Operation
MagnaTran 7.1 User’s Manual
Wafer Presence Sensors- Radial Motion
MN-003-1600-00
Brooks Automation
6-38
Revision 2.2
Wafer Presence Sensors- Radial Motion
Radial Motion Sensors detect wafer presence on the specified arm while the arm is
traveling in radial (R axis) motion. The R_MT sensor will verify the success of any
wafer transfer operation (PICK/PLACE/GOTO/XFER).
The Radial Motion Sensor (R_MT) feature was designed to determine the load on the
end effector of the Brooks Automation Leapfrog arm set. Because of the “same-side”
design of the Leapfrog, it is not possible to determine which arm has a wafer on the
end effector when the arms are retracted.
However, the R_MT sensors may be used in any application where the sensors are
placed outside of the normal robot retract position.
R_MT Wafer Sensing Technique
The R_MT type wafer presence sensors work with the PICK, PLACE, XFER, and
GOTO (with MAT option) commands only. During MOVE operations, no wafer sen-
sor are active. During these operations, all motions will follow the speed and acceler-
ation profiles according to the arm load status in the robot memory map. The speed
and acceleration that the robot moves during the PICK, PLACE, XFER, and GOTO
operations is dependent on the load status of the end effector as discussed in
R_MT Placement Criteria
The placement of the wafer sensor with respect to the robot retract position deter-
mines the success of the sensing technique.
The best position for the R_MT wafer sensor is as close as possible to the wafer outer
edge while the arm is retracted. With this criteria, the robot can check the sensor to
determine if an operation has failed early in the beginning of the motion where the
robot has not reached it’s maximum velocity, acceleration, or inertia.
If the above scenario is not possible, as in the case of Leapfrog same-side arms, the
sensor can be placed underneath the wafer at the retracted position. In this scenario,
the wafer sensors are validated during the T-axis part of the motion to a station. The
sensor should be placed as close as possible to the outer edge of the wafer while in the
retract position and in the same T coordinates as the station. If the sensor has to be off-
set from the station T coordinates, then the offset must be specified in the station
setup.
