All too often, booms on cherry pickers are not locked down, resulting in accidental damage to bridges and overpasses, trees, and power and telephone wires. Booms should be fully retracted, secured, and checked by drivers prior to movement. Without some means of indication of change or a lockout provision, however, these devices can move from their travel position without the driver's notice, exposing the equipment and surrounding structures to danger.
Historically, limit switches have been utilized for this type of indication, but they tend to wear. They also have moving parts, seals, levers, and rollers that are subject to failure as they are exposed to the elements.
To help manufacturers ensure booms and outriggers are in the carry position prior to vehicle movement, Contrinex Inc., Old Saybrook, Conn., suggests installing inductive proximity sensors on the machinery. According to Contrinex's Ed Leese, “Proximity sensors are a viable alternative to limit switches because they are fully sealed with no moving parts, are small in size, and mount unobtrusively.” Nor do they require periodic maintenance or adjustment.
Leese continues: “The inductive proximity sensor alone does not comprise a system, but when coupled with redundant circuitry and visible or audible annunciation in the cab of the truck, it affords operators the extra security of knowing cargo is in the proper position and that travel is safe.”
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