1.  Field of the Invention
The invention is the field of conveying flat, bendable objects, in particular of printed products, and concerns a device according to the generic term of the independent claim.  The device serves for the separation of individual flat, bendable objects from the underside of a stack of such objects and for the onward transportation of the objects, in particular for the separation of individual printed products from the underside of a stack of printed products and for onward transportation of the printed products. 
2.  Description of Related Art
From publication EP1226083, a device is known which serves the purpose named above.  For separation of individual printed products from the underside of the stack of printed products, the device comprises a carrier wheel, arranged below the stack, rotating on a substantially horizontal axis, on the periphery of which pairs each consisting of a suction device and a gripper allocated to the suction device are arranged.  The device further comprises a supporting means, which on the one hand supports the stack from below, on the other hand comprises at least one extraction opening, through which the lowermost printed product may be gripped and for separation may be bent away from the stack towards the gripper allocated to the suction device.  The carrier wheel is arranged and driven such that the suction device and gripper are moved in parallel to a pair of edges of the stacked printed products and approximately centrally between these edges below the stack.  The suction devices are rotated in a controlled manner during the rotation of the carrier wheel and connected to a suction pipe and de-coupled from it.  The grippers are closed and re-opened in a controlled manner during the rotation.  When a suction device is moved through underneath the stack, it grips the lowermost printed product in the region of the edge orientated transversally to its direction of movement it meets first, and when moving further it bends this edge region downwards through the extraction opening in the supporting means into the open allocated gripper, which then grips the printed product and removes it completely from the stack during its further movement. 
In an embodiment described in publication EP1226083, the supporting means on which the stack rests is a roll bed conveyor, which comprises a plurality of rollers arranged horizontally and in parallel to each other and are mounted to be freely rotatable, and which are aligned to the suction devices and grippers but are moved through below the stack on a substantially rectilinear and horizontal path.  Hereby, the movements of the rollers and the suction devices are adjusted in relation to one another such that the suction device may grip the lowermost printed product of the stack in-between two successive rollers and may draw out its edge region, and the upstream roller of the two may move in-between the printed product gripped by the suction device and the printed product resting thereupon.  The roll bed conveyor thus forms a succession of extraction openings orientated in parallel to the rollers and to the printed product edges gripped by the suction devices, which openings successively move through beneath the stack.  In order for the stack to be securely supported and for the extraction openings to be large enough all the same, it is suggested to move the rollers through beneath the stack in groups of three, wherein the rollers within the groups of three are at smaller distances from each other and wherein between succeeding groups a larger interspace is provided and only this interspace is used as an extraction opening.  The rollers forming the roll bed conveyor underneath the stack consist of two mutually aligned roller sections, which are at a distance from each other.  Thus, it is prevented that the suction devices conflict with the rollers.  A circulating chain is provided on each side of the carrier wheel, one for the left roller sections and one for the right roller sections, wherein the roller sections are coupled to these chains and revolve with the chain at constant distances to each other.  The orbit of the chains on both sides runs around a deflection roller arranged coaxially to the carrier wheel and around a further deflection roller with a parallel axis, which is arranged such that an upper part of the orbits is approximately horizontal between the deflection rollers.  The stack is arranged above this region of the orbit of the rollers. 
The device according to EP1226083, thus, comprises a revolving roll bed conveyor with extraction openings, wherein the stack is arranged on the outside of this roll bed conveyor.  When separated from the stack of printed products, the printed products are drawn through an extraction opening to the inner side of the circulating roll bed conveyor, from where they need to reach its outer side for being conveyed further.  For this purpose the roller sections in the corresponding region are rotated into a substantially vertical position in their orbit.  In this region the printed products are laid down on a conveying belt and released by the grippers, wherein the conveying belt follows the circular movement of the grippers in a substantially tangential manner. 
The device described in publication EP1226083 works without problems and without requiring much space.  It is, however, a costly device, and is restricted regarding the direction of onward transportation. 
In publication WO 2008/0000099, a device is described which serves the same purpose.  Again, a roll bed conveyor is on hand, wherein the rollers of the roll bed conveyor are fitted to a roller wheel, which e.g. circulates on the same axis as the carrier wheel.  The drawn out printed products are, however, not drawn completely into the inner region of the roll bed conveyor, but only partly.  In this position, the printed products are conveyed in synchrony with the roll bed conveyor over a certain distance and then deposited on a transport track.  Thus it is not—as in EP1226083—necessary to open the roll bed conveyor in a certain region in order to transport the printed products outwards from the inside of the roll bed conveyor.  Therefore, the orientation of the rotation axis of the rollers remains unchanged and the rollers circulate on a non-circular orbit, on which the distances between the rollers are varied.  For this purpose the rollers are flexibly linked to the roller wheel by means of levers, such that the levers are rotatable in parallel to the rotation plane of the roller wheel.  A definite orbit and a definite and consistent course of movement of the rollers along this orbit are defined by a roller guidance, which controls the movement of the rollers along the orbit. 
Publication EP1254855 also shows a roll bed conveyor, in which the rollers are fitted to a roller wheel.  In order to open the roll bed conveyor in a certain region, the rollers are tilted away on a tilting axis, which is substantially radial or secantial respectively in relation to the roller wheel.  For rotating the rollers, a cam control is provided.  A wheel rolling on a cam moves the rollers via a lever mechanism with several levers.  Because of unfavourable leverage due to the relatively long rollers and the tilting point of the rollers being near the lever mechanism the forces developed on the lever mechanism, are considerable and conversely the resulting movement of the rollers is not defined to complete precision.