Patent Publication Number: US-6216590-B1

Title: Light weight intaglio printing press

Description:
This application is a continuation-in-part of U.S. application Ser. No. 09/368,679 filed Aug. 5, 1999, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a printing press, and in particular to a press for intaglio printing, including printing of etchings and engravings. 
     2. Description Relative to the Prior Art 
     The art of intaglio printing dates back at least to the 15th century, where it was practiced by such well known artists as Rembrandt and Durer. It has developed over time and continues as a method of graphic artistic expression to the present. 
     The forms of intaglio printing are characterized by having the art work incised on a flat plate (i.e., a printing block plate); either into a ground layer covering the plate or into the surface of the plate itself. The plate surface used, and the means of forming the lines of the print determine the actual classification of the work. However, all intaglio processes involve filling the incised lines of the plate&#39;s finished drawing with ink, and carefully removing all remnants of ink from the flat, uncut surfaces of the plate. The plate is then covered with an appropriately wetted print paper (i.e., print fabricating material) which is in turn covered with resilient layers of material such as felt, and then run through a press which applies pressure to the felt and paper forcing it down into the inscribed lines of the plate so that ink is picked up and transferred to the paper. 
     Because paper fibers must be forced down into the lines and grooves of the inked plate to effect the ink transfer, large forces, uniform across the width of the plate, must be applied to the felt/paper layers as they traverse the press. Presses of the prior art utilize a fixed structure on which is mounted a massive movable bed onto which the plate is laid for printing. The bed is generally propelled by a lower driven roller which causes the plate to move on auxiliary rollers along the length of the table carrying the plate beneath the fixed print roller. The print roller, supported on end bearings fixed in heavy brackets secured to the table, is pressed down onto the felt/paper layers with pressure sufficient to effect the ink/paper transfer as the bed is rolled along the table in a plane parallel to, and at a fixed distance from, the print roller axis, by an appropriate motive means. In the prior art, the print rollers have been substantial steel cylinders with diameters of from 4″ and up, and the lower rollers consisting of steel cylinders with diameters of from 3″ and up. These heavy rollers are used to provide uniform pressure and to maintain straightness and parallelism over their full widths of the bed from 12″ to several feet, and require heavy, rigid support structures. The bed itself must be weighty to resist flexing under the printing forces. Thus the intaglio press of the prior art is a heavy and unwieldy structure. The present invention provides performance equivalent to that obtainable by the presses of the prior art, but with a substantial reduction in complexity and weight. 
     SUMMARY OF THE INVENTION 
     Rather than using a heavy bed to support an intaglio plate and moving the bed and plate under a fixed print roller, the present invention teaches using a lighter weight fixed bed to support the intaglio plate and mounting the print roller on a movable trolley which is advanced across the intaglio plate causing the pressure of the print roller to effect the printing. The trolley is fabricated from light weight beams substantially forming the sides of a hollow box beam, and the print roller is stiffened by support of rollers tied to a trolley beam and in contact with the print roller at several intermediate points. These intermediate rollers, fixed to the upper beam, preclude the print roller from flexing under the load presented by the intaglio plate and the associated paper and felt material as the print roller under pressure traverses the plate. This allows the use of a lighter, smaller diameter print roller, and further reduces the weight and complexity of the print roller support assembly. Handwheels attached to the trolley provide spring loaded pressure to control the pressure of the print roller on the intaglio plate assembly. The trolley is driven across the bed and plate either by a manually operated external drive wheel or a geared motor, which causes the print roller to rotate under pressure across the plate effecting printing as it rolls. Below the bed of the table is a lower roller attached to the trolley and circumfirentially in contact with the lower bed face. This roller provides support to the underside of the fixed bed to prevent its flexure under the pressure of the print wheel pressing on the plate assembly at the upper surface of the bed. Also supporting this lower roller are intermediate rollers secured to the horizontal lower trolley beam to further provide uniform pressure and structural support during the printing process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with respect to the drawings of which: 
