# US 8,542,454 B2 · Magnetic reading and writing device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,542,454 B2 - Document ID: US8542454B2 - Status: Granted - Kind: B2 - Application number: 13/271,176 - Filed: 2011-10-11 - Published: 2012-07-12 - Granted: 2013-09-24 - Earliest claimed: 2011-01-06 - Assignees: Fuji Electric Co., Ltd. - Applicants: Takashi Hayashi - Inventors: Takashi Hayashi - Web page: https://patentgrep.com/patent/US8542454B2 ## CPC - G11B 5/6029: {Measurement using values derived from the data signal read from the disk} - G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence) - G11B 5/607: {using thermal means} - G11B 27/36: Monitoring, i.e. supervising the progress of recording or reproducing {(for digital recording G11B20/00 and s.gr.; for monitoring, testing or measuring of TV recorders of the type covered by H04N5/76 and subgroups, see H04N17/06)} - G11B 20/10388: {control of the read or write heads, e.g. tracking errors, defocus or tilt compensation} - G11B 2005/001: {Controlling recording characteristics of record carriers or transducing characteristics of transducers by means not being part of their structure} - G11B 2220/2516: Hard disks - 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 In a magnetic reading/writing device, a controller derives at each radius of a recording medium a slope of a curve of track-averaged write performance with respect to an adjustment parameter, and determines a first set of fitting coefficients of a first equation approximating the derived slopes in terms of a first variable representing each radius. The controller acquires write performance dependence on a variable representing each of multiple circumferential positions of the medium by measuring track average write performance with respect to the circumferential positions, and determines a second set of fitting coefficients to approximate by a periodic function the acquired dependence in terms of the first variable. The controller corrects a condition value representing the adjustment parameter by subtracting from the condition value an adjustment value obtained from functions calculated with the first and second sets of fitting coefficients. ## Claims ### Claim 1 A magnetic reading and writing device, comprising: a magnetic head for performing a magnetic reading/writing and a flying height control; a magnetic recording medium from and on which the reading/writing is performed by the magnetic head; nonvolatile memory which stores a set of condition values at each radius of a plurality of radii of the medium, the stored condition values being selected such that a recording density is maximized at each radius; first means for deriving, at each radius, a respective slope of a curve of track-averaged write performance with respect to an adjustment parameter, for determining a first set of fitting coefficients of a first equation approximating the derived slopes in terms of a first variable representing each radius, and for storing the first set of fitting coefficients in the memory; second means for acquiring write performance dependence on a second variable representing each of a plurality of circumferential positions of the medium by measuring, under a condition set by the stored set of condition values at each radius, track average write performance with respect to the plurality of circumferential positions, for determining a second set of fitting coefficients to approximate by a periodic function the acquired dependence in terms of the first variable, and for storing the determined second set of fitting coefficients in the memory; and correction means for correcting a condition value among the stored condition values at a particular radius, which is a value representing the adjustment parameter, by subtracting from the condition value an adjustment value obtained from a first function and a second function that are respectively calculated with the first and second sets of fitting coefficients. ### Claim 2 (depends on 1) The magnetic reading and writing device according to claim 1, wherein the adjustment value is the ratio of a shift value at the particular radius and a particular circumferential position, to a slope value obtained from the first function at the particular radius, the shift value being the difference between a track-averaged performance value at the particular radius and a local write performance value obtained from the second function at the particular radius and the particular circumferential position. ### Claim 3 (depends on 1) The magnetic reading and writing device according to claim 1, wherein the set of condition values includes values representing a write current, a track pitch, a linear recording density and a flying height control heater power. ### Claim 4 (depends on 1) The magnetic reading and writing device according to claim 1, wherein the adjustment parameter is a write current. ### Claim 5 (depends on 1) The magnetic reading and writing device according to claim 1, wherein the adjustment parameter is a flying height control heater power. ### Claim 6 (depends on 1) The magnetic reading and writing device according to claim 1, wherein the second set of fitting coefficients is a set of fitting coefficients of a second equation approximating a relation between a set of coefficients of the periodic function and the first variable. ### Claim 7 (depends on 6) The magnetic reading and writing device according to claim 6, wherein the first and second equations are polynomial equations. ### Claim 8 (depends on 7) The magnetic reading and writing device according to claim 7, wherein the respective degree of the first and second polynomial equations is greater than or equal to 3 and smaller than or equal to 5. ### Claim 9 A controller for optimizing condition values of a magnetic reading and writing device that includes a magnetic head for performing a magnetic reading/writing and a flying height control and a magnetic recording medium from and on which the reading/writing is performed by the magnetic head, the controller comprising: storing means for storing in a nonvolatile memory a set of condition values at each radius of a plurality of radii of the medium, the stored condition values being selected such that a recording density is maximized at each radius; first means for deriving, at each radius, a respective slope of a curve of track-averaged write performance with respect to an adjustment parameter, for determining a first set of fitting coefficients of a first equation approximating the derived slopes in terms of a first variable representing each radius, and for storing the first set of fitting coefficients in the memory; second means for acquiring write performance dependence on a second variable representing a plurality of circumferential positions of the medium by measuring, under a condition set by the stored set of condition values at each radius, track average write performance with respect to the plurality of circumferential positions, for determining a second set of fitting coefficients to approximate by a periodic function the acquired dependence in terms of the first variable, and for storing the determined second set of fitting coefficients in the memory; and correction means for correcting a condition value among the stored condition values at a particular radius, which is a value representing the adjustment parameter, by subtracting from the condition value an adjustment value obtained from a first function and a second function that are respectively calculated with the first and second sets of fitting coefficients. ### Claim 10 (depends on 9) The controller according to claim 9, wherein the adjustment value is the ratio of a shift value at the particular radius and a particular circumferential position, to a slope value obtained from the first function at the particular radius, the shift value being the difference between a track-averaged performance value at the particular radius and a local write performance value obtained from the second function at the particular radius and the particular circumferential position. ### Claim 11 (depends on 9) The controller according to claim 9, wherein the set of condition values includes values representing a write current, a track pitch, a linear recording density and a flying height control heater power. ### Claim 12 (depends on 9) The controller according to claim 9, wherein the adjustment parameter is a write current. ### Claim 13 (depends on 9) The controller according to claim 9, wherein the adjustment parameter is a flying height control heater power. ### Claim 14 (depends on 9) The controller according to claim 9, wherein the second set of fitting coefficients is a set of fitting coefficients of a second equation approximating a relation between a set of coefficients of the periodic function and the first variable. ### Claim 15 (depends on 14) The controller according to claim 14, wherein the first and second equations are polynomial equations. ### Claim 16 (depends on 15) The controller according to claim 15, wherein the respective degree of the first and second polynomial equations is greater than or equal to 3 and smaller than or equal to 5.