Abstract:
A turning unit for sheet-like substrates has at least one first turning element with a basic body having an outer, round substrate contact surface for deflecting the substrate. The deflection is from a first sheet conveying direction to a second sheet conveying direction describing a predetermined angle to the first sheet conveying direction. Furthermore, a channel structure is provided that is formed in the substrate contact surface and onto which open a plurality of gas outlet openings which are in fluid communication with a gas supply.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device for turning sheet-like substrates, in particular sheet-like substrates in a printing press, that are to undergo verso printing following recto printing. 
       BACKGROUND OF THE INVENTION 
       [0002]    In printing technology, turning units are known which following recto printing use deflecting elements to turn sheet-like print materials for verso printing. A turning unit of this type is described for example in DE 43 35 473. The turning unit described there has two fixed turning elements rotated 90° to one another and a deflecting element positioned in a sheet running direction between the turning elements. The turning elements are each inclined 45° to a running direction of a substrate sheet, as a result of which they each provide a 90° turn. 
         [0003]    The turning elements can guide the substrate sheet in a sliding and contacting manner, or, as described in DE 43 35 473, over an air cushion between the substrate sheet and the turning element. To generate the air cushion, the turning elements are provided with a cavity and a plurality of openings connected to said cavity and opening onto the circumference of the turning element. To generate an air cushion between the substrate sheet and the turning element which reduces the friction between them, the cavity is supplied with compressed air which exits through the openings in the turning elements. 
         [0004]    A drawback of a design of this type is the high air consumption needed to generate a sufficient air cushion over the width of a substrate sheet. A high air consumption of this nature is concomitant with correspondingly high energy consumption for generating the required air quantity. In edge areas of the substrate sheet, there fluttering of the substrate sheet may also result from high air flows, which can impair the guidance accuracy of the substrate sheet. Furthermore, a heavy noise development can result from this and/or from strong air flows. 
         [0005]    The printing of sheet-like print materials requires a high degree of accuracy in respect of the guidance of the print material. The guidance accuracy can be impaired by repeated turning of print material sheets in a turning unit of the above type. 
       SUMMARY OF THE INVENTION 
       [0006]    The object underlying the present invention is to provide a device for turning a sheet-like substrate of the above type and for eliminating at least one of the aforementioned drawbacks, in particular permitting lower air consumption for generating the air cushion. 
         [0007]    In accordance with the invention, this object is achieved by a turning unit according to claim  1 . Further embodiments of the invention are detailed in the respective sub-claims. 
         [0008]    In particular, a turning unit for sheet-like substrates is provided with at least one first turning element having a basic body with an outer, round substrate guide surface angled relative to a sheet conveying direction. 
         [0009]    Furthermore provided are a channel structure that is formed in the substrate guide surface, and a plurality of gas outlet openings opening onto the channel structure and which can be supplied with gas in order to provide a gas flow to the channel structure. 
         [0010]    The channel structure in the substrate guide surface permits an improved and more even distribution of air between the turning element and a substrate sheet passing over it. As a result, the air quantity used and hence the energy expended to form a sufficient air cushion can be reduced. As a result, low noise development can be achieved. In particular in edge areas of the substrate sheet, the channel structure can provide a controlled air flow, as a result of which fluttering of the substrate sheet and the associated noise development can if necessary be reduced. The first turning element can for example be arranged fixed at a 45° angle to a first sheet conveying direction, where said first sheet conveying direction is the sheet running direction of the substrate sheet before it is turned by the turning element. This would result in a 90° turn relative to the first sheet conveying direction. 
         [0011]    In a preferred embodiment, at least two turning elements are provided which are each arranged at an angle to a sheet conveying direction and also relative to one another. As a result, a double turn of the substrate sheet and hence for example a 180° turn can be provided. The turning elements can be arranged in the known manner each at 45° to the sheet conveying direction and intersecting one another at a 90° angle. In a sheet running direction, a pivot-mounted intermediate roller can be provided between the turning elements, by which the sheet-like print material is deflected after the first turn to the second turning element. An arrangement of this type permits in known manner a compact arrangement of the turning unit. 
