Manual, Passive Compliant Force Control
Document #9610-50-1036-04
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4.3.1 Gravity Compensation
The PCFC sensor kit supports gravity compensation. This feature allows the tool to automatically
adjust the compliance force as the tool’s orientation changes with respect to gravity. A sensor built
into the tool tracks the tool’s movements and notes when the tool rotates about X or Y. As this
change occurs, a signal is sent to a programmable regulator to adjust the air pressure being sent to
the retract air‑port. This increase or decrease in air pressure allows the tool to compensate for the
changing forces applied to the workpiece by the weight of the tool. It is important to note that if a
user is planning to use gravity compensation, the weight of the tooling cannot exceed 50% of the
PCFC’s maximum compliance force. This is because when the PCFC is pointed straight down, the
force of the retract pressure must equal two times the weight of the tooling in order to properly bias
out the weight over the entire range of motion.
Without gravity compensation, it is possible to maintain consistent force between a workpiece and
tool through the various tool orientations necessary in complex motions, but it can be very difficult
and time consuming. In standard operation, the force applied would be subject to the orientation
of the tool. When the workpiece is “above” the tool, the pistons push the tool “up” toward the
workpiece while gravity counteracts the pistons and pulls the tool “away” from the workpiece.
However, when the tool rotates and the workpiece is now “below” the tool, the pistons still push
with the same amount of force toward the workpiece, but now that force combines with the effect
of gravity which pulls the tool “toward” the workpiece, creating a large increase on force applied
to the workpiece. This range in force (compliance force +/‑ weight of tool) can be severe and as
varied as the tools that are fixed to the PCFC. Varying force can lead to inconsistent results and
poor process performance.
