Method for controlling stretching and contracting operations of telescopic multistage boom.

摘要

A method for controlling operating cylinders during extension and contraction of a multistage telescopic boom including a base boom portion, an intermediate boom portion and a fore boom portion, the method comprising: detecting the length of the boom by means of a boom length detector; permitting extension or contracting of a cylinder of the intermediate boom portion alone when the value (1) of a detected length is smaller than a first preset reference value (L-b) which is determined by substracting a preset arbitrary length (b) from an actual length (L) of the boom with the intermediate boom protion fully extended relative to the base boom protion and the fore boom portion fully contracted relative to the intermediate boom portion; permitting extension or contraction of a cylinder of the fore boom portion alone when the detected value (1) is greater than a second preset reference value (L+b); detecting variation per unit time (v) of the detected value (1) when the value (1) is in the range between the first and second reference values (L-b) and (L+b); continuing the boom extension or contraction by a currently operating cylinder while the variation is greater than a predetermined value; and switching the operation to the boom extension or contraction by a cylinder of the next stage as soon as the variation becomes smaller than the predetermined value.