| 摘要 |
This is an improvement in an extendible boom assembly having a lower section and an upper section and an intermediate section mounted for telescopic movement with respect to one another. The boom assembly has power means connected to the lower and upper sections for extending and retracting the boom assembly. The improvement comprises latch members carried by the upper and intermediate sections. One of the latch members is movable to a latched position wherein it retentively engages the other of the latch members so as to cause the upper and intermediate sections to be locked together for movement in unison. This one latch member is movable from its latched position to a release position wherein it releases the other latch member from retentive engagement. A bearing surface slidably engages the latch member during extension of the upper and intermediate sections, and holds the latch member in its latched position until the boom assembly extends to a predetermined point at which time it permits the latch member to move to its release position. The engagement between the two latch members is such that the movable latch member is urged towards its release position whenever the upper section extends with the latch members in retentive engagement with one another.
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