Simple direction-dependent rhythmic movements and partial somesthesis of a marionette

The simple rhythmic movements of a multi-link sagittal marionette with many muscle-like actuators are considered in this paper. The marionette is standing on the ground, and contact with surrounding objects is not permitted. Every actuator has two inputs: a firing rate, analogous to the collective action of the alpha motoneurons of a muscle, and a threshold signal, analogous to the effective action of the gamma motoneurons that excite the sensory organ of the natural muscle-the spindle. The system possesses intrinsic position and velocity feedback due to the structure of its actuators, and extrinsic feedback with transmission delays between the actuators and the control system. The extrinsic feedback is nonlinear and is fashioned after the spindle response in natural systems. Force and length sensors convey information from which the angular position of the marionette is estimated by simultaneous solution of a redundant set of equations. Thus, the marionette is endowed with partial somesthesis: awareness of the whereabouts of its limbs. A control strategy for simple rhythmic movements is developed. This is a preliminary effort to develop an analytical structure for a multiactuator system. The long range findings may shed some light on the elaborate control structure of the central nervous system in natural systems.<>