In this paper, we introduce the key elements of a computational tool and a comprehensive methodology for enabling simulation-informed design of robotic ankle prostheses. Our approach is based on trajectory optimization methods for predicting human walking gait applied to a model of a bilateral lower leg amputee with robotic ankle prostheses. The goal of this simulation tool and design methodology is to provide a means to evaluate the performance of a prosthetic design and its effect on adapting human walking gait before involving human subject studies. The gait prediction problem is formulated as a multi-objective trajectory optimization of a multibody dynamic system within the existing framework of the open-source biomechanics package, OpenSim. Our approach models the effects of a planar human model with legs and torso, Hill-type muscle actuators, a closed-loop linkage for the robotic prosthetic device, and a DC motor dynamics model. To demonstrate the gait prediction process in use for design evaluation, we include a pair of example design evaluation simulations. In the first example, the gait prediction method shows that the initially proposed prosthesis design fails to improve the human effort estimated by cubic muscle excitations. In the second example, after the selection of a different actuator, the gait prediction method shows that the modified design has the potential to relieve some of the effort of walking required from the amputee. These examples combine to demonstrate how our methodology may be useful for design.

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