软数控实时任务的时间特性对加工精度的影响

Effect of Time Characteristics of Software NC Real-Time Tasks on Manufacturing Accuracy

为分析软数控实时任务的不确定性与加工精度的关系,提出一种基于模型的加工误差分析方法.首先研究采样抖动、输入-输出抖动、数控任务可调度及加工误差评估等相关理论;然后建立二轴数控系统加工误差分析仿真模型;最后对任务抖动、任务不可调度及实时突发任务等与加工误差的相关性进行仿真.结果表明:采样抖动时间为任务周期的80%时,误差达4.7%;输入-输出抖动时间为任务周期的80%时,误差达1.2%;40%的事务不能在时间限内完成时,误差达13.4%.该结果说明不可调度事务会引起较大的加工误差.

In order to reveal the relationship between the uncertainty of software numerical control （NC） real-time tasks and the manufacturing accuracy, a model-based analysis method of mismachining tolerance is presented. First, the relevant theories concerning the sampling jitter, the input-output jitter, the NC task schedulability and the mismachining tolerance evaluation are analyzed. Then, a two-axis NC simulation model is established. Finally, some simulations are performed to reveal the relationships between the mismachining tolerance and the factors such as task jitter, task non-schedulability and aperiodic real-time tasks. The results show that the mismachining tole- rance respectively reaches 4.7% and 1.2% when the sampling jitter time and the input-output jitter time are both 80% of the task period, and that the tolerance is up to 13.4% when 40% of jobs fail to meet their deadlines. It is thus concluded that non-schedulable jobs may result in a noticeable mismachining tolerance.