Abstract:
This invention relates to a system and method for intelligently placing in a periodic and/or random manner a plurality of whetting areas which facilitate lubricating and/or cooling a doctor blade in a printing press when the cylinder is placed therein. The system and method includes one or more routines which analyzes engraving/etching data and any associated white-span length. One or more whetting areas are placed in a periodic or random pattern in response thereto. The whetting areas facilitate lubricating and/or cooling the doctor blade so that it does not heat beyond a predetermined level, thereby avoiding scoring of the cylinder and problems associated with deterioration of print quality or length of cylinder life resulting from thermo-dynamic expansion and/or undesired evaporation of ink associated with areas which make up the image.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a system and method for improving printing and, more particularly, to a system and method for providing a plurality of whetting areas on a workpiece for the purpose of cooling and/or lubricating a doctor blade of a printing press when the workpiece is used therein. 
     2. Description of the Related Art 
     During a gravure printing process, a workpiece, such as a cylinder, is situated in the press with a portion thereof submerged in ink. As the cylinder rotates, areas on the cylinder receive ink and transmit the ink to a substrate, such as paper, plastic, film and the like in a manner conventionally known. 
     The press typically had a doctor blade which engaged a surface of the workpiece and wiped the excess ink off the surface, so that ink within the areas would be transmitted to the substrate. 
     Typically, the workpiece would be engraved with a plurality of areas which collectively correspond to one or more images. Unfortunately, when there were significant spans between adjacent areas along a circumferential direction, then the doctor blade began to heat to undesired levels, such as in excess of 200 degrees Fahrenheit. One problem with the doctor blade heating is that when it first encountered the ink associated with an image edge of the engraved image area which defined the image to be printed, the doctor blade would be so hot that it would cause the ink along such image edge to evaporate. 
     Another problem with the doctor blade heating beyond a desired level is that it would begin to scratch the surface of the cylinder as the blade undergoes a thermo-dynamic expansion. 
     In the past, microcracks in the surface of the cylinder facilitated lubricating and cooling the doctor blade. Oftentimes, however, the microcracks were not deep enough to hold an appreciable amount of ink or did not provide enough lubrication to lubricate and/or cool the doctor blade. A workpiece which has very little engraved or etched area, will need more lubrication and, consequently, require more and deeper microcracks. Likewise, a cylinder which has a large portion of its surface area engraved or etched, requires less and shallower microcracks because the engraved or etched portion facilitates lubricating and/or cooling the doctor blade as it preforms its function. 
     In the past, small non-printing cells known as “scum dots” were placed on the surface in response to a visual inspection of the cylinder in an attempt to overcome this problem. This empirical approach oftentimes resulted in too few or too many dots being situated on the cylinder, resulting in a doctor blade which was either not lubricated enough or lubricated to much. 
     Unfortunately, the processes heretofore known could not be selectively turned up or down to suit a cylinders specific lubrication needs. Furthermore, a leading edge of an engraved or etched area oftentimes does not print correctly. Because the doctor blade removes or causes some of the ink at the leading edge to be removed or evaporated. Surface tension and adhesion of the ink within an engraved or etched area to the walls defining the engraved or etched area is also thought to be a cause of poor printing quality. 
     What is needed, therefore, is a system and method for evaluating data and strategically positioning an appropriate number of whetting areas to facilitate eliminating or reducing the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the invention to provide a system and method for lubricating and/or cooling a doctor blade in a manner not previously known. Another object of the invention is to provide a system and method for strategically placing a plurality of whetting areas upstream of an engraved or etched image area, so that the resultant printing along a leading edge of an image associated with the engraved or etched area is improved. 
     In one aspect, this invention comprises a method for engraving/etching a plurality of whetting areas on a workpiece to facilitate lubricating and/or cooling a doctor blade when the workpiece is situated on a printing press, the method comprising the step of providing a system for engraving/etching a plurality of whetting areas at predetermined positions on the workpiece, the predetermined positions being determined in response to an image to be engraved or etched, a plurality of whetting areas being capable of holding ink for lubricating and/or cooling of the doctor blade when the workpiece is used in a printing press. 
     In another aspect, this invention comprises a method for locating a plurality of whetting areas on a workpiece to facilitate cooling and/or lubricating a doctor blade during a printing process, providing a whetting pattern determinor for determining a whetting pattern defining a plurality of whetting areas which facilitate cooling and/or lubricating the doctor blade in response to an image to be engraved or etched and providing a system for engraving/etching the whetting pattern and an image pattern corresponding to the image. 
