Dynamic magnetic information storage or retrieval – Checking record characteristics or modifying recording...
Reexamination Certificate
2001-10-30
2004-11-30
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
Checking record characteristics or modifying recording...
C360S031000, C360S046000, C360S051000, C360S078120, C360S078090
Reexamination Certificate
active
06826002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring method for use in a recording unit including a circular recording medium, in particular, to a measuring apparatus and a measuring method for measuring performance characteristics of a recording unit including a circular recording medium such as a hard disk, a floppy disk or an optical disk such as CD, DVD, a magneto-optical disk (of ROM, write once type, rewriting type), or the like, and components such as a head for recording a data signal on the above recording medium, and the like.
2. Description of the Prior Art
Upon testing either a fixed type magnetism fixture magnetic disk drive unit (referred to as a hard disk unit hereinafter) for driving a hard disk, the above hard disk, or a magnetic head, there is the practice of evaluating the performance characteristics of the above hard disk, the disk drive unit and the circuit therefor, and the testing process includes the following steps:
(a) inserting a spindle into a center hole of the hard disk and supporting the magnetic head so as to electromagnetically couple the magnetic head with the surface of the hard disk in a non-contact manner;
(b) executing either a data writing process or a data reading process on the hard disk by means of the magnetic head while rotating the spindle by means of a spindle motor; and
(c) evaluating the performance characteristics of the hard disk unit including the hard disk.
As performance evaluation items the following ones can be enumerated. The performance evaluation items include the following:
(a) track average signal amplitude (Track Averaged Amplitude: referred to as a TAA hereinafter);
(b) asymmetry of a signal amplitude;
(c) pulse width (PW);
(d) asymmetry of a pulse width;
(e) base line;
(i) non-linear type bit shift amount (Non-linear Transition bit Shift: NLTS);
(g) overwrite characteristic (OverWrite: OW);
(h) bit error rate (Bit Error Rate: BER);
(i) margin, and so on.
When evaluating the performance of a hard disk, it is required to set parameters for measurement, and the parameters include the following:
(a) position of a magnetic head (referred to as a head position hereinafter);
(b) head angle (skew);
(c) spindle rotation speed;
(d) signal frequency;
(e) write data pattern;
(f) write current amount;
(g) write compensation amount (concretely, an amount of compensation for compensating for the write change timing);
(h) MR (Magnetic Resistance) head bias current, and so on.
In this case, the signal frequency, the write data pattern, the write current amount, the write compensation amount, the head position and the MR head bias current are write parameters for the hard disk, while the head position, the head angle and the MR head bias current are read parameters for the hard disk.
A procedure in measuring the above evaluation items has a sequence of parameter setting, writing onto a disk, reading out and evaluating the characteristics of the read signal. Conventionally, it has been a common practice to obtain a parameter dependency of the measured values of the evaluation items by changing set values of the above-mentioned parameters in small steps and repetitively executing a similar measurement. According to the conventional technique, such a measurement has been executed by writing data with one fixed parameter for one rotation of the disk when the spindle is rotated by one turn, and reading out the written data during another turn, thereby obtaining the measurement data for one point. By repeating this sequence a plurality of times while changing the parameter, a graph is obtained according to the measuring method based on the conventional technique (referred to as a first prior art hereinafter). That is, according to the conventional technique, one parameter has been set per one round of the track.
There is sometimes such a case that the state of a read element is disadvantageously changed by a magnetic field in the writing stage, then consequently this leads to an unstable characteristic (referred to as instability hereinafter). This phenomenon may be a kind that occurs only once per several times or another kind that occurs as a variation measurement. Therefore, in measuring such a characteristic it is a common practice to repeat the write and read operations many times, and then statistically evaluate the measured values of read signals. When measuring the above-mentioned instability by a conventional technique (referred to as a second prior art hereinafter), static data including the average value and variance of the measured value data are obtained by executing a plurality of times, a process including the steps of, first of all, writing desired data on the whole track of the disk, writing data which will be abandoned for a part of the track, and thereafter reading out the data on the rest of the track.
The above-mentioned prior art measuring method and measuring apparatus have had such a problem that the measuring time is relatively long.
Furthermore, when executing the measurement by switching the measurement item upon evaluating the performance characteristics of a hard disk, it takes much measuring time according to the prior art methods in an attempt at viewing the influences on the parameters requiring a significantly long time for convergence. As the parameters requiring a significantly long time for convergence, there can be enumerated the frequency, the head position and so on. For example, a relationship between the head position and the read signal amplitude is shown, where the relationship is called the track profile. Such a measurement (referred to as a third prior art hereinafter) takes a long time for moving the head position as compared with that of the rotation of the spindle, and this leads to such a problem that the measuring time is elongated.
In order to solve the above-described problems, the Japanese patent laid-open publication No. 11-053701 discloses, for example, a measuring apparatus for use in a recording unit for measuring performance characteristics of the recording unit including a record medium on which one track is divided into a plurality of sectors, where the measuring apparatus can measure performance characteristics at a speed higher than that of the prior art, by writing a write signal with a write parameter value changed for respective sectors, by reading out the written write signal, with predetermined read parameters for respective sectors, and by measuring the read-out write signal as a read signal.
Recently, a magnetic head in which a micro actuator (MA) is mounted as a new technology for higher concentration of the recording density of a hard disk has come into practical use. A magnetic head is mounted at the tip of a suspension, where the magnetic head is constituted by a slider
4
c
, a write element
4
a
and a read element (MR element)
4
b
, as shown in
FIG. 21. A
conventional system where these elements are moved together with the suspension for following the track cannot be no longer untreatable in the system having narrower tracks. Therefore, as shown in
FIGS. 16 and 17
, such an idea has been proposed that a small actuator which is called a micro actuator (MA)
6
is mounted at the tip of the suspension (or it may be provided at the root of the suspension) so as to facilitate following of the track by moving only the magnetic head
4
.
It has become necessary for manufactures of the magnetic head
4
to measure the performance of the micro actuator
6
in addition to the characteristics of the conventional magnetic head
4
itself. As a typical measurement item, there is a static operational characteristic, and in order to obtain the characteristic, a relationship between a movement distance and a control voltage is measured by applying a control voltage Vc to the micro actuator
6
to determine the amount of distance by which the magnetic head
4
has moved, as shown in
FIG. 18. A
method for measuring the movement distance X of the micro actuator
6
according to a prior art therefor will b
Agilent Technologie,s Inc.
Faber Alan T.
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