0049] Figure 11 A diagram showing the temperature drift of the eddy current sensor in the experimental platform is shown.

[0050] Element number explanation

[0051] 100 sensor probe

[0052] 110 column skeleton

[0053] 111 arc-shaped boss

[0054] 120 detection coil

[0055] 121 first PCB board

[0056] 122 first coil

[0057] 130 reference coil

[0058] 131 second PCB board

[0059] 132 second coil

[0060] 140 cable

[0061] 150 reference object

[0062] 160 shield

[0063] 200 preamplifier

[0064] 210 signal providing circuit

[0065] 211 first signal source module

[0066] 212 second signal source module

[0067] 213 power amplification module

[0068] 220 signal processing circuit

[0069] 221 differential amplification module

[0070] 222 phase sensitive detection module

[0071] 222a first phase sensitive detection branch

[0072] 222b second phase sensitive detection branch

[0073] 2221a first multiplication unit

[0074] 2221b second multiplication unit

[0075] 2222a first amplification unit

[0076] 2222b second amplification unit

[0077] 2223a first filter unit

[0078] 2223b second filter unit

[0079] 223 processor module

[0080] 300 motion stage

[0081] 400 laser interferometer

[0082] 500 target plate DETAILED DESCRIPTION

[0083] The present application is herein described, by way of example only, with the

[0084] Please refer to Figures 1 to 11 . It is to be understood that all the drawings described by this specification are only schematic and the sizes of the components shown in the drawings can not be to scale. The specific embodiments of the present application will be described in detail below with reference to the drawings.

[0085] Embodiment One

[0086] As Figure 1 and Figure 2As shown, this embodiment provides a sensor probe 100, which includes: a column frame 110, a detection coil 120, a reference coil 130, a cable 140, and a reference object 150; further, the sensor probe 100 also includes: a shield 160 and a sealant (not shown in the figure).

[0087] The column frame 110 is a cylindrical frame structure formed by column walls, used to fix the detection coil 120 and the reference coil 130; when the reference object 150 is set in the column frame 110, it is also used to fix the reference object 150; when the sensor probe 100 also includes a shield 160, the column frame 110 is also used to fix the shield 160.

[0088] Specifically, such as Figure 3 As shown, the corresponding inner wall of the column frame 110 is also provided with an arc-shaped boss 111 for fixing corresponding components, such as the detection coil 120 and the reference coil 130; wherein, the number of arc-shaped bosses 111 is greater than or equal to one. In practical applications, the number of arc-shaped bosses 111 is generally greater than or equal to two, and the corresponding components can be fixed to the arc-shaped bosses 111 using adhesive. Of course, an annular boss can also be used to replace the arc-shaped bosses 111, that is, an annular boss can be provided on the corresponding inner wall of the column frame 110, which has no substantial impact on the implementation of the scheme in this embodiment.

[0089] To better achieve the fixing function, the column frame 110 should be made of materials with high mechanical strength, such as non-metallic materials like plexiglass and PPS engineering plastics, or metallic materials like aluminum and copper.

[0090] When the column frame 110 is made of non-metallic material, since non-metallic material does not have shielding function, the detection coil 120 and reference coil 130 are easily affected by external magnetic field interference. Therefore, a shielding layer made of metallic material (not shown in the figure) is usually wrapped on the outer wall of the column frame 110 to reduce external magnetic field interference.

[0091] When using metal materials to construct the column frame 110, since the column frame 110 itself has a shielding function, there is no need to form a shielding layer, making the structure simpler. In this embodiment, the column frame 110 is made of aluminum metal, such as aluminum alloy, which achieves the fixing function while also shielding against external magnetic field interference.

[0092] The detection coil 120 and the reference coil 130 are arranged in the columnar framework 110 and are led out through the cable 140; at least part of the cable 140 is arranged in the columnar framework 110 and is connected to the detection coil 120 and the reference coil 130 respectively to transmit signals. In use, the detection coil 120 is close to an external measured object and interacts to generate an eddy current effect, and the reference coil 130 is close to a reference object 150 and interacts to generate an eddy current effect.

