IMU: Difference between revisions

{{See also|Terms|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 [[accelerometer]]s, [[gyroscope]]s, and often [[magnetometer]]s.<ref name="TDK_IMU_Overview">“MEMS Motion Sensors – Inertial Measurement Units.” TDK InvenSense. https://invensense.tdk.com/ (accessed 2 May 2025).</ref> IMUs are fundamental components in [[virtual reality|Virtual Reality (VR)]] and [[augmented reality|Augmented Reality (AR)]] systems, tracking the orientation of [[Head‑Mounted Display|HMDs]] and [[Input Devices]] like controllers.

* '''[[Accelerometer]]s''': Measure proper acceleration (g‑force), including gravity.<ref name="Woodman_IMU_Tutorial">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</ref>

* '''[[Gyroscope]]s''': Measure [[angular velocity]] about one or more axes.<ref name="Woodman_IMU_Tutorial" />

* '''[[Magnetometer]]s''' (optional): Sense the local [[magnetic field]], providing an absolute yaw reference.<ref name="Woodman_IMU_Tutorial" />

An IMU containing all three sensors is called a 9‑axis IMU or a [[MARG]] (Magnetic, Angular‑Rate, and Gravity) sensor.<ref>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</ref>

== Sensor Fusion ==

Raw data are noisy or drift; [[Sensor fusion]] algorithms such as complementary or [[Kalman filter]]s combine the signals to yield a stable estimate.<ref name="Mahony_Filter">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</ref>

IMUs provide the sub‑millisecond [[rotational tracking]] needed for [[immersion]] and for avoiding [[motion sickness]].<ref name="LaValle_VR_Book">LaValle, S. M. (2016) ''Virtual Reality'' – Chapter 9. https://lavalle.pl/vr/vrch9.pdf</ref>

=== 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.<ref>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</ref>

* '''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 update]]s (ZUPTs).<ref>Cadena, C. et al. (2016) “Past, Present, and Future of SLAM.” arXiv:1606.05830.</ref>

== IMU Specifications for VR/AR ==

* Integrated processing / basic fusion<ref name="TDK_Homepage">“Motion Sensors – Product Portfolio.” TDK InvenSense. https://invensense.tdk.com/products/motion-tracking/ (accessed 2 May 2025).</ref>

Trends include lower power draw, on‑sensor machine‑learning, and reduced drift.<ref>Yole Group (2024) ''Status of the MEMS Industry 2024'' (report brochure). https://www.yolegroup.com/product/report/status-of-the-mems-industry-2024/</ref>

== Key IMU Manufacturers ==

* [[TDK]]‑[[InvenSense]]<ref name="TDK_Homepage" />

* [[Bosch Sensortec]]<ref name="Bosch_Homepage">“Inertial Measurement Units (IMUs).” Bosch Sensortec. https://www.bosch-sensortec.com/products/motion-sensors/imus/</ref>

* [[STMicroelectronics]]<ref name="ST_Homepage">“MEMS and Sensors.” STMicroelectronics. https://www.st.com/en/mems-and-sensors.html</ref>

* [[Analog Devices]]

* [[Xsens]]

== Notable IMU Models in VR/AR ==

* '''MPU‑6050''': Low‑cost 6‑axis IMU, used in early [[Oculus Rift]] prototypes.<ref name="MPU6050_Datasheet">*MPU‑6000/6050 Product Specification* Rev 3.4. InvenSense Inc., 2013. https://invensense.tdk.com/wp-content/uploads/2015/02/MPU-6000-Datasheet1.pdf</ref>

* '''MPU‑9250''': 9‑axis IMU adding a magnetometer.<ref name="MPU9250_Datasheet">*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</ref>

* '''ICM‑42688‑P''': High‑performance 6‑axis IMU in the Meta [[Quest 2]].<ref name="Quest2_Teardown_iFixit">iFixit (2021) “Meta Quest 2 Teardown: Into the Metaverse.” https://www.ifixit.com/News/56892/oculus-quest-2-teardown-into-the-metaverse</ref>

* '''BMI085/BMI270''': Bosch IMUs used in [[Valve Index]] controllers.<ref>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</ref>

* '''LSM6DSO(X)''': STMicroelectronics 6‑axis IMUs found in the [[HoloLens 2]].

== References ==

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