Abstract:
A method for trimming multiple edges of a print product over the course of several processing steps of a processing cycle using a trimming apparatus is disclosed. The method comprises the processing steps of feeding the print product from a stacking device to a trimming device using a feeding device, pressing the print product onto a trimming table using a pressing die, trimming the print product positioned on the trimming table using knives associated with the trimming device, releasing the pressing die from the trimming table, and removing the trimmed print product from the trimming table. The pressing die and the knives are driven by separate drives that are controlled by a control unit. The steps of feeding, pressing down, and releasing are time-variable, while the step of trimming includes a respectively time-constant knife movement for trimming the print product.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the priority of European Patent Application No. 04405649.7-1262, filed on Oct. 18, 2004, the entire content of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a method and apparatus for trimming multiple edges of a print product over the course of several processing steps of a processing cycle. The trimming apparatus comprises a stacking device for holding the print products, and a feeding device for transporting the print products from the stacking device to a trimming device. The trimming device includes a pressing die for pressing the print products onto the trimming table, and knives for trimming the print products positioned on the trimming table. The pressing die and the knives have separate drives controlled by a control unit. The processing cycle comprises the following processing steps: 
        feeding the print products from the stacking device to the trimming device;     pressing the print products onto the trimming table of the trimming device;     trimming the print products while they are positioned on the trimming table of the trimming device;     releasing the pressing die from the trimming table of the trimming device and conveying the print products away from the trimming table.        
 
         [0007]     Three-way trimmers are known which trim the goods (e.g. stacks of brochures, book blocks, or the like) by pressing the goods against trimming bars. Three-way trimmers of this type can trim a stack (e.g., a stack consisting of at least one book and/or book block) completely and on all three sides while remaining in the same position. The clamped-in good to be trimmed is aligned while on a trimming table and is then trimmed along the head, foot and fore edge. Depending on the design of the three-way trimmer, the sequence of the trimming steps can also be reversed.  
         [0008]     Also known are three-way trimmers that trim the fore-edge and the head and foot during separate machine cycles or processing steps. In that case, the good being trimmed must be transported between trimming operations from one trimming station to the next, which has a negative affect on the desired trimming quality.  
         [0009]     During the trimming operation, a pressing die presses the good against the trimming table to prevent any movement caused by the resulting cutting forces. To maintain a stable geometry for the good to be trimmed during the trimming operation, it must be ensured that any air which may still be trapped inside the freshly bound good can escape prior to the trimming. Air that is still present in the good during the trimming operation is damaging in several aspects. First, the friction value between pages is reduced because the air acts in the manner of, an air cushion, thus causing the pages to shift relative to each other during the trimming operation. Second, the enclosed air may increase the thickness of the good in certain regions, which can increase the spring-deflection of the good during trimming, causing the upper layers of the good to be cut longer. Both effects reduce the trimming quality.  
         [0010]     German reference DE 42 06 329 A, for example, discloses a method for trimming a good which makes use of a pressing device comprising a drive for adjusting pressing elements on the basis of a predetermined characteristic while taking into account the lowest structural mass. The lifting movement of the pressing element can be predetermined in dependence on the operational height for the good to be trimmed. Also provided is a unit for selecting the pressing force and the lifting height. The desired values for the pressing force and the lifting height are input by an operator. However, the disclosed device does not solve the problems caused by enclosed air and the associated reduced trimming quality.  
         [0011]     A three-way trimmer is also disclosed in reference EP 0 740 983 A. The disclosed device includes two side-trimming knives and one fore-edge trimming knife. The knives are provided with separate drives operated by digitally controlled servomotors or stepping motors. The movement sequences of the knives are synchronized with the aid of a joint control computer. A pressing die is also provided with a separate drive, which has a digitally controlled servomotor or stepping motor, and is synchronized, thereby resulting in a reduction of the mechanical expenditure and the space required for the coupling elements.  
         [0012]     Reference DE 30 11 090 A discloses a trimming apparatus with a mechanically operated pressing device, for which the pressing force can be adjusted hydraulically. The pressing device is positioned automatically, based on the height of the previous good to be trimmed.  
       SUMMARY OF THE INVENTION  
       [0013]     It is an object of the present invention to provide a method and apparatus for trimming multiple edges of a print product, which results in a higher trimming quality.  
         [0014]     One exemplary embodiment of the present invention relates to a method for trimming multiple edges of a print product over the course of several processing steps of a processing cycle using a trimming apparatus. The method comprises the processing steps of feeding the print product from a stacking device to a trimming device using a feeding device; pressing the print product onto a trimming table using a pressing die; trimming the print product positioned on the trimming table using knives associated with the trimming device; and releasing the pressing die from the trimming table and removing the trimmed print product from the trimming table. The pressing die and the knives are driven by separate drives that are controlled by a control unit. The steps of feeding, pressing down, and releasing are time-variable, while the step of trimming includes a respective knife movement for trimming the print product that is substantially constant in duration.  
