Abstract:
A developing solution carrier configured to mix developing solution containing therein toner stored in a developing solution tank and convey the developing solution to a predetermined location includes a housing including a first opening connected to the developing solution tank and a second opening formed close to the predetermined location and two rotatable members located inside the housing. The rotatable members are configured to be engaged with each other, so as to generate force at the interface therebetween in a direction toward the second opening from the first opening while rotating.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a developing solution carrier configured to convey developing solution containing toner in carrier solution to a predetermined location, and to a wet type image forming apparatus, which is provided with such a developing solution carrier, configured to form an image with the developing solution.  
         [0002]     Apparatuses that transfer toner to a recording paper to thereby form an image include, for example, a dry type image forming apparatus, which applies powder toner to the surface of a developing roller to form an image, and a wet type image forming apparatus, which applies developing solution containing toner in carrier solution to the surface of a developing roller (more strictly, a “developing solution carrying roller”) to form an image, as disclosed in Japanese Unexamined Patent Publication No. 2000-250318. The toner employed in the latter apparatus is finer than that employed in the former. Accordingly, the latter provides images of higher quality.  
         [0003]     In a wet type image forming apparatus as described in Japanese Unexamined Patent Publication. No. 2000-250318, a tube pump is employed to deliver liquid toner (i.e., developing solution) stored in a toner container to a location above an applicator roller. In addition, the toner that has not been consumed for developing is collected into the toner container for recycling. The collected toner is unevenly distributed or aggregated in the solution. Accordingly, the toner container generally includes a mixer for uniformly distributing the toner all over the solution.  
         [0004]     In most of conventional wet type image forming apparatuses including the one according to Japanese Unexamined Patent Publication No. 2000-250318, however, the developing solution carrier that conveys the developing solution is complicatedly configured. Besides, the developing solution carrier and the mixer are independently installed from each other. Such a configuration constitutes a bottleneck in reducing the overall dimensions of the wet type image forming apparatus, as well as the manufacturing cost thereof.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is advantageous in that a developing solution carrier with a simple structure, yet capable of both mixing and conveying developing solution, and a wet type image forming apparatus that includes such a developing solution carrier, is provided.  
         [0006]     According to an aspect of the invention, there is provided a developing solution carrier configured to mix developing solution containing therein toner stored in a developing solution tank and convey the developing solution to a predetermined location, which includes a housing including a first opening connected to the developing solution tank and a second opening formed close to the predetermined location and two rotatable members located inside the housing, the rotatable members being configured to be engaged with each other, so as to generate force at the interface therebetween in a direction toward the second opening from the first opening while rotating.  
         [0007]     Optionally, the rotatable members may be cylindrical-shaped helical members having respective spiral tooth leads formed thereon. Optionally, at least one of the rotatable members may be a helical gear supported by a rotatable shaft.  
         [0008]     Optionally, the rotatable members may have the spiral tooth leads formed in different directions from each other.  
         [0009]     Still optionally, the engagement ratio of the rotatable members may be gradually increased in a direction toward the second opening from the first opening.  
         [0010]     Further optionally, one of the rotatable members may be caused to rotate by rotation of the other.  
         [0011]     Optionally, at least one of the rotatable members is formed of elastic material.  
         [0012]     Yet optionally, at least one of the rotatable members may be configured with a plurality of rotatable members being joined to one another.  
         [0013]     Optionally, at least one of the rotatable members is formed by resin molding.  
         [0014]     According to another aspect of the invention, there is provided a wet type image forming apparatus configured to form an image with developing solution containing toner in carrier solution stored in a developing solution tank, which includes a latent image carrying roller on which a latent image to be developed by the toner is formed, a developing solution carrying roller configured to carry the developing solution so as to supply the toner to the latent image carrying roller, a developing solution applicator roller configured to uniformly apply the developing solution to a surface of the developing solution carrying roller, and a developing solution carrier configured to mix the developing solution in the developing solution tank and convey the developing solution toward the developing solution applicator roller. The developing solution carrier includes a housing including a first opening connected to the developing solution tank and a second opening formed above the developing solution applicator roller, and two rotatable members located inside the housing. The rotatable members are configured to be engaged with each other, so as to generate force at the interface therebetween in a direction toward the second opening from the first opening while rotating. 
