A planar micro rotary actuator for endoscopic optical scanning

Abstract

Optical endoscopy is an essential technique for diagnosing disease in modern medicine. Side-viewing endoscopic probes with an embedded distal actuator that circumferentially scans an imaging light within an organ’s lumen are expected to significantly enhance the imaging ability of the probes. To this end, this work develops and experimentally analyzes an electromagnetic micro rotary actuator with a planar and hollow architecture. The actuator uses a liquid-phase bearing based on ferrofluid that is self-sustained on the magnetic rotor to eliminate complex bearing structures and enable low-friction actuation. Compared to preceding tubular designs, the planar topology allows for 83% downsizing in the actuator’s axial size, which helps preserve probe flexibility. Furthermore, the hollow design provides an unobstructed optical path through the actuator body, which removes imaging blind spots. A proof-of-concept scanner device is prototyped using flex-circuit microfabrication and 3D printing techniques for its electromechanical characterization. The prototype is successfully driven to revolve the rotor with 45° steps on a ring-shaped planar stator, which are then cycled at high frequencies to continuously spin the rotor up to a maximum rate of 2000 rpm with a device temperature below 45 °C, a safety threshold for tissue damage. The demonstrated stepwise and high-speed modes of laser scanning suggests the feasibility of the scanner design for multimodal imaging application toward advancing optical endoscope technology.