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

Feasibility of Using Neuro-Fuzzy Subject-Specific Models for Functional Electrical Stimulation Induced Hand Movements

Functional Electrical Stimulation (FES) is a technique that artificially elicits muscle contractions and it is used to restore motor/sensory functions in both assistive and therapeutic applications. The use of multi-field surface electrodes is a novel popular approach in transcutaneous FES applications. Lately, hybrid systems that combine artificial neural networks and fuzzy logic have also been proposed for many applications in different areas. This paper presents the possibility of combining both approaches for obtaining subject-specific models of FES induced hand movements for grasping applications. Data of the hand and finger motion from two subjects affected by acquired brain injury were used to train two different approaches: coactive neuro-fuzzy inference system and recurrent fuzzy neural network. Preliminary results show that these approaches can be considered in modelling applications for their ability to learn and predict main characteristics of the system, as well as providing useful information from the original system that could be interpreted as subject-specific knowledge

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

Controle rítmico para aplicações de estimulação elétrica funcional usando modelos musculoesqueléticos detalhados

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2017.O objetivo principal deste trabalho é projetar novos controladores para exercícios rítmicos assistidos por FES, como ciclismo e remo. Este trabalho faz parte de um esforço de pesquisa mais amplo baseado na reabilitação de SCI com base em princípios de neuro-engenharia e robótica integrados com fisioterapia orientada. Uma estrutura básica para simulação de modelos musculoesqueléticos detalhados foi desenvolvida para acelerar a prototipagem de novas estratégias de controle. O controle básico possui um controlador de estado finito no nível superior e um controlador de nível inferior que calcula a intensidade da ativação dos músculos. Um controlador com primitivas de movimento com base na dinâmica de atratores foi desenvolvido para o exercício de remo e osciladores acoplados foram adicionados aos controladores para exercícios de remo e ciclismo. Além disso, algoritmos genéticos foram utilizados para estimar os parâmetros dos controladores, minimizar o nível geral da estimulação elétrica aplicada e aumentar a robustez em ambientes com configurações diferentes. No caso do exercício de ciclismo, os mesmos parâmetros foram utilizados em simulações com ruído, fadiga, diferentes cargas e escalas. Além da avaliação de desempenho, a eficiência do gasto energético metabólico dos modelos musculoesqueléticos também foi calculada como método alternativo para comparar diferentes aplicações FES. Os resultados demonstraram que a adição de osciladores acoplados aumentou a eficiência em ambos os exercícios. Além disso, o ciclismo assistido por FES parece ser mais adequado para participantes com deficiência motora que têm músculos fracos e baixa resistência devido à sua menor ativação muscular e ao gasto de energia metabólica. O remo assistido por FES pode ser usado depois para melhorar a potência dos músculos.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).The main objective of this work concerns the design of new controllers for rhythmic exercises assisted by functional electrical stimulation (FES), such as cycling and rowing. This work is part of a broader research effort targeting spinal cord injury rehabilitation based on principles of neuro-engineering and robotics integrated with goal-directed physical therapy. We developed a basic framework for simulation of detailed musculoskeletal models to accelerate the prototyping of new control strategies. The basic control features a higher level finite state controller and a lower level controller which calculates the activation level of the muscles. A controller with motor primitives based on attractor dynamics was developed for the rowing exercise, and coupled oscillators were added to controllers of both cycling and rowing exercises. Furthermore, we used genetic algorithms to estimate the controllers parameters, minimize the overall level of applied electrical stimulation and increase the robustness in environments with different configurations. In the case of the cycling exercise, we used the same parameters in simulations with noise, fatigue, different loads, and scales. Besides the performance evaluation, we also calculated the efficiency of the metabolic energy expenditure of the musculoskeletal models as an alternative method to compare different FES applications. Results demonstrated that the addition of coupled oscillators increased the efficiency in both exercises. Also, FES cycling seems to be more suitable for participants with motor disabilities who have weak muscles and low endurance due to its lower muscle activation and metabolic energy expenditure. FES rowing can be used later for improving the power of the muscles

Feedback control of cycling in spinal cord injury using functional electrical stimulation

This thesis is concerned with the realisation of leg cycling by means of FES in SCI individuals with complete paraplegia. FES lower-limb cycling can be safely performed by paraplegics on static ergometers or recumbent tricycles. In this work, different FES cycling systems were developed for clinical and home use. Two design approaches have been followed. The first is based on the adaptation of commercially available recumbent tricycles. This results in devices which can be used as static trainers or for mobile cycling. The second design approach utilises a commercially available motorised ergometer which can be operated while sitting in a wheelchair. The developed FES cycling systems can be operated in isotonic (constant cycling resistance) or isokinetic mode (constant cadence) when used as static trainers. This represents a novelty compared to existing FES cycling systems. In order to realise isokinetic cycling, an electric motor is needed to assist or resist the cycling movement to maintain a constant cadence. Repetitive control technology is applied to the motor in this context to virtually eliminate disturbance caused by the FES activated musculature which are periodic with respect to the cadence. Furthermore, new methods for feedback control of the patient’s work rate have been introduced. A one year pilot study on FES cycling with paraplegic subjects has been carried out. Effective indoor cycling on a trainer setup could be achieved for long periods up to an hour, and mobile outdoor cycling was performed over useful distances. Power output of FES cycling was in the range of 15 to 20 W for two of the three subjects at the end of the pilot study. A muscle strengthening programme was carried out prior and concurrent to the FES cycling. Feedback control of FES assisted weight lifting exercises by quadriceps stimulation has been studied in this context

