An inductive displacement sensor

Abstract

The present invention relates to the field of sensor technology, and discloses an inductive displacement sensor, comprising a substrate, two pairs of rectangular receiving coils fixedly arranged on the surface of the substrate, and a spiral linear excitation coil, an initial plane coordinate system is created with the center of the substrate as the origin, the two receiving coils of each pair are arranged in parallel, the two pairs of receiving coils are arranged vertically, and the excitation coil is located on the side of the receiving coil away from the substrate and is arranged parallel to the surface of the substrate; in the initial state, the projection of the center point of the excitation coil on the substrate coincides with the origin of the initial plane coordinate system, and the receiving coil has a relative position to the excitation coil. xy When the displacement occurs within the plane, the two pairs of coils output x and y The invention can measure displacement in two directions at the same time, realize high-precision and high-stability measurement of displacement signals, and has good dynamic response characteristics, reducing errors caused by the movement of mechanical parts.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, in particular to 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] LVDT (Linear Variable Differential Transformer) is a typical traditional inductive displacement sensor that uses the principle of electromagnetic induction to achieve the conversion of displacement to electrical signals. This sensor has the characteristics of high resolution, high stability, good linearity and insensitivity to environmental changes, and is suitable for various harsh environments and high-precision applications. However, LVDT also has some limitations. For example, LVDT has a complex structure and a large volume, and is easily affected by small-angle rotation and deflection during measurement, resulting in reduced measurement accuracy. In addition, LVDT has the problem of insufficient dynamic response when used at high frequencies, which limits its application in the field of high-speed dynamic measurement.

[0005] A typical inductive displacement sensor LVDT usually consists of multiple parts, including a coil, an iron core, and a housing, which may lead to a complex structure, difficult to miniaturize, and difficult to manufacture and maintain. Due to the large number of components and large mass, the iron core is driven by the object being measured to change the mutual inductance or self-inductance of the coil to output a displacement signal. In high-speed dynamic measurements, the LVDT may not provide sufficient response speed, resulting in an inability to accurately track rapidly changing displacements. It is usually designed for single-axis measurement. Although multi-axis measurement can be achieved by using multiple LVDTs, this will increase the complexity and cost of the system. Summary of the invention

[0006] In view of the above-mentioned defects and shortcomings, the present invention aims to provide a new type of two-degree-of-freedom inductive displacement sensor, which can simultaneously perform displacement measurement in two directions, achieve high-precision and high-stability measurement of displacement signals, and has good dynamic response characteristics, and is suitable for a wider range of application scenarios. The sensor can reduce errors caused by rotation or deflection of mechanical parts while maintaining high measurement accuracy.

[0007] In order to solve the above technical problems, a technical solution adopted by the present invention is:

[0008] An inductive displacement sensor includes a substrate, two pairs of long sides fixedly arranged on the surface of the substrate, and l , the short side length is h The number of turns is n A rectangular receiving coil with an outer radius of R 1. The inner radius is R 2 spiral linear excitation coil, with the center of the substrate as the origin, and two mutually perpendicular central axes as x Axis and y The initial plane coordinate system is created by the axis, in which a pair of two receiving coils are arranged parallel and symmetrically at x The two sides of the axis, the symmetry lines of the two short sides and y The axes coincide with each other, and the two receiving coils of the other pair are arranged parallel and symmetrically at y The two sides of the axis, the symmetry lines of the two short sides and x The axes coincide, and the symmetry lines of the two long sides of any receiving coil are parallel to it. x axis / y The vertical distance between the axes is h 0, the excitation coil is located on the side of the receiving coil away from the substrate and is set parallel to the surface of the substrate. The minimum vertical distance between the surface of the excitation coil and the surface of the substrate is H ;

[0009] In the initial state, the projection of the center point of the excitation coil on the substrate coincides with the origin of the initial plane coordinate system, and the receiving coil has xy When the displacement occurs within the plane, the two pairs of coils output x and y The relative displacement in two directions can be decoupled at the same time.

[0010] Furthermore, the method for obtaining various size parameters of the excitation coil and the receiving coil includes the following steps:

[0011] S1. Set the initial value:

[0012] Set the outer radius of the excitation coil R 1 and inner radius R2. The minimum vertical distance between the surface of the excitation coil and the surface of the substrate is H , the excitation voltage frequency of the excitation coil is f ;

[0013] S2. Obtain the magnetic flux density function:

[0014] The two-dimensional axisymmetric model is used for modeling and simulation to obtain the The magnetic flux density function in the z-axis direction , and the corresponding function curve;

[0015] S3. Calculate the magnetic flux in the single-turn coil area of ​​the receiving coil:

