Abstract:
In the method for monitoring the position of a sheet ( 36, 38, 48 ) transported in a folding machine, during the transport of the sheet ( 36, 38, 48 ), at a detection location, the positions of a sheet edge ( 37, 39, 49 ) running substantially in the transport direction (TR) are determined by a detection device ( 32, 34, 46 ). Measured values corresponding to the positions detected are then passed on to a processor device by the detection device ( 32, 34, 46 ). The processor device calculates a measured curve (MK 1,  MK 2,  MK 3 ) on the basis of the detected measured values and the travel of the sheet ( 36, 38, 48 ) through the detection location and compares this with a previously determined reference curve (RK). The processor device outputs an error signal if the measured curve (MK 1,  MK 2,  MK 3 ) deviates from the reference curve (RK).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a method for monitoring the position of a sheet transported in a folding machine.  
         [0003]     2. Description of the Background Art  
         [0004]     In a folding mechanism of a folding machine, a sheet is to be folded in such a way that, after the folding operation, all the edges of the sheet lie congruently on one another. A precondition for this is that the sheet has been cut absolutely rectangularly, the sheet is inserted at right angles to the longitudinal axes of the folding rollers, and the folding rollers exhibit the same pulling force over their working width. In the case of folding in a folding pocket, it is necessary that the folding pocket is not set obliquely with respect to the transport direction of the sheet and its clear width between the pocket rods is selected optimally. In addition, the sheet stop in the folding pocket must be set at right angles to the transport direction.  
         [0005]     In order to correct possible faults, adjusting devices are provided at the appropriate points of the folding machine.  
         [0006]     As a rule, not all the folded sheets of a job are cut with a cut on one cutting machine. Therefore, during the cutting of a job, it is possible for the rectangularity of the sheets and thus the folding result to change. In addition, a mechanical adjusting device, for example when its clamping to the folding machine is loosened, can change its position unnoticed. In addition, the position of a fold in a folding pocket depends on the speed. If the speed is changed during continuous production, the position of the fold changes, depending on the difference in speed, the sheet format, the folding length in the folding pocket and the characteristics of the paper.  
         [0007]     A change in the folding result is detected by an operator of the folding machine only if the quality of the finally folded sheet is monitored continuously. Then, by using the folded product, the operator must detect the point in the folding machine at which a correction must be made in order that the folding quality is optimal again. This is very complicated and requires a very great deal of experience on the part of the operator.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention is based on the object, by using constructionally simple means, of providing a method for monitoring the position of a sheet transported in a folding machine which makes it possible for the operator to quickly detect the source of a fault during the folding of a sheet and to carry out suitable corrective measures.  
         [0009]     According to the invention, this object is achieved by a method for monitoring a position of a sheet transported in a folding machine, in which during transport of said sheet, at at least one detection location, positions of a sheet edge running substantially in a transport direction are determined by a detection device, measured values corresponding to said positions detected are passed on to a processor device by said detection device, said processor device calculates a measured curve on the basis of said detected measured values and said travel of said sheet through said detection location, said processor device compares said measured curve with a previously determined reference curve, said processor device outputs an error signal if said measured curve deviates from said reference curve.  
         [0010]     As soon as the measured curve, determined during the passage of a sheet, deviates from the reference curve by more than a previously determined extent, the attention of the operator of the folding machine is drawn to the erroneous position of the sheet by the error signal from the processor device. The operator detects immediately the point in a folding machine at which the fault has first occurred. He can then take the necessary measures to rectify the erroneous position of the sheet.  
         [0011]     In the event of a slight deviation of the measured curve from the reference curve, the correction can be carried out by the operator during operation.  
         [0012]     If the deviations of the measured curve from the reference curve are too great, however, the processor device can give a command to stop the folding machine after the output of the error signal.  
         [0013]     An intervention of an operator would not be possible if, following the output of the error signal, the drives of the folding machine that are responsible for the deviation are driven automatically by the processor device in such a way that, in the case of the following sheets, the measured curve and the reference curve coincide.  