         [0015]     Another exemplary embodiment of the present invention relates to a trimming apparatus for trimming multiple edges of a print product using a processing cycle. The apparatus comprises a stacking device; a feeding device; a pressing die operated by at least a first drive; a trimming device that operates jointly with the pressing die and includes several knives, the knives being operated by at least a second drive; a measuring device adapted to measure the thickness of the print product; and a control unit connected to the first drive, the second drive, and the measuring device. The processing cycle includes the steps of feeding the print product with the feeding device, pressing down the print product with the pressing die, trimming the print product with the trimming device, and releasing the pressing die from the print product. The control unit divides the processing cycle between the time-constant trimming step of constant duration, and at least one of the feeding, pressing, and releasing steps.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     These and other features and advantages of the invention will be further understood from the following detailed description of the preferred embodiments with reference to the accompanying drawings to which reference is made for all details not expressly mentioned in the text, wherein:  
         [0017]      FIG. 1  is a schematic representation of a trimming apparatus according to an exemplary embodiment of the present invention;  
         [0018]      FIG. 2  is a diagram, representing the steps of conveying, pressing, and trimming of the fore-edge and the head/foot, at the maximum possible clocking rate for one processing cycle;  
         [0019]      FIG. 3  is a diagram similar to  FIG. 2 , showing double the cycle time for the processing cycle;  
         [0020]      FIG. 4  is diagram similar to  FIG. 3 , showing an extended pressing time, and  
         [0021]      FIG. 5  is a diagram illustrating the fluffiness and dependence of the thickness on the pressing force in order to determine the spring characteristic for the trimming good.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 1  shows an exemplary trimming apparatus  1  for trimming print products, such as books or book blocks, according to the present invention. The trimming apparatus  1  includes a mechanical charging device  2 , a feeding device  7 , and a trimming device  17 . The mechanical charging device  2  comprises a conveying means for supplying the print products  5  in the direction of arrow  60  to a stacking device  4 , where a stack of print products  5  is formed. The good  10  to be trimmed (also referred to as the trimming good  10 ) consists of at least one print product  5 . The print products can include, for example, newspapers, catalogues, paperback books, or the like. The thickness of the print products produced during one production run can vary.  
         [0023]     A pusher  3  pushes the trimming good  10  from the stacking device  4  onto the feeding device  7 . The pusher  3  can have its height adjusted to be equal to or smaller than the minimum height of the trimming good  10 . The feeding device  7  includes a lower withdrawing roller  9  and an upper withdrawing roller  8 . Both withdrawing rollers  8 ,  9  can be driven with the aid of a motor  43  and a drive means  44 . The motor  43  can be connected via a signal line  45  to a control unit  30 . The lower withdrawing roller  9  can be mounted on the machine frame (not shown), while the upper withdrawing roller  8  can be mounted on guides  13  that allow the roller  8  to move vertically up and down against the force of a compression spring  12 . Compression spring  12  generates a force in the direction of arrow  15 . The vertical position of the upper withdrawing roller  8  can be detected by a measuring device  11  having a connection  14  that moves in response to movement of the roller  8  in the vertical direction. The measuring device  11  can be connected via a signal line  32  to the control unit  30 .  
         [0024]     Once the trimming good  10  leaves the feeding device  7  in the direction of the trimming device  17 , the trimming good  10  is conveyed by means of a conveyor  42  to a trimming table  18  on the trimming device  17 . After this, the pusher  3  moves back to its starting position, ready to push out the next trimming good  10 .  
         [0025]     On the trimming table  18 , the trimming good  10  is aligned positively in the longitudinal and transverse directions with the aid of an alignment means (not shown), and is then pressed with a pressing die  19  against the trimming table  18 , securing the trimming good  10  in place. The pressing die  19  can be arranged at the lower end of a spindle  20  which is operationally connected to a servomotor  21  that is controlled by a servo-drive  29  via a line  35 . The servo-drive  29  can be connected via a signal line  34  to a sensor  22  which detects the position of the pressing die  19 , which is moved up and down by turning the spindle  20 . The servo-drive  29  can be connected via signal lines  36 ,  37  to the control unit  30 . Once the trimming good  10  is pressed against the trimming table  18  and is thus secured in place, it is subsequently trimmed with a fore-edge knife  23  along the fore edge and with two side knives  24  along the head and foot. The sequence of trimming steps can also be reversed in that the head and foot can be trimmed first and then the fore edge. The fore-edge knife  23  moves vertically up and down in the directions of double arrow  25  while the two side knives  24  move in the direction of double arrow  26  for the trimming operation. The movement paths are shown with dashed lines  27  and  28  in  FIG. 1 .  
