A non-contact three-dimensional displacement sensor

Abstract

The present invention discloses a non-contact three-dimensional displacement sensor, comprising a mechanical probe and a detection circuit. The mechanical probe part comprises a differential fixed block and an end cross beam. A first differential coil and a second differential coil are fixedly arranged on two parallel inner side surfaces of the differential fixed block respectively. A first target conductor located directly below the first differential coil is fixedly arranged on the top surface of the suspended end of the cross beam, and a second target conductor located directly above the second differential coil is fixedly arranged on the bottom surface. A pair of receiving coils are fixedly arranged on the top surface of the first target conductor or / and on the bottom surface of the second target conductor along the horizontal x direction. L x A pair of receiving coils are fixedly arranged along the horizontal y direction L y The two pairs of receiving coils form a "well" structure. The non-contact three-dimensional displacement sensor of the present invention has better quasi-static resolution and displacement sensitivity in three directions, realizes all-directional decoupling, and has excellent performance in linearity, range and other indicators.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, in particular to a non-contact three-dimensional displacement sensor based on a differential eddy current displacement sensor and an inductive displacement sensor. Background Art

[0002] With the development of industrial automation and intelligent manufacturing, the demand for precision displacement measurement technology is growing. As a key component in the automation system, the performance of the displacement sensor directly affects the position control accuracy and stability of the entire system.

[0003] Non-contact displacement measurement is a very important direction in the development of displacement measurement technology. Compared with contact displacement sensors, non-contact displacement sensors have been increasingly widely used because they have no direct mechanical coupling with the target to be measured, small load effect, no wear during the measurement process, long life, and high reliability. Especially for the measurement of high-speed motion, non-contact displacement sensors are the only choice. Among many non-contact displacement sensors, inductive sensors measure the displacement between coils based on the electromagnetic induction effect between coils. Compared with capacitive displacement sensors and eddy current displacement sensors, inductive sensors can detect the displacement of coils by measuring the mutual inductance between coils. They have the characteristics of high resolution, large measurement range, and simple structure. At the same time, since the mutual inductance of the coils is almost insensitive to factors such as environmental humidity, it can maintain good stability even in harsh environments.

[0004] Three-dimensional non-contact measurement is widely used in many occasions. For example, the displacement feedback of the x, y, and z degrees of freedom translation stage requires displacement measurement in three directions. Traditional three-dimensional displacement sensors are mostly simple superpositions of the same type of probes, such as eddy current displacement sensors in all three directions. The disadvantage is that the ranges in all three directions are small; if a laser interferometer is selected, the cost will be high; if a laser displacement sensor is selected, its resolution is low; if a strain gauge displacement sensor is selected, it is a contact measurement with low resolution. Summary of the invention

[0005] In view of the above-mentioned defects and shortcomings, the present invention aims to provide a non-contact three-dimensional displacement sensor, which is based on a differential eddy current displacement sensor (Eddy Current Sensor, hereinafter referred to as ECS) and an inductive displacement sensor (Inductive Displacement Senso, hereinafter referred to as IDS), organically integrating the structures of the two sensors into one, simplifying the structure of the entire three-dimensional displacement sensor, reducing production and use costs, and being able to simultaneously perform non-contact measurement of displacements in three coordinate directions. It naturally has a high bandwidth, and has extremely low nonlinearity and excellent resolution in each direction within the range.

[0006] In order to solve the above technical problems, a technical solution adopted by the present invention is:

[0007] A non-contact three-dimensional displacement sensor, comprising a mechanical probe and a detection circuit, wherein the mechanical probe portion comprises a differential fixed block of a "U"-shaped structure and a crossbeam whose end is suspended inside the differential fixed block, a first differential coil and a second differential coil are fixedly arranged on two parallel inner side surfaces of the differential fixed block, a first target conductor located directly below the first differential coil is fixedly arranged on the top surface of the suspended end of the crossbeam, and a second target conductor located directly above the second differential coil is fixedly arranged on the bottom surface;

[0008] A pair of receiving coils are fixedly arranged on the top surface of the first target conductor and / or on the bottom surface of the second target conductor along the horizontal x direction. L x A pair of receiving coils are fixedly arranged along the horizontal y direction L y , the two receiving coils of each pair are arranged in parallel, and the two pairs of receiving coils are arranged vertically to form a "well" structure;

[0009] When the first differential coil and the second differential coil are input with an excitation signal, when the differential fixed block and the cross beam undergo relative displacement, the signal output difference between the two input ends of the first differential coil and the second differential coil is demodulated by the measurement circuit and output as Uz, which is used to characterize the relative displacement between the cross beam and the differential fixed block in the z direction, and the z direction is perpendicular to the two parallel inner side surfaces of the differential fixed block;

[0010] The signal difference at the output ends of the two receiving coils of each pair is demodulated by the measurement circuit and output as Ux and Uy, which are used to characterize the relative displacement in the x-direction and y-direction between the beam and the differential fixed block, respectively. The planes in the x-direction and y-direction are parallel to the two parallel inner sides of the differential fixed block.

[0011] Furthermore, the first differential coil and the second differential coil have the same structure, and both are double-layer structures that are stacked and connected in series end to end.

[0012] Further, the detection circuit includes an excitation power supply, a differential amplifier, an x-direction instrumentation amplifier, a y-direction instrumentation amplifier, a z-direction phase-sensitive detector, an x-direction phase-sensitive detector and a y-direction phase-sensitive detector, one end of the first differential coil and the second differential coil are commonly grounded, and the other ends are respectively connected in series with matching resistors Rs, the other ends of the two matching resistors Rs are commonly connected to the output end of the excitation power supply, the two connection points of the two differential coils and the two matching resistors Rs are respectively connected to the two signal input ends of the differential amplifier, the output end of the differential amplifier and the output end of the excitation power supply are respectively connected to the two input ends of the z-direction phase-sensitive detector, and the z-direction phase-sensitive detector outputs Uz;

[0013] Two receiving coils Lx / Two receiving coils L y One end of the two phase-sensitive detectors is grounded, and the other end is connected to the two input ends of the x-direction instrumentation amplifier / y-direction instrumentation amplifier respectively. The output end of the x-direction instrumentation amplifier / y-direction instrumentation amplifier and the output end of the excitation power supply are connected to the two input ends of the x-direction phase-sensitive detector / y-direction phase-sensitive detector. The x-direction phase-sensitive detector / y-direction phase-sensitive detector outputs Ux / Uy.

