Method for straightening non-straightened corners capable of straightening

Abstract

A method for straightening a non-straightened corner that can be straightened belongs to the field of digital manufacturing technology for aircraft structural parts. The main process includes: (1) discretely taking points on the corner surface to create a discrete point set; (2) respectively calculating the normal direction of each point in the discrete point set on the corner surface, pointing to the concave side of the corner, and calculating the corner axis point corresponding to each discrete point to form a corner axis point set; (3) using the least squares method to perform spatial straight line fitting on the points of the axis point set to obtain the fitted corner axis; (4) in the corner axis point set, calculating the deviation of the corner axis fitting, retrieving and recording the axis point with the smallest fitting deviation; (5) obtaining the normal plane of the fitted axis through the point with the smallest axis fitting deviation; (6) intersecting the normal plane with the corner surface and the cut-in surface and cut-out surface to obtain the intersection line; (7) using the intersection line as the contour line and the fitted axis as the guide line to create a swept surface to obtain the fitted ruled surface.

Description

Technical Field

[0001] The present invention relates to a method for straightening non-straight corners, belonging to the technical field of digital manufacturing of aircraft structural parts. The method can assist in realizing the rapid compilation of non-straight corner machining numerical control programs. Background Art

[0002] As the complexity of aviation products increases, the design of aircraft structural parts contains more complex curved surfaces. Accordingly, the transition between complex curved surfaces will form non-straight lateral corners (Note: the corners mentioned in the article refer to lateral corners). For this type of corner, engineering usually combines the manufacturing tolerance requirements of the structural parts to measure whether the corner can be straight-lined. For non-straight corners that can be straight-lined, when using CAM software for CNC programming, directly selecting the corner surface in the structural part as a geometric parameter will result in the tool path being unable to be calculated or the tool axis direction suddenly changing at the center of the circle. The programmer needs to repeatedly adjust the parameters or manually interactively construct the straight surface as a geometric parameter or use the method of machining the curved surfaces on both sides and stopping the tool at the corner axis. Therefore, in the CNC programming of non-straight corners that can be straight-lined, there are problems such as low programming efficiency and difficulty in ensuring the quality of corner processing. Therefore, it is urgent to propose an effective technical solution to improve the research and development efficiency and quality of aircraft structural parts to meet the rapid development needs of the current aviation manufacturing industry. Summary of the invention

[0003] The present invention proposes a method for straight-graining a non-straight-grained corner that can be straight-grained, which provides geometric parameters for the compilation of numerical control programs for non-straight-grained corners, assists in realizing fast corner programming, and improves the quality of corner processing.

[0004] The technical solution of the present invention:

[0005] A method for straightening a non-straightened corner that can be straightened, the main process of which includes: (1) discretely taking points on the corner surface to create a discrete point set; (2) respectively calculating the normal direction of each point in the discrete point set on the corner surface, pointing to the concave side of the corner, and calculating the corner axis point corresponding to each discrete point to form a corner axis point set; (3) using the least squares method to perform spatial straight line fitting on the points of the axis point set to obtain the fitted corner axis; (4) in the corner axis point set, calculating the deviation of the corner axis fitting, and retrieving and recording the axis point with the smallest fitting deviation; (5) obtaining the normal plane of the fitted axis through the point with the smallest axis fitting deviation; (6) intersecting the normal plane with the corner surface and the cut-in surface and the cut-out surface to obtain the intersection line; (7) using the intersection line as the contour line and the fitted axis as the guide line to create a swept surface to obtain the fitted straightened surface.

[0006] Beneficial effects of the invention: The invention provides a scientific engineering implementation method for the ruled fitting of non-straight corner surfaces, is a key technology for realizing rapid programming of corner features, can solve the problems of tool path calculation failure and poor corner processing quality in CNC programming of non-straight corners, and is of great significance for high-quality and efficient manufacturing of aircraft structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 Schematic diagram of corner features.

[0008] Figure 2 Schematic diagram of discrete point extraction for corner surfaces.

[0009] Figure 3 This is a schematic diagram for calculating the axis points of the corner surface.

[0010] Figure 4 Schematic diagram for calculating the distance between a spatial point and a straight line.

[0011] Figure 5 Schematic diagram of the calculation of the ruled contour line of the corner surface. DETAILED DESCRIPTION

[0012] The present invention proposes a method for straightening a non-straightened corner that can be straightened and manufactured, which is based on a CAD / CAM system platform, realizes the rapid straightening of complex corner surfaces, and solves the problem of complex corner numerical control programming in the processing of aircraft structural parts. The following is a detailed description of the implementation example of the present invention in conjunction with the accompanying drawings. This implementation example is implemented on the premise of the invention technical solution, and a detailed implementation method and a specific implementation process are given, but the protection scope of the present invention is not limited to the following implementation example.

