GB624500A - Improvements in load limit warning devices for jib cranes - Google Patents

Abstract

624,500. Jib cranes. RANSOMES, SIMS, & JEFFERIES, Ltd., and WILLIAMS, A. H. May 9, 1947, No. 12641. [Class 78 (iv)] A warning device for indicating when the maximum permissible load at any position of the jib is being exceeded which device deflects the hoisting rope from its line of action and operates a switch controlling a signal circuit or motor, the switch being an electric switch, one contact of which, responsive to and dependent on the tension of the hoisting rope for effecting closure of the switch, is attached to, and movable with, the jib of the crane, this contact oscillating relatively to the other contact which ensures closure of the circuit before overloading at any angle, this latter contact being in a fixed position and shaped eccentric to the pivot about which the movable contact oscillates so that the distance between the two contacts is greater when the jib is at its maximum angular height than when the jib is horizontal. As shown in Fig. 4, the jib 2 has a tail pulley 19 and is fulcrummed on a shaft 3 which carries a fixed contact 16 eccentrically mounted with respect to the shaft. The hoisting cable 20 passes under fixed pulleys 4 and 5 and over a movable pulley 6, the pulleys being supported by a bracket 1 attached to the iib. The pulley 6, Fig. 2 is mounted on a spindle 9.in a movable jaw 10 which carries a contact 14. A member 11 fixed to the jaw slides in a guide 12 fixed to the bracket 1 and against a spring 13. On increasing the tension in the cable, the pulley 6 is thus moved inwards against the action of a spring 13. At maximum load the contact 14 touches the member 16 and closes the circuit. The distance through which the contact has to move increases with the angle of the jib, and the tension can therefore be correspondingly increased and hence the maximum load possible. A micro switch can be incorporated as an alternative switch.