A comparison of serial, parallel, and dual Passive Assist Devices (PADs) designed using energy minimization based on a known maneuver is presented. Implementation of a PAD can result in an improvement in system performance with respect to efficiency, reliability, and/or safety. In previous work we demonstrated this concept experimentally on a single link robot arm augmented with a torsional spring in parallel. Here we show that the concept can extended to serial and dual systems as well. To make the optimization converge more quickly we introduce a new initial design using a weighted force displacement curve fit. We provide engineering insight into why different types of PADs perform differently depending on the maneuver and offer guidelines on how to select a specific type based on the application. Finally, we demonstrate this design process and selection procedure on a 3-link manipulator arm and show that a combination of parallel and dual PADs could reduce energy consumption by up to 78%.

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