CN114659464B - Airplane complete machine shape waviness measuring method based on measured three-dimensional data - Google Patents
Airplane complete machine shape waviness measuring method based on measured three-dimensional data Download PDFInfo
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Abstract
The invention discloses an aircraft complete machine appearance waviness measuring method based on actual measurement three-dimensional data, which comprises the following steps: removing outliers from original point cloud data of the whole machine, and then registering a theoretical point cloud model and an actual point cloud model of the whole machine in an optimal fitting mode; extracting a theoretical curve of the outline to be measured from the theoretical point cloud model, and taking point cloud data near a projection plane where the theoretical curve is located as candidate points of the curve to be measured; calculating the corresponding points of each discrete point in the candidate point set according to the discrete theoretical curve; adjusting the position of each discrete point according to the displacement of each discrete point generated under the action of gravity and internal force until an iteration termination condition is reached; and extracting a waviness curve according to the distance between the discrete points of the theoretical curve and the corresponding points of the theoretical curve and calculating a waviness parameter. The method combines three-dimensional point cloud data, and realizes accurate and efficient extraction of the waviness information of the curved surface to be detected based on the registered theoretical model and the point cloud model.
Description
Technical Field
The invention belongs to the field of measurement of the overall appearance waviness of an aircraft, and particularly relates to a method for measuring the overall appearance waviness of the aircraft based on actually measured three-dimensional data.
Background
The waviness of the aircraft profile has a great influence on both the aerodynamic performance and the flight performance of the aircraft. At present, the waviness of the outer shape of an airplane is detected by a method using a material sample strip, but the method has the defects of low measurement precision, low efficiency, large workload and the like, and is gradually abandoned. Most of the existing waviness measurement methods are mechanical measurement methods, manual sampling is needed, sampling time is long, and sampling data are susceptible to influence of human factors to generate errors. Therefore, in general, a mature measuring method for measuring and analyzing waviness is lacking at present.
With the development and popularization of laser radar and three-dimensional scanning technologies (the technologies are widely applied to the fields of surveying and mapping, power line inspection, digital cities, historic building protection, military equipment measurement, digital twins and the like), some methods for measuring and analyzing the waviness based on laser radar point cloud also appear in recent years, although the methods are different, the methods all have certain defects, and collected laser point cloud data cannot be fully utilized.
Disclosure of Invention
The invention provides a method for measuring the overall profile waviness of an airplane based on actually measured three-dimensional data, aiming at overcoming the defects in the prior art, and solving the problems of poor measurement precision and low efficiency of the overall profile waviness of the airplane in the prior art.
In order to realize the purpose, the invention adopts the following technical scheme:
a method for measuring the overall shape waviness of an aircraft based on measured three-dimensional data comprises the following steps:
s1, performing outlier removal operation on original point cloud data of the whole machine, and then registering a theoretical point cloud model and an actual point cloud model of the whole machine in a best fitting mode;
s2, extracting a theoretical curve of the external surface to be measured from the theoretical point cloud model, and taking point cloud data near a projection plane where the theoretical curve is located as candidate points of the curve to be measured;
s3, calculating corresponding points of each discrete point in the candidate point set according to the discrete theory curve, and projecting each discrete point and the corresponding point to the same horizontal plane;
s4, adjusting the position of each discrete point according to the displacement of each discrete point generated under the action of gravity and internal force until an iteration termination condition is reached;
and S5, extracting a waviness curve according to the distance between the discrete points of the theoretical curve and the corresponding points of the theoretical curve and calculating a waviness parameter.
Further, step S1 specifically includes the following steps:
s101, removing outliers from original point cloud data of the whole machine to obtain an actual point cloud model;
s102, randomly sampling on a theoretical curved surface model of the whole machine to obtain a corresponding theoretical point cloud model;
and S103, registering the actual point cloud model and the theoretical point cloud model by adopting an ICP (inductively coupled plasma) algorithm, and converting the actual point cloud model and the theoretical point cloud model into the same coordinate system.
