Abstract:
A friction driven printing device capable of delivering high-resolution images on the vertical surface of corrugated boxes, shipping cases, chip board, and the like, has a print cylinder assembly that is housed in a print carriage that is mountable on a conveyor line. The print cylinder has a wall that is perforated and includes a stencil and a screen mounted on the print cylinder. Ink from an ink cartridge is pumped into the print cylinder via an ink feed tube and deposited in the print cylinder. A roller squeegee is used to meter the ink uniformly across the print area of the print cylinder and ultimately onto the printer substrate.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/330,951, filed on Nov. 5, 2001. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   This invention is directed to a printing system for delivering high-resolution images on vertical surfaces of recording media having a non-negligible third dimension. 
   2. Description of Related Art 
   A variety of printing methods are familiar to most people, including offset, letter press and gravure lithography, inkjet printing, laser printing, and impact printing. A technique that has nearly vanished over the past 20 years is mimeography. 
   Mimeography was widely used in the 1940s and 1950s in schools, hospitals and the military as an alternative to commercial printing. Traditional mimeography is inexpensive and can be accomplished “in house” with little capital investment and a high level of flexibility. A user needs only a typewriter or an impact printer, a mimeograph printer, which is about the size of a small photocopier, stencils, ink and paper. The heart of the traditional mimeograph system is the stencil, which is traditionally made of a natural fiber tissue and coated to block the flow of ink. To create an image, the stencil is placed in a typewriter. The typing keys remove the coating on impact. The stencil is then mounted on the mimeograph print cylinder. Ink, flowing from inside the cylinder through a porous metal cylinder surface and then through the voids created in the stencil by the typewriter, transfers the image to the paper substrate. Print quality is not comparable to typed memos or letters. As a result, use of the traditional mimeograph process was limited in commercial offices. Schools, hospitals and the military used this traditional mimeograph process because the copy is legible, but more importantly, inexpensive. 
   Mimeography in its original form has virtually disappeared in the industrial world. It has been largely replaced by photocopier equipment. However, recently mimeography was reborn when a “digital stencil” was developed. Digital stencils are made of a non-woven backing of natural and polyester fibers laminated to a polyester thin film of about 6-8 gauges. The digital stencil is imaged by using thermal printheads such as those used in facsimile machines and a wide variety of label printers. Such thermal printheads have a resolution of about 200 to 600 dots per inch. The digital stencil system, also known commercially as a digital duplication system, offers vastly improved print quality over traditional mimeograph equipment. 
   Thermal printheads accept digital data. As a result, stenciled images may be created in computers or digital scanners, as opposed to old-fashioned typewriters and impact printers. From the standpoint of print quality, digital duplicator systems are not comparable with photocopying. However, the improved print quality and low operating cost is useful in many traditional office settings. 
   The typical digital duplicator looks and performs very much like a small photocopier. An original image is placed on the machine&#39;s plate scanner, which scans and digitizes the image and downloads a copy to a thermal imager. The thermal imager burns holes in a plastic stencil at 300 or 400 dots per inch. The stencil is automatically loaded onto the print cylinder and paper is automatically fed into the printer, printed and discharged. The operator need only enter the quantity of copies desired and select the print speed. In some machines, a computer can be used for the digitizing process where an original does not exist. Thus, the operator can create an image having text, graphics, and the like on a personal computer and download the image directly to the thermal imager to start the automatic printing process. 
   SUMMARY OF THE INVENTION 
   Various conventional embodiments of digital duplicators have many features in common, such as only printing on a horizontal plane and requiring the use of fine print paper, which is necessary because fine print paper offers a very consistent surface. In all conventional digital duplication machines, an opposing impression roll is pressed against the underside of the print medium to force un-used ink back into the print cylinder to prevent ink from building up under the stencil, and thus creating an image quality problem. Because the opposing impression roller is required, conventional digital duplicators cannot simultaneously print on opposing sides of the print medium. Additionally, all conventional digital duplication machines automatically feed and control the path of the paper. Conventional digital duplicators primarily reside in an office environment, because conventional digital duplicators are not designed for use in a factory setting that is often too harsh for sensitive electronic equipment. 
