Abstract:
A printing apparatus and a method suitable for printing on two sides of medium, such as paper by using an intermediate transfer surface. The device consists of a print head, an intermediate transfer surface and a medium path such that as the medium is transported along the medium path the print head prints a first image on the transfer surface, then sequentially prints a second image to one face of medium while the transfer surface is transferring the first image to the other face of a medium by pressing the transfer surface against the medium. A method for printing is also disclosed comprising of the steps of printing a first image on a transfer surface, printing a second image directly onto one face of the medium, then transferring the first image onto the other face of the medium.

Description:
TECHNICAL FIELD 
     The invention relates in general to electronic printers and copiers, and in particular to printers and copiers where both the front and back surface of a paper document are to be printed. 
     BACKGROUND INFORMATION 
     When using electronic cash registers and point of sale printers, it is often necessary to print on the front and back surface of a document, such as a check. This is sometimes accomplished by a salesperson physically inserting a check into the path of a print head so that one side can be printed, removing the check, turning it around and reinserting the other side of the check so the other side can be printed. This procedure is time consuming and often the sales person inserts the wrong side of the document into the path of the printer head. 
     Some cash registers and point of sale printers, known as “duplex printers” are capable of printing on both sides of a document without the need for human intervention. Depending on the design scheme, duplex printers use one or multiple print stations. Duplex printers that use a single printer station physically turn the document so that printing occurs sequentially on both surfaces of the document. A turning mechanism must be supplied to turn or flip the document. Such a mechanism was disclosed in U.S. Pat. No. 5,865,547, issued Feb. 2, 1999 to Harris. These mechanisms are relatively more expensive. Furthermore, turning or flipping the document greatly increases the probability that a paper jam will occur. As such, these mechanisms often have relatively higher maintenance costs. 
     Another approach is the use of two print stations. However, the cost of the printer or register is significantly increased because the print station is typically one of the more expensive parts of the printer. Furthermore, the use of two print stations increases the overall failure rate of the printer and increases maintenance costs. 
     What is needed, therefore, is a device which economically and reliably allows printing on both sides of a document without the use of a turning mechanism or two printer stations. 
     SUMMARY OF THE INVENTION 
     The previously mentioned needs are fulfilled with the principle of the present invention. Accordingly, there is provided, in a first form of the present invention a printing apparatus consisting of a print head, a transfer surface and a medium path such that as the medium is transported along the medium path the print head prints a first image on the transfer surface, then sequentially prints a second image to one face of a medium while the transfer surface is transferring the first image to the other face of the medium by pressing the transfer surface against the medium. 
     A method for printing is also disclosed comprising the steps of printing a first image on a transfer surface, printing a second image directly onto one face of the medium, then transferring the first image onto the other face of the medium. 
     These and other features, and advantages, will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It is important to note the drawings are not intended to represent the only form of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an isometric view of one embodiment of the present invention as shown used in a point of sale printer during one stage of the print cycle; 
     FIG. 2 is an isometric view of the embodiment of FIG. 1 showing another stage of the print cycle; and 
     FIG. 3 is an isometric view of the embodiment of FIG. 1 used in a point of sale printer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in FIGS. 1-3 of the drawings, in which like numbers designate like parts. In the following description, well-known elements are presented without detailed description in order not to obscure the present invention in unnecessary detail. For the most part, details unnecessary to obtain a complete understanding of the present invention have been omitted inasmuch as such details are within the skills of persons of ordinary skill in the relevant art. Details regarding control circuitry or mechanisms used to control the rotation of the various elements described herein are omitted, as such control circuits are within the skills of persons of ordinary skill in the relevant art. 
     FIG. 1 illustrates an embodiment of the present invention as used in a point of sale printer. Other embodiments could include copiers, computer printers or fax machines. The printer housing and supports have been removed to illustrate interior detail and a portion of the elements of the present invention. In this embodiment, a recording medium, such as a check, or paper  102  is to receive the printed images. However, the medium could consist of plastic, paper or another suitable material. FIG. 1 shows paper  102  sandwiched between feed rollers  100 A and  100 B. Feed rollers  100 A and  100 B are elongated cylindrical shafts each having two sets of paper rollers. One set of paper rollers  101 A and  101 B are visible in FIG.  1 . Paper rollers  101 A and  101 B are cylindrical rollers made of rubber or other materials which have a high coefficient of friction. A relatively high coefficient of friction is necessary so that paper  102  will move along paper path  104  as feed rollers  100 A and  100 B rotate. Paper path  104  is the route or direction paper  102  takes as it is moved through the present invention and the printer. In this embodiment, it is the route the paper takes from the time it enters slot  302  (see FIG. 3) to the time it exits slot  304  (see FIG.  3 ). 
