More Like this

1. Stable Cadence Tracking of Admitting Functional Electrical Stimulation Cycle

   https://doi.org/10.1115/DSCC2018-8989  

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

   Rehabilitation robotics and functional electrical stimulation (FES) are two promising methods of rehabilitation for people with neurological disorders. In motorized FES cycling, both the rider and the motorized cycle must be controlled for cooperative human-machine interaction. While rehabilitation goals vary widely, FES cycling traditionally rejects rider disturbances to accomplish cadence and power tracking; however, this paper ensures that the cycle accommodates the rider without rejecting rider disturbances as a means to promote function and strength recovery while ensuring rider safety. A cadence and admittance controller are developed to activate the cycle’s electric motor and the rider’s leg muscles through FES when kinematically efficient. Using a single set of combined cycle-rider dynamics, a Lyapunov-like switched systems analysis is conducted to conclude global exponential cadence tracking. A subsequent passivity analysis is conducted to show the admittance controller is passive with respect to the rider. For a desired cadence of 50 RPM, preliminary experiments on one able-bodied participant and one participant with spina bifida demonstrate tracking errors of −0.07±2.59 RPM and −0.20±3.86 RPM, respectively. *Note this paper does not properly cite the specific NSF project number. 

   more » « less
2. Saturated Control of a Switched FES-Cycle with an Unknown Time-Varying Input Delay

   Allen, B. C. ; Stubbs, K. J. ; Dixon, W. E. ( December 2020 , IFAC Conference on Cyber-Physical Human-Systems)

   A common rehabilitation for those with lower limb movement disorders is motorized functional electrical stimulation (FES) induced cycling. Motorized FES-cycling is a switched system with uncertain dynamics, unknown disturbances, and there exists an unknown time-varying input delay between the application/removal of stimulation and the onset/removal of muscle force. This is further complicated by the fact that each participant has varying levels of sensitivity to the FES input, and the stimulation must be bounded to ensure comfort and safety. In this paper, saturated FES and motor controllers are developed for an FES-cycle that ensure safety and comfort of the participant, while likewise being robust to uncertain parameters in the dynamics, unknown disturbances, and an unknown time-varying input delay. A Lyapunov-based stability analysis is performed to ensure uniformly ultimately bounded cadence tracking. 

   more » « less
3. Cadence Tracking for Switched FES Cycling with Unknown Input Delay

   Allen, B. ; Cousin, C. ; Rouse, C. ; Dixon, W. ( January 2019 , 2019 IEEE 58th Conference on Decision and Control (CDC))

   Functional electrical stimulation (FES) induced cycling provides a means of therapeutic exercise and functional restoration for people affected by neuromuscular disorders. A challenge in closed-loop FES control of coordinated motion is the presence of a potentially destabilizing input delay between the application of the electrical stimulation and the resulting muscle contraction. Moreover, switching amongst multiple actuators (e.g., between FES control of various muscle groups and a controlled electric motor) presents additional challenges for overall system stability. In this paper, a closed-loop controller is developed to yield exponential cadence tracking, despite an unknown input delay, switching between FES and motor only control, uncertain nonlinear dynamics, and additive disturbances. Lyapunov-Krasovskii functionals are used in a Lyapunov-based stability analysis to ensure exponential convergence for all time. 

   more » « less
4. Cadence and Admittance Control of a Motorized Functional Electrical Stimulation Cycle

   https://doi.org/10.1109/CDC.2018.8618685  

   Cousin, Christian A. ; Duenas, Victor H. ; Rouse, Courtney A. ; Dixon, Warren E. ( December 2018 , Proc. IEEE Conference on Decision and Control)

   Functional electrical stimulation (FES) can be combined with a motorized cycle to offer various rehabilitation options for individuals with neurological conditions. Typically, FES cycling controllers use cooperating muscles and an electric motor to track cadence. In this paper, in addition to cooperative cadence tracking, the motorized cycle tracks an admittance trajectory generated using torque feedback. This method allows the cycle to deviate from the desired cadence trajectory and admit to the rider-applied torque, ensuring safe human-machine interaction. Two sets of uncertain, nonlinear dynamics are presented, one for the human rider and one for the robot, linked by a common measurable interaction torque. After developing cadence and admittance controllers, a Lyapunov-like switched system stability analysis is provided to prove global exponential tracking of the cadence error system, and a passivity analysis is conducted to prove passivity of the cycle’s admittance controller with respect to the rider’s interaction torque. *Note this paper does not properly cite the specific project. 

   more » « less
5. 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. 

   more » « less