Abstract
BackgroundThe purpose of this study was to determine the comparative effectiveness of feedback control systems for maintaining standing balance based on joint kinematics or total body center of mass (COM) acceleration, and assess their clinical practicality for standing neuroprostheses after spinal cord injury (SCI).MethodsIn simulation, controller performance was measured according to the upper extremity effort required to stabilize a three-dimensional model of bipedal standing against a variety of postural disturbances. Three cases were investigated: proportional-derivative control based on joint kinematics alone, COM acceleration feedback alone, and combined joint kinematics and COM acceleration feedback. Additionally, pilot data was collected during external perturbations of an individual with SCI standing with functional neuromuscular stimulation (FNS), and the resulting joint kinematics and COM acceleration data was analyzed.ResultsCompared to the baseline case of maximal constant muscle excitations, the three control systems reduced the mean upper extremity loading by 51%, 43% and 56%, respectively against external force-pulse perturbations. Controller robustness was defined as the degradation in performance with increasing levels of input errors expected with clinical deployment of sensor-based feedback. At error levels typical for body-mounted inertial sensors, performance degradation due to sensor noise and placement were negligible. However, at typical tracking error levels, performance could degrade as much as 86% for joint kinematics feedback and 35% for COM acceleration feedback. Pilot data indicated that COM acceleration could be estimated with a few well-placed sensors and efficiently captures information related to movement synergies observed during perturbed bipedal standing following SCI.ConclusionsOverall, COM acceleration feedback may be a more feasible solution for control of standing with FNS given its superior robustness and small number of inputs required.
Highlights
The purpose of this study was to determine the comparative effectiveness of feedback control systems for maintaining standing balance based on joint kinematics or total body center of mass (COM) acceleration, and assess their clinical practicality for standing neuroprostheses after spinal cord injury (SCI)
We have previously developed comprehensive functional neuromuscular stimulation (FNS) control systems utilizing either proportionalderivative joint feedback [7] or total body center of mass (COM) acceleration feedback [8] to drive an artificial neural network (ANN) trained to output changes in muscle excitation levels and maintain standing posture against disturbances
Controller gain tuning The optimal controller gains determined by the global search algorithm for minimizing upper extremity (UE) loading against external force-pulse perturbations are listed in Table 1 for all three controller cases
Summary
The purpose of this study was to determine the comparative effectiveness of feedback control systems for maintaining standing balance based on joint kinematics or total body center of mass (COM) acceleration, and assess their clinical practicality for standing neuroprostheses after spinal cord injury (SCI). The goal of this study was to assess the potential performance of control systems employing feedback of total body center of mass (COM) acceleration and proportionalderivative joint feedback from the ankles, knees, hips, and trunk for comprehensive control of standing after spinal control of stimulation is necessary to provide automatic postural adjustments that reduce the UE effort necessary for stabilization. We have previously developed comprehensive FNS control systems utilizing either proportionalderivative joint feedback [7] or total body center of mass (COM) acceleration feedback [8] to drive an artificial neural network (ANN) trained to output changes in muscle excitation levels and maintain standing posture against disturbances. The simulated performance of the FNS control systems were mainly assessed according to minimization of the UE loading applied during postural perturbations
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