VCM PWM to linear mode transition offset optimization to improve PES

Patent metadata

Field	Value
Publication number	US-12254909-B2
Application number	US-202318446612-A
Country	US
Kind code	B2
Filing date	Aug 9, 2023
Priority date	May 11, 2022
Publication date	Mar 18, 2025
Grant date	Mar 18, 2025

Abstract

Various illustrative aspects are directed to a data storage device comprising one or more disks, an actuator arm assembly comprising one or more disk heads and a voice coil motor (VCM), the VCM configured to operate in a PWM mode and a linear mode, and one or more processing devices configured to: seek the VCM towards a target track in the PWM mode; transition the VCM from the PWM mode to the linear mode, wherein the transitioning comprises switching an offset compensation value from a first offset compensation value to a second compensation offset value to compensate for a transition offset induced while transitioning the VCM from the PWM to the linear mode, wherein the first and the second offset compensation values correspond to the PWM and linear modes, respectively, and seek the VCM towards the target track in the linear mode for a linear mode time.

First claim

What is claimed is:

1. A data storage device comprising:
one or more disks;
an actuator arm assembly comprising one or more disk heads and a voice coil motor (VCM), the VCM configured to operate in a first mode and a second mode, the first mode and the second mode each comprising one of a pulse width modulation (PWM) mode and a linear or current control loop (CCL) mode, the first mode being different from the second mode; and
one or more processing devices or components, configured, individually or in combination, to:
perform a calibration routine, wherein performing the calibration routine comprises:
identifying a mapping between offset compensation values and a track arrival position error signal (PES), wherein each offset compensation value translates to a current offset applied to the VCM in the first mode or the second mode;
and wherein the mapping is identified by one or more of:
measuring the track arrival PES for one or more of different seek lengths and different directions, the directions selected from a group consisting of an inner diameter (ID) to an outer diameter (OD) direction and an OD to ID direction;
measuring the track arrival PES for different offset compensation values after seek completion; and
incrementally reducing a linear mode time and measuring a corresponding track arrival PES.

2. The data storage device of claim 1 , wherein the one or more processing devices or components are further configured, individually or in combination, to:
determine an optimal offset compensation value, wherein the optimal offset compensation value corresponds to a lowest track arrival PES measured while measuring the track arrival PES for different offset compensation values after seek completion.

3. The data storage device of claim 1 , wherein incrementally reducing the linear mode time and measuring the corresponding track arrival PES comprises:
determining an optimal offset compensation value, wherein the optimal offset compensation value corresponds to a lowest track arrival PES measured while measuring the track arrival PES for different offset compensation values after seek completion;
setting an initial linear mode time for operating the VCM in the second mode, wherein the second mode comprises the linear or CCL mode;
decreasing the linear mode time by an interval amount; and
measuring the corresponding track arrival PES after each decrease in the linear mode time to identify an optimal linear mode time corresponding to a minimal or no increase in the track arrival PES.

4. The data storage device of claim 1 , wherein the one or more processing devices or components are further configured, individually or in combination, to:
set an initial linear mode time for operating the VCM in the second mode, the second mode comprising the linear mode;
set an initial offset compensation value;
adjust one or more of the initial linear mode time and the initial offset compensation value and measure the corresponding track arrival PES to determine an optimal linear mode time and offset compensation value combination for optimizing the track arrival PES; and
calibrate firmware to utilize the optimal linear mode time and offset compensation value combination during seek operations.

5. The data storage device of claim 1 , wherein identifying the mapping further comprises:
identifying a mapping of transition current offsets with respect to one or more of PWM frequencies, slew rates, and linear mode time for different current levels applied to the VCM.

6. The data storage device of claim 1 , wherein each offset compensation value corresponds to a trimming value for trimming a current sense amplifier (CSA) offset, and wherein the one or more processing devices or components are further configured, individually or in combination, to:
trim the CSA offset to generate the current offset applied to the VCM to compensate for a transition current offset, wherein the transition current offset corresponds to a steady-state offset or error between the first and the second modes.

7. A method of operating a data storage device, comprising:
performing a calibration routine to identify a mapping between offset compensation values and a track arrival position error signal (PES) for a voice coil motor (VCM) of the data storage device, wherein the VCM is configured to operate in a pulse width modulation (PWM) mode and a linear or current control loop (CCL) mode, and wherein identifying the mapping comprises at least:
measuring the track arrival PES for one or more of different seek lengths and different directions, the directions selected from a group consisting of an inner diameter (ID) to an outer diameter (OD) direction and an OD to ID direction;
measuring the track arrival PES for different compensation values after seek completion; and
incrementally reducing a linear mode time and measuring a corresponding track arrival PES.

8. The method of claim 7 , further comprising:
determining an optimal offset compensation value, wherein the optimal offset compensation value corresponds to a lowest track arrival PES measured while measuring the track arrival PES for different offset compensation values.

9. The method of claim 7 , wherein incrementally reducing the linear mode time and measuring the corresponding track arrival PES comprises:
determining an optimal offset compensation value, wherein the optimal offset compensation value corresponds to a lowest track arrival PES measured while measuring the track arrival PES for different offset compensation values;
setting an initial linear mode time for operating the VCM in the linear or CCL mode;
decreasing the linear mode time by an interval amount; and
measuring the corresponding track arrival PES after each decrease in the linear mode time to identify an optimal linear mode time corresponding to a minimal or no increase in the track arrival PES.

10. The method of claim 7 , further comprising:
setting an initial linear mode time for operating the VCM in the linear or CCL mode;
setting an initial offset compensation value; and
determining an optimal linear mode time and offset compensation value combination for optimizing the track arrival PES, based at least in part on:
adjusting one or more of the initial linear mode time and the initial offset compensation value and measuring the corresponding track arrival PES.

11. The method of claim 10 , further comprising:
calibrating firmware (FW) of the data storage device, based at least in part on determining the optimal linear mode time and offset compensation value combination; and
utilizing the optimal linear mode time and offset compensation value combination for one or more subsequent seek operations, based at least in part on calibrating the FW.

12. The method of claim 7 , wherein identifying the mapping further comprises:
identifying a mapping of transition current offsets with respect to one or more of PWM frequencies, slew rates, and linear mode times for different current levels applied to the VCM.

13. The method of claim 7 , wherein each offset compensation value corresponds to a trimming value for trimming a current sense amplifier (CSA) offset, and wherein the method further comprises:
trimming the CSA offset to generate the current offset applied to the VCM.

14. The method of claim 13 , wherein:
the current offset compensates for a transition current offset; and
the transition current offset corresponds to a steady-state offset or error between the PWM mode and the linear or CCL mode.

15. The method of claim 14 , wherein the transition current offset between the PWM mode and

Assignees

• Western Digital Tech Inc

Inventors

• Byoun Jaesoo
• Johnson Brian
• Ito Hideaki
• Ikedo Gaku
• Kagami Naoyuki

Classifications

• G11B5/5543

  servo-format therefor · CPC title

• G11B5/5547 Primary

  "Seek" control and circuits therefor (G11B5/5556 takes precedence) · CPC title