Recently, power shortages have become a major problem all over Japan, due to the Great
East Japan Earthquake, which resulted in the shutdown of a nuclear power plant. As a consequence,
production scheduling has become a problem for factories, due to considerations
of the availability of electric power. For factories, the contract with the electric power company
sets the maximum power demand for a unit period, and in order to minimize this, it is
necessary to consider the peak power when scheduling production. There are conventional
studies on flowshop scheduling with consideration of peak power. However, these studies
did not consider fluctuations in the processing time. Because the actual processing time is
not constant, there is an increase in the probability of simultaneous operations with multiple
machines. If the probability of simultaneous operations is high, the probability of
increasing the peak power is high. Thus, we consider inserting idle time (delay in inputting
parts) into the schedule in order to reduce the likelihood of simultaneous operations. We
consider a robust schedule that limits the peak power, in spite of an unexpected fluctuation
in the processing time. However, when we insert idle time, the makespan gets longer, and
the production efficiency decreases. Therefore, we performed simulations to investigate the
optimal amount of idle time and the best point for inserting it. We propose a more robust
production scheduling model that considers random processing times and the peak power
consumption. The results of experiments show that the effectiveness of the schedule produced
by the proposed method is superior to the initial schedule and to a schedule produced
by another method. Thus, the use of random processing times can limit the peak power.