Controlling the gaze direction of a humanoid robot with redundant joints

Abstract

Due to their high number of joints, humanoid robots typically have kinematic redundancies to achieve end- effector poses. Examples for such redundancies are the kinematic chains of pitch and yaw joints that allow the robot to turn towards a gaze target. Our humanoid communication robot currently uses its spine, its neck, and its eye joints to direct its cameras towards an object. In this paper, we propose a control strategy that considers three factors, namely tracking error, discomfort, defined at the joint level, and "effort" to control the pitch and yaw joints. Our strategy is based on gradient descent on a cost function. During the optimization, we use different step sizes to reflect the different inertia of the moved parts. Our control scheme produces human-like motions, where smaller, light-weight parts such as the eyes of the robot move quickly towards the target and then move back while the larger joints turn towards the target. We present experiments to evaluate the proposed strategy qualitatively and quantitatively.