(57) A ladder with a locking device comprises a pair of inner rotating plates (102, 103)
provided with a plurality of hinge holes spaced apart at predetermined angles; a rotating
plate (106) with notch portions (105) corresponding to the hinge holes, said rotating
plate rotating on an outer surface of the inner rotating plates (102, 103) to selectively
open the hinge holes; a resilient member (107) biasing the rotating plate (106) to
an initial state of closing the hinge holes, one end of said resilient member (107)
being secured to the rotating plate (106) and the other end secured to one of the
inner rotating plates (102); a pair of outer rotating plates (109, 110) with fixing
holes formed on one side and supporting said inner rotating plates (102, 103) rotatably;
and a locking key (114) including a guide pin (112) for securing the rotating plate
(106), inner rotating plates (102, 103) and outer rotating plates (109, 110), and
a fixing pin (113) for selective insertion into the hinge holes, said locking key
(114) being adapted to lock after the ladder has been spread by rotating the inner
rotating plates (102, 103) with respect to the outer rotating plates (109, 110), this
being possible when the fixing pin (113) has been released from the hinge holes by
the pressing of a push cover (115). The releasing of the hinge assembly due to an
external force is prevented, thereby preventing accidents whilst facilitating the
use of the ladder by enabling easy control of the locking and releasing of the assembly.
Furthermore, the number of operations for assembling the ladder is reduced, thereby
increasing the workability. Also, clearance between hollow beams of the ladder and
the hinge assembly is obviated, thereby increasing the durability of the ladder. Furthermore,
the number of parts for assembling the ladder is reduced, which in turn reduces the
cost for manufacturing the ladder considerably.
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