GB723070A - Improvements in safe-load indicating devices for cranes or the like - Google Patents

Abstract

723,070. Load indicators for cranes. AITKEN, R. L. Oct. 15, 1953 [Oct. 15, 1952], No. 25831/52. Class 78 (4). A safe load indicator for crane or the like comprises a lever pivotally mounted in a fixed casing, means for applying a substantially constant restoring force on the lever, a second lever lying in the central plane of the first lever, one lever operating an alarm circuit on reaching a predetermined deflection, means for applying a turning moment to the second lever indicative of the load and a moving member between the two levers and in contact therewith at a point automatically varied in accordance with the radius of the crane operation. A pair of parallel levers 3 is pivoted to a bracket 4 mounted in a casing 1 attached to the crane jib and has a vertical part 5 supporting contacts 9, the other contacts 10 of a micro-switch being mounted on the casing. A spring 7 connects the part 5 with an adjustable anchorage 8. A lever 11 lies above the levers 3 and is pivoted to a bracket 12 on the casing. A lever 15 has a roller 16 which lies between and contacts levers 3 and 11, a steadying roller 17 on the lever 15 is positioned between the levers 3. The lever 15 is connected to a lever 18 which is pivoted at 19 to the casing and carries a roller 21 urged by a spring 22 to contact a cam 20 on a shaft 23. A member on the shaft outside the casing is connected to a fixed part of the crane by a link whereby, as the angle of the jib changes, the cam rotates and moves the levers 18, 15, changing the position of the rollers 16. The hoisting rope passes round a pulley 27 on a pivoted bell-crank lever 26, one arm of which extends within the casing and has a sheave 28 round which a wire rope passes which is anchored to an eccentrically-mounted member 31 which has an extension connected by link 14 to the link 11. As the load increases the lever 26 rocks and tensions the rope 30, causing rotation of the member 31 about its eccentric mounting, moving the links 14 and 11 down wards to depress the links 3 and operate the microswitch to give a warning first of the approach of a dangerous load, then the actual danger signal. When a crane has two distinct ratings a different part of the cam surface is used by rotating the cam 20 on the shaft 23 for the different rating. To give an indication to the operator for which rating the cam has been adjusted, a cam 36 is mounted integrally with the cam 20, the cam 36 contacts a switch 37 to illuminate a signal.