GB1253813A - Improvements in or relating to safe load indicating devices - Google Patents

Abstract

1,253,813. Safe load indicators for jib-cranes. ROBERT McALPINE & SONS Ltd., and K. McALPINE. 22 Nov., 1968 [24 Nov., 1967], No. 53609/67. Heading B8B. A safe load indicator with an alarm device for a jib-crane comprises a product box 19 with five cams 27, each with a pair of surfaces respectively associated with a switch 45 and each cam 27 corresponding to a different configuration of the crane, the associated pair of switches 45 being selected by means of a switch 51. The switches 45 are moved with respect to the cams 27 in accordance with the load on the jib 12 through an hydraulic sensing device 16 arranged to sense the tension in suspension ropes 14, the jib 12 being pivoted at 13. The pressure from the device 16 is led through pipe 18 to the product box and thus to a plunger (not shown) connected to the switches 45. The cams 27 are mounted on an axle 26 which is rotated in accordance with the movement of the jib 12 through a cable 17 which gives a measure of the horizontal displacement of the load from the standing to which the crane is attached. Each surface on each cam 27 has a cam follower 37 loaded by a spring 46. The switch 45 is operated when a ball 44 is lifted by a ramp 42 on the end of the cam follower 37 remote from the cam 27. One of each pair of associated cam surfaces gives a warning when the predetermined safe limit is approached, the other when it has been reached, an electric cable 21 leading from the product box 19 to warning lights 22 for this purpose. The alarm may operate in conjunction with the warning lights which may include an indication of safe loading conditions. Limit switches operate the alarm if the hydraulic fluid leaks out or if the cable breaks (not shown).