[0014] Furthermore, the output ends of the z-direction phase-sensitive detector, the x-direction phase-sensitive detector and the y-direction phase-sensitive detector are all connected to a low-pass filter.

[0015] Furthermore, within the z-direction detection range, the resistance change of the first differential coil and the second differential coil is ΔR, and the inductance change is ΔL, but the change directions are opposite, so that the differential output U of the two differential coils of the AC bridge is diff for:

[0016]

[0017] The expression of the bridge output signal after demodulation by the differential amplifier and the z-direction phase-sensitive detector is:

[0018]

[0019] in,

[0020]

[0021] E is the excitation voltage The amplitude of the excitation voltage is ω, K 1 is the signal gain of the differential amplifier, K 2 is the signal gain of the z-direction phase-sensitive detector, Rs is the matching resistance value, R is the equivalent resistance of the first differential coil and the second differential coil, and L is the equivalent inductance of the first differential coil and the second differential coil.

[0022] Furthermore, a pair of receiving coils in the x direction L x and a pair of receiving coils in the y direction L y The mutual inductance with the first differential coil or the second differential coil is M x and M y When the first differential coil and the second differential coil are connected with a frequency of ω , the amplitude is I When the excitation current is L x and a pair of receiving coilsL y The induced voltage amplitude at both ends V x and V y They are:

[0023]

[0024] V x and V y The expression after demodulation by the corresponding instrument amplifier and the corresponding phase-sensitive detector is:

[0025]

[0026] in, K 3 is the signal gain of the instrumentation amplifier, K 4 is the signal gain of the phase sensitive detector.

[0027] Furthermore, the first target conductor and the second target conductor are both made of metal plates, preferably aluminum plates.

[0028] Further, in the initial state, the z-direction distance between the first differential coil and the first target conductor is equal to the z-direction distance between the second differential coil and the second target conductor, and the two receiving coils L x The y-distance between the two receiving coils L y The x-direction distances between the two pairs of receiving coils are equal, and the intersection point of the center lines of the two pairs of receiving coils is located on the line connecting the centers of the first differential coil and the second differential coil.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The present invention organically integrates an eddy current displacement sensor (ECS) and an inductive displacement sensor (IDS), that is, the eddy current coil of the eddy current displacement sensor is used as the excitation coil of the inductive displacement sensor, and the metal targets required by the two sensor probes are also combined into one, thereby simplifying the structure of the entire three-dimensional displacement sensor, thereby reducing the production and use costs;

[0031] 2. The non-contact three-dimensional displacement sensor of the present invention can simultaneously measure the displacement in three coordinate directions in a non-contact manner. The range in the x and y directions reaches 3mm, the nonlinearity of the full range is as low as ±0.3%, and the quasi-static resolution in the bandwidth of 0.1~10Hz reaches 9nm; the range in the z direction is 200μm, the quasi-static resolution is 0.3nm, and the nonlinearity is as low as ±0.028%. Generally, it is not necessary to digitally linearize the sensor output, and it naturally has a high bandwidth. The sensor has extremely low nonlinearity and excellent resolution in the range of 200μm in the z direction, as well as a large range of up to 3mm in the x and y directions and nanometer-level resolution. It has good performance and thus has a wide range of applications.

[0032] 3. The present invention directly connects the instrument amplifier at the output position of the induction receiving coil and utilizes the high input impedance of the instrument amplifier to make the current in the induction coil almost zero. There is no current inside the induction coil and the magnetic field will not be excited, thereby not affecting the signal of the eddy current coil itself and the performance of the eddy current probe, thereby achieving decoupling of the z direction from the x and y directions, and correcting the displacement sensitivity of the induction coil in the x and y directions by the value in the z direction measured by the eddy current probe, thereby achieving the final decoupling of the x, y and z directions and ensuring the stability of the measurement performance in each direction and the accuracy of the precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the overall structure of the non-contact three-dimensional displacement sensor of the present invention;

[0034] Figure 2 It is a schematic diagram of the exploded structure of the non-contact three-dimensional displacement sensor of the present invention;

[0035] Figure 3 It is a simplified structural schematic diagram of the non-contact three-dimensional displacement sensor of the present invention in a side view;

[0036] Figure 4 Model the structure and size diagram of the simulation model;

[0037] Figure 5 It is a schematic diagram of a top view of the structure in which the receiving coil of the present invention is arranged on the first target conductor;

[0038] Figure 6 The magnetic flux density simulation results obtained by the simulation model, where Figure 6 (a) is a schematic diagram of magnetic flux density distribution. Figure 6 (b) is a schematic diagram of the distribution of magnetic flux density contours in the z direction;

[0039] Figure 7The inductance variation and nonlinear simulation results of the single-ended ECS probe coil and the differential ECS coil within a range of 200 μm at a distance of 0.6 mm from the surface of the target conductor, where: Figure 7 (a) is the simulation result of inductance change. Figure 7 (b) is the nonlinear simulation result;

[0040] Figure 8 The figure is a schematic diagram showing the influence of the number of turns of the receiving coil on sensitivity and nonlinearity under different ranges, where: Figure 8 (a) is the result corresponding to the measuring range of ±1mm, Figure 8 (b) is the result corresponding to the measuring range of ±1.5 mm. Figure 8 (c) is the result corresponding to the measuring range of ±2mm;

