CN118089558A - Terahertz-based coating thickness detection method and system - Google Patents

Abstract

The invention relates to the technical field of thickness detection, and discloses a terahertz-based coating thickness detection method and a terahertz-based coating thickness detection system, wherein the method comprises the following steps: establishing a robot base coordinate system, and calibrating a mapping relation of a flange center point; calibrating the mapping of the laser ranging sensor and the flange coordinate system by a planar method; determining the detection distance of a laser ranging sensor by using a terahertz calibration plate; detecting a detected object and obtaining modeling data; the robot is controlled to locate and collect local plane data, and the local plane data is compared with the normal vector of the measured object, and the robot is automatically adjusted; judging whether to adjust the position of the robot according to the angle difference value; collecting environment information and correcting a measurement distance, and comparing the measurement distance with a detection distance to obtain a final measurement distance; and finally, carrying out terahertz time-domain spectrum measurement according to the final measurement distance. The invention has the advantages of automation, high precision, non-contact and the like, improves the precision and the degree of automation of the thickness measurement of the coating, and reduces the technical dependence of operators.

Description

Terahertz-based coating thickness detection method and system

Technical Field

The invention relates to the technical field of thickness detection, in particular to a terahertz-based coating thickness detection method and system.

Background

Protective coatings are commonly used in automotive, marine, aerospace manufacturing and other applications. The coating process is complicated, and the detection process is complicated. Wherein coating thickness is an important indicator for characterizing the quality and integrity of the coating. If the thickness of the coating does not meet the specified requirements, the properties of corrosion resistance, rust resistance, attractive appearance and the like of the product are directly affected, so that various coating defects are caused, and the effective service life of the coating is directly affected.

The traditional coating thickness measuring technology comprises a magnetic induction thickness measuring method, an eddy current thickness measuring method, an ultrasonic thickness measuring method, a ray thickness measuring method and the like, and the traditional coating thickness measuring technology has some defects in practical application. The magnetic thickness measurement method is sensitive to the performances of the geometric shape, the surface roughness, the magnetic permeability, the conductivity and the like of the test sample; the ultrasonic detection method is suitable for thinner paint film coatings, has low laser signal-to-noise ratio, is difficult to stably use for a long time, and has higher cost and complex operation. The radiometric method can use a radioactive source and has certain radiation hazard.

Terahertz waves are located between microwaves and infrared rays in electromagnetic wave spectrums, and have the unique advantages of strong penetrability, safety to human bodies and the like. Compared with the traditional coating detection means, the terahertz wave is safe to human bodies, the terahertz spectrum technology and the characteristics of terahertz pulse such as high transmittance and low scattering are utilized, the terahertz detection technology can be applied to the field of paint film coating thickness measurement, nondestructive measurement of the thickness of a multilayer paint film coating, evaluation of distribution uniformity, thickness distribution measurement, non-contact online measurement of the thickness of the paint film coating and the like are realized, and the test process is not limited by the electric or magnetic characteristics of a substrate. However, in the current technology of applying terahertz to thickness detection, a great deal of manual intervention is required, which results in lower automation degree of operation, limits the efficiency and repeatability of measurement, and the terahertz thickness measurement technology has higher requirements on the operation level of personnel, and easily causes that the detection result is interfered by the environment and lacks accuracy.

Therefore, there is a need to design a terahertz-based coating thickness detection method and system for solving the current problems.

Disclosure of Invention

In view of the above, the invention provides a terahertz-based coating thickness detection method and a terahertz-based coating thickness detection system, which aim to solve the problems existing in the current coating thickness measurement technology.

In one aspect, the invention provides a terahertz-based coating thickness detection method, which comprises the following steps:

establishing a robot base coordinate system, calibrating a flange center point by using a probe method, and obtaining a mapping relation between the flange and the robot base coordinate system;

Calibrating the mapping relation between the laser ranging sensor and the flange coordinate system by using a planar method;

determining the detection distance of the laser ranging sensor by using a terahertz calibration plate with a coating;

After the detection distance is determined, detecting the detected object; when a detected object is detected, carrying out image acquisition on the detected object, acquiring modeling data of the detected object, and determining initial sampling coordinates according to the modeling data;

After the control robot moves to the initial sampling coordinate, collecting the vector direction and the measurement distance of the laser ranging sensor from the local plane of the sampling point, comparing the normal vector of the plane target of the measured object with the vector direction, and judging whether to adjust the robot according to the comparison result;

The method comprises the steps of obtaining an angle difference delta theta between a normal vector of the plane target and a vector direction, comparing the angle difference delta theta with a preset angle difference threshold value theta max, and judging whether to adjust the robot according to a comparison result;

when delta theta is larger than theta max, judging to adjust the robot;

When delta theta is less than or equal to theta max, judging that the robot is not regulated;

When judging whether to adjust the robot, collecting the measuring distance of the laser ranging sensor, collecting environmental information, correcting the measuring distance according to the environmental information, and obtaining the corrected measuring distance;

comparing the corrected measurement distance with the detection distance, and judging whether to adjust the corrected measurement distance according to the comparison result to obtain a final measurement distance;

and after the final measurement distance is obtained, controlling the terahertz sensor to conduct terahertz time-domain spectrum measurement.

Further, the establishing a robot base coordinate system, calibrating the center point of the flange by using a probe method and obtaining the mapping relation between the flange and the robot base coordinate system, includes:

Establishing a three-dimensional coordinate system by taking the robot base as an origin, and marking the three-dimensional coordinate system as a robot base coordinate system O _R;

Establishing a three-dimensional coordinate system by taking the central point of the flange plate as an origin, and marking the three-dimensional coordinate system as a flange coordinate system O _F;

And mounting a standard probe on the flange, and controlling the probe to contact the same contact under different postures to obtain the position conversion relation of the base coordinate system O _R and the flange coordinate system O _F in a three-dimensional space.

Furthermore, the calibrating the mapping relation between the laser ranging sensor and the flange coordinate system by using the planar method comprises the following steps:

Constructing a position parameter constraint equation of the laser ranging sensor through a calibration plane to construct a mapping relation between the laser ranging sensor and a flange coordinate system;

The construction of the position parameter constraint equation of the laser ranging sensor is achieved through the following formula:

An, bn, cn represent the plane equation coefficient of the calibration plate in the nth calibration, n is the calibration times, and n is more than 6; x0, y0, z0 are represented as spatial coordinates to be calibrated, and l _n represents a ranging value of the nth laser displacement sensor.

