IMU
- See also: Terms and Technical terms
An Inertial Measurement Unit (IMU) is an electronic sensor device that measures and reports a body's specific force, angular rate, and sometimes orientation using a combination of accelerometers, gyroscopes, and often magnetometers.[1] IMUs are fundamental components in Virtual Reality (VR) and Augmented Reality (AR) systems, tracking the orientation of HMDs and Input Devices like controllers.
Components and Function
A typical IMU integrates multiple sensor types onto a microchip:
- Accelerometers: Measure proper acceleration (g‑force), including gravity.[2]
- Gyroscopes: Measure angular velocity about one or more axes.[2]
- Magnetometers (optional): Sense the local magnetic field, providing an absolute yaw reference.[2]
An IMU containing all three sensors is called a 9‑axis IMU or a MARG (Magnetic, Angular‑Rate, and Gravity) sensor.[3]
Sensor Fusion
Raw data are noisy or drift; Sensor fusion algorithms such as complementary or Kalman filters combine the signals to yield a stable estimate.[4]
Role in VR/AR
IMUs provide the sub‑millisecond rotational tracking needed for immersion and for avoiding motion sickness.[5]
6DoF Tracking Systems
For full 6DoF tracking, IMU data are fused with camera‑based inside‑out tracking or external lighthouse tracking systems to correct long‑term drift.[6]
Limitations and Correction
- Sensor drift from gyroscopes
- Magnetic interference
- No positional data without external references
Drift is mitigated by visual corrections, complementary filters, and periodic resets such as Zero‑velocity updates (ZUPTs).[7]
IMU Specifications for VR/AR
- Latency < 2 ms
- Update rate 500–1000 Hz
- Gyro drift < 0.01 °/s
- Low‑noise accelerometers
- Integrated processing / basic fusion[8]
Future Developments
Trends include lower power draw, on‑sensor machine‑learning, and reduced drift.[9]
Key IMU Manufacturers
Notable IMU Models in VR/AR
- MPU‑6050: Low‑cost 6‑axis IMU, used in early Oculus Rift prototypes.[12]
- MPU‑9250: 9‑axis IMU adding a magnetometer.[13]
- ICM‑42688‑P: High‑performance 6‑axis IMU in the Meta Quest 2.[14]
- BMI085/BMI270: Bosch IMUs used in Valve Index controllers.[15]
- LSM6DSO(X): STMicroelectronics 6‑axis IMUs found in the HoloLens 2.
References
- ↑ “MEMS Motion Sensors – Inertial Measurement Units.” TDK InvenSense. https://invensense.tdk.com/ (accessed 2 May 2025).
- ↑ 2.0 2.1 2.2 Woodman, O. J. (2007) An Introduction to Inertial Navigation. Technical Report UCAM‑CL‑TR‑696, University of Cambridge Computer Laboratory. https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-696.pdf
- ↑ Madgwick, S. O. H.; Harrison, A. J. L.; Vaidyanathan, R. (2011) “Estimation of IMU and MARG Orientation Using a Gradient Descent Algorithm.” Proc. IEEE ICORR, 1‑7. https://vigir.missouri.edu/~gdesouza/Research/Conference_CDs/RehabWeekZürich/icorr/papers/Madgwick_Estimation_of_IMU_and_MARG_orientation_using_a_gradient_descent_algorithm_ICORR2011.pdf
- ↑ Mahony, R.; Hamel, T.; Pflimlin, J.‑M. (2008) “Nonlinear Complementary Filters on the Special Orthogonal Group.” IEEE T‑AC 53 (5): 1203‑1218. https://doi.org/10.1109/TAC.2008.923738
- ↑ LaValle, S. M. (2016) Virtual Reality – Chapter 9. https://lavalle.pl/vr/vrch9.pdf
- ↑ Ercan, A. O.; Erdem, A. T. (2011) “On Sensor Fusion for Head Tracking in Augmented Reality Applications.” Proc. ACC, 1286‑1291. https://doi.org/10.1109/ACC.2011.5991077
- ↑ Cadena, C. et al. (2016) “Past, Present, and Future of SLAM.” arXiv:1606.05830.
- ↑ 8.0 8.1 “Motion Sensors – Product Portfolio.” TDK InvenSense. https://invensense.tdk.com/products/motion-tracking/ (accessed 2 May 2025).
- ↑ Yole Group (2024) Status of the MEMS Industry 2024 (report brochure). https://www.yolegroup.com/product/report/status-of-the-mems-industry-2024/
- ↑ “Inertial Measurement Units (IMUs).” Bosch Sensortec. https://www.bosch-sensortec.com/products/motion-sensors/imus/
- ↑ “MEMS and Sensors.” STMicroelectronics. https://www.st.com/en/mems-and-sensors.html
- ↑ *MPU‑6000/6050 Product Specification* Rev 3.4. InvenSense Inc., 2013. https://invensense.tdk.com/wp-content/uploads/2015/02/MPU-6000-Datasheet1.pdf
- ↑ *MPU‑9250 Product Specification* Rev 1.1. InvenSense Inc., 2016. https://invensense.tdk.com/wp-content/uploads/2015/02/PS-MPU-9250A-01-v1.1.pdf
- ↑ iFixit (2021) “Meta Quest 2 Teardown: Into the Metaverse.” https://www.ifixit.com/News/56892/oculus-quest-2-teardown-into-the-metaverse
- ↑ Nield, D. (29 May 2022) “These realityOS trademarks hint at an imminent Apple AR/VR headset launch.” TechRadar. https://www.techradar.com/news/these-realityos-trademarks-hint-at-an-imminent-apple-arvr-headset-launch