CN111536876A - A method for in-situ measurement of sealing surface of triple eccentric butterfly valve - Google Patents

Abstract

The invention discloses an in-situ measurement method for a sealing surface of a triple eccentric butterfly valve, comprising: acquiring coordinate information of data points on the outer contour of a workpiece to be measured placed on a turntable; The space straight line equation; select the optimal generatrix equation according to the preset cone angle from the first space line equation; obtain the first conical surface equation by fitting the optimal generatrix equation; obtain the coordinates of m fitted center points, The coordinates of are substituted into the equation of the first conical surface, and the corresponding equations of m second conic surfaces are obtained; the second conical surface corresponding to the set with the smallest error is selected from the set of minimum distance values from the data point to the m second conical surfaces: Best fit conic surface. Through the above algorithm, it is possible to measure at the same time of processing, grasp the processing error at any time, and avoid the secondary processing error caused by the disassembly of the workpiece after offline measurement.

Description

A method for in-situ measurement of sealing surface of triple eccentric butterfly valve

technical field

The invention relates to the technical field of measurement, in particular to an in-situ measurement method of a sealing surface of a triple eccentric butterfly valve.

Background technique

At present, most of the mechanical manufacturing process adopts offline measurement technology. Using the offline measurement method requires processing and measurement to be carried out on professional equipment respectively, and the processed parts need to be moved to the measurement equipment for testing. This method is suitable for mass production. The disadvantage is that it will inevitably bring about problems such as secondary clamping error, prolonged processing cycle and workpiece turnover process damage, which will affect the production progress and efficiency.

Commonly used offline measurement methods include: caliper measurement, three-coordinate measuring instrument, etc. Caliper measurement has the advantages of low price and convenient use due to the use of standardized tools such as vernier calipers, micrometers and calipers. However, the unique inclined cone structure of the triple eccentric butterfly valve leads to the fact that the maximum dimension from the straight edge to the inclined edge is only the distance between the two points on the largest straight edge and the largest oblique edge, so the measurement often depends on the operator's feel, and the measurement repeatability is very high. There are also large differences in the results of different worker measurements. In addition, the triple-eccentric zero-leakage seal requires complete surface contact of the sealing surface, and the dimensional error will cause the contact part to be only a line, so it is difficult to achieve zero-leakage requirements, let alone two-way zero-leakage sealing requirements. In addition, the current three-coordinate measuring instrument cannot accurately measure the butterfly valve with a large diameter due to the size limitation; and the use of the three-coordinate measuring instrument must remove the workpiece from the lathe processing table, and the error obtained at this time cannot be measured. The workpiece is then subjected to secondary tool compensation processing. Because if the secondary processing is to be performed after the measurement, the workpiece must be re-clamped. Due to the asymmetry of the shape of the sealing surface of the triple eccentric butterfly valve, the secondary clamping will inevitably produce a large error, even if it is re-clamped on the lathe Reprocessing is also not possible. For workpieces that only slightly exceed the allowable tolerance range, only scrapping can be selected.

In-situ measurement means that the workpiece is not disassembled after being machined, but is still clamped on the machine tool, and the machined part is measured on the machine tool. If the measurement result is unqualified, the machine tool is directly and quickly Rework can avoid the secondary machining error caused by disassembling the workpiece after offline measurement, and further improve the machining accuracy.

Therefore, how to use the in-situ measurement method for the workpiece, measure at the same time as processing, grasp the processing error at any time, and avoid the secondary processing error caused by the disassembly of the workpiece after offline measurement has become an urgent problem to be solved.

SUMMARY OF THE INVENTION

In view of this, the embodiment of the present invention provides an in-situ measurement method for the sealing surface of a triple eccentric butterfly valve, so as to solve the problem of secondary processing error caused by the use of offline measurement to disassemble the workpiece in the prior art.