Further, after obtaining the mapping relation between the laser ranging sensor and the flange coordinate system, the determining the detection distance of the laser ranging sensor by using the terahertz calibration plate with the coating further includes:

Moving the robot to enable the terahertz sensor to be perpendicular to the terahertz calibration plate, collecting signal intensity Q0 of the terahertz sensor, comparing the signal intensity Q0 with a preset intensity threshold Qmin, and judging whether to adjust the position of the terahertz sensor according to a comparison result;

when Q0 is more than or equal to Qmin, judging that the position of the terahertz sensor is not adjusted, recording the coordinate position of the terahertz sensor at the moment, and obtaining a detection distance L1 according to the coordinate position;

when Q0 is smaller than Qmin, the position of the terahertz sensor is judged to be adjusted, the robot is moved until Q0 is larger than or equal to Qmin, the coordinate position of the terahertz sensor at the moment is recorded, and the detection distance L1 is obtained according to the coordinate position.

Further, when it is determined whether to adjust the robot, collecting a measurement distance of the laser ranging sensor and collecting environmental information, correcting the measurement distance according to the environmental information, and obtaining a corrected measurement distance, including:

The environment information comprises an environment temperature W0, an environment humidity S0 and a dust concentration H0;

Presetting a first preset environmental temperature W1, a second preset environmental temperature W2 and a third preset environmental temperature W3, wherein W1 is more than W2 and less than W3; presetting a first preset distance correction coefficient J1, a second preset distance correction coefficient J2 and a third preset distance correction coefficient J3, wherein J1 is less than J2 and less than J3; selecting a distance correction coefficient according to the magnitude relation between the environment temperature W0 and each preset environment temperature to correct the measured distance L0, and obtaining a corrected measured distance;

When W1 is less than or equal to W0 and less than W2, selecting the third preset distance correction coefficient J3 to correct the measured distance L0, and obtaining corrected measured distance L0×J3;

when W2 is less than or equal to W0 and less than W3, selecting the second preset distance correction coefficient J2 to correct the measured distance L0, and obtaining corrected measured distance L0×J2;

when W3 is less than or equal to W0, the first preset distance correction coefficient J1 is selected to correct the measured distance L0, and corrected measured distance L0×J1 is obtained.

Further, after the i-th preset distance correction coefficient Ji is selected to correct the measured distance L0 and the corrected measured distance l0×ji is obtained, i=1, 2,3, the measured distance is corrected according to the environmental information, and the corrected measured distance is obtained, which further includes:

presetting a first preset environmental humidity S1, a second preset environmental humidity S2 and a third preset environmental humidity S3, wherein S1 is more than S2 and less than S3; selecting a distance correction coefficient according to the magnitude relation between the ambient humidity S0 and each preset ambient humidity, and carrying out secondary correction on the corrected measured distance L0×Ji to obtain a measured distance after secondary correction;

when S1 is less than or equal to S0 and less than S2, selecting the third preset distance correction coefficient J3 to carry out secondary correction on the corrected measured distance L0×Ji to obtain a secondary corrected measured distance L0×Ji×J3;

when S2 is less than or equal to S0 and less than S3, selecting the second preset distance correction coefficient J2 to carry out secondary correction on the corrected measured distance L0×Ji to obtain a secondary corrected measured distance L0×Ji×J2;

And when S3 is less than or equal to S0, selecting the first preset distance correction coefficient J1 to carry out secondary correction on the corrected measured distance L0×Ji, and obtaining the measured distance L0×Ji×J1 after secondary correction.

Further, after selecting the i-th preset distance correction coefficient Ji to perform secondary correction on the corrected measurement distance l0×ji to obtain the measurement distance l0×ji×ji after the secondary correction, i=1, 2,3, and correcting the measurement distance according to the environmental information to obtain the corrected measurement distance, the method further includes:

Presetting a first preset dust concentration H1, a second preset dust concentration H2 and a third preset dust concentration H3, wherein H1 is more than H2 and less than H3; selecting a distance correction coefficient according to the size relation between the dust concentration H0 and each preset dust concentration, and carrying out three times of correction on the measured distance L0×Ji×Ji after the secondary correction to obtain the measured distance after the three times of correction;

when H1 is less than or equal to H0 and less than H2, selecting the third preset distance correction coefficient J3 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction to obtain the measured distance L0×Ji×Ji×J3 after the three times of correction;

When H2 is less than or equal to H0 and less than H3, selecting the second preset distance correction coefficient J2 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction to obtain the measured distance L0×Ji×Ji×J2 after the three times of correction;

when H3 is less than or equal to H0, selecting the first preset distance correction coefficient J1 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction, and obtaining the measured distance L0×Ji×Ji×J1 after the three times of correction.

Further, the measured distance L0×Ji×Ji after correction is corrected three times by selecting the i-th preset distance correction coefficient Ji, after the measurement distances l0×ji×ji×ji after three corrections are obtained, i=1, 2,3, comparing the corrected measurement distance with the detection distance, judging whether to adjust the corrected measurement distance according to the comparison result, and obtaining a final measurement distance, wherein the method comprises the following steps:

when 0.9L1 < L0.times.Ji.times.Ji.times.Ji.times.Ji < 1.1L1, it is determined that the corrected measurement distance is not adjusted, and the corrected measurement distance L0×Ji× Ji x Ji as the final measured distance;

When 0.9L1 is equal to or less than L0×Ji×Ji×Ji or when L0×Ji×Ji×Ji is not less than 1.1L1, it is determined to adjust the corrected measured distance, and taking the adjusted measured distance as the final measured distance.

Further, when it is determined to adjust the corrected measured distance, it includes:

when 0.9L1.ltoreq.L0.times.Ji.times.Ji.times.Ji.times.Ji, obtaining a distance difference Δl=l 0 XJiXJiXJiXJiXJi-0.9L1, and the distance difference delta L is regulated after being expressed in the flange coordinate system;

acquisition distance difference Δl= obtain the distance difference Δl= 1.1L1-L0XJiXJiXJiXJiXJi, and the distance difference delta L is regulated after being expressed in the flange coordinate system.

Compared with the prior art, the invention has the beneficial effects that: the coordinate system of the robot base is established, the center point of the flange plate is calibrated through a probe method, and the accurate mapping relation between the flange plate and the coordinate system of the robot base is realized. The mapping relation between the laser ranging sensor and the flange coordinate system is calibrated by adopting a planar method, so that the consistency of data during the action of the robot is improved, and the accuracy and the reliability of measurement are further improved. The terahertz calibration plate with the coating is used for determining the detection distance of the laser ranging sensor, so that calibration and inspection before measurement are realized, and the reliability of measurement data is improved. In the coating detection process, the measurement direction of the laser ranging sensor can be aligned with the normal vector on the surface of the measured object through automatic robot adjustment, so that the technical dependence of operators is reduced, and the measurement precision and stability are improved. Environmental information correction is introduced to correct the measured distance, so that the accuracy of measurement is improved, whether the corrected measured distance needs to be adjusted or not can be automatically judged, and the reliability of a final measurement result is ensured.

