Design and evaluation of a stiffness compensating ankle-foot orthosis

Design and evaluation of a stiffness compensating ankle-foot orthosis

Verbakel, F.

De Vlugt, E. (mentor)
De Groot, J.H. (mentor)

Mechanical, Maritime and Materials Engineering

BioMechanical Engineering

BMD

2013-04-18

This study proposes an ankle-foot orthosis (AFO) based on a novel concept to compensate increased ankle joint stiffness by adding negative stiffness to the joint. The negative stiffness working principle is a mechanism consisting of a spring generating force around a rotation axis, with a variable moment arm. The spring force is decreasing, when rotating the axis, less than the moment arm is increasing and torque thus increases. A mathematical model has been used to dimension different design parameters. The negative stiffness working principle has been realized with the first negative stiffness orthosis (NSO). Ten able-bodied subjects with an artificially increased ankle joint stiffness performed passive and active Range of Motion (RoM) tasks while wearing the NSO. The NSO increases ankle angles for constant torque input. Maximal active dorsiflexion angle increased as well, while dorsiflexor muscle EMG-activity decreased for equal ankle angles. The results show that the negative stiffness mechanism is able to partly compensate stiffness and support a better dorsiflexion angle to force ratio, which is especially beneficial in UMND patients with weaker muscles than normal. A prototype, suitable for walking, is to be developed.

ankle-foot orthosis
negative stiffness

http://resolver.tudelft.nl/uuid:c22a5bb4-c450-40fa-826f-f628b83a87ff

2018-03-18

Student theses

master thesis

(c) 2013 Verbakel, F.