Adaptive suppression of biodynamic interference in helmet-mounted displays and head teleoperation

This paper addresses errors caused by vibration or turbulence in airborne helmet displays and teleoperation. It is shown by analysis and computer simulations that a modified version of the least-mean-squares adaptive noise suppression algorithm facilitates the separation of the large voluntary head movements from the vibrationinduced small nonvoluntary head motion. Thus, the effects of the biodynamic interference can be essentially removed. The results also indicate that errors in head-tracking teleoperated devices can essentially be suppressed. Extensive man-in-the-loop laboratory simulations that validate the method are described. YSTEM teleoperation by pilot head motion and presentation of computer-gene rated symbols and flight information in helmet-mounte d displays is emerging as a promising technology in modern avionic systems. Head teleoperation is potentially an effective method for instinctive and rapid aiming of radar antennas, missile seeker heads, or laser designators. In addition, it relieves the hands of the pilot for other vital manual tasks in increasingly complex airborne environments. Helmet-mounted displays (HMD) can, in principle, be the ultimate solution in merging computer-generated displays with the outside scene, thus embracing the entire field of view available to the pilot. Therefore, the HMD potentially relieves the pilot from the troublesome need to share his attention between the all-aspect outside scene and a restrictive cockpitmounted panel or head-up display. However, a potential shortcoming of head teleoperation and HMDs is their vulnerability to biodynamic interference resulting from vibration, atmospheric turbulence, or self-induced vehicle motion. These interferences can cause substantial random aiming errors and apparent display blurring that may seriously impair pilot performance. Two kinds of biodynamic interference exist, namely, 1) additive interferences due to nonvoluntary limb motions caused by, and correlated with, vibration,1'2 and 2) nonadditive interferences resulting from the disturbances in the central nervous system caused by the body and head vibrations, uncorrelated with them, but monotonically increasing with their intensity.3'4 Head vibration causes relative angular motion of the HMD with respect to the line of sight of the eye, which is inertially stabilized by the vestibular system. Consequently, as a result of the apparent display shift, image blurring occurs, resulting in substantial degradation of reading speed and probability of correct character recognition.5'6 This neuromotor stabilization, known as the vestibulo-ocular reflex (VOR), is effective in the frequency range of 2-10 Hz.7 Wells and Griffin6'8 conducted experiments to cancel this blurring by shifting the display in the opposite direction with an amplitude equal to the measured head motion which was determined by an approximate double integration of head angular acceleration. They succeeded in demonstrating the effectiveness of the concept, but the imperfection of the integration caused substantial transients in the display position in the presence of large angular head motion.