The subreflector's adjusting mechanism of the 65 meters radio telescope in Shanghai observatory is a Stewart parallel robot. In order to find out the problems of this robot's precision decline in time, caused by mechanical wear or error accumulation, inclinometers are used to measure the orientation of the mobile robot platform. Comparing the RMS (root mean square) error of the measured platform orientation with the expected orientation precision, thereby the user can judge whether maintenance or homing is required. For improving the easy maintenance of the parallel robot, two ways of homing are set up, by using photoelectric sensor and magnetic linearity displacement transducer (MLDT) respectively. The principles of the two ways of homing are analyzed, particularly that of calibrating the precision of the photoelectric sensor and the MLDT by using the homing operation. What's more, different conditions under which the parallel robot needs homing operation are summarized, and the corresponding homing control strategies are proposed. Test shows that the homing strategy proposed is an effective tool to solve homing problem of the parallel robot.
[1] Taghirad H D, Nahon M A. Kinematic analysis of a macro-micro redundantly actuated parallel manipulator[J]. Advanced Robotics, 2008, 22(6/7): 657-687.[2] Koch P M, Kesteven M, Nishioka H, et al. The AMiBA hexapod telescope mount[J]. Astrophysical Journal, 2009, 649(2): 1670-1684.[3] 张明辉,黄田.Diamond 机构的弹性动力分析与试验研究[J].机械设计,2004,24(11): 6-8. Zhang M H, Huang T. Research on elastic dynamic analysis and test for Diamond mechanism[J]. Journal of Machine Design, 2004, 24(11): 6-8.[4] 赵永生,郑魁敬,李秦川,等.5-UPS/PRPU 5自由度并联机床运动学分析[J].机械工程学报,2004,40(2): 12-16. Zhao Y S, Zheng K J, Li Q C, et al. Kinematic analysis of 5-UPS/PRPU 5-DOF parallel machine tool[J]. Chinese Journal of Mechanical Engineering, 2004, 40(2): 12-16.[5] Duan B Y. A new design project of the line feed structure for large spherical radio telescope and its nonlinear dynamic analysis[J]. Mechatronics, 1999, 9(1): 53-64. [6] 刘红军,龚民,赵明扬.一种四自由度并联机构的误差分析及其标定补偿[J].机器人,2005,27(1): 6-9. Liu H J, Gong M, Zhao M Y, et al. Error analysis and calibration of a 4-DOF parallel mechanism[J]. Robot, 2005, 27(1): 6-9.[7] 刘含玮,王洪光,李树军,等.一种3自由度并联柔索驱动机器人的精度研究[J].机器人,2008,30(5): 392-397. Liu H W, Wang H G, Li S J, et al. On accuracy of a three DOF parallel wire driven robot[J]. Robot, 2008, 30(5): 392-397.[8] 高建设,陶征,程丽,等.新型五自由度并联机床回零研究[J].机床与液压,2009,37(6): 41-44. Gao J S, Tao Z, Cheng L, et al. Homing research of a new type of 5-DOF parallel machine tool[J]. Machine Tool & Hydraulics, 2009, 37(6): 41-44.[9] Wang J S, Wu J, Wang L P, et al. Homing strategy for a redundantly actuated parallel kinematic machine[J]. Journal of Mechanical Design, 2008, 130(4): 044501-1-5.[10] Ding Q Y, Sun L N, Ji J H, et al. Calibration of a 2-DOF planar parallel robot: Home position identification and experimental verification[C]//IEEE International Conference on Mechatronics and Automation. Piscataway, NJ, USA: IEEE, 2005: 510-515.[11] Wang L P, Liu D W, Li T M. Homing strategy for a 4RRR parallel kinematic machine[J]. Chinese Journal of Mechanical Engineering, 2011, 24(3): 399-405. [12] 贺静.6PUS-UPS控制系统开发与实验研究[D].秦皇岛:燕山大学,2010. He J. Development of control system and experimental investigation for 6PUS-UPS parallel manipulator[D]. Qinhuangdao: Yanshan University, 2010.