CN100538261C - Unknown free curved face self-adapting measuring method and gauge head unit based on the method for exploring the way - Google Patents

Abstract

The invention discloses a kind of unknown free curved face self-adapting measuring method and gauge head unit based on the method for exploring the way.Contact measuring head is installed in the middle of two laser feelers, and whole device is installed on the Z axle of three coordinate measuring machine, utilizes the signal of two laser feelers to explore the way, and contact measuring head is used for measuring; When contact measuring head moves to the process of next tested point from current measurement point, laser feeler is explored the way to the measuring route of front with the sampling step length of 0.5～2mm, and with the measurement data that obtains after treatment, fits to the Uniform B-spline curve three times; Then the curve after the match is pressed amount of curvature, be separated into adaptive sampled point, generate the corresponding barrier point of keeping away simultaneously with sampled point; Again with these sampled points, keep away barrier point and instruct contact type measurement, realize adaptive measuring to unknown free curved face.This method algorithm is easy, and apparatus structure is simple, is easy to realize.

Description

Unknown free curved face self-adapting measuring method and gauge head unit based on the method for exploring the way

Technical field

The present invention relates to the measurement of irregular surface or profile, especially relate to a kind of unknown free curved face self-adapting measuring method and gauge head unit based on the method for exploring the way.

Background technology

In mechanical manufacturing field, relate to the parts that contain free form surface in a large number, as car body covering, engine air flue, turbine blade, aircraft wing etc.The design of these parts, manufacturing and detection problem are directly connected to the digitized measurement of free form surface, promptly are the sampled point extraction curved surface original-shape information with series of discrete.Three coordinate measuring machine with characteristics such as its high precision, intellectualities being most widely used aspect the free form surface digitized measurement.

When with three coordinate measuring machine free form surface being carried out digitized sampling, one of key is to determine the rational method of sampling.In order to realize requiring the method for sampling to have adaptive characteristic to efficient, the high-precision measurement of free form surface, promptly the layout of sampled point changes with the variation of curvature of curved surface, and curvature is big more, and sampled point is close more, otherwise sampled point is thin more.At present, the unknown free curved face digitized sampling method that is widely used mainly contains four kinds:

(1) equidistant scanning method: the sampling step length that follow procedure is set in advance and keep away barrier dot generation method, equidistant scanning survey is carried out in each cross section of free form surface, be digitized sampling method commonly used at present.It can improve sampling precision by dwindling sampling interval, but can significantly reduce the efficient of digitized measurement, and because the remarkable increase of measuring point, has increased the difficulty of subsequent treatment greatly.

(2) adaptive prediction method: some points that will record earlier fit to a certain curve, according to predetermined sampling precision, adjust parameter of curve again, and extrapolation is obtained next sensing point and kept away the barrier point adaptively, realizes adaptive measuring.

(3) thick-smart two step method: under the integrated environment of multiple survey sensor, earlier measuring object is carried out bigness scale amount (measuring as CCD), utilize the model information of bigness scale amount reconstruct again, instruct accurate measurement amount (as contact type measurement), realize adaptively sampled.

(4) segmentation process of iteration: earlier tested curved surface is carried out equidistantly evenly bigness scale, and form grid.Then the grid that does not meet accuracy requirement is segmented measurement, so loop iteration all meets the predetermined accuracy requirement up to all grids.This method has triangle segmentation iteration and rectangle to segment two kinds of iteration at present.

In the above method, equidistantly scanning method is simple, but does not embody adaptive characteristic.The adaptive prediction method is based on " prediction algorithm ", can realize adaptively sampledly, but prediction algorithm is often very complicated, and can not predict each situation accurately.Slightly-smart two step method is a kind of more satisfactory in theory method, but need integrated quick bigness scale sensor (as ccd sensor), and quick reconfiguration roughcast type has certain degree of difficulty.In addition, bigness scale and accurate measurement are series processes, can influence efficiency of measurement.This method also is in the further exploration.Segment in the process of iteration, the definite of initial mesh size has very big influence to measuring process, but because surface model the unknown so can follow the not rational foundation of determining of initial network size, is generally set initial mesh by rule of thumb.This method is used less in practice.Simultaneously, more than four kinds of methods itself all do not have the Boundary Recognition ability, all require before measurement the artificial Measured Boundary of setting free form surface.

