Optimizing the power and energy consumption of powered prosthetic ankles with series and parallel elasticity

Abstract

Several works have shown that series and parallel elasticity can reduce peak power and energy consumption in prosthetic ankles. Setting the right stiness of the elastic elements is essential to unlock this potential. In this work, we perform a thorough optimization of series and parallel elastic elements for a prosthetic ankle driven by a geared DC motor. Through simulation, we study the eect of drivetrain limitations and compare dierent mechanical and electrical optimization objectives. The results highlight the importance of selecting a motor and gearbox in an early stage of the design process. Drivetrain inertia causes peaks in electrical power in the swing phase, which would go unnoticed in an optimization based solely on mechanical power. Furthermore, limitations of the drivetrain and controller reduce the range of applicable springs. This has a direct inuence on the optimized spring stiness values, which, as a result, are dierent from other works. Overall, the results suggest that, by integrating motor selection into the early stages of the design process, designs can be made lighter, more compact and more ecient.

Design and Analysis of Novel Actuation Mechanism with Controllable Stiffness

“…That is: (12) where n = n(θ 0 ) from the rolling contact constraints (Equations (6) and 7). Therefore, using this relationship and Equations (10) and (11), a single nonlinear equation in θ 0 is obtained, which can be solved using a tool such as Matlab's fsolve or a custom line search. Additionally, parameters a and b can be found by this process.…”

“…The following abbreviations are used in this manuscript: End deflections a and b presented in Equations (10) and (11) of Section 3.2 are defined by using a set of homogeneous coordinate transformations (translation and rotation), which is presented in the following:…”

“…SEA design may be optimized with the goal of decreasing energy consumption by proper selection of the compliant element's stiffness [9]. Furthermore, optimization techniques may be used to select the motor and the mechanism parameters [10][11][12].…”

A Short Review on the Cost, Design, Materials and Challenges of the Prosthetics Leg Development and Usage

“…Studies have shown that adding an active element in prosthesis can aid in attaining the similar energy as if in the real limb and reduced metabolic cost but somehow it increases the weight that is also correspond to added energy during walking and resulting in asymmetric gait [29]. In order to prevent these comorbidities, many researches have been done to investigate the series and parallel elasticity for power amplification and energy storage and at the same time reduces the actuation unit weight as shown in Figure 2 [30]. Addition of series and parallel elasticity can reduce the peak power and reducing the torque values where reducing the energy consumption at the same time [31].…”

“…Addition of series and parallel elasticity can reduce the peak power and reducing the torque values where reducing the energy consumption at the same time [31]. Addressing motor design, gearbox and springs and studying the operating range for each component in the actuated prosthesis is necessary to reduce the energy consumption, perform a better dynamic response, reduce size and weight [30].…”