# US 2021/0341900 A1 · Airplane structure stiffener repair method based on measured data

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- Number: US 2021/0341900 A1
- Document ID: US20210341900A1
- Status: Published application
- Kind: A1
- Application number: 17/026,262
- Filed: 2020-09-20
- Published: 2021-11-04
- Earliest claimed: 2020-04-29
- Assignees: Nanjing University of Aeronautics and Astronautics
- Applicants: Nanjing University of Aeronautics and Astronautics
- Inventors: Jun WANG; Zeyong WEI; Honghua CHEN
- Web page: https://patentgrep.com/patent/US20210341900A1

## CPC

- B64F 5/40: Maintaining or repairing aircraft
- G05B 19/402: characterised by control arrangements for positioning, e.g. centring a tool relative to a hole in the workpiece, additional detection means to correct position (G05B19/19 takes precedence)
- G01M 5/0016: {of aircraft wings or blades}
- G05B 2219/32228: Repair, rework of manufactured article
- G05B 2219/35519: Machining data and tool data
- B64F: GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR
- G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G)
- G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR

## Abstract

The present invention relates to an airplane structure stiffener repair method based on measured data guidance. The method includes: respectively measuring point cloud data on a surface of a structure stiffener and point cloud data on a surface of a to-be-assembled position of a body; respectively extracting all assembly plane features in two point cloud data based on an RANSAC algorithm; performing pre-alignment according to the plane features; performing accurate alignment based on a signed distance constraint according to repair tolerance requirements; and calculating a repair allowance, and generating a machining path to serve as an accurate machining basis. According to the method in the present invention, a repair amount can be accurately calculated by virtue of an alignment algorithm of the signed distance constraint, and an envelope relationship during model matching is met.

## Claims

### Claim 1

An airplane structure stiffener repair method based on measured data guidance, comprising the following steps:
S1: respectively scanning to acquire point cloud data P on a surface of an airplane structure stiffener and point cloud data Q on a surface of a to-be-assembled position of a body;
S2: respectively extracting all assembly plane features in the point cloud data P and Q;
S3: performing pre-alignment based on the extracted assembly plane features according to a structural assembly relationship between the airplane structure stiffener and the to-be-assembled position of the body;
S4: performing accurate alignment based on a signed distance constraint according to repair tolerance requirements; and
S5: calculating a repair allowance, and generating an accurate machining path to serve as an accurate machining basis on a machining platform.

### Claim 2 (depends on 1)

The airplane structure stiffener repair method based on measured data guidance according to claim 1, wherein the step S1 comprises:
S101: scanning to acquire the point cloud data P={p1, p2, . . . , pm} on the surface of the airplane structure stiffener, wherein m is the number of points in the point cloud data P; the point cloud data P comprises a normal Np={n1p, n2p, . . . , nmp} by default; if no normal exists, normal information may be calculated by a PCA method; and
S102: scanning to acquire the point cloud data Q={q1, q2, . . . , ql} on the surface of the to-be-assembled position of the body, wherein 1 is the number of points in the point cloud data Q; the point cloud data Q comprises a normal Nq={n1q, n2q, . . . , nlq} by default; if no normal exists, normal information may be calculated by a PCA method.

### Claim 3 (depends on 1)

The airplane structure stiffener repair method based on measured data guidance according to claim 1, wherein the step S2 comprises:
S201: for the point cloud data P, extracting all assembly plane features by an RANSAC algorithm; and
S202: for the point cloud data Q, extracting all assembly plane features by the RANSAC algorithm.

### Claim 4 (depends on 3)

The airplane structure stiffener repair method based on measured data guidance according to claim 3, wherein the step S3 comprises:
S301: determining correspondence of assembly planes between the point cloud data P and the point cloud data Q according to the structural assembly relationship between the airplane structure stiffener and the to-be-assembled position of the body;
S302: performing pre-alignment on the point cloud data Q and the point cloud data P by an SVD method according to the assembly relationship in correspondence and the extracted assembly plane features.

