Study On Control Strategy And Error Compensation Method For Atomic Force Microscopy Positioning System

At present, the atomic force microscope (AFM) has been widely used in many fileds such as microelectronics, micromechanics new material science, electro- magnetism, chemistry, biological medicine, nanotechnology, nano-fabrication and nano-operational. However, the operation speed and positioning precision has become the bottleneck of AFM technology, mainly because the existing control technology in AFM system cannot overcome the problem of slowly measurement speed and narrowband, etc.From the perspective of control, the paper focuses on the research of the control and compensation methods on high-speed AFM system, the concrete content is as follows:First, the positioning and control method for AFM system in which the core is piezoelectric actuator is studied, and the key points that limit the operation speed of current AFM is pointed out: slow operation speed and narrowband measuring .To solve the problem of high-speed AFM positioning, the limitation of traditional control method is analyzed, and the advanced control method is necessarily proposed.Second, aiming at the problems on slow operation speed and narrowband measuring in AFM-based nanomechanical measurement, the control methods to compensate for dynamic characteristic of AFM positioning system in x-axis/z-axis direction are proposed. the open-closed loop PID type iterative learning algorithm in time domain for positioning control is presented toimprove the precision in the x-axis direction; a set of feed-forward control link based on model-less inversion-based iterative learning control method is proposed, thereby increasing the bandwidth of the system and improving the precision of the system during tracking the expected input signal.At last, nanometer measurement on material viscoelasticity based on moded-less inersion-based iterative learning control is presented. This method increases the bandwidth of the system and improves the precision of the system during tracking the expected input signal. The proposed approach is illustrated by implementing it to measure the viscoelasticity of poly (dimethylsiloxane) (PDMS) over a broad frequency range of 3 orders of magnitude (1Hz~4.5 kHz). Moroever, for the residual dynamic characteristic of AFM system which coupled in measured date, a homomorphic adaptive filter is designed to improve the precision of AFM-based nano-measurment.