Naji Alibeji | University of Pittsburgh (original) (raw)

Papers by Naji Alibeji

To date, a functional electrical stimulation (FES)-based walking technology is incapable of enabl... more To date, a functional electrical stimulation (FES)-based walking technology is incapable of enabling a paraplegic user to walk more than a few hundred meters. This is primarily due to the rapid onset of muscle fatigue, which causes limited torque generation capability of the lower-limb muscles. A hybrid walking neuroprosthesis that combines FES with an electric motor can overcome this challenge, since an electric motor can be used to compensate for any reduction in force generation due to the muscle fatigue. However, the hybrid actuation structure creates an actuator redundancy control problem; i.e., a closed-loop controller must optimally distribute torque between FES and an electric motor. Further, the control inputs to FES and an electric motor must adapt as a skeletal muscle fatigues. We consider these issues as open research control problems. In this paper, we propose that a model predictive control (MPC)-based control design can be used to optimally distribute joint torque, and can adapt as the muscle fatigue sets in. Particularly, a customized quadratic programming solver (generated using CVXGEN) was used to simulate MPC-based control of the hybrid neuroprosthesis that elicits knee extension via FES and an electric actuator.

Springer eBooks, Oct 13, 2016

The walking duration of gait restoration systems that use functional electrical stimulation (FES)... more The walking duration of gait restoration systems that use functional electrical stimulation (FES) is severely limited by the rapid onset of muscle fatigue. Alternatively, fully actuated orthoses can also be employed to restore walking in paraplegia. However, due to the high power consumption of electric motors the walking duration of such devices are limited by the charge of the batteries. This paper proposes that a hybrid system, which uses FES and an actuated orthosis, is capable of achieving greater walking durations than an FES only system and more energetically efficient than a lower-limb exoskeleton. This is illustrated through results of optimizations of a musculoskeletal gait model for three actuation cases: FES only, electric motors only, and a hybrid system. The presented results illustrate that a hybrid system may be capable of greater walking durations than FES-based systems while using half the energy of a lower-limb exoskeleton.

A hybrid neuroprosthesis is a device that uses a combination of electric motors and functional el... more A hybrid neuroprosthesis is a device that uses a combination of electric motors and functional electrical stimulation (FES) to provide gait assistance. Its closed-loop control performance can be potentially affected by the presence of electromechanical delay (EMD) during FES. In this paper, a tracking control scheme for a hybrid walking neuroprosthesis that combines electric motor actuation at the hip and FES actuation at the knee is presented. The knee joint controller uses a delay compensation technique to compensate for EMD during FES. This neuroprosthesis controller is combined within a finite state machine that also features gait detection, wherein force sensors in the foot can detect gait phases and create a fully automated and functional assisted gait cycle. Experiments were performed on an able bodied subject to demonstrate the efficacy of the tracking control scheme. Results from the experiments show a maximum error at the hip of less than 1 degree and a maximum error at the knee of 13.66 degrees. The maximum error at the knee is attributed to overshoot caused by the unidirectional actuation of the FES.

A combination of functional electrical stimulation (FES) and an orthosis can be used to restore l... more A combination of functional electrical stimulation (FES) and an orthosis can be used to restore lower limb function in persons with paraplegia. This artificial intervention may allow them to regain the ability to walk again, however, only for short time durations. To improve the time duration of hybrid (FES and orthosis) gait, the muscle fatigue due to FES and the fatigue in arms, caused by a user’s supported weight on a walker, needs to be minimized. In this paper, we show that dynamic optimization can be used to compute stimulation/torque profiles and their corresponding joint angle trajectories which minimize electrical stimulation and walker push or pull forces. Importantly, the computation of these optimal stimulation or torque profiles did not require a predefined or a nominal gait trajectory (i.e., a tracking control problem was not solved). Rather the trajectories were computed based only on pre-defined end-points. For optimization we utilized the recently developed three-link dynamic walking model, which includes both single and double support phases and muscle dynamics. Moreover, different optimal actuation strategies for FES and orthosis aided gait under various scenarios (e.g., use of a powered or an unpowered orthosis combined with stimulation of all or few selected lower-limb muscles) were calculated. The qualitative comparison of these results depict the advantages and disadvantages of each actuation strategy. The computed optimal FES/orthosis aided gait were also compared with able-bodied trajectories to illustrate how they differed from able-bodied walking.

Biosystems & biorobotics, Oct 13, 2016

Hybrid neuroprostheses that use both electric motor drives and functional electrical stimulation ... more Hybrid neuroprostheses that use both electric motor drives and functional electrical stimulation for the restoration of walking in persons with paraplegia have a promising potential. However, the hybrid actuation structure introduces effector redundancy, making the system complex and difficult to control. In this paper, preliminary experimental results of a recently developed low-dimensional controller, which is inspired from the muscle synergy principle, are presented. The experiments were performed on an able-bodied subject in a configuration where only one leg is actuated in a cycling manner while the contralateral leg was fixed.

