CN106932271B - A kind of ball indentation test impression dimension measurement method based on reverse-engineering - Google Patents
A kind of ball indentation test impression dimension measurement method based on reverse-engineering Download PDFInfo
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Abstract
The present invention proposes a kind of ball indentation test impression dimension measurement method based on reverse-engineering, in particular to for examining the ball indentation test impression dimension measurement method of heat resistance of nonmetal material in a kind of electrical safety standards, method includes: 1) to scan impression sample surfaces using three-dimensional laser scanner, obtains impression sample surfaces three-dimensional point cloud coordinate data；2) point cloud data is pre-processed；3) impression curved surface is rebuild with the B-spline surface approximating method based on Triangle Cell Parameterization；4) cutting impression curved surface obtains indentation feature curve；5) impression diameter is measured.The method of the present invention can accurately distinguish transition indented area and true indented area, precise measurement impression size, measurement accuracy height；After the point cloud data for collecting impression sample to be measured, subsequent measurement process is automatically performed by algorithm, measuring speed is fast, easy to operate；It also can determine whether load biases occur in impression forming process according to the form of the impression curved surface pattern of reconstruction or indentation feature curve.
Description
Technical field
The present invention relates to a kind of impression dimension measurement method, in particular to one kind is non-for examining in electrical safety standards
The ball indentation test impression dimension measurement method of metal material heat resistance.
Background technique
High temperature can electric property, mechanical strength and hardness to nonmetallic materials impact.Especially temperature is increased to
After first-class degree, the characteristics of some nonmetallic materials can essential changes have taken place, as under the condition of high temperature or when the hurried variation of temperature
It can melt or gradually soften, mechanical strength dramatic decrease, insulation resistance reduce.In electronics, electrical equipment, for heat damage
May influence afterwards the case member of equipment safety, other external insulation parts, supporting part dangerous voltage insulating materials should be abundant
Heat-resisting, otherwise high temperature is easy to cause the failure of equipment, and short circuit can be caused when serious, causes the accidents such as fire, electric shock.Ball indentation test
It is common test electronics, one of method of heat resistance of nonmetal material in electric product, is electronics, electric product associated safety
The important content of Product Safety, " the safety first part of household and similar applications electric appliance: general GB4706.1 are examined in standard
It is required that " the 30.1st article of regulation be " for exterior part made of nonmetallic materials, for supporting the exhausted of charging member (including connection)
Edge material parts and offer superinsulation or the thermoplastic material part for reinforcing insulation, deterioration may cause utensil and do not meet mark
Alignment request, should be sufficiently heat-resisting ".Also similar rule have been made in the standards such as GB2099.1 " household with similar applications electrical appliance plug jack "
It is fixed.
Clear stipulaties are made that the judgment method of the requirement of ball indentation test and heat resistance of nonmetal material in national standard: by ball
Compression testing device and sample holder are put into heater box together, are heated to that test specimen is placed on sample after temperature as defined in standard
About center position on support, then pressure ball is placed on sample center position and applies a 20N at the appointed time
The down force of ± 0.2N, then removes pressure ball from sample, and it is 20 DEG C ± 5 that test specimen, which is immersed temperature, in 10s
In DEG C water and after being kept for 6min ± 2min time, test specimen is taken out from water, moisture removal is removed in 3min later and is measured
Impression size d, if diameter d is no more than 2.0mm, the heat resistance of insulating materials meets national standard.Defined in national standard
Impression diameter d refers to that pressure ball in ball indentation test is in contact the maximum gauge in region with sample.Ball indentation test is formed by impression shape
True indented area and the part of transition indented area two can be divided by becoming region, wherein the part being in contact with pressure ball is true impression
Area, does not contact with pressure ball but the region that deformation occurs is transition indented area.In national standard clear stipulaties obtain the method for impression with
Step, but the specific method of impression diameter measurement is not provided.There are mainly three types of sides for Inspection Unit's measurement impression diameter at present
Method: sciagraphy, patterning method and it is measured microscopically method.But impression size is small, and patterning method is difficult accurately along center line to impression
It carries out cutting and cutting process is easily destroyed impression sample.And it projects or is measured microscopically method, and there are complex steps, true
The problems such as indented area can not be accurately identified with transition indented area, and testing staff's subjective impact is big.For a long time, it is pressed in ball indentation test
The accuracy and objectivity of trace measurement result is always to perplex a big problem of quality inspection personnel.