[0016] According to the obtained magnetic flux density function , in the single-turn coil area D The length of the short side is calculated by integrating the magnetic flux density inside. h The magnetic flux in the rectangular box at time:

[0017] (1)

[0018] Calculate the magnetic flux with respect to the short side length h Magnetic flux distribution curve;

[0019] S4. Obtain the symmetry line position of the single-turn coil of the receiving coil h 0:

[0020] Intercept the symmetrical part of the magnetic flux distribution curve about the length of the short side to obtain the symmetry line position of the symmetrical part of the magnetic flux curve h 0, h 0 is the midpoint of the short side of the coil;

[0021] S5. Obtain the fitting function of the symmetrical part of the magnetic flux distribution curve of the single-turn coil of the receiving coil:

[0022] The symmetrical part of the magnetic flux distribution curve is fitted with a second-order function to obtain the corresponding curve function:

[0023] (2)

[0024] Among them, the parameters a ∈ R , b ∈ R , the specific value is determined according to the discrete value of the symmetrical part of the corresponding magnetic flux distribution curve;

[0025] The symmetry line and straight line of the two long sides of a single-turn coil h = h 0 coincides, the straight line where the two long sides lie h =h 1 and h = h 2 The magnetic flux values ​​at the two points where it intersects the magnetic flux curve are equal, , the magnetic flux inside the coil is , the output of the coil is 0, and the single-turn coil is at the origin;

[0026] S6. Output sensitivity and linearity evaluation of single-turn receiving coil:

[0027] When the single-turn coil moves from the origin along the symmetry line of the two short sides When the displacement is M D Changes occur, coil output M O Also changes accordingly, the output M O for:

[0028] (3)

[0029] Output and displacement of a single-turn coil There is a good linear relationship between them;

[0030] Among them, the short side length of a single-turn coil is w= ( h 1 -h 2) is the sensitivity coefficient of the output, w The larger the value, the higher the corresponding sensitivity, and vice versa;

[0031] S7. Determine the number of turns of the receiving coil n :

[0032] 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. The number of turns of the receiving coil needs to be selected through the design of nonlinearity and maximum sensitivity. n ;

[0033] S8, x, y Direction decoupling performance optimization:

[0034] Select the length of the innermost long side l For receiving coils of different specifications, with other parameters being the same and determined, the magnetic flux inside the coil is calculated using formula (1): M D ,as well as M D Displacement in the long side direction The influence of formula (2) and formula (3) are used to calculate the displacement of receiving coils of different specifications in the short side direction. , the offset in the long side direction is The long side offset in the case of The results of the influence on the displacement sensitivity in the short side direction are used to find the minimum value of the innermost long side length that satisfies the decoupling performance of the receiving coil in two directions.

[0035] Furthermore, the outermost short side length of the receiving coil w max The constraints are:

[0036] (4).

[0037] Furthermore, the substrate is made of a metal plate, preferably an aluminum substrate.

[0038] Furthermore, the excitation coil is a double-layer structure that is superimposed and connected in series end to end.

[0039] Furthermore, the innermost wire ends of the four receiving coils are connected in parallel and symmetrically arranged at x The two outermost wire ends of the two receiving coils on both sides of the axis serve as y The signal output terminal of the direction displacement is symmetrically set at y The two outermost wire ends of the two receiving coils on both sides of the axis serve as x Directional displacement signal output terminal.

[0040] A data processing system using the inductive displacement sensor as described above is also provided, comprising a signal source for applying an excitation signal to an excitation coil, y The two signal output terminals of the direction displacement are connected y Direction signal processing circuit, and x The two signal output terminals of the direction displacement are connected x Direction signal processing circuit, respectively y Direction signal processing circuit and x an analog-to-digital converter connected to the output end of the direction signal processing circuit and a central processing unit connected to the digital-to-analog converter;

[0041] When the excitation signal is fed into the excitation coil, the receiving coil has a xy When the displacement is within the plane, the symmetry is set at x The two receiving coils on both sides of the shaft output induction signals to y Direction signal processing circuit, symmetrically arranged at y The two receiving coils on both sides of the shaft output induction signals to x Direction signal processing circuit: The signal processing circuits of the two directions process the sensing signals respectively and input them into the digital-to-analog converter, and then the digital-to-analog converter converts the analog signals into corresponding digital signals and transmits them to the central processing unit.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] 1. The present invention realizes high-precision and high-stability measurement of displacement signals through the innovative sensor probe coil structure design, and has good dynamic response characteristics, which is suitable for a wider range of application scenarios, including but not limited to industrial automation, aerospace, medical equipment, and precision instruments. The sensor can reduce the error caused by the rotation or deflection of mechanical parts while maintaining high measurement accuracy.

