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FEATURE
SENSORS & SENSING SYSTEMS
Safe travelS - the autonomouS way
James Fennelly,
ACEINNA Inc. product manager – Inertial
Measurement Systems, looks into the technology that
enables autonomous vehicles to safely travel
P
recise lane level positioning is a critical enabler for increasing autonomy in vehicles of all types – from personal cars to trucks,
and from robo-taxis to agricultural machines and heavy construction equipment. Agricultural equipment needs to know where
exactly it is on a field for planting and harvesting, especially if it is operating on a side of a hill or curved rows. Cranes, excavation and other equipment need to accurately know where they are operating on a construction site. For cars and trucks, this capability helps autonomous vehicles to safely switch lanes, make turns and take corners in a secure manner. More importantly, however, when combined
with other perception sensors, precise positioning helps autonomous vehicles anticipate the next manoeuvre and increase the safety. It can also improve the performance – such as safety, reliability etc. – of many ADAS functions such as lane centering, lane change assistance, and lane departure warning. Other transportation functions such as ride
sharing, autonomous parking and ride hailing applications will also benefit from the improved positioning. Consider, for example, robot vehicles that, after being summoned from your smart phone, drive up to your location and then take you wherever you want to go. And then, after the ride is completed, the vehicle makes its way back to its home base.
accurate poSItIonIng
One of the most critical questions required for the success and safe operation of self-driving vehicles is: Where am I? Modern autonomous vehicles can use what is known as Inertial Navigation System (INS) guidance and navigation technology to enable them to locate where they are. An INS system is typically composed of a Global Navigation Satellite System (GNSS) receiver and an Inertial Measurement Unit (IMU), as well as very advanced algorithms that combine the data from these sources to calculate an accurate location. INS uses standard GNSS positioning techniques
14 DESIGN SOLUTIONS SEPTEMBER 2022
By combining IMU and wheel speed sensor data with precision location correction, the Inertial Navigation System is an integral part of the sensor suite that enables autonomous vehicles to safely and accurately navigate from one location to the next
to generate location accuracies of a few meters. For autonomous driving applications that require lane level accuracy, additional carrier-based positioning techniques, such as Real Time Kinematic (RTK), is required to provide centimeter level accuracy. For instance, when the vehicle is approaching
a fork on the highway, the lane would usually become wider. Having cm level accuracy can aid the autonomous vehicles to mitigate the sharp steering motion and make it safer and smoother for the vehicle to exit the highway.
the Imu
Unlike perception sensors like LiDar, radar, cameras, etc., IMU sensors measure the forces of gravity, angles of movement and acceleration, and are not impacted by outside environmental conditions like heavy rain, dust, mud, dirt or darkness. An IMU sensor is often composed of two
sets of sensors – three gyroscopes and three accelerometers. The gyroscope measures angular rate of three orthogonal axes. Integrating the angular rate along the three axes
over time will generate roll, pitch, and yaw, which is the attitude of an object. Similarly, the accelerometer measures linear acceleration in three orthogonal axes. Integrating acceleration over time will provide velocity; and integrating velocity over time will yield distance travelled. An IMU with gyroscopic and accelerometer sensors can provide measurement over 6 degrees of freedom (6-DOF). In ACEINNA’s inertial products, such as the
RTK330LA, duplicate IMUs of each type (three accelerometers and three gyroscopes) are used to construct a triple-redundant sensor architecture. ACEINNA’s proprietary fusion algorithm processes the data from the various sensors to ensure that the system only generates valid IMU measurements. Any defective sensor output or errant dataset will be ignored or de-rated in importance. Not only does this architecture ensure the reliability of the system, it also simultaneously improves overall performance and accuracy.
ACEINNA
www.aceinna.com/inertial-systems
IMU sensors are immune from harsh environmental conditions and physical obstructions like tunnels and foliage and will therefore continue to operate
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