On the other hand, the application also provides a terahertz-based coating thickness detection system, which comprises:

control computer, robot and terahertz spectrometer; the control computer comprises a mapping unit, a calibration unit, an acquisition unit, a judgment unit, a correction unit, an adjustment unit and a measurement unit; the control computer is electrically connected with the robot and the terahertz spectrometer, the terahertz spectrometer is electrically connected with the robot, and the terahertz spectrometer is used for analyzing spectrum data;

The mapping unit is configured to establish a robot base coordinate system, calibrate a flange center point by using a probe method and obtain a mapping relation between the flange and the robot base coordinate system;

The mapping unit is further configured to calibrate the mapping relation between the laser ranging sensor and the flange coordinate system by using a planar method;

The calibration unit is configured to determine the detection distance of the laser ranging sensor by using a terahertz calibration plate with a coating;

The acquisition unit is configured to detect an object to be detected after the detection distance is determined; when a detected object is detected, carrying out image acquisition on the detected object, acquiring modeling data of the detected object, and determining initial sampling coordinates according to the modeling data;

The judging unit is configured to control the robot to move to the initial sampling coordinate, collect the vector direction and the measuring distance of the laser ranging sensor from the local plane of the sampling point, compare the normal vector of the plane target of the measured object with the vector direction, and judge whether to adjust the robot according to the comparison result;

The method comprises the steps of obtaining an angle difference delta theta between a normal vector of the plane target and a vector direction, comparing the angle difference delta theta with a preset angle difference threshold value theta max, and judging whether to adjust the robot according to a comparison result;

when delta theta is larger than theta max, judging to adjust the robot;

When delta theta is less than or equal to theta max, judging that the robot is not regulated;

The correction unit is configured to collect the measured distance of the laser ranging sensor and environmental information after judging whether to adjust the robot, correct the measured distance according to the environmental information and obtain the corrected measured distance;

The adjusting unit is configured to compare the corrected measured distance with the detection distance, and judge whether to adjust the corrected measured distance according to the comparison result to obtain a final measured distance;

the measuring unit is configured to control the terahertz sensor to conduct terahertz time-domain spectroscopy measurement after the final measurement distance is obtained.

It can be appreciated that the terahertz-based coating thickness detection method and system have the same beneficial effects and are not described in detail herein.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:

Fig. 1 is a flowchart of a terahertz-based coating thickness detection method provided by an embodiment of the invention;

fig. 2 is a schematic structural diagram of a terahertz-based coating thickness detection system according to an embodiment of the present invention;

fig. 3 is a functional block diagram of a control computer in the terahertz-based coating thickness detection system provided by the embodiment of the invention.

100, A control computer; 110. the mapping unit, 120, the calibration unit; 130. an acquisition unit; 140. a judging unit; 150. a correction unit; 160. an adjusting unit; 170. a measuring unit; 200. terahertz spectrometer; 300. a robot; 310. a laser ranging sensor; 320. a terahertz sensor; 400. an object to be measured.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.

With the rapid development of coating technology and modern industry, the industrialization degree is continuously improved, and the industrial materials used for coating and substrate are continuously improved and optimized in terms of cost and quality, so that higher requirements and more demands are placed on the control of the quality of the coating, and the method mainly comprises the following three aspects: (1) nondestructive testing requirements. The nondestructive coating thickness detection method has the advantages of high detection speed, no damage to the coating and the substrate, low measurement cost, and on-line, dynamic and real-time detection on the basis of nondestructive thickness measurement. (2) multiple coating thickness detection requirements. The important fields of automobiles, aerospace and the like are urgent in detection of the thickness of multiple coatings, a paint system is generally a multi-layer structure comprising a primer, a middle coating, a colored paint and a varnish, and the thickness of each layer has an important influence on the whole coating system. (3) safety requirements. The safety detection is critical, and the technical research and popularization and application of the coating thickness detection method are all carried out by taking the safety as a precondition.

The traditional detection technology has respective defects, and the novel terahertz detection technology is non-contact nondestructive detection, is safe to human bodies, can realize real-time and rapid measurement of the thickness of a plurality of coatings and the thickness of each single-layer coating, uniformity of the thickness of the coatings, defect distribution and the like, and has good application prospects in practical industrial application. Therefore, it is necessary to design a terahertz-based coating thickness detection method and system.

Referring to fig. 1-2, in some embodiments of the application, a terahertz-based coating thickness detection method includes:

Step S100: and establishing a robot base coordinate system, calibrating a central point of the flange by using a probe method, and obtaining a mapping relation between the flange and the robot base coordinate system. The mapping relation between the laser ranging sensor 310 and the flange coordinate system is calibrated by a planar method.

Step S200: the detection distance of the laser ranging sensor 310 is determined using a coated terahertz calibration plate.

Step S300: after the detection distance is determined, the object 400 is detected. When the object 400 is detected, image acquisition is performed on the object 400, modeling data of the object 400 is acquired, and initial sampling coordinates are determined according to the modeling data.

S400: after the control robot 300 moves to the initial sampling coordinates, the vector direction and the measurement distance of the laser ranging sensor 310 from the local plane of the sampling point are collected, the normal vector of the plane target of the measured object 400 is compared with the vector direction, and whether the robot 300 is adjusted is judged according to the comparison result.

The angle difference value delta theta between the normal vector of the plane target and the vector direction is obtained, the angle difference value delta theta is compared with a preset angle difference value threshold value theta max, and whether the robot 300 is adjusted is judged according to the comparison result.

When Δθ > θmax, it is determined to adjust the robot 300.

When Δθ is equal to or smaller than θmax, it is determined that no adjustment is performed on the robot 300.

S500: after determining whether to adjust the robot 300, the measured distance of the laser ranging sensor 310 is collected and environmental information is collected, and the measured distance is corrected according to the environmental information to obtain a corrected measured distance.

S600: and comparing the corrected measured distance with the detection distance, and judging whether to adjust the corrected measured distance according to the comparison result to obtain the final measured distance.

S700: when the final measurement distance is obtained, the terahertz sensor 320 is controlled to perform terahertz time-domain spectroscopy measurement.

