Fast-Head Unloading Scheme

Fast-Head Unloading Scheme

      Disclosed is a method of fast unloading to the ramp for a Hard
Disk Drive (HDD) which has read/write heads and disks and load/unload
function assembly.  The unloading function requires a calibration of
back-ElectroMotive Force (EMF) sensing circuit (*) which is provided
for a constant velocity servo of a Voice Coil Motor (VCM) actuator.
The AD  input in Fig. 1 shows the following value V_ad (2):
V_ad=R7/(R6+R7)*(Vref+R4/R2*(V_bemf+I_vcm*Rvcm)-Rg/R1*Rsens*I_vcm) =
R7/(R6+R7)*Vref + R7/(R6+R7)*R4/R2*V_bemf  +
R7/(R6+R7)*R4/R2*I_vcm(Rvcm-Rg/R1*Rsens) ..........(1) =A*(V_ref +
B*(Vbemf + I_vcm*R_delta))..................(2) assume R3=R4,R5=R6
where offset =R7/(R6+R7)*Vref  A=R7/(R6+R7)  B=R4/R2  R_delta=
Rvcm-Rg/R1*Rsens......(3)

      Fig. 2 shows this calibration process in an actual HDD
application.  Voltage of the VCM coil(y-axies), Time(x-axies) is
shown in Fig. 2.  By measuring DACOUT values of VCM and AD converter
values at the different two positions (Point A at inner and B at
outer in Fig. 2) on the disk y averaging for certain period, above
R_delta(3) is obtained by the following equation (4):
  R_delta=(AD(cylinder=x1)-AD(cylinder=x2))/
   (DAC(cylinder=x1)-DAC(cylinder=x2)......(4)

      Fig. 3 shows an example of the relationship between cylinder
position vs. DACOUT value at following mode.

      Fig. 4 shows an example of the relationship between
expected AD conversion value and DACOUT value.  By usin...