User:Jaison2050/sandbox

Functional electrical stimulation (FES) in Spinal Cord Injury is a technique that is used to generate a locomotion pattern in patients with spinal cord injury (SCI), head injury, stroke and other neurological disorders using electrical stimulation of major neuronal pathways innervating limb muscles. It is also used to correct gait in patients with neuromuscular disabilities where those affected are unable to coordinate their muscle movements in a pattern required for stepping like motion and balance.

Background
The neuromuscular response to electrical stimulation is nonlinear and any external perturbation might result in unpredictable responses with varying latencies. Stimulation of the lumbar region of the spinal cord at certain frequencies ranging from 2 Hz to 50Hz in known to activate certain locomotor neural pathways that activate muscle synergies responsible for cycling stepping like coordinated movements required for walking. There have been several open loop functional electrical stimulation (FES) systems that have been used to improve motor function in SCI patients during their Locomat-assisted rehabilitation training. These systems however fail to use the bodies sensory feedback system that could stabilize/ correct locomotor pattern in response to variations in external perturbation.

Proportional-Integral-Derivative
The Proportional-Integral-Derivative (PID) is a commonly used linear control algorithm due to its simplicity, reliability and its well established tuning methods. However PID controller can only be used to control linear time-invariant systems and does not react well to external disturbances that change the system. A more dynamic version of the PID controller could improve FES performance.

Gain scheduling
The Gain scheduling control involves linearizing the system at a series of operating points representing the operating region. Then a local linear controller is designed for each linearized segment. The scheduling variable is one that can model the non-linearity of the system and change slowly with respect to system dynamics. The scheduling variable is also used to interpolate between local linear models at fixed operating points. This controller works well when operating within the operating region but shows reduced accuracy when outside the operating span. A common scheduling variables chosen in FES walking systems is the knee angle and muscle lengths. However the such variables cannot capture the non-linearities introduced by muscle fatigue, fitness and spasticity. Therefore choosing an ideal scheduling variable and and tuning the controller across an operating region can be lengthy and expensive process.

Sliding mode control
The sliding mode control system involves defining a control rule that causes the state of the system to converge toward a chosen sliding manifold in finite time and evolve along the sliding manifold toward a goal state possibly in infinite time. Such a control algorithm provides good tracking, requires few parameters to be tunes and is adaptive to system dynamics. If an accurate system model is used, the sliding mode system also guarantees a stability. In light of all the aforementioned advantages, the sliding model is note designed to work with time-varying systems. Its performance falls when muscle fatigue is introduced also this control system is susceptible to 'chattering' - rapid back and forth switching between different control actions resulting in controller failure.

Currently available FES systems
Some of the commercially available FES cycling systems for SCI patients include:

+ The RT300 by Restorative Therapies, Inc., Baltimore, MD. + The Ergys 2 by Therapeutic Alliances, Inc., Fairborn, OH. + The NESS H200 FES grasping system by Bioness, Inc., Santa Clarita, CA. + The ODFS Pace FES to correct foot drop by Odstock Medical, Ltd., Wiltshire, U.K. + The WalkAide to correct foot drop by Innovative Neurotronics, Inc., Austin, TX + The L300 Bioness, Inc.