Summary of the invention

Deficiency at existing unknown free curved face digitized sampling method the purpose of this invention is to provide a kind of unknown free curved face self-adapting measuring method and gauge head unit based on the method for exploring the way.Be installed on the Z axle of three coordinate measuring machine contact measuring head and point laser feeler are parallel, wherein the signal of laser feeler is explored the way, and contact measuring head is used for measuring.In the measuring process, instruct contact type measurement, thereby realize adaptive measuring with the detection data of laser feeler.

The technical solution adopted for the present invention to solve the technical problems is:

One, a kind of unknown free curved face self-adapting measuring method based on the method for exploring the way:

Contact measuring head is installed in the middle of two laser feelers, and whole device is installed on the Z axle of three coordinate measuring machine, wherein utilizes the signal of two laser feelers to explore the way, and contact measuring head is used for measuring; During measurement, when contact measuring head moves to the process of next tested point from current measurement point, laser feeler is explored the way to the measuring route of front with the sampling step length of 0.5～2mm, and with the measurement data that obtains after treatment, fit to the Uniform B-spline curve three times; Then the curve after the match is pressed amount of curvature, be separated into adaptive sampled point, generate the corresponding barrier point of keeping away simultaneously with sampled point; Again with these sampled points, keep away barrier point and instruct contact type measurement, realize adaptive measuring to unknown free curved face.

Described laser feeler is to adopt point laser feeler to explore the way, and contact measuring head adopts touch trigger probe to measure.

Describedly obtain data before fitting to curve, handle through the denoising point of articulation from laser feeler.

Three Uniform B-spline curves after the described match carry out adaptive discrete with the difference of corresponding chord length as pre-value with arc length.

According to the signal of laser feeler from having to do not having or the sudden change of growing out of nothing, the border of identification curved surface.

Two, a kind of unknown free curved face self-adapting measuring apparatus based on the method for exploring the way:

Right laser feeler is fixed on the substrate; Substrate is installed in the Right Inboard of " Π " shape gauge head pedestal; Left side laser feeler is inboard with the left side that same form is installed in the gauge head pedestal; Pitman on the contact measuring head passes the centre that connecting hole is placed on the gauge head pedestal; Left and right laser feeler is symmetrical distribution with relative contact measuring head on the gauge head pedestal; Whole gauge head unit is installed on the Z axle of three coordinate measuring machine; Have four connecting holes and clamp device to be connected with four connecting holes on the gauge head pedestal on the three coordinate measuring machine Z axle, clamp device clamps the pitman of contact measuring head.

The measuring staff place straight line of described left and right sides laser feeler emitted laser bundle and contact measuring head is in the same plane, and the XOZ plane parallel of this plane and measuring machine coordinate system of machine.

Described four pedestal mounting holes, contact measuring head connecting hole and substrate mounting hole are dowel hole.

The bottom surface of described left and right laser feeler equals the measurement headroom of laser feeler to the vertical range h of the survey ball of contact measuring head.

The beneficial effect that the present invention has is:

1) measurement data with point laser feeler is guidance, generates sampled point and keeps away the barrier point, realizes adaptive measuring.

2) in measuring process, point laser feeler and contact measuring head concurrent working, the efficient that does not influence contact type measurement is measured in exploring the way of point laser feeler.

3) point laser feeler is measured except that exploring the way, can realize the automatic identification of surface boundary.

4) apparatus structure is simple and easy, and path planning algorithm is simple, is easy to realize.

Description of drawings

Fig. 1 is the free-form surface self-adaptive measurement mechanism structural representation of the method for exploring the way;

Fig. 2 is the three-view diagram of gauge head base construction;

Fig. 3 is an adaptive measuring process synoptic diagram;

Fig. 4 is the location diagram of three adjacent measuring points;

Fig. 5 is laser measurement data contrast figure before and after the denoising point of articulation;

Fig. 6 is the even B-spline Curve figure that fits to;

Fig. 7 is the sampling point distributions synoptic diagram after the B-spline curves adaptive discrete;

Fig. 8 hinders the some synoptic diagram with adaptively sampled corresponding keeping away.