A position-synchronization controller for functional electrical stimulation (FES)-based telerehab... more A position-synchronization controller for functional electrical stimulation (FES)-based telerehabilitation was designed. The developed controller synchronizes an FES-driven human limb with a remote physical therapist’s manipulator despite constant bilateral communication delays. The control design overcomes a major stability analysis challenge: the unknown and unstructured nonlinearities in the FES-driven musculoskeletal dynamics. To address this challenge, the nonlinear muscle model was estimated through two neural networks with online update laws. A Lyapunov-based stability analysis was used to prove the globally uniformly ultimately bounded tracking performance. The control performance of the state synchronization controller is depicted using a simulation of an FES-elicited elbow extension that is remotely controlled by a manipulator.Copyright © 2014 by ASME

2017 8th International IEEE/EMBS Conference on Neural Engineering (NER)

Converging Clinical and Engineering Research on Neurorehabilitation II, 2016

Volume 3: Industrial Applications; Modeling for Oil and Gas, Control and Validation, Estimation, and Control of Automotive Systems; Multi-Agent and Networked Systems; Control System Design; Physical Human-Robot Interaction; Rehabilitation Robotics; Sensing and Actuation for Control; Biomedical Sy..., 2014

Volume 1: Aerial Vehicles; Aerospace Control; Alternative Energy; Automotive Control Systems; Battery Systems; Beams and Flexible Structures; Biologically-Inspired Control and its Applications; Bio-Medical and Bio-Mechanical Systems; Biomedical Robots and Rehab; Bipeds and Locomotion; Control Des..., 2013

2016 American Control Conference (ACC), 2016

IFAC-PapersOnLine, 2015

Hybrid neuroprostheses that use both electric motor drives and functional electrical stimulation ... more Hybrid neuroprostheses that use both electric motor drives and functional electrical stimulation for the restoration of walking in persons with paraplegia have a promising potential. However, the hybrid actuation structure introduces effector redundancy, making the system complex and difficult to control. In this paper we design a low-dimensional controller inspired from the muscle synergy principle. The new controller requires few control signals to actuate multiple effectors in a hybrid neuroprostheses. The development of the controller and a Lyapunov stability analysis, which yielded semi-global uniformly ultimately boundedness is presented in this paper. Computer simulations were performed to test the new controller on a 2 degree of freedom fixed hip model.

IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, Jan 2, 2015

Electromechanical delay (EMD) and uncertain nonlinear muscle dynamics can cause destabilizing eff... more Electromechanical delay (EMD) and uncertain nonlinear muscle dynamics can cause destabilizing effects and performance loss during closed-loop control of neuromuscular electrical stimulation (NMES). Linear control methods for NMES often perform poorly due to these technical challenges. A new predictor-based closed-loop controller called proportional integral derivative controller with delay compensation (PID-DC) is presented in this paper. The PID-DC controller was designed to compensate for EMDs during NMES. Further, the robust controller can be implemented despite uncertainties or in the absence of model knowledge of the nonlinear musculoskeletal dynamics. Lyapunov stability analysis was used to synthesize the new controller. The control effectiveness of the new controller was validated and compared with two recently developed nonlinear NMES controllers, through a series of closed-loop control experiments on four able-bodied human subjects. Experimental results depict statistically...

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014

Through the application of functional electrical stimulation (FES) individuals with paraplegia ca... more Through the application of functional electrical stimulation (FES) individuals with paraplegia can regain lost walking function. However, due to the rapid onset of muscle fatigue, the walking duration obtained with an FES-based neuroprosthesis is often relatively short. The rapid muscle fatigue can be compensated for by using a hybrid system that uses both FES and an active orthosis. In this paper, we demonstrate the initial testing of a semi-active hybrid walking neuroprosthesis. The semi-active hybrid orthosis (SEAHO) supports a user during the stance phase and standing while the electric motors attached to the hip section of the orthosis are used to generate hip flexion/extension. FES in SEAHO is mainly used to actuate knee flexion/extension and plantar flexion of the foot. SEAHO is controlled by a finite state machine that uses a recently developed nonlinear controller for position tracking control of the hip motors and cues from the hip angle to actuate FES and other components.

Frontiers in bioengineering and biotechnology, 2015

A hybrid neuroprosthesis that uses an electric motor-based wearable exoskeleton and functional el... more A hybrid neuroprosthesis that uses an electric motor-based wearable exoskeleton and functional electrical stimulation (FES) has a promising potential to restore walking in persons with paraplegia. A hybrid actuation structure introduces effector redundancy, making its automatic control a challenging task because multiple muscles and additional electric motor need to be coordinated. Inspired by the muscle synergy principle, we designed a low dimensional controller to control multiple effectors: FES of multiple muscles and electric motors. The resulting control system may be less complex and easier to control. To obtain the muscle synergy-inspired low dimensional control, a subject-specific gait model was optimized to compute optimal control signals for the multiple effectors. The optimal control signals were then dimensionally reduced by using principal component analysis to extract synergies. Then, an adaptive feedforward controller with an update law for the synergy activation was ...

Springer eBooks, Oct 13, 2016

Biosystems & biorobotics, Oct 13, 2016

2017 8th International IEEE/EMBS Conference on Neural Engineering (NER)

Converging Clinical and Engineering Research on Neurorehabilitation II, 2016

2016 American Control Conference (ACC), 2016

IFAC-PapersOnLine, 2015

Hybrid neuroprostheses that use both electric motor drives and functional electrical stimulation ... more Hybrid neuroprostheses that use both electric motor drives and functional electrical stimulation for the restoration of walking in persons with paraplegia have a promising potential. However, the hybrid actuation structure introduces effector redundancy, making the system complex and difficult to control. In this paper we design a low-dimensional controller inspired from the muscle synergy principle. The new controller requires few control signals to actuate multiple effectors in a hybrid neuroprostheses. The development of the controller and a Lyapunov stability analysis, which yielded semi-global uniformly ultimately boundedness is presented in this paper. Computer simulations were performed to test the new controller on a 2 degree of freedom fixed hip model.

IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, Jan 2, 2015

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014

Frontiers in bioengineering and biotechnology, 2015