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

Neuroprostheses control interfaces based on body motion in persons with spinal cord injury

Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2019.A lesão medular (LM) é uma condição médica que frequentemente leva a deficiências motoras severas. Pessoas com LM podem ter paraplegia ou tetraplegia, e perder suas habilidades de realizar tarefas básicas como locomoção, alimentação e higiene. Ela afeta centenas de milhares de pessoas apenas no Brasil e muito poucos se recuperam totalmente. Tratamentos tradicionais como fisioterapia normalmente têm resultados limitados. Uma pessoa com LM pode não conseguir controlar seus membros superiores e inferiores, mas normalmente as estruturas locais, como músculos e neurônios motores, são preservados. Portanto estimulação elétrica funcional (EEF) pode ser usada para induzir contração nesses músculos e gerar movimento em membros paralisados. Neste trabalho eu desenvolvi uma plataforma de técnicas para interfaces de usuário que explora capacidades motoras residuais que usuários com LM podem ainda ter para controlar neuropróteses. Para obter informações de movimento, uso unidades de medida inercial (UMI). Eu desenvolvi e avaliei algoritmos para detecção e classificação de movimentos de usuários com paraplegia e tetraplegia. O objetivo é que os usuários possam usar seus próprios movimentos residuais, dependendo do seu nível de lesão, para ativar diferentes comandos de dispositivos assistivos. Eu usei as técnicas desenvolvidas em três cenários de aplicações com pessoas com LM. Primeiro eu executei um experimento em que três participantes com paraplegia ativaram um dispositivo ativado por EEF para auxílio em transferências sentado-pivô (TSP). Eu analisei dados cinemáticos dos troncos para investigar a viabilidade de usar essa informação para ativar a EEF nos seus membros inferiores durante a TSP. Depois eu desenvolvi uma interface com a qual nove participantes com tetraplegia usaram movimentos de ombro para controlar uma mão robótica simulando um dispositivo de auxílio de preensão manual. Eu usei dados de acelerômetros e giroscópios e uma análise de componente principal para classificá-los. Então eu mapeei esses movimentos em três comandos na mão robótica. Em seguida eu desenvolvi uma interface que usa dados cinemáticos de membros superiores para ativar uma neuroprótese acionada por EEF em membros inferiores de pessoas com paraplegia durante remo assistido por EEF. Eu usei uma máquina de estados finitos e análise discriminante linear para classificar todos os movimentos de membro superior do usuário em três comandos de fases diferentes no remo. Eu avaliei esse sistema com um participante e um remo ergômetro adaptado para remadores com LM. No experimento de transferência, cada participante moveu seu tronco de uma forma similar em todas as repetições, com desvios padrão de ângulos menores que 5°, o que significa que eu posso usar essa técnica para automatizar a ativação da EEF. Os participantes que utilizaram a interface de simulação de preensão manual conseguiram controlar a mão robótica com sucesso, corretamente executando 91% dos comandos solicitados. Por fim, o participante do protocolo de remo foi capaz de remar com a interface desenvolvida utilizando apenas os movimentos de membros superiores. O sistema ativou a neuroprótese em seus membros inferiores em sincronia com os seus membros superiores. Esses resultados mostram que pessoas com LM conseguem usar seus movimentos residuais para controlar dispositivos assistivos nas condições observadas.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Apoio à Pesquisa do Distrito Federal (FAP/DF) e Instituto de Engenheiros Eletricistas e Eletrônicos (IEEE).Spinal cord injury (SCI) is a serious medical condition that often leads to severe motor disabilities. Persons with SCI may have paraplegia or tetraplegia, greatly decreasing their ability to perform basic tasks such as locomotion, feeding and hygiene. It affects hundreds of thousands of people in Brazil alone and very few people totally recover from it. Traditional recovery treatments such as physiotherapy typically have limited results. A person with SCI may not be able to control their upper or lower limbs, but often the local structures, such as muscles and motoneurons, are preserved. Therefore functional electrical stimulation (FES) can be used to induce contraction on these muscles and generate movement in paralyzed limbs. However, due to their own motor disabilities, patients usually find it hard in their daily lives to operate FES assistive devices. This limits their performance and usability. In this work, I developed a framework of techniques for user interfaces that explore residual motor capabilities that users with SCI may still possess to control neuroprostheses. In order to acquire movement information I use inertial measurement units (IMUs). I developed and evaluated algorithms for detection and classification of movements by users with paraplegia and tetraplegia. They use their own residual movements, depending on their injury levels, to activate different commands in assistive devices. I applied the developed techniques in three application scenarios with persons with SCI. First I performed an experiment in which three users with paraplegia activated an FES device to aid in sitting pivot transfers (SPT). I analyzed their trunk kinematics to investigate the feasibility of using that information to activate the FES on their lower limbs during the SPT. Then I developed an interface with which nine users with tetraplegia used shoulder movements to control a robotic hand, which simulated an upper limb grasping assisted device. In this case, I used accelerometer and gyroscope data along a threshold technique to detect movements, and a principal component analysis (PCA) to classify them. I then mapped these movements into different commands on the robotic hand. Next I developed an interface that uses upper limb kinematics to properly activate an FES neuroprosthesis on lower limbs of persons with paraplegia during FES-rowing. I used a finite state machine and linear discriminant analysis (LDA) to constantly classify every upper limbs movement from the user into three different rowing phases commands. I evaluated it with one participant and an adapted rowing machine for rowers with SCI. On the transfer experiment, each participant moved their trunk in a similar way across trials, with angles standard deviations less than 5°, which means I can use it to automate the FES activation. Using the upper limb grasping simulation interface, participants were able to successfully control the robotic hand, correctly performing 91% of the robotic hand commands I instructed them to. Finally, the rowing protocol participant was capable of rowing with the developed interface with only their upper limbs movements. The system activated his lower limbs neuroprosthesis in sync with the upper limbs rowing motion. Also, he could start and control the FES by stopping or moving his arms. These results show that persons with SCI are successful in using residual motor capabilities to control assistive devices under the observed conditions