Among the figure: 1, gauge head pedestal, 2, contact measuring head, 3, left laser feeler, 4, right laser feeler, 5, substrate, 6, gib screw, 7, socket head cap screw, 8, laser beam, 9, measuring staff, 10, survey ball, 11, pedestal mounting hole, 12, connecting hole, 13 substrate mounting holes, 14, pitman.

Embodiment

As shown in Figure 1 and Figure 2, the right laser feeler 4 among the present invention is fixed on the substrate 5 by socket head cap screw 7; Substrate 5 is installed in the right side of " Π " shape gauge head pedestal 1 by gib screw 6 and substrate mounting hole 13.Left side laser feeler 3 is inboard with the left side that same form is installed in gauge head pedestal 1; Pitman 14 on the contact measuring head 2 passes the centre that connecting hole 12 is placed on gauge head pedestal 1; Left and right laser feeler 3,4 is symmetrical distribution with relative contact measuring head on gauge head pedestal 1; Whole gauge head unit is installed on the Z axle of three coordinate measuring machine; Have four connecting holes and clamp device to be connected with four connecting holes 11 on the gauge head pedestal 1 on the three coordinate measuring machine Z axle, clamp device clamps the pitman 14 of contact measuring head 2.

The measuring staff 9 place straight lines of described left and right sides laser feeler 3,4 emitted laser bundles 8 and contact measuring head 2 are in the same plane, and the XOZ plane parallel of this plane and measuring machine coordinate system of machine.

Described four pedestal mounting holes 11, contact measuring head connecting hole 12 and substrate mounting hole 13 are dowel hole.

The bottom surface of described left and right laser feeler 3,4 equals the measurement headroom of laser feeler 3,4 to the vertical range h of contact measuring head 2 survey balls 10.

Shown in Fig. 2 (a), Fig. 2 (b), the substrate mounting hole 13 on " Π " shape gauge head pedestal 1 is designed to dowel hole.The position of laser feeler 3,4 can be adjusted up and down like this, so that the bottom surface that makes laser feeler 3,4 is to the distance h of surveying ball 10, equal the measurement headroom (the laser feeler bottom surface converges the distance of focus to laser beam) of laser feeler, to reach best measurement effect.

Before measuring beginning, whole device will be installed on the Z axle of three coordinate measuring machine.Four connecting holes and a clamp device are arranged on the Connection Block of three coordinate measuring machine Z axle, and wherein four connecting holes are corresponding with four mounting holes 11 on the gauge head pedestal 1 respectively, are used for fixing gauge head pedestal 1.Clamp device is used to clamp the pitman 14 of contact measuring head 2, with fixing contact measuring head 2.

Shown in Fig. 2 (c), four mounting holes 11 on the gauge head pedestal 1 also are designed to the key-way shape hole.The front and back position of laser feeler 3,4 and contact measuring head 2 can be adjusted like this, so that make left and right sides laser feeler 3,4 emitted laser bundles 8 and measuring staff 9 place straight lines in same plane.Simultaneously, this plane should with the XOZ plane parallel of measuring machine coordinate system of machine.

Employed laser feeler is a point laser feeler among the present invention, and the contact measuring head that uses is touch trigger probe.

