On the control of paraplegic standing using functional electrical stimulation
This thesis is concerned with the restoration of upright standing after spinal cord injury (SCI) by the means of Functional Electrical Stimulation. In particular, the work presented in this thesis is concerned with unsupported standing, i.e. standing without any support by the arms for stabilisation. Firstly, the experimental apparatus and feedback control approach is described. Secondly, the experimental work is divided into three parts. The motivation, experimental setup and procedure as well as results and conclusions are given for each of them. The feasibility of the investigated approach was usually tested on a neurologically intact subject. The results were subsequently confirmed with a paraplegic subject. First the feasibility and fundamental limitations of unsupported standing were investigated. Assuming the subject as a single-link inverted pendulum, an improved fully dynamic control approach was employed in the first step, confirming existing results. Here, the voluntary influence by the central nervous system was minimised. However, it is naturally desirable to take advantage of the residual sensory-motor abilities of the paraplegic subject to ease the task of stabilising the body. Ankle stiffness control has been proposed in the literature to accomplish this task. Hitherto, ankle stiffness was provided by artificial actuators. In the second part we investigated the feasibility and limitations of ankle stiffness control by means of FES. The same single-link approach was employed as above. Ankle stiffness control by FES was used in the third part to enable paraplegic standing. Here, the subject was required to participate actively in the task of stable standing and, while doing so, behaving like a double-link inverted pendulum. It could be shown that FES-controlled ankle stiffness contributed crucially to the subject's ability to stand. The thesis concludes with propositions for future work.