The term IMU stands for “Inertial Measurement Unit,” and we use it to describe a collection of measurement tools. When installed in a device, these tools can capture data about the device’s movement. IMUs contain sensors such as accelerometers, gyroscopes, and magnetometers.
How Does an IMU Work?
IMUs can measure a variety of factors, including speed, direction, acceleration, specific force, angular rate, and (in the presence of a magnetometer), magnetic fields surrounding the device.
Each tool in an IMU is used to capture different data types:
- Accelerometer: measures velocity and acceleration
- Gyroscope: measures rotation and rotational rate
- Magnetometer: establishes cardinal direction (directional heading)
IMUs combine input from several different sensor types in order to accurately output movement.
What is an IMU Used For?
You commonly see IMUs used in navigational devices or as components of navigational equipment, such as:
- Manned and unmanned aircraft. A connected (or onboard) computer can use an IMU’s measurements to calculate altitude and relative position to a reference frame, making them exceedingly useful in aircraft applications.
- GPS positioning systems IMUs serve as a supplement to GPS positioning systems, allowing the navigational device to continue with an estimated position and heading if it loses satellite connection.
Beyond their obvious applications in navigation, you can apply an IMU in nearly any field where motion detection comes into play:
- Most smartphones, tablets and fitness tracking devices contain a low-cost IMU
- IMUs are involved in sports training applications that need to measure, for example, the precise angle and force of a swing in golf or baseball.
- IMUs drive the self-balancing systems of personal transportation devices like Segways and hoverboards.
Disadvantages of IMUs
The principal disadvantage of an IMU is that they are prone to error that accumulates over time, also known as “drift.” Because the device is always measuring changes relative to itself (not triangulating against an absolute or known outside device), the IMU constantly rounds off small fractions in its calculations, which accumulate over time. Left uncorrected, these tiny imprecisions can add up to significant errors.
Still, when coupled with a corrective technology or a human operator, IMUs can be a beneficial supplement to other sensors. In precision applications, you can suspend the sensors from shock absorbers to mitigate errors as well as protect the unit.
IMU Sensors Explained
IMUs are sensing devices that incorporate at least two (and often three) types of sensors to measure a host device’s location in three-dimensional space. They are a valuable supplement to GPS or other navigational technologies. Additionally, they are present in a wide variety of consumer electronics that contain motion sensors (such as smartphones).
In most consumer applications, drift of negligible importance since an IMU doesn’t require a high degree of long-term precision. In more precise applications, users should ensure the accuracy of the sensor readings and enact occasional controls to correct for drift, especially in positioning.