     
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0015]      FIG. 1  is a schematic cross-sectional side view showing a structure of a wet type printer according to a first embodiment of the present invention;  
         [0016]      FIG. 2  is an enlarged cross-sectional side view showing a structure around a developing solution carrier according to the first embodiment of the present invention;  
         [0017]      FIG. 3  is a schematic perspective view showing only helical gears and rotating shafts thereof out of the developing solution carrier according to the first embodiment of the present invention;  
         [0018]      FIG. 4  is a schematic perspective view showing a helical gear and a helical roller incorporated in a wet type printer according to a second embodiment; and  
         [0019]      FIG. 5  is a schematic perspective view showing a helical gear and a helical roller incorporated in a wet type printer according to a third embodiment. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0020]     Hereinafter, referring to the accompanying drawings, wet type printers, which are wet type image forming apparatuses of embodiments according to the present invention, will be described hereunder.  
       First Embodiment  
       [0021]      FIG. 1  is a cross-sectional side view showing a structure of a wet type printer  100  according to an embodiment (first embodiment) of the present invention. The wet type printer  100  is an apparatus that forms an image with a developing roller that carries, on its surface, developing solution DS containing toner in carrier solution, and more specifically an apparatus that prints out a letter or image information inputted from an external apparatus such as a computer on a recording paper P by an electrophotography process utilizing a laser beam.  
         [0022]     The wet type printer  100  generally includes a control unit  20  that controls a printing process, carrying operation and so on, a driving unit  30  that drives various mechanisms, a laser scanning unit (hereinafter, abbreviated as “LSU”)  40  that outputs a laser beam modulated according to printing information, a developing unit  50  that develops a latent image formed according to a letter or printing information with the developing solution DS by electrophotography, a transfer unit  70  that sets a toner image developed by the developing unit  50  at a transfer position and thereby transfers the image on the recording paper P, a carrying mechanism that carries the recording paper P, and a fixing unit  80  that fixes the toner image transferred onto the recording paper P supplied by the carrying mechanism.  
         [0023]     The driving unit  30  serving as a driving source of the mechanisms in the wet type printer  100  includes a plurality of actuators that drive the respective mechanisms. All of these actuators are connected to the control unit  20 , to be driven under the control of the control unit  20 . The driving unit  30  can cause a rotation of, for example, a developing roller  55  (developing solution carrying roller) and photoconductive drum  61  (latent image carrying roller) included in the developing unit  50 , and a heat roller  81  included in the fixing unit  80 .  
         [0024]     On a side face of a housing of the wet type printer  100 , a paper inlet  12  is provided, through which the recording paper P is introduced into the printer, and a paper tray  11  for storing the recording paper P is attached at the paper inlet  12 . On the opposite side face of the housing, a paper outlet  15  and a receiver tray  16  are provided. The recording paper P, upon being introduced into the wet type printer  100  through the paper inlet  12 , is carried along a paper path  13  to reach the transfer position defined by the transfer unit  70 , where the toner is transferred onto the surface of the recording paper P according to the printing information. Thereafter the recording paper P is carried along a paper path  14  to reach a fixing position defined by the fixing unit  80  for fixation of the toner, and discharged through the paper outlet  15  out of the wet type printer  100 .  
         [0025]     The transfer unit  70  forms an image as follows, with the toner representing the printing information to be transferred to the recording paper P. Firstly a latent image is generated by the control unit  20  and the LSU  40 . The LSU  40  is an example of exposure methods to form the latent image on the surface of the photoconductive drum  61 , and includes a laser diode  41  serving as a light source, a collimator lens  42 , a cylindrical lens  43 , a polygon mirror  44 , an image forming lens  45  and a deflecting mirror  46 . Here, an LED (Light Emitting Diode) or a reducing optical system may be employed as the exposure method, instead of the LSU  40 .  
         [0026]     The laser diode  41  emits a laser beam. The laser diode  41  is driven under the control of the control unit  20 , so as to turn on and off (i.e., be modulated) according to the letter and image information inputted thereto. The laser beam emitted by the laser diode  41  enters the collimator lens  42  to be thereby converted from diffuse rays into parallel rays, and then enters the polygon mirror  44  via the cylindrical lens  43 .  
         [0027]     The laser beam converted into parallel rays is converged by the cylindrical lens  43  solely in an auxiliary scanning direction, near a reflecting surface of the polygon mirror  44 . It is noted that the auxiliary scanning direction herein referred to designates a direction parallel to the sheet of  FIG. 1  (a direction orthogonal to the rotating shaft of the photoconductive drum  61 , i.e., a tangent on a circumferential surface thereof), while a direction orthogonal to the auxiliary scanning direction, i.e., a direction in which the laser beam is scanned on the photoconductive drum  61  (an axial direction on the photoconductive drum  61 ) is herein defined as a main scanning direction.  