         [0012]    In an embodiment of the invention, the channel structure inside the substrate contact surface has a plurality of circumferential channels spaced apart and extending in the circumferential direction of the round substrate guide surface, and at least one transverse channel extending transversely to the circumferential channels and being in fluid communication with at least two circumferential channels. As a result, a good distribution of air can be achieved between the turning element and the substrate sheet. The at least one transverse channel can here extend in the circumferential direction of the circumferential channels and centrally thereto. The circumferential channels preferably each have the same distances relative to one another. However, another arrangement of the circumferential channels can also be provided. With an arrangement of this type of the circumferential channels and of the at least one transverse channel, supplied gas or air can easily be distributed in the respective channels, thereby achieving an even air cushion between the turning element and the substrate sheet. 
         [0013]    In one embodiment, at least some of the gas outlet openings open onto at least one transverse channel in order to provide a good distribution of supplied gas over a width of a substrate sheet. 
         [0014]    In an alternative embodiment, the channel structure has channels distributed statistically in the substrate contact surface. As a result, a particularly even distribution of supplied gas can be achieved over the substrate guide surface. 
         [0015]    Preferably, a control unit is provided which is able to supply gas to the gas outlet openings individually or in groups. This makes it possible to supply gas substantially only to those gas outlet openings which are covered during operation by a substrate sheet in order to reduce leakage flows. An adaptation to differing widths of substrate sheets is thus possible. As a result, the entire air quantity and an energy consumption connected thereto, and if applicable also the noise development, can be reduced. 
         [0016]    In an embodiment, a cavity is provided inside the basic body of the turning element which is in fluid communication with the gas outlet openings and which can be supplied with gas. A cavity of this type permits a particularly simple supply of gas to the gas outlet openings. It can for example be subdivided in order to achieve easily by this subdivision an individual or grouped controllability of the gas outlet openings. Inside the cavity, a slider can also be movably mounted such that it permits selective supplying of gas to gas outlet openings via the cavity. A slide of this type permits a continuous adjustment of the area of the cavity via which gas outlet openings can be supplied with gas. This permits an approximately continuous adjustment to the width of a substrate sheet. Two slides can be provided here that are movable from opposite ends into the cavity to permit an adjustment to a position and width of the substrate sheet. 
         [0017]    Alternatively or additionally, a plurality of valves can also be provided for individual or grouped supplying of gas to gas outlet openings. 
         [0018]    The substrate guide surface can have a plurality of separate channel structure segments arranged adjacently over a width of the substrate guide surface, where a respective channel structure is in fluid communication with at least one gas outlet opening. The individual channel structure segments could each be separated from one another by areas without channels of the substrate guide surface. The respective channel structure segments are preferably thus not in fluid communication with one another via channels. An arrangement of this type of channel structure segments permits ready adjustment to the width of a sheet-like substrate in particular with a segment-by-segment supply to the gas outlet openings. The separation of the channel structure segments allows a reduction of leakage flows via the respective channel structure. Preferably, gas inlet opening(s) associated with a respective channel structure segment can be supplied with gas in groups. 
         [0019]    The channels preferably extend over a maximum of 180° in the circumferential direction of the substrate guide surface in order to reduce leakage flows. In particular, the channels should extend in the circumferential direction of the substrate guide surface at most over one winding area of the substrate sheet. 
         [0020]    In accordance with a preferred embodiment, the channel structure has a depth of 0.1 to 1 mm, which on the one hand permits a good distribution of gas and on the other hand prevents excessive leakage flows. The channel structure can for example be provided in the surface of the basic body by milling, etching or with the aid of lasers. It can of course also be formed in other ways. The gas outlet openings preferably have a diameter of 0.3 to 0.5 mm. 
