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CN-121804307-B - Eddy current sensor calibration method for small-diameter metal ball

CN121804307BCN 121804307 BCN121804307 BCN 121804307BCN-121804307-B

Abstract

The application relates to the technical field of eddy current sensors and voltage calibration. The calibration method for the eddy current sensor of the small-diameter metal ball comprises four parts of coordinate system establishment, calibration data acquisition, calibration sample set construction and calibration equation coefficient optimization. According to the application, through innovative coordinate system definition and position parameterization and combination of an intelligent optimization algorithm, a voltage-position relation model capable of accurately representing the fact that the spherical center of the small-diameter metal sphere deviates from the actual effective measuring axis of the sensor is successfully established, and nonlinear measuring errors caused by the fact that the spherical center is eccentric, the surface is high in curvature and the axis deviation of the sensor is effectively compensated.

Inventors

  • LIANG HONGQIN
  • JIANG LEI
  • ZHONG QIHONG
  • PENG JIA
  • WANG JUNJIE
  • ZHANG YALI

Assignees

  • 西南交通大学

Dates

Publication Date
20260508
Application Date
20260309

Claims (9)

  1. 1. The calibration method of the eddy current sensor for the small-diameter metal ball is characterized by comprising the following steps of: The method comprises the steps of 1, constructing a calibration coordinate system O C -X C Y C Z C ,X C axis, a Y C axis and a Z C axis which are parallel to the motion direction of the degree of freedom of a calibration instrument by taking the lowest measuring range point on the central axis of an eddy current sensor as an origin O C ; Constructing a measurement coordinate system O S -X S Y S Z S by taking a point, in the range of the eddy current sensor, of which the spherical center coordinate of the small-diameter metal sphere is closest to the plane of the eddy current sensor probe as an origin O S , and taking the direction of the maximum voltage change gradient as a Z S axis; the relative position relation between the sphere center of the small-diameter metal sphere and the electric vortex sensor is described by l and r; Wherein l represents the distance between the center of the small-diameter metal ball and the X S O S Y S plane in the measurement coordinate system, and r represents the distance between the center of the small-diameter metal ball and the Z S axis in the measurement coordinate system; constructing a voltage-position calibration equation according to the position relation between the spherical center of the small-diameter metal sphere and the center of the eddy current sensor; Step 2, moving the small-diameter metal ball along a preset calibration track in a calibration coordinate system to obtain a plurality of calibration points and voltage readings corresponding to the calibration points; Step 3, taking the calibration point and the voltage reading corresponding to the calibration point as a calibration sample, and obtaining all the calibration samples to obtain a calibration sample set; Step 4, dynamically updating fitting coefficients in the voltage calibration equation by adopting a particle swarm algorithm to obtain an accurate voltage-position calibration equation; the voltage-position calibration equation is: ; k 1 ~k 10 are 10 fitting coefficients to be calibrated.
  2. 2. The method for calibrating an eddy current sensor for a small diameter metal ball according to claim 1, wherein step 2 comprises the steps of: Step 21, dividing calibration points of the effective range of the eddy current sensor according to fixed intervals delta X, delta Y and delta Z on an X C axis, a Y C axis and a Z C axis of a calibration coordinate system to form equidistant calibration points; step 22, taking a Z C axis as a starting row of small-diameter metal balls, and sequentially passing through equidistant calibration points; Step 23, acquiring the readings of the eddy current sensor of the small-diameter metal ball at each equidistant calibration point.
  3. 3. The method according to claim 2, wherein in step 23, a voltage threshold is preset, readings of the small-diameter metal ball near the equidistant calibration points are monitored in real time, and when the readings of the eddy current sensor are smaller than the voltage threshold, the readings of the eddy current sensor at the moment are taken as effective calibration voltages of the calibration points, and an average value of the effective calibration voltages is taken as the calibration voltages of the calibration points.
