Abstract:
A printing device, system and method are disclosed for measuring and displaying the amount of wear experienced by printing rolls. A wear detection mechanism is employed in connection with rolls, such as anilox-type rolls that transfer ink to a substrate in forming a printed image. A wear detection mechanism is engraved, etched, or the like into the outer circumferential surface of the roll to provide an indication of the amount of wear experienced by the roll. Portions provided in series at predetermined depths may be correlated with a depletion scale indicia to display the wear condition of a particular roll in a printing system. A depletable wear strip comprising multiple engraved portions which correlate with values upon a depletion scale may be employed.

Description:
BACKGROUND OF THE INVENTION 
     Modern printing rolls may be formed in a number of ways, including by overcoating a smooth metallic core with a metal layer, followed by applying an outer ceramic coating. The outer ceramic coating then may be engraved using a laser to form a desired cell pattern in the ceramic. Various printing rolls or sleeves exemplified by anilox rolls, engraved rolls, form rolls, meter rolls, knurled rolls, ink applicator rolls, sleeves, ink transfer rolls, and the like may utilize the present invention if they wear during use. Printing rolls and/or sleeves typically include a series of engraved cells or the like upon their outer surface. The cells are configured to receive and transfer colorants such as ink in the formation of an image or coloration on a substrate. 
     In the operation of flexographic printers, for example, ink from a reservoir is transferred to a roll, such as an anilox roll. The anilox roll then transfers the ink to a printing plate, which may be mounted to the surface of a print cylinder. The web or substrate is printed when the print cylinder and inked printing plate roll over the web, transferring the image to the web. This process may be repeated thousands of times. 
     The outer surface of printing rolls, such as an anilox rolls, may experience significant amounts of wear, which are the subject of this invention. As the outer surface wears, cells in the outer surface of the roll are worn away and their volumes are reduced. These cells, which sometimes form an inverted pyramid or a hexagon, supply a fixed quantity of ink that is passed to the web or substrate during printing, based on the volume of the cell. 
     As the roll wears, and the cells erode, a significant reduction in ink volume is transferred to the printing substrate by each cell. For example, a 20% reduction of depth in an inverted pyramid cell may lead to a 40-50% reduction in volume of ink transferred depending upon the screen count and cutting angle. This undesirably may result in a noticeable decrease in print density in the transferred image. 
     Printing personnel may compensate for such wear by adjusting the intensity of ink applied to the roll. In the past, as a roll is used, the amount of wear has been estimated, and the ink concentration applied to the roll was periodically adjusted to increase the intensity of the ink, thereby compensating for such wear. To determine the actual amount of wear, it has usually been required that the roll be removed from service, and examined with a magnifying apparatus, such as a microscope. The periodic compensation for roll wear to maintain a consistent image is a significant challenge in conducting such printing processes. 
     For example, it is often difficult to determine how much wear a particular roll has experienced. The degree of wear, however, is necessary information for ink adjustments. Furthermore, estimates of the ink concentration necessary to produce the desired image are not always accurate. Errors easily can be made in the amount of ink applied to the roll, sometimes resulting in an undesirable or inconsistent image or coloration applied to the substrate. 
     What is needed in the printing industry is an apparatus and method for accurately and quickly determining the amount of wear that has been experienced by a roll. An apparatus that provides to printing personnel updated or “real time” information regarding the amount of wear experienced by the outer surface of such rolls would be very desirable. Such an apparatus and method of use of same could enable more accurate and more convenient adjustment of the amount of colorant or ink applied, thereby improving the continuity of high quality, consistent printing. An apparatus or method that could supply wear data or information without requiring that the roll be dismounted and examined by magnification devices would be particularly useful. 
     Sometimes, the print machinery is out of alignment, resulting in uneven wear along the length of the roll, or a roll when provided is “out of round”. It would also be important for printing personnel to be aware of such abnormalities which can lend to off quality production. Wear indicating apparatus and methods that could alert to uneven wear, out of round rolls and the like would be therefore quite useful. 
     SUMMARY OF THE INVENTION 
     In the present invention, a printing device for applying colorant to a substrate is provided. A roll having an outer circumferential surface with a plurality of transferring cells receives colorant from a reservoir to a substrate. A wear indicator mechanism is configured to detect wear and transfer the colorant of the outer circumferential surface of the roll. In some applications, the roll may be an anilox roll with a ceramic coating on its outer surface. In some applications, an outer sleeve is applied to the exterior surface. 
     In another embodiment of the invention, a system for determining the amount of wear that has been experienced by a roll or sleeve in a printing system is provided. In the system, a reservoir supplies colorant to the roll which is metered by a doctor blade, with respect to the plurality of transferring cells located on the outer surface of the roll. The transferring cells receive colorant from the reservoir and transfer the colorant to a substrate. One or more doctor blades wipe across the surface of the roll, metering colorant to the transferring cells. The doctor blades function as a dam or barrier for the colorant reservoir. The printing roll rotates while bearing against the doctor blade(s), and the portion of the outer circumferential surface on the roll that is engaged by a doctor blade defines a wear surface, and does wear during use. 
