Abstract:
In a sheet feeder for a sheet processing machine, such as a sheet-fed rotary printing press, and initial torque spike when the sheet feeder is first switched into the system is reduced with a switch-on torque limiter. The torque limiter is disposed in the drive train between the sheet processing machine and the sheet feeder, so that a torque surge which occurs when the sheet feeder is coupled in at an increased basic speed of the sheet processing machine can be absorbed.

Description:
BACKGROUND OF THE INVENTION  
       FIELD OF THE INVENTION  
         [0001]    The invention lies in the field of sheet-processing machines. More specifically, the invention relates to a sheet feeder for a sheet-processing machine, such as a sheet-fed printing press.  
           [0002]    In sheet feeders having a clutch for the drive connection to the sheet processing machine, such as a printing press, there exists the problem that the sheet feeder is not usually connected until the printing press has a very high operating speed. A joltlike drive torque caused by the coupling process firstly stresses the drive means with a torque surge and leads to heavy wear of the drive, as well as of driven components and the driving components.  
           [0003]    To solve the above-described problem, German published patent application DE 100 40 070 A1 discloses a switchable sheet feeder which, in addition to the actual feeder clutch, has an additional torsionally elastic clutch that diminishes the coupling surge. In order to suppress oscillations between the machine and the feeder in operation, the torsionally elastic clutch is bypassed via a further, torsionally rigid clutch after the coupling process.  
           [0004]    A clutch configuration of that type, however, is complicated in construction terms and it is relatively expensive.  
         SUMMARY OF THE INVENTION  
         [0005]    It is accordingly an object of the invention to provide a sheet feeder for a sheet-processing machine which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a sheet feeder that can be coupled in and has a device for absorbing the torque surges caused by the coupling process.  
           [0006]    With the foregoing and other objects in view there is provided, in accordance with the invention, a sheet feeder for the synchronized feeding of sheets to a sheet processing machine having a machine drive, the sheet feeder comprising:  
           [0007]    drive assemblies for driving the sheet feeder and a drive train connecting the drive assemblies to the machine drive of the sheet processing machine;  
           [0008]    a clutch selectively switchable with a determined angular position into the drive train between the drive assembly of the sheet feeder and the machine drive of the sheet processing machine; and  
           [0009]    a switch-on torque limiter with a pretensioned spring element connected in the drive train.  
           [0010]    Arranging a switch-on torque limiter according to the invention in the drive train of the feeder leads to a reduction of the torque surge when coupling the feeder to the rotating machine, for example sheet processing machine, in particular printing press, while ensuring the correct phase relation between the latter in operation and reducing oscillations between the feeder and machine.  
           [0011]    In one advantageous refinement, a pretensioned elastic element is incorporated into the drive train, which becomes active after a threshold load is exceeded (for example during the coupling process) and limits the torque surge.  
           [0012]    This threshold load is higher than the torques to be transmitted during feeder operation, so that the elastic element is not effectively loaded and the feeder is rigidly coupled to the machine.  
           [0013]    In one advantageous development of the subject matter of the invention, it is possible to integrate the switch-on torque limiter into a phase adjusting mechanism.  
           [0014]    In accordance with an added feature of the invention, the switch-on torque limiter is disposed between the machine drive of the sheet processing machine and the clutch. Alternatively, the switch-on torque limiter is disposed between the clutch and the drive assemblies of the sheet feeder.  
           [0015]    In accordance with a specific embodiment of the invention, the switch-on torque limiter includes four stationary and symmetrically disposed deflection rollers and two displaceable deflection rollers.  
           [0016]    Furthermore, there may be provided an endless belt that is part-way wrapped around each of the deflection rollers (the four stationary deflection rollers and the two displaceable deflection rollers).  
           [0017]    In accordance with another feature of the invention, there is provided a carriage that supports the displaceable deflection rollers, and a second spring element holding the carriage in a pretensioned state in an operating position.  
           [0018]    In accordance with again a further feature of the invention, the first above-mentioned pretensioned spring element configured to absorb a torque surge introduced when the machine drive is first connected to the drive assemblies of the sheet feeder, and a second spring element is configured to cushion a recoil movement of the switch-on torque limiter.  
           [0019]    In accordance with a preferred embodiment of the invention, the first spring element and the second spring element are disposed coaxially inside one another.  
           [0020]    In accordance with a concomitant feature of the invention, an actuating motor is operatively associated with the carriage for adjusting the carriage specifically to adjust a phase between the machine drive and the drive assemblies of the sheet feeder. Specifically, the actuating motor is operatively associated with the carriage for adjusting a phase between a pinion of the machine drive and a pulley wheel in the drive train.  
           [0021]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0022]    Although the invention is illustrated and described herein as embodied in a sheet feeder having a drive for the synchronized feeding of sheets to a sheet processing 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.  
