Control Safety Margins for Telescoping-Boom Mechatronic Lifts

High-reach aerial lifts often use telescoping booms to lift workers, tools, and supplies to elevated positions. The personnel working on such machines are secured to the platform with lanyards to prevents falls; however, they are still subjected to the potentially deadly tip-over accident. In order to mitigate tip-over accidents, aerial lift manufacturers have developed countermeasures, such as widening the base of support of the machines with expanding wheel bases or outriggers, adding counterweights to offset the extended boom, using sensors and control algorithms to limit the configurations of the machine to within the stable envelope. The size of the stability margin that keeps the machine away from tip-over conditions is mandated by industrial standards that limit the rated load capacity to a percentage of the actual load capacity. Such load-based safety margins attempt to provide a butter against sensor errors, wind loads, ground undulations, payload movement, etc. This paper investigates new types of safety margins that better account for the types of uncertainties associated with aerial lifts. Rather than use a safety margin tied to the load weight, safety margins are also expressed in terms of the boom angle and boom extension lengths. The analysis indicates that the industry standard load limits give inconsistent margins, as well as relatively low safety margins for cases when the boom is extended a significant amount.