Disk drive employing momentum based unload during power failure
View Patent ↗A disk drive is discloses comprising a disk, a head connected to a distal end of an actuator arm, and a voice coil motor (VCM) for rotating the actuator arm about a pivot in order to actuate the head radially over the disk. If when a power failure occurs the radial location of the head is less than a predetermined distance from the outer diameter of the disk, the VCM is controlled to move the head toward the inner diameter of the disk and stopping the head before it reaches the inner diameter of the disk. The VCM is then controlled to move the head toward the outer diameter of the disk until the actuator arm unloads onto a ramp.
1. A disk drive comprising:
(a) a disk;
(b) an actuator arm;
(c) a head connected to a distal end of the actuator arm;
(d) a voice coil motor (VCM) for rotating the actuator arm about a pivot to actuate the head radially over the disk;
(e) a ramp positioned near an outer diameter of the disk;
(d) disk control circuitry for executing an unload operation to unload the actuator arm onto the ramp during a power failure by:
monitoring a radial location of the head;
if the radial location of the head is greater than a predetermined distance from the outer diameter of the disk when the power failure occurs, controlling the VCM to move the head toward the outer diameter of the disk until the actuator arm unloads onto the ramp; and
if the radial location of the head is less than the predetermined distance from the outer diameter of the disk when the power failure occurs:
controlling the VCM to move the head toward the inner diameter of the disk and stopping the head before it reaches the inner diameter of the disk; and
controlling the VCM to move the head toward the outer diameter of the disk until the actuator arm unloads onto the ramp.
2. The disk drive as recited in claim 1 , further comprising a spindle motor for rotating the disk, wherein a back EMF voltage generated by the spindle motor is used to power the VCM during the unload operation.
3. The disk drive as recited in claim 1 , wherein:
(a) the VCM generates a back EMF voltage;
(b) the disk control circuitry estimates a velocity of the actuator arm from the back EMF voltage generated by the VCM; and
(c) the disk control circuitry controls the velocity of the actuator arm in response to the estimated velocity.
4. The disk drive as recited in claim 1 , wherein the disk control circuitry controls the VCM to rotate the actuator arm at a predetermined velocity for a first interval in order to move the head toward the inner diameter of the disk, wherein the disk control circuitry stops the head after the first predetermined interval.
5. The disk drive as recited in claim 4 , wherein the disk control circuitry controls the VCM to rotate the actuator arm at a predetermined velocity for a second interval in order to move the head toward the outer diameter of the disk.
6. The disk drive as recited in claim 5 , wherein the disk control circuitry computes at least one of the first and second intervals in response to the radial location of the head when the power failure occurs.
7. A method of unloading an actuator arm onto a ramp in a disk drive during a power failure, the disk drive comprising a disk, the actuator arm, a head connected to a distal end of the actuator arm, a voice coil motor (VCM) for rotating the actuator arm about a pivot to actuate the head radially over the disk, and the ramp positioned near an outer diameter of the disk, the method comprising the steps of:
(a) monitoring a radial location of the head;
(b) if the radial location of the head is greater than a predetermined distance from the outer diameter of the disk when then power failure occurs, controlling the VCM to move the head toward the outer diameter of the disk until the actuator arm unloads onto the ramp; and
(c) if the radial location of the head is less than the predetermined distance from the outer diameter of the disk when the power failure occurs:
controlling the VCM to move the head toward the inner diameter of the disk and stopping the head before it reaches the inner diameter of the disk; and
controlling the VCM to move the head toward the outer diameter of the disk until the actuator arm unloads onto the ramp.
8. The method as recited in claim 7 , wherein the disk drive further comprises a spindle motor for rotating the disk, wherein a back EMF voltage generated by the spindle motor is used to power the VCM during the unload operation.
9. The method as recited in claim 7 , wherein the VCM generates a back EMF voltage, further comprising the steps of:
(a) estimating a velocity of the actuator arm from the back EMF voltage generated by the VCM; and
(b) controlling the velocity of the actuator arm in response to the estimated velocity.
10. The method as recited in claim 7 , wherein the step of controlling the VCM to move the head toward the inner diameter of the disk comprises the steps of:
(a) rotating the actuator arm at a predetermined velocity for a first interval in order to move the head toward the inner diameter of the disk; and
(b) stopping the head after the first predetermined interval.
11. The method as recited in claim 10 , wherein the step of controlling the VCM to move the head toward the outer diameter of the disk comprises the step of rotating the actuator arm at a predetermined velocity for a second interval in order to move the head toward the outer diameter of the disk.
12. The method as recited in claim 11 , further comprising the step of computing at least one of the first and second intervals in response to the radial location of the head when the power failure occurs.