Abstract:
The invention is a print head for a thermal printer having a print region, a plurality of heating elements arranged in the print region, and actuating electronics by which the heating elements can be actuated. One or more additional heating elements are arranged outside the print region, wherein at least one of the additional heating elements has a property, that differs from a normal property, of the heating elements arranged in the print region. There is included a method for production of the print head. The device electronics further comprises a testing circuit for verification of the print head, in which the print head has one or more additional heating elements whose properties differ in regard to at least one normal property of the heating elements and the testing circuit for verification of the print head is designed to check this property at least on some of the heating elements.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from European Patent Application Serial No. 09 013898.3, filed Nov. 5, 2009, the entire contents of which is herein incorporated fully by reference. 
       FIGURE FOR PUBLICATION 
       [0002]      FIG. 1A . 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a print head for a thermal printer and the method of making the print head. More specifically, the present invention relates to a print head for a thermal printer with a print region for imprinting a print medium, a plurality of heating elements arranged in at least one line in the print region, and actuating electronics. The print head further comprises one or more additional heating elements arranged outside the print region, wherein at least one of the additional heating elements has a property that differs from a normal property of the heating elements arranged in the print region. 
         [0005]    2. Description of the Related Art 
         [0006]    The term thermal printer in the sense of this patent application comprises printers in which the desired local heating of the print head brings about a color change on the medium being printed directly or indirectly. Three subcategories of such printers are currently of practical significance: thermodirect printers; thermotransfer printers; and, thermosublimation printers. 
         [0007]    In thermodirect printers, a special heat-sensitive print medium is used, which changes color at a place where the print head is heated locally. Thermodirect printers enable a fast and cheap printing process with a very simple layout of the printer; their main drawback is that the print medium is sensitive to light and temperature in the long term, so that often aging processes occur in the print medium, which may have the result that a printout is no longer legible after a long time, such as several years. 
         [0008]    Thermotransfer printers are distinguished in that they can achieve a very high resolution of the print image and therefore they find broad use. 
         [0009]    The basic principle of thermotransfer printing is that a special ink film with an ink layer, the thermotransfer film, is led between the medium being printed and the print head. The printing mechanism of the print head usually extends over the entire width of the medium being printed upon; the print widths are standardized. The print head, more specifically the printing mechanism of the print head, has a plurality—typically over 1000—of heating elements, which are typically designed with pointlike heads, or so-called “dots”, and arranged in a line. The individual heating elements are activated by actuation electronics, which processes the print data received via the printer from the host computer. If a heating element is actuated, its head is heated, and as a consequence the ink layer melts and the ink is transferred to the medium being printed. 
         [0010]    The heating elements must be actuated quickly and with high precision. Basically, it is desirable to print as fast as possible; at present, a printing of up to 1000 mm of print medium per second can be achieved. With a print quality of 300 dpi (dots per inch), an ink spot must be laid down every 0.085 mm, which means that even disregarding the [missing word—likely “time”] for feeding of the print medium and the ink transfer film, the melting and ink transfer process must be completed in less than one millisecond. 
         [0011]    Thermo sublimation printers are similar to thermotransfer printers in their basic principle. In contrast to thermotransfer printing, with thermosublimation printing the ink layer deposited on the substrate film is directly evaporated by furnishing heat (sublimated). The ink gas then penetrates into the material being printed or is precipitated thereupon. The quantity of ink transferred depends decisively on the energy supplied by the heating element, which makes it possible to work with very high color resolution, but at the same time requires a very exact actuation of the print head. 
         [0012]    Of critical importance to the print quality achieved with all the aforementioned types of thermal printers is the use of print heads that are precisely attuned to the respective thermal printer. Only this can ensure that the color change of the print medium (in thermodirect printers) or the melting or evaporating of the ink layer (in thermotransfer or thermosublimation printers) will in fact occur in optimal manner in the time up to the next relative movement between print medium and print head or ink transfer film and print head, so that a satisfactory and high-quality printing outcome is achieved. 
         [0013]    It is customary to provide print heads for thermal printers with a printer-specific coding, which is polled by the respective printer and an error message is sent if the polling reveals that the wrong code is present. The coding systems known thus far can basically be divided into two classes. On the one hand, mechanical codes in the form of a perforation pattern are used. But these are easy to imitate, as they can be easily evaluated visually. On the other hand, it is known how to arrange electronic codes on the print heads, for which a key number is saved in an electronic storage module, such as a flash memory or an EPROM, and the electronic storage module is read out during each printing process. But, what is not appreciated by the prior art is the relatively high expense associated with it, which leads to substantial costs. 