[0093] Specifically, the detection coil 120 is a PCB coil, and a first coil 122 is obtained by etching a metal layer between first PCB plates 121; the first PCB plates 121 are circular plates, the first coil 122 is a ring-shaped planar coil, the first PCB plates 121 are coaxially designed with the first coil 122, and the diameter of the first PCB plates 121 should be greater than the outer diameter of the first coil 122 to avoid eddy current loss of the electromagnetic field of the first coil 122 on the columnar framework 110. In order to minimize the gap between the detection coil 120 and the inner wall of the columnar framework 110, the diameter of the first PCB plates 121 should be equal to the inner diameter of the columnar framework 110, so that the detection coil 120 is coaxial with the columnar framework 110.

[0094] The reference coil 130 is a PCB coil, and a second coil 132 is obtained by etching a metal layer between second PCB plates 131; the second PCB plates 131 are circular plates, the second coil 132 is a ring-shaped planar coil, the second PCB plates 131 are coaxially designed with the second coil 132, and the diameter of the second PCB plates 131 should be greater than the outer diameter of the second coil 132 to avoid eddy current loss of the electromagnetic field of the second coil 132 on the columnar framework 110. In order to minimize the gap between the reference coil 130 and the inner wall of the columnar framework 110, the diameter of the second PCB plates 131 should be equal to the inner diameter of the columnar framework 110, so that the reference coil 130 is coaxial with the columnar framework 110.

[0095] Using a PCB coil as the detection coil 120 and the reference coil 130 can make the detection coil 120 and the reference coil 130 have good stability and consistency, and ordinary winding coils cannot achieve high stability and consistency. Even if two winding coils are in the same environment, the temperature drift may have a large difference in the influence on the two coils, so using a PCB coil effectively reduces the different influence of temperature drift on the two coils. In application, the detection coil 120 and the reference coil 130 are preferably made in the same batch.

[0096] Specifically, the above-mentioned PCB coil uses a copper layer as the metal layer between the plates to block the electromagnetic fields of the two coils and reduce the interaction between the two coils. In addition, the cable 140 electrically connecting the above-mentioned PCB coil and the outside can be a coaxial cable, and the coaxial cable can be routed at the inner ring of the two coils.

[0097] In fact, the number of turns and the diameter of the coil of the detection coil 120 and the reference coil 130 are completely same, so as to reduce the influence of temperature drift by the difference of the two coil measurement values, and improve the measurement accuracy; wherein, the number of turns and the diameter of the coil should be set according to the specific requirements, and the embodiment does not limit this. It should be noted that the diameter of the coil of the detection coil 120 refers to the diameter of the first coil 122, and the diameter of the coil of the reference coil 130 refers to the diameter of the second coil 132.

[0098] The reference object 150 is arranged on the side of the reference coil 130 away from the detection coil 120, and the reference object 150 has a preset distance from the reference coil 130, and the material of the reference object 150 is the same as that of the measured object.

[0099] Specifically, the reference object 150 can be arranged outside the columnar skeleton 110, or arranged in the columnar skeleton 110; when arranged outside the columnar skeleton 110, it can be fixed on one side of the reference coil 130 by any fixing method. As a preferred scheme, the reference object 150 is arranged in the columnar skeleton 110; wherein, the reference object 150 can be arranged in the columnar skeleton 110 by fixed installation or detachable installation, which has no substantial influence on the implementation of the embodiment.

[0100] In fact, for different application scenarios, the material of the measured object may be different, which requires replacing the reference object 150 of the same material, and the detachable installation of the reference object 150 can make the same sensor probe 100 applicable to different application scenarios, and only the reference object 150 needs to be replaced.

[0101] Specifically, the preset distance between the reference object 150 and the reference coil 130 is related to the range of the sensor, and as a preferred scheme, the preset distance between the reference object 150 and the reference coil 130 in the embodiment is between 0-0.3mm (including both end point values 0 and 0.3mm), that is, the preset distance is less than or equal to 0.3mm, so that the eddy current sensor provided by the embodiment can have a range of 0-3mm. It should be noted that for the sensor probe 100, the preset distance between the reference object 150 and the reference coil 130 is a fixed value, which is usually equal to the initial distance between the measured object and the detection coil 120.