After measurement mechanism installs, need the locus of contact measuring head 2 and two laser feelers 3,4 is demarcated, so that they are unified under same measurement coordinate system.Concrete grammar is as follows: before measuring beginning, placing a standard ball on the worktable of measuring machine, is initial point with the centre of sphere of standard ball, three respectively with X, the Y of coordinate system of machine, the Z axle is parallel and direction is consistent, sets up measurement coordinate system oxyz.Use contact measuring head 2 then, get some points (being no less than 7 points), the coordinate figure (be actually the positional value of measuring machine on grating chi) of record each point under coordinate system of machine at the diverse location of standard ball sphere.Then use least square method, resulting machine coordinate figure is fitted to a ball, and try to achieve the sphere centre coordinate (X of this match ball _Co, Y _Co, Z _Co).Be located in the later measuring process, the corresponding machine coordinate figure of contact measuring point is (X _c, Y _c, Z _c), so, its coordinate figure in oxyz can be described as (X _c-X _Co, Y _c-Y _Co, Z _c-Z _Co).Using the same method can be in the hope of left and right laser feeler 3,4 pairing match sphere centre coordinate (X _Lo, Y _Lco, X _Lo), (X _Ro, Y _Ro, Z _Ro), if in the measuring process afterwards, the measuring point of left and right laser feeler 3,4, pairing machine coordinate figure is respectively (X _l, Y _l, Z _l), (X _r, Y _r, Z _r), their coordinate figures in oxyz can be described as (X so _l-X _Lo, Y _l-Y _Lo, Z _l-Z _Lo), (X _r-X _Ro, Y _r-Y _Ro, Z _r-Z _Ro).Through handling like this, system has just arrived three gauge head unifications under the same measurement coordinate system oxyz.In calibration process, can also obtain the distance D between two laser 8 place straight lines and the measuring staff 9 place straight lines ₁, D ₂, wherein

${\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="C200710156129E00152.png"\; state="\{\{state\}\}">D</figure-callout>}}_1=\sqrt{{(X_{\mathrm{lo}}-X_{\mathrm{co}})}^2+{(Y_{\mathrm{lo}}-Y_{\mathrm{co}})}^2+{(Z_{\mathrm{lo}}-Z_{\mathrm{co}})}^2}$

${\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">D</figure-callout>}}_2=\sqrt{{(X_{\mathrm{ro}}-X_{\mathrm{co}})}^2+{(Y_{\mathrm{ro}}-Y_{\mathrm{co}})}^2+(Z_{\mathrm{ro}}-Z_{\mathrm{co}})}$

The adaptive measuring process is finished the measurement to a cross section as shown in Figure 3, comprises seven stages.

One, laser feeler is visited the border:

Shown in Fig. 3 (a), mobile gauge head open right laser feeler 4, and left laser feeler 3 wouldn't be worked to starting point.Fixing a certain coordinate figure (as Y-axis) allows gauge head edge+X-direction move.When right laser feeler 4 was gone into surface boundary E, its output signal can be undergone mutation (the present invention only considers the border that suddenlys change, and the feature of not suddenling change in the hypothesis curved surface), and at this moment Survey Software is immediately to this sudden change coordinate figure (x ₀, y ₀, z ₀) carry out record, and save as frontier point A ₀

Two, the laser feeler measurement of exploring the way, contact measuring head is visited the border:

Shown in Fig. 3 (b), after right laser feeler 4 entered border E, measuring system was opened three threads immediately, and the work of each thread is as follows:

Thread I: laser measurement control thread, be used to control right laser feeler 4 with etc. step-length (according to the measurement experience, to get 0.5～2mm more reasonable when step-length) to the cross section profile l of curved surface ₁Measure.

Thread II: thread is judged on the border, is used to judge whether contact measuring head 2 enters surface boundary E.Can be by center and the frontier point A that relatively surveys ball 10 ₀Between coordinate figure judge.

Thread III: laser data processing threads, it is topmost thread, it obtains measurement data to right laser feeler 4 in real time and handles, and comprises measurement data pre-service, three Uniform B-spline curve fittings, variable curvature adaptive discrete and keeps away four parts of barrier dot generation.

(1) measurement data pre-service comprises and removes noise point and repeat a little two parts.

