Automatic focus control for assembly alignment in a lens module process

This study proposes an auto focusing method for multi-focus images in assembling lens modules in digital camera phones. A camera module in a camera phone is composed of a CCD sensor, an IR glass, a lens and a PCB board. The alignment of the components is one of the most important factors in determining the product quality. Auto-focus is essential to adjust the image quality of the IR glass, but there are two focal points in the captured image, due to the thickness of the IR glass. Therefore, the sharpness, probability and scale factor are used to find the desired focus from a multi-focus image. The sharpness is defined as the clarity of the image. The variation of the probability and scale factors are analyzed to find the focus after pattern recognition with a registered image. The presented algorithm was applied to a lens assembly machine which has 5 axes, two vacuum chucks and an inspection system. The desired focus can be determined on the local maximum of the sharpness, the probability and the scale factor in the experiment.