On Fri, 13 Apr 2012, Kirk Wallace wrote: > > As for cogging, this only comes into play when a motor is driven by a > constant voltage or current supply. The shaft speed or torque will vary > slightly as the poles pass each other. Some motors are designed to > minimize this by twisting the rotor poles or by adjusting the pole > geometry in others ways. For CNC, the motion control system compensates > for the cogging, so this rarely becomes an issue. Although stepper > motors need strong cogging in order to define step locations. >
Cogging in BLDC/PMSMs is because of square wave drive currents in simple drives (like PC fan motors) A three phase PMSM motor has about 13% torque cogging with pure Hall signal square wave drive. Cogging is reduced to negligible amounts with sine or space vector drive. This is similar to a full or 1/2 step step motor drive versus a say 256 uStep drive. With a high u-step ratio, there is negligible cogging. Peter Wallace Mesa Electronics ------------------------------------------------------------------------------ For Developers, A Lot Can Happen In A Second. Boundary is the first to Know...and Tell You. Monitor Your Applications in Ultra-Fine Resolution. Try it FREE! http://p.sf.net/sfu/Boundary-d2dvs2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
