Internal Model Control for Spiral Trajectory Tracking With MEMS AFM Scanners.

We demonstrate the application of internal model control for accurate tracking of spiral scan trajectories, where the reference signals are orthogonal sinusoids whose amplitudes linearly vary with time. The plant is a 2-D microelectromechanical system nanopositioner equipped with in situ differential electrothermal sensors and electrostatic actuators. This device is used as the scanner stage in an atomic-force microscope. Additional internal model components are included in the controllers to compensate for the residual tracking errors due to plant nonlinearities. In a large scan range with a diameter of 16 m, we achieved tracking of 1430-Hz spiral sinusoids, a frequency beyond the undamped fundamental resonance of the plant at 1340 Hz. This leads to a video-rate scan speed of 18 frames/s.