Optimization and Evaluation of a Proportional Derivative Controller for Planar Arm Movement

In most clinical applications of functional electrical stimulation (FES), the timing and amplitude of electrical stimuli have been controlled by open-loop pattern generators. The control of upper extremity reaching movements, however, will require feedback control to achieve the required precision. Here we present three controllers using proportional derivative (PD) feedback to stimulate six arm muscles, using two joint angle sensors. Controllers were first optimized and then evaluated on a computational arm model that includes musculoskeletal dynamics. Feedback gains were optimized by minimizing a weighted sum of position errors and muscle forces. Generalizability of the controllers was evaluated by performing movements for which the controller was not optimized, and robustness was tested via model simulations with randomly weakened muscles. Robustness was further evaluated by adding joint friction and doubling the arm mass. After optimization with a properly weighted cost function, all PD controllers performed fast, accurate, and robust reaching movements in simulation. Oscillatory behavior was seen after improper tuning. Performance improved slightly as the complexity of the feedback gain matrix increased

Doctor of Philosophy

dissertationHigh-count microelectrode arrays implanted in peripheral nerves could restore motor function after spinal cord injury or sensory function after limb loss via electrical stimulation. The same device could also help restore volitional control to a prosthesis-using amputee, or sensation to a Spinal cord Injury (SCI) patient, via recordings from the still-viable peripheral nerves. The overall objective of these dissertations studies is to improve the usefulness of intrafascicular electrodes, such as the Utah Slanted Electrode Array (USEA), for neuroprosthetic devices for limb loss or spinal cord injury patients. Previous work in cat sciatic nerve has shown that stimulation through the USEA can remain viable for months after implant. However, stimulation parameters were not stable, and recordings were lost rapidly and were subject to strong contamination by myoelectrical activity from adjacent muscles. Recent research has shown that even when mobility is restored to a patient, either through prosthesis or functional electrical stimulation, difficulties in using the affected limbs arise from the lack of sensory input. In the absence of the usual proprioceptive and cutaneous inputs from the limb, planning and executing motions can be challenging and sometimes lead to the user's abandonment of prostheses. To begin to address this need, I examined the ability of USEAs in cat hindlimb nerves to activate primary sensory fibers by monitoring evoked potentials in somatosensory cortex via skull-screw electrodes. I iv also monitored evoked EMG responses, and determined that it is possible to recruit sensory or motor responses independently of one another. In the second study of this dissertation, I sought to improve the long-term stability of USEAs in the PNS by physically and electrically stabilizing and protecting the array. To demonstrate the efficacy of the stabilization and shielding technique, I examined the recording capabilities of USEA electrodes and their selectivity of muscle activation over the long term in cat sciatic nerve. In addition to long-term viability, clinically useful neuroprosthetic devices will have to be capable of interfacing with complex motor systems such as the human hand. To extend previous results of USEAs in cat hindlimb nerves and to examine selectivity when interfacing with a complex sensorimotor system, I characterized EMG and cortical somatosensory responses to acute USEA stimulation in monkey arm nerves. Then, to demonstrate the functional usefulness of stimulation through the USEA. I used multi-array, multi-electrode stimulation to generate a natural, coordinated grasp

Achieving Practical Functional Electrical Stimulation-driven Reaching Motions In An Individual With Tetraplegia

Functional electrical stimulation (FES) is a promising technique for restoring the ability to complete reaching motions to individuals with tetraplegia due to a spinal cord injury (SCI). FES has proven to be a successful technique for controlling many functional tasks such as grasping, standing, and even limited walking. However, translating these successes to reaching motions has proven difficult due to the complexity of the arm and the goaldirected nature of reaching motions. The state-of-the-art systems either use robots to assist the FES-driven reaching motions or control the arm of healthy subjects to complete planar motions. These controllers do not directly translate to controlling the full-arm of an individual with tetraplegia because the muscle capabilities of individuals with spinal cord injuries are unique and often limited due to muscle atrophy and the loss of function caused by lower motor neuron damage. This dissertation aims to develop a full-arm FES-driven reaching controller that is capable of achieving 3D reaching motions in an individual with a spinal cord injury. Aim 1 was to develop a complete-arm FES-driven reaching controller that can hold static hand positions for an individual with high tetraplegia due to SCI. We developed a combined feedforward-feedback controller which used the subject-specific model to automatically determine the muscle stimulation commands necessary to hold a desired static hand position. Aim 2 was to develop a subject-specific model-based control strategy to use FES to drive the arm of an individual with high tetraplegia due to SCI along a desired path in the subject’s workspace. We used trajectory optimization to find feasible trajectories which explicitly account for the unique muscle characteristics and the simulated arm dynamics of our subject with tetraplegia. We then developed a model predictive control controller to iii control the arm along the desired trajectory. The controller developed in this dissertation is a significant step towards restoring full arm reaching function to individuals with spinal cord injuries

Problemy techniczne i medyczne w zakresie szerszego wykorzystania neuroprotez u pacjentów neurologicznych

