Stability Margins of Heavy-Lifting Machines with a Telescoping Boom and Jib

Machines that use a telescoping boom with an attached jib to raise loads to great heights have deadly tip-over hazards. To keep machines safely away from tip-over conditions, machine producers provide a variety of countermeasures, such as outriggers that increase the width of the stability base, counterweights, configuration sensors, control input smoothing, and control computers that stop the machines from moving out of the stable envelope of reachable positions. The computers are programmed to have a stability margin that restricts machine motion well within the envelope of actual stability. These stability margins are set by industry standards that limit the allowable payload weight. However, margins created by payload limits do not provide good margins for other machine parameter variations and configuration errors. This paper calculates stability margins that are not considered by industry standards. The results indicate that these neglected stability margins can be both small and inconsistent throughout the reachable workspace. Therefore, telescoping-boom machines with attached jibs pose safety hazards that are neither well understood, nor adequately addressed by industry standards.