Research On The Feedrate Look-Ahead Algorithms In The CNC System And Their Applications

Numerical control technology is the critical technology of modern equipment manufacturingindustry, which plays an important role in aviation, marine, automobile and other projects. Itdetermines the function and performance of manufacture equipment. Overshooting, mechanicalharmful vibrations and data starvation directly impact on the maching quality. This paper proposed alook-ahead algorthm that can analyze tool path, find dangerous points and deal with sensitivesituations in machining automatically. This method can guarantee speed change smoothly andimprove machining efficiency and machining quality.Supported by natural science fundation of Jiangsu province (No.BK2003005), National NaturalScience Foundation of China (No.51005122)and Aeronautical Science Foundation of China (No.2008ZE52049), this dissertation places emphases on acceleration and deceleration algorithm,consecutive line blocks look-ahead algorithm, and an adaptive parametric look-ahead interpolationalgorithm. And an S shape acceleration and deceleartion for the NURBS look-ahead algorithm alsohas been reaseached in the dissertation.In terms of configuration of look-ahead algorithm, the basic is acceleration and declelerationalgorithm. By analyzing the acceleration and decleration mathematical model in the look-aheadalgorithm, the ralationship between the speed, acceleration and decleration distance can be determined,that laies a foundation for the look-ahead algorithm.At present, in most CNC system the tool path is discreted consecutive line blocks. So theconsective look-ahead algorithm is proposed in the paper. By presenting the mathematical modeladjust the velocity automatically to achieve maximum in machining of consecutive line blocks withhigh speed, and the high curvature points are found according the speed. Then the optimal look-aheadblocks and velocity characteristic are estimated. Then the algorithm can make velocity changingsmoothly.Then a look-ahead interpolation algorithm for parametric curves is studied. This method improvedthe machining accuracy and detected the sensitive points by confining the chord error in a limitedrange. Through dividing look-ahead distance into two parts, sensitive points were analyzed, acontinuous velocity and accelerating profile were found out which reduced the jerk relate problem.This satisfied not only machining accuracy but also acceleration and deceleration performace ofmachine tools.Based on the parametric curves look-ahead algorithm, the NURBS look-ahead algorithm based on S shape is researched. By dividing the curve into curvature increased segment and curvaturedecreased segment according to he different curvature movement and re-planning the velocity curvesin the velocity changing frequently tool path to reduce computation. This algorithm can meet the realtime requirements to look ahead in CNC system.The experimental results are provided to verify the feasibility and precision of the proposedinterpolation algorithm. The machining qualitiy and efficiently are greatly improved.