Study Of Velocity Planning And Contour Error Estimation Method Based On PH Curve

Compared with the traditional grid modeling, NURBS (Non-Uniform RationalB-Splines) can control the angularity of object surface well, thus create vividly andlifelike modeling. NURBS has a strong ability of industry modeling, which makes itwidely used and become the industry standard gradually. NURBS is an outstandingmodeling method, which is widely supported in the three dimensional modelingsoftware. Therefore, NURBS curve interpolation technology is a hot research areaand is widely used in numerical control system.Interpolator is vital to CNC system, because the quality of interpolator decidesthe quality of CNC system and affects the machining quality directly. The formerinterpolators mostly concentrate on designing interpolation algorithms andoptimizing servocontrols instead of modifying the original curves to compensate theerrors which the servocontrols produce. This article focuses on the areas that willcause large counter errors on the original curve. The modifications made on theseareas will compensate the errors which the servocontrol produces, and then themachining quality will get improved. The main researches of this article focus onthree points as following:All the sharp corners should be found out based on the in-depth analysis of theoriginal curve, and then be replaced by PH (Pythagorean Hodograph) which aresimple and easy to be interpolated. The construction parameters of the PH will beoptimized by pattern search method to reduce the counter error. The finalinterpolation will be simplified and achieve a higher accuracy.A new curve can be obtained after modification, and the final interpolation willbe carried on that curve. Keeping the machine tool steady will guarantee themachining accuracy, therefore, S-curve velocity planning algorithm is adopted toachieve smooth feedrates. The PCI (Predictor-Corrector Interpolator) is adopted toestimate and correct the interpolation points instead of the traditional Taylorexpansion.The proposed algorithm will be tested and verified by simulations andexperiments. The IDE used to write C code is VC++6.0. MATLAB is used tosimulate the S-curve velocity planning algorithm, the counter optimizing algorithmand so on. The simulation results will confirm the validity of the proposedinterpolator. The algorithm will be realized on the hardware platform based on DSPand the X-Y platform, then compare the experiment results and the simulationresults.