Motion and force analysis of slow-speed multi-trailer systems

Comparing with the tractor-trailer systems for the road haulage, which must cope with some typical undesired trends, such as high-speed instability, over- or under-steering and off-tracking, the multi-trailer systems for the transport of luggage in the airports or in the railway stations, or for the transfer of goods in the warehouses, run at quite low speeds, but must manage to steer clear of the many obstacles encountered along their path. This type of vehicle is not subject to tire cornering phenomena, because the speed is just low and the wheels are generally stiff. Hence, the vehicle movement is in practice ruled by the non-holonomic rolling constraint of the wheels and by the steering device mounted on the trailers, which may consist in drawbars integrated with the front axles and rotating around a central pin (dolly-semitrailer systems), or else in roulettes set back with respect to their vertical connection pins to the trailer chassis (caster-trailer systems). The present analysis addresses all the interconnected aspects of the mechanical behaviour of these types of multi-trailer systems in an organic whole, starting from the kinematical analysis of the possible paths and their stability, giving guidelines for the proper layout of the vehicle units to eliminate the steady off-track, and ending with the calculation of the traction forces through the various links and the road forces at the ground prints, in order to gain information useful to check the stress state of the various structural elements.