Chinese patent CN201773041U disclose a bulb compacting test impression dimension measuring device, be equipped with lighting device,
Optical information transformation system 2CCD video camera, image pick-up card, white dynamic focusing objective table and computer.The patent described device makes
Vickers indentation is measured with the method that optical information converts, but optical information transformation system requires height to each eyeglass assembly precision, it is micro-
Small rigging error may cause the biggish error of measurement result, and the patent does not provide the scaling method of measuring device, survey
Amount device is not easy to demarcate.
Summary of the invention
It is an object of the invention to overcome the deficiency of the prior art, proposes a kind of ball indentation test impression based on reverse-engineering
Dimension measurement method, by obtaining impression sample surfaces three-dimensional point cloud coordinate data, being pre-processed to point cloud data, with being based on
The B-spline surface approximating method of Triangle Cell Parameterization rebuilds impression curved surface and cutting impression curved surface obtains indentation feature curve,
Impression diameter is measured, the method for the present invention can accurate, rapid survey impression size.
The technical solution adopted by the present invention to solve the technical problems is:
A kind of ball indentation test impression dimension measurement method based on reverse-engineering, comprising:
Step 1, impression sample surfaces are scanned using 3 D laser scanning equipment, obtains the three-dimensional point cloud of impression sample surfaces
Data；
Step 2, point cloud data is pre-processed, comprising: establish point cloud data topological relation；Reduce point cloud noise；Essence
Simple point cloud data；
Step 3, impression curved surface is rebuild with the B-spline surface approximating method based on Triangle Cell Parameterization, comprising:
3.1) triangle gridding discrete point cloud data forms a triangle mesh curved surface；
3.2) fairing processing is carried out to triangle gridding, homogenizes triangular plate, long and narrow triangular plate is avoided to influence curve reestablishing；
3.3) trigonometric framework lattice are obtained using Triangle Cell Parameterization method；
3.4) trigonometric framework lattice Reparameterization is obtained into quadrangle control grid；
3.5) B-spline surface fitting is carried out to quadrangle control grid, rebuilds impression curved surface；
Step 4, cutting impression curved surface obtains indentation feature curve, comprising:
4.1) transverse cross sectional impression sample obtains impression horizontal section；
4.2) the marginal point coordinate for obtaining impression horizontal section determines the circle of impression horizontal section by Hough circle transformation
Heart coordinate crosses the impression horizontal section center of circle and makees impression center line；
4.3) it crosses impression center line and makees cutting planes longitudinally cutting impression sample, obtain the longitudinal profile of impression, obtain pressure
Trace indicatrix L1；
4.4) longitudinally cutting plane is rotated clockwise into 120 ° and 240 ° of longitudinally cutting pressures respectively using impression center line as axis
Trace sample obtains 120 ° and 240 ° corresponding indicatrix L of longitudinally cutting Plane Rotation2、L3；
Step 5, impression diameter is measured, comprising:
5.1) indentation feature curve L is determined1Center, and by Hough circle transformation calculate pressure ball center；
5.2) each point on indentation feature curve is calculated to be accurately identified to the distance at pressure ball center according to the situation of change of distance
The separation of true indented area and transition indented area；
5.3) linear distance between true indentation curves and transition indentation curves separation is calculated, impression diameter is obtained
One measured value d1；
5.4) the indicatrix L obtained according to step 4.4)2、L3, it is corresponding to respectively obtain 120 ° of longitudinally cutting Plane Rotation
The measured value d2 of the impression diameter and measured value d3 for rotating 240 ° of corresponding impression diameters, last pressure trace diameter measurements are put down
Mean value d=(d1+d2+d3)/3 are used as measurement result.
Further, the method for point cloud data topological relation is established described in step 2 are as follows: using based on point cloud data space
The K neighborhood search method of division.
Further, the method for the point of reduction described in step 2 cloud noise are as follows: according to the K neighborhood topology relationship established, make
Noise reduction process is carried out to cloud with median filtering algorithm.
Further, point cloud data is simplified described in step 2, point cloud data is simplified using the algorithm of simplifying based on curvature, wrap
It includes:
A) the least square tangent plane for being fitted the K neighborhood of each point calculates the normal vector of each point；
B) global normal vector is adjusted, all normal vectors is made to be directed to the same side of curved surface to be reconstructed；
C) using normal vector direction as the direction local coordinate system z, by least square method, the K neighborhood of each point Xi is fitted
One paraboloid, and use the curvature of paraboloid at this point as the estimation result of the curvature；
D) point cloud data is simplified according to the average curvature of the curvature of each point and point cloud data.
