When industrial robots are used for automatic drilling of aircraft components, their accumulative errors inevitably result in poor positioning accuracy. An on-machine positioning error compensation method is proposed, utilizing the homographic hand-eye relation to measure 3D error of robot driving coordinates. Firstly, the geometric relations among the coordinate frames involved in the robot drilling system are established by using an external measurement device. In the calibration stage, a planar calibration target is specifically installed to coincide with the working plane, and the robot-carried camera, which mounted at an angle, takes one image of the calibration target that is in front of the drilling bit. The homographic relation between the vision image plane and the working plane is then calculated according to the image of the calibration target. In the drilling process, with the aid of range sensor and monocular, the robot adjusts its pose, which corresponding to the theoretical coordinates of the datum hole, to the ideal pose above the datum hole. The practical driving coordinates corresponding to datum holes are calculated by utilizing the calibrated hand-eye homography. And then the 3D transformational matrix is calculated based on a group of 3D driving errors of datum holes. The position errors of the holes to be drilled/riveted are then compensated based on the 3D transformational matrix. The proposed error compensation method is verified by stimulated drillings on an experimental aircraft structural part. The results show that the ranges of measured value of positioning and normal error of the drilling holes before compensation are 2.28-2.85 mm and 2.09°-3.93° respectively, and the average errors are 2.55 mm and 3.30° respectively. After compensation, the maximum error of the drilling errors is within 0.30 mm and 0.21°, respectively, meeting the requirement of aircraft structure drilling.
WANG Longfei
,
ZHANG Liyan
,
YE Nan
. An on-line compensation technology for robotic drilling error suitable for curved structure[J]. ACTA AERONAUTICAET ASTRONAUTICA SINICA, 2019
, 40(10)
: 422871
-422871
.
DOI: 10.7527/S1000-6893.2019.22871
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