Design of a precision grinder with closed loop optical feedback for the manufacture of micro electro discharge machining electrodes

This research focuses on the design of a precision grinder for the manufacture of electrodes used in micro-electro discharge machining (EDM). Electrodes used in micro- EDM can range in size from 10 - 500 microns in diameter and are typically produced through conventional precision grinding. Variability in grinding parameters such as vibration, spindle run out, electrode positioning, and electrode deflection at high lengthto- diameter aspect ratios result in increased grinding time and difficult to achieve repeatability. To mitigate this variability and to provide for a faster automated solution, the precision grinder developed incorporates a high resolution optical measurement system, precision air bearing spindle, and air bearing x-y positioning stage. The integrated high resolution optical measurement system allows for automated compensation for electrode positioning errors and other associated grinding variations. Sub micron resolution is achieved in the optics design allowing for in process resolution of the electrode diameter to within +/- 1 micron. Electrode positioning is achieved through use of an air bearing x-y stage with closed loop feedback position from a linear optical encoder with 100 nanometer (nm) resolution. A diamond grinding wheel is mounted on a precision air bearing spindle for minimal run out, vibration dampening, and stiffness. This grinder is demonstrated through the production of a series of electrodes with emphasis on the repeatability and tolerances achieved.