[0044] 2. The inductive displacement sensor of the present invention adopts a split design, consisting of a spiral excitation coil and a flexible rectangular receiving coil, and can accurately measure the displacement of the receiving coil on the coil plane. This design not only simplifies the structure of the sensor and reduces the manufacturing cost, but also improves the installation flexibility and convenience of the sensor.

[0045] 3. By optimizing the geometry and size of the receiving coil, the present invention can achieve high sensitivity and high resolution detection of displacement changes. At the same time, the extremely small nonlinearity also eliminates the need for secondary correction, and the bandwidth of the sensor is also guaranteed, meeting the needs of modern automation and control fields for high-precision displacement measurement.

[0046] 4. The two-degree-of-freedom inductive displacement sensor designed by the present invention can measure displacement in two directions at the same time, which is very useful in complex mechanical systems, such as robot joints or multi-degree-of-freedom automation equipment. At the same time, the non-contact measurement feature makes its working bandwidth much larger than that of LVDT, with a wider range of applications, suitable for high-speed dynamic measurement, and simple structure, which helps to reduce manufacturing costs and improve reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a structural schematic diagram of the inductive displacement sensor of the present invention;

[0048] Figure 2 Modeling structure and size diagram of the simulation model to obtain the magnetic flux density function;

[0049] Figure 3 The simulation results of magnetic flux density distribution obtained for the simulation model;

[0050] Figure 4 Schematic diagram of the spatial coordinate system for constructing the magnetic flux density function;

[0051] Figure 5 Schematic diagram of the magnetic flux density distribution curve obtained by the simulation model;

[0052] Figure 6It is a schematic diagram of the top view of the preliminary design of the receiving coil of the present invention;

[0053] Figure 7 It is a calculation model of magnetic flux in a rectangular frame of a single-turn coil and a schematic diagram of the distribution curve of magnetic flux in rectangular frames of different widths;

[0054] Figure 8 This is a schematic diagram of the initial position design of the receiving coil and the displacement result analysis;

[0055] Fig. 9 This is a schematic diagram showing the influence of the number of turns of the receiving coil on sensitivity and nonlinearity;

[0056] Fig.10 This is a schematic diagram showing the influence of different ranges of the receiving coil on the maximum sensitivity and minimum nonlinearity;

[0057] Fig.11 The receiving coil is inside the rectangular frame y Schematic diagram of position offset in direction;

[0058] Fig.12 is the magnetic flux distribution curve in the rectangular frame of the receiving coil at different offsets;

[0059] Fig.13 For the receiving coil x Displacement in the same direction y Schematic diagram of position offset with different offset directions;

[0060] Fig.14 for y Direction offset to coil x Schematic diagram of the influence trend of directional displacement sensitivity;

[0061] Fig.15 A structural block diagram of the inductive sensor data processing system of the present invention;

[0062] Fig.16 A schematic diagram of a top view of the receiving coil designed for experimental testing of the present invention;

[0063] Fig.17 It is a schematic diagram of the structure of the experimental device used for the performance test of the inductive sensor;

[0064] Fig.18 For experimental x, y The corresponding displacement direction y Output result of direction coil;

[0065] Fig.19 The sensitivity test results of receiving coils with different numbers of turns are shown below;

[0066] Fig. 20The experimental test results of the inductive displacement sensor output displacement noise.

[0067] In the figure: 1, substrate; 2, receiving coil; 3, exciting coil; 11, base; 12, first cantilever beam; 13, second cantilever beam; 14, winding z Axis turntable; 15. xy Direction displacement stage; 16, around x Axis turntable; 17. z Direction translation stage. DETAILED DESCRIPTION

[0068] 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.

[0069] 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.

[0070] 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.

[0071] The present invention provides an inductive displacement sensor, such as Figure 1 As shown, the inductive displacement sensor includes a substrate 1, two pairs of long sides with lengths of l , the short side length is h The number of turns is n The receiving coil 2 is rectangular and has an outer radius of R 1. The inner radius is R The spiral linear excitation coil 3 of 2 has the center of the substrate 1 as the origin and two mutually perpendicular central axes as x Axis and y The initial plane coordinate system is created by the axis, in which a pair of two receiving coils 2 are arranged parallel and symmetrically at x The two sides of the axis, the symmetry lines of the two short sides and y The axes coincide, and the two receiving coils 2 of the other pair are arranged in parallel and symmetrically. yThe two sides of the axis, the symmetry lines of the two short sides and x The axes coincide, and the symmetry lines of the two long sides of any receiving coil 2 are parallel to it. x axis / y The vertical distance between the axes is h 0, the excitation coil 3 is located on the side of the receiving coil 2 away from the substrate 1 and is arranged parallel to the surface of the substrate 1. The minimum vertical distance between the surface of the excitation coil 3 and the surface of the substrate 1 is H ;

[0072] In the initial state, the projection of the center point of the excitation coil on the substrate coincides with the origin of the initial plane coordinate system, and the receiving coil has xy When the displacement occurs within the plane, the two pairs of coils output x and y The relative displacement in two directions can be decoupled at the same time.

