Measurement of articulation angle by image template matching

Articulated heavy goods vehicles and long combination vehicles offer improved efficiency and emissions but reduced low-speed manoeuvrability and high-speed stability compared to rigid lorries. Active control systems can help to address these issues but require additional instrumentation, particularly articulation angle sensing. Existing commercial and research solutions for articulation sensing are limited either in terms of measurement accuracy or practicality. In this paper, a camera-based articulation angle sensing concept using template-matching and an Unscented Kalman Filter is investigated, including detailed simulation and full-scale vehicle experiments. The effects of aliasing and trailer pitch angle are studied, and a correction model for trailer pitch is proposed. The sensing system demonstrates superior measurement accuracy compared to the published literature, with root mean square errors of 0.8°–1.8° for articulation angles up to 37° in full-scale experiments. The sensor solution proposed in this work addresses more of the practical criteria for this problem than the comparable solutions in the literature. It does so through the novel camera and image processing system which is unique to this application. The proposed sensor offers acceptable measurement accuracy in real-time, is non-contact, requires minimal knowledge of trailer parameters and is compatible with semi-trailers and rigid draw-bar trailers.