   Because of the limitations of conventional digital duplicators, conventional digital duplicators are inappropriate for printing on inconsistent surfaces, such as, for example, those found on chipboard and corrugated shipping boxes. Corrugated shipping boxes have a very irregular and abrasive surface. Not only is the quality of the “surface linear fall” inferior to that of the fine paper that is necessary for conventional digital duplicators, the surface also undulates as a result of the underlying corrugations. Further, the quality of the surface print area of corrugated shipping boxes is inconsistent due to wide variations in wood pulp makeup, processing variations from paper mill to paper mill, and in the percentage of recycled fiber. Although printing on such inconsistent surfaces is discussed above, printing on other surfaces, including consistent surfaces such as, for example, printing on paper, textiles, metals, or the like, is contemplated. 
   This invention provides systems and methods for delivering high-resolution images on the vertical surface of recording media, such as corrugated sheets, corrugated boxes and shipping cases, chip board, or any other recording medium that has a non-negligible third dimension, such as filled shipping cases. 
   In various exemplary embodiments, a print cylinder assembly is housed in a print carriage that is, in various exemplary embodiments, detachably mountable on a conveyor line to print images on such recording media. 
   In various exemplary embodiments, the systems and methods of this invention include applying a pseudoplastic ink within a vertically mounted print cylinder having a wall. The print cylinder wall has a perforated surface formed using a metal or mesh material. A stencil is mounted on the exterior surface of the print cylinder. Ink from an ink cartridge, or reservoir, is pumped into the print cylinder via an ink feed tube and deposited in the print cylinder. A roller squeegee is used to meter the ink uniformly across the print area of the print cylinder and ultimately onto the printed substrate. In an exemplary embodiment of the invention, the ink is deposited on the floor of a vertically mounted print cylinder proximally to the cylinder wall and the squeegee. 
   A sensor, mounted on an ink sensor assembly proximally to the ink feed tube and the surface of the print cylinder, maintains the level of ink within the print cylinder near or at a desired level of ink by regulating the amount of ink pumped from the ink reservoir through the ink feed tube. In various exemplary embodiments, the ink feed tube may be constructed of copper, plastic, or the like. In various exemplary embodiments, the sensor may be a capacitive sensor and the ink may be a pseudoplastic ink. Shear forces may cause the pseudoplastic ink to rise forming a vertical bead on the wall of the cylinder. 
   In various exemplary embodiments, the stencil is mounted on the print cylinder and attached by a stencil hold-down device. The stencil hold-down device maintains the proper tension on both the leading and trailing ends of the stencil to provide a compressive force usable to force unused ink back into the print cylinder. This tends to reduce ink buildup under the stencil. To assist in this process, in various exemplary embodiments, the squeegee has a serrated surface that provides channels for any excess ink to flow back into the print cylinder. In various exemplary embodiments of the invention, the stencil hold-down device may be a mechanical, leveraged stencil hold-down device. 
   The print cylinder assembly is housed in a print carriage that is, in various exemplary embodiments, detachably mountable on a conveyor line. In various exemplary embodiments, the stencil hold down device has an arm extending outwardly from the print carriage into the path of items traveling on the conveyor line. The arm of the stencil hold down device catches the leading edge of an item as it travels on the conveyor line and causes the print cylinder to turn. This causes the print cylinder to apply an image to the item. This also tends to reduce the friction of the item on the stencil, because the stencil is in motion with the item as the item passes by the print cylinder. Because many items, such as corrugated boxes, have extremely abrasive surfaces, it is desirable to reduce the friction on the stencil and the print cylinder to increase the useful life of these desirable components. 
   In various exemplary embodiments of the invention, upper and lower O-rings may be provided on the surface of the print cylinder to further reduce the amount of friction to the stencil caused by a passing print surface. The O-rings also provide a drive surface to rotate the print-cylinder. In various exemplary embodiments, the O-rings are formed using rubber, or the like, which provides a high coefficient of friction between the passing item and the print cylinder. 
   In various exemplary embodiments of the systems and methods according to this invention, the print cylinder includes a cam that advances the print cylinder when it is displaced from a home position forward to the home position. In various exemplary embodiments, the cam rides on an elliptically shaped interior surface of the print cylinder. Because of the elliptical interior surface, the print cylinder returns to the “home” or starting position after a full or a partial rotation. Thus, in such exemplary embodiments the print cylinder remains in registration, and is always ready to print the following item. The full rotation also ensures that all ink is cleared from the surface of the print cylinder so ink does not build-up under the surface of the stencil. 
   In various exemplary embodiments, to reduce the force of impact from the items to be printed on the device, the print carriage is spring-loaded. In various exemplary embodiments, to overcome the recoil in the springs caused by the impact of the moving items, a shock absorber may be used. In various exemplary embodiments, to deal with convex and concave variations in the vertical print surface of the items, the carriage includes a gimbal for the print cylinder to allow the surface of the print cylinder to remain in contact with an uneven print surface. 
