A stepping micromotor based on ferrofluid bearing for side-viewing microendoscope applications

This paper reports a catheter-based electromagnetic micro rotary motor targeting at enabling side-viewing microendoscopes designed for the Raman spectroscopic modality. The micromotor uses the magnetic rotor that is levitated with thin ferrofluid layers inside the polymeric tube and electromagnetically driven with the stator coils circumferentially patterned around the tubular substrate. The device with a new miniaturized design is both theoretically and experimentally shown to provide performance benefits over the preceding design, including 4 × higher revolution speeds per given power and >95% reduction in temperature rise at low-speed operation. The precision stepping control of fabricated prototypes with angular steps down to 22.5° is demonstrated with an average positioning error as small as <2%. This is achieved with only two stator coils defined on the tube substrate via controlled power distribution to the coils, uniquely enabling fine stepping actuation with a limited number of stator coils that could be integrated within a microendoscope device. The developed micromotor is suitable for application to side-viewing Raman probes that typically require fine circumferential stepping of laser beam.