| 摘要 |
453,968. Loft-ladders. LOFT LADDERS, Ltd., Broadway Works, Bromley, and GORHAM, P. H., 25, Degema Road, Chislehurst, both in Kent. June 14, 1935, No. 17242. Addition to 392,940 and 428,560. [Class 20 (ii)] A loft-ladder according to the parent Specifications, is now provided with a cam 4 or like varying-radius device for automatically varying the leverage of the upward pull on the ladder. The chain, cord or the like 1 is secured to a plunger 2 acting on the spring or series of springs 3 and is secured to and entrained over the cam 4. The cam is secured to a shaft which carries also a pulley 5 to which is secured the cable 6 connected to the ladder. The pulley may have a longer radius then the greatest radius of the cam to provide a reduction gear between the chains 1 and 6. The effective cam radius is a maximum when the ladder is raised and a minimum when the ladder is lowered. In a modification the spring and cam-pulley devices are carried by the ladder the chain from the pulley being anchored to a fixed point, for instance to the side of the loft opening. |
