The vertical travel is accomplished through motor, gearbox, lead screw and nut arrangements. Vertical travel is synchronized to get smooth vertical movement of the entire platform and avoid tilting on any side. The drive arrangement such as geared motor and the Connecting Rods connect the 4 nuts and are mounted below the platform. The radial adjustment of the platform, (opening – closing) is accomplished through a wire rope drum pulley mechanism and linear motion Guide rails. The platform is in a four segment construction to maintain the circularity of the aperture.