[0073] The following describes in detail the process of determining and optimizing the structural dimensions of each component of the inductive displacement sensor, so that the inductive displacement sensor has the expected high sensitivity to displacement changes in two directions in the plane and the resolution detection performance.

[0074] The method for obtaining various size parameters of the excitation coil and the receiving coil comprises the following steps:

[0075] S1. Set the initial value:

[0076] Set the outer radius of the excitation coil R 1 is 9.85mm, inner radius R 2 is 2.15 mm. Preferably, in order to increase the magnetic flux in the receiving coil, the excitation coil adopts a double-layer structure, that is, two identical coils are superimposed and connected in series end to end as a whole. The design of the receiving coil needs to take into account the The magnetic flux density in the plane, in this embodiment, uses simulation technology to confirm the magnetic flux density and optimize the structural design of the receiving coil 2.

[0077] According to Figure 1 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 2 As shown in the figure, according to the actual situation, the coil is a double-layer structure, and its inner and outer diameters are 2.15mm and 9.85mm respectively. The substrate 1 adopts an aluminum-based target plate with a radius of 30mm and a thickness of 0.1mm. The vertical distance between the upper surface of the excitation coil and the lower surface of the aluminum-based target plate (that is, the minimum vertical distance between the surface of the excitation coil 3 and the surface of the substrate 1 is H) is set to 0.6mm, and the excitation voltage frequency of the excitation coil f Set to 1MHz.

[0078] The distribution of the magnetic flux density and other related parameters in the radial direction of the lower surface of the substrate 1 is simulated and calculated in the software, such as Figure 3 As shown. The magnetic flux density is the largest in the area between the excitation coil 3 and the substrate 1, but Figure 3 From the directions of the contour lines in part (a), it can be seen that the main magnetic flux is concentrated in r direction. We are more concerned about z The magnetic flux in the direction, Figure 3 Part (b) of z The magnetic flux density in the direction is higher than that in r A lot smaller in direction.

[0079] S2. Obtain the magnetic flux density function:

[0080] In the COMSOL software, the following is established on the surface of substrate 1: Figure 4 The spatial coordinate system shown in Figure 2. Since the simulation model is rotationally symmetric, it is easy to know that Figure 4 Within the dotted circle, the radial length changes Δr When <<1mm, the magnetic flux density at any point in the ring is equal, that is, at any point on the surface of substrate 1 of z Magnetic flux density in the direction is the radius of the point r Function , and the angle with this point θ In COMSOL software, any point on the surface of substrate 1 is exported. of z The magnetic flux density function curve of the direction is as follows Figure 5 shown.

[0081] Figure 6 The dotted circle in the middle represents the excitation coil 3, and the solid rectangle represents the four receiving coils 2. As mentioned above, the excitation coil 3 is a plane spiral, and the receiving coils 2 are four rectangles, and the long side of the rectangular coil 2 is much larger than the short side. The receiving coil 2 marked with ① in the figure (referred to as coil ①) is used as an example to illustrate the decoupling principle of the structural design. Figure 5 The simulation results shown in FIG. z Magnetic flux density in the direction ρ In radius r The area outside >15mm is close to 0. Coil ① y When the direction of the coil moves, the magnetic flux passing through it changes very little, and its voltage output hardly changes, that is, the output of coil ① is the same as yThe displacement in the direction is irrelevant. x When moving in the direction, the moving range is r When the diameter is less than 10mm, the magnetic flux passing through it changes greatly, and the corresponding voltage output is large. y Direction displacement is insensitive to x Directional displacement-sensitive decoupling.

[0082] The output of the receiving coil 3 has different sensitivities in the two directions. The sensitivity in the sensitive direction (short side direction) is much greater than that in the insensitive direction (long side direction). Figure 6 In the figure, the sensitive directions of the two receiving coils 2 marked ① and ④ are x Direction, the sensitive direction of the two receiving coils 2 marked ② and ③ is y Direction. From the perspective of decoupling, the ideal sensor probe design needs to ensure that the output of the receiving coil remains unchanged when moving in the insensitive direction. In addition, linearity is also a factor that needs to be considered in optimizing the sensor probe design. The sensor probe needs to have good linearity, which means that it can provide a consistent output signal throughout the entire measurement range, which is critical for precise control. The subsequent design mainly takes good decoupling capability and linearity as optimization goals, and tries to increase the sensitivity of the sensor as much as possible while meeting the first two requirements.

