Printer, in particular matrix pin printer
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a printer, and in particular to matrix pin printer with a frame. A print substrate support, extending in longitudinal direction, is disposed at the frame, and a longitudinal guide for a slider with a print head is disposed opposite and in parallel to the print substrate support. A paper guide is provided for individual sheets and/or for a continuous paper web. The paper guide and the print-head slider are drivable and controllable by way of drive motors. The frame is surrounded by a two-part or multiple-part plastic casing. 
     2. Brief Description of the Background of the Invention Including Prior Art 
     Such printers exhibit in most cases a metallic base frame and a two-part or multiple-part plastic casing. The printer width is determined according to the predetermined length of the print substrate support and by the path of the print head, which passes approximately over the full length of the print substrate support. This path is adapted to the printable width of the paper to be processed. 
     It is known from the German Patent Application Laid Out DE-B1-2,343,858 that the control electronics printed circuit board is disposed in a floor pan of the printer and that the drive motors for the print-head slider or, respectively, for the paper guide are disposed in their respective coordination relative to the respective drive component groups. This coordination is associated with disadvantages for two reasons. First, printers cannot be produced to employ alternatively paper of different widths. Second, there exists the difficulty that component groups, cycled with high frequencies, such as, for example, microprocessors, step electromotors and the like, emit undesirable electromagnetic interference radiations, which can be shielded individually only with difficulties and in a substantially uneconomical manner. 
     SUMMARY OF THE INVENTION 
     1. Purposes of the Invention 
     It is an object of the present invention to provide a printer of a simple and economical construction which operates alternatively with papers of different widths. 
     It is a further object of the present invention to provide a matrix printer construction which substantially shields against electromagnetic radiation emitted from high-frequency component groups. 
     It is yet another object of the present invention to furnish a matrix printer, which substantially separates the mechanical from the electrical components for easy servicing. 
     These and other objects and advantages of the present invention will become evident from the description which follows. 
     2. Brief Description of the Invention 
     According to a first embodiment, the present invention provides that the printer frame, following to the end of an elongated paper guide or, respectively, of an elongated print substrate support or, respectively, of the longitudinal guide for the print-head slider, forms a separated, substantially enclosed space. At least one printed circuit board for the electronics, an interface printed circuit board, and the paper-guide drive motor, as well as the print-head-slider drive motor, are disposed in said separated space. This construction is associated with the advantage that all lengths of the print substrate support, of the longitudinal guide, and of the guide rods and axles required for the longitudinal guide, can now be shortened or extended in a simple way in order to obtain a printer of a predetermined paper width, and production technology is thereby simplified. At the same time, there results in general the shortest possible connection lines among the electrical or, respectively, electronic component groups. 
     According to a second embodiment of the invention, all parts of the printer frame, with the exception of the metallic guide rods and axles, are produced of a synthetic plastic material and all electrical or, respectively, electronic components, as well as their connection elements, are disposed in a separated space. In addition to the already recited main advantages, the further advantage of an additional improvement in production technology results in a lower-cost production of the printer. 
     The two embodiments described above can be further improved by shielding the separated space with a sheet-metal casing for shielding the outside from emission of interfering electromagnetic radiation. 
     The invention structure can be further enhanced by furnishing a frame wall, made of electrically conductive plastic material, disposed facing toward the paper guide or, respectively, toward the print substrate support or, respectively, toward the longitudinal guide for the print-head slider. The guide rods, the axles, and the like, are electrically conductively supported in the frame wall. The print substrate support is also supported in the frame wall. 
     Additional improvements furnished by the invention provide that the space, shielded against interfering electromagnetic radiation, is subdivided into several levels. On one level there is furnished an interface printed circuit board and a control-logic printed circuit board, which are functionally connected by way of a connection plug. This results in advantages for the servicing of the printer, which advantages will become clearer in the following. 
