Patent GB-377209-A (GB)
Title: Improvement in or relating to load indicators for cranes and the like
IPC: B66C15/00
Filed: 1931-04-14
Abstract: 377,209. Load indicators for cranes &c. WYLIE, H. N., 5, Clement's Inn, London. April 14, .1931, Nos. 10969 and 34954. [Classes 78 (iv) and 78 (v).] A device for giving a decisive indication or signal at a predetermined load, or successive signals under successive predetermined loads, applicable to cranes and other appliances, comprises compression heads 3, 4 movable towards one another against the resistance of an elastic or jointed strut 2 which on yielding operates a signal or a succession of signals or may cut off power from the crane &c. The device may be loaded by engagement with a deflected tension member such as the lifting or luffing rope of a crane. As shown in Fig. 1, the strut consists of a group of thin steel plates clipped together at the centre at 6, and with squared ends. The plates are given a small initial deflection by a set-screw 7, and the amount of this deflection determines the critical load. When the load on the heads'3, 4 reaches the critical value, the plates bend decisively and operate a plunger 8 and lever 10 to close a lamp circuit 14. The load supported by this form of strut decreases as the deflection increases, but if the ends are bevelled as in Figs. 2 or 3 so that the load is not axial the resistance may decrease only slightly or may even increase with increasing deflection. As shown in Fig. 2, a tension applied to the pins 16, 18 causes a compression load on the heads 3, 4 and bends the strut 2 towards the left, causing the rod 8 to close a circuit 14, at a predetermined load. The strut 2 then acts upon a compression head 19 and as the load increases further, a second strut 20 is deflected and closes a circuit 23 to give a second signal at a predetermined higher load. The struts are held in place when not under load by a spring 25. The circuit 23 may give an audible signal or interrupt the main current supply to a crane or other machine. Another arrangement for indicating two predetermined loads is shown in Fig. 3. The plunger 8 bears on a block 27 hinged at 29 and carrying a lever arm 30. This arm operates a signal arm 34 bv a cord 32 at the first critical load and then picks up a weighted rod 38 which gives an audible alarm on a further decisive deflection of the strut. The lever 30 carries a weight 31, which may be varied in magnitude or position to adjust the critical load. In a modification, Fig. 4, the strut is replaced by two rigid bars 45 supported between knife-edges and initially inclined as shown and restrained under load by two or more springs 48, 49 which come into action in succession, the device giving successive signals by means of rods and levers operating as before. This device may be arranged to deflect decisively, or gradually, according to the strength of the springs. The springs may be replaced by a weighted lever. As shown in Fig. 5, the apparatus is mounted within the overhaul weight 54 of a crane which is clamped on the hoisting rope 55 above the load hook. The rope is held centrally on the weight at 57 and is deflected at the centre by the compression head 56. The strut 2 operates a lever 30 against the action of springs 48, 49, and moves a signal arm 59 normally lying in a groove in the weight, and at a higher load the lever 30 operates a bell 65 which may be of the clockwork type. Alternatively the device may operate electric signals, insulated wires being led to the weight 54 from spring drums on the jib. In a modification, Fig. 6, the lifting rope 73 of a crane is deflected by a pulley 75 carried by the load-indicating device 74 pivotally mounted on the mast at 76.