| 摘要 |
<p>A climbing mast assembly (40), including a mast (42) having multiple recesses (45) thereon spaced longitudinally along the mast. A pair of ratchet housings (56) is mounted to be relatively slideable along the mast and including means to mount one or more jacks (55) for coupling the housings and operable to adjust the relative separation of the housings along the mast. First ratchet elements (60a) are mounted on the respective ratchet housings for reciprocatory sliding movement, transversely of the mast, and selectively positionable to successively engage said recesses to limit return travel of the respective housing as it is advanced up the mast by operation of said jack(s). Second ratchet elements (60b) are mounted on the respective ratchet housings for reciprocatory sliding movement, transversely of the mast, and selectively positionable to successively engage said recesses to allow lifting of the mast by the jack(s) and to limit return travel of the mast when it is being raised relative to the respective housings.</p> |
