Andrzej Ordys

Ashwin Needham

Journal of Foot and Ankle Research

PubMed

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MEETING ABSTRACT Open Access
Active control of a powered ankle-foot prosthesis
Ashwin Needham*, Andrzej Ordys
From 4th Congress of the International Foot and Ankle Biomechanics (i-FAB) Community
Busan, Korea. 8-11 April 2014
Amputees suffer a higher metabolic demand on their
bodies. Passive prostheses seek to reduce this deficit
through elastic distribution of the energy inherently dis-
sipated in walking. Yet with no capacity to generate tor-
que they lack truly biomimetic function. The active
prosthesis is a solution to this and opens up a world of
active control in the timing and magnitude of energy
return. Being able to also modulate the dynamic charac-
ter of the replaced joint, in impedance and position,
brings us closer to a true model of the ankle-foot com-
plex. And so the ankle-foot complex can be seen to be
modelled as a visco-elastic system with loading and
unloading phases and active power output.
It was identified that the concept of the active auto-
mobile suspension system designed by Bose has the
capacity to satisfy these functional demands and so was
investigated as a viable model for a prosthetic device. In
using this model, the ankle joint was modelled as a
motor, driven in drive and dynamo modes to convert an
elastic system into an electromagnetic system based
around a battery. Low power drain derived from signifi-
cant power recovery makes this concept particularly
interesting. The versatility of this concept is regarded as
approaching that of the human beyond those devices
that rely on passive or fixed elastic systems. This is
active elasticity.
A CAD model was generated along with a correspond-
ing control scheme. The control system is proposed as a
viable and innovative concept for future prosthetics with
great potential for development.
This proposal makes use of underfoot sensors to deter-
mine the displacement of the fore and aft sections of the
* Correspondence: ashwin.needham@hotmail.co.uk
School of Mechanical and Automotive Engineering, Kingston University,
London, UK
Figure 1 Torque-angle, or stiffness profile derived from exponential function. (Figure 1 inspired largely by [1] as a means of comparison to a
typical torque-angle profile.)
Needham and Ordys Journal of Foot and Ankle Research 2014, 7(Suppl1):A60
http://www.jfootankleres.com/content/7/S1/A60
JOURNAL OF FOOT
AND ANKLE RESEARCH
© 2014 Needham and Ordys; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
foot above ground, and is proposed as an effective sen-
sory concept to facilitate handling of various terrain
including slopes and stairs. The concept is seen as highly
versatile in this respect. Models for both slope and stair
walking have been implemented.
An exponential function was proposed as a model for
the action of impedance at the ankle. This is a highly ver-
satile function that can be matched, using discrete tuning
parameters, to each phase of stance against a majority of
samples during level walking. This function also facilitates
the smooth and controlled contact between the foot and
the ground when combined with the underfoot sensors.
The concept is not fully developed but has been
initiated. Much further work is possible.
Thesis Supervisor: Professor Andrzej Ordys.
November 2013.
Published: 8 April 2014
Reference
1. Au SK: Powered ankle-foot prosthesis for the improvement of amputee
walking economy. Ph.D. dissertation, Massachusetts Inst. Technol Cambridge,
MA; 2007, 21.
doi:10.1186/1757-1146-7-S1-A60
Cite this article as: Needham and Ordys: Active control of a powered
ankle-foot prosthesis. Journal of Foot and Ankle Research 2014
7(Suppl1):A60.
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Needham and Ordys Journal of Foot and Ankle Research 2014, 7(Suppl1):A60
http://www.jfootankleres.com/content/7/S1/A60
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Active control of a powered ankle-foot prosthesis

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Active control of a powered ankle-foot prosthesis

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