Abstract: As a key factor of shoe last numerical machining, zooming is the most important determinant which affects the similarity among the shoe lasts of same series with different size and which will ultimately determine the quality of the products. By analyzing the traditional process of zooming with mechanical explorator and the zooming principle of the data at the center of the measuring head, the major causes of the zooming error are discovered. An zoom arithmetic with high precision for shoe last machining is proposed. The zooming data of shoe lasts surface are calculated by B-spline offsetting. The increment of polar distance after zooming can be calculated by using the zoom factor and the increment along the normal vector of the measuring point can also be calculated by rotation mapping of the vector. Finally, the accurate data of the shoe lasts surface after zooming can be obtained. With simulation and experimental results, it is verified that the method discussed has high precision and high efficiency.

Key words: Error analysis, Model girth, Shoe last, Zoom arithmetic