New Track Pitch Calculation

New Track Pitch Calculation

      Disclosed is a track pitch calculation method which is suited
for Rotary type Servo Track Writer (STW).

      Fig. 1 shows the current method of track pitch calculation for
Rotary type STW.  Track pitch angle is calculated as follows.
  Track pitch angle (ta) = (angle-a) - (angle-b)
  angle-a = ArcCos((A(2)  + R(2)  - r1(2))/(2 * A * R))
  angle-b = ArcCos((A(2)  + R(2)  - r2(2))/(2 * A * R))
  A :  length between Disk center and Pivot center
  R :  length between Pivot center and head gap
  r :  length between Disk center and target track position

      In above method, all values are estimated as same as nominal
value.  The error of actual length which differ from nominal value
does not influence accuracy of track pitch.  But, consider about the
position error of Pivot center and Rotation axis center of Rotary
positioning equipment.  This error is caused by the following errors:
  1.  Cumulative error of mechanical dimensions of clamping fixture.
  2.  Repeatability of Hard Disk loading position.
  3.  Mechanical accuracy of position of pivot center from standard
       datum position.

      This error depends on construction of clamping fixture.  But,
from our experience, this error can be .5 mm as maximum.  .5 mm of
this error causes more than 2% error of track pitch accuracy.

      This new technology is to compensate this error by measuring
between Outer Crush Stop (Outer stopper) and Inner Crush stop (Inner
stopper).  To measure this angle, we utilize current change sense
function of Rotary Positioning equipment.  The following is a
detailed
description.
  1.  Measure between Outer Crush stop and Inner Crush stop
      a.  The case of pusher touch from outer side (Fig. 2)
          o  Give bias force to VCM (Voice Coil Motor ) of HDD from
              inner to outer
          o  Move pusher of Rotary positioning equipment from outer
to
              inner.  Sense current change point of Rotary
positioning
              equipment.  Define this point as Outer Crush point.
          o  Move pusher of Rotary positioning equipment to inner.
              Sense current change point of Rotary positioning
              equipment.  Define this point as Inner Crush stop
              position.
      b.  The case of pushe...