CN109141325B - Non-contact measuring method and device for coating thickness on metal surface - Google Patents
Non-contact measuring method and device for coating thickness on metal surface Download PDFInfo
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- CN109141325B CN109141325B CN201811074878.4A CN201811074878A CN109141325B CN 109141325 B CN109141325 B CN 109141325B CN 201811074878 A CN201811074878 A CN 201811074878A CN 109141325 B CN109141325 B CN 109141325B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/026—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring distance between sensor and object
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
- G01B7/023—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring distance between sensor and object
Abstract
A non-contact measuring method and device for the thickness of the coating on the metal surface are disclosed, which correspondingly select a non-contact eddy current detection probe for calibration according to the size of a piece to be tested so as to obtain a relation curve between eddy current signals and corresponding lift-off distances and establish an eddy current distance measurement model of the metal substrate of the piece to be tested, obtain the eddy current signals of an eddy current sensor in the detection process, calculate the distance from the central point of the eddy current area of the metal substrate to the end face of the eddy current probe according to the eddy current distance measurement model of the metal substrate of the piece to be tested, further measure the distance from the central point of the outer surface of the coating of the eddy current area to the plane where the projection point of a laser distance measurement sensor group is located, namely the detection plane pi according to the laser distance. The invention can realize stable and reliable nondestructive non-contact detection, has simple data processing method, and is easy to implement on-line detection, thereby saving a large amount of economic cost and time.
Description
Technical Field
The invention relates to a technology in the field of machining, in particular to a non-contact measuring method and a non-contact measuring device for the thickness of a coating layer on a metal surface based on an eddy current sensor and a laser ranging sensor.
Background
In engineering applications, in order to increase the burning resistance and corrosion resistance of metal containers and pipelines, ablation-resistant and corrosion-resistant non-metallic materials are generally adhered or sprayed on the inner surface or the outer surface of the metal containers and pipelines. The thickness of these coatings plays an extremely important role in the characterization, quality control, workability, and stability, reliability, and life of the entire test piece.
The existing coating layer thickness nondestructive detection methods include a magnetic thickness measurement method, an ultrasonic thickness measurement method, a laser thickness measurement method and an eddy current thickness measurement method. Among the methods, eddy current thickness measurement is widely used with the advantages of no need of a coupling agent, high sensitivity, simple structure, no influence of an oil stain medium, high detection speed, easiness in realization of automation and the like, is commonly used in the measurement of the thickness of a coating layer on the surface of a planar metal substrate, a probe is tightly attached to the surface of the coating layer in the measurement process, the lifting distance of the probe is the thickness of the coating layer, the method is generally used for the measurement of a dry coating layer, is basically contact-type measurement, sometimes causes the damage of the surface of the coating layer, and for a curved substrate, the finally obtained thickness value comprises datum deviation caused by curvature.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a non-contact measuring method and a non-contact measuring device for the thickness of a coating layer on a metal surface.
The invention is realized by the following technical scheme:
the invention relates to a non-contact measuring method of the thickness of a metal surface coating, which correspondingly selects a non-contact eddy current detection probe for calibration according to the size of a to-be-tested piece so as to obtain a relation curve of eddy current signals and corresponding lift-off distance and establish an eddy current distance measurement model of a metal matrix of the to-be-tested piece, obtains the eddy current signals of an eddy current sensor in the detection process, calculates the distance from the central point of the eddy current area of the metal matrix to the end face of the eddy current probe according to the eddy current distance measurement model of the to-be-tested piece, further measures the distance from the central point of the outer surface of the coating of the eddy current area to the plane where the projection point of a laser distance measurement sensor group is positioned, namely the detection plane pi according to the laser distance.
The non-contact eddy current detection probe is a shielding probe but not limited to the shielding probe.
Correspondingly selecting an eddy current detection probe according to the size of a to-be-detected test piece: when the measured surface is a plane, the diameter of the measured surface is more than 1.5 times of the diameter of the head of the probe by taking a point which is opposite to the central line of the probe as a center; when the measured surface is the arc surface of a cylindrical cylinder and the center line of the probe is orthogonal to the axis, the diameter of the cylinder is generally required to be more than 3 times of the diameter of the probe.