   The design of the print device, as described above, makes it possible for the printing device to be friction driven. Because, in various exemplary embodiments, the print cylinder revolves as the result of the driving force of the item to be printed as that item passes by the print cylinder, no external power source is needed to drive the print cylinder. Thus, in such exemplary embodiments, it is not necessary to match the print cylinder speed to the speed of the item passing the printing cylinder. Normally, this force is provided by the conveyor which conveys the item past the print cylinder. However, in various exemplary embodiments, the drive force can also be accomplished by manually pushing the item past the printing device on a non-driven conveyor or table. In other words, in various exemplary embodiments, the device does not control the item being printed. Rather, the item being printed controls the device. 
   In various exemplary embodiments, a mounting system for the device allows the entire device to be adjustably mounted on a conventional conveyor system, such that the location of the print image on the item may be at any desired height. Further, additional devices may be added, or “stacked”, on the mounting system to allow for multiple images to be deposited on the item in a single pass. The devices may also be mounted opposing each other on the conveyor to allow for two sides of item to be printed simultaneously. 
   In various exemplary embodiments, the system may be used with a conventional personal computer and existing commercial software to create stencils useable with the system. 
   These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various exemplary embodiments of the systems and methods of this invention will be described in detail, with reference to the following figures, wherein: 
       FIG. 1  is a perspective view of one exemplary embodiment of a printing device and the mounting frame according to this invention; 
       FIG. 2  is a perspective front view of one exemplary embodiment of a printing device according to this invention; 
       FIG. 3  is a side view of one exemplary embodiment of a printing device and the mounting frame according to this invention; 
       FIG. 4  is a top view of one exemplary embodiment of a printing device with a cover and the mounting frame according to this invention; 
       FIG. 5  is a detailed top view of one exemplary embodiment of a printing device without the cover according to this invention; 
       FIG. 6  is a detailed top view of one exemplary embodiment of a print cylinder and a cam configuration of the printing device according to this invention without print cylinder mount; 
       FIG. 7  is a detailed top view of the print cylinder and ink feed tube configuration of the printing device according to this invention without end cap; and 
       FIG. 8  is a detailed top view of the stencil hold-down device of the printing device according to this invention. 
       FIG. 9  is a detailed top view of the stencil hold-down device and a gusset according to this invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     FIG. 1  illustrates one exemplary embodiment of a printing device  20  and mounting frame  10  according to this invention. As shown in  FIG. 1 , the printing device  20  includes a print cylinder mount  40  that is pivotably attached to a print carriage  30  by a print cylinder mount pivot  140 . The printing device  20  is adjustably attached to a mounting frame  10  by a vertical adjust control device  100 . The vertical adjust control device  100  allows the printing device  20  to be adjusted in a vertical direction at the desired location. The mounting frame  10 , and the attached printing device  20 , are horizontally adjustable by a horizontal adjustment control device  110 . The horizontal adjustment control device  110  allows the printing device  20  to be horizontally positioned relative to a conveyor system  2  at any desired location. In various exemplary embodiments of the invention, the horizontal adjust control  110  includes a crank (not shown) for fine horizontal positioning of the printing device  20 . 
     FIG. 2  shows front view of one exemplary embodiment of the printing device  20  of  FIG. 1 . As shown in  FIG. 2 , the printing device  20  includes the print cylinder mount  40  that is pivotably attached to the print carriage  30  by a pair of print cylinder mount pivots  140 . The print cylinder  90  has top and bottom end caps  94  attached at upper and lower ends, respectively, of a perforated metal screen  93  that forms an exterior wall or surface of the print cylinder  90 . The print cylinder  90  is rotationally attached to the print cylinder mount  40  by a number of print cylinder fasteners  112 . A stencil hold-down device  70  retains a stencil  92  on the outer surface of the print cylinder  90 . One or more metal gussets  71  ( FIG. 9 ) are disposed at the top and bottom of the stencil hold-down device  70  to protect the stencil  92 , silk screen (not shown), and O-rings  91  when an item to be printed  1  contacts the printing device  20 . A guide foot  80  is attached to the print carriage  30  and aligns the item  1  to be printed so that the item to be printed  1  is properly positioned relative to the printing device  20  for receiving a print image. The guide foot  80  also protects the print cylinder  90  and the stencil  92  from damage that would otherwise occur by impact with the item to be printed  1 . 
