# US 8,786,978 B2 · Magnetic disk device and method of controlling head position > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,786,978 B2 - Document ID: US8786978B2 - Status: Granted - Kind: B2 - Application number: 13/473,365 - Filed: 2012-05-16 - Published: 2013-08-01 - Granted: 2014-07-22 - Earliest claimed: 2012-01-31 - Assignees: Kabushiki Kaisha Toshiba - Applicants: Shinsuke Akiya - Inventors: Shinsuke Akiya - Web page: https://patentgrep.com/patent/US8786978B2 ## CPC - G11B 5/59627: {Aligning for runout, eccentricity or offset compensation (G11B5/5534, G11B5/59677, G11B5/59688 take precedence)} - 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 reference head select module selects any one of magnetic heads as a reference head; a follow-up controller executes a follow-up control of a trajectory of the reference head based on a signal read by the reference head; and an eccentric controller executes an eccentric control of a trajectory of a magnetic head other than the reference head in order that an eccentric error between the trajectory of the reference head and the trajectory of the corresponding magnetic head is close to zero. ## Claims ### Claim 1 A magnetic disk device comprising: at least one magnetic disk; a plurality of magnetic heads for a disk surface of each magnetic disk; a reference head select module configured to select any one of the magnetic heads as a reference head; a follow-up controller configured to execute a follow-up control of a trajectory of the reference head based on a signal read by the reference head; and an eccentric control unit configured to execute an eccentric control of a trajectory of a magnetic head other than the reference head, causing an eccentric error between the trajectory of the reference head and the trajectory of the corresponding magnetic head to be effectively zero, wherein a read post code for the reference head is deleted so as to decrease a length of a servo gate for the reference head by a length corresponding to the deleted read post code. ### Claim 2 (depends on 1) The magnetic disk device of claim 1, further comprising: a repeatable runout (RRO) corrector configured to correct a repeatable runout based upon the read post code. ### Claim 3 (depends on 1) The magnetic disk device of claim 1, wherein a coefficient of a virtual-circle control of the magnetic head is acquired, and the trajectory of eccentric control for the magnetic head other than the reference head is acquired by subtracting the coefficient of the virtual-circle control of the magnetic head other than the reference head from the coefficient of the virtual-circle control of the reference head. ### Claim 4 (depends on 3) The magnetic disk device of claim 3, wherein the coefficient of the virtual-circle control of the magnetic head is obtained for each zone. ### Claim 5 A magnetic disk device comprising: at least one magnetic disk; a plurality of magnetic heads for a disk surface of each magnetic disk; a reference head select module configured to select any one of the magnetic heads as a reference head; a self-servo write controller configured to write a servo pattern on the respective disk surfaces using the respective magnetic heads; a first follow-up controller configured to execute a follow-up control of a trajectory of the reference head based on a signal read by the reference head; and a second follow-up controller configured to execute, for the magnetic head other than the reference head, a follow-up control of a trajectory of the magnetic head that is on a bank same as the bank of the reference head, wherein a read post code for the reference head and the magnetic heads other than the reference head is deleted so as to decrease a length of a servo gate for the reference head and the magnetic heads other than the reference head by a length corresponding to the deleted read post code. ### Claim 6 A method of controlling a head position comprising: selecting any one of magnetic heads provided for a disk surface of each magnetic disk as a reference head; executing a follow-up control of a trajectory of the reference head based upon a signal read by the reference head; and executing an eccentric control of a trajectory of a magnetic head other than the reference head, causing an eccentric error between the trajectory of the reference head and the trajectory of the corresponding magnetic head to be effectively zero, wherein a read post code for the reference head is deleted so as to decrease a length of a servo gate for the reference head by a length corresponding to the deleted read post code. ### Claim 7 (depends on 6) The method of controlling the head position of claim 6, wherein a repeatable runout is corrected based upon the read post code. ### Claim 8 (depends on 6) The method of controlling the head position of claim 6, wherein a coefficient of a virtual-circle control of the magnetic head is acquired, and the trajectory of eccentric control for the magnetic head other than the reference head is acquired by subtracting the coefficient of the virtual-circle control of the magnetic head other than the reference head from the coefficient of the virtual-circle control of the reference head. ### Claim 9 (depends on 8) The method of controlling the head position of claim 8, wherein the coefficient of the virtual-circle control of the magnetic head is obtained for each zone. ### Claim 10 A method of controlling a head position comprising: selecting any one of magnetic heads provided for a disk surface of each magnetic disk as a reference head; writing simultaneously a servo pattern for the magnetic heads on the disk surface by each of the magnetic heads; executing a follow-up control of a trajectory of the reference head based upon a signal read by the reference head; and executing, for the magnetic head other than the reference head, a follow-up control of a trajectory of the magnetic head that is on a bank same as the bank of the reference head, wherein a read post code for the reference head and the magnetic heads other than the reference head is deleted so as to decrease a length of a servo gate for the reference head and the magnetic heads other than the reference head by a length corresponding to the deleted read post code.