Further, fairing processing is carried out to the triangle gridding of point cloud data in step 3.2) to use based on Laplce's change
The Smoothing Algorithm changed.
Further, trigonometric framework lattice are obtained using Triangle Cell Parameterization method described in step 3.3), comprising:
Using the Triangle Cell Parameterization method optimized based on strain energy of distortion, by each edge in triangle gridding as one
The boundary of triangle gridding is first mapped on the polygon pre-defined by a spring, then by minimizing triangle gridding
Elastic potential energy parameterizes inner space point, obtains trigonometric framework lattice.
Further, trigonometric framework lattice Reparameterization is obtained into quadrangle control grid, packet described in step 3.4)
It includes:
Triangular surface piece in trigonometric framework lattice is combined, quadrangularly patch is combined two-by-two, to obtain B
Quadrangle required for spline-fit controls grid.
Further, B-spline surface fitting is carried out to quadrangle control grid described in step 3.5), comprising:
It is fitted using the biquadratic and bi-cubic B spine of tensor product type, distance function is used during fitting
To control error of fitting.
The invention has the following beneficial effects:
(1) measurement accuracy is high, can accurately distinguish transition indented area and true indented area, it is correct identify transition indented area with very
The separation of real indented area, precise measurement impression size；
(2) measurement process is easy to operate, and measuring speed is fast；The method of the invention is programmed and is realized, three-dimensional laser is used
After scanner collects the point cloud data of impression sample to be measured, the measurement of impression diameter can be automatically performed using program；
(3) according to the form of the impression curved surface pattern of reconstruction or indentation feature curve can determine whether in impression forming process whether
Load biases occur, and further judge whether impression acquired in ball indentation test meets national standard.
Invention is further described in detail with reference to the accompanying drawings and embodiments, but one kind of the invention is based on reverse work
The ball indentation test impression dimension measurement method of journey is not limited to the embodiment.
Detailed description of the invention
Fig. 1 is flow diagram of the invention；
Fig. 2 is the three dimensional point cloud of impression sample surfaces；
Fig. 3 is the impression sample surfaces rebuild；
Fig. 4 is impression model schematic；
Fig. 5 is transverse cross sectional impression sample schematic diagram；
Fig. 6 is impression horizontal section；
Fig. 7 is the determination of impression center line；
Fig. 8 is the longitudinally cutting of impression；
Fig. 9 is the longitudinal profile of impression；
Figure 10 is indentation feature curve；
Figure 11 is characterized the determination at curve upper pressing ball center；
Figure 12 is characterized curve each point at a distance from pressure ball center.
Appended drawing reference: M1, reference planes, M2, transverse cuts plane, M3, longitudinally cutting plane, N1, impression horizontal section,
N2, impression longitudinal profile, O1, the impression horizontal section center of circle, O2, pressure ball center, the center line of L, impression, Q, indicatrix, Q1,
True indentation curves, Q2, transition indentation curves, C, central point, A1 and A2, separation.
Specific embodiment
As shown in Figure 1, a kind of ball indentation test impression dimension measurement method based on reverse-engineering provided by the invention, passes through
5 steps realize the precise measurement of ball indentation test impression size, wherein step 2~5 with Visual Studio be that exploitation is flat
Platform is programmed using C Plus Plus and is realized, i.e., after the point cloud data of acquisition indentation surface, can be automatically performed by program subsequent
Impression dimensional measurement process.Measurement method of the invention is described further with reference to the accompanying drawing.
Step 1, the three dimensional point cloud of impression sample surfaces is obtained.
Impression sample surfaces to be measured, which are scanned, using the 3 D laser scanning equipment scanned based on line-structured laser obtains pressure
The three dimensional point cloud of trace sample surfaces, point cloud data is by measurement point set discrete one by one at each measurement point records one
Independent three-dimensional coordinate data.Line-structured laser scanning survey method is also known as light cross-section method, is a kind of based on principle of triangulation
Active structure light coding measuring technique.Relative to laser dot scans method and projection grating method, light cross-section method in measurement accuracy and
Two aspect of speed is all more satisfactory.Fig. 2 is the three dimensional point cloud of impression sample surfaces acquired in 3 D laser scanning equipment, point
There are about 2,000,000 measurement points in cloud, and measurement point is in disordered state at random, without apparent geometry distribution characteristics.
Step 2, point cloud data is pre-processed.