         [0021]    Furthermore, a device for printing on a substrate sheet is provided which has at least one printing unit for application of a print medium onto the substrate sheet and a turning unit of the above type. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention is explained in more detail in the following with reference to the drawings, which show in: 
           [0023]      FIG. 1  a schematic side view of a printing press with turning unit in accordance with the invention; 
           [0024]      FIG. 2  a schematic detailed view of a turning unit in accordance with the invention with two turning elements and one intermediate roller; 
           [0025]      FIG. 3  a schematic plan view onto a movement area of a substrate sheet in the view from line A in  FIG. 1 ; 
           [0026]      FIG. 4  a schematic plan view onto a turning element in accordance with the invention; 
           [0027]      FIG. 5  a schematic plan view onto an alternative turning element in accordance with the invention; 
           [0028]      FIG. 6  a schematic detailed view of a channel structure in a surface of a turning element in accordance with an embodiment of the invention; 
           [0029]      FIG. 7  a schematic sectional view through the turning element in accordance with  FIG. 6  along the line B-B in  FIG. 6 ; and 
           [0030]      FIG. 8  a schematic detailed view of a channel structure in a surface of a turning element in accordance with an alternative embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    The position and direction information provided in the following description relates primarily to the illustrations in the drawings and should therefore not be deemed to be restrictive. It can however also relate to a preferred final arrangement. 
         [0032]      FIG. 1  shows a schematic side view of a printing press  1  with a feeder/delivery area  2 , a print area  3  and a turning area  4 . The print area  3  is arranged between the feeder/delivery area  2  and the turning area  4 . 
         [0033]    In the feeder/delivery area  2 , a first print material roll  5  is provided from which a print material sheet  6  is fed to the print area  3  for printing. The feeder/delivery area  2  is furthermore provided with a second (not shown) print material roll for receiving the print material sheet  6  returning from the print area  3  after being turned in the turning area  4 , as described in detail in the following. 
         [0034]    A plurality of rollers  8  for guiding the print material sheet  6  and a plurality of printing units  10  are provided in the print area  3 .  FIG. 1  shows schematically seven of the rollers  8 , although as a rule a larger number are provided to convey the print material sheet  6  along a non-linear transport path through the print area  3 . 
         [0035]      FIG. 1  shows four printing units  10  so that the printing press  1  in accordance with  FIG. 1  would be suitable for four-color printing. It is however also possible to provide a different number of printing units  10 . The printing units  10  are preferably inkjet printing units, but can also be of another digital type. 
         [0036]    A plurality of deflecting rollers  12  and a turning unit  14  are provided in the turning area. The deflecting rollers  12  are arranged such that they guide the print material sheet  6  out of the print area  3  to the turning unit  14  and from the turning unit  14  back to the print area  3 . The turning unit  14 , which is explained in the following in greater detail, effects a 180° turn of the print material sheet  6  and also a lateral movement of the latter. Thanks to the lateral movement of the print material sheet  6 , it is possible to guide the print material sheet  6  in opposite directions through the print area  3  and the printing units  10 , as indicated schematically in  FIG. 3 .  FIG. 3  here shows schematically the opposed and laterally offset movement of the print material sheet  6  over a roller  8  positioned in the area of a printing unit. 
         [0037]      FIG. 2  shows schematically a perspective view of the turning unit  14  with a first turning element  20 , an intermediate deflecting roller  22  and a second turning element  24 .  FIG. 2  furthermore shows the substrate sheet  6  as it is passed through the turning unit  14 . The first turning element  20  is arranged at an angle of 45° relative to an entry running direction of the print material sheet  6  indicated by the arrow in  FIG. 2 , and comprises a fixed hollow tube as explained in greater detail in the following. The print material sheet  6  is passed around the first turning element  20  and is as a result deflected by 90°, so that after the deflection it runs at a right angle transversely to the entry running direction. 
         [0038]    The intermediate deflecting roller  22  is a pivot-mounted deflecting roller arranged laterally offset to the first turning element  20  and extending parallel to the entry running direction of the print material sheet  6 . It is arranged such that it deflects the print material sheet  6 , running transversely to the entry direction after the first deflection, by 180°. As a result, the print material sheet runs after deflection in the opposite direction but still transversely to the entry running direction. 
         [0039]    The second turning element  24  has the same design as the first one and is arranged at a 90° angle to it. For a lateral offset of the print material sheet, the first and second turning elements  20 ,  24  can be arranged transversely to the entry running direction and offset relative to one another. 
