Electric load management in spindle run-up and run-down for multi-spindle machine tools via optimal power-torque trajectories and peak load synchronization

Electrical energy consumed during machine tool spindle run-up and run-down has a non-negligible impact on overall spindle energy performance. A model-based efficiency analysis of a common spindle unit architecture, with a separate induction motor, is conducted to investigate different loss sources. The identified model is exploited to define optimized motor torque trajectories for spindle run-up/run-down, exploiting the idle time typically available on the fastest machining modules in a transfer machine tool. Study reveals that savings can be achieved, both in terms of peak power and energy losses, by adopting optimal values for the acceleration rate and power limit. To reduce power peaks at the machine level, a unit synchronization algorithm is proposed which avoids simultaneous acceleration/deceleration of multiple spindles. The overall cycle time is preserved by prioritizing the execution of the slowest processing unit. The proposed methodologies have been applied to a three spindles flexible transfer machine tool, estimating the corresponding gains in terms of energy losses and power peak reduction.