AN AUTOFOCUSING PROBE FOR PROFILE MEASUREMENT

K. C. Fan, W. J. Lin, S. Chen, J. H. Ho

Abstract

In this research, a low cost high-precision auto-focus laser probe system was developed. Modified from the pickup head of a market available compact disc player as basis, it can detect the Focus Error Signal (FES) of the object with a built-in four-quadrant photodiode. The FES will feedback to the developed controller through which the objective lens can be adjusted to remain in focus using a voice coil motor (VCM). The driving current (converted from Servo FES) of the VCM and objective lens displacement is one to one linearly related within few hundred micrometers. Because of this relationship, the surface profile of the tested object can be realized. Experimental results showed that the designed probe has 200 µm linearity range, 0.2 accuracy and 0.0854 µm resolutions. Some applications are given to show the applicability of this probe system.

Keywords

CD pickup head, auto-focus, voice coil motor, Focus Error Signal

Download

IMEKO-WC-2000-MNT-P483.pdf

DOI

-

Back to the proceedings