Hi,
high power, high speed induction motors certainly make good spindle drives but they are not so good at position control.
An induction motor relies on the rotating magnetic field of the stator windings being faster than the rotation of the rotor, the difference, called slip
is what 'induces' current in the squirrel cage rotor and how induction motors get their name. If it were necessary to back the rotor up half a turn say,
as in a position control application, the field windings have to reverse and sufficiently so that there is enough slip for the rotor to be magnetized. If the rotor
overshot then the field windings would have to reverse again including the required slip. Induction motors are not good for position control.
If the rotor is permanently magnetized as they are in servos there is no need for slip. The rotor is synchronous with the field windings. The resulting position
control is way tighter than an induction, also called asynchronous, motor. Additionally there is no requirement for the field windings to supply the induced
rotor current. As a consequence permanent magnet servos are smaller than induction motors for the same power. Further the torque characteristics of a servo
are linear with current and extend to zero rpm. You can use a servo as a torque motor, many thousands are used in this manner in printing presses which is
possible but harder to ensure than with an induction motor.
Induction motors are simple and cheap but if you want position control they are not the right way to go.
There is a warning to, most induction motors are designed for 50-60 Hz line frequency. A motor driven by a VFD has a much higher insulation requirement.
If you use an ordinary induction motor on a VFD it will work provided your not silly but it may also blow up because of the extra insulation required.
'Inverter Ready' motors are available but not so cheap. I wouldn't trust a cheap Chinese induction motor.
Craig