Method and system for detecting coplanarity of nut post

Abstract

The application relates to the technical field of coplanarity detection, in particular to a nut post coplanarity detection method and a detection system, which comprises the following steps: analyzing the discrete characteristics of three-dimensional coordinate data and angle data of the same bit sequence on all circle threads to obtain discrete characteristic values of each bit sequence; obtaining the collinear deviation of each bit sequence based on the deviation generated by straight line fitting of the three-dimensional coordinate data of the same bit sequence on all circle threads; analyzing the deviation between the fitting straight line and the fitting curved surface corresponding to two adjacent bit sequences based on the difference and distribution between the collinear deviations of each adjacent bit sequence to obtain the trajectory continuity between each adjacent bit sequence; analyzing the distance change characteristics and rotation change characteristics between the three-dimensional coordinate data of the thread points of all adjacent bit sequences on all circle threads to obtain the thread coplanar stability of the nut post, and obtaining the coplanarity detection result of the nut post. The application aims to improve the accuracy of the coplanarity detection result of the nut post.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of coplanarity detection, in particular to a nut post coplanarity detection method and system. BACKGROUND

[0002] The nut post is an important mechanical connecting component, widely used in the fields of automobiles, aerospace, electronic equipment, mechanical manufacturing, etc. It is usually used to fix multiple components together to achieve fastening and connecting functions, ensuring the stability and reliability of the structure. Therefore, the quality and precision of the nut post play a crucial role in the overall performance and safety of the product. Coplanarity measures whether multiple surfaces or points are on the same plane. Through coplanarity detection, it can be analyzed whether the production quality of the nut post meets the standard and whether the internal threads can be evenly contacted with the bolts, thereby avoiding connection failure problems caused by thread slipping or local stress concentration.

[0003] The prior art focuses on the collinearity or plane deviation of the thread points on a single cross-section when detecting the coplanarity of the nut post, mainly focusing on the consistency of the thread height on the same cross-section. However, this method does not fully consider the path deviation caused by the change of the internal thread spiral path of the nut post, which may cause errors in the coplanarity detection results of the nut post, thereby affecting the subsequent production quality detection of the nut post. SUMMARY

[0004] In view of the above, it is necessary to provide a nut post coplanarity detection method and system to solve the above problems.

[0005] The first aspect of the application provides a nut post coplanarity detection method, which comprises:

[0006] Collecting three-dimensional coordinate data of each thread point along the thread sequence of the nut post spirally upwards, obtaining angle data corresponding to the projection points of the three-dimensional coordinate data of all thread points on each thread;

[0007] Extracting three-dimensional coordinate data and angle data of the same bit sequence on all threads, obtaining a discrete feature value of each bit sequence according to the variation characteristics of each three-dimensional coordinate data and the discrete characteristics of the angle data, and obtaining a collinearity deviation of each bit sequence based on the deviation generated by linear fitting of the three-dimensional coordinate data of the same bit sequence on all threads;

[0008] Based on the difference and distribution between the collinearity deviations of each adjacent bit sequence, obtaining the collinearity deviation difference between each adjacent bit sequence, extracting the fitting surface of the thread points on all threads, analyzing the deviation between the fitting straight line corresponding to each adjacent bit sequence and the fitting surface, and obtaining the trajectory continuity between each adjacent bit sequence;

[0009] The distance variation characteristics and the rotation variation characteristics between the three-dimensional coordinate data of the thread points of each adjacent bit sequence on the threads of all turns are analyzed to obtain variation characteristic values between each adjacent bit sequence, and the thread coplanarity stability of the nut column is obtained in combination with the trajectory continuity between all adjacent bit sequences.

[0010] Based on the numerical characteristics of the thread coplanarity stability, a coplanarity detection result of the nut column is obtained.

[0011] Preferably, the angle data corresponding to the projection point of the three-dimensional coordinate data is specifically:

[0012] The projection point of each three-dimensional coordinate data in a two-dimensional coordinate system constructed by the X axis and the Y axis is obtained, the connecting line between the projection point and the origin of the two-dimensional coordinate system is extracted, and the angle data composed of the connecting line and the X positive half-axis is obtained.

[0013] Preferably, the process of obtaining the discrete characteristic value of each bit sequence is:

[0014] The discrete degree of the coordinate data of all thread points of each bit sequence on the X axis is recorded as a first discrete degree, and the discrete degree of the coordinate data of all thread points of each bit sequence on the Y axis is recorded as a second discrete degree.

