Human characteristics at multi-variable control when the operator changes over the plant-lines

In this paper, we experimentally investigate the human characteristics when the operator changes over the plant-lines. Observing the human behaviour under stable experimental conditions, it was noticed that the time between the change-overs of the controllers is almost constant, that is, the operator seems to change over the controller according to a rhythm (we call it 'rhythmic operation'). Control by rhythmic operation presents two striking differences from that by conventional operation without the rhythm: one is the ability to predict the movement of the controlled quantity exactly, and the other is that there is little differences between cognition and performance. Therefore, we consider a way of calculating the rhythm for the experimental conditions, and attempt to introduce the rhythmic operation over all experimental conditions. As the result of a verification experiment with the rhythmic operation, the control error decreased considerably and the validity for the rhythmic operation was confirmed. Furthermore, we found that the operator's mental workload decreased because the number of indefinite factors involved in the decision making at the change-overs of the controller decreased.