Abstract:
A sheet feeder for feeding printed sheets to a conveying device, with a gripper drum that has at least one gripper for removing the printed sheets one at a time from a stack; a pocket is permanently mounted essentially in the peripheral area of the gripper drum wherein the printed sheets are aligned against a stop with the fold forward and set down on the conveying device with reversal of direction; and with a decelerating device for slowing the speed of the printed sheets downstream towards the stop. The decelerating device has at least one secondary stop, which rotates in the same direction as the gripper drum, has a slower speed than the gripper drum for slowing down the printed sheets, and on which the printed sheets are slowed down upstream of the stop.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a sheet feeder for feeding printed sheets to a conveying device. The sheet feeder has a gripper drum with at least one gripper for removing the printed sheets one at a time from a stack; a pocket, which is permanently mounted essentially in the peripheral area of the gripper drum and in which the printed sheets can be aligned against a stop with the fold forward and set down on the conveying device with reversal of direction; and a decelerating device, which slows the speed of the printed sheets downstream towards the stop. 
         [0003]    2. Description of the Related Art 
         [0004]    Sheet feeders of this type are known especially as signature feeders of gathering and stitching machines. These have a gripper drum, with which printed sheets in a stack are tipped at a front edge, gripped and guided one at a time to stops, also known as register stops, on which the printed sheets are aligned. During this process, the sheets are held in the peripheral area of the drum by guides, which form a pocket and are mounted in a stationary way. The printed sheets are pulled from this pocket one at a time by their rear edges and opened with opening drums. They are then set down in roof-like fashion on a gathering line. 
         [0005]    The printed sheets are often provided with an overlay fold to allow them to be opened. The different length of the front side and rear side of the folded printed sheets thus allows central opening. During the further processing of the gathered printed sheets, these overlay folds must be cut off in a cutting device to realize a clean appearance of the printed products. The overlay fold thus serves only for correct processing of the printed sheets and ultimately winds up as waste, which, of course, must be kept low. Conflicting with this goal is the fact that in a high-speed sheet feeder, the printed sheets strike at high speed in the pocket and do not have time to stabilize in this position. Especially the end of the printed sheet that is located in the pocket thus lies unsteadily and inexactly, which makes it more difficult to realize reliable gripping and opening with the smaller overlay fold that is desired. Therefore, in high-capacity sheet feeders, the overlay fold must be made longer than would be desirable from the standpoint of waste production. 
         [0006]    To stabilize the printed sheets in the pocket, the sheet feeder disclosed by EP 0 716 995 A has a pocket with a rubber stop, which is meant to dampen the impact of the printed sheets. In the sheet feeder described by DE 197 38 920 A, an endless belt is provided, which is intended to stabilize the printed sheets in the pocket with frictional contact. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the invention is to create a sheet feeder of the aforementioned type, which is intended to allow reliable gripping and opening of the sheets at their rear edge at high processing speeds. 
         [0008]    In a sheet feeder of this general type, the solution to this problem is provided by the fact that the decelerating device has at least one secondary stop, which rotates in the same direction as the gripper drum, has a slower speed than the gripper drum for slowing down the printed sheets, and on which the printed sheets are slowed down upstream of the stop. 
         [0009]    In the sheet feeder of the invention, the printed sheets are slowed down significantly by the secondary stop before the stop is reached. The speed at which the printed sheets strike the stop in the pocket is thus significantly lower than the speed of the printed sheets after they have been pulled from the stack. Before the change in direction, the printed sheets are thus decelerated in two stages. The speed can be reduced, for example, by half on the secondary stop. Since the printed sheets strike the stop at a reduced speed in the pocket, the end of the sheet, i.e., the rear edge of the printed sheet, is positioned much more steadily and exactly. Therefore, the overlay fold can be made shorter, which reduces the amount of waste, since in most cases the overlay fold is cut off. Due to the lower speed of the printed sheets in the pocket, the rear edge or the overlay fold can thus be gripped more reliably, and the printed sheet can be opened. The stop in the pocket is also acoustically quieter, which is another advantage. The sheet feeder of the invention is thus quieter at the same output. 
         [0010]    In accordance with a further development of the invention, it is provided that the one or more secondary stops bring the slowed printed sheet into the vicinity of the pocket. The printed sheet remains with its front edge on the secondary stop until it is slowed down on the stop. To this end, in accordance with another refinement of the invention, it is provided that the one or more secondary stops have holding means for gripping the front edge of the braked printed sheet. The front edge of the printed sheet can be gripped especially reliably if, in accordance with another refinement of the invention, the holding means have a spring element for gripping one printed sheet at a time. The front edge of the printed sheet can then be gripped on the secondary stop. This allows especially reliable transfer of the braked printed sheets to the pocket. 