         [0014]     The detection device in a preferred embodiment is formed by a light curtain which, depending on the coverage by the sheet, passes on an electrical signal as measured value to the processor device. Such a light curtain is, for example, the FAV30-01 photo sensor with analog output from SensoPart. The electrical signal can be a voltage value, for example from 0 to 10 V, a current value, for example from 0 to 20 mA, a serial data interface, a parallel interface or the like.  
         [0015]     The detection and evaluation can, however, also be carried out by an image processing system comprising camera, processor device and suitable software.  
         [0016]     The reference curve is preferably determined during the passage of a calibration sheet which is optimally folded after passing through the folding machine. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Exemplary embodiments of the invention will be explained in more detail below using drawings, in which  
         [0018]      FIG. 1  shows, in schematic form, a plan view of a first embodiment of a folding machine having two folding mechanisms,  
         [0019]      FIG. 2  shows a pocket folding mechanism in schematic form,  
         [0020]      FIG. 3  shows a U-S reference curve of a calibration sheet,  
         [0021]      FIG. 4  shows a first measured curve as compared with the reference curve,  
         [0022]      FIG. 5  shows a second measured curve as compared with the reference curve,  
         [0023]      FIG. 6  shows a third measured curve as compared with the reference curve,  
         [0024]      FIG. 7  shows, in schematic form, a plan view of a second embodiment of a folding machine having two folding mechanisms. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     The folding machine shown in  FIG. 1  has a first folding mechanism  23  having two folding rollers  24 ,  26  and a second folding mechanism  29  having folding rollers  28 ,  30  connected downstream of the first folding mechanism  23 . Arranged upstream of the first folding mechanism  23  is a first inclined roller table which, in a known manner, contains an alignment rule  20  which extends in the transport direction TR 1  of the sheet  36 . In the ideal case, the sheet  36  will be brought into contact with the alignment rule  20  by the first inclined roller table  16  and then guided in the transport direction TR 1  between the folding rollers  24 ,  26  and folded by the latter. After the passage through the folding rollers  24 ,  26 , the folded sheet  39  is conveyed onto a second inclined roller table  18 , of which the transport direction TR 2  runs at right angles to the transport direction TR 1  of the first inclined roller table  16 . By means of the inclined rollers, the sheet  39  is brought into contact with an alignment rule  22  and then guided between the folding rollers  28 ,  30  of the second folding mechanism  29  and folded once more.  
         [0026]     Immediately before the folding rollers  24 ,  26  of the first folding mechanism  23  there is arranged a light curtain  32  as a detection device, whose longitudinal direction runs at right angles to the longitudinal direction of the alignment rule  20 . In the region in which the light curtain  32  is arranged, the sheet  36  should already be resting on the alignment rule  20 , in order then to be introduced between the folding rollers  24 ,  26  in the transport direction TR 1 .  
         [0027]     The light curtain  32  is arranged in such a way that it extends in the direction of the alignment rule  20  beyond the sheet edge  37  facing away from the alignment rule  20 , in order to be able to detect the sheet edge  37 . Depending on the coverage of the light curtain  32  by the sheet  36 , the light curtain  32  passes on a measured value to a processor device (not shown). The light curtain is, for example, an FAV30-01 photosensor with analog output from the SensoPart company. This photosensor passes on a voltage of 0 to 10 V to the processor device, depending on the coverage by the sheet  37 .  
         [0028]     A similar light curtain  34  is arranged in front of the second folding mechanism  29 .  
         [0029]      FIG. 2  shows, in schematic form, a folding pocket  40  having a plurality of pocket rods  42  forming a pocket gap and a stop  44  limiting the travel of a sheet running into the folding pocket  48 . Shortly after the pocket inlet, parallel to the stop  44 , there is arranged a light curtain  46 , which extends beyond the right-hand edge  49  of a sheet in  FIG. 2 . As indicated by the double arrow TR, the sheet  48  is inserted until it strikes the stop  44 . The sheet  48  is then conveyed out of the folding pocket  40  again.  