[0102] In one embodiment, in order to further reduce the interaction between the detection coil 120 and the reference coil 130, a shield 160 can be added between the two, i.e. the shield 160 is arranged in the columnar skeleton 110 and between the detection coil 120 and the reference coil 130. In this embodiment, the shield 160 is arranged at a middle position between the detection coil 120 and the reference coil 130, i.e. the distance from the shield 160 to the detection coil 120 is equal to the distance from the shield 160 to the reference coil 130.

[0103] In this embodiment, the shield 160 is in a columnar structure, in order to better achieve the shielding effect, the diameter of the columnar structure should be equal to the inner diameter of the columnar skeleton 110, so as to minimize the gap between the shield 160 and the inner wall of the columnar skeleton 110. In addition, the shield 160 is made of metal material, such as aluminum material, and its thickness can be the same as the thickness of the columnar skeleton 110.

[0104] In another embodiment, in order to further reduce the interaction between the detection coil 120 and the reference coil 130, without adding the shield 160, the distance between the detection coil 120 and the reference coil 130 can be set, for example, the distance between the detection coil 120 and the reference coil 130 is greater than 5 times the coil diameter.

[0105] Of course, in other embodiments, the distance between the detection coil 120 and the reference coil 130 can be set to be greater than 5 times the coil diameter while the shield 160 is added between the detection coil 120 and the reference coil 130, so as to minimize the interaction between the detection coil 120 and the reference coil 130.

[0106] The columnar skeleton 110 is also filled with sealant to fill and seal all gaps between the various components arranged in the columnar skeleton 110 by the sealant; wherein the sealant is epoxy resin glue.

[0107] In the prior art, the sensor probe usually only contains a detection coil, and the reference coil is usually arranged in the preamplifier circuit connected to the sensor probe. In this way, the distance between the two coils is relatively far, and the working environment of the two coils is different, which makes the temperature around the two coils also have a large difference. Since temperature has a great influence on the parameters of the coil, when the temperature difference between the two coils is large, it will be difficult to effectively eliminate the influence of temperature drift.

[0108] The sensor probe 100 with double coils according to this embodiment has the detection coil 120 and the reference coil 130 symmetrically arranged on the columnar skeleton 110, and the equivalent circuit is as shown in Figure 4As shown, the detection coil 120 is equivalent to inductance L1 and internal resistance R01, and the reference coil 130 is equivalent to inductance L2 and internal resistance R02. When the two coils are connected to the two sampling resistors in the preamplifier circuit, the corresponding circuit can be regarded as a bridge circuit. The advantage of a bridge circuit is that it can obtain a more accurate electrical signal. However, when a bridge circuit is used in an eddy current sensor, it needs to overcome the influence of different temperatures between the coils. If the two coils have different temperatures, causing different changes in the coils, this will disrupt the balance of the bridge arms in the bridge circuit, and the output electrical signal will produce a larger error.

[0109] In this embodiment, the detection coil 120 and the reference coil 130 are in the same environment, and the use of a PCB coil ensures the consistency of the two coils. The temperature effects on the two coils are almost identical, thus having little impact on the bridge circuit. Therefore, the differential measurement values ​​of the two coils can eliminate the influence of temperature drift, that is, eliminate sensor measurement errors caused by temperature changes, improve the sensor's measurement accuracy, and make it possible to achieve nanometer-level accuracy. Furthermore, using a columnar frame 110 to fix the detection coil 120 and the reference coil 130 can improve the sensor's mechanical strength and stability, protecting the coils and other critical components from external interference.

[0110] Example 2

[0111] like Figure 5 As shown, this embodiment provides an eddy current sensor, which includes a sensor probe 100 and a preamplifier 200, wherein the sensor probe 100 and the preamplifier 200 are connected by a cable 140 (coaxial cable).

[0112] The sensor probe 100 is the probe structure described in Embodiment 1. For a detailed description of the relevant components, please refer to Embodiment 1. It will not be repeated here.

[0113] The preamplifier 200 includes a signal providing circuit 210 and a signal processing circuit 220. In applications, the preamplifier 200 is typically placed in a metal enclosure and encapsulated with sealant (such as epoxy resin) to shield against external interference signals.