### Claim 5 (depends on 4)

The airplane structure stiffener repair method based on measured data guidance according to claim 4, wherein the step S4 comprises:
S401: finding out a corresponding closest Euclidean distance point pi in the point cloud data P for any point qi in the point cloud data Q according to a closest distance relationship in accordance with a pre-alignment result of the point cloud data P and the point cloud data Q;
S402: constructing optimization functions based on a signed distance constraint according to the repair tolerance requirements:
min
T
⁢
∑
i
=
1
l
⁢
(

T
⁡
(
q
i
)
-
p
i

2
-
θ
)
2
(
1
)
n
i
p
·
(
T
⁡
(
q
i
)
-
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<
0
(
2
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in the formulas (1) and (2), min represents a minimum value; T is a to-be-solved transformation matrix; ∥*∥2 is 2-norm; θ is repair tolerance; T(qi) is the transformed point qi by the transformation matrix T; and nip is the normal at the point pi;
S403: repeating the steps S401 and S402; solving the T that makes the (1) minimum by an iteration method; stopping iteration when the number of iterations reaches a preset value (generally 10) or an error is less than a preset threshold after alignment; and performing transformation on the Q with the T so as to acquire point cloud data Q′ after accurate alignment of the point cloud data P.

### Claim 6 (depends on 5)

The airplane structure stiffener repair method based on measured data guidance according to claim 5, wherein the step S5 comprises:
S501: calculating a closest Euclidean distance di from each point in the point cloud data P to the point cloud data Q′ after accurate alignment according to an accurate alignment result;
S502: obtaining a minimum spanning tree from the point cloud at the to-be-assembled position of the body structure after accurate alignment by using a Prim algorithm, and solving the longest path therein (e.g., a critical path, using a general algorithm for graphs), that is, a machining path, as shown by a heavy line in FIG. 2;
S503: providing the machining path and the repair amount for a machining center, and performing accurate repair machining.

### Claim 7 (depends on 2)

The airplane structure stiffener repair method based on measured data guidance according to claim 2, wherein the step S2 comprises:
S201: for the point cloud data P, extracting all assembly plane features by an RANSAC algorithm; and
S202: for the point cloud data Q, extracting all assembly plane features by the RANSAC algorithm.

### Claim 8 (depends on 7)

The airplane structure stiffener repair method based on measured data guidance according to claim 7, wherein the step S3 comprises:
S301: determining correspondence of assembly planes between the point cloud data P and the point cloud data Q according to the structural assembly relationship between the airplane structure stiffener and the to-be-assembled position of the body;
S302: performing pre-alignment on the point cloud data Q and the point cloud data P by an SVD method according to the assembly relationship in correspondence and the extracted assembly plane features.

### Claim 9 (depends on 8)

The airplane structure stiffener repair method based on measured data guidance according to claim 8, wherein the step S4 comprises:
S401: finding out a corresponding closest Euclidean distance point pi in the point cloud data P for any point qi in the point cloud data Q according to a closest distance relationship in accordance with a pre-alignment result of the point cloud data P and the point cloud data Q;
S402: constructing optimization functions based on a signed distance constraint according to the repair tolerance requirements:
min
T
⁢
∑
i
=
1
l
⁢
(

T
⁡
(
q
i
)
-
p
i

2
-
θ
)
2
(
1
)
n
i
p
·
(
T
⁡
(
q
i
)
-
p
i
)
<
0
(
2
)
in the formulas (1) and (2), min represents a minimum value; T is a to-be-solved transformation matrix; ∥*∥2 is 2-norm; θ is repair tolerance; T(qi) is the transformed point qi by the transformation matrix T; and nip is the normal at the point pi;
S403: repeating the steps S401 and S402; solving the T that makes the (1) minimum by an iteration method; stopping iteration when the number of iterations reaches a preset value (generally 10) or an error is less than a preset threshold after alignment; and performing transformation on the Q with the T so as to acquire point cloud data Q′ after accurate alignment of the point cloud data P.

### Claim 10 (depends on 9)

The airplane structure stiffener repair method based on measured data guidance according to claim 9, wherein the step S5 comprises:
S501: calculating a closest Euclidean distance di from each point in the point cloud data P to the point cloud data Q′ after accurate alignment according to an accurate alignment result;
S502: obtaining a minimum spanning tree from the point cloud at the to-be-assembled position of the body structure after accurate alignment by using a Prim algorithm, and solving the longest path therein (e.g., a critical path, using a general algorithm for graphs), that is, a machining path, as shown by a heavy line in FIG. 2;
S503: providing the machining path and the repair amount for a machining center, and performing accurate repair machining.