Specifically, in the case of curved surface sample detection using a reflection-type terahertz wave transmission optical path, it is necessary to adjust the terahertz sensor 320 (including the light source and the receiver) to the normal pose of the sampling point local geometric plane at each sampling point. The preferred application introduces three laser positioners for the robot 300. The device applied by the application comprises a robot base, the robot 300 is fixedly connected to the base, a flange clamp is fixed at the other end of the robot 300, a terahertz sensor 320 is fixed in the center of the flange clamp, and a laser ranging sensor 310 is fixed around the terahertz sensor 320. The distance between the laser ranging sensors 310 is equal. And establishing a robot base coordinate system, and calibrating a center point of the flange by using a probe method to obtain a mapping relation between the flange and the robot base coordinate system. Meanwhile, the mapping relation between the laser ranging sensor 310 and the flange coordinate system is calibrated through a planar method, so that the accuracy of the measured space reference is ensured. Once the detection distance is determined, the effective measurement distance of the terahertz sensor 320 starts to be detected using the terahertz calibration plate. The terahertz sensor 320 is calibrated by means of a terahertz signal calibration plate with uniform coating thickness. The robot 300 is moved, so that the terahertz sensor 320 at the tail end of the industrial robot is perpendicular to the terahertz calibration plate, and the signal receiving condition of the terahertz sensor 320 is observed. And if the terahertz signal intensity is too low, adjusting the distance and the detection angle between the robot 300 and the terahertz calibration plate. When the terahertz return signal strength is higher than the reception threshold, the distance at this time is recorded as the detection distance because this distance data is obtained by the detection of the laser ranging sensor 310 and is also referred to as the detection distance of the laser ranging sensor 310. After determining the effective measurement distance of the terahertz sensor 320, the detection of the object 400 starts. If the object 400 is detected, image acquisition is performed and modeling data of the object 400 is acquired. These data are used to determine initial sampling coordinates. And selecting the closest point from the modeling data to the probe for measurement. After the control robot 300 moves to the initial sampling coordinate position, the laser ranging sensor 310 is used to measure the vector direction and the measurement distance of the local plane of the sampling point. Then, the normal vector of the plane target of the object 400 is compared with the direction of the measurement vector to determine whether the robot 300 needs to be adjusted. And calculating and obtaining an angle difference delta theta between the normal vector of the planar target and the direction of the measurement vector. The delta theta is compared to a preset angle difference threshold value θmax to determine whether adjustments to the robot 300 are needed. If Δθ > θmax, the robot 300 may perform position adjustment according to the angle difference to ensure accuracy in measurement. Environmental information is collected after the angle adjustment is correct, and then the measured distance is corrected by using the information. This is to ensure accuracy of measurement results in consideration of the influence of environmental factors on measurement. The corrected measured distance is compared with the previously obtained detected distance. It is determined whether further adjustments to the corrected measured distance are required to obtain a final measured distance. The terahertz sensor 320 is controlled to perform coating thickness measurement on the object 400 at the final measurement distance.

It will be appreciated that accurate measurement of coating thickness is achieved by using a number of techniques including robotic control, terahertz techniques, image processing and automated adjustment. Not only improves the accuracy of measurement, but also reduces the dependence of manual operation, and is favorable for high-precision and automatic coating quality detection.

In some embodiments of the present application, establishing a robot base coordinate system, calibrating a center point of a flange using a probe method and obtaining a mapping relationship between the flange and the robot base coordinate system, including: a three-dimensional coordinate system is established by taking a robot base as an origin, and is marked as a robot base coordinate system O _R. And (3) establishing a three-dimensional coordinate system by taking the central point of the flange plate as an origin, and marking the three-dimensional coordinate system as a flange coordinate system O _F. And mounting a standard probe on the flange, and controlling the probe to contact the same contact under different postures to obtain the position conversion relation of the base coordinate system O _R and the flange coordinate system O _F in a three-dimensional space.

Specifically, the established robot base coordinate system O _R is a three-dimensional coordinate system with the base of the robot 300 itself as the origin, the flange coordinate system O _F is a three-dimensional coordinate system with the center point of the flange fixture as the origin, the origin of the terahertz coordinate system O _C is taken at the start point of the terahertz emission beam, and 3 laser ranging sensors 310 are preferably installed around the terahertz sensor 320 and jointly determine a ranging sensor coordinate system O _S.

It can be understood that before calibrating the laser sensor, the standard probe is first replaced on the flange plate, and the same contact point is contacted under 4 different postures, so that the position conversion relationship between the robot base coordinate system O _R and the flange coordinate system O _F in the three-dimensional space is deduced. By accurately locating the relationship between the robot base coordinate system and the flange coordinate system, it is ensured that the robot 300 is able to accurately perform tasks in subsequent operations, particularly for coating thickness measurement tasks that require accurate positioning and control. Providing a reliable reference for subsequent coating thickness measurement, and helping to improve the accuracy and repeatability of measurement, thereby ensuring the consistency of product quality and performance.

In some embodiments of the present application, calibrating the mapping relationship between the laser ranging sensor 310 and the flange coordinate system by using a planar method includes: and constructing a mapping relation between the laser ranging sensor 310 and a flange coordinate system by calibrating a plane to construct a position parameter constraint equation of the laser ranging sensor 310.

The positional parameter constraint equation for laser ranging sensor 310 is constructed by:

An, bn, cn represent the plane equation coefficient of the calibration plate in the nth calibration, n is the calibration times, and n is more than 6; x0, y0, z0 are represented as spatial coordinates to be calibrated, and l _n represents a ranging value of the nth laser displacement sensor.

Specifically, the calibration method of the laser sensor can be classified into a planar calibration method and a spherical calibration method according to the difference of the calibration surfaces; according to the motion relation of the calibration surface, the following steps are respectively: the robot is static, the calibration surface moves, the robot moves, and the calibration surface is static. Because the motion error of the robot is generally larger than the measurement error of the laser sensor, if a calibration mode of the movement of the robot is adopted, the real-time pose of the robot is accurately positioned through additional measurement equipment, so that the calibration process is more complex; by adopting a robot static calibration scheme, the calculation of the fitting value of the calibration surface is easier by planar calibration than by spherical calibration. Therefore, the application adopts a plane calibration method under the static condition of the robot, and the position calibration of the laser ranging sensor 310 and the flange coordinate system O _F is completed in a mode that the robot 300 moves the plane calibration surface for a plurality of times.

Specifically, the laser ranging sensor 310 is installed under the flange coordinate system, the calibration plane is marked as pi, and the calibration of the laser ranging sensor 310 and the flange coordinate system of the fixture requires the construction of a position parameter constraint equation of the sensor through the calibration plane. When calibrating the laser ranging sensor 310, the position of the calibration surface pi is continuously changed, and the effective measurement distance value of each sensor on the plane is recorded. The position of each laser ranging sensor 310 is calculated in the same manner, so one of the solutions is taken as an example.

