On-machine precision measurement technology of tool electrode

The paper introduces precision measuring technology of tool electrode and its importance for micro-electrical discharge machining system. The paper describes the self-developed machine by type of μEDM-50 which is designed to satisfy high precision machining requirement of miniature characters of parts. The optical measurement system is constructed. It includes special light source, high ratio zoom microscope lens, CCD camera, frame grabber and a set of accessories. A special image processing soft is programmed for the measurement system. In experiment, calibration of the system is firstly finished so that scale ratio can be known between single image pixel and real distance. Then, tool electrode is magnified through optical route in the system and its digital image is captured clearly in CCD camera. Sub-pixel edge processing algorithm is applied to calculate edge information of tool electrode in image. Measuring error can be less than 1 micrometer. The measurement system can be used for any tool electrode whose diameter is between 1 micrometer and 1 millimeter. It is useful to compensate wear of tool electrode and manufacture miniature characters accurately.