- Award ID(s):
- 2002261
- NSF-PAR ID:
- 10333463
- Date Published:
- Journal Name:
- Sensors
- Volume:
- 22
- Issue:
- 1
- ISSN:
- 1424-8220
- Page Range / eLocation ID:
- 335
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Functional electrical stimulation (FES) is a potential technique for reanimating paralyzed muscles post neurological injury/disease. Several technical challenges including difficulty in measuring and compensating for delayed muscle activation levels inhibit its satisfactory control performance. In this paper, an ultrasound (US) imaging approach is proposed to measure delayed muscle activation levels under the implementation of FES. Due to low sampling rates of US imaging, a sampled data observer (SDO) is designed to estimate the muscle activation in a continuous manner. The SDO is combined with continuous-time dynamic surface control (DSC) approach that compensates for the electromechanical delay (EMD) in the tibialis anterior (TA) activation dynamics. The stability analysis based on the Lyapunov-Krasovskii function proves that the SDO-based DSC plus delay compensation (SDO-DSC-DC) approach achieves semi-global uniformly ultimately bounded (SGUUB) tracking performance. Simulation results on an ankle dorsiflexion neuromusculoskeletal system show the root mean square error (RMSE) of desired trajectory tracking is reduced by 19.77 % by using the proposed SDO-DSC-DC compared to the DSC-DC without the SDO. The findings provide potentials for rehabilitative devices, like powered exoskeleton and FES, to assist or enhance human limb movement based on the corresponding muscle activities in real-time.more » « less
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Abstract Introduction Optimal frequency modulation during functional electrical stimulation (FES) may minimize or delay the onset of FES‐induced muscle fatigue.
Methods An offline dynamic optimization method, constrained to a modified Hill‐Huxley model, was used to determine the minimum number of pulses that would maintain a constant desired isometric contraction force.
Results Six able‐bodied participants were recruited for the experiments, and their quadriceps muscles were stimulated while they sat on a leg extension machine. The force–time (F–T) integrals and peak forces after the pulse train was delivered were found to be statistically significantly greater than the force–time integrals and peak forces obtained after a constant frequency train was delivered.
Discussion Experimental results indicated that the optimized pulse trains induced lower levels of muscle fatigue compared with constant frequency pulse trains. This could have a potential advantage over current FES methods that often choose a constant frequency stimulation train.
Muscle Nerve 57 : 634–641, 2018 -
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 compensating for the FES-induced muscle fatigue and ensuring performance despite highly nonlinear and uncertain skeletal muscle behavior. This study develops a bi-level hierarchical control design for shared control of a powered exoskeleton and FES to overcome these challenges. A higher-level neural network–based iterative learning controller (NNILC) is derived to generate torques needed to drive the hybrid system. Then, a low-level model predictive control (MPC)-based allocation strategy optimally distributes the torque contributions between FES and the exoskeleton’s knee motors based on the muscle fatigue and recovery characteristics of a participant’s quadriceps muscles. A Lyapunov-like stability analysis proves global asymptotic tracking of state-dependent desired joint trajectories. The experimental results on four non-disabled participants validate the effectiveness of the proposed NNILC-MPC framework. The root mean square error (RMSE) of the knee joint and the hip joint was reduced by 71.96 and 74.57%, respectively, in the fourth iteration compared to the RMSE in the 1st sit-to-stand iteration.more » « less
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null (Ed.)Introduction: Functional electrical stimulation (FES) induced cycling has been shown to be an effective rehabilitation for those with lower limb movement disorders. However, a consequence of FES is an electromechanical delay (EMD) existing between the stimulation input and the onset of muscle force. The objective of this study is to determine if the cycle crank angle has an effect on the EMD. Methods: Experiments were performed on 10 participants, five healthy and five with neurological conditions resulting in movement disorders. A motor fixed the crank arm of a FES-cycle in 10 degree increments and at each angle stimulation was applied in a random sequence to a combination of the quadriceps femoris and gluteal muscle groups. The EMD was examined by considering the contraction delay (CD) and the residual delay (RD), where the CD (RD) is the time latency between the start (end) of stimulation and the onset (cessation) of torque. Two different measurements were used to examine the CD and RD. Further, two multiple linear regressions were performed on each measurement, one for the left and one for the right muscle groups. Results: The crank angle was determined to be statistically relevant for both the CD and RD. Conclusions: Since the crank angle has a significant effect on both the CD and RD, the angle has a significant effect on the EMD. Therefore, future efforts should consider the importance of the crank angle when modelling or estimating the EMD to improve control designs and ultimately improve rehabilitative treatments.more » « less
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Functional electrical stimulation (FES) is commonly used for people with neurological conditions. As the muscle geometry changes (i.e., muscle lengthening/ shortening), the force induced by static electrode placement may also change. Experimental results indicate that muscle forces can be increased by spatially switching stimulation as the muscle geometry changes with joint angle. In this letter, an electric field is switched between multiple electrodes placed across the biceps brachii to track a desired trajectory. A switched systems approach is used to develop a position-based switching law, including a switched robust sliding mode controller that successfully tracks the desired angular trajectory about the elbow, despite changes in muscle geometry. Lyapunovbased methods for switched systems are used to prove global exponential tracking. Experimental results from nine able-bodied subjects are presented and the developed control system achieves an average position and velocity error of −0.21 ± 1.17 deg and −0.43 ± 5.38 deg/s, respectively, and, on average, reduces fatigue by 13.6%, as compared to traditional single-electrode methods, demonstrating the performance of the uncertain nonlinear switched control system.more » « less