Further, step S2 specifically includes the following steps:
s201, determining two points A on two boundary curves of the external surface to be detected in the theoretical curved surface model by giving the percentage K of the theoretical curved surface waviness detection 0 、A 1 So that A is 0 、A 1 The percentage of the arc length from the two points to the starting position of each boundary line to the total arc length of the boundary lines is equal to K, A 0 、A 1 Line A formed by connecting two points 0 A 1 Projecting the data to a theoretical point cloud model to obtain a theoretical curve L t ；
S202, converting the theoretical curve L t All points within 10mm of the two sides of the projection plane are used as candidate points of the curve to be measured to form a candidate point set P j (j＝0,1,...,M)。
Further, step S3 specifically includes the following steps:
s301, according to the straight line A 0 A 1 According to a parameter equation of the linear system, selecting a point T on the straight line according to a certain length interval i (i =0,1,.. Times.n), M > N > 1, and point T i (i =0,1,.., N) is projected to theoretical curve L t To obtain a theoretical curve L t Discrete point of (T) i ′(i＝0,1,...,N)；
S302, respectively calculating the distance d between each discrete point and each candidate point in the candidate point set j (j =0,1.., M), the candidate point with the smallest distance is taken as the corresponding point T of the discrete points i "(i =0,1,. And N), and the distance between them is taken as the theoretical distance;
and S303, projecting each discrete point and the corresponding point thereof on the same horizontal plane.
Further, step S4 specifically includes the following steps:
s401, respectively calculating each discrete point T i ' (i =0,1.., N) curvature ρ i (i =0,1.., N) and corresponding normal vector α i (i =0,1,.., N), the theoretical curve L t All the discrete points on the graph move for a certain distance along the direction opposite to the normal direction of the point with the minimum curvature, and whether each discrete point is regarded as an immovable point or not is judged;
s402, calculating a theoretical curve L t Upper discrete points T i ' (i =0,1., N) is displaced under the dual action of gravity and internal force, and the corresponding point is moved to a new position according to the displacement and whether the corresponding point is regarded as an immovable point is judged;
s404, repeating the step S402 until all the discrete points are immovable points or the distances between the discrete points and the corresponding points are less than the set threshold value.
Further, in S402, the formula
Calculating the theoretical curve L t Upper discrete points T i ' (i =0,1.., N) displacement due to both gravity and internal force, wherein Y is i (T) represents a point T i ' (i =0,1.., N) position at time t, F out (Y i And t) represents the point at time t at position Y i External forces applied thereto, including gravity and forces generated by collisions with other points, F ind (Y i And t) represents the point at time t at position Y i When internal forces are generated due to the action between discrete points, m represents the point T i ' (i =0,1.., N);
considering only gravitational effects, from the formula
Calculating the displacement, where Δ t is the time step, G represents the gravity coefficient, and X (t + Δ t), X (t- Δ t), and X (t) respectively represent the value at t +Δ t, t- Δ t, the position of the t time point;
taking the theoretical curve L into account only when the internal force acts t Upper two adjacent discrete points T i ′、T i+1 ', if both the two points are movable points, moving the two points in opposite directions by the same displacement amount d, if one of the points is an immovable point, moving the movable point by the displacement amount d, and if both the two points are immovable points, not operating;
the displacement amount
Wherein p is 0 For the currently prepared point to move, p i Is p 0 Of the adjacent point of the light source,
b is 1 when there is a movable point, and b is 0 when both points are non-movable points.
Further, the basis for determining the immovable point is as follows: and if the distance between the discrete point and the corresponding point after the displacement is less than or equal to the theoretical distance, regarding the discrete point as a non-movable point and fixing the position of the point.
Further, step S5 specifically includes the following steps:
s501, calculating the distance between each discrete point and the corresponding point on the theoretical curve after iteration is terminated;
s502, linear interpolation is carried out on all the intervals to obtain the value of 2 J Original signal y formed by discrete points J (x) Decompose y according to Mallat's algorithm J (x)：
Wherein the number of decomposition layers is l, l is less than J, and the approximate component of decomposition of each layer is
The detail component is
c j,k Is an approximation coefficient, d j,k In order to be a coefficient of detail,
for the scale function, ψ (x) is a wavelet function, J = (J, J-1,.., J-l + 1);
taking the approximate component of the l layer decomposition as a final waviness curve;
s503, determining the phases of the wave crest and the wave trough according to the slope change of the waviness curve: scanning a waviness curve from left to right, wherein the position of the slope changing from positive to negative is a wave crest, and the position of the slope changing from negative to positive is a wave trough; the amplitude of the wave peak is the maximum value of the original signal between adjacent wave troughs, and the amplitude of the wave trough is the minimum value of the original signal between adjacent wave peaks; after the phases and amplitudes of the wave crests and the wave troughs are determined, the wave amplitude and the wave length are calculated according to the definition of the waviness.
The invention has the beneficial effects that:
compared with the existing mechanical waviness measuring method with the problems of low measuring precision, high manual operation time cost, low efficiency and the like, the method provided by the invention measures the waviness of the appearance of the airplane by combining a point cloud data model of the appearance of the whole airplane obtained by the three-dimensional laser scanner and adding the action of internal force and external force to a discrete theoretical curve, and has the advantages of high measuring precision, high efficiency, less manual operation and the like.