[0015] A first-order difference sequence of a sequence composed of the coordinate data of all thread points of each bit sequence on the Z axis is obtained, and the discrete degree of the elements of the first-order difference sequence is recorded as a third discrete degree.

[0016] The discrete degree of the angle data of all thread points of each bit sequence is recorded as a fourth discrete degree.

[0017] The mean value of all discrete degrees obtained for each bit sequence is taken as the discrete characteristic value of each bit sequence.

[0018] Preferably, the step of obtaining the collinearity deviation degree of each bit sequence is:

[0019] The mean value of the distances between the three-dimensional data coordinates of all thread points on each bit sequence and the fitting straight line is taken as the point-line distance mean value of each bit sequence.

[0020] The discrete characteristic value and the point-line distance mean value of each bit sequence are positively fused to obtain the collinearity deviation degree of each bit sequence.

[0021] Preferably, the collinearity deviation difference between each adjacent bit sequence is specifically:

[0022] The absolute value and the mean value of the difference between the collinearity deviation degrees of each adjacent bit sequence are calculated, and the product of the absolute value and the mean value is taken as the collinearity deviation difference between each adjacent bit sequence.

[0023] Preferably, the process of obtaining the trajectory continuity between each adjacent bit sequence is specifically:

[0024] The direction vector of the fitting straight line corresponding to each bit sequence is extracted, the similarity between the direction vectors of each adjacent bit sequence is analyzed, and the parallelism between each adjacent bit sequence is obtained.

[0025] The average distance between the two fitting straight lines corresponding to each adjacent bit sequence and the fitting curved surface is obtained, which is recorded as the average line-surface distance between each adjacent bit sequence.

[0026] The sum of the collineation deviation difference between each adjacent bit sequence and the average line-surface distance is obtained; the negative correlation mapping result of the sum is positively fused with the absolute value of the parallelism corresponding to the absolute value, and the trajectory continuity between each adjacent bit sequence is obtained.

[0027] Preferably, the process of obtaining the change characteristic value between each adjacent bit sequence is specifically:

[0028] The distance between the two thread points of each adjacent bit sequence in each turn is obtained, and the dispersion degree of the distance of each adjacent bit sequence on all turns is recorded as the distance dispersion value.

[0029] The dispersion degree of the helix angle vector of each adjacent bit sequence in each turn in each dimension is obtained, and the average of the dispersion degrees in all dimensions is taken as the turning angle dispersion value; wherein, the helix angle vector is determined by the difference value of the coordinates of the thread point with larger bit sequence and the coordinates of the thread point with smaller bit sequence in each adjacent bit sequence corresponding to the dimension.

[0030] The average of the distance dispersion value and the turning angle dispersion value corresponding to each adjacent bit sequence is taken as the change characteristic value between each adjacent bit sequence.

[0031] Preferably, the process of obtaining the thread coplanar stability of the nut column is specifically:

[0032] The positive fusion result of the negative correlation mapping result of the change characteristic value of each adjacent bit sequence and the trajectory continuity is calculated, and the average of the positive fusion results obtained by all adjacent bit sequences is taken as the thread coplanar stability of the nut column.

[0033] Preferably, the coplanarity detection result of the nut column is specifically:

[0034] The thread coplanar stability of the nut column is normalized, and if the normalized value is greater than or equal to a preset threshold, it is determined that the coplanarity detection of the nut column is qualified; otherwise, the coplanarity detection of the nut column is unqualified.

[0035] In a second aspect, the embodiments of the present application also provide a nut column coplanarity detection system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, and the processor implements the steps of the method in any of the above aspects when executing the computer program.

[0036] The present application has at least the following beneficial effects:

[0037] The embodiments of the present application can quantify the linear consistency of the same bit sequence thread point on each thread in the axial direction by constructing the collinear deviation degree, and further assess whether there are problems such as uneven thread height and processing skip; the trajectory continuity degree is constructed, so as to reflect whether the adjacent thread points belong to the same plane, and further judge the spatial stability of the internal structure of the nut column; the thread coplanarity smoothness is constructed, so as to jointly analyze the stability of the thread plane relationship and the spiral rising path between adjacent thread points, and finally evaluate the production quality of the nut column.

