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1. Split-Crank Cadence Tracking for Switched Motorized FES-Cycling with Volitional Pedaling

   Rouse, Courtney ; Cousin, Christian ; Allen, Brendon ; Dixon, Warren E. ( July 2019 , Proc. American Control Conference)

   A wide variation in muscle strength and asymmetry exists in people with movement disorders. Functional electrical stimulation (FES) can be used to induce muscle contractions to assist and a motor can be used to both assist and resist a person’s volitional and/or FES-induced pedaling. On a traditional cycle with coupled pedals, people with neuromuscular asymmetries can primarily use their dominant (i.e., stronger) side to successfully pedal at a desired cadence, neglecting the side that would benefit most from rehabilitation. In this paper, a multi-level switched system is applied to a two-sided control objective to maintain a desired range of cadence using FES, an electric motor, and volitional pedaling. The non-dominant leg tracks the cadence range while the dominant leg tracks the position (offset by 180 degrees) and cadence of the first leg. Assistive, uncontrolled, and resistive modes are developed based on cadence and position for the non-dominant and dominant legs, respectively. Lyapunov-based methods for switched systems are used to prove global exponential tracking to the desired cadence range for the combined FES-motor control system. 

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2. Teleoperated Motorized Functional Electric Stimulation Actuated Rehabilitative Cycling

   https://doi.org/10.1115/DSCC2020-3131  

   Stubbs, Kimberly J. ; Allen, Brendon C. ; Dixon, Warren E. ( October 2020 , ASME Dynamic Systems and Control Conference)

   null (Ed.)

   Many people are affected by a wide range of neuromuscular disorders, many of which can be improved through the use of Functional Electrical Stimulation (FES) rehabilitative cycling. Recent improvements in nonlinear, Lyapunov-based FES muscle control with motor assistance in unstimulated regions of the cycle-crank rotation have led to a reduction in muscle fatigue, allowing rehabilitation time to be extended. Studies in rehabilitation have shown that the addition of coordinated movement between the upper limbs and lower limbs can have a positive effect on neural plasticity leading to faster restoration of walking in those who have some neurological disorders. In this paper, to implement coordinated motion during rehabilitation, a strongly coupled bilateral telerobotic system is developed between a hand-cycle system driven by the participant’s volitional efforts and a split-crank leg-cycle system driven by the switched application of FES with motor assistance. A variable operator is applied to the leg-cycle’s motor input during the FES stimulation regions to provide assistance as required. Lyapunov-based analysis methods are used on the combined leg and hand-cycle system to prove global exponential stability. Analysis further proves that all switched system inputs are bounded, thus the states of the telerobotic master (i.e., hand-cycle system) are bounded, therefore, the telerobotic system is stable. 

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3. Cadence and Position Tracking for Decoupled Legs during Switched Split-Crank Motorized FES-Cycling

   Esquivel Estay, Fidel ; Rouse, Courtney ; Cohen, Max ; Cousin, Christian ; Dixon, Warren E. ( July 2019 , Proc. American Control Conference)

   Functional electrical stimulation (FES) has proven to be an effective method for improving health and regaining muscle function for people with limited or reduced motor skills. Closed-loop control of motorized FES-cycling can facilitate recovery. Many people with movement disorders (e.g., stroke) have asymmetries in their motor control, motivating the need for a closed-loop control system that can be implemented on a split-crank cycle. In this paper, nonlinear sliding mode controllers are designed for the FES and electric motor on each side of a split-crank cycle to maintain a desired cadence and a crank angle offset of 180 degrees, simulating standard pedaling conditions. A Lyapunov-like function is used to prove stability and tracking of the desired cadence and position for the combined cycle-rider system. One experimental trial on an able-bodied individual demonstrated the feasibility and stability of the closed-loop controller, which resulted in an average cadence error of 2.62 ± 3.54 RPM for the dominant leg and an average position and cadence error of 39.84±10.77 degrees and −0.04 ± 8.79 RPM for the non-dominant leg. 

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4. Varying Motor Assistance During Biceps Curls Induced via Functional Electrical Stimulation

   https://doi.org/10.1115/DSCC2018-9083  

   Rouse, Courtney A. ; Cousin, Christian A. ; Duenas, Victor H. ; Dixon, Warren E. ( September 2018 , Proc. ASME Dynamic Systems and Control Conference)

   Robot-assisted therapy has been established as a useful rehabilitation tool for motor recovery in people with various neurological impairments; however, balancing human and robot contribution, such that the target muscle is sufficiently exercised, is necessary to improve the outcome of rehabilitation protocols. Functional Electrical Stimulation (FES) can assist a person to move their limb by contracting the muscle; however, motor assistance is often necessary to accurately follow a desired limb trajectory, especially since stimulation can be limited due to various factors (e.g., subject comfort, stimulation saturation). In this paper, a motor is tasked with intermittently assisting the FES-activated biceps brachii in tracking a desired forearm trajectory whenever the FES input reaches a pre-set comfort threshold. A Lyapunov-like switched systems stability analysis is used to prove exponential stability of the human-robot system. Preliminary experiments demonstrate the feasibility and performance of the controller on two subjects with neurological impairments. *Note this paper does not properly cite the specific project number. 

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5. Switched Control of Motor Assistance and Functional Electrical Stimulation for Biceps Curls

   https://doi.org/10.3390/app10228090  

   Rouse, Courtney ; Allen, Brendon ; Dixon, Warren ( November 2020 , Applied Sciences)

   null (Ed.)

   Rehabilitation robotics is an emerging tool for motor recovery from various neurological impairments. However, balancing the human and robot contribution is an open problem. While the motor input can reduce fatigue, which is often a limiting factor of functional electrical stimulation (FES) exercises, too much assistance can slow progress. For a person with a neurological impairment, FES can assist by strategically contracting their muscle(s) to achieve a desired limb movement; however, feasibility can be limited due to factors such as subject comfort, muscle mass, unnatural muscle fiber recruitment, and stimulation saturation. Thus, motor assistance in addition to FES can be useful for prolonging exercise while still ensuring physical effort from the person. In this paper, FES is applied to the biceps brachii to perform biceps curls, and motor assistance is applied intermittently whenever the FES input reaches a pre-set comfort threshold. Exponential stability of the human–robot system is proven with a Lyapunov-like switched systems stability analysis. Experimental results from participants with neurological conditions demonstrate the feasibility and performance of the controller. 

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