     A wear indicator mechanism or means provided on the outer circumferential surface of the roll measures the amount of wear experienced by the roll. In one embodiment, the wear indicator includes a plurality of indicator cells at various predetermined depths upon the outer circumferential surface of the roll. In other embodiments, a single indicator cell is employed. The indicator cells may be provided in alignment with a wear scale, which provides numerical or other indication of the amount of wear that has been experienced by the wear surface of a roll. However, other embodiments do not employ a scale or other indicia, but instead rely upon erasure of a textured surface to indicate the degree of wear upon a roll. 
     In yet another application of the invention, a method for detecting the amount of wear experienced by a printing roll is provided. The method includes providing a cylindrical roll having a wear-detection mechanism configured to detect depletion of the outer surface of the cylindrical roll. The roll is rotated, thereby transferring ink from a supply to a substrate. As the wear surface of the roll is depleted, the wear indicator mechanism makes it possible to observe the amount of roll wear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full and enabling disclosure of this invention, including the preferred embodiment, is set forth in this specification. The following Figures are illustrative of embodiments of the invention: 
     FIG. 1 is a perspective view of a printing system that includes a wear indicator according to the present invention; 
     FIG. 2 shows a cross-sectional view of the printing system of FIG. 1 taken along line  2 — 2 ; 
     FIG. 3 depicts a perspective view of a print roll  22  according to the present invention, illustrating a preferred embodiment of a wear indicator mechanism; 
     FIG. 4A shows a cross sectional view of the wear indicator mechanism having multiple indicator cells of varying predetermined depth, the cross section taken along a line  4 A— 4 A; 
     FIG. 4B shows a cross-sectional view of the embodiment shown in FIG. 4A, except that FIG. 4B illustrates a roll after it has experienced some wear and the wear indicator mechanism is indicative of that wear; 
     FIG. 4C illustrates another embodiment of the invention in which the depth of a single indicator cell is varied, thereby forming a sloped wall in a continuous uninterrupted line from the outer surface of the roll to a bottom point of the indicator cell; 
     FIG. 4D illustrates a top view of a cell in yet another embodiment of the invention in which concentric rings of varying depth are provided within a single indicator cell; 
     FIG. 4E illustrates a cross sectional view of the cell in FIG. 4D; and 
     FIG. 5 is a perspective view of further embodiments of wear indications according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in this invention without departing from the scope or spirit of the invention. 
     Turning to FIG. 1, a printing system generally  20  is shown in which a colorant supply unit  21  supplies colorant to a roll  22 . Colorant supply unit  21  transfers colorant which is held within a reservoir  27  of a body  26 . A first doctor blade  28  and a second doctor blade  29  (shown in phantom in FIG. 1) form the limits of reservoir  27 , and bear against the outer surface of the roll  22  to meter colorant into transferring cells of the roll (cells not shown). The portion of the roll subject to the respective first and second doctor blades  28 - 29  is shown as wear surface zone  39  in FIG.  3 . FIG. 1 shows one embodiment of a wear indicator mechanism generally  25  which will be fully described herein. Once colorant has passed to roll  22 , it is transferred to image carrier  23 , and then to a substrate or flexible web (not shown) that rotates upon drum  24 . Colorant within the reservoir  27  may be ink or any other substance that provides a color or visually perceptible image. Ink is typically used as a colorant in such apparatus. 
     In FIG. 2, a cross sectional view along lines  2 — 2  of FIG. 1 is provided. A clamping bar  30  holds in place first doctor blade  28 , which bears against roll  22 . The wear indicator mechanism  25  is shown in phantom passing beneath the first doctor blade  28 . Alignment pin  31  is shown at the upper portion of the first doctor blade  28 , and a bolt  32  holds the clamping bar  30  in place against the body  26  of the inking unit  34 , though any suitable arrangement for securing doctor blades  28 - 29  may be provided. An elastic seal  33  is provided between the first doctor blade  28  and the body  26  to seal reservoir  27  at that point. In other applications, an outer sleeve is employed. The use of “roll” herein shall be construed to also cover the use of transfer sleeves and the like. 
