GB1282627A - Overload safety device for jib cranes - Google Patents

Abstract

1282627 Safe-load indicator for cranes L PIETZSCH 19 Sept 1969 [16 Oct 1968 23 Nov 1968 24 Jan 1969] 46356/69 Heading G1N An overload device, Fig.1, for a jib crane comprises a plurality of strain gauges in a bridge 8 to produce a first voltage indicative of jib loading, and an arrangement which displaces the slider 4 of a potentiometer 3 in accordance with jib radius (horizontal projection of jib length), the potentiometer having a plurality of supply connections, C1 to Cn, to each of which a supply voltage is fed through adjustable switches S 1 to S n which supply voltages represent the maximum values of jib loading permissible for the respective actual values of jib radius corresponding to positions of the slider when set to the respective tapping points of the potentiometer. The slider voltage is compared with the first voltage by a discriminator 10 which actuates a relay 11 when the voltages are equal to actuate an alarm or switch off the crane. An arrangement for indicating jib radius Fig.5, includes a lead-screw spindle 11' rotatablymounted orthogonally of the axis of a telescopic jib 1', a nut 13' on the spindle, fixed against rotation, but movable longitudinally of the spindle when the latter is rotated by pulley 7' and cable 10' due to extension of the jib. A pin 18' extends from the nut to support an end of a rod 16' of which the other end is fixed orthogonally of a sleeve 17' slidable longitudinally of a pendulum bar 15', which pendulum is suspended from a fixed point 14 on the spindle axis. A rope 20' is fixed at one end to the sleeve and at the other to the drift shaft 19' of a potentiometer slider 4. Thus the distance a' between the point 14 and the sleeve varies as the jib radius lsinα where 1 is jib length and α is the angular displacement of the jib from the vertical. Alternative arrangements for indicating jib radius are illustrated in Figs.6, 7, 8 (not shown). Fig.4 (not shown) illustrates a circuit for compensating the jib load signal for variations caused by tilting of the jib. Fig.3 illustrates an alternative circuit to that of Fig.1 for use with a crane having a telescopic jib and incorporates a sine potentiometer R sα the slider 23 of which is driven by a jib angle α measuring device W, the potentiometer output voltage U α being fed to resistances R 1 , R 2 and R L in series of which R L is a potentiometer of which the slider 24 is operated by the output shaft 25 of the jib length measuring device L. So voltage U L at slider 24 is a function of lsinα where 1 is jib length. A reference voltage Ur corresponding to the position of slider 4 is taken from the slider 26 of a linear potentiometer R R across which a constant supply voltage U o is connected through resistors R 3 , R 4 . The differential voltage U L -U r is fed through an amplifier 27 to a motor M which operates sliders 26 and 4 to bring U r into equality with U L so that the slider 4 is automatically adjusted proportionally to jib radius.