A precision soft-touch end effector has a mounting plate attached to a
robot arm. The plate supports a stepper motor. The output shaft of the
stepper motor is connected through a spring to an elongated finger that
slides in a central longitudinal slot of the plate and supports a first
wafer gripping post, while on the end opposite to the first wafer
gripping post the mounting plate pivotally supports two L-shaped fingers
with a second and third wafer gripping posts on their respective ends.
The mounting plate in combination with the first sliding finger and two
pivotal fingers forms the end effector of the robot arm which is thin
enough for insertion into a wafer-holding slot of a wafer cassette. The
end effector is equipped with a mapping sensor for detecting the presence
or absence of the preceding wafer, wafer position sensors for determining
positions of the wafer with respect to the end effector, and force
sensors for controlling the wafer gripping force. Several embodiments
relate to different arrangements of gripping rollers and mechanisms for
control of the gripping force and speed of gripping required for gripping
the wafer with a soft and reliable touch.