  4. 4. The method for calibrating an eddy current sensor for a small-diameter metal ball according to any one of claims 1 to 3, wherein step 4 comprises the steps of: Step 41, loading a voltage-position calibration equation, defining a definition field Uj of a fitting coefficient kj , wherein j represents an index of the fitting coefficient, and j epsilon {1, 2..10 }, and Uj represents a definition field of a j-th fitting coefficient; Step 42, randomly taking values of each fitting coefficient in a definition domain to generate 1 particle xi , randomly generating N particles to obtain an initialized population, wherein i represents the index of the particles; , representing the value of the jth fitting parameter in the ith particle; ; Step 43, defining a fitness function F (x), and enabling the calculated voltage and the actually measured voltage error of each calibration sample to be minimum after the particle swarm parameters are substituted into a calibration equation; and 44, calculating the fitness function value of each particle, and iterating according to the fitness function value of the population until the preset termination condition is reached.
  5. 5. The method of calibrating an eddy current sensor for a small diameter metal ball as recited in claim 4, wherein step 44 comprises the steps of: Step 441, calculating fitness function values F ( xi ) of all particles in the initialized population N 0 to obtain probability of each particle being selected as a cross population , Indicating particles Probability of selection as cross population; ; ; representing the sum of fitness function values of all particles; step 442, based on the probability of each particle Mapping each particle into a closed circle, wherein the area of a sector area mapped by each particle is ; ; Representing the total area of the circle; 443, randomly generating discrete points with the same number of particles in the population at the t time of iteration in a circle, and extracting particles corresponding to the area where each discrete point is located to obtain a cross population; Step 444, randomly pairing particles in the crossed population in pairs, and randomly generating a cross point G for the paired particles xa 、 xb ; ; Representing the j-th fitting parameter in particle xa ; ; representing the j-th fitting parameter in particle xb ; Crossing particles xa 、 xb at crossing point G to form new particles ca 、 cb ; ; The G-th fitting parameter in ca is shown; ; the G-th fitting parameter in cb is shown; Step 445 fitting parameters to the new particles Based on the update probabilities upj , a choice is made as to whether to perform the update, and if not, the parameters are fitted For the original value, if an update is needed, the update formula is as follows: ; representing fitting parameters Updated values Lj represents the lower limit of the jth fitting parameter, Uj represents the jth fitting parameter The upper limit of the fitting parameters is set, Representing random numbers, wherein the range is 0-1; step 446, repeatedly executing steps 442-445 until the termination condition is reached.
  6. 6. The method of calibrating an eddy current sensor for a small diameter metal ball as recited in claim 5, wherein in step 444, the random intersection point G is generated as follows: 4441, generating an initial selection factor p 1 ~p 10 for all fitting parameters k 1 ~k 10 to generate crossing points, wherein the initial selection factor gradually increases; Step 4442, updating the selection factor p G for the cross point G selected last time during each iteration to obtain a new selection factor p G '; ; Wherein, the Representing the number of particles in the population at the t-th iteration, The number of particles in the population at each iteration, Representing the selection factor after the update, Represents the selection factor before update, G represents the index of the selection factor, g= {1, 2,..10 }; 4443, replacing the new selection factor p G ' with the selection factor of the corresponding fitting parameter, and randomly selecting a new fitting parameter as an intersection point based on a wheel disc algorithm; The probability of the fitting parameter j being selected as the intersection is Ptj ; ; Representing the selection factor of the G-th fitting parameter at the t-th iteration.
  7. 7. The method of calibrating an eddy current sensor for a small diameter metal ball as recited in claim 6, wherein in step 445, the update probability upj is related to the number of iterations and the number of items; ; Wherein t represents the iteration number, l represents the sum of the number of terms of the fitting parameter, e represents a natural constant, and f (t) represents an iteration function; When t is less than 80, the number of times, ; When the t is more than or equal to 120 and more than or equal to 80, ; When T is more than or equal to T >120, B 0 is a constant factor.
  8. 8. The method of calibrating an eddy current sensor for a small diameter metal ball as recited in claim 7, wherein the fitness function value F ( xi ) in step 441 is the mean square error of all samples; ; Where q represents the sample index, R represents the total number of samples, Representing the voltage corresponding to the index point of the q-th sample, The voltage calculated for the voltage-position calibration equation.
  9. 9. The method according to claim 7, wherein the termination condition is that the optimal direction change gradient for the number of iterations reaching a preset threshold or fitness function value is smaller than a preset value.

