Development of a novel 5-DOF controlled maglev local actuator for high-speed electrical discharge machining

A compact, five-degrees-of-freedom (5-DOF) controlled maglev local actuator (MLA) for realizing high-speed electrical discharge machining (EDM) has been developed. It includes a magnetic coupling mechanism that not only transmits torque from the motor to the spindle shaft, but also feeds a discharge current to an electrode attached to the spindle shaft. The spindle shaft is levitated by a 5-DOF controlled magnetic bearing system and is rotated by following the rotation of a power-supply ring, utilizing a magnetic coupling. Conductive flexible wire connecting the power-supply ring to the spindle shaft feeds the discharge current to the electrode, avoiding direct contact between the power-supply brushes and the spindle shaft. Experimental results show that a prototype MLA possesses sub-micron positioning resolution with an angular resolution of several micro-radians, bandwidths greater than 200 Hz in the 5-DOF directions, and positioning strokes of 2 mm in the thrust direction, 180 μm in the radial direction and 3.6 mrad in tilt direction, respectively. Moreover, the spindle shaft can be rotated smoothly at up to 2,000 min−1 with vibration amplitudes of less than 1.5 μm and 30 μrad, while the discharge current can be fed to the electrode while the spindle shaft is rotating without any friction force induced by the power-supply brushes.