CN1534276A - Measuring method of free curved surface - Google Patents

Abstract

A method for measuring free curved surface by use of integrated flexible laser machining system, three-coordinate measurer, or numerally controlled machine-tool includes dividing the free curved surface into equadistance cross-sections, measuring each cross-section, and obtaining the whole free curved surface. A method for measuring each cross-section is also disclosed. Its advantage is high efficiency and precision.

Description

A kind of measuring method of free form surface

Technical field

The present invention relates to the automatic control survey technical field, particularly a kind of measuring method of free form surface.

Background technology

Because free form surface does not have analytic expression truly, so its digitizing is the difficult point in the engineering always.At present, some scholar has proposed measuring method to the known free form surface of mathematical model according to center of mass theorem, but measurement for the free form surface of unknown mathematical model, then general by waiting distance measurement method, the mode of step-length such as promptly use to come free form surface is measured, its defective is not consider the characteristics of curved surface itself, even for changing more violent curved surface also with being desirous of peace the same step-length of smooth curved surface, the measurement data of Huo Deing just can not reflect the truth of free form surface sometimes like this, and efficiency of measurement is lower.

Summary of the invention

The objective of the invention is to: overcome the truth that can not reflect curved surface when waiting distance measurement method to measure the free form surface of unknown mathematical model, and the low shortcoming of efficiency of measurement, thereby a kind of measuring method of free form surface is provided.

The object of the present invention is achieved like this: the measuring method of a kind of free form surface of the present invention, utilize integrated flexible laser system of processing, three-coordinate measuring machine or numerically-controlled machine, feature according to free form surface is divided into equidistant cross section with free form surface, then, each cross section curve is measured, generate next sensing point and the corresponding barrier point of keeping away adaptively, and can in measuring process, constantly revise the irrational measurement point in front, to measure free form surface.

The measuring method of a kind of free form surface of the present invention is characterized in that, the step of this method comprises:

(1) determines the measurement range of curved surface to be measured, and will measure curved surface and be divided into N cross section, cross section sequence number variable m is set;

(2) measuring four starting point P on this curve with automatic equidistant from the step-length measuring method on the curve in m cross section ₁, P ₂, P ₃, P ₄Three dimensional space coordinate, and 4 coordinate figure deposited in the measurement data file in the computing machine;

(3) according to 4 P that recorded ₁, P ₂, P ₃, P ₄, calculate straight line P ₂P ₃With straight line P ₃P ₄Between acute angle theta;

(4) again according to 4 P that recorded ₁, P ₂, P ₃, P ₄With three Bessel's equation matched curves, again with θ for declaring apart from adaptive adjustment variable element Δ t, obtain next sensing point P ' ₅, and obtain its correspondence keep away a barrier point P _{B, 5}, utilize sensing point P ' ₅Hinder some P with keeping away _{B, 5}Record P ₅The 3 d space coordinate value, and coordinate figure deposited in the measurement data file, if variable element Δ t＞0, then with P ₂, P ₃, P ₄, P ₅Give P ₁, P ₂, P ₃, P ₄

(5) if variable element Δ t＜0 illustrates P ₅Point is back measuring point, i.e. P ₄Point is at P ₅P is then used in the front of point ₁, P ₂, P ₃, P ₅The value of point is measured next sensing point and is kept away the barrier point;

(6) repeat above-mentioned steps (3), (4) and (5) until the border, and make cross section sequence number value m=m+1; When m=N, finish to measure.

Describedly declare apart from θ≤1 °, then Δ t=1/3+0.10; If 1 °＜θ≤3 °, then Δ t=1/3+0.05; If 3 °＜θ≤6 °, then Δ t=1/3; If θ＞6 °, then Δ t=-1/6.

