Design And Research On Micro-displacement Measurement System For PZT Actuated HGA

With the development of the hard disk drive technology, the two servo drivetechnology was more and more widely used in hard disk, and the head gimbleassembly (HGA) using piezoelectric ceramic (PZT) as the second level of driverwas first used for commercial purposes. As the PZT is quite fragile, defects, such aschips, cracks inevitably occur during the production process. Appropriate indicatorsneed to be selected for testing to ensure the quality of products. For eligibleproducts, under specific excitation voltage, PZT carries out push-pull movement,and will actuate the HGA head movement, and the micro-displacement (nano) is inthe design range. While for the the flawed HGA, it will be less than the designedvalue, therefore, it can be used for quality detection.As HGA product requirements is increasingly stringent, the measurement ofHGA Micro displacement actuated by PZT attracts more and more attention. Inorder to meet the needs of the market, the automatic measurement need to berealized. The micro displacement measurement system is used to measures the HGAhead micro displacement under particular PZT excitation voltage, when the HGA inflight status on the disk. It has the following features: HGA flight status simulation,the HGA micro-displacement measurement using LDV and the LDV laser automaticalignment. The main contents of this paper are as follows:Firstly, through access to the relevant technical information and on-siteevaluation experiments, an overall design was completed. Machine vision andimage processing were researched and applied to control the HGA head surface andthe disk surface distance. And a necessary HGA deflection angle measurement wasconducted to prepare parameter for achieving automatic alignment of the LDV laser.Secondly, an analysis to the collected signal were conducted in Matlab tocomplete the reaserach on the calculation of the HGA micro displacement.Lastly, HGA deflection angle repeatability measurements, LDV alignmentreliability analysis, stability testing of the micro-displacement were carried out, soas to evaluate the performance of the measurement system.