A Multi-Rate Control Scheme for a Robotic Eye/Head System Integrating Visual and Self-Motion Cues

Abstract

In primates, the vestibulo-ocular reflex (VOR) is known to stabilize gaze during head perturbations. Also, the internal brain circuits controlling eye movements are found to operate with neural delays much smaller than delays in visual processing pathways (~2ms vs 150 ms). Based on these biological findings, we present a unified multi-rate biomimetic gaze controller integrating VOR mechanisms (self-motion cues) with tracking (pursuit and saccades) for a robotic head with two cameras. The controller uses automatic parametric switching in shared premotor circuits to alternate between two movement types: smooth pursuit (slow phase) relying on visual feedback, and fast blind corrective jumps (fast phase) producing nystagmus. During fixation or tracking of a target (slow phase), a head-motion sensor (VOR) detects head rotation direction and drives the cameras in the opposite direction so that gaze in space remains on the visual target. A multi- rate control scheme is used to overcome inherent delays in the visual system limited to a 30Hz frame rate. Adding prediction and memory (PDI controller) in the visual feedback copes better with visual delays and allows slow tracking bandwidths near 2Hz. The rest of the controller operates at 600Hz: since the saccade circuit is effectively blind, the higher rate controller operation allows increasing saccade bandwidths without ringing to over 30Hz. In this paper, we describe the controller model and we present simulation results to demonstrate its performance.