The embodiment of the present invention provides an in-situ measurement method for the sealing surface of a triple eccentric butterfly valve, including:

Obtain the coordinate information of the external contour data points of the workpiece to be measured placed on the turntable;

establishing a first space straight line equation by least square fitting to the coordinate information of the data points;

Select the optimal busbar equation from the first space straight line equation according to the preset cone angle;

The first conical surface equation is obtained by fitting the optimal generatrix equation;

Obtain the coordinates of m fitting center points, and substitute the coordinates of the center points into the first conical surface equation to obtain the corresponding m second conical surface equations; among them, the center point is from the plane where the cone vertex of the workpiece to be measured is located. Select from the preset area, the plane is parallel to the upper surface of the turntable, the preset area is a circular area with a radius r containing the vertices of the cone, or, the preset area is a square area with a side length r containing the vertices of the cone, m is a natural number greater than or equal to 1;

From the set of minimum distance values from the data point to the m second conical surfaces, the second conical surface corresponding to the set with the smallest error is selected as the best fitting conic surface.

Optionally, acquiring the coordinate information of the outer contour data points of the workpiece to be measured placed on the turntable includes: when the turntable rotates by a predetermined angle, the laser sensor performs a collection operation on the workpiece to be measured; The axis is moved down a predetermined distance in preparation for the next acquisition operation.

Optionally, before establishing the first space straight line equation by least squares fitting on the coordinate information of the data points, the method further includes:

The optimal data that meets the requirements in the data points is set as the standard point, and the remaining data points are the data points to be screened;

Set the relative distance deviation threshold;

Calculate the relative distance between the data points to be screened and the standard points. If the relative distance is less than or equal to the relative distance deviation threshold, the data points to be screened are qualified data points.

Optionally, selecting the optimal generatrix equation from the first space straight line equation according to the preset taper angle includes:

Obtain the direction vector of the first space straight line equation;

Obtain the angle between the first space straight line and the standard straight line according to the direction vector;

Calculate the cone angle of the cone with the first space straight line as the generatrix according to the included angle;

All the first space straight lines whose taper angle ranges from 18° to 23° are used as the second space straight lines;

A straight line is selected from the second space straight line as the optimal generatrix.

Optionally, obtaining the direction vector of the first space straight line equation includes:

Calculate the residual sum of squares of the first space straight line equation;

The coefficient of the first space straight line equation and the direction vector of the first space straight line are obtained by derivation of the residual sum of squared residuals.

Optionally, the coordinates of m fitted center points are obtained, and the coordinates of the center points are substituted into the first conical surface equation, and the corresponding m second conic surface equations are obtained, including:

Substitute the equation of the second space straight line into the general equation of the first conical surface to obtain the equation of the second conical surface, and the equation of the second conical surface is related to the coefficient of the first space straight line equation.

Optionally, selecting the second conical surface corresponding to the set with the smallest error from the set of minimum distance values from the data point to the m second conical surfaces as the best fitting conic surface includes:

The general expression for obtaining the minimum distance from the data point to the m second conical surfaces by using the Lagrange multiplier method of the conditional extrema of the multivariate function;

Substitute the data point into the general expression of the minimum distance, and obtain the minimum distance value set from the data point to the m second conical surfaces;

Errors are calculated respectively for the minimum distance value set from the data point to the m second conical surfaces, and the second conical surface corresponding to the minimum distance value set with the smallest error is selected as the best fitting conic surface.

Optionally, the general expression for obtaining the minimum distance from the data point to the m second conical surfaces using the Lagrangian multiplier method of the conditional extrema of the multivariate function includes:

Obtain the Lagrangian function according to the coordinates of the data points;

Differentiate the Lagrangian functions according to the three-dimensional coordinate parameters, and obtain the coordinate algebraic expressions related to the Lagrangian parameters and the coordinates of the data points;

Substitute the coordinate algebra into the equation of the second conical surface to obtain the third conical surface equation related to the Lagrangian parameters;

By calculating the extreme value of the third conical surface equation, the specific value of the Lagrangian parameter is obtained;

The minimum distance from the data point to the m second conical surfaces is obtained through the coordinate algebra formula related to the Lagrangian parameter and the coordinate of the data point.

The embodiment of the present invention provides an in-situ measurement method for the sealing surface of a triple eccentric butterfly valve. The workpiece of the triple eccentric butterfly valve to be measured is placed on a turntable, and the coordinate information of the sealing surface data points of the workpiece to be measured is collected by a laser sensor. The data collected by the laser sensor is transmitted to the computer; by calculating the distance from the data point (except the data point of the fitting space line) to the conic surface, it is judged whether the data point can be fitted to the conical surface; otherwise, find the next The center point of the plane, continue to fit to obtain a conic surface, and then calculate the distance from the remaining data points to the conic surface to judge whether the data point can be fitted to the conic surface; repeat the above steps, the fitting error is until |Δ _ij ≤Δ ₀₀ |, indicating that the conic surface is the best fitting surface.

