METHOD FOR CALIBRATING ROTATION CENTER BASED ON BLADE LOCAL LEADING-EDGE CURVE FEATURE

Abstract

The present disclosure provides a method for calibrating a rotation center based on a blade local leading-edge curve feature. The method acquires a blade local leading-edge curve feature before and after rotation, solves centroid coordinates according to maximum values in the blade local leading-edge curve features in the two times, and then solves a rotation center according to the centroid coordinates, thereby calibrating a coordinate of the rotation center. Compared with a point calibration method in the prior art, the present disclosure has a more accurate result by curve calibration and is more suitable for a real rotation center; and the method also has a more accurate blade measurement result when applied to measuring a blade cross-section curve feature.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit and priority of Chinese Patent Application No. 202011134900.7, filed on Oct. 22, 2020, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure belongs to the field of blade measurement, and in particular, relates to a method for calibrating a rotation center based on a blade local leading-edge curve feature.

Description of the Related Art

Blades are core components of aviation engines, gas turbines, steam turbines and other devices, and play a vital role in conversion from heat energy to mechanical energy. The profile and quality of the blades directly affect the energy conversion efficiency and service life of the complete machines. The blades are difficult to be measured because the cross sections are irregularly free-form surfaces and each cross-section profile is different.

A Chinese invention patent 201911267259.1 discloses a method for measuring a blade based on line structured light. The method calibrates the center of the turntable by using a feature that the blade leading-edge profile has a maximum value on the cross section. Although solving the error arising from the transfer of a calibration sphere in the prior art, the method has a certain error in itself as it calibrates the center of the turntable by approximating the line between two points as a tangent line. Moreover, the method has a certain limitation, and is only applicable to blades having small curvature radii of leading-edge profiles.

BRIEF SUMMARY OF THE INVENTION

An objective of the present disclosure is to provide a method for calibrating a rotation center based on a blade local leading-edge curve feature. The method calibrates the center of the turntable with the blade leading-edge curve feature to achieve a wider application scope and a higher blade measurement accuracy.

To achieve the above objective, the present disclosure uses the following technical solutions:

A method for calibrating a rotation center based on a blade local leading-edge curve feature includes the following steps:

(1) putting a blade onto a turntable plane, and adjusting a pose of a line structured-light sensor such that a laser plane of the line structured-light sensor intersects with a leading-edge curve feature of the blade, the line structured-light sensor acquiring profile data V₁∈^2×n1 of the leading-edge curve feature of the present blade, selecting the maximum value V_1m in the profile data V₁, and respectively taking n points along left and right sides of the V_1m to form a data set v₁=[V_1m−n . . . V_1m . . . V_1m+n]_1×(2n+1) of a blade local leading-edge curve feature;

(2) ensuring that the pose of the line structured-light sensor is unchanged, the laser plane of the line structured-light sensor still intersects with a leading-edge curve feature of the blade after rotation of the turntable, and a rotation angle θ is 1-3°, acquiring profile data V₂∈^2×n2 of the leading-edge curve feature at this time, first selecting a maximum value V_2m in the profile data V₂, finding a point V_2m-r corresponding to the maximum value V_1m in step (1) near the maximum value V_2m, respectively taking c reference points V_2m-r∈[V_2m-c . . . V_2m . . . V_2m+c]_1×(2c+1) along left and right sides of the V_2m, and forming a profile data set v_2m-r=[V_(2m-r)-n . . . V_2m-r . . . V_(2m-r)+n]_1×(2n+1) of a blade local leading-edge curve feature with n points in left and right sides of the V_2m-r;

(3) calculating covariance matrixes of the profile data sets v₁ and V_2m-r of the blade local leading-edge curve features, solving eigenvectors and eigenvalues according to the covariance matrixes, and then establishing a matching function M between the maximum values V_1m and V_2m-r according to the eigenvectors and the eigenvalues:

