FOGs vs. MEMS: Challenges of Highly Dynamic Environments

KVH, FOG, fiber optic gyro, MEMS gyro, highly dynamic environments, IMU, inertial measurement unit

What’s so hard about navigation in highly dynamic environments?

Navigating, positioning, or stabilizing an autonomous or manned system in highly dynamic environments presents a series of unique challenges. When pressed back into your seat during an airplane takeoff, you might be experiencing 1.2 or 1.3 Gs. The launch and acceleration of a missile, rocket or jet plane, however, imposes much greater kinetic energy on the platform’s components. That kinetic energy is further impacted by speed, wind shear, and temperature changes.

These types of extreme environments require navigation or positioning/stabilization solutions that are designed to provide continuous operating performance through shock, vibration, and temperature changes. The gyros or inertial systems used to provide navigation data, positioning, or stabilization are either based on Fiber Optic Gyro (FOG) technology or Micro-Electro-Mechanical Systems (MEMS) technology. Although MEMS are sometimes used, usually as a means of reducing cost, the MEMS technology is poorly suited for these highly dynamic environments.

Key attributes that designers require for performance in dynamic environments include Angle Random Walk (ARW) or noise and Bias Instability or drift. FOGs provide a very low noise floor, which enables very accurate navigation. High noise translates to positional inaccuracy. Bias Instability is also a key characteristic as maintaining position and delivering precise turning measurements is essential to staying on track.

While MEMS gyros and inertial units are typically smaller, lighter, and cheaper than FOG-based systems, MEMS-based systems cannot handle the levels of vibration during operation that occur in highly dynamic environments. In fact, MEMs technology performance is hindered in higher vibration environments such landing, take-off, turbulence or rough terrain. In addition, MEMS solutions have higher Bias Instability, which results in degraded navigation or stabilization/pointing solutions. MEMS gyros and inertial systems thermal sensitivity at the extremes of range also impacts their bias and Scale Factor performance – attributes that are critical in both stabilization and navigation applications.

FOGs and FOG-based inertial products such as KVH’s 1775 IMU and DSP-1760 gyro are the favored solutions for manned, unmanned, and autonomous aerial systems operating in extreme environments in which shock, vibration, and thermal changes are typical, and high performance is critical. Engineers designing applications for these harsh environments are using the high performance KVH 1775 IMU, now available with either 10g accelerometers or 25g accelerometers, to handle all the demands of highly dynamic environments.

 

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About Pam Cleveland 25 Articles
Manager, Inertial Navigation Marketing and Global Proposals

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