Method of operating hard disk drives, corresponding control circuit, hard disk drive and processing device
A voice coil motor (VCM) in a hard disk drive having a VCM resistance is driven based on a value of the back electromotive force (BEMF) of the VCM reconstructed from a voltage drop indicative of the intensity of a current flowing towards the VCM detected by an amperometry resistance. The BEMF of the VCM is reconstructed as a function of the voltage drop via a first gain value, determined as the ratio of the VCM resistance to the amperometry resistance. A calibrated gain value, indicative of the ratio of the actual VCM resistance to the amperometry resistance is produced by applying a correction factor to the first gain value. The VCM is driven continuously based on a value of the BEMF of the VCM reconstructed by applying to the voltage drop the calibrated gain value.
1 . A method of operating a voice coil motor (VCM) in a hard disk drive, the VCM being driven based on a value of a back electromotive force (BEMF) of the VCM reconstructed as a function of a voltage drop indicative of an intensity of a current flowing towards the VCM detected by an amperometry resistance, the BEMF of the VCM being reconstructed as a function of the voltage drop via a first gain value determined as a ratio of a first VCM resistance to the amperometry resistance, the method comprising:
producing a calibrated gain value indicative of a second ratio of an actual VCM resistance to the amperometry resistance by applying a correction factor to the first gain value; and
driving the VCM continuously based on a reconstructed value of the BEMF of the VCM, reconstructed by applying to the voltage drop the calibrated gain value.
2 . The method of claim 1 , comprising applying the correction factor to the first gain value, by multiplying the first gain value by the correction factor.
3 . The method of claim 1 , comprising calculating the correction factor as a function of the reconstructed value of the BEMF of the VCM, a drive voltage applied to the VCM, and a BEMF voltage from the VCM.
4 . The method of claim 3 , comprising calculating the correction factor as a function of a third ratio of:
a difference between the drive voltage applied to the VCM and the BEMF voltage from the VCM; and
a difference between the drive voltage applied to the VCM and the reconstructed value of the BEMF of the VCM.
5 . The method of claim 1 , comprising forcing at least one signal pulse through the VCM concurrently with or prior to producing the calibrated gain value.
6 . The method of claim 5 , comprising forcing through the VCM a plurality of signal pulses, at least one of a VCM speed or a VCM position prior to producing the calibrated gain value being restored in response to the plurality of signal pulses being forced through the VCM.
7 . The method of claim 6 , wherein the plurality of signal pulses forced through the VCM comprises pulses of opposed polarity.
8 . The method of claim 6 , comprising producing respective calibrated gain values subsequent to forcing through the VCM the signal pulses in the plurality of signal pulses.
9 . A control circuit configured to operate a voice coil motor (VCM) in a hard disk drive, the VCM configured to be driven based on a value of a back electromotive force (BEMF) of the VCM reconstructed as a function of a voltage drop indicative of an intensity of a current flowing towards the VCM detected by an amperometry resistance, the BEMF of the VCM being reconstructed as a function of the voltage drop via a first gain value determined as a ratio of a first VCM resistance to the amperometry resistance, the control circuit comprising:
retract logic circuitry configured to be coupled to the VCM and to, during a retract phase:
produce a calibrated gain value indicative of a second ratio of an actual VCM resistance to the amperometry resistance by applying a correction factor to the first gain value; and
drive the VCM continuously based on a reconstructed value of the BEMF of the VCM, reconstructed by applying to the voltage drop the calibrated gain value.
10 . The control circuit of claim 9 , wherein the retract logic circuitry is configured to apply the correction factor to the first gain value, by multiplying the first gain value by the correction factor.
11 . The control circuit of claim 9 , wherein the retract logic circuitry is configured to calculate the correction factor as a function of the reconstructed value of the BEMF of the VCM, a drive voltage applied to the VCM, and a BEMF voltage from the VCM.
12 . The control circuit of claim 11 , wherein the retract logic circuitry is configured to calculate the correction factor as a function of a third ratio of:
a difference between the drive voltage applied to the VCM and the BEMF voltage from the VCM; and
a difference between the drive voltage applied to the VCM and the reconstructed value of the BEMF of the VCM.
13 . The control circuit of claim 9 , wherein the retract logic circuitry is configured to force at least one signal pulse through the VCM concurrently with or prior to producing the calibrated gain value.
14 . The control circuit of claim 13 , wherein the retract logic circuitry is configured to force through the VCM a plurality of signal pulses, at least one of a VCM speed or a VCM position prior to producing the calibrated gain value being restored in response to the plurality of signal pulses being forced through the VCM.
15 . The control circuit of claim 14 , wherein the plurality of signal pulses forced through the VCM comprises pulses of opposed polarity.
16 . The control circuit of claim 14 , wherein the retract logic circuitry is configured to produce respective calibrated gain values subsequent to forcing through the VCM the signal pulses in the plurality of signal pulses.
17 . A hard disk drive, comprising:
at least one voice coil motor (VCM); and
a control circuit configured to operate the VCM, the VCM configured to be driven based on a value of a back electromotive force (BEMF) of the VCM reconstructed as a function of a voltage drop indicative of an intensity of a current flowing towards the VCM detected by an amperometry resistance, the BEMF of the VCM being reconstructed as a function of the voltage drop via a first gain value determined as a ratio of a first VCM resistance to the amperometry resistance, the control circuit comprising retract logic circuitry coupled to the VCM and configured to, during a retract phase:
produce a calibrated gain value indicative of a second ratio of an actual VCM resistance to the amperometry resistance by applying a correction factor to the first gain value; and
drive the VCM continuously based on a reconstructed value of the BEMF of the VCM, reconstructed by applying to the voltage drop the calibrated gain value.
18 . The hard disk drive of claim 17 , wherein the retract logic circuitry is configured to apply the correction factor to the first gain value, by multiplying the first gain value by the correction factor.
19 . The hard disk drive of claim 17 , wherein the retract logic circuitry is configured to calculate the correction factor as a function of the reconstructed value of the BEMF of the VCM, a drive voltage applied to the VCM, and a BEMF voltage from the VCM.
20 . The hard disk drive of claim 17 , wherein the retract logic circuitry is configured to force at least one signal pulse through the VCM concurrently with or prior to producing the calibrated gain value.