[0114] The signal providing circuit 210 is used to provide a first excitation signal, a second excitation signal, a detection signal and a reference signal, wherein the phase difference between the first excitation signal and the second excitation signal is 90°.

[0115] As an example, the signal providing circuit 210 includes: a first signal source module 211, a second signal source module 212, a power amplification module 213, a first resistor R1 and a second resistor R2, wherein the first resistor R1 and the second resistor R2 are sampling resistors.

[0116] The first signal source module 211 is configured to provide a first excitation signal, and the second signal source module 212 is configured to provide a second excitation signal. In an application, the first signal source module 211 and the second signal source module 212 are implemented by using a programmable waveform generator, such as an AD9833 chip.

[0117] In the prior art, a combination of one signal source and a phase shift module is usually used to generate two signals with a phase difference of 90°, but the signals obtained by this method have certain errors and cannot meet the measurement requirements of nanometer precision. In the present application, two AD9833 chips are used to realize double signal output, the amplitude and phase of the output excitation signal are set digitally, the phase difference of the two excitation signals can be accurately set to 90°, the measurement requirements of nanometer precision are met, and in addition, the AD9833 chip has low power consumption, and the temperature change has a great influence on the eddy current sensor, so the low power consumption also has the effect of suppressing temperature drift.

[0118] The power amplification module 213 is connected with the first signal source module 211 and is configured to perform power amplification output on the first excitation signal. The power amplification module 213 is implemented by using a power amplifier, and the input end of the power amplifier is connected with the first excitation signal, so that the first excitation signal is output with large power.

[0119] The first end of the first resistor R1 is connected with the power amplification module 213, and the second end is connected with the detection coil 120 in the sensor probe 100 and outputs a detection signal. The first excitation signal amplified by the power amplification module 213 is applied to the detection coil 120 (equivalent to the inductance L1 and the internal resistance R01 in the figure) through the first resistor R1, so that the detection coil 120 generates a detection signal based on the eddy current effect and outputs the detection signal through the second end of the first resistor R1.

[0120] The first end of the second resistor R2 is connected with the power amplification module 213, and the second end is connected with the reference coil 130 in the sensor probe 100 and outputs a reference signal. The first excitation signal amplified by the power amplification module 213 is applied to the reference coil 130 (equivalent to the inductance L2 and the internal resistance R02 in the figure) through the second resistor R2, so that the reference coil 130 generates a reference signal based on the eddy current effect and outputs the reference signal through the second end of the second resistor R2.

[0121] The signal processing circuit 220 is connected with the signal providing circuit 210 and is configured to perform quadrature demodulation on a difference signal between the detection signal and the reference signal according to the first excitation signal and the second excitation signal to obtain an output voltage signal.

[0122] As an example, the signal processing circuit 220 includes a differential amplification module 221, a phase-sensitive detection module 222, and a processor module 223.

[0123] The differential amplification module 221 is connected with the signal providing circuit 210, and is configured to perform differential amplification on the detection signal and the reference signal to obtain a difference signal. The differential amplification module 221 is implemented by using a differential amplifier, the first input end of the differential amplifier is connected with the detection signal, the second input end is connected with the reference signal, and the output end generates the difference signal.

[0124] The phase-sensitive detection module 222 is connected with the signal providing circuit 210 and the differential amplification module 221, and is configured to perform phase-sensitive detection on the difference signal according to the first excitation signal to obtain a real part voltage signal, and perform phase-sensitive detection on the difference signal according to the second excitation signal to obtain an imaginary part voltage signal.

[0125] Specifically, the phase-sensitive detection module 222 includes: a first phase-sensitive detection branch 222a and a second phase-sensitive detection branch 222b, which have the same structure; the first phase-sensitive detection branch 222a includes: a first multiplication unit 2221a, a first amplification unit 2222a and a first filtering unit 2223a, and the second phase-sensitive detection branch 222b includes: a second multiplication unit 2221b, a second amplification unit 2222b and a second filtering unit 2223b.