[0083] S3. Calculate the magnetic flux in the single-turn coil area of ​​the receiving coil:

[0084] Establish as Figure 7 In the function coordinate system shown in part (a), the dotted circle is the projection of the excitation coil 3 on the surface of the substrate 1, the center of the circle is the vertical projection of the center of the excitation coil 3 on the substrate 1, and the solid rectangle represents the single-turn coil of the receiving coil 2. The length of the long side of the rectangular frame is l Set to 60mm and the long side on the left y The axes coincide, and the short side is h (0< h <30mm). Any point in the known rectangular frame The magnetic flux density is , in the single-turn coil area D The length of the short side is calculated by integrating the magnetic flux density inside. h When the rectangular frame z Directional magnetic flux:

[0085] (1)

[0086] because The simulation results are discrete, and the above integrals are also discretized accordingly. The calculation results are calculated by programming in the mathematical software MATLAB, as shown in Figure 7 As shown in part (b).

[0087] S4. Obtain the symmetry line position of the single-turn coil of the receiving coil h 0:

[0088] Take the symmetrical part of the magnetic flux distribution curve about the length of the short side, such as Figure 7 The part of the curve covered by the rectangular box in part (b) of the figure. It can be seen that the magnetic flux distribution curve is h = 1.08~10mm This range is almost all about straight lines h =5.54mm symmetrical. Therefore, the symmetry line positions of the two long sides of the single-turn coil of the receiving coil are h 0 is 5.54mm.

[0089] S5. Obtain the fitting function of the symmetrical part of the magnetic flux distribution curve of the single-turn coil of the receiving coil:

[0090] The symmetrical part of the magnetic flux distribution curve is fitted with a second-order function, and the goodness of fit is R 2 =0.9976, and the corresponding curve function is obtained:

[0091] (2)

[0092] Among them, the parameters a ∈ R , b ∈ R , the specific value is determined according to the discrete value of the symmetrical part of the corresponding magnetic flux distribution curve;

[0093] like Figure 8 As shown in part (a) of the figure, the receiving coil (only 4 layers of coils are drawn in the figure, and the long side length of the innermost coil is l 0≥30mm). Taking the outermost circle as an example, when the receiving coil is about the straight line h =5.54mmWhen placed symmetrically, that is, the symmetry line of the two long sides of the single-turn coil and the straight line h = h 0 coincides, the straight line where the two long sides lie h = h 1 and h = h 2 The magnetic flux values ​​at the two points where the magnetic flux curve intersects (points A and B as shown in the figure) are equal. , the magnetic flux inside the coil is , , the output of the coil is 0, and the single-turn coil is at the origin, which is also the initial origin position of the receiving coil;

[0094] S6. Output sensitivity and linearity evaluation of single-turn receiving coil:

[0095] When a single-turn coil is Figure 8 The origin position shown in part (a) moves along the symmetry line of the two short sides (left and right direction) When the displacement is M D Changes occur, coil output M O Also changes accordingly, the output M O for:

[0096] (3)

[0097] It can be seen that the output and displacement of the outermost coil The inner coil has good linearity. The output of the rectangular coil has good linearity. It shows good linearity. Among them, the short side length of the single-turn coil w= ( h 1 -h 2) is the sensitivity coefficient of the output, w The larger the value, the higher the corresponding sensitivity, and vice versa.

[0098] To facilitate processing, set the innermost coil width w 0 = 0.8 mm, obviously, Figure 8 In part (a), the outermost long side of the coil cannot cross the y axis, otherwise the coil output has a large nonlinearity. Therefore, the length of the short side of the outermost layer of the receiving coil is w max The constraints are:

[0099] (4).

[0100] S7. Determine the number of turns of the receiving coil n :

[0101] First, the effect of the number of coil turns on the sensitivity and nonlinearity of the sensor is calculated and analyzed. Fig. 9 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). y The sensitivity of the coils with different numbers of turns shown on the axis is relative to the sensitivity of a single inner coil.

[0102] 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 x and yNo matter how the direction moves, the long side of the induction coil cannot be crossed Figure 8 The midpoint of part (a) y axis. Therefore, if you want a large range, the number of coil turns cannot be too many, and the number of turns and 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 how much the range is set, there is an optimal number of turns that minimizes nonlinearity. For example, Fig. 9 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.

[0103] 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.10 As shown in the figure, it can be seen 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 2 and the excitation coil 3 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 design of nonlinearity and maximum sensitivity needs to be compromised, so as to select the number of turns of the receiving coil. n .

[0104] S8, x, y Direction decoupling performance optimization:

[0105] In the above maximum sensitivity and minimum nonlinear optimization analysis, no consideration was given to x, y Decoupling requirements in both directions, that is, the default receiving coil 2 is only x (or y ) in one direction. In fact, since the receiving coil 2 of the inductive sensor is allowed to have a xy The displacement in the plane needs to be analyzed, so the factors that affect the decoupling performance need to be analyzed. x A single coil in the direction of the analysis y Effect of directional offset on coil output.