   The O-rings  91  are disposed around the peripherally of the stencil  92  on the surface of the print cylinder  90  to provide a drive surface to aid in rotating the print cylinder  90  as the item to be printed  1  passes the printing device  20  for printing. The O-rings  91  also aid in protecting the stencil  92  and silk screen (not shown) from impact and friction caused by the item to be printed  1  as the item to be printed passes the printing device  20 . 
     FIG. 3  shows a side view of one exemplary embodiment of the printing device  20  of  FIG. 1 . As shown in  FIG. 3 , the mounting frame  10  may be attached to the conveyor system  2  and allows the printing device  20  to be adjustably positioned relative to the conveyor system  2  and the items to be printed  1  that are placed on the conveyor  2 . As shown in  FIG. 3 , in various exemplary embodiments of the systems and methods according to the invention, an impression roller  50  is adjustably attached to the mounting frame  10  opposite to the printing device  20  to assist in the proper alignment of the item to be printed  1  and to provide a resistant force to maintain the vertical surface of the item to be printed  1  in contact with the print cylinder  90 . 
     FIG. 4  shows a top view of one exemplary embodiment of the printing device  20  of  FIG. 1  with a top cover  32  in place and the impression roller  50  positioned opposite to the printing device  20 , each being adjustably attached to the mounting frame  10 . 
   As the item to be printed  1  approaches the printing device  20 , the item to be printed  1  is properly aligned by the guide foot  80  and the impression roller  50 . The item to be printed  1  then engages the stencil hold-down device  70  and the O-rings  91 . The stencil hold-down device  70  is securely attached to the print cylinder  90  at a number of end caps  94  by mounting plates (not shown). In various exemplary embodiments, the surface of the end caps  94  may be knurled to provide a bonding surface to adhere the metal screen  93 . The stencil hold-down device  70  receives a leading edge of the item to be printed  1  as the item to be printed  1  passes by the printing device  20 . As a result, the print cylinder  90  rotates, and the item to be printed  1  engages the O-rings  91  to provide a drive force to the print cylinder  90 . As the print cylinder  90  rotates, an image is printed on the vertical surface of the item to be printed  1  as the item to be printed  1  passes by and contacts the printing device  20 . The impression roller  50  holds the item  1  against the print cylinder  90  as the item to be printed  1  is printed. As the print cylinder  90  rotates, ink deposited in the print cylinder  90  is uniformly distributed on the wall  93  of the print cylinder  90  by the squeegee  280 . The ink is forced through the cylinder wall  93 , the stencil  92 , and the silkscreen (not shown), to print an image on the item to be printed  1 . The silkscreen may be comprised of silk, metal mesh, stainless steel, or another appropriate known or later-developed material that is suitable for the purposes of the invention. Although, the above described exemplary embodiments describe ink passing through each of the cylinder wall  93 , the stencil  92  and the silkscreen (not shown), the invention also contemplates the ink passing through only the cylinder wall  93 , or any combination of the cylinder wall  93 , the stencil  92  and the silkscreen. 
     FIG. 5  shows a detailed top view of one exemplary embodiment of the printing device  20  of  FIG. 1  without the cover  32 . As shown in  FIG. 5 , the print cylinder  90  is rotatably attached to the print cylinder mount  40  and is pivotably attached to the print carriage  30  at the print cylinder mount pivots  140 . A gimbal  130  is disposed between opposing sides of the print carriage  30  and in front of the front cross-member  150  to allow the print cylinder  90  and the print cylinder mount  40  to rotate in a horizontal plane. This allows contact to be maintained between the stencil  92  and the item to be printed  1  as the image is printed onto the item to be printed  1 , regardless of minor inclinations of the vertical surface of the item to be printed  1  from true vertical relative to the surface of the printing cylinder  90 . A print cylinder lock  60 , which can be disposed on the surface of the print cylinder mount  40 , may be used to lock the print cylinder  90  in place to prevent the print cylinder  90  from rotating when desired, such as while changing the stencil  92  or during shipping of the printing device  20 . 
   When the item to be printed  1  that is traveling down the conveyor system  2  is received by the stencil hold-down device  70 , the force of the impact of the item to be printed  1  on the printing device  20  is absorbed by a number of springs  160  and/or a shock absorber  170 . In various exemplary embodiments, the first ends of the one or more springs  160  are attached to the front cross-member  150  and the second ends of the one or more are attached to a carriage dampener  162 . In various exemplary embodiments, the shock absorber  170  is attached to the carriage dampener  162  at a first end and is in contact at a second end with a shock absorber block  180 . In various exemplary embodiments, the shock absorber block  180  is attached to the front cross member  150 . Upon impact with the item to be printed  1 , the one or more springs  160  and the shock absorber  170  absorb the impact. The print carriage  30  may travel relative to the mounting frame  10  by at most the distance of a number of elongated holes  190 . 
