Fuzzy-logic control of cutting forces in CNC milling processes using motor currents as indirect force sensors

A fuzzy-logic controller (FLC) is designed to automatically adjust feed rate in order to regulate the cutting force of milling processes in a vertical machining center The FLC has a double-loop structure consisting of the inner PD (proportional-derivative) velocity-control loop for a feed servo and the outer fuzzy logic force-control loop Reference cutting forces are well maintained in both numerical simulation and experiments when the cutting-depth profile of an aluminum workpiece (Al6061-T6) is varying step-wise or continuously In order to replace expensive and impractical tool dynamometers ac-induction-motor currents in the feed system and the spindle system are analyzed and then compared as a cutting-force sensor The bandwidth of both systems are not high enough to sense the cutting dynamics for common spindle speeds Thus quasi-static quantities (i e average or maximum resultant cutting force per spindle revolution) are compared instead The spindle-motor current i chosen because quasi static sensitivity is much higher (i e 5 415 x 10(-3) vs 2 128 x 10(-4) A/N) Reference cutting forces (230 and 330 N) are well maintained when the depth of cut is less than 4 mm (C) 2010 Elsevier Inc All rights reserved