CAN bus IMU improves autonomous car safety

CAN (Controller Area Network) is a robust and mature vehicle bus standard that allows devices to communicate with each other. Now over thirty years old, CAN is used on virtually all passenger vehicles as well as heavy equipment. 

As autonomous vehicles require many sensors to reliably exchange data, CAN is now recognised as an excellent interface choice for a variety of low and medium speed vehicle sensors such as the Wheel Speed Sensor, Steering Angle Sensor, Throttle Position Sensor, and the Inertial Measurement Unit.

Inertial Measurement Units (IMU’s) consist of three axes of acceleration plus three axes of angular rate measurements that are the linear and rotational components of a vehicle respectively. Not to be confused with single chip accel/gyro integrated circuit solutions, a temperature compensated and calibrated IMU module delivers nearly zero bias drift over temperature and operating conditions. An IMU may also include three axis of magnetic field measurement used for electronic compass functionality. 

In an autonomous vehicle, CAN is used to pass IMU data to other sensors as well as the main vehicle control such as, the vehicle’s brain. It is possible to use the CAN bus to share IMU data with up to 20 other vehicle subsystems. This can include LIDAR, Camera, Radar as well as primary compute engines all benefiting from one centrally mounted high-performance IMU on the vehicle.

A CAN bus based IMU application can also listen to other messages on the bus. This is a quite powerful feature. For example, the Dynamic Tilt algorithm could be performance enhanced by listening to messages such GPS/INS for precise localisation and Odometer or Vehicle Speed to better compensate for the influence of linear acceleration on dynamic roll and pitch. 

This whitepaper cites two ‘out of the box’ example applications and how to develop custom applications, the first using CAN2.0A and the second using CAN2.0B with J1939.