Study And Realize Of The Look-ahead Control Technology For A CNC System

High-speed and high-precision motion control technology is one of the key technologies of the Computerized Numerical Control(CNC)system.Look-ahead control is the guarantee of the CNC system,which can machine workpieces with high speed.Machining with high speed is not real high speed processing if it is without look-ahead control.Therefore,it is extremely significant to realize the technology of the look-ahead control technology through the deeper analyses the control theory of look-ahead of CNC system.In this thesis,the look-ahead control theory of CNC system is analyzed in detail.Then the look-ahead control technology is researched and realized in the motion controller which developed by us.The contents of the research are as following:(1)In actual machining process,the trajectories are mostly consisted with line trajectory and circular trajectory.Here,a look-ahead control algorithm is presented,which is based on the asymmetric S-curve acceleration and deceleration.This algorithm can be used to realize smooth transition of speed for four modes:the transition for line trajectory to line trajectory,circular trajectory to line trajectory,line trajectory to circular trajectory,and circular trajectory to circular trajectory.(2)Under the traditional constraints,the path length constraint taking into account the asymmetric S-curve acceleration and deceleration control are presented.If it is applied to the building of the models of two adjacent trajectories,the number of trajectories for look-ahead is not need to set in advance any more.The velocity for the transition of two trajectories can be solved as long as the conditions of the two trajectories are taken into account.Therefore,more trajectories can be taken to the look-ahead control in the same hardware.(3)The control strategy of interpolation precision has been studied.In the phase of acceleration and deceleration,a round strategy is presented to adapt to the asymmetric S-curve acceleration and deceleration control algorithm.In the phase of calculating the parameters for interpolation,an integer computing strategy is presented.(4)An experimental platform is built.Then three experiments are designed to verify the asymmetric S-curve acceleration and deceleration control algorithm and the interpolation precision control strategy,the effect of the transition of two trajectories,the processing efficiency and the trajectory precision in the case of accelerating and decelerating frequently and in micro-segments.These results indicate that the look-ahead algorithm that based on the asymmetric S-curve acceleration and deceleration control algorithm can plan all kinds of trajectories efficiently.The velocity can transit smoothly in the joint of two trajectories.The position precision and processing efficiency can be improved effectively.