Stability and movement of a one-link neuromusculoskeletal sagittal arm

The stability and point-to-point and rhythmic movements of a one-link sagittal arm are studied. The system is highly nonlinear. Its major physiological characteristics are simultaneous activation of a pair of nonlinear muscle-like actuators for control purposes, existence of nonlinear spindle-like sensors, and actions of gravity and loading. Transmission delays are included in the afferent and efferent neural paths to account for a more accurate representation of the reflex loops. An algorithm for computation of the actuator forces and the feedback signals in the system is provided. It automatically renders positive forces and positive neural signals. The positiveness of the forces represents the unidirectional character of muscular forces. The positiveness of the neural signals implies that these signals can correspond to firing rates. The system is designed to perform stable point-to-point movement. The effects of presetting the input signals, of the nonlinearities in the dynamics, actuators, and feedback signals, and of the delays and gain in the feedback loops in destabilizing the system, and the consequent undesirable oscillations, are studied by simulation.<>