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Régulateur numérique pour contrôleur de mouvement de haute précision

This bachelor's thesis was done in partnership with a company looking to develop a new 3-axes motorized stage for the automatic positioning of electronic circuits under scanning electron or optical microscopes.

The goal of this project was to develop a regulation algorithm to insure fast and precise positioning on the two axes that control the horizontal position of the stage. The expected regulation precision is ±200nm. The third axis for the vertical positioning of the stage is out of the scope of this project.

The actuators used for the three axes are piezoelectric. This is the main challenge of this project as piezoelectric actuators do not behave linearly and many complex effects affect the movement, such as creep and hysteresis. The piezoelectric actuators of the X and Y axes work in shear mode and can move in two ways : scanning (applying a DC voltage) and stick-and-slip (applying a sawtooth voltage).

The work consisted of studying the system using a Simulink model of the stage, predesigning a regulator using the same model, characterizing the real system, and adjusting the regulator. The algorithm was implemented in C language on a microcontroller card and tested on the stage. While the main objective of this bachelor's thesis was the regulation of the X and Y axes, a lot of time was spent characterizing the axes as the stage was being developed simultaneously.

Due to difficulties with moving the X axis and a lack of time, a regulator for the X axis was not implemented. However, a similar approach to the regulation for the Y axis can be followed.

In the end, a regulation algorithm was written for the Y axis using a combination of a sawtooth signal for errors over the range attainable by scanning, and a scanning signal with an amplitude regulated by a PID controller to ensure a smooth target attainment. Due to a lack of time, the precision of ±200nm was not attained for targets over 460nm.

The specification of the maximal regulation time of 3 seconds was achieved.