The calibration refers to: changing the lifting distance every 0.1mm to obtain eddy current signals, namely voltage or current analog quantity, output by the eddy current sensor at different lifting distances; calibrating the eddy current signal and the lift-off distance through a multimodal Gaussian fitting function, and establishing a metal matrix eddy current distance measurement model to be tested, wherein the multimodal Gaussian curve is as follows:
wherein: a isi、bi、ciIs constant, x is the eddy current signal, and y is the calibrated lift-off distance.
The calibration preferably performs detection of the eddy current signal after preheating the eddy current sensor, so as to reduce the influence of the ambient temperature on the measurement result.
The relation curve refers to: the eddy current signal in the form of a voltage or current is a function of the actual lift-off distance.
The metal matrix eddy current distance measurement model of the to-be-tested piece takes an eddy current signal of the to-be-tested piece as input, and takes an actual lift-off distance as output.
The central point of the metal matrix eddy current region is as follows: the interface of the metal matrix/the coating layer is specifically as follows: when the eddy current probe is loaded with a sine wave current exciting coil to be close to the surface of the metal matrix test piece, eddy current is generated in the test piece to be tested due to the influence of an alternating magnetic field around the coil, the central point of the outer surface of the area corresponds to the distance from the central point to the end face of the eddy current probe, and particularly, an eddy current signal is obtained through an eddy current sensor and substituted into an eddy current distance measurement model to calculate the distance from the central point of the eddy current area of the metal matrix to the end face of the eddy current probe.
The distance between the central point of the outer surface of the coating and the plane where the projection point of the laser ranging sensor group is located is approximately obtained in a three-point and one-surface mode according to the distance between the projection axis of the laser ranging sensor and the contact point of the coating surface, namely the distance between the characteristic point and the distance between the central point of the outer surface of the coating of the metal matrix eddy current area and the detection plane pi, wherein the distance between the detection plane pi and the end face of the eddy current probe is a fixed value.
The thickness of the coating layer on the surface of the metal matrix is obtained by subtracting the distance from the central point of the coating layer on the eddy current region of the metal matrix to the end face of the eddy current probe from the distance from the central point of the coating layer on the eddy current region of the metal matrix to the detection plane pi and the distance from the detection plane pi to the end face of the probe of the eddy current sensor.
The invention relates to a system for realizing the method, which comprises the following steps: non-contact eddy current inspection probe and encircle its three laser rangefinder sensor that sets up, wherein: the three laser distance measuring sensors are symmetrically arranged on the periphery of the eddy current sensor at an included angle of 120 degrees and used for detecting and outputting the distance from the central point of the coating layer surface of the metal matrix eddy current area to a detection plane pi, and the thickness of the coating layer on the metal surface is calculated by combining the eddy current signal output by the eddy current sensor.
Technical effects
Compared with the prior art, the method solves the problems of large error and low precision of the distance measurement of the curved metal matrix through the eddy current distance measurement model; the three laser ranging sensors are utilized to form an approximate measuring surface, stable and reliable nondestructive non-contact detection can be realized in the process of measuring the thickness of the coating layer on the surface of the metal substrate, the data processing method is simple, and online detection is easy to implement, so that a large amount of economic cost and time are saved.
Drawings
FIG. 1 is a block diagram of a circuit configuration of a measuring apparatus according to an embodiment;
FIG. 2 is a schematic diagram of a measuring device constructed in accordance with an embodiment;
FIG. 3 is a flow chart of eddy current ranging model calibration used in the present invention;
FIG. 4 is a schematic diagram of the eddy current ranging principle used in the present invention;
fig. 5 is a schematic diagram illustrating a principle of ranging by the laser ranging sensor group according to the embodiment.