[0038] Further, the present application considers the thread spiral path change characteristics which are not fully considered in the prior art, which may lead to false detection, by constructing the thread coplanarity smoothness, which can consider the coplanarity of adjacent collection points in the nut column, and simultaneously evaluate the continuity and direction stability of the thread path in the spiral direction. This method can comprehensively reflect the distribution characteristics of the thread points in the three-dimensional space, thereby improving the accuracy and robustness of the coplanarity detection. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 A step flowchart of the nut column coplanarity detection method provided by an embodiment of the present application is shown in the figure;

[0040] Figure 2 A schematic diagram of thread point three-dimensional coordinate data collection provided by an embodiment of the present application is shown in the figure;

[0041] Figure 3 A schematic diagram of thread point corresponding angle data collection provided by an embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0042] In the description of the embodiments of the present application, the words "exemplary", "or", "for example" are used to mean as an example, illustration, or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the words "exemplary", "or", "for example" are used in the specific manner to present the relevant concept.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0044] In addition, it should be pointed out that the terms "first", "second" in the present application and the drawings are used to distinguish similar objects, and are not used to describe a specific order or sequence. The method disclosed in the embodiments of the present application or the method shown in the flow chart includes one or more steps for implementing the method, and the execution order of the steps can be interchanged with each other without departing from the scope of the present application, and some steps can also be deleted.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0046] The specific scheme of the nut column coplanarity detection method and detection system provided by the present application will be described in detail below in combination with the drawings.

[0047] Please refer to Figure 1 , which shows the step flow chart of the nut column coplanarity detection method provided by an embodiment of the present application, and the method includes the following steps:

[0048] The first step: uniformly collecting three-dimensional coordinate data of each thread point along the thread sequence of the nut column and spirally upward, and obtaining angle data corresponding to the projection point of the three-dimensional coordinate data of all thread points on each thread.

[0049] The present application collects the coordinate and angle data of the thread point by using a contact three-coordinate measuring instrument with a micro probe, as follows:

[0050] First, build the coordinate system: when collecting the coordinate data of the thread point, fix the nut column, take the center of the bottom of the nut column as the center of the circle, take the front as the Y positive axis, take the right as the X positive axis, and take the top as the Z positive axis to build a three-dimensional coordinate system. At the same time, build a two-dimensional coordinate system with the same position of the X axis and the Y axis.

[0051] Define the initial contact point at the thread top of the bottom of the nut column, collect the coordinate data of each thread point along the thread sequence spirally upward with a preset step length, and stop collecting at the thread top of the uppermost end of the nut column, so as to obtain the three-dimensional coordinate data of all thread points in the nut column, wherein the thread point three-dimensional coordinate data collection schematic diagram is shown in Figure 2 Figure 2 ​The nut column bottom thread tooth top position 1, the nut column top thread tooth top position 2, and the threaded spiral path 3 are included. Meanwhile, angle data corresponding to the projection points of each thread point in the two-dimensional coordinate system is recorded during data acquisition, and the angle data is the angle formed by the connecting straight line between each projection point and the origin and the x positive axis direction. The thread point corresponding angle data acquisition schematic is shown in Figure 3 Figure 3 The angle of the projection point corresponding to the thread point of the i-th bit sequence is β i It should be understood that one angle corresponds to multiple thread points in an ideal state.

[0052] In the present application, the preset step length formula is: In the formula, T is the length of one upward spiral of the thread, and J is a preset value. Since the angle of one rotation of the thread is 360 degrees, J is 360 in the present example.

[0053] According to the time sequence order of data acquisition, the three-dimensional coordinate data and angle value data of all thread points collected on each thread are used to construct the x sequence, y sequence, z sequence, and angle sequence corresponding to each thread of the nut column.

[0054] In order to eliminate the dimensional influence between data, all data is normalized. Normalization methods include Z-score, tanh normalization, maximum and minimum value normalization, etc. In the present embodiment, maximum and minimum value normalization is used.

[0055] The second step is to extract the three-dimensional coordinate data and angle data of the same bit sequence on all threads, obtain the discrete characteristic value of each bit sequence according to the variation characteristics of each dimensional coordinate data and the discrete characteristics of the angle data, and obtain the collinearity deviation of each bit sequence based on the deviation generated by the straight line fitting of the three-dimensional coordinate data of the same bit sequence on all threads.

