Abstract:
An apparatus for estimating a lifetime of a cutter for cutting a sheet comprising: a detector for detecting a value of a parameter representing a cutting resistance during sheet cutting; a comparator for comparing the detected value of the parameter with a predetermined reference value; and an output element for outputting a result based on the comparison

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method and apparatus for estimating a life-span of a cutter by which a sheet member that is conveyed on conveyor rollers or the like, is cut. The sheet member may be a paper strip, thin film, cloth or the like that is adapted for image-formation.  
           [0003]    2. DESCRIPTION OF THE RELATED ART  
           [0004]    In an ordinary thermal-transfer type image-forming apparatus in which an image exposed on a photosensitive material is thermally transferred onto an image-receiving sheet, the photosensitive material is firstly unwound and pulled out by a certain length from a magazine, and thereafter a piece or sheet of photosensitive material is cut off therefrom. The sheet-form piece of photosensitive material is then conveyed to an exposure section.  
           [0005]    In the exposure section, an image is exposed onto the photosensitive material. The image-exposed photosensitive material then has water applied thereto, and is thereafter conveyed to a transfer section. In the transfer section, the photosensitive material is overlapped with the image-receiving sheet, wound together with the image-receiving sheet around a heating drum, and pressed onto the heating drum for a predetermined length of time, so that the image on the photosensitive material is thermally transferred to the image-receiving sheet.  
           [0006]    The image-receiving sheet is accommodated in a magazine in a wound state. After a predetermined length of the image-receiving sheet has been unwound, a desired length of the image-receiving sheet is cut off by a sheet cutter  92  for cutting the image-receiving sheet, as shown in FIG. 9. The cut-off image-receiving sheet is then conveyed to a transfer section.  
           [0007]    The sheet cutter  92  features a rotary blade  98  and a fixed blade  94  with an elongated plate shape. When the rotary blade  98  moves along the fixed blade  94  while rotating, an image-receiving sheet P which is conveyed and disposed over the fixed blade  94  is cut by an engaging portion between the rotary blade  98  and the fixed blade  94 .  
           [0008]    As the number of cuttings increases, the edge of the rotary blade  98  becomes worn or unfit for use. Due to this wear, during cutting, burrs K and warp would inevitably be generated at an edge of the piece of the image-receiving sheet P, as shown in FIG. 10. Thus, when the sheet piece was overlapped with a photosensitive material, a small space is generated therebetween due to burrs and warp, which might cause a poor picture, e.g., a so-called “white clarity”. Sheet jamming would also be generated due to poor cutting.  
           [0009]    At present, in general, the rotary cutter is not regarded as unfit for use and is not replaced until immediately before problems such as poor picture, jamming and the like become apparent. In brief, the method of replacing a cutter in use with a new one is not a systematic method based on predetermined criteria.  
         SUMMARY OF THE INVENTION  
         [0010]    In light of the above-mentioned fact, a primary object of the present invention is to provide a method and/or apparatus for estimating a life-span of a cutter wherein the cutter is reliably changed before burrs and warp are generated at an edge of a sheet piece that is cut by the cutter, by estimating when the cutter is unfit for use.  
           [0011]    In order to solve the aforementioned problems, according to the present invention, there is provided an apparatus of estimating a lifetime of a cutter for cutting a sheet comprising: a detector for detecting a value of a parameter representing a cutting resistance during sheet cutting; a comparator for comparing the detected value of the parameter with a predetermined reference value; and an output element for outputting a result based on the comparison.  
           [0012]    In accordance with another aspect of the present invention, there is provided a method of estimating a lifetime of a cutter for cutting a sheet comprising the steps of: (a) detecting a value of a parameter representing a cutting resistance during sheet cutting; (b) comparing the detected value of the parameter with a predetermined reference value; and (c) outputting a result based on the comparison.  
           [0013]    In accordance with yet another aspect of the present invention, there is provided a sheet cutter for cutting a sheet piece from a sheet by shearing, the sheet cutter comprising a fixed blade; a movable blade which is movable along the fixed blade; and a life estimation element for estimating a life span of the movable blade.  