         [0014]    Accordingly, there is a need for an improved print head for a thermal printer that can be encoded in a secure, and at the same time, economical manner, and a thermal printer with such a print head. 
       ASPECTS AND SUMMARY OF THE INVENTION 
       [0015]    An aspect of the present invention is to provide a print head for a thermal printer that can be encoded in a secure and at the same time economical manner, and the provision of a thermal printer with such a print head. 
         [0016]    The problem is solved by a print head for a thermal printer with a print region for imprinting a print medium, a plurality of heating elements arranged in at least one line in the print region, and actuating electronics. The print head further comprises one or more additional heating elements arranged outside the print region, wherein at least one of the additional heating elements has a property that differs from a normal property of the heating elements arranged in the print region. 
         [0017]    The print head for a thermal printer according to the invention has a print region for imprinting a print medium, a plurality of heating elements arranged in at least one line in the print region, an actuating electronics by which the heating elements can be actuated, and a plug connector. According to the invention, one or more additional heating elements are also arranged outside the print region, being likewise actuated by the actuating electronics, wherein at least one of the additional heating elements has a property, especially an electrical resistance, that differs from a normal property, especially the electrical resistance, of the heating elements arranged in the print region. 
         [0018]    The basic notion of the invention thus consists in providing additional heating elements with respective actuating electronics outside of the print region, which is always clearly distinguishable on account of the customary use in thermal printers of a stationary print head and standardized widths of the medium being printed upon, and to achieve the coding in that properties, especially the electrical resistance, of a selection of these additional heating elements of the print head are specifically changed in a processing step. 
         [0019]    By the print region of the print head is meant the region in which the print head can perform its intended function, i.e., where any given combination of dots can be used for the color change on the print medium. Explicitly included in the notion of the invention is therefore the possibility of decreasing the print region originally provided for a print head designed for a given usable width by modifying some of the heating elements arranged at the margin of the original print region in an additional processing step. 
         [0020]    In view of the fact that typical print heads for thermal printers have over 1000 heating elements for the standard usable width of 104 mm, for example, corresponding to a spacing between individual dots formed by the heating elements of 0.085 mm for 300 dpi, the providing of a few additional heating elements is so slight in terms of cost as a reducing of the print region by a few dots, say, 2; but the coding formed by the specific selection or arrangement of the altered heating elements, and which can also vary within the same type of device, can only be ascertained with great expense and is therefore very secure. 
         [0021]    To achieve good heat dissipation, it is advantageous for the print head to have an aluminum body. 
         [0022]    An especially compact and easy to produce print head is obtained if the actuating electronics is integrated in a circuit board or in a substrate that is actuated by a circuit board. If utilizing an aluminum body, an especially good heat dissipation is achieved when the aluminum body lies at least partly on the circuit board and/or the substrate. In order not to impair the heat conduction by intermediate layers, it is especially advantageous in this case to connect the aluminum body to the circuit board at fastening points. 
         [0023]    The method of the invention for production of a print head for a thermal to printer specifies at least the steps of preparing a substrate with a plurality of heating elements, having at least one line of heating elements, and an actuating electronics, by means of which the heating elements can be actuated; the establishing of a print region of the print head, in which a print medium can be imprinted by the print head, wherein the print region is established such that one or more heating elements lie outside the print region; and the producing of a specific change of properties of one or more of the heating elements lying outside the print region. The sequence of these steps is essentially variable. In particular, it is possible to carry out the steps in the above-indicated order; but it would also be possible to first specifically change a row of heating elements, then establish the print region on a substrate and then to mount heating elements whose property has been changed at one or more selected sites outside the print region during the preparation of the substrate. 
         [0024]    A property which is especially easy to change by means of a thermal treatment is the resistance of one or more of the heating elements lying outside the print region. This can be done, in particular, by a specific supplying of current to the heating elements, which can be done in particular with an especially high current or for an especially long time. 
         [0025]    One advantageous possibility of supplying the current is to control the current supply during the thermal treatment by the actuating electronics. 
         [0026]    The thermal printer according to the invention has device electronics for actuating a print head and a print head which can be actuated by the device electronics with a plurality of heating elements, wherein the device electronics has a testing circuit for verification of the print head. The print head has one or more heating elements whose properties differ in regard to at least one normal property of the heating elements and the testing circuit for verification of the print head is designed to check this property at least on some of the heating elements. 
