This study proposes an integrated optical system for flat panel display (FPD) substrate inspection. For such a system,
auto-focusing is a challenging problem since the microscope magnification ratio is as large as 10X to 50X and the
corresponding depth of field (DOF) can thus reduced to 5 µm. Considering its low-cost and its capability in maintaining
the depth of field that may be deteriorated by the increase of magnification ratio, this work uses the digital versatile disc
(DVD) pickup head is used as the auto-focusing sensor. To verify the auto focus can be achieved. We construct
experiment to simulate the real vibration. Change different position from lens to FPD substrate DVD calculate focus
error signal (FES) to control PZT stage return to focus position immediately in 0.5 sec.