   In various exemplary embodiments, a rear cross-member  152  is disposed between opposing sides of the print carriage  30 . In various exemplary embodiments, an ink cartridge  200  is detachably connected to the ink pump  210 . In various exemplary embodiments, the ink cartridge  200  and the ink pump  210  are mounted rearward of the rear cross-member  152  and between opposing sides of the print carriage  30 . 
     FIG. 6  shows a detailed top view of one exemplary embodiment of the print cylinder  90  and a cylinder rotation assembly  240  of  FIG. 1  without the print cylinder mount  40  in place. As shown in  FIG. 6 , the print cylinder  90  has an end cap  94  at the top end of the print cylinder  90 . A cam ring  230 , which has an elliptical inner surface  232 , is affixed to the end cap  94 . A roller wheel  250  is maintained in contact with an elliptical inner surface  232  of the cam ring  230  by a cam spring  260 . This assembly causes the print cylinder  90  to rotate by about 360° when the stencil hold-down device  70  engages a leading edge of the item to be printed  1  traveling on the conveyor system  2 . In various exemplary embodiments of the invention, the roller wheel  250  is maintained in forceable contact with the elliptical inner surface  232  of the cam ring  230  by one or more cam springs  260 . In various exemplary embodiments, the tension of the one or more cam springs  260  may be selected based on the temperature of the operating environment of the printing device  20  and/or the viscosity of the ink. 
     FIG. 7  shows a detailed top view of one exemplary embodiment of the print cylinder  90  and the ink feed tube  120  without the end cap  94  in place. As shown in  FIG. 7 , a roller squeegee  280 , which has, in various exemplary embodiments, a plurality of diamond shaped cuts forming a serrated surface, is disposed against the inner wall of the print cylinder  90 . Ink from the ink cartridge  200  is pumped by the ink pump  210  through the ink feed tube  120  and deposited on the bottom end cap  94 , or floor, of the print cylinder  90 . Shear forces cause the ink to rise vertically up the wall  93  of the print cylinder  90 . The roller squeegee  280  forces the ink through the wall  93  of the print cylinder  90  as the print cylinder  90  rotates due to an item to be printed  1  engaging the stencil hold-down device  70 . The flow of ink through the feed tube  120  is controlled by a sensor  320 , which activates an ink pump  210  to pump ink from the ink cartridge  200  when ink is required. As the print cylinder  90  rotates, the roller squeegee  280  presses ink through the wall  93  of the print cylinder  90 , the stencil  92 , and the silk screen (not shown). Once the ink has passed through the print cylinder  90  the wall  93 , the silk screen (not shown) and the stencil  92 , the ink is deposited in an image-wise pattern on the vertical surface of the item to be printed  1 . 
   The stencil  92  is held in place on the outer surface of the wall  93  of the print cylinder  90  by the stencil hold-down device  70 . In various exemplary embodiments, the stencil hold-down device  70  is attached to the print cylinder  90  at the end caps  94  by mounting plates (not shown). As shown in  FIG. 8 , in various exemplary embodiments, the stencil hold-down device  70  includes a first stencil lock  290 , shown in an open position, and a second stencil lock  292 , shown in a closed position. The first and second stencil locks  290  and  292  securely fasten the two ends of the stencil  92  over the mesh screen and around the print cylinder  90 . 
   Although the above exemplary embodiments have been described using ink, and more specifically a pseudoplastic ink, other fluids are contemplated by this invention. Such fluids may include, for example, paints, pigments, dyes, stains, adhesives, or the like, and any combination thereof. 
   Although the above exemplary embodiments are described using a screen disposed over the wall  93  of the print cylinder  90 , the invention contemplates the use of a pad  95  ( FIG. 9 ), or cushion, disposed between the wall  93  of the print cylinder  90  and the screen (not shown), to provide a cushioned and/or resilient surface of the print cylinder  90 . The pad  95  may be formed using felt, neoprene, nylon, or other known or later developed material suitable for the stated purpose. Although  FIG. 9  shows the pad  95  disposed on the print cylinder  90  and the gusset  71  connected to the stencil hold-down device  73 , it should be appreciated that either the gusset  71  or the pad  95  may be used without the other. 
   While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.