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Control aspects of the single-fiber scanning endoscope

The Single Fiber Scanning Endoscope (SFSE) is a new class of endoscopes being developed at the University of Washington's Human Interface Technology lab which uses combinations of a resonating optical fiber and a single photodetector to produce large field of view, high-resolution images from a small flexible package. Although current prototypes show the validity of the concept, the nonlinear response of the resonant optical fiber under open loop control creates image distortion or limits the frame rate. Due to low damping and nonlinear effects in the fiber, open loop control, phase lock loops, PID control, classical and modern controllers are all unable to produce accurate, reproducible, robust high frequency 2D scans. A nonlinear control scheme, feedback linearization, is capable of accurately producing a scan and is robust to most of the unavoidable manufacturing and environmental variability in the resonant scanner. Through theoretical analysis and simulations, this paper reviews the application of the following variety of open loop and closed loop controllers to the nonlinear scanner of the SFSE: open loop control, modelless closed loop control (phase lock loop and PID control), feedforward plus feedback classical and modern state space tracking control, and nonlinear feedback linearization control.