In this paper, a piezoelectric tube of the type typically used in scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) is considered. Actuation of this piezoelectric tube is hampered by the presence of a lightly damped low-frequency resonant mode. The resonant mode is identified and damped using a positive velocity and position feedback (PVPF) controller, a control technique proposed in this paper. Input signals are then shaped such that the closed-loop system tracks a raster pattern. Normally, piezoelectric tubes are actuated using voltage amplifiers. Nonlinearity in the form of hysteresis is observed when actuating the piezoelectric tubes at high amplitudes using voltage amplifiers. It has been known for some time that hysteresis in piezoelectric actuators can be largely compensated by actuating them using charge amplifiers. In this paper, high-amplitude actuation of a piezoelectric tube is achieved using a charge amplifier.
Abstract-Piezoelectricstack-actuated parallel-kinematic nanopositioning platforms are widely used in nanopositioning applications. These platforms have a dominant first resonant mode at relatively low frequencies, typically in the hundreds of hertz. Furthermore, piezoelectric stacks used for actuation have inherent nonlinearities such as hysteresis and creep. These problems result in a typically low-grade positioning performance. Closed-loop control algorithms have shown the potential to eliminate these problems and achieve robust, repeatable nanopositioning. Using closed-loop noise profile as a performance criterion, three commonly used damping controllers, positive position feedback, polynomial-based pole placement, and resonant control are compared for their suitability in nanopositioning applications. The polynomial-based pole placement controller is chosen as the most suitable of the three. Consequently, the polynomial-based control design to damp the resonant mode of the platform is combined with an integrator to produce raster scans of large areas. A scanning resolution of approximately 8 nm, over a 100 m 100 m area is achieved.
Abstract-An XYZ nanopositioner is designed for fast the atomic force microscopy. The first resonant modes of the device are measured at 8.8, 8.9, and 48.4 kHz along the X-, Y-, and Z-axes, respectively, which are in close agreement to the finite-element simulations. The measured travel ranges of the lateral and vertical axes are 6.5 μm × 6.6 μm and 4.2 μm, respectively. Actuating the nanopositioner at frequencies beyond 1% of the first resonance of the lateral axes causes mechanical vibrations that result in degradation of the images generated. In order to improve the lateral scanning bandwidth, controllers are designed using the integral resonant control methodology to damp the resonant modes of the nanopositioner and to enable fast actuation. Due to the large bandwidth of the designed nanopositioner, a field programmable analog array is used for analog implementation of the controllers. Highresolution images are successfully generated at 200-Hz line rate with 200×200 pixel resolution in closed loop.Index Terms-Field-programmable analog array (FPAA), flexure-guided positioners, high-speed atomic force microscope (AFM), integral resonant control (IRC), nanopositioner, piezoelectric actuators.
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