Nonlinear robust control of functional electrical stimulation system for paraplegia

The study was directed towards enhancing Functional Electrical Stimulation (FES) for sit-to-stand movement restoration in paraplegia subjects. The scarcity of FES assistive devices was due to the inability of the developed equipment to attain clinical acceptance. Applications of control systems have shown fruitful results. And based on the literature, further improvements in model, trajectory and control systems are needed. Model with a higher level of accuracy and continuous as well as bump-free trajectories are essential ingredients for better control systems. The control systems can be enhanced by giving considering to changes in mass of the subject, disturbance rejection and stability. Hence, the comprehensive control scheme is necessary for this application as well as a better model and trajectory. In modelling an additional joint has been considered to improve the accuracy. In trajectory planning, the six-order polynomial has been used to refine the desired trajectory. The comprehensive control systems have been designed with consideration of robustness, disturbance rejection, and stability. Three nonlinear control approaches have been investigated; the Sliding Mode Control (SMC), Feedback Linearisation Control (FLC), and Back-Stepping Control (BSC). Results reveal improvements in the accuracy of the kinematic model by 24%, and the dynamic model by 47%. The trajectory planning parameters are continuous, and not susceptible to jerks or spikes. Execution time enhanced by 11%, the upper and lower terminal velocities improved by 16.9% and 20.9% respectively. The system response without disturbance shows good results with the SMC, FLC, and BSC. Revelations by robustness examination also maintain remarkable enhancements in the parameters with both 53% and 126% mass. The results for disturbance rejection examinations with fatigue, spasm, tremor, and combined disturbance effects showed sustenance of refinement in the response parameters. Therefore, indicating improvements despite the changes to the system. The BSC showed the best performance, followed by the FLC, and the SMC. Hence, the BSC is recommended for such systems

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

Computer modelling and experimental design of a gait orthosis for early rehabilitation of walking

Walking is a fundamental human activity [1]. Rehabilitation of walking is one of the essential goals for patients with spinal cord injury (SCI) or other neurological impairments [2, 3]. Early rehabilitation is desirable to maximise the beneficial effects, so training programmes should be initiated even when patients are still on bed rest. In order to promote early rehabilitation of patients with incomplete spinal cord injury who cannot maintain an upright posture, a Gait Orthosis for Early Rehabilitation (GOER) of walking was designed [2] and evaluated in this PhD work. This research started with a gait analysis experiment, through which the kinematics and kinetics of overground walking were investigated. Based on experimental walking data from able-bodied subjects, a least squares algorithm was developed to approximate the foot trajectories with circles. The determination of the best-fit circle for the toe trajectory over the whole gait cycle provided the basis for inducing toe movement by a rigid bar. Therefore a model of a two-bar mechanism was developed in Matlab/SimMechanics to simulate supine stepping. The simulated kinematics, including the angles of the hip, knee and ankle joints, showed comparable ranges of motion (ROMs) to the experimental walking performance in able-bodied subjects. This two-bar model provided the basis for the development of the GOER system. The intersegmental kinetics of the lower limb motion during supine stepping were investigated through computer simulation. A model of a leg linkage was firstly developed to simulate upright walking. After the model was validated by successful simulation of dynamic performance similar to experimental overground walking, the model was rotated by 90o to simulate stepping movement in a supine posture. It was found that the dynamics of the hip joint were significantly influenced by the position change from upright to supine, which highlighted the importance of a leg-weight support during supine stepping. In contrast, the kinetics of the ankle joint were much influenced by the forces applied on the foot sole which mimicked the ground reaction occurring during overground walking. Therefore a suitable force pattern was required on the foot sole in order to train the ankle joint during supine stepping. The simulated kinematic and kinetic results provided the basis for the design process of the GOER system. A GOER prototype with mechanisms for one leg was manufactured, which included a bar linkage to move the leg frame upwards and downwards and a cam-roller mechanism to rotate the shoe platform. The bar-cam GOER prototype achieved coordinated movements in the leg frame through constant rotation of an electric motor. Preliminary tests were carried out in three able-bodied subjects who followed the movements produced by the GOER prototype. The subjects felt walking-like stepping movement in the lower limb. Synchronised motion in the hip, knee and ankle joints was obtained, with the ROMs in the physiological ranges of motion during overground walking. The experimentally obtained joint profiles during supine stepping matched the simulated supine stepping and were close to the profiles during overground walking. Apart from inducing proprioceptive feedback from the lower limb joints, the GOER system required dynamic stimulation from the shoe platform to mimic load occurring during the stance phase of overground walking. Activated by pneumatic components, the shoe platform managed to apply forces on the foot sole with adjustable amplitudes. The pneumatic shoe platform was evaluated in ten able-bodied subjects and managed to induce walking-like pressure sensation on the foot sole with physiological responses from the leg muscles. In summary, this thesis developed and evaluated a new gait training robotic system targeting supine stepping for patients who are still restricted to a lying position. The conceptual design process was developed through computer modelling and it was implemented as a prototype. Evaluation tests on able-bodied subjects proved the technical feasibility of the robotic system for supine stepping and led to recommendations for further development