M(V_1m,V_2m-r)=Σ_d=1²∥λ_d^r1χ_d^r1−λ_d^r2m(R_θχ_d^r2m)∥²

where, λ_d^r1 is the eigenvalue of the covariance matrix of the data set v₁; χ_d^r1 is the eigenvector of the covariance matrix of the data set v₁; λ_d^r2m is the eigenvalue of the covariance matrix of the data set V_2m-r; λ_d^r2m is the eigenvector of the covariance matrix of the data set v_2m-r; and

$R_{\theta }=\left[\begin{array}{cc}\cos \theta & \sin \theta \\ -\sin \theta & \cos \theta \end{array}\right]$

is a rotation matrix;

(4) selecting the data set v_2m-r formed by different reference points V_2m-r, finding a reference point V_2m-k corresponding to a minimum value in the matching function M, and taking n points along left and right sides of the reference point V_2m-k to form a data set v₂=[V_(2m-k)-n . . . V_2m-k . . . V_(2m-k)+n]_1×(2n+1) of the blade local leading-edge curve feature; and

(5) solving centroid coordinates v₁ and v₂ according to the profile data sets v₁ and v₂ of the blade local leading-edge curve features: v_t=(Σ_i=1²ⁿ⁺¹v_ti)/(2n+1), t=1, 2, and v₁ and v₂ being respectively the centroid coordinates of the data sets v₁ and v₂ of the blade local leading-edge curve features; and solving a rotation center O_b according to the two centroid coordinates v₁ and v₂.

Further, the data set v₁ of the blade local leading-edge curve feature in step (1) may be established through the following steps:

selecting the maximum value V_1m in the profile data V₁ as a reference point, and nth points V_1m+n and V_1m−n along the left and right sides of the V_1m; and calculating a distance d_Ln from the maximum value V_1m to a line connecting the V_1m+n and the V_1m−n, and selecting the V_1m+n and the V_1m−n having the d_Ln more than or equal to an optimal measuring interval d_z of the line structured-light sensor as endpoints of a blade local leading-edge data set, namely, the profile data set v₁=[V_1m−n . . . V_1m . . . V_1m+n]_1×(2n+1) of the blade local leading-edge curve feature:

$d_{\mathrm{Ln}}=\frac{K{x}_{1m}-y_{1m}+\left(y_{1m-n}-{\mathrm{Ky}}_{1m-n}\right)}{\sqrt{K^2+1}},$

where, d_Ln is the distance from the maximum value V_1m to the line connecting the V_1m+n and the V_1m−n; and K is a slope of the line connecting the V_1m+n and the V_1m−n.

Further, the rotation center coordinate O_b may be solved with a following model:

o _b=[x y]^T=(R_θ−E)⁻¹(R_θv₂−v₁)

where, (x, y) is coordinate data of the rotation center O_b in a data coordinate system;

$R_{\theta }=\left[\begin{array}{cc}\cos \theta & \sin \theta \\ -\sin \theta & \cos \theta \end{array}\right]$

is the rotation matrix;

$E=\left[\begin{array}{cc}1& 0\\ 0& 1\end{array}\right]$

is a 2*2 identity matrix; and v₁ and v₂ are respectively the centroid coordinates of the data sets v₁ and v₂ of the blade local leading-edge curve features.

The method for calibrating a rotation center based on a blade local leading-edge curve feature is used to measure a blade cross-section profile, the blade cross-section profile being P=[V₁^ob V₂^ob . . . V_i^ob . . . V_n^ob], V_i^ob=R_ϕi(V_i+o_so_b), where R_ϕi is a rotation matrix of a turntable at an ith time; V_i is data acquired by a line structured-light sensor at the ith time; and o_so_b is a vector from an origin of a data coordinate system to a rotation center.

The present disclosure calibrates the rotation center by matching the blade local leading-edge curve features. Compared with the prior art in which the rotation center is calibrated by single-point matching, the present disclosure achieves the more accurate result and the better robustness because of the introduction of more feature points. Next, owing to the improved precision for calibrating the rotation center, the present disclosure further reduces the subsequent reconstruction error of the blade profile, to improve the blade measurement precision.

Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:

FIG. 1 is a schematic diagram of a measurement apparatus according to the present disclosure.

FIG. 2 is a schematic diagram of a measurement for calibrating a rotation center with a local leading-edge curve feature according to the present disclosure.

FIG. 3 is a schematic diagram of a measured local leading-edge curve feature according to the present disclosure.

FIG. 4 is an overlapped schematic diagram of transformation of leading-edge curve features in two times to a rotation center according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

With the measurement of a blade cross-section profile as an example, the calibration of a rotation center based on a blade leading-edge curve feature provided by the present disclosure as well as the measurement of the blade cross-section profile will be described in detail in the embodiment.

The embodiment provides a method for measuring a blade cross-section profile based on a blade leading-edge curve feature at a high precision, including the following steps:

(1) Calibration on Measurement Apparatus Before Blade Installation

As shown in FIG. 1, the measurement apparatus includes a line structured-light sensor 100, a translational drive (S_X, S_Y, S_Z) for controlling motion of the line structured-light sensor within a moving coordinate system O-XYZ, and a rotational drive W for controlling rotation of a turntable. The turntable has a rotation center certainly. There is a need to calibrate the measurement apparatus before installation of the blade 200, to ensure the subsequent acquisition accuracy. The calibration includes pose calibration on the line structured-light sensor 100 and calibration on the turntable plane. The calibration method is the same as the prior art, and will not be repeated in the embodiment.

(2) Calibration on Rotation Center of Turntable

(a) Put the blade 200 onto the turntable plane, and adjust a pose of the line structured-light sensor 100 such that a laser plane of the line structured-light sensor 100 intersects with a leading-edge curve feature of the blade 200. As shown in FIG. 2, the solid line of the blade 200 is the blade cross-section profile in a present state, and the curve intersecting with the line structured-light sensor 100 is the leading-edge curve feature. The line structured-light sensor 100 acquires profile data V₁∈^2×n1 of the leading-edge curve feature of the present blade 200.

(b) Select a maximum value V_1m in the profile data V₁, and sequentially select nth points V_1m+n and V_1m−n along left and right sides of the V_1m; and calculate a distance d_Ln from the maximum value V_1m to a line connecting the V_1m+n and the V_1m−n,

$d_{\mathrm{Ln}}=\frac{K{x}_{1m}-y_{2m}+\left(y_{1m-n}-{\mathrm{Ky}}_{1m-n}\right)}{\sqrt{K^2+1}},$

where, d_Ln is the distance from the maximum value V_1m to the line connecting the V_1m+n and the V_1m−n, K=(Y_1m−n−y_1m+n)/(x_1m−n−x_1m+n) is a slope of the line connecting the V_1m+n and the V_1m−n, x_1m and y_1m are data values of the V_1m, x_1m+n and y_1m+n are data values of the V_1m+n, and x_1m−n and y_1m−n are data values of the V_1m−n.

Select the V_1m+n and the V_1m−n having the d_Ln just more than an optimal measuring value d_z of the line structured-light sensor 100 as endpoints of a blade local leading-edge data set. The line structured-light sensor selected during implementation has the optimal measuring value d_z=0.25 mm, and has the high precision. The embodiment selects the V_1m+n and the V_1m−n having the d_Ln just more than 0.25 mm as the endpoints of the blade local leading-edge data set, namely, a profile data set v₁=[V_1m−n . . . V_1m . . . V_1m+n]_1×(2n+1) of a blade local leading-edge curve feature.

