GB1060089A - Safe load indicator for cranes - Google Patents

Abstract

1,060,089. Safety devices on cranes. STAR CRANES Ltd. Sept. 27, 1965 [Oct. 22, 1964], No. 43105/64. Heading B8B. A safe-load device for a crane, e.g. a tower crane, having a travelling trolley on a horizontal jib, includes a microswitch having two interacting contacts 24, 25, Fig. 2, which are respectively moved towards each other by the load on the crane hook and the outward movement of the trolley. The trolley 13, Fig. 1 (not shown), is moved in both directions by a cable 14 operated by a drum 15 and the hook 16 is moved vertically by a hoist cable 17 operated by a drum 18. The dead end of the cable 17 is anchored to a rod 21 which is restrained from being displaced by a compression spring 22 disposed in a housing 23 attached to the tower 11. The contact 24 is carried by the rod 21 so that it moves in dependence upon the load. The contact 25 is carried by an arm 26 which is pivoted at 27 and has a camfollower 31 co-operating with a snail cam 28 which is driven by rotation of the drum 15 through gearing including gears 30, 29, so that the contact 25 moves in dependence upon the movement of the trolley. Operation of the switch gives warning or operates a cut-out to stop the crane. In a second embodiment (not shown), the trolley cable is a single length passing round a winch drum and maintained taut by a friction pulley and tension device, and a separate cable extends from the trolley to the cam-shaft. The device may be duplicated, one device giving an audible and/or visible warning and the second device causing a cut-out a little later. In a third embodiment (not shown), the spring 22 has associated with it a further spring or a set of Belleville washers to control the rate of the spring 22.