Abstract:
A structure in which length-measuring roll including an elastic body is rotated by movement of a continuously fed web is employed, an amount of deformation of the length-measuring roll changes according to changes in a web speed, and a circumference of the length-measuring roll changes as a result. An error is generated in length measurement of the web, and therefore, web cutting accuracy by a cutter cannot be maintained. Therefore, timing of cutting by the cutter is controlled according to a fed length of the web and web speed information to maintain web cutting accuracy.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a device and method for cutting a web of a photosensitive planographic printing plate precursor, or the like, to a predetermined size.  
           [0003]    2. Description of the Related Art  
           [0004]    Generally, for producing a photosensitive planographic printing plate precursor (hereinafter referred to as a “PS plate”), a sheet-like or coil-like aluminum plate is subjected to a surface treatment or a suitable combination of surface treatments such as graining, anodic oxidation, chemical conversion treatment. Then, the aluminum plate is coated with a photosensitive solution and dried (hereinafter, a product thus processed is called a “web”), and then cut to a desired size.  
           [0005]    That is, a trimming width (width size) of a PS plate is determined by continuously cutting the web using a slitter. Then, a cutting length L (length in a conveyance direction) of the PS plate  12 A is determined by continuous cutting by a flying shear  50 , shown in FIG. 8, disposed at a downstream side of the slitter.  
           [0006]    Timing of cutting by the flying shear  50  (timing of rotation) is controlled by measuring, with an encoder  56 , the number of rotations of a length-measuring roll  54 , which feeds a web  12 , and calculating a fed length of the web  12  in a cutter controller  58 .  
           [0007]    In recent years, in order to eliminate adverse effects on a surface of the PS plate  12 A, rubber rolls have been used for the length-measuring roll  54  instead of metal rolls that measure more accurately. However, as shown in FIG. 9, circumferences of rubber rolls  60  change because deformation conditions at a nip portion of the rubber rolls  60  change slightly depending on a speed of travel of the web  12 .  
           [0008]    Therefore, although the number of rotations of the rubber rolls  60  is constant, measured lengths of the web  12  vary depending on the speed of the web  12 , and this causes irregularities in accuracy of the cut lengths of PS plate.  
         SUMMARY OF THE INVENTION  
         [0009]    In view of the aforementioned drawbacks, a task of the present invention is to become able to ensure accurate cutting even when a web speed changes.  
           [0010]    A device for cutting a web according to a first aspect of the present invention comprises: a roll comprising an elastic body, the roll being rotatably mounted in contact with a web and rotating when the web is fed past the roll due to contact between the web and roll; a cutter for cutting the web disposed downstream of the roll relative to feed direction of the web; a length-measuring device for measuring length of the web fed past the roll; and a controller which communicates with the cutter and the length-measuring device and receiving the information from the length-measuring device, with the controller controlling timing of cutting by the cutter according to fed length of the web and web speed information based on data from the length-measuring device.  
           [0011]    In the above-described structure, since the rolls having elastic bodies (hereinafter, elastic rolls) are rotated by the movement of the continuously fed web, there is no risk of damaging the surface of the web, as there is when metal rolls are used. However, an amount of crushing of the elastic rolls changes according to changes in the web speed, and the circumferences of the elastic rolls change.  
           [0012]    Since the length-measuring device measures the fed length of the web by counting the number of rotations of the elastic rolls, errors are generated in a measurement of the length of the web, and therefore, accurate cutting of the web (hereinafter, web cutting accuracy) cannot be maintained.  
           [0013]    Therefore, the controller controls the timing of cutting by the cutter on the basis of the fed length of the web and the web speed information, thereby maintaining accurate web cutting.  
           [0014]    The device for cutting a web according to the present invention is preferably characterized in that the web speed information includes acceleration/deceleration information of the web, based on data received from the length-measuring device at a time of previous cutting and at a time of current cutting.  
           [0015]    In the structure described above, whether the web is in a state of acceleration or deceleration is continuously determined on the basis of a web speed at a time of previous cutting and a web speed at a time of current cutting to ensure web cutting accuracy.  
           [0016]    Further, the device for cutting a web according to the present invention is preferably characterized in that the timing of cutting by the cutter is controlled so as to compensate for errors in length measurement according to hysteresis of acceleration and deceleration, the hysteresis of acceleration and deceleration being the acceleration/deceleration information.  
           [0017]    In the structure described above, the different changed states of the circumference of the elastic rolls according to hysteresis of acceleration and deceleration of the web are noted. Then, since errors in length measurement of the web can be accurately understood, web cutting accuracy can be improved.  
