Contact-less revolving stage using transverse flux induction principle

To expand the inherently limited-rotating range of existing ultra-precision stage, a revolving stage, with a magnetically suspended rotor capable of making 360° turns without contact, is suggested. The system rotates, suspends, and moves in the planar direction infinitesimally, using the vector forces by three-separate transverse flux circular induction motor (TFCIM) located at regular intervals around the circumference. This paper discusses the entire process for the successful implementation of the stage, including the modeling of the magnetic force across the air-gap and the sensing mechanism, adopting only the proximity transducer. Particularly, because thrust force and normal force of TFCIM are strongly cross-coupled with main input variables, slip frequency and ac magnitude, the novel method controlling both forces independently is suggested, using new variables through dc-biased multi-phase inputs. Finally, roundness test and rotational step test results are given to verify the system performance.