Through the in-situ measurement method of the sealing surface of the triple eccentric butterfly valve provided in the above embodiment, more complete correct measurement data of the workpiece can be obtained, so as to improve the measurement accuracy of the measurement system and play a guiding role in subsequent processing. It realizes the measurement at the same time of processing, grasps the processing error at any time, and avoids the secondary processing error caused by the disassembly of the workpiece after offline measurement.

Description of drawings

The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way, in which:

1 shows a flow chart of a method for in-situ measurement of a sealing surface of a triple eccentric butterfly valve in an embodiment of the present invention;

Fig. 2 shows the relationship diagram between the collected data points and the qualified data points of the sealing surface of a triple eccentric butterfly valve in an embodiment of the present invention;

FIG. 3 shows a flowchart of another in-situ measurement algorithm of the sealing surface of the triple eccentric butterfly valve in the embodiment of the present invention.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

At present, in-situ measurement obtains several discrete data of the processed surface through in-situ measurement. According to these data, we hope to obtain a continuous surface that is consistent with the known data. This process is a surface fitting process. Surface fitting technology has a wide range of applications in computer graphics, numerical computing and other fields. At present, the commonly used surface fitting methods are: least squares method, interpolation method, shrinkage algorithm and so on.

The interpolation method is to construct an n-degree polynomial P _n (x) according to the interpolation principle, so that the data of P _n (x) at each test point just passes the measured point; although the interpolation method can retain the original data points, but, in general, in order to A lot of data points are collected to reflect the actual situation as much as possible, resulting in a high degree of interpolation polynomial P _n (x), which not only increases the amount of calculation, but also affects the fitting accuracy, which is not conducive to the actual production process of the project. Surface fitting of the workpiece in . The shrinkage algorithm is a direct iterative algorithm with the basic characteristics of shrinking and expanding the search space. Under the condition that the search space is relatively simple, the shrinkage algorithm can achieve the best fit without providing suitable initial values. When the space is complicated, its search efficiency will decrease, and it is difficult to implement for multi-parameter nonlinear problems. The least squares method is to select an approximate function f(x) according to the known data, so that the root mean square error of the function f(x) is the smallest. Although the least squares fitting is insufficient in retaining some original data points, the biggest advantage of the least squares fitting is that the fitting accuracy can be regulated, and different fitting accuracies can be selected according to the actual usage. The least squares method of linearly fitting the surface is more simple, direct and easy to operate, which is conducive to the feedback of the actual processing process.

The embodiment of the present invention provides an in-situ measurement method for the sealing surface of a triple eccentric butterfly valve, as shown in FIG. 1 , including:

In step S10, the coordinate information of the outer contour data points of the workpiece to be measured placed on the turntable is obtained.

In this embodiment, the workpiece of the triple eccentric butterfly valve to be tested is placed on the turntable, the coordinate information of the data points of the sealing surface of the workpiece to be tested is collected by the laser sensor, and the encoder transmits the data collected by the laser sensor to the computer.

Step S20, establishing a first space straight line equation by least squares fitting on the coordinate information of the data points.

In this embodiment, the workpiece of the triple eccentric butterfly valve to be tested rotates with the turntable, and the laser sensor collects information on the sealing surface of the workpiece of the triple eccentric butterfly valve to be tested to obtain the three-dimensional coordinate information of the sealing surface of the workpiece of the triple eccentric butterfly valve to be tested. The points are linearly fitted to obtain a plurality of equations of the first space straight lines.

The least squares method is to select an approximate function f(x) according to the known data, so that the root mean square error of the function f(x) is the smallest. Although the least squares fitting is insufficient in retaining some original data points, the biggest advantage of the least squares fitting is that the fitting accuracy can be regulated, and different fitting accuracies can be selected according to the actual usage. The least squares method of linearly fitting the surface is more simple, direct and easy to operate, which is conducive to the feedback of the actual processing process.

In this embodiment, using the least squares method to linearly fit the curved surface under the condition of in-situ measurement can timely feedback the machining error, and provide technical guidance for the subsequent machining, so as to further improve the machining accuracy of the workpiece.