     A service improvement and simplification comprises that the interface printed circuit board can be withdrawn or, respectively, can be reinserted along a lateral direction or, respectively, rearwardly along a guide. 
     A further simplification of the printer structure is achieved in that the paper-guide drive motor is supported at the frame wall made of an electrically conductive plastic. 
     A more favorable space subdivision of the separated space is further achieved in that the electrical connection line terminals for the paper-guide drive motor or, respectively, for the slider drive motor are guided to a printed circuit board for the power electronics, disposed in the area of the side wall of the separated space. 
     Furthermore, it is provided that the main power terminal part is disposed at the rear wall of the separated space. The main power terminal part is thus disposed outside of the paper guide path and is accessible easier than hitherto even in case of a pulled-in paper web. 
     The same advantage of having the connection line disposed outside of the paper sheet or paper web path during operation is achieved by having a plug-contact strip for the interface printed circuit board and a main power cable at the rear side of the separated space. 
     It is further advantageous that an operating field or key board is disposed on the side of the shielded space. With such a structure, there will result the shortest possible connection lines and supply lines. 
     According to a further feature of the invention, the keys of the operating keyboard are protruding through openings of the removable plastic casing. 
     The novel features which are considered as characteristic for the invention are set forth in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the accompanying drawing, in which are shown several of the various possible embodiments of the present invention: 
     FIG. 1 is a top plan view onto a printer according to the invention where the upper part of the casing is removed; 
     FIG. 2 is a top plan view onto the separated space in the rear region in an enlarged representation at the level of the interface printed circuit board; 
     FIG. 3 is a top plan view onto the complete separated space at the level of the drive motors and of the grid connection part; 
     FIG. 4 is a vertical sectional view through the separated space illustrated in FIG. 2; 
     FIG. 5 is a top plan view onto the separated space in the region of the keyboard, and 
     FIG. 6 is a partial sectional view according to the section line VI--VI according to FIG. 5. 
    
    
     DESCRIPTION OF INVENTION AND PREFERRED EMBODIMENT 
     The accompanying drawings are illustrating a serial matrix printer of the pin print head construction type. However, the invention can also be employed in many kinds of printers independent of the pin print principle. In particular, the invention can be employed with printers using a slider moving along a substrate. 
     The printer exhibits a frame 1 made of metal or of plastic. A print substrate support 3 and a longitudinal guide 4, disposed parallel and opposite to the print substrate support 3, are disposed at the frame 1 and extend in longitudinal direction 2. The longitudinal guide 4 comprises a guide rod 5 and an axle 6 for a print-head slider 7 including a print head 8. In addition, a paper guide 9 for individual sheets and such a paper guide 9a for a continuous paper web or sheet paper path is furnished. The paper guides 9 or, respectively, 9a can be driven and controlled by way of a paper-guide drive motor 10 and of a print-head-slider drive motor 11. The complete unit with the frame 1 is surrounded by a two-part plastic casing 12 which keeps dust and dirt away from the inner space and insulates printer noises from the inside toward the outside. 
     Following to the end 13 of the paper guides 9, 9a or, respectively following to the end of the print substrate support 3 or, respectively, of the longitudinal guide 4 for the print-head slider 7, the frame 1 is formed as a separated space 14. At least one control-logic printed circuit board 15, an interface printed circuit board 16, and the paper-guide drive motor 10, as well as the print-head-slider drive motor 11 are disposed in this special separated space 14. 
     All parts of the frame 1, with the exception of the metallic guide rods 5 and the axles 6, are made of a moldable synthetic material or of a synthetic plastic which can be plastified. All electrical or, respectively, electronic device components and their connection elements are disposed in the separated enclosed space 14. The separated enclosed space 14 is surrounded by a sheet-metal casing 17. The sheet-metal casing 17 comprises advantageously a removable sheet-metal cover 17a, as illustrated in FIG. 4. 
