Apparatus to reject disk drive disturbance
View Patent ↗Track mis-registration (TMR) correction is conditionally made in a hard disk drive using servo data in a closed loop servo control scheme, along with one or more alternative sensing schemes when an external shock or vibration occurs. The alternative sensing schemes include measurement of spindle motor speed using a frequency of servo markers read from a rotating disk, voice control motor (VCM) back emf, spindle motor speed back emf, and accelerometer readings. The predicted TMR resulting from the signal generated by the alternative sensing scheme(s) is simulated based upon a model of the disk drive system, and corrections are applied only if the expected TMR due to the disturbances is large enough that application of the corrections using the alternative sensing scheme would be likely to reduce the overall TMR. In one case, actual operation is occasionally performed with and without corrective TMR feedback from the selected sensing scheme(s), and the actual values are compared with predictions from the system model and the results are used to update the system model.
1. A servo system for a hard disk drive that controls track alignment of a transducer head relative to a desired tracking location using at least two measurements,
(a) a first measurement made from servo data position error signals (PES) read from a rotatable disk by the transducer head; and
(b) a second measurement made from a feed forward signal indicative of a disturbance applied to the hard disk drive, the second measurement being used to control the track alignment only when the servo system determines that use of the second measurement will likely reduce track alignment error, wherein the servo system determines that use of the second signal will likely reduce the track alignment error when a threshold is exceeded, the threshold being determined from a computer model enabling comparison of predicted PES amounts with and without the use of the second signal, wherein the feed forward signal comprises two or more of the following:
an accelerometer signal provided from the accelerometer sensing movement of the disk;
a first spindle motor speed indication signal provided from a frequency of servo markers passing the transducer head as read from the disk rotated by the spindle motor;
a second spindle motor speed indication signal provided from a back emf signal received from a winding of the spindle motor; and
a voice control motor (VCM) movement indication signal provided from a back emf signal received from a winding of the VCM.
2. A servo system for a hard disk drive that controls track alignment of a transducer head relative to a desired tracking location using at least two measurements,
(a) a first measurement made from servo data position error signals (PES) read from a rotatable disk by the transducer head; and
(b) a second measurement made from a feed forward signal indicative of a disturbance applied to the hard disk drive, the second measurement being used to control the track alignment only when the servo system determines that use of the second measurement will likely reduce track alignment error, wherein the servo system determines that use of the second signal will likely reduce the track alignment error when a threshold is exceeded, the threshold being set with hysteresis so that the threshold has a first value when use is made of the second measurement and a second value when switching back to not using the second measurement.
3. A servo system for a hard disk drive that controls track alignment of a transducer head relative to a desired tracking location using at least two measurements,
(a) a first measurement made from servo data position error signals (PES) read from a rotatable disk by the transducer head; and
(b) a second measurement made from a feed forward signal indicative of a disturbance applied to the hard disk drive, the second measurement being used to control the track alignment only when the servo system determines that use of the second measurement will likely reduce track alignment error, wherein when the second measurement is used, track alignment correction is provided using the feed forward signal without the PES signal.
4. A servo system for a hard disk drive that controls the track alignment of a transducer head relative to a desired tracking location using at least two measurements,
a first measurement made from servo data position error signals (PES) read from the rotatable disk by the read/write head; and
a second measurement made from a feed forward signal indicative of external disturbances applied to the hard disk drive, the second measurement being used to determine the track alignment only when a threshold value related to the disturbance is detected, wherein the threshold value is provided with hysteresis, so that the threshold has a first value when use is made of the second measurement and a second value when switching back to not using the second measurement.
5. The servo system of claim 4 , wherein the threshold value comprises a PES signal magnitude.
6. The servo system of claim 4 , wherein the threshold value comprises a disturbance magnitude.
7. A servo system for a hard disk drive that controls track alignment of a transducer head relative to a desired tracking location using at least two measurements,
(a) a first measurement made from servo data position error signals (PES) read from a rotatable disk by the transducer head; and
(b) a second measurement made from a feed forward signal indicative of a disturbance applied to the hard disk drive, the second measurement being used to control the track alignment only when the servo system determines that use of the second measurement will likely reduce track alignment error, wherein the servo system determines that use of the second signal will likely reduce the track alignment error when a threshold is exceeded, wherein the feed forward signal comprises at least one of the following:
an accelerometer signal provided from the accelerometer sensing movement of the disk;
a first spindle motor speed indication signal provided from a frequency of servo markers passing the transducer head as read from the disk rotated by the spindle motor;
a second spindle motor speed indication signal provided from a back emf signal received from a winding of the spindle motor; and
a voice control motor (VCM) movement indication signal provided from a back emf signal received from a winding of the VCM.
8. The servo system of claim 7 , wherein the servo system determines that use of the second signal will likely reduce the track alignment error when the threshold indicating a limit for a magnitude for the disturbance is exceeded.
9. The servo system of claim 7 , wherein the servo system determines that use of the second signal will likely reduce the track alignment error when the threshold indicating a limit of the PES signal is exceeded.
10. The servo system of claim 7 , wherein the servo system determines that use of the second signal will likely reduce the track alignment error when the threshold indicating a limit of both the disturbance and the PES signal is exceeded.
11. The servo system of claim 7 , wherein the servo system comprises:
a memory storing data indicating the threshold; and
a processor coupled to the memory and to the read/write head, the processor configured to determine when the servo system will determine track alignment control using the second measurement based on whether the threshold is exceeded.