Jib relief speed regulating device null of tower crane for construction

摘要

PURPOSE:To make stable lifting work performable by setting a jib's derricking angle range to be plural stages so much as it is uprighted, and controlling it so as not to cause force-up speed of the jib by a hydraulic cylinder to be suddenly operated. CONSTITUTION:When a derricking angle of a jib exceeds a range of 47 degrees, it is detected by a derricking angle detector 40, and since a limit switch LS1 is operated by a cam and comes to ON, a relay R1 operates, its contact Lr1 opens but another contact Lr1' closes instead, so that a command signal is selected to a command for throttling a feed oil quantity by an amplifier Am. Therefore a current value to solenoids 32', 32' of a solenoid proportional valve 32 is controlled so as to cause an output signal of the amplifier Am to execute an intermediate restriction, whereby a working supply to a derricking hydraulic cylinder 6 is reduced, thus a jib 3 is uprighted at slow speed. When the jib 3 is uprighted and exceeds a range of 60 degrees, a limit switch LS2 is operated by a cam of the detector 20, and contacts Lr2, Lr2' of a relay LR2 are opened or closed and thereby the command signal at the amplifier Am is selected.