         [0040]    The print material sheet  6  running transversely to the entry running direction after the intermediate deflecting roller  22  is passed around the second turning unit  24  and is again deflected here by 90° so that it is again running in the entry running direction. The multiple deflections however turn the print material sheet by 180°, so that the previously upward-facing side now faces downwards. 
         [0041]    The turning elements  20 ,  24  can have the same design, so that the following describes in detail only differing embodiments of the turning element  20 . 
         [0042]      FIG. 4  shows a schematic plan view onto the tube-like turning element  20 . The plan view shows in particular the area of the turning element  20  wrapped around by the print material  6  during operation of the turning unit  14 . The turning element  20  has in this area a surface referred to in the following as the substrate guide surface  30 . In the area numbered  32  of the substrate guide surface, a continuous channel structure is provided, the design of which is described in greater detail in the following. The area  32  extends approximately over the entire width of the turning element  20 . In the circumferential direction, the area  32  and hence the channel structure provided therein extends over approximately 180° of the turning element  20 . It should preferably not extend by more than 180° in the circumferential direction of the turning element. 
         [0043]      FIG. 5  shows a schematic plan view onto the tube-like turning element  20  in accordance with an alternative embodiment. The plan view again shows the area of the turning element  20  wrapped around by the print material  6  during operation of the turning unit  14 . The turning element  20  here again has a surface referred to in the following as the substrate guide surface  30 . In the areas numbered  45 , continuous channel structures are provided in each case, the design of which is explained in greater detail in the following. The areas  45  are arranged adjacently to one another over the width. Inside the respective areas  45 , the channel structures are continuous, i.e. all areas of the channel structure are connected via corresponding channels of the same. There is however no connection to the channel structures of adjacent areas  45 . For this, the areas  46  are provided, which each indicate an area of the substrate guide surface  30  without channels. The substrate guide surface  30  thus has several segments or areas  45  with channel structures provided therein and areas  46  between these without such channel structures. The areas  45  are arranged adjacently to one another over approximately the entire width of the turning element  20 . In the circumferential direction, the areas  45  and hence the channel structures provided therein extend over approximately 180° of the turning element  20 . They should preferably not extend by more than 180° in the circumferential direction of the turning element. 
         [0044]      FIG. 6  shows a schematic detailed view of a continuous channel structure  60  in a substrate guide surface  30  of a turning element  20  in accordance with a first embodiment. The channel structure  60  can be designed in the form shown both in the area  32  in accordance with  FIG. 4  and in the areas  45  of  FIG. 5 . 
         [0045]    The channel structure  60  has a plurality of parallel-extending circumferential channels  62  and a transverse channel  64  provided in the substrate guide surface  30 . The circumferential channels  62  extend in the circumferential direction of the turning element  20 . The respective circumferential channels  62  are connected to one another via the transverse channel  64 , the latter centrally intersecting the circumferential channels  62  in the circumferential direction of the turning element. It would of course also be possible to provide several transverse channels intersecting the circumferential channels  62  in the circumferential direction of the turning element at different points. 
         [0046]    The circumferential channels  62  and the transverse channel  64  have the same depth, preferably in the range from 0.1 to 1 mm. It is however also possible to provide different depths for the circumferential and transverse channels  62 ,  64 . The circumferential and transverse channels  62 ,  64  can for example be provided in suitable manner by means of laser machining, etching or milling in the substrate guide surface  30 . Thanks to the circumferential and transverse channels  62 ,  64  in the substrate guide surface  30 , surface elements  70  are created between the circumferential channels  62 . 
         [0047]    In the area of the intersection points of the circumferential channels  62  and the transverse channel  64 , a gas outlet opening  68  is provided in each case in the form of a passage opening that connects the interior of the hollow tube to the outside, as can be easily discerned in  FIG. 7 . The hollow tube defines in the interior a cavity  80  limited in the radial direction by the inner wall  82 . The gas outlet opening  68  extends here from the cavity  80  into the transverse channel  64  in the substrate guide surface  30 . The section shown in  FIG. 7  along the line B-B from  FIG. 6  also shows one of the many circumferential channels  62 . It can be readily discerned that the circumferential channel  62  extends over 180° in the circumferential direction of the turning element, corresponding in operation approximately to the wrapped area of a print material sheet  6 . 
