Glossary for Inertial Measurement Unit (IMU)

1. Accelerometer

A sensor within the IMU that measures linear acceleration along one or more axes, including the effects of gravity.

2. Gyroscope

A sensor in the IMU that measures angular velocity, which is the rate of rotation around an axis.

3. Magnetometer

An optional sensor in some IMUs used to measure magnetic field strength and direction, helping to determine heading.

4. Angular Velocity

The speed of rotation around a particular axis, typically measured in degrees per second (°/s) or radians per second (rad/s).

5. Linear Acceleration

The rate of change of velocity along a straight line, excluding rotational motion, as measured by the accelerometer.

6. Orientation

The spatial alignment of the IMU in three-dimensional space, described using roll, pitch, and yaw, or sometimes using quaternions.

7. Roll, Pitch, Yaw

The three axes of rotation:

• Roll - Rotation around the longitudinal axis
• Pitch - Rotation around the lateral axis
• Yaw - Rotation around the vertical axis

8. Quaternions

A mathematical representation of orientation in 3D space that avoids issues like gimbal lock seen with Euler angles.

9. Bias

A systematic offset in sensor readings that causes errors in measurements over time if not corrected.

10. Bias Drift

The slow and continuous change in sensor bias, leading to errors in measurements over time.

11. Dynamic Range

The range of values (e.g., acceleration or angular velocity) a sensor can accurately measure before saturating.

12. Sensor Noise

Random fluctuations or variations in sensor output, causing inaccuracies in measurements.

13. Temperature Drift

Variations in sensor performance caused by changes in temperature, requiring compensation to maintain accuracy.

14. Scale Factor

A constant that converts raw sensor readings into meaningful physical units like m/s² or rad/s.

15. Alignment

The process of calibrating the IMU’s sensors to align with a known reference frame.

16. Calibration

A process of correcting sensor errors such as bias, noise, and scale factor to improve measurement accuracy.

17. G-force

A unit of acceleration equal to the acceleration due to gravity (9.8 m/s²). IMUs measure accelerations in terms of g-forces.

18. Initial Alignment

A procedure to establish the IMU’s orientation relative to a fixed reference point before beginning measurements.

19. Specific Force

The non-gravitational force per unit mass measured by the accelerometer, reflecting motion-induced acceleration.

20. Error Propagation

The accumulation of small errors in IMU data over time, leading to inaccuracies in position or orientation calculations.

21. Integration Drift

Errors that accumulate when integrating sensor data over time to calculate velocity or position.

22. Strapdown IMU

An IMU configuration where sensors are rigidly attached to the platform or vehicle, requiring mathematical transformations instead of mechanical stabilization.

23. Tactical Grade IMU

A classification of IMUs with moderate precision, often used in military and commercial applications.

24. Industrial Grade IMU

IMUs designed for robust performance in harsh industrial environments, with moderate accuracy and durability.

25. Consumer Grade IMU

Low-cost IMUs used in everyday devices like smartphones and fitness trackers, with less precision compared to tactical or industrial-grade units.

26. Navigation Grade IMU

High-precision IMUs used in applications like aircraft and submarines, where very low drift is required.

27. Sensor Fusion

The process of combining data from accelerometers, gyroscopes, and magnetometers to provide a more accurate estimate of motion and orientation.

28. Gravity Compensation

A correction applied to accelerometer readings to remove the effects of gravity from the measured acceleration.

29. Heading

The direction of travel or orientation of the IMU, typically relative to true north or magnetic north.

30. Zero Bias

The output of a sensor when there is no external stimulus, ideally zero but often requiring correction in real-world sensors.

31. Sampling Rate

The frequency at which sensor measurements are taken, typically measured in Hz (samples per second).

32. Time Synchronization

The alignment of measurements across sensors to ensure that data corresponds to the same moment in time.

33. Turn Rate

The rate at which the IMU rotates around an axis, as measured by the gyroscope.

34. Dead Reckoning

A navigation technique where position is calculated based on previously known positions and IMU measurements, without external signals.

35. MEMS (Micro-Electro-Mechanical Systems)

Miniaturized IMUs commonly used in consumer electronics, drones, and robotics.

36. Gimbal Lock

A condition where two axes of rotation align, causing a loss of one degree of freedom in orientation measurements.

37. Heading Drift

The gradual error in heading estimation due to gyroscope bias and drift.

38. Zero Velocity Update (ZUPT)

A method to correct velocity drift by resetting measurements when the IMU is stationary.

39. Stabilization

Techniques used to maintain consistent sensor measurements despite movement or vibrations.

40. Redundancy

The inclusion of multiple sensors in an IMU to improve reliability and detect potential sensor failures.