The laser source position of the laser ranging sensor 310 is in the flange coordinate system as followsMay be represented as a location parameter that is a function of the location parameter,

The unit vector of the laser irradiation direction isThe direction parameter is indicated as a direction parameter,

Let the laser point coordinates of the calibration plane beThe distance measurement value of the laser ranging is l,

The plane equation of the plane pi under the robot base coordinate system O _R can be calculated through the measuring equipment, the expression form of the calibration plane under the flange coordinate system O _F can be solved according to the translational rotation relation between O _R and the flange coordinate system O _F, and the expression form is recorded as

Π:Ax+By+Cz+D＝0；

Therein also has laser pointsBelonging to plane pi, so that the plane equation is satisfied, there can be

A(x₀+l·n_x)+B(y₀+l·n_y)+C(z₀+l·n_z)+D＝0；

The industrial robot needs to be limited from 6 degrees of freedom, in order to obtain accurate position parameters of the laser ranging sensor 310, the calibration times n of the calibration plane are made to be more than 6, after the calibration plane is moved n times, plane equations of n positions can be obtained,

And (3) deforming the equation set into a thread equation set form, and solving the calibration parameters (x ₀,y₀,z₀,n_x,n_y,n_z) of the equation set to finish the calibration of the laser coordinate sensor.

It can be understood that by accurately calibrating the position and direction of the sensor, measurement errors can be effectively eliminated, and the performance of the system is improved, so that the reliability and precision of the detection of the thickness of the coating are ensured, and the product quality and the production efficiency are improved. In addition, the static calibration mode of the robot 300 is adopted, compared with the moving mode of the robot 300, the calibration process is simplified, the complexity is reduced, and the calibration feasibility is improved.

In some embodiments of the present application, after obtaining the mapping relationship between the laser ranging sensor 310 and the flange coordinate system, determining the detection distance of the laser ranging sensor 310 using the terahertz calibration plate with the coating further includes: the mobile robot 300 is perpendicular to the terahertz calibration plate, acquires the signal intensity Q0 of the terahertz sensor 320, compares the signal intensity Q0 with a preset intensity threshold Qmin, and judges whether to adjust the position of the terahertz sensor 320 according to the comparison result. When Q0 is more than or equal to Qmin, the position of the terahertz sensor 320 is judged not to be adjusted, the coordinate position of the terahertz sensor 320 at the moment is recorded, and the detection distance L1 is obtained according to the coordinate position. When Q0 is smaller than Qmin, the position of the terahertz sensor 320 is judged to be adjusted, the robot 300 is moved until Q0 is larger than or equal to Qmin, the coordinate position of the terahertz sensor 320 at the moment is recorded, and the detection distance L1 is obtained according to the coordinate position.

Specifically, the terahertz sensor 320 is calibrated by means of a terahertz signal calibration plate with a uniform coating thickness. The robot 300 is moved, so that the terahertz sensor 320 at the tail end of the industrial robot is perpendicular to the terahertz calibration plate, and the signal receiving condition of the terahertz sensor 320 is observed. And if the terahertz signal intensity is too low, adjusting the distance and the detection angle between the robot 300 and the terahertz calibration plate. When the terahertz return signal strength is higher than the reception threshold, the system records the detection distance of the robot 300.

It can be appreciated that by detecting the signal strength of the terahertz sensor 320 in real time, the system can automatically detect and adjust the distance and angle between the terahertz sensor 320 and the detection object, ensuring that an accurate detection distance is obtained. By comparing the signal intensity with a preset intensity threshold, the system can judge whether the position of the sensor needs to be adjusted, so that the measurement error is reduced to the greatest extent, and the accuracy of the measurement of the thickness of the coating is improved. The method is beneficial to improving the stability and reliability of the system and ensuring that consistent and accurate coating thickness measurement results are obtained in the production process.

In some embodiments of the present application, when determining whether to adjust the robot 300, collecting the measured distance of the laser ranging sensor 310 and collecting environmental information, correcting the measured distance according to the environmental information, and obtaining the corrected measured distance includes: the environmental information includes an environmental temperature W0, an environmental humidity S0, and a dust concentration H0. The method comprises the steps of presetting a first preset environment temperature W1, a second preset environment temperature W2 and a third preset environment temperature W3, wherein W1 is more than W2 and less than W3. The first preset distance correction coefficient J1, the second preset distance correction coefficient J2 and the third preset distance correction coefficient J3 are preset, and J1 is smaller than J2 and smaller than J3. And selecting a distance correction coefficient according to the magnitude relation between the ambient temperature W0 and each preset ambient temperature to correct the measured distance L0, and obtaining the corrected measured distance. When W1 is less than or equal to W0 and less than W2, a third preset distance correction coefficient J3 is selected to correct the measured distance L0, and corrected measured distance L0×J3 is obtained. When W2 is less than or equal to W0 and less than W3, a second preset distance correction coefficient J2 is selected to correct the measured distance L0, and corrected measured distance L0×J2 is obtained. When W3 is less than or equal to W0, a first preset distance correction coefficient J1 is selected to correct the measured distance L0, and corrected measured distance L0×J1 is obtained.

Specifically, different preset ambient temperatures and distance correction coefficients are preset for different ambient temperature ranges. The temperature rise causes the optical element to expand, inducing a small structural change in the optical path. These variations cause shifts or changes in the focal position of the light, which in turn cause inaccuracies in the optical measurements. In particular, when the element expands, the light may defocus on the lens or mirror, resulting in a change in the focal position, resulting in a larger measurement, and the measuring device may misinterpret the focal position of the light as farther from the actual position. Therefore, in a high temperature environment, accurate optical measurement needs to take into account and correct optical system variations caused by temperature to ensure accuracy and reliability of measurement results.

It will be appreciated that the temperature induced errors can be corrected by calibration to obtain more accurate and reliable measurements.

In some embodiments of the present application, after the i-th preset distance correction coefficient Ji is selected to correct the measured distance L0 to obtain a corrected measured distance l0×ji, i=1, 2,3, and correcting the measured distance according to the environmental information to obtain a corrected measured distance, the method further includes: the first preset environmental humidity S1, the second preset environmental humidity S2 and the third preset environmental humidity S3 are preset, and S1 is more than S2 and less than S3. And selecting a distance correction coefficient according to the magnitude relation between the ambient humidity S0 and each preset ambient humidity, and carrying out secondary correction on the corrected measured distance L0×Ji to obtain the measured distance after secondary correction. When S1 is less than or equal to S0 and less than S2, selecting a third preset distance correction coefficient J3 to carry out secondary correction on the corrected measured distance L0×Ji, and obtaining the measured distance L0×Ji×J3 after secondary correction. When S2 is less than or equal to S0 and less than S3, a second preset distance correction coefficient J2 is selected to carry out secondary correction on the corrected measured distance L0×Ji, and the measured distance L0×Ji×J2 after secondary correction is obtained. When S3 is less than or equal to S0, a first preset distance correction coefficient J1 is selected to carry out secondary correction on the corrected measured distance L0×Ji, and the measured distance L0×Ji×J1 after secondary correction is obtained.