[0126] The first multiplication unit 2221a is connected with the signal providing circuit 210 and the differential amplification module 221, and is configured to perform logical multiplication operation on the difference signal and the first excitation signal to obtain a first product signal; the first amplification unit 2222a is connected with the first multiplication unit 2221a, and is configured to perform differential amplification on the first product signal and the direct current modulation signal to obtain a first product amplification signal; and the first filtering unit 2223a is connected with the first amplification unit 2222a, and is configured to filter out high-frequency components in the first product amplification signal to obtain the real part voltage signal.

[0127] The second multiplication unit 2221b is connected with the signal providing circuit 210 and the differential amplification module 221, and is configured to perform logical multiplication operation on the difference signal and the second excitation signal to obtain a second product signal; the second amplification unit 2222b is connected with the second multiplication unit 2221b, and is configured to perform differential amplification on the second product signal and the direct current modulation signal to obtain a second product amplification signal; and the second filtering unit 2223b is connected with the second amplification unit 2222b, and is configured to filter out high-frequency components in the second product amplification signal to obtain the imaginary part voltage signal.

[0128] The first multiplication unit 2221a and the second multiplication unit 2221b are implemented by using a multiplier; the first amplification unit 2222a and the second amplification unit 2222b are implemented by using a differential amplifier, and the direct current component of the output voltage signal is adjusted by introducing the direct current modulation signal; and the first filtering unit 2223a and the second filtering unit 2223b are implemented by using a low-pass filter.

[0129] In the first phase-sensitive detector branch 222a, the first excitation signal is multiplied with the difference signal, and then amplified and low-pass filtered to remove high-frequency components to obtain the real part voltage signal. In the second phase-sensitive detector branch 222b, the second excitation signal, which has a 90° phase difference with the first excitation signal, is multiplied with the difference signal, and then amplified and low-pass filtered to remove high-frequency components to obtain the imaginary part voltage signal. In this way, the difference signal and the first excitation signal can be adjusted to be in the same phase, eliminating nonlinear distortion in the signal, that is, eliminating the nonlinear error of the sensor, improving the accuracy and reliability of the sensor, and making it possible to achieve measurement accuracy at the nanometer level.

[0130] The processor module 223 is connected to the phase-sensitive detector module 222 and is used to obtain the output voltage signal based on the real part voltage signal and the imaginary part voltage signal, and to obtain the displacement of the object under test based on the output voltage signal, thereby realizing the displacement measurement of the object under test.

[0131] Accordingly, this embodiment also provides a measurement method for the eddy current sensor as described above, which includes the following steps.

[0132] Step 1) Provide a set of excitation signals with a 90° phase difference, including a first excitation signal and a second excitation signal.

[0133] Specifically, a first excitation signal and a second excitation signal are provided by two signal source modules (such as a programmable waveform generator), and the two excitation signals can be made to have a precise 90° phase difference by digitally setting the phase.

[0134] Step 2) Apply a first excitation signal to the detection coil 120 and reference coil 130 in the sensor probe 100, so that the detection coil 120 and reference coil 130 generate detection signals and reference signals based on the eddy current effect.

[0135] Specifically, after the first signal source module 211 generates the first excitation signal, it is amplified by the power amplification module 213 and output. Then, it is applied to the detection coil 120 and the reference coil 130 through the first resistor R1 and the second resistor R2, respectively. The detection coil 120 and the reference coil 130 generate detection signals and reference signals respectively based on the eddy current effect.

[0136] Step 3) Perform quadrature demodulation on the difference signal between the detection signal and the reference signal based on the first excitation signal and the second excitation signal to obtain the output voltage signal.

[0137] Specifically, the method for obtaining the output voltage signal includes: performing phase-sensitive detection on the difference signal based on the first excitation signal and the second excitation signal to obtain the real part voltage signal and the imaginary part voltage signal, and then applying the formula... The output voltage signal is obtained; where U is the output voltage signal, Q is the real part of the voltage signal, and I is the real part of the voltage signal.m is a real part voltage signal.

[0138] The real part voltage signal and the imaginary part voltage signal are obtained by the processor module 223 executing the formula to obtain an output voltage signal.

[0139] Step 4) obtaining the displacement of the measured object according to the output voltage signal.