Described three Bessel's equations are P ' ₅=T (1+ Δ t) MP, wherein T (1+ Δ t)=[(1+ Δ t) ³(1+ Δ t) ²(1+ Δ t) 1], be the variable element matrix, M is the constant coefficient matrix of three Bezier basis functions, $M=\left[\begin{array}{cccc}-1& 3& -3& 1\\ 3& -6& 3& 0\\ -3& 3& 0& 0\\ 1& 0& 0& 0\end{array}\right];$ P is the matrix of the 3 d space coordinate of four points obtaining of up-to-date measurement, and P=[p ₁p ₂p ₃p ₄] ^T

The invention has the advantages that: the measuring method of a kind of free form surface of the present invention, based on three times specific Bezier mathematical models, curve on the equidistant cross section of adaptive measuring, efficiency of measurement height not only, and, the truth that can reflect curved surface has realized the digitizing of free form surface with degree of precision.

The drawing explanation

Fig. 1 is the instrumentation plan of frontier point in the free curved face measurement method of the present invention

Fig. 2 is the curved measurement synoptic diagram in the free curved face measurement method of the present invention

Fig. 3 is the measurement result data plot of free curved face measurement method embodiment of the present invention

Fig. 4 is the schematic flow sheet of free curved face measurement method of the present invention

Embodiment

Utilizing a most preferred embodiment of free curved face measurement method of the present invention that the present invention is made further specifies.

The China Patent No. that adopts Chinese Academy of Sciences's mechanics study to be authorized is that ZL98101217.5 a kind of has flexible the transmission and multi-shaft interlocked laser processing device, also can adopt three coordinate measuring machine, utilize contact measuring head (or contactless gauge head) and be equipped with and measure that auxiliary circuit links to each other with the I/O communication port of planer type numerical control lathe and the equipment such as measurement processing machine that are transformed into, free form surface to a bight of stamping die of automotive covering part is measured, as shown in Figure 4, its concrete measuring process is as follows:

1, determines the measurement range of curved surface to be measured earlier, as shown in Figure 1, look, go out the lower left corner frontier point P of curved surface to be measured with the measuring head manual measurement along the Y-axis forward _s, its three dimensional space coordinate value is (2072.342-1324.306-314.720); Upper left corner frontier point P _e, its three dimensional space coordinate value is (2072.342-1225.630-286.319); Upper right corner frontier point P _c, obtain its 3 d space coordinate value and be (2145.276-1225.630-260.691).

Determine according to the precision of measurement requirement between per two cross sections of free form surface apart from d=4mm, the row who calculates required measurement counts N=12, and memory variable cross section sequence number m is set, for first cross section that will measure, getting the m value is 1.

2, from the cross section initial point, as shown in Figure 2, control survey head equidistant steps will is that the automatic equidistant step-length measuring method of 4mm measures 4 P on m cross section of free form surface to be measured ₁, P ₂, P ₃, P ₄Three dimensional space coordinate, with P ₁, P ₂, P ₃, P ₄For software setting is global memory's variable, and four space of points D coordinates value are deposited in the measurement data file by text mode by measurement control software;

3, according to 4 P that record ₁, P ₂, P ₃, P ₄, utilize formula

$\mathrm{\θ}=\arccos \left(\frac{(p_3-p_2)\·(p_4-p_3)}{|p_3-p_2||p_4-p_3|}\right)---\left(2\right)$

Calculate straight line P ₂P ₃With straight line P ₃P ₄Between acute angle theta, again with θ for declaring distance, adaptive adjustment variable element variable Δ t: if θ≤1 °, then Δ t=1/3+0.10; If 1 °＜θ≤3 °, Δ t=1/3+0.05; If 3 °＜θ≤6 °, Δ t=1/3; If θ＞6 °, Δ t=-1/6 returns and surveys a bit.

