Brooks Automation 5. Software Reference
Part Number: 603988 Rev. A
Controlling the PreciseFlex
Servo Gripper
For this case it is more exact to know the exact number of tcnts to oppose the spring at various
openings. For the portrait mode opening of 83 mm it takes 1600 tcnts to oppose the spring. For the
landscape mode opening of 123 mm it takes 2200 tcnts to oppose the spring.
If the rated torque of the motor has been set to its maximum value of 1.26 A, the formula for setting
parameter 10352 is (Spring force at position) +((-<Contents of 10352>-<tcnts to oppose spring
force>)/4378) X18 N, where 4378 is the number of tcnts corresponding to 1.26 A or the rated torque
of the motor. For example, for portrait mode the spring force is about 6 N, and if the contents of
10352 are -3200, this value will be 6 N + (3200-1600)/4378) X18 N or about 12.5 N. If the value of
10352 is -1600, the squeeze will be 6 N which is the spring force only.
In a similar manner parameter 10351 can be used to limit the gripper opening force. In this case the
value for the opening force is ((<Contents of 10351>-<tcnts to oppose spring force>)/4378)X18 N –
(Spring force at position). For example, in landscape mode the spring force is about 8 N, and if the
contents of 10351 are 5200, this value will be (5200-2200)/4378X18 N -8 N or 4.3 N. Note that 5200
is about as low a value as one would want to use in landscape mode for parameter 10351, to ensure
there is enough force to oppose the spring and open the gripper all the way to the homing position.
For many cases, 10351 can be left at its default value of 0, in which case it is disabled.
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 18 N. 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 tcnts, or about 18 N. 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.
Copyright © 2023 Brooks Automation, Inc.
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