What is an IMU?

Honeywell’s N580+HRVS

The Basics

An IMU (Inertial Measurement Unit), very simply, is a small box or "puck" with embedded sensors that track essential movement/location info. These are often very small, meant to be tucked away on a test device to work alongside other systems.

Applications

IMU's are very common on aircraft as well as ground vehicles. Applications can include "production line machines, robotic devices, vehicles, autonomous systems, gimbals, machine tools, and even robotic prosthetics." ¹

Internal Sensors Overview

Usually, an IMU consists of the below

• Gyroscopes: providing a measure angular rate

• Accelerometers: providing a measure specific force/acceleration

• Magnetometers (optional): measurement of the magnetic field surrounding the system ²

Inside: Accelerometers and "Gyros" aka Angular Rate Sensors

Image depicting the accelerometers and gyroscopes in the three axes of movement. Each accelerometer and gyroscope is positioned at 90 ° to the others (orthogonally). Accelerometers measure motion along each axis and each gyroscope measures angular velocity around each axis. [Advanced Navigation]

• Acceleration Data:

  • The IMU uses accelerometers to measure linear acceleration in three axes (X, Y, and Z)

  • Integration this data over time allows the system to estimate changes in position (displacement)

• Rotation Data:

  • The gyroscopes in the IMU measure angular velocity, or how fast the platform is rotating around each axis (pitch, roll, yaw).

Inside: Magnetometers

The red axis depicts “magnetic north” as it is aligned with the Earth’s magnetic fields. The blue axis represents “true north” as it is the actual axis that the Earth spins around. [Advanced Navigation]

Determining an article's heading can be crucial, and doing so without GPS or some other complex system can be a game changer. Here is where magnetometers can come in.

"A magnetometer is used to detect and measure the strength and direction of the Earth’s magnetic fields in order to determine heading.

Magnetic heading derives north-related direction using a combination of the Earth’s magnetic field strength. Three magnetometers measure the magnetic field strength to provide a three-dimensional orientation, with respect to magnetic north. Note that magnetic north is not the same as “true” (geographical) north, which is the axis that the Earth revolves around." ¹

Confusion with AHRS

Many times during calls with clients, the term "attitude" or "orientation/heading" comes up, and it's important to make sure we understand which technology is providing what. The Advanced Navigation site breaks this down nicely as well.

IMU versus AHRS [Advanced Navigation]

"The IMU is often confused with AHRS (attitude, heading and reference system) devices. The main difference being that an AHRS will provide orientation/heading data in addition to motion data." ¹

Confusion with General Data Systems

Saying "what kind of IMU is that?" when looking at a complex data acquisition system (DAS) is a bit like looking at an engine on the floor and asking "Whoa, what kind of Lamborghini is that"? It might take the conference room audience a second to understand what you meant. Still, if the reps in the room are worth your time, they'll say something like "It's... it's our light Lamborghini model."

While a DAS could mean a huge variety of devices, sensors, and operation types, an IMU is in fact a very specific system, intended for a narrower (but essential) mission. It too, can be an exquisite system, perhaps very expensive, depending on what is demanded of it in the field.

Example Products

VectorNav

VectorNav VN-100 (IMU) [VectorNav]

VectorNav is another common manufacturer in the A&D space. These IMU's are very small which is a frequent demand for aerospace systems. They make units with AHRS capabilities as well.

Honeywell

Honeywell N580+HRVS and Related Tech [Honeywell]

Products like Honeywell’s N580+HRVS solution can use IMU tech for GPS-Denied environments where these measurements are critical. ³

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• All statements in this article are the sole opinions of the original author and do not represent the stance or perspective of any associated companies or groups.

• Any mention of specific products is not an endorsement but rather an illustrative example. Please do your own research and due diligence before pursuing any solution mentioned on this site.

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Works Cited

¹ Harris, Simon. “Inertial Measurement Unit (IMU) - an Introduction.” Advanced Navigation, advancednavigation.com, 12 Feb. 2023, www.advancednavigation.com/tech-articles/inertial-measurement-unit-imu-an-introduction/. Accessed 16 Dec. 2024.

² vectornav. “What Is an Inertial Measurement Unit?” VectorNav, 2024, www.vectornav.com/resources/detail/what-is-an-inertial-measurement-unit. Accessed 16 Dec. 2024.

³ Wylie, Abi. “Advancing Navigation in GNSS-Denied Environments: Honeywell’s N580+HRVS Solution on Display at InterGeo 2024 | UST.” Unmanned Systems Technology, 19 Sept. 2024, www.unmannedsystemstechnology.com/2024/09/advancing-navigation-in-gnss-denied-environments-honeywells-n580hrvs-solution-on-display-at-intergeo-2024/. Accessed 16 Dec. 2024.