Abstract: Apparatus for determining the position and orientation of a helmet worn by a crew member in a vehicle including a generator, associated with the vehicle, which produces a rotating magnetic and electric field of fixed strength, orientation and frequency within at least a portion of the vehicle. The apparatus also includes a plurality of detectors each of which generates a signal proportional to at least one of the electric or magnetic fields at least one point associated with the helmet and calculation circuitry responsive to the signal for ascertaining the coordinates of the at least one point with respect to the generator and for determining the position and orientation of the helmet.

Abstract: Apparatus for determining the position and orientation of a helmet worn by a crew member in a vehicle including a generator, associated with the vehicle, which produces a rotating magnetic and electric field of fixed strength, orientation and frequency within at least a portion of the vehicle. The apparatus also includes a plurality of detectors each of which generates a signal proportional to at least one of the electric or magnetic fields at least one point associated with the helmet and calculation circuitry responsive to the signal for ascertaining the coordinates of the at least one point with respect to the generator and for determining the position and orientation of the helmet.

Abstract: A helmet system having a visor attached to a support bracket mounted on a helmet wherein the support bracket is formed with an extension operative to block the visor from lifting upwards when the visor is pushed toward the helmet by wind pressure while not obstructing the normal circumferential movement of said visor in the absence of wind pressure.

Abstract: A system and method for measuring the operation of a device is disclosed. A plurality of virtual sensors which define a multi-dimensional virtual sensor space sense the operation of the device. A normal operation determiner determines at least one region of normal operation for the device. An abnormal condition determiner provides a warning when the operation does not fall within the normal operation region which is defined within the multi-dimensional virtual sensor space. A maintenance method and system are also disclosed for maintaining at least one device. The maintenance system includes a measurement system and an abnormality processor. The measurement system measures the operation of the device and provides an indication of when the device is not operating normally. The abnormality processor predicts, based on the output of the measurement system, when the device is likely to fail.

Abstract: A display, for example, for a visor attached to a helmet, the visor having a partially reflecting semi-transparent portion in the view of the wearer and an optical projector for projecting an image onto the semi-transparent portion for reflection therefrom. The semi-transparent portion has a relatively higher reflectivity in a central area thereof and a relatively lower reflectivity in an annular area outside the central area. In one aspect of the invention, the head mounted display includes a projector having a display source whereon an image is formed and an optical system for focusing the image at separate sagittal and tangential foci between the image-forming surface and the semi-transparent portion.