Step S30, select the optimal busbar equation from the first space straight line equation according to the preset taper angle.

In this embodiment, since the sealing surface of the workpiece of the triple eccentric butterfly valve to be tested is approximately a conical surface, a straight line should be selected from the equations of the plurality of first space straight lines in step S20 as the optimal fitting of the conical surface. busbar. The optimal busbar is selected according to the size of the cone angle between the first space straight line equation and the standard straight line.

Step S40, obtaining the first conical surface equation by fitting the optimal generatrix equation.

In this embodiment, by determining a line segment and a cone angle in the world coordinate system, a plurality of conical surfaces can be obtained, and the vertices of these conical surfaces are not determined.

In step S50, the coordinates of the m fitted center points are obtained, and the coordinates of the center points are substituted into the first conical surface equation to obtain the corresponding m second conic surface equations. The center point is selected from a preset area in the plane where the cone vertex of the workpiece to be tested is located, the plane is parallel to the upper surface of the turntable, and the preset area is a circular area with a radius r containing the cone vertex, or, the preset area is a square area with side length r containing the vertices of the cone, where m is a natural number greater than or equal to 1.

In this embodiment, the laser sensor collects data on the vertex coordinates of the sealing surface of the workpiece of the triple eccentric butterfly valve to be tested. During the rotation of the workpiece to be tested with the turntable, the x-axis and y-axis coordinates of the sealing surface of the workpiece to be tested may occur. changes, and the z-axis coordinate of the apex of the sealing surface of the workpiece to be tested generally does not change. If the workpiece of the triple eccentric butterfly valve to be tested is placed, the vertex of its sealing surface is just above the center of the turntable, the coordinates of the vertex of the sealing surface of the workpiece to be tested will not change during the rotation of the turntable.

Taking a circular area as an example, in any measurement process, determine a circular area with the coordinates of the vertex of the sealing surface as the center and r as the radius, and divide the circular area into m unit areas according to the preset size. The coordinate of the center of the unit area is the center point of the fitting, and the coordinates of the m fitting center points are substituted into the first conical surface equation in step S40 to obtain m equations of the second conical surface. The values of radius r and m can be set according to actual needs.

Step S60, selecting the second conical surface corresponding to the set with the smallest error from the set of minimum distance values from the data point to the m second conical surfaces as the best fitting conical surface.

In this embodiment, it is determined whether the data point can be fitted to the conic surface by calculating the distance from the data point (except the data point of the fitting space straight line) to the conic surface; otherwise, find the next plane center point, and continue A conic surface is obtained by fitting, and then the distance from the remaining data points to the conic surface is calculated to determine whether the data point can be fitted to the conic surface; repeat the above steps, the fitting error is until |Δ _ij ≤Δ ₀₀ |, indicating that the The conic surface is the best fit surface.

Through the in-situ measurement method of the sealing surface of the triple eccentric butterfly valve provided in the above embodiment, more complete correct measurement data of the workpiece can be obtained, so as to improve the measurement accuracy of the measurement system and play a guiding role in subsequent processing. It realizes the measurement at the same time of processing, grasps the processing error at any time, and avoids the secondary processing error caused by the disassembly of the workpiece after offline measurement.

As an optional embodiment, the coordinate information of the outer contour data points of the workpiece to be measured placed on the turntable is obtained: after each rotation of the turntable by a predetermined angle, the laser sensor performs a collection operation on the workpiece to be measured; Move down a predetermined distance along the Z axis for the next acquisition operation.

In this embodiment, the workpiece to be measured is placed on the turntable, and the turntable drives the workpiece to rotate at a constant speed. The laser measures data once every time the workpiece to be measured rotates by the same angle. After one rotation, the laser sensor completes one measurement; The Z axis moves downward by a suitable distance, and the laser measures the data every time the workpiece rotates at the same angle. After one rotation, the laser sensor completes one measurement. Repeat the above operation to finally obtain all data points.

All measured data points are characterized by the presence of one data band with the same value and another data band with the same value.

The turntable drives the workpiece to rotate at a constant speed, and the data points can be divided into columns of data points according to the average rotation angle.

As an optional implementation manner, before step S20, it also includes:

In step S11, the optimal data that meets the requirements in the data points is set as the standard point, and the remaining data points are the data points to be screened.

