Cataloged from PDF version of article.Thesis (Ph.D.): Bilkent University, Department of Electrical and Electronics Engineering, İhsan Doğramacı Bilkent University, 2017.Includes bibliographical references (leaves 94-100).Passive dynamic walking models are capable of capturing basic properties of walking
behaviors and can generate stable human-like walking without any actuation
on downhill surfaces. The passive compass gait model is among the simplest of
such models, consisting of a planar point mass and two stick legs. A number of
di erent actuation methods have been proposed both for this model and its more
complex extensions to eliminate the need for a downhill sloped ground, balancing
collision losses using gravitational potential energy. In this thesis, we introduce
and investigate an extended compass gait model with series-elastic actuation at
the ankle towards a similar goal, realizing stable walking on various terrains such
as level ground, inclined surfaces and rough terrains. Our model seeks to capture
the basic structure of how humans utilize toe push-o prior to leg lifto , and
is intended to eventually be used for controlling the ankle joint in a lower-body
robotic orthosis.
We derive hybrid equations of motion for this model and obtain limit cycle
walking on level and inclined grounds. We then numerically identify xed points
of this system and and show numerically through Poincar e analysis that it can
achieve asymptotically stable walking on level and inclined ground for certain
choices of system parameters. The dependence of limit cycles and their stability
on system parameters such as spring precompression and sti ness for level ground
walking is identi ed by studying the bifurcation regimes of period doubling of this
model, leading to chaotic walking patterns. We show that feedback control on
the initial extension of the series ankle spring can be used to improve and extend
system stability on level ground walking. Then, we investigate and identify the
period doubling bifurcation regions of our model for spring precompression and
ground slope parameter leading to various maps that we utilize for rough terrainwalking. Furthermore, we evaluate the performance of our model on rough terrains
by applying ground slope feedback controllers on the spring precompression.
Thereafter, we demonstrate that slope feedback along with stance leg apex velocity
feedback control on the extension of the series ankle spring improves walking
performance on rough terrains.
The implementation of series elastic actuation on the ankle joint is realized
with an experimental instantiations of active ankle foot orthosis system for the
patients walking unnaturally and ine ciently with impaired ankles. Finally, we
integrate the active ankle foot orthosis platform with an active knee orthosis
platform where the experimentation results indicate that the integrated platform
can generate e cient walking patterns.by Deniz Kerimoğlu.Ph. D