AHRS In Action

Posted on April 22, 2008
Filed Under Auto Accessories |

AHRS in Action

AHRS is normally used to provide continuous outputs of position, velocity, and attitude of the vehicle during those intervals of time between successive inputs from instruments and observations which are most precise. For example, an aircraft in which the present invention may be installed, may be capable of obtaining precise radio navigation information at intervals, and AHRS is capable of responding to these more precise inputs to provide continuous position outputs. Even if the reference dynamic variable from the more precise instruments is available continuously, the AHRS system can use that information as an input to provide more accurate estimation of certain other dynamic variables. For example, in the present invention an estimator of heading angle is obtained by mathematical integration of the sensed rate of change of heading angle. Simultaneously, a measurement of heading angle is made by a flux sensor and this magnetic heading is used as a reference dynamic variable and is continually compared with the estimator of heading angle. The updated estimator of heading angle is used in turn to obtain estimates of the vehicle’s latitude and longitude and to obtain a correction for earth rate which is used in calculating the pitch and roll attitude angles of the vehicle.

The AHRS of the present invention is of the type known as a “strapdown” inertial measurment instrument. This means that the instrument, specifically the sensors from which the instrument obtains information, are rigidly fixed to the frame of the vehicle. For example, a linear accelerometer is mounted to the vehicle with its sensitive axis fixed in the direction of the longitudinal axis of the vehicle, which may differ from the direction of motion of the vehicle. Thus, the information that is obtained by the instruments for use by the system of the present invention is referenced to the vehicle rather than to the earth. In this sense, the instruments and their measurements are referred to as “vehicle-oriented” rather than “earth-oriented”. The present invention includes provision for converting the vehicle-oriented measurements to earth-oriented measurements.

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