Description

Eddy current sensor calibration method for small-diameter metal ball Technical Field The application relates to the technical field of eddy current sensors and voltage calibration, in particular to an eddy current sensor calibration method aiming at a small-diameter metal ball. Background The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. The eddy current sensor operates based on the eddy current effect. The exciting coil in the probe is fed with high-frequency alternating current to generate alternating magnetic field. When the magnetic field acts on the surface of the metal ball, closed annular current, namely electric vortex, is induced on the surface layer of the ball. The eddy current itself generates a reverse magnetic field in a direction opposite to the original magnetic field, thereby changing the equivalent impedance (mainly represented by the change of inductance and resistance) of the probe coil. The change of the impedance of the coil (which is usually converted into a voltage signal to be output) is detected by a measuring circuit, so that the distance information between the probe and the surface of the metal ball can be reflected. When a plane or a metal ball with a large diameter (usually 5-10 times of the diameter of the probe) is measured, the magnetic induction lines are distributed relatively uniformly, eddy current coupling is stable, and a relatively linear corresponding relation can be established between the output voltage of the sensor and the distance, so that the distance measurement with relatively high precision is realized. When measuring small diameter metal balls (the diameter is smaller than 5 times of the diameter of the probe), the surface curvature of the small balls is large, so that the magnetic field generated by the probe is seriously unevenly distributed on the spherical surface, and the eddy current coupling area and the strength are obviously changed. Especially when the centre of the sphere of the pellet is not exactly aligned to the theoretical axis of the sensor, the local curvature at the measurement point will further increase, so that a complex nonlinear relationship between the sensor output voltage and the real distance is presented, resulting in significant measurement errors. And the current vortex sensor itself may cause incomplete coincidence between a theoretical central axis and an actual effective measurement axis due to factors such as zero drift, coil material difference, non-uniformity of a winding process, non-ideal internal magnetic field distribution and the like. This axis deviation directly affects the position determination of the measurement point relative to the center of the sphere, further exacerbating the deviation of the output voltage from the ideal voltage. At present, an accurate relation model between the spatial position (comprising the distance and the eccentric amount) of a small-diameter metal ball (especially in the case of off-axis spherical center) and the output voltage of the eddy current sensor is not effectively established. At the same time, a mature compensation method is lacking to effectively reduce the nonlinear influence of the high curvature surface and the axis deviation of the sensor on the measurement voltage. Disclosure of Invention The summary of the application is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. The summary of the application is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Some embodiments of the present application provide an eddy current sensor calibration method for a small-diameter metal ball, so as to solve the technical problems mentioned in the background section above. As a first aspect of the present application, some embodiments of the present application provide an eddy current sensor calibration method for a small diameter metal ball, comprising the steps of: The method comprises the steps of 1, constructing a calibration coordinate system O C-XCYCZC,XC axis, a Y C axis and a Z C axis which are parallel to the motion direction of the degree of freedom of a calibration instrument by taking the lowest measuring range point on the central axis of an eddy current sensor as an origin O C; Constructing a measurement coordinate system O S-XSYSZS by taking a point, in the range of the eddy current sensor, of which the spherical center coordinate of the small-diameter metal sphere is closest to the plane of the eddy current sensor probe as an origin O S, and taking the direction of the maximum voltage change gradient as a Z S axis, wherein the O S and the central axis are not collinear; the relative position relation between the sphere center of the small-diameter metal sphere and the electric vortex