Micropositioning mechatronics system based on FPGA architecture

In this paper a micropositioning mechatronics system is conceived and described. Its mechanical design is optimized in order to achieve high precision displacements. High speed closed-loop feedback control is obtained by using both PID and ramp control algorithms programmed as virtual instruments (VI) on an FPGA (Field Programmable Gate Array) module. User controls are programmed in an independent Host VI. A Linear Variable Differential Transformer (LVDT) is employed as a position feedback sensor, while positioning accuracy and repeatability are experimentally assessed by using a Michelson-type laser Doppler interferometric system. Different experiments with point-to-point positioning are conducted. In the first set of experiments, positioning with 100 μm steps is performed. In a second step, 10 mm positioning experiments are done. The system shows a marked nonlinearity when longer positioning steps are used; this nonlinearity influences significantly the output error. It is hence found that the main contribution to system´s nonlinearity is caused by the LVDT. The error is compensated via system linearization by an experimentally obtained analytical function which is programmed in the LabVIEW Host VI. Positioning accuracy and repeatability are finally assessed experimentally again and true micrometric positioning is achieved.