Abstract: The present invention relates to a movable conveyor for construction sites. The platform includes: (a) a stage having two opposite end portions for conveying objects thereon; (b) a pair of elongated arms attached to the respective end portion of the stage, slidable and rotatable with respective to the stage in a horizontal plane; (c) a plurality of holders installed in the arms, the holders being adapted to grasp the structure and to hang therefrom; (d) a driving mechanisms to slide and rotate the elongated arms with respect to the stage and the holders; and (e) controller for sliding and rotating the driving mechanisms and for holders and releasing the holding, whereby the stage is conveyed with respect to the structure.

Abstract: A power transmission mechanism in which a small rotatable screw thread is arranged symmetrically with a large rotatable screw thread. The pitch and the pitch circle diameter of the large screw thread are the same integer times the pitch and the pitch circle diameter of the small screw thread. The screw thread grooves are connected through ball means and a convenient combination of screw threads provides an input shaft and an output shaft either in parallel or in alignment. This arrangement provides a power transmission mechanism of a compact size and a simple structure with an enhanced ratio of power increase and decrease.

Abstract: A ball-retaining structure in a power transmission apparatus for transmitting power by means of magnetic balls arranged between non-magnetic rotating bodies is disclosed, in which a magnet or magnets are arranged within either one of the rotating bodies in the vicinity of the balls.