# US 2021/0280210 A1 · Magnetic disk device

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- Number: US 2021/0280210 A1
- Document ID: US20210280210A1
- Status: Published application
- Kind: A1
- Application number: 16/935,494
- Filed: 2020-07-22
- Published: 2021-09-09
- Earliest claimed: 2020-03-05
- Assignees: Kabushiki Kaisha Toshiba; Toshiba Electronic Devices & Storage Corporation
- Applicants: Kabushiki Kaisha Toshiba; Toshiba Electronic Devices & Storage Corporation
- Inventors: Takuji Matsuzawa
- Web page: https://patentgrep.com/patent/US20210280210A1

## CPC

- G11B 5/5573: {Details of the magnetic circuit, e.g. of actuators}
- G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence)
- G11B 5/4873: {the arm comprising piezoelectric or other actuators for adjustment of the arm}
- G11B 5/82: Disk carriers
- G11B 5/5552: {using fine positioning means for track acquisition separate from the coarse (e.g. track changing) positioning means}
- G11B 5/5556: {with track following after a "seek"}
- G11B 5/556: {control circuits therefor}
- G11B 5/5578: {Multiple actuators addressing the same disk, e.g. to improve data rate or access rate}
- G11B 5/5586: {Minimising seek noise, e.g. actuator noise}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

According to one embodiment, a magnetic disk device includes a magnetic disk, a magnetic head, a first actuator that moves the magnetic head to a predetermined position on the magnetic disk, a second actuator that is provided in the first actuator and adjusts a position of the magnetic head, a control unit that controls operations of the first actuator and the second actuator, and a storing unit that stores a coefficient of an approximation polynomial calculated based on an approximation formula for approximating voltage dependency of a gain of the second actuator. When controlling the operation of the second actuator, the control unit calculates the gain amplitude of the second actuator from the approximation polynomial in which the coefficient is used and amplitude of a voltage input to the second actuator.

## Claims

### Claim 1

(canceled)

### Claim 2

A magnetic disk device comprising:
a magnetic disk;
a magnetic head that reads data from and writes data in the magnetic disk;
a first actuator that moves the magnetic head to a predetermined position on the magnetic disk;
a second actuator that is provided in the first actuator and adjusts a position of the magnetic head;
a control unit that controls operations of the first actuator and the second actuator, and
a storing unit that stores a first coefficient of an approximation polynomial calculated based on an approximation formula for approximating voltage dependency of a first gain of the second actuator, wherein
when controlling the operation of the second actuator, the control unit calculates the first gain of the second actuator from the approximation polynomial in which the first coefficient stored in the storing unit is used, a second coefficient of an odd number times angle of a sine wave when an output of the second actuator calculated from an input sine wave voltage is represented as a sum of odd numbers times angle of a fundamental frequency of the sine wave, and a desired displacement of the second actuator.

### Claim 3 (depends on 2)

The magnetic disk device according to claim 2, wherein
the control unit represents the output of the second actuator as a sum of odd numbers times angle of a fundamental frequency of the sine wave voltage, and
when the odd numbers are represented as 2k+1, where k is 0, 1, 2, . . . ,
calculates the first gain by adding up all the second coefficients of the odd numbers times angle when k is an even number or subtracting all the second coefficients when k is an odd number.

### Claim 4 (depends on 2)

The magnetic disk device according to claim 2, wherein the first coefficient is calculated from a plurality of second gains by measuring the first gain of the second actuator by the discrete Fourier transform at a number of measurement points greater than a degree of the approximation polynomial and the second coefficient of a sine wave fundamental frequency of the output of the second actuator as a sum of odd numbers times angle of a fundamental frequency of the sine wave voltage.

### Claim 5

(canceled)