     FIG. 1 is a cross-sectional drawing of an end view of the press of the invention, 
     FIG. 2 a  is a cross-sectional drawing of a prior art mechanism for applying pressure to a print roll, 
     FIG. 2 b  is a plot of the pressure v. screw position for the mechanism of FIG. 2 a,    
     FIG. 3 is a drawing of a side elevation view of the trolley that is part of the press of the invention, 
     FIG. 4 is a plot of the pressure v. screw position for the screw mechanism of the invention, 
     FIG. 5 is a plot of the pressure v. screw position for the screw mechanism of the invention for a dual action spring, 
     FIG. 6 is a drawing illustrating the screw mechanism of the invention with a dual action pressure generating spring, 
     FIG. 7 a  is a partial elevation drawing of a pressure indicator for measuring the force applied by the print roller onto the intaglio plate, and 
     FIG. 7 b  is a partial drawing of the scale of the pressure indicator of FIG. 7 a  shown rotated through 90 degrees relative to FIG. 7 a.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the press  10  of the invention consists of a fixed table structure  12  having an attached top flat bed  14  extending the full width and full length of the table  12 , and fixed to it. In the process of printing an etching or engraving, an incised intaglio inked plate (not shown) will be secured to the bed  14  in a fixed position with its top surface overlaid with the print paper and a resilient felt blanket. Pressure onto the felt blanket provides the forcible contact between the paper and the incised plate. Along the width edges of the bed&#39;s  14  top surface are rigid sides  16  extending downwards, and attached to these sides  16  are inwardly facing platforms  18  extending the length of the table  14 . A print roller  20 , not fixed relative to the table structure  12 , is part of a trolley assembly  22  whose travel across the bed  14  drives the print roller  20  over the stationary inked plate/paper/felt assembly positioned on the flat bed  14 . 
     The trolley  22  has two vertical box like members  28 , 30  that form the sides of the trolley  22 , and an upper beam  24 , and lower beam  26  that form the top and bottom of the trolley  22 . Referring to FIG. 1, the side members  28 , 30  are positioned alongside the rigid sides  16  of the table top  12 , and the trolley is completed by the upper cross beam  24  tying the box members  28 , 30  together at the top end of the trolley,  22 , i.e. above the bed  14 , and the lower cross beam  26  tying them together at the bottom end of the trolley, i.e. below the bed  14 . Thus the structure of the trolley  22  is substantially a hollow-like box enveloping the table  12 . Attached to the vertical member  30  are two roller bearings of which only one,  34 , is seen in FIG. 1, and to the vertical member  28  to be attached are two roller bearings  32 , 33 , of which only one,  32 , is seen in FIG. 1, which bear against the rigid sides  16  of the flat bed  14  and transversely guide the trolley  22  while it rolls the length of the table  12 . Additionally, fixed to the upper surface of the lower beam  26  are the inner rings of radial bearings  48 , 50  whose outer races ride on the fixed platform  18 , which support the lower portion of the trolley  22 . (Corresponding bearings, of which one,  51 , is seen in FIG. 3 are in mirror image positions relative to the bearings  48 , 50 .) 
     The print roller  20  extending the width of the flat bed  14  is mounted in bearings  47 , 49  secured to the trolley&#39;s vertical members  28 , 30  so that the print roller  20  rides with the trolley  22 . As will be explained below in connection with the operation of the pressure generating handwheels  40 , 42 , pressure is applied downwardly at the ends of the print roller  20  to uniformly force it across the felt blanket covering the paper which is to be printed by the intaglio plate. Further extending from the upper beam  24  are two auxiliary roller bearings  36 , 38  in contact with the upper surface of the print roller  20  to maintain print roller  20  rigidity and parallelism against the considerable upward pressure exerted through the felt from the intaglio plate. A drive wheel  44  is coupled to the print roller  20  through bearings  47 , 49  and rotation of the drive wheel  44  propels the trolley  22  and the print roller  20  across the paper/felt/intaglio plate for printing. By a simple modification, a motor drive (not shown) may be used for moving the trolley  22  across the table in place of the drive wheel  44 . 