In the measuring process, because the influence of factors such as mechanical vibration, system noise, illumination and curved surface roughness to be measured, make to be mixed with noise spot (burr or deviation point) in the laser measurement data inevitably, before measurement point fits to B-spline curves, should remove noise point earlier.Method is as follows: investigating the angle theta between certain point and adjacent 2 lines, if θ less than a certain predetermined value, then rejects this point, is rational measurement point otherwise look this point.As shown in Figure 4, establish V _I-1(x _I-1, y _I-1, z _I-1), V _i(x _i, y _i, z _i), V _I+1(x _I+1, y _I+1, z _I+1) be up-to-date adjacent 3 points that record, then V _i(x _i, y _i, z _i) whether be that the deterministic process of noise point is:

1. calculate corresponding vector of unit length T ₁(a, b, c) and T ₂(m, n, k)

$(a,b,c)=(x_{i+1}-x_i,y_{i+1}-y_i,z_{i+1}-z_i)/\sqrt{{(x_{i+1}-x_i)}^2+{(y_{i+1}-y_i)}^2+{(z_{i+1}-z_i)}^2}$

$(m,n,k)=(x_i-x_{i-1},y_i-y_{i-1},z_i-z_{i-1})/\sqrt{{(x_i-x_{i-1})}^2+{(y_i-y_{i-1})}^2+{(z_i-z_{i-1})}^2}$

2. calculate the angle theta between them

${\mathrm{\&theta;}}_i=\arccos \left(\frac{(a,b,c)\&CenterDot;(m,n,k)}{\sqrt{a^2+{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">b</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}\&times;\sqrt{{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">m</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">n</figure-callout>}}^2+k^2}}\right)=\arccos ((a,b,c)\&CenterDot;(m,n,k))$

3. judge θ _iGreater than certain preassigned angle δ (the present invention is according to the measurement experience, get δ=70 °), if less than δ, then this point may be a noise point, can reject, otherwise should keep.

Obtain next measurement point V _I+2After, same by investigating V _I+1With V _i, V _I+2Angle between the line is judged V _I+1Rationality, so circulation finishes to explore the way measurement until laser feeler.The laser measurement data are removed the contrast relationship before and after the noise point, as shown in Figure 5.

(2) B-spline curves match.In current CAD/CAM system, B-spline curves, curved surface have become the core of geometric modeling.Consider the free form surface of actual diel, its order reaches the requirement of measuring system to real-time between 2～4, and the present invention adopts three Uniform B-spline curves to approach the laser measurement point.If V _i, V _I+1, V _I+2And V _I+3Be four up-to-date acquisitions, rational measurement point, then with V _i, V _I+1, V _I+2And V _I+3For three Uniform B-spline segment of curve at reference mark can be expressed as

$P_i\left(u\right)=\frac{1}{6}\left[\begin{array}{cccc}{u}^3& u^2& u& 1\end{array}\right]\left[\begin{array}{cccc}-1& 3& -3& 1\\ 3& -6& 3& 0\\ -3& 0& 3& 0\\ 1& 4& 1& 0\end{array}\right]\left[\begin{array}{c}{V}_i\\ V_{i+1}\\ V_{i+2}\\ V_{i+3}\end{array}\right]---\left(1\right)$

Write as with formula and be

$P_i\left(u\right)=\underset{j=0}{\overset{3}{\mathrm{\&Sigma;}}}{B}_{j,3}\left(u\right)V_{i+j}---\left(2\right)$

U is a parameter in the formula, u ∈ [0,1]; V _i, V _I+1, V _I+2And V _I+3Be the feature polygon vertex.

B _{J, 3}(u), j=0,1,2,3 is the basis function of cubic B-spline, its expression formula is respectively:

$\left\{\begin{array}{c}{B}_{\mathrm{0,3}}\left(u\right)=\frac{1}{6}{(1-u)}^3\\ {\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="C200710156129E00152.png"\; state="\{\{state\}\}">B</figure-callout>}}_{\mathrm{1,3}}\left(u\right)=\frac{1}{6}({3u}^3-{6\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">u</figure-callout>}}^2+4)\\ {\mathrm{<figure-callout\; id="2"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">B</figure-callout>}}_{\mathrm{2,3}}\left(u\right)=\frac{1}{6}({-3\mathrm{<figure-callout\; id="3"\; label="u"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">u</figure-callout>}}^3+{3\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">u</figure-callout>}}^2+3u+1)\\ {\mathrm{<figure-callout\; id="3"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">B</figure-callout>}}_{\mathrm{3,3}}\left(u\right)=\frac{1}{6}{u}^3\end{array}\right.---\left(3\right)$

Obtain next reasonably measurement point V _I+4After, system will be with V _I+1, V _I+2, V _I+3And V _I+4Be new reference mark, come next section of match curve.So circulation finishes to explore the way measurement until laser feeler.B-spline curves after the match as shown in Figure 6.

