GB574571A - Improvements in or relating to extending ladders - Google Patents

Abstract

574,571. Extending ladders. GRAVITY LADDERS, Ltd., and PRITCHARD, C. W. Dec. 17, 1943, No. 21248. [Class 20 (ii)] An extending ladder of the lazy-tongs type, e.g., for providing emergency escape to the ground, has a locking device at its lower end which operates automatically upon the ladder reaching the ground in order to prevent further relative movement of the bottom rungs. The ladder, composed of links 10 with pivots 11 and rings 12 has one pair of upper links pivoted at 14 to a pair of parallel members 13 which may be secured to the crane or other overhead structure, the other upper links having a pivot 15 sliding in a curved guide 16 of such form that the ladder takes up a bowed form when extended. The lower links are pivoted, one pair at 17 and the other pair on a bar 23 mounted in a guide slot 20 in a pair of parallel foot members 18. A member 27 carrying a pulley 30 for the cable 31 operating the ladder, is pivoted to a link 28 pivoted to the foot members 18 and to a link 26 coupled to a locking member 22 which is pivoted in the foot members at 21 and has a notch 23 to engage the slidable bottom rung, and a bearing surface 24 to engage the foot members. On the cable 21 being operated to lift the member 27, the locking member 22 releases the bottom rung thereby allowing it to slide along the foot member as the ladder is collapsed upwardly. In the folded position a hook 32 on the member 27 engages a bar 33 between the members 13. In a modification the member 27 may be connected directly to one end of the locking member 22. Means are provided to damp the motion of the ladder to prevent too rapid an extension, e.g., the upper pulley over which the cable runs may have a centrifugal clutch or brake, or a hydraulic dash-pot of the type consisting of vanes rotating in oil. The speed of extension may be controlled by a separate rope running over a centrifugal or other speed-limiting device, this arrangement preventing the ladder from dropping if the operating rope should break. To prevent collapse should a side-link break, bars are provided at intervals, pivoted on one rung and having a slot to receive the opposite rung.