Multiple motor-unit muscle models for the design of FES systems

Many functional electrical stimulation (FES) controllers have been developed using a simulation approach, the performance of these controllers depends on the muscle model accuracy. Realistic models of neuro-musculoskeletal systems can provide a safe and convenient environment for the design and evaluation of FES controllers. A typical FES system consists of FES controller, an electrical stimulator, electrodes and sensors.During FES, the stimulation level can change in a continuous fashion such that different motor-units are recruited at different muscle lengths and at different times. Furthermore, it is also not accurate to use the instantaneous length as input to the force-length relationship in dynamic (non-isometric) situations. Although instantaneous CE length is commonly used in FES control studies, empirical data from the literature were reviewed and it was concluded that the CE length at initial recruitment is a key parameter influencing total muscle force. The author presents a new multiple motor-unit Hill-type muscle model that accounts for different motor units being recruited at different CE lengths and different times. Hence the model can account for a continuously changing recruitment level whilst using the individual motor unit lengths at initial recruitment as input to the force-length relationship. Moreover, the model is capable of modelling fatigue and force enhancement & depression for the individual motor-units (i.e. the recruitment and time history effects). The model can also take account of the different force-length and force-velocity relationships for different fibre types by modelling these properties for the individual motor-units.The new multiple motor-unit model is described in detail, implemented and tested in Matlab. Open-loop simulation protocols are made on single/multiple motor-unit models using different CE lengths for the force-length relationship; on single/multiple motor-unit fatigue sub-models; and on single/ multiple motor-unit force enhancement & depression sub-models.A general model that can be used to represent all relevant models from the literature was developed. This model can also be used to build new models at different levels of complexity. Such a “General Model” could be used to study the effect of model complexity on FES controller design so that appropriate trade-offs between model complexity and accuracy could be determined. Results, limitations and possible future work are discussed

Investigation and Quantification of FES Exercise – Isometric Electromechanics and Perceptions of Its Usage as an Exercise Modality for Various Populations

Functional Electrical Stimulation (FES) is the triggering of muscle contraction by use of an electrical current. It can be used to give paralyzed individuals several health benefits, through allowing artificial movement and exercise. Although many FES devices exist, many aspects require innovation to increase usability and home translation. In addition, the effect of changing electrical parameters on limb biomechanics is not entirely understood; in particular with regards to stimulation duty cycle. This thesis has two distinct components. In the first (public health component), interview studies were conducted to understand several issues related to FES technology enhancement, implementation and home translation. In the second (computational biomechanics component), novel signal processing algorithms were designed that can be used to measure mechanical responses of muscles subjected to electrical stimulation. These experiments were performed by changing duty cycle and measuring its effect on quadriceps-generated knee torque. The studies of this thesis have presented several ideas, toolkits and results which have the potential to guide future FES biomechanics studies and the translatability of systems into regular usage for patients. The public health studies have provided conceptual frameworks upon which FES may be used in the home by patients. In addition, they have elucidated a range of issues that need to be addressed should FES technology reach its true potential as a therapy. The computational biomechanics studies have put forward novel data analysis techniques which may be used for understanding how muscle responds to electrical stimulation, as measured via torque. Furthermore, the effect of changing the electrical stimulation duty cycle on torque was successfully described, adding to an understanding of how electrical stimulation parameter modulation can influence joint biomechanics