(3) variable curvature adaptive discrete.

The purpose of B-spline curves after the match being carried out adaptive discrete is: for contact type measurement provides rational sampled point.The density of adaptive discrete requirement sampled point changes with the variation of curvature of curve, and the big more then sampled point of curvature is close more, and vice versa.The present invention is a pre-value with the difference of arc length and corresponding chord length, carries out adaptive discrete.With i segment of curve P (u) is example, and departure process is as follows:

1. get Δ u=0.001 (can get the per mille of laser measurement step-length), with P (u) be separated into a P (0), P (Δ u), P (2 Δ u) ..., P (1), and to establish starting point P (s) earlier be P (0), i.e. s=0.

2. in order zequin P (s) to each point P[(s+1 thereafter) Δ u], P[(s+2) Δ u] ... P[(s+k) Δ u] arc length S and corresponding chord length L:

$S\&ap;\underset{i=s}{\overset{k}{\mathrm{\&Sigma;}}}|P\left[(i+1)\mathrm{\&Delta;u}\right]-P\left(\mathrm{i\&Delta;u}\right)|$ (arc length with the chord length approximate representation arc length that adds up)

L＝|P(kΔu)-P(s)|

Cyclic process 2., up to S-L 〉=η (η is predefined pre-value, is taken as 0.0008mm among the present invention), enter process 3..

3. establish S-L 〉=during η, corresponding terminal point is P (n Δ u), then P (n Δ u) is saved as adaptively sampled point, be ground zero with P (n Δ u) then, i.e. s=n, and 2. the continuation process so circulates, until the segment of curve border.Adaptively sampled some distribution situation after discrete as shown in Figure 7.

(4) keep away the barrier dot generation.

Keep away one of three big key elements that the barrier point is a measuring route (the barrier point is vowed, kept away to nominal measure point, nominal measure point method), whether the layout of keeping away the barrier point is reasonable, and Measuring Time, measuring accuracy, security are all had very big influence.Among the present invention, the generation method of keeping away the barrier point is as follows: establish P (u _i) be an adaptively sampled point, then it keeps away barrier point P ' (u _i) can be expressed as

P′(u _i)＝P(u _i)+Δp

Wherein Δ P is for keeping away the barrier vector, and Δ P=dn, d are the length of keeping away the barrier vector, according to practical experience, can be made as 0.5～2mm, and n is that curve P (u) is at P (u _i) per unit system located vows that the solution procedure of n is:

If curve P (u) is at a P (u _i) unit that locates cuts and vow and be t, then

$t=[\frac{x\&prime;\left(u\right)}{\sqrt{{(x\&prime;\left(u\right))}^2+{(y\&prime;\left(u\right))}^2+(z\&prime;{\left(u\right)}^2)}},\frac{y\&prime;\left(u\right)}{\sqrt{{(x\&prime;\left(u\right))}^2+{(y\&prime;\left(u\right))}^2+{(z\&prime;\left(u\right))}^2}},\frac{z\&prime;\left(u\right)}{\sqrt{{(x\&prime;\left(u\right))}^2+{(y\&prime;\left(u\right))}^2+{(z\&prime;\left(u\right))}^2}}]$

$=[\frac{x\&prime;\left(u\right)}{|P\&prime;\left(u\right)|},\frac{y\&prime;\left(u\right)}{|P\&prime;\left(u\right)|},\frac{z\&prime;\left(u\right)}{|P\&prime;\left(u\right)|}]$

In the formula

$P\&prime;\left(u\right)=\underset{j=0}{\overset{3}{\mathrm{\&Sigma;}}}{B}_{j,3}^{\&prime;}\left(u\right)P_{i+j}$

$x\&prime;\left(u\right)=\underset{j=0}{\overset{3}{\mathrm{\&Sigma;}}}{B}_{j,3}^{\&prime;}\left(u\right)x_{i+j}$