Before rebuilding impression curved surface, point cloud data is pre-processed first, establishes topological relation, the drop of point cloud data
Low spot cloud noise, the number for reducing effective measurement point in point cloud data.
2.1) foundation of point cloud data topological relation
Original point cloud data is in disordered state at random, without apparent topological relation, is divided using based on point cloud data space
K neighborhood search method establish the syntople between each measurement point, song to be reconstructed is reflected using the neighborhood relationships of every bit
The shape information of face at this point.
Space division is carried out to point cloud data first: reading in point cloud data, calculates the X of point cloud data, Y, Z coordinate is most
Small, maximum value surrounds all data points to form a cuboid bounding box parallel with reference axis；Calculate son cube
Body side length Len, and cuboid bounding box is divided by m × n × l sub-cube according to Len；Where judging each data point
Sub-cube, and the serial number of data point is appended in the corresponding linear linked list of the cube, it is stored with ltsh chain table structure each
The data point for including in a sub-cube.Call number direct addressing of the Hash table by cubic lattice in tri- directions X, Y, Z.
If the min coordinates of point cloud data be Min_x, Min_y, Min_z, maximum coordinates Max_x, Max_y, Max_z,
The then calculation formula of the sub-cube side length L of point cloud data are as follows:
In formula, N is the sum of point cloud data, and K is the number of neighbor point.After cube side length Len is determined, sub-cube exists
The number of three coordinate directions are as follows:
WhereinFor to round up.
For any point Xi (xi, yi, zi), the hash function of the sub-cube where the point is asked to be:
WhereinTo be rounded downwards；I is integer, and xi indicates that the coordinate value on X-coordinate direction, yi indicate Y-coordinate direction
On coordinate value, zi indicate Z coordinate direction on coordinate value；T, j, k are respectively the call number of sub-cube where the point.
After carrying out space division to all the points in cloud, the sub-cube for not including data point is deleted, to reduce
Need the sub-cube quantity searched for.
Next on the basis of space divides, K neighborhood search is carried out, the K neighborhood of point Xi is denoted as Nbhd (Xi), K is adjacent
The searching method in domain are as follows: according to the coordinate value Xi (xi, yi, zi) of each candidate point, find out the index of the sub-cube where it
Number t, j, k, using this cube as initial search area；Calculate the point to six faces of cube shortest distance ds；This is counted to search
The number N1 of rope region point calculates the maximum distance dmax of other points in the point and region of search if N1 is not less than k, if
Dmax is less than ds, and k point is the K neighborhood point of the point before taking, and search finishes, and circle work is otherwise extended to the outside centered on this region
It is re-searched for for new region of search.
2.2) cloud noise reduction is put
During obtaining impression sample surfaces three dimensional point cloud, due to the measurement accuracy and measurement of equipment itself
Vibration, mirror-reflection, human factor of environment etc. so that the obtained point cloud data of measurement inevitably have it is a degree of
Noise.Noise be with testee configuration of surface wide of the mark geological information, upset 3-D geometric model to a certain extent
Authenticity.In order to weaken the influence of noise, impression dimensional measurement precision is improved, is opened up based on the point cloud data K neighborhood established
Relationship is flutterred, noise reduction process is carried out to cloud using median filtering algorithm.Median filtering can preferably eliminate data burr can also
Preferably keep the minutia of model.
2.3) point cloud data is simplified
3 D laser scanning equipment retouches a data points up to a million in the available scanning area of impression sample surfaces.Point cloud number
According to very intensively, there are bulk redundancies, if huge time and resource consumption will be brought by being directly used in curved surface structure, and excessively
Intensive point cloud data is easy the fairness for influencing to rebuild curved surface, and it is constant to give the storage of data and transmission belt, and is keeping surveying
Under conditions of enough critical-geometry characteristic informations needed for measuring object subsequent processing link, point cloud data is carried out maximum
Degree simplifies the efficiency and quality for handling and will greatly improving point cloud surface reconstruction.
Point cloud model curvature is corresponding with the distribution of impression geometrical characteristic, and the big region of curvature corresponds to the true of impression sample
Real indented area and transition indented area, the region are the key areas of impression measurement, and the lesser region of curvature corresponds to impression sample
In non-indented region, the partial region will not influence impression measurement accuracy.Impression is simplified using the algorithm based on curvature
Point cloud data retains the geometrical characteristic that enough points carry out expression model in the big region of curvature, and relatively small in curvature
Data area is significantly simplified, and a small amount of point is only retained, and utmostly reduces the redundancy of data point.
