Inertial measurement unit

An IMU allows a GPS receiver to work when GPS-signals are unavailable, such as in tunnels, inside buildings, or when electronic interference is present.

An inertial measurement unit works by detecting linear acceleration using one or more accelerometers and rotational rate using one or more gyroscopes.

[4] Typical configurations contain one accelerometer, gyro, and magnetometer per axis for each of the three principal axes: pitch, roll and yaw.

IMUs are often incorporated into Inertial Navigation Systems, which utilize the raw IMU measurements to calculate attitude, angular rates, linear velocity, and position relative to a global reference frame.

The IMU equipped INS forms the backbone for the navigation and control of many commercial and military vehicles, such as crewed aircraft, missiles, ships, submarines, and satellites.

The data collected from the IMU's sensors allows a computer to track craft's position, using a method known as dead reckoning.

In a navigation system, the data reported by the IMU is fed into a processor which calculates altitude, velocity and position.

[11] Positional tracking systems like GPS[12] can be used to continually correct drift errors (an application of the Kalman filter).

[13] A very wide variety of IMUs exists,[14] depending on application types, with performance ranging: To get a rough idea, this means that, for a single, uncorrected accelerometer, the cheapest (at 100 mg) loses its ability to give 50-meter accuracy after around 10 seconds, while the best accelerometer (at 10 μg) loses its 50-meter accuracy after around 17 minutes.

Sensors and IMU models are computed in factories through a dedicated calibration sequence using multi-axis turntables and climatic chambers.

These shock absorbers are required to master three effects: Suspended IMUs can offer very high performance, even when submitted to harsh environments.

However, to reach such performance, it is necessary to compensate for three main resulting behaviors: Decreasing these errors tends to push IMU designers to increase processing frequencies, which becomes easier using recent digital technologies.