     Pressure roller  106  is further along paper path  104  from feed rollers  100 A and  100 B. Pressure roller  106  is a cylinder made of rubber or another elastic material capable of deforming in such a way that it exerts a relatively uniform pressure in response to a pressure applied to its surface. Pressure roller  106  is rotationally mounted to shaft  107  which is rotatably attached to fixed supports (not shown) in the printer housing  301  (See FIG.  3 ). Further along paper path  104  from pressure roller  106  is a print head  108 . In this embodiment, another stepper motor and gearing (not shown) moves print head  108  back and forth in a direction parallel to direction  110 . Direction  110  is substantially perpendicular to the direction of paper path  104 . Print head  108  is illustrated as an ink jet print head. A print head is the part of a printer that controls the printing of characters or images on paper. An ink jet print head is of the type which prints an image by ejecting ink droplets from a plurality of nozzles in response to a recording signal. In other embodiments, print head  108  could be any print head capable of printing on transfer surface  115  and paper  102 . Such print heads include laser print heads, thermal transfer print heads, in-line ink jet print heads. A laser print head uses electrophotographic technology similar to technology used in by photocopiers. Thermal transfer print include print heads which use heat to generate an image on a specially treated surface and print heads which use heat to melt colored wax onto paper to create an image. An in-line ink jet print head has hundreds of nozzles that span the width of paper  102  and would eliminate the need to move the print head across the paper path. These print heads are familiar to those who are in the art of designing electronic printers. 
     In FIG. 1, print head  108  is positioned to print a reverse image  112  on transfer roller  114 . A positioning assembly consisting of a series of rollers, gearing, and supports (not shown) positions transfer roller  114  so that it is in apposition to print head  108 . It also positions pressure roller  106  and platen  116 . Such positioning assembles are known to those in the art of designing electronic printers. Transfer roller  114  is cylindrical in shape and comprises a transfer surface  115  and an internal drum rotatably mounted on a support shaft  113  which is secured to the positioning assembly (not shown). Surface  115  is made from stainless steel or similar material that does not absorb or disperse the ink from print head  108 . Downstream of transfer roller  114  and further along paper path  104  is platen  116 . Platen  116  is made of material capable of supporting the back surface of paper  102  when print head  108  is printing an image  200  on the front surface  202 A of paper  102  (See FIG.  2 ). Transfer roller cleaning station  118  is partially shown in FIG. 1 behind transfer roller  114 . 
     FIG. 2 shows paper  102  at a different point further along paper path  104 . FIG. 2 also shows the relative positions after the positioning assembly has positioned pressure roller  106 , transfer roller  114 , and platen  116 . In FIG. 2, pressure roller  106  is now in apposition to transfer roller  114  such that paper  102  is sandwiched between transfer roller surface  115  and the surface of pressure roller  106 . Platen  116  has also been positioned such that it is in apposition to print head  108 . At this point, print head  108  can now print image  200  directly on face  202 A of paper  102 . 
     FIG. 3 shows the embodiment of FIGS. 1 and 2 as part of a point of sale printer  300 . A portion of the walls of printer housing  301  have been removed to illustrate interior detail and configuration of some of the elements of the present invention. For brevity and clarity, a description of those parts which are identical or similar to those described in connection with the first embodiment illustrated in FIGS. 3 and 4 will not be repeated here. Paper  102  is shown before it enters slot  302  of printer housing  301 . After paper  102  follows paper path  104  (FIGS. 1 and 2) it will exit from slot  304 . Slot  304  is only partially shown because the walls of printer housing  301  have been removed. 
