Abstract:
A method for controlling the feed of sheets to a sheet-fed printing press is provided for a sheet feeder unit comprising an individual drive assigned to each of a plurality of components provided for supplying the sheets in a stack, separating the sheets from a stack and supplying the sheets to the press. The method includes stopping at least two of the individual drives in a predefined position in a targeted manner when shutting down the feeder unit. The individual drives are operated in synchronization with one another during printing operation. The synchronization between the at least two individual drives is canceled when the sheet feeder unit is shut down. These drives are shut down individually and synchronized with one another when the sheet feeder unit is started up again such that in shutdown, each individual drive assumes a predefinable position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Patent Application Serial No. 102007051945.3 filed Oct. 31, 2007, the entirety of which is incorporated herein by reference thereto. 
     BACKGROUND 
     The invention relates to a method for controlling the feed of sheets to a sheet-fed printing press having a sheet feeder comprising multiple components, each component being assigned an individual drive and these components being provided for supplying the sheets in a sheet stack, for separating the sheets from a sheet stack and for feeding the sheets to the sheet-fed printing press. 
     DE 195 05 560 A1 discloses a method for controlling the sheet feed in a sheet processing printing press. In this printing press, the sheets to be printed are taken from the top of a feeder unit stack and conveyed to the installation of the printing press over a predefined conveyor path. At the beginning of the conveyor path, a sheet inspection is performed with regard to double sheets and defective sheets and the sheet conveyance is stopped, depending on the result of the sheet inspection. On detection of a double sheet or defective sheet, withdrawal of additional sheets from the feeder unit stack is stopped immediately and the number of sheets that can still be conveyed into the printing press and printed there before the double sheet or defective sheet in the direction of sheet on the conveyor path reaches the front mark of the installation conveyance is determined. The ink feed is stopped even before the last sheet situated upstream from the double sheet or defective sheet in the direction in conveyance of the sheet enters the printing press. After withdrawal of a sheet from the feeder unit stack has been stopped, sheet conveyance is stopped exactly when the double sheet or defective sheet has reached the installation. Then the number of sheets yet to be fed into the printing press is determined from the distance between the installation and the sheet inspection in combination with the degree of underfeeding in the case of underfed sheet feeding and the format length of the sheets. 
     One disadvantage of this approach is that in shutdown of the sheet conveyor belt, the underfed sheets may be displaced with respect to one another and cannot approach the printing press again in this state without problems. 
     EP 1 281 647 B1 therefore presents a method for conveying sheets in a sheet feeder unit of a sheet processing machine by means of which this disadvantage is to be avoided. With this printing press, the rate of travel of the conveyor belt for conveying the fed sheets is variable, independent of the operating speed of the machine in accordance with the predefined speed profiles, so that when starting or stopping of the feeder unit, the conveyor belt can be stopped and/or started in accordance with a predetermined acceleration profile. 
     DE 102 16 135 A1 discloses a method for controlling the sheet feed to a sheet processing machine having a sheet feeder unit which comprises, among other things, a sheet separator for separating the sheets from a stack and a table with belts or a suction table with belts. The sheets are conveyed to the machine and inspected with regard to double sheets, defective sheets or skewed sheets. If there is such a sheet or if there is a disturbance in the downstream machine, the sheet feed is stopped, in which a sampling device that detects the height level of the stack is provided and the drive of the sheet feeder unit is provided by individual drives, which are controlled by means of an electronic processing unit that is connected to a control unit of the downstream machine. After breaking the connection between the electronic processing unit and the machine control unit, the synchronization of the individual drives is eliminated, so that the individual drives can be operated at will. The individual drives may also be operated optionally in different directions of rotation or brought to a standstill. 
     This process takes places directly on stoppage of the feeder unit. The disadvantage here is that other driven components of the feeder unit are stopped in an undefined position which makes renewed startup difficult. 
     Therefore, the object of the present invention is to develop a method by means of which at least two drives of components of the feeder unit are brought to a standstill in a defined position in a targeted manner when the feeder unit is shut down. 
     SUMMARY 
     According to the invention, this object is achieved by a method for controlling the feed of sheets to a sheet-fed printing press with a sheet feeder unit comprising multiple components such that these components are provided for supplying the sheets in a stack for separating the sheets from the stack and for conveying the sheets to the feeder printing mechanism of the sheet-fed printing press. An individual drive is assignable to each of these components. These individual drives are operable in synchronization with one another during the printing by the sheet-fed printing press. The synchronization between at least two individual drives is eliminated when the sheet feeder is shut down, wherein these individual drives are shut down individually and synchronized in relation to one another again in resuming operation of the sheet feeder unit such that they assume a predefinable position for each individual drive when the individual drives are shut down. 
