A new algorithm for thread cutting entrance

To minimize the entrance error of thread cutting, a new algorithm is proposed in this paper. On one hand, some special processing for counter of spindle encoder is taken on the Field Programmable Gate Array(FPGA), when zero pulse(Z) signal of encoder coming the counter is cleared to zero. On the other hand, encoder is read once per interpolation circle when threads are interpolated. Thread interpolation processing is handled just after the zero signal and the offset is distributed averagely into the acceleration area to ensure the accuracy and repeatability of entry point when threads cutting is operated. Applying this new method, the pitch errors are between -0.006 mm and 0.008 mm. While with zero signal interruption method, the errors are between -0.030 mm and 0.032 mm. Experiment results show that this new approach ensures the smoothness of position control, reduces entrance error, and is better for application.