Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2002-04-15
2003-11-11
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C324S225000, C360S075000, C360S240000, C360S290000
Reexamination Certificate
active
06646436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a head holding apparatus that is used in devices that test one or both of the head and disk of a hard disk drives, and relates to a device having a means for controlling the amount of head displacement per unit of time with exposure to heat, so that fluctuations in test results are controlled.
2. Discussion of the Background Art
Hard disk drives (HDDs) are widely used for information recording media for recording large volumes of digital data, beginning with electronic computers.
HDDs generally comprise a substrate, one or more magnetic disks, which is a non-magnetic disk material covered with a magnetic thin film, a rotating spindle that is anchored to the substrate and rotates the magnetic disk at high speed, a slider with a head, which is the recording element and reproducing element, at its surface, head gimbal assemblies (HGAs) with the sliders at its end, a suspension arm that supports the HGA, and a rotary actuator that is anchored to the substrate and drives the arm. Furthermore, one 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 that 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 trace between the outer periphery and the innermost periphery of the magnetic disk forms an arc. Moreover, when information is being recorded or retrieved, the slider that is above the magnetic disk maintains a tilted posture so that a wedge-shaped space is formed with the magnetic disk as the slider floats a very small distance above the magnetic disk in the air current that is produced on the surface of the magnetic disk that is 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 retrieved by the reproducing element attached to the same slider.
Furthermore, recording and retrieving of information are performed in the memory area that has been made by physically subdividing the magnetic disk recording surface. For instance, reading and writing are performed on an circular memory area 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 retrieving of information. A head testing device that records or retrieves 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 a conventional head testing device
10
is shown in
FIG. 1A
, and a side view of the same head testing device
10
is shown in FIG.
1
B. Head testing device
10
in
FIGS. 1A and 1B
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
horizontally with respect to reference table
11
, head loading mechanism (HLM)
14
that positions piezo stage
13
perpendicularly with respect to reference table
11
, stage
15
anchored above reference table
11
that coarse-positions HLM
14
horizontally with respect to reference table
11
, and disk rotating device drive
50
anchored above 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
is rotated around its axis using motor
52
.
Cassette
30
has head holding part
31
that holds head
20
, connector
32
, support
33
that is connected to carriage
12
by connector
32
and supports head holding part
31
, and amplifier
35
that is connected to head
20
via signal line
34
and processes electrical signals transmitted to and received from head
20
. Cassette
30
can be disconnected from the head testing device as needed because it has connector
32
and therefore, the heads that are the subject of tests performed by the head testing device can be replaced as needed when heads are loaded on each cassette.
Moreover, although not illustrated, in addition to the above-mentioned structural elements, head testing device
10
has external arithmetic and control unit M and input-output unit P. Arithmetic and control unit M controls stage
15
, HLM
14
, piezo stage
13
and disk rotating device drive
50
based on commands that are input by the user through input-output unit P, and further, is connected to amplifier
35
and transmits and receives electrical signals to and from amplifier
35
in order to process and analyze the electrical signals that are transmitted and received, etc. In addition, the analysis results and operating status, etc., are further input to input-output unit P and communicated to the user as needed.
A summary of the effects of the above-mentioned structure is as follows: Piezo positioner or stage
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 above 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: the track average amplitude (TAA), which is the average amplitude of retrieving signals that are output from the head; the track profile (TP) representing the distribution of TAAs relative to displacement from the track center line (TCL) within a track; the overwrite (OW), which is represented by the attenuation factor of the lowest frequency signals (LF signals hereafter) when the highest frequency signals (HF signals hereafter) are overwritten on LF recorded on a magnetic disk; the bit error rate (BER); etc. The intensity of the magnetic field generated by the magnetic information that has been written on the magnetic disk changes with the position of the head within a track. Consequently, the head positioning accuracy (positioning accuracy hereafter) in the direction of track width above the magnetic disk has a strong effect on the measurement accuracy of the test items when evaluating the above- mentioned test items. Particularly high head-positioning accuracy is needed in BER tests, etc., because determination time is long in comparison to the other test items.
Nevertheless, it has become difficult to achieve the head-positioning accuracy that is now required with the progress that has been made in HDD technology. The reason for this is that signals that are transmitted to and received from the head have become faster as a result of the recent increase in the data transmission speed of the HDD. The amplifier of the head testing device must be placed near the head in order to control the attenuation of faint signals from the head, and there are many cases where the amplifier is loaded on the cassette. However, the amplifier begins to generate heat at the same time when the measurements are started. Therefore, the dimensions of the cassette change as it expands when exposed to the heat generated by the amplifier. As a result, the head slips (drifts hereafter) from the predetermined position within the determination track and there is a marked compromise of measurement reliability.
A cross section of cassette
30
is shown in FIG.
2
. It is an e
Kita Toshiki
Mihara Takahisa
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