Brooks Automation
P/N: PFD0-DI-00010, Rev 5.0.0, April 9, 2022
Gripper Support
Copyright © 2022, Brooks Automation, Inc.
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210002. This input can be viewed in the Web Browser under Control Panels/Remote IO/Network Node 2
IO. At power up this sensor can be checked to determine if the gripper is fully closed, and thus not
holding a plate. If the gripper is not fully closed it will be holding a plate, and the operator should be
directed to remove the plate before homing the robot, which will open the gripper to the maximum hard
stop.
Grip Test and Squeeze Check
It may be desirable to check if a plate is gripped by checking the gripping torque value. The output torque
to the motor is available in Parameter 12304, value 5 in the parameter data base. For a non-spring
gripper, this value varies between 0 and 4378 tcnts for a maximum gripper force of 18N. For a spring
gripper, per above, for a portrait grip, the spring adds about 1600 tcnts to the squeeze and for a
landscape grip, it adds about 2200 torque counts to the squeeze. Since this value is taken into account
by the spring compensation and is offset from the torque commanded to the motor in Parameter 12304,
when checking Parameter 12304 to determine squeeze the spring compensation must be subtracted from
the torque value in Parameter 12304. For example, if the gripper is at the portrait position and not holding
a plate, it must servo against the spring. In this case the value in Parameter 12304 will be about 1600
tcnts. To determine the effective squeeze torque, subtract 1600 tcnts from this value, which results in
zero tcnts of squeeze force. If the value in 12304 is -2700, then the gripper motor is squeezing with -
2700 tcnts, and the spring is adding -1600 tcnts, and the effective squeeze is -4300 tncts, or about
18N. The exact spring compensation value is stored in field 5 of Parameter 12331. For the best
accuracy in determining effective squeeze force at any gripper opening, subtract this value from the value
in 12304.
Servo Gripper Controller Digital Inputs and Outputs
The Servo Gripper Controller PCA (GSBP) adds 3 general optically isolated digital outputs and 3 general
optically isolated digital inputs to the standard digital I/O found on the PreciseFlex™ Controller. Like the
other general inputs and outputs, they can be assigned for various control purposes during system setup,
or they can be used directly by a GPL procedure. Digital output 3 has a 1,000ohm resistor in series with
the output to limit current to LED indicator lights.
Unlike the controller's standard digital I/O that are directly accessed on demand, these I/O are scanned
by the controller. The scanning period is nominally 4 milliseconds, so your application must be able to
handle a delay of up to 4 milliseconds for signal changes to propagate through the system. Note that two
IO pins have optional assignments based on jumpers. For J4 connect pins 2 and 3 to connect Digital
Input 1 to pin 6 and connect pins 1 and 2 to connect pin 6 to a line that goes back to the controller RS232
RXD input. For J7 connect pins 2 and 3 to connect Digital Output 3 to pin 3 and connect pins 1 and 2 to
connect pin 3 to a line that goes back to the controller RS232 TXD input.