[0041] Fig. 9 This is a schematic diagram showing the influence of different ranges of the receiving coil on the performance trend, where: Fig. 9 (a) is a schematic diagram of the maximum sensitivity trend change. Fig. 9 (b) is the number of turns corresponding to the maximum sensitivity, Fig. 9 (c) is a schematic diagram of the minimum nonlinear trend change. Fig. 9 (d) is the number of turns corresponding to the minimum nonlinearity;

[0042] Fig.10 is the magnetic flux distribution curve in the rectangular frame of the receiving coil at different offsets, where: Fig.10 (a) is the length of the long side l= The corresponding results for 22mm are: Fig.10 (b) is the length of the long side l= The corresponding results for 56mm;

[0043] Fig.11 for y Direction offset to receiving coil x Schematic diagram of the influence trend of directional displacement sensitivity;

[0044] Fig.12 The measurement circuit schematic diagram of the ECS in the present invention;

[0045] Fig.13 It is the principle diagram of the measurement circuit of IDS in the present invention;

[0046] Fig.14 This is a schematic diagram of the phase-sensitive detection circuit structure based on MC1496;

[0047] Fig.15 Schematic diagram of the equivalent model of the sensing process of the three-dimensional sensor;

[0048] Fig.16 The displacement sensitivity simulation results of the IDS receiving coil at different distances z;

[0049] Fig.17 It is a schematic diagram of the structure of the experimental device used for ECS sensitivity measurement;

[0050] Fig.18 The sensitivity test results of the three-dimensional displacement sensor in the z direction;

[0051] Fig.19 is the output displacement noise result of the three-dimensional displacement sensor in the z direction, where: Fig.19 (a) is the output displacement noise result at a sampling rate of 600Hz. Fig.19 (b) is the output displacement noise result at a sampling rate of 10Hz;

[0052] Fig. 20 It is a schematic diagram of the experimental device structure used for IDS performance testing;

[0053] Fig.21 The corresponding displacements in different directions obtained from the experiment y The output of the direction coil, where Fig.21 (a) is the output result when the displacement is in the y direction. Fig.21 (b) is the output result when the displacement is in the x direction;

[0054] Fig. 22 The sensitivity test results of receiving coils with different numbers of turns are shown in Figure 2. Fig. 22 (a) is the test result when the number of turns is 15. Fig. 22 (b) is the test result when the number of turns is 20;

[0055] Fig.23 This is the experimental test result of IDS output displacement noise, where: Fig.23 (a) is the test result at 600Hz sampling rate. Fig.23 (b) is the test result at a sampling rate of 10 Hz.

[0056] In the figure: 1. differential fixed block; 2. crossbeam; 3. first differential coil; 4. second differential coil; 5. first target conductor; 6. second target conductor; 11. first base; 12. first cantilever beam; 13. second cantilever beam; 14. turntable around z-axis; 15. xy-direction translation stage; 16. turntable around x-axis; 17. z-direction translation stage; 21. piezoelectric translation stage; 22. air floating platform; 23. fixed pressure block; 24. test fixture; 25. second base. DETAILED DESCRIPTION

[0057] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0058] It should be noted that when a component is referred to as being "mounted on" another component, it may be directly on the other component or there may be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may be a central component at the same time. When a component is considered to be "fixed to" another component, it may be directly fixed on the other component or there may be a central component at the same time.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0060] The present invention provides a non-contact three-dimensional displacement sensor, including a mechanical probe and a detection circuit, such as Figures 1 to 3 As shown, the mechanical probe part includes a differential fixed block 1 of a "U"-shaped structure and a crossbeam 2 whose end is suspended inside the differential fixed block 1. In actual application, the differential fixed block 1 and the crossbeam 2 are respectively fixedly connected to the two ends of the relative motion of the position to be detected, or directly replaced by the two ends of the relative motion.

[0061] The first differential coil 3 and the second differential coil 4 are fixedly arranged on the two parallel inner side surfaces of the differential fixing block 1, and the first target conductor 5 located directly below the first differential coil 3 is fixedly arranged on the top surface of the suspension end of the crossbeam 2, and the second target conductor 6 located directly above the second differential coil 4 is fixedly arranged on the bottom surface. Specifically, grooves are respectively provided on the two parallel inner side surfaces of the differential fixing block 1, and the first differential coil 3 and the second differential coil 4 have the same structure and are symmetrically fixed and bonded to the bottom surfaces of the two grooves, and the center line of the two differential coils is perpendicular to the two parallel inner side surfaces of the differential fixing block 1. A wiring groove is provided on one side of the groove and the side surface of the differential fixing block 5 for laying the connection lines of the two differential coils. The first differential coil 3 and the second differential coil 4 are both double-layer structures that are superimposed and connected in series end to end, that is, two identical coils are connected in series as a whole to increase the displacement sensitivity of the coil. In this embodiment, the inner and outer radii of the ECS probe coil (the first differential coil 3 and the second differential coil 4, i.e., the eddy current coil) are 2.15 mm and 9.85 mm, respectively. The first target conductor 5 and the second target conductor 6 have the same structure, and are both rectangular metal plates, preferably pure aluminum plates in this embodiment, with a side length of 60 mm and a thickness of 0.1 mm. The first target conductor 5 and the second target conductor 6 are symmetrically fixed and bonded to the upper and lower surfaces of the beam 2, respectively, and are parallel to the two parallel inner side surfaces of the differential fixing block 1.

