GB1364323A - Overload safety devices for cranes - Google Patents

Abstract

1364323 Crane safety devices LEO GOTTWALD KG 7 Feb 1972 5632/71 Heading B8B A crane overload safety device 11 is attached by a bracket 13 to a crane jib 12. A number of cams 21, each corresponding to a particular length of jib 12, is mounted on a shaft 16. A damped pendulum 24 maintains the cams 21 in position corresponding to the vertical position of the pendulum 24, automatically compensating for any slope of a vehicle on which the jib 12 is mounted. A shaft 15 carries arms 42 associated in pairs with the cams 21 and carrying either a lamp, e.g. 43 or a photo-cell, e.g. 44. The shaft 15 is counterbalanced and may be rotated by a cable 49 attached to a wheel 48, passing over a pulley 51 and connected to a lever 56 of a strain gauge 52. The strain gauge comprises a tension rod 59 attached to the lower side of the jib 12 and prestressed by an amount equal to the maximum load allowable, the mountings 55 releasing the rod 59 should it be no longer stressed. Each cam 21 is arranged to have its four quadrants corresponding to a particular arrangement of the crane, the particular quadrant being selected by operation of a motor 38. Movement of the arms 42 cuts off the light passing between, e.g. lamp 43 and photo-cell 44, when the cam 21 intervenes and this results in preventing operation of the crane to increase the load further. A preliminary warning is given by, e.g. lamp 43a and photo-cell 44a. A controller pendulum 27 pivoted on a pin 26 above the shaft 16 ensures, through a photo-cell and light source 25, 28 that the device operates only when the two pendulums 24, 27 are in line. Should the cable 49 break a return spring 54 moves the arms 42 to a safety light trap 62 which cuts the light beam between the arms 42. The various lamps 43 &c. may be replaced by light supplied from a central source by way of optical fibre light conductors. Other beam emitters and receivers, such as ultrasonic beam emitters and receivers (not shown) may replace the light sources and photo-cells.