           [0014]    In accordance with yet another aspect of the present invention, there is provided a sheet cutter for cutting a sheet piece from a sheet by shearing, the sheet cutter comprising: a fixed blade; a movable blade which is movable along the fixed blade; a receiving element which receives the sheet piece that is cut off from the sheet, the receiving element being structured so as to be movable together with the movable blade; and a life estimation element for estimating a life span of the movable blade.  
           [0015]    The foregoing and other objects, features and advantages of the present invention will be apparent from the following description of a preferred embodiment of the invention, as illustrated in the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a general side view of an image-forming device in which a life-span estimation apparatus of a cutter according to a first embodiment of the present invention is provided.  
         [0017]    [0017]FIG. 2 is a perspective view illustrating a sheet cutter according to the first embodiment of the present invention.  
         [0018]    [0018]FIG. 3 is a cross sectional view illustrating the sheet cutter of the life-span estimation apparatus of a cutter according to the first embodiment of the present invention.  
         [0019]    [0019]FIG. 4 is an overall perspective view including a block diagram which illustrates the sheet cutter incorporating the life-span estimation apparatus according to the first embodiment of the present invention.  
         [0020]    [0020]FIG. 5 is a flowchart of the life-span estimation apparatus of a cutter according to the first embodiment of the present invention.  
         [0021]    [0021]FIG. 6 is a chart showing an endurance test result obtained in the life-span estimation apparatus of a cutter according to the first embodiment of the present invention.  
         [0022]    [0022]FIG. 7 is an overall perspective view including a block diagram which illustrates a sheet cutter according to a second embodiment of the present invention.  
         [0023]    [0023]FIG. 8 is a chart showing an endurance test result obtained in the life-span estimation apparatus of a cutter according to the second embodiment of the present invention.  
         [0024]    [0024]FIG. 9 is a perspective view illustrating a conventional cutter in a state in which it is cutting a paper sheet.  
         [0025]    [0025]FIG. 10 is a view illustrating a sheet in which there are burrs at a sheet edge of an image-receiving sheet. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    In FIG. 1, there is generally shown an image-forming apparatus  10  provided with a life-span estimation apparatus of a cutter according to an embodiment of the present invention.  
         [0027]    At a lower side within a housing  16  of the image-forming apparatus  10  is disposed a photosensitive material magazine  18  in which a photosensitive material  12  is set and wound-up around a supply reel  20 . The supply reel  20  is driven for rotation by a driving means (not illustrated) so as to unwind the photosensitive material  12 .  
         [0028]    A distal end of the photosensitive material  12  is nipped by pulling-out rollers  22  that are provided at a securing section for the photosensitive material magazine  18 . Under predetermined conditions, the pulling-out rollers  22  pull the photosensitive material and feed the same toward guide plates  24  or define a further buffer (indicated by a two-dotted line).  
         [0029]    On passing through the guide plates  24 , the photosensitive material  12  is wound around an exposure drum  14  and then image-exposed by a scanning head  28 . Because the photosensitive material  12  is wound onto the exposure drum  14  and image-exposed in the manner described above, it is possible to avoid generation of winkles or creases with respect to the widthwise direction of the photosensitive material  12 . Thus, flatness of the exposed surface can be maintained at a high level.  
         [0030]    The image-exposed photosensitive material  12  is sandwiched between a support table  34  and a pressure plate  36 , and is supplied with water by an application member  40  (a sponge or the like). The application member  40 , which is water absorptive, is provided at an application tank  38 .  
         [0031]    The water-applied photosensitive material  12  is wound around a heating drum  42  with a predetermined constant pressure by tension rollers  44  and  46 . The heating drum  42  has a halogen lamp incorporated therein. While the wound photosensitive material is heated, it is superposed with an upper surface of an image-receiving sheet hereinafter referred to as a “sheet”) P described in detail hereinbelow, onto which the image is transferred.  