[0140] Specifically, the output voltage signal and the displacement of the measured object are in a linear relationship, satisfying the formula U=kX+b, and the processor module 223 executes the above formula on the output voltage signal to obtain the displacement of the measured object; wherein U is the output voltage signal, X is the displacement, k and b are characteristic parameters (k is the slope and b is the initial voltage).

[0141] More specifically, the method for determining the values of the characteristic parameters k and b includes: collecting data of the measured object by the displacement measuring device and the eddy current sensor as described above to obtain multiple sets of displacement and corresponding output voltage signals; and determining the values of the characteristic parameters k and b by data fitting on the multiple sets of displacement and output voltage signals. The slope k is affected by the material of the measured object and the coil, and in specific applications, the material of the measured object and the coil are determined, so the slope k can be regarded as a constant value; the initial voltage b is the voltage corresponding to the zero displacement, which is affected by the external temperature. The sensor probe structure of the double coil in the embodiment can reduce or even eliminate the influence of temperature change on the linear formula, and improve the linearity.

[0142] The displacement measuring device includes a laser interferometer or a grating ruler; the displacement of the measured object is measured by the displacement measuring device, and the output voltage signal corresponding to the displacement is measured by the eddy current sensor; multiple sets of displacement and output voltage signals can be obtained by continuously moving the measured object. When data fitting is performed on the multiple sets of displacement and output voltage signals, methods such as least squares method can be used.

[0143] Next, based on the eddy current sensor of the embodiment, an experimental platform is built, and the linear relationship between the output voltage signal of the eddy current sensor of the embodiment and the displacement of the measured object is illustrated by displacement measurement experiments.

[0144] A prototype of the eddy current sensor of this embodiment was fabricated, wherein the number of turns of the detection coil 120 and the reference coil 130 is 15, the inner diameter of the coil is 3.124 mm, the outer diameter of the coil is 9.5 mm, and the material of the reference object 150 is titanium alloy TC4.

[0145] An eddy current sensor, a fixed bracket, and a motion table of 300 mm were used to construct the following structure: Figure 6 The experimental platform shown is used for displacement measurement experiments, and the motion distance of the motion stage 300 is corrected by an IDS3010 laser interferometer 400. When setting up the experimental platform, the eddy current sensor is fixed to the external steel frame of the motion stage 300 by a fixed bracket. Then, the target plate (i.e. the object being measured) 500 is installed close to the sensor probe 100 to ensure that the front end of the sensor probe 100 is parallel to the target plate 500. At this time, the eddy current sensor is at the starting position of the range.

[0146] To reduce vibration-induced errors and improve experimental accuracy, the entire experimental platform was placed on an optical platform and the entire experiment was conducted in a cleanroom; the temperature in the cleanroom was 24℃ and the humidity was 50%. During the experiment, the frequency of the first excitation signal and the amplitude of the second excitation signal were 1MHz and 1V respectively.

[0147] Experimental Procedure: After the eddy current sensor output stabilized, the target plate 500 was moved backward 15 steps (3 mm total) by moving the motion stage 300 by 0.2 mm each time. The output voltage signal of the eddy current sensor was recorded after each step of movement, and the linearity was calculated. Experimental results are as follows: Figure 7 As shown, the approximate linear function after fitting is y = 3.0245x + 0.534, where y is the voltage value and x is the displacement value, i.e., U = 3.0245X + 0.534, with a linearity of 0.50523% FSO.

[0148] Repeatability error typically refers to the error caused by the inherent instability of the sensor and other random factors under the same experimental conditions. Experimental verification shows that the outgoing repeatability of the eddy current sensor in this embodiment is as follows: Figure 8 As shown, the repeatability is 0.6692 μm; the retrace repeatability is as follows: Figure 9 As shown, the repeatability is 0.9639 μm.

[0149] The displacement resolution of the sensor was measured at 11 points from 0 to 3 mm, with a step size of 0.3 mm. The measurement method for each point was repeated as for the first point. The effective value resolution (RMS) was calculated based on the peak value of the recorded output noise. The RMS resolution is numerically equal to 1 / 6.6 of the peak resolution. Figure 10 As can be seen, the minimum resolution is 11.95nm and the maximum resolution is 94.17nm.

