A High Precision Servomechanism of a Constant Speed for NC Machines

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The NC machine is useful for mass production. In particular, it is suitable for producing a complex machine element. However, the NC machine is not suitable for making a special component such as gears. For example, until several years ago, it had been unable to get high precision gears by NC cutting or NC grinding process. It is because a high precisely synchronized servomechanisms are required for NC gear process.T. Emura of the head of this research project developed a very high precision servomechanism about ten years ago, and he tried to apply his servomechanism to gear cutting machines of NC type. Then he succeeded in cutting high precision gears by a NC hobber.This research work is carried out in order to increase cutting or grinding speed by means of a direct-drive technique. Since the equivalent moment of inertia of the direct-drive servomechanism is extremely small, an inertial damper was used and the position loop-gain of the servomechanism was increased sufficiently in order to decrease the rotary vibration of a servo- spindle. Moreover the authors applied a new PLL developed by T. Emura to their high speed servo-spindle. After experiments, they succeeded in rotating their spindle at a speed of 4,000rpm and with the accuracy of 20"pp. These speed and accuracy are high enough for NC gear hobbers and NC gear grinders.