Inertial Orientation Trackers With Drift Compensation

Invention could enable the paralyzed to control machines via head motions.

A class of inertial- sensor systems with drift compensation has been invented for use in measuring the orientations of human heads (and perhaps other, similarly sized objects). These systems can be designed to overcome some of the limitations of prior orientation- measuring systems that are based, variously, on magnetic, optical, mechanical-linkage, and acoustical principles. The orientation signals generated by the systems of this invention could be used for diverse purposes, including controlling head-orientation-dependent “virtual reality” visual displays or enabling persons whose limbs are paralyzed to control machinery by means of head motions.

The inventive concept admits to variations too numerous to describe here, making it necessary to limit this description to a typical system, the selected aspects of which are illustrated in the figure. A set of sensors is mounted on a bracket on a band or a cap that gently but firmly grips the wearer’s head to be tracked. Among the sensors are three drift-sensitive rotation-rate sensors (e.g., integrated-circuit angular-rate-measuring gyroscopes), which put out DC voltages nominally proportional to the rates of rotation about their sensory axes. These sensors are mounted in mutually orthogonal orientations for measuring rates of rotation about the roll, pitch, and yaw axes of the wearer’s head.

The outputs of these rate sensors are conditioned and digitized, and the resulting data are fed to an integrator module implemented in software in a digital computer. In the integrator module, the angular- rate signals are jointly integrated by any of several established methods to obtain a set of angles that represent approximately the orientation of the head in an external, inertial coordinate system. Because some drift is always present as a component of an angular position computed by integrating the outputs of angular-rate sensors, the orientation signal is processed further in a drift-compensator software module.

Also mounted on the bracket are two drift-compensating angular-position sensors. One of these sensors is typically a twoaxis bubble inclinometer that generates voltages proportional to tilts, relative to the gravitational field, about the roll and pitch axes. The other sensor is typically a fluxgate compass that measures the flux densities of the ambient magnetic field along the roll and pitch axes. In principle, the combination of the magnetic-field information and the tilt information can be used to determine the heading in the horizontal plane or, equivalently, the angular position in rotation about the vertical (gravitational) axis.