Abstract:
An apparatus for depositing sheets onto a stack permits improved alignment of the sheets on the stack. At least one conveying element provides for cyclical forward movement of the sheets into a position above the stack. At least one reciprocating aligning element is provided for stacked sheets. A device for controlling movements of the aligning element includes a computer. At least one linear actuator moves the aligning element and may be controlled by the computer.

Description:
BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0001]     The invention relates to an apparatus for depositing sheets onto a stack, including at least one conveying element for the cyclical forward movement of the sheets into a position above the stack. At least one reciprocating aligning element moves stacked sheets. A device for controlling the movements of the aligning element includes a computer.  
         [0002]     German Published, Non-Prosecuted Patent Application DE 198 06 100 A1 discloses a configuration for controlling two or more sheet joggers in the delivery of a sheet-fed printing press. In that configuration, a stop plate is moved to and fro or reciprocatingly periodically with a pneumatic drive. Time profiles of the movements of the stop plate are adapted to different parameters, such as machine speed, format, printing material and subject. A control valve serves as an actuating element for the pneumatic drive. An instant for actuation of the control valve, synchronously with the machine, is calculated by using a computer that accesses memories in which characteristic curves are stored which contain parameters that influence the depositing behavior. In that apparatus, the instant for the actuation of the control valve is set by using the fixed characteristic curves, with the movement sequence remaining uninfluenced.  
         [0003]     In an apparatus for forming a sheet stack in the delivery of a sheet-fed printing press according to German Published, Non-Prosecuted Patent Application DE 196 27 241 A1, corresponding to U.S. Pat. No. 5,890,713, vibratory plates are suspended so as to oscillate freely, for example on springs, and are connected to an oscillation exciting device which oscillates independently of the delivery cycle. The vibratory plates are coupled to the oscillation exciting device in a contactless manner. A plunger-type coil serves as an oscillation exciting device. The plunger-type coil operates at a fixed oscillation frequency which lies in the vicinity of, but not exactly at, the resonant frequency of the elastically suspended vibratory plate. The movement profile is substantially sinusoidal due to the suspension and remains unchanged.  
         [0004]     In a delivery of a sheet-fed printing press according to German Published, Non-Prosecuted Patent Application DE 34 13 179 A1, it is possible to switch over the movement of a sheet jogger with a computer and stored characteristic curves from an individual stroke per sheet to a vibratory movement. A characteristic curve is selected by using input data relating to the weight of the paper, the sheet format and the rotational speed of the sheet-fed printing press. The profile of the movement of the sheet jogger in the individual stroke mode and in the vibratory mode is stipulated fixedly.  
         [0005]     German Patent DE 196 16 422 C1 describes a device for controlling lateral stops in sheet delivery systems of sheet-fed printing presses. In that device, the instant of the action of a lateral stop on the sheet is varied by hand as a function of the specific conditions of the sheet to be deposited, by displacing a rotary slide supplying the lateral stops periodically with compressed air. The movement sequence remains constant during the action of the lateral stop.  
         [0006]     In a stacking device for sheet-fed printing presses according to German Published, Non-Prosecuted Patent Application DE 29 42 855 A1, a drive for a vibratory device is configured as an electromagnetic oscillator, having an oscillation frequency which is reduced considerably via a control device, as compared with the mains frequency. In one variant, the oscillation frequency is superimposed by the mains frequency, with the result that, in addition to slow stroke movements, rapid vibratory movements are produced on vibratory plates. Linear vibrators having an exciter winding and an armature shaft which are coupled to the vibratory plates can be used as an oscillator. The to and fro or reciprocating movement of the vibratory plates is produced by superimposing two approximately sinusoidal movements.  
         [0007]     German Published, Non-Prosecuted Patent Application DE 40 01 565 A1 shows a sheet delivery of a sheet-fed printing press, in which a sheet stop is activated as a function of parameters, in particular operating parameters, that influence the sheet depositing behavior. The parameters are fed to a computer and used to form actuating signals for the actuation of the sheet stop. The actuating signals lead to a defined retardation of the movement sequence of the sheet stop, with the movement sequence itself remaining unchanged.  
