Spindle speed control using feed-forward estimation in a hard disk drive

1. A method to reduce a range in variation of a target spin speed for a rotatable medium in a data storage device having a head operably associated with a rotary actuator, the method comprising:

rotating the rotatable medium at the target spin speed;

determining an initial position of the head relative to a surface of the rotatable medium;

determining a target position of the head relative to the surface of the rotatable medium;

determining an adjusted spin speed based at least in part on an approximately repeatable variation in the target spin speed due to motion of the rotary actuator in arranging the head between the initial position and the target position;

sending a signal to rotate the rotatable medium at the adjusted spin speed;

repositioning the head from the initial position to the target position; and

sending a signal to rotate the rotatable medium at the target spin speed.

2. A method to reduce a range in variation of a target spin speed for a rotatable medium in a data storage device, the method comprising:

rotating the rotatable medium at the target spin speed;

determining an initial position of a head relative to a surface of the rotatable medium;

determining a target position of the head relative to the surface of the rotatable medium;

determining an amount of initial drag at the initial position;

determining an amount of target drag at the target positions;

determining an adjusted spin speed based on the initial drag and the target drag;

sending a signal to rotate the rotatable medium at the adjusted spin speed;

repositioning the head from the initial position to the target position; and

sending a signal to rotate the rotatable medium at the target spin speed.

3. The method of claim 2 , wherein determining an adjusted spin speed further comprises calculating a net change in drag based on the initial drag and the target drag.

4. The method of claim 3 , wherein the adjusted spin speed is determined to compensate for the net change in drag.

5. The method of claim 1 , wherein determining an adjusted spin speed includes calculating the adjusted spin speed using an algorithm.

6. The method of claim 1 , wherein determining an adjusted spin speed includes obtaining the adjusted spin speed from a database.

7. A method to reduce a range in variation of a target spin speed for a rotatable medium in a data storage device, the method comprising:

rotating the rotatable medium at the target spin speed;

determining an initial position of a head relative to a surface of the rotatable medium;

determining a target position of the head relative to the surface of the rotatable medium;

determining a sequence of adjusted spin speeds based on the initial position and the target position;

sending a signal to rotate the rotatable medium through the sequence of adjusted spin speeds;

repositioning the head from the initial position to the target position; and

sending a signal to rotate the rotatable medium at the target spin speed.

8. The method of claim 1 , wherein determining an initial position of a head relative to a surface of the rotatable medium includes reading servo information from the surface of the rotatable medium with the head.

9. The method of claim 2 , wherein:

determining an amount of initial drag at the initial position includes accessing the initial drag from memory based on the initial position; and

determining an amount of target drag at the target position includes accessing the target drag from memory based on the target position.

10. A system to reduce a range in variation of a target spin speed for a rotatable medium in a data storage device having a head operably associated with a rotary actuator, the system comprising:

an actuator assembly including a head adapted to access the rotatable medium;

a processor having instruction to:

rotate the rotatable medium at the target spin speed;

determine an initial position of the head relative to a surface of the rotatable medium;

determine a target position of the head relative to the surface of the rotatable medium;

determining an adjusted spin speed based at least in part on an approximately repeatable variation in the target spin speed due to motion of the rotary actuator in arranging the head between the initial position and the target position;

send a signal to rotate the rotatable medium at the adjusted spin speed;

reposition the head from the initial position to the target position; and

send a signal to rotate the rotatable medium at the target spin speed.

11. A system to reduce a range in variation of a target spin speed for a rotatable medium in a data storage device, the system comprising:

an actuator assembly including a head adapted to access the rotatable medium;

a processor having instruction to:

rotate the rotatable medium at the target spin speed;

determine an initial position of a head relative to a surface of the rotatable medium;

determine a target position of the head relative to the surface of the rotatable medium;

determine an amount of initial drag at the initial position;

determine an amount of target drag at the target position;

determining an adjusted spin speed based on the initial drag and the target drag;

send a signal to rotate the rotatable medium at the adjusted spin speed;

reposition the head from the initial position to the target position; and

send a signal to rotate the rotatable medium at the target spin speed.

12. The method of claim 11 , wherein the instruction to determine an adjusted spin speed further includes an instruction to calculate a net change in drag based on the initial drag and the target drag.

13. The method of claim 12 , wherein the adjusted spin speed is determined to compensate for the net change in drag.

14. The method of claim 10 , wherein the instruction to determine an adjusted spin speed includes an instruction to calculate the adjusted spin speed using an algorithm.

15. The method of claim 10 , wherein the instruction to determine an adjusted spin speed includes an instruction to obtaining the adjusted spin speed from a database.

16. The method of claim 10 , wherein the instruction to determine an initial position of a head relative to a surface of the rotatable medium includes an instruction to read servo information from the surface of the rotatable medium with the head.

17. The method of claim 11 , wherein:

the instruction to determine an amount of initial drag at the initial position includes accessing the initial drag from memory based on the initial position; and

the instruction to determine an amount of target drag at the target position includes accessing the target drag from memory based on the target position.