     Similarly, a lower roller  46 , equal approximately in length to the width of the bed  14 , is located below the bed  14 , and this roller is supported by intermediate bearings of which only  60 ,  62 ,  64  are seen in FIG.  1 . These bearings are mounted in blocks connected to the lower beam  26 . The lower roller  46  is in contact with the underside of the bed  14 , and the lower roller&#39;s rigidity prevents the bed  14  from flexing during printing. 
     Before describing the inventive spring loading of the printing roll  20  disclosed in the present invention, it is advantageous to consider the method of positioning, and the pressure exerted by, the print roller as practiced in the prior art. Referring to FIG. 2 a,  a print roller  91  is shown positioned above a bed  89  covered by a felt/paper layer  81 . The shaft  87  of the print roller  91  is fitted into a bearing pillow block  85  whose upper surface is in contact with the bottom of the screw  95 . Rotation of the screw  95  by handle  93  pushes down on the bearing pillow block  85  to set the pressure of the print roller  91  on the bed  89  and felt  81 . The felt,  81  which distributes the force over the plate, being comprised of organic fibers, has a relatively steep spring constant. From FIG. 2 b  which shows the linear relationship,  92 , between the movement of the screw  95  and the pressure on the felt  81 , it will be seen that a slight movement ( 94 ) of the screw  95  results in a relatively large change in the pressure ( 96 ) on the felt  81 . The pressure control of the present invention solves this problem, as described below. 
     Referring to FIG. 3 one of the handwheel assemblies, e.g.  40 , is seen in a detailed side view of the trolley  22 . The structure of the other hand wheel assembly, e.g.  42  is substantially its mirror image. The side member of the trolley  22  labelled  28 , (FIG.  1 ), viewed from the side is in the form of a box beam with a top member  52 , side members  54 ,  56 , and bottom member  58 . Flat bed  14 , rigid side wall  16  and platform  18  are shown oriented in the longitudinal direction, i.e. the direction of trolley  22  movement during printing. 
     Pressure is applied to the print roller  20  in the following manner. The print roller  20  is mounted on a bracket  66  which passes through holes  68 , 70  in the cross beam  52 , so that bracket  66  is captive but can move vertically with respect to cross beam  52 . Screw  72  clears a hole  74  in the top of the bracket  66 , and the end of the screw  72  is locked by the nut  82  so it cannot move vertically with respect to the cross beam  52  of the trolley  22 . The lower end of the screw  72  is mounted in bearings  78 , 79  which allows the screw  72  to solely rotate relative to the bracket  66  and to the cross beam  52 . The lower end of the spring  80  is against the top of bracket  66 , and the upper end of the spring  80  is against the bottom of the plate  84 . The screw  72  is threaded through the nut  76  which is locked into place by being welded to a square plate  84 . A housing  86  has a partially opened top surface through which the screw  72  easily passes, and the side walls of the housing  86  are adjacent to the edges of the plate  84  which restrict any rotational movement of the square plate  84 . Rotation of the screw  72  by means of handle  40  compresses or relieves the spring  80  due to the vertical movement of the screw  72  relative to plate  84  and the nut  76 . Hence, the advance or retraction of screw  72  and the resultant vertical movement of the plate  84  controls the degree of compression of spring  80  which generates the force applied between the top of the bracket  66  and square plate  84 . The spring pressure applied to bracket  66  forces the bracket  66  down, (or allows it to move up), controlling the pressure at the line of contact of the print roller  20  against the felt  83  on the intaglio plate. 
