So i've recently came into a few dirt cheap piezo actuators. Was considering turning them into a x-y-z positioning stage then maybe a micromill or something. My one issue is I'm unsure of what is best to use for feedback control in the sub-micrometer range. Only thing I know that accurate is an interferometer. I also wouldn't 100% know how to guarantee that through mechanical means as most other means are temperature sensitive. Any help?