           [0018]    Furthermore, the device for cutting a web according to the present invention is preferably characterized in that the controller controls the timing of cutting by the cutter by correcting a set cutting length value of the web on the basis of a correction value obtained by multiplying the web speed, a cutting length of the web, and a correction coefficient together.  
           [0019]    In the structure described above, the fact that errors in the measurement of the cutting length by the elastic rolls become larger when the cutting length becomes larger is noted, and the timing of cutting by the cutter is controlled so that a set cutting length of the web which is input to the controller is controlled using a correction value calculated by multiplying a cutting length of the web.  
           [0020]    In addition, the device for cutting a web according to the present invention is preferably characterized in that the controller controls the timing of cutting by the cutter by correcting a set cutting length value of the web on the basis of at least one of a correction value obtained by multiplying the web speed, a unit length of the web, and a correction coefficient together, and a correction value obtained by multiplying the web speed, a circumference of the roll and a correction coefficient together.  
           [0021]    In the structure described above, all cutting lengths from long to short can be swiftly corrected on the basis of the web measurement errors.  
           [0022]    A method for cutting a web according to another aspect of the present invention comprises the steps of: (a) feeding the web past a rotatably mounted roll comprising an elastic body, with the roll contacting the web so that the roll rotates due to contact between the roll and the web, (b) measuring fed length and speed information of the web based on rotation of the roll; and (c) cutting the web so as to compensate for an error in the fed length measured which error varies according to the speed information of the web. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a perspective view showing all of a line in which a device for cutting a web according to an embodiment of the present invention is used.  
         [0024]    [0024]FIG. 2 is a block diagram for explaining the device for cutting a web according to the embodiment of the present invention.  
         [0025]    [0025]FIG. 3 is a graph showing a relationship between hysteresis at times of acceleration and deceleration of the web and errors in cutting length.  
         [0026]    [0026]FIG. 4 is a flow chart showing a procedure for calculating correction values.  
         [0027]    [0027]FIG. 5 is a graph showing differences between errors in cutting length of the web when the correction has been performed and when the correction has not been performed.  
         [0028]    [0028]FIG. 6 is a graph showing amounts of errors due to differences in set cutting lengths of the web when the correction has not been performed.  
         [0029]    [0029]FIG. 7 is a graph showing amounts of errors due to differences in set cutting lengths of the web when the correction has been performed.  
         [0030]    [0030]FIG. 8 is a block diagram for explaining a conventional device for cutting a web.  
         [0031]    [0031]FIG. 9 is a sectional view showing an aspect of deformation of rubber rolls due to changes in speed. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    Hereinafter, an embodiment of the present invention will be described with reference to the figures.  
         [0033]    First, an outline of a cutting line will be described.  
         [0034]    As shown in FIG. 1, a feeding device  14  for feeding a roll-shaped web  12  is disposed at an upstream side of a processing line. The web  12  is fed from the feeding device  14 , and then, a charged interleaf sheet  18  is superposed on the web  12  at feeding rolls  16 . Then, the web  12  is conveyed to a notcher  20 .  
         [0035]    The notcher  20  punches holes in edge portions or a central portion of the web  12  so that upper trimming blades  22  and lower trimming blades  24  of a slitter  10  can move in a width (transverse) direction of the web  12  at the punched portions. Thus, trimming widths (width sizes) of the web  12  can be changed during continuous cutting (cutting the interleaf sheet and the web). Further, as necessary, the web  12  may be cut and divided down the central portion thereof by a center-cutting blade  26  to form two webs.  
         [0036]    In this manner, the web  12  is trimmed to a predetermined trimming width. Then, a length-measuring roll  42  of a web-cutting device  40 A detects a fed length of the web, and a cutter  34  cuts the web  12  with an instructed timing to produce PS plates  12 A having a set size.  
         [0037]    The PS plates  12 A are loaded onto a conveyer  36  and conveyed to a collecting site  46 . Then, after a predetermined number of the PS plates  12 A which were conveyed to the collecting site  46  are piled up, the PS plates are packaged in, for example, a corrugated board box to be shipped. Defective products sorted by a sorting device  48  are conveyed to a dumping site by an ejection conveyer  48 .  
         [0038]    Next, the web-cutting device will be described with reference to FIG. 2.  
         [0039]    The length-measuring roll  42  comprises rubber roll portions  42 A as elastic bodies, which nip the web  12  from the upper side and the lower side and which are rotated by movement of the web  12 . By making portions of the rolls contacting the web  12  out of rubber, there is no risk of damaging the surface of the web  12 .  