     The invention has the advantage that an optimal stop point is achieved for the components of the sheet feeder so that operation can be resumed without problems. 
     The invention will now be explained in greater detail below on the basis of an exemplary embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a sheet-fed printing press formed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The respective drawing shows a sheet feeder unit  1  with a table with belts  2 . The table with belts  2  is designed as a suction table with belts  2 . 1 . The inventive approach is explained on the example of a sheet feeder unit  1  with a suction table with belts  2 . 1 , in which sheets  8  are held by vacuum on suction belts  26 . 1 , such that the inventive approach may also be implemented on a sheet feeder unit  1  with a table with belts  2  in which the sheets  8  are guided in a known way through pressure rollers arranged on a rod grating against conveyor belts  26  of the table with belts. A feeder table  3  with front marks  4 , a vibrating system  5  and a feed cylinder  6  of a feed printing mechanism  7  of a sheet-fed printing press are arranged downstream from the suction table with belts  2 . 1 . 
     The sheet feeder unit  1  consists of multiple components, each component being assigned an individual drive  19 ,  28 ,  31 . 
     A stack  9  consisting of the sheets  8  is positioned on a stack plate  10  in the sheet feeder unit  1 . The stack plate  10  is attached to conveyor means  11 , which are connected to a lift (not shown). A sheet separator  12  is assigned as an additional component to the top of the stack  9 . The sheet separator  12  has separation suction cups  13  and conveyor suction cups  14  as well as undercut edge stops  15 . The sheet separator  12  is provided so that it is adjustable in height by means of an actuator drive  16  in the sheet feeder unit  1 . In addition, the sheet separator  12  may be displaced in or against a direction of conveyance  17  for adaptation of the format. In the exemplary embodiment, a sampling device  18  is assigned to the sheet separator  12  to detect the height level of the stack  9 . The sampling device  18  may also be provided at any other location on the sheet feeder unit  1 . The sheet separator  12  is driven by means of a first individual drive  19 , which may be designed as an electric motor, for example. Blowers  36  are also provided on the rear side and optionally on the sides of the stack  9  for predrying the sheets  8  on the stack  9  and for blowing under the sheets  8  during conveyance. To be able to form an air cushion that will support the sheets  8 , side plates  20  are arranged on the sides of the stack  9 . However, it is also possible to assign laterally bordering guide elements  20 . 1  to the stack  9 . 
     On the front side of the stack  9 , a shaft  21  extends over the width of the stack  9  as an additional component of the sheet feeder unit  1 , its drive being provided by a third individual drive  31 . Downstream from this a blow pipe  22  whose direction of blowing runs approximately opposite a direction of conveyance  17 . 
     The suction table with belts  2 . 1  as an additional component of the sheet feeder unit  1  comprises a drive roller  23  and a reversing roller  24 , between which a suction box  25  is provided, at least one suction belt  26 . 1  being wrapped around the rollers  23 ,  24 . The suction belt  26 . 1  is put under tension by tension rollers  27 . The suction belt  26 . 1  is provided with suction openings in a known way, coming into operative connection with suction bores provided in the suction box  25  in their movement in the direction of conveyance  17 , driven by the drive roller  23 . The drive roller  23  is driven by a second individual drive  28 , e.g., an electric motor. Stepping wheels  29  correspond to the drive roller  23  and are controlled periodically against the drive roller  23  within an operating cycle. 
     The front marks  4  are controlled into an operating position against the feeder table  3  downstream from the suction table with belts  2 . 1  from a catch position beneath the feeder table  3 . An inspection device  32  is provided for the feeder table  3 . The vibrating system  5  arranged downstream from the feeder table  3  has a sheet holding system  30  and executes a pivoting movement between the feeder table  3  and the feeder cylinder  6  of the feeder printing mechanism  7 . 
     The individual drives  19 ,  28 ,  31  that drive the sheet separator as well as the sheet conveyor means, the actuator drive  16  and the inspection device  32  are connected to an electronic processing unit  33  of the sheet feeder unit  1  which is in turn connected to a control unit  34  of the downstream sheet-fed printing press. The sheet feeder unit  1  is readjusted in synchronization with the sheet-fed printing press via the machine control unit  34  and the electronic process unit  33 . 
