The impact of deadline misses on the control performance of high-end motion control systems

In high-end motion control systems, the real-time computational platform must execute tasks from multiple control loops operating at high sampling rates. In recent years, traditional special-purpose platforms have been replaced by general-purpose multiprocessor platforms, which introduce significant fluctuations in execution times. While considering worst-case execution times would severely reduce the sampling rates, accepting deadline misses and assuring that the control system still meets the desired specifications is challenging. In this paper, we provide a framework to model and assert the impact of deadline misses in a real-time control loop. We consider stochastic models for deadline misses and characterize the mean and the variance of closed-loop output variables based on a time-domain analysis. We illustrate the usefulness of our framework in the control of a benchmark motion control experimental setup and in the control of a wafer stage in a lithographic machine.