Abstract:
In order to manufacture a discharging roller which discharges a recording medium from a recording apparatus, there are a first die formed with a first recess extending in an axial direction of a shaft portion of the discharging roller, and a second die formed with a second recess extending in the axial direction. The first die and the second die are combined such that the first recess and the second recess face to form a continuous cavity. Synthetic resin is injected into the cavity to mold a bore portion of the shaft portion.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a discharging roller which discharges a recording medium on which data recording has been performed, a method of manufacturing the discharging roller, and a recording apparatus incorporating the discharging roller.  
           [0002]    An ink jet printer that is one of recording apparatuses is generally constituted so as to supply a sheet stored in a sheet feeding tray to a sheet feeding roller, transport the supplied sheet to a recording section while holding between a sheet feeding roller pair, cause a recording head to eject an ink droplet onto the sheet to perform recording, and discharge the sheet to a sheet ejection tray while holding between a discharging roller pair. Since recording on the sheet is thus performed between the discharging roller pair and the feeding roller pair, a rotary speed of the discharging roller is set slight higher than that of the feeding roller to tense the sheet between the discharging roller and the feeding roller, whereby the sheet becomes flat to improve recording accuracy.  
           [0003]    [0003]FIG. 13A is a perspective view showing a first related-art discharging roller as disclosed in Japanese Patent Publication No. 10-129910A. This discharging roller  1  is formed so that a shaft portion  2  made of plastics becomes longer than at least recordable maximum sheet width, and plural roller portions  3  made of rubber are fitted in the shaft portion  2  with constant intervals. As shown in FIG. 13B, such the discharging roller  1  is formed so that a circular portion of a sectional shape of the shaft portion  2  has diameter Ds and a cross-shaped portion thereof has thickness t, and the diameter Ds must be smaller than diameter Dr of the roller portion  3 . Specifically, the diameter Ds is 6.80 mm and the diameter Dr is 11.26 mm. Therefore, the proportion of the outer diameter of the shaft portion to the outer diameter of the roller portion is 60.4%.  
           [0004]    [0004]FIG. 14 is a section view showing a second related-art discharging roller as disclosed in Japanese Patent Publication No. 10-291874A. This discharging roller comprises a cylindrical body  30  and shaft portions  20  extended from both longitudinal ends of the cylindrical body  30  and having a smaller diameter than that of the cylindrical body  30 . The cylindrical body  30  and the shaft portions  20  are made of plastics. The shaft portions respectively have a hollowed portion which are formed by a core  75  or a resin injection port  77 . One of the hollowed portion is communicated with a cavity  31  formed inside the cylindrical body  30 .  
           [0005]    In case that the first related-art discharging roller  1  is formed of synthetic resin, it is necessary to provide thickness deletion (thick removal) so as not to make the discharging roller thick in order to prevent deformation or sink of the shaft caused by internal stress in molding. Therefore, only rigidity of a certain level can be secured. Further, since the rotation speed of the discharging roller  1  is set so as to become higher than that of the feeding roller, power pulled onto the feeding roller side acts on the discharging roller. Therefore, there is anxiety that deformation such as a flexure is produced in the discharging roller  1 .  
           [0006]    Since the deformation of the discharge roll  1  such as the flexure is restored when a rear end of the sheet is released from the feeding roller pair, there are instances where a so-called flip phenomenon of sheet is produced at this time. In case that an ink jet printer can record data on the whole surface of sheet or the nearly whole surface thereof, recording is continued to the rear end of the sheet even after the rear end of the sheet is released from the feeding roller pair. Therefore, in case that the above flip phenomenon is produced, a bad influence is exerted on recording accuracy.  
           [0007]    Regarding the second related-art discharging roller shown in FIG. 14, the sink  34  tends to be produced when auxiliary cavities  40  are filled with the injected resin. This causes deformation or the rigidity reduction of the discharging roller surface. Moreover, if flashes are formed on an outer circumferential surface of the shaft portions  20  and the cylindrical body  30  at the plastic molding process performed by the gas injection method, for example, there is anxiety that the flashes cause sliding load increase of a bearing portion or deterioration of sheet feeding accuracy.  
         SUMMARY OF THE INVENTION  
         [0008]    It is therefore an object of the invention to provide a discharging roller which can prevent the flip phenomenon at the discharging time of a recording medium, a method of manufacturing such a discharging roller, and a recording apparatus incorporating such a discharging roller.  