         [0027]    Thus, with the help of the testing circuit, one can establish which heating elements have a deviation from the normal property. This outcome is then compared to a nominal outcome, which is deposited in the thermal printer, preferably in a storage element. If an outcome deviating from the nominal outcome is determined by the testing circuit, an error message is put out, which is shown in a printer display or on a monitor screen of a device controlling the printer, such as a computer or a computerized cash register. The error message can be a warning message that is temporarily or permanently acknowledged by a confirmation, or it can also prevent any further use of the printer. 
         [0028]    An especially easy to realize testing is possible if the testing circuit for verification of the print head is designed to test the electrical resistance of at least some of the heating elements. 
         [0029]    It is especially advantageous if the print head has a print region in which some of the heating elements are arranged at least in one line, while one or more additional heating elements are arranged outside the print region. 
         [0030]    In one especially simple embodiment, the testing circuit is designed only for testing of heating elements that are arranged outside the print region. 
         [0031]    A more costly embodiment calls for the testing circuit to be designed for the testing of all heating elements. This makes it possible, by means of the testing circuit for checking the coding, to perform a checking of the functional capability of the print head at the same time, since a deviation of a given heating element from the normal property, especially the resistance, leads to a deviation in the ink transfer. 
         [0032]    The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1   a  is a pictorial representation of a print head for a thermal printer, shown slanted from below. 
           [0034]      FIG. 1   b  is a pictorial representation of the print head of  FIG. 1   a , shown slanted from above. 
           [0035]      FIG. 2  is a block diagram of the components of a thermal printer. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    Reference will now be made in detail to several embodiments of the invention that are illustrated in the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. The drawings are in simplified form and are not to precise scale. For purposes of convenience and clarity only, directional terms, such as top, bottom, up, down, over, above, and below may be used with respect to the drawings. These and similar directional terms should not be construed to limit the scope of the invention in any manner. The words “connect,” “couple,” and similar terms with their inflectional morphemes do not necessarily denote direct and immediate connections, but also include connections through mediate elements or devices. 
         [0037]    F  1   a  shows a simplified representation of a print head  10  for a thermal printer, shown slanted from below as compared to its typical direction of installation. In other words, in  FIG. 1   a  one is looking at the side of the print head  10  that faces the medium being imprinted during operation of the thermal printer. One notices a substrate  11 , on or in which an actuating electronics  2  and a plurality of heating elements  1  oriented in line fashion are arranged. The simplification of the representation consists in that, in a real print head, a very much larger number of heating elements  1  is provided, typically more than 1000 heating elements  1  for print heads that are designed to imprint a print medium at a width of 104 mm. 
         [0038]    The substrate  11  is arranged on a circuit board  3 , by means of which the substrate can be actuated. In the perspective view of  FIG. 1   a , there is an aluminum block  5  underneath the circuit board  3  in surface contact with the underside of the circuit board  3  and the substrate  11 . The circuit board  3  is studded with a number of contact pins  7 , which communicate with the actuating electronics  2  via conductor tracks of the circuit board (not shown). The contact pins  7  lead to a plug connector  6 , which serves to connect the print head to a thermal printer. 
         [0039]    Moreover, two broken lines A, A′ are shown in  FIG. 1   a . The print region (A-A′) of the print head  10  lies between these two lines. Outside the print region are additional heating elements  8 ,  9 —two in this simplified example—that can likewise be actuated by the actuating electronics  2 . While the heating elements  1  are used to carry out the thermal printing, the additional heating elements  8 ,  9  serve for the coding of the print head. The deviation of a property of at least one of the additional heating elements  8 ,  9  from the corresponding property of the heating elements  1  is used as logical one and the agreement of the corresponding property is used as logical zero, or vice versa. Specifically, e.g., the resistance of the respective heating elements can be used, which can be influenced, specifically in regard to a normal resistance, by a deliberate thermal alteration of heating elements by supplying very high currents or for a lengthy time. For example, heating elements  1  with a normal resistance of 1 kΩ can be used and resistances of 2-10 kΩ can be produced in one or both of the additional heating elements  8 ,  9  by long-term supplying of current. This long-term current supply can come, for example, from an appropriate actuation by the actuating circuit  2 . 
         [0040]    Thus, for two additional heating elements  8 ,  9 , there are four conceivable codes: both of the additional heating elements  8 ,  9  might have the normal resistance (code 00), the additional heating element  8  might have the normal resistance and the additional heating element  9  a deviating resistance (code 01), only the additional heating element  9  might have the normal resistance and the additional heating element  8  a deviating resistance (code 10), or both additional heating elements  8 ,  9  might have a deviating resistance (code 11). 