         [0008]     In an apparatus for sample sheet removal at a delivery of a sheet-fed printing press according to German Published, Non-Prosecuted Patent Application DE 198 08 310 A1, a sheet stop can be displaced into a second stop position which is set away from the sheet stack. The sheet delivery can be set in such a way that the front edge of a sample sheet is conveyed as far as the sheet stop which is set away from the sheet stack, and the sheet stop can be displaced from the second stop position into a removal position. The sheet stop is seated fixedly in the respective stop position.  
       SUMMARY OF THE INVENTION  
       [0009]     It is accordingly an object of the invention to provide an apparatus for depositing sheets onto a stack, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which permits improved alignment of the sheets on the stack.  
         [0010]     With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for depositing sheets onto a stack. The apparatus comprises at least one conveying element for cyclical forward movement of the sheets into a position above the stack. At least one reciprocating aligning element is provided for stacked sheets. A device, including a computer, controls movements of the at least one aligning element. At least one linear actuator, to be controlled by the computer, moves the at least one aligning element.  
         [0011]     According to the invention, at least one linear actuator which can be controlled by a computer is provided to move an aligning element for sheets. It is thus possible to move the aligning element according to a movement profile which can be defined freely, with the result that the stack formation is improved. The movement of the aligning element can be synchronized with respect to the phase relation of a machine which delivers the sheets and in relation to other settings of the machine. The computer-controlled linear actuator, in particular a plunger-type coil actuator, can move the aligning element flexibly with a freely programmable controller. It is thus possible to adapt the aligning process of the sheets to different operating types, in particular to a specific type of printing material, thickness of printing material and format of printing material. The position of the aligning element can be sensed continuously with a sensor, such as with a Hall sensor with direct sensing of a magnetic field. The linear actuator and the aligning element can be decoupled mechanically by an elastic coupling. If the apparatus is used in a sheet-fed printing press with transport of the sheets in grippers, the linear actuator can set the phase relation of the aligning element in relation to the machine cycle, the position of the gripper opening, the position of the leading edge of the sheets, the effect of a sheet brake and the position of a further aligning element. Furthermore, it is possible to set the starting and stopping position of the aligning element for easy removal of a sheet. Additionally, the apparatus makes it possible to displace a sheet for marking in the stack in a targeted manner.  
         [0012]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0013]     Although the invention is illustrated and described herein as embodied in an apparatus for depositing sheets onto a stack, 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.  
         [0014]     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  
       [0015]      FIG. 1  is a fragmentary, diagrammatic, partly-sectional, top-plan view and block diagram of an apparatus for depositing sheets onto a stack; and  
         [0016]      FIGS. 2 and 3  are graphs showing different movement profiles of a vibratory plate. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen an illustration of an apparatus for forming a stack  1  in a delivery of a sheet-fed printing press. Two vibratory units are disposed on both sides of the stack  1 , although only one is shown in  FIG. 1 . The vibratory unit includes a reciprocating aligning element or vibrating plate  2  which is suspended on a machine frame  5  on return springs  3 ,  4 . An elastomeric coupling element  6  is fastened centrally on a side of the vibrating plate  2  which faces away from the stack  1 . The coupling element  6  is connected to a tie rod  7  of at least one plunger-type linear coil actuator  8 , such as a linear motor stepping drive. An exciter winding  9  of the plunger-type coil actuator  8  is fastened in a fixed position to the machine frame  5 . Movement of the vibrating plate  2  is sensed by a Hall sensor  10  which is oriented toward a magnet or magnetic part  11  that is fastened to the vibrating plate  2 . As an alternative, the magnetic field of the plunger-type coil actuator  8  could be used to detect the travel of the vibrating plate  2 .  
         [0018]     The output of the Hall sensor  10  is connected to a control device  12  which has further inputs for a rotary encoder  13  of the machine angle of the sheet-fed printing press and for a sensor  14  for the movement profile of the vibrating plate  2 . The control device  12  includes a computer  22  for processing data from the Hall sensor  10 , the rotary encoder  13  and the sensor  14  and for controlling the vibrating plate  2 . Furthermore, a sensor  15  for a speed profile of the vibrating plate  2  and a sensor  16  for a force or torque profile of the vibrating plate  2  or for a current with which the exciter winding  9  is to be actuated, are connected to the control device  12 . The control device  12  is connected to a power output stage  17  which is connected to the exciter winding  9 .  