           [0009]    In order to achieve the above object, according to the invention, there is provided a discharging roller which discharges a recording medium from a recording apparatus, comprising a hollowed shaft portion comprised of synthetic resin.  
           [0010]    Preferably, the synthetic resin is comprised of an additive to enhance stiffness of the shaft portion.  
           [0011]    Preferably, the discharging roller further comprises a roller portion formed on an outer periphery of the shaft portion. Here, a proportion of an outer diameter of the shaft portion with respect to an outer diameter of the roller portion is not less than 60.5%.  
           [0012]    According to the invention, there is also provided a die for molding a discharging roller which discharges a recording medium from a recording apparatus, the die comprising;  
           [0013]    a first die, formed with a first recess extending in an axial direction of a shaft portion of the discharging roller; and  
           [0014]    a second die, formed with a second recess extending in the axial direction, the second die combined with the first die such that the first recess and the second recess face to form a continuous cavity for molding a bore portion of the shaft portion.  
           [0015]    Preferably, the first recess is formed on a bottom face of a recessed portion of the first die, and the second recess is formed on a convex portion of the second die which is fitted into the recessed portion.  
           [0016]    Here, it is preferable that an entrance corner of the recessed portion and a corner portion opposing to the entrance corner are tapered.  
           [0017]    Preferably, at least one of the first die and the second die is formed with a fluid passage through which a fluid for cooling the cavity flows.  
           [0018]    According to the invention, there is also provided a method of manufacturing a discharging roller which discharges a recording medium from a recording apparatus, the method comprising steps of:  
           [0019]    providing a first die, formed with a first recess extending in an axial direction of a shaft portion of the discharging roller;  
           [0020]    providing a second die, formed with a second recess extending in the axial direction;  
           [0021]    combining the first die and the second die such that the first recess and the second recess face to form a continuous cavity; and  
           [0022]    injecting synthetic resin into the cavity to mold a bore portion of the shaft portion.  
           [0023]    Preferably, the manufacturing method further comprises a step of regulating temperature of the cavity such an extent that the injected synthetic resin is solidified in a state where it is adhered onto an inner face of the cavity.  
           [0024]    Preferably, the manufacturing method further comprises a step of injecting gas into the cavity to form a void in the injected synthetic resin in the cavity.  
           [0025]    Since the discharging roller molded by the above die or manufactured by the above method has enhanced flexural rigidity, even if force in the opposite direction to the discharging direction is applied onto the discharging roller, the deformation of the discharging roller such as a flexure can be suppressed. Accordingly, the flip phenomenon of the recording medium due to the discharging roller can be prevented, and particularly recording accuracy in recording on the whole surface can be improved.  
           [0026]    According to the invention, there is also provided a recording apparatus comprising the above discharging roller. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0028]    [0028]FIG. 1 is a perspective view of the whole of the exterior structure of an ink jet printer, in a state where a sheet ejection port is closed;  
         [0029]    [0029]FIG. 2 is a perspective view of the ink jet printer, in a state where the sheet ejection port is opened;  
         [0030]    [0030]FIG. 3 is a perspective view of the whole of the internal structure of the ink jet printer in a state where an upper housing is removed;  
         [0031]    [0031]FIG. 4 is a sectional side view of an essential portion of the ink jet printer;  
         [0032]    [0032]FIG. 5A is a perspective view showing a discharging roller in the ink jet printer;  
         [0033]    [0033]FIG. 5B is a section view of the discharging roller;  
         [0034]    [0034]FIG. 6 is a perspective view showing an upper die and a lower die used in molding of the discharging roller, according to a first embodiment of the invention;  
         [0035]    [0035]FIG. 7A is a plan view of the upper die and the lower die;  
         [0036]    [0036]FIG. 7B is a section view taken along the line A-A in FIG. 7A;  
         [0037]    [0037]FIGS. 8A and 8B are perspective views showing the lower die;  
         [0038]    [0038]FIG. 9 is a side view showing a fitting part of the upper die and the lower die;  
         [0039]    [0039]FIG. 10A is a plan view of the lower die, showing a fluid passage for cooling liquid;  
         [0040]    [0040]FIG. 10B is a section view taken along the line B-B in FIG. 10A;  
         [0041]    [0041]FIG. 11 is a section view of an injection molding machine incorporating the dies;  
         [0042]    [0042]FIG. 12 is a section view showing a die used in molding of the discharging roller with a gas injection method, according to a second embodiment of the invention;  
         [0043]    [0043]FIG. 13A is a perspective view showing a first related-art discharging roller;  
         [0044]    [0044]FIG. 13B is an enlarged perspective view of the first related-art discharging roller, and  
         [0045]    [0045]FIG. 14 is a section view showing a die used in molding of a second related-art discharging roller with a gas injection method. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    Preferred embodiments of the invention will be described below in detail with reference to accompanying drawings.  
