An on-line measurement system was proposed. It is composed of a halogen type light source

a zoom lens

a CCD camera and a bracket that has 6-degree of freedom. It has a resolution of 1.61 μm and a magnification of 113~729. Based on the Linux operating system

an image capturing program was developed with the V4L2 API

in which the image data was acquired with the method of mmap() memory map. The conversion between the data structure of IplImage and the class of QImage was implemented. Therefore the image could be processed by using OpenCV

as well as showed with Qt. The contour of micro electrodes can be extracted by means of the Canny edge detector. Furthermore

the G code for on-line measurement was also developed. The experiment of block electrodes Electrical Discharge Machining (EDM) grinding was carried out. It shows that the relative error between the on-line measurement system (OMS) and the scanning electron microscope (SEM) is less than 5%. It also shows that the system can be used to deal with the difficulties in micro electrodes on-line fabrication and measurement in micro EMD.