Energy Efficient State Control of Machine Tool Components: A Multi-sleep Control Policy

Energy efficient control policies that switch off/on machine tools aim to reduce the energy consumed while not producing parts. Commonly, a transitory is required before resuming the service; thus, to switch off/on the machine might be not advantageous. This paper analyzes a time-based threshold policy that disables/enables machine components with separated control commands instead of controlling the whole machine simultaneously. According to the subset of controlled components, multiple sleeping states and transitory duration can be defined. Machine idle times are assumed stochastic and the expected value of the energy consumed per produced part is reduced while assuring a certain target of machine utilization. A simulation optimization algorithm is used to search for the optimum. The analysis is based on two real CNC machining centers. Potential benefits are compared to state-of-the-art policies and discussed for a set of realistic numerical cases representing several production environments.