         [0047]    As shown in FIGS. 1 and 2, an ink jet printer  100  which is one of recording apparatuses comprises an upper housing  101  and a lower housing  102 . The upper housing  101  and the lower housing  102  are engaged with each other by snap fitting.  
         [0048]    On the rear side of the upper housing  101 , a sheet feeding port  103  is formed. In this sheet feeding port  103 , a sheet feeding tray  110  on which sheets to be supplied are stacked is attached. The sheet feeding tray  110  is attached so as to protrude to the diagonally upper backside, and holds the sheets in a slanting state. On the front side of the upper housing  101 , a sheet ejection port  104  is formed. On the front sides of the upper housing  101  and lower housing  102 , a stacker  120  on which the ejected sheets are stacked is provided.  
         [0049]    The stacker  120  is attached to the front sides of the upper housing  101  and lower housing  102  pivotably about a rotary shaft located at its lower portion. When the stacker  120  is not used, it is pivoted upward to close the sheet ejection port  104 . When it is used, it is pivoted downward to open the sheet ejection port  104 , and stops at a position where it protrudes from the lower housing  102  to the diagonally upper front side to receive the sheet in the slanting state. This stacker  120  has two-stage structure comprising a first stacker member  121  and a second stacker member  122  which is slidably attached to the first stacker member  121  at a distal end portion thereof. The second stacker member  122  is housed in the first stacker member  121  when it is not used, and pulled out from the first stacker member  121  when it is used.  
         [0050]    A window  105  is formed from the upper portion of the upper housing  101  to the front surface thereof. This window  105  is covered with a transparent or semitransparent openable cover  106 . By opening this cover  106 , an exchanging work of ink cartridge and a maintenance work of the internal mechanism can be readily performed. Further, a push button type of power switch  131  and operational switches  132 ,  133  are provided on the left backside of the upper housing  101 .  
         [0051]    As shown in FIG. 3, in the lower housing  102 , a control board  130  constituting a printer controller is placed vertically, and a recording section  140  constituting a print engine, a sheet feeder  150  and a transporter  160  shown in FIG. 4 are installed.  
         [0052]    A control element and a memory element such as CPU, ROM, RAM, ASIC (they are not shown), and other various circuit elements are mounted on the control board  130 . At the upper end of the control board  130 , light emitting diodes  133  and  134  are located protrusively, which emit lights respectively when the power switch  131  or the operational switches  132 ,  133  are pushed on, whereby a user can confirm switch-ON.  
         [0053]    The recording section  140  comprises a carriage  141 , a recording head  142 , a carriage motor  143 , a timing belt  144 , and a suction pump  145 . On a sheet transported by the transporter  160 , data is recorded by the recording head  142  mounted on the carriage  141  scanned by the carriage motor  143  and the timing belt  144 . From ink cartridges  146  of four colors, for example, yellow, magenta, cyan, and black, housed in the carriage  141 , each color ink is supplied to the recording head  142  so that full color printing can be performed.  
         [0054]    The feeder  150  comprises the sheet feeding tray  110 , a sheet feeding guide  111 , a sheet feeding roller  151 , a hopper  152 , and a separation pad  153 . Sheets P stacked on the sheet feeding tray  110  and aligned by the sheet feeding guide  111  are pushed against the sheet feeding roller  151  with the separation pad  153  by rising of the hopper  152  with rotation of the sheet feeding roller  151 , separated one by one from the uppermost sheet P, and transported to the transporter  160 .  
         [0055]    The transporter  160  comprises a feeding roller  161 , a driven roller  162 , a discharging roller  163 , a serrated roller  164 , a sheet feeding motor  165 , and the stacker  120 . The sheet P supplied from the feeder  150  is transported to the recording section  140  while being held between the feeding roller  161  driven by the sheet feeding motor  165  and the driven roller  162 , and further transported to the ejected sheet stacker  120  while being held between the discharging roller  163  driven by the sheet feeding motor  165  and the serrated roller  164 .  
