Abstract:
In the present invention, a flat platen having a flat surface opposed to a print head is fixed to a platen supporting member by a fixing member, and a first impact absorbing member is disposed elastically between the platen and the platen supporting member. Accordingly, the propagation of vibration between the platen and the platen supporting member is prevented by a vibration absorbing action of the first impact absorbing member and vibrations in a vibration generation source are absorbed quickly. Thus, according to the present invention, a printing noise can be damped effectively.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    The present application is based on Japanese Priority Document 2000-270927 filed on Sep. 7, 2000, the content of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a platen supporting device for supporting a platen of a printer.  
           [0004]    2. Discussion of the Background  
           [0005]    As a platen of a printer, not only a platen called platen roller having a paper feed function, but also a flat platen not having a paper feed function is known. In such a platen, both ends thereof are fixed to platen supporting members such as frames opposed to each other. A more concrete description will be given below with reference to FIGS. 7 and 8, of which FIG. 7 is an exploded perspective view showing a part of a platen supporting structure and FIG. 8 is a side view thereof.  
           [0006]    A platen  15  is a flat type and is disposed in opposition to a wire dot head  20 . Mounting holes  15   a  are formed in both longitudinal ends of the platen  15 . Mounting screws  26  are inserted respectively through the mounting holes  15   a  and are threadedly engaged with platen supporting members  25  formed in frames  24  for example, whereby the platen  15  is fixed.  
           [0007]    In the printer, however, there occurs noise during conveyance of paper, during movement of a carriage with the wire dot head  20  mounted thereon, or when the wire dot head  20  is driven during movement of the carriage. Particularly, in case of using an impact type wire dot head  20 , the platen  15  is a loudest noise generation source because it is struck by the wire dot head  20 .  
           [0008]    As shown in FIGS. 7 and 8, in the case where the platen  15  is mounted directly to the platen supporting members  25 , vibrations of the platen  15  are transmitted to the platen supporting members  25 . The vibrations are propagated to the frames  24  and are amplified thereby, thus generating a loud printing noise. For damping this noise there has been adopted, for example, a measure of affixing a sound absorbing material to an inner surface of a case of the printer. However, a further anti-noise measure is demanded because the striking sound of the wire dot head  20  is very high.  
           [0009]    Moreover, in the case of a flat platen  15 , the surface of the platen  15  opposed to the tip of the wire dot head  20  is sometimes not parallel to the head tip. More particularly, for example if paper is conveyed from left to right in FIG. 8 and if a gap between the wire dot head  20  and the print head  15  on an upstream side in the paper conveying direction is a and that on a downstream side is b, the a and b are sometimes not equal to each other. In this case, there occurs a difference in print density between the upstream side and the downstream side, with consequent deterioration of the print quality. To eliminate such a difference there has been developed a mechanism for adjusting an inclination of the platen  15 , but the structure of the mechanism and the adjusting work are complicated.  
         SUMMARY OF THE INVENTION  
         [0010]    In certain embodiment, there is a platen having an impact absorbing element, it possible to damp a printing noise quickly in its generation source.  
           [0011]    According to embodiment of the present invention, a platen having a surface opposed to a print head is fixed to a platen supporting member by a fixing member. In this case, a first impact absorbing member is interposed elastically between the platen and the platen supporting member. With a vibration absorbing action of the impact absorbing member, it is possible to prevent propagation of vibration between the platen and the platen supporting member. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 is a side view in vertical section, showing an internal structure of a printer to which the present invention is applied;  
         [0014]    [0014]FIG. 2 is an exploded perspective view showing the construction of a platen supporting device according to a first embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a side view in vertical section thereof;  
         [0016]    [0016]FIG. 4 is a side view in vertical section of a platen supporting device according to a second embodiment of the present invention;  
         [0017]    [0017]FIG. 5 is an exploded perspective view showing the construction of a platen supporting device according to a third embodiment of the present invention;  
         [0018]    [0018]FIG. 6 is a side view in vertical section thereof;  
         [0019]    [0019]FIG. 7 is an exploded perspective view showing a part of a conventional platen supporting structure; and  
         [0020]    [0020]FIG. 8 is a side view thereof. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    A first embodiment of the present invention is now explained with reference to FIGS.  1 - 3 .  
