It should be possible to construct a motorized ladder consisting of a chain of linked crossbars which form a loop half of which is inside and half on the outside of a rectangular tube through which the loop passes and which is the length of the ladder. A motor on the base of the tube would drive the chain to either lift or lower somebody on the ladder. The user would stand on one of the crossbars and could control the ladder with a hand-held switch which might be connected as a wireless control to the drive motor. This device would work as a portable escalator and might be useful for firemen who are carrying people out of windows or anybody who might have to carry a heavy load up or down a vertical surface. It probably would be possible to eliminate the tube and have the chain of steps move on a vertical element with some sort of bracket to keep the moving elements away from the ground and the wall.
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This is a vertical conveyor, used prior to the 1970s (to my knowledge) in some buildings in Europe in lieu of traditional (and safe) elevators. A portable model wouldn't be light or easily carried, and would require a good amount of power (read that: electric) to operate.
I was thinking of the apparatus on a fire truck where the extensible ladder could be powered by the truck. A fireman rescuing a victim or carrying heavy equipment could be helped by an automatic raising or lowering system.