| 摘要 |
<p>A multi-section telescopic lifting boom which is extended and retracted at least in part by chains having their ends secured to one section, engaging sprockets carried by another section and connected at an intermediate point to a third section. Telescopic elements which are completely separated during boom extension are provided with inclined guide surfaces to insure entry of the smaller element into the surrounding element. Extension and retraction is effected by a linear hydraulic motor connected to a cylinder box which is pivoted to section adjacent the the base section; anti-friction pads are carried at the bottom of the outer end of the cylinder box and engage longitudinally extending tubes on the bottom plate of the next section, the tubes extending higher than the extension and retraction chains, which are positioned between the tubes. The chains are provided in parallel, at least one end of each chain being connected to a yoke which is adjustably secured by a threaded member.</p> |
