Wednesday, November 29, 2023

How ADAS Equipped With Inertial Measurement Sensors Promotes Safe Driving

By Nidhi Agarwal

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Want to drive safely? Discover how IMU-equipped ADAS systems are revolutionising vehicle safety and autonomy through advancements like sensor fusion and triple redundancy,
shaping the future of driving for safer and smarter experiences.

Inertial Measurement Unit (IMU) is crucial to present and future navigation and safety systems in autonomous vehicles and advanced driver assistance systems (ADAS). IMUs collaborate with diverse perception sensors, including light detection and ranging (Lidar) cameras and radar odimetry, etc, to maintain accurate vehicle trajectory. ADAS technologies assist drivers in various aspects of their driving tasks and provide an extra layer of safety. In this article, we will discuss how an IMU-equipped ADAS system ensures safety and what developments are happening in this field.

Incorporating inertial measurement sensors with ADAS promotes safe driving in the following ways.

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Adaptive cruise control (ACC). ACC allows users to relax while driving, especially on highways, by automatically adjusting the car’s speed by matching the speed of the vehicles in front. The IMU utilised in the ACC system maintains a safe distance between vehicles by measuring the vehicle’s acceleration and deceleration. If a change in speed is encountered in the lead vehicle, inertial sensors enable the system to respond quickly, thus promoting safe and comfortable driving.

Lane departure warning (LDW). The LDW system provides users with a stress-free parking experience in crowded garages by minimising concerns about collision-related damage to the vehicle. While driving, the LDW system ensures safety by warning drivers about leaving the marked lanes without giving proper indicators. The inertial sensors monitor the vehicle’s lateral motion and orientation and detect when the car unintentionally drifts out of its lane. Fast alerts are triggered, avoiding collisions.

Electronic stability control (ESC). ESC is a crash avoidance system which activates automatically when loss of control over the vehicle is detected. The system applies the brakes on individual wheels, preventing the car from skidding and avoiding severe accidents. Inertial sensors continuously monitor the vehicle’s acceleration, angular velocity, and orientation. The system can then selectively apply braking force to individual wheels and adjust engine torque to help the driver maintain control during movements like sharp turns. IMU helps detect vehicle rollover by activating stability control measures or issuing drivers warnings, thereby ensuring safety.

Autonomous emergency braking (AEB). As the name suggests, AEB comes into action in critical situations. AEB system’s primary function is to turn crashes into close calls. In short, it recognises the dangers and applies the brakes for the driver. Inertial sensors are utilised in AEB systems to detect potential collisions and assist in avoiding or mitigating their severity. Responsiveness and accuracy of ABE systems are enhanced using inertial sensors by providing data to the system and helping to make decisions.

Although not all ADAS come with all these features, several car manufacturers, including Tesla, BMW, Hyundai, Audi, Honda, Kia and many more, offer vehicles with ADAS systems that incorporate a comprehensive set of common features.

Understanding and utilising IMUs
An IMU is typically a combination of accelerometers, gyroscopes, and magnetometers. Magnetometers are optional.
• The accelerometers measure the specific force/acceleration of the body in different directions.
• The gyroscopes measure the angular rate of the body around different axes.
• When included, the magnetometers measure the magnetic field around the system and determine the body’s orientation relative to the Earth’s magnetic field.
• Combining the readings from these sensors, an IMU provides complete information about the motion and orientation of a body in real time.
With their ability to deliver accurate measurements, IMUs are well-suited for tasks demanding precision, such as medical applications, robotics, motion capture, and so on. The low power consumption of IMU makes them ideal for battery-powered applications. The cost-effectiveness positions them as an affordable solution across various domains.

Advancement in IMU-based ADAS functionalities

In recent years, several advancements in ADAS, including IMUs, led to notable improvements in the performance, accuracy, and safety of ADAS functionalities. Some of the advances in this technology comprise the following.

Sensor fusion. Sensor fusion involves information from multiple sources like vehicle position, orientation, and sensor error characteristics and maintaining an updated record. IMUs provide valuable information on the vehicle’s movement and orientation that can be combined with data from other sensors, such as cameras, lidar, and radar, to create a more comprehensive understanding of the vehicle’s surroundings. For example, IMU provides information on the vehicle’s acceleration and angular velocity, yielding a more accurate environmental map when combined with lidar data. In sensor fusion, many sensors are involved. Still, IMU is the key sensor as it can blend the characteristics of all other sensors and, with simple math, come up with integrated results. The IMU, along with other sensors in autonomous vehicles, can better determine the position, speed, and trajectory of objects in the vehicle’s vicinity and take appropriate actions to avoid collisions.