     FIG. 3 shows a perspective view of a roll  22  which has been removed from a printing system such as  20  for purposes of illustration, and which forms an embodiment of the invention. The outer circumferential surface  40  of the roll  22  carries a wear indicator mechanism  25 . The wear surface zone  39  is shown as that portion of the roll contacting colorant between and/or beneath respective doctor blades  28 - 29 . In the embodiment shown in FIG. 3, a wear strip  41  is provided in the outer surface of roll  22  just outside the intended image area. Wear strip  41  includes of a plurality of wear indicator cells  43   a-g  (see FIG.  4 A). The wear indicator cells  43   a-g  each correlate with a depletion indicia or value  44  juxtaposed thereto. The wear indicator cells  43   a-g  and depletion indicia or values  44  typically are positioned just outside the image pattern (but still within the wear zone of the first doctor blade  28 ) though could be placed within the image pattern if acceptable. The printed or engraved depletion indicia or values  44  are generally unaffected by wear upon wear surface zone  39  of roll  22 , but again, could be worn away along with its corresponding cell or cell portion. 
     The depletion indicia or values  44  may be provided in the form of a depletion scale, using numerals, or other indicia. The depletion indicia or values  44  (or scale) may provide the percentage of wear that has been experienced by a roll  22 . Just by way of example the first wear cell to the left of “10” represents about 10 percent of the original colorant transferring via the transferring cell, and when worn off, indicates that the cells have lost about 10 percent of their depth or the like. This is only one means of detecting wear. 
     In other applications of the invention, it is possible to provide geometric shapes, lettering, or other visible means of indicating the amount of wear that has been experienced by the wear strip  41  of the wear indicator mechanism  25  and the roll  22 . Depletion values  44 , however, may not be necessary if an operator has knowledge of the amount of wear represented by each indicator cell  43   a-g . The operator may simply note the number of wear indicator cells  43   a-g  which are absent or remaining at any given time and will thereby ascertain the degree of wear. In some embodiments, a cross-hatching or texture may be provided upon the lower surface of indicator cells, and when such texture is removed, immediately provides a visual cue to the degree of wear. 
     In FIG. 4A, a partial cross sectional view of the wear strip  41  of the wear indicator mechanism  25  is shown. Engraved areas may be provided on the outer surface of the roll  22 . In some applications, the engraved areas are cut into a hardened outer surface of the roll using a laser, such as a carbon dioxide laser. For example, wear indicator cell  43   a  may be engraved to a predetermined depth, while wear indicator cell  43   b  is engraved to an even greater depth. Successively greater depths have been engraved into the outer circumferential surface  40  of the roll as one proceeds along the outer periphery of the roll from  43   a - 43   g . In FIG. 4A, the deepest and last wear indicator cell  43   g  is shown near the far right side of the Figure. In the application of the invention, there is no limit to the number of wear indicator cells  43   a-g  that may be provided. Furthermore, the wear indicator cells  43   a-g  could be provided within only one indicator cell, or could be spread among many such indicator cells. Etching or other suitable technique may be employed instead of engraving, to produce the wear indicator cell or cells. 
     FIG. 4B shows the roll previously seen in FIG. 4A, except that the roll has experienced wear which has depleted the outer circumferential surface  40  as shown down to the depth of indicator cell  43   d . In FIG. 4B, wear indicator cells  43   a ,  43   b , and  43   c  are no longer visible, having been worn away during operation of roll  22 . Thus, an operator observing roll  22  which is shown in FIG. 4B could readily observe that the wear indicator cell  43   d  is in alignment with a roll depletion value of about “40” (for example, as shown in FIG.  3 ). Or course, it would be possible to provide any number of wear indicator cells  43   a-g , and the scale could be fine or coarse, or in any convenient units, depending upon the particular application. Furthermore, it is not always necessary to use numerical values adjacent to indicator cells  43   a-g , because the mere absence of such indicator cells  43   a-g  may indicate to an experienced operator that a given amount of wear has occurred. That is, an operator who is aware that rolls begin with a total of seven wear indicator cells  43   a-g  (as an example) would know that by observing only five of them, that two have been worn off, indicating to him a certain value of wear by the absence of a predetermined number of such positions  43   a-g.    
     FIG. 4C illustrates yet another embodiment of the invention in which a wear detection means  64  includes a single wear indicator cell  65 . Wear indicator cell  65  is configured to have a predetermined depth. When the depth is diminished by wear, a visual indicator is provided to reveal the amount of wear of said wear indicator cell  65  upon the printing roll  66 . The visual indication may be provided by the loss of a visible texture or other marking which is prepositioned upon the sloping surface  69  of the wear indicator cell  65 . The sloping surface  69  extends from the outer circumferential surface  67  of the printing roll  66  to a bottom point  68  of the wear indicator cell  65 . The absence of such a texture would shorten the total length of the sloping surface  69 , indicating to an operator the degree of wear that has been experienced by printing roll  66 . 