Detailed Description
As shown in fig. 1 and fig. 2, the on-line thickness measuring device for the heat insulating layer of the cylinder according to the present embodiment includes: eddy current sensor 1, laser rangefinder sensor group 2 and the master control calculation subsystem 3 of the built-in ARM chip circuit who links to each other with it respectively, wherein: a transmitter for directly outputting 4-20 mA after linearization and normalization processing of displacement signals collected by the sensors is arranged between the eddy current sensor 1 and the main control computing subsystem 3, a preamplifier for amplifying voltage signals is arranged between each laser ranging sensor in the laser ranging sensor group 2 and the main control computing subsystem 3, and the output ends of the transmitter and the preamplifier are respectively connected with an analog-to-digital conversion unit in the main control computing subsystem 3.
The ARM chip circuit analyzes and comprehensively processes all sampled data to obtain the thickness of a coating layer of a measured point, a control signal can be provided for the displacement servo system through the digital output driving circuit, and meanwhile, each limit switch signal can be received through the digital input driving circuit.
The main control computing subsystem 3 is preferably further connected with an ethernet interface circuit, an RS485 interface circuit, and a CAN Bus interface circuit, and is used for digital communication, and any one digital interface CAN be selected to realize communication between the measuring device and an upper control system, including sending control decision information to the upper control system, sending measurement status and data to the upper control system, receiving instructions from the upper control system, and the like.
The on-line measuring device of heat insulation layer thickness in further be equipped with the driver that is used for providing control signal and gathers the real-time operating mode of motor to the displacement servo drive motor of automatic equipment of polishing, wherein: the main control computing subsystem 3 receives an instruction of an upper control system through a digital input driving circuit, obtains real-time working condition information of the motor through a driver, sends a motor control signal, and outputs a reset signal to the driver when a limit switch signal is triggered so as to control the motor to rotate to a standby position.
The embodiment relates to a measuring method of the device, which comprises the following steps:
step 1: as shown in fig. 3, the eddy current distance measurement calibration is performed on the metal matrix, and the method specifically comprises the following steps:
1.1) selecting a proper eddy current sensor according to the size, the measurement precision and the detection frequency of a cylinder to be measured, determining an initial distance according to the measurement range of the sensor, and initializing a calibration device;
1.2) lifting off within the measuring range, changing the lifting-off distance every 0.1mm, measuring 5 times of output voltage signals for each lifting-off distance in order to reduce measuring errors in operation, taking the average value of the output voltage signals, fitting the vortex signals and the lifting-off distances by selecting a multimodal Gaussian function, and establishing a vortex distance measuring model of the to-be-tested piece.
The multimodal gaussian function is:
wherein: a isi、bi、ciIs constant, x is the eddy current signal, and y is the calibrated lift-off distance.
And obtaining a prediction output according to the vortex distance measurement model, comparing the prediction output with the real lift-off distance to obtain a prediction error, further judging that when the error exceeds a specified range, updating model parameters according to the prediction error of the vortex distance measurement model, and otherwise, stopping calculation and updating the vortex distance measurement model to complete the establishment of the vortex distance measurement model.
The updating means that: and adjusting the undetermined parameters in the multimodal Gaussian function according to the criterion of reducing the prediction error.
Step 2: as shown in fig. 2, the distance measurement model of the non-contact eddy current sensor is obtained, an eddy current signal output by the eddy current sensor is obtained, the eddy current distance measurement model obtained in step 1 is called, and the distance from the central point C of the eddy current area of the metal matrix to the end face a of the eddy current probe is calculated.
And step 3: as shown in fig. 1, the measured distances are output by three laser ranging sensors in a voltage manner, and in order to ensure the optimal measurement accuracy, the output voltage is preferably adjusted to the range position of the master control computing subsystem 3, and the distance between the detection plane pi and the end face of the eddy current probe is obtained by three points and one surface.