[0062] like Figure 5 As shown, a pair of receiving coils are fixedly arranged on the top surface of the first target conductor 5 along the horizontal x direction. L x A pair of receiving coils are fixedly arranged along the horizontal y direction L y , the two receiving coils of each pair are arranged in parallel, and the two pairs of receiving coils are arranged vertically to form a "well" structure. In this embodiment, the innermost coil long side of a single receiving coil is 38mm in length, the innermost width is 0.8mm, the number of turns is 20, and the line width and line spacing are both 75μm. The structures of the four receiving coils are exactly the same. In the initial state, the z-direction distance between the first differential coil 3 and the first target conductor 5 and the z-direction distance between the second differential coil 4 and the second target conductor 6 are equal, which is set to 0.6mm in this embodiment; the two receiving coils L x The y-distance between the two receiving coils L y The x-direction distance between the two pairs of receiving coils is equal, which is set to 5.54 mm in this embodiment; and the intersection of the center lines of the two pairs of receiving coils is located on the line connecting the centers of the first differential coil 3 and the second differential coil 4. L x The symmetry line is the x-axis, and the two receiving coils L yThe symmetry line of the circuit is the y-axis, the line connecting the centers of the two differential coils is the z-axis, and the intersection of the three axes is the origin to establish a spatial coordinate system.

[0063] According to Figure 1 and Figure 2 The structure shown in the figure is modeled and simulated using a two-dimensional axisymmetric model in COMSOL Multiphysics 6.2 software. The two-dimensional axisymmetric simulation can greatly reduce the amount of calculation and the accuracy is almost unaffected. Figure 4 As shown, according to the actual situation, the differential coil is a double-layer structure, and its inner and outer diameters are 2.15mm and 9.85mm respectively.

[0064] The software simulates and calculates the distribution of relevant parameters such as the magnetic flux density in the radial direction of the target conductor surface, such as Figure 6 The magnetic flux density is greatest in the region between the differential coil and the target conductor, but is Figure 6 From the direction of the contour lines in part (a), we can see that the main magnetic flux is concentrated in the r direction. We are more concerned about the magnetic flux in the z direction. Figure 6 Part (b) shows the magnetic flux density in the z direction. It can be seen that the magnetic flux density in this direction is much smaller than that in the r direction.

[0065] The ECS range can generally maintain good linearity at the sub-millimeter level. Figure 7 The inductance variation and nonlinearity of a single-ended ECS probe coil (i.e., only one eddy current coil and one target conductor) and a differential ECS coil (with two eddy current coils) are simulated within a range of 200μm at a distance of 0.6mm from the surface of the target conductor.

[0066] Figure 7 (a) in the figure shows that the output sensitivity of the differential coil is 17.66μH / mm, which is twice the sensitivity of the single-ended coil (8.83μH / mm). Figure 7 (b) in the figure shows that the nonlinearity of the differential coil is ±0.01%, which is much smaller than the nonlinearity of the single-ended coil of ±0.95%. Therefore, the use of differential form in ECS has ensured higher sensitivity and excellent nonlinearity. Figures 1 to 3 The ECS probe in the device can realize displacement measurement in the z direction.

[0067] Calculate and analyze the effect of the number of turns of the receiving coil on the sensitivity and nonlinearity of the inductive displacement sensor (IDS). Figure 8 Parts (a), (b), and (c) in the figure respectively show the effect of the number of turns on sensitivity and nonlinearity when the range is ±1mm, ±1.5mm, and ±2mm. The coil wire diameter and wire spacing are both set to 3mil (75μm). In the figure, the sensitivity of the coils with different numbers of turns shown on the left y-axis is relative to the sensitivity of a single inner coil.

[0068] As can be seen from the figure, the larger the range, the smaller the number of turns that can be wound. This is because no matter how the x and y directions move, the long side of the receiving coil cannot cross the symmetrical center line parallel to it. Therefore, if you want a large range, the number of coil turns cannot be too many. The number of turns and the range are contradictory. And the more turns, the greater the sensitivity, which is obvious. Therefore, a large range and high sensitivity are contradictory and cannot be achieved at the same time. From the perspective of nonlinear optimization, no matter what the range is set to, there is an optimal number of turns that minimizes nonlinearity. For example, Figure 8 As shown in part (b), when the measuring range is ±1.5 mm and the number of turns is 20, the nonlinearity can be as small as ±0.11%. At this time, the sensitivity is 107 times that of the innermost coil.

[0069] Taking sensitivity, nonlinearity and range as optimization directions, the maximum sensitivity and minimum nonlinearity that can be obtained by the induction coil under different ranges and the corresponding number of turns for these two situations are calculated, such as Fig. 9 As shown in the figure. It can be seen from the figure that the larger the range, the smaller the maximum sensitivity. This is because a large range means fewer turns, and the mutual inductance between the receiving coil and the eddy current coil is small. The larger the range, the greater the minimum nonlinearity. However, under any range, the number of turns corresponding to the minimum nonlinearity is not necessarily equal to the number of turns corresponding to the maximum sensitivity, that is, the nonlinearity and maximum sensitivity design need to be compromised, so as to select the number of turns of the receiving coil. In this embodiment, the number of turns of the receiving coil is selected as 20, which meets the performance requirements.

[0070] Decoupling performance optimization in x and y directions:

[0071] In the above maximum sensitivity and minimum nonlinear optimization analysis, the decoupling requirements in the x and y directions are not considered, that is, the receiving coil is assumed to move only in the x (or y) direction. In fact, since the receiving coil of the inductive sensor is allowed to move in the xy plane relative to the eddy current coil, it is necessary to analyze the factors that affect the decoupling performance. L x Take the example to analyze the influence of y-direction offset on coil output.

[0072] Fig.10 Parts (a) and (b) show the length of the long side. l= 22mm and l= The internal magnetic flux of two 56mm rectangular frames with different offsets in the y direction. Fig.10 It can be seen that the length of the long side of the rectangular frame l= When the diameter is 22 mm, the internal magnetic flux is affected by the offset much more than l= 56mm. Therefore, the length of the receiving coil lCannot be too small. To quantify the length l and offset Δ y The influence of displacement sensitivity of the receiving coil is calculated by calculating the change of magnetic flux when the receiving coil is displaced relative to the eddy current coil, which is used to characterize the output of the coil and obtain the effect of the y-direction offset on the receiving coil. L x The influence of displacement sensitivity in the x direction is as follows Fig.11 shown.