Specifically, when the humidity is high, the concentration of water vapor in the air increases, which causes an increase in the refractive index of the light passing through the humidity, resulting in a larger measurement result, and the sensor misperceives the propagation speed of the light as faster, resulting in a larger measurement distance.

It can be understood that the light refraction error can be corrected more accurately by selecting different distance correction coefficients for secondary correction according to the actual humidity condition, so that the accuracy of measuring the distance is ensured.

In some embodiments of the present application, after selecting the i-th preset distance correction coefficient Ji to perform secondary correction on the corrected measured distance l0×ji, obtaining the measured distance l0×ji×ji after the secondary correction, i=1, 2,3, correcting the measured distance according to the environmental information, and obtaining the corrected measured distance, further including: the first preset dust concentration H1, the second preset dust concentration H2 and the third preset dust concentration H3 are preset, and H1 is smaller than H2 and smaller than H3. And selecting a distance correction coefficient according to the size relation between the dust concentration H0 and each preset dust concentration, and carrying out three times of correction on the measured distance L0×Ji×Ji after the secondary correction to obtain the measured distance after the three times of correction. When H1 is less than or equal to H0 and less than H2, selecting a third preset distance correction coefficient J3 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction, and obtaining the measured distance L0×Ji×Ji×J3 after the three times of correction. When H2 is less than or equal to H0 and less than H3, selecting a second preset distance correction coefficient J2 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction, and obtaining the measured distance L0×Ji×Ji×J2 after the three times of correction. When H3 is less than or equal to H0, a first preset distance correction coefficient J1 is selected to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction, and the measured distance L0×Ji×Ji×J1 after the three times of correction is obtained.

In particular, the dust particles may interact with the light, resulting in scattering or absorption of the light, thereby attenuating the light signal received by the sensor. The sensor may erroneously estimate the propagation distance of the light as a further distance, again making the measurement larger. In particular, in environments with high dust concentrations, light rays can interact with suspended dust particles on their way through the air. These particles can cause scattering of the light, which changes direction during propagation, thus affecting the accuracy of the measurement.

It can be understood that by selecting different distance correction coefficients for three times according to the actual dust concentration condition, the attenuation of the optical signal caused by dust can be corrected more accurately, and the accuracy of measuring the distance can be ensured. The reliability of measurement is improved, and errors caused by dust are reduced.

In some embodiments of the present application, after selecting an i-th preset distance correction coefficient Ji to perform three corrections on the corrected measurement distance l0×ji×ji, obtaining the measurement distance l0×ji×ji after three corrections, i=1, 2,3, comparing the corrected measurement distance with the detection distance, and determining whether to adjust the corrected measurement distance according to the comparison result, to obtain a final measurement distance, including: when 0.9L1 < L0.times.Ji.times.Ji.times.Ji.times.Ji < 1.1L1, it is determined that the corrected measurement distance is not adjusted, and the corrected measurement distance L0X Ji X Ji as the distance is finally measured. L0×Ji x Ji x l0×ji×ji× when the Ji is more than or equal to 1.1L1, and judging to adjust the corrected measured distance, and taking the adjusted measured distance as a final measured distance.

In some embodiments of the application, when determining to adjust the corrected measured distance, it comprises: when 0.9L1.ltoreq.L0.times.Ji.times.Ji.times.Ji.times.Ji, obtaining a distance difference Δl=l 0 XJiXJiXJiXJiXJi-0.9L1, and the distance difference DeltaL is adjusted after being expressed in a flange coordinate system. Acquisition distance difference Δl= obtain the distance difference Δl= 1.1L1-L0XJiXJiXJiXJiXJi, and the distance difference DeltaL is adjusted after being expressed in a flange coordinate system.

It will be appreciated that the number of components, corrected measurement distance L0×Ji× JixJi has higher accuracy, the measurement error is reduced. The actual measurement distance is adjusted according to the comparison result by comparing the measurement distance with the effective detection distance of the terahertz sensor 320, so that the terahertz sensor 320 is always in the optimal measurement position during measurement, the reliability and consistency of the detection result are improved, and the detection precision is improved.

In conclusion, the application establishes the robot base coordinate system, and calibrates the center point of the flange plate by a probe method, thereby realizing the accurate mapping relation between the flange plate and the robot base coordinate system. The mapping relation between the laser ranging sensor 310 and the flange coordinate system is calibrated by adopting a planar method, so that the consistency of data during the action of the robot is improved, and the accuracy and the reliability of measurement are further improved. The terahertz calibration plate with the coating is used for determining the detection distance of the laser ranging sensor 310, so that calibration and inspection before measurement are realized, and the reliability of measurement data is improved. In the coating detection process, the measurement direction of the laser ranging sensor 310 can be aligned with the normal vector of the surface of the measured object 400 through automatic robot adjustment, so that the technical dependence of operators is reduced, and the measurement precision and stability are improved. Environmental information correction is introduced to correct the measured distance, so that the accuracy of measurement is improved, whether the corrected measured distance needs to be adjusted or not can be automatically judged, and the reliability of a final measurement result is ensured.

In another preferred mode based on the above embodiment, referring to fig. 3, the present embodiment provides a terahertz-based coating thickness detection system, including:

Control computer 100, robot 300, and terahertz spectrometer 200; the control computer 100 includes a mapping unit 110, a calibration unit 120, an acquisition unit 130, a judgment unit 140, a correction unit 150, an adjustment unit 160, and a measurement unit 170; the control computer 100 is electrically connected with the robot 300 and the terahertz spectrometer 200, the terahertz spectrometer 200 is electrically connected with the robot 300, and the terahertz spectrometer 300 is used for analyzing spectral data;

The mapping unit 110 is configured to establish a robot base coordinate system, calibrate a center point of the flange by using a probe method, and obtain a mapping relationship between the flange and the robot base coordinate system;

The mapping unit 110 is further configured to calibrate the mapping relationship between the laser ranging sensor 310 and the flange coordinate system by using a planar method;

the calibration unit 120 is configured to determine a detection distance of the laser ranging sensor 310 using a coated terahertz calibration plate;

the collection unit 130 is configured to perform detection on the object 400 after determining the detection distance; when the detected object 400 is detected, image acquisition is carried out on the detected object 400, modeling data of the detected object 400 are obtained, and initial sampling coordinates are determined according to the modeling data;

