Abstract:
A method of feeding sheets to a printing-technology machine includes individually separating sheets from a sheet pile, conveying the sheets against movable lays for effecting an alignment thereof, and cyclically conveying the sheets from the lays to the machine. A control device coordinates movement of the lays with the individual separation of the sheets from the sheet pile and onward conveyance of the sheets to the machine. Data related to characteristics of the sheets are processed in the control device for generating actuating signals for a separate, controllable drive system. The lays are moved by the drive system. A device for performing the method is also provided.

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention relates to a method and a device for feeding sheets to a machine pertinent to printing technology or, in short, a printing-technology machine. 
   In printing presses, sheets from a sheet pile or stack are conveyed individually or in overlapped form against feed lays on a feed table set at an angle thereto. The feed lays may be formed as front and top lays, the top lays serving to catch a sheet to be aligned, and the front lays forming a feed line for aligning the sheets at the leading edge thereof. In order to move the feed lays from the operating position thereof into a position underneath the feed table, in a construction shown in German Published, Non-prosecuted Patent Application DE 42 43 585 A1, the feed lays are disposed on coupling rods of four-bar linkages constructed as double swinging arms. A drive element of the four-bar linkage is coupled to the drive of the printing press. The top lays can be set to the thickness of the sheets being advanced for processing. 
   In German Published, Non-prosecuted Patent Application DE 199 01 699 A1, corresponding to U.S. Pat. No. 6,241,241, a method of eliminating rhythmic register faults in sheet-fed rotary presses is described, wherein front lays can be moved into two different alignment positions on a feed table by being pivoted from a position outside the conveying path of the sheets by a cyclically driven shaft. The pivoting movement of the front lays is controlled via a cam mechanism which is connected to the main drive of the sheet-fed printing press. 
   In a drive for a swinging pregripper in a sheet-fed printing press shown in German Published, Non-prosecuted Patent Application DE 196 16 755 A1, corresponding to U.S. Pat. No. 6,000,694, additional acceleration and braking torques are introduced with the aid of a linear drive. The drive for the reciprocating movement can therefore be load-relieved. 
   In all the aforementioned constructions, the movements of the lays or gripper systems are controlled by mechanical elements which have a connection to the main drive of the printing-technology machine. The mechanical drive elements are subjected to fixed movement sequences, so that an adaptation to different conveying speeds and sheet thicknesses is able to be carried out only with increased effort. 
   As shown and described in German Published, Non-prosecuted Patent Application DE 31 38 540 A1, corresponding to U.S. Pat. No. 4,458,893, a device for feeding sheets separated on a feed table and aligned according to the leading and side edge is provided with a computer for evaluating rotary encoder signals. The computer serves for driving a motor for a feed cylinder which, for transferring a sheet, is moved cyclically from a minimum circumferential speed or from a standstill to the circumferential speed of a printing-press cylinder. The drive for the sheet feed device is separated from the other printing-press drive. The alignment of the sheets on the leading and side edge is performed in a conventional manner. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide a method and a device for feeding sheets to a printing-technology machine, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which permit flexible adaptation to machine and process conditions, with little outlay. 
   With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of feeding sheets to a printing-technology machine, which comprises individually separating sheets from a sheet pile. The sheets are conveyed against movable lays for effecting an alignment thereof. The sheets are cyclically conveyed from the lays to the machine. A control device coordinates movement of the lays with the individual separation of the sheets from the sheet pile and onward conveyance of the sheets to the machine. Data related to characteristics of the sheets for generating actuating signals for a separate, controllable drive system are processed in the control device. The lays are moved by the drive system. 
   In accordance with another mode, the method of the invention further includes additionally processing data containing information relating to at least one of machine speed, machine configuration and a then occurring machine process, in the control device. 
   With the objects of the invention in view, there is also provided a device for feeding sheets to a printing-technology machine, comprising a device for individually separating sheets from a sheet pile. A conveying device is used for conveying the individually separated sheets against liftable and lowerable lays. Drive elements are provided for lifting and lowering the lays. A further conveying device is present for conveying the individually separated sheets from the lays to the machine. At least one control device is connected to the separating device and to the conveying devices for setting a course of movement of the lays based upon characteristics of the sheets. Equipment is provided for feeding data relating to the sheet characteristics to the control device for lifting and lowering the lays. 