[0073] For the receiving coil L x For example, the displacement in the insensitive direction (y direction) of the coil affects the sensitivity in the sensitive direction (x direction), but this effect varies with the size of the coil in the insensitive direction (long side length). l ) increases and decreases rapidly. The size of the coil in the insensitive direction l When the sensitivity is ≥36mm, the effect of a 1.5mm offset on the sensitivity is less than 0.02%, and the effect of a 3mm offset on the sensitivity is less than 0.07%. To ensure the decoupling of the coils in both directions, the length of the innermost layer of the coil should not be less than 36mm. Therefore, in this embodiment, the innermost length of the four receiving coils is selected to be 38mm, which meets the performance requirements.

[0074] When the first differential coil 3 and the second differential coil 4 are input with an excitation signal, and when the differential fixed block 1 and the beam 2 undergo relative displacement, the signal output difference between the two input ends of the first differential coil 3 and the second differential coil 4 is demodulated by the measuring circuit and output as Uz, which is used to characterize the relative displacement in the z direction between the beam 2 and the differential fixed block 1; the signal difference at the output ends of the two receiving coils of each pair is demodulated by the measuring circuit and output as Ux and Uy, which are respectively used to characterize the relative displacement in the x direction and the y direction between the beam 2 and the differential fixed block 1.

[0075] Specifically, Fig.12 and Fig.13 As shown, the detection circuit includes an excitation power supply, a differential amplifier, an x-direction instrumentation amplifier, a y-direction instrumentation amplifier, a z-direction phase-sensitive detector, an x-direction phase-sensitive detector and a y-direction phase-sensitive detector. One end of the first differential coil 3 and the second differential coil 4 are commonly grounded, and the other ends are respectively connected in series with matching resistors Rs. The other ends of the two matching resistors Rs are commonly connected to the output end of the excitation power supply. The two connection points of the two differential coils and the two matching resistors Rs are respectively connected to the two signal input ends of the differential amplifier. The output end of the differential amplifier and the output end of the excitation power supply are respectively connected to the two input ends of the z-direction phase-sensitive detector. The z-direction phase-sensitive detector outputs Uz.

[0076] Two receiving coils L x / Two receiving coils Ly One end of the two phase-sensitive detectors is grounded, and the other end is connected to the two input ends of the x-direction instrumentation amplifier / y-direction instrumentation amplifier respectively. The output end of the x-direction instrumentation amplifier / y-direction instrumentation amplifier and the output end of the excitation power supply are connected to the two input ends of the x-direction phase-sensitive detector / y-direction phase-sensitive detector. The x-direction phase-sensitive detector / y-direction phase-sensitive detector outputs Ux / Uy.

[0077] Preferably, the output ends of the z-direction phase-sensitive detector, the x-direction phase-sensitive detector and the y-direction phase-sensitive detector are all connected to a low-pass filter (LPF).

[0078] Differential ECS signal demodulation: Fig.12 In the differential ECS signal processing circuit shown in FIG. 1 , a probe wound with a single eddy current coil can be electrically equivalent to a series connection of a series resistor R and a series inductor L. The difference between the two differential coil signals output by the AC bridge in the circuit is U diff For a pair of differential coils of the differential probe, when the distance change is very small (sub-millimeter), within the z-direction detection range, the resistance change of the first differential coil 3 and the second differential coil 4 are both ΔR, and the inductance change is both ΔL, but the change direction is opposite, so the differential output U of the two differential coils of the AC bridge is diff for:

[0079]

[0080] The expression of the bridge output signal after demodulation by the differential amplifier and the z-direction phase-sensitive detector is:

[0081]

[0082] in,

[0083]

[0084] E is the excitation voltage The amplitude of the excitation voltage is ω, K 1 is the signal gain of the differential amplifier, K 2 is the signal gain of the z-direction phase-sensitive detector, Rs is the matching resistance value, R is the equivalent resistance of the first differential coil and the second differential coil, and L is the equivalent inductance of the first differential coil and the second differential coil.

[0085] From formula (2), we can see that the output U of ECS is z It is proportional to the change in coil inductance ΔL, which is consistent with the above analysis.

[0086] In this embodiment, Fig.12 The phase sensitive detector (PSD) in the circuit is designed based on the MC1496 modulation and demodulation chip. The specific circuit diagram is as follows: Fig.14 MC1496 works in the nonlinear region and acts as a switch multiplier to demodulate weak signals.

[0087] Signal demodulation of inductive displacement sensor (IDS): Fig.15 As shown, the equivalent model of the three-dimensional sensor of the present invention. There are four induction coils (receiving coils), which are combined into two pairs. For the convenience of display, only one coil is drawn in the model. The induction coil and the excitation coil (the first differential coil 3 and the second differential coil 4, that is, the eddy current coil) work based on the electromagnetic induction effect. In order to avoid the newly added induction coil affecting the performance of the ECS, the impedance of the induction coil should be as large as possible (above 1GΩ). To achieve this goal, Fig.15 The input impedance Z of the operational amplifier connected in series with the non-inverting terminal and the inverting terminal is in Greater than 1GΩ. When the inductive coil loop impedance Z in When the current in the receiving coil is greater than 1GΩ, it is negligible compared to the eddy current of the target conductor. Therefore, the receiving coil is equivalent to an open circuit and will not directly generate a magnetic field to affect the excitation coil, nor will it increase the load of the excitation coil. The performance of the excitation coil as an eddy current coil will not be affected by the receiving coil. The addition of the receiving coil will not affect the performance of the eddy current sensor.

[0088] like Fig.13 As shown, in order to meet the high impedance requirement of the receiving coil side, both ends of the receiving coil are directly connected to the instrument amplifier. The instrument amplifier model selected in this embodiment is AD8421, which is a high-performance instrument amplifier designed and produced by Analog Devices. Its differential mode and common mode input impedance are both as high as 30GΩ, which meets the requirement that the newly added IDS does not affect the original performance of the ECS.

