| 摘要 |
<p>PURPOSE:To lessen tension by fitting a fourth boom into a third boom after hooking 2N numbers of wire ropes around the third boom when the number of wire ropes to be hooked around a first and a third boom of a three section boom, expanding and contracting simultaneously and in the same amount, is more than two. CONSTITUTION:A three section boom is composed of a first boom section BS1, a second boom section BS2 and a third boom section BS3 while BS2 and BS2 are expanded and contracted by means of a hydraulic cylinder 5 and each BS1 through BS3 are expanded and contracted simultaneously and in the same amount by means of expansion and contraction synchronizing devices 6, 7. When BS4 is fitted into BS3, one end of a wire rope WR31, which is hooked around an expansion synchronizing device 34, is fastened 32 to the tip of BS3 and, after hooking it around pulleys 28, 29, it is hooked around pulleys 29 and 30 for four times and the other end is fastened 32 to the tip of BS3. While N numbers (drawing shows two ropes) of WR are hooked around BS1 and BS3, 2N numbers of WR are hooked around BS3 and BS4. Thus a four section boom, expanding and contracting simultaneously and in the same amount, is formed and, furthermore, the tension imposed upon a wire rope is lessened.</p> |