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FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is a schematic diagram of the process carried out in the examples.
Detailed Description
The present invention will now be described in further detail with reference to the accompanying drawings.
The invention provides an aircraft complete machine appearance waviness measuring method based on measured three-dimensional data, as shown in figure 1, the method mainly comprises the following steps:
s1, removing outliers from original point cloud data of the whole machine, and then registering a theoretical point cloud model and an actual point cloud model of the whole machine in a best fitting mode, wherein the method specifically comprises the following steps:
s101, removing outliers from original point cloud data of the whole machine to obtain an actual point cloud model;
s102, randomly sampling on a theoretical curved surface model of the whole machine to obtain a corresponding theoretical point cloud model;
and S103, registering the actual point cloud model and the theoretical point cloud model by adopting an ICP (inductively coupled plasma) algorithm, and converting the actual point cloud model and the theoretical point cloud model into the same coordinate system.
And S2, extracting a theoretical curve of the external surface to be measured from the theoretical point cloud model, and taking point cloud data near a projection plane where the theoretical curve is located as candidate points of the curve to be measured. The method comprises the following steps:
s201, giving a percentage K of theoretical surface waviness detection, and determining two points A on two boundary curves of the external surface to be detected in a theoretical surface model 0 、A 1 So that A is 0 、A 1 The percentage of the arc length from the two points to the starting position of each boundary line to the total arc length of the boundary lines is equal to K, and A is 0 、A 1 Line A formed by connecting two points 0 A 1 Projecting the data to a theoretical point cloud model to obtain a theoretical curve L t ；
S202, converting the theoretical curve L t All points within 10mm of the two sides of the projection plane are used as candidate points of the curve to be measured to form a candidate point set P j (j＝0,1,...,M)。
Step S3, discrete theory curve L t And calculating corresponding points of the discrete points in the candidate point set, and projecting the discrete points and the corresponding points thereof on the same horizontal plane. The method comprises the following steps:
s301, according to the straight line A 0 A 1 Selecting points T on the straight line according to a certain length interval i (i =0,1,. Ann, N), M > N > 1, and point T i (i =0,1,.., N) is projected to theoretical curve L t To obtain a theoretical curve L t Discrete point of (T) i ′(i＝0,1,...,N)；
S302, respectively calculating the distance d between each discrete point and each candidate point in the candidate point set j (j =0,1.., M), the candidate point with the smallest distance is selectedCorresponding point T as discrete point i "(i =0,1,.., N), and the distance between the two is taken as the theoretical distance
And S303, projecting each discrete point and the corresponding point thereof on the same horizontal plane.
And S4, adjusting the positions of the discrete points according to the displacement of the discrete points under the action of gravity and internal force until an iteration termination condition is reached. The method comprises the following steps:
s401, respectively calculating each discrete point T i ' (i =0,1.., N) curvature ρ i (i =0,1.., N) and corresponding normal vector α i (i =0,1,.., N), the theoretical curve L t All the discrete points on the graph move 50mm along the direction opposite to the normal direction of the point with the minimum curvature, as shown in FIG. 2, and whether each discrete point is regarded as an immovable point is judged;
s402, formula
Calculating the theoretical curve L t Upper discrete points T i ' (i =0,1.., N) displacement due to both gravity and internal force, wherein Y is i (T) represents a point T i ' (i =0,1.., N) position at time t, F out (Y i And t) represents the point at time t at position Y i External forces applied thereto, including gravity and forces generated by collision with other points, F ind (Y i And t) represents the point at time t at position Y i When internal forces are generated due to the action between discrete points, m represents the point T i ' (i =0,1.., N) is taken to be 1.
Taking into account the displacement produced by gravity only, i.e. internal factors F ind (Y i T) is set to 0, then the result is obtained
Calculating the displacement, moving the discrete point to a new position according to the calculated displacement, and determining whether the discrete point is regarded as an immovable point, wherein delta t isThe time step, set to 0.5 in this example, represents the gravity coefficient, and in this example, 9.8, X (t + Δ t), X (t- Δ t), and X (t) represent the positions at the time points t + Δ t, t- Δ t, and t, respectively.
S403, driving F by internal factors only ind (Y i T) taking the theoretical curve L t Upper two adjacent discrete points T i ′、T i+1 If both the two points are movable points, the two points are moved toward each other by the same displacement d, and if one of the points is an immovable point, the movable point is moved by the displacement d; if the points are all immovable points, no operation is performed.
