Abstract:
The invention relates to a device for turning sheets. A sheet to be turned is guided into a gap between two transport elements moving in opposite directions and is pressed against the reverse-moving transport element or the forward-moving transport element depending on whether or not said sheet should be turned. The following transport elements then guide the turned or unturned sheet to the output of the device. The device preferably is configured such that the same transport time is required for turned and unturned sheets so that the order of the sheets and the interval between the sheets upstream and downstream of the turning device remain the same.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for turning sheets. Such devices are known, for example, in connection with letter sorting equipment. In this regard, the turning device serves to manipulate letters inserted in an arbitrary orientation, such that a side of preference in the transport system or in the pigeonholes at all times comes to lie on one specific side, such that the address of letters is visible and legible. The function of turning is discussed as follows. The letters to be turned are fed to a short, dead-end-like section of the transport system, are stopped there and accelerated again in reverse direction, thereby leaving the transport system in inverted manner. Due to the fact that the intervals between the letters in the transport system of the letter sorting apparatus are narrow and decelerating as well as accelerating take a long time, two turning devices must be arranged in parallel in the letter sorting apparatus in order to be able to continuously process the stream of letters. Moreover, the drive systems for decelerating and accelerating are relatively complex due to the masses of the transport elements involved. However, devices for turning sheets are known as well in connection with banknote sorting machines. For example, the banknotes to be turned can be clamped between two elastic flat belts guided across rollers in a manner arranged on top of each other and twisted by 180°. Such a device is shown also in EP 0 532 217 A1 for example. Although such a device permits continuous processing of the banknotes, the known device nevertheless entails the disadvantage that the banknotes, due to the twisting of the belts, are subject to mechanical loads during turning, whereby the banknotes may be damaged. Due to the system, there is moreover the disadvantage that only sheets arriving symmetrically can be passed on to the subsequent transport system in uniform manner. However, this constitutes considerably restricting marginal conditions in sorting banknotes, e.g. in singularizing, scanning and stacking. 
     U.S. Pat. No. 5,048,814 reveals a device for turning documents, which turns all of the documents fed to the device. To this end, there is provided a lever that is biased by the documents entering the device and presses the documents, after the same have fully entered the device, onto a belt running in the opposite direction. The documents then are transported out of the device in the opposite direction and thus are turned. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to suggest a device for turning sheets which, with low technical expenditure, renders possible continuous processing of the sheets, however, without subjecting the sheets to mechanical loads during turning. 
     This object is met by the features indicated in the main claim. 
     According to the invention, the sheets to be turned are fed into a gap between two transport elements continuously driven in opposite directions, with the particular sheet being pressed against the forward-moving or reverse-moving transport element by means of guiding elements actuated by an actuator. Preferably, the transport elements are in the form of elastic flat belts and the guiding elements are in the form of guide plates which, either with or without pressing rollers, press the sheet toward the one or other belt. Due to the low mass of the guide plates, e.g. a simple lifting magnet may be used as actuator, moving the guide plates in linear manner. Due to this, the switching times may be kept so short that, observing the minimum distance between two sheets, these can be processed in continuous manner. Additional advantages and further developments of the invention are set forth in the dependent claims as well as in the embodiments of the specification with reference to the drawings wherein 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side view of a first preferred embodiment, 
     FIG. 2 shows a side view of a second embodiment, 
     FIG. 3 shows a side view of a third embodiment, 
     FIG. 4 shows a side view of a fourth embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a first preferred embodiment of the invention in a schematic diagram. The sheet  10  transported in the direction of the arrow is guided, by means of a switch means  205 , into a gap formed by two transport belts  101 ,  102  moving in opposite directions; in the region of said gap, there are arranged the guiding elements, e.g. in the form of guide plates  202  and  203 . For turning the sheet present between guide plates  202  and  203 , an actuator  204 , such as a lifting magnet configured to press the sheet via guide plate  202  against transport belt  102  moving in reverse direction with respect to the direction of transport of the sheet. The sheet thus is moved in reverse direction and is guided by switch means  205  between transport belts  102  and  103 . To this end, the switch means  205  is controlled correspondingly e.g. via an actuator  206 . The guide plates  202 ,  203  may have pressing rollers, not shown here, for guiding and accelerating the sheet. In the event that the particular sheet is not to be turned, the actuator  204  urges the sheet by way of guide plate  203  against the transport belt  101  moving in the direction of transport of the sheet. In that event, the sheet moves along a V-shaped path formed by the transport belts  101 ,  102 . In the present embodiment, part of the turning length is utilized as well for the transport path of the unturned sheet, thereby reducing the expenditure for this second transport path. This V-shaped transport path is used as well to simulate the loss in time caused by turning of the sheet. It is thus possible that both turned and unturned sheets have equal transport times in the turning device. The sheets thus may be introduced almost at the same intervals into an additional transport system, not shown here, of a sorting device. 