[0106] like Fig.11 As shown, it is the length of the long side l= 22mm single turn rectangular coil y There is an offset Δ in the direction y The long side of the coil is y The axes coincide, as described above, using formula (1) to calculate the short side h Magnetic flux in the frame when changing M D . Fig.12Parts (a) and (b) show the length of the long side. l= 22mm and l= Two 56mm rectangular frames y Internal magnetic flux for different directional offsets.

[0107] from Fig.12 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 2 l Cannot be too small. To quantify the length l and offset Δ y The influence on the displacement sensitivity of the receiving coil 2 is calculated by combining formula (2) and formula (3) to calculate the change in magnetic flux when the receiving coil 2 is displaced relative to the exciting coil 3, so as to characterize the output of the coil. Fig.13 The coil is shown in y Direction offset is 0 and Δ y When x The displacement in the direction is Δ x Schematic diagram of the change of coil position when . For the convenience of calculation, the coil is set to 20 layers, the innermost layer width is 0.8mm, and the length is l , the line width and line spacing are both 75μm. y Direction offset to coil x The influence of directional displacement sensitivity is as follows Fig.14 shown.

[0108] For receiving coil 2, in the coil insensitive direction ( y direction) affects the coil sensitive direction ( x direction), but this effect decreases with the size of the coil in the insensitive direction (length of the long side). l ) increases and decreases rapidly. The size of the coil in the insensitive direction l When the sensitivity is ≥36mm, the effect of 1.5mm offset on sensitivity is less than 0.02%, and the effect of 3mm offset on 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.

[0109] The innermost wire ends of the four receiving coils are connected in parallel and symmetrically arranged at x The two outermost wire ends of the two receiving coils on both sides of the axis serve as y The signal output terminal of the direction displacement is symmetrically set at y The two outermost wire ends of the two receiving coils on both sides of the axis serve as x Directional displacement signal output terminal.

[0110] like Fig.15 As shown, a data processing system using the inductive displacement sensor as described above includes a signal source for applying an excitation signal to an excitation coil, and y The two signal output terminals of the direction displacement are connected y Direction signal processing circuit, and x The two signal output terminals of the direction displacement are connected x Direction signal processing circuit, respectively y Direction signal processing circuit and x an analog-to-digital converter (ADC) connected to the output end of the direction signal processing circuit and a central processing unit (such as a computer) connected to the analog-to-digital converter;

[0111] When the excitation signal is fed into the excitation coil, the receiving coil has a xy When the displacement is within the plane, the symmetry is set at x The two receiving coils on both sides of the shaft output induction signals to y Direction signal processing circuit, symmetrically arranged at y The two receiving coils on both sides of the shaft output induction signals to x Direction signal processing circuit, the signal processing circuits in two directions process the sensing signals respectively and input them into the digital-to-analog converter, and then the digital-to-analog converter converts the analog signals into corresponding digital signals and transmits them to the central processing unit, which can then display, save or export the data.

[0112] Performance test experimental device:

[0113] In this experiment, the inner and outer radii of the excitation coil 3 are 2.15 mm and 9.85 mm respectively. According to the simulation results, two receiving coils 2 are designed. The structures are as follows: Fig.16 The specific size parameters of one receiving coil 2 are: inner layer width 0.8mm, length 38mm, outer layer length 42.5mm, total 15 turns; the specific size parameters of another receiving coil 2 are: inner layer width 0.8mm, length 38mm, outer layer length 44mm, total 20 turns.

[0114] like Fig.17 The figure shows a performance test system for the aforementioned inductive sensor. The excitation coil 3 is fixedly attached to the lower surface of the top suspension plate of the first cantilever beam 12, the substrate 1 is fixedly attached to the upper surface of the top suspension plate of the second cantilever beam 13, and the receiving coil 2 is fixedly attached to the top surface of the substrate 1. The windings are stacked below the first cantilever beam 12. z Axis rotary table 14 and xy Directional displacement platform 15, the second cantilever beam 13 is stacked below the winding x Axis rotary table 16 and z Direction displacement stage 17, xyDirection translation stage 15 and z The direction displacement platform 17 is fixedly connected to both sides of the top surface of the base 11. z The shaft turntable 14 can adjust the rotation of the first cantilever beam 12 so that xy The two moving directions of the direction displacement stage 15 are respectively arranged in parallel with the two sensing directions of the receiving coil 2 . xy The direction displacement stage 15 realizes the excitation coil 3 and the receiving coil 2 xy Relative displacement on a plane; x The axis turntable 16 adjusts the plane position of the receiving coil 2 so as to make it parallel to the plane where the exciting coil 3 is located. z The direction displacement stage 17 is used to adjust the vertical distance between the receiving coil 2 and the exciting coil 3. For example, in this experiment, the vertical distance is set to 0.6 mm.