         [0056]    As shown in FIGS. 5A and 5B, the discharging roller  163  is formed so that a shaft portion  163   a  made of plastics elongates longer than at least recordable maximum sheet width and has a hollowed portion  163   c  extending axially. Further, plural roller portions  163   b  made of elastomer such as rubber are joined to the shaft portion  163   a  at a constant interval. The shaft portion  163   a  of the discharging roller  163  is molded by an injection method or a gas injection method which generates a void that can prevent a sink and a warp by suppressing internal stress produced when molding is performed using a die. The roller portion  163   b  of the discharging roller  163  is molded on the shaft portion  163   a  by an injection method.  
         [0057]    Since the shaft portion  163   a  of the discharging roller  163  is thus formed in the hollowed shape having larger sectional area than sectional area of the related-art discharging roller  1 , flexural rigidity of this discharging roller  163  can be enhanced more than that of the related-art discharging roller  1 . Specifically, the diameter Dr1 (see FIG. 5B) is 11.26 mm and the diameter Ds1 is 8.25 mm. Therefore, the proportion of the outer diameter of the shaft portion to the outer diameter of the roller portion is 73.3%. Consequently, when the sheet is tensed between the discharging roller  163  and the feeding roller  161 , deformation of the discharging roller  163  such as a flexure can be suppressed. Therefore, a flip phenomenon caused by the discharging roller  163  can be avoided, and particularly recording accuracy in recording on a whole surface can be improved.  
         [0058]    As a material of the shaft portion  163   a  of the discharging roller  163 , thermoplastic resin is used, for example, ABS (copolymer of acrylonitrile, butadiene and styrene), PS (polystrene), POM (polyacetal), modified PPE (polyphenylene ether), PC (polycarbonate), PBT (polybutylene terephthalate), and alloy system. Further, in order to heighten more the flexural rigidity, an additive such as GF (glass fiber), GR (glass beads), carbon, nylon, or potassium titanate is added. The amount of this additive is preferably 5 to 50% and particularly 10 to 30% in order to further enhance the flexural rigidity.  
         [0059]    As shown in FIG. 6, in a die  200  used in molding of the shaft portion  163   a  of the discharging roller  163 , according to a first embodiment of the invention, cavity portions  201  and  202  are formed in order to mold one shaft portion  163   a  of the discharging roller  163 , and the die  200  comprises an upper die  210  and a lower die  220  that are divided in the radial direction of the discharging roller  163 . Here, since the conventional shaft portion of the discharging roller, formed of metal is high in rigidity, distortion can be prevented by double point support structure in which both ends are supported. However, since the shaft portion  163   a  of the discharging roller  163  according to the invention is formed of plastics that is lower in rigidity than the metal, five point support structure in which not only the both ends but also intermediate portions are supported is adopted to prevent the distortion.  
         [0060]    Since molding accuracy of each bore part in the shaft portion  163   a  of the discharging roller  163  affects greatly accuracy of rotation of the discharging roller  163 , in order to improve the molding accuracy, the upper die  210  and the lower die  220  are respectively divided into three parts at portions where a part other than the bore portions is molded. In other words, each bore section including at least one bore portion is molded by a single die (a first upper die  211 , a second upper die  212 , a third upper die  213 , a first lower die  221 , a second lower die  222 , and a third lower die  223 ) as shown in FIGS. 6, 7A and  7 B.  
         [0061]    Thus, through-work such as wire cut electrical discharge machining or cutting can be performed at the time of manufacturing the die, working accuracy of the die can be enhanced, and a die manufacturing cost can be reduced. Accordingly, the molding accuracy of the shaft portion  163   a  of the discharging roller  163  can be improved, and the eccentric rotation of the discharging roller  163  can be suppressed. Further, since the sectional shape of the shaft portion  163   a  of the discharging roller  163  is simplified, a cost of the discharging roller  163  can be reduced.  
         [0062]    Due to limitation of a shape in the vicinity of each bore portion, there may be portions where the cavity portions  201  and  202  cannot be collectively formed. However, insert dies  214  and  224  are inserted into these portions to obtain desired shape of the cavity portions. FIGS. 8A and 8B are perspective views showing the second lower die  222  in detail. In this second lower die  222 , five insert dies  224  are inserted. Each insert die  224 , is inserted into a through hole  222   a  from a bottom face  222   c  side to constitute a part of the cavity portion  202 . Though not shown, the first upper die  211 , the second upper die  212 , the third upper die  213 , the first lower die  221 , the third lower die  223  have also the similar structure.  
         [0063]    As shown in FIG. 9, a fitting part  215  of the upper die  210  and a fitting part  225  of the lower die  220  are formed in the shapes of concave and convex that can be fitted to each other, and lower corners  215   a  of the upper fitting part  215  and the upper corners  225   a  of the lower fitting part  225  are tapered so as to facilitate the fitting operation.  