Triple redundant IMU in ADAS. A triple redundant IMU is used in ADAS to enhance reliability and accuracy through redundancy. IMU triple redundancy utilises three separate IMUs to create a sensor architecture providing its measurements of acceleration, angular rate, and orientation. These IMUs operate independently and are cross-checked against each other to identify any inconsistencies or discrepancies in the data. By comparing the outputs from the redundant IMUs, the system can detect sensor faults or anomalies and take appropriate actions. Bosch utilises triple redundant IMUs in their ADAS systems to enhance the reliability and accuracy of motion sensing. Many automotive technology providers, like Aptiv, Aptiv, etc, also use triple redundant IMUs in their ADAS solutions.

Autonomous driving. IMU operates independently of external conditions, relying on gravity and the laws of physics; hence in the event of other sensors’ failure or worst weather conditions, IMU continues to provide data ensuring safety until the vehicle comes to a secure stop or the complete system resumes functioning. By eliminating data interruption and increasing operational safety, the IMU accelerates the realisation of Level 5 fully autonomous driving. The accuracy of an IMU’s performance is solely determined by the precision of its own sensor’s acceleration measurements. The IMU is considered more affordable compared to other sensors in ADAS. A high-performance IMU plays a vital role in achieving highly accurate positioning in autonomous vehicles.

Challenges and opportunities
The automotive industry is undergoing a significant transformation with the introduction of electric vehicles (EVs), bringing challenges and opportunities for the use of IMUs in advanced ADAS systems.
•The complex electrical/electronic architectures in vehicles include many electronic control units (ECUs) hindering innovation.
• A paradigm shift is needed from distributed hardware to software and services that pave the way for new opportunities in ADAS development within electric vehicles.
• Ensuring the accuracy and calibration of IMU sensors in varying environmental conditions is a different challenge.
• Integrating IMU data with inputs from other sensors requires sophisticated sensor fusion algorithms and precise calibration.
• Processing the vast amounts of real-time data generated by IMUs demands efficient algorithms and computational resources.
• IMU-equipped ADAS systems can enhance safety by accurately measuring a vehicle’s motion, enabling collision avoidance, lane-keeping assist, and emergency braking.
• Vehicle dynamics and control can be improved, leading to optimised traction, stability, and adaptive suspension systems.
• IMUs are crucial in autonomous driving, enabling precise localisation, mapping, and path planning.
• Sensor fusion with IMU data enhances the perception and object detection capabilities.

The way ahead

IMU-equipped ADAS holds the potential for development and advancement in future. Nowadays, engineers work on designing the automatic communication between cars, called Vehicle to Vehicle (V2V), and between cars and surrounding infrastructure, called Vehicle to Infrastructure (V2I). These advancements in automotive technology are revolutionising how vehicles interact with each other and their environment, paving the way for safer and more efficient driving experiences. However, IMUs are not directly involved in the communication aspect. They provide crucial data supporting accurate positioning, orientation, and motion tracking, which is essential for effective V2V and V2I interactions. The development of advanced motion control algorithms can utilise IMU data to optimise vehicle stability. Integrating artificial intelligence (AI) and machine learning (ML) techniques with IMU data will enable intelligent and adaptive ADAS functionalities. Finally, the ongoing development includes evolving safety features, such as collision detection and avoidance systems, pedestrian and cyclist detection, and improved emergency braking systems.

Autonomous electric cars with artificial intelligence self driving on metropolis road, 3d rendering

IMUs have already made a significant impact on ADAS. Looking to the future, IMUs can further enhance ADAS systems in several ways. IMUs are expected to benefit from advancements in sensor technology, including higher accuracy, improved reliability, and reduced power consumption. This will enable them to contribute to developing advanced safety features in ADAS. IMUs will remain integral to achieving high-precision positioning and navigation in autonomous driving. The miniaturisation of IMUs and advancements in manufacturing techniques will likely lead to smaller, more affordable, and mass-market-ready IMU solutions. This will facilitate their widespread adoption in various ADAS applications, making them a standard component in future vehicles.

The author, Nidhi Agarwal, works as a tech journalist at EFY


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