Strasbaugh Mechanical Description
Version 4.0 - February 1998 4 - 9
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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