[0089] exist Fig.13 In the figure, a pair of receiving coils facing in the x direction L x and a pair of receiving coils in the y direction L y The mutual inductance with the first differential coil 3 is M x and M y When the first differential coil 3 and the second differential coil 4 are connected with a frequency of ω , the amplitude is I When the excitation current is L x and a pair of receiving coils L y The induced voltage amplitude at both ends V x and Vy They are:

[0090]

[0091] V x and V y The expression after demodulation by the corresponding instrument amplifier and the corresponding phase-sensitive detector is:

[0092]

[0093] in, K 3 is the signal gain of the instrumentation amplifier, K 4 is the signal gain of the phase sensitive detector.

[0094] It can be seen that the output in the x direction U x At the same time, the mutual inductance M x And the excitation current amplitude I The output in the y direction is U y At the same time, the mutual inductance M y And the excitation current amplitude I When the shape, size, number of turns and other parameters of the excitation coil and the receiving coil are determined, when the excitation current is constant and the distance between the excitation coil and the receiving coil in the z direction is determined, the mutual inductance M x and M y It is only determined by the relative position of the excitation coil and the receiving coil in the horizontal direction. x and U y , the measurement of two-dimensional displacement in the x and y directions on the horizontal plane can be realized. The number of turns, shape and size of the receiving coil will affect its mutual inductance with the excitation coil. By optimizing the above parameters of the receiving coil, the sensitivity of the IDS can be improved and its nonlinearity can be reduced.

[0095] Mutual Induction M x and M y In addition to being affected by the relative positions of the receiving coil and the excitation coil in the x and y directions, it is also affected by the relative positions of the coils in the z direction, that is, the displacement in the z direction will also change the output of the inductive sensor in the x and y directions. The outputs in these two directions are not decoupled from the displacement in the z direction. The following simulation analyzes the specific impact of the displacement in the z direction on the output in the x and y directions and provides a solution to eliminate this impact.

[0096] Set the distance from the first target conductor 5 to the first differential coil 3 as z, and simulate the displacement sensitivity of the IDS receiving coil in the x and y directions when the distance z is different. The simulation results are as follows: Fig.16 As shown, for the convenience of comparison, the relative displacement sensitivity values ​​at different distances in the figure are the ratios of the sensitivity at that location to the sensitivity at z=0.6mm.

[0097] from Fig.16 It can be seen that when the inner and outer radii of the excitation coil are 2.15mm and 9.85mm respectively, the distance z between the excitation coil and the corresponding target conductor has a great influence on the displacement sensitivity of the IDS receiving coil in the x and y directions. When the crossbeam 2 of the ECS is located at the symmetrical equilibrium position in the middle of the differential fixed block 1, that is, z=0.6mm, the displacement sensitivity of the IDS receiving coil is 1; when z=0.5mm, the displacement sensitivity increases to 1.13; when z=0.7mm, the displacement sensitivity decreases to 0.90. The displacement sensitivity of the IDS receiving coil in the x and y directions can be well fitted by a second-order polynomial, and the maximum fitting error is ±0.19% of the full scale.

[0098] In order to reduce the influence of the displacement in the z direction on the sensitivity of the IDS in the x and y directions, the present invention proposes that the displacement recorded by the ECS in the z direction can be used to correct the output of the IDS in the x and y directions, thereby achieving the purpose of decoupling in the three directions. In this way, the eddy current displacement sensor ECS for measuring the displacement in the z direction and the inductive displacement sensor IDS for measuring the x and y directions are combined into the three-dimensional displacement sensor proposed by the present invention.

[0099] Performance experiment:

[0100] (1) ECS sensitivity measurement

[0101] The high-performance piezoelectric translation stage (model: N-565) from German PI (Physik Instrumente) was selected to measure the performance of ECS in the z direction. Fig.17As shown, the piezoelectric displacement stage 21 is fixed on the air floating platform 22, the differential fixed block 1 with the differential coil is fixed on the test fixture 24 on the top of the second base 25 through the fixed pressure block 23, and the crossbeam 2 with the receiving coil is fixed on the test fixture 24 on the top of the piezoelectric displacement stage 21 through the fixed pressure block 23, and the crossbeam 2 is located in a balanced position in the differential fixed block 1. The side of the test fixture 24 is rotatably connected with a horizontally arranged threaded rod, and a knob is fixedly arranged at the end of the threaded rod; through holes are provided on the differential fixed block 1 and the crossbeam 2, and the threaded rod passes through the through holes respectively; the fixed pressure block 23 is threadedly sleeved on the outside of the threaded rod, and the outer edge is fixedly connected to the side of the differential fixed block 1 or the crossbeam 2 by screws. By waving the corresponding knob, the threaded rod can be rotated, so that the horizontal distance between the fixed pressure block 23 and the test fixture 24 is adjusted by threaded cooperation, so that the differential fixed block 1 and the crossbeam 2 are fixed on the corresponding test fixture 24.

[0102] The piezoelectric displacement stage 21 is controlled to take a step every 10 μm within a range of 200 μm, and a total of 20 steps are taken to complete the whole range. The output data of the ECS part of the three-dimensional displacement sensor is recorded. The processed data results are as follows: Fig.18 As shown. Fig.18 It can be seen that the displacement sensitivity of the three-dimensional displacement sensor in the z direction is 18.579mV / μm, and the maximum nonlinearity of the full range is ±0.028%, which is slightly larger than Figure 7 The simulation results in Fig.18 The horizontal coordinate 0μm in the figure is the symmetric position of ECS at z=0.6mm.