Nervous system disorders may seriously impair motor, sensory or cognitive functions. Present neurorehabilitation in selected cases can cause significant functional recovery e.g. in the area of locomotor pattern generation and balance, but in the most severe cases this recovery still remains incomplete. Use of neuroprostheses broadens possibilities of rehabilitation and care. Neuroprostheses are electronic devices substituting lost sensory, motor or cognitive functions. They significantly help to restore or replace functions lost as a result of neural damage. Clinical used neuroprostheses proved to be effective in achieving a greater patients’ independence in daily activities.Further development of neuroprostheses need for increased involvement of medical staff in the area of clinical research on clear and safe medical procedures. This progress can make another breakthrough in the therapy, rehabilitation and care of patients with nervous system deficits. (PNN 2012;1(3):119-123)Schorzenia układu nerwowego mogą poważnie zaburzyć funkcje motoryczne, sensoryczne lub poznawcze. Współczesna rehabilitacja neurologiczna w części przypadków może przynieść znaczącą poprawę funkcjonalną, m.in. w obszarze generacji wzorców lokomocji i równowagi, lecz w najcięższych przypadkach ta poprawa jest wciąż niepełna. Wykorzystanie neuroprotez rozszerza tu możliwości rehabilitacji i opieki. Neuroprotezy są urządzeniami elektronicznymi zastępującymi utracone funkcje sensoryczne, motoryczne lub poznawcze. Mogą one znacząco pomóc w przywróceniu lub zastąpieniu funkcji utraconych wskutek uszkodzenia układu nerwowego. Neuroprotezy wykorzystywane klinicznie udowodniły swoją efektywność w przywracaniu pacjentom większej samodzielności w codziennych czynnościach. Dalszy rozwój neuroprotez wymaga zwiększonego zaangażowania personelu medycznego w obszarze badań klinicznych nad przejrzystymi i bezpiecznymi procedurami medycznymi. Postęp ten może spowodować kolejny przełom w terapii, rehabilitacji i opiece nad pacjentami neurologicznymi. (PNN 2012;1(3):119-123

An optimized proportional-derivative controller for the human upper extremity with gravity

When Functional Electrical Stimulation (FES) is used to restore movement in subjects with spinal cord injury (SCI), muscle stimulation patterns should be selected to generate accurate and efficient movements. Ideally, the controller for such a neuroprosthesis will have the simplest architecture possible, to facilitate translation into a clinical setting. In this study, we used the simulated annealing algorithm to optimize two proportional-derivative (PD) feedback controller gain sets for a 3-dimensional arm model that includes musculoskeletal dynamics and has 5 degrees of freedom and 22 muscles, performing goal-oriented reaching movements. Controller gains were optimized by minimizing a weighted sum of position errors, orientation errors, and muscle activations. After optimization, gain performance was evaluated on the basis of accuracy and efficiency of reaching movements, along with three other benchmark gain sets not optimized for our system, on a large set of dynamic reaching movements for which the controllers had not been optimized, to test ability to generalize. Robustness in the presence of weakened muscles was also tested. The two optimized gain sets were found to have very similar performance to each other on all metrics, and to exhibit significantly better accuracy, compared with the three standard gain sets. All gain sets investigated used physiologically acceptable amounts of muscular activation. It was concluded that optimization can yield significant improvements in controller performance while still maintaining muscular efficiency, and that optimization should be considered as a strategy for future neuroprosthesis controller design

Are We the Robots? : Man-Machine Integration

We experience and interact with the world through our body. The founding father of computer science, Alan Turing, correctly realized that one of the most important features of the human being is the interaction between mind and body. Since the original demonstration that electrical activity of the cortical neurons can be employed to directly control a robotic device, the research on the so-called Brain-Machine Interfaces (BMIs) has impressively grown. For example, current BMIs dedicated to both experimental and clinical studies can translate raw neuronal signals into computational commands to reproduce reaching or grasping in artificial actuators. These developments hold promise for the restoration of limb mobility in paralyzed individuals. However, as the authors review in this chapter, before this goal can be achieved, several hurdles have to be overcome, including developments in real-time computational algorithms and in designing fully implantable and biocompatible devices. Future investigations will have to address the best solutions for restoring sensation to the prosthetic limb, which still remains a major challenge to full integration of the limb into the user's self-image

Multi-contact epineural electrical stimulation to restore upper-limb functions

International audienceWe investigated the feasibility of a novel approach aiming at restoring functional movements in completely paralyzed upper limbs using neural stimulation. Two multi-contact cuff electrodes were wrapped around radial and median nerves, unilaterally, in 2 individuals with complete high tetraplegia. Electrodes were maintained for 28 days. Advanced stimulation configurations were implemented to achieve selective activation of fascicles and elicit different graspings. A control interface was developed to allow users to pilot movements of their hand by triggering stimulation. Both participants were able to execute palmar and key pinch grasping during functional tasks

