Abstract:
Apparatus for depositing sheets on a stack, which permits essentially free access to the stack and can be implemented with a low outlay of materials and costs. The apparatus includes on the side of the stack ( 1 ) that faces a machine, tongues ( 5, 6 ) with which frictional elements ( 3, 4 ) can be brought into and out of contact and which can be moved in the conveying direction ( 10 ) of the sheets ( 2 ) and in the opposite direction, and can be lowered onto the stack ( 1 ), and wherein on the side of the stack ( 1 ) that faces the machine, at least one hold-down ( 7 ) is provided which can be moved in the conveying direction ( 10 ) of the sheets ( 2 ) and in the opposite direction, and can be lowered onto the stack ( 1 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to an apparatus for depositing sheets on a stack. 
     BACKGROUND OF THE INVENTION 
     Apparatus is known for depositing sheets on a stack, which apparatus is arranged downstream, for example, of a printing machine. Such apparatus uses grippers that are arranged on endless chains, open under cam control and allow a sheet to fall in order to form a stack. Allowing the sheet to fall can be improved by using suction air and blower devices, by the conveying speed being retarded considerably and by the falling movement being accelerated. In order to improve the exactness of the stack formation, the sheets to be deposited are brought up against a stop and aligned using rectilinear joggers acting on side edges. In the environment of the stack there is a large number of constructional elements requiring high outlay of materials and costs, which also impair operator accessibility to the stack for handling and inspection activities. The moving parts in the sheet stack area of a printing machine constitute a safety risk, so that the sheet stack area is enclosed to the greatest possible extent. In order to remove a proof sheet, appropriate additional apparatus, such as flaps or diverters, can be provided, which necessitates additional outlay. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to develop an apparatus for depositing sheets on a stack, which permits essentially free access to the stack and can be implemented with a low outlay of materials and costs. 
     The elements provided for depositing the sheets are located essentially so as to face the sheet-processing or sheet-inspecting machine. The elements act on the trailing end of the sheets and occupy only a low volume. Free accessibility to three sides of the stack is provided. If the sheets are deposited with the imprint on the top, the printed image can be inspected easily, since only a small area is covered by such elements and the light conditions for the inspection are optimal. The stack can be transported away without hindrance. If the frictional elements are independently driven rollers, a skewed position of a sheet can be compensated for. If, in addition, the frictional elements can be moved transversely with respect to the conveying direction of the sheets, the lateral position of the sheets can be adjusted. The apparatus has only a few elements with a low volume. Stops or deposit containers predefining the form of the stack are not necessary. The widest possible range of sheet format can be deposited, without adjustments of any kind being needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is to be explained in more detail below using the exemplary embodiments. In the drawings: 
         FIGS. 1.1  through  1 . 11  show a schematic side view of the apparatus, at various stages of operation; 
         FIG. 2  shows a schematic plan view of the apparatus; and 
         FIGS. 3 through 7  show an embodiment with control cams. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Those parts of the apparatus, which are essential to the invention are illustrated schematically in side view and plan view in  FIGS. 1.1  through  1 . 11  and  2 .  FIGS. 1.1  through  1 . 11  show a stack  1 , onto which sheets  2  are to be deposited horizontally upon one another. For this purpose, two rollers  3 ,  4 , two tongues  5 ,  6 , and hold-down  7  are provided. The axes of rotation of the rollers  3 ,  4  are aligned along a line  8 , which is parallel to the upper, rear stack edge  9  and perpendicular to the conveying direction  10 . In the lateral direction, the rollers  3 ,  4  are arranged symmetrically with respect to the mid-line  11  of the stack  1 , in the vicinity of the side edges  12 ,  13  of the stack  1 . The rollers  3 ,  4  are driven independently of one another by stepping motors, so that the rollers  3 ,  4  can rotate at different speeds in the direction of the arrow  16 . 
     The rollers  3 ,  4 , together with the stepping motors, are fixed to a common frame  17 . The frame  17  with the rollers  3 ,  4  is provided such that it can be raised and lowered in the vertical direction  18  and positioned in the lateral direction  19 . On their surface, the rollers  3 ,  4  are provided with an elastic material, so that when they are in contact with a sheet  2 , the result is a high coefficient of friction. The tongues  5 ,  6  are located in the lateral direction at the level of the rollers  3 ,  4 . The tongues  5 ,  6  are very flat, arranged parallel to the surface of the stack  1  and fixed to a frame  20 . The frame  20  with the tongues  5 ,  6  can be positioned in the vertical direction  18  and in the horizontal direction  21 . The surface  22  of the tongues  5 ,  6  facing the rollers  3 ,  4  is polished and, in relation to the sheet material, has a low coefficient of friction. The surface  23  of the tongues  5 ,  6  facing the upper side of the stack can have a high coefficient of friction in relation to the sheet  2  located underneath. The hold-down  7  acts in the center on the rear stack edge  9 . The hold-down  7  is likewise arranged such that it can be positioned in the horizontal and vertical direction  18  and  21 . The underside  24  of the hold-down  7  has a high coefficient of friction in relation to the sheet  2  located underneath. 
