In this paper, the problem of dual actuation in the atomic force microscope (AFM) is analyzed. The use of two actuators to balance the trade-off between bandwidth, range, and precision has been recently extended to nano-positioning systems. Despite existing demands, this concept undergoes fundamental limitations towards its extension to AFMs. This is attributed to the non-conventional requirement imposed on the control signal response, as it used to create the image of the characterized surface.
This paper develops a model and control scheme for nano-manipulation systems based on atomic force microscopes (AFM). The model includes the micro-cantilever's and piezotube actuator's coupled dynamics. An identification-based controller is proposed for piezotube scanner positioning accounting for the piezotube's nonlinear sensitivity and axes coupling. A novel robust adaptive controller is developed to compensate for large parametric uncertainties including time varying and switching parameters due to probe-surface contacts as well as time varying and impulsive forces due to contact and impact. Discussions and simulations are presented for typical nano-manipulation tasks.
In this paper, new designs for hybrid PID and lag controllers with state resetting are presented. Lyapunov stable designs are shown for first and second order plants, which in case of integral reset for first order plants reduces to that of a Clegg integrator but differs from the First Order Reset Elements (FORE)'s commonly used in the literature for nonintegral lag controllers. Furthermore, the proposed PID and lag designs utilize different resetting conditions especially for second order plants, which is an important class of systems for motion control. Different solutions to retain a linear integrator's steady-state disturbance rejection capability are presented. Simulations and experiments for motion control of a typical servo motor driven positioning stage show the performance benefits of these hybrid controllers and verify the analysis.
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