In this paper we present the force distribution analysis for a dual input actuator called parallel force/velocity actuator (PFVA). We present five physical quantities that are relevant to the design and operation of PFVA-based systems. For each of them we (i) follow a first principles approach to develop a model, (ii) define dimensionless parameters and criteria that indicate the relative distribution of the quantity between the two inputs of the PFVA, (iii) express the basic model in terms of these dimensionless parameters, (iv) provide numerical examples using five candidate designs with commercial off-the-shelf components, (v) investigate the limiting case as the two inputs become more and more kinematically distinct, and (vi) suggest design guidelines based on our analysis. We studied four aspects of PFVA design: (i) mixing of position uncertainties of the two inputs, i.e., force actuator (FA) and velocity actuator (VA), (ii) distribution of static and inertia torques between the inputs for a given output loading condition, (iii) acceleration responsiveness, and lastly, (iv) effective stiffness of the PFVA system with respect to some basic design parameters of the PFVA. As an example result, we observed that the PFVA's effective stiffness will be at least 40% greater than that of the VA if the FA is 85% as efficient as the VA, the FA is 17% less stiff than the VA, and the kinematic scaling between the two inputs (FA and VA) is approximately 11.5. The results we obtained are organized into five design guidelines for the PFVA. To demonstrate the utility of this analysis and the guidelines, we present a design case study that describes a PFVA prototype. The results of this paper assist in better designing PFVA-based systems with a focus on the coupling between the two inputs.

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