Working with motion sensors in AR and VR designs

Motion sensing is a key ingredient in the portable designs built around augmented reality (AR) and virtual reality (VR) applications. But while motion sensors are bridging the real and virtual worlds, a more specialized device, the inertial measurement unit (IMU), is ideally suited to serve the nascent AR/VR markets.

AR/VR applications are now a key battleground for smartphones as well as wearable devices such as smart glasses and head-mounted displays (HMDs). At the same time, however, AR/VR designs demand highly sensitive, precise, robust and responsive motion sensors.

Here, the IMU, a combination of an accelerometer and a gyroscope, provides the accuracy of fast-motion measurements and the granularity of slow-motion measurements. So smartphone and wearable designs can create a more authentic and immersive AR and VR experience for users and engage them with real and virtual environments for longer periods without requiring frequent breaks.

This article will provide a detailed treatment of how IMUs facilitate a much more realistic and pleasant experience in the exciting worlds of augmented and virtual reality. Besides application-suitability needs, it will also delve into the latest IMU design enhancements like the integration of processing cores and improved image stabilization aiming to bolster AR/VR designs.

Anatomy of an IMU
IMUs ensure stability in environments with high motion fluctuations often encountered in HMDs and AR gizmos like smart glasses. It begins with accuracy, a critical requirement in the lightning-fast high-definition AR/VR applications.

The ultra-precise and instantaneous detection of head movements, for example, reduces the time lag to an almost imperceptible minimum. That, in turn, reduces motion-sickness effects like nausea. The negative physical effects can also be mitigated with a low-noise accelerometer and low-drift gyroscope.

For example, in the BMI085 , Bosch Sensortec’s six-axis IMU, the accelerometer ensures temperature stability with a low temperature coefficient offset (TCO) of typically less than 0.2 mg/K and temperature coefficient sensitivity (TCS) of 0.002 %/K. In addition, it achieves a noise density of under 120 μg/√Hz.

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