         [0026]     The trimming good  10  is preferably trimmed during a single processing cycle. The guided knives  23  and  24  can be driven with the aid of crank drives  46 ,  47  and via push rods  48 ,  49 . The crank drives  46 ,  47  in turn are driven by a motor  50  to which they are connected via a drive means  51 . The motor  50  can be connected via line  52  to the control unit  30 . Servomotors can be used for the motors  43 ,  50 , in which case, one servo-drive is installed between each of the motors  43 ,  50  and the control unit  30 .  
         [0027]     Once the good  10  has been trimmed and the pressure removed by lifting the pressing die  19 , the good  10  is removed from the trimming table  18  by means of a transporting device that is not shown.  
         [0028]     The device for removing the good can be, for example, a pusher, a gripper, or a conveyor-belt system. It is preferable that the next trimming good  10  is fed in at the same time as the previous trimming good  10  is being removed. The machine angle M (e.g., the angular position of the motor  50  and/or crank drives  46 ,  47  with respect to one full revolution), is preferably determined by a sensor  31  that is connected via a signal line  33  to the control unit  30 .  
         [0029]     The individual steps of the processing cycle include feeding the trimming good  10  by pushing it out of the stacking device  4  and transferring the good  10  to the trimming device  17 , pressing the good  10  onto the trimming table  18  with the pressing die  19 , making the fore-edge cut with the fore-edge knife  23  and making the side cuts with the side knives  24 , and finally releasing the pressing die  19  from the good  10 .  
         [0030]     The aforementioned steps are illustrated by curves  38  to  41  in  FIG. 2  for a processing cycle with a time interval T, and in dependence on the machine angle M.  
         [0031]     The curve  38  represents the trimming good  10  being fed from the stacking device  4  to the trimming table  18 , at a machine angle ranging from 130° to 260° along the transport path W. Shortly before the good  10  arrives in the position for trimming on the trimming table  18 , the pressing die  19  moves downward by the pressing stroke D, as represented by curve  39 , and reaches its lowest position on the trimming good  10  when the machine angle is approximately 300°. The curve  40  illustrates the movement S F  of the fore-edge knife  23 , which starts to move in the downward direction at a machine angle of approximately 270° and, shortly after the pressing die has reached its lower end position, starts the trimming of a thick good  10  with thickness D D , after reaching 300°. With a thin trimming good having a thickness of D d , the trimming operation is delayed by approximately 30°, for example, to a machine angle of approximately 330°. The lower end position of the fore-edge knife is reached at 0° from which the fore-edge knife  23  starts the return movement to the upper end position, immediately following the trimming operation. Curve  41  illustrates that the movement of the side knives is analogous to that of the fore-edge knife, but is phase-displaced by 110° (in the present example) in order to prevent a collision of the knives  23  and  24 . The total stroke S F  of the fore-edge knife  23  and S S  of the side knives  24  is always the same, regardless of all other parameters.  
         [0032]     The curve  39  shows that immediately after trimming with the side knives  24 , the pressing force is removed and the trimmed good  10  is conveyed away from the trimming table  18 . The next trimming good  10  is supplied at the same time and the above-described processing cycle is repeated. The curve  39 ( a ) in  FIG. 2 , representing the course of the pressing operation, corresponds to pressure applied to the thickest and most fluffy trimming good  10 . A smaller stroke as well as a flatter course for the curve  39 ( b ) results if the trimming good  10  is less fluffy. The trimming operation for a thin trimming good  10  with thickness D d  starts at approximately 333°. Additional time is thus available for the pressing operation and the course of the pressing curve  39  becomes even flatter, as shown with the curve  39 ( c ). The time available for pressing down on the good during the trimming of a thin trimming good  10  as compared to a thick trimming good is consequently increased considerably from 0.21 T to 0.30 T, as shown in  FIG. 2 . As a result of the longer pressing-down time, more of the air enclosed in the trimming good  10  can escape and a considerably more stable stack results due to higher friction between the individual sheets. As previously mentioned, this has a positive effect on the trimming quality. One example of this is the adaptation of the pressing-down movement to the varied thickness D D  and/or D d  of the trimming good  10 . Alternatively or additionally, the time gained can be used, for example, to extend the alignment operation or the time for transporting the trimming good  10 .  
