GPS World, June 2017
COVERSTORY Photo Fuyu Liu Shutterstock INERTIAL PERFORMANCE Enhanced Tightly Coupled Dead Reckoning T he number of available options in inertial navigation systems INS has grown substantially over the last several years Major advances have been made not only in inertial measurement unit IMU technology but also in the ability to exploit sensor information to its fullest extent In both cases the largest impact can be seen in the micro electrical mechanical systems MEMS sensors MEMS sensors are typically much smaller lower power and less expensive than traditional IMUs The net result of these improvements is a proliferation of INS systems at much lower cost than were previously available and therefore greatly increased accessibility to technology that has historically seen limited deployment Selecting the appropriate sensor and fusion 10 GPS WORLD WWW GPSWORLD COM JUNE 2017 solution for a particular application can be very challenging due to the large and confusing spectrum of solutions The IMUs will be examined in the context of new enhancements to sensor fusion algorithms such as the use of INS profiles The concept of INS profiles applies environment specific constraints to improve performance in certain types of vehicles or motion profiles External sensors such as odometers and dual antenna operation can also aid the solution considerably but will be unused in this analysis except for occasional comparisons These external aiding sensors are extremely helpful in many cases and are available to use with a proprietary tightly coupled GNSS INS solution called SPAN but this paper seeks to evaluate what performance can be achieved without such aids Real world test results will be examined using a selection of IMUs with the latest SPAN algorithms to illustrate what kind of performance can be achieved with different sensors in difficult conditions Despite their major advances over the past few years there are many challenges involved with utilizing MEMS technology to provide a robust navigation solution particularly during limited GNSS availability or low dynamics The measurement error characteristics of these devices have improved dramatically but are BY Ryan Dixon and Michael Bobye NOVATEL I N C FIGURE 1 Equipment set up not to scale EXPLORING IMU SPECIFICATIONS and correlating them to performance of a final product can be daunting as differences between MEMS sensors are not always apparent This article presents achievable performances in fusion technology across a range of IMUs among the best in their respective performance categories
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