The judging unit 140 is configured to control the robot 300 to move to the initial sampling coordinate, collect a vector direction and a measurement distance of the laser ranging sensor 310 from a local plane of the sampling point, compare a normal vector of a plane target of the measured object 400 with the vector direction, and judge whether to adjust the robot 300 according to a comparison result;

the method comprises the steps of obtaining an angle difference delta theta between a normal vector of the plane target and a vector direction, comparing the angle difference delta theta with a preset angle difference threshold value theta max, and judging whether to adjust the robot 300 according to a comparison result;

When Δθ > θmax, determining to adjust the robot 300;

when Δθ is less than or equal to θmax, it is determined that no adjustment is performed on the robot 300;

The correction unit 150 is configured to collect a measured distance of the laser ranging sensor 310 and collect environmental information after determining whether to adjust the robot 300, correct the measured distance according to the environmental information, and obtain a corrected measured distance;

The adjusting unit 160 is configured to compare the corrected measured distance with the detected distance, and determine whether to adjust the corrected measured distance according to the comparison result, so as to obtain a final measured distance;

The measurement unit 170 is configured to control the terahertz sensor 320 to perform terahertz time-domain spectroscopy measurement after the final measurement distance is obtained.

It can be appreciated that the terahertz-based coating thickness detection method and system have the same beneficial effects and are not described in detail herein.

It will be appreciated by those skilled in the art that embodiments of the application may be provided as methods, systems, or computer program products. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flowchart and/or block of the flowchart illustrations and/or block diagrams, and combinations of flowcharts and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.

Claims (10)

1. The terahertz-based coating thickness detection method is characterized by comprising the following steps of:

Establishing a robot base coordinate system, calibrating a flange center point by using a probe method, and obtaining a mapping relation between the flange and the robot base coordinate system; calibrating the mapping relation between the laser ranging sensor and the flange coordinate system by using a planar method;

determining the detection distance of the laser ranging sensor by using a terahertz calibration plate with a coating;

After the detection distance is determined, detecting the detected object; when a detected object is detected, carrying out image acquisition on the detected object, acquiring modeling data of the detected object, and determining initial sampling coordinates according to the modeling data;

After the control robot moves to the initial sampling coordinate, collecting the vector direction and the measurement distance of the laser ranging sensor from the local plane of the sampling point, comparing the normal vector of the plane target of the measured object with the vector direction, and judging whether to adjust the robot according to the comparison result;

The method comprises the steps of obtaining an angle difference delta theta between a normal vector of the plane target and a vector direction, comparing the angle difference delta theta with a preset angle difference threshold value theta max, and judging whether to adjust the robot according to a comparison result;

when delta theta is larger than theta max, judging to adjust the robot;

When delta theta is less than or equal to theta max, judging that the robot is not regulated;

When judging whether to adjust the robot, collecting the measuring distance of the laser ranging sensor, collecting environmental information, correcting the measuring distance according to the environmental information, and obtaining the corrected measuring distance;

comparing the corrected measurement distance with the detection distance, and judging whether to adjust the corrected measurement distance according to the comparison result to obtain a final measurement distance;

and after the final measurement distance is obtained, controlling the terahertz sensor to conduct terahertz time-domain spectrum measurement.

2. The terahertz-based coating thickness detection method of claim 1, wherein the establishing a robot base coordinate system, calibrating a flange center point using a probe method and obtaining a mapping relationship between the flange and the robot base coordinate system, includes:

Establishing a three-dimensional coordinate system by taking the robot base as an origin, and marking the three-dimensional coordinate system as a robot base coordinate system O _R;

Establishing a three-dimensional coordinate system by taking the central point of the flange plate as an origin, and marking the three-dimensional coordinate system as a flange coordinate system O _F;

And mounting a standard probe on the flange, and controlling the probe to contact the same contact under different postures to obtain the position conversion relation of the base coordinate system O _R and the flange coordinate system O _F in a three-dimensional space.

3. The terahertz-based coating thickness detection method according to claim 2, wherein calibrating the mapping relation between the laser ranging sensor and the flange coordinate system by a planar method includes:

Constructing a position parameter constraint equation of the laser ranging sensor through a calibration plane to construct a mapping relation between the laser ranging sensor and a flange coordinate system;

The construction of the position parameter constraint equation of the laser ranging sensor is achieved through the following formula:

Wherein An, bn, cn represent the plane equation coefficient of the calibration plate when calibrating for the nth time, n is the calibration times, and n is more than 6; x0, y0, z0 are represented as spatial coordinates to be calibrated, and l _n represents a ranging value of the nth laser displacement sensor.

4. The terahertz-based coating thickness detection method of claim 3, wherein the determining a detection distance of the laser ranging sensor using a terahertz calibration plate with a coating after obtaining a mapping relation of the laser ranging sensor and a flange coordinate system, further comprises:

Moving the robot to enable the terahertz sensor to be perpendicular to the terahertz calibration plate, collecting signal intensity Q0 of the terahertz sensor, comparing the signal intensity Q0 with a preset intensity threshold Qmin, and judging whether to adjust the position of the terahertz sensor according to a comparison result;

when Q0 is more than or equal to Qmin, judging that the position of the terahertz sensor is not adjusted, recording the coordinate position of the terahertz sensor at the moment, and obtaining a detection distance L1 according to the coordinate position;

when Q0 is smaller than Qmin, the position of the terahertz sensor is judged to be adjusted, the robot is moved until Q0 is larger than or equal to Qmin, the coordinate position of the terahertz sensor at the moment is recorded, and the detection distance L1 is obtained according to the coordinate position.

5. The terahertz-based coating thickness detection method of claim 4, wherein after determining whether to adjust the robot, collecting a measurement distance of the laser ranging sensor and collecting environmental information, correcting the measurement distance according to the environmental information, and obtaining a corrected measurement distance, comprising:

The environment information comprises an environment temperature W0, an environment humidity S0 and a dust concentration H0;

Presetting a first preset environmental temperature W1, a second preset environmental temperature W2 and a third preset environmental temperature W3, wherein W1 is more than W2 and less than W3; presetting a first preset distance correction coefficient J1, a second preset distance correction coefficient J2 and a third preset distance correction coefficient J3, wherein J1 is less than J2 and less than J3; selecting a distance correction coefficient according to the magnitude relation between the environment temperature W0 and each preset environment temperature to correct the measured distance L0, and obtaining a corrected measured distance;

When W1 is less than or equal to W0 and less than W2, selecting the third preset distance correction coefficient J3 to correct the measured distance L0, and obtaining corrected measured distance L0×J3;

when W2 is less than or equal to W0 and less than W3, selecting the second preset distance correction coefficient J2 to correct the measured distance L0, and obtaining corrected measured distance L0×J2;

when W3 is less than or equal to W0, the first preset distance correction coefficient J1 is selected to correct the measured distance L0, and corrected measured distance L0×J1 is obtained.

