Is it possible to use a VFD with a standard AC Motor with shaft encoder for linear position?  The axis would be rack and pinion drive.  I only need to hold about +/- 0.030".

I am looking for higher accel and speed than steppers provide.  I know servo motors are an option but they are fairly pricey.

This is for a new project.  It will be a 3 axis pick and place robot.

Any thoughts would be appreciated.