World’s largest technical professional group focuses on inertial

April 2, 2019  - By
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Inertial 2019, the sixth annual Institute of Electrical and Electronics Engineers (IEEE) International Symposium on Inertial Sensors and Systems, took place in Florida earlier this month. Events of particular note included two keynote talks from experts at the U.S. Defense Advanced Research Projects Agency (DARPA) and the Air Force Institute of Technology (AFIT), and a technical paper on the “Design and Performance of Wheel-mounted MEMS Inertial Measurement Unit (IMU) for Vehicular Navigation.”

Miniature Sensors. Ronald Polcawich from DARPA addressed “Miniature Navigation Grade Inertial Sensors: Status and Outlook.” The agency’s Precise Robust Inertial Guidance for Munitions (PRIGM) program has focused for more than three years on developing inertial sensor technologies to enable PNT in GPS-denied environments. PRIGM has developed a navigation-grade inertial measurement unit (NGIMU) based on micro-electromechanical systems (MEMS) platforms. The device has a mechanical/electronic interface compatible with drop-in replacement for existing tactical-grade IMUs on legacy U.S. Department of Defense (DoD) platforms.

PRIGM’s second main area of interest is advanced inertial micro sensor (AIMS) technologies for future gun-hard, high-bandwidth, high-dynamic-range, GPS-free navigation. It explores alternative technologies and modalities for inertial sensing, including photonic and MEMS-photonic integration, as well as novel architectures and materials systems.

Map-Matching. Aaron Canciani from AFIT educated the many computer scientists, software developers, information technology professionals, physicists and electrical and electronics engineering attendees on “The Importance of INS Accuracy for Map-Matching Navigation.”

The GPS-alternative technique matches measurements from a sensor to a map to provide navigation information. With repeatable measurements, almost any map may be used to navigate. Common maps used for navigation include terrain height, gravity, magnetic fields, Wi-Fi RSS and more. The inertial navigation system often plays a critical role in the accuracy of these methods, and increased INS accuracy plays a synergistic role in an overall map-matching navigation system.

Inertial wheel sensor mounted on wheel rim. (Image: Jussi Collin)

Inertial wheel sensor mounted on wheel rim. (Image: Jussi Collin)

WHEEL-MOUNTED IMUS

In today’s automobiles, MEMS gyroscopes and accelerometers provide essential measurements for enhancing stability and control. Both types of sensors have significant noise at low frequencies, limiting the measurement accuracy, particularly in low-dynamic conditions. Further, uncompensated accelerometer tilt causes large bias to acceleration estimates. For gyroscopes, physical rotation of the sensor can remove the constant part of the gyro errors and reduce low-frequency noise. In ground vehicles, such rotation occurs conveniently in wheels.

When inertial sensors are attached to the wheel, both types of sensors provide information on the rotation, gyroscopes naturally and accelerometers via specific force measurement. As a result of carouseling, accurate wheel heading, roll and pitch estimation can be estimated with high resolution, and the result is nearly bias-free. Combining the wheel orientation to distance traveled via known radius enables classic dead-reckoning mechanization (assuming zero slip) and other vehicle dynamics monitoring systems (considering wheel slip as unknown to be solved).

Authors Jussi Collin of JC Inertial Oy, Finland, and Oleg Mezentsev, Pacific Inertial Systems Inc., Canada, provided details of wheel-mounted inertial system hardware and algorithms and showed test results for several system configurations and applications. They discussed future system improvements — in particular, system miniaturization and an energy-harvesting development progress for next-generation inertial systems.

They have designed a wheel-mountable sensor system that contains MEMS sensors, battery, Bluetooth module and electronics to run computations and navigation algorithms on board. It operates in several programmable modes:

  • Computes navigation parameters real time and sends them via Bluetooth to an onboard computer (can be any other integrated system, data logger or a tablet).
  • Sends real-time raw data to an onboard computer.
  • Records high-rate raw sensor data (up to 2 kHz) to an embedded micro-SD card.

The onboard computer is a MEMS-array IMU with 48 gyro and accelerometer channels, with a BT receiving and sync controller, data storage and Wi-Fi interface. They can connect up to four such units to one onboard computer and have all their data in sync with the in-cabin inertial data. All of this data can be used for navigation, wheel dynamics measurements or road quality monitoring applications.

Position estimation of the researchers’ PI-WINS device in two modes versus in-car GNSS/inertial system. (Graphic: Collin/Mezentzev)

Position estimation of the researchers’ PI-WINS device in two modes versus in-car GNSS/inertial system. (Graphic: Collin/Mezentzev)

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