     In FIG. 4D, yet another embodiment of the invention is illustrated in a top plan view, with a single indicator cell  74  providing a wear detection means by employing multiple depth portions or steps  75   a-d  in a concentric circular pattern upon the outer circumferential surface  77  of the printing roll  78 . A bottom point  76  is centered, and forms the deepest portion of the indicator cell  74 . A cross section of the indicator cell  74  of FIG. 4D taken along line  4 E— 4 E is provided in FIG.  4 E. Wear experienced by indicator cell  74  would deplete the printing roll  78  by first erasing depth position  75   a , which would simply make the indicator cell  74  appear smaller in diameter. Further wear would deplete the indicator cell  75   b , and then indicator cell  75   c , and then indicator cell  75   d ; until only bottom point  76  would be left. Then, bottom point  76  would be depleted by additional wear. Thus, the size of the indicator cell  74  in total visible diameter would indicate the degree of wear experienced by the printing roll  78 . 
     FIG. 5 illustrates further embodiments of the invention in which it is possible to provide a roll  150  with wear indicator means  152   a-h . For example, wear indicator means  152   a-d  are located on the first end  154  of the roll  150 , whereas wear indicator mechanism or means  152   e-h  are shown on the second end  155  of the roll  150 . Wear experienced by the outer circumferential surface  156  of the roll  150  may be measured at various positions around the roll, at both ends of the roll, or both. 
     The embodiment shown in FIG. 5 provides an operator with the ability to determine if a roll is out of round, or otherwise not cylindrically oriented in correct alignment (showing uneven wear along the length of the roll). Wear indicator sets  152   a-h  could be provided in differing numbers of sets and at different locations around the circumference of the roll. For example, as shown in FIG. 5 such wear indicator sets  152   a-d  are provided at 90 degrees from each other. In other applications, such wear indicator sets  152   a-h  may be provided at differing degree intervals, e.g. when three wear indicator sets are positioned around a roll  22 . Such sets  152   a-h  may be equally spaced to correlate evenness of wear around the roll. 
     FIG. 5 also illustrates the wear indicator sets  152   a-h  at both ends of a roll, e.g.  152   a  and  152   e . Using such an arrangement, one can observe the two wear strips during use and ascertain the location at which wear is even along the roll. 
     It should be noted that FIG. 5 shows in combination two different features, that is, one feature of providing said wear indicator sets  152   a-h  on both ends of a roll, and a second feature providing said wear indicator sets in spaced groups around the circumference of a roll. One or both features may be employed independently. Some embodiments of the invention may employ both the first and second feature, as does the roll in FIG.  5 . 
     Printing rolls include transferring cells or transferring cell structures that may be of several types, including, without limitation, trihelical, pyramidal, quadrangular, hexagonal, or hexagonal. Other shapes are possible as well. A pyramidal shaped cell may be employed in the invention. Transferring cells usually are very small, and are not illustrated in FIGS. 1-5 although it is understood that such transferring cells appear on the outer circumferential surface of such printing rolls. Rolls may be provided in many different forms in the application of the invention. The invention of this application is not limited to any particular type of roll, but may apply to numerous roll types. 
     Laser engraved rolls may include plasma sprayed ceramic coating (e.g. chromium oxide) that is ground and honed to a very smooth finish. A ceramic coating typically is extremely hard. Hardness is widely used as a guide to strength, wear, and erosion resistance of a coating. 
     Typically, lasers of any type may be used in laser engraving. For example, carbon dioxide (CO 2 ) lasers can be used to manufacture laser engraved rolls. Such lasers may be used to generate pulses of energy, whereby each pulse is responsible for producing an impression in the ceramic. Usually, to create a cell in a ceramic substrate, a laser beam must be focused upon the ceramic surface using special lenses. Commercially available lasers may be used available to persons of skill in the art. It should be understood, however, that the present invention is not limited to laser cut rolls. Any roll with cells that wear could be employed regardless of how the cells are processed. Just by way of example cells (both colorant transfer and wear indicator cells) could be either engraved, milled or the like. 
     Doctor blades are typically installed near the edge of the roll and are subject to significant pressure. For that reason, they typically are made of steel, such as stainless steel. 
     In the practice of the invention, a wear strip  41  (see FIG. 3, as example). The wear strip  41  includes a plurality of engraved positions or cells at varying depths upon the outer circumferential surface of the roll. The wear indicator cells  43   a-g  may be provided in alignment with a depletion scale, enabling correlation of positions of the depletable wear strip with depletion scale values. In this way, an indication of the amount of wear experienced by a roll is provided. 
     Furthermore, experienced operators may readily observe the degree of wear upon a roll simply by noting the number of wear indicator cells  43   a-g  that have been worn off during roll usage. If an operator knows the number of indicator cells  43   a-g  that are provided upon a new roll, he or she may immediately know the degree of wear without the necessity to dismount the roll and/or observe the cells of a roll under a high magnification microscope, which is a significant operational advantage. 
     It is understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. The invention is shown by example in the appended claims.