SERVO WRITING SYSTEM TO BE USED IN DATA RECORDING DISK DRIVING DEVICE

PROBLEM TO BE SOLVED: To provide a non-entrance type servo writing system which is to be used in a data recording disk drive. SOLUTION: A system measures the position of an actuator and generates a reference clock by using a semiconductor laser 200. The reference of the internal position is provided by reflection diffraction gratings mounted on an actuator arm and a spindle hub. A wave front reproducing optical system corrects aberration in the gratings. Moreover, optical sensors detect change of difference of a diffraction pattern to be generated by the gratings to exclude sensitivity with respect to a frequency drift. A decoding circuit converts data of the optical sensors into the measurement value of the position of the actuator. A control circuit drives a voice coil motor 118 in the disk drive and the motor positions a write-in transducer in order to record servo information to be provided in a servo pattern generator. Then, a servo writing device performs a writing to the drive which is completely assembled and is hermetically sealed through a transmission window in a head and disk assembly cover.