The step of impression Cloud Points Reduction based on curvature, is as follows:
A) calculating of normal vector
For point Xi, normal vector direction is equivalent to the normal vector direction that the point rebuilds the tangent plane of curved surface at this point.
It is intended to seek the tangent plane of point Xi, the K neighborhood Nbhd (Xi) of reply point Xi first carries out surface fitting, rebuilds curved surface in the point.Due to
Point cloud data is intensive, and each point in Nbhd (Xi) has similar curvature, therefore Nbhd (Xi) can be fitted to plane, with this
The reconstruction tangent plane to a surface of plane approximation expression point Xi.It is used herein as least square method and Nbhd (Xi) is fitted to plane, point
The normal vector of Xi is the normal vector of the least square plane.The solution of the normal vector, which can be converted into, solves covariance matrix CV's
The corresponding feature vector of minimal eigenvalue:
In formula, tiFor the center of the tangent plane,K indicates the number put in K neighborhood in formula, and x is the K
The abscissa put in neighborhood, if λ i is feature vector corresponding to the smallest characteristic value of absolute value of CV, then normal vector ni=± λ
i。
B) adjustment of global normal vector
Each point on curved surface to be reconstructed has two contrary normal vectors, is respectively directed to the inside of curved surface to be reconstructed
And outside, the adjustment of global normal vector are exactly to adjust normal vector direction at random, and all normal vectors is made to be directed to song to be reconstructed
The same side in face.
For adjacent discrete point, if curved surface to be reconstructed is more smooth and puts that cloud density is larger, adjacent is discrete
Point tangent plane be almost it is parallel, normal vector also be almost it is parallel.If discrete point X1, X2 are adjacent on curved surface to be reconstructed
Point, n1、n2The respectively normal vector of point X1, X2, i.e. n1×n2≈±1.If the direction of the normal vector of tangent plane is directed toward one
It causes, then has n1×n2≈ 1, otherwise normal vector is contrary, and one of normal vector needs reversed.
The key step of normal vector adjustment is as follows: finding the maximum data point of Z coordinate value and adjusts as normal vector
Starting point, adjust the direction of its normal vector, be allowed to be greater than 0 with the dot product of vector (0,0,1), normal vector adjusted is directed toward bent
On the outside of face；Then in the K contiguous range of starting point, the adjustment in normal vector direction is carried out, until the normal vector of all the points adjusts
It finishes.
C) paraboloid fitting process seeks curvature
Utilize the local curvature of normal vector adjusted and K neighborhood relationships estimated data's point of data point.Using minimum
The K neighborhood Nbhd (Xi) of data point Xi is fitted a parabolic surface by square law, and use the curvature of this curved surface at this point as
The estimation result of the curvature.Specific step is as follows:
If paraboloid equation are as follows:
Z=ax2+bxy+cy2
In above formula, x indicates that the coordinate value on X-coordinate direction, y indicate that the coordinate value on Y-coordinate direction, z indicate Z coordinate side
Upward coordinate value.
Using some point Xi in point cloud data as local coordinate system origin, the normal vector direction of the point is local coordinate system Z
Following system of linear equations can be obtained by K neighborhood point Nbhd (Xi) coordinate transform of Xi to the local coordinate system in direction:
AX=Z
In formula
X=[a b c]T
Z=[z1 z2 … zk]T
System of linear equations is solved using SVD converter technique, acquires the coefficient a, b, c of paraboloid equation.
To calculate the curvature Hi=a+c at Xi.
Above procedure is repeated, the curvature H of point cloud data each point is obtainedi, and by the curvature H of each pointiCalculate point cloud all the points
Average curvature
D) point cloud data is simplified
On the basis of point cloud data space divides, point cloud data is simplified according to the average curvature of point cloud data, it is specific to walk
It is rapid as follows: to calculate the mean value of the average curvature of all the points in each sub-cubeIfShow that the cube surrounds
Point be in the biggish region of Curvature varying, when simplifying retain sub-cube in all average curvatures be more than or equal toPoint, to the greatest extent
Possible reservation object geometrical characteristic information outstanding；IfIt is smaller that the point that then cube surrounds is in Curvature varying
Region, only retain in sub-cube when simplifying average curvature values closest toPoint.
Step 3, impression curved surface is rebuild with the B-spline surface approximating method based on Triangle Cell Parameterization.