         [0019]     A sheet may be released in a conveying direction  18  by at least one conveying element for cyclical forward movement of the sheets into a position above the stack  1 . The at least one conveying element may be grippers  19  of a gripper bridge  20  on a transport chain  21 . If the sheet is released, the plunger-type coil actuator  8  is actuated in such a way that the vibrating plate  2  makes contact with the sheet which is still falling or floating and aligns it with respect to the sheets which have already been deposited. One goal is correct stack formation with vertical lateral surfaces of the stack  1  without protruding sheets. The plunger-type coil actuator  8  is actuated via the control device  12  and the power output stage  17 . The elastomeric coupling element  6  or another spring element between the tie rod  7  and the vibrating plate  2  brings about mechanical decoupling and overload safeguard. The position of the vibrating plate  2  transversely with respect to the conveying direction  18  is sensed continuously by the Hall sensor  10 . The signals of the Hall sensor  10  are the actual signals for positional regulation of the vibrating plate  2 . A movement profile is stipulated for the plunger-type coil actuator  8  by the sensor  14 . A check is made in the control device  12  as to whether or not the actual movement deviates from the setpoint movement profile. If there are deviations between the setpoint value and the actual value, compensating actuating variables are generated through the use of the computer  15  and fed to the exciter winding  9  via the power output stage  17 . During the stipulation of the movement profile with the sensor  14 , the stroke and the frequency of the vibrating plate  2  are defined individually and regulated. External and internal forces on the vibrating plate  2  can be compensated for by overdriving. The positional regulation of the vibrating plate  2  can be triggered by using the machine angle of the sheet-fed printing press which is sensed by the rotary encoder  13 , and can thus be operated in a phase-adjustable manner in relation to the machine cycle and other machine elements. A feed current I which occurs between the power output stage  17  and the exciter winding  9  can be measured continuously and can be processed together with the signals of the Hall sensor  10  for overload monitoring. In the event of a current failure, the vibrating plate  2  is moved by the action of the return springs  3 ,  4  into a desired initial position. A marking apparatus  23  for sheets, such as an ink jet, is associated with the stack and has a control signal. The at least one aligning element or vibrating plate  2  may be set as a function of the control signal for the marking apparatus  23 .  
         [0020]      FIGS. 2 and 3  show setpoint movement profiles for paperboard and sheets of low thickness, as they are stipulated by the sensor  14 . A direction of travel s of the vibrating plate  2  which lies perpendicular to the conveying direction  18  is plotted against time t. Information about the sheet thickness is input into the control device  12 , whereupon the correct movement profile is selected automatically. A trapezoidal movement profile according to  FIG. 2  is selected when paperboard sheets are being printed. The rising sides or flanks of the waveform are sufficiently steep to have sufficient impact energy available for the alignment of the paperboard sheet as a result of relatively powerful impacts of the vibrating plate  2  against a falling paperboard sheet. In the event of thin sheets, a sinusoidal movement profile shown in  FIG. 3  is stipulated, with which the sheets are moved gently to a setpoint position above the stack  1 . If required, the stroke and the frequency of the movement profiles can be adapted to the actual conditions. In the movement profiles according to  FIGS. 2 and 3 , the result is three hard impacts per paperboard sheet and only one soft impact in the event of thin sheets, which approximates gentle pushing of the sheet.  
         [0021]     In an analogous manner, trapezoidal or sinusoidal profiles can be stipulated with the sensors  15 ,  16  for the profile of the speed and the force of the vibrating plate  2 , as a function of the machine angle or as a function of the opening angle of grippers which convey the sheets.  
         [0022]     This application claims the priority, under 35 U.S.C. § 119, of German Patent Application 10 2004 049 189.5, filed Oct. 8, 2004; the entire disclosure of the prior application is herewith incorporated by reference.