High-precision measurement of defocus amount for laser welding by analyzing image definition

The defocus amount is of great importance to laser welding quality of tight butt joint formed by two sheet metal according to laser welding process. A high-precision measurement system mainly consists of microscopic enlarger lens, CCD camera and LED light source is presented in this article. This measure system which is based on the principle of depth from focus can ensure an accurate defocus amount in tight butt joint welding. The depth position of the weld seam in the optical axis direction is measured by analyzing image definition of the weld seam micrograph. Measurement range and precision of the seam centerline in depth direction are ±0.45mm and ±10μm respectively.