     In still another aspect, this invention comprises a system for locating a plurality of whetting areas for facilitating cooling and/or lubricating a doctor blade on an printing press, comprising a whetting pattern determinor for determining a whetting pattern in response to an image to be engraved or etched, the whetting pattern determinor generating the whetting pattern of a plurality of whetting areas which facilitate cooling and/or lubricating the doctor blade in response to the image. 
     In yet another aspect, this invention comprises an engraving/etching system comprising a system for engraving/etching a workpiece with a plurality of areas defining an image pattern, a whetting pattern determinor for analyzing job data and for generating whetting data corresponding to a whetting pattern of whetting areas in response thereto and a signal generator for receiving the job data and the whetting data and for generating a signal in response thereto so that whetting pattern is engraved or etched relative to the engraved or-etched image pattern such that the whetting pattern facilitates cooling and/or lubricating a doctor blade in a printing press when the workpiece is used therein. 
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
     FIG. 1 is a general perspective view of an engraving/etching system in accordance with one embodiment of the invention; 
     FIG. 2 is a perspective view of a cylinder engraved or etched in accordance with features of the present invention; 
     FIG. 3 is a schematic diagram of a transition based whetting pattern generator in accordance with one embodiment of the invention; 
     FIG. 4 is a schematic diagram of a periodic whetting pattern insertion routine in accordance with another embodiment of the invention; 
     FIG. 5 is a general fragmentary view of a surface of a cylinder illustrating various whetting areas to facilitate lubricating and/or cooling a doctor blade; 
     FIG. 6 is a fragmentary view of a surface of the cylinder showing a line of whetting areas; 
     FIG. 7 is a fragmentary view of a surface of the cylinder showing a random pattern of whetting areas generated in accordance with features of this invention; and 
     FIG. 8 is a view of a plurality of waveforms illustrating engraving/etching signals generated by engraving/etching signal generator  90  in response to engraving/etching data input represented in a sinusoidal waveform. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a general perspective view of a preferred embodiment of a system which incorporates features of this invention. For ease of illustration, the invention is described for use on an engraving system, designated generally as engraver  10 ; however, it should be appreciated that the features of this invention may also be used in connection with other types of systems, such as laser engraving, laser etching or even chemical etching systems. In the embodiment being described, the engraver  10  is an electro-mechanical engraver, but the invention may be suitable for use in other engravers, such as a laser engraving or etching. The engraver  10  may have a surrounding, slidable safety cabinet structure which is not shown for ease of illustration. 
     Engraver  10  comprises a base  12  having a headstock  16  and a tailstock  18  slidably mounted in a track  20  such that the headstock  16  and tailstock  18  can move towards and away from each other. In this regard, engraver  10  comprises a plurality of linear actuators or first drive motor means or first drive motor  46  and a second drive motor means or second drive motor  48  which are capable of driving the headstock  16  and tailstock  18 , respectively, towards and away form each other. For example, the drive motors may cause the headstock  16  and tailstock  18  to be actuated to a fully retracted position (not shown) or to a cylinder support position shown in FIG.  1 . 
     The drive motors may be selectively energized to cause headstock  16  and tailstock  18  to be actuated either independently or simultaneously. Although not shown, a single drive motor may be used with a single leadscrew (not shown) having reverse threads on which either end causes the headstock  16  and tailstock  18  to move simultaneously towards and away from each other as the leadscrew is driven. Driving both headstock  16  and tailstock  18  permits cylinders  14  of varying lengths to be loaded by an overhead crane, for example, whose path is perpendicular to the axis of rotation of the cylinder  14 . Although not shown, it should be appreciated that a stationary headstock  16  or tailstock  18  may be used with a driven headstock  16  or tailstock  18 , respectively. 
     The headstock  16  and tailstock  18  comprise a first support cone or shaft  16   a  and a second support cone or shaft  18   a , respectively. The support shaft  16   a  and  18   a  each comprise a conically shaped end which is suitable for engaging and rotatably supporting cylinder  14  at an engraving station  15  of engraver  10 . In this regard, the cylinder  14  comprises a first end  14   a  and a second end  14   b , each having a receiving opening for a receiving end, respectively. The receiving openings in ends  14   a  and  14   b  are conically shaped in cross-section so as to matingly receive the ends of cone  16   a  and  18   a.    
     Although not shown, if a shafted cylinder (not shown) was to be engraved or etched, then headstock  16  and tailstock  18  would each include a gripping device or chuck (not shown) for receiving the shafts and also for rotatably supporting the cylinder  14  at the engraving station  15 . 
     The engraver  10  also comprises an engraving head  22  having an engraving device, such as a cutting tool or stylus  23 , for engraving a surface  13  of cylinder  14 . In the embodiment being described, the engraving device  23  preferably has a diamond stylus; however, it should be appreciated that the invention may be used with other types of engraving devices, including, for example, laser engraving or etching devices. 