         [0033]     Additional advantages are achieved if the trimming operation with the fore-edge knife  23  and the side knives  24  is realized at maximum speed for all operating conditions, which is explained in the following with the aid of  FIGS. 3 and 4 . If the trimming device  1  operates at half the speed, as illustrated by the diagram in  FIG. 3 , the cycle time Z is doubled to 2 T. With rigidly connected sequences, all time intervals for the individual steps are thus changed proportional to the cycle time. The corresponding courses for the curves  38 ′,  39 ′,  40 ′ and  41 ′ show the extension of the individual processing steps, for example, a longer transport time as shown with curve  38 ′. If, as illustrated in  FIG. 4 , the speed of the trimming operation is not cut in half correspondingly, but is maintained for the trimming operation, the same amount of time as shown in the diagram in  FIG. 2  is then required for the trimming operation, meaning 0.45 T. The trimming operation share of a processing cycle is then reduced in favor of the remaining processing steps. As a result, significantly more time is available for the remaining processing steps which are relevant to the quality. This additional time can be distributed over the other processing steps. According to the diagram in  FIG. 4 , for example, the pressing-down time is 1.19 T, as compared to 0.60 T for a proportional distribution according to the diagram in  FIG. 3 , which still results in a comparably long pressing-down time of 1.11 T for a trimming good  10  with comparably large thickness D D . As a result of this considerably longer pressing-down time, a correspondingly large amount of air can be squeezed from the trimming good. Since the thickness of a trimming good  10  consisting of several print products  5  can vary over a certain range, it is advantageous if the effective relative thickness S R  for the trimming good  10  is known before each pressing operation, so that the processing steps can be adapted continually and optimally for each processing cycle with the aid of values determined during a preceding calibration operation and by continuously measuring the feeding device  7 .  
         [0034]     Calibration Procedure:  
         [0035]     The trimming device  1  must first be adjusted to the dimensions of the print products and/or the trimming good. This may require, in some circumstances, replacing parts of the device, such as the trimming table  18  or the pressing die  19 . The pressing die  19  is then lowered to the trimming table  18  in order to detect the zero point, and the measuring system of the servo drive  29  is calibrated accordingly. This is already standard procedure for machines according to prior art. The new, additional calibration operation is shown with the diagram in  FIG. 5  and comprises the following steps: 
        Determining the relative thickness of a trimming good  10  by measuring the distance S R  between the withdrawing rollers  8 ,  9  with the measuring device  11 , at the force F R  required for the withdrawing, and storing the measured value S R  (0) in the control unit  30 . As shown in  FIG. 1 , the measuring device  11  is connected to the control unit  30  via signal line  32 .     Conveying the trimming good  10  to the trimming table  18 , with the pressing die  19  located in an upper position.     Lowering the pressing die  19  to the thickness D L  and storing the measured value D L (0) in the control unit  30 , wherein this thickness corresponds to the supplied trimming good  10  before the air is pressed out of it. The first contact between pressing die  19  and trimming good  10  occurs at this thickness. This position can be detected visually by the operator or by means of optoelectronic sensors. The value measured for the position of the pressing die  19  can be polled at the servo drive  29 , which is connected via the signal line  34  to the sensor  22  of the servomotor  21 .     Build-up of the pressing-down force F 2 , which should correspond at least to the pressing-down force required for the production, as well as measuring of the thickness D 2 (0).     Build-up of the pressing-down force F 1 , which should be considerably smaller than the pressing-down force F 2 , as well as measuring of the thickness D 1  and storing of the measured value D 1 (0).        
 
         [0041]     A specific force is built up at the pressing die by generating a corresponding torque at the servomotor  21  with the aid of the servo drive  29 . With the aid of points P 1 (0) and P 2 (0), it is possible to compute the increase in the spring characteristic, using the Formula C=(F 2 −F 1 )/(D 2 (0)−D 1 (0)), and the point P 0 (0). It is only necessary to carry out this calibration on the first trimming good  10 . Once the spring characteristic C has been determined, it can be considered a constant because the differences for the thickness S R  within a production run are relatively small. Making the assumption that with all print products  5  of a series, the values D 0 −S R , D B  and C of the trimming good  10  are constant, all other points such as P 0 (n), P 1 (n), P 2 (n) and P L (n) can be computed based on the continuously measured thickness S R (n).  
         [0042]     The thickness D L  of a loose trimming good  10  can be computed, for example, with the following formula: 
 
 D   L ( n )= D   L (0)+( S   R ( n )− S   R (0) ) 
 
 The drives are coordinated via the control unit  30 , which is connected via the lines  37 ,  45 ,  52  to the drives or motors. The control unit  30  is supplied via the signal lines  32 ,  33 ,  36  with the required measuring values and signals. 
 
         [0043]     It is obvious from the above explanations that a considerable reduction in the press-down speed, above all in the acceleration, is possible by optimizing the pressing stroke, especially for stiff and/or thin print products  5 . Independent of the production speed, the trimming device  17  can always operate at the maximum speed which in this case is limited not by the trimming speed, but by the limits predetermined by the mechanics. It is furthermore essential that the cycle time Z, which is longer for a slower machine speed, is available for the transporting, aligning, and pressing down operations, since the same amount of time is always needed for the trimming operation.  
         [0044]     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.