The Use of a Steering Shaping Function to Improve Human Performance in By-Wire Vehicles

Report No. ARL-TR-4387
Authors: Susan G. Hill, Jason S. Metcalfe, and Kaleb McDowell
Date/Pages: March 2008; 35 pages
Abstract: The U.S. Army is examining evolutionary concepts for the command and control of military vehicles. Currently, there is a performance issue regarding vehicle control at higher speeds for some indirect vision, by-wire tactical vehicles. By-wire vehicles are those in which mechanical links between the driver and control devices are replaced by electronic or computerized signals. Specifically, an operators ability to maintain reliable control of by-wire military vehicles while driving appears to be progressively compromised as vehicle speed increases. Several factors have been identified as possible sources of this difficulty, including lags in the system control loop, characteristics of the steering interface (such as its shaping function or lack of force feedback), inadequate visual display, and physical effects of vehicle motion on the operator (McDowell et al., 2007a). This report is a review of the current state of knowledge regarding the steering shaping function, which specifies the dynamic spatial relationship between steering input from the driver and vehicle heading direction. The overall goal of the review is to identify design parameters critical to improving current by-wire implementation in military tactical vehicles, thereby identifying design elements to optimize human-vehicle system performance for secure mobile operations. Through a review of general automotive literature related to variable gear ratio steering systems as well as steer-by-wire design and implementation, three main factors affecting steering control were identified. The primary factors of influence that were reviewed included the overall range of motion (throw) of the steering device, the steering shaping function, and modifications of the shaping function because of vehicle motion characteristics. In addition, variations in performance were observed to be a consequence of dynamic characteristics of the operator and the vehicle and most importantly, the interaction between the operator and the vehicle. This review concludes that the shaping function is a central influence over system performance, and further, it is apparent that no single shaping function will suffice across all driving scenarios. Owing to noteworthy driver performance issues at higher vehicle speeds (particularly with nonstandard steering devices, such as joysticks), a call is made for further research to extend the current understanding of steering control. Specifically, we suggest that the achievement of optimal steering characteristics will most likely come with a greater understanding of the dynamic variations needed within shaping functions in order to accommodate different vehicle, task, and operator characteristics.
Distribution: Approved for public release
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Last Update / Reviewed: March 1, 2008