Safety device for cranes

Claim 1

An anti-two block system adapted to be used with a crane, the crane having a boom with a boom point and adapted to lift loads with a lifting line having a travelling member therewith, the crane having hoisting and braking levers for controlling operations thereof, comprising: sensor means mounted with the boom point of the crane for detecting the close proximity of the travelling member adjacent the boom point of the crane during lifting operations of the travelling member with the crane, said sensor means including: a body member mounted with the boom point, said body member having a bore formed therethrough for receivably mounting the lifting line of the crane therein and a fluid cavity formed about said bore; a sleeve having a first end and a second end, said first end adapted to be disposed in said fluid cavity in said body member and said second end adapted to be engaged by the travelling member, said fluid cavity between said first end of said sleeve and said body member forming a fluid chamber; hoisting actuator means mounted adjacent the hoisting lever of the crane for co-action therewith; and, means operatively connecting said hoisting actuator means and said fluid chamber of said sensor means, said fluid chamber providing a fluid output from said sensor means as a result of longitudinal movement of said sleeve with respect to said body member within said fluid cavity from a first unactivated position to a second engaged position wherein said hoisting actuator means, in communication with said fluid chamber, is activated by said fluid output for effecting movement of the hoisting lever to discontinue the lifting force exerted on the lifting line when the travelling member engages said sensor means.