GB1138019A - Safety control systems for cranes - Google Patents

Abstract

1,138,019. Jib cranes. AUGUST BILSTEIN. 7 Aug., 1967 [6 Aug., 1966], No. 36185/67. Headings B8B and B8H. A control system for limiting the loadmoment applied to a vehicle having a slewing crane mounted thereon and having an hydraulic support leg at each side thereof, comprises electrical circuit means controlling the crane drive and including a switch controlled by a pressure measuring device coupled to a pressure cylinder of one of the legs and arranged to measure the hydraulic pressure in the cylinder as it varies in dependence upon the load-moment, the switch being arranged to prevent operation of the crane drive in a load-moment increasing sense when the hydraulic pressure exceeds a predetermined value. In a first embodiment, Fig. 1, a crane mounted on a vehicle 3 has a jib 1 which is extensible and adjustable as to its height, and a pillar 2 on which the jib is mounted. The vehicle has support legs comprising hydraulic rams 6, 7 hinged at 4, 5 on the vehicle and having footplates 8, 9. Gauges 12, 13 are connected to the pressure side of the ram cylinders which when operational are pressurized to a predetermined pressure limited by pressure valves, for example. The pressure in the rams 6, 7 will vary in dependence on the loadmoment. For example, with the jib positioned as shown in Fig. 1 the pressure in the ram 6 will increase with increased load-moment until the gauge 12 operates the control switch. In a second embodiment, Fig. 2, a single gauge 15 registers the pressure difference between the rams 6, 7 and operates the control switch on a predetermined pressure difference being reached. The electrical circuit means, Fig. 3, comprises a circuit A including a relay 18<SP>1</SP> controlling a switch 18, and a voltage source 19, the circuit A having terminals c, d for connection to the pressure gauges, a circuit B including the switch 18, a load-moment limit switch 29 mounted on the pillar 2, a jib-extension drive relay 20, a voltage source 21, and a single-pole, two-way switch 22, and a circuit C including a jibretraction relay 23, the voltage source 21 and the switch 22. The switch 29 comprises an electrically conductive arm 24 secured to the pillar 2 and having a contact g coacting with a second contact h fixed on the pillar. If the loadmoment on the pillar exceeds a predetermined value it will bend sufficiently to open the contacts g, h. In normal operation the switch 18 is closed and the switch 22 engages contact e. If the vehicle is laterally overloaded the switch 18 is opened to de-energize the relay 20. By moving the switch 22 to contact f the relay 23 is energized to retract the jib. The switch 29 ensures that the jib is not overloaded when it extends longitudinally of the vehicle. The reaction of the control system can be transmitted to the crane drive mechanically or hydraulically. A limit can be placed on the maximum load which can be lifted by the crane with the jib set along the longitudinal axis of the vehicle by limiting the fluid pressure driving the hoist chain. The crane may have a counterweight.