Reinforcement mechanism for multi-stage telescopic boom

In a multi-stage boom having a plurality of boom members including a first boom member, at least one intermediate boom member and a last boom member, each boom member being slideably inserted into its subordinate boom member to undergo telescopic expansion and contraction, the improvement comprising:

• an operating shaft connected pivotably at its bottom portion erectly to a peripheral lower end portion of the last boom member;
• a plurality of adjusting shafts, each adjusting shaft being disposed pivotably at its bottom portion erectly to a peripheral upper end portion of respective ones of the boom members except the first boom member;
• a first tension cable connected at its one end to a lower end portion of the first boom member, lead thereform through an upper end opening of a subordinate boom member, turned forwardly at a top portion of the adjusting shaft disposed at a peripheral upper end portion of the subordinate boom member, and connected at its other end to an upper end portion of the first boom member;
• at least one intermediate tension cable connected at its one end to a lower end portion of a corresponding intermediate boom member, lead therefrom through an upper end opening of a subordinate boom member, turned forwardly at a top portion of the adjusting shaft disposed on a peripheral upper end portion of the subordinate boom member, and connected at its other end to a top portion of another adjusting shaft disposed on a peripheral upper end portion of the corresponding intermediate boom member;
• a last tension cable connected between a top portion of the operating shaft and a top portion of the adjusting shaft disposed on a peripheral upper end portion of the last boom member;
• and means for controlling a tilting angle of the operating shaft according to the expansion amount of the multi-state boom to tension a chain of the first, intermediate and last tension cables.