Multiple sleeping states for energy saving in CNC machining centers

Energy efficient control policies that switch off/on the machine have been proposed in recent literature. However, such policies control the whole machine simultaneously and consider only one stand-by state. This paper extends a time-based threshold policy by modeling several sleeping states and controlling machine components. Machine idle time is stochastic and the expected value of the energy consumed per produced part is minimized while assuring a certain productivity target. Technological constraints for control applicability are discussed. Results are based on a 5-axes Computer Numerical Control (CNC) machining center and savings are significant compared with that of state-of-the-art policies.