Abstract: The interrupt of data flow in the full software computer numerical control (CNC) system will extend the machining time and degrade the machining accuracy. To prevent the interrupt from happening, a new feedback real-time scheduling scheme FSF-DF is proposed. FSF-DF can adjust the period of tasks in CNC system according to the system state. FSF-DF sets an overflow warning line in the buffer on the data flow, and carries out real time monitoring of the data quantity so as to determine whether it goes beyond the overflow warning line, thereby identifying whether there is a hazard of data interrupt. When the data flow is about to interrupt, FSF-DF adjusts the execution frequency and priority of related tasks, so as to maintain the stability of CNC system. Statistical methods such as Markov chain are used to reduce the adjustment times of execution frequency, so that FSF-DF may have a low system overhead. The scheduling scheme, including monitor, controller and basic scheduler, is used to integrate the adjusting rules into real-time operating system. The FSF-DF is implemented in RTAI real-time operating system, and is verified for its effectiveness. Test result shows that the FSF-DF can efficiently prevent the data flow interrupt and improve the whole performance and machining speed of CNC system.

Key words: Data flow in computer numerical control (CNC), Data starvation, Feedback scheduling, Full software CNC system, Real-time operating system