     As illustrated in FIG. 2, the interface printed circuit board 16, together with its plug contact strip 18, can be easily demounted and removed. A frame wall 1a,  facing toward the paper guides 9, 9a or, respectively, the print substrate support 3 or, respectively, the longitudinal guide 4 for the print-head slider 7, is made of an electrically conductive plastic, such as a plastic comprising carbon fibers. The guide rod 5 and the axle 6 are electrically conductively supported in this frame wall 1a. The print substrate support 3 is also disposed in this frame wall 1a, which is made of an electrically conductively synthetic plastic. The electrical conductivity serves in this case for the discharge of electrostatic voltages which could affect the operating personnel. 
     The separated enclosed space 14, shielding against interfering electromagnetic radiation, is subdivided into different levels 19 and 20. The upper level 19, as illustrated in FIG. 2, is formed by the printed circuit boards for the control logic 15 and for the interface 16. The lower level 20 is represented, amongst others, by the paper-guide drive motor 10 and the print-head-slider drive motor 11, as illustrated in FIG. 3. The control-logic printed circuit board 15 and the interface printed circuit board 16 are mechanically and electrically connected to each other by way of a connection plug 21, illustrated in FIG. 2. 
     The interface printed circuit board 16 can be pulled sideways toward the left first out of a catch 22 against a spring arm 24 and then out of the connection plug 21, as illustrated by a position shown as dashed lines in FIG. 2. The interface printed circuit board 16 can be further pulled out of a guide 23, which comprises the spring arm 24 for a disengageable clamping and interlocking. The interface printed circuit board 16 comprises device components such as, for example, an EPROM 25 which contains the control program. The remaining device components 26 through 34 form the required device modules for the interface functions. 
     The paper-guide drive motor 10 is supported at the frame wall 1a, furnished of an electrically conductive plastic, in the lower level 20, as illustrated in FIG. 3. The electrical connection line terminals 34a and 35 for the paper-guide drive motor 10 and the electrical conduction line terminals 36 and 37 are led to a printed circuit board 38 for the power electronics. This power-electronics printed circuit board 38, furnishing a power supply, is disposed outside at the separated space 14 below the sheet-metal casing 17. Device components, such as a capacitor 39, storage device modules 40, 41, driver device modules 42 and the like, are furnished at the printed circuit board 38. 
     A main power connection 43, a power switch 44, and a power plug 45 are disposed at the rear wall side 46 of the separated space 14. 
     In addition, the plug-contact strip 18 for the interface printed circuit board 16 and the power cable 47 are disposed at the rear wall side 46 of the separated space 14 and are therefore all accessible even in case a paper web has been inserted into the printer. 
     An operating field or keyboard 48 is disposed on the side of the shielded, enclosed and separated space 14 such that the operating field or keyboard 48 can be disposed on the right or on the left at the printer. 
     The keys 49 of the keyboard 48 are led through openings 50 of the removable plastic casing 12 and protrude correspondingly. Even though a main power transformer 51, the paper-guide drive motor 10, and the print-head-slider driver motor 11, disposed in the lower level 20, as illustrated in FIG. 3, have to be considered as heat-loss generators, heat and thermal energy can be removed sufficiently by the highly thermally conductive sheet-metal casing 17 without forced ventilation to the surrounding outside of the plastic casing 12. 
     The sheet-metal casing 17 is also furnished as a bottom panel, as illustrated in FIG. 4, and is in electrical and mechanical contact with the otherwise U-shaped sheet casing. The two arms of the U furnish the front side 52 and the rear wall side 46, as illustrated in FIG. 3. The sheet-metal casing 17 is furthermore furnished with bent protrusions 52a and 52b. In addition, the individual key device groups 53 as well as the support plate 54, receiving the keys, are shown in FIGS. 5 and 6. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of printing and paper-employing apparatus differing from the types described above. 
     While the invention has been illustrated and described as embodied in the context of a matrix pin printer, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.