6. The terahertz-based coating thickness detection method of claim 5, wherein after selecting an i-th preset distance correction coefficient Ji to correct a measured distance L0 and obtaining a corrected measured distance l0×ji, i=1, 2,3, correcting the measured distance according to the environmental information, obtaining a corrected measured distance, further comprising:

presetting a first preset environmental humidity S1, a second preset environmental humidity S2 and a third preset environmental humidity S3, wherein S1 is more than S2 and less than S3; selecting a distance correction coefficient according to the magnitude relation between the ambient humidity S0 and each preset ambient humidity, and carrying out secondary correction on the corrected measured distance L0×Ji to obtain a measured distance after secondary correction;

when S1 is less than or equal to S0 and less than S2, selecting the third preset distance correction coefficient J3 to carry out secondary correction on the corrected measured distance L0×Ji to obtain a secondary corrected measured distance L0×Ji×J3;

when S2 is less than or equal to S0 and less than S3, selecting the second preset distance correction coefficient J2 to carry out secondary correction on the corrected measured distance L0×Ji to obtain a secondary corrected measured distance L0×Ji×J2;

And when S3 is less than or equal to S0, selecting the first preset distance correction coefficient J1 to carry out secondary correction on the corrected measured distance L0×Ji, and obtaining the measured distance L0×Ji×J1 after secondary correction.

7. The terahertz-based coating thickness detection method of claim 6, wherein after selecting an i-th preset distance correction coefficient Ji to secondarily correct the corrected measurement distance l0×ji to obtain the secondarily corrected measurement distance l0×ji×ji, i=1, 2,3, the correcting the measurement distance according to the environmental information to obtain the corrected measurement distance, further comprising:

Presetting a first preset dust concentration H1, a second preset dust concentration H2 and a third preset dust concentration H3, wherein H1 is more than H2 and less than H3; selecting a distance correction coefficient according to the size relation between the dust concentration H0 and each preset dust concentration, and carrying out three times of correction on the measured distance L0×Ji×Ji after the secondary correction to obtain the measured distance after the three times of correction;

when H1 is less than or equal to H0 and less than H2, selecting the third preset distance correction coefficient J3 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction to obtain the measured distance L0×Ji×Ji×J3 after the three times of correction;

When H2 is less than or equal to H0 and less than H3, selecting the second preset distance correction coefficient J2 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction to obtain the measured distance L0×Ji×Ji×J2 after the three times of correction;

when H3 is less than or equal to H0, selecting the first preset distance correction coefficient J1 to perform three times of correction on the measured distance L0×Ji×Ji after the secondary correction, and obtaining the measured distance L0×Ji×Ji×J1 after the three times of correction.

8. The terahertz-based coating thickness detection method of claim 7, the measurement distance L0×Ji×Ji after correction is corrected three times by selecting the i-th preset distance correction coefficient Ji, after the measurement distances l0×ji×ji×ji after three corrections are obtained, i=1, 2,3, comparing the corrected measurement distance with the detection distance, judging whether to adjust the corrected measurement distance according to the comparison result, and obtaining a final measurement distance, including:

when 0.9L1 < L0.times.Ji.times.Ji.times.Ji.times.Ji < 1.1L1, it is determined that the corrected measurement distance is not adjusted, and the corrected measurement distance L0×Ji× Ji x Ji as the final measured distance;

When 0.9L1 is equal to or less than L0×Ji×Ji×Ji or when L0×Ji×Ji×Ji is not less than 1.1L1, it is determined to adjust the corrected measured distance, and taking the adjusted measured distance as the final measured distance.

9. The terahertz-based coating thickness detection method according to claim 8, wherein when it is determined to adjust the corrected measured distance, comprising:

when 0.9L1.ltoreq.L0.times.Ji.times.Ji.times.Ji.times.Ji, obtaining a distance difference Δl=l 0 XJiXJiXJiXJiXJi-0.9L1, and the distance difference delta L is regulated after being expressed in the flange coordinate system;

acquisition distance difference Δl= obtain the distance difference Δl= 1.1L1-L0XJiXJiXJiXJiXJi, and the distance difference delta L is regulated after being expressed in the flange coordinate system.

10. A terahertz-based coating thickness detection system, applying the method according to any one of claims 1 to 9, comprising:

control computer, robot and terahertz spectrometer; the control computer comprises a mapping unit, a calibration unit, an acquisition unit, a judgment unit, a correction unit, an adjustment unit and a measurement unit; the control computer is electrically connected with the robot and the terahertz spectrometer, the terahertz spectrometer is electrically connected with the robot, and the terahertz spectrometer is used for analyzing spectrum data;

The mapping unit is configured to establish a robot base coordinate system, calibrate a flange center point by using a probe method and obtain a mapping relation between the flange and the robot base coordinate system;

The mapping unit is further configured to calibrate the mapping relation between the laser ranging sensor and the flange coordinate system by using a planar method;

The calibration unit is configured to determine the detection distance of the laser ranging sensor by using a terahertz calibration plate with a coating;

The acquisition unit is configured to detect an object to be detected after the detection distance is determined; when a detected object is detected, carrying out image acquisition on the detected object, acquiring modeling data of the detected object, and determining initial sampling coordinates according to the modeling data;

The judging unit is configured to control the robot to move to the initial sampling coordinate, collect the vector direction and the measuring distance of the laser ranging sensor from the local plane of the sampling point, compare the normal vector of the plane target of the measured object with the vector direction, and judge whether to adjust the robot according to the comparison result;

The method comprises the steps of obtaining an angle difference delta theta between a normal vector of the plane target and a vector direction, comparing the angle difference delta theta with a preset angle difference threshold value theta max, and judging whether to adjust the robot according to a comparison result;

when delta theta is larger than theta max, judging to adjust the robot;

When delta theta is less than or equal to theta max, judging that the robot is not regulated;

The correction unit is configured to collect the measured distance of the laser ranging sensor and environmental information after judging whether to adjust the robot, correct the measured distance according to the environmental information and obtain the corrected measured distance;

The adjusting unit is configured to compare the corrected measured distance with the detection distance, and judge whether to adjust the corrected measured distance according to the comparison result to obtain a final measured distance;

the measuring unit is configured to control the terahertz sensor to conduct terahertz time-domain spectroscopy measurement after the final measurement distance is obtained.