Numerically Control of Servo-Spindle for Machine Tools by Two-phase Type PLL Method

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Recently, Machine tools have been rapidly changing to NC machines, however, it has been difficult to make NC gear cutting or grinding machines. For example, NC hobbing machines were not suitable for making high precision gears as compared with full-mechanical ones. To overcome the difficulty, T. Emura, the head investigator of this project, tried to make a high precision and high speed servo-spindle suitable for gear manufacturing machines using the direct-drive techniques which were obtained through the investigation about waudng robots. The two-phase type PLL(phase-locked loop), proposed by T. Emura, was applied to controlling the servo-spindle in order to obtain high precision and high stiffness rotational motion.The summary of this research results-are as follows. we made the servo-spindle which was composed of a build-in motor, a magnetic scale and a dynamic balancing mechanism necessary for high speed rotation(maximum 12, 000 rpm). In order to improve the adaptivity to the periodic disturbance, the repetitive control method were used. In addition, a meshing mechanism is usually necessary for NC gear grinding machines to check and correct the relative displacement between the tool and the work. We proposed a new meshing method using image processing and proved that it is very useful.As a result of the experiments using the NC gear grinding machine using the servo-spindle controlled with the two-phase type PLL, it was proved that we can very quickly get high precision gears whose cumulative error is less than 10".