[0056] When the production and processing quality of the nut column meets the standard, the internal thread height and thread spacing should remain consistent, so as to play a good connection and fixing role. At this time, the thread points at the same bit sequence should be located on the same straight line, and since more than three points exist in the straight line collinearity, it can reflect that they are in the same plane. Therefore, if the production of the nut column meets the standard, the thread points of the internal thread of the nut column at the same bit sequence have coplanar characteristics. If the production and processing quality of the nut column does not meet the standard, the internal thread height is inconsistent and no longer has the coplanarity degree characteristics, which may cause problems such as thread slippage and local stress concentration, thereby affecting the stability and service life of the nut column.

[0057] Taking the i-th bit sequence thread point as an example for analysis, it is detected whether the i-th bit sequence thread points on all threads are collinear. ​

[0058] Specifically, the elements of the i-th bit sequence are extracted from the x sequence of all turns of threads, and the x sub-sequence corresponding to the i-th bit sequence is constructed according to the sequence of data acquisition. Correspondingly, the y sub-sequence, the z sub-sequence and the angle sub-sequence corresponding to the i-th bit sequence are extracted based on the y sequence, the z sequence and the angle sequence by using the same method.

[0059] If the nut column production quality is good, according to the equal interval and equal height of the threads and the spiral ascending characteristics, the internal elements of the x sub-sequence and the y sub-sequence should be strictly the same, the internal elements of the z sub-sequence show linear growth, and the distance between adjacent points is consistent.

[0060] The first-order difference sequence of the z sub-sequence is obtained, which can reflect the interval between each adjacent element in the z sub-sequence.

[0061] For the i-th bit sequence, the dispersion degree of the x sub-sequence is recorded as the first dispersion degree, the dispersion degree of the y sub-sequence is recorded as the second dispersion degree, the dispersion degree of the first-order difference sequence of the z sub-sequence is recorded as the third dispersion degree, and the dispersion degree of the elements of the angle sub-sequence is recorded as the fourth dispersion degree. The mean value of all the dispersion degrees is recorded as the dispersion characteristic value of the i-th bit sequence. The dispersion characteristic value can reflect the consistency and spiral ascending uniformity of all turns of threads under the i-th bit sequence; the smaller the value, the more consistent and uniform the threads of all turns of threads under the i-th bit sequence. The calculation method of the dispersion degree includes variance, coefficient of variation, information entropy, etc. In this embodiment, the variance is calculated.

[0062] Further, the x sub-sequence, the y sub-sequence and the z sub-sequence are arranged in the order of x, y and z to construct the thread point coordinate matrix corresponding to the i-th bit sequence in the order of column-by-column insertion. Each row of data in the matrix is the three-dimensional coordinate data of the thread point on the i-th bit sequence of each turn in the data acquisition process.

[0063] All the thread point coordinates corresponding to the i-th bit sequence, i.e. the three-dimensional coordinates corresponding to all the rows of the thread point coordinate matrix, are taken as the input of the straight line fitting algorithm for three-dimensional straight line fitting, and the point-line distance between the three-dimensional coordinates corresponding to each row of data and the three-dimensional straight line is calculated. The mean value of all the point-line distances is recorded as the point-line distance mean value of the i-th bit sequence. The point-line distance mean value can reflect the average distance between all the thread points of the same bit sequence and the fitted straight line; the smaller the value, the greater the possibility that all the thread points corresponding to the i-th bit sequence are located on the same straight line. It should be noted that the three-dimensional straight line fitting algorithm is not limited to the least square method and the RANSAC algorithm, and the least square method is used in this embodiment.

[0064] The discrete characteristic value of the i-th bit sequence is fused with the average of the point line distance to obtain the collinearity deviation of the i-th bit sequence. In this embodiment, the calculation method of multiplication is used for the forward fusion of multiple variables.

[0065] It should be understood that the collinearity deviation can reflect the regularity and stability of the thread point distribution. The greater the collinearity deviation, the greater the degree of deviation of the thread points in the i-th bit sequence from the straight line, the poorer the co-planarity of the thread points in the i-th bit sequence, and the greater the possibility of unevenness of the thread structure of the nut column.