         [0032]    Next, the image-transferred photosensitive material  12  is wound around a scrap reel  30 . As described above, the photosensitive material  12  is delivered not in a cut-off sheet manner but in a consecutive web manner from the supply reel  20  to the scrap reel  30 . Therefore, the photosensitive material  12  itself functions as a timing belt which applies a certain constant pressure to the sheet P.  
         [0033]    At an upper side within the housing  16  is disposed a sheet magazine  32 , in which the sheet P is wound around a supply reel  20 . The sheet P is nipped and unwound by nipping rollers  26  and  27 , and thereafter a sheet piece having a predetermined length is cut off therefrom by a sheet cutter  50 , details of which will be described hereinbelow. Then, the sheet piece is conveyed by guidance of conveyor rollers  48  and guide plates  49  and wound around the heating drum  42  together with the photosensitive material in an overlapping manner.  
         [0034]    The image recorded on the photosensitive material  12  is transferred to the sheet piece P. Thereafter, the image-transferred sheet piece is separated from the heating drum  42  and from the photosensitive material by a separation claw (not illustrated), conveyed under guidance of conveyor rollers  13  and guide plates  15 , and led to a receiving tray  17 .  
         [0035]    With reference to FIGS. 2 and 3, the sheet cutter  50  will now be described in detail. A guide rail  52  is disposed in the sheet cutter  50  substantially perpendicular to a sheet conveying direction (indicated by bidirectional arrow), i.e., a sheet width direction. To this guide rail  52  is secured a fixed blade  54  of elongated plate shape, whose length is greater than the width of the sheet P that is coiled and stored in the sheet magazine  32 .  
         [0036]    The sheet P is conveyed through an elongated slit formed in the guide rail  52  and conveyed over the fixed blade  54 . Above the fixed blade  54  is disposed an upper housing  60  which accommodates a (single-edged) rotary blade  58 , part of which is exposed.  
         [0037]    The rotary blade  58  has a rotatable shaft  62  with two ends, both of which ends are rotatably supported by bearings  64  and  66 . The bearing  64  is secured to a cantilever-type plate member  68 . Between the plate member  68  and a disk plate  61 A is provided a coil spring which biases the rotary blade  58  toward the fixed blade  54 . Thus, a side surface  58 A of the rotary blade  58  is pressed to the fixed blade  54  at a cutting point C (see FIG. 3). The fixed blade  54  has an upper surface and an inclined, relief surface, with these surfaces meeting at the cutting point C and forming an angle (θ) with each other (e.g., around 80°). When the rotary blade  58  is moved along the fixed blade  54 , the rotary blade  58  rotates due to friction, so that the sheet P is reliably cut at the cutting point C.  
         [0038]    Also, a disk plate  70  is concentrically fixed to the rotatable shaft  62  of the rotary blade  58 . The disk plate  70  has a groove  72  circumferentially defined in the external surface thereof. A seal ring, that is, an O-ring  74 , is received in this groove  72 . The O-ring  74  is in a slightly compressed state when moved on the upper surface of the fixed blade  54  during rotation.  
         [0039]    A slider  76  is disposed under the fixed blade  54  such that the slider  76  opposes the O-ring  74 . The slider  76  is connected to the upper housing  60  via a connection plate  78  and slides along a back surface of the fixed blade  54 . The fixed blade  54  is maintained between the O-ring  74  and the slider  76  such that up and down movement of the rotary blade  58  with respect to the fixed blade  54  is restricted.  
         [0040]    Further, to the slider  76  is fixed an endless wire  80  which is wound around pulleys  96  and  102 , as shown in FIG. 4. The pulleys  96  and  102  are disposed at each end of the guide rail  52 . Power from a motor (e.g., a stepping motor) is transmitted to the pulley  102  through a reduction gear (not illustrated).  
