Abstract:

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.

Key words: numerical control, mismachining tolerance, time characteristic, scheduling algorithm, non-schedulable job