| 摘要 |
A jib stretching and folding mechanism for a jib crane having a boom, a jib pivotally supported at the base end thereof on jib support pins provided at the distal end of the boom, and jib cylinders each having one end pivotally joined to the jib support pin and the other end fixed to the corresponding base end of the jib. The jib stretching and folding mechanism includes guide cylinders each having one end fixedly connected to the piston rod of the jib cylinder so as to be able to receive entirely the cylinder tube of the same jib cylinder as the jib cylinder is contracted, and guide members fixed to the cylinder tubes of the jib cylinders so as to engage guide grooves formed in the corresponding guide tubes, respectively. The guide groove formed in one of the guide tubes has a helical section formed in an angular range corresponding to an angle through which the jib suspended from one of the jib support pins is turned in stretching and in folding the same, so that the jib is turned automatically when the jib cylinders are operated for stretching and for folding the jib by the movement of the guide member along the helical section of the guide groove.
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