Point cloud data, will be from using the B-spline surface approximating method based on Triangle Cell Parameterization after pretreatment
The step of scattered impression point cloud data is redeveloped into continuous impression curved surface, rebuilds impression curved surface is as follows:
3.1) triangle gridding of discrete point cloud data
The triangle gridding of discrete point cloud data is exactly that will be mutually connected in the form of triangle between each point in discrete point cloud
It connects, forms one or several sheets triangle mesh curved surface.The present embodiment uses zone broadening algorithm by discrete point cloud data triangle gridding
Change, specific steps are as follows: select three points in the K neighborhood Nbhd (Xi) of some point of impression point cloud data Xi, establish one initially
Triangle is added in triangular plate set queue TS, and then each triangular plate Tc in TS containing boundary edge is carried out down
State iterative calculation: for the boundary edge of Tc, traversal search obtains an optimal active point O (maximum can be used in judgment criteria in P
Subtended angle principle), it is connected with boundary edge and generates a new triangular plate Tn, and is added in TS queue；Update the state of reference point in P
Neighbouring relations between TS intermediate cam piece carry out next iteration.Algorithm is due to using the optimal active point of whole traversal search
With subtended angle maximum principle, all data points in original point cloud data can be effectively utilized to generate triangular plate.
3.2) fairing of triangle gridding
Discrete data is easy the presence of a large amount of long and narrow triangular plates after triangle gridding, the reconstruction of affecting parameters curved surface,
Lead to many defects for rebuilding curved surface.In order to avoid the reconstruction defect that strait triangle introduces, the present embodiment uses Laplce
Smoothing method carries out fairing adjustment to model and homogenizes triangular plate to eliminate noise.Laplacian method method defines one to each vertex
A Laplace operator adjusts grid by moving vertex along adjustment direction with certain speed to determine adjustment direction.Tool
Body implementation method is as follows:
If triangle gridding M={ V, F }, wherein V is the set of n fixed point, and F is the set of tri patch.This method is to fixed
Point ViThe discrete Laplace operator of definition indicates are as follows:
In formula, N is Np(Vi) set element number, Laplace operator L (Vi) it is that its week is shifted on the vertex in grid
The position of form center for enclosing neighborhood makes the noise of the apex scatter into its neighborhood, so promote grid intermediate cam piece shape and
Distribution gradually tends to uniformity.Laplacian method method is exactly to pass through L (Vi) opposite vertexes are adjusted:
Vnew=Vold+μ·L(Vi)
μ is a positive constant, and the different values of μ can control the speed of Mesh smoothing.By multiple to each vertex
After iteration, it can be obtained and ideal meet fairing requirement and grid is distributed relatively uniform model.
3.3) Triangle Cell Parameterization obtains trigonometric framework lattice: using the triangle gridding parameter optimized based on strain energy of distortion
Change method regards each edge in triangle gridding as a spring, is first mapped to the boundary of triangle gridding and pre-defines
Polygon on, then inner space point is parameterized by minimizing the elastic potential energy of triangle gridding, to obtain triangle control
Grid processed.
3.4) trigonometric framework lattice Reparameterization quadrangularly is controlled into grid
Triangular surface piece in trigonometric framework lattice is combined, quadrangularly patch is combined two-by-two, to obtain B
Quadrangle required for spline-fit controls grid
3.5) B-spline surface fitting is carried out to quadrangle control grid, rebuilds impression curved surface.
It is fitted using the biquadratic of tensor product type, bi-cubic B spine, and distance function is added in fit procedure,
The precision for rebuilding impression curved surface is improved using least square fitting multi-Step Iterations algorithm, so that point cloud data point is with curved surface S's
Range error is minimum.The distance function being added in fit procedure are as follows:
E in formuladistFor the quadratic sum of the range error of point cloud data point and curved surface, point cloud data D by N number of group of data points at
D={ pi=(xi,yi,zi)T| i=1,2 ... ..., N }, every bit X in point cloud dataiCorresponding parameter value is (ui,vi)。
The indentation surface model that above-mentioned steps are rebuild is as shown in Figure 3.Fig. 4 is impression model schematic, according to whether occurring
Deformation, impression sample surfaces are divided into indented area and non-indented area.Wherein, indented area be ball indentation test in due to pressure ball extruding and
Make the region that deformation occurs for sample, indented area can be further divided into transition indented area and true indented area again, wherein true impression
Area is the region that is in contact with pressure ball in indented area, and excessive indented area is the not region with pressure ball joint in indented area.National standard
Described in impression diameter refer to the diameter of true indented area, next just based on indentation surface model shown in Fig. 3,
Indentation feature curve is obtained, transition indented area and true indented area are distinguished, identifies the boundary of transition indented area and true indented area
Point measures impression size.
