Browse Prior Art Database

Improved Back Electromagnetic Force Voice Coil Motor Controller

IP.com Disclosure Number: IPCOM000116862D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Related People

Eaton, RE: AUTHOR [+2]

Abstract

Disclosed is a method for the compensation of the coil resistance of a Voice Coil Motor (VCM) in hard disk drives to simplify the measurement of the back Electromagnetic Force (EMF) voltage of the VCM for actuator load/unload control.

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This is the abbreviated version, containing approximately 52% of the total text.

Improved Back Electromagnetic Force Voice Coil Motor Controller

      Disclosed is a method for the compensation of the coil
resistance of a Voice Coil Motor (VCM) in hard disk drives to
simplify the measurement of the back Electromagnetic Force (EMF)
voltage of the VCM for actuator load/unload control.

      Many disk drives today use the back EMF voltage generated
according to Lenz's law to measure the velocity of the actuator in a
disk drive.  Actuator Loading and Unloading (L/U) is performed by
measuring the back EMF voltage across the VCM while controlling the
VCM current to maintain a constant back EMF voltage, meaning a
constant velocity for the actuator arm.

      The back EMF voltage is small compared to the voltage across
the VCM needed to move the actuator onto the disk.  The back EMF
voltage is measured as follows:  First the total coil voltage is
measured and converted to the digital domain by an A/D convertor.
Next, the calculated ohmic portion of the coil voltage is subtracted.
Assuming enough time has elapsed to allow any inductive transients to
die out, the result is the back EMF voltage which is proportional to
the velocity of the actuator.

      The ohmic part of the coil voltage is calculated from the
measured coil resistance and the VCM current (which is typically
controlled with a DAC).  The resistance is usually measured before
the load or unload operation by applying a VCM current, which will
produce no actuator motion, and then measuring the coil voltage.

      The A/D convertor range currently needed in the control loop to
load/unload the head is given by the maximum voltage across the coil
consisting o...