| Description |
Paralysis due to spinal cord injury or stroke can leave a person with intact peripheral nerves and muscles, but deficient volitional motor control, thereby reducing their health and quality of life. Functional neuromuscular stimulation (FNS) has been widely studied and employed in clinical devices to aid and restore lost or deficient motor function. Strong, selective, and fatigue-resistant muscle forces can be evoked by asynchronously stimulating small independent groups of motor neurons via multiple intrafascicular electrodes on an implanted Utah slanted electrode array (USEA). Determining the parameters of asynchronous intrafascicular multi-electrode stimulation (aIFMS), i.e., the per-electrode stimulus intensities and the interelectrode stimulus phasing, to evoke precise muscle force or joint motion presents unique challenges because this system has multiple-inputs, the n independently stimulated electrodes, but only one measurable output, the evoked endpoint isometric force or joint position. This dissertation presents three studies towards developing robust real-time control of aIFMS. The first study developed an adaptive feedforward algorithm for selecting aIFMS per-electrode stimulus intensities and interelectrode stimulus phasing to evoke a variety of isometric ankle plantar-flexion force trajectories. In simulation and experiments, desired step, sinusoidal, and more-complex time-varying isometric forces were successfully evoked. The second study developed a closed-loop feedback control method for determining aIFMS per-electrode stimulus intensities to evoke precise single-muscle isometric ankle plantar-flexion force trajectories, in real-time. Using a proportional closed-loop force-feedback controller, desired step, sinusoid, and more complex time-varying forces were evoked with good response characteristics, even in the presence of nonlinear system dynamics, such as muscle fatigue. The third study adapted and extended the closed-loop feedback controller to the more demanding task of controlling joint position in the presence of opposing joint torques. A proportional-plus-velocity-plus-integral (PIV) joint-angle feedback controller evoked and held desired steps in position with responses th a t were stable, consistent, and robust to disturbances. The controller evoked smooth ramp-up (concentric) and ramp-down (eccentric) motion, as well as precise slow moving sinusoidal motion. The control methods developed in this dissertation provide a foundation for new lower-limb FNS-based neuroprostheses that can generate sustained and coordinated muscle forces and joint motions that will be desired by paralyzed individuals on a daily basis. proportional-plus-velocity-plus-integral (PIV) joint-angle feedback controller evoked and held desired steps in position with responses th a t were stable, consistent, and robust to disturbances. The controller evoked smooth ramp-up (concentric) and ramp-down (eccentric) motion, as well as precise slow moving sinusoidal motion. The control methods developed in this dissertation provide a foundation for new lower-limb FNS-based neuroprostheses that can generate sustained and coordinated muscle forces and joint motions that will be desired by paralyzed individuals on a daily basis. |
