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Any autonomous machine—whether passenger car, tractor, delivery robot, or unmanned aerial vehicle (UAV)—must understand its global and relative position accurately and in all conditions for safe and reliable operation. This is especially challenging when geolocation signals such as those generated by the Global Navigation Satellite System (GNSS) or Global Positioning System (GPS) regularly experience signal blockages while on-board visual sensors (LIDAR, radar, camera) are susceptible to blindness by weather conditions, bright sun, and spoofing attacks. To overcome the environmental limitations of these sensors, a high performance inertial measurement unit (IMU) is used to independently determine a vehicle’s acceleration, heading angle, and relative position. The IMU relies on the principles of gravity and inertia instead of the external environment, offering a constant and complementary data source for the autonomous precision navigation system.
A robust legacy …
Analog Devices’ iSensor® IMU technology was first to market and has played a key role in the rapid rise of autonomous machines over the past decade. ADI IMUs guide more L4-capable ground and air vehicles deployed worldwide than all our competitors combined. Our portfolio spans tactical-grade stability and ultralow noise, delivering up to 10 degrees of motion freedom, all with full factory calibration and optimized embedded sensor conditioning. The portfolio is constantly expanding, with avionics certified IMUs available now and automotive qualification in the works.
… and a bright future
Analog Devices is expanding our industrial IMU portfolio into automotive, marking the first time that tactical-grade performance will be available with automotive qualification and enhanced diagnostics. ADI’s iSensor IMUs have dominant market share in the emerging autonomous robo-taxi field trials occurring around the world. In addition, we are developing ASIL-certified compact IMUs for partially automated systems (often referred to as SAE Level 3) targeted at functions such as Highway Pilot and Automated Valet Parking.
Inertial Performance Matters
While many IMU suppliers claim to offer impressive performance with bias stability levels below one degree per hour, in reality, lab performance rarely translates to performance in the field. In-run bias stability, a popular measure for calculating how stable an IMU will be, is always measured when the IMU is at rest in a quiet environment. When that same IMU is deployed to the field, the dynamic threats of the environment, such as vibration from a bumpy road, can cause key specifications including the bias stability to degrade significantly. This is where a precision navigation system excels.
ADI prides itself on being able to offer conservative specifications that hold up in all the conditions that matter, not just on a test bench. Shown in the table below is a comparison of ADI against three well-known competitors. While some suppliers appear to offer similar bias stability to ADI , once vibration  and cross-axis  errors are introduced, the performance gap between ADI and the competition widens by over a factor of 10.
 In-Run Bias Stability (dph)
A measure of IMU stability assessed in a quiet lab environment
 Linear g (dps/g)
IMU vibration performance
 Cross-Axis (dph)
IMU cross-axis performance under 5deg of tilt
 Achievable Bias Stability (dph)
IMU bias stability  once  and  are accounted for
 Accumulated Error (m)
Localization error of a vehicle traveling 30 mph after 30 seconds
The stability of ADI’s IMUs enables an autonomous vehicle to precisely track its position for over a minute at a time before requiring a correction from the GPS or visual sensors. This allows the vehicle to maintain lane-level accuracy during blockages or outages for 10 times longer than what is offered by legacy IMUs installed in production vehicles today.
Hands-Free Highway Pilot
This system is an advanced version of cruise control, which allows a vehicle to automatically steer and adapt its speed in order to stay centered in its lane and a safe distance from the vehicle in front of it.
Automated Valet Parking
This feature enables a vehicle to automatically pull into an open parking spot. More advanced versions do not require a driver to be present, allowing the car to autonomously locate a spot within a parking garage.
This is a method for calculating a vehicle’s position by estimating the direction and distance traveled from a known starting point. This is required whenever GNSS/GPS satellite signals are lost and the IMU heading must be used.
In the event that an autonomous vehicle detects a fault in its system and cannot continue to operate safely, rotation and acceleration data from the IMU is used to help bring the vehicle to a safe and controlled stop.
GNSS/GPS blockage can occur whenever tall buildings, tunnels, overhead bridges, or dense trees block the satellite signal from reaching the vehicle. During these events the vehicle relies on its perception and IMU sensors to navigate.
Perception blindness occurs whenever the on-board camera, LIDAR, and radar sensors are negatively impacted by environmental conditions such as precipitation, bright sun, or the accumulation of mud and dirt.
Analog Devices’ IMUs are utilized in a wide variety of GNSS/GPS systems. ADI’s partner Septentrio has seen the value of ADI’s innovative product portfolio of IMUs and chosen the ADIS16505. Septentrio’s offerings span a complete set of sought-after GNSS features, including a multifrequency, multiconstellation engine and specialized signal processing hardware and algorithms that offer enhanced protection against jamming and spoofing attacks. Septentrio recently released the AsteRx-i D UAS evaluation board to the market, which combines these features together with the power of the ADIS16505 in a compact form factor appropriate for UAVs and automated driving applications.
Precision, Six Degrees of Freedom Miniature MEMS IMU
See Autonomous Precision Navigation in Action at CES 2020!
Race to Autonomy: Enabling Trusted Navigation & Reliable Perception
Learn more about ADI’s advanced sensor technologies, including Inertial Measurement Units and LIDAR, supporting critical aspects of navigation and perception as well as real-time condition monitoring of infrastructure in this live video from the show floor.
Featured Navigation Sensing Resources
Tactical-Grade Inertial Measurement Unit (IMU) with Industry’s Lowest SWaP+C
Our advancements in MEMS inertial sensing enable tactical-grade stability at a fraction of the size and cost of existing solutions.
Whether you are new in INS or an expert in navigation systems, this webinar will help you to learn the latest advancements and understand better the broad landscape of GNSS/INS and what’s the right choice for you.
With the longest history in the industry for supplying to autonomous precision navigation systems, ADI stands ready to provide application-level support based on our comprehensive knowledge of the dynamics and challenges these systems face. Furthermore, ADI is exploring innovative vehicle precision navigation architectures that combine a high performance IMU with visual sensors (camera, radar, and LIDAR) to offer trusted positioning information at low latency and high update.
For more information on how our Trusted Motion UnitTM architecture can enable your system to make faster, safer decisions in all conditions, please contact your local Analog Devices sales office. To learn more about this architecture and other cutting-edge technologies from ADI, visit Analog Garage.
With an extensive background in automotive and avionics safety applications, ADI is able to offer autonomous system designers an expanded suite of products via our complete Drive360™ portfolio.