A magnetic disk mounted on a hard magnetic disk drive (HDD) used for storing data memory of a computer system is written with servo information (servo signal) for controlling a position of the magnetic disk by a servo track writer. In the recent HDD using mini-disk, it is usual to use one or two mini-disks and use a sector servo system in which servo information is set correspondingly to tracks of each disk.
In the sector servo system, identical servo information is written in predetermined positions of every sector of each of tracks on both surfaces of one disk. The technique of this kind is described in, for example, JP-A-10-106194.
On the other hand, in a magnetic head tester and the magnetic disk tester, a magnetic head electrically functions by writing predetermined data in a track according to servo information set in a disk and reading the data according to the servo information.
As a magnetic head for HDD, a composite magnetic head having GMR head, TMR head, etc., which will be referred to MR head, hereinafter, and installed on a reading side is used recently. The recent recording density of the composite magnetic head is several tens Giga/Inch and the number of tracks exceeds 10,000/inch. Further, recent width of each track is 2.0 μm or narrower.
It is a main stream that the size of magnetic disk is mainly 3.3 inches or smaller and a glass material is used as a substrate of the magnetic disk. The HDD with using a single magnetic disk becomes popular. In such HDD, a slider having an area of a tenth part mm×1 mm is provided on a top end of a suspension spring which is 15 mm to 20 mm long. A gap between a thin film magnetic head and a disk is as close as several nm to 10 nm.
In the magnetic head tester and the magnetic disk tester which use a high density recording disk of such type, highly precise head positioning in a track is required. Therefore, a head carriage has a fine movement piezo stage for fine positioning in addition to a coarse movement stage. The magnetic head accesses a track of a magnetic disk by driving the head carriage using the coarse movement stage and the fine movement stage. This kind of head carriage and the positioning control thereof are described in detail in U.S. Pat. No. 7,035,039 corresponding to JP-A-2003-272326.
With the improvement of recording density of the magnetic disk device, it is requested to improve preciseness of head positioning in the magnetic head tester or magnetic disk tester. Further, the recent rotation speed of magnetic disk is increased to 7,200 rpm˜15,000 rpm or more.
In a tester for testing a magnetic head or magnetic disk by writing servo information in the magnetic disk having current track density and recording density by using the sector servo system, it has to write the servo information in the magnetic disk every time when a magnetic head assembly is replaced.
The reason for this is that the writing position of the servo information is deviated due to variation of configuration of the magnetic head assembly.
That is, the tester has to move the magnetic head to an aimed track by the coarse moving stage and position it in a predetermined position by the fine movement stage (a piezo stage for fine positioning) and, then, to write the servo information in a predetermined track. However, the moving range of the fine movement stage is limited in a range from 100 to 200 tracks. For example, when the servo information is written in 100 to 200 tracks, the tester moves the magnetic head to next tracks by the coarse movement stage, positions it in the next tracks by the fine movement stage and then writes the servo information in the next tracks.
Due to the recent track width of several μm, variation of length of the magnetic head assembly and variation of magnetic head mounting position of the magnetic head assembly influence the writing positions of the next tracks every time when the positioning of the magnetic head in the aimed tracks is performed by the coarse movement stage.
The writing position of next tracks in which servo information is written by the magnetic head moved by the coarse movement stage and the fine movement stage and a writing gap corresponding to the track are determined correspondingly to variation of the magnetic head assembly with using the position of the coarse movement stage as a reference. Therefore, there is no consistency between the servo information thus written and servo information written by a magnetic head of another magnetic head assembly. In other words, the servo information becomes discontinuous correspondingly to variation of the configuration of the magnetic head assembly every time when a magnetic head is moved by the coarse movement stage. That is, a deviation of servo information in radial direction occurs in tracks of a magnetic disk.
So long as the same magnetic head assembly is used, there is no substantial problem in accessing the magnetic head to tracks even when the writing position of servo information is discontinuous since the combination of the fine movement stage and the coarse movement stage is unchanged. However, when a magnetic head assembly is replaced by another assembly, servo information is written in the discontinuous location due to variation of configuration of the magnetic head assembly, so that the positioning of a magnetic head of the another magnetic head assembly becomes unstable. Therefore, there is a problem that it becomes impossible to normally test a magnetic head or a magnetic disk.
As a result, the tester has to newly set servo information correspondingly to tracks by a new magnetic head every time the magnetic head assembly is replaced. However, through-put of the test of magnetic head or magnetic disk is lowered.