Abstract:
In a device for reducing the frictional force between a guiding or carrying element for sheets in a sheet-processing machine, in particular rotary printing machines, guiding and carrying elements acted upon by throttled blowing air include a sheet surface, orifices fluidically connected to a hollow interior, and a throttle disposed in the hollow interior. The elements are to be connected to an air source for blowing air out through the orifices and for generating an air cushion between a sheet and the sheet surface. Each of the orifices is preceded by the throttle with respect to a direction of air from the air source.

Description:
BACKGROUND OF THE INVENTION  
       FIELD OF THE INVENTION  
         [0001]    The invention relates to a device for reducing the frictional force between a guiding or carrying element for sheets in a sheet-processing machine.  
           [0002]    It is disclosed in German Published, Non-Prosecuted Patent Application DE 25 05 762 B, corresponding to U.S. Pat. No. 3,951,401 to Marass, to employ for sheets or sheet stacks carrying bars that are used to carry an auxiliary stack, particularly in the case of nonstop feed or delivery. To reduce the frictional force between the carrying bars and the sheet stack, blowing air is blown into the spaces between the carrying bars located at a distance from one another. Seals prevent the blowing air from flowing out and assist the buildup of an appropriate dynamic pressure.  
         SUMMARY OF THE INVENTION  
         [0003]    It is accordingly an object of the invention to provide guiding and carrying elements with throttled blowing air that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that reduces frictional force between guiding and carrying elements and sheets of a sheet-processing machine by using blowing air.  
           [0004]    With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for reducing a frictional force between sheets and guiding and carrying devices for sheets in a sheet-processing machine including a sheet transporting element defining a hollow interior, the sheet transporting element having a sheet surface, orifices fluidically connected to the hollow interior, and a throttle disposed in the hollow interior, the sheet transporting element to be connected to an air source for blowing air out through the orifices and for generating an air cushion between a sheet and the sheet surface of the sheet transporting element, and each of the orifices preceded by the throttle with respect to a direction of air from the air source.  
           [0005]    One advantage of the invention is that additional sealing measures in the outer region of the sheet stack are no longer necessary.  
           [0006]    Throttled nozzles that are disposed directly on the top side and the underside of the carrying bars generate, at the surfaces of contact between carrying bar and sheet, a high dynamic pressure along with a low throughflow. Advantageously, therefore, only a little blowing air escapes from nozzles that are not covered.  
           [0007]    In accordance with another feature of the invention, throttled nozzles are used on so-called “separating shoes” that are disposed in the region of the front lay marks on the feed table. The separating shoes are guiding elements that are acted upon by blowing air and are disposed at a distance from one another transversely to the sheet transport direction such that the transporting and aligning device are disposed between the separating shoes. On an underside facing the sheet, the separating shoes have a number of orifices, from which throttled blowing air emerges, and the frictional force between the separating shoes and the sheet is, thus, reduced. Ideally, the sheet is guided, completely free of contact, below the separating shoes. It is advantageously proposed, furthermore, that cover marks be acted upon from inside by throttled blowing air that can emerge from orifices, in particular, on the top side of the cover marks, so that a sheet drawn by the front lay marks comes into contact as little as possible, preferably free of contact, with the cover marks.  
           [0008]    In accordance with a further feature of the invention, the throttle is a throttle section.  
           [0009]    In accordance with an added feature of the invention, the sheet transporting element is one of a sheet guiding element and a sheet carrying element.  
           [0010]    In accordance with an additional feature of the invention, the orifices are throttled air nozzles.  
           [0011]    In accordance with yet another feature of the invention, advantageously, the configuration of the throttled nozzles is such that each of the orifices is connected to an air pressure generator through an air throttle. The air throttle may be integrated into the air guidance system at a distance from the respective throttled air nozzle. However, the air throttle and the air nozzle throttled by the air throttle may form a structural unit in the form of a throttle nozzle. In the last-mentioned case, each of the throttled air nozzles is assigned its own air throttle. However, an air throttle may also be provided that is connected pneumatically to a plurality of throttled air nozzles simultaneously through the air guidance system.  
           [0012]    In accordance with yet a further feature of the invention, the air throttle has located in it, as its integral part, a so-called packing column, the small packing bodies of which form flow resistances for the suction or blowing air flowing through the air throttle and generated by the air pressure generator.  
