The invention is situated in the field of materials handling technology and concerns a conveying device in accordance with the generic term of the independent claim.  The device serves to convey piece goods, i.e., to convey a large number of identical or at least similar objects on a conveyor track, for example to a processing point, through the processing point and away from the processing point.  The objects are for example printed products.  During conveyance they are held individually or in small groups in a defined position. 
For gripped conveyance printed products are usually freely hanging, being individually held in the region of an upper edge oriented substantially transverse to the conveying direction.  The advantage of such conveyance consists in the fact, that each product has its own individual place within the conveyed stream, that the products therefore at any time can be individualized, that nonetheless, however, the product spacings can be small relative to the product size, which already in the case of relatively low conveying speeds renders high conveying capacities possible. 
If printed products, which are conveyed in such a dense conveyed stream, need to be processed during conveyance, it is in many cases necessary to not only change their relative position temporarily, but if so required also to increase the spacings between the printed products at least temporarily, so that the individual printed products are sufficiently accessible for processing. 
Conveying devices for the named conveying tasks, for example comprise a plurality of holding elements, which are driven in circulation on a closed-in-itself track more or less independently of one another, wherein a part of this track is utilized as conveyor track and the remainder of the track is used for returning the holding elements from the end of the conveyor track to its beginning.  Each of the holding elements has a body movable along a rail in a rolling or sliding manner and a gripper mounted on the body.  The grippers are closed in a controlled manner on taking over an object and are opened in a controlled manner on releasing the object.  The movable rolling or sliding bodies are advantageously designed in such a manner, that they can be driven closely adjacent to one another, for example by pushing, and that in such pushed operation there are precisely defined, regular minimum spacings between the grippers, resp.,  between the objects held by the grippers.  A conveying device of this type is, for example, described in the publication WO-99/33733. 
If in a conveying device of the type described above not only precisely defined minimum spacings, but at least in certain zones also precisely defined other spacings larger than the minimum spacings, are to be established, then the device needs to comprise means for establishing the desired spacings and a corresponding conveying speed as well as means for maintaining during conveyance the desired established spacings and speed.  A conveyor system comprising such means is e.g. described in the publication U.S. Pat.  No.  5,261,520 (Duke).  The system described comprises holding elements which are independent of one another and which are moved by four different driving organs along a closed-in-itself track.  On a first part of the track, a first endless driving organ with a first conveying speed and with conveying cams defining a first holding element spacing is active, on a second part of the track a second endless driving organ with a second conveying speed differing from the first one and with conveying cams defining a second holding element spacing different from the first one is active.  Between the two parts of the track there is in each case a screw drive having a screw pitch getting larger, resp.,  smaller in the conveying direction, which screw drives bring the holding elements from one spacing to the other, i.e., phase or time them from the one type of conveyance to the other.  Such a conveying device can be expanded to as many zones with different holding element spacings as required, wherein for every zone with a certain holding element spacing a driving organ and between every two zones of this kind always a means for phasing or adjusting have to be provided. 
Conveying systems with grippers installed on a circulating traction organ can also be equipped for a gripper spacing change in specific zones.  In the publication EP-0300170, a device of this type is described.  The traction organ is a chain comprising a plurality of chain links being joined together in an articulated manner by hinge pins.  The hinge pins are equipped with guide rollers, with which they are alternately guided in two guideways in such a manner, that the distance between the two guideways determines the angles between the links and therefore also the length of the links in conveying direction and the spacing between adjacent grippers installed on every fourth hinge pin.  In zones of the conveyor track, in which the holding means are to have greatest possible spacings, the guideways are arranged in such a way (smallest possible distance between the guideways), that the chain is substantially stretched out.  In such conveyor track zones, in which the holding means are to have the smallest possible spacings, the guideways are arranged in such a manner (greatest possible distance between the guideways), that the chain is compressed to a maximum degree. 
The object of the invention is to create a conveying device for conveying piece goods.  The conveying device comprises in per se known manner a rail track and holding elements with grippers being movable substantially independently of one another along the track, the holding elements being designed in such a manner, that in pushed operation a uniform, minimum spacing between the grippers is established.  In at least one zone of the track (adjustment zone) the gripper spacing is to be larger than the minimum spacing in a precisely defined way.  The inventive device shall be simpler than corresponding devices according to prior art and shall be utilizable with as few limitations as possible.  Furthermore, the inventive device shall make it possible, also in a simple manner, to within an adjustment zone choose one specific spacing increase from a plurality of possible spacing increases and/or to optionally activate or de-activate the spacing increase. 
This objective is achieved by the conveying device as defined by the independent claim.  The dependent claims define preferred embodiments of the inventive conveying device. 
The inventive conveying device comprises a rail track and holding elements movable along the rail track independently of one another.  The inventive conveying device further comprises at least one drive for conveying the holding elements tightly ranged together towards an adjustment zone and advantageously again tightly ranged together away from the adjustment zone, wherein gravity can possibly be exploited as driving means.  Furthermore, the device comprises in the adjustment zone a means for increasing the spacings between the holding elements in a controlled manner.  This means is an endless circulating, compressible adjusting chain, which is adapted to the holding elements and which is arranged in such a manner, that a part of its circulating track runs parallel to the rail track and the chain is in engagement with holding elements on the rail track.  Cooperating with the adjusting chain there is a means for defining the local compression of the adjusting chain in this part of the circulating track such that chain compression in the area of the adjustment zone is decreased from a value corresponding to the minimum spacing of the holding elements to a value corresponding to a predetermined larger holding element spacing. 
The holding elements conveyed with minimum spacings enter into engagement with the adjusting chain, which at the point of engagement is compressed in correspondence with the minimum spacing.  While the holding elements are conveyed onwards in engagement with the adjusting chain, the compression decreases, i.e., the adjusting chain is expanded, so that the holding elements are pushed apart.  In passing through the adjustment zone, the degree of compression corresponds to the predefined, increased holding element spacing and is maintained constant.  After the adjustment zone, the degree of compression of the adjusting chain increases again, until it once again corresponds to the minimum spacing of the holding elements.  Thereupon, the holding elements are released from engagement with the adjusting chain. 
While holding elements and adjusting chain are in engagement with one another, the adjusting chain is driven, for example, by the holding elements (for example, pushed).  It goes without saying, that it is also possible to drive the holding elements through the adjusting chain.  It is furthermore possible, to drive both chain and holding elements, obviously with the same speed. 
The compressible adjusting chain has e.g. links joined together in an articulated manner and being designed in such a way, that the chain can be compressed like a concertina.  The means for adjusting the chain compression are e.g. control rollers located on the chain links or on the link joints and rolling alternately on two stationary cams or guideways, wherein the distance between the cams defines the chain compression. 
For allowing selective adjustment of a plurality of different holding element spacings larger than the minimum spacing, the means for adjusting compression of the adjusting chain have to be designed to be adjustable and furthermore, means for compensating a change in the length of the adjusting chain must be provided, the change in chain length being caused by a local change in chain compression.  For a selectable activation/de-activation of the spacing increase, either similar compensating means as for selective adjustment can be utilized or the adjusting chain can be arranged to be displaceable in such a manner, that the engagement with the holding elements is selectively activated or de-activated.