Re: [ATM] Voice coil actuators was: DC Motor for grinding machine question

[Richard <cnc@cncservo.co.uk>]

Hi Mike,

Tuesday, November 21, 2006, 4:00:12 PM, you wrote:

ML> "noise" will swamp out any periodic vibrations introduced by the
ML> bearings

Think of the path of a single ball in a race as it orbits. Let's
say the outer race is fixed and the inner race rotates. The
periperal velocity of the ball is the same as the peripheral
velocity of the track of the inner race that it rolls in. Where
is the ball after one revolution of the shaft?. It depends
entirely on the ratio of the ball diameter to race track
diameter, oil film thickness and if there is and skidding of the
contact. The chances of it having undergone an integer number of
revolutions of the shaft and hence contributing *harmonic*
forces are remote IMO.

Of course, the ball is orbiting, but for each orbiting ball
there is likely to be an equal and opposite orbiting ball
cancelling any cyclic forces. Yes, there can be an odd number of
balls, so better put, the vector sum of the ball cyclic forces
cancel. One of the reasons that high speed precision bearings
have high accuaracy cages. And one of the reasons I have used
expensive bearings in my computer controlled polisher.

-- 

Best regards,
  Richard in the UK

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