Strasbaugh Machine Description
Version 4.0 - February 1998 2 - 25
ELEVATOR ASSEMBLY
The elevator assembly, located at the left of the machine, consists of two
functional units, send and receive. The left and right send elevators, located
at the rear of the machine, raise and lower cassettes loaded with unprocessed
wafers. The left and right receive elevators, located near the middle of the
machine, raise and lower cassettes loaded with processed wafers.
The elevator back support houses a polymer nut and two pillow block
bearings. The bearings travel on a rail supported by the framework of the
elevator slide assembly. The polymer nut is stationary, and a lead screw is
rotated inside the nut. The lead screw is supported at both ends by bearings
mounted on the slide assembly. The lead screw is belt-driven by a brushless
DC motor with a tooth belt and two pulleys.
The motor has uses encoder feedback to monitor speed and position. The
elevator home switch, located two to three inches from the end of travel, is
used to tell the control computer when the elevator has reached the bottom
limit of travel. This information is used to “home” the elevator. Note that
the elevators are water-resistant.
Each of the four cassette sensor arms has a mechanical microswitch located
in the end of the arm. Lowering an arm onto a cassette trips the
microswitch, informing the control computer that a cassette has been placed
on the elevator.
The elevators sit in tanks supplied with water from an air operated valve
controlled by a solenoid valve mounted on the valve panel located at the
lower left side of the machine.
The elevator light sensor option detects any wafer not correctly (and
safely) positioned in its cassette slot. The incorrectly positioned wafer will
break an invisible infrared light beam. When the beam is broken, indicating
the wafer is not positioned close enough to the rear of the slot, downward
movements of the elevator, which could break the wafer, are not permitted.
After a five-second delay, an alarm will sound, and a message will be
displayed on the monitor screen. The five-second alarm delay prevents false
alarms from normal light beam interruptions such as the robot inserting a
wafer. The light sensor detection is active only if the elevator arm is
lowered onto a cassette.
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