Abstract
This article investigates the application of optimal feedback control to trajectory planning in voluntary human arm movements. A nonlinear model predictive controller (NMPC) with a finite prediction horizon was used as the optimal feedback controller to predict the hand trajectory planning and execution of planar reaching tasks. The NMPC is completely predictive, and motion tracking or electromyography data are not required to obtain the limb trajectories. To present this concept, a two degree of freedom musculoskeletal planar arm model actuated by three pairs of antagonist muscles was used to simulate the human arm dynamics. This study is based on the assumption that the nervous system minimizes the muscular effort during goal-directed movements. The effects of prediction horizon length on the trajectory, velocity profile, and muscle activities of a reaching task are presented. The NMPC predictions of the hand trajectory to reach fixed and moving targets are in good agreement with the trajectories found by dynamic optimization and those from experiments. However, the hand velocity and muscle activations predicted by NMPC did not agree as well with experiments or with those found from dynamic optimization.
Highlights
The human central nervous system (CNS), consisting of brain, and spinal cord, is responsible for controlling and maintaining body motions
This study investigates the use of anticipatory planning with continuous error correction by the CNS during reaching tasks
The first goal of this study is to study the effects of varying the prediction horizon on the hand trajectory and muscle activities in a reaching task
Summary
The human central nervous system (CNS), consisting of brain, and spinal cord, is responsible for controlling and maintaining body motions. The early observations of reaching and pointing tasks led to the well-known “Minimum-X” models [e.g., minimum-jerk model (Flash and Hogan, 1985; Wada et al, 2001), minimum-torque-change model (Uno et al, 1989), minimum-variance model (Harris and Wolpert, 1998), and minimumwork model (Soechting et al, 1995)] to predict the hand trajectory. These models hypothesize that the CNS coordinates the body movement such that an exertion (X) is minimized. This hypothesis is extended to consider physiologically-motivated exertions such as muscle activation effort (Crowninshield and Brand, 1981; Happee and Van der Helm, 1995; Ackermann and van den Bogert, 2010), metabolic energy expenditure (Anderson and Pandy, 2001; Peasgood et al, 2006), and muscle fatigue (Sharif Razavian and McPhee, 2015)
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