         [0022]    [0022]FIG. 1 is a side view in vertical section, showing an internal structure of a printer, FIG. 2 is an exploded perspective view showing the construction of a platen supporting device, and FIG. 3 is a side view in vertical section thereof.  
         [0023]    First, with reference to FIG. 1, a description will be given about the construction of a printer P. An opening  3  is formed in a front side  2  of a printer body  1 , with a manual feed tray  4  being disposed in the opening  3  so as to be movable in opening and closing directions with respect to the opening  3 . A paper feed port  5  is formed in a lower portion of the front side  2  of the printer body  1 , while on a rear side  6  is provided a discharged paper receiving portion  7 . Further, an opening/closing cover  9  is supported pivotably along an upper surface  8  of the printer body  1 .  
         [0024]    At a center of the printer body  1 , a paper conveying passage  10  is formed. An upstream side of the paper conveying passage  10  is connected to both a paper feed passage  11  disposed on an extension plane of the manual feed tray  4  as opened and a paper feed passage  12  communicating with the paper feed port  5 , while a downstream side of the paper conveying passage  10  is connected to the discharged paper receiving portion  7 . A tractor  13  is disposed in the paper feed passage  12  and a pair of conveyance rollers  14  as paper conveying members and a platen  15  are disposed in the paper conveying passage  10 . A delivery roller  16  is disposed in an inlet of the discharged paper receiving portion  7 . A presser roller  17  is brought into pressure contact with the delivery roller  16  and it is supported pivotably on a free end side of the opening/closing cover  9 . A carriage  19  is slidably fitted on a carriage shaft  18  which is parallel to axes of the conveyance rollers  14 . A wire dot head  20  as a print head is mounted on the carriage  19  and an ink ribbon cassette  21  is supported removably by the carriage.  
         [0025]    In case of using a slip  22  as printing paper in such a printer, the slip is fed from the manual feed tray  4 , while in case of using continuous paper  23  as printing paper, the paper is fed from the paper feed port  5 . No matter which printing paper may be used, the paper used is conveyed by the conveyance rollers  14  and is discharged to the discharged paper receiving portion  7  by the delivery roller  16 . While the paper is thus conveyed, the carriage  19  is moved in the longitudinal direction of the platen  15  (in the direction perpendicular to the paper surface in FIG. 1) and printing is performed by the wire dot head  20 .  
         [0026]    Next, the construction of a platen supporting device A for supporting the platen  15  will now be described with reference to FIGS. 2 and 3. The platen  15  is a flat type having a square sectional shape, provided it may have another sectional shape insofar as its surface opposed to the wire dot head  20  is flat. Although only one side of the platen  15  is illustrated in FIG. 2, mounting holes  15   a  are formed respectively in both longitudinal ends of the platen  15 . Frames  24  opposed to each other are provided at both longitudinal ends of the platen  15  and are respectively formed with platen supporting members  25  which are bent to support the platen  15 . In each platen supporting member  25  is formed a tapped hole  27  for threaded engagement therewith of a mounting screw  26  as a fixing member.  
         [0027]    A first impact absorbing member  28  of cylindrical shape is fitted on each end portion of the platen  15 . Through holes  29  for insertion therethrough of the mounting screw  26  are formed in both sides in the vertical direction of the first impact absorbing member  28 .  
         [0028]    Further provided are a second impact absorbing member  30  which is cylindrical and which is inserted into a mounting hole  15   a  formed in the platen  15  and a third impact absorbing member  32  which is brought into contact with a lower surface of the associated platen supporting member  25  and which has a through hole  31  for insertion therein of the mounting screw  26 . An inside diameter of the second impact absorbing member  30  is set at a value which permits the mounting screw  26  to be press-fitted therein, while an overall length of the second impact absorbing member  30  is set at a value which permits both ends thereof to come into contact with a ceiling surface and a bottom surface, respectively, of the first impact absorbing member  28 . The first, second and third impact absorbing members  28 ,  30 ,  32  are formed using an elastically deflectable material having a high vibration absorbing characteristic such as rubber or a soft synthetic resin.  