   In accordance with an added feature of the invention, the data-feeding equipment serves for additionally feeding data relating to at least one of printing speed, machine configuration and a then occurring machine process to the control device for lifting and lowering the lays. 
   In accordance with an additional feature of the invention, the sheet-feeding device further includes an electric motor for actuating the drive elements for lifting and lowering the lays. 
   In accordance with yet another feature of the invention, the motor is coupled directly with a shaft whereon the lays are disposed. 
   In accordance with yet a further feature of the invention, the shaft is coupled with a rotary encoder connected to the control device for lifting and lowering the lays. 
   In accordance with yet an added feature of the invention, the lays are disposed on a shaft, and the motor is a linear motor coupled via a pivoting lever with the shaft for lifting and lowering the lays. 
   In accordance with a concomitant feature of the invention, the sheet-feeding device further includes a gear transmission provided between the lays and the motor for lifting and lowering the lays. 
   Due to the fact that the lays are moved by a separate, controllable drive system, it is possible to adapt the time available for aligning and stabilizing a sheet continuously to the then occurring machine speed. The feed register is thereby improved. The lays are able to be positioned with small drive torques, due to which the excitation to oscillations is reduced. The movement of the lays can be controlled so that no mechanical damage to the sheet and no formation of waves in the sheet occur. 
   In printing-technology machines with front and top lays, a preferably electromotive drive is provided therefor which is independent of the rest of the machine, that can be subjected to different courses of movement by an open-loop and closed-loop control device. In order to determine a then occurring course of movement, information relating to the sheet characteristics, the machine speed, the machine configuration and the machine process is processed in the open-loop and closed-loop control device. The information can be entered manually, taken from a memory or obtained by detectors. For example, a sensitive board, i.e., cardboard or pasteboard or the like, in a printing press having a large number of printing units requires a course of movement for the lays wherein the risk of scratching a sheet by the lays is reduced at the expense of the feed register and the excitation to oscillations. If, by contrast, thin paper is to be processed, a course of movement will then be provided which as much as possible prevents the formation of waves in the incoming sheet. In a machine having a small number of printing units, the course of movement is optimized so that the feed register is improved and the stabilizing time of the sheet is lengthened. In machines having a large number of printing units, these criteria are not important, because a sheet can be printed in final form in a single pass. The courses of movement of the lays can also be coordinated with the courses of movement of the sheet conveying devices disposed upstream and downstream, in particular if those sheet conveying devices are likewise driven separately. 
   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 method and a device for feeding sheets to a printing-technology machine, 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 DRAWINGS 
       FIG. 1  is a diagrammatic and schematic view of a printing press having a device for performing the method according to the invention; 
       FIG. 2.1  is a fragmentary, highly diagrammatic side-elevational view of  FIG. 1 , showing front lays; 
       FIG. 2.2  is a front-elevational and schematic view of  FIG. 2.1 ; and 
       FIG. 3  is a plot diagram of the sheet travel distance with respect to the machine angle in degrees, thereby depicting the course of movement of the front lays. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a printing press having a feeder  1 , two printing units  2  and  3 , and a delivery  4 . A sheet pile or stack  5  of sheets  6  which is provided in the feeder  1  can be separated individually or singly from above by a suction head  7 . The uppermost sheet  6  is lifted off the stack  5  by the suction head  7  and fed to transport rollers  8  to  11 . The transport rollers  8  to  11  and non-illustrated transport belts convey the sheets  6  individually and successively, in underlapped form, on a feed table against front lays  13 . The front lays  13  are pivotable from a working position, as illustrated, into a position underneath the feed table  12  with the aid of a motor  14 . The first and second printing units  2  and  3 , respectively, have inking and dampening rollers  15 ,  16 , a plate cylinder  17 ,  18 , a transfer cylinder  19 ,  20  and an impression cylinder  21 ,  22 , which are all coupled via a gear train. Connected between the impression cylinders  21 ,  22  is a transfer drum  23 , which is drivable by a belt drive  24  to  26 . 