Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2002-05-14
2003-11-25
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S132000, C318S254100, C318S500000, C318S700000, C318S767000
Reexamination Certificate
active
06653809
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to recording devices in general and in particular, to high-speed positioning of the read-write head of recording devices. The high-speed positioning technology of the present invention is ideal for use in spin stands of recording devices that are used to determine performance and properties of recording devices.
2. Discussion of the Background Art
Hard disk drives (HDD) are widely used in information recording media for recording large volumes of digital data, beginning with electronic computers.
HDDs generally comprise a substrate, a magnetic disk, which is a non-magnetic disk covered with magnetic thin film, a spindle motor that is anchored to the substrate and rotates the magnetic disk at high speed, a slider that has a recording element and a head, which is the reproducing element, on its surface, a head gimbal assembly (HGA) with the slider at its end, an arm with suspension that supports the HGA, and a rotary actuator that is anchored to the substrate and drives the arm. Furthermore, a single HDD has several magnetic disks and heads depending on the recording capacity of the HDD.
The working principle of the HDD is as follows: The center of a magnetic disk is held by a spindle and rotates at high speed from 4,000 to 15,000 rotations per minute. The slider is guided by an arm that is driven by a rotary actuator and moved so that the space between the outer periphery and the innermost periphery of the magnetic disk forms an arc. Moreover, when information is being recorded or reproduced, the slider that is above the magnetic disk maintains an inclined posture so that a wedge-shaped space is formed with the magnetic disk as it floats at a very small distance above the magnetic disk under the air current that is produced on the surface of the magnetic disk rotating at a high speed. Once the slider has been positioned at a predetermined position on the magnetic disk by the rotary actuator, the magnetic disk is magnetized and information is recorded by the recording element attached to the slider. Moreover, the magnetic field from the magnetic disk is detected and information is reproduced by the reproducing element attached to the same slider.
Furthermore, recording and reproduction of information is performed on the memory region that has been made by physically subdividing the magnetic disk recording surface. For instance, reading and writing are performed on an annular memory region called a track having a predetermined width that has been made along the concentric circumference of the magnetic disk.
The HDD accumulates information and therefore, each part comprising the HDD undergoes rigorous testing because there must be complete reliability during recording and reproduction of information. A head testing device that records or reproduces information on a magnetic disk for testing and evaluates the performance and properties of the head is used to test heads.
An oblique view of the conventional head testing device
10
is shown in FIG.
1
. Head testing device
10
in
FIG. 1
consists of reference table
11
, cassette
30
that holds head
20
at the end, carriage
12
that holds cassette
30
, piezo stage
13
that fine-positions carriage
12
horizontal with respect to reference table
11
, head-loading mechanism (HLM)
14
that positions piezo stage
13
perpendicular with respect to reference table
11
, stage
15
anchored to reference table
11
that coarse-positions HLM
14
horizontal with respect to reference table
11
, and disk rotating device
50
anchored to reference table
11
that holds the center of magnetic disk
40
with rotating shaft
51
so that magnetic disk
40
is horizontal with respect to reference table
11
and magnetic disk
40
rotates around its axis using motor
52
.
A summary of the effects of the above-mentioned structure is as follows: Piezo positioner
13
is coarse-positioned by stage
15
and then carriage
12
is fine-positioned by piezo stage
13
. Head
20
is positioned at a predetermined position over magnetic disk
40
by these positioning operations. Furthermore, head
20
is moved up and down above magnetic disk
40
by HLM
14
and floats above the surface of magnetic disk
40
or rests above the surface of magnetic disk
40
. Head
20
generates a magnetic field when it floats above the surface of magnetic disk
40
and writes information on magnetic disk
40
or detects a magnetic field and reads information from the magnetic disk.
The following are items evaluated by a head testing device. These include the track average amplitude (TAA), which is the average amplitude of reproduction signals that are output from the head; the track profile (TP) representing the TAA distribution relative to displacement from the track center line (TCL) within a track; the overwrite (OW), which is represented by the attenuation factor of the LF signals when the highest frequency signals (HF signals hereafter) are overwritten on the lowest frequency signals (LF signals hereafter) recorded on a magnetic disk; the bit error rate (BER), etc. For instance, the head moves in micro-increments from one side of the track width to the other in order to determine the TAA distribution in the direction of width with the track center line serving as the center in the track profile determinations. Moreover, it also moves between tracks because there are fluctuations, etc., in determination results between the inner and outer periphery of the magnetic disk. Thus, in addition to the magnetic disk being read by the head, the head also frequently moves during head tests.
When determining the above-mentioned evaluation items, mechanical and electrical parameters are established for the head testing device. The following are the mechanical parameters: The radius, which is represented by distance when the center of the disk is the reference point; the skew angle, which is the angle formed between the head and the circumferential tangent of the magnetic disk; spindle rotational speed, etc., all of which are absolute positions of the magnetic disk. The following are the electric parameters: The signal frequency, the signal current, the data pattern, the MR head bias current, etc., when magnetic signals are being written or read.
Head testing device
10
determines the above-mentioned evaluation items while simulating operation of the hard disk. For instance, the head is moved by the rotary actuator while describing an arc above the magnetic disk, as previously mentioned, and therefore, the head skew angle increases as the head moves from the side of the inner periphery to the outer periphery. The skew angle relative to the radius varies with each type of HDD, even if the radius remains the same. Therefore, head testing device
10
calculates the position on magnetic disk
40
that satisfies both the radius and the skew angle and positions the head at the position obtained by calculation. Head
20
moves in micro-increments within the track above the magnetic disk while moving between tracks in order to determine fluctuations in the determination results when head
20
is being tested, for instance, during track profile determinations. The testing time for head
20
includes movement such as movement within a track and movement between tracks, etc., and therefore, it is preferred that head
20
linearly move the shortest distance so that the movement time for head
20
will be curtailed in order to reduce the testing time of head
20
. Nevertheless, when head
20
moves linearly above magnetic disk
40
, there is a chance that head
20
or cassette
30
holding head
20
will impact spindle
51
holding magnetic disk
40
, etc.
A specific example of impact is shown in FIG.
2
.
FIG. 2
is a diagram of head
20
attached to cassette
30
and magnetic disk
40
held by spindle
51
, seen from above. The skew angle of head
20
is 0 degrees directly beneath with spindle
51
in the center, that is, when head
20
is at 3 o'clock, but when the head moves toward 2 o'clock,
Agilent Technologie,s Inc.
Masih Karen
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