Inertial Measurement Unit

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