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. 2017 Nov 17;12(11):e0188266.
doi: 10.1371/journal.pone.0188266. eCollection 2017.

Optimal design and control of an electromechanical transfemoral prosthesis with energy regeneration

Farbod Rohani  1   2 , Hanz Richter  2 , Antonie J van den Bogert  2
Affiliations

Optimal design and control of an electromechanical transfemoral prosthesis with energy regeneration

Farbod Rohani et al. PLoS One. .

Abstract

In this paper, we present the design of an electromechanical above-knee active prosthesis with energy storage and regeneration. The system consists of geared knee and ankle motors, parallel springs for each motor, an ultracapacitor, and controllable four-quadrant power converters. The goal is to maximize the performance of the system by finding optimal controls and design parameters. A model of the system dynamics was developed, and used to solve a combined trajectory and design optimization problem. The objectives of the optimization were to minimize tracking error relative to human joint motions, as well as energy use. The optimization problem was solved by the method of direct collocation, based on joint torque and joint angle data from ten subjects walking at three speeds. After optimization of controls and design parameters, the simulated system could operate at zero energy cost while still closely emulating able-bodied gait. This was achieved by controlled energy transfer between knee and ankle, and by controlled storage and release of energy throughout the gait cycle. Optimal gear ratios and spring parameters were similar across subjects and walking speeds.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Schematic diagram of the electromechanical prosthetic system with motors at ankle (left) and knee (right).
Fig 2
Fig 2. The tradeoff between energy cost and RMS tracking error shown as a Pareto front.
Fig 3
Fig 3. Optimal joint angles, capacitor energy, control signals, and tracking errors for three walking speeds in the zero-energy case for subject 1.
Time is expressed as a percentage of the gait cycle, from heel strike to the next heel strike. See text for further details.
See this image and copyright information in PMC

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