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Inertial sensors enhance autonomous systems

Mon, 10/25/2010 - 5:47am
Fritz Martin, Senior Product Design Manager, MicroStrain

The adoption rate for unmanned systems continues to increase in the military, defense, aerospace and robotics industries, and is now also being embraced in many new markets across a variety of applications. The benefits of autonomous mobility, improved safety, remote operation, remote data collection, and improved repeatability are just a few of the reasons why the field of unmanned systems is poised for growth.

As the prevalence of unmanned systems increases, the push for technology to make these systems smaller, more accurate, and multi-functional also increases. Inertial micro-electrical-mechanical systems (MEMS) are the enabling technology for smaller, more precise attitude heading reference systems. However, MEMs sensors, by themselves, are not yet accurate enough for many of the more demanding tasks such as dead reckoning navigation. Fortunately, the performance of MEMs sensors can be greatly enhanced by proper temperature compensation, precision calibration, and fine tuned sensor fusion algorithms, to the point where the best inertial MEMs sensors are becoming viable for applications that are currently dominated by mechanical and optical technologies.

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3DM-GX3-25With the introduction of the 3DM-GX3 series of inertial sensors, MicroStrain entered its fourth generation of inertial MEMs products starting with the 3DM-G, 3DM-GX1, and 3DM-GX2 series. With each generation, the size of the sensors is reduced and the performance is enhanced.

In the design of the 3DM-GX3-25, MicroStrain’s lightest and smallest attitude heading reference system, the triaxial accelerometer, triaxial gyro, and triaxial magnetometer are combined with the temperature sensors and run through a sophisticated sensor fusion algorithm by the on-board processor. This provides accurate and more reliable measurements while minimizing drift due to inherent imperfections in the individual sensors.
To enhance the accuracy of these sensors even further, in-factory calibrations are executed to reinforce optimal effectiveness. Each sensor is manipulated in robotic chambers to ensure full temperature compensation, promoting measurement integrity in extreme temperatures. The sensors are also tested to calculate misalignment and each unit is burned with an alignment matrix. In addition to these in-factory calibrations, the tiny AHRS can be field calibrated for hard and soft iron interference using an enhanced graphical user interface. This allows the end user to easily compensate for any distortion due to ferromagnetic materials or altered magnetic fields while the sensor is positioned in an application.

An additional step in improving performance and versatility of AHRS in unmanned systems is the integration of global positioning systems. Data collected from a high sensitivity GPS receiver which runs parallel to and is synchronized with data from an AHRS provides unprecedented precision, and creates a more cost-effective, robust navigation system.

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