Patent GB-419287-A (GB)
Title: An improved load indicator for cranes and the like
IPC: B66C23/90
Filed: 1933-04-27
Abstract: 419,287. Dynamometers. WYLIE, H. N., 3, Clement's Inn, London. April 27, 1933, Nos. 12335 and 31408. [Class 106 (ii).] Relates to apparatus for indicating or signalling a predetermined tension in a crane member which changes its inclination with change of inclination of the jib, for example, the jib-tie rope or chain. The indicator is mounted on or forms part of the tension member in such a manner as to impose deflections on the tension member at least two of which are automatically varied by change of inclination of the tension member, whereby the desired indication is given under different tensions at different jib inclinations. The signals may be given by a pointer on a dial, by a steam whistle, by coloured electric lamps, by electrical or mechanical bells, &c., or by combinations of these. As shown in Fig. 1, the indicator is fitted on the standing end of the derricking rope 2 which passes over a rest 3 on the crane frame 1. The indicator comprises a pair of parallel plates 4 rigidly secured to the rope 2 by a clamp 6. The plates are also connected with the rope by a supporting piece 5 and a deflecting piece 7. The piece 5 carries a roller 19, the plates 4 carry a roller 20, and the lower end of the plates 4 is spaced from the rope 2 by a wedge 17 passing between the rollers 19, 20. The wedge 17 is pivoted on the crane frame 1 at 18 so that the position of the lower end of the plates 4 relative to the rope 2 varies with the inclination of the jib. The deflecting piece 7 is pivoted to a bolt 11 mounted in links 12 adjustably pivoted on the plates 4 at 13, and the bolt 11 forms one end of a load-sensitive unit comprising a pair of spring plates connected by bolts 9, 10, 11 and forming a bendable strut 8 as described and claimed in Specifications 377,209 and 400,428, supported on the plates 4 at 10. Tension in the rope 2 tends to straighten the rope and the toggle-joint at 11, placing the strut 8 in compression, and the deflection of the centre of the strut moves a pointer 15 over a plate 16, seen in edge view, marked "safe," "caution," "danger." The contour of the wedge 17 is determined by trial so that the danger indication is given when the known maximum safe load is on the crane in given positions of the jib. The indicator may operate a steam whistle 21 by means of a rod 24 passing through a tube 24 which is connected with the plates 4 by a ball-and-socket joint 25 and is pivoted at 26 to a member 27 swivelling in a fixed bracket 28. The rod 22 is moved longitudinally by the bending of the strut and operates the whistle through a lever 30 pivoted on the swivel member 27, and a rod 23. In a modification, Fig. 4, the lower end of the plates 4 is spaced from the rope 2 by a lever 33 pivoted to the plates at 19 and to the support 5 at 20, and bearing on a rest 34 on the crane frame 1. The shape of the rest 34 is formed by trial so that the danger indication is given when the known maximum safe load is on the crane in different positions of the jib, and in some cases the rest may be a pin or if the necessary shape is a circular arc a radius rod may be used. In another modification, Fig. 6, the indicator comprises a lever 12,pivoted at 6 on a frame 4. The rope 2 bends over a pin 7 on the lever 12, under the pivot pin 6 and over a pin 5 on the frame 4, and tension tending to straighten the rope is opposed by a bendable strut 8 clamped to the frame 4 at 11 and to the lever 12 at 10. A roller 35 on the frame 4 bears upon a rest 36. In another modification, Fig. 7, the frame 4 is supported only at 6 and 35, the pin 5 being omitted. If the rope 2 passes over the pin 7 and under the pin 6 the rest 36 is arranged to bear downwardly on the frame 4, but as shown, the rope passes under the pin 7 and over the pin 6 and the strut 8 of Fig. 6 is replaced by a tension spring. The pointer 15 is pivoted on the lever 12 and is operated by a multiplying lever 37 pivoted on the frame 4 at 38 and slotted to engage a pin 37<1> on the lever 12. As shown in Fig. 8, the indicator comprises the parts 4, 8, 12 as in Fig. 6, the lever 12 is connected with the end 2 of the jib-supporting chain, and the frame 4 is connected at 5 with a short link 40 connected to the crane frame 1. The shaped end 36 of the frame 4 bears on a roller 35 on the crane frame. The line of pull is shown by the chain line which is deflected at 5, 6 and 7. In a modification of this arrangement, Fig. 9, the chain 2 is connected with the frame 4 of the indicator, and the lever 12 is pivoted at 5 to the link 40 extending beyond the pivot 6. The deflections in the line of pull at the points 5, 6, 7 are shown by the zig-zag chain-line. The lever extension 36 may be attached to either of the levers 4, 12 ; for example the lever 12 in Fig. 9 may be extended to engage the roller 35. The sensitive member may be in tension. As shown in plan in Fig. 10, the indicator 48 is arranged between the standing ends of a pair of derricking chains 2 which pass over pulleys 46. The indicator 48 deflects both the chains, and the deflection increases as the pulleys 46 pass from A to B in luffing the jib. If the indicator is adjusted for these two positions it is usually correct for intermediate positions. A strut 50 may be placed between the chains in order to keep the deflection of the chains by the indicator constant while the pulleys move from C to B, and shaped rests 51 may be placed on the frame of the crane so as to vary the deflection of the chains by the indicator at different inclinations of the jib. The indicator may be applied to running ropes instead of standing ropes. According to the first Provisional Specification the indicator may comprise a rigid base pivoted on an eccentric bush at the point where the flexible member 2 pivots on the crane frame ; the wedge 17, Fig. 1, may act upon the indicator frame 4 through a lover; instead of using the wedge 17, the indicator may be connected to a suitable point on the crane frame by a link ; and the indicator may be applied to the burden rope.