Browse Prior Art Database

Voice Coil Motor Driver DC Offset Compensation by Micro Controller

IP.com Disclosure Number: IPCOM000114683D
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Fukushima, Y: AUTHOR [+4]

Abstract

Disclosed is a method for DC-offset of Voice Coil Motor (VCM) Driver compensation on closed loop servo system hard disk drive without any additional hardware.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 85% of the total text.

Voice Coil Motor Driver DC Offset Compensation by Micro Controller

      Disclosed is a method for DC-offset of Voice Coil Motor (VCM)
Driver compensation on closed loop servo system hard disk drive
without any additional hardware.

      VCM driver outputs VCM current to control head position.  VCM
current is bi-directional and direction of head moving is decided by
direction of VCM current and current control acceleration of head.
VCM
current is controlled by differential input Vctrl and Vref
(Fig. 1).  Ideally, VCM current must be zero when Vctrl=Vref.  But
actual VCM driver has DC offset and VCM current exists when
Vctrl=Vref
(Fig. 2).  The offset causes imbalance of VCM current.

      This disclosure describes measurement and compensation method
of the DC offset using head position information written on a disk
surface.

      DC-offset can be calculated from acceleration when Vctrl=Vref.
Measurement step is as follows (Fig. 3):
  1.  Set Vctrl=Vref.
  2.  Read head position (CYL.A)
  3.  Wait
  4.  Read head position (CYL.B)
  5.  Wait
  6.  Read head position (CYL.C)
  7.  Calculate DC-offset
      VelocityAB = CYL.B - CYL.A
      VelocityBC = CYL.C - CYL.B
      Acceleration = Velocity BC - Velocity AB
                   = (CYL.C - CYL.B) - (CYL.B - CYL.A)
                   = CYL.C - 2 x CYL.B + CYL.A
             DC-Offset in Vctrl = Constant x Acceleration.
  Offset...