GB616022A - Improvements in or relating to safe-load indicators for cranes and like hoisting apparatus - Google Patents

Abstract

616,022. Cranes; winding and paying-out apparatus; lifting and lowering. AITKEN, R. L. Aug. 20, 1946, No. 24808. [Classes 78 (ii), 78 (iv) and 78 (v)] In a safe load indicator of the kind in which a change of tension in a member is arranged to react on spring means, the deflection of which is arranged to operate indicating and/or control means, the spring means comprises two springs having different natural periods of vibration forming a vibration damper. Clamps 24, 25, Figs. 1 and 2, secure the indicator between two parallel cables under tension, which are anchored to, and remain fixed with relation to, a part of the crane, said indicator serving to deflect the cables out of the straight so that variations of cable tension transmit a reaction transverse to the length of the cables to the two concentrically arranged springs 18, 19, having different natural periods of oscillation and constituting a vibration damper, contained between the yoke pieces 10, 11, the latter being free to slide along rods 12 towards the yoke 10 which is fixed thereto. Movement of the yoke 10 moves the micro-switch 23 into engagement with the abutment 22 adjustably secured to the casing 20. In a further embodiment, the indicator is attached at 36, Fig. 4, to a fixed part of the crane and at 29 to a tension member 30 which swings with the jib and which when under tension moves a yoke piece 26, carrying micro-switches 38, 39, against the action of vibration damping springs 18, 19. The switches are operated by a bridge piece 40 carried at the end of a spindle 41, the other end of which is attached to a cam-following roller 44 which is moved against the action of a spring 45 by cams which are shaped to correspond to two possible loading conditions of the crane.