Comments on “Extensions and Performance/Robustness Tradeoffs of the EWMA Run-to-Run Controller by Using the Internal Model Control Structure”

Adivikolanu and Zafiriou proposed an RtR-internal model control scheme with some particular parameters and two tuning hyper-parameters for semiconductor manufacturing processes to completely and efficiently compensate against process shifts and drifts even in the presence of modeling error and metrology delay. In their scheme, these particular parameters are very important for further analyzing the robust stability and performance of the closed-loop system. However, it is found that the analytic expressions of these particular parameters and the consequent robust stability condition are not completely correct. In this paper, we derive the exact analytic expressions of these particular parameters and the corresponding robust stability condition.