         [0011]    In accordance with another further development of the invention, it is provided that the one or more secondary stops are located on a lever. The lever allows simple and nevertheless reliable control of the secondary stop. This is especially simple and reliable if, in accordance with a further development of the invention, the lever is rotatably mounted on a driven disk. Preferably, two disks of this type are provided, with the gripper drum arranged between the two disks. Naturally, before the printed sheets strike the secondary stop, they are released. In this refinement, the printed sheets are thus slowed down on two levers arranged some distance apart. 
         [0012]    In accordance with a further development of the invention, it is provided that the lever is a two-armed lever and that the one or more secondary stops are located at the rear end of the lever. The lever can be controlled, for example, by a cam disk. A suitable cam roller, which runs on the cam of the cam disk, is then mounted on the front end of the lever. Naturally, if there are two levers, two such cam disks can be provided accordingly. The cam disks are rigidly mounted. 
         [0013]    In accordance with a further development of the invention, it is provided that the one or more secondary stops are controlled in such a way that they are swiveled into a position that is shifted back relative to the periphery of the gripper drum after the pocket with respect to the direction of flow and that they are swiveled to the periphery of the gripper drum before the pocket to slow down the printed sheets. In this connection, the secondary stop is preferably swiveled radially inward or radially outward. If the secondary stop is swiveled inward into an inactive position, the printed sheets can be moved past the secondary stop. If the secondary stop is swiveled into the peripheral area of the gripper drum, printed sheets which follow strike this secondary stop. 
         [0014]    In accordance with a further development of the invention, at least two, preferably three, and even more preferably four or more than four secondary stops are provided, which are spaced apart from one another. They are preferably spaced equal distances apart. 
         [0015]    In accordance with a further development of the invention, the secondary stop has a speed of rotation that is about 50% of the speed of rotation of the gripper drum. The speed of impact of the printed sheets on the stop of the pocket can thus be essentially halved. 
         [0016]    In accordance with a further development of the invention, it is provided that at least one secondary stop can be swiveled outward upstream of the pocket in such a way that it deflects the trailing end of a preceding printed sheet radially outward. This secondary stop thus acts here not as a stop for slowing a printed sheet but rather as a guide device for guiding the rear edge into the intended position for the reversal of direction. The aforesaid end of the sheet is already being deflected outward by gravity. However, this deflection is guided by the secondary stop and thus takes place more precisely. 
         [0017]    The printed sheets are preferably provided with a leading fold and are preferably so-called signatures. The sheet feeder of the invention preferably has opening drums, with which the printed sheets, after the aforesaid reversal of direction has occurred, are opened, so that they can be set down on the conveying device. However, this is not absolutely necessary. In principle, after the reversal of direction, the printed sheets can also be further conveyed unopened. 
         [0018]    The sheet feeder of the invention is suitable especially for a gathering and stitching machine. However, use for a gathering and stitching machine is not absolutely necessary. 
         [0019]    Other advantageous features are specified in the dependent claims and the following description and are apparent from the drawings. 
         [0020]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING IN THE DRAWING 
         [0021]      FIG. 1  is a schematic view of a sheet feeder of the invention. 
           [0022]      FIG. 2  is a cross section through part of the sheet feeder of the invention along line II-II of  FIG. 1 . 
           [0023]      FIG. 3  is a schematic partial view of the sheet feeder of the invention. 
           [0024]      FIG. 4  is schematic view of a lever that forms a secondary stop. 
           [0025]      FIG. 5  shows schematically the transfer of a printed sheet to a bin. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The sheet feeder  1  shown in  FIG. 1  has a gripper drum  2 , with which printed sheets  7  are separated and removed from a stack  6  in a way which in itself is already well known. The printed sheets  7  are preferably signatures and have a front edge  8  and a rear edge  9 . The printed sheet is usually folded at the front edge  8 . The rear edge  9  is furnished with an overlay fold. To separate the printing sheets  7 , a suction device  11  or other suitable type of gripping device is provided. 
