On the conflict between energy, stability and robustness in production schedules

Paper in proceedings, 2016

In this paper, a novel contribution to highlight the conflict between energy efficiency, robustness and stability is presented. Energy optimization is combined with robust scheduling techniques to analyze the trade-off. In rescheduling, slack is often used in order to protect a schedule from disruptions. However, results from the literature on energy minimization show that a reduction in energy consumption is achieved by extending the execution time of operations. Thus, slack in schedules is eliminated on behalf of longer execution times. A continuous-time formulation is proposed using a mixed-integer nonlinear programming model including a multi-objective corresponding to energy, robustness, stability and makespan. Surrogate slack-based measures are used to evaluate robustness and stability. Previous work connecting the two research fields use simulation for analyzing the impact of disruptions in order to generate robust production schedules. Our results show that an increase in energy efficiency comes at a cost of reducing stability and robustness and hence becoming more sensitive to disruptions.