In-Situ Mechanical Impedance of Air Bearing in Hard Disk Drive

This paper describes a novel method used to realize in-situ mechanical impedance measurement of air bearing in hard disk drive (HDD). It is originated from simultaneously sensing and actuating (SSA) method. In this method, an active cantilever is merged into a slider of HDD. It works with a patch of PZT, coating onto its top surface. This PZT cantilever is capable of sensing the mechanical impedance when the HDD is in the operational state. During HDD´s operation, a certain voltage will be input to the PZT. As the piezoelectricity occurs inside the PZT, it will expand in the length direction. This expansion will cause the cantilever to be deformed. Because of the cantilever´s deformation, the shape of the air bearing will be modified, which leads to the variation of the aerodynamic force produced on the cantilever. At the same time, the inverse piezoelectricity will occur due to the deformation of the cantilever. This inverse piezoelectricity results into the variation of the output electrical impedance of the PZT. In our method, the PZT cantilever is viewed as a four-pole device. Once the transduction matrix of it has been obtained, the mechanical impedance of air bearing on tip of cantilever could be achieved from the input electrical impedance of the PZT. This capability of the PZT cantilever has been validated by a well established finite element procedure and it has been used to measure the mechanical impedance of air bearing by numerical simulation. A good consistence between our numerical results and other researcher´s experimental results shows the effectiveness of the new method