Utilize formula P ' ₅=T (1+ Δ t) MP (3)

P _b，5＝P′ ₅+(0?0?10) (4)

Generate next sensing point P ' ₅Hinder some P with keeping away _{B, 5}

4, utilize sensing point P ' ₅Hinder some P with keeping away _{B, 5}Drive gauge head and obtain measurement point P ₅The 3 d space coordinate value, and coordinate figure is deposited in the measurement data file of text formatting;

If 5 variable element Δ t＞0 are then with P ₂, P ₃, P ₄, P ₅Give P ₁, P ₂, P ₃, P ₄If variable element Δ t＜0 illustrates P ₅Point is back measuring point, i.e. P ₄Point is at P ₅P is then used in the front of point ₁, P ₂, P ₃, P ₅The value of point is measured next sensing point and is kept away the barrier point;

6, calculate P ₅With P _eBetween distance D _s, if D _s＜0.5mm then finishes to measure; Otherwise repeating step 3～5 is until end; And make cross section sequence number value m=m+1, carry out the measurement in next cross section.

When m=N, finish to measure.The measurement result that obtains adopts the origin mapping software to show at last, as shown in Figure 3.

Claims (4)

1, a kind of measuring method of free form surface, utilize integrated flexible laser system of processing, three-coordinate measuring machine or numerically-controlled machine, feature according to free form surface is divided into equidistant cross section with free form surface, then, each cross section curve is measured, generate next sensing point and the corresponding barrier point of keeping away adaptively, and can in measuring process, constantly revise the irrational measurement point in front, to measure free form surface.

According to the measuring method of the described free form surface of claim 1, it is characterized in that 2, the step of this method comprises:

(1) determines the measurement range of curved surface to be measured, and will measure curved surface and be divided into N cross section, cross section sequence number variable m is set;

(2) measuring four starting point P on this curve with automatic equidistant from the step-length measuring method on the curve in m cross section ₁, P ₂, P ₃, P ₄Three dimensional space coordinate, and 4 coordinate figure deposited in the measurement data file in the computing machine;

(3) according to 4 P that recorded ₁, P ₂, P ₃, P ₄, calculate straight line P ₂P ₃With straight line P ₃P ₄Between acute angle theta;

(4) again according to 4 P that recorded ₁, P ₂, P ₃, P ₄With three Bessel's equation matched curves, again with θ for declaring apart from adaptive adjustment variable element Δ t, obtain next sensing point P ' ₅, and obtain its correspondence keep away a barrier point P _{B, 5}Utilize sensing point P ' ₅Hinder some P with keeping away _{B, 5}Record P ₅The 3 d space coordinate value, and coordinate figure deposited in the measurement data file, if variable element Δ t＞0, then with P ₂, P ₃, P ₄, P ₅Give P ₁, P ₂, P ₃, P ₄

(5) if variable element Δ t＜0 illustrates P ₅Point is back measuring point, i.e. P ₄Point is at P ₅P is then used in the front of point ₁, P ₂, P ₃, P ₅The value of point is measured next sensing point and is kept away the barrier point;

(6) repeat above-mentioned steps (3), (4) and (5) until the border, and make cross section sequence number value m=m+1; When m=N, finish to measure.

3, according to the measuring method of the described free form surface of claim 2, it is characterized in that, describedly declare apart from θ≤1 °, then Δ t=1/3+0.10; If 1 °＜θ≤3 °, then Δ t=1/3+0.05; If 3 °＜θ≤6 °, then Δ t=1/3; If θ＞6 °, then Δ t=-1/6.

According to the measuring method of the described free form surface of claim 2, it is characterized in that 4, described three Bessel's equations are P ' ₅=T (1+ Δ t) MP, wherein T (1+ Δ t)=[(1+ Δ t) ³(1+ Δ t) ²(1+ Δ t) 1], be the variable element matrix, M is the constant coefficient matrix of three Bezier basis functions, $M=\left[\begin{array}{cccc}-1& 3& -3& 1\\ 3& -6& 3& 0\\ -3& 3& 0& 0\\ 1& 0& 0& 0\end{array}\right];$ P is the matrix of the 3 d space coordinate of four points obtaining of up-to-date measurement, and P=[p ₁p ₂p ₃p ₄] ^T

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