A carrier includes a base, a number of wheels attached to the base, and a spring biasing device for engaging with the stairs and for biasing the base while the base is moved relative to stairs, in order to facilitate the base of the carrier upstairs or downstairs. One or more posts are secured to the...http://www.google.sh/patents/US20030098552?utm_source=gb-gplus-sharePatent US20030098552 - Carrier having device for assisting stair climbing