$y\&prime;\left(u\right)=\underset{j=0}{\overset{3}{\mathrm{\&Sigma;}}}{B}_{j,3}^{\&prime;}\left(u\right)y_{i+j}$

$z\&prime;\left(u\right)=\underset{j=0}{\overset{3}{\mathrm{\&Sigma;}}}{B}_{j,3}^{\&prime;}\left(u\right)z_{i+j}$

$B_{j,3}^{\&prime;},j=\mathrm{0,1,2,3}$ Expression formula be respectively

$\left\{\begin{array}{c}{\mathrm{<figure-callout\; id="3"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">B</figure-callout>}}_{\mathrm{0,3}}^{\&prime;}\left(u\right)=-\frac{1}{2}{(1-u)}^2\\ {\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="C200710156129E00152.png"\; state="\{\{state\}\}">\; <figure-callout\; id="3"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">B</figure-callout>\; </figure-callout>}}_{\mathrm{1,3}}^{\&prime;}\left(u\right)=\frac{1}{2}({3u}^2-4u)\\ {\mathrm{<figure-callout\; id="2"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">\; <figure-callout\; id="3"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">B</figure-callout>\; </figure-callout>}}_{\mathrm{2,3}}^{\&prime;}\left(u\right)=\frac{1}{2}({-3\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">u</figure-callout>}}^2+2u+1)\\ {\mathrm{<figure-callout\; id="3"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">\; <figure-callout\; id="3"\; label="B"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">B</figure-callout>\; </figure-callout>}}_{\mathrm{3,3}}^{\&prime;}\left(u\right)=\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="C200710156129E00131.png"\; state="\{\{state\}\}">u</figure-callout>}}^2\end{array}\right.$

Because Y-axis is fixed, so y ' (u)=0, promptly $t=[\frac{x\&prime;\left(u\right)}{|P\&prime;\left(u\right)|},0,\frac{z\&prime;\left(u\right)}{|P\&prime;\left(u\right)|}].$

Again because t ⊥ n, so $[-\frac{z\&prime;\left(u\right)}{|P\&prime;\left(u\right)|},0,\frac{x\&prime;\left(u\right)}{|P\&prime;\left(u\right)|}]$

The position of keeping away barrier point and adaptively sampled point concerns as shown in Figure 8.

Three, contact type measurement, the contactless concurrent working of exploring the way:

Shown in Fig. 3 (c), after contact measuring head 2 entered surface boundary E, thread II (border judgement thread) stopped, and new thread IV opens.Thread IV is a contact type measurement control thread, and its work is: the adaptively sampled point that provides with thread III (laser data processing threads) and corresponding to keep away the barrier point be foundation, and control 2 pairs of curved surfaces of contact measuring head and carry out adaptive measuring.In the contact type measurement process, thread I and III (laser measurement control thread and laser data processing threads) be operate as normal still.

Four, right laser feeler 4 leaves surface boundary E, and contact type measurement continues:

Shown in Fig. 3 (d), when right laser feeler 4 left surface boundary E, its output signal can be undergone mutation, and at this moment Survey Software is immediately to this sudden change coordinate figure (x ₁, y ₁, z ₁) carry out record, and save as frontier point A ₁, right then laser feeler 4 quits work.This moment, the working condition of each thread was:

Thread I and III (laser measurement control thread and laser data processing threads) stop.

Thread II (border judgement thread) restarts, by center and the frontier point A that relatively surveys ball 10 ₁Between coordinate figure, judge whether contact measuring head 2 leaves surface boundary E.

Thread IV (contact type measurement control thread) operate as normal.

Five, contact measuring head 2 leaves surface boundary E:

Shown in Fig. 3 (e), after contact measuring head 2 left surface boundary E, thread II, IV (thread and contact type measurement control thread are judged in the border) all stopped.Simultaneously, left laser feeler 3 is unlocked, and system continues the control gauge head unit and moves to+X-direction.

