| Since the invention of the hard disk, its storage density and access speed continues to increase. As an important part of the hard disk, the head positioning technology, also developed from beginning of the rail orientation to the voice coil which widespread use in current drive. Meanwhile, the positioning accuracy and speed have been greatly improved. However, if the storage density reaches 10TB/in~2 in the future, the current unipolar voice coil motor will be unable to meet the needs.This paper presents dual-stage micro-actuators on the basis of voice coil motor in a unipolar orientation. Head positioning is a complex system, which has relationship with not only the voice coil motor and dual-stage actuator, but also some of the natural properties of the arm. This paper introduces the basic structure and working principle of the hard disk. Then we created a solid model for the arm and calculated the natural frequencies, mode shapes, and other important parameters of the arm by finite element method. A mathematical transfer function model of the voice coil motor is given. Based on this, control relationship between secondary positioning system and the first-stage positioning system is analyzed. The basic requirements of the dual-stage micro actuator are described. We present two types of micro-actuators in the form of the piezoelectric and electromagnetic and deduce the two kinds of micro actuator physical model. Static displacement of the two types of micro-actuator could be more than 20nm by calculating with ANSYS simulation, which is in line with the static stroke requirements of the micro actuator. However, compared with the driving voltage and structure effects, the electromagnetic actuator is more suitable for the HDD. By transient performance analysis and performance analysis of electromagnetic micro-actuator, the resonant frequency is over 10kHz. Finally, specific parameters of micro-actuator model are obtained by system identification with the results of dynamic analysis. |
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