         [0029]    Further, a metallic, cylindrical cover  33  is provided which has a size capable of covering both the platen  15  and the first impact absorbing member  28  fitted in each end portion of the platen. A through hole  34  for insertion therethrough of the mounting screw  26  is formed on an upper surface of the cover  33 , a slit  35  which permits the mounting screw  26  to project therethrough is formed in a bottom of the cover  33 , and two tapped holes  38  for threaded insertion therein of clamp screws  37  are formed in a side face  36  of the cover  33 , the clamp screws  37  being arranged in upper and lower positions respectively.  
         [0030]    The following description is now provided about an assembling work for mounting the platen  15  to the platen supporting members  25 . Since this assembling work is common to both end sides of the platen  15 , reference will here be made to only one end side. With the second impact absorbing member  30  inserted into the mounting hole  15   a  of the platen  15 , the first impact absorbing member  28  is fitted on the end portion of the platen  15 , the cover  33  is fitted on the first impact absorbing member  28  from the outside, then the cover  33  is disposed so that the bottom thereof is positioned below the platen supporting member  25  and the third impact absorbing member  32  which is located below the platen supporting member, then in this state the mounting screw  26  is inserted successively through the through hole  34  of the cover  33 , the upper through hole  29  of the first impact absorbing member  28 , the second impact absorbing member  30 , the lower through hole  29  of the first impact absorbing member  28 , and the slit  35  of the cover  33 , and the tip of the mounting screw  26  is brought into threaded engagement with the tapped hole  27  of the platen supporting member  25 . In this way the platen  15  is mounted to the platen supporting member  25 , as shown in FIG. 3.  
         [0031]    In this construction, during printing, the platen  15  vibrates because it is struck by the wire dot head  20 , but since the bottom of the first impact absorbing member  28  cylindrical in shape which surrounds the platen  15  comes into abutment against the platen supporting member  25 , the propagation of vibration between the platen  15  and the platen supporting member  25  can be prevented by a vibration absorbing action of the first impact absorbing member  28 . Besides, since the second impact absorbing member  30  cylindrical in shape is press-fitted on the mounting screw  26  inserted into the mounting hole  15   a  of the platen  15 , the propagation of vibration between the platen  15  and the mounting screw  26  can be prevented by a vibration absorbing action of the second impact absorbing member  30 .  
         [0032]    Further, since the first impact absorbing member  28  is cylindrical and comes into contact with the platen  15  over a wide area, the vibration absorbing action thereof is further enhanced. In this case, because of a cylindrical shape, the first impact absorbing member has a large surface area and is apt to be deformed under the influence of heat and a change with the lapse of time. However, since the outside of the first impact absorbing member is compressed by the cover  33 , it is possible to diminish the influence of heat and a change with time and hence possible to maintain the vibration absorbing performance over a long period.  
         [0033]    The cylindrical cover  33  also covers the platen supporting member  25 , but since the third impact absorbing member  32  is interposed between the bottom of the cover  33  and the platen supporting member  25 , even if the vibration of the platen  15  is propagated to the cover  33 , the propagation of the vibration between the cover  33  and the platen supporting member  25  can be prevented by a vibration absorbing action of the third impact absorbing member  32 .  
         [0034]    As shown in FIG. 3, when the two upper and lower clamp screws  37  threadedly engaged with the tapped holes  38  formed in the side face  36  of the cover  33  are tightened, a pressure induced by the tightening of the screws is exerted on the platen  15  through the first impact absorbing member  28 . Therefore, by adjusting the tightening force for the upper and lower clamp screws  37 , it becomes possible to adjust the inclination of the platen  15  relatively with respect to the tip of the wire dot head  20 .  
         [0035]    In this case, since a periphery of the platen  15  is compressed by the cylindrical, first impact absorbing member  28  in the interior of the cover  33 , the posture of the platen in its tilting direction can be rendered stable without the need of using any other fixing means.  
         [0036]    In this inclination adjustment for the platen  15  the second impact absorbing member  30  also permits the tilting motion of the platen  15  by deflection, but if the second impact absorbing member  30  is omitted, the inclination angle of the platen  15  can be adjusted by an amount corresponding to the clearance between the mounting hole  15   a  of the platen  15  and the mounting screw  26 .  
