Operation and Maintenance Manual Model 7AA Wafer Grinder
3 - 8 Version 1.2 - April 18, 1996
crossmember on the bed. The rear of the upright is secured by a
nut affixed to the rear end of the bed. The forward-rear tilt of the
spindle is adjusted by rotating the upright bolt through the nut.
The grind spindle itself slides within a precision honed bore located
in a casting affixed to the upright. This casting is secured to the
upright with four bolts and a hinge pin to provide side-to-side
alignment adjustment. The spindle bore is periodically lubricated
by the automatic lubricator to maintain smooth stick-free spindle
movement.
GRIND SPINDLE FEED MECHANISM
The grind spindle feed mechanism provides for precise control
of the grind spindle feed rate and position. The grind spindle is
supported by two pivot points on either side of the spindle
attached to a cast iron lever arm. The front of the lever arm
rests on a floating post just forward of the grind spindle. The
rear end of the lever rests on a platform affixed to a threaded
sleeve. The ratio of the pivot point location to overall lever arm
length provides a 5:1 ratio between feed platform travel and
spindle travel. This provides increased resolution for control of
spindle position. The sleeve sustaining the feed platform travels
on a fine pitch lead screw located inside the sleeve. The screw
is driven by a timing belt running on the lead screw and z axis
servo motor pulleys. Whenever conditions exist that prevent the
spindle from following the platform travel (e.g. excessive feed
rate while grinding or jogging wheels to contact wafer chuck
surface) the platform will continue to travel downward and the
lever arm will be suspended above the platform. This scheme
prevents the spindle from being forced to apply excessive force
on the wafer or chuck surface.
A counterbalance weight suspended by wire rope applies a
lifting force on the lever arm. Since the weight of the grind
spindle yields excessive grind forces this counterweight acts to
lift the spindle lever arm to reduce the maximum downforce to
an acceptable level.
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