STRETCHING SPEED CONTROL DEVICE FOR MULTI-STAGE BOOM

摘要

PURPOSE:To keep the stretching speed of a tip boom at a prescribed value so that the tip boom is easily operated by an operator by providing a position detector of the tip boom against a base boom, and suppressing the stretching speed of a drive boom in response to the detected signal. CONSTITUTION:The telescopic boom of a mobile crane vehicle is constituted of a vertical boom 2 and a horizontal boom 3, individual booms constituting the vertical boom 2 are stretched by an stretching cylinder, and individual booms constituting the horizontal boom 3 are stretched by a three-stage stretching cylinder and a two-stage wire synchronization stretching mechanism. A position detector 40 of a tip boom 20 fitted with an auxiliary hook 7 is fitted to the base boom of the horizontal boom 3. The feed oil pressure to the third hydraulic cylinder driving the third boom is controlled by a proportional flow control valve so that the stretching speed of the tip boom 20 becomes equal to the stretching speed of the second hydraulic cylinder driving the second boom of the horizontal boom 3 based on the output signal of the position detector 40.