         [0037]    A second embodiment of the present invention is now explained with reference to FIG. 4. The same parts as those in the first embodiment are designated by the same reference numerals and are not again explained herein.  
         [0038]    [0038]FIG. 4 is a side view in vertical section of a platen supporting device according to a second embodiment of the present invention.  
         [0039]    The platen supporting device of this embodiment, indicated at B, uses an eccentric cam  39  instead of the clamp screws  37 . The eccentric cam  39  is provided on only one side with the mounting screw  26  as the center so as to press a lower end of the platen  15 . Therefore, when the eccentric cam  39  is rotated, the platen  15  changes posture in its tilting direction while causing the first and second impact absorbing members  28 ,  30  to be deformed elastically. In this case, it is necessary that a cutout portion  28   a  for placing the eccentric cam  39  therein be formed in the first impact absorbing member  28 .  
         [0040]    As shown in FIG. 4, in the case where the eccentric cam  39  is to be journaled in a direction perpendicular to the paper surface in the same figure, this can be attained by providing a side wall orthogonal to the side face  36  of the cover  33  and allowing the side wall to support the eccentric cam  39 . Of course, the eccentric cam  39  may be journaled rotatably by the side face  36  of the cover  33  as is the case with the clamp screws  37 .  
         [0041]    A third embodiment of the present invention is now explained with reference to FIGS. 5 and 6. The same parts as those in the first embodiment are designated by the same reference numerals and are not again explained herein.  
         [0042]    [0042]FIG. 5 is an exploded perspective view showing the construction of a platen supporting device according to a third embodiment of the present invention and FIG. 6 is a side view in vertical section thereof.  
         [0043]    In the platen supporting device of this embodiment, indicated at C, a cover  40  is formed in a turned square U-shape whose underside is open, with lugs  43  being formed centrally of lower edges  42  of both side faces  41 . Fitting holes  44  for fitting therein of the lugs  43  are formed in the platen supporting member  25 . The height of the cover  40  from a ceiling surface thereof which comes into contact with the upper surface of the first impact absorbing member  28  to each lower edge  42  is set at a value which permits pressing the first impact absorbing member  28  with a predetermined certain pressure.  
         [0044]    Next, a description will be given about an assembling work for mounting the platen  15  to the platen supporting member  25 . Since this mounting work is common to both end portions of the platen  15 , reference will here be made to only one end portion. With the second impact absorbing member  30  inserted into the mounting hole  15   a  of the platen  15 , the first impact absorbing member  28  is fitted on the end portion of the platen  15  and in this state is placed on the platen supporting member  25 , then the cover  40  is applied onto the first impact absorbing member  28 , allowing the lugs  43  to be fitted in the fitting holes  44 . In this state, the mounting screw  26  is inserted successively through a through hole  34  formed in the cover  40 , the upper through hole  29  of the first impact absorbing member  28 , the second impact absorbing member  30 , and the lower through hole  29  of the first impact absorbing member  28 , and the tip of the mounting screw  26  is brought into threaded engagement with a tapped hole  27  formed in the platen supporting member  25 . In this way the platen  15  is mounted to the platen supporting member  25 , as shown in FIG. 6.  
         [0045]    According to this construction, the lugs  43  of the cover  40  are fitted in the fitting holes  44  and the lower edges  42  thereof come into abutment against the upper surface of the platen supporting member  25 , so that even if the mounting screw  26  is tightened with a strong force, the amount of compression of the first and second impact absorbing members  28 ,  30  are constant. Therefore, the height of the platen  15  can be kept constant.  
         [0046]    Further, the lower edges  42  of the cover  40  come into abutment against the upper surface of the platen supporting member  25  and function to define the amount of compression of the first and second impact absorbing members  28 ,  30 . Thus, the cover  40  exhibits a function as a pressing member which adjusts the inclination of the platen  15  by adjusting the position of the lower edges  42 .  
         [0047]    The platen supporting device of the third embodiment may also be provided with the third impact absorbing member.  
         [0048]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.