[0115] Performance test results:

[0116] (1) Decoupling performance test of inductive displacement sensor

[0117] Test the 15-turn receiving coil 2. x Direction fixed, y Equilibrium position in the direction ±1.5 mm In the range of 250μm step y Move the exciting coil 3 in the direction of the clockwise rotation and record the output of the receiving coil 2. A total of 5 sets of tests are performed. x The positions of the directions are -1000 μm, -500 μm, 0 μm, 500 μm, and 1000 μm, respectively.

[0118] Five different x Displacement Inductive Sensor y The sensitivity test result obtained by the output of the direction receiving coil 2 is as follows Fig.18 As shown in part (a) of . From the results, we can see that y The output of the direction receiving coil 2 is y Directly proportional to the displacement, with good linearity; different x The curves corresponding to the values ​​are basically coincident, which indicates that the inductive sensor y The direction receiving coil output is basically not affected by x The influence of the change of direction displacement.

[0119] Still keep the receiving coil 2 fixed and keep y Direction fixed, x The equilibrium position in the direction is within ±1.5mm with a step size of 250μm. x Move the exciting coil 3 in the direction of the receiver coil 2 and record the output structure of the receiving coil 2. A total of 5 sets of tests are performed. yThe positions of the directions are -1000 μm, -500 μm, 0 μm, 500 μm, and 1000 μm, respectively.

[0120] y Direction output in x The test results when the directional displacement changes are as follows Fig.18 As shown in part (b) of . From the results, we can see that y The output of the direction receiving coil 2 is almost entirely related to y The displacement in the direction y When the direction position is fixed and the direction displacement changes, y The output direction is almost parallel to x The straight line of the axis further verifies the inductive sensor y The direction receiving coil output is basically not affected by x In summary, the decoupling performance of the inductive sensor is good, which is consistent with the simulation results.

[0121] (2) Sensitivity and nonlinearity test of inductive displacement sensor

[0122] according to Fig. 9 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.

[0123] 15 turns coil and 20 turns coil y The displacement sensitivity test results in the direction are as follows Fig.19 During the test, keep x The direction remains unchanged at the equilibrium position and is fixed at 0 μm. Only the excitation coil is changed. y Displacement in direction.

[0124] 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.

[0125] (3) Resolution test of inductive displacement sensor

[0126] 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. 20 As shown, 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.

[0127] 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 at a sampling rate of 600 Hz is 60 nm, and the quasi-static resolution of the sensor at 0.1-10 Hz is 9 nm.

[0128] 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.

[0129] 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. An inductive displacement sensor, characterized in that: The invention comprises a substrate, two pairs of long sides fixedly arranged on the surface of the substrate having a length of l , the short side length is h The number of turns is n A rectangular receiving coil with an outer radius of R 1. The inner radius is R 2 spiral linear excitation coil, with the center of the substrate as the origin, and two mutually perpendicular central axes as x Axis and y The initial plane coordinate system is created by the axis, in which a pair of two receiving coils are arranged parallel and symmetrically at x The two sides of the axis, the symmetry lines of the two short sides and y The axes coincide with each other, and the two receiving coils of the other pair are arranged parallel and symmetrically at y The two sides of the axis, the symmetry lines of the two short sides and x The axes coincide, and the symmetry lines of the two long sides of any receiving coil are parallel to it. x axis / y The vertical distance between the axes is h 0 The excitation coil is located on the side of the receiving coil away from the substrate and is arranged parallel to the surface of the substrate. The minimum vertical distance between the surface of the excitation coil and the surface of the substrate is H ; In the initial state, the projection of the center point of the excitation coil on the substrate coincides with the origin of the initial plane coordinate system, and the receiving coil has xy When the displacement occurs within the plane, the two pairs of coils output x and y The relative displacement in two directions can be decoupled at the same time.