     OPERATION 
     The manner of using the duplex printer mechanism can be illustrated by describing it as a part of a point of sale printer. A document, such as a check or paper  102  is partially inserted into the printer slot  302  (see FIG.  3 ). The printer housing  301  is used as a guide to position paper  102  in the space defined between rollers  100 A and rollers  100 B. A sensor (not shown) activates a circuit which drives a document feed mechanism (not shown). Rotation and torque from the document feed mechanism is transmitted by gearing (not shown) to feed rollers  100 A and  100 B. 
     FIG. 1 illustrates the relative position of platen  116 , print head  108 , transfer roller  114 , and pressure roller  106  after image  112  is printed onto surface  115 . Feed roller  100 A rotates counter-clockwise about its longitudinal axis as viewed from FIG. 1 in direction  120 A. Feed roller  100 B rotates clockwise about its longitudinal axis as viewed from FIG. 1 in direction  120 B. The combined rotation of feed rollers  100 A and  100 B moves paper  102  along paper path  104 . The check verification information is then printed as reverse image  112  onto surface  115  of transfer roller  114  by print head  108 . An elongated piece of image  112  which is parallel to direction  110  or “row” of information is printed as print head  108  moves in a direction substantially parallel to direction  110 . After a row of information is printed, transfer roller  114  is rotated in a clockwise direction about its longitudinal axis as viewed from FIG.  1 . After transfer roller  114  is rotated, another row of information is printed onto surface  115  as print head  108  moves back across transfer roller  114 . This cycle of printing and clockwise rotating continues until all of image  112  is printed onto surface  115 . The circumference of transfer roller  114  must be slightly larger than the number of rows necessary to complete the printing of the image. 
     In FIG. 2, the positioning assembly (not shown) has moved transfer roller  114  adjacent to pressure roller  106 . Platen  116  has been positioned such that platen  116  is in apposition to the path of print head  108  and paper  102  is between platen  116  and print head  108 . In another embodiment, for example, platen  116  and transfer roller  114  could remain stationary while the positioning system moves print head  108  and pressure roller  106 . The position system consists of gearing and guides (not shown, but familiar to those who are in the art of designing electronic printers). 
     Pressure roller  106  has been positioned such that it is adjacent to transfer roller  114  and paper  102  is sandwiched between transfer roller  114  and pressure roller  106 . The pressing of surface  115  against the surface of pressure roller  16  creates an elongated area of pressure. Transfer roller  114  rotates counterclockwise about its longitudinal axis when viewed from FIG. 2 while pressure roller  106  turns clockwise. The pressure between the two surfaces is sufficient to cause image  112  (see FIG. 1) to be pressed onto surface  202 B of paper  102  such that image  112  is entirely transferred off from transfer surface  115  to paper  102  as the pressure roller  106  and transfer roller  114  rotate. 
     Furthermore, as paper  102  moves between platen  116  and print head  108 , print head  108  prints ink on surface  202 A as image  200 . A part of image  200  consisting of a row of information is printed as print head  108  moves forward in a direction substantially parallel to direction  110 . After a row of information is printed, paper  102  is moved in a direction substantially parallel to direction  104  by feed rollers  100 A and  100 B and by the rotation of transfer roller  114  pressing against pressure roller  106 . After paper  102  is moved, another row of information is printed onto surface  202 A as print head  108  moves back across platen  116 . This cycle of rotation and printing continues until all of image  200  is printed. 
     After the ink on surface  115  of transfer roller  114  has been transferred to paper  102 , surface  115  rotates to cleaning station  118 . Cleaning station  118  removes any residue left from image  112  on surface  115 . One embodiment of cleaning station  118  consists of a solvent and ink adsorbing roller or similar device in combination with an elastic blade or body of rubber or the like with is pressed against transfer surface  115 . Such blades and cleaning stations are familiar to those who are in the art of designing electronic printers. 
     Unlike the arrangements of the related art that use a paper turning mechanism, the present invention prints on both sides of the paper without turning the paper. Because paper turning mechanisms often jam, the present invention is more reliable, resulting in lower maintenance costs. Furthermore, the present invention uses only one print head and print station in contrast to related art that use two print heads and two printer stations. The printer stations are often the most expensive parts of a printer, thus, the use of a single print station results in a more economical and reliable design. 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.