[0103] In addition, the noise at a displacement of 50 μm in the z direction was recorded when the sensor was in a stable state, as shown in Fig.19 shown. Fig.19 Part (a) shows that when the sampling rate is 600 Hz, the peak-to-peak value of the noise in the z direction is 5.8 nm; Fig.19 Part (b) shows that the peak-to-peak value of the noise is 2nm at a sampling rate of 10Hz. At a confidence level of 99.9%, the peak-to-peak value of the noise signal is about 6.6 times the effective value. Therefore, the resolution of the sensor in the z direction at a sampling rate of 600Hz is 0.88nm, and the quasi-static resolution from 0.1 to 10Hz is 0.30nm.

[0104] (2) Performance test of inductive sensor IDS

[0105] like Fig. 20As shown, it is a performance test system for the aforementioned inductive sensor. The excitation coil is fixedly attached to the lower surface of the top suspension plate of the first cantilever beam 12, and the target conductor with the receiving coil is fixedly attached to the upper surface of the top suspension plate of the second cantilever beam 13. A z-axis turntable 14 and an xy-direction displacement stage 15 are stacked below the first cantilever beam 12, and a x-axis turntable 16 and a z-direction displacement stage 17 are stacked below the second cantilever beam 13. The xy-direction displacement stage 15 and the z-direction displacement stage 17 are fixedly connected to both sides of the top surface of the first base 11 respectively. The z-axis turntable 14 can adjust the rotation of the first cantilever beam 12, so that the two moving directions of the xy-direction displacement stage 15 are respectively arranged in parallel with the two induction directions of the receiving coil. The xy-direction displacement stage 15 realizes the relative displacement of the excitation coil and the receiving coil in the xy plane; the x-axis turntable 16 adjusts the plane position of the receiving coil so that it is parallel to the plane where the excitation coil is located. The z-direction translation stage 17 is used to adjust the vertical distance between the receiving coil and the exciting coil. For example, in this experiment, the vertical distance is initially set to 0.6 mm.

[0106] 1) Decoupling performance test of inductive displacement sensor

[0107] Test the 15-turn receiving coil. The receiving coil is fixed, the x-direction is kept fixed, and the excitation coil is moved in the y-direction within the range of ±1.5mm of the equilibrium position in the y-direction with a step of 250μm, and the output results of the receiving coil are recorded. A total of 5 groups of tests are performed, and the positions in the x-direction are -1000μm, -500μm, 0μm, 500μm, and 1000μm respectively.

[0108] Inductive sensor at five different x-displacements y The sensitivity test results obtained from the output of the direction receiving coil are as follows Fig.21 As shown in part (a) of the figure, the output of the receiving coil in the y direction is proportional to the displacement in the y direction and has good linearity; the curves corresponding to different x values ​​basically overlap, which shows that the output of the receiving coil in the y direction of the inductive sensor is basically not affected by the displacement in the x direction.

[0109] Still keeping the receiving coil fixed and the y direction fixed, move the excitation coil in the x direction within the range of ±1.5mm of the equilibrium position in the x direction with a step distance of 250μm, and record the output structure of the receiving coil. A total of 5 groups of tests were performed, and the positions in the y direction were -1000μm, -500μm, 0μm, 500μm, and 1000μm respectively.

[0110] The test results when the y-direction output changes in the x-direction displacement are as follows Fig.21As shown in part (b) of . It can be seen from the results that the output of the y-direction receiving coil is almost only related to the displacement in the y-direction. When the y-direction position is fixed and the displacement changes, the y-direction output is almost a straight line parallel to the x-axis, which further verifies that the y-direction receiving coil output of the inductive sensor is basically not affected by the displacement change in the x-direction. In summary, the decoupling performance of the inductive sensor is good, which is consistent with the simulation results.

[0111] 2) Sensitivity and nonlinearity test of inductive displacement sensor

[0112] according to Figure 8 The simulation results of nonlinearity and sensitivity shown in part (b) show that when the range is ±1.5mm and the number of turns is 15, the nonlinearity reaches the minimum of ±1.06%, and when the number of turns is 20, the nonlinearity is ±0.11%. The displacement sensitivity of 20 turns is 1.751 times that of 15 turns.

[0113] The displacement sensitivity test results of the 15-turn coil and the 20-turn coil in the y direction are as follows: Fig. 22 During the test, the x-direction is kept at the equilibrium position and fixed at 0 μm, and only the displacement of the exciting coil in the y-direction is changed.

[0114] The experimentally measured nonlinearity of the 15-turn coil is ±1.1%, which is consistent with the simulation results. The nonlinearity of the 20-turn coil is ±0.3%, which is greater than the simulation result. The main reason is that the displacement operation of the hand-twisted differential head introduces errors. However, the nonlinearity of ±0.3% is still much better than the ±1.1% of the 15-turn coil. The overall trend of the nonlinear measured results is consistent with the simulation. The experimentally measured displacement output fitting straight line slope of the 15-turn coil is 0.616mV / μm, which is the displacement sensitivity of the coil; the displacement sensitivity of the 20-turn coil is 1.081mV / μm, which is 1.755 times the former, and is almost completely consistent with the simulation results. The effectiveness of the optimization measures proposed in the present invention is proved.

[0115] 3) Inductive displacement sensor resolution test

[0116] In order to analyze the noise of the sensor, the displacement output noise at the maximum displacement of 1.5mm is measured when the sensor is in a stable state. Fig.23 As shown in the figure, the peak-to-peak value of the noise is 390nm when the sampling rate is 600Hz, and the peak-to-peak value of the noise is 60nm when the sampling rate is 10Hz. At a confidence probability of 99.9%, the peak-to-peak value of the noise signal is about 6.6 times the effective value. Therefore, the resolution of the sensor at a sampling rate of 600Hz is 60nm, and the quasi-static resolution of the sensor at 0.1~10Hz is 9nm.