Step 4, cutting impression curved surface obtains indentation feature curve.
The step is specifically divided into following three step:
4.1) transverse cross sectional impression sample obtains impression horizontal section；
It is flat with reference planes M1 by creation by the M1 as a reference plane of the plane where the non-indented region of impression sample
Capable transverse cuts plane M2, carries out transverse cross sectional for impression, obtains impression horizontal section N1, as shown in Figure 5, Figure 6.
4.2) the marginal point coordinate for obtaining impression horizontal section N1 determines impression horizontal section N1 by Hough circle transformation
Center location O1, cross impression horizontal section center of circle O1 make a straight line L vertical with reference planes M1, then L be impression center line,
As shown in Figure 7.
4.3) make a longitudinally cutting plane M3 for crossing impression center line L, longitudinally cutting impression sample obtains the longitudinal direction of impression
Section N2 obtains indentation feature curve Q, as seen in figs. 8-10；
Step 5, impression diameter is measured.Specifically:
Such as the indicatrix Q that Figure 10 is impression, the key of impression diameter measurement is to distinguish true pressure from indicatrix Q
Trace curve Q1 and transition indentation curves Q2, accurately identifies separation A1, A2 of true indentation curves Q1 Yu transition indentation curves Q2.
The measuring process of impression diameter particularly may be divided into following four step:
5.1) the intersection point C of indicatrix Q and center line L is characterized the central point of curve Q, the spy near the two sides central point C
Sign curve corresponds to true indented area, and true indented area is the part with pressure ball joint, is the circular arc of standard.From central point C
The point that certain amount is respectively taken on indicatrix near two sides can calculate true indentation curves Q1 by Circle Hough Transform
The center of circle, which is also pressure ball center O2, as shown in figure 11.
5.2) each point on indicatrix Q is calculated to be identified according to the situation of change of distance true to the distance of pressure ball center O2
Separation A1, A2 of indentation curves Q1 and transition indentation curves Q2.On true indentation curves Q1 each point away from pressure ball center O2 away from
From equal, on transition indentation curves Q2 each point, distance center point C is remoter, also bigger at a distance from the O2 of pressure ball center, such as Figure 12
It is shown.The point that identification mutates at a distance from the O2 of pressure ball center on indicatrix Q, can accurately identify true indentation curves
Separation A1, A2 of Q1 and transition indentation curves Q2.
5.3) linear distance between true indentation curves and transition indentation curves separation A1, A2 is calculated, impression is obtained
One measured value d1 of diameter.
5.4) in step 4.3), longitudinally cutting plane M3 is rotated clockwise 120 ° respectively using impression center line L as axis
And longitudinally cutting impression sample after 240 °, and step 5.1), 5.2), 5.3) is successively executed, respectively obtain longitudinally cutting plane M3
Measured value d2, d3 of 120 ° and 240 ° corresponding impression diameters are rotated, the average value of last pressure trace diameter measurements is as pressure
The measurement result of trace diameter d, d=(d1+d2+d3)/3。
The foregoing is merely presently preferred embodiments of the present invention, is not intended to limit the invention, it is all in spirit of the invention and
Within principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.