           [0013]    In accordance with yet an added feature of the invention, the air throttle has located in it, as its integral part, a throttle piece, resembling an air filter, which forms a flow resistance for the suction or blowing air. For example, the throttle piece is a textile layer that may be woven or nonwoven. However, the throttle piece may also be a porous and, therefore, air-permeable sponge that is foamed from a plastic.  
           [0014]    In accordance with yet an additional feature of the invention, the air throttle is fitted with air barriers that project into the flow path of the suction or blowing air and that delimit swirl chambers that are disposed between each of the projecting air barriers.  
           [0015]    In accordance with again another feature of the invention, the air throttle is configured as a so-called perforated-plate labyrinth. The plates are disposed one above the other and swirl chambers are disposed between each of the perforated plates.  
           [0016]    In accordance with again a further feature of the invention, the throttle is a spiral air duct.  
           [0017]    In accordance with again an added feature of the invention, the throttled air nozzles are blowing nozzles.  
           [0018]    In accordance with again an additional feature of the invention, the orifices are blowing nozzles.  
           [0019]    With the objects of the invention in view, there is also provided a device for reducing a frictional force between sheets and an auxiliary stack table for sheets in a feeder of a sheet-processing machine including a rake bar defining a hollow interior. The rake bar has a sheet surface, orifices fluidically connected to the hollow interior, and a throttle disposed in the hollow interior. The rake bar is connected to an air source for blowing air out through the orifices and for generating an air cushion between a sheet and the sheet surface of the rake bar. Each of the orifices is preceded by the throttle with respect to a direction of air from the air source.  
           [0020]    With the objects of the invention in view, there is also provided a device for reducing a frictional force between sheets and an auxiliary stack table for sheets in a delivery of a sheet-processing machine including a rake bar defining a hollow interior. The rake bar has a sheet surface, orifices fluidically connected to the hollow interior, and a throttle disposed in the hollow interior. The rake bar is connected to an air source for blowing air out through the orifices and for generating an air cushion between a sheet and the sheet surface of the rake bar. Each of the orifices is preceded by the throttle with respect to a direction of air from the air source.  
           [0021]    With the objects of the invention in view, there is also provided a sheet-fed rotary printing machine including sheet guiding and carrying devices and a sheet transporting element for reducing a frictional force between sheets and the guiding and carrying devices. The sheet transporting element cooperates with the sheet guiding and carrying devices to convey sheets in a printing machine. The sheet transporting element defines a hollow interior. The sheet transporting element has a sheet surface, orifices fluidically connected to the hollow interior, and a throttle disposed in the hollow interior. The sheet transporting element is connected to an air source for blowing air out through the orifices and for generating an air cushion between a sheet and the sheet surface of the sheet transporting element. Each of the orifices is preceded by the throttle with respect to a direction of air from the air source.  
           [0022]    Other features that are considered as characteristic for the invention are set forth in the appended claims.  
           [0023]    Although the invention is illustrated and described herein as embodied in guiding and carrying elements with throttled blowing air, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0024]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a diagrammatic cross-sectional view of a sheet-processing machine according to the invention;  
         [0026]    [0026]FIG. 2 is a diagrammatic cross-sectional view of a rake bar for carrying a sheet stack of FIG. 1;  
         [0027]    [0027]FIG. 3 is a diagrammatic cross-sectional view of a separating shoe and a cover mark in the region of the front lay marks of FIG. 1; and  
         [0028]    [0028]FIG. 4 is a fragmentary, cross-sectional view of an embodiment of the air throttle of FIG. 2;  
         [0029]    [0029]FIG. 5 is a fragmentary, cross-sectional view of a second embodiment of the air throttle of FIG. 2;  
         [0030]    [0030]FIG. 6 a  is a fragmentary, cross-sectional plan view of a third embodiment of the air throttle of FIG. 2;  
         [0031]    [0031]FIG. 6 b  is a fragmentary, cross-sectional side view of the embodiment of FIG. 6 a;    
         [0032]    [0032]FIG. 7 a  is a fragmentary, cross-sectional plan view of a fourth embodiment of the air throttle of FIG. 2;  
         [0033]    [0033]FIG. 7 b  is a fragmentary, cross-sectional side view of the embodiment of FIG. 7 a;  and  
         [0034]    [0034]FIG. 8 is a fragmentary, cross-sectional view of a fifth embodiment of the air throttle of FIG. 2. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Related applications having the Application Serial Nos. (Attorney Docket Nos. A-2905, A-2935, and A-2936) are hereby incorporated herein by reference.  
