Development and evaluation of an on-machine optical measurement device

Demand for fabricating micro-features such as fine holes, micro-cavity for injection moulding, and micro-pin using both conventional (turning, milling, etc.) and non-conventional edge detection method (EDM), wire cut EDM, etc.) processes is increasing significantly. To successfully achieve micro-machining, development of a miniature machine tool, process technology, and on-machine measurement is essential. However, in such tool-based micro-machining processes, proper tool shape monitoring, precision processing, and dimensional control require significant attention. Since these are tool-based machining processes, tool shape monitoring and control are also important technologies to be established. In this study, an on-machine measuring device was developed based on non-contact optical method to inspect dimensions of the fabricated tools (e.g. electrodes for EDM) as well as the wear of tools used for the respective processes. The developed inspection system uses a laser light source and a photo-electronic device. To minimize errors due to the change of tool measurement position and the Fresnel diffraction of laser light, an edge detection algorithm using a linear discrimination function is proposed in this study. Furthermore, an intensity measuring method was added for specimen with a smaller diameter. The experimental results show that the developed on-machine optical inspection system has the accuracy and stability to effectively monitor the fine dimensions of tools and their wear. (C) 2006 Elsevier Ltd. All rights reserved.