The three-point one-surface mode is shown in fig. 5, and specifically comprises the following steps: three laser ranging sensors can measure the projection point M in the measuring processi(i ═ 1, 2, 3) and the corresponding three feature points Vi(i-1, 2, 3) by a distance Di(i is 1, 2, 3), so point Vi(i-1, 2, 3) has a z-coordinate of
Wherein:
the included angle between the projected light of the laser distance measuring sensor and the z-axis is provided, the radius of the circle E is R, and three characteristic points V can be obtained according to the geometric property of an equilateral trianglei(i-1, 2, 3) has x and y coordinates of
Since θ is 30 °, the characteristic point Vi(i-1, 2, 3) has coordinates of
And 4, step 4: the main control computing subsystem 3 obtains a thickness Δ H of the coating layer facing the central point of the eddy current probe, namely PC in fig. 2, according to the distance from the central point C of the metal matrix eddy current region to the end face a of the eddy current probe obtained in the step 2 and the distance from the central point P of the outer surface of the coating layer of the matrix eddy current region obtained in the step 3 to the detection plane pi, where: and delta L is the distance between the detection plane pi and the end face A of the probe of the eddy current sensor.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (11)
1. A non-contact measuring method for the thickness of a coating on a metal surface is characterized in that a non-contact eddy current detection probe is correspondingly selected according to the size of a piece to be tested for calibration, so that a relation curve of eddy current signals and corresponding lift-off distances is obtained, an eddy current distance measurement model of the metal matrix of the piece to be tested is established, eddy current signals of an eddy current sensor are obtained in the detection process, the distance from the central point of a vortex area of the metal matrix to the end face of the eddy current probe is calculated according to the eddy current distance measurement model of the metal matrix of the piece to be tested, the distance from the central point of the outer surface of the coating of the vortex area to the plane where a light projection point of a laser distance measurement sensor group is located is further measured according to the laser distance measurement sensor group, namely the;
the distance from the central point of the outer surface of the coating layer to the plane where the projection point of the laser ranging sensor group is located is obtained by the following method: three laser ranging sensors can measure the projection point M in the measuring processiI is 1, 2, 3, and corresponding three feature points ViA distance D betweeniTherefore point ViHas a z coordinate of
Wherein:
the included angle between the projection ray of the laser ranging sensor and the z-axis is formed, the radius of a circle E is r, and three characteristic points V are obtained according to the geometric property of an equilateral triangleiHave x and y coordinates of
Since θ is 30 °, the characteristic point ViThe coordinates of (a) are:
2. The method of claim 1, wherein the eddy current test probe is selected according to the size of the test object: when the measured surface is a plane, the diameter of the measured surface is more than 1.5 times of the diameter of the head of the probe by taking a point which is opposite to the central line of the probe as a center; when the measured surface is the arc surface of a cylindrical cylinder and the center line of the probe is orthogonal to the axis, the diameter of the cylinder is generally required to be more than 3 times of the diameter of the probe.
3. The method of claim 1, wherein said calibrating comprises: changing the lifting distance every 0.1mm to obtain eddy current signals, namely voltage or current analog quantity, output by the eddy current sensor at different lifting distances; calibrating the eddy current signal and the lift-off distance through a multimodal Gaussian fitting function, and establishing a metal matrix eddy current distance measurement model to be tested, wherein the multimodal Gaussian curve is as follows:
wherein: a isi、bi、ciIs constant, x is the eddy current signal, and y is the calibrated lift-off distance.
4. A method according to claim 1 or claim 3, wherein calibration is performed by preheating the eddy current sensor and then detecting the eddy current signal to reduce the effect of ambient temperature on the measurement.
5. The method of claim 1, wherein said relationship is: the eddy current signal in the form of a voltage or current is a function of the actual lift-off distance.
6. The method of claim 1, wherein the metal matrix vortex region center point is: the interface of the metal matrix/the coating layer is specifically as follows: when the eddy current probe is loaded with a sine wave current exciting coil to be close to the surface of the metal matrix test piece, eddy current is generated in the test piece to be tested due to the influence of an alternating magnetic field around the coil, the central point of the outer surface of the area corresponds to the distance from the central point to the end face of the eddy current probe, and particularly, an eddy current signal is obtained through an eddy current sensor and substituted into an eddy current distance measurement model to calculate the distance from the central point of the eddy current area of the metal matrix to the end face of the eddy current probe.
