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Low-Noise Spindle Motor for Small Hard Disk Drive

IP.com Disclosure Number: IPCOM000105907D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Ando, H: AUTHOR [+3]

Abstract

This disclosure describes how to prevent beating tone in a small Hard Disk Drive. The cause of the beating tone is interference in vibrations which are generated by two bearings of spindle motor. For the solution, ball Pitch Circle Diameter (PCD) of the bearings in the spindle motor is changed to eliminate the beating tone.

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Low-Noise Spindle Motor for Small Hard Disk Drive

      This disclosure describes how to prevent beating tone in a
small Hard Disk Drive.  The cause of the beating tone is interference
in vibrations which are generated by two bearings of spindle motor.
For the solution, ball Pitch Circle Diameter (PCD) of the bearings in
the spindle motor is changed to eliminate the beating tone.

      The factors which influence the vibration frequency of a ball
bearing are mainly ball diameter and ball Pitch Circle Diameter.  The
equations which show the vibration frequency of a ball bearing are as
follows.

     ball revolution frequency:
          fa = (1/2) * { 1 - (D/dp) * cos A } * fr
     inner race undulation frequency (axial) :
          feT = n * Z * ( fr - fa )
     inner race undulation frequency (radial) :
          feR = feT  fr
where:  D: ball diameter    dp: ball pitch circle diameter
        A: contact angle    fr: revolutional speed
        Z: ball number      n : number ( 1,2,3,.....)

      A beating tone is generated by interference in very closed
frequency vibration.  In this case, the problem caused by beating
tone is interference in closed frequency vibrations which are
generated by two bearings of spindle motor.  The same size bearings
generate very closed frequency vibration (slightly difference)
because of their machining variance.  Therefore, one of the problem
solutions is to cha...