For the seam feature measurement of the tight butt joint without misalignment in laser welding

current vision sensor cannot obtain the seam gap width and seam position stable and reliable enough. In this paper

a seam measurement method based on the micro depth of field is proposed. A hight optical magnification lens

a CCD(Charge Coupled Device)/CMOS(Complementary Metal-Oxide-Semiconductor Transistor) camera and an external LED(Light-Emitting Diode) lighting unit are used to constitute the non-contact measurement system. The measurement system can be used for the tight butt joint in laser welding. The angle between the seam surface and the optical axis of the camera is about 45°. The installation method solves the problem that the depth of field and the field of view are too small to measure the tight butt joint with the multi-time magnification image measurement system. Experiments indicate that the measurement system can obtain the seam gap width and seam position stable and correctly. With this measure method

the seam surface normal vector also can be measured. The measurement accuracy for the seam gap width and seam position is 5 μm and 6 μm

respectively. Furthermore

the narrowest welding seam gap that can be measured is 0.02 mm

which fully satisfies the demand of the seam measurement in laser welding.