Folding crane boom

Claim 1

A truck-mounted, fully collapsible boom for material handling and the like which carries at least 100 feet of boom within reasonable highway limitations when in the traveling position, the overhang thereof when in the traveling position being substantially equally distributed between the front and the rear of the carrying vehicle to provide improved maneuverability and weight distribution on the axles of the carrying vehicle, which comprises: a. a truck chassis; b. a base mounted on said chassis for pivotal movement about a vertical axis; c. a boom base section pivotally connected at one end to said base for vertical swinging movement about a horizontal axis; d. a boom point section pivotally connected at one end to the end of said base section remote from said base for vertical swinging movement about a horizontal axis; e. gantry means including a pair of parallel telescoping rear legs adjacent ends of which are pivotally mounted on said base for vertical swinging movement about a horizontal axis, said rear legs being spaced from said boom base section, at least one front leg one end of which is pivotally connected to the other adjacent ends of said rear gantry legs and the other end of which is pivotally connected for vertical swinging movement about a horizontal axis on said base between the pivot connections on said base for said boom base section and said rear gantry legs adjacent said pivot connection on said base for said boom base section, the connection between said rear and front gantry legs forming a gantry peak; f. a boom harness joining said gantry peak with the upper end of said boom point section, the end of said boom harness joining said gantry peak being attached to a floating block provided with linkage means, whereby when said boom is in the working position said boom harness is tensioned, and when said boom is in the traveling position said linkage means is connected to said boom point and base sections substantially at the pivot connection therebetween and said boom harness is in a relaxed position; g. a pair of parallel telescoping backstops adjacent ends of which are pivotally mounted on said base adjacent said rear gantry legs for vertical swinging movement about a horizontal axis and the other adjacent ends of which are pivotally mounted near the lower end of said boom point section for vertical swinging movement about a horizontal axis; and h. means joining said boom harness and acting with the lower end of said point section and the upper end of said base section for extending and retracting said boom to a working position and to a traveling position, respectively; said base, boom base section, boom point section and backstops forming a four-bar linkage, said four-bar linkage being aided by a two-scissors system, which at one point during extension and retraction of said boom comprises the stiff, piVotally fixed front leg of said gantry means and said telescoping, parallel backstops, and at another point during extension and retraction of said boom comprises the rear legs of said gantry means and said telescoping, parallel backstops, the common members of said four-bar linkage and said two-scissors system being said backstops, said backstops during retraction of said boom telescoping inwardly, becoming solid and starting to act as compression members, then acting as tension members, and finally telescoping extensibly during the remainder of the retraction of said boom.