         [0027]    The gripper drum  2  has several grippers  12  which in themselves are already well known. Each gripper  12  can be rotated about its axis  13  under automatic control. These grippers  12  seize each separated printed sheet  7  by its front edge and convey it on a peripheral area  17  formed by the gripper drum  2  in the direction of the arrow  14  and thus in the counterclockwise direction in  FIG. 1 . In a lower area of the gripper drum  2 , a supporting lever  25  is installed, which can be swiveled about an axis of rotation  26  between the positions indicated by the solid lines and the broken lines. The supporting lever  25  serves to guide small formats. After this supporting lever  25 , the printed sheets  7 , with the folded front edge  8  forward, are fed into an essentially stationary pocket  15 , which is formed by several guides. The pocket  15  is thus mounted on a frame, which is not shown here. In principle, however, the pocket  16  could also be provided with limited movement, so that, for example, if the printed sheets  7  become jammed, it could give way. A stop  16 , which the front edges  8  of the printed sheets  7  strike, is located near the pocket  15 . To accommodate different formats, the stop  16  can be shifted in the peripheral direction, as indicated by the double arrow  29 .  FIG. 3  shows a stop  16 ′ that is adjusted for a comparatively small format. 
         [0028]    If a printed sheet  7  is located in the stop position against the stop  16 , it is seized at its rear edge  9  by a gripper  27  of an opening drum  3  and pulled out of the pocket  15  with reversal of its direction. The gripper  27  or the two grippers  27  that are provided here are swiveled about an axis  28  under automatic control. The opening drum  3  cooperates with another opening drum  4  to open the printed sheet gripped at its rear edge  9  and set it down on a gathering chain  5  or other conveying device. In this operation, the opening drums  3  and  4  are driven in the directions of the arrows  30  and  31 . The gathering chain  5  is especially part of a gathering and stitching machine, the rest of which is not shown here. In principle, the gathering chain  5  can also be some other type of conveying device. The printed sheets  7  can also be dropped onto the conveying device unopened. 
         [0029]    As  FIG. 2  shows, the gripper drum  1  is mounted on a shaft  33 , which is driven and controlled by a drive (not shown). A gripper disk  37  is mounted nonrotatably on this shaft  33 , and the aforementioned grippers  12  are supported on the gripper disk  37  in such a way that they can rotate about an axis of rotation  13 . The grippers  12  are controlled by a toothed segment  48  on a cam  38 , on each of which a cam roller  43  rests. The cam  38  is mounted on a support  32 , which is joined with a feeder table  36  or the machine frame. When the shaft  33  rotates, the grippers  12  are controlled in such a way that they seize or release a printed sheet  7  at the desired moment. 
         [0030]    The gripper disk  37  is disposed between two secondary stop disks  40 , each of which is nonrotatably joined with sleeves  44 , which are arranged coaxially with the shaft. The sleeves  44  are synchronously driven by a drive (not shown here). It is also possible for the secondary stop disks to be driven by their own drive, for example, a servomotor. This makes it possible to optimize the sequence of motions of the secondary stops and/or to reduce the number of secondary stops. With a suitable gear ratio, this drive can simultaneously serve as the drive for the shaft  33 . The secondary stop disks  40  each serve to support four levers  18 , which, as shown in  FIG. 1 , are two-armed levers. As shown in  FIG. 2 , these levers  18  are each rotatably supported, with an axis of rotation  19 , on one of the two secondary stop disks  40 . At one end, each of the levers  18  has a cam roller  20 , which runs on a cam  24  of a cam disk  39 . The two cam disks  39  are also rigidly connected with the support  32 . The course of the cam  24  is shown in  FIG. 1  as a dot-dash line. Instead of a cam disk  39 , other control mechanisms can also be used for controlling the levers  18 . 
         [0031]    In addition, the levers  18  have a secondary stop  21  at one end, as shown in  FIGS. 1 and 4 . The secondary stop  21  has a more or less conically tapering recess  23 , which is bounded on one side by a spring element  22  and on the other side by a tongue  46 . The spring element  22  is designed especially as a leaf spring. The recess  23  is arranged some distance from the axis of rotation  19  and at the opposite end of the lever  18  from the cam roller  20 . Each two-armed lever  18  thus has the cam roller  20  at one end and the aforesaid secondary stop  21  at the other end. The spring element  22  and the tongue  46  form holding means, with which the decelerated printed sheet  7  can be seized by its front edge  8 . 
         [0032]    The two secondary stop disks  24  are driven in the same direction as the gripper disk  37 . However, the speed of rotation of the two secondary stop disks  40  is slower than the speed of rotation of the gripper disk  37 . If the gripper disk  37  is driven at a speed V, then the two secondary stop disks  40  are driven at a speed V′. The speed V′ is significantly lower than the speed V. The two secondary stop disks  40  are driven at the same speed and synchronously with each other. In the illustrated embodiment, the speed V′ is 50% of the speed V. However, other speed ratios are also possible here; in particular, the speed V can be varied by a controlled drive during a rotation of the secondary stop disks. 