     The engraving head  22  is slidably mounted on a carriage  24  such that a third drive means or third drive motor  21  can drive the engraving head  22  towards and away from the surface  13  of cylinder  14  in a direction which is generally radial with respect to the rotational axis of cylinder  14 . The carriage  24  is also slidably mounted on base  12  such that it traverses the entire surface  13  of cylinder  14  in the direction of double arrow  26  in FIG. 1, which is generally parallel to the axis of the cylinder  14 . The engraver  10  also comprises a lead screw (not shown) and drive motors (not shown) for causing the carriage  24  to move in the direction of double arrow  26 . The engraving head  22 , carriage  24  and transverse movement thereof is similar to that shown in U.S. Pat. Nos. 5,438,422, 5,424,845 and 5,329,215 which are assigned to the same assignee as the present invention and which are incorporated herein by reference and made a part hereof. 
     The engraver  10  also comprises drive means or a drive motor  28  for rotatably driving the support member  16   a , cylinder  14 , and support member  18   a . The drive motor  28  is also operatively coupled to the controlled  17 , as shown. 
     The engraver  10  further comprises a programmable controller, processor or computer  17  which controls the operation of the engraver  10  and which also controls drive motors  21 ,  28 ,  46  and  48  mentioned earlier herein. 
     Although not shown, the engraver  10  may further comprise a support or support means for supporting the cylinder  14  between headstock  16  and tailstock  18 , for example, during loading and unloading. 
     Computer  17  is also coupled to engraving head  22  and is capable of energizing engraving head  22  to engrave at least one controlled-depth area or cell as carriage  24  traverses surface  13  of cylinder  14  in a manner described later herein. 
     In accordance with an embodiment of the invention, an improved engraving/etching method and system is provided for providing a plurality of whetting areas or “scum” dots on surface  13  of cylinder  14  in response to an engraved etch job to facilitate lubricating and/or cooling of a doctor blade (as illustrated in FIGS. 5-7) in a printing press when the workpiece or cylinder  14  is used therein. Advantageously, this facilitates improving the printing performed by the press, particularly at the edges of the printing. 
     As illustrated in FIGS.  2  and  5 - 6 , an engraved or etched pattern  50  comprises a plurality of areas, such as areas  52  and  54  on surface  13  of cylinder  14  (FIGS.  2  and  5 - 7 ). It should be appreciated that FIGS.  2  and  5 - 7  illustrate only a fragmentary portion of surface  13  of cylinder  14  and of the pattern  50 . It should also be appreciated that during printing, cylinder  14  is rotated about its cylindrical axis to produce a surface motion or rotation indicated by arrow A in FIG.  2 . Notice that a transition or edge area  56  is defined along line E in FIG. 2 which represents a transition between the pattern  50  and a non-engraved area  60 . In general, the areas  52  and  54  are arranged in a series of nested columns, each having a plurality of lead cells or areas  62  and  64 , respectively, which begin a plurality of vertical columns (as viewed in FIG.  2 ). It should be appreciated that these adjacent columns and cavities of areas are produced by oscillating the engraving/etching device or stylus  23  (FIG.1) into engraving/etching contact with surface  13  of cylinder  14  during rotation of cylinder  14 . 
     As best illustrated in FIGS. 5-7, a feature of the present invention is that it is capable of placing one or more whetting areas, such as whetting areas  66  and  68 , integrally adjacent to the engraved or etched image pattern  50  (as illustrated in FIG. 5) or immediately adjacent, but not integral (as illustrated in FIG.  6 ). As described later herein, the whetting areas may be generated by the system and method of the present invention in a periodic, non-random or uniform order. Alternatively and as shown in FIG. 7, the whetting areas may be placed in a non-periodic, random or non-uniform arrangement if desired. In any event, the whetting areas facilitate lubricating and/or cooling the doctor blade (FIGS. 5-7) when the cylinder  14  is used in a printing press (not shown). 
     In general, features of this invention are achieved by determining whether the whetting areas  66  and  68  need to be engraved in surface  13  of cylinder  14 . In this regard, the system and method for generating the whetting areas utilizes job data which may be input from a remote computer (not shown), scanning device (not shown) or other suitable means which is ultimately stored on computer  17 . The data is used to determine transitions between an engraved/etched area and a non-engraved/etched or white-span area for the purpose of determining whether a whetting pattern of whetting areas, such as pattern  70  shown in FIG.  7  and pattern  72  shown in FIG.  6 . It should be appreciated that the job data may include image data corresponding to an image which represents both continuous tone image and/or linework image and the white-span data corresponding to non-engraved or white-span areas. 
