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Control system implementation on an AFM prototype
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Orientador(es)
Resumo(s)
This work deals with the implementation of a fine and coarse tip-sample distance control as well as
with the tuning of several other features that will make one AFM prototype more user friendly. The main
goal was to design and integrate a PI (Proportional-Integral) Analog Controller with digitally controllable
gains.
The development of the controller started by identifying and characterizing the system, with emphasis
on the Z-axis Scanner’s response, which in turn allowed to build models for all the different components
that make up the AFM.
The PI Controller’s gains were arranged to be independently tuned via a digital potentiometer in
conjunction with an analog multiplexer. The digital potentiometer provides a fine gain adjustment while
the analog multiplexer increments the gains by an order of magnitude. These devices receive instructions
from a microcontroller.
In parallel, several other important enhancements were carried out, which include an implementation
of an Auto-Approach functionality that automatically approaches the probe and sample without crashing
onto each other. In order to achieve this, it was conducted an experimental study of the instrument’s
motorized coarse motion structure.
All the new features developed here were integrated in the existing prototype via the Arduino platform.
To interface the signals outputted by the AFM circuitry and the microcontroller, as well as providing
robust tolerance against faulty use, additional circuitry was included. This allows the reading of important signals within the instrument’s context, such as the deflection signal, amplitude signal and controller
output. By taking advantage of the microcontroller’s features, it was designed a voltage source that
serves as an adjustable setpoint via the PWM outputs from the Arduino.
Finally, it was design and developed a GUI providing the user direct control of the tasks mentioned
above and also displaying some quantitative and qualitative data, acquired by the microcontroller, about
the state of the AFM.
Descrição
Tese de Mestrado Integrado, Engenharia Física, 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Microscopia de Força Atómica Controlador PI Analógico com ganhos digitais Instrumentação Arduino Algoritmo Auto-Approach Teses de mestrado - 2023