         [0041]    In this structure, when the sheet P has advanced to a cutting position, the motor  104  usually rotates according to the later described timing, and the upper housing  60  and the slider  76  are moved along the fixed blade  54 . At this time, the rotary blade  58  cuts the sheet P in the sheet width direction at the cutting point C defined with the fixed blade  54 . When the motor is operated in a reverse direction, the slider  76  and the upper housing  60  are pulled back to a standby position.  
         [0042]    Further, a lower housing  82  is fixed to the connection plate  78  and moves integrally with the upper housing  60 . The lower housing  82  includes a rotation shaft  88  and a receiving roller  84 , which serves as a receiving member, is made of metal, and is rotatably supported by the rotation shaft  88 . The receiving roller  84  has a groove  86  circumferentially defined in the external surface thereof such that the edge of the rotary blade  58  is accommodated in the groove  86 .  
         [0043]    Specifically, in the present embodiment, in which the rotary blade  58  and the receiving roller  84  are moved integrally, at the time the image-receiving sheet P is cut, a trailing edge portion of a piece of image-receiving sheet, which is cut off, is bent down and enters into the groove  86 , as shown in FIG. 3. In short, a bent-down or hung-down portion P 1  of the sheet edge of the piece is purposely formed so as to suppress or eliminate generation of burrs.  
         [0044]    Next, description will be made of the life-span estimation apparatus of a cutter of the embodiment with reference to FIGS.  4  to  6 .  
         [0045]    The motor  104  which transmits power to the pulley  102  as described above, is connected to a current measurement equipment  94  which is in turn connected to a central processing unit (hereinafter referred to as a “CPU”)  90 . At the time the sheet P is cut by the rotary blade  58 , the current measurement equipment  94  measures the value of electric current of the motor  104 . The CPU  90  then compares this value with a reference current value.  
         [0046]    The CPU  90  is connected to a display control unit  106  which is in turn connected to a display  108 . When the current value measured exceeds the reference, the CPU  90 , via the display control unit  106 , causes the display  108  to indicate that the rotary blade  58  should be replaced.  
         [0047]    Specifically, if the cutting edge of the rotary blade  58  has worn out, cutting resistance would increase, thereby resulting in a large load on the motor  104 , and therefore, the current value of the motor would necessarily go up. By using this phenomenon to determine when the rotary blade  58  should be replaced because it is unfit for use, it is possible to ensure that the rotary blade or cutter is replaced with a new one in a timely manner and thus prevent burrs and warp from being generated on the sheet P.  
         [0048]    Operation of the life-span estimation apparatus of a cutter will now be described with reference to a flowchart shown in FIG. 5.  
         [0049]    At step S 200 , the present current value I of the motor  104  is input, and at step S 202 , it is determined whether the present current value I exceeds the predetermined reference current value Io. If the former exceeds the latter, the CPU  90 , via the display control unit  106 , causes the display  108  to display an indication, e.g., a message indicating that the rotary blade  58  should be replaced.  
         [0050]    Next, at step S 206 , it is determined whether the sheet cutting by the rotary blade  58  has been completed. When the cutting has been completed, at step S 208 , rotation of the motor  104  for driving the rotary blade to move is stopped. At step S 210 , it is determined whether the rotary blade  58  has been replaced.  
         [0051]    After replacing the rotary blade, the message in the display  108  is cleared at step S 212 . The routine is returned to step S 200 . At step S 202 , if the current value I does not exceed the predetermined reference current value, the routine loops back to step S 200 .  
         [0052]    A description will now be made of the relationship between the cutting time and the number of cuttings (or the number of sheets cut), with reference to FIG. 6 showing a cutter or blade endurance test chart.  
         [0053]    It will be noted that attention should be paid to variation or changing (i.e., shape or curves) in the plot of electric current rather than current value itself.  
         [0054]    In the initial period of use of a rotary blade or when using a new rotary blade, the rotary blade is not accustomed to cutting, and therefore, cutting resistance is fairly large, thereby resulting in a high load on the motor  104 . For example, the electric current value of the motor sometimes tends to go up to around 350 [mA] when cutting a sheet However, when the number of sheets cut exceeds about 1,000, the rotary blade starts to become accustomed to cutting, and therefore, the electric current value decreases to around 270 [mA] and is stably maintained at such a lower level. When the number of sheet cutting is over around 120,000, the electric current value gradually goes up. Those numbers are only examples and vary depending on several factors, i.e., sheet material, cutter material, parts dimensions, etc.  