Non-invasive activation of cervical spinal networks after severe paralysis

© Copyright 2018, Mary Ann Liebert, Inc. 2018. Paralysis of the upper extremities following cervical spinal cord injury (SCI) significantly impairs one's ability to live independently. While regaining hand function or grasping ability is considered one of the most desired functions in tetraplegics, limited therapeutic development in this direction has been demonstrated to date in humans with a high severe cervical injury. The underlying hypothesis is that after severe cervical SCI, nonfunctional sensory-motor networks within the cervical spinal cord can be transcutaneously neuromodulated to physiological states that enable and amplify voluntary control of the hand. Improved voluntary hand function occurred within a single session in every subject tested. After eight sessions of non-invasive transcutaneous stimulation, combined with training over 4 weeks, maximum voluntary hand grip forces increased by ∼325% (in the presence of stimulation) and ∼225% (when grip strength was tested without simultaneous stimulation) in chronic cervical SCI subjects (American Spinal Injury Association Impairment Scale [AIS] B, n = 3; AIS C, n = 5) 1-21 years post-injury). Maximum grip strength improved in both the left and right hands and the magnitude of increase was independent of hand dominance. We refer to the neuromodulatory method used as transcutaneous enabling motor control to emphasize that the stimulation parameters used are designed to avoid directly inducing muscular contractions, but to enable task performance according to the subject's voluntary intent. In some subjects, there were improvements in autonomic function, lower extremity motor function, and sensation below the level of the lesion. Although a neuromodulation-training effect was observed in every subject tested, further controlled and blinded studies are needed to determine the responsiveness of a larger and broader population of subjects varying in the type, severity, and years post-injury. It appears rather convincing, however, that a "central pattern generation" phenomenon as generally perceived in the lumbosacral networks in controlling stepping neuromodulator is not a critical element of spinal neuromodulation to regain function among spinal networks

Development of an Upper Limb Neuroprosthesis: Conquering Weakness and Fatigue

Neuroprosthetics are devices that substitute for or supplant motor, sensory or cognitive modalities damaged as a result of spinal cord injury or stroke. Functional electrical stimulation (FES) neuroprosthetics utilize artificial stimulation to restore motor function in paralyzed muscles, where control exerted by higher nervous system centers over muscle may be impaired. Although promising, FES has failed to gain widespread acceptance due in part to weak contraction strength and rapid fatigue observed with artificial stimulation. This dissertation documents an attempt to create an upper limb FES neuroprosthetic and subsequently to address the issues of weakness and fatigue. To exploit the capabilities of the musculoskeletal system the neural drive to muscle first must be decoded. Decoding the neural drive for specific movements has been approached using either a deterministic (engineering) or machine learning model. While a deterministic model accounts for all components of a limb, number of joints, degrees of freedom, limb length, muscle length, etc, machine learning characterizes the relationship between select variables, in this case whole muscle electromyographic data (EMG) and limb kinematics. Ultimately, the output of both approaches is used to predict the neural drive required to generate movements. In this study we first attempt to build an upper limb FES neuroprosthetic. Utilizing machine learning, we characterize the relationship between limb kinematics and EMG. Then, predict EMG based solely on limb kinematics. Finally, stimulation pulses were generated and delivered via intramuscular electrodes to produce movement. Additionally, to address force generation we hypothesized that due to the distributed nature of motor axons within a muscle stimulating with multiple spatially distributed electrodes would activate a larger muscle volume thus generating additional force. This in turn would facilitate load sharing among muscle fibers, and reduce fatigue. To evaluate fatigue we compared interleaved and synchronous patterns of stimulation as well as single electrode vs multiple electrode stimulation. We approached these questions and aims with a combination of strategies and techniques including machine learning, implantation of stimulating electrodes in a non-human primate model and finally human subjects. While machine learning provided EMG predictions with high R values, we were unable to generate substantive movements activating all the muscle in a complete joint system. However, we were able to generate movements stimulating a single muscle in an intact joint system. We found that single electrode force could be augmented with multiple electrodes. Additional results indicate that multiple electrode stimulation was less fatiguing than single electrode stimulation. Interleaved stimulation however, did not result in less fatigue than synchronous stimulation

Patient preferences for reconstructive interventions of the upper limb in tetraplegia

Subjects with an SCI suffer from many health problems such as pain, spacticity, pressure sores, urinary tract infections, etc. However, despite these health problems, the satisfaction with life as a whole of subjects with SCI living in the community does not differ significantly from the life satisfaction of a population group, as demonstrated by Post et al. The results of studies carried out by Post et al and Francescini showed that in SCI the levels of social and psychological functioning and the degree of autonomy are more important predictors of life satisfaction and quality of life than the seriousness of the injury. However, these studies also showed that subjects with tetraplegia, related to impairment of the upper extremities (UE), are less satisfied with self-care ability and also have an inferior degree of autonomy, which has a negative impact on satisfaction and quality of life. In this respect, treatment of the UE in subjects with a cervical SCI is of utmost importance