Trajectory Planning For Direct Drive X-Y Table Based On NURBS Interpolator

Taking the National Natural Science Fund Project (51175349) as the background, thisthesis focuses on the research of direct-drive X-Y table servo control system, aims atimproving the precision reduction problem caused by the disturbance factors existingduring the contour machining process by establishing reasonable trajectory planningstrategy.The accuracy of the motion control system depends on three factors: precisecommand paths, servo control scheme and mechanical structure. While due to thelimitation of the manufacturer, the mechanical part has exceeded engineers’ controllablerange. So a reasonable motion controller and an accurate command interpolator must beincorporated during the designing process of control system. The relationship betweencommand path and motion controller are mutual dependable, so an appropriate adjustablemethod who make the two parts compatible with each other become a key research topic.This thesis takes the command path planning part and the integrated motion controllerdesign part as the core task and auxiliary task respectively to analyze and research the XYtable driven by two linear motors during the following tasks.While in the command path giving part, due to the advantage that NURBSinterpolator can accurately represent both the analytical and free-form curves, thecommand position is generated by NURBS real-time interpolator firstly which conducts asthe communication bridge between the CAD/CAM and CNC, thus accordingly achieve ahigh speed and high precision system. While come to the acc/dec planning part, the digitalconvolution method is adopted to make sure the velocity curve more smooth and thusaccordingly the computation time is greatly reduced compared to the polynomial operationmode.Besides, the look-ahead planning method is added during the NURBS interpolation.The planning method combines the advantages of conventional method and direct digitalconvolution method together and ably avoid the inherent disadvantages of the twosimultaneously which make the whole interpolation process more flexible and continuous, and it can thus satisfy the requirements of high speed and high precision indirectly. Inorder to verify the effectiveness of the proposed hybrid look-ahead planning method, asimulation on four-section cam curve is conducted, through the comparison result ofvelocity planning and contour curves, the advantage of the proposed method exhibitsvividly.Finally, in order to cooperate with the acc/dec strategy above mentioned, thecontroller is designed as the auxiliary part, the model-based disturbance attenuationmethod is adopted in single axis to reduce the disturbance and friction, while due to thefunction that cross-coupled controller can adjust the speed of dynamic response and reducethe contour error, the late-model CCC scheme with position error compensation function isincorporated during the coordinate control which aims at through pre-compensationscheme to reduce both the tracking error and the contour error simultaneously. Thesimulation results of heart contour verified the effectiveness of the proposed method.