  Multi-agent human-robot co-manipulation is a poorly understood process with
many inputs that potentially affect agent behavior. This paper explores one
such input known as interaction force. Interaction force is potentially a
primary component in communication that occurs during co-manipulation. There
are, however, many different perspectives and definitions of interaction force
in the literature. Therefore, a decomposition of interaction force is proposed
that provides a consistent way of ascertaining the state of an agent relative
to the group for multi-agent co-manipulation. This proposed method extends a
current definition from one to four degrees of freedom, does not rely on a
predefined object path, and is independent of the number of agents acting on
the system and their locations and input wrenches (forces and torques). In
addition, all of the necessary measures can be obtained by a self-contained
robotic system, allowing for a more flexible and adaptive approach for future
co-manipulation robot controllers.
