A marionette-based strategy for stable movement

A strategy is developed for stable movement of a marionette under a system of unidirectional muscle-like actuators. It is shown that the strategy provides positive forces and positive inputs to the actuators that can be made analogous to monotonic function of the firing rate of natural muscles. The strategy requires more pairs of actuators than the degrees of freedom of the system-hence a need for synergistic actuators. In contrast to string-pulled marionettes where the length of the string is controlled, the tension of the string is controlled. Consequently the actuators are supplied with spindle-like position and velocity sensors and with independent input signals from higher control centers analogous to gamma inputs in living systems. Furthermore, ideal transmission delays are included in the feedforward and feedback paths to imitate neural transmission delays in living systems. To test the control strategy a three-link ten-actuator system is modeled and its stability, point to point movement, and tremor-like oscillations are shown by simulation.<>