GB566767A - Improvements in level luffing jib cranes - Google Patents

Abstract

566,767. Jib cranes. WELLMAN SMITH OWEN ENGINEERING CORPORATION, Ltd., and KAY, I. March 15, 1943, No. 4219. [Class 78 (iv)] A level-luffing jib crane has a balanced jib which (1) has a C.G. moving in a substantially horizontal path during luffing of the jib, and (2) is supported by links or the equivalent in such a way that the end of the jib remote from the load moves in a substantially-vertical path during luffing. In the diagrammatic form shown in Fig. 3, the jib AB has its C.G. at L and is constrained by two radius arms H, F, the arm H being pivoted to the crane frame (not shown) at J and to the jib at a point C such that the arm H equals the part B of the jib. The arm F is pivoted to the crane frame at G and also at E to an arm D which is rigid with the jib and the length CE of which is equal to the parts B, H. The pivots J, G and the rear end of the jib are all in the same vertical plane, the pivot J is arranged to be in the same horizontal plane as the point L of the jib, and the arms H and F if produced meet at a point K which is vertically below the point L and is in the same horizontal plane as the rear end of the jib. This applies in all positions of the jib, so that it follows that the point L moves in a horizontal path. In order to reduce the height of the crane post necessitated by the high position of the arm H, this may be replaced by an arm O pivoted to the crane frame at P and to the arm D at Q, the point P being on the line joining the points J and E and the point Q being on the line joining the points P and K. If the C.G. of the jib is at its centre of length, a single hoisting rope willserve, since the pulls M, N of its two ends balance each other, but if, e.g. the C.G. at the point L is at a distance from the rear end of the jib equal to “ the length of the jib, as shown in Fig. 7, then the single rope fall M at the jib-head must be balanced by a triple rope-fall N<1> at the rear end. For this purpose, the hoisting rope passes from the 'load hook T over pulleys R, S on the jib and then as three falls N<1> over a pulley G to the hoisting drum V. A second load hook T' may be suspended from a rope having two falls M<1>, M<2> and passing over a pulley R<1>, another pulley S and three falls similar to N<1> to a hoisting drum V<1>, the two falls M<1>, M<2> being used because of the position of the pulley R<1> midway between L and R. The jib is preferably luffed by a screw Y pivoted at Y<1> to the jib near the point L and engaged by a motor-driven nut Z pivoted to the crane frame at Z<1>.