[0013] The detailed steps of implementing the present invention are as follows:

[0014] (1) Calculation of discrete point sets on corner surfaces

[0015] Taking the corner surface as the object, three sets of isoparametric curves are created on the corner surface in the U and V directions (the corner surface parameters are 0.25, 0.5, and 0.75 respectively), and the intersection points of the isoparametric curves are selected as discrete points on the corner surface. The discrete point set PC of the corner surface is obtained as follows:

[0016] P c =∪p ij , (i, j=1, 2, 3).............(1)

[0017] (2) Calculate the axis point set of the rotation surface

[0018] Take the discrete point set P of the corner surface c Any point p in ij , click p ijThe normal direction at the corner surface is v p , v p If the corner is concave to one side, the axis point corresponding to this point is o ij for:

[0019] o ij =p ij +r*v p .............(2)

[0020] Where r is the nominal radius of the corner.

[0021] According to the algorithm, the axis point corresponding to each point in the corner surface discrete point set PC is calculated in turn to obtain the corner axis point set O. c for:

[0022] O c =∪o ij , (i, j=1, 2, 3).............(3)

[0023] (3) Angle surface axis fitting

[0024] The least square method is used to calculate the rotation axis point set O c Perform spatial straight line fitting to obtain the fitting axis of the corner surface. The fitting method is as follows:

[0025] The standard equation of a straight line in space is:

[0026]

[0027] Transformed into projective form:

[0028]

[0029] make

[0030] The projective equation simplifies to:

[0031]

[0032] From this equation, we can know that a straight line in space is regarded as the intersection of two planes. Therefore, the fitting of a straight line in space is the fitting of these two equations. The sum of the residual squares of the two equations is calculated separately to obtain:

[0033]

[0034]

[0035] According to the least squares principle, we have

[0036]

[0037] Set the corner axis point set O c Substitute the point data into the above equation, solve the equation group, calculate the coefficients m, n, s, t, and thus, you can get the fitting space straight line, which is the fitting axis A of the corner surface. c .

[0038] (4) Retrieve the axis point with the smallest straight line fitting deviation

[0039] Set point ij is the axis point set O c For any point in ij To axis A c The distance d ij .

[0040] The axis A is obtained by calculation in step (3) c The equation of the line is:

[0041]

[0042] The axis A c Direction vector Axis A c A point on (x 0 ,y 0 , z 0 );

[0043] Assume that point o ij (x i ,y i , z i ) Make axis A c The perpendicular line of d ,y d , z d ), then:

[0044]

[0045] The converted parameter forms are:

[0046]

[0047] At the same time, ij The perpendicular line o ij The direction vector of D

[0048] From axis A c With o ij The vertical relationship of D can be obtained:

[0049]

[0050] Right now:

[0051] a(x d -x i )+b(y d -y i )+c(z d -z i )=0.............(13)

[0052] By combining formula (12) and (13), we can obtain:

[0053]

[0054] At this point, we will find point o ij To axis A c The distance d ij Convert to point o ij (x i ,y i , z i ) and D(x d ,y d , z d )The distance between two points can be obtained

[0055]

[0056] According to the above method, calculate the rotation surface axis point set O in sequence c Each point in the fitting axis A of the corner surface c Deviation, comparative analysis, retrieve the axis point with the minimum deviation o min :

[0057] o min =min(d ij ), (i, j=1, 2, 3).............(16)

[0058] Where d ij Representative point o ij To axis A c distance.

[0059] (5) Calculate the intersection plane

[0060] Minimum axis point of deviation o min , create the fitting axis A of the corner surface c The normal plane F is the intersection plane.

[0061] Assume point o min (x min ,y min , z min ), axis A c The direction vector is Then the equation of the normal plane F can be obtained as:

[0062] a(xx min )+b(yy min )+c(zz min )=0.............(17)

[0063] (6) Calculate the contour line of the corner surface ruled processing

[0064] Fitting the axis A with the angle surface c The normal plane F and the corner surface S c , Corner cut-in surface S i , Corner cut-out surface S o Perform intersection and obtain the intersection line, which is the contour line l of the corner surface ruled:

[0065] l=F∩(S i ∪S c ∪S o ).............(18)

[0066] (7) Straightening of non-straight corner surfaces

[0067] The fitting axis A of the corner surface c is the guide line, the contour line l is the sweep contour line, and the sweep surface S is created to achieve the ruled processing of the non-ruled corner surface:

[0068] S=f(A c , l).............(19).