Step S12, setting a relative distance deviation threshold.

Step S13: Calculate the relative distance between the data point to be screened and the standard point. If the relative distance is less than or equal to the relative distance deviation threshold, the data point to be screened is a qualified data point.

In this embodiment, the relative distance deviation is used to remove abnormal data points; each time the measurement completes a circle, the data points of this group of data will have two values that are significantly different, and the group of data with the smaller value is closer to the standard numerical value. Assuming that there is optimal data that meets the requirements in the collected data point column, set it as the standard point. As shown in Figure 2, set the standard point set according to the above method, calculate the relative average distance D between other data points and the standard point set, and set the relative distance deviation threshold ε according to the requirements. requirements, and finally obtain all the data points that meet the requirements.

As an optional implementation manner, step S30 includes:

Step S301, obtaining the direction vector of the first space straight line equation.

Step S302, obtaining the included angle between the first space straight line and the standard straight line according to the direction vector.

Step S303: Calculate the taper angle of the cone with the first spatial straight line as the generatrix according to the included angle.

In step S304, all the first space straight lines with the taper angle ranging from 18° to 23° are used as the second space straight lines.

In step S305, a straight line is selected from the second spatial straight line as the optimal generatrix.

In this embodiment, a straight line with a taper angle of 20° is selected as the optimal bus bar.

As an optional implementation manner, step S301 includes:

Calculate the residual sum of squares of the first space straight line equation;

The coefficient of the first space straight line equation and the direction vector of the first space straight line are obtained by derivation of the residual sum of squared residuals.

In this embodiment, it is assumed that the equation of the straight line is:

为激光传感器采集到的待测三偏心蝶阀工件密封面的数据点坐标。in

It is the data point coordinates of the sealing surface of the workpiece of the triple eccentric butterfly valve to be tested collected by the laser sensor.

The residual sum of squares is obtained as:

Q _ij and Q _{i, j+1} are the optimization criteria, and the derivation of Q _ij and Q _{i, j+1} is obtained respectively:

The coefficients of the first space straight line equation are:

空间直线的方向向量为

It can be known from the plane vertical normal vector that the standard line direction vector

The direction vector of a straight line in space is

可以计算出第一空间直线l_ij和标准直线的之间的夹角为

Then in step S302, the angle between the first space straight line and the standard straight line is obtained according to the direction vector: according to

The angle between the first space straight line l _ij and the standard straight line can be calculated as

Step S303, calculating according to the included angle, the taper angle of the cone with the first spatial straight line as the generatrix is α _ij .

As an optional implementation manner, step S50 includes: substituting the equation of the second space straight line into the general equation of the first conical surface to obtain the equation of the second conical surface, the equation of the second conic surface and the coefficients of the equation of the first space straight line related.

In this embodiment, the second space straight line is a first space straight line with a taper angle α _ij of 20° between the standard straight line and the second space straight line l ₂ :

Substitute into the equation of the conical surface: G(x,y,z)=a ² (x ² +y ² )-z ² , the coefficient a in this equation is obtained by fitting and calculating according to the data points on the second space straight line.

Get the equation of the conic surface:

Determine the center point C _m (x, y, z), and substitute the center point coordinates C _m (x, y, z) into the equation of the conical surface to get:

As an optional implementation manner, step S60 includes:

Step S601 , using the Lagrange multiplier method of the conditional extremum of the multivariate function to obtain a general expression of the minimum distance from the data point to the m second conical surfaces.

Specifically, step S601 includes:

Step S6011 obtains the Lagrangian function according to the coordinates of the data points.

List the Lagrange functions:

_{Li ij} =(xx _ij ) ² +(yy _ij ) ² +(zz _ij ) ² +λ[a ² (x ² +y ² )-z ² ]

Wherein, (x, y, z) are points on the conic surface, and (x _ij , y _ij , z _ij ) are points on the second space straight line l ₂ .

Step S6012: Differentiate the Lagrangian functions according to the three-dimensional coordinate parameters, and obtain a coordinate algebraic formula related to the Lagrangian parameters and the coordinates of the data points.

