Oxford Technical Solutions (OxTS) has recently provided a GPS-aided inertial navigation system for integration in a new revolutionary piece of technology. Dynamic Research, Inc. (DRI) has collaborated with Anthony Best Dynamics (ABD) to develop an Integrated ABD/DRI Guided Soft Target (GST) vehicle, with DRI being responsible for the design and development of the chassis, and ABD integrating their software and driverless control system technology. As part of the control system, an OxTS GPS/INS is used to provide high-precision position measurements for accurate path-following control.
The GST is designed for use in Advanced Driver Assistance Systems (ADAS) testing. In particular, the GST is well suited for the testing and evaluation of Advanced Crash Avoidance Technologies (ACATs) such as vehicle collision detection and crash mitigation systems.
Ideal for ADAS Testing
ADAS are becoming more and more popular in new vehicles. Some, such as Autonomous Emergency Braking (AEB), are essential for achieving a Euro NCAP 5-star rating.
When it comes to testing systems such as AEB, there is a great likelihood of a collision occurring. This puts test personnel and potentially expensive prototype test vehicles at significant risk of damage or injury. In recent years, balloon cars have been developed to reduce the impact should a collision occur. Although a great improvement, balloon targets still have the disadvantages of bursting on impact in high speed collisions, the need for a tow vehicle, and the lack of realistic motion that can be coordinated with a test vehicle.
The GST consists of a low-profile robotic vehicle (LPRV) and a separate foam panel body styled to look like a standard mid-sized car. It is designed to withstand collision speeds up to 120 km/h, and to do so without damaging the test vehicle or any personnel inside. When a collision occurs, the foam panel body separates from itself and the LPRV, causing minimal impact to the test vehicle. The LPRV can then be driven over as a result of the durable low profile and sloping design, causing the LPRV wheels to retract into the chassis. This protects the suspension of the LPRV and the test vehicle by providing the minimum possible shock input.
Housed within the armoured structure of the LPRV is the inertial navigation system (INS) used for motion control. OxTS’s flagship RT3000 INS is used to ensure maximum accuracy and reliability in the guidance, navigation and control systems. Like all INS products in the OxTS RT series, the RT3000 contains an inertial measurement unit and a high accuracy GPS receiver. It blends the inertial and GPS data together to deliver accurate position, velocity, acceleration, and orientation data even in poor GPS environments.
Thanks to the RT, the GST can also coordinate its motion with the test vehicle and adjust its speed and position to ensure meetings at precise, predetermined potential impact locations. This makes it ideal for ADAS tests such as Collision Mitigation Braking systems, Forward Collision Warnings, Automatic Collision Avoidance Steering, and Vehicle-to-Vehicle Communication systems.
Accurate Path-Following with RT
The GST features a differential GPS (DGPS) antenna which allows the RT to receive differential corrections in real time from reference stations such as the portable OxTS GPS-Base. With the corrections the RT can achieve a position accuracy of 2 cm, allowing extremely accurate path following capabilities. Jordan Silberling, Senior Staff Engineer at DRI commented, ‘Integrating the RT into the Guided Soft Target (GST) system has substantially improved its path following and high speed stability due to the RT’s accuracy and low latency measurements of the vehicle state. Also, the RT’s ability to provide accurate data during periods of non-optimal GPS satellite reception, as compared to GPS-only solutions, makes the GST system more reliable.’
The GST can be controlled manually via remote control, or set up in fully automatic mode. Fully automatic mode is used for situations where consistent, repeatable tests need to be done, or where complex manoeuvres need to be performed with great precision. In this mode a path is set and a target speed at a specific point is programmed. However, the exact speed and position of the GST as it travels along the path can be coordinated with the speed and position of the test vehicle.
The RT calculates and outputs data in real-time at a high refresh rate of 100 Hz, and with a very low latency of 3.5 ms. With another RT in the test vehicle, its position can be continuously broadcast over WLAN to the GST. The on-board processor then compares the measured position of the test vehicle to a predefined path it is expected to follow. This allows the GST to adjust its speed and position in real-time, and automatically and continuously drive to each position on its own path that corresponds to the test vehicles measured position.
As a result of the 2 cm accurate capabilities and fast, real-time update rate, the GST can provide precise control and coordination in time and space. This enables test engineers to create complex test scenarios with straight, curved, or other complicated paths, with varying speed profiles. They can also design and reliably recreate intricate test vehicle and collision partner interactions, such as rear-end, crossing path, and side swipe, to thoroughly evaluate a test system.