     To do so, a rotary angle sensor  35  may be assigned, for example, to the feed cylinder  6 , which is connected to the machine control unit  34 . The individual drives  19 ,  28 ,  31  run in synchronization with one another over 360° of a single-turn shaft as well as within a unit of time. 
     In synchronized readjustment of the sheet feeder unit  1 , the top sheet  8  is separated from the stack  9  by the separating suction cups  13  driven by the first individual drive  19  assigned to the sheet separator  12  and is transferred to the conveyor suction cups  14  which convey the separated sheets  8  in the direction of conveyance  17 . The separation of the sheets  8  is supported by the fact that the stack  9  is loosened by blowers  36  and air is blown by the additional blowers  36  under the respective sheets  8  conveyed by the conveyor suction cups  14 . The sheets  8  conveyed by the conveyor suction cups  14  are guided by the stepping wheels  29  that make contact in cycles against the drive roller  23  and are then released by the conveyor suction cups  14 . The shaft  21  driven by the third individual drive  31  is pivoted out of the path of the sheets  8  and the blowing air feed to the blow pipe  22  is interrupted. The sheets  8  guided by the stepping wheels  29  against the drive roller  23  are picked up by the suction belts  26 . 1 , which are constantly being acted upon by a vacuum via the suction box  26 , and then are conveyed as a stack of sheets onto the feeder table  3  and with the front edge toward the front marks  4  in the working position. In the exemplary embodiment, an inspection device  32  which detects the sheets  8  is provided for the feeder table  3 . It is also possible to provide multiple measurement devices that inspect the sheets  8  and distribute them over the path of the sheets  8  as they travel from the sheet feeder unit  1  to the front marks  4 . 
     If no sheets  8  that are subject to defects are detected by the inspection device  32 , then the sheet  8  in contact with the front marks is transferred by the sheet holding system  30  of the vibrating system  5  and conveyed to the feed cylinder  6  whereby the front marks  4  are pivoted into their position beneath the feeder table  3 . If a sheet  8  subject to defects is detected by the inspection device  32 , a signal is supplied from the inspection device  32  to the electronic processing unit  33  and the synchronization between at least two individual drives  19 ,  28 , 31  is canceled thereby. In the exemplary embodiment, these include the first individual drive  19  and the second individual drive  28 . It is also possible to eliminate the synchronization of all individual drives  19 ,  28 ,  31 . 
     The individual drives  19 ,  28  are shut down individually. The conveyor belt  26  is stopped within the shortest possible amount of time in a process that is optimized for acceleration. This takes place in such a way that the conveyor belt  26  experiences a negative acceleration when stopped such that it comes to standstill in a technologically minimal time while maintaining the distance between the sheet  8  of the stack of sheets. 
     In shutdown of the individual drives  19 ,  28 , they assume a position predefined for each individual drive  19 ,  28 . Thus, for example, the sheet separator  12  moves into a position which allows it to start up again with no problem. The goal here is for the sheet separator  12  to reach this predefinable position within a technologically minimal amount of time. The sheet separator  12  may move in the direction of conveyance  17  or opposite the direction of conveyance  17 . 
     After removing the defective sheet  8  from the feeder table  3 , removal of the sheets  8  on the suction table with belts  2 . 1  is initiated by a startup signal supplied manually to the electronic processing unit  33 . In doing so the blowing air and suction air supply to the sheet separator  12  as well as the blowing air supplied to the blowers  36  are interrupted and the blow pipe  22  is acted upon by blowing air. 
     When the sheet feeder unit  1  is started up again, the first individual drive  19  and the second individual drives  28  are synchronized with one another again. The actuator drive  16  of the sheet separator  12  is lowered into its working position, the suction air and blowing air supplied to the sheet separator  12  and the blowing air supplied to the blowers  36  are activated and the blowing air supplied to the blow pipe  22  is interrupted. At the same time, the individual drives  19 ,  28  are activated such that the original direction of rotation of the second individual drive  28  is restored, so that the sheets  8  are removed from the stack  9  in the direction of conveyance  17  and can be sent to the front marks  4 . After aligning the first sheet  8  with the front marks  4 , the connection between the electronic processing unit  33  and the machine control unit  34  is restored and the sheet feeder unit  1  is connected to the suction table with belts  2  within one working cycle. 
     The present invention is not limited just to the exemplary embodiment described above. Other components of the sheet feeder unit  1 , not specified in the exemplary embodiment but provided with individual drives, may be operated in the manner described here.