Tower crane crab overload protection equipment - allows two-or four-fall working and lowering when near tower

摘要

The equipment incorporates a switching cam moving on the jib in proportion to the crab movement, having one profile representing maximum load for when the crab is close to the tower, and a second one representing maximum tipping moment when it is further from it. A stop switch moved by the hoist rope dependent on the load works in conjunction with the cam. The hoist mechanism can be used for either two- or four-full working, there being a separate stop switch with its corresponding cam profile for each condition. When the crab is on a first part (a) of the jib nearest the tower a locking mechanism for a pair of rope falls allows lowering but when it is on the other part of the jib prevents it. When the crab travels out of the zone nearest the tower and this pair of falls is lowered a changeover mechanism is actuated.