         [0064]    Since the cavity portion  201  in the upper die  210  and the cavity portion  202  in the lower die  220  can be faced with each other with high accuracy, occurrence of flash extending in the axial direction of the periphery of the shaft portion  163   a  can be suppressed and the molding accuracy can be improved, so that the eccentric rotation of the discharging roller  163  can be suppressed.  
         [0065]    As shown in FIGS. 10A and 10B, the cavity portions  201  and  202  are heat-regulated. Inside of this second lower die  222 , a fluid passage  204  through which cooling liquid (e.g., water) for heat regulation of the cavity portion  202  flows is formed. As shown in FIG. 10B, the fluid passage  204  extends perpendicularly from a bottom face  222   c  at one end face  222   b  side, it turns at a nearly right angle, extends from one end face  222   b  side to the other end face  222   d  side, and thereafter turns at a nearly right angle to run through the bottom face  222   c  at the other end face  222  side. Such the fluid passages  204 , as shown in FIG. 10A, are formed respectively on both widthwise sides of the cavity portion  202 . Though not shown, the similar fluid passages are formed in the first lower die  221  and the third lower die  223 .  
         [0066]    [0066]FIG. 11 is a section view showing a state where the die  200  is attached to a die attaching portion  300  of an injection molding machine. In the die attaching portion  300  of the injection molding machine, a fluid passage  301  through which cooling liquid (e.g., water) for heat-regulating the die attaching portion  300  itself flows is formed. Moreover, a fluid passage  302  through which cooling liquid for heat-regulating the cavity portions  201 ,  202  is formed so as to communicate to the fluid passage  204  of the die  200 .  
         [0067]    Hereby, since the inner surfaces of the cavity portions  201 ,  202  can be cooled, when the melted plastic is injected, the outer surface of plastic is solidified in a state where it is adhered onto the inner surfaces of the cavity portions  201 ,  202 , and void is easy to be produced on the inside thereof. Therefore, occurrence of internal stress of molded products for the shaft portion  163   a  can be suppressed, so that a sink and a warp can be prevented. Further, dimensional accuracy of outer diameter of the shaft portion  163   a  can be improved, so that the eccentric rotation of the discharging roller  163  can be suppressed. Further, since the die  200  is cooled relatively quickly, an operation cycle for molding can be reduced.  
         [0068]    Further, as the injection method, a gas injection method can be adopted. FIG. 12 shows this configuration as a second embodiment of the invention. To a die attaching portion of an injection molding machine of this embodiment, a die  400  and a die  450  are attached. The die  400  has the similar structure as the die  200 , in which cavity portions  401 ,  402  for molding one shaft portion  163   a  of a discharging roller  163  are formed. An auxiliary cavity  451  is attached to an exhaust port  404 .  
         [0069]    Under a condition that the cavity portions  401 ,  402  of the die  400  are heat regulated at a predetermined temperature, the predetermined amount of the melted plastic is injected from an injection port  403  of the die  400 . Subsequently, the predetermined amount of gas is injected from the injection port of the die  400 . Hereby, a plastic outer surface coming into contact with the inner surfaces of the cavity portions  401 ,  402  is quickly cooled and pressed by gas pressure from the plastic inside. Therefore, the plastic is solidified in a state where it is adhered onto the inner surfaces of the cavity portions  401 ,  402 .  
         [0070]    Melting plastic inside the plastic between the injection port  403  of the die  400  and the exhaust port  404  is pushed out from the exhaust port  404  by gas and fed out into the auxiliary cavity  451 . Hereby, occurrence of internal stress of molded products for the shaft portion  163   a  of the discharging roller  163  can be suppressed, so that the sink and the warp can be prevented. Further, the dimensional accuracy of outer diameter of the shaft portion  163   a  can be improved, and a uniform hollowed portion  163   c  can be formed stably in the shaft portion  163   a  throughout the entire region in the axial direction. Therefore, the eccentric rotation of the discharging roller  163  can be suppressed.  
         [0071]    Though the invention has been described in the above various embodiments, it is not limited the above embodiments but may be applied also to other embodiments within the scope of the appended claims. For example, though the ink jet printer has been described as an example of a recording apparatus, the invention is not limited to this but can be applied to another recording apparatus having a discharging roller, for example, a thermal transfer type printer, and an ink jet type or thermal transfer type facsimile or copying machine.