Geometrical Parameter Measurement of Contact Lens with Imaging Method

摘要

As the decisive features of diopter of contact lens, fore radius r_1 and retral radius r_2 and central thickness d are key parameters of contact lens. It is very important to measure these geometrical parameters precisely and accurately. Being made of a bibulous and soft macromolecule material, contact lens is prone to be distorted when pressed or dehydrated. For this reason, it is very difficult to measure its geometrical parameter with high precision. In order to address this problem, geometrical and material characteristics of contact lens are discussed in details. Considering the advantages of non-contact measurement and imaging magnification, the imaging method is put forward. In imaging method, contact lens is projected into an enlarged image with a projecting lens. An imaging sensor is used to acquire the enlarged image, and a single board computer is adopted to process the image and to do the calculation of parameters. In addition, a glass ring emerged in the liquid was introduced to hold contact lens without any distortion or dehydration. An example of system is provided. With the system, the thickness t can be measured directly, and fore radius r_1 and retral radius r_2 can be calculated with the help of h_1 and h_2 and d_1 and d_2. With an imaging system of 20 tunes magnification, and a 512 pixels CCD linear imaging sensor of a 50 μm pixel spacing, the system has a resolution of 5 um, which is much higher than the accuracy requirement of measurement 0.01 millimeter.