Vahidreza Molazadeh's research while affiliated with National Institutes of Health and other places

Publications (13)

Article
Full-text available
A hybrid exoskeleton comprising a powered exoskeleton and functional electrical stimulation (FES) is a promising technology for restoration of standing and walking functions after a neurological injury. Its shared control remains challenging due to the need to optimally distribute joint torques among FES and the powered exoskeleton while compensati...
Article
A hybrid exoskeleton that combines functional electrical stimulation (FES) and a powered exoskeleton is an emerging technology for assisting people with mobility disorders. The cooperative use of FES and the exoskeleton allows active muscle contractions through FES while robustifying torque generation to reduce FES-induced muscle fatigue. In this a...
Article
In this paper, a switched control method for a class of wearable robotic systems that prioritizes the use of human skeletal muscles in an assistive rigid powered exoskeleton is derived. A general N-degree-of-freedom (N-DOF) human-robot model is proposed to consider the challenges induced by the wearable system that include uncertainties and nonline...
Chapter
In this paper a lower-limb powered exoskeleton is combined with functional electrical stimulation of the quadriceps muscle to achieve a standing-up motion. As two actuation mechanisms (FES and the motors) act on the knee joints, it is desirable to optimally coordinate them. A feedback controller that stabilizes the desired standing-up motion is der...
Article
Currently controllers that dynamically modulate functional electrical stimulation (FES) and a powered exoskeleton at the same time during standing-up movements are largely unavailable. In this paper, an optimal shared control of FES and a powered exoskeleton is designed to perform sitting to standing (STS) movements with a hybrid exoskeleton. A hie...
Conference Paper
Full-text available
In this paper, a novel neural network based iterative learning controller for a hybrid exoskeleton is presented. The control allocation between functional electrical stimulation and knee electric motors uses a model predictive control strategy. Further to address modeling uncertainties, the controller identifies the system dynamics and input gain m...
Article
In this paper, a robust iterative learning switching controller that uses optimal virtual constraint is designed for a hybrid walking exoskeleton that uses functional electrical stimulation and a powered exoskeleton. The synthesis of iterative learning control with sliding-mode control improves tracking performance and accuracy. The motivation for...
Article
Mobility disorders caused by spinal cord injury (SCI), stroke, or progressive neurological diseases such as multiple sclerosis and amyotrophic lateral sclerosis, lead to a deterioration in quality of life. Resulting sequelae, such as pressure ulcers, depression, and urinary infections, require constant medical care throughout a patient's lifetime....
Article
Full-text available
A hybrid walking neuroprosthesis that combines functional electrical stimulation (FES) with a powered lower limb exoskeleton can be used to restore walking in persons with paraplegia. It provides therapeutic benefits of FES and torque reliability of the powered exoskeleton. Moreover, by harnessing metabolic power of muscles via FES, the hybrid comb...

Citations

... Compared to our previous simulation studies by Molazadeh et al. (2019), Bao et al. (2020b), and Molazadeh et al. (2018a,b), the study presents a more detailed derivation of the controller, improved robustness to modeling uncertainties, and supporting stability analysis. Furthermore, extensive sit-to-stand experiments with a hybrid exoskeleton validated the approach on four participants with no disabilities. ...
... Open-loop control of FES replays a predetermined pattern of stimulation triggered by FSM [142], [143]. Instead, Closed-loop control of FES relies on indirect measurement of muscle performance to modulate the stimulation in real time [144], [145]. In the spectrum of hybrid exoskeletons, the ones with fully active robotic actuation and closed-loop FES control have been the focus of research in recent years. ...
... Firstly, to control the HES, an allocation strategy is needed to coordinate FES and the powered exoskeleton based on the onset of FES-induced muscle fatigue. Our previous paper [2] extended a fatigue based switching control design in [3] for allocating FES and exoskeleton a multi degrees of freedom (DOF) walking. In an * Contact author: nis62@pitt.edu ...
... Compared to our previous simulation studies by Molazadeh et al. (2019), Bao et al. (2020b), and Molazadeh et al. (2018a,b), the study presents a more detailed derivation of the controller, improved robustness to modeling uncertainties, and supporting stability analysis. Furthermore, extensive sit-to-stand experiments with a hybrid exoskeleton validated the approach on four participants with no disabilities. ...
... The desired trajectories are generated from normal human sitting-to-standing profiles. The trajectories of knee angles are computed offline by polynomial fitting while the trajectories of hip angles are generated online as functions of the actual measured knee angles according to a designed virtual constraint (Molazadeh, Sheng, Bao, & Sharma, 2019) between the knee and hip joints. For both left and right part, the feedback control gains used in control mode I were: α = 20, β = 2, K u = 4, K ρ = 10, ρ s,1 = 0.5, ρ s,2 = 0 (no soft actuator assigned at hip joints), Q 4 = ( ρ m,ij ) 2×2 obtained by online solving the linear algebraic equation, ...
... A fundamental research question for the development of hybrid exoskeletons is how to allocate or segregate the control design for the powered actuators and muscles (Alibeji et al., 2018a;Alibeji et al., 2018b;Ha et al., 2016). Kinematic tracking has been the primary control objective for rehabilitation devices and machines that combine FES and powered actuation, where the desired trajectories can be tracked by muscles, electric motors (i.e., the machine or robot) or both during walking and cycling (Alibeji et al., 2018b;Duenas et al., 2019;Cousin et al., 2021). ...
... A closed-loop adaptive control design using iterative learning and neural networks was developed to distribute the control between FES and electric motors to perform sit-to-stand tasks . Switched control between two modes was developed for a wearable exoskeleton with FES to address nonlinearities and uncertainties in the overall system (Sheng et al., 2021). A controller inspired by the principle of synergies was used to address the problem of actuator redundancy in simulation to control muscles via FES and electric motors (Alibeji et al., 2015). ...
... Notably, the NN-based control approach is derived to iteratively increase the feed-forward learning component and decrease the high-level torque generator's high gain feedback component. The feed-forward learning is an improvement over our recent approach that used a high-gain position tracking controller for high-level torque generation for an experimental study on sit-to-stand tasks (Bao et al. (2020a)). Unlike most exoskeleton controllers that follow a time-dependent desired joint trajectory Contreras-Vidal et al. (2016); Alibeji et al. (2018b); Bae and Tomizuka (2012)) or a desired timedependent or EMG-generated torque trajectory (Zhang et al. (2015)), the designed NN-based approach follows statedependent desired joint trajectories known as virtual constraints (Westervelt et al. (2007); Gregg and Sensinger (2014)). ...
... A preliminary conference paper on a 5-DOF lower-limb human-robot model with a uniform input delay at knee joints was presented in Sheng, Molazadeh, and Sharma (2018). In the current paper, the theoretical results have been extended to a general N-DOF system with different input delays of each soft actuator at each joint. ...
... Hybrid exoskeletons provide postural support, coordinate motion across multiple joints, and apply bursts of electrical stimulation. Several hybrid exoskeletons have incorporated direct joint actuation and implemented closed-loop controllers for the powered machines and FES (Ha et al., 2016;Alibeji et al., 2018a). Hybrid orthoses have been designed to lock and unlock leg joints as a function of the gait cycle to provide upright stability and leg assistance using postural controllers (Kobetic et al., 2009). ...