[0150] Figure 11 For at 0.3mm, the temperature is increased by 10℃, 20℃, 22℃, 24℃, 26℃, 28℃, 30℃, 40℃, 50℃ in turn within one hour, the change trend of the analog quantity with the temperature is observed, and the temperature drift of the sensor is calculated according to the method. The temperature drift of the sensor is less than ±0.035%FSO / ℃.

[0151] It can be seen that the eddy current sensor of the embodiment utilizes the symmetric design of the double coils to make the temperature of the double coils balanced and weaken the influence of the temperature on the coils as much as possible; the signals collected by the double coils are subjected to orthogonal demodulation processing, and the nonlinearity problem of the sensor is solved. Through the analysis of the performance of the sensor, the range is 3mm, the resolution is less than 100nm, the linearity is 0.50523%FSO, the repeatability is less than 1μm, and the temperature drift is less than ±0.035%FSO / ℃. In the embodiment, the linear function approximation of the output voltage signal of the eddy current sensor and the displacement of the displacement is y=3.0245x+0.534, wherein y is the voltage value, and x is the displacement value, that is, U=3.0245X+0.534. After the linear function relationship is obtained, the displacement of the detected object at any position can be calculated through the value of the output voltage signal of the eddy current sensor.

[0152] It should be noted that the verification result of the embodiment is only to illustrate that there is a linear relationship between the voltage output signal of the eddy current sensor of the embodiment and the displacement of the detected object. In other embodiments, the characteristic parameters k and b in the linear relationship U=kX+b can also be other values, and the specific values depend on the material of the detected object, the size of the coil, the number of turns of the coil, the environmental temperature and the like. The verification process is basically the same, and therefore will not be illustrated one by one.

[0153] In summary, the sensor probe, the eddy current sensor and the measurement method of the embodiment can symmetrically design the detection coil and the reference coil on the column skeleton, so that the two coils are subjected to almost the same temperature influence. Thus, the difference between the measurement values of the two coils can eliminate the influence of the temperature drift, that is, eliminate the measurement error of the sensor caused by the temperature change, and improve the measurement accuracy of the sensor, that is, the resolution. At the same time, the detection signal and the reference signal are subjected to orthogonal demodulation processing by a group of excitation signals with a phase difference of 90°, which can eliminate the nonlinearity error of the sensor and improve the accuracy and reliability of the sensor. The eddy current sensor of the embodiment solves the problems of temperature drift and nonlinearity, and can reach the nanometer level resolution under the range of 3mm. Therefore, the embodiment effectively overcomes the shortcomings in the prior art and has high industrial utilization value.

[0154] The above embodiments are only illustrative of the principles of the present application and its efficacy, and are not intended to limit the present application. Any modification or change made by any person skilled in the art without departing from the spirit and scope of the present application shall be covered by the claims of the present application.

