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.
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