Smart agile lens remote optical sensor for three-dimensional object shape measurements

Abstract

We demonstrate what is, to the best of our knowledge, the first electronically controlled variable focus lens (ECVFL)-based sensor for remote object shape sensing. Using a target illuminating laser, the axial depths of the shape features on a given object are measured by observing the intensity profile of the optical beam falling on the object surface and tuning the ECVFL focal length to form a minimum beam spot. Using a lens focal length control calibration table, the object feature depths are computed. Transverse measurement of the dimensions of each object feature is done using a surface-flooding technique that completely illuminates a given feature. Alternately, transverse measurements can also be made by the variable spatial sampling scan technique, where, depending upon the feature sizes, the spatial sampling spot beam size is controlled using the ECVFL. A proof-of-concept sensor is demonstrated using an optical beam from a laser source operating at a power of 10 mW and a wavelength of 633 nm. A three-dimensional (3D) test object constructed from LEGO building blocks forms has three mini-skyscraper structures labeled A, B, and C. The (x, y, z) dimensions for A, B, and C are (8 mm, 8 mm, 124.84 mm), (24.2 mm, 24.2 mm, 38.5 mm), and (15.86 mm, 15.86 mm, 86.74 mm), respectively. The smart sensor experimentally measured (x,y,z) dimensions for A, B, C are (7.95 mm, 7.95 mm, 120 mm), (24.1 mm, 24.1 mm, 37 mm), and (15.8 mm, 15.8 mm, 85 mm), respectively. The average shape sensor transverse measurement percentage errors for A, B, and C are +/-0.625%, +/-0.41%, and +/-0.38%, respectively. The average shape sensor axial measurement percentage errors for A, B, and C are +/-4.03%, +/-3.9%, and +/-2.01%, respectively. Applications for the proposed shape sensor include machine parts inspection, 3D object reconstruction, and animation.