         [0028]     The polygon mirror  44  is rotated by a motor not shown, and hence the laser beam incident upon the polygon mirror  44  is deflected so as to scan in the main scanning direction. Then the laser beam incident upon the image forming lens  45  is thereby converted so as to scan in the main scanning direction at a predetermined speed on the photoconductive drum  61 . The laser beam thus converted is deflected by the deflecting mirror  46  toward the photoconductive drum  61 , to thereby form an image on the photoconductive drum  61 . At this stage, since the laser beam is modulated with the progress of the main scanning, a scanning line according to the letter and image information is formed on the photoconductive drum  61 . Also, since the photoconductive drum  61  rotates in the auxiliary scanning direction, a plurality of scanning lines is formed in the auxiliary scanning direction on the photoconductive drum  61 . As a result, a two-dimensional latent image representing the letter and image information is generated on the photoconductive drum  61 .  
         [0029]     The developing unit  50  includes a developing solution tank  51 , a developing solution carrier  52 , a measuring roller (=developing solution applicator roller)  53 , an adjusting blade  54 , a developing roller  55 , a developing roller charging corona  56 , and a developing roller cleaning blade  58 .  
         [0030]     Close to the developing unit  50 , there are located the photoconductive drum  61 , on which a latent image is developed by the toner supplied by the developing roller  55  upon formation of the latent image by the LSU  40  based on the printing information, and a photoconductive drum charging corona  62  that uniformly charges the photoconductive drum  61 . Also, there is located close to the developing unit  50  a photoconductive drum cleaning blade  63  for scraping off the toner remaining on the surface of the photoconductive drum  61  without being transferred to an intermediate transfer roll  71 , to be later described, included in the transfer unit  70 .  
         [0031]     The developing solution tank  51 , which serves as a housing sustaining the components of the developing unit  50 , is capable of storing therein the developing solution DS. The developing solution tank  51  also receives the unconsumed toner that has been collected for recycling, as will be described later. Accordingly, the toner is unevenly distributed or aggregated in the developing solution DS in the developing solution tank  51 . Here, the temperature of the developing solution stored in the developing solution tank  51  is controlled by a temperature control mechanism, which is not shown.  
         [0032]      FIG. 2  is an enlarged cross-sectional side view showing a structure around a developing solution carrier according to the first embodiment. The developing solution carrier  52  includes a tube  52   a,  a housing  52   b,  helical gears  52   c,    52   d,  and a supply roller  52   e.    
         [0033]     The tube  52   a  has one end portion disposed in the developing solution tank  51  so as to be dipped in the developing solution DS, and the other end portion connected to a portion of the housing  52   b.  The housing  52   b  is provided with two openings, namely an intake port  521   b  and a discharge port  522   b.  The intake port  521   b  is connected with the other end portion of the tube  52   a.  Accordingly, the developing solution DS in the developing solution tank  51  can flow through the tube  52   a  to be introduced into the housing  52   b.    
         [0034]     Inside the housing  52   b,  two helical gears  52   c,    52   d  are retained in parallel with each other. The helical gears  52   c,    52   d  are rotatably supported by the housing  52   b  via rotating shafts  521   c,    521   d,  respectively.  
         [0035]      FIG. 3  is a schematic perspective view showing only the helical gears  52   c,    52   d  and the rotating shafts thereof  521   c,    521   d  out of the developing solution carrier  52  according to the first embodiment.  
         [0036]     The helical gears  52   c,    52   d  are of a cylindrical shape, and provided with a spiral tooth lead formed on the surfaces. The spiral tooth lead on the surface of the helical gear  52   c  and that on the surface of the helical gear  52   d  are formed in different directions. In the case, for example, where the spiral tooth lead on the surface of the helical gear  52   c  is directed clockwise, the spiral tooth lead on the surface of the helical gear  52   d  is directed counterclockwise.  
         [0037]     The helical gears  52   c,    52   d  are mutually engaged. The helical gear  52   c  is rotated by the driving unit  30  in a direction indicated by the arrow B. The helical gear  52   d  is caused to rotate by the rotation of the helical gear  52   c,  in a direction indicated by the arrow C.  
         [0038]     When the helical gears  52   c,    52   d  rotate, thrust force (shearing force) is generated at the interface therebetween in an axis direction (thrust direction) of these gears, i.e., in the direction of the arrow A. Such force introduces the developing solution DS in the developing solution tank  51  into the housing  52   b  through the tube  52   a  and the intake port  521   b.  The developing solution DS thus introduced is kneaded between the teeth of the helical gears  52   c,    52   d  at a position where the teeth are mutually engaged, and flows inside the housing in the direction of the arrow A, taken along the spiral tooth lead. The toner in the developing solution DS is mixed to be uniformly distributed, and the toner that has been aggregated is diffused again, while the developing solution DS is being kneaded between the engaged teeth of the helical gears  52   c,    52   d.  Thus, the developing solution DS is conveyed in the housing  52   b  in the direction of the arrow A while being mixed by the helical gears  52   c,    52   d.    
