  Presented in this paper is an actuator concept, called a Parallel
Force/Velocity Actuator (PFVA), that combines two fundamentally distinct
actuators (one using low gear reduction or even direct drive, which we will
call a Force Actuator (FA) and the other with a high reduction gear train that
we will refer to as a Velocity Actuator (VA)). The objective of this work is to
evaluate the effect of the relative scale factor, RSF, (ratio of gear
reductions) between these inputs on their dynamic coupling. We conceptually
describe a Parallel Force/Velocity Actuator (PFVA) based on a
Dual-Input-Single- Output (DISO) epicyclic gear train. We then present an
analytical formulation for the variation of the dynamic coupling term w.r.t.
RSF. Conclusions from this formulation are illustrated through a numerical
example involving a 1-DOF four-bar linkage. It is shown, both analytically and
numerically, that as we increase the RSF, the two inputs to the PFVA are
decoupled w.r.t. the inertia torques. This understanding can serve as an
important design guideline for PFVAs. The paper also presents two limitations
of this study and suggests future work based on these caveats.
