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Modeling and control of the resonant fiber scanner of a novel scanning scope

The single fiber scanning endoscope is designed with a resonant fiber scanner at the distal end of a thin flexible shaft to produce a flying spot scan for image acquisition purposes. Dynamic nonlinearities during large amplitude vibrations of the resonant fiber scanner result in distortions in the two-dimensional scan pattern and the acquired images. The nonlinearities produce nonlinear amplitude and phase responses, jump and whirl. A dynamic model which includes the fibers dynamic nonlinearities, as well as its piezotube actuators nonlinearities, has been developed to understand the nonlinear behavior and as the basis of a controller to remove the scan distortion. A robust state-space controller with feedback linearization has been implemented to force the resonant fiber scanner to follow three reference scan patterns: raster, propeller, and spiral formats. Acquired images at 250/spl times/250 pixel resolution demonstrate improved image fidelity over previous images taken with open-loop scanning.