     The engraving/etching data is typically stored in computer  17  (FIG.  1 ), and it provides a binary representation which indicates the area in which the continuous tone or linework data is to be placed. The job data relative to white-span areas along a cylindrical or helical track which are not engraved or etched is also stored as part of the job data. For each revolution of cylinder  14 , a calculation of the non-engraved area for each cylindrical or helical track is determined in accordance with the routines described relative to FIGS. 3 and 4. In general, if a white-span (WHT.SPN.LENGTH) length or circumferential length of the white-span area is greater than a predetermined dimension, as described below, then the computer  17  causes a whetting pattern, such as patterns  70  (FIG. 7) or  72  (FIG. 6) or some combination thereof, to be engraved, chemically etched, or laser etched. The system and method for generating the whetting pattern, such as patterns  70  and/or  72 , will now be described relative to FIGS. 1,  3  and  4 . 
     Computer  17  comprises a whetting pattern determinor  80  (FIG. 1) comprising an analyzer  80   a  for receiving the job data comprising both image data associated with the image to be engraved or etched and data associated with white-span areas. Computer  17  further comprises a signal generator  90  for receiving the image data and whetting data from the whetting pattern determinor  80  and for generating an engraving/etching signal in response thereto. This facilitates ensuring the whetting pattern (such as pattern  70  or  72  in FIGS. 7 and 6, respectively) is engraved or etched relative to the engraved or etched image pattern  50  in order to facilitate cooling and/or lubricating the doctor blade (not shown) in a printing press (not shown) when the cylinder or workpiece  14  is used therein. 
     In the embodiment being described, the whetting pattern determinor  80  comprises a calculator or calculating means for calculating a white-span dimension in a given direction, such as a circumferential direction, an axial direction or a diagonal direction. The white-span dimension is then used by the whetting pattern determinor  80  to generate whetting data if the dimension exceeds a predetermined dimension. The whetting pattern determinor  80  analyzes the engraving/etching data and generates whetting data in accordance with the routines described in FIGS. 3 and 4 which will now be described. 
     FIG. 3 discloses a transition based whetting pattern insertion routine resident on computer  17  which begins at block  89  with the start of the engraving/etching data. At block  92 , a white-span length (“WHT.SPAN.LENGTH”) is set in a buffer in computer  17  to zero. The analyzer  80   a  determines the white-span length using the engraving/etching data in a given direction, such as a circumferential direction as viewed in FIG. 2 (block  94 ). 
     At decision block  96 , it is determined whether the calculated white-span length is greater than a predetermined length, such as a circumferential length, which is represented by the double arrow X in FIG.  2 . If it is, then the routine places a whetting cell or engraved or etched area or a pattern of whetting areas before a transition to an image area, such as the transition (indicated by arrow E in FIG.  6 ). It should be appreciated that the white-span length in the embodiment being described corresponds to the number of consecutive areas with a zero percent video density value or, stated another way, the number of zero percent density value areas between transitions between images. 
     It should also be appreciated that the predetermined dimension in the embodiment being described corresponds to the minimum number of zero percent density value areas which require the placement of a whetting pattern, such as pattern  72  in FIG. 6, to facilitate maintaining the temperature of a doctor blade in a printing press below a predetermined or desired temperature. It should further be appreciated that the predetermined dimension may be determined in response to at least one of the following characteristics: copper hardness, rotational speed of the cylinder during printing, ink type, surface finish, roughness or smoothness, doctor blade type, blade pressure, or the general lack of a lubricating agent to lubricate the doctor blade. In general, any characteristic that would tend to cause the doctor blade to become heated beyond the desired temperature will cause the predetermined dimension to become shorter. The predetermined dimension may increase up to a point where the doctor blade achieves a temperature which requires cooling. By way of example, it has been found that when the doctor blade achieves temperatures in excess of 200 degrees fahrenheit it is desirable to engrave a whetting pattern in order to facilitate avoiding the problems associated with overheating the doctor blade. 
     In the embodiment being described, the computer  17  generates a signal in response to the image data and whetting data which results in the whetting pattern being positioned as described. For ease of illustration, FIG. 8 illustrates an engraving/etching data input received by whetting pattern determinor  80  and which is used by the signal generator  90  to generate an engraving/etching signal in response to the image data and whetting pattern data. Notice, for example, that the engraving/etching data represented by the sinusoidal waveform  91  correlates to an image which does not have any appreciable white-span length greater than a distance X in FIG.  8 . Accordingly, the engraving/etching signal generator  90  does not generate any whetting areas or pattern in response thereto as illustrated by the engraving/etching signal waveform  91   a.    