The amount of displacement is represented by the formula
The calculation is carried out according to the calculation,
wherein b is 1 when the points are movable points, and b is 0,p when the points are all immovable points 0 For the currently prepared point to move, p i Is p 0 Of the adjacent point of the light source,
and moving the corresponding point to a new position according to the displacement d and judging whether the corresponding point is regarded as an immovable point.
And S404, repeating the steps S402 and S403 until all the discrete points are immovable points or the distances between the discrete points and the corresponding points are less than a set threshold value e =3mm.
Further, the basis for judging the immovable point is as follows: and if the distance between the discrete point and the corresponding point after the displacement is less than or equal to the theoretical distance, regarding the discrete point as a non-movable point and fixing the position of the point.
S5, extracting a waviness curve according to the distance between discrete points of the theoretical curve and corresponding points of the discrete points, and calculating related parameters:
s501, calculating a theoretical curve L after iteration is ended t Upper point T i ' (i =0,1.., N) and its corresponding point T i The spacing D between "((i =0,1.., N)) i (i＝0,1,...,N)。
S502, for all the distances D i (i =0,1.., N) is obtained by 2 J Original signal y formed by discrete points J (x) Decompose y according to Mallat's algorithm J (x) .1. The The number of decomposition layers is l, l < J, and J =20 and l =6 in this example.
The approximate component of each layer decomposition is
The detail component is
Wherein J = (J, J-1., J-l + 1), c) j,k Is an approximation coefficient, d j,k In order to be a coefficient of detail,
for the scale function, ψ (x) is a wavelet function. Approximate component y of the l-th decomposition J-l (x) And reflecting basic fluctuation in the original signal, and taking the basic fluctuation as a final waviness curve.
And S503, determining the phases of the wave crest and the wave trough according to the slope change of the waviness curve. And scanning a waviness curve from left to right, wherein the position where the slope changes from positive to negative is a peak, and the position where the slope changes from negative to positive is a trough. The amplitude of the wave peak is the maximum value of the original signal between the adjacent wave troughs, and the amplitude of the wave trough is the minimum value of the original signal between the adjacent wave peaks. After the phases and amplitudes of the wave crests and the wave troughs are determined, the wave amplitude h and the wavelength l are calculated according to the definition of the waviness.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.
Claims (6)
1. A method for measuring the overall appearance waviness of an aircraft based on measured three-dimensional data is characterized by comprising the following steps:
s1, performing outlier removal operation on original point cloud data of the whole machine, and then registering a theoretical point cloud model and an actual point cloud model of the whole machine in a best fitting mode;
s2, extracting a theoretical curve of the external surface to be measured from the theoretical point cloud model, and taking point cloud data near a projection plane where the theoretical curve is located as candidate points of the curve to be measured;
s3, calculating corresponding points of each discrete point in the candidate point set according to the discrete theory curve, and projecting each discrete point and the corresponding point to the same horizontal plane;
s4, adjusting the position of each discrete point according to the displacement of each discrete point generated under the action of gravity and internal force until an iteration termination condition is reached; the method specifically comprises the following substeps:
s401, respectively calculating each discrete point T i ' (i =0,1.., N) curvature ρ i (i =0,1.., N) and corresponding normal vector α i (i =0,1,.., N), the theoretical curve L t All the discrete points on the graph move for a certain distance along the direction opposite to the normal direction of the point with the minimum curvature, and whether each discrete point is regarded as an immovable point or not is judged;
s402, calculating a theoretical curve L t Upper discrete points T i ' (i =0,1., N) is displaced under the dual action of gravity and internal force, and the corresponding point is moved to a new position according to the displacement and whether the corresponding point is regarded as an immovable point is judged; in particular, from the formula
Calculating a theoretical curve L t Upper discrete points T i ' (i =0,1.., N) displacement due to both gravity and internal force, wherein Y is i (T) represents a point T i ' (i =0,1.., N) position at time t, F out (Y i And t) represents the point at time t at position Y i Is subjected toExternal forces, including the forces of gravity and collision with other points, F ind (Y i T) represents the point at time t at position Y i When internal forces are generated due to the action between discrete points, m represents the point T i ' (i =0,1.., N);
considering only the gravitational effect, from the formula
Calculating the displacement, wherein delta t is a time step, G represents a gravity coefficient, and X (t + delta t), X (t-delta t) and X (t) respectively represent the positions of time points t + delta t, t-delta t and t;
taking into account only internal acting forces, taking the theoretical curve L arbitrarily t Upper two adjacent discrete points T i ′、T i+1 If both the two points are movable points, moving the two points in opposite directions by the same displacement d, if one of the points is an immovable point, moving the movable point by the displacement d, and if both the two points are immovable points, not operating;
the displacement amount
Wherein p is 0 For the currently prepared point to move, p i Is p 0 Of the adjacent point of the light source,
b is 1 when there is a movable point, and b is 0 when both points are non-movable points;
s403, repeating the step S402 until all the discrete points are immovable points or the distances between the discrete points and the corresponding points are less than a set threshold value;
and S5, extracting a waviness curve according to the distance between the discrete points of the theoretical curve and the corresponding points of the theoretical curve and calculating a waviness parameter.