[0066] The third step: based on the difference and distribution between the collinearity deviations of each adjacent bit sequence, the collinearity deviation between each adjacent bit sequence is obtained, the fitting surface of the thread points on all the threads is extracted, the deviation between the fitting straight line corresponding to each adjacent bit sequence and the fitting surface is analyzed, and the trajectory continuity between each adjacent bit sequence is obtained.

[0067] Further, after obtaining the collinearity degree of the thread points in the same bit sequence, the co-planarity of the thread points between adjacent bit sequences in the nut column can be further analyzed by analyzing the difference in collinearity degree of the thread points between each adjacent bit sequence, thereby providing a data basis for subsequent production quality detection of the nut column as a whole.

[0068] Taking the i-th bit sequence and the i+1-th bit sequence as an example for analysis. The collinearity deviation of the i+1-th bit sequence is obtained by the calculation method of the collinearity deviation of the i-th bit sequence.

[0069] The absolute value and the average of the difference between the collinearity deviations of the i-th bit sequence and the i+1-th bit sequence are calculated, and the product of the absolute value and the average is taken as the collinearity deviation between the i-th bit sequence and the i+1-th bit sequence. The collinearity deviation can reflect whether the collinearity degree of the thread points of adjacent bit sequences is consistent; the smaller the value, the better the collinearity of the corresponding thread points of the i-th bit sequence and the i+1-th bit sequence, and the greater the possibility that the thread points of the two bit sequences are located on two straight lines.

[0070] Further, according to the geometric axiom: two parallel straight lines must belong to the same plane, and the plane is uniquely determined. Therefore, whether all the thread points between adjacent bit sequences are co-planar can be calculated by analyzing the parallel degree between the straight lines to which the thread points of the i-th bit sequence and the i+1-th bit sequence belong.

[0071] When using the least square method to fit a three-dimensional straight line, the least square method first calculates a center point and a covariance matrix by all data points to be fitted, and then fits a three-dimensional straight line according to the center point and the covariance matrix. At this time, the eigenvalue decomposition is performed on the covariance matrix, and the vector corresponding to the maximum eigenvalue is the direction vector of the fitted three-dimensional straight line, which represents the direction angle of the straight line in the three-dimensional space.

[0072] Therefore, by performing eigenvalue decomposition on the covariance matrix in the three-dimensional straight line fitting process respectively, the direction vectors of the three-dimensional fitting straight lines corresponding to the i th and i+1 th thread orders can be directly obtained. The two direction vectors are unitized respectively, and then the parallelism between the two unit direction vectors is calculated as the parallelism between the i th and i+1 th thread orders. The calculation method of the vector parallelism is not limited to the cosine similarity and the dot product. In this embodiment, the cosine similarity is used. The greater the parallelism, the greater the possibility that the three-dimensional straight lines corresponding to the i th and i+1 th thread orders are in parallel relationship.

[0073] Further, a three-dimensional curved surface is fitted by all thread points corresponding to all thread orders, and then the average of the line-surface distances between the three-dimensional straight lines corresponding to the i th and i+1 th thread orders and the fitted curved surface is calculated, which is recorded as the line-surface average distance between the i th and i+1 th thread orders. The smaller the line-surface average distance, the greater the possibility that the three-dimensional straight lines corresponding to the i th and i+1 th thread orders belong to the same integral threaded curved surface.

[0074] The three-dimensional curved surface fitting algorithm is not limited to the least square method curved surface fitting and the B-spline curved surface fitting algorithm. In this embodiment, the least square method curved surface fitting algorithm is used. The line-surface distance calculation method in the three-dimensional space includes the projection method and the gradient method. In this embodiment, the projection method is used for calculation, and the number of projection points is the number of turns of the thread in the nut column. The three-dimensional straight line and curved surface fitting based on the least square method, the eigenvalue decomposition, the vector unitization, the cosine similarity, and the projection method are all known technologies, which will not be described here.

[0075] The sum of the collinear deviation difference between the i th and i+1 th thread orders and the line-surface average distance is calculated. The negative correlation mapping result of the sum is fused with the absolute value of the corresponding parallelism in a positive direction to obtain the trajectory continuity between the i th and i+1 th thread orders.

