Method for automatically evaluating errors of three-dimensional geometrical shapes

A technology for three-dimensional geometry and error evaluation, applied in special data processing applications, measuring devices, instruments, etc., can solve the problems that cannot fully reflect the true shape information of the measured workpiece, and the measurement and evaluation process is cumbersome.

Inactive Publication Date: 2014-09-17
BEIJING UNIV OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The measurement and evaluation process of these two methods is relatively cumbersome, and only a small number of measuring points on the surface of the measured workpiece can be extracted, which cannot fully reflect the true shape information of the measured workpiece.
It is relatively simple to use a coordinate measuring machine to measure flatness errors ( image 3 ), the coordinate measuring machine 6 can quickly collect a large number of data points on the measured workpiece 1, and the coordinate measurement software can directly calculate the error evaluation results, but the measurement operator still needs to construct the plane features before the error evaluation can be performed during the measurement process

Method used

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  • Method for automatically evaluating errors of three-dimensional geometrical shapes
  • Method for automatically evaluating errors of three-dimensional geometrical shapes
  • Method for automatically evaluating errors of three-dimensional geometrical shapes

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Experimental program
Comparison scheme
Effect test

Embodiment 1

[0035] 1) Obtain the coordinate values ​​p of n sampling points of the measurement point set P i =(x i ,y i ,z i ), i=1,2,...,n, the surface normal vector n corresponding to the n points is calculated by the discrete point k neighborhood differential plane fitting method i =(x ni ,y ni ,z ni ), i=1,2,...,n;

[0036] 2) Use the coordinate value p of the measurement point set i and its corresponding normal vector coordinate value n i , calculate the eigenvalues ​​and eigenvectors of the discriminant matrix N, and get k=3, α 1 =0,ω 2,3 =0,ω 1 ≠0, according to Table 1, it is determined that the surface category corresponding to the point set is plane C P , and the unit normal vector T of the plane where the measuring point set is located P = ω 1 =(a P ,b P ,c P ), where a P , b P 、c Pis the coordinate value of the unit normal vector;

[0037] 3) Determine the error evaluation mathematical model according to the identification and judgment results

[0038] ...

Embodiment 2

[0045] 1) Obtain the coordinate values ​​p of n sampling points of the measurement point set P i =(x i ,y i ,z i ), i=1,2,...,n, the surface normal vector n corresponding to the n points is calculated by the discrete point k neighborhood differential plane fitting method i =(x ni ,y ni ,z ni ), i=1,2,...,n;

[0046] 2) Use the coordinate value p of the measurement point set i and its corresponding normal vector coordinate value n i , calculate the eigenvalues ​​and eigenvectors of the discriminant matrix N, and get k=3, α 1,2,3 =0,ω 1,2,3 ≠0, according to Table 1, it is determined that the surface category corresponding to the point set is spherical C S ;

[0047] 3) Determine the error evaluation mathematical model according to the identification and judgment results

[0048] min t , x max e ( p i ...

Embodiment 3

[0058] 1) Obtain the coordinate values ​​p of n sampling points of the measurement point set P i =(x i ,y i ,z i ), i=1,2,...,n, the surface normal vector n corresponding to the n points is calculated by the discrete point k neighborhood differential plane fitting method i =(x ni ,y ni ,z ni ), i=1,2,...,n;

[0059] 2) Use the coordinate value p of the measurement point set i and its corresponding normal vector coordinate value n i , calculate the eigenvalues ​​and eigenvectors of the discriminant matrix N, and get k=2, α 1 = ω 2 =0,ω 1 = α 2 , according to Table 1, it is determined that the surface category corresponding to the point set is a cylindrical surface C C , and the axis direction vector T of the cylindrical surface C = ω 1 = α 2 =(a C ,b C ,c C ), where a C , b C 、c C is the coordinate value of the unit direction vector;

[0060] 3) Determine the error evaluation mathematical model according to the identification and judgment results

[0061]...

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Abstract

The invention relates to a method for automatically evaluating errors of three-dimensional geometrical shapes and belongs to the technical field of precise measurement. Based on the evaluation method, three-dimensional measurement is performed on a certain functional surface of a workpiece with a coordinate measuring machine, three-dimensional coordinate values of measured points are obtained, the coordinate values are analyzed and calculated to directly obtain the error evaluation result, parameters of the shape of the measured surface do not need to be provided, and measuring factors do not need to be constructed manually. The three-dimensional geometrical shapes can be divided into planes, spherical surfaces, cylindrical surfaces, columnar surfaces, revolution surfaces, helicoidal surfaces and composite surfaces according to the inherent translation and rotation invariance and characteristic. The invariance number and the characteristic vectors of a measured object are calculated according to the coordinate values of the measured points, the types of the measured shapes are recognized, an error evaluation mathematical model meeting the minimum region evaluation criteria is further built, a fitting problem is solved to obtain the optimum fitting factors, and then the error evaluation result can be figured out. The initial values of the parameters required by solving the fitting problem can be obtained through calculation of the coordinate values of the measured points and the recognized characteristic vectors. Through the evaluation method, the errors of the shapes of measured workpieces can be reflected comprehensively and really, human intervention is reduced, and the shape error evaluation process is made intelligent and easier to operate.

Description

technical field [0001] The invention belongs to the technical field of precision measurement, and in particular relates to an automatic evaluation method for three-dimensional geometric shape errors. Background technique [0002] The control of product geometric accuracy is a very important process in precision machinery manufacturing, and geometric error detection is an important means to ensure the processing quality of the workpiece and meet the design requirements. Among them, shape error measurement is the most basic detection link, and the error evaluation result directly determines whether the product quality is qualified. At present, the shape error measurement is mainly realized by special measuring instruments and general measuring instruments such as three-coordinate measuring machines, and the error evaluation results are calculated by measuring software. The traditional measurement method needs to know the shape parameters of the measured object or the CAD mode...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G06F19/00G01B21/04
Inventor 石照耀张华
Owner BEIJING UNIV OF TECH
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