Claims

1. An eddy current sensor, characterized by, The eddy current sensor comprises a sensor probe and a preamplifier, the sensor probe is connected with the preamplifier through a cable; The sensor probe comprises a column skeleton, a detection coil, a reference coil, a cable and a reference object; the detection coil and the reference coil are arranged in the column skeleton and are led out through the cable, the reference object is arranged on the side of the reference coil away from the detection coil and has a preset distance with the reference coil; wherein the detection coil and the reference coil adopt PCB coils, the detection coil is used to generate eddy current effect with an external measured object, the reference coil is used to generate eddy current effect with the reference object, and the measured object and the reference object are made of the same material; The preamplifier comprises a signal providing circuit and a signal processing circuit; the signal providing circuit is used to provide a first excitation signal, a second excitation signal, a detection signal and a reference signal, wherein the signal providing circuit provides the first excitation signal and the second excitation signal through two signal source modules respectively and makes the phase difference of the two signals 90° through digital phase setting; the signal processing circuit is connected with the signal providing circuit and is used to obtain an output voltage signal through quadrature demodulation of the difference signal of the detection signal and the reference signal according to the first excitation signal and the second excitation signal; The signal providing circuit comprises a first signal source module, a second signal source module, a power amplification module, a first resistor and a second resistor; the first signal source module is used to provide the first excitation signal; the second signal source module is used to provide the second excitation signal; the power amplification module is connected with the first signal source module and is used to perform power amplification output on the first excitation signal; the first end of the first resistor is connected with the power amplification module, the second end is connected with the detection coil in the sensor probe and outputs the detection signal; the first end of the second resistor is connected with the power amplification module, the second end is connected with the reference coil in the sensor probe and outputs the reference signal; The signal processing circuit comprises a differential amplification module, a phase-sensitive detection module and a processor module; the differential amplification module is connected with the signal providing circuit and is used to perform differential amplification on the detection signal and the reference signal to obtain the difference signal; the phase-sensitive detection module is connected with the signal providing circuit and the differential amplification module and is used to obtain a real part voltage signal through phase-sensitive detection of the difference signal according to the first excitation signal and obtain an imaginary part voltage signal through phase-sensitive detection of the difference signal according to the second excitation signal; the processor module is connected with the phase-sensitive detection module and is used to obtain the output voltage signal according to the real part voltage signal and the imaginary part voltage signal and obtain the displacement of the measured object according to the output voltage signal. The phase-sensitive detection module comprises a first phase-sensitive detection branch and a second phase-sensitive detection branch, both of which have the same structure and comprise a multiplication unit, an amplification unit and a filtering unit; the multiplication unit is connected with the signal providing circuit and the differential amplification module, and is used for performing logical multiplication operation on the difference signal and the first excitation signal or the second excitation signal to obtain a product signal; the amplification unit is connected with the multiplication unit, and is used for performing differential amplification on the product signal and a direct current modulation signal to obtain a product amplification signal; and the filtering unit is connected with the amplification unit, and is used for filtering out high-frequency components in the product amplification signal to obtain the real part voltage signal or the imaginary part voltage signal.

2. The eddy current sensor of claim 1, wherein, The sensor probe further comprises a shield arranged in the columnar framework and located between the detection coil and the reference coil.

3. The eddy current sensor according to claim 1 or 2, characterized in that The detection coil and the reference coil have equal coil diameters, and the distance between the detection coil and the reference coil is greater than 5 times the coil diameter.

4. The eddy current sensor of claim 1, wherein, The reference object is arranged in the columnar framework in a fixed mounting manner or a detachable mounting manner.

5. The eddy current sensor according to claim 1 or 4, characterized in that The preset distance between the reference object and the reference coil is less than or equal to 0.3 mm.

6. The eddy current sensor of claim 1, wherein, The columnar framework is made of aluminum metal, and the columnar framework is further filled with sealant.

7. A method of measuring an eddy current sensor as claimed in any one of the claims 1-6, characterized in that, The measurement method comprises: providing a set of excitation signals with a phase difference of 90°, including a first excitation signal and a second excitation signal; applying the first excitation signal to the detection coil and the reference coil, so that the detection coil and the reference coil generate detection signals and reference signals based on the eddy current effect; performing quadrature demodulation on a difference signal of the detection signal and the reference signal according to the first excitation signal and the second excitation signal to obtain an output voltage signal; obtaining the displacement amount of the measured object according to the output voltage signal.

8. The measurement method of an eddy current sensor according to claim 7, characterized in that, The method for obtaining the output voltage signal comprises: performing phase-sensitive detection on the difference signal according to the first excitation signal and the second excitation signal respectively to obtain a real part voltage signal and an imaginary part voltage signal, and obtaining the output voltage signal according to the formula wherein U is the output voltage signal, Q is the real part voltage signal, and I m is the imaginary part voltage signal.

9. The measurement method of an eddy current sensor according to claim 7, characterized by, The output voltage signal and the displacement amount are in linear relationship, satisfying the formula wherein U is the output voltage signal, X is the displacement amount, and k and b are characteristic parameters.

10. The measurement method of an eddy current sensor according to claim 9, wherein, The method for determining the values of the characteristic parameters k and b comprises: collecting data of the measured object by the displacement measuring device and the eddy current sensor to obtain a plurality of sets of displacement amounts and corresponding output voltage signals; and determining the values of the characteristic parameters k and b by data fitting on the plurality of sets of displacement amounts and output voltage signals.

Images