[0117] The non-contact three-dimensional displacement sensor proposed in the present invention has a quasi-static resolution of 9nm in the x and y directions, and a resolution of 60nm under 600Hz sampling. It also has a large range of 3mm and a maximum nonlinearity of ±0.3% of the full range. The quasi-static resolution of the sensor in the z direction has reached the sub-nanometer level, which is 0.3nm. The resolution in the z direction under a sampling rate of 600Hz can also reach 0.88nm, and the maximum nonlinearity within the full range of 200μm is ±0.028%. By correcting the displacement sensitivity in the x and y directions through the displacement measurement value in the z direction, the purpose of decoupling the output in the x and y directions from the z direction can be achieved, and the output in the x and y directions is also decoupled. Therefore, the three-dimensional displacement sensor in the present invention achieves decoupling in three directions and has excellent performance in indicators such as linearity and range.

[0118] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A non-contact three-dimensional displacement sensor, characterized in that: The invention comprises a mechanical probe and a detection circuit, wherein the mechanical probe part comprises a differential fixed block of a "U"-shaped structure and a crossbeam whose end is suspended inside the differential fixed block, a first differential coil and a second differential coil are fixedly arranged on two parallel inner side surfaces of the differential fixed block, a first target conductor located directly below the first differential coil is fixedly arranged on the top surface of the suspended end of the crossbeam, and a second target conductor located directly above the second differential coil is fixedly arranged on the bottom surface; A pair of receiving coils are fixedly arranged on the top surface of the first target conductor and / or on the bottom surface of the second target conductor along the horizontal x direction. L x A pair of receiving coils are fixedly arranged along the horizontal y direction L y , the two receiving coils of each pair are arranged in parallel, and the two pairs of receiving coils are arranged vertically to form a "well" structure; When the first differential coil and the second differential coil are input with an excitation signal, when the differential fixed block and the cross beam undergo relative displacement, the signal output difference between the two input ends of the first differential coil and the second differential coil is demodulated by the measurement circuit and output as Uz, which is used to characterize the relative displacement between the cross beam and the differential fixed block in the z direction, and the z direction is perpendicular to the two parallel inner side surfaces of the differential fixed block; The signal difference at the output ends of the two receiving coils of each pair is demodulated by the measurement circuit and output as Ux and Uy, which are used to characterize the relative displacement in the x-direction and y-direction between the beam and the differential fixed block, respectively. The planes in the x-direction and y-direction are parallel to the two parallel inner sides of the differential fixed block.

2. A non-contact three-dimensional displacement sensor according to claim 1, characterized in that: The first differential coil and the second differential coil have the same structure, and both are double-layer structures that are stacked and connected in series end to end.

3. The non-contact three-dimensional displacement sensor according to claim 1, characterized in that: The detection circuit includes an excitation power supply, a differential amplifier, an x-direction instrumentation amplifier, a y-direction instrumentation amplifier, a z-direction phase-sensitive detector, an x-direction phase-sensitive detector and a y-direction phase-sensitive detector. One end of the first differential coil and the second differential coil are commonly grounded, and the other ends are respectively connected in series with matching resistors Rs. The other ends of the two matching resistors Rs are commonly connected to the output end of the excitation power supply. The two connection points of the two differential coils and the two matching resistors Rs are respectively connected to the two signal input ends of the differential amplifier. The output end of the differential amplifier and the output end of the excitation power supply are respectively connected to the two input ends of the z-direction phase-sensitive detector. The z-direction phase-sensitive detector outputs Uz. Two receiving coils L x / Two receiving coils L y One end of the two phase-sensitive detectors is grounded, and the other end is connected to the two input ends of the x-direction instrumentation amplifier / y-direction instrumentation amplifier respectively. The output end of the x-direction instrumentation amplifier / y-direction instrumentation amplifier and the output end of the excitation power supply are connected to the two input ends of the x-direction phase-sensitive detector / y-direction phase-sensitive detector. The x-direction phase-sensitive detector / y-direction phase-sensitive detector outputs Ux / Uy.

4. The non-contact three-dimensional displacement sensor according to claim 3, characterized in that: The output ends of the z-direction phase-sensitive detector, the x-direction phase-sensitive detector and the y-direction phase-sensitive detector are all connected to a low-pass filter.

5. A non-contact three-dimensional displacement sensor according to claim 3 or 4, characterized in that: In the z-direction detection range, the resistance change of the first differential coil and the second differential coil is ΔR, and the inductance change is ΔL, but the change direction is opposite, so the differential output U of the two differential coils of the AC bridge is diff for: The expression of the bridge output signal after demodulation by the differential amplifier and the z-direction phase-sensitive detector is: in, E is the excitation voltage The amplitude of the excitation voltage is ω, K 1 is the signal gain of the differential amplifier, K 2 is the signal gain of the z-direction phase-sensitive detector, Rs is the matching resistance value, R is the equivalent resistance of the first differential coil and the second differential coil, and L is the equivalent inductance of the first differential coil and the second differential coil.

6. A non-contact three-dimensional displacement sensor according to claim 3 or 4, characterized in that: A pair of receiving coils in the x direction L x and a pair of receiving coils in the y direction L y The mutual inductance with the first differential coil or the second differential coil is M x and M y When the first differential coil and the second differential coil are connected with a frequency of ω , the amplitude is I When the excitation current is L x and a pair of receiving coils L y The induced voltage amplitude at both ends V x and V y They are: V x and V y The expression after demodulation by the corresponding instrument amplifier and the corresponding phase-sensitive detector is: in, K 3 is the signal gain of the instrumentation amplifier, K 4 is the signal gain of the phase sensitive detector.

7. A non-contact three-dimensional displacement sensor according to any one of claims 1 to 4, characterized in that: The first target conductor and the second target conductor are both made of metal plates.

8. A non-contact three-dimensional displacement sensor according to any one of claims 1 to 4, characterized in that: In the initial state, the z-direction distance between the first differential coil and the first target conductor and the z-direction distance between the second differential coil and the second target conductor are equal, and the two receiving coils L x The y-distance between the two receiving coils L y The x-direction distances between the two pairs of receiving coils are equal, and the intersection point of the center lines of the two pairs of receiving coils is located on the line connecting the centers of the first differential coil and the second differential coil.

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