In this paper, proactive feedforward control is recommended to be combined with the
traditional reactive feedback control for process improvement, and the feasibility
condition of feedforward control is illustrated from a disturbance decomposition
viewpoint. Some disturbance models, including the periodic shift models and random step
change models are discussed, and their feedback and feedforward control equations are
proposed. Some issues on process monitoring, feedback control and feedforward control
are discussed, which provide some insights on the necessity of feedforward control, the
relationship between process monitoring and process adjustment are investigated, and the
rationale for our disturbance decomposition viewpoint is further illustrated.