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Manufacturing accuracy, especially position
accuracy of fastener holes, directly affects service life and security of aircraft.
The traditional modification has poor robustness, while the modification based on
laser tracker costs too much. To improve the relative position accuracy of aircraft
assembly drilling, and ensure the hole-edge distance requirement, a method was presented
to modify the coordinates of drilling holes. Based on online inspecting two positions
of pre-assembly holes and their theoretical coordinates, the spatial coordinate
transformation matrix of modification could be calculated. Thus the straight drilling
holes could be modified. The method improves relative position accuracy of drilling
on simple structure effectively. And it reduces the requirement of absolute position
accuracy and the cost of position modification. And the process technician also
can use this method to decide the position accuracy of different pre-assembly holes
based on the accuracy requirement of assembly holes.
By rigidizing the input joints, all
possible combinations of drive selecting for the 4-PPPS parallel mechanism are
analyzed based on the screw theory in this paper, and the five of them are
proved to be reasonable. Then choosing the one as mechanical actuators, the
workspace of the 4-PPPS parallel mechanism is deduced according to the rational
input scheme. Finally the rationality of input scheme for this mechanism is
identified on the basis of the continuity of the workspace.