Research On State Detection And Path Optimization Of EDM Micro Hole Based On FPGA Control System

Small hole machine is a kind of EDM machine specially designed for high-speed piercing,which is widely used in aerospace,medical devices and other fields.On the one hand,whether the motion controller is stable and accurate is the key factor to produce high quality small holes.On the other hand,whether the control program of small hole machine is easy to operate and whether the function is complete will affect the processing efficiency.The discharge state of micro EDM can directly reflect the machining situation.The discharge state directly affects the machining efficiency and surface roughness,so it is necessary to accurately detect the discharge state.In the process of machining,the electrode needs to move frequently.When there are many holes and mass production,the optimization of the path can improve the machining efficiency.This paper aims to build a numerical control system of small hole machine,and improve the efficiency and stability of small hole machining by improving the accuracy and efficiency of discharge state detection and optimizing the machining path of group holes.Firstly,in order to facilitate the program transplantation and improve the stability and specificity of the motion controller,a motion controller based on FPGA and a C # host computer program are developed to form a small hole machine numerical control system.The upper computer is divided into man-machine interface and command control format.The lower computer program includes communication module,command analysis module,motion control module,servo motion control module,pulse power supply control module,switch control module,limit state detection module and discharge state detection module.In order to verify the accuracy of FPGA program module,the timing simulation is carried out,and the results show that each module meets the expected control requirements.Secondly,in order to solve the problem that the voltage threshold method can not count the open circuit time well and adjust the voltage threshold when changing the discharge voltage.A pulse recognition method based on slope ratio and variable statistical period is proposed.This method makes the detection device directly used in micro EDM rough grinding and fine grinding with two different open circuit voltages.It does not need to adjust the voltage threshold and can effectively count the open circuit time,so as to improve the detection efficiency and accuracy.The Ni acquisition card and Lab VIEW software are used to develop the pulse recognition system.The system can display the gap voltage,continuously store the gap voltage and split the file.Then the slope ratio method and the variable statistical period method are analyzed theoretically,and the pulse recognition and statistical program are written.The experimental verification of discharge state detection is carried out.The results show that the method can identify different pulses and is suitable for different discharge voltages,and the program results are in good agreement with the actual results,which proves the effectiveness and practicability of the method.Thirdly,in order to shorten the electrode moving time,the machining path of group holes is optimized.The nearest neighbor algorithm,greedy insertion algorithm and ant colony algorithm are compared and analyzed.The results show that the time complexity of nearest neighbor algorithm is the lowest,but the optimization effect is not as good as greedy insertion algorithm.The optimization effect of ant colony algorithm is good,but the optimization time is much longer than nearest neighbor algorithm and ant colony algorithm.Therefore,the greedy insertion algorithm is selected in the numerical control system.Finally,in order to verify and debug the CNC system of the small hole machine,the lower computer program is simulated and verified,and then the command format of the upper computer program is detected.Finally,the small hole processing experiment is carried out,and the steel drilling experiment is carried out by using 0.8mm hollow copper bar.The results show that the CNC system runs stably,the peripheral equipment debugging is normal,the small hole processing speed is high,and the surface quality is good.