Overhead cranes carry the load

Machine shops, foundries, and other plants routinely move loads weighing from several to 600 tons on overhead cranes such as the ER-2000 from Whiting Corp., Monee, Ill. (whitingcorp.com). Such cranes are built around wide-flange and welded-box girders forming a moving bridge that carries a hoist on a trolley. The hoist can use a variety of brakes in addition to a solenoid-encapsulated self-adjusting (SESA), shoe-type holding brake. These include a mechanical-load brake, an eddycurrent brake, and flux-vector control brake. Both

the trolley and bridge can be controlled by adjustablefrequency Ultra-Drive, a device that uses low-maintenance ac squirrel-cage motors and electronically balanced speed and horsepower for smooth operation, minimal energy use, and precise positioning. And Ultra-Drive controls can be configured as two or three speed, or infinitely variable. The hoist uses a triple reduction helical and spur gear reducer for smooth operation under load. A single operator can control the crane from a 24-V pendant.