         [0039]     It is to be noted that the helical gears  52   c,    52   d  have diameters gradually increasing in the direction of the arrow A. Accordingly, the engagement ratio of the helical gears  52   c,    52   d  gradually increases in a direction toward the discharge port  522   b  from the intake port  521   b.  Therefore, the developing solution DS is kneaded by greater force as the developing solution DS is conveyed farther inside the housing  52   b.  Such a configuration also serves to increase the load in the thrust direction, thereby ensuring the developing solution DS being conveyed in the direction of the arrow A. Actually, however, the increase in diameter of the helical gears  52   c,    52   d  is very slight. Alternatively, the helical gears  52   c,    52   d  may be formed in constant diameters so that the engagement ratio remains constant all the way.  
         [0040]     The developing solution DS, which has been stirred and conveyed in the direction of the arrow A by the rotation of the helical gears  52   c,    52   d,  is discharged through the discharge port  522   b  out of the housing  52   b.  The discharge port  522   b  is located above the supply roller  52   e  and the measuring roller  53 . Accordingly, the developing solution DS which has been discharged through the discharge port  522   b  falls toward the supply roller  52   e  and measuring roller  53 .  
         [0041]     Thus, the developing solution carrier  52  according to the first embodiment has a simple structure, yet is capable of effectively mixing the developing solution DS and conveying the same to the measuring roller  53 .  
         [0042]     The supply roller  52   e  and the measuring roller  53  are rotatably butted to each other. Also, the supply roller  52   e  and the measuring roller  53  are provided with wall portions (not shown) on the respective end portions. The supply roller  52   e,  the measuring roller  53  and the wall portions thus disposed define a space that is widely open upward, between the supply roller  52   e  and the measuring roller  53 . Since the developing solution DS discharged through the discharge port  522   b  falls into this space, and thereby pools between the supply roller  52   e  and the measuring roller  53 , as shown in  FIG. 2 .  
         [0043]     As shown in  FIG. 2 , the supply roller  52   e  rotates clockwise, while the measuring roller  53  rotates counterclockwise. When the developing solution DS stuck to the surface of the supply roller  52   e  in the aforementioned space passes through the rotation interface with the measuring roller  53 , a portion of the developing solution DS falls in the developing solution tank  51 , while the rest remains stuck to the supply roller  52   e.  In addition, the developing solution DS stuck to the surface of the measuring roller  53  in this space passes through the rotation interface with the supply roller  52   e,  and then reaches the position where the adjusting blade  54  is in contact with the measuring roller  53 .  
         [0044]     Then a portion of the developing solution DS stuck to the surface of the measuring roller  53  is scraped off (i.e., adjusted) by the adjusting blade  54  engaged with the measuring roller  53 . It is noted that the measuring roller  53  is provided with a plurality of grooves formed at a predetermined interval on its surface. Accordingly, another portion of the developing solution DS stuck to the measuring roller  53  is exempted from being scraped off, since such portion is retained in the grooves. Therefore, it is only the portion retained in the grooves, i.e., the accurately adjusted portion of the developing solution DS, that remains on the surface of the measuring roller  53 , and consequently the developing solution DS can be uniformly applied to the developing roller  55 , which is in rotational contact with the measuring roller  53 .  
         [0045]     The developing solution DS contains the toner in a uniform concentration, immediately after the application to the developing roller  55  from the measuring roller  53 . Accordingly, the toner is uniformly distributed in the carrier solution, in a region close to the interface between the measuring roller  53  and the developing roller  55 . The developing roller  55  rotates in the clockwise direction, as shown in  FIG. 1 . Therefore, the developing solution DS having a uniform concentration is carried by the surface of the developing roller  55 , thereby passing under the developing roller charging corona  56 .  
         [0046]     The developing roller  55  has a surface formed from a conductive material, so that such surface is uniformly charged by a corona charging effect of the developing roller charging corona  56 . The charging effect generates an electric field between the surfaces of the developing roller  55  and the developing solution DS, and thereby causes the toner, which has been uniformly distributed in the carrier solution, to move toward the surface of the developing roller  55  and to closely stick thereto. In other words, the developing solution DS is split into two layers, namely a layer containing only the carrier solution and the other layer containing the toner in a higher concentration than the initial state in the carrier solution. Obviously, it is the latter layer that contacts the surface of the developing roller  55 .  
