Patent ID: 8408361

Claim:
A ladder assembly, comprising: a ladder; two wheel carriers mounted on the ladder movably and rotatably; two wheels each rotatably mounted on a respective one of the two wheel carriers; two fastening members each extended through a respective one of the two wheel carriers and each secured on the ladder to attach the respective wheel carrier to the ladder; a support rack pivotally mounted on the ladder; wherein each of the two wheel carriers has a surface formed with an elongate oblique guide slot which is slidable on the respective fastening member so that each of the two wheel carriers moves and rotates about the ladder as a direct result of being pushed into the respective fastening member which sits within and directly contacts the respective guide slot for guiding the respective wheels carriers; the ladder includes a front frame and a rear frame pivotally connected with the front frame; each of the two wheel carriers has a lower end provided with a washer abutting the support rack; the support rack has a side provided with two pivot brackets each pivotally mounted on the front frame of the ladder and each abutting the washer of a respective one of the two wheel carriers; each of the two pivot brackets of the support rack is pivotally mounted on the front frame of the ladder by a respective one of two pivot shafts; each of the two pivot brackets of the support rack has an upper abutting edge that is movable to abut the washer of the respective wheel carrier and a front abutting edge that is movable to abut the washer of the respective wheel carrier; a distance between the upper abutting edge of each of the two pivot brackets and the respective pivot shaft is greater than that between the front abutting edge of each of the two pivot brackets and the respective pivot shaft; each of the pivot shafts is eccentrically mounted on the respective pivot bracket of the support rack; the ladder assembly further comprises: two fixing sleeves each secured on the front frame of the ladder; two compression springs each mounted on the front frame of the ladder and each biased between a respective one of the two fixing sleeves and a respective one of the two wheel carriers to push the respective wheel carrier toward the support rack.