Analysis and control of FES-assisted paraplegic walking with wheel walker.

The number of people with spinal cord injury (SCI) is increasing every year and
walking has been found to be the most exciting and important prospect to these
patients to improve their quality of life. Many individuals with incomplete SCI
have the potential to walk and everyone of them wants to try. Unfortunately up to
now, there is less than one third of patients could walk again after SCI. Residual
function, the orthotic support, energy expenditure, patient motivation and control
technique are some of the factors that influence the walking outcome of spinal cord
injured people. In this thesis, a series of studies are carried out to investigate the
possibility of enhancing the performance of the functional electrical stimulation
(PES) assisted paraplegic walking with wheel walker through the development and
implementation of intelligent control technique and spring brake orthosis (SBO)
with full utilization of the voluntary upper body effort. The main aim of this thesis
is to enable individuals with complete paraplegia to walk again with maximum
performance and the simplest approach as possible.
Firstly, before simulation of the system can be made, it is important to select the
right model to represent the actual plant. In this thesis, the development of a
humanoid and wheel walker models are carried out using MSC.visualNastran4D
(vN4D) software and this is integrated with Matlab Simulink® for simulation. The
newly developed quadriceps and hamstrings muscle models from the series of
experiments are used to represent subject muscles after comparison and validation
with other two well-known muscle models are performed.
Several experiments are conducted to investigate the effect of stimulation frequency
and pulse-width in intermittent stimulation with isometric measurement from
paraplegic subjects. The results from this work can serve as a guidance to determine
the optimum stimulation parameters such as frequency and pulse-width to reduce
muscle fatigue during PES application. The ability test is introduced to determine
the maximum leg force that can be applied to the specific paraplegic subject during
FES functional task with minimum chance of spasm and leg injury.
Investigations are carried out on the control techniques implemented for FES
walking with wheel walker. PID control and fuzzy logic control (FLC) are used to
regulate the electrical stimulation required by the quadriceps and hamstrings
muscles in order to perform the FES walking manoeuvre according to predefined
walking trajectory. The body weight transfer is introduced to increase the efficiency
of FES walking performance. The effectiveness of body weight transfer and control
strategy to enhance the performance of FES walking and reduce stimulation pulses
required is examined.
Investigations are carried out on the effectiveness of spring brake orthosis (SBO)
for FES assisted paraplegic walking with wheel walker. A new concept in hybrid
orthotics provides solutions to the problems that affect current 'hybrid orthosis,
including knee and hip flexion without relying on the withdrawal reflex or a
powered actuator and foot-ground clearance without extra upper body effort. The
use of SBO can also eliminate electrical stimulation pulses required by the
hamstrings muscle for the same FES walking system.
Further improvement of the FES walking system is achieved by introducing finite
state control (FSC) to control the switching time between springs, brakes and
electrical stimulation during FES assisted walking with wheel walker with the
combInation of FLC to regulate the electrical stimulation required for the knee
extension. The results show that FSC can be used to accurately control the
switching time and improve the system robustness and stability.