Optical distance control for a multi focus image in camera phone module assembly

Camera phones are very popular these days and mass production is essential for manufacturing the camera modules used in the phones. This study aims at developing a focusing method for use in the camera module assembly process. The camera module is composed of small components and machine vision is necessary to align them before their assembly. The inspected images usually have multiple areas with different focal distances, due to the different thicknesses of the components. Sharpness is the evaluation of focus, calculated by determining its absolute derivative and used for determining the focal point. A dynamic focus region (DFR) is defined to find the object of interest to be focused on. The DFR is built from the edge fragments detected using several narrow ROIs across the vision screen. An assembly machine was constructed to attach lens mounts to a PCB for the experiment. The distance between the lens mount and vision camera was adjusted to find the focus position by means of the sharpness and DFR. The result shows that the desired object is brought into focus and the proposed method can be applied to the camera module assembly process.