7. The method as claimed in claim 1, wherein the thickness of the coating on the surface of the metal substrate is obtained by subtracting the distance from the central point of the eddy current region of the metal substrate to the end face of the eddy current probe from the distance from the central point of the outer surface of the coating on the eddy current region of the substrate to the detection plane pi and the distance from the detection plane pi to the end face of the eddy current sensor probe.
8. An apparatus for implementing the method of any preceding claim, comprising: non-contact eddy current inspection probe and encircle its three laser rangefinder sensor that sets up, wherein: the three laser distance measuring sensors are symmetrically arranged on the periphery of the eddy current sensor at an included angle of 120 degrees and used for detecting and outputting the distance from the central point of the coating layer surface of the metal matrix eddy current area to a detection plane pi, and the thickness of the coating layer on the metal surface is calculated by combining the eddy current signal output by the eddy current sensor.
9. The apparatus of claim 8, further comprising a master computing subsystem with built-in ARM chip circuitry coupled to the eddy current sensor and the laser range sensor, respectively, wherein: a transmitter for directly outputting 4-20 mA after linearization and normalization processing of displacement signals collected by the sensors is arranged between the eddy current sensor and the master control computing subsystem, a preamplifier for amplifying voltage signals is arranged between each laser ranging sensor in the laser ranging sensor group and the master control computing subsystem, and the output ends of the transmitter and the preamplifier are respectively connected with an analog-to-digital conversion unit in the master control computing subsystem.
10. The device as claimed in claim 9, wherein the main control computing subsystem is further connected with an ethernet interface circuit, an RS485 interface circuit and a CANBus interface circuit, and is used for digital communication, and the device for realizing the non-contact measurement method of the thickness of the metal surface coating layer is communicated with an upper control system by selecting any one digital interface, and comprises the steps of sending control decision information to the upper control system, sending measurement state and data to the upper control system, and receiving instructions from the upper control system for operation.
11. The apparatus of claim 9, further comprising a driver for providing control signals to a displacement servo drive motor of the automatic polishing apparatus and for collecting real-time operating conditions of the motor, wherein: the main control computing subsystem receives an instruction of the upper control system through the digital input driving circuit, obtains real-time working condition information of the motor through the driver and sends a motor control signal, and when the limit switch signal is triggered, the main control computing subsystem outputs a reset signal to the driver so as to control the motor to rotate to a standby position.
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| CN111486782A (en) * | 2019-01-26 | 2020-08-04 | 保定长空科技有限公司 | Glass steel coating film thickness non-contact monitoring facilities |
| CN110260778A (en) * | 2019-07-19 | 2019-09-20 | 华中科技大学无锡研究院 | Chamfering measurement method and device based on electromagnetic principle |
| JP2021028535A (en) * | 2019-08-09 | 2021-02-25 | 三桜工業株式会社 | Pipe joint and tube with pipe joint |
| CN111023960B (en) * | 2019-12-31 | 2021-04-27 | 新余学院 | Non-contact paint film thickness nondestructive testing system and method based on transparent conductive film electrode material |
| CN113514539A (en) * | 2021-04-12 | 2021-10-19 | 爱德森（厦门）电子有限公司 | Method and device for detecting temperature resistance and relative expansion coefficient of metal surface coating |
| CN114383493B (en) * | 2022-02-28 | 2024-01-30 | 中国工程物理研究院总体工程研究所 | Non-contact metal surface non-conductive coating thickness measuring method |
| CN116242239B (en) * | 2022-12-09 | 2023-07-28 | 江汉大学 | Method and device for detecting thickness of nodular cast iron pipe |
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| CN104748666A (en) * | 2013-12-30 | 2015-07-01 | 中核武汉核电运行技术股份有限公司 | Deep defect quantifying method based on eddy rotating probe signal |
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