[0076] In this embodiment, the trajectory continuity of the thread points between the i th and i+1 th thread orders is recorded as F i,i+1 , and the specific formula form is as follows: In the formula, D i,i+1 is the collinear deviation difference between the i th and i+1 th thread orders; Q i,i+1 is the line-surface average distance between the i th and i+1 th thread orders; and |Gi,i+1 | is the absolute value of the parallelism between the third straight line corresponding to the i-th and the i+1-th pitch sequence. τ is a tuning coefficient, which is taken from the range (0.005, 0.01) to avoid the denominator being zero, and the value has little effect on the calculation and can be ignored. The implementer can take the value by himself.

[0077] It should be understood that the trajectory continuity can not only reflect whether the thread points of the i-th and the i+1-th pitch sequence belong to the same plane in the three-dimensional space, but also reflect whether they belong to the same thread surface. The greater the value, the more likely that the thread points of the i-th and the i+1-th pitch sequence are located on the fitting straight line, and the fitting straight line is parallel and belongs to the thread surface, thereby further reflecting that the change of the thread trajectory is more continuous and more consistent with the overall spiral change.

[0078] The fourth step is to analyze the distance change characteristics and rotation change characteristics between the three-dimensional coordinate data of the thread points of each adjacent pitch sequence on all circle threads, obtain the change characteristic value between each adjacent pitch sequence, and obtain the thread coplanar stability of the nut column in combination with the trajectory continuity between all adjacent pitch sequences.

[0079] Further, considering that even if the thread points under the adjacent pitch sequence have coplanar degree, the up and down offset of the thread path may still occur; therefore, the spiral change characteristics of the thread points under the adjacent pitch sequence can be used to further characterize whether the spiral path of the nut column exists offset between the adjacent pitch sequences and whether it may cause uneven contact of the bolt.

[0080] The i+1-th thread point coordinate matrix is constructed in the construction manner of the i-th thread point coordinate matrix.

[0081] Since the internal thread of the nut column with good production quality has the characteristic of stable spiral rising, when the thread points change from the i-th pitch sequence to the i+1-th pitch sequence in each circle, the distance and the turning angle of each change will be consistent.

[0082] The distance between the three-dimensional coordinate data of each row of the two thread point coordinate matrices is recorded as the row sequence distance, and the dispersion degree between all row sequence distances is calculated. The dispersion degree between all row sequence distances is recorded as the distance dispersion value between the i-th and the i+1-th pitch sequence. The distance dispersion value can reflect the consistency of the thread distance change between the adjacent pitch sequences in different turns of the nut column. The smaller the distance dispersion value, the more consistent the spiral change distance of the thread in the nut column. The distance calculation method of the three-dimensional coordinate data is not limited to Euclidean distance, Manhattan distance, DTW distance, and the Euclidean distance is adopted in this embodiment.

[0083] The coordinate data L of the thread point corresponding to the i th position sequence and the i+1 th position sequence of the nut post in the L th turn i (L i,x ,L i,y ,L i,y ) and L i+1 (L i+1,x ,L i+1,y ,L i+1,y ) can be calculated to obtain the helix angle vector of the i th position sequence to the i+1 th position sequence in the L th turn The helix angle vector can reflect the direction change of the adjacent two thread points on the helical path in the three-dimensional space in the same turn. The dispersion degree of the helix angle vector of the i th position sequence and the i+1 th position sequence in all turns in each dimension is calculated, and the average of the dispersion degrees obtained in all dimensions is taken as the steering angle dispersion value. The steering angle dispersion value can reflect whether the direction change of the thread path between the adjacent position sequences in the three-dimensional space is consistent. The smaller the steering angle dispersion value is, the more the same steering change of the helix angle is reflected.

[0084] The average of the distance dispersion value and the steering angle dispersion value is taken as the change characteristic value between the i th position sequence and the i+1 th position sequence. The change characteristic value can reflect the stability of the thread helix between the i th position sequence and the i+1 th position sequence.

[0085] The negative correlation mapping result of the change characteristic value of the adjacent two position sequences and the positive fusion result of the trajectory continuity are calculated, and the average of the positive fusion results obtained by all adjacent position sequences is taken as the thread coplanar stability of the nut post. In this embodiment, the formula of the thread coplanar stability W of the nut post is: In the formula, J is the number of thread points of each turn of the thread of the nut post, which is 360 in this embodiment; F i,i+1 is the trajectory continuity between the i th position sequence and the i+1 th position sequence; H i,i+1 is the change characteristic value between the i th position sequence and the i+1 th position sequence.