         [0033]    The cam  24  has an inwardly curved area  24 ′, which is located approximately in the 4 o&#39;clock position in  FIG. 1 . In this area  24 ′, the cam rollers  20  thus move radially inward and then radially outward again. Accordingly, the secondary stop  21  first moves radially outward and then radially inward again. The outward movement causes the secondary stop  21  to enter the peripheral region  17 , on which the printed sheets  7  are also being conveyed. The corresponding secondary stop  21  is now controlled in such a way that, upstream of the stop  16  or upstream of the pocket  15 , it forms a stop for a printed sheet  7  trailing it. 
         [0034]    Since the levers  18  are moved at a lower speed than the printed sheets  7 , the aforementioned printed sheet  7  is slowed down on the secondary stop  21  to the speed of the secondary stop  21 . Since, as explained earlier, two secondary stop disks  40  are provided, a printed sheet  7  simultaneously strikes two levers  18  or two secondary stops  21  that are some distance apart. Before the printed sheet  7  hits the two secondary stops  21 , it is released by the corresponding gripper  12 . The two levers  18 , on which the printed sheet  7  is stopped, now guides this printed sheet  7  farther until it reaches the pocket  15 , in which the printed sheet is finally slowed down to a speed of zero on the stop  16 . 
         [0035]    If the front edge  8  of a printed sheet  7  runs into the two secondary stops  21 , it then passes under the spring element  22  until finally, at the end of the recess  23 , it is gripped by said spring element  22  and thus stabilized. This is shown in  FIGS. 4 and 5 . In this way, the slowed printed sheet  7  can be safely transferred to the pocket  15  in the direction of the arrow  47 , as shown in  FIG. 5 . If the printed sheet  7  has been slowed to a speed of zero on the stop  16 , then the corresponding lever  18  can immediately detach itself from the printed sheet  7  due to the spring action of the spring element  22  and thus continue to be moved with undiminished speed. 
         [0036]    The end of the lever  18 , on which the secondary stop  21  is mounted, has a finger-like construction, as  FIG. 4  shows, and has a curved outer guide surface  45 . This guide surface  45  makes it possible, by suitable control of the lever  18 , to guide the rear edge  9  of a printed sheet  7  that is entering the pocket  15  in order to transfer the overlay fold  10  to one of the grippers  27 . The given lever  18  does not act as a secondary stop in this case but rather acts to guide the given printed sheet  7 , as just described. This process will now be described in greater detail with reference to  FIG. 3 . 
         [0037]    As  FIG. 3  shows, the rear edge  9  of a printed sheet  7  that has entered the pocket  15  is moved radially outward, which allows it to be gripped by one of the grippers  27 . This radially outwardly directed movement basically occurs even without the guidance of a lever  18 . However, the lever  18  assists this movement by the swiveling movement shown in  FIG. 3 . In this movement, the aforesaid guide surface  45  is moved radially outward beyond the peripheral area  17  upstream of the guide roller  41 . This movement begins as soon as the corresponding cam roller  20  moves into the aforementioned area  24 ′ of the cam  24 . The guide surface  25  then briefly moves in the outward direction and then back in the inward direction. Approximately in the vicinity of the guide roller  41 , the guide surface  45  is again located in the peripheral area  17 . 
         [0038]      FIG. 1  shows three printed sheets  7   a ,  7   b , and  7   c  in different phases during the transfer from the stack  6  to the opening drums  3  and  4 . A gripper  12  grips the front edge  8  of the printed sheet  7   a  approximately in the 10 o&#39;clock position. The lever  18 , whose secondary stop  21  is located in the vicinity of the front edge  8 , is inactive at this time. 
         [0039]    The front edge  8  of the printed sheet  7   b  is located at the secondary stop  21  of the lever  18 ″. The printed sheet  7   b  has thus been slowed or is being slowed. The printed sheet  7  is guided by the supporting lever  25  and is now being transferred on the stop  21  of the lever  18 ″ to the pocket  15 . This transfer is also shown in  FIG. 5 . When the rear edge  9  of the printed sheet  7   b  has left the supporting lever  25 , this rear edge  9  is guided by the following lever  18 ′ in such a way, as explained above, that this rear edge  9  can be securely gripped by one of the grippers  27 . 
         [0040]    The rear edge  9  of the printed sheet  7   c  has already been gripped by a lever  27  and is being pulled by this lever  27  out of the pocket  15  by the rotational motion of the opening drum  3 . Finally, the printed sheet  7   c  is opened by means that are already well known and dropped on the gathering chain  5 . 
         [0041]    The function of the lever  18 ′ as a guide device is advantageous during the transfer of the printed sheets  7  to the opening drums but is not essential to the invention. It would thus be conceivable to have a design in which the rear edge  9  is deflected in a way that in itself is already well known and is then gripped by a gripper  27 . 
         [0042]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.