The present invention relates to a data storage apparatus and its control method. In particular, the invention relates to a data storage apparatus that compensates the motion of the head for vibration detected by a sensor and a control method for such a data storage apparatus.
Data storage devices using various types of media such as optical disks and magnetic tapes are known in the art. Among them, hard disk drives have become popular as storage devices for computers to such an extent that they are one type of the storage devices indispensable for today's computers. Further, not limited to computer systems, the hard disk drives are expanding more and more in application because of its excellent characteristics. For example, hard disk drives are used for moving picture recording/reproducing devices, car navigation systems, and removable memories for use in digital cameras.
Each magnetic disk used in hard disk drives (HDDs) has a plurality of tracks formed concentrically and each track is partitioned into a plurality of sectors. In each sector, servo data and user data are stored. The servo data includes the address of each sector and burst signals. Data can be written to and read from a desired address by the head element unit which accesses the sector according to the address information therein. That is, the HDD allows the head element unit to move to a desired track on the magnetic disk by controlling the current supplied to the voice coil motor (VCM). While following the center of the track according to the burst signals, the head element unit reads or writes data.
The head element unit may be displaced from the track center when the HDD is subject to external vibration. To solve this off-track problem, a variety of methods have been developed. For example, if off-track condition occurs during write, data in another track may be overwritten. One method to solve this problem is to set an acceleration sensor in the HDD to detect vibration and shock. In this method, write is halted if vibration or shock is detected by the acceleration sensor. However, this method deteriorates the performance of the HDD.
Another off-track control method is disclosed in, for example, Patent Document 1 (Japanese Patent Laid-open No. 2003-346439). In the disclosed data storage apparatus, compensating data from acceleration sensors is added to the servo loop. In this method, this head position compensating signal is entered to control the current supplied to the VCM. In addition, injecting the compensating signal into the servo loop is stopped at prescribed timings in this method.
In this method, however, the head happened to move to a wrong position in some cases. For example, if noise is introduced into the output signal of the sensors while there is no vibration, compensation is made based on the noise-introduced signal, perhaps resulting in moving the head to a wrong position. In this case, the HDD deteriorates in performance since data cannot accurately be read/written. Such prior art HDDs having sensors installed therein to detect vibration have this problem in that data cannot accurately be read/written.