         [0048]    The cavity  80  extends at first substantially over the entire length of the hollow tube. At its ends, the hollow tube can be closed in suitable manner by end walls. At least one gas inlet opening is provided for supplying the cavity with gas, in particular with compressed air, in the end walls and/or in a circumferential area of the hollow tube outside the substrate guide surface  30 . This in turn allows the gas outlet openings  68  to be supplied with a gas flow. 
         [0049]    In the longitudinal direction of the hollow tube, the cavity  80  can also be limited by respective slide elements (sliders), not shown. This permits a change in the cavity and hence a selective supply to gas outlet openings  68 , in order for example to apply gas only where the substrate sheet wraps around the turning element. A selective supply of this type is for example also possible by corresponding subdivisions of the cavity with individual gas supply to its subdivisions, for example via valves. Direct gas feed lines could also be provided for the individual gas outlets openings, which for example can be supplied with gas individually or in groups. 
         [0050]      FIG. 8  shows a schematic detailed view of an alternative continuous channel structure  100  in a substrate guide surface  30  of a turning element  20  in accordance with a second embodiment. The channel structure  100  can be designed in the form shown both in the area  32  in accordance with  FIG. 4  and in the areas  45  of  FIG. 5 . 
         [0051]      FIG. 8  shows a statistical distribution of one or more channels of the channel structure  100 , with the following relating to only one channel. The channel is continuous, i.e. designed such that every point inside the channel is connected via the channel to any other point in the channel. 
         [0052]    The distribution of the channel forming the channel structure  100  inside the substrate guide surface corresponds to a statistical distribution. The distribution of the channel structure  100  substantially follows a uniform distribution, but can have any required distribution. The channel forming the channel structure  100  has a depth of preferably 0.1 to 1 mm. 
         [0053]    Gas outlet openings  68  are again provided and each open into the channel of the channel structure  100 . The gas outlet openings  68  can also be statistically distributed in the substrate guide surface. The gas outlet openings  68  preferably have a diameter of 0.3 to 0.5 mm. 
         [0054]      FIG. 2  is intended to explain in greater detail the mode of operation of the turning unit  2  in accordance with the invention. 
         [0055]    A print material sheet  6  conveyed in a first sheet conveying direction is passed around the first fixed turning element  20  and deflected due to its alignment transverse to the entry direction of the print material sheet  6  into a second sheet conveying direction transverse to the first sheet conveying direction. Then it is deflected by the intermediate deflecting roller  22  into a third sheet running direction opposite to the second one and then passed around the second fixed turning element. The alignment of the latter transverse to the third sheet running direction of the print material sheet  6  deflects the latter into a fourth sheet conveying direction transverse to the third one. The first and the fourth sheet conveying directions have the same orientation, and the sheet is turned by the deflections such that the side originally on top is now facing downwards. 
         [0056]    During operation, gas, in particular air, is introduced into the respective cavity  80  in corresponding gas inlet openings of the turning elements  20 ,  24 . The gas thus supplied flows via the gas outlet openings  68  into the channel structure  60 ,  100  formed in the wrapped area of the substrate guide surface  30 . The gas spreads substantially evenly via the respective channels  62 ,  64  over the substrate guide surface  30  and forms a uniform air cushion between the substrate guide surface  30  and the print material sheet  6 . A gas flow thus distributed creates an air cushion which extends over the entire substrate guide surface  30 . The print material  6  is thus deflected with reduced friction into the respective second or fourth sheet conveying direction. By selective control of the areas  45  or also of individual gas outlet openings  68 , the gas flow can be limited substantially to the wrapping area of the print material sheet. 
         [0057]    The first and second turning elements  20 ,  24  are as already mentioned arranged fixed, so that the print material  6  is always passed around the same circumferential area of the turning elements  20 ,  24 . 
         [0058]    The turning unit can turn a print material sheet printed on one side in the print area  3  in the manner stated above and make it available for verso printing. 
         [0059]    The invention was described on the basis of preferred embodiments without being restricted to these.