         [0030]      FIG. 3  shows by way of example a U(voltage)-S(travel) reference curve RK of a calibration sheet, which is determined by the processor device by using the measured values which had been determined by the optical sensor  32  during the passage of a calibration sheet.  
         [0031]     This is an optimal U-S curve, which leads to exact folding of the calibration sheet. The voltage U is passed on to the processor device by the light curtain. The travel S is determined via a rotary encoder on the appropriate folding mechanism. This rotary encoder is firmly connected to the sheet transport system. Each pulse on the rotary encoder corresponds to a specific travel of the sheet transport system. The processor device can therefore determine the sheet travel S and thus the U-S curve from the number of pulses.  
         [0032]      FIG. 4  shows a measured curve MK 1  from a sheet  36  passing through obliquely in the region of the light curtain  32 . The measured curve MK 1  shows that the sheet edge  37 , as it runs through the light curtain  32 , is located closer to the alignment rule  20  than the sheet edge  37  of the calibration sheet. At the end of the passage of the sheet  36 , the distance of the sheet edge  37  corresponds substantially to the distance of the sheet edge of the calibration sheet.  
         [0033]     The measured curve MK 2  shown in  FIG. 5  reveals that the sheet running direction of the sheet  36  is parallel to the sheet running direction of the calibration sheet. However, the sheet  36  covers the light curtain  32  further than the calibration sheet, so that a higher voltage is output by the light curtain  32 . The sheet  36  corresponding to the measured curve MK 2  is thus at a distance from the alignment rule  20 .  
         [0034]      FIG. 6  shows a measured curve MK 3  from a sheet  36  which is transported exactly along the alignment rule  20  and the width of which corresponds to the width of the calibration sheet. However, the leading sheet edge of the incoming sheet  36  runs into the light curtain  32  at a later time than that of the calibration sheet.  
         [0035]     If the processor device determines a measured curve MK 1 , MK 2  or MK 3 , it outputs an error signal which indicates that the sheet  36  is not transported in accordance with the calibration sheet. After the error signal has been output, by taking account of the differences of the measured curves MK 1 , MK 2  and MK 3  in relation to the reference curve RK, the suitable measures can be taken by an operator or, if appropriate, automatically.  
         [0036]     The second embodiment of the folding machine  50 , shown in  FIG. 7 , differs from the folding machine shown in  FIG. 1  in that the pairs of folding rollers  23 ,  29  in each case have a pair of knife cylinders  52  and  54  arranged after them, by means of which perforations or creases can be formed in a folded sheet folded by the pairs of folding rollers  23 ,  29 , weakening the sheet along a fold line.  
         [0037]     As viewed in the sheet transport direction TR, a further light curtain  58  is provided after the pair of knife cylinders  52  of the first folding mechanism  12 , such that it detects the lateral sheet edge  62  of a sheet  60  running out of the first folding mechanism  12 , which has been folded by the pair of folding rollers  23  and perforated by the pair of knife cylinders  52 . Since the lateral sheet edge  62  always runs parallel to the perforation or crease lines formed by the pair of knife cylinders  52 , it is possible to use the light curtain  58  in the manner described by using FIGS.  3  to  6  to detect whether the perforation or crease lines run exactly.  
         [0038]     Correction of oblique perforation lines is normally carried out by pulling a sheet diverter (not shown) arranged upstream of the pair of knife cylinders  52  in the folding mechanism  12  to the leading side. The pulling action forces a lengthening of the travel when passing through the sheet diverter, and therefore the lead is compensated for. The use of the light curtain  58  after the pair of knife cylinders  52  permits the monitoring of the straight exit of the emerging lateral sheet edge  62  and therefore the perforation line produced in the pair of knife cylinders  52 .  
         [0039]     Any deviation of a determined measured curve from a reference curve can be signaled to the operator by means of an error signal from the processor device, so that the appropriate sheet diverter can be pulled.