AHRS Attitude Heading Reference System

Overview

Copyright: DFKI GmbH, Robotics Innovation

Affordable MEMS AHRS

Affordable MEMS AHRS’ were introduced just after 2000, when inertial sensors prices dropped and accuracy improved, to enable the mass introduction of ESP, airbags and built-in car navigation. The improved inertial sensors were used by companies such as Xsens to design AHRSs that provide 3D orientation for a broad range of applications from human motion to navigation of unmanned vehicles and the stabilization of antenna and camera systems. The Xsens MTi 10-series and MTi 100-series are proven products in the industrial applications market place.

Kalman filtering

In order to cope with transient accelerations, magnetic disturbances and vibrations, the sensor fusion algorithm needs to be adapted for specific applications. Xsens offers the best performance by applying filter setting profiles that are optimized for the customer’s application.

GPS enhanced AHRSs

To improve the AHRS performance under long-lasting accelerations and under conditions with severe magnetic disturbance, Xsens offers the MTi-G-700 GPS/INS. The MTi-G-700 uses GPS to determine accelerations and velocity, which can be used to make the referencing with gravity more robust, resulting in a robust roll and pitch. Using the heading and course of the GPS, it is also possible to retrieve heading without using the magnetometers.

The MTi-G-700 is often used in applications that are high-dynamic. Test results and testimonials can be found here:

> MTi-G in a jet aircraft
> MTi-G on a racing track

MEMS AHRSs as a replacement for high-grade IMUs?

Traditional IMUs (e.g. Honeywell, Sagem and Northrop Grumman/Litef) are used in many applications for navigation, control, and stabilization. With the Xsens AHRSs, it is, however, possible to get similar performance in a smaller package allowing to use them in more applications, such as antenna and camera stabilization, small unmanned vehicles and even hand-held applications.

It also makes the use of orientation sensors possible where an orientation sensor had not been considered before. A few examples can be found at the Xsens website:

• Stabilizing an antenna for EM Solutions; EM Solutions provides a stabilized antenna system in challenging, mission-critical environments. The accuracy of the Xsens MTi-G is sufficient to cope with vibrations and dynamic movements.
• MTi’s steering a fleet of robots; the number of robots in a fleet (6 or more) makes the use of conventional orientation sensors very expensive. Using MTi’s gives the fleet manager information on every single robot.