Six, surface boundary E leaves in the gauge head system:

Shown in Fig. 3 (f), when the output signal of left laser feeler 3 can be undergone mutation, show that the gauge head system left surface boundary E.In order to prevent to bump with surface boundary, software will continue the control gauge head unit and move a wide distance D of putting to+X-direction _AThe wide distance D of putting _ASize relevant with Δ y (amount of feeding of Y direction), can get D _A=3 Δ y, the value of Δ y can be got 1～5mm, also can be as the case may be, by the man-machine interaction adjustment.

Seven, begin next section gauge:

Shown in Fig. 3 (g), system control gauge head unit, increment Delta y of feeding on+Y direction, then the gauge head system will move along-X-direction, at new measurement cross section l ₂On, continue above-mentioned adaptive measuring.

Seven step cycle work are until the adaptive measuring of finishing whole curved surface.The measurement data that obtains will import the postorder process software, rebuild the geometric model of free form surface.

Claims (9)

1. unknown free curved face self-adapting measuring method based on the method for exploring the way, it is characterized in that: contact measuring head is installed in the middle of two laser feelers, and above three gauge heads are installed on the Z axle of three coordinate measuring machine, wherein utilize the signal of two laser feelers to explore the way, contact measuring head is used for measuring; During measurement, when contact measuring head moves to the process of next tested point from current measurement point, laser feeler is explored the way to the measuring route of front with the sampling step length of 0.5～2mm, and with the measurement data that obtains after treatment, fit to the Uniform B-spline curve three times; Then the curve after the match is pressed amount of curvature, be separated into adaptive sampled point, generate the corresponding barrier point of keeping away simultaneously with sampled point; Again with these sampled points, keep away barrier point and instruct contact type measurement, realize adaptive measuring to unknown free curved face.

2. a kind of unknown free curved face self-adapting measuring method based on the method for exploring the way according to claim 1 is characterized in that: described laser feeler is to adopt point laser feeler to explore the way, and contact measuring head adopts touch trigger probe to measure.

3. a kind of unknown free curved face self-adapting measuring method based on the method for exploring the way according to claim 1 is characterized in that: the measurement data of described acquisition is handled through the denoising point of articulation before fitting to curve.

4. a kind of unknown free curved face self-adapting measuring method based on the method for exploring the way according to claim 1 is characterized in that: described three Uniform B-spline curves that fit to, carry out adaptive discrete with the difference of corresponding chord length as pre-value with arc length.

5. a kind of unknown free curved face self-adapting measuring method based on the method for exploring the way according to claim 1 is characterized in that: according to the signal of laser feeler from having to do not having or the sudden change of growing out of nothing, the border of identification curved surface.

6. gauge head unit that is used for adaptive measuring, it is characterized in that: right laser feeler (4) is fixed on the substrate (5); Substrate (5) by gib screw (6) and substrate mounting hole (13) be installed in "

" Right Inboard of shape gauge head pedestal (1); Left side laser feeler (3) is inboard with the left side that same form is installed in gauge head pedestal (1); Pitman (14) on the contact measuring head (2) passes the centre that connecting hole (12) is placed on gauge head pedestal (1); Left and right laser feeler (3,4) is symmetrical distribution to go up relative contact measuring head at gauge head pedestal (1); Whole gauge head unit is installed on the Z axle of three coordinate measuring machine; Have four connecting holes and clamp device to be connected with four pedestal mounting holes (11) on the gauge head pedestal (1) on the three coordinate measuring machine Z axle, clamp device clamps the pitman (14) of contact measuring head (2).

7. a kind of gauge head unit that is used for adaptive measuring according to claim 6, it is characterized in that: measuring staff (9) the place straight line of described left and right sides laser feeler (3,4) emitted laser bundles (8) and contact measuring head (2), be in the same plane, and the XOZ plane parallel of this plane and measuring machine coordinate system of machine.

8. a kind of gauge head unit that is used for adaptive measuring according to claim 6 is characterized in that: described four pedestal mounting holes (11), contact measuring head connecting hole (12) and substrate mounting hole (13) are dowel hole.

9. a kind of gauge head unit that is used for adaptive measuring according to claim 6, it is characterized in that: the bottom surface of described left and right laser feeler (3,4) equals the measurement headroom of laser feeler (3,4) to the vertical range h of the survey ball (10) of contact measuring head (2).

Images