# US 8,787,125 B1 · Disk drive calibrating fly height actuator to enable laser biasing during non-write mode > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,125 B1 - Document ID: US8787125B1 - Status: Granted - Kind: B1 - Application number: 13/802,583 - Filed: 2013-03-13 - Granted: 2014-07-22 - Earliest claimed: 2013-03-13 - Assignees: Western Digital Technologies, Inc. - Applicants: Western Digital Technologies, Inc. - Inventors: Tehri S. Lee - Web page: https://patentgrep.com/patent/US8787125B1 ## CPC - G11B 5/607: {using thermal means} - G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence) - G11B 5/5534: {Initialisation, calibration, e.g. cylinder "set-up"} - G11B 5/6058: {using piezoelectric means} - G11B 2005/0021: {Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal} - 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 A disk drive is disclosed comprising a disk, a head comprising a laser operable to heat the disk while writing data to the disk, and a fly height actuator (FHA) operable to actuate the head vertically over the disk. A setting is applied to the FHA to maintain a fly height of the head. An approximately zero bias laser power is applied to the laser during a non-write mode, and a first write laser power is calibrated during a write mode. A non-zero bias laser power is applied to the laser during the non-write mode, and a second write laser power is calibrated during the write mode. When the second write laser power is different than the first write laser power, the setting of the FHA is adjusted to adjust the fly height of the head. ## Claims ### Claim 1 A disk drive comprising: a disk; a head comprising a laser operable to heat the disk while writing data to the disk; a fly height actuator (FHA) operable to actuate the head vertically over the disk; and control circuitry operable to: apply a setting to the FHA to maintain a fly height of the head; apply a zero bias laser power to the laser during a non-write mode and calibrate a first write laser power during a write mode; apply a non-zero bias laser power to the laser during the non-write mode and calibrate a second write laser power during the write mode; and when the second write laser power is different than the first write laser power, adjust the setting of the FHA to adjust the fly height of the head. ### Claim 2 (depends on 1) The disk drive as recited in claim 1, wherein the control circuitry is further operable to adjust the setting of the FHA to adjust the fly height of the head until the second write laser power substantially matches the first write laser power. ### Claim 3 (depends on 1) The disk drive as recited in claim 1, wherein prior to applying the non-zero bias laser power to the laser, the control circuitry is further operable to adjust the setting to the FHA to increase the fly height of the head. ### Claim 4 (depends on 1) The disk drive as recited in claim 1, wherein the non-zero bias laser power reduces a turn-on time of the laser at a beginning of the write mode. ### Claim 5 (depends on 1) The disk drive as recited in claim 1, wherein the non-zero bias laser power causes the head to protrude toward the disk thereby reducing the fly height. ### Claim 6 (depends on 1) The disk drive as recited in claim 1, wherein the control circuitry is operable to calibrate the first and second laser powers based on a target quality metric. ### Claim 7 (depends on 1) The disk drive as recited in claim 1, wherein the control circuitry is operable to calibrate the first setting applied to the FHA by calibrating a touchdown setting applied to the FHA that causes the head to contact the disk. ### Claim 8 (depends on 1) The disk drive as recited in claim 1, wherein the setting of the FHA comprises a substantially constant value during at least part of the non-write mode. ### Claim 9 (depends on 8) The disk drive as recited in claim 8, wherein the control circuitry is further operable to adjust the setting of the FHA preceding the write mode to lower the fly height during a pre-heat interval. ### Claim 10 (depends on 8) The disk drive as recited in claim 8, wherein the control circuitry is further operable to adjust the setting of the FHA at a beginning of the write mode to compensate for a heating effect of the write laser power. ### Claim 11 (depends on 1) The disk drive as recited in claim 1, wherein when the second write laser power is different than the first write laser power, the control circuitry is operable to adjust the setting of the FHA to adjust the fly height of the head based on a difference between the second write laser power and the first write laser power. ### Claim 12 (depends on 1) The disk drive as recited in claim 1, wherein the non-zero bias laser power applied to the laser during the non-write mode does not significantly reduce a coercivity of the disk. ### Claim 13 (depends on 1) The disk drive as recited in claim 1, wherein the non-zero bias laser power applied to the laser during the non-write mode is approximately fifty percent of the first write laser power. ### Claim 14 A method of operating a disk drive comprising a disk, a head comprising a laser operable to heat the disk while writing data to the disk, and a fly height actuator (FHA) operable to actuate the head vertically over the disk, the method comprising: applying a setting to the FHA to maintain a fly height of the head; applying zero bias laser power to the laser during a non-write mode and calibrate a first write laser power during a write mode; applying a non-zero bias laser power to the laser during the non-write mode and calibrate a second write laser power during the write mode; and when the second write laser power is different than the first write laser power, adjusting the setting of the FHA to adjust the fly height of the head. ### Claim 15 (depends on 14) The method as recited in claim 14, further comprising adjusting the setting of the FHA to adjust the fly height of the head until the second write laser power substantially matches the first write laser power. ### Claim 16 (depends on 14) The method as recited in claim 14, wherein prior to applying the non-zero bias laser power to the laser, further comprising adjusting the setting to the FHA to increase the fly height of the head. ### Claim 17 (depends on 14) The method as recited in claim 14, wherein the non-zero bias laser power reduces a turn-on time of the laser at a beginning of the write mode. ### Claim 18 (depends on 14) The method as recited in claim 14, wherein the non-zero bias laser power causes the head to protrude toward the disk thereby reducing the fly height. ### Claim 19 (depends on 14) The method as recited in claim 14, further comprising calibrating the first and second laser powers based on a target quality metric. ### Claim 20 (depends on 14) The method as recited in claim 14, further comprising calibrating the first setting applied to the FHA by calibrating a touchdown setting applied to the FHA that causes the head to contact the disk. ### Claim 21 (depends on 14) The method as recited in claim 14, wherein the setting of the FHA comprises a substantially constant value during at least part of the non-write mode. ### Claim 22 (depends on 21) The method as recited in claim 21, further comprising adjusting the setting of the FHA preceding the write mode to lower the fly height during a pre-heat interval. ### Claim 23 (depends on 21) The method as recited in claim 21, further comprising adjusting the setting of the FHA at a beginning of the write mode to compensate for a heating effect of the write laser power. ### Claim 24 (depends on 14) The method as recited in claim 14, wherein when the second write laser power is different than the first write laser power, further comprising adjusting the setting of the FHA to adjust the fly height of the head based on a difference between the second write laser power and the first write laser power. ### Claim 25 (depends on 14) The method as recited in claim 14, wherein the non-zero bias laser power applied to the laser during the non-write mode does not significantly reduce a coercivity of the disk. ### Claim 26 (depends on 14) The method as recited in claim 14, wherein the non-zero bias laser power applied to the laser during the non-write mode is approximately fifty percent of the first write laser power.