(c) Ensure that the pose of the line structured-light sensor 100 is unchanged, the laser plane of the line structured-light sensor 100 still intersects with a leading-edge curve feature of the blade 200 after rotation of the turntable, and a rotation angle is θ. In the embodiment, the θ is 1°, 2° or 3°. As shown in FIG. 2, the dotted line is the rotated blade cross-section profile, and profile data V₂∈^2×n2 of the leading-edge curve feature at this time is acquired. The maximum value in the V₂ is V_2m. As the θ is relatively small, the point corresponding to the maximum value V_1m of the V₁ in the V₂ is certainly located near the V_2m, and thus the reference point V_2m-r optimally corresponding to the V_1m is found in the V₂. Sequentially take c points in left and right sides of the V_2m as V_2m-r∈[V_2m-c . . . V_2m . . . V_2m+c]_1×(2c+1) and then take n points in left and right sides of the V_2m-r selected each time to form a profile data set v_2m-r=[V_(2m-r)-n . . . V_2m-r . . . V_(2m-r)+n]_1×(2n+1) of a blade local leading-edge curve feature.

(d) Calculate covariance matrixes COV(v₁)=Σ_i=1²ⁿ⁺¹(v_1i−v₁)(v_1i−v₁)^T and COV(v_2m-r)=Σ_i=1²ⁿ⁺¹(v_2i−v_2m-r)(v_2i−v_2m-r)^T of the profile data sets v₁ and v_2m-r of the blade local leading-edge curve features, where v₁=(Σ_i=1²ⁿ⁺¹v_1i)/(2n+1) and v_2m-r=(Σ_i=1²ⁿ⁺¹v_(2m-r)i)/(2n+1) are respectively centroid coordinates of the data sets v₁ and v_2m-r of the blade local leading-edge curve features; and solve an eigenvector χ_d^r1 and an eigenvalue λ_d^r1 according to the covariance matrix COV(v₁), solve an eigenvector λ_d^r2m and an eigenvalue λ_d^r2m, according to the covariance matrix COV(v_2m-r) and then establish a matching function between the maximum values V_1m and V_2m-r according to the eigenvectors χ_d^r1 and χ_d^r2m and the eigenvalues and λ_d^r2m,

M(V_1m,V_2m-r)=Σ_d=1²∥λ_d^r1χ_d^r1−λ_d^r2m(R_θχ_d^r2m)∥²

where, λ_d^r1 is the eigenvalue of the data set v₁; χ_d^r1 is the eigenvector of the data set v₁; λ_d^22m is the eigenvalue of the data set v_2m-r; χ_d^r2m is the eigenvector of the data set v_2m-r; and

$R_{\theta }=\left[\begin{array}{cc}\cos \theta & \sin \theta \\ -\sin \theta & \cos \theta \end{array}\right]$

is a rotation matrix.

(e) Select different reference points V_2m-r to establish the data set v_2m-r of the local leading-edge curve feature, and find a reference point V_2m-k corresponding to a minimum value in a target function M, n points in left and right sides of the reference point V_2m-k forming the data set v₂=[V_(2m-k)-n . . . V_2m-k . . . V_(2m-k)+n]_1×(2n+1) of the blade local leading-edge curve feature.

(f) Solve centroid coordinates v₁=(Σ_i=1²ⁿ⁺¹v_1i)/(2n+1) and v₂=(Σ_i=1²ⁿ⁺¹v_2i)/(2n+1) according to the profile data sets v₁ and v₂ of the blade local leading-edge curve features, and solve a rotation center O_b according to the two centroid coordinates. Set that a vector of the O_b to an origin O_s of a data coordinate system o_s-x_sy_s is o_so_b=[x y]=(R_θ−E)⁻¹(R_θv₂−v₁); (x, y) is coordinate data of the rotation center O_b in the data coordinate system;

$R_{\theta }=\left[\begin{array}{cc}\cos \theta & \sin \theta \\ -\sin \theta & \cos \theta \end{array}\right]$

is the rotation matrix;

$E=\left[\begin{array}{cc}1& 0\\ 0& 1\end{array}\right]$

is a 2*2 identity matrix; and v₁ and v₂ are respectively the centroid coordinates of the data sets v₁ and v₂ of the blade local leading-edge curve features.

