Flexible link 2, designed as a chain, runs over chain sprockets 1 and 3. Flexible link 5, another chain, runs over sprockets 4 and 6. Attached to one chain are links 7 and 8 and to the other, links 9 and 10. These links are connected by turning pairs a and b to link 11. The lengths of all these links are designed so that points a and b always lie on a vertical line. Then, as the chains move over the sprockets, platforms e, perpendicular to links 11 and intended for holding the boards, will always be horizontal. Thus, as the chains go around the sprockets, the figure formed by links 7, 8, 9, 10 and 11 changes but points a and b remain on a vertical line and platforms e, carrying boards, remain horizontal. Sprockets 1 and 4 are the driving members and have a common drive.
$2021$FL,MH$