> I get some used PMSM from auctions. Replacing the > bearings gives them a second life. Keep the angle position > of the resolver on the rotor! So you can test it with > an old (with analog velocity input) 3 phase power supply. > Usually this motors run very smooth if the stator pack > is twisted giving nearly no torque ripple (assuming > rotating magnets). > > Motors with torque ripple maybe used as a drive > if the control can do a predistortion to the > current to compensate for the ripple. But I > have not seen this until now with my eyes.
I can see you've be seriously dealing with the internals of PMSM, and I would like to discuss a little bit about the subject,as I'm facing some problems related to torque rippling issue. I agree with your comments, but it looks like complicated, as some sort of identification/calibration should be needed. Plus a resolver, I mean you need to track the absolute position of the shaft during a single revolution (may be, there are suitable encoders for that work). Plus, I think that the logic should be implemented directly in the electronics driving directly the motor, as the compensation strategy should be fairly quick. Driving a variable intensity command from EMC will certainly limit the strategy to low rpm. I've seen some guys trying to do such compensation dealing with this when using linear motors, that I presume are very similar to PMSM. I suppose that this problem important to them probably because the aforementioned lack of twisting, but also because it is a Direct-Drive application. That is, no reduction, and then low velocity. What do you think about this?: I've seen referred this torque ripple as "cogging", I can feel it in my setup (www.imac.unavarra.es/~cnc) rotating the shaft by hand my motors switched off. I'm pretty sure that this is the main responsable of the vibrations I feel in the robot at low velocities. I'm using an almost direct driving. Do you think that this is an indication that my stator is not twisted?. So I'm thinking about using pulleys to introduce some sort of reduction, but I'm not sure if this is going to lower the problem. I mean, for a frictionless reduction strategy, I would get a increase in rotor velocity, but also a lower level of torque. I see a benefit as the rippling frequency will be increased. But wouldn't worsen the ripple to torque ratio, and then introduce more problems?. I've been thinking about increasing the bandwidth of the PID (I'm controlling intensity), hoping that the feedback can be able to compensate the cogging, but may be then other sources of noise can become more important. Then may be an identification + feedforward compensation can be the best solution. I think it can be implemented in EMC, up to some bandwidth. Identification can be the hard part, but if a good homing strategy is available, is looks like possible. I'm thinking about making such a implementation. Do you think that it can improve things?. Also what is your position about the best motor/driver type for direct-drive position control applications. I hope this discussion helps some body else to enlighten thing. It certainly helps me. Cheers, Javier ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