     Likewise, signal  93  in FIG. 8, illustrates a white-span length (identified by arrow Y) which is not greater than the predetermined dimension X. Consequently, no whetting areas are generated by generator  90  in the ultimate corresponding engraving/etching signal output ( 93   a ). 
     Conversely, waveforms  95  and  97  illustrate engraving/etching data which has a white-span length which is greater than the predetermined dimension (identified by double arrow X in FIG.  8 ). In this example, whetting pattern determinor  80  and analyzer  80   a  cause the whetting pattern (e.g., patterns  70  and  72 ) to be generated. Engraving/etching signal generator  90  receives whetting data corresponding to the whetting pattern, as well as the image data, and ultimately generates engraving/etching signals  95   a  and  97   a.    
     The signals  95   a  and  97   a  are received by engraving head  22  after being converted by D/A convertor  19  and amplified by amplifier  29 . The head  22  engraves whetting areas ( 66  and  68  in FIGS. 5 and 6, for example) to define a pattern of whetting areas, such as pattern  70  relative to signal  97   a  or pattern  72  relative to signal  95   a.    
     As mentioned previously herein, the whetting areas  66  and  68  may be placed randomly, non-uniformly or non-periodically (as illustrated in FIG. 7) or non-randomly, periodically and uniformly as illustrated in FIG.  5 . Thus, as illustrated in FIG. 5, the whetting pattern determinor  80  may cause the whetting areas or cells to be situated integrally with and adjacent to the pattern  50  corresponding to the image. This provides a line  112  of whetting areas, such as areas  66  and  68  in FIG. 5, which facilitate lubricating or cooling the doctor blade before it encounters and ink in the pattern  50  corresponding to the image. Notice that the whetting areas  66  and  68  shown in FIG. 5 are in fluid communication with the pattern  50 . 
     If the decision at decision block  96  is negative or after the placement of the whetting areas at block  98 , it is determined at decision block  100  whether all engraving/etching data for a job has been processed. If it has, then the routine is complete. Otherwise, it loops to block  102  where further engraving/etching data is obtained and processed beginning at block  92  as shown. 
     FIG. 4 illustrates another, simplified, embodiment of the invention where periodic whetting areas or a pattern of whetting areas are automatically inserted in the engraving/etching data at predetermined intervals of a white-span length. In this embodiment, analyzer  80   a  of whetting pattern determinor  80  of computer  17  begins at the start of the engraving/etching data (block  102  in FIG.  4 ). At block  104 , computer  17  scans the engraving/etching data for a predetermined number of areas. At decision block  106 , it is determined whether all the areas which were scanned each had a video density value of zero percent, thereby indicating that each area was a “white” area. If it is, then the routine proceeds to block  108  where whetting pattern determinor  80  generates a whetting area or a pattern of whetting areas which signal generator  90  then uses to modify the job data to generate a signal in response thereto. Thereafter or if the decision at decision block  106  is negative, it is determined at decision block  110  whether the job is complete. If it is, then the routine is finished and all job data has been processed. If it is not, however, then the job data for the next revolution of cylinder  14  is obtained for analysis by whetting pattern determinor (block  112 ). Thereafter, the routine proceeds to block  104  as shown. 
     It should be appreciated that the predetermined dimension X referred to relative to FIGS. 3 and 8 or the number of areas selected relative to block  104  in FIG. 4 are defined by a user and, again, correlate to a threshold distance at which it is desired to begin cooling the doctor blade of the printing press before the blade encounters the ink received in the areas which make up the image pattern  50  (FIG.  2 ). 
     In the embodiment being described, the predetermined dimension X referred to in FIG. 3 corresponds to a length, such as the circumferential length X shown in FIG. 2, of at least 25 mm. Also, the whetting areas themselves are typically very small relative to the areas which make up the pattern  50 . Moreover, the typical volume of an engraved or etched whetting area  66  or  68  is less than about 800 cubic microns. 
     Advantageously, this system and method provides convenient means for prelubricating and cooling a doctor blade in a printing press so that it does not vaporize or remove ink from the engraved or etched pattern corresponding to the image to be printed. This, in turn, provides improved cylinder engraving/etching which results in improved printing characteristics, especially at the edges of an image pattern where a doctor blade initially engages the ink in the engraved or etched pattern. 
     While the methods herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims. For example and as alluded to earlier herein, it is contemplated that features of the invention may be used in systems which are not restricted to mechanical engraving. Such systems include chemical etching, laser etching, laser engraving, electron beam engraving and the like.