     The addition of the spring  80  to the screw assembly  72  allows the print roller  20  to move up and down with changes in print plate thickness, or with changes of the felt&#39;s spring constant due to varying moisture in the felt while maintaining substantially the same pressure on the plate and paper being printed. Referring to FIG. 4, the corresponding relation between screw motion and pressure at the roller for the spring assembly of the invention is seen. The overall slope of the spring rate/felt rate curve  98  may be made flatter, since it is controlled by the spring  80  rather than by the randomly variable spring constant of the felt  83 . A small, readily controllable, change is screw position  100  results in a small pressure change of the roller on the felt  102 , as compared to the large change  96  illustrated in FIG. 2 b,  as practiced in the prior art. 
     Additionally, the spring force may be made non-linear relative to rotation of the screw. Referring to FIG. 5, the initial spring rate ( 104 ) is seen to be very low, increasing ( 106 ) as the print roller continues to press into the felt. This allows the initial setup of the felt/paper at a minimal force between the print roller  20  and the felt/paper using a coarse adjustment of the screw  72 , and after the felt/paper have been correctly position under the roller, a few additional screw turns generates the high pressure needed for printing. 
     At the four corners of the top lip of the housing  86  four screws are threaded through the lip, of which only screws  88 , 90  are seen in the view of FIG.  3 . The positions of these threaded screws limit the upward motion of the plate  84 , and accordingly the rise of the print roller  20  above the bed  14  under control of the handle  40 . 
     In a second embodiment of the invention, a structure implementing a multiple constant spring is shown in FIG. 6, which may be used in setting print roll  20  pressure in place of the spring system of FIG. 3. A spring  108  (corresponding to the spring  80  of FIG. 3) surrounds a screw  73  (corresponding to screw  72 ). The spring  108  consists of a series of stacked Belleville disc spring washers , and it will be appreciated that by selecting differing heights and thicknesses for these washers  108 , and stacking them in proper order, a dual constant spring arrangement may be effected. That is, a less stiff upper set of discs, followed by stiffer lower discs will provide the dual spring constant. FIG. 5 shows the resultant spring constant of the dual spring constant structure. Initially, the low spring constant ( 104 ) controls the pressure, but when this spring segment is full compressed, the stiffer spring constant ( 106 ) takes over. Other types of spring elements may be placed in series in an equivalent manner. 
     In a third embodiment of the invention, a pressure measuring indicator  100  is mounted on the bracket  66 ′. (In the drawings, different but related elements are identified with the same reference characters, albeit that corresponding elements in the various drawings are distinguished by primes.) The pressure measuring indicator  100  has an arm  102  that is pivoted at the point  104 . A boss  106  on the arm  102  is in contact with the underside of plate  84 ′. As the handwheel  40 ′ compresses the spring  80 ′ by moving the plate  84 ′, the arm  102  is deflected about the pivot point  104  due to the force on the boss  106  exerted by the plate  84 ′. A pointer  108  is mounted on the free end of the arm  102 , and a juxtaposed pressure scale  110  is secured to the bracket  66 ′. Depending on the compression of the spring  80 ′, the pointer  108  indicates on the scale  110  the corresponding pressure applied to the print roller. It will be noted that the boss  106  may be located anywhere along the portion of the arm adjacent to the plate  84 ′; the closer the boss  106  is to the pivot point  104  the greater the magnification of the swing of the pointer  108  over the scale  110  relative to the movement of the plate  84 ′. A light spring  112  biases the arm  112  so that the boss  106  remains in contact with the bottom of the plate  84 ′. It will be appreciated that in practice two of the disclosed indicators  100  are used on the press of the invention; each in association with a corresponding handwheel  40 ,  42 , so that controlled pressures may be applied to each end of the print roller  20  (FIG.  1 ). 
     The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, while the invention has been described in terms of printing of etchings or engravings from an intaglio plate, it will appreciated that other forms of printing such as lithography, printing from handset type, or wood blocks may be practiced on the press of the invention. Applicant generically refers to use of “printing blocks” to inclusively cover the above broad printing techniques.