Design analysis of a grating interferometer sensor for HDD servo-track writing

A grating interferometer (GI) system for the measurement of a hard disk drive (HDD) actuator arm during the servo-track writing (STW) process has been designed and analyzed. Attractive features of this GI based system over current measurement systems such as the mechanical and optical push-pin techniques are that it does not require contact with the actuator arm and only needs a single servo loop to control the actuator arm position. In this paper, the theory necessary for the design of a GI based system to perform a non-contact direct measurement of a HDD actuator arm for use in STW is presented. The theoretical background related to the linear type GI is presented, and this theory is extended to the measurement of the angular displacement of a HDD actuator arm using a linear grating. Finally, experimental results with a prototype GI measurement system are presented and discussed