Inertial Measurement Units (IMU)

Owned by Former user (Deleted)
May 05, 2021
2 min read

Introduction

"An Inertial Measurement Unit (IMU) is a device that can measure and report specific gravity and angular rate of an object to which it is attached." 

An IMU typically contains the following sensors:

  • Gyroscope
    • Measures Angular Direction
  • Accelerometers
    • Measures Angular Force


This data is helpful when attempting to determine the forces acting on and the current direction of an IMU.

Some IMU's contain a magnetometer, which measures the magnetic field surrounding a system.


How does it work?

From: https://www.ceva-dsp.com/ourblog/what-is-an-imu-sensor/

  • Accelerometer: The most commonly used type of motion sensor is the accelerometer. It measures acceleration (change of velocity) across a single axis, like when you step on the gas in your car or drop your phone. Accelerometers measure linear acceleration in a particular direction. An accelerometer can also be used to measure gravity as a downward force. Integrating acceleration once reveals an estimate for velocity, and integrating again gives you an estimate for position. Due to the double integration and the state of today’s technology, an accelerometer is not a recommended method of distance estimation.
  • Gyroscope: While accelerometers can measure linear acceleration, they can’t measure twisting or rotational movement. Gyroscopes, however, measure angular velocity about three axes: pitch (x axis), roll (y axis) and yaw (z axis). When integrated with sensor fusion software, a gyro can be used to determine an object’s orientation within 3D space. While a gyroscope has no initial frame of reference (like gravity), you can combine its data with data from an accelerometer to measure angular position. For an in-depth look at the different types of gyroscopes, look to our 2nd blog titled, Exploring the Application of Gyroscopes.
  • Magnetometer: A magnetometer, as the name suggests, measures magnetic fields. It can detect fluctuations in Earth’s magnetic field, by measuring the air’s magnetic flux density at the sensor’s point in space. Through those fluctuations, it finds the vector towards Earth’s magnetic North. This can be fused in conjunction with accelerometer and gyroscope data to determine absolute heading. As you’ve seen, IMUs are used to measure acceleration, angular velocity and magnetic fields, and, when combined with sensor fusion software, they can be used to determine motion, orientation and heading. They’re found in many applications across consumer electronics and the industrial sector. In our next blog post, we’ll dive deeper into gyroscopes and what they’re used for.

Disadvantages:

  • Drift
    • Since an IMU measures relative to itself, drift may become a concern when using an IMU for localization purposes
    • Arrow.com recommends that in "more precise applications, users should ensure the accuracy of the sensor readings and enact occasional controls to correct for drift, especially in positioning"


Sources:

  1. https://www.vectornav.com/resources/what-is-an-imu
  2. https://de.mathworks.com/help/fusion/gs/model-imu-gps-and-insgps.html
  3. https://www.arrow.com/en/research-and-events/articles/imu-principles-and-applications
  4. https://www.ceva-dsp.com/ourblog/what-is-an-imu-sensor/