Design and control of a knee exoskeleton powered by pleated pneumatic artificial muscles for robot-assisted gait rehabilitation

Student thesis: Doctoral Thesis


Research in robot-assisted rehabilitation of gait has known a paradigm shift towards
a more human-centered approach, focusing on assistance-as-needed, increased
functionality and adaptability of the environment displayed by the device.
Physical human-robot interaction (pHRI) is a key aspect in this approach. From
an engineering viewpoint the improvement of pHRI is sought in wearable design,
high performance actuator technologies and dedicated control strategies.
In this dissertation a combination of lightweight, intrinsically compliant actuators
with high force output (pleated pneumatic artificial muscles) and safe, adaptable
guidance along a target trajectory is investigated for end use in a full lower limb
exoskeleton. A powered knee exoskeleton, KNEXO, has been developed for this
In its design, emphasis was laid on optimising the actuator system conguration
and on the adaptability of the human-robot interface.
As for control, two different, but complementary control strategies have been studied
by means of simulations and experiments: a torque controller and a trajectory
tracking based assistive controller. The torque controller supports an unassisted
walking mode, that serves as a baseline for the performance evaluation of robotic
assistance and that enables the recording of reference and target trajectories. The
assistive controller uses proxy-based sliding mode control (PSMC) in conjunction
with a non-model based support torque to provide an assisted walking mode that
safely allows for deviations from the target trajectory.
Treadmill walking experiments have been performed in unimpaired subjects wearing
KNEXO in order to assess wearability and to investigate controller performance
in view of impaired subject testing. Experimental results verified that the combination
of intrinsically compliant actuators with proxy-based sliding mode control
achieves compliant guidance and at the same time exhibits a safe and tunable response
to human-robot interaction torques. Following this positive evaluation, a
hemiparetic stroke patient and a multiple sclerosis patient participated in a series
of pilot assisted walking experiments. Provided a patient-specific controller tuning,
based on experience gained from experiments with unimpaired subjects, KNEXO
effectively supports and compliantly guides the subject's impaired knee. Both in
unimpaired and impaired subjects gait kinematics measurements and muscle EMG
measurements have been performed to quantify human-robot interaction.
Considering these promising results, the methods proposed in this work contribute
towards a more human-centered rehabilitation of gait.
Date of Award20 Dec 2010
Original languageEnglish
SupervisorDirk Lefeber (Promotor), Michael Van Damme (Jury), Bram Vanderborght (Jury), Annick Hubin (Jury), Rik Pintelon (Jury), Romain Meeusen (Jury), Sunil K. Agrawal (Jury) & Eugenio Guglielmelli (Jury)


  • rehabilitation robotics
  • gait rehabilitation
  • powered exoskeleton
  • physical human-robot interaction
  • compliant actuator
  • pleated pneumatic artificial muscle
  • adaptable compliance
  • assistance-as-needed
  • robot-assisted walking
  • proxy-based sliding mode control

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