GB1310012A - Safe load indicating systems for extensible jib cranes and the like - Google Patents

Abstract

1310012 Crane safe-load indicators B & A ENG CO Ltd 19 March 1970 [5 Feb 1969 12 Dec 1969] 6313/69 and 60842/69 Heading B8B A crane safety device gives warning of incipient tipping and incorporates supplementary safety features, giving warning, for example, of approach to the limit of the structural strength of the jib and of bending of the jib under load increasing the danger of tipping. As shown in the drawing accompanying provisional Specification 1,310,012 hydraulic actuators 6, 7 connected to the top and bottom of a luffing ram (not shown) act on a lever 8 pivoted at 9 and transmit a force representative of the load through a plunger 10 to a lever 11 pivoted at 12. A cam lever 17 is acted upon by a cam 18 rotated through lever 20 in response to the jib angle and moves a fulcrum 16 between the lever 11 and an operating lever 14 pivoted at 15 and having its rotation resisted by a spring strut 21. Certain preselected moments applied to the lever 14 result in switches 22a and 22b being closed in turn to give warning when the rated load is approached and exceeded. A rod 23 is attached to a spring 24 secured to a cam roller lever 26 pivoted at 27 and following the contour of a cam 29 rotated in response to either the crane operating radius or to the jib extension, through a lever 31. The other end of the rod 23 is attached to the lever 14 and thus provides a supplementary force acting thereon. The device shown in the drawing accompanying the complete Specification 1,310,012 provides a supplementary force to a crane safety device operating lever (such as 14 above) through a rod 20. A first lever 5 pivoted at 6 is loaded by a spring 7 against a first cam 3 rotated in response to jib extension. The spring 7 also acts on a first member 8 of a compound lever arrangement to pivot it about a pivot 9 and transmit a force through movable fulcrum 10 to the other member 18 of the compound lever arrangement. The position of the movable fulcrum 10 is determined by a second cam 16 rotated in response to the crane operating radius to rotate a lever 13 about a pivot 14 and thus adjust the position of a rod 12 attached to the movable fulcrum 10. The supplementary force transmitted by the rod 20 thus depends on both the jib extension and on the crane operating radius. In the full line position shown the supplementary force is zero and corresponds to minimum jib extension. The dotted line position corresponds to maximum jib extension and minimum operating radius.