By putting the profile data V₁ and V₂ acquired by the line structured-light sensor 100 for the leading-edge curve feature of the present blade 200 into V₁^ob=V₁+o_so_b and V₂^ob=R_θ(V₂+o_so_b) in the data coordinate system o_s-x_sy_s, the blade local leading-edge feature curve is as shown in FIG. 4.

(3) Measurement on Blade Cross-Section Profile

Set that an n field of view (FOV) is employed by the cross section to acquire the complete cycle of profile data, the rotation angle corresponding to the FOV i is ϕ_i, the translational parameter is T_i=[x_i y_i]^T, and the cross-section curve profile is P=[V₁^ob V₂^ob . . . V_i^ob . . . V_n^ob], V_i^ob=R_ϕi(V_i+o_so_b); R_ϕi being a rotation matrix of a turntable at the ith time, V_i being data acquired by a line structured-light sensor at the ith time, and o_so_b being a vector from an origin of a data coordinate system to a rotation center.

Adjust the line structured-light sensor such that a laser plane intersects with a next target measured cross section, and repeat the above steps, thereby completely all measurement work of the blade.

Of note, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes”, and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

As well, the corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Having thus described the invention of the present application in detail and by reference to embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims as follows:

Claims

1. A method for calibrating a rotation center based on a blade local leading-edge curve feature, comprising the following steps: (1) putting a blade onto a turntable plane, and adjusting a pose of a line structured-light sensor such that a laser plane of the line structured-light sensor intersects with a leading-edge curve feature of the blade, the line structured-light sensor acquiring profile data V1∈2×n1 of the leading-edge curve feature of the present blade, selecting a maximum value V1m in the profile data V1, and respectively taking n points along left and right sides of the V1m to form a data set v1=[V1m−n . . . V1m . . . V1m+n]1×(2n+1) of a blade local leading-edge curve feature;(2) ensuring that the pose of the line structured-light sensor is unchanged, the laser plane of the line structured-light sensor still intersects with a leading-edge curve feature of the blade after rotation of the turntable, and a rotation angle θ is 1-3°, acquiring profile data V2∈2×n2 of the leading-edge curve feature at this time, first selecting a maximum value V2m in the profile data V2, finding a point V2m-r corresponding to the maximum value V1m in step (1) near the maximum value V2m, respectively taking c reference points V2m-r∈[V2m-c . . . V2m . . . V2m+c]1×(2c+1) along left and right sides of the V2m, and forming a profile data set v2m-r=[V(2m-r)-n . . . V2m-r . . . V(2m-r)+n]1×(2n+1) of a blade local leading-edge curve feature with n points in left and right sides of the V2m-r;(3) calculating covariance matrixes of the profile data sets v1 and v2m-r of the blade local leading-edge curve features, solving eigenvectors and eigenvalues according to the covariance matrixes, and then establishing a matching function M between the maximum values V1m and V2m-r according to the eigenvectors and the eigenvalues, M(V1m,V2m-r)=Σd=12∥λdr1χdr1−λdr2m(Rθχdr2m)∥2

2. The method for calibrating a rotation center based on a blade local leading-edge curve feature according to claim 1, wherein the data set v1 of the blade local leading-edge curve feature in step (1) is established through the following steps: selecting the maximum value V1m in the profile data V1, and nth points V1m+n and V1m−n along the left and right sides of the V1m; and calculating a distance dLn from the maximum value V1m to a line connecting the V1m+n and the V1m−n, and selecting the V1m+n and the V1m−n having the dLn more than or equal to an optimal measuring value dz of the line structured-light sensor as endpoints of the blade local leading-edge data set, namely, the profile data set v1=[V1m−n . . . V1m . . . V1m+n]1×(2n+1) of the blade local leading-edge curve feature:

3. The method for calibrating a rotation center based on a blade local leading-edge curve feature according to claim 1, wherein the rotation center coordinate Ob is solved with a following model: ob=[x y]T=(Rθ−E)−1(Rθv2−v1)