         [0036]    Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a rotary printing machine, for example, a sheet-processing printing machine  1  having a feeder  2 , at least one printing unit  3 ,  4 , and a delivery  6 . The sheets  7  are taken from a sheet stack  8  and fed, individually or imbricated, to the printing units  3 ,  4  through a feed table  9 . These printing units each contain a conventional plate cylinder  11 ,  12 . The plate cylinders  11  and  12  each have a device  13 ,  14  for fastening flexible printing plates. Furthermore, each plate cylinder  11 ,  12  is assigned a device  16 ,  17  for the semiautomatic or fully automatic change of a printing plate.  
         [0037]    The sheet stack  8  lies on a stack plate  10  capable of being raised in a controlled manner. The sheets  7  are taken from the top side of the sheet stack  8  by a so-called suction head  18  that has inter alia a number of lifting and dragging suckers  19 ,  21  for the individual separation of the sheets  7 . Moreover, a blowing device or means  22  for loosening the upper sheet layers and tracer elements  23  for stack tracking are provided. A number of lateral and rear stops are provided for the alignment of the sheet stack  8 , in particular, of the upper sheets  7  of the sheet stack  8 .  
         [0038]    After the processing of the sheets  7 , the sheets  7  are deposited onto a depositing stack  24  in the delivery  6 . New sheet stacks  8  must be fed to the feeder  2  and the sheet stacks  24  of the delivery  6  must be removed so that printing can be carried out without interruption. Holding elements in the form of rake bars  27  disposed parallel and next to one another are provided so that the respective remaining stacks  26  can be carried. The rake bars  27  have a number of blowing orifices  28 , out of which throttled blowing air flows, so that the rake bars  27  can be pushed in between the sheet layers with little effort. The throttled blowing air has the effect that an air cushion that reduces the frictional force between sheet and rake bar  27  is built up in the vicinity of the surface of the rake bars  27 . Due to the use of throttled blowing air, only a little blowing air flows out of the blowing orifices  28 . Thus, even when the rake bar  27  is pushed in, when still not all the blowing orifices  28  are covered, a sufficiently high air pressure prevails at the orifices  28  of the rake bar  27  that are covered by the sheets. A common blowing-air source  29  supplies the rake bars  27  disposed next to one another through a common hollow crossmember  31 .  
         [0039]    In a second exemplary embodiment, pivotable front lay marks  33  are provided at a front edge  32  of the feed table  9 , at which the sheets  7  are aligned in the circumferential direction. Furthermore, a pregripper  34  picks up the aligned sheets  7  by its pregripper gripper  36  and transfers them onto a first sheet-guiding cylinder of the printing machine  1 . A number of pivotable cover marks  37 , disposed parallel and next to one another with clearances, prevent a sheet  7  from shooting over the front lay marks  33  during alignment. Disposed parallel and next to one another in the clearances between the cover marks  37  are a number of guiding bars  38 , otherwise referred to as “separating shoes”, which form a guide for the sheets  7  transported by the pregripper  34  and, thus, prevent a sheet  7  from being overturned during its transport from the feed table  9 . Thus, a sheet  7  is led through between a top side of the cover marks  37  and an underside of the separating shoes  38 . To reduce the frictional force between the sheets  7  and the cover marks  38  or separating shoes  38 , they are acted upon from inside by throttled blowing air from a blowing-air source  40 , which can flow out of correspondingly disposed blowing orifices  39 ,  41 . In such a case, the throttled blowing air forms, particularly in the vicinity of the top side of the cover mark  37  and of the underside of the separating shoes  38 , a high-pressure air layer, at the same time with a low volume flow. The air layer reduces the frictional force between the sheet  7  and the separating shoes  38  or cover marks  37  to such an extent that the sheets  7  are ideally guided free of contact. Undesirable marking, particularly on already preprinted sheets  7 , is, thus, avoided.  
