This article deals with a novel hybrid control of an atomic force microscope (AFM) for the robust characterization of interaction tip/sample force regions. The hybrid structure is composed of several position and force controllers and a specific switch compensation structure. A single selected controller is online at a time, and a robust bumpless switch between different control laws is designed. The objectives are the robustness of each controller and switch compensator with respect to uncertain parameters of the AFM. The method uses discrete points in the range of uncertainties. For each operating point, the hybrid controller is designed by an eigenstructure assignment. The method is generalized by a multimodel approach considering only uncertainties defined by a worst-case analysis, thus reducing the conservatism. The order of the controller is related to the number of observers selected by the user. This offers the possibility to design a low-order controller depending on the control specifications. The experimental results demonstrate the effectiveness of the hybrid controller for a fully automated landing procedure of the AFM tip on a sample surface and for force distance curve cycle characterization. Thanks to the robustness of the control method, landing and cycles are reproducible despite actuator uncertainties, friction variation due to aging, and instrumental issues such as the real-time data acquisition.
Active force sensors are based on the principle of force balancing using a feedback control. They allow, unlike passive sensors, the static characterization of forces without interference of the sensor mechanical properties on the estimated stiffness of the object to be studied. This capability is fundamental when dealing with the mechanical characterization of samples Q1 having a wide range of stiffness. This paper deals with the modeling and the experimental characterization of a new active MEMS based force sensor. This sensor includes Q2 folded-flexure type suspensions and a differential comb drive actuation allowing a linear force/voltage relationship. A control oriented electromechanical model is proposed and validated experimentally in static and dynamic operating modes using a stroboscopic measurement system. This work is a first step towards new MEMS active force sensor with high resonant frequency (>2kHz) and high linear measurement force range (50 µN). The advantage of this structure is to be able to change the sensor operating point without changing the sensor dynamics. Thus simplifying the control law. Modifying the operating point allows performing an accurate self positioning of the probe Q3 in close proximity to the surface to be studied.
The Atomic Force Microscope (AFM) is a reliable tool 6 for 3D imaging and manipulation at the micrometer and nanometer 7 scales. When used inside a Scanning Electron Microscope (SEM), 8 AFM probes can be localized and controlled with a nanometer res-9 olution by visual feedback. However, achieving trajectory control 10 and obstacles avoidance is still a major concern for manipulation 11 tasks. We propose a Model Predictive Control (MPC) to address 12 these two issues while AFM probes are actuated by Piezoelectric 13 Inertia type Actuators (PIA). The novelty of this letter is that the 14 model of our MPC-based approach relies on a velocity map of PIAs.
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