Abstract
A multivariable deterministic extremum seeking (ES) is being evaluated to construct an adaptive Proportional-Integral-Derivative (PID) control law for the functional Neuromuscular Electrical Stimulation (NMES) of stroke patients. The developed scheme is applied to control the position of the patient's arm so that movements of flexion/extension for its elbow can be produced. The true limitations of a PID controller for these types of applications is that a PID controller is designed for linear systems, but the system which is being controlled is nonlinear. Moreover, it is worth mention that clinicians' knowledge of control systems is limited. Therefore, their expertise in tuning controllers is limited. Also, in NMES applications each patient is unique and requires a unique set of PID parameters. Since it can be time consuming and difficult to find proper parameters for each patient, a better procedure, or a more intelligent adaptive controller, is needed. The PID parameters are updated by means of ES in order to minimize a cost function which brings the desired performance attributes. Experiments are performed with healthy volunteers and stroke patients, including significant advances based on real data and validation. Quantitative results show a reduction of 64:1% in terms of RMSE (Root-Mean-Square Error) - from 8:94º to 3:21º - when comparing the tracking curves of the last cycle to the first cycle in the experiments with all stroke patients.
Highlights
Neuromuscular Electrical Stimulation (NMES) is a technique based on the artificial activation of the second motor neurons using exogenous electrical impulses (Sheffler and Chae 2007)
NMES can be divided in two branches: the applications used as functional substitute and those ones intended to therapeutic intervention
The tests indicate that the Root-Mean-Square Error (RMSE) are statistically less for the last cycle of evaluation for the proposed extremum seeking (ES) based PID controller when compared to the first cycle, representing a reduction of 64% in terms of the RMSE
Summary
Neuromuscular Electrical Stimulation (NMES) is a technique based on the artificial activation of the second motor neurons using exogenous electrical impulses (Sheffler and Chae 2007). It has been shown that the open-loop devices are not well suited to promote an adequate association between the subject’s intended movement and the artificial activation produced by NMES In this context, Proportional-Integral-Derivative (PID) controllers continue to represent a good option to closed-loop control the NMES electrical current amplitude based on the angular displacement of the arms because it has a simple implementation and its behavior is well known (Freeman et al 2009). Of our previous publication based on healthy volunteers (Oliveira et al 2016), experimental results are presented for stroke patients We believe this is a meaningful and relevant contribution since the self-tuning of PID controllers for NMES-based rehabilitation would make their use much more practical in clinical settings by means of closed-loop control. To the best of our knowledge, the present paper is the first work which proposes the use of deterministic ES as a tool for adaptation of NMES closed-loop controllers experimental validation with stroke patients
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