1  and a gear  26 . 2 . A feed drum  27  is assigned to the impression cylinder  21 . An oscillating or swinging gripper  28  which is provided in order to convey the sheets  6  from the front lays  13  to the feed cylinder  27 , is coupled to the gear  26 . 2  via a transmission or gearbox  29 . The cylinders and drive elements which are coupled to one another via the aforedescribed gear train are connected, respectively, by a double line  30  in FIG.  1 . In the delivery  4 , there is a chain gripper system  31 , which conveys the finally printed sheets  6  from the impression cylinder  22  onto a delivery pile or stack  32 . A main drive motor  33  is coupled to the belt drive  24  for driving the printing press. A rotary encoder  34  is provided in the gear train of a transfer drum  23  for determining or registering the rotational angle. The pivoting movement of the front lays  13  is determined or registered by a further rotary encoder  35 . The drive of the front lays  13  has no mechanical connection to the main drive train of the printing press. The motors  14 ,  33  for the front lays  13  and the main drive of the printing press, and the rotary encoders  34 ,  35  are connected to a control device  36 . In the sheet path over the feed table  12 , there is disposed a sensor unit  37  for detecting characteristics of the sheets  6 , such as sheet thickness, format, weight, weight distribution, moisture content and the like. The sensor unit  37  is connected to the control device  36 . Also connected to the control device  36  is an input unit  38  for information relating to the sheet characteristics, the machine configuration and the transpiring machine process. The input unit  38  permits entry of the information by an operator, by transfer from a memory or as an interface to sensors for the information concerning the machine process, such as the then existing register deviations, for example. 
     FIGS. 2.1  and  2 . 2  show details from the range of action of the front lays  13 . According to  FIG. 2.1 , the front lays  13  in the working position rest against a stop  39  underneath the feed table  12 . In the working position, the front lays  13  form a stop line for an oncoming sheet  6 , while a previously arrived sheet  6  is being conveyed over the front lays  13  to the feed drum  27  by the oscillating gripper  28 . As shown in  FIG. 2.2 , the front lays  13  on the drive side AS and on the operating side BS of the printing press are held with a pivot shaft  40  in bearings  42  and  41 , respectively, the pivot shaft  40  being coupled directly to the motor  14 . Starting from the working position, the front lays  13  can be moved reciprocatingly over an angular range of about 50° by the motor  14 . In order to determine or register the rotational position, a screen disk  35 . 2  belonging to the rotary encoder  35  is fixed to the pivot shaft  39 . 
   From the information relating to the sheet characteristics and from the additional information relating to the machine speed, the machine configuration and the machine process, the optimum course of movement for the front lays  13  is determined in the control device  36  with the aid of a computer. Appropriate signals are fed to the motor  14 , so that the front lays  13  assume a calculated rotational position in the pivoting range in accordance with the machine angle determined by the rotary encoder  34 . 
   When the sheets  6  are thin, they are unstable and, when being conveyed from the front lays  13  to the feed drum  27 , they cling readily to the prescribed construction space. The risk that the thin sheets  6  will come into contact with machine, i.e., press, parts and will be scratched is quite low, when compared with thick, and therefore rigid, grammage. When thin sheets  6  are being conveyed from the front lays  13  to the feed drum  27 , it is sufficient for those sheets to be supported by conventional sheet guide elements, which can be constructed in the form of a rake. Additional support by the front lays  13  during the onward movement thereof from the stop  39  is not required. However, because of the instability of the thin sheets  6 , they are difficult to align on the front lays  13 . The motor  14  is therefore controlled in a manner that the front lays  13  arrive early into the working position thereof at the stop  39 , and therefore a greater time interval is available for aligning thin sheets. During the relatively long dwell time of a thin sheet  6  on the front lays  13 , the sheet  6  comes to rest in terms of movement, which consequently improves the alignment in the conveying direction and in the lateral direction, and the sheet  6  can be gripped exactly by the oscillating gripper  28 . 