         [0041]      FIG. 1   b  shows the print head  10  from  FIG. 1   a , seen from the opposite direction. From this direction, one looks at an aluminum block  5 , which is arranged on a surface segment of a circuit board  3  and the substrate  11  concealed by the aluminum block  5  in  FIG. 1   b  and fastened to the latter by fastening points  4 . A plug connector  6  is connected by contact pins  7  to the circuit board or, more precisely, to conductor tracks of the circuit board (not shown). 
         [0042]      FIG. 2  shows a block diagram of the components of a thermal printer  20 . One notices a print head  21 , for example, like that depicted in  FIG. 1   a  and  FIG. 1   b , with a plug connector  22  arranged at the print head side and a device electronics  26 , which has a testing circuit  25  for verification of the print head and a plug connector  24  at the device electronics side, connected to the testing circuit  25  via a signal pathway  27 . A connection cable  23  connects the plug connector  22  arranged at the print head side and the plug connector  24  at the device electronics side. 
         [0043]    The testing circuit  25  for verification of the print head is designed to check whether at least the additional heating elements  8 ,  9  have the normal property for the heating element  1 , i.e., whether the heating elements  8  and  9  represent a logical one or a logical zero. This testing can be done, e.g., each time the thermal printer  20  is turned on or during each print command sent to the thermal printer  20 . 
         [0044]    For example, if a resistance of the heating element  1 ,  8 ,  9  of 1 kΩ is used as the normal property, the testing circuit could send commands to the actuating electronics  2  to apply in succession a definite voltage to each of the heating elements  1 ,  8 ,  9  of interest and then, if the actuating electronics is so designed, either to measure the resulting current flowing through the heating element  1 ,  8 ,  9  of interest and relay the measured value to the testing circuit  25 , or to relay the response signal from the heating element  1 ,  8 ,  9  of interest via the connection cable to the testing circuit  25 , which in this case evaluates the response signal either by a measurement of current or by comparison with a reference current corresponding to the normal signal. 
         [0045]    In this way, the proper functioning of the heating element can be checked for heating elements  1  lying inside the print region. For the additional heating elements  8 ,  9  lying outside the print region, one determines in this way whether they represent a logical one or a logical zero. 
         [0046]    In order to ascertain from this information whether the correct print head  10 ,  21  is being used, it is necessary to store the code for the correct print head  10 ,  21  in the device electronics  26 , for example, in a storage element of the device electronics  26  or the testing circuit  25 , and to make a comparison between the correct code and the code that is detected. In the present example, with only two additional heating elements  8 ,  9  for a given thermal printer  20 , one of four different codes could be the correct one. 
         [0047]    If the device electronics  26  ascertains that a print head  10 ,  21  with a wrong code has been installed, a corresponding alarm signal can be triggered on a display of the thermal printer  20  or a device in control of it. This can be, e.g., a warning message to the user that adequate print results cannot be achieved with the print head  10 ,  21 , and it can be acknowledged permanently or for a certain length of time, e.g., 10 minutes. Of course, it is also conceivable that an alarm signal will result in termination of the print command, so that a thermal printer  20  with the wrong print head  10 ,  21  is no longer usable. 
         [0048]    Which print head  10 ,  21  to be delivered when the current print head  10 ,  21  is used up can be determined by a certified replacement parts vendor, for example, by using a device number displayed when ordering a new print head  10 ,  21 . A manufacturer of print heads  10 ,  21  that do not satisfy the quality standards does not receive this information. He must then either deliver a print head  10 ,  21  trusting to luck, which even with 2 additional heating elements  8 ,  9  is only successful in 25% of the cases, or the customer of the lower-quality manufacturer must temporarily hand over his printer to him so that he can test out all the possibilities. 
         [0049]    Thus, the invention reliably ensures that an ideal print quality of a thermal printer  20  can be constantly achieved by use of the optimally adapted print head  10 ,  21 . 
         [0050]    In the claims, means or step-plus-function clauses are intended to cover the structures described or suggested herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, for example, although a nail, a screw, and a bolt may not be structural equivalents in that a nail relies on friction between a wooden part and a cylindrical surface, a screw&#39;s helical surface positively engages the wooden part, and a bolt&#39;s head and nut compress opposite sides of a wooden part, in the environment of fastening wooden parts, a nail, a screw, and a bolt may be readily understood by those skilled in the art as equivalent structures. 
         [0051]    Having described at least one of the preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes, modifications, and adaptations may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.