         [0040]    To generate throttled blowing air at the orifices  28  of the rake bars  27 , the orifices  41  of the separating shoes  38  and the orifices  39  of the cover marks  37 , the following air throttles are proposed. Components marked by reference symbols  47  to  51  explained in detail in FIG. 4 are also found again in the variants of the air throttles  516 ,  616 ,  716 ,  816  illustrated in FIGS.  5  to  8 , thus, the reference symbols  47  to  51  in FIGS.  5  to  8  are used again without further explanation. In the variant of the air throttle  516 , as shown in FIG. 5, the packing  52  of FIG. 4 is replaced by a textile throttle piece  54 , such as, for example, a woven or a nonwoven fabric, inserted into the throttle chamber  51 . To fill the throttle chamber  51  from the throttle bottom  50  to the throttle top  48  with the throttle piece  54 , the throttle piece  54  may be made of a single sufficiently bulky layer or be wound up into a multilayered insert or be stretched open in the throttle chamber  51 . The blowing air flowing through the throttle piece  54  is throttled as a result of accumulations of threads or fibers and of turbulences in pores of the throttle piece  54 .  
         [0041]    [0041]FIGS. 6 a  (a horizontal section along the sectional line VIa-VIa in FIG. 6 b ) and  6   b  (a vertical section along the sectional line VIb-VIb in FIG. 6 a ) illustrate an air throttle  616 , the air guide walls  55  and  56  of which are disposed orthogonally together in the throttle chamber  51 , so that an air duct  57  in the form of a polygonal spiral, guiding the blowing air between the air guide walls  55  and  56  from the throttle inlet  47  to the throttle outlet  49 , is obtained. The suction or blowing air flowing through the air duct accumulates in corner angles  58 ,  59  of the air duct  57  and swirls at corner edges  60 ,  61  of the air guide walls  55  and  56 , so that the airstream is throttled. The air guide walls  55 ,  56  have very high surface roughness that is brought about, for example, by sandblasting, that contributes to reducing the flow velocity of the blowing air in the air duct  57  by an increase in friction.  
         [0042]    In the case of the air throttle  716  - cf. FIG. 7 a  (a horizontal cross-section) and  7   b  (a vertical cross-section), the throttle chamber  51  is fitted with air barriers  62 ,  63  in the form of baffle walls. The air barriers  62 ,  63  are disposed alternately in two rows and so as to overlap one another with the exception of narrow air gaps  64 ,  65 . Located between the air barriers  62 ,  63  are swirl chambers  74 ,  75  that, together with the air gaps  64 ,  65 , form a meanderlike air duct that leads from the throttle inlet  47  to the throttle outlet  49  and in which the blowing air is throttled.  
         [0043]    [0043]FIG. 8 illustrates a cross-section through the air throttle  816  that is made of perforated plates  68 ,  69  disposed one above the other in a sandwich form of construction in the throttle chamber  51 . Each of the perforated plates  68 ,  69  has at least one hole  70 ,  71  that is disposed in the plate plane so as to be offset to at least one hole  71 ,  70  of the respectively adjacent perforated plate. The holes  70 ,  71  are, thus, out of alignment with one another and overlap with closed plate surfaces of the perforated plates  68 ,  69 . The spacer pieces  72 ,  73  hold the perforated plates  68 ,  69  at a distance from one another and define volumes of swirl chambers  74 ,  75  that are located between the perforated plates  68 ,  69  and through that the blowing air flows. The blowing air flows accumulate in front of the holes  70 ,  71  constituting narrow points in the flow path and swirls in the swirl chambers  74 ,  75 . The throttling action of the air throttle  816  is based, in exactly the same way as the throttling action of the air throttles  616  and  716 , on a reduction in the flow velocity of the blowing air by a multiple deflection of the air flow in the throttle chamber  51 .  
         [0044]    Further advantages are provided by the invention. In the case of the combination of the air throttle  416 ,  516 ,  616 ,  716 , or  816  with an orifice  28 ,  39 ,  41 , the air throughflow becomes so small that, on one hand, large quantities of blowing air do not have to be discharged and, on the other hand, too much air cannot escape in the case of orifices that are not covered. A blowing force is exerted on the print carrier sheet by the throttled blowing nozzle, which, with an increasing distance of the sheet from the blowing nozzle, decreases more than linearly. Thus, a desirable, much thinner air cushion can be generated between an orifice  28 ,  39 ,  41  provided with the throttled blowing nozzle, for example, on the surface of the rake bar  27 , the cover mark  37 , or separating shoe  38  of the sheet  7 , than is possible with conventional, in other words, unthrottled blowing nozzles.