Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2001-09-12
2004-10-05
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S077020
Reexamination Certificate
active
06801377
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of testing a performance of a head gimbal assembly (HGA) with a precise positioning actuator for a thin-film magnetic head element used in a magnetic disk drive unit and, more particularly, to a method of testing a displacement performance of the actuator.
2. Description of the Related Art
In a magnetic disk drive apparatus, thin-film magnetic head elements for writing magnetic information into and/or reading magnetic information from magnetic disks are in general formed on magnetic head sliders flying in operation above the rotating magnetic disks. The sliders are supported at top end sections of suspensions of HGAs, respectively.
Recently, recording and reproducing density along the radial direction or along the track width direction in the magnetic disk (track density) has rapidly increased to satisfy the requirement for ever increasing data storage capacities and densities in today magnetic disk drive apparatus. For advancing the track density, the position control of the magnetic head element with respect to the track in the magnetic disk by a voice coil motor (VCM) only has never presented enough accuracy.
In order to solve this problem, an additional actuator mechanism is mounted at a position nearer to the magnetic head slider than the VCM so as to perform fine precise positioning that cannot be achieved by the VCM only. The techniques for achieving precise positioning of the magnetic head are described in for example U.S. Pat. No. 5,745,319 and Japanese patent publication No. 08180623 A.
As an example of such a precise positioning actuator, there is a piggy-back structure actuator using a piezoelectric material. This piggy-back structure actuator is formed by piezoelectric material member of PZT in an I-character shape with one end section to be fixed to a suspension, and the other end section to be fixed to a magnetic head slider and a pillar shaped movable arms connected between these end sections. By applying voltage across electrode layers sandwiching the piezoelectric material member, the actuator will displace to precisely position the thin-film magnetic head element.
In order to test a displacement performance of this precise positioning actuator, a displaced amount has been conventionally measured by using a laser Doppler vibration meter. Namely, when the actuator is driven, a laser beam is irradiated to the displaced section of the actuator and then the displaced amount is measured. By this test method of the displacement performance, a displaced amount and a response speed of the actuator in response to an applied drive signal can be accurately measured.
However, during manufacturing and testing processes of an HGA, such displacement measurement using a laser Doppler vibration meter will cause the following various problems:
(1) Because of the laser Doppler vibration meter itself is expensive, a manufacturing cost of the HGA increases;
(2) Because the measurement using the laser Doppler vibration meter requires a long time period, the inspection time becomes huge causing the manufacturing cost also to increase;
(3) Introduction of the laser Doppler vibration meter which is not included in the normal inspection instruments for testing the magnetic head element will complicate the inspection process and also increase the number of the inspection process; and
(4) Introduction of the laser Doppler vibration meter increases the footprint of the inspection instruments.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a performance test method of an HGA with a precise positioning actuator, whereby a displacement performance of the actuator can be easily obtained in a short time without increasing a manufacturing cost of the HGA.
According to the present invention, a method of testing a performance of an HGA includes a step of obtaining a displacement performance of a precise positioning actuator by driving this actuator to displace and by executing a track profile measurement of at least one thin-film magnetic head element.
Because the displacement performance of the actuator is obtained by driving the actuator and by executing the track profile measurement which is one of the electromagnetic conversion performance measurements of the thin-film magnetic head element, it is not necessary to introduce a new inspection instrument resulting a manufacturing cost of the HGA to prevent from increasing. Also, because the displacement performance test can be executed simultaneously with the normal test of the electromagnetic conversion performance of the HGA using a dynamic performance (DP) tester or a read/write (R/W) tester, the number of the inspection processes will not increase although the inspection item increases. Therefore, the displacement performance of the actuator can be easily obtained in a short time. In addition, because of no enlarging of a footprint of the inspection instruments, the manufacturing cost of the HGA can be further prevented from increasing.
In this specification, riving an actuator to displace or riving an actuator for displacement is not equivalent to merely applying a drive signal to the actuator but means to control the drive signal of the actuator so that the actuator displaces from its initial position. Namely, depending upon a bias voltage applied to the actuator, the actuator may displace without applying a drive signal or the actuator may not locate at its initial position when a medium valued drive signal is applied thereto.
It is preferable that the driving of the actuator includes applying a DC drive signal or an AC drive signal to the actuator.
It is also preferable that the driving of the actuator is executed only during a reading out operation or a writing operation of the at least one thin-film magnetic head element.
According to the present invention, also, a method of testing a performance of an HGA provided with a magnetic head slider with at least one thin-film magnetic head element, a support and an actuator for displacing the magnetic head slider with respect to the support so as to precisely position the at least one thin-film magnetic head element, includes a step of writing at least one track of information on a magnetic medium with no displacement of the actuator, a step of executing a track profile measurement of the head gimbal assembly using the written at least one track of information with no displacement of the actuator to obtain a reference track average amplitude profile (reference TAA (track average amplitude) profile) with respect to an off-track distance, a step of measuring a TAA at each position displaced by driving the actuator, and a step of obtaining a displacement performance of the actuator from the reference TAA profile and the measured TAAs.
It is preferable that the driving of the actuator includes applying a DC drive signal to the actuator. In this case, the DC drive signal may be a DC voltage signal with a variable voltage, or DC voltage signals with voltages for driving the actuator to the maximum displacement thereof.
It is also preferable that the driving of the actuator is executed only during a reading out operation of the at least one thin-film magnetic head element.
It is preferable that the writing step includes a step of writing one track or two tracks on the magnetic medium. In the latter case, the written two tracks are preferably spaced by a distance substantially corresponding to the maximum displacement of the actuator from one side to the other side.
According to the present invention, furthermore, a method of testing a performance of an HGA provided with a magnetic head slider with at least one thin-film magnetic head element, a support and an actuator for displacing the magnetic head slider with respect to the support so as to precisely position the at least one thin-film magnetic head element, includes a step of writing at least one track of information on a magnetic medium with no displacement of the actuator, a step of executing a track profil
Honda Takashi
Kasajima Tamon
Shiraishi Masashi
Tomita Katsuhiko
Wada Takeshi
Armstrong Kratz Quintos Hanson & Brooks, LLP
Faber Alan T.
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