[0086] It should be understood that the thread coplanar stability W can reflect the coplanar degree of the thread points between the adjacent position sequences and the stability of the helical path in the nut post. The larger W is, the better the production quality of the nut post is reflected, the more consistent the height and helical direction of the thread are, the better the coplanar degree is, the more uniform the connection stress between the nut post and the bolt is, and the better the fixing effect is.

[0087] The fifth step: based on the numerical characteristics of the thread coplanar stability, the coplanar degree detection result of the nut post is obtained.

[0088] The thread coplanarity stability of the nut column is sigmoid normalized, if the normalized value is greater than or equal to a preset threshold value 0.5, it is determined that the coplanarity detection of the thread in the nut column is qualified, the connection quality of the nut column is stable, and the production quality meets the standard; if the normalized value is less than the threshold value 0.5, it is determined that the coplanarity detection of the thread in the nut column is unqualified, and problems such as thread slipping and connection stress concentration may occur, and the production quality is unqualified and needs to be reprocessed.

[0089] Based on the same inventive concept as the above method, the embodiments of the present application also provide a coplanarity detection system for a nut column, comprising a memory, a processor and a computer program stored in the memory and running on the processor, and the processor executes the computer program to realize the steps of any one of the above coplanarity detection methods for the nut column.

[0090] In summary, the present application can quantify the linear consistency of the same bit sequence thread points on each thread in the axial direction by constructing the collinear deviation, and further evaluate whether there are problems such as uneven thread height and processing skip; by constructing the trajectory continuity, it can reflect whether the adjacent bit sequence thread points belong to the same plane, and further judge the spatial stability of the internal structure of the entire nut column; by constructing the thread coplanarity stability, it can jointly analyze the stability of the thread plane relationship and the spiral rising path between adjacent bit sequence thread points, and finally evaluate the production quality of the nut column.

[0091] Further, the present application aims at the problem of false detection in the prior art due to insufficient consideration of the change characteristics of the thread spiral path. The present application constructs the thread coplanarity stability, which not only considers the coplanarity of the thread points under adjacent collection bit sequences in the nut column, but also synchronously measures the path continuity and direction stability in the spiral direction, thereby comprehensively reflecting the distribution characteristics of the thread points in the three-dimensional space and improving the robustness of the coplanarity detection.

[0092] The computer program product of the present application can be a computer program implemented on one or more computers. The program instructions can be stored on a computer-readable medium, such as a floppy disk, CD-ROM, and the like. The computer program product can also include computer programs that are transmitted over a network via, for example, telephone line, LAN, wireless instrument, or others. Accordingly, the computer program product of the present application can be an article of manufacture including a computer usable medium having computer readable program code means distributed therein. The computer readable program code means is means for causing a computer to operate in a specific and predefined manner. The present application can also be embodied in a computer readable medium including transitory signals. Accordingly, the present application can be a product, an article of manufacture, and / or a machine.

[0093] It is apparent that a person skilled in the art can make various modifications to the embodiments described in the application, without departing from the spirit and scope of the application. Therefore, the described embodiments are to be considered in all respects as illustrative and not restrictive. Any modification, equivalent replacement, or improvement made to the technical solutions described in the embodiments of the present application, without departing from the spirit and scope of the embodiments of the present application, shall fall within the scope of the protection of the present application.

Claims

1. A method for detecting the coplanarity of a nut column, characterized in that, The method includes the following steps: The three-dimensional coordinate data of each thread point is collected evenly along the spiral upward sequence of the nut thread to obtain the angle data corresponding to the projection point of the three-dimensional coordinate data of all thread points on each turn of the thread. Extract the three-dimensional coordinate data and angle data of the same position sequence on all ring threads. Based on the variation characteristics of each dimension coordinate data and the discrete characteristics of the angle data, obtain the discrete feature value of each position sequence. Based on the deviation generated by the linear fitting of the three-dimensional coordinate data of the same position sequence on all ring threads, obtain the collinearity deviation of each position sequence. Based on the difference and distribution of collinear deviation between each adjacent position, the collinear deviation difference between each adjacent position is obtained. The fitted surface of the thread points on all threads is extracted. The deviation between the fitted straight line and the fitted surface corresponding to each adjacent position is analyzed to obtain the trajectory continuity between each adjacent position. Analyze the distance and rotation characteristics between the three-dimensional coordinate data of each adjacent thread position on all the threads, obtain the characteristic value of the change between each adjacent position, calculate the negative correlation mapping result of the characteristic value of the change between each adjacent position and the positive fusion result of the trajectory continuity, and take the average of the positive fusion results obtained from all adjacent positions as the thread coplanar stability of the nut column. Based on the numerical characteristics of the coplanar stability of the thread, the coplanarity test results of the nut column are obtained.

