Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-12-11
2001-10-09
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053450
Reexamination Certificate
active
06301207
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an information storage device and a servo gain compensating method of compensating a servo gain when in a seek operation and in a positioning process in the information storage device for reading or reading/writing information from and to a storage medium by a head, and more particularly to an information storage device and a servo gain compensating method of setting a servo gain corresponding to a measured temperature.
2. Description of the Related Art
An information storage device such as a magnetic disk device, etc. has been widely utilized as a storage device of a computer, etc. This type of information storage device has a servo loop for driving an actuator in accordance with position signal read from the head.
A scatter in terms of characteristics of a magnet and a coil of a voice coil motor (VCM) for moving the magnetic head, might be a factor for causing problems in a loop gain of a servo control system. Further, the scatter in gain of a control loop system circuit of a power amplifier, etc. also leads to a scatter in the loop gain of the servo control system. The scatter in the characteristic of the VCM and the scatter in the gain of the control system circuit may be integrated and conceived as a scatter in a servo loop gain of the control system.
In the magnetic disk device, the servo control is executed by compensating the above scatter (a gain compensation) when in the seek operation and in the positioning process on a target track. This servo gain value changes depending on an environment temperature of the device, and hence there must be a necessity for compensating the servo gain at an interval of a fixed time (5 min-10 min).
A calibration seek may be a general method as the one described above. According to the calibration seek, a drive current having a fixed value flows to the VCM for a fixed period of time, thereby executing a seeking process of the VCM. This method is that when in this seeking process, a quantity of displacement is measured from the positional information of the magnetic head, and a servo gain is measured based on the quantity of displacement. According to this calibration seek method, a precise servo gain value at that point of time can be measured. However, the seek operation is carried out, during which there is a necessity for having a host request wait. Therefore, a technology of compensating the servo gain without having the host request wait is needed.
FIG. 7
is a diagram showing a construction in the prior art.
FIG. 8
is an explanatory diagram showing the prior art.
As illustrated in
FIG. 7
, a magnetic disk drive
91
includes a magnetic disk
92
and a magnetic head
90
. The magnetic disk
92
, on which a servo signal is recorded per sector, is rotated by a spindle motor
93
. The magnetic head
90
reads and writes information from and to the magnetic disk
91
.
The magnetic head
90
is moved in a track traversing direction on the magnetic disk
91
by a voice coil motor (VCM)
98
. A control circuit
96
detects a present position of the head in accordance with a position signal given from the magnetic head
90
, and generates a control value corresponding to a distance from a position to be sought.
For compensating scatters in characteristics of the VCM
98
and of the power amplifier
95
, the control value is multiplied by the servo gain value. A drive value is outputted to the power amplifier
95
, thereby driving the VCM
98
.
This servo gain value changes depending on the temperature. A parameter table stored with the servo gain values at the respective temperatures is therefore prepared. This parameter table is, as shown in
FIG. 8
, stored with the servo gain value at every temperature. Further, the magnetic disk drive
91
is provided with a temperature sensor
94
for detecting a temperature of the drive
91
.
In such a construction, the control circuit
96
periodically measures the temperature of the drive through the temperature sensor
94
. Then, the control circuit
96
obtains a servo gain from the measured temperature referring to the parameter table in the memory
97
. The servo control is executed based on this servo gain.
Thus, according to the prior art, the servo gain is compensated to a servo gain value corresponding to the temperature of the device without performing the calibration seek.
There arise, however, the following problems inherent in the prior art.
With downsizing of the magnetic disk device, the magnetic disk device is built in an electronic appliance such as a portable computer etc. In this case, the magnetic disk device receives heat from other units (such as, e.g., a host processor and a display unit) of the electronic appliance. These other units emit heat when operated but do not emit heat when not operated.
Therefore, the environment temperature of the magnetic disk device changes. The small-sized magnetic disk device has a small thermal capacity, and hence the temperature might change depending on the environment temperature. The temperature sensor measures the characteristics of the VCM and of the power amplifier from the temperature of the device. If the environment temperature changes abruptly, the characteristics of the VCM and of the power amplifier do not follow up the change in the temperature.
Accordingly, when using the servo gain in the table created on the assumption of the temperature change due to the emission of heat from the VCM and the power amplifier, the problem is that the servo gain can not be compensated to the servo gain value suited to the characteristics of the VCM and the power amplifier.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a servo gain compensating method in an information storage device, of making compensation to a precise servo gain.
It is another object of the present invention to provide a servo gain compensating method in an information storage device, of making compensation to a precise servo gain no matter how a temperature may change.
It is still another object of the present invention to provide a servo gain compensating method in an information storage device, of making compensation to a servo gain accurately coincident with characteristics of a VCM and of a power amplifier in accordance with a change in temperature.
According to a first aspect of the present invention, an information storage device comprises a storage medium, a head for reading information from the storage medium, an actuator for moving the head, a control circuit for generating a control quantity for positioning the head from positional information read from the storage medium by the head and calculating a drive quantity with the control quantity compensated by a servo gain value, and a driving circuit for driving the actuator based on the drive quantity.
And according to the first aspect of the present invention, a servo gain compensating method comprises a step of periodically measuring a temperature of the information storage device through a temperature detecting element for measuring the temperature of the information storage device, a step of judging whether or not a difference between the measured temperature and the temperature measured last time is over a fixed value, a first step of obtaining, if the difference is not over the fixed value, a servo gain value corresponding to the measured temperature with reference to a first table stored with a first servo gain characteristic, and a second step of obtaining, if the difference is over the fixed value, a servo gain value corresponding to the measured temperature with reference to a second table stored with a second servo gain characteristic.
According to the first aspect of the present invention, there are provided the first table stored with the servo gain at each temperature when the temperature does not change abruptly, and the second table stored with the servo gain at each temperature when the temperature changes abruptly. Then, it is judged whether or not the temperature
Abe Yukio
Isokawa Hiroshi
Fujitsu Limited
Greer Burns & Crain Ltd.
Huber Paul W.
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