referring to fig2 the shelf assembly 10 includes four shelves 11 , 12 , 13 , 14 rotatably - mounted about a horizontal axis x -- x . documents are placed on edge on the shelves , as books are usually placed on bookshelves , and arranged perpendicular to the horizontal axis x -- x . referring to fig1 each of the four shelves is an elongate channel of three successively - connected rectangular flat plates including a first bottom or shelf plate 21 , a second back plate 22 , and a third top plate 23 . the bottom plate 21 and the top plate 23 are parallel with each other and perpendicular to the back plate 22 . referring to fig2 and 3 , the four shelves are arranged around the horizontal axis x -- x . a cylindrical , elongate rod 16 , coaxial with the horizontal axis x -- x , is used to rotatably - mount the shelves to a support structure ( not shown ). the shelves are arranged such that the corner edge formed by the intersection of the first bottom plate and the second back plate of each shelf is adjacent to and parallel with the elongate rod 16 and such that the bottom plate of one shelf is perpendicular to the bottom plate of adjacent shelves . the ends of the shelves are closed - off by polygonal or circular end plates 17 . the end plates 17 are arranged perpendicular to the horizontal axis x -- x and connected to the ends of the shelves . the elongate rod 16 protrudes through the external faces of the plates 17 so that the shelves may be rotatably mounted to the support structure ( not shown ). referring to fig4 and 5 , a retainer plate 18 extends along the longitudinal edge of the bottom plate 21 of each shelf for retaining the documents on the shelves during rotation and for preventing the documents from falling off the shelves when in a rotated or upside - down position . each retainer plate is pivotally - mounted between the end plates 17 to pivot about a horizontal axis x &# 39 ;-- x &# 39 ; which is parallel to the horizontal axis x -- x . each retainer plate has an angular cross - sectional shape with one leg extending inwardly toward the back plate 22 and the other leg extending to overlap the top plate of an adjacent shape . the shape of the cross - section and the position of the axis of each retainer plate 18 can vary so long as they prevent documents from falling off the shelf as it rotates . the retainer plate 18 is positioned between the end plates 17 and pivotally - mounted on an axis parallel to the axis x -- x by any one of a number of conventional means . also , a conventional fixing device is provided for affixing the retainer plate 18 in either a position preventing the documents from falling off the shelf or a position permitting the documents to be inserted on or removed from the shelf . in operation , documents are inserted in or removed from the unit by rotating any one of the four shelves to an upright position . the retainer plate is then unlatched and pivoted or moved to a position allowing insertion or removal of a document from the shelf . afterwards , the retainer plate is pivoted or moved to a position which prevents the documents from falling out and affixed or latched in this position to retain the documents on the shelf during rotation . referring to fig6 a preferable and alternative design of the above - described shelf assembly is shown . the four shelves are integrally - joined together such that the bottom plate 21 &# 39 ; of each shelf also forms the back plate 22 &# 39 ; of an adjacent shelf . accordingly , the four integrally - joined shelves form an integral shelf assembly having a cross - section shaped like a swastika cross . the integral assembly rotates about a horizontal axis x -- x which is coaxial with the linear intersection of the four shelves , i . e . the center axis of the swastika cross . end plates 17 &# 39 ; and retainer plates 18 &# 39 ; are provided on the integral shelf assembly in the same manner as previously described . a pin 16 &# 39 ;, coaxial with the horizontal axis x -- x , protrudes from each of the end plates for rotatably - mounting the shelf assembly to rotate about the horizontal axis x -- x .
a system of revolving shelves for filing documents having the same rectangular format is disclosed . the system consists of four shelves revolving around a horizontal axis on which the documents to be filed are replaced .