4 Study on a Digital Inspection Method for Aircraft Tubing Assembly
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theoretical location coordinates of the clamp positioning point on the tubing
centreline can be determined. If the locating point of the clamp cannot be
determined, the tangent point to the bent section with largest distance from the
two tubing endpoints, PLmax, can be used to replace that, so that obtaining the
theoretical triangle with the largest area and minimize the inspection error.
(2) Determination of the theoretical barycenter of the triangle: the theoretical
triangle S 0 is composed of two theoretical tubing endpoints and the locating
point of the clamp, and its barycenter is determined as G 0 .
(3) Determination of the measured barycenter of the triangle: the measured triangle
S 1 is composed of two measured tubing endpoints and the locating point of the
clamp, and its barycenter is determine as G 1 .
(4) Comparison and matching of the datum: rotating and moving the measured
triangle S 1 , and making S 0 coplanar with S 1 , G 0 coincide with G 1 and Line0
connecting theoretical tubing endpoints parallel to Line1 connecting measured
tubing endpoints, so as to realize the locating of the measured and the theoretical
tubing based on the three assembly points.
4.2.4 Inspection Datum Fitting
Because the actual shape of the measured tubing can be completely expressed by the
coordinates of two endpoints and bent tangent points, only the above tubing points
need to be taken as deviation calculation points. And the shape deviation of tubing
was divided into the axial deviation, the radial deviation and the angle deviation, as
shown in Fig. 4.1.
Axial deviation: projecting the calculation deviation points of the measured tubing
on the centreline of the theoretical tubing, the distance between the projection point
and theoretical point is the axial deviation. If the deviation calculation point is the
end point of tube, the axial deviation corresponds to the butt clearance of tubing
assembly.
Radial deviation: projecting the deviation calculation point of the measured tubing
on the cross section of theoretical tubing, the distance between the projection point
and the theoretical point is the radial deviation. If the deviation calculation point is
the tubing endpoint, the radial deviation corresponds to the misalignment of tubing
assembly.
Angle deviation: the angle value between the centreline of the deviation calculation point of the measured tubing and the centreline of theoretical tubing is considered
as the angle deviation. If the deviation calculation point is the tubing endpoint, the
angle deviation corresponds to the angle deviation of tubing assembly.
In order to improve the inspection accuracy, the digitized equipment is used to
measure the tube shape and the accuracy shall not be less than one third of the
deviation of the tubing shape, at least 0.1 mm. In the process of numerical calculation,
the calculation accuracy shall not be less than one thousandth of the deviation of
tubing shape, at least 0.0001 mm.
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theoretical location coordinates of the clamp positioning point on the tubing
centreline can be determined. If the locating point of the clamp cannot be
determined, the tangent point to the bent section with largest distance from the
two tubing endpoints, PLmax, can be used to replace that, so that obtaining the
theoretical triangle with the largest area and minimize the inspection error.
(2) Determination of the theoretical barycenter of the triangle: the theoretical
triangle S 0 is composed of two theoretical tubing endpoints and the locating
point of the clamp, and its barycenter is determined as G 0 .
(3) Determination of the measured barycenter of the triangle: the measured triangle
S 1 is composed of two measured tubing endpoints and the locating point of the
clamp, and its barycenter is determine as G 1 .
(4) Comparison and matching of the datum: rotating and moving the measured
triangle S 1 , and making S 0 coplanar with S 1 , G 0 coincide with G 1 and Line0
connecting theoretical tubing endpoints parallel to Line1 connecting measured
tubing endpoints, so as to realize the locating of the measured and the theoretical
tubing based on the three assembly points.
4.2.4 Inspection Datum Fitting
Because the actual shape of the measured tubing can be completely expressed by the
coordinates of two endpoints and bent tangent points, only the above tubing points
need to be taken as deviation calculation points. And the shape deviation of tubing
was divided into the axial deviation, the radial deviation and the angle deviation, as
shown in Fig. 4.1.
Axial deviation: projecting the calculation deviation points of the measured tubing
on the centreline of the theoretical tubing, the distance between the projection point
and theoretical point is the axial deviation. If the deviation calculation point is the
end point of tube, the axial deviation corresponds to the butt clearance of tubing
assembly.
Radial deviation: projecting the deviation calculation point of the measured tubing
on the cross section of theoretical tubing, the distance between the projection point
and the theoretical point is the radial deviation. If the deviation calculation point is
the tubing endpoint, the radial deviation corresponds to the misalignment of tubing
assembly.
Angle deviation: the angle value between the centreline of the deviation calculation point of the measured tubing and the centreline of theoretical tubing is considered
as the angle deviation. If the deviation calculation point is the tubing endpoint, the
angle deviation corresponds to the angle deviation of tubing assembly.
In order to improve the inspection accuracy, the digitized equipment is used to
measure the tube shape and the accuracy shall not be less than one third of the
deviation of the tubing shape, at least 0.1 mm. In the process of numerical calculation,
the calculation accuracy shall not be less than one thousandth of the deviation of
tubing shape, at least 0.0001 mm.