Derivation of the Lagrangian function in step S6011:

Let L' _x = 0, L' _y = 0, and L' _z = 0 to obtain the xyz coordinate algebraic formula for λ and the coordinates of the data points:

Step S6013: Substitute the coordinate algebraic formula into the equation of the second conical surface to obtain the third conical surface equation related to the Lagrangian parameters.

Substitute the xyz coordinate algebraic expression in step S6012 into the equation G(x, y, z) of the conical surface to obtain:

Step S6014, by calculating the extreme value of the third conical surface equation, obtain the specific value of the Lagrangian parameter.

The value of λ can be obtained by finding the extreme value of G(λ).

Step S6015, obtain the minimum distance from the data point to the m second conical surfaces by using the coordinate algebraic formula related to the Lagrangian parameter and the coordinates of the data point.

Given the set of data points X∈{x=(x _ij ,y _ij ,z _ij )}, calculate the distance from the spatial point (x _ij ,y _ij ,z _ij ) to the conic surface:

Step S602: Substitute the data point into the general expression of the minimum distance, and obtain a set of minimum distance values from the data point to the m second conical surfaces.

以及步骤S6014中求出的λ的值，代入距离公式d_ij中，求出数据点到m个第二圆锥面的距离最小值。Known from step S6012,

And the value of λ obtained in step S6014 is substituted into the distance formula d _ij to obtain the minimum distance from the data point to the m second conical surfaces.

Step S603: Calculate errors respectively for the minimum distance value sets from the data point to the m second conical surfaces, and select the second conical surface corresponding to the minimum distance value set with the smallest error as the best fitting conic surface.

当Δ_ij小于0.2％时，停止迭代，此时，可以找到最佳的拟合圆锥曲面。make

When _Δij is less than 0.2%, the iteration is stopped, at this time, the best fitting conic surface can be found.

As shown in Figure 3, the algorithm of using least squares to linearly fit the sealing surface of triple eccentric butterfly valve under the condition of in-situ measurement includes the following steps:

Step 1: During the laser measurement, the workpiece is placed on the turntable, and the turntable drives the workpiece to rotate at a constant speed. The laser measures data every time the workpiece rotates at the same angle. After one rotation, the laser sensor completes a measurement; then the laser sensor moves down with the Z axis. For a suitable distance, the laser measures the data every time the workpiece rotates at the same angle. After one rotation, the laser sensor completes one measurement. Repeat the above operation to finally obtain all data points. The encoder transmits the collected and measured data to the computer.

Step 2: Use the relative distance deviation to remove abnormal data points; each time the measurement completes a circle, the data points of this group of data will have two values that are significantly different. At this time, the group of data with the smaller value is closer to the standard value. Set the standard point set according to the above method, calculate the relative average distance D between other data points and the standard point set, and set the relative distance deviation threshold ε according to the requirements. If D≤ε, the data point meets the requirements, and finally all Data points that meet the requirements.

Step 3: By establishing the spatial straight line equation of the data points and performing least squares fitting; by obtaining the "optimization criterion" - the sum of squares of residuals, the spatial straight line l _ij and the direction vector of the straight line are finally obtained:

Step 4: Calculate the cone angle according to the obtained space straight line and perform fitting to obtain the three-dimensional surface constraint as a conical surface, and obtain the general equation of the conic surface.

Step 5: For the obtained general conical surface equation, obtain the further fitted conical surface in turn by determining the center point C _m (x, y, z); use the Lagrange multiplier method of the conditional extreme value of the multivariate function to obtain The distance equation d _ij between the data point set and the conical surface; by calculating the mean value Δ _ij of the distance equation d _ij between the data point set and the conical surface, it is judged that the conical surface obtained by the final fitting is the optimal solution.

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the present invention, such modifications and variations falling within the scope of the appended claims within the limited range.