     FIG. 1 shows a first preferred embodiment of the invention in a schematic diagram. The sheet  10  transported in the direction of the arrow is guided, by means of a switch means  205 , into a gap formed by two transport belts  101 ,  102  moving in opposite directions; in the region of said gap, there are arranged the guiding elements, e.g. in the form of guide plates  202  and  203 . For turning the sheet present between guide plates  202  and  203 , an actuator  204 , e.g. a lifting magnet, presses the sheet via guide plate  202  against transport belt  102  moving in reverse direction with respect to the direction of transport of the sheet. The sheet thus is moved in reverse direction and is guided by switch means  205  between transport belts  102  and  103 . To this end, the switch means  205  is controlled correspondingly e.g. via an actuator  206 . The guide plates  202 ,  203  may have pressing rollers, not shown here, for guiding and accelerating the sheet. In the event that the particular sheet is not to be turned, the actuator  204  urges the sheet by way of guide plate  203  against the transport belt  101  moving in the direction of transport of the sheet. In that event, the sheet moves along a V-shaped path formed by the transport belts  101 ,  102 . In the present embodiment, part of the turning length is utilized as well for the transport path of the unturned sheet, thereby reducing the expenditure for this second transport path. This V-shaped transport path is used as well to simulate the loss in time caused by turning of the sheet. It is thus possible that both turned and unturned sheets have equal transport times in the turning device. The sheets thus may be introduced almost at the same intervals into an additional transport system, not shown here, of a sorting device. 
     FIG. 2 shows a schematic diagram of a second embodiment. The functional principle is the same as with the first embodiment; the essential difference resides in the design of the guiding elements. The guiding elements  209  and  210  are rigidly mounted, whereas the relatively small guiding elements  202  and  203  are movable. The guiding elements  202  and  203  may be operated e.g. by one or two actuators  204 . The sheet not shown here is transported in the direction of the arrow and is passed by rigid guiding element  210  in downward direction into the vertical transport path. If the sheet is to be turned, the guiding elements  202  and  203  are shifted towards the right as soon as the rear edge of the sheet is in the region of said guiding elements  202  and  203 , thereby eliminating firstly the contact between guiding element  203 , downward-moving transport element  101  and the sheet arranged therebetween, and establishing secondly contact between guiding element  202 , upward-moving transport element  102  and the sheet arranged therebetween. The sheet thus is accelerated in reverse direction and, due to the horizontal displacement of guiding elements  202  and  203 , is introduced at the right-hand edge of the rigid guiding element  210  into the transport path formed by transport elements  102  and  103  and leaves the device on this transport path. The guiding elements  202  and  203  preferably contain rollers to safely guide and accelerate the sheets. If a sheet is not to be turned, the guiding element  203  presses the sheet against transport element  101  and conveys the same downwardly and then towards the upper right out of the device. It is advantageous in this embodiment that the moving masses of the guiding elements and thus the switching times can be further reduced in comparison with the first embodiment. Moreover, the region between the transport elements  101  and  102  running in opposite directions, which is subject to the risk of transport disturbances, has been reduced to a minimum. The uncontrolled condition of movement of the sheet during the switching operation has been reduced considerably thereby, whereby the occurrence of transport disturbances in this region can be avoided. 
     FIG. 3 shows the schematic diagram of a third embodiment. The functional principle is the same as with the first embodiment; the essential difference resides in the arrangement and control of switch means  207 . In the event a sheet is not to be turned, the switch means  207  is actuated such that the sheet conveyed in the direction of the arrow is allowed to directly pass through the turning device. This embodiment permits a simple transport path for the unturned sheet that is not susceptible of disturbance. However, uniform transport intervals of turned and unturned sheets are no longer possible. 
     FIG. 4 shows the schematic diagram of a fourth embodiment. The difference from the first and fourth embodiments resides in the path of the unturned sheet which is fed into a separate, parallel transport path by a switch means  208 . The transport path  105  may be matched in length in such a manner that uniform transport intervals of turned and unturned sheets are possible.