Detecting head landings on a data zone of a data storage disc
View Patent ↗Method and apparatus for detecting head landings on a data zone of a data storage disc. A disc drive includes an actuator which controllably positions a head adjacent a disc and nominally retracts the head to a parked position when the drive is deactivated. The actuator moves in response to current applied to an actuator coil immersed in a magnetic field. During disc drive initialization, the disc is accelerated to a velocity sufficient to allow the head to be aerodynamically supported over the disc, and current is passed through the actuator coil to urge the head toward the parked position. The current is monitored to detect generation of a back electromotive force (bemf) voltage induced by movement of the coil. An error condition is logged indicating that an initial position of the head was over a data zone of the disc when bemf voltage is detected.
1. A method for determining whether a head has been moved to a parked position by steps comprising:
completing a park routine;
subsequently moving a disc at a sufficient velocity so that the head has aerodynamic support adjacent the disc;
energizing an actuator coil to urge the head in a direction toward the parked position;
monitoring an actuator coil current to detect generation of a beck electromotive force (bemf) voltage indicating the head was not in the parked position after completing the parked routine.
2. The method of claim 1 , wherein the energizing step comprises applying a substantially constant voltage across the actuator coil, and wherein the monitoring step comprises detecting the generation of the bemf voltage in relation to a reduction in die current passing through the actuator coil as the actuator coil moves.
3. The method of claim 1 , further comprising electrically shooting the actuator coil to brake the actuator coil prior to the energizing step.
4. The method of claim 3 , further comprising obtaining a brake current sample value indicative of a magnitude of current passing through the actuator coil during the electrically shorting step, and wherein the brake current sample value is used during the monitoring step to detect the generation of the bemf voltage.
5. The method of claim 1 , further comprising obtaining a maximum retract current sample value indicative of a maximum magnitude of current passing through the actuator coil during the energized step, and wherein the maximum retract current sample value is used during the monitoring step to detect the generation of the bemf voltage.
6. The method of claim 1 , further comprising adjusting retract characteristics of the disc drive in response to detection of the bemf voltage.
7. The method of claim 1 , wherein the monitoring step comprises establishing a threshold current magnitude level and detecting the generation of the bemf voltage when the current passing through the actuator coil crosses over the threshold current magnitude level.
8. The method of claim 1 , further comprising:
electrically shorting the actuator coil to brake the actuator coil prior to the energizing step;
obtaining a brake current sample value indicative of a magnitude of current passing through the actuator coil during die electrically shorting step;
obtaining a maximum retract current sample value indicative of a maximum magnitude of current passing through the actuator coil during the energizing step; and
calculating a threshold current magnitude level in relation to the brake current sample value and the maximum retract current sample value, wherein the threshold current magnitude level is used during the monitoring step to detect the generation of the bemf voltage.
9. The method of claim 8 , wherein the threshold current magnitude level of the calculating step is determined as an average of the brake current sample value and the maximum retract current sample value.
10. A disc drive data storage device configured to perform the method of claim 1 .
11. A servo circuit adapted for passing current through an actuatorcoil immersed in a magnetic field to move a data head across a data storage surface, wherein the servo circuit selectively moves the data head from a data zone to a parked position of the data storage surface, and wherein the servo circuit subsequently determines whether the data head failed to move to the parked position during a most recently performed move operation by moving the data storage surface to a velocity sufficient to cause the data head to attain aerodynamic support adjacent the data storage surface, passing current through the actuator coil to urge the data head in a direction toward the parked position while monitoring the current to detect generation of a back electromotive force (bemf) voltage indicating that the data head was over the data zone at the conclusion of the most recently performed move operation.
12. The servo circuit of claim 11 adapted for passing the current through the actuator coil by applying a substantially constant voltage across the actuator coil, and wherein the servo circuit further detects the generation of the bemf voltage in relation to a reduction in the current passing through the actuator coil as the actuator coil moves with respect to the magnetic field.
13. The servo circuit of claim 11 adapted for electrically shorting the actuator coil to brake the actuator coil prior to passing the current through the actuator coil.
14. The servo circuit of claim 11 adapted for obtaining a maximum retract current sample value indicative of a maximum magnitude of current passing through the actuator coil and using the maximum retract current sample value to detect the generation of the bemf voltage.
15. The servo circuit of claim 11 adapted for establishing a threshold current magnitude level and detecting the generation of the bemf voltage when the current passing through the actuator coil crosses over the threshold current magnitude level.
16. A data storage device, comprising:
an actuator which supports a data transducing head adjacent a data storage surface and which supports an actuator coil in a magnetic field, wherein passage of current through the actuator coil induces movement of the head across the data storage surface, and wherein the actuator selectively moves the head from a data zone to a parked position of the data storage surface; and
first means for determining whether the actuator failed to move the head to the parked position during die most recently performed move operation.
17. The storage device of claim 16 , wherein the first means comprises a servo circuit which passes current through the actuator coil to move the head across the data storage surface, wherein the servo circuit is configured to move the data storage surface to a velocity sufficient to cause the head to attain aerodynamic support adjacent the data storage surface, pass current through the actuator coil to urge the head in a direction toward the parked position while monitoring the current to detect generation of a back electromotive force (bemf) voltage indicating that the head was over the data zone at the conclusion of the most recently performed move operation.
18. The data storage device of claim 17 , wherein the servo circuit passes the current though the actuator coil by applying a substantially constant voltage across the actuator coil, and wherein the servo circuit further detects the generation of the bemf voltage in relation to a reduction in the current passing through the actuator coil as the actuator coil moves with respect to the magnetic field.
19. A servo circuit that retracts a head to a parked position and subsequently determines whether the head failed to retract.