Research On Open CNC Servo System Model And Position Control Technology

Advanced NC machine tool is the most valuable and representative production in modern NC industry. And it is a critical criterion to assess the manufacturing level of a country. The position control technology of servo system is one of the core technologies that decide the machining precision of NC machine tools.Basing on the character of open CNC system, a hardware platform whose core is IPC and common industry interface card is designed and constructed associating with digital copying technology and 3-axis linkage NC manufacturing. This platform supports 4 routes of impulse counter for the quadrature encoder, 4 routs of D/A outputs, 16 channels single or 8 channels difference A/D input and 48 channels I/O. Control circuit is highly integrated, and is added into anti-jamming technology. All provides strong support and guarantee to the realization of high speed and high accuracy machining NC system. Advanced quintic spline interpolation technology and Look-Ahead control method are all applied in the complex free curve disposal model.According to the function requirement of morden high precision NC system, kernel arithmetics of the key software technology of CNC system is researched and optimaized. G code is translated line by line through the establishment of buffers and code distributary. Data sample interpolation technology is used to dispose the line and circle information in G code. Every module is optimazed to realize increment operation and iterative calculation. So computing speed is improved remarkably when high accuracy algorithm is used.Basing on the CNC software arithmetic optimazed, a CNC software kernel which bases on open structure is developed on VC platform with language C. Since this open structure CNC kernel has been modularized, it has outstanding interoperability, scalability, portability and scalability. Not only is the hardware structure predigested, but also the cost of system is reduced remarkably.A 4th order model of servo system in high running speed condition is constructed and researched basing on CNC system platform established. The response characters of high speed 4th order model, low speed 1st order model and middle speed 2nd order model which use the same position controller parameters are compared by their step response. It shows that with the increasing speed of servo system, system performance would deteriorate for the parameter error of position controller. The parameters in the 4th order model of high speed servo system are optimized through poles allocation. And then the rapid system response character without oscillation and overshoot is got.For improving the system stability, a neural PID controller is initialized by the parameters optimized. And then a neural PID controller is established basing on the parameters optimized. Simulation results identify that this method would decrease the peak value of disturb by 10 percents when it still keep the good characters after optimization.