     The mode of action of the apparatus is to be explained using eleven component pictures  FIGS. 1.1  through  1 . 11 : in the initial state ( FIG. 1.1 ) the rollers  3 ,  4  and the tongues  5 ,  6  are raised, in each case, in their uppermost vertical position. The hold-down  7  presses with its underside  24  on the top sheet of the stack  1  and fixes it. The rollers  3 ,  4  rotate at a circumferential speed, which corresponds to the conveying speed of a sheet  2  output from a printing machine. The conveying direction  10  is inclined with respect to the horizontal direction  21  in such a way that the sheet  2 , beginning with its leading edge  25 , can slide along on the smooth surface  22  of the tongues  5 ,  6 . 
     In the state shown in  FIG. 1.2 , the tongues  5 ,  6  have been lowered onto the stack  1 , and the rollers  3 ,  4  have been lowered to about half their maximum height above the stack  1 . As the sheet  2  is advanced further, the leading end is located under the rollers  3 ,  4 , as illustrated in  FIG. 1.3 . The rollers  3 ,  4  press the sheet  2  against the surface  22 . The sheet  2  is conveyed onward by the rotation of the rollers  3 ,  4 . The stepping motors of the rollers  3 ,  4  are stopped when the trailing edge  26  of the sheet  2  has reached the rear stack edge  9 . This state is shown in  FIG. 1.4 . 
     After the rollers  3 ,  4  have stopped, the hold-down  7  is lifted off the stack  1  and, as illustrated specifically in  FIG. 1.5 , displaced in the horizontal direction  21  in the direction opposite to the conveying direction  10  of the sheet  2 , so that the front end  27  of the hold-down  7  is still located in front of the rear stack edge  9 . At the same time, the sheet  2  is deposited onto the stack  1  in the area between the tongues  5 ,  6 . As the hold-down  7  is drawn away, the sheet  2  remains fixed in position by the rollers  3 ,  4 . As shown in  FIGS. 1.6  and  1 . 7 , the hold-down  7  is placed onto the rear end of the stack  1  again by a horizontal movement and a vertical movement. The hold-down  7  then takes over the action of fixing the top sheet  2  in position. 
     The rollers  3 ,  4  can be lifted off the stack  1 , as shown in  FIG. 1.8 . In subsequent steps ( FIGS. 1.8  and  1 . 9 ), the tongues  5 ,  6  are lifted off the stack  1  and drawn back in the horizontal direction  21  to such an extent that the front end  27  of the tongues  5 ,  6  is still located in front of the rear stack edge  9 . The sheet  2 , which continues to be fixed by the hold-down  7 , is deposited entirely on the stack  1 . In a last step, as illustrated in  FIG. 1.11 , the tongues  5 ,  6  are moved back into the position above the stack  1  and under the rollers  3 ,  4 . The rollers  3 ,  4  are set rotating, which produces the initial state, described in  FIG. 1.1 , for the deposition of the next sheet  2 . 
     The stepping motors of the rollers  3 ,  4  can be constituent parts of a position control loop for the sheets. For this purpose, detectors for the position of the sheet  2  in relation to the stack edges can be provided. By comparing the actual position with a desired position, actuating signals can be derived which, in the step according to  FIG. 1.3 , drive the rollers  3 ,  4  at different circumferential speeds in such a way that a skewed position of a sheet is compensated for. In the step according to  FIG. 1.4 , the frame  17  with the rollers  3 ,  4  can be positioned further in the direction  19 , by which any lateral offset of the sheet  2  in relation to the stack  1  can be compensated for or can be produced deliberately. 
       FIGS. 3 through 7  show an exemplary embodiment in which two tongues  101 ,  102  and a hold-down  103  arranged between the tongues  101 ,  102  can be raised and lowered from a stack (not further illustrated) with the aid of cam disks  104 – 106 . The cam disks  104 – 106  are firmly seated on a shaft  107 , which is mounted in a frame  108 . In order to drive the shaft  107 , a toothed-belt gear mechanism is used, having toothed-belt pulleys  109 – 111 , a toothed belt  112 , and a motor  113  fixed to the frame  108 . The tongues  101 ,  102  are connected via rotary joints  114 ,  115  to a common holding plate  116  which is essentially arranged horizontally and which is mounted such that it can be pivoted on a shaft  117  held in the frame  108 . The hold-down  103  is likewise connected via a rotary joint  118  to a holding plate  119 , which is also mounted such that it can be pivoted on the shaft  117 . 
