Inertial Measurement Unit

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The Inertial Measurement Unit (IMU) is typically a combination of three sensors: accelerometer, gyroscope, and magnetometer. IMUs can directly produce measurements of acceleration, angular velocity, and heading. Sensor fusion techniques can be used to estimate orientation in 3D space.

Overview

Measurement: Linear acceleration (accelerometer), angular velocity (gyroscope), heading (magnetometer/compass). 3D orientation (roll/pitch/yaw) when values are combined using sensor fusion techniques.

Ideal operating conditions: Can be used in nearly any conditions. Magnetometer needs to avoid EM noise and ferrous materials.

Sensor Pros:

  • Can be used in nearly any conditions – indoor/outdoor, day/night, uneven surfaces. Requires few assumptions to use. This versatility makes the IMU a useful addition to any sensor setup.
  • Good for mitigating discrete jumps in position and orientation measurement when fused with other sensors.
  • Useful in both 2D and 3D applications.
  • Produces a reasonable 3D orientation estimate.
  • Acceleration measurements can be integrated to estimate velocity and position. However, these estimates are noisy and will accumulate error over time. Fusing the acceleration data with other sensors is a better approach.
  • Very inexpensive. Decent IMUs are available for less than $20.

Sensor Cons:

  • Requires initial calibration
  • It is difficult to work directly with raw IMU data due mainly to noise. Filtering algorithms are needed to extract useful information. Higher end IMUs can filter the data before outputting it.
  • Gyroscopes are susceptible to drift.
  • Magnetometer/compass output is unreliable. Must be corrected based on where it is being used in the world. Even then the compass heading is inaccurate (+-20 degrees or worse). Also vulnerable to external magnetic sources.

Products

MinIMU-9 v5
UM7-LT Orientation Sensor
UM7 Orientation Sensor
MPU-6050

IMU Components

Accelerometer

Gyroscope

Magnetometer