Global calibration method for laser-tracking measurement system based on vision guiding

Aiming at the problems of low efficiency, low automatization and high cost existing in traditional laser tracking measurement system widely used in digital flexible assembly technique, a combined homing measurement system for large-scale part assembly is proposed. A laser tracker and a monocular vision system are combined in the system to fulfill the homing measurement of 3D coordinates of benchmarks in parts. To calibrate the system, a new global calibration method based on spatial planes is proposed. Global calibration is fulfilled by acquiring plane equations of planar target at diverse positions and orientations in the coordinate frames of both the vision system and laser tracker respectively, and calculating the transformation matrix between the two coordinate frames. The data measured in the vision system are then combined with those measured in the laser tracker. A mathematical model was established, and simulation was carried out. To evaluate the precision of the method, global calibration experiment was accomplished. The plane equations of planar target measured at 30 diverse positions and orientations were taken into calibration. Experiment results show that this method features simple operation, high stability and bright future for practical application; the RMS errors for the angle between planes measured by the calibrated vision system and laser tracker, and the distance difference between laser tracker origin and the planes are 0.13° and 1.50 mm, respectively.