     Mounted in the frame  108  is a further shaft  120 , which is located parallel to the shaft  107  and on which cam disks  121 – 123  are fixed. The cam disks  121 – 123  roll on grooved ball bearings  124  ( FIG. 5 ), which are located in the U-shaped holding plates  116 ,  119 . As the bottom view of  FIG. 4  reveals, the cam disks  104 – 106  slide on sliding coverings  125 – 127 , which are located under the tongues  101 ,  102  and under the hold-down  103 . The shaft  120  is driven synchronously with the shaft  107  by the toothed-belt pulley  110 . In order to prevent the tongues  101 ,  102 , the hold-down  103  and the holding plates  116 ,  119 , all of which are moved in operation, from lifting off the cam disks  104 – 106 ,  121 – 123 , tension springs  128 – 130  are provided, which are fixed to a shaft  131  fixed in the frame  108 . On the shaft  117 , close to the holding plate  119 , a tension holding plate  132  is mounted such that it can be pivoted. Provided in the tension holding plate  132  is a further grooved ball bearing  133 , which interacts with a cam disk  134 , which is likewise fixed to the shaft  120 . A tension spring  135  connects the hold-down  103  to the grooved ball bearing  133  in the tension holding plate  132 . 
     Mounted above the elements described in  FIGS. 3 through 5  is a subassembly shown in more detail in  FIGS. 6 and 7 . The subassembly contains offset rollers  136 ,  137 , which interact with the tongues  101 ,  102 . The offset rollers  136 ,  137  are fixed to an aluminum tube  138 . The aluminum tube  138  is guided in sliding bearings such that it can be displaced on a drive shaft  139 . By a bushing  140  which is provided with a longitudinal slot, and with the aid of a pin that is screwed into the drive shaft  139 , the torque is transmitted to the offset rollers  136 ,  137  by the drive shaft  139 , which is driven by a stepping motor. A stepping motor  141  with attached spindle effects the lateral displacement of the offset rollers  136 ,  137  on the drive shaft  139 . The forces for the lateral displacement of the offset rollers  13 . 6 ,  137  are transmitted by an articulated head  142 , which is secured against rotation on the spindle. 
     Guided in the articulated head  142  is a rod  143 , which is screwed into a setting ring  144 , which is not rotated at the same time. The articulated head  142  and the rod  143  are necessary in order to raise the offset rollers  136 ,  137  off the tongues  101 ,  102 . When the offset rollers  136 ,  137  are being raised, the rod  143  is able to slide through the articulated head  142  with a clearance fit. The raising action is achieved via lateral lever arms  145 ,  146 . The lever arms  145 ,  146  are mounted in a holder  147  such that they can be pivoted about a shaft  148 . 
     When the upper subassembly is put together with the lower subassembly, grooved ball bearings  149  fixed on the lever arms  145 ,  146  rest on cam disks  150 ,  151  which are fixed to the shaft  107 . The upper subassembly includes a paper feed  152 , a pair of rollers  153  being provided in the transport path of the sheets. The rollers of the pair of rollers  153  can be driven independently of one another by motors, by which a skewed sheet can be aligned by accelerating one of the rollers. Following the alignment of a sheet, its lateral position can be registered, for example using a linear CCD. Using computing means, the difference between the center of the sheet and the theoretically accurate central position of the sheet can be determined, and can be corrected with the aid of the lateral displacement of the offset rollers  136 ,  137 . The correction to the deviation of the sheet centers from the center of the paper path is carried out in a similar manner as well during the production of sheet stacks with sheets located so as to be offset. 
     The cam disks  104 – 106 ,  121 – 123 ,  134 ,  150 , and  151  have the corresponding phase angles and geometries corresponding to the movement sequence already described in relation to  FIGS. 1.1  through  1 . 11  and  2 . The entire holding and depositing procedure is run through with one revolution of the shaft of the motor  113 . 
     In the following text, the intention is to discuss the function of the above-described elements in more detail. The tension holding plate  132  and the tension spring  135 , in conjunction with the cam disk  134 , have the effect of completely relieving the tension on the hold-down  103  shortly before the hold-down  103  is drawn out of the interspace between a newly deposited sheet and the stack already formed. In this state, the hold-down  103  does not exert any holding forces on the stack. While the hold-down  103  is being relieved of tension and drawn out of the stack, the tongues  101 ,  102  perform the clamping of the top sheets. The sheet newly deposited above the tongues  101 ,  102  is held by the offset rollers  136 ,  137 . 
