Extensible crane

Claim 1

A crane comprising means for hoisting a load including a winch and a hoisting cable; a telescoping boom assembly carrying said hoisting cable on sheaves for compensation of free cable length upon extension and retraction, said boom assembly including a first boom and a second boom extensible from said first boom by means of a boom extending piston in a cylinder carried by said first boom, said boom extending piston carrying a pinion for cooperation with gear racks on said first and second booms to double the extension distance produced by motion of said boom extending piston; means for rotating said boom assembly with respect to a base to swing a load; means including a generally horizontally mounted boom elevating piston and cylinder assembly, the cylinder of said boom elevating assembly being pivotally mounted for limited motion with respect to the horizontal upon elevation of the boom, a linkage operatively coupling a forward end of the boom elevating piston to the boom for conversion of substantially horizontal piston motion to topping movement oF the boom, said linkage comprising a crosshead carried by the boom elevating piston, a pair of generally rearwardly extending arms carried by said crosshead, a relatively short linkage pivotally connected to a rear end of each of said arms and to a part of the boom which moves down as the boom is elevated, and a relatively long, generally L-shaped link pivotally connected near the rear end of each said arm and to a fixed frame element; said hoisting, telescoping, swinging and elevating means being concurrently and independently operable for transporting a load by any combination of hoisting, telescoping, elevating and swinging.