   When the sheets  6  are thick, they are rigid and heavy and, when being conveyed from the front lays  13  to the feed drum  27 , need additional support from the front lays  13 , which are of non-scratching construction, while the front lays  13  are moving onward from the stop  39 . This prevents the thick sheet  6  from colliding with other machine parts. Due to the great rigidity of the thick sheet  6 , the alignment thereof on the front lays  13  is not critical. The motor  14  serves for moving the front lays in a manner that they dwell on the stop  39  for only a short time, and as much time as possible is available for supporting the thick sheet  6 . 
   During the conveyance of sheets  6  having a small format, and being formed of very rigid board, the motor  14  is driven in a manner that the front lays  13  follow the sheet trailing edge  47 . 
   The course of movement for two sheets  6  is illustrated in FIG.  3 . In the ordinate direction, the plot diagram or graph of  FIG. 3  shows the machine angle φ which results from the signals transmitted by the rotary encoder  34 . The sheet travel path s is plotted in the abscissa direction. The sheet travel path s is 0 when the sheet  6  rests aligned on the front lays  13 . The curves  43  and  44  show the path of the leading edge  45  of a first and a second sheet  6 , respectively. The curve  46  shows the path of the trailing edge  47  of the first sheet  6 . 
   The curve  46  lies parallel to parts of the curves  43  and  44 . The distance between the curves  43  and  46  represents the sheet length L of the first sheet  6 . The curves  48  and  49  show the paths of the front lays  13  with two different sheet thicknesses. Curve  50  shows the course of the movement of the oscillating gripper  28 . 
   According to curve  43 , the first sheet  6  is conveyed with uniform speed against the front lays  13  and reaches the stationary front lay  13  at the machine angle φ 1 . At a machine angle φ 2 , the oscillating gripper  28  reaches the leading edge  45  of the first sheet  6 . The first sheet  6  is gripped by the swinging gripper  28 . As far as a machine angle φ 3 , the leading edge  45  of the first sheet  6  is located in the oscillating gripper  28  and on the front lays  13 . Starting from the angle φ 3 , the front lays  13  are pivoted away from the working position of the stop  39  by the motor  14 . The front lays  13  open the path for the transport of the first sheet  6  to the feed cylinder  27  by the oscillating gripper  28 . 
   Depending upon the sheet thickness, the front lays  13  are again moved into the working position either earlier or later. According to the curve  49 , the front lays  13  already reach the working position at the machine angle φ 4 . This course of movement is advantageous for thinner sheets  6 . In the case of thick sheets  6  such as board, the course of movement is set in accordance with the curve  48 . The front lays  13  reach the working position only at the machine angle φ 5 , but yet in sufficient time to receive the next sheet  6 . As  FIG. 3  illustrates, the leading edge  45  of the second sheet  6  reaches the front lay  13  at the angle φ 6 . The further courses of movement are repeated as described hereinabove with respect to the first sheet  6 . 
   In an alternative non-illustrated embodiment, the pivot or swing shaft  39  is pivoted by a linear motor and a lever mechanism. In principle, the setting of the courses of movement remains the same. The embodiment in terms of construction depends upon the available construction space. 
   The method serves both for the front lays  13  and for top lays. The top lays can likewise be driven by separate actuators. The movement of the top lays is not a pure pivoting movement, but rather, a lifting and pivoting movement, for which purpose two actuators, such as rotating or linear electric motors, for example, can serve. 
   The invention of the instant application is applicable not only for a direct coupling between an actuator and a front lay  13  or top lay. Gear mechanisms, such as cams or coupling mechanisms, can be connected between an actuator and a drive element of a lay. By such a gear mechanism, parts of the course of movement of the lays can be defined or determined, for example, a lifting movement or a pivoting movement in a defined angular range. When a gear mechanism is applied for moving lays, the method according to the invention is realized by a non-uniform drive of the gear mechanism, so that the same movement path of a lay is traversed with a variable time pattern.