Neuro-fuzzy modeling of multi-field surface neuroprostheses for hand grasp

154 p.Las neuroprótesis aplican pulsos eléctricos a los nervios periféricos con el objetivo de sustituir funciones motrices/sensoriales perdidas, dando asistencia e influyendo positivamente en la rehabilitación motriz de personas con disfunciones motrices causadas por trastornos neurológicos. La complejidad de la neuroanatomía del antebrazo y la mano, su dimensionalidad, las diversas tareas no-cíclicas, la variabilidad de movimientos entre sujetos y la reducida selectividad de las neuroprótesis superficiales, ha dado lugar al diseño de un número reducido de neuroprótesis orientadas a agarres básicos. La posibilidad de hacer más selectiva la estimulación mediante los electrodos multi-campo, junto con el conocimiento sobre la incomodidad y los movimientos que genera la aplicación de la estimulación eléctrica funcional (FES por sus siglas en inglés) en miembro superior, podrían ser base fundamental para el desarrollo de neuroprótesis de agarre más avanzadas. La presente tesis describe un análisis de incomodidad como resultado de FES en el miembro superior, y propone modelos neuro-difusos para neuroprótesis de agarre tanto para personas sanas como para personas con trastornos neurológicos. El conocimiento generado respecto a la incomodidad puede ser utilizado como guía para desarrollar aplicaciones de FES de miembro superior más cómodas. Del mismo modo, los modelos propuestos en esta tesis pueden ser utilizados para apoyar el diseño y la validación de sistemas de control avanzados en neuroprótesis dirigidas a la función de agarre.Tecnalia; Intelligent Control Research Grou

Model based experimental investigation on Powered Gait Orthosis (PGO)

Research on rehabilitation showed that appropriate and repetitive mechanical movements can help spinal cord injured individuals to restore their functional standing and walking. The objective of this paper was to achieve appropriate and repetitive joint movements and approximately normal gait through the PGO by replicating normal walking, and to minimize the energy consumption for both patients and the device. A model based experimental investigative approach is presented in this dissertation. First, a human model was created in Ideas and human walking was simulated in Adams. The main feature of this model was the foot ground contact model, which had distributed contact points along the foot and varied viscoelasticity. The model was validated by comparison of simulated results of normal walking and measured ones from the literature. It was used to simulate current PGO walking to investigate the real causes of poor function of the current PGO, even though it had joint movements close to normal walking. The direct cause was one leg moving at a time, which resulted in short step length and no clearance after toe off. It can not be solved by simply adding power on both hip joints. In order to find a better answer, a PGO mechanism model was used to investigate different walking mechanisms by locking or releasing some joints. A trade-off between energy consumption, control complexity and standing position was found. Finally a foot release PGO virtual model was created and simulated and only foot release mechanism was developed into a prototype. Both the release mechanism and the design of foot release were validated through the experiment by adding the foot release on the current PGO. This demonstrated an advancement in improving functional aspects of the current PGO even without a whole physical model of foot release PGO for comparison