The secrets inside of autonomous car safety

31st July 2019

ACEINNA

Alex Lynn

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There is a lot of debate about the safety of autonomous vehicles. What happens when an autonomous vehicle with no steering wheel has a major system fault while speeding down a highway? People can die. Safe Stop is the industry term for, when things go wrong, by which an autonomous vehicle is able to stop without human intervention.

The need for safe stop can arise from numerous conditions such as severe weather which temporarily blinds the vehicle’s sensors or complex driving scenarios which challenge the computing system’s ability to safely manoeuvre the vehicle. Or more simply, one of the sensors or connections, fails or goes bad.

The autonomous vehicles being developed today are complex computing systems that fuse data from arrays of 20 or more sensors. These systems are some of the most complex robotics systems being developed in any industry or field. As the systems move into SAE Level 4 and 5 vehicles, the option to hand off to a human driver in the case of a system fault or error is no longer possible.

The Level 4 and Level 5 systems must be able to handle all road, weather and computing conditions that may arise. Since no system, however well designed, is perfect, the concept of a vehicle Safe Stop has been gaining traction in the autonomous development segment.

The unsung hero in the Safe Stop mitigation scheme is the inertial measurement unit (IMU) sensor.

The IMU is a sensor which measures the forces of acceleration and movement of the vehicle. The IMU is particularly well suited for a Safe Stop application because it is the one sensor that does not require inputs from the external world outside the vehicle.

The IMU senses the movement of the vehicle and is immune to things occurring outside the vehicle. Knowing the vehicle’s position before the system encounters lethal problems, the IMU measures the vehicle’s forces of motion and can calculate the estimated position.

How long would it take to complete a Safe Stop manoeuvre? Typically, system engineers plan for a Safe Stop manoeuvre to take between 15 and 30 seconds.

That time is enough to allow a quickly moving vehicle to decelerate and come to a complete stop. The IMU allows the vehicle to calculate its position during the deceleration and ensure that it is still driving in the intended path. Depending on the situation, the IMU could potentially guide the vehicle towards safely pulling off the road as well.

The IMU can guide the vehicle to a Safe Stop and ensure the safety of all passengers as well as nearby moving vehicles and pedestrians.