2. The inductive displacement sensor according to claim 1, characterized in that: The method for obtaining various size parameters of the excitation coil and the receiving coil comprises the following steps: S1. Set the initial value: Set the outer radius of the excitation coil R 1 and inner radius R 2. The minimum vertical distance between the surface of the excitation coil and the surface of the substrate is H , the excitation voltage frequency of the excitation coil is f ; S2. Obtain the magnetic flux density function: A two-dimensional axisymmetric model is used for modeling and simulation calculation, and a spatial coordinate system is established on the surface of the substrate to obtain the coordinates of any point on the substrate surface. The magnetic flux density function in the z-axis direction , and the corresponding function curve, where is the polar coordinate value corresponding to the point in the spatial coordinate system; S3. Calculate the magnetic flux in the single-turn coil area of ​​the receiving coil: According to the obtained magnetic flux density function , in the single-turn coil area D The length of the short side is calculated by integrating the magnetic flux density inside. h The magnetic flux in the rectangular box at time: （1） Calculate the magnetic flux with respect to the short side length h Magnetic flux distribution curve; S4. Obtain the symmetry line position of the single-turn coil of the receiving coil h 0: Intercept the symmetrical part of the magnetic flux distribution curve about the length of the short side to obtain the symmetry line position of the symmetrical part of the magnetic flux curve h 0, h 0 is the midpoint of the short side of the coil; S5. Obtain the fitting function of the symmetrical part of the magnetic flux distribution curve of the single-turn coil of the receiving coil: The symmetrical part of the magnetic flux distribution curve is fitted with a second-order function to obtain the corresponding curve function: （2） Among them, the parameters a ∈ R , b ∈ R , the specific value is determined according to the discrete value of the symmetrical part of the corresponding magnetic flux distribution curve; The symmetry line and straight line of the two long sides of a single-turn coil h = h 0 coincides, the straight line where the two long sides lie h = h 1 and h = h 2 The magnetic flux values ​​at the two points where it intersects the magnetic flux curve are equal, , the magnetic flux inside the coil is , the output of the coil is 0, and the single-turn coil is at the origin. h 1 and h 2 is located on the straight line h = h Symmetrical points on both sides of 0; S6. Output sensitivity and linearity evaluation of single-turn receiving coil: When the single-turn coil moves from the origin along the symmetry line of the two short sides ∆h When the displacement is M D Changes occur, coil output M O Also changes accordingly, the output M O for: （3） Output and displacement of a single-turn coil ∆h There is a good linear relationship between them; Among them, the short side length of a single-turn coil is w= ( h 1 -h 2) is the sensitivity coefficient of the output, w The larger the value, the higher the corresponding sensitivity; S7. Determine the number of turns of the receiving coil n : Taking sensitivity, nonlinearity and range as optimization directions, the maximum sensitivity and minimum nonlinearity of the inductive coil under different ranges and the corresponding number of turns of these two cases are calculated. The number of turns of the receiving coil required for the design of nonlinearity and maximum sensitivity is selected. n ; S8, x, y Direction decoupling performance optimization: Select the length of the innermost long side l For receiving coils of different specifications, with other parameters being the same and determined, the magnetic flux inside the coil is calculated using formula (1): M D ,as well as M D Displacement in the long side direction ∆l The influence of formula (2) and formula (3) are used to calculate the displacement of receiving coils of different specifications in the short side direction. ∆h , the offset in the long side direction is ∆l The long side offset in the case of ∆l The results of the influence on the displacement sensitivity in the short side direction are used to find the minimum value of the innermost long side length that satisfies the decoupling performance of the receiving coil in two directions.

3. An inductive displacement sensor according to claim 2, characterized in that: The length of the shortest side of the receiving coil w max The constraints are: （4）。 4. An inductive displacement sensor according to any one of claims 1 to 3, characterized in that: The base plate is made of a metal plate.

5. An inductive displacement sensor according to any one of claims 1 to 3, characterized in that: The excitation coil is a double-layer structure that is superimposed and connected in series end to end.

6. An inductive displacement sensor according to any one of claims 1 to 3, characterized in that: The innermost wire ends of the four receiving coils are connected in parallel and symmetrically arranged at x The two outermost wire ends of the two receiving coils on both sides of the axis serve as y The signal output terminal of the direction displacement is symmetrically set at y The two outermost wire ends of the two receiving coils on both sides of the axis serve as x Directional displacement signal output terminal.

7. A data processing system using the inductive displacement sensor according to claim 6, characterized in that: A signal source for applying an excitation signal to an excitation coil, and y The two signal output terminals of the direction displacement are connected y Direction signal processing circuit, and x The two signal output terminals of the direction displacement are connected x Direction signal processing circuit, respectively y Direction signal processing circuit and x an analog-to-digital converter connected to the output end of the direction signal processing circuit and a central processing unit connected to the digital-to-analog converter; When the excitation signal is fed into the excitation coil, the receiving coil has a xy When the displacement is within the plane, the symmetry is set at x The two receiving coils on both sides of the shaft output induction signals to y Direction signal processing circuit, symmetrically arranged at y The two receiving coils on both sides of the shaft output induction signals to x Direction signal processing circuit: The signal processing circuits of the two directions process the sensing signals respectively and input them into the digital-to-analog converter, and then the digital-to-analog converter converts the analog signals into corresponding digital signals and transmits them to the central processing unit.

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