Disk drive and method of measuring frictional characteristics

1. A disk comprising:

a head in contact with a disk by a head suspension;

a controller configured to move the head to a position on a track by controlling a driving force generated by a voice coil motor;

a head position detector configured to detect the position on the track of the head as head position information; and

a calculator configured to calculate a frictional force between the disk and the head based on the driving force of the voice coil motor and the head position information detected by the head position detector, wherein the calculator is configured to calculate the frictional force when the voice coil motor vibrates the head in the radial direction of the disk by the controller.

2. The disk drive of claim 1 , wherein the controller is configured to control the voice coil motor at a substantially high frequency for measurement exceeding a servo frequency band in order to move the head in the radial direction of the disk.

3. The disk drive of claim 1 , further comprising an actuator configured to change the pressing force of the head suspension, wherein

the calculator is configured to calculate the frictional force at steps of the pressing force when the pressing force is changed stepwise by the actuator, and to calculate the friction coefficient based on an amount of change in the pressing force and an amount of change in the frictional force.

4. The disk drive of claim 3 , wherein the calculator is configured to calculate the normal force between the head and the disk by dividing the frictional force by the friction coefficient.

5. The disk drive of claim 4 , wherein the calculator is configured to calculate the attraction force between the head and the disk based on the normal force and the pressing force.

6. The disk drive of claim 5 , wherein the calculator is configured to subtract the aerodynamic force between the disk and the head due to an airflow concomitant with the rotation of the disk from the attraction force calculated based on the normal force and the pressing force.

7. The disk drive of claim 3 , wherein the actuator is configured to change the pressing force by applying a voltage to a piezoelectric element on the head suspension.

8. The disk drive of claim 3 , further comprising load fluctuation measuring module on the head suspension, configured to measure fluctuation in the load passively induced from geometrical undulation of the disk, and to provide the measured load fluctuation to the calculator.

9. The disk drive of claim 1 , wherein the calculator is configured to calculate the frictional force between the head and the disk based on an amplitude of a sinusoidal current corresponding to the driving force of the voice coil motor and a vibration amplitude of the head calculated from the head position information.

10. A method of measuring frictional characteristics in a disk drive which comprises a head being in contact with a disk by a head suspension, the method comprising:

controlling a driving force generated by a voice coil motor in such a manner that the head moves to a position on a track in the radial direction of the disk;

calculating a frictional force between the disk and the head based on the driving force of the voice coil motor and the head position information detected by a head position detector; and

controlling the voice coil motor at a substantially high frequency for measurement exceeding a servo band to move the head in the radial direction of the disk.

11. The method of claim 10 , further comprising:

changing the pressing force of the head suspension by an actuator;

calculating the frictional force at steps of the pressing force; and

calculating the friction coefficient based on an amount of change in the pressing force and an amount of change in the frictional force.

12. The method of claim 11 , further comprising calculating the normal force between the head and the disk by dividing the frictional force by the friction coefficient.

13. The method of claim 12 , further comprising calculating the attraction force between the head and the disk based on the normal force and the pressing force.

14. The method of claim 13 , further comprising subtracting the aerodynamic force between the disk and the head due to an airflow concomitant with the rotation of the disk from the attraction force calculated based on the normal force and the pressing force.

15. The method of claim 11 , further comprising changing the pressing force by applying a voltage to a piezoelectric element provided on the head suspension.

16. The method of claim 11 , further comprising measuring passive load fluctuation from geometrical undulation of the disk at the head suspension, and using the measured load fluctuation in the calculating.

17. The method of claim 10 , further comprising calculating the frictional force between the head and the disk based on an amplitude of a sinusoidal current corresponding to the driving force of the voice coil motor and a vibration amplitude of the head calculated from the head position information.