2. The method for measuring the overall profile waviness of the aircraft based on the measured three-dimensional data as claimed in claim 1, wherein the step S1 specifically comprises the following steps:
s101, removing outliers from original point cloud data of the whole machine to obtain an actual point cloud model;
s102, randomly sampling on a theoretical curved surface model of the whole machine to obtain a corresponding theoretical point cloud model;
and S103, registering the actual point cloud model and the theoretical point cloud model by adopting an ICP (inductively coupled plasma) algorithm, and converting the actual point cloud model and the theoretical point cloud model into the same coordinate system.
3. The method for measuring the overall profile waviness of the aircraft based on the measured three-dimensional data as claimed in claim 1, wherein the step S2 specifically comprises the following steps:
s201, determining two points A on two boundary curves of the external surface to be detected in the theoretical curved surface model by giving the percentage K of the theoretical curved surface waviness detection 0 、A 1 So that A is 0 、A 1 The percentage of the arc length from the two points to the starting position of each boundary line to the total arc length of the boundary lines is equal to K, A 0 、A 1 Line A formed by connecting two points 0 A 1 Projecting the data to a theoretical point cloud model to obtain a theoretical curve L t ；
S202, converting the theoretical curve L t All points within 10mm of the two sides of the projection plane are used as candidate points of the curve to be measured to form a candidate point set P j (j＝0,1,...,M)。
4. The method for measuring the overall profile waviness of the aircraft based on the measured three-dimensional data as claimed in claim 3, wherein the step S3 specifically comprises the following steps:
s301, according to the straight line A 0 A 1 According to a parameter equation of the linear system, selecting a point T on the straight line according to a certain length interval i (i =0,1,. Ann, N), M > N > 1, and point T i (i =0,1.., N) is projected onto theoretical curve L t To obtain a theoretical curve L t Discrete point of (T) i ′(i＝0,1,...,N)；
S302, respectively calculating the distance d between each discrete point and each candidate point in the candidate point set j (j＝0,1,...,M) Taking the candidate point with the minimum distance as the corresponding point T of the discrete point i "(i =0,1,. And N), and the distance between them is taken as the theoretical distance;
and S303, projecting each discrete point and the corresponding point thereof to the same horizontal plane.
5. The method for measuring the overall appearance waviness of an aircraft based on measured three-dimensional data of claim 1, wherein the basis for judging the immovable points is as follows: and if the distance between the discrete point and the corresponding point after the displacement is less than or equal to the theoretical distance, regarding the discrete point as a non-movable point and fixing the position of the point.
6. The method for measuring the overall profile waviness of the aircraft based on the measured three-dimensional data as claimed in claim 1, wherein the step S5 specifically comprises the following steps:
s501, calculating the distance between each discrete point and the corresponding point on the theoretical curve after iteration is ended;
s502, linear interpolation is carried out on all the intervals to obtain the value of 2 J Original signal y formed by discrete points J (x) Decompose y according to Mallat's algorithm J (x)：
Wherein the number of decomposition layers is l, l is less than J, and the approximate component of decomposition of each layer is
The detail component is
c j,k Is an approximation coefficient, d j,k In order to be a coefficient of detail,
for scale functions,. Phi. (x) for wavelet functions, j＝(J,J-1,...,J-l+1)；
Taking the approximate component of the l layer decomposition as a final waviness curve;
s503, determining the phases of the wave crest and the wave trough according to the slope change of the waviness curve: scanning a waviness curve from left to right, wherein the position of the slope changing from positive to negative is a wave crest, and the position of the slope changing from negative to positive is a wave trough; the amplitude of the wave peak is the maximum value of the original signal between adjacent wave troughs, and the amplitude of the wave trough is the minimum value of the original signal between adjacent wave peaks; after the phases and amplitudes of the wave crests and the wave troughs are determined, the wave amplitude and the wave length are calculated according to the definition of the waviness.
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