Abstract:
A device and a method for raising and positioning an object, for example a sheet from a sheet stack, uses a whirlwind to generate a negative pressure for generating a retaining force and uses interference air for releasing the retaining force.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2014 001 756.7, filed Feb. 10, 2014; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a device and a method for suctioning a sheet, in particular for separating a sheet from a sheet stack. The invention also relates to a sheet-fed rotary printing machine and a punch having the device. 
     In feeders of machines for processing sheets, so-called suction heads are typically used for separating sheets from a sheet stack. 
     European Patent EP 0 734 983 B1, corresponding to U.S. Pat. No. 5,685,534, provides suction cups which are to be impinged or charged with suction air, which grasp the sheet and which are driven by a suction-element drive to transfer the sheet to a downstream conveying belt. The suction cups are supplied with suction air in a centralized manner from a suction-air generator. 
     German Utility Model DE 20 2011 107 531 U1, corresponding to International Publication No. WO 2013/068307 A1, shows a device for lifting an object, wherein the object clings to a housing by using a suction force. The suction force is generated directly in the housing by a rapidly rotating impeller. An adjustable aperture which is disposed on the housing is provided for releasing the retaining force. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a device and a method for suctioning a sheet from a sheet stack and positioning an object and a sheet-fed rotary printing machine and a punch having the device, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices, methods, printing machines and punches of this general type and in which a retaining force is generated by an impeller and releasing the retaining force is controllable pneumatically. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a device for suctioning and positioning an object. The device comprises a housing having a suction opening formed therein, a device disposed in the housing for generating a negative pressure using a whirlwind for suctioning the object, and the housing having at least one flow duct for supplying or discharging interference air centrally into an interior of the whirlwind. 
     With the objects of the invention in view there is concomitantly provided a method for suctioning and positioning an object. The method comprises providing a housing having a suction opening formed therein, having at least one flow duct formed therein and having a ventilating device disposed therein, generating a negative pressure using the ventilating device creating a whirlwind suctioning the object through the suction opening, and supplying or discharging interference air through the at least one flow duct centrally into an interior of the whirlwind to disrupt the suctioning of the object. 
     It is a particular advantage of the invention that a tornado module which is configured by using an impeller is controllable in a pneumatic manner at a predetermined operational cycle rate, for example at the cycle rate of a machine processing sheets. In this case, a clocked interference air, for example a blown air or a suction air, is directed counter to the whirlwind generated by the impeller for suctioning an object, for example a sheet, in such a way that a previously generated negative-pressure area collapses. 
     The clocked interference air may be controlled by a rotary valve or solenoid valves. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a device for suctioning a sheet from a sheet stack and a sheet-fed rotary printing machine and a punch having the device, it is nevertheless not intended to be limited to the details shown, since 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. 
     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 SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic, longitudinal-sectional view of a sheet-fed rotary printing machine; 
         FIG. 2  is an enlarged, vertical-sectional view of a tornado module according to the invention, having central interference air; 
         FIG. 3  is a vertical-sectional view of a tornado module having lateral interference air; 
         FIG. 4  is a vertical-sectional view of a tornado module having a plurality of interference air supply ducts; and 
         FIG. 5  is a vertical-sectional view of a tornado module having suction ducts. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a machine, for example a printing machine  1 , for processing sheets  7 , having a feeder  2 , at least one respective printing unit  3  and  4  and a delivery  6 . The sheets  7  are removed from a sheet stack  8  and separated or fed in an imbricate manner over a feed table  9  to the printing units  3  and  4 . The printing units  3  and  4  each contain a plate cylinder  11 ,  12 , in a known manner. The plate cylinders  11  and  12  in each case have a device  13 ,  14  for fastening flexible printing plates. Moreover, each plate cylinder  11 ,  12  is assigned a device  16 ,  17  for semi-automatically or fully automatically changing printing plates. 
     The sheet stack  8  lies on a main stack plate  10  which can be raised in a controlled manner. Removal of the sheets  7  takes place from the upper side of the sheet stack  8 , by using at least one gripper  18  which can be pneumatically charged. Moreover, blowing devices for loosening upper sheet layers are provided with sensing elements for stack tracking. A number of lateral and rear stops are provided for orienting the sheet stack  8 , in particular the upper sheets  7  of the sheet stack  8 . 
     According to  FIG. 2 , the pneumatic gripper  18  is composed substantially of a housing  19  in which a rapidly rotating impeller  21  is disposed. The housing is configured so as to be open toward the bottom, in the direction of the object to be raised, for example a sheet  7  to be separated or singularized, in such a way that a first air circuit (whirlwind) which is generated by the impeller  21  and which corresponds to a tornado whirlwind can be generated. The first air circuit  22  itself generates a second air circuit  23 , by way of which a negative-pressure area  24  is generated. 
     The negative-pressure area  24  is utilized for suctioning and retaining the sheet  7 . 
     In order to release the suction force and thus to let go of the sheet  7 , the air circuits  22 ,  23  are interrupted by regulated interference air  26  (for example, blowing air). Due to this measure, the negative-pressure area  24  collapses and the sheet  7  is surrendered by the gripper  18 . 
     In the case of the exemplary embodiment according to  FIG. 2 , the interference air  26  is supplied centrally into the interior of the tornado or first air circuit  22  by using a flow duct  28  which is disposed in a drive shaft  27  of the impeller  21 . The interference air  26  is thus directed counter to the rotational direction of the second air circuit  23 , due to which the negative-pressure area  24  is cancelled or released. 
     A second exemplary embodiment according to  FIG. 3  provides for two interference air flows  28  which are directed counter to the second flow circuit  23  to be generated. The two interference air flows  28  are supplied to the housing  19  by using laterally disposed flow ducts  25 ,  30 . 
     In the case of the exemplary embodiment according to  FIG. 4  it is provided that two interference air flows  32 ,  33  are supplied to the housing  19  in a decentralized manner. The interference air flows  32 ,  33  make their way through passage arcs or conduits  34 ,  35  into the effective region of the impeller  21 , in such a way that the second flow circuits  23  which are generated by the latter are disturbed, due to which the negative-pressure area  24  collapses. 
     An exemplary embodiment according to  FIG. 5  provides for suction air to be used as interference air  36 , for example. In this case, the lateral flow ducts  25 ,  30  are impinged upon by suction air, due to which the second air flow circuit  23  is disturbed, in such a way that the negative-pressure area  24  collapses. 
     In all of the exemplary embodiments according to  FIGS. 2 to 5  it is provided for the interference air (suction air  36 , blowing air  26 ) to be made available in a clocked or timed manner, in particular at the cycle rate of the machine  1  processing the sheets. Rotary valves or control valves operating with solenoids are particularly suitable for generating clocked or timed air flows, as illustrated in  FIG. 4 . 
     The use of the device described above on a machine for processing sheets is particularly advantageous for retaining and separating sheets from a sheet stack, for example of a sheet-fed rotary printing machine  1 , a punch, or a folding machine.