Optical Shape Sensor Using Electronically Controlled Lens

Abstract

Proposed is a single viewing axis optical Three-Dimensional (3-D) shape sensor using an electronically controlled variable focus lens (ECVFL) for non-contact smallest transverse resolution reconstructions at all axial direction target planes. The demonstrated completely automated sensor design also involves input beam aperture control for balancing aberration and diffraction effects, enabling minimum focused sampling beam diameter. Sensor design analysis is presented, including the derivation of the depth of field of the camera used in the 3-D sensor. A computer-controlled sensor system using a liquid ECVFL is built and experimentally calibrated for a 40-mm-depth scan with a better than $52~\mu \text{m}$ transverse resolution over a $400~\textrm {mm} \times 400$ mm mechanically implemented transverse scan zone. The 3-D sensor system is successfully deployed to measure the borehole depths in a 3-D sample containing 12 boreholes, image the pin regions of a 16-pin Integrated Circuit (IC) Thin-Shrink Small Outline Package (TSSOP), and reconstruct the shape of a 3-D aircraft part. The sensor gave a ±3% average measurement error for the borehole test sample compared with a vernier caliper measurement. The proposed single viewing axis sensor is ideal for applications requiring cavity or borehole inspections as well as parts requiring high transverse resolution imaging.