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Browse Prior Art Database

Hard Disk Drive

IP.com Disclosure Number: IPCOM000117082D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Fukushima, Y: AUTHOR

Abstract

Disclosed is a function to recover a read error which is caused by an asperity on disk surface. If MR type head hits the asperity, data on the disk sometimes can't be read because the characteristics of MR element is obstructed by a temperature rise (Fig. 1). To read such errors, head flying height is increased by changing the spindle motor speed upward in a error recovery function. Then the possibility of reading the error portion can be increased because the hitting ratio between the asperity and the MR element is decreased. When data on the desk is read on higher spindle motor speed, following parameters should be change to appropriate values, - Servo clock frequency for decoding Gray code - read/write channel PLL (phase locked loop) source clock frequency

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Hard Disk Drive

      Disclosed is a function to recover a read error which is caused
by an asperity on disk surface.  If MR type head hits the asperity,
data on the disk sometimes can't be read because the characteristics
of MR element is obstructed by a temperature rise (Fig. 1).  To read
such errors, head flying height is increased by changing the spindle
motor speed upward in a error recovery function.  Then the
possibility of reading the error portion can be increased because the
hitting ratio between the asperity and the MR element is decreased.
When data on the desk is read on higher spindle motor speed,
following parameters should be change to appropriate values,
  - Servo clock frequency for decoding Gray code
  - read/write channel PLL (phase locked loop) source clock frequency

      Fig. 2 shows an example of this function.  The oscillated
frequency of Xtal-2 is higher than that of Xtal-1.  Usually OSC
(oscillator) is connected to Xtal-1.  In case of error recovery,
Xtal-1 is switched to Xtal-2.  Then the MPU clock is higher and the
spindle motor speed is faster because the speed is controlled by MPU.
On the other side, the clock of OSC is supplied to read/write channel
module.  So the PLL oscillated frequency is raised.  And the OSC
clock is supplied to Servo logic which decodes the Gray code.  As the
result, an error which is caused by an asperity can be read during
higher spindle motor speed.