Operation and Maintenance Manual Model 7AA Wafer Grinder
7 - 28 Version 1.2 - April 18, 1996
CASSETTE SLOT LOCATION
The elevator uses a lead screw to raise and lower the cassette
platform. The lead screw has a 1/8" thread pitch with a two
lobe encoder affixed to the screw. The screw rotation is
measured by an inductive proximity switch that senses each
lobe during screw rotation. Since cassette slot spacing is 3/16"
each slot occurs every three pulses (1-1/2 screw revolutions) of
the lobe switch.
The reference point for the platform position is a limit switch
that trips at the top end of the lead screw travel. Each time the
elevator returns to this limit the lobe counter is reset. The top
reference position is defined as the first lobe sensed after the
top limit switch is tripped. Therefore whenever elevator
adjustment is performed it should be such that the limit switch is
activated while the proximity sensor is between lobes. This will
eliminate any timing conflicts and assure that the reset function
will always occur on the same lobe.
With the top position as a reference all wafer slots are
determined to be at consecutive multiples of three encoder
lobes. To adjust the slot height requires adjustment of the set
screw that trips the top limit switch. To raise the reference
position (and thus each slot location) requires that the platform
extend higher. This requires that the set screw be lowered by
rotating clockwise. The set screw end is accessible through an
access hole in the conveyor roller assembly. To lower the
platform position extend the set screw.
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