Claims (8)

1. an in-situ measurement method for a sealing surface of a triple eccentric butterfly valve, is characterized in that, comprising: Obtain the coordinate information of the external contour data points of the workpiece to be measured placed on the turntable; establishing a first space straight line equation by least squares fitting to the coordinate information of the data points; Select the optimal generatrix equation from the first space straight line equation according to the preset taper angle; The first conical surface equation is obtained by fitting the optimal generatrix equation; Obtain the coordinates of m fitted center points, and substitute the coordinates of the center points into the equation of the first conical surface to obtain the corresponding equations of m second conical surfaces; The conical vertex of the workpiece is selected from a preset area in a plane where the plane is parallel to the upper surface of the turntable, and the preset area is a circular area with a radius r containing the conical vertex, or, the The preset area is a square area containing the vertices of the cone with a side length r, where m is a natural number greater than or equal to 1; From the set of minimum distance values from the data point to the m second conical surfaces, the second conical surface corresponding to the set with the smallest error is selected as the best fitting conic surface. 2. The method for in-situ measurement of the sealing surface of a triple eccentric butterfly valve according to claim 1, wherein obtaining the coordinate information of the outer contour data points of the workpiece to be measured placed on the turntable comprises: When the turntable rotates by a predetermined angle, the laser sensor performs a collection operation on the workpiece to be tested; after the turntable rotates for one cycle, the laser sensor moves down a predetermined distance along the Z axis for the next collection operation . 3. The in-situ measurement method of the sealing surface of a triple eccentric butterfly valve according to claim 1, characterized in that, before establishing the first space straight line equation by least square fitting to the coordinate information of the data points, it also comprises: The optimal data that meets the requirements in the data points is set as the standard point, and the remaining data points are the data points to be screened; Set the relative distance deviation threshold; Calculate the relative distance between the to-be-screened data point and the standard point, and if the relative distance is less than or equal to the relative distance deviation threshold, the to-be-screened data point is a qualified data point. 4. The in-situ measurement method of the sealing surface of a triple eccentric butterfly valve according to claim 1, wherein the selection of the optimal busbar equation according to the preset cone angle from the first space straight line equation comprises: obtaining the direction vector of the first space straight line equation; Obtaining the included angle between the first space straight line and the standard straight line according to the direction vector; Calculate the cone angle of the cone with the first space straight line as the generatrix according to the included angle; Taking all the first space straight lines with the cone angle ranging from 18° to 23° as the second space straight lines; A straight line is selected from the second space straight line as the optimal generatrix. 5. The in-situ measurement method for the sealing surface of a triple eccentric butterfly valve according to claim 4, wherein obtaining the direction vector of the first space straight line equation comprises: calculating the residual sum of squares of the first space straight line equation; The coefficient of the first space straight line equation and the direction vector of the first space straight line are obtained by derivation of the residual sum of squared residuals. 6. The in-situ measurement method for the sealing surface of a triple eccentric butterfly valve according to claim 5, wherein the coordinates of m fitting center points are obtained, and the coordinates of the center points are substituted into the first conical surface equation , the corresponding m second conic surface equations include: Substitute the equation of the second space straight line into the general equation of the first conical surface to obtain the equation of the second conical surface, and the equation of the second conical surface is related to the coefficient of the equation of the first space straight line . 7. The method for in-situ measurement of the sealing surface of a triple eccentric butterfly valve according to claim 6, characterized in that, in the set of minimum distance values from the data point to the m second conical surfaces, the set with the smallest error is selected. The corresponding second conical surface is the best fitting conical surface including: The general expression for obtaining the minimum distance from the data point to the m second conical surfaces by using the Lagrange multiplier method of the conditional extreme value of the multivariate function; Substitute the data point into the general expression of the minimum distance, and obtain the minimum distance value set from the data point to the m second conical surfaces; Errors are calculated respectively for the minimum distance value set from the data point to the m second conical surfaces, and the second conical surface corresponding to the minimum distance value set with the smallest error is selected as the best fitting conic surface. 8 . The in-situ measurement method for the sealing surface of a triple eccentric butterfly valve according to claim 7 , wherein the data points are obtained by using the Lagrangian multiplier method of the conditional extreme value of a multivariate function to obtain m the second The general expression for the minimum distance of a conical surface includes: obtaining a Lagrangian function according to the coordinates of the data points; Differentiate the Lagrangian functions according to the three-dimensional coordinate parameters, and obtain the coordinate algebraic expressions related to the Lagrangian parameters and the coordinates of the data points; Substitute the coordinate algebra into the equation of the second conical surface to obtain the third conical surface equation related to the Lagrangian parameter; Obtain the specific value of the Lagrangian parameter by calculating the extreme value of the third conical surface equation; The minimum value of the distances from the data point to the m second conical surfaces is obtained through a coordinate algebraic formula related to the Lagrangian parameter and the coordinates of the data point.

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