     Before the tongues  101 ,  102  are drawn back out of the stack and the hold-down  103  takes over the clamping of the sheet stack, the tongues  101 ,  102  are first raised considerably from the sheet stack by the cam disks  104 ,  106 . It would also be possible to implement a tension-relieving operation as has already been described in relation to the hold-down  103 . A few milliseconds before the tongues  101 ,  102  are raised, the raising of the offset rollers  136 ,  137  begins, brought about by the cam disks  150 ,  151 . This premature raising of the offset rollers  136 ,  137  off the tongues  101 ,  102  is necessary in order that the sheet conveyed out between the offset rollers  136 ,  137  and the tongues  101 ,  102  is released and ultimately held only by the hold-down  103 . As the tongues  101 ,  102  are raised, the two lateral sheet edges are raised to a slight extent at the same time. When the tongues  101 ,  102  are drawn away from the sheet stack  1 , by the cam disks  121 ,  122  in the next step, then the sheet stack  1  is released by tongues  101 ,  102 , and the conveyed sheet is deposited on the already existing stack  1 . 
     The cam disks  104 ,  106 ,  121 ,  122  are such that as the tongues  101 ,  102  are advanced quickly over the stack, the tongues  101 ,  102  remain in a raised position, so that they can be moved safely over the stack. Only shortly before the final position of the tongues  101 ,  102  as they are advanced rapidly over the stack are the tongues  101 ,  102  lowered onto the stack by the cam disks  104 ,  106 . A newly conveyed sheet can subsequently move onto the stack over the tongues  101 ,  102 , the offset rollers  136 ,  137  still being in a raised position because of the cam disks  150 ,  151 ; that is to say, there is no contact between the tongues  101 ,  102  and the offset rollers  136 ,  137 . Before the offset rollers  136 ,  137  are lowered by the cam disks  150 ,  151 , the offset rollers  136 ,  137  are brought up to sheet advance speed. After the offset rollers  136 ,  130 . 7  have been lowered, these take over the sheet transport onto the stack still before the pair of rollers  153  releases the sheet in the paper feed  152 . The correction to the skewed position of a sheet by the pair of rollers  153  is concluded before the offset rollers  136 ,  137  are placed on said sheet. 
     In the paper feed  152 , in the conveying path of the sheet and directly downstream of the pair of rollers  153 , two detectors for the sheet trailing edge can be provided spaced apart from one another perpendicularly in the conveying direction. As a result, the sheets can be deposited irrespective of their format. The detector signals are used to start the motor  113  and to correct the skewed position of the sheets. Following each deposition cycle, the deposition system finds itself in a rest position, in which the hold-down  103  rests on the sheet stack, the tongues  101 ,  102  are in the withdrawn position and the offset rollers  136 ,  137  are raised. 
     In addition to the variants described above, however, the sheet leading edge can also be detected. For this purpose, the information relating to the sheet length must be made available to the deposition system. Using this information, the appropriate time delay for the starting point of the deposition cycle is then determined. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           1  Stack 
           2  Sheet 
           3 ,  4  Roller 
           5 ,  6  Tongue 
           7  Hold-down 
           8  Line 
           9  Stack edge 
           10  Conveying direction 
           11  Mid-line 
           12 ,  13  Side edges 
           14 ,  15  Stepping motors 
           16  Arrow 
           17  Frame 
           18  Direction 
           19  Direction 
           20  Frame 
           21  Direction 
           22 ,  23  Surface 
           24  Underside 
           25  Leading edge 
           26  Trailing edge 
           27  End 
           101 ,  102  Tongue 
           103  Hold-down 
           104 – 106  Cam disks 
           107  Shaft 
           108  Frame 
           109 – 111  Toothed-belt pulleys 
           112  Toothed belt 
           113  Motor 
           114 ,  115  Rotary joint 
           116  Holding plate 
           117  Shaft 
           118  Rotary joint 
           119  Holding plate 
           120  Shaft 
           121 – 123  Cam disk 
           124  Grooved ball bearing 
           125 – 127  Sliding covering 
           128 – 130  Tension spring 
           131  Shaft 
           132  Tension holding plate 
           134  Cam disk 
           135  Tension Spring 
           136 ,  137  Offset roller 
           138  Aluminum tube 
           139  Drive shaft 
           140  Bush 
           141  Stepping motor 
           142  Articulated head 
           143  Rod 
           144  Setting ring 
           145 ,  146  Lever arms 
           147  Mounting 
           148  Shaft 
           149  Grooved ball bearing 
           150 ,  151  Cam disk 
           152  Paper feed 
           153  Pair of rollers