Estimation of trailer off-tracking using visual odometry

High Capacity Vehicles (HCVs) have been shown to be highly effective in reducing emissions associated with road freight transport. However, the reduced manoeuvrability of long vehicles often necessitates the use of active trailer steering. Path-following trailer steering systems are very effective in this regard, but are currently limited to on-highway applications due to the manner in which trailer off-tracking is estimated. In this work, a novel trailer off- tracking measurement concept is introduced which is independent of wheel slip and ground surface conditions, and requires no additional sensor measurements or parameter data from the tractor. The concept utilises a stereo camera pair affixed to the trailer and a visual odometry-based algorithm to calculate off-tracking. The concept was evaluated in detailed simulation and full-scale vehicle tests, demonstrating its feasibility and highlighting some important characteristics. RMS measurement errors of 0.11-0.12 m (3.3-3.6%) were obtained in a challenging visual environment.CSIR, South Africa; Cambridge Commonwealth, European and International Trust, UK; Cambridge Vehicle Dynamics Consortium

Vision-based trailer pose estimation for articulated vehicles

Articulated Heavy Goods Vehicles (HGVs) are more efficient than conventional rigid lorries, but exhibit reduced low-speed manoeuvrability and high-speed stability. Technologies such as autonomous reversing and path-following trailer steering can mitigate this, but practical limitations of the available sensing technologies restrict their commercialisation potential. This dissertation describes the development of practical vision-based articulation angle and trailer off-tracking sensing for HGVs. Chapter 1 provides a background and literature review, covering important vehicle technologies, existing commercial and experimental sensors for articulation angle and off-tracking measurement, and relevant vision-based technologies. This is followed by an introduction to pertinent computer vision theory and terminology in Chapter 2. Chapter 3 describes the development and simulation-based assessment of an articulation angle sensing concept. It utilises a rear-facing camera mounted behind the truck or tractor, and one of two proposed image processing methods: template-matching and Parallel Tracking and Mapping (PTAM). The PTAM-based method was shown to be the more accurate and versatile method in full-scale vehicle tests. RMS measurement errors of 0.4-1.6$^\circ$ were observed in tests on a tractor semi-trailer (Chapter 4), and 0.8-2.4$^\circ$ in tests on a Nordic combination with two articulation points (Chapter 5). The system requires no truck-trailer communication links or artificial markers, and is compatible with multiple trailer shapes, but was found to have increasing errors at higher articulation angles. Chapter 6 describes the development and simulation-based assessment of a trailer off-tracking sensing concept, which utilises a trailer-mounted stereo camera pair and visual odometry. The concept was evaluated in full-scale tests on a tractor semi-trailer combination in which camera location and stereo baseline were varied, presented in Chapter 7. RMS measurement errors of 0.11-0.13 m were obtained in some tests, but a sensitivity to camera alignment was discovered in others which negatively affected results. A very stiff stereo camera mount with a sub-0.5 m baseline is suggested for future experiments. A summary of the main conclusions, a review of the objectives, and recommendations for future work are given in Chapter 8. Recommendations include further refinement of both sensors, an investigation into lighting sensitivity, and alternative applications of the sensors.This work was supported by a "CSIR South Africa Cambridge Scholarship", funded jointly by the Cambridge Commonwealth, European & International Trust and the Council for Scientific & Industrial Research (CSIR South Africa)

Performance-based standards for South African car-carriers

Until recently, car-carriers in South Africa operated under abnormal load permits allowing a finite relaxation of legal height and length limits. This practice is being phased out, and exemption will only be granted if a car-carrier complies with the Australian Performance-Based Standards (PBS) scheme. A low-speed turning model was developed in Matlab®, and used to benchmark the tail swing performance of the existing South African car-carrier fleet. About 80 per cent of the fleet were shown to not comply with the 0.30 m tail swing limit, due to South Africa’s inadequate rear overhang legislation which permits tail swing of up to 1.25 m. TruckSim® was used to conduct detailed PBS assessments of two car-carrier designs. Critical performance areas were identified; most notably yaw damping and tail swing for the truck and tag-trailer combination, and maximum of difference and difference of maxima for the tractor and semitrailer combination. These were remedied through appropriate design modifications. The Matlab® model was shown to be versatile, accurate and efficient, with potential for future application. The TruckSim® assessments highlighted complexities unique to car-carriers in a PBS context and showed how these may be addressed. This research has shown the benefit of PBS for heavy vehicles, and has guided car-carrier design to improve safety

Dataset supporting publication entitled: 'Estimation of trailer off-tracking using visual odometry'

Zip file containing raw dat

Research data supporting 'Camera-based measurement of cyclist motion'

A set of .fig files, that can be opened by Matlab or Octave, providing all data needed to generate the figures in the paper