Abstract: According to the setting and safety of docking assembly for large cylinder-tail nozzles， a new method for precise docking assembly is proposed based on LD-PSD to improve the assembly accuracy and efficiency. First， the calibration block marker coordinates are obtained by using laser trackers， and the least square model is established according to the deviation between theoretical coordinate and the measured coordinate of the mark point. Precise spatial registration is implemented between measured coordinate and global coordinate by using singular value decomposition(SVD). Then， the tracking instrument is used to obtain the coordinate of the key point of the nozzle and cylinder. The mathematical model of the current position of nozzle cylinder is established using the least squares and HSF. 6-DOF CNC equipment is developed， and taking the posture of the cylinder as a reference， posture preconditioning is done by the anti-solution of nozzle pose parameters. The online feedback system is launched to detect the pre-assembly error. By planning micro rotation and micro translational path， the position of the nozzle is corrected several times to meet the requirement of a given assembly accuracy. The test results in a power plant show that the assembly process is smooth and efficient， and it can realize the precise docking assembly of large cylinder-tail nozzles.

Key words: mechanical arm, laser tracker, key pose vector, least square method, closed loop calibration