Optimal time-varying postural control in a single-link neuromechanical model with feedback latencies
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ORIGINAL ARTICLE
Optimal time-varying postural control in a single-link neuromechanical model with feedback latencies Kamran Iqbal1 Received: 26 February 2020 / Accepted: 20 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Maintaining balance during quiet standing is a challenging task for the neural control mechanisms due to the inherent instabilities involved in the task. The feedback latencies and the lowpass characteristics of skeletal muscle add to the difficulty of regulating postural dynamics in real-time. Inverted-pendulum (IP) type robotic models have served as a popular paradigm to investigate control of postural balance. In this study, an in-depth neuromechanical postural control model is developed from physiological principles. The model comprises a single-segment IP robotic model, Hill-type muscle model, and proprioceptive feedback from the muscle spindle (MS) and golgi tendon organ (GTO). An optimal proportional-integral-derivative (PID) controller is proposed to realize effective postural control amid latencies in sensory feedback. The neural commands for postural stabilization are generated by a time-varying PID controller, tuned using linear quadratic regulator (LQR) principles. Computer simulations are used to assess the efficacy of the tuned PID-LQR controller. Sensitivity analysis of the controlled system shows a delay tolerance of 300ms. Preliminary empirical data in support of the mathematical model were obtained from perturbation experiments. The model response to perturbation torque, measured in terms of the center of mass (COM) excursion in the anterior-posterior (AP) direction, displays a high degree of correlation with the empirical data (ρ = 0.91). Keywords Neuromechanical postural control model · Inverted-pendulum · Feedback latencies · Optimally tuned PID controller
1 Introduction This study aims to develop a physiologically relevant postural control representation of a standing human. An additional aim of the study is to design an optimal time-varying representation of the control processes underlying postural adjustments. The neuromechanical model developed in this study includes an inverted-pendulum (IP) representation of a standing human in the sagittal plane. The robotic IP model is actuated by dual muscle-like actuators based on the Hill-type muscle model. The actuators represent the anti-gravity muscles including the tricep surae muscle (gastrocnemius and the soleus) responsible for planterflexion and tibialis anterior muscle responsible for dorsiflexion. Further, the musclelike actuators generate stabilizing moments to counter the Communicated by Benjamin Lindner.
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Kamran Iqbal [email protected] University of Arkansas Little Rock, Little Rock, AR 72204, USA
destabilizing gravitational torques at the ankle joint. The neuromechanical postural control model includes proprioceptive sensing of muscle length, rate of muscle shortening, and the muscle tone using simple models of muscle spindle (MS) and golgi tendon organ (GTO). The model includ
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