Abstract：For the visual problem of the contact lines on planar double-enveloping, the worm pairs Ⅰ, Ⅱ andⅢ type contact line and their formation reasons are studied. By using the function of the Matlab numerical calculation and image processing, the animation of contact line formation process is gained under different transmission type on the worm gear tooth surface. The research method provides evidence to study the structure of the tooth surface on worm pairs. Theoretically it is proved the characteristics of the worm drive and the relationship between the transformation point and a variety of contact line type. It provides the guidance to further explore complex the structure on worm gear.

Keyword：double-enveloping;contact line;transformation point;visualization;