Servotrack writing system using dual laser scales for high track-per-inch recording

A servotrack writing (STW) system using dual laser scales (DLSs) has been developed. Two very small and lightweight laser scales are mounted on both the head arm and spindle motor, respectively, detecting the arm position and clock signal by the grating interferometer head. DLS-STW is a drive-level servotrack writer that eliminates the need for a clean room. A 5-nm step VCM control has been achieved by using a mechanically improved prototype small hard disk drive.