Claims

1. A method for straightening a non-straightened corner that can be straightened, characterized in that: Here are the steps: (1) Discrete points are taken on the corner surface to create a discrete point set; (2) Calculate the normal direction of each point in the discrete point set on the corner surface, pointing to the concave side of the corner, and calculate the corner axis point corresponding to each discrete point to form a corner axis point set; (3) Using the least square method to fit the points of the axis point set into a spatial straight line, a fitted rotation axis is obtained; (4) In the set of corner axis points, the deviation of the corner axis fitting is calculated, and the axis point with the smallest fitting deviation is retrieved and recorded; (5) Find the normal plane of the fitting axis through the point where the axis fitting deviation is minimum; (6) Intersecting the normal plane, the corner plane, the entry plane, and the exit plane to obtain the intersection line; (7) Using the intersection line as the contour line and the fitting axis as the guide line, the scanned surface is created to obtain the fitted ruled surface.

2. The method for straightening non-straightened corners according to claim 1, characterized in that: The specific steps are as follows: (1) Calculation of discrete point sets on corner surfaces Taking the corner surface as the object, three sets of isoparametric curves are created on the corner surface in the U and V directions. The intersection points of the isoparametric curves are selected as discrete points on the corner surface to obtain the discrete point set P of the corner surface. C for: P c =∪p ij ,i,j=1,2,3...........(1) (2) Calculate the axis point set of the rotation surface Take the discrete point set P of the corner surface c Any point p in ij , click p ij The normal direction at the corner surface is v p , v p If the corner is concave to one side, the axis point corresponding to this point is o ij for: O ij =p ij +r*v p ............(2) Where r is the nominal radius of the corner; According to the algorithm, the discrete point set P of the corner surface is calculated in sequence. C Each point in the axis point corresponds to the axis point, and the angle axis point set O is obtained. c for: O c =∪o ij ,i,j=1,2,3.............(3) (3) Angle surface axis fitting The least square method is used to calculate the rotation axis point set O c Perform spatial straight line fitting to obtain the fitting axis of the corner surface; the fitting method is as follows: The standard equation of a line in space is: Transformed into projective form: make The projective equation simplifies to: From this equation, we can know that a straight line in space is regarded as the intersection of two planes. Therefore, the fitting of the straight line in space is the fitting of these two equations. The sum of the squares of the residuals of the two equations is obtained: According to the least squares principle, we have Set the corner axis point set O c Substitute the point data into the above equation, solve the equation group, calculate the coefficients m, n, s, t, and thus, you can get the fitting space straight line, which is the fitting axis A of the corner surface. c ; (4) Retrieve the axis point with the smallest straight line fitting deviation Set point oi j is the axis point set O c For any point in ij To axis A c The distance d ij ; The axis A is obtained by calculation in step (3) c The equation of the line is: The axis A c Direction vector Axis A c A point on is (x0, y0, z0); Assume that point o ij (x i ,y i , z i ) Make axis A c The perpendicular line of d ,y d , z d ), then: The converted parameter forms are: At the same time, ij The perpendicular line o ij The direction vector of D From axis A c With o ij The vertical relationship of D can be obtained: Right now: a(x d -x i )+b(y d -y i )+c(z d -z i )=0.............(13) By combining formula (12) and (13), we can obtain: At this point, we will find point o ij To axis A c The distance d ij Convert to point o ij (x i ,y i , z i ) and D(x d ,y d , z d )The distance between two points can be obtained According to the above method, calculate the rotation surface axis point set O in sequence c Each point in the fitting axis A of the corner surface c Deviation, comparative analysis, retrieve the axis point with the minimum deviation o min : oh min =min(d ij ),i,j=1,2,3...........(16) Where d ij Representative point o ij To axis A c distance; (5) Calculate the intersection plane Minimum axis point of deviation o min , create the fitting axis A of the corner surface c The normal plane F is the intersection plane; Assume point o min (x min ,y min , z min ), axis A c The direction vector is Then the equation of the normal plane F can be obtained as: a(x-x min )+b(y-y min )+c(z-z min )=0.............(17) (6) Calculate the contour line of the corner surface ruled processing Fitting the axis A with the angle surface c The normal plane F and the corner surface S c , Corner cut-in surface S i , Corner cut-out surface S o Perform intersection and obtain the intersection line, which is the contour line l of the corner surface ruled: l=F∩(S i ∪S c ∪S o ).............(18) (7) Straightening of non-straight corner surfaces The fitting axis A of the corner surface c is the guide line, the contour line l is the sweep contour line, and the sweep surface S is created to achieve the ruled processing of the non-ruled corner surface: S=f(A c ,l).............(19)。

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