2. The method for detecting the coplanarity of a nut-shaped column as described in claim 1, characterized in that, The angle data corresponding to the projection point of the obtained three-dimensional coordinate data is specifically as follows: Obtain the projection point of each three-dimensional coordinate data onto the two-dimensional coordinate system constructed by the X-axis and Y-axis, extract the line connecting the projection point and the origin of the two-dimensional coordinate system, and obtain the angle data formed by the line and the positive X-axis.

3. The method for detecting the coplanarity of a nut-oriented column as described in claim 1, characterized in that, The process of obtaining the discrete feature value of each bit sequence is as follows: The degree of dispersion of the X-axis coordinate data of all thread points in each sequence is denoted as the first degree of dispersion; the degree of dispersion of the Y-axis coordinate data of all thread points in each sequence is denoted as the second degree of dispersion. Obtain the first-order difference sequence of the sequence of coordinate data of all thread points on the Z-axis for each sequence, and denote the degree of discretization of the elements of the first-order difference sequence as the third degree of discretization. The degree of dispersion of the angle data of all thread points in each sequence is denoted as the fourth degree of dispersion. The mean of all discretenesses obtained for each order is used as the discrete characteristic value of each order.

4. The method for detecting the coplanarity of a nut-oriented column as described in claim 1, characterized in that, The step of obtaining the collinearity deviation of each bit sequence is as follows: The average distance between the three-dimensional data coordinates of all thread points in each sequence and the fitted straight line is taken as the average point-to-line distance of each sequence. The collinearity deviation of each sequence is obtained by positively fusing the discrete feature value of each sequence with the mean distance between the point and the line.

5. The method for detecting the coplanarity of a nut-oriented column as described in claim 1, characterized in that, The collinear deviation difference between each adjacent position is obtained specifically as follows: Calculate the absolute value and mean of the difference between the collinearity deviations of each adjacent position, and use the product of the absolute value and the mean as the collinearity deviation difference between each adjacent position.

6. The method for detecting the coplanarity of a nut-oriented column as described in claim 1, characterized in that, The process of obtaining the trajectory continuity between each adjacent position is specifically as follows: Extract the direction vector of the fitted line corresponding to each position, analyze the similarity between the direction vectors of each adjacent position, and obtain the parallelism between each adjacent position. The average distance between the two fitted lines and the fitted surface corresponding to each adjacent position is obtained and denoted as the average line-surface distance between each adjacent position. The sum of the collinear deviation difference between each adjacent position and the average distance between the line and the surface is used to obtain the trajectory continuity between each adjacent position by positively fusing the negative correlation mapping result of the sum with the corresponding absolute value of parallelism.

7. The method for detecting the coplanarity of a nut-oriented column as described in claim 1, characterized in that, The process of obtaining the change feature value between each adjacent position is as follows: Obtain the distance between two thread points of each adjacent position in each turn, and record the dispersion of the distance between each adjacent position in all turns of the thread as the distance dispersion value; The dispersion of the helical angle vector between two adjacent thread points in each revolution is obtained in each dimension, and the average of the dispersion in all dimensions is used as the discrete value of the steering angle; wherein, the helical angle vector is determined by the difference in the corresponding dimension between the coordinates of the thread point with the larger position and the thread point with the smaller position in each adjacent sequence. The mean of the discrete distance and the discrete turning angle values ​​corresponding to each adjacent position is used as the characteristic value of the change between each adjacent position.

8. The method for detecting the coplanarity of a nut-oriented column as described in claim 1, characterized in that, The coplanarity test results of the nut column are obtained as follows: The coplanarity of the nut column thread is normalized. If the normalized value is greater than or equal to the preset threshold, the coplanarity of the nut column is deemed to be qualified; otherwise, the coplanarity of the nut column is deemed to be unqualified.

9. A coplanarity detection system for a nut post, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1-8.

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