           [0023]    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  
       [0024]    [0024]FIG. 1 is a diagrammatic representation of a section taken through a sheet-fed rotary printing press;  
         [0025]    [0025]FIG. 2 is a diagrammatic representation of a section through a drive for the feeder of the sheet-fed rotary printing press;  
         [0026]    [0026]FIG. 3 is a diagrammatic view of the switch-on torque limiter according to the invention in the switched operating state of the feeder;  
         [0027]    [0027]FIG. 4 is a similar view of the switch-on torque limiter during absorption of the switch-on torque surge; and  
         [0028]    [0028]FIG. 5 is a similar view of the switch-on torque limiter during the cushioning of the recoil movement. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a rotary press, e.g. a printing press  1  which processes sheets  7 , has a feeder  2 , at least one printing unit  3  or  4  and a delivery  6 . The sheets  7  are taken from a stack of sheets  8 , a sheet pile  8 , and, separated or overlapped, are fed over a feed table  9  to the printing units  3  and  4 . Each of the printing units  3 ,  4  contains a respective 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 semiautomatic or fully automatic printing plate change.  
         [0030]    The sheet pile  8  is stacked on a pile board  10  which can be raised under control. The removal of the sheets  7  takes place from the top of the sheet pile  8  by way of a suction head  18 , which inter alia has a number of lifting and dragging suckers  19 ,  21  to separate the sheets  7 . Furthermore the blowing devices  22  for loosening the top sheet layers and sensing elements  23  for tracking the stack are provided. In order to align the sheet pile  8 , in particular the top sheets  7  of the sheet pile  8 , a number of side and rear stops  24  are provided.  
         [0031]    The sheet feeder  2  is driven from a drive shaft  26  of the machine drive. A switchable clutch  27  connects the drive of the sheet-processing machine  1  to the drive assemblies of the sheet feeder  2 , for example the drive  28  for the suction head mechanism and air control means; a drive  29  for the intermittently operated roller and flap shaft; and a drive  31  for the transport belt. The drive shaft  26  is provided with a pinion  32  for an endless belt  33 . The belt  33  wraps around a pulley wheel  34  of the clutch  27 .  
         [0032]    A device for absorbing a torque surge of the belt  33  is disposed on a side frame  36 . The device will be referred to as a “switch-on torque limiter  37 ” in the following text. It substantially comprises four stationary deflection rollers  38 ,  39 ,  41 ,  42  that are symmetrically arranged and two further, non-stationary deflection rollers  43 ,  44 . It will be understood that the term “stationary” refers to the respective axes of the rollers only. The rollers are rotatably supported. The rollers  43 ,  44  can be displaced together. The rollers  43 ,  44  are disposed on a displaceable carriage  46 . The belt  33  is wrapped around all the deflection rollers  38 ,  39 ,  41 ,  42 ,  43 ,  44 . In the drive direction shown in FIGS.  3  to  5  (counter-clockwise), the deflection roller  44  is disposed in the region of the load run and the deflection roller  43  is disposed in the region of the empty run.  
         [0033]    At its end adjacent to the deflection roller  44 , the carriage  46  has a guide  47  with a stop  48  for a first spring element  49 . The spring element  49  is configured as a helical spring, and one end of it is supported on the stop  48  and the other end is supported on a plate  51  which can be displaced along the guide  47 . As the spring element  49  is installed in a pretensioned state (approximately 2 to 3 times the operating moment), it pushes the plate  51  against a stop  50  of a housing  53 . A second spring element  52  encloses the spring element  49 , and one end of the former is likewise supported on the plate  51  and the second end is supported on the housing  53  which encloses the spring elements  49 ,  52 , the plate  51  and the guide  47 . The second spring element  52  is also constantly in a pretensioned state. When the sheet feeder  2  or its stationary drive assemblies are coupled to the sheet processing machine  1  which is already rotating at a rotational speed, the result is a not inconsiderable torque surge which acts on the belt  33 . The load is applied here to the load run. This tension leads to the deflection roller  44  being deflected upward in the direction of the arrow in FIG. 4. Together with the carriage  46  and the deflection roller  43 , said deflection occurs counter to the force of the first spring  49 . As a result of this measure, the torque surge is absorbed by the spring deflection when the sheet feeder  2  is coupled in, that is to say it is limited to an amount which corresponds to the spring force.  
         [0034]    [0034]FIG. 4 shows the carriage  46  extended upward counter to the force of the first spring element  49 . The carriage  46  is pressed back into the operating position by the action of the first spring element  49 . Here, as shown in FIG. 5, the carriage  46  swings beyond the operating position, to be precise in such a manner that the second spring element  52  is now compressed, while the first spring element  49  is relieved to its original pretensioned state. The carriage can thus oscillate back and forth a number of times, depending on the magnitude of the coupling torque. After a short time, the switch-on torque limiter  37  is again situated in its stationary initial position, the operating position. Here, the pretensioned spring elements  49 ,  52  are designed to be so stiff that operational torques cannot lead to a deflecting movement of the carriage  46 .  
         [0035]    In the preferred exemplary embodiment, the switch-on torque limiter  37  is also simultaneously used as a phase adjusting mechanism. There is provision here for the housing  53  to be provided with an actuating motor  56  via a gear mechanism  54 , for example a threaded rod and hole. The actuating movement is transmitted to the carriage  46  via the stiffly designed second spring element  52  and therefore ensures specific deflection of the load run and empty run which results in phase adjustment of the drive pinion  32  with respect to the pulley wheel  34 .