         [0047]     The developing solution DS split into two layers then reaches the position to contact the photoconductive drum  61 . On the surface of the photoconductive drum  61 , the latent image based on the printing information is formed by the beam outputted from the LSU  40 . The photoconductive drum  61  is charged so as to gain a higher potential than the developing roller  55 , by the photoconductive drum charging corona  62 . However, the region where the latent image is provided based on the printing information by the laser beam gains a lower potential than the developing roller  55 , because of an effect of the laser beam. Accordingly, between the region excluding the latent image on the photoconductive drum  61  and the surface of the developing roller  55 , the toner remains closely stuck to the lower-potential region, i.e., the surface of the developing roller  55 , without being transferred to the region where the latent image is not provided. Consequently, the region excluding the latent image is not developed. By contrast, between the latent image region on the surface of the photoconductive drum  61  and the surface of the developing roller  55 , the toner is electrophoresed toward the lower-potential region, i.e., the latent image region on the surface of the photoconductive drum  61 , thus to adhere thereto. Thereby, the latent image on the photoconductive drum  61  is developed, to turn into a toner image.  
         [0048]     The developing solution DS containing the toner, which has not been utilized in the developing process, is scraped off by the developing roller cleaning blade  58  disposed in contact with the surface of the developing roller  55 , and collected into the developing solution tank  51 .  
         [0049]     The toner image developed on the surface of the photoconductive drum  61  is transferred to the recording paper P by the transfer unit  70 . The transfer unit  70  includes an intermediate transfer roll  71 , a carrier solution squeeze roll  72 , a carrier solution cleaning blade  73 , a secondary transfer roll  74 , and an intermediate transfer roll cleaning unit  75 .  
         [0050]     To the intermediate transfer roll  71 , a transfer bias of a reverse polarity to the toner is applied, so that the toner image developed on the surface of the photoconductive drum  61  is primary-transferred to the intermediate transfer roll  71 , at the interface between the photoconductive drum  61  and the intermediate transfer roll  71 . At this stage, the portion of the toner remaining on the surface of the photoconductive drum  61  without being transferred at the interface is scraped off from the surface, by the photoconductive drum cleaning blade  63 . Also, the carrier solution that has adhered to the surface of the intermediate transfer roll  71  together with the toner image is squeezed off from the surface by the carrier solution squeeze roll  72 . Such residual carrier solution is then removed from the surface of the carrier solution squeeze roll  72  by the carrier solution cleaning blade  73 , and is collected as waste toner in a waste toner box (not shown).  
         [0051]     The intermediate transfer roll  71  and the secondary transfer roll  74  are disposed so as to oppose each other across the paper path for the recording paper P, and mutually butted at a predetermined nip pressure. The toner image transferred to the surface of the intermediate transfer roll  71  is transferred to the recording paper P to be carried along the paper path at the interface with the secondary transfer roll  74 , by the effect of a transfer electric field, the nip pressure and so on. The intermediate transfer roll  71 , interposed between the secondary transfer roll  74  and the photoconductive drum  61 , also serves to prevent the nip pressure of the secondary transfer roll  74  from being directly applied to the photoconductive drum  61 . Further, the toner that remains on the surface of the intermediate transfer roll  71  after the transference to the recording paper P is removed by the intermediate transfer roll cleaning unit  75 , and is collected as waste toner in the aforementioned waste toner box.  
         [0052]     The recording paper P on which the toner image has been transferred is carried to the fixing unit  80  along the paper path  14 . The fixing unit  80  serves to apply heat and pressure to the recording paper P, so as to fix the toner image (i.e., the printing information) onto the recording paper P, and includes a heat roller  81  that heats up the recording paper P, and a press roller  82  that faces the heat roller  81  across the paper path and holds the recording paper P between itself and the heat roller  81  to apply a pressure to the recording paper P. The recording paper P, on which the image according to the printing information has been fixed by the fixing unit  80 , is discharged through the paper outlet  15 .  
         [0053]     Although the present invention has been described based on the first embodiment, it is to be understood that the present invention is not limited thereto, but various modifications may be made without departing from the scope and spirit of the present invention.  
         [0054]     Hereinafter, a few examples of the modifications of the present invention will be described with reference to the associated drawings. In the relevant drawings, the same constituents as those of the wet type printer  100  according to the first embodiment shown in FIGS.  1  to  3  are given identical reference numbers and detailed description thereof will be omitted.  
       Second Embodiment  
       [0055]      FIG. 4  is a schematic perspective view showing a helical gear  52   c  and a helical roller  52   f  incorporated in a wet type printer  100  according to another embodiment (second embodiment). The helical roller  52   f  is of a cylindrical shape, and provided with a spiral tooth lead