On High-precision Subpixel-based Drilling Technique for Suture Needles with Thread

Tiebo Sun*, Hong Li
Mechanical and Electrical Engineering Department, Jiangsu Food & Pharmaceutical Science College, Jiangsu Huai’an, 223003, China

© 2014 Sun and Li

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: ( This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Mechanical and Electrical Engineering Department, Jiangsu Food & Pharmaceutical Science College, Mingyuan Road, Jiangsu Huai’an 223003, China; Tel: 8613861659701; Email:


In order to improve the automation of end-hole drilling process in the production of suture needles with thread, a high-precision subpixel-based drilling method is proposed. According to the edge detection principle in mathematical morphology, combined with the characteristics of the magnified images of the ends of suture needles to be drilled, the morphological edge detection operators with variable structural elements are constructed to achieve noise suppression and fully extract the detailed information of edges of images of needle end holes to be drilled. Then, the subdivision method of spatial moments is adopted to realize the subpixel positioning of pixel-level edges. Finally, least squares fitting method is used to achieve the high-precision positioning of center of needle end hole to be drilled. The experimental results of the 0.5 mm needle samples show that the drilling method proposed in this study has a concentricity error no more than ± 0.2 μm and an average drilling time of 0.65S. Moreover, the method also boasts good real-time performance and stability and meets the automated production needs of drilling process of suture needles with thread.

Keywords: Least squares fitting, machine vision, mathematical morphology, subpixel, suture needles with thread.