Claims (8)
1. a kind of ball indentation test impression dimension measurement method based on reverse-engineering, it is characterized in that, comprising:
Step 1, impression sample surfaces are scanned using 3 D laser scanning equipment, obtains the three-dimensional point cloud number of impression sample surfaces
According to；
Step 2, point cloud data is pre-processed, comprising: establish point cloud data topological relation；Reduce point cloud noise；It simplifies a little
Cloud data；
Step 3, impression curved surface is rebuild with the B-spline surface approximating method based on Triangle Cell Parameterization, comprising:
3.1) triangle gridding discrete point cloud data forms a triangle mesh curved surface；
3.2) fairing processing is carried out to triangle gridding, homogenizes triangular plate, long and narrow triangular plate is avoided to influence curve reestablishing；
3.3) trigonometric framework lattice are obtained using Triangle Cell Parameterization method；
3.4) trigonometric framework lattice Reparameterization is obtained into quadrangle control grid；
3.5) B-spline surface fitting is carried out to quadrangle control grid, rebuilds impression curved surface；
Step 4, cutting impression curved surface obtains indentation feature curve, comprising:
4.1) using the plane transverse cuts pressure-like product parallel with plane where non-indented region, impression horizontal section is obtained；
4.2) the marginal point coordinate for obtaining impression horizontal section determines that the center of circle of impression horizontal section is sat by Hough circle transformation
Mark crosses the impression horizontal section center of circle and makees the straight line vertical with horizontal section, obtains impression center line；
4.3) it crosses impression center line and makees cutting planes longitudinally cutting impression sample, obtain the longitudinal profile of impression, it is special to obtain impression
Levy curve L1；
4.4) longitudinally cutting plane is rotated clockwise into 120 ° and 240 ° of longitudinally cutting impression samples respectively using impression center line as axis
Product obtain 120 ° and 240 ° corresponding indicatrix L of longitudinally cutting Plane Rotation2、L3；
Step 5, impression diameter is measured, comprising:
5.1) indentation feature curve L is determined1Center, which is characterized the intersection point of curve L1 Yu impression center line, and passes through
Hough circle transformation calculates pressure ball center；
5.2) each point on indentation feature curve is calculated to be accurately identified really to the distance at pressure ball center according to the situation of change of distance
The separation of indented area and transition indented area；
5.3) linear distance between true indentation curves and transition indentation curves separation is calculated, one of impression diameter is obtained
Measured value d1；
5.4) according to the indicatrix L of step 4.4) acquisition2、L3, respectively obtain 120 ° of corresponding impressions of longitudinally cutting Plane Rotation
The measured value d2 of the diameter and measured value d3 for rotating 240 ° of corresponding impression diameters, the average value of last pressure trace diameter measurements
D=(d1+d2+d3)/3 are used as measurement result.
2. the ball indentation test impression dimension measurement method based on reverse-engineering as described in claim 1, which is characterized in that step
The method of point cloud data topological relation is established described in 2 are as follows: using the K neighborhood search method divided based on point cloud data space.
3. the ball indentation test impression dimension measurement method based on reverse-engineering as described in claim 1, which is characterized in that step
The method of the point cloud noise of reduction described in 2 are as follows: according to the K neighborhood topology relationship established, using median filtering algorithm to a cloud
Carry out noise reduction process.
4. the ball indentation test impression dimension measurement method based on reverse-engineering as described in claim 1, which is characterized in that step
Point cloud data is simplified described in 2, and point cloud data is simplified using the algorithm of simplifying based on curvature, comprising:
A) the least square tangent plane for being fitted the K neighborhood of each point calculates the normal vector of each point；
B) global normal vector is adjusted, all normal vectors is made to be directed to the same side of curved surface to be reconstructed；
C) using normal vector direction as the direction local coordinate system z, by least square method, the K neighborhood of each point Xi is fitted one
Paraboloid, and use the curvature of paraboloid at this point as the estimation result of the curvature；
D) point cloud data is simplified according to the average curvature of the curvature of each point and point cloud data.
5. the ball indentation test impression dimension measurement method based on reverse-engineering as described in claim 1, which is characterized in that step
3.2) fairing processing is carried out to the triangle gridding of point cloud data in and uses the Smoothing Algorithm based on Laplace transform.
6. the ball indentation test impression dimension measurement method based on reverse-engineering as described in claim 1, which is characterized in that step
3.3) trigonometric framework lattice are obtained using Triangle Cell Parameterization method described in, comprising:
Using the Triangle Cell Parameterization method optimized based on strain energy of distortion, by each edge in triangle gridding as a bullet
The boundary of triangle gridding is first mapped on the polygon pre-defined by spring, then passes through the elasticity of minimum triangle gridding
Potential energy parameterizes inner space point, obtains trigonometric framework lattice.
7. the ball indentation test impression dimension measurement method based on reverse-engineering as described in claim 1, which is characterized in that step
3.4) trigonometric framework lattice Reparameterization is obtained into quadrangle control grid described in, comprising:
Triangular surface piece in trigonometric framework lattice is combined, quadrangularly patch is combined two-by-two, to obtain B-spline
Quadrangle required for being fitted controls grid.
8. the ball indentation test impression dimension measurement method based on reverse-engineering as described in claim 1, which is characterized in that step
3.5) B-spline surface fitting is carried out to quadrangle control grid described in, comprising:
It is fitted using the biquadratic and bi-cubic B spine of tensor product type, is controlled during fitting using distance function
Error of fitting processed.
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