         [0040]    An encoder  28  is attached at a shaft of the length-measuring roll  42 . By counting pulses of the encoder  28  using a counter, a rotation angle (the number of rotations) of the length-measuring roll  42  can be measured.  
         [0041]    Based on this, a fed amount of the web  12  from the length-measuring roll  42  is calculated by the cutter controller  30 , and the cutter  34  is rotated at a predetermined timing on the basis of a cutting length of an inputted product size to cut the web  12  continuously.  
         [0042]    However, when the above-described control method is used, the web  12  cannot be cut to a correct product size since a circumference of the length-measuring roll  42  changes depending on the speed of the web  12 . Therefore, a correction calculation device  32  is provided for continuously correcting irregularities in cutting accuracy due to changes in the speed of the web  12 , so that accuracy of cutting can be ensured in any speed range and in any state of acceleration or deceleration.  
         [0043]    Specifically, a current web speed is calculated on the basis of length-measuring pulses input to the correction calculation device  32  from the encoder  28 . By comparing the current speed with a previously measured speed, namely, a speed measured at the time of previous cutting, it is determined whether the web  12  is in a state of acceleration, constant speed, or deceleration.  
         [0044]    As shown in FIG. 3, a determination of the state of the web speed is carried out because errors in the cutting length with respect to the set cutting value vary due to hysteresis at the times of acceleration and deceleration. Therefore, the set cutting value which is input to the cutter controller  30  is corrected using a correction value according to each state of the speed. Thus, timing of cutting by the cutter  34  is modified.  
         [0045]    The correction calculation is given by: 
         α=( A·v+B ) x×   
         [0046]    where α is a correction value, v is a web speed, x is a cutting length of a product size, a correction coefficient A=−4.56939×10 −6 , and a correction coefficient B=3.55513×10 −4 .  
         [0047]    Note that, as shown in FIG. 4, when the web speed is less than 60 m/min and accelerating or at a constant speed, (x+α) is input to the cutter controller  30  as a set cutting value. However, when the web speed is 60 m/min or more and decelerating or at a constant speed, x is input to the cutter controller  30  as a set cutting value without correction.  
         [0048]    Further, when the web speed is less than 30 m/min and in the deceleration range, (x+α/2) is input to the cutter controller  30  as a set cutting value, and when the web speed is 30 m/min or more and in the deceleration range, x is input to the cutter controller  30  as a set cutting value without correction.  
         [0049]    The reason why the correction of the set cutting value differs between these cases can be seen from results of an experiment shown in FIG. 5. When the web is in the acceleration range and correction is not performed, errors in the cutting length are large at the web speed of less than 60 m/min. Therefore, the boundary of whether the correction is performed or not is around the web speed of 60 m/min.  
         [0050]    On the other hand, when the web is in the deceleration range and the web speed is less than 30 m/min, errors are smaller than those are when the web is in the acceleration range. Therefore, one half of a calculated correction value is used as a correction value. Further, when the web speed is 30 m/min or more, errors are small except around the web speed of 40 m/min. Therefore, correction is not performed.  
         [0051]    In addition, errors generated by using the rubber length-measuring roll  42  are caused by changes in the circumference of the length-measuring roll  42 . Therefore, if the cutting length is doubled, even if the error per unit of length is the same, the absolute value of the error will become twice as large.  
         [0052]    [0052]FIGS. 6 and 7 are graphs showing dimensional errors when the set cutting value has not been corrected and when it has been corrected, respectively. As can be seen from the graphs, as the length of the PS plate increases to 550 mm, 800 mm and 1200 mm, the dimensional error also increases.  
         [0053]    Accordingly, if a correction value per unit of cutting length or a correction value per single rotation of the length-measuring roll is calculated, a correction value for a set cutting length can be calculated on the basis of the correction value for the unit cutting length or the correction value per rotation of the length-measuring roll.  
         [0054]    As described above, in the present embodiment, by continuously correcting irregularities in accuracy of cutting due to the web speed, accuracy of cutting required for products can be ensured in all speed ranges from a speed immediately after the line starts operation to a maximum web speed, and from the maximum web speed to the speed when the line stops operation.  
         [0055]    Further, although the description has been made based on PS plates in the present embodiment, the printing plate may be of a type with which image recording is carried out using a laser beam, such as a CCP printing plate. The present invention can be applied to all products that are produced by cutting a long sheet to a set size.  
         [0056]    Since the present invention has the above-described structure, it is less likely to damage the web, and it can ensure accuracy of cutting even when the web speed changes.