         [0055]    As described above, in the present embodiment, a life span of a blade or cutter can be estimated by measuring an electric current value of a motor for driving the blade or cutter. Further, blade trouble like blade breakage and/or generation of sheet jamming can be anticipated. In place of or in addition to displaying a message that the blade or cutter should be replaced, visual or audible warning to users may simply be provided.  
         [0056]    Next, a life-span estimation apparatus of a cutter of another embodiment according to the present invention will be described with reference to FIGS. 7 and 8.  
         [0057]    As shown in FIG. 7, this structure is provided with two touch sensors  110  and  112 , each of which is disposed in the vicinity of each end of the fixed blade  54 . As soon as the rotary blade  58  starts cutting of the sheet P, the slider  76  is brought out of contact with the touch sensor  110 . At this moment, an electric circuit included in the touch sensor  110  accordingly operates and outputs a signal (i.e., a cutting start signal) to the CPU  90 . Next, as soon as the rotary blade  58  completes cutting of the sheet P, the slider  76  is brought into contact with the touch sensor  112 . Correspondingly, the touch sensor  112  outputs a signal (i.e., a cutting completion signal) to the CPU  90 .  
         [0058]    In the CPU  90 , time between receiving the cutting start signal and receiving the cutting completion signal is regarded as a cutting time required for the rotary blade  58  to cut the sheet P. Then, the CPU compares this time with the predetermined reference cutting time.  
         [0059]    When the cutting time measured exceeds the predetermined reference time for cutting, the CPU  90  causes the display  108 , via the display control unit  106 , to indicate that the rotary blade  58  should be replaced.  
         [0060]    Description will now be made of the relationship between the cutting time and the number of cuttings (or the number of sheets cut), with reference to FIG. 8 which shows an endurance test chart for cutters or blades.  
         [0061]    It will be noted that attention should be paid to variation or changing (i.e., shape or curves) in the plot of cutting time rather than the value of cutting time itself.  
         [0062]    In the initial period of use of a rotary blade or when using a new rotary blade, the rotary blade is not accustomed to cutting, and therefore, cutting resistance is fairly large, thereby resulting in a long cutting time. For example, the cutting time sometimes tends to go up to around 710 [msec] when cutting a sheet. However, when the number of sheet cutting is over around 5,000, the rotary blade starts to get use to cutting, and therefore, the cutting time value decreases to around 700˜690 [msec] and is stably maintained at such a lower level. When the number of sheet cutting exceeds about 120,000, the cutting time gradually increases. Those numbers are only examples and vary depending on several factors, i.e., sheet material, cutter material, parts dimensions, etc.  
         [0063]    As described above, in the present embodiment, a life span of a rotary blade  58  can be estimated by measuring a cutting time when the blade cuts a sheet.  
         [0064]    According to the above exemplary structures of the present invention, life span of a cutter or blade can be precisely estimated, and therefore, the cutter or blade can be replaced in a timely manner to prevent poor cutting which may cause burrs and warp at sheet edges during cutting.  
         [0065]    Incidentally, it is conceivable that by counting a frequency of cutting or number of times a rotary blade is used, a life span of the rotary blade can be estimated. However, the frequency or number of cutting varies depending on properties of materials constituting the rotary blade. Therefore, in this way of estimation, it is difficult to achieve an accurate or timely estimation with respect to the rotary blade. Namely, this may result in an undesirable situation in which the rotary blade is replaced although it is not yet the time for the rotary blade to be replaced or the rotary blade is not replaced although it is past the time for the rotary blade to be replaced.  
         [0066]    In this respect, according to the instant invention, there is provided an improved estimating system in which the above-described problems are eliminated.