On 12/11/2013 11:53 AM, Jon Elson wrote: > On 12/11/2013 06:25 AM, Leonardo Marsaglia wrote: >> Working on my tuning I find that the vibration/oscillation I have is due to >> torque. The charriot that the screw is moving is vertical and weights like >> 100 kg so there's a lot of force for the motor to do to lift the charriot. >> That's when I get the vibrations, on the way up. On the other side, when I >> move the charriot down there is no vibration and the motor runs smooth. >> >> I know this is due to torque but I don't know how to compensate this. If I >> use low speed on the way up theres almost no vibration. >> >> The vfd without LinuxCNC handled well both up and down so I don't think >> it's too much for the VFD and motor. >> >> > Note that typical AC induction motors with straight stator > windings and > straight rotor bars will give a strong torque (and current) > ripple as > the induced poles slip around the rotor. There are motors > that have > either the rotor or stator slots twisted a bit to reduce > this effect. > If these are typical AC induction motors not intended for servo > use, then I think this may be the problem. It is possible > that there > is a resonance going on, and avoiding the resonant speed may > get around the worst of this. When the motor slip frequency > matches > the natural resonance of the mechanical elements, it may become > more pronounced. > > Jon >
If standard AC induction motors could be used exactly the same as a servo drive, few people would be buying servo drives and motors. Standard AC motors require rotor to field slip in order to magnetize the rotor. No field slip, no rotor magnetization. When I was working for Siemens 10 years ago the best we could do at the time with a standard induction motor was to move to and then stop at a position. This would be similar to putting a spindle in position for a tool change. Holding torque was terrible so they recommended some type of brake if the load required holding torque when stopped. To do this required a full vector drive (MM440) with encoder feedback. This was worlds away from servo operation performance that can have 100% torque at zero speed and incrementally move very small distances at high speed. I'm sure that VFD control has improved since then but the motors are pretty much the same. Siemens had hybrid motors that were not standard induction motors at the time that could do better positioning but they were as expensive ore more expensive than other companies servo drive systems and were generally only used for very large HP/torque applications that required some level of positioning at high power levels. Think big $$. Dave ------------------------------------------------------------------------------ Rapidly troubleshoot problems before they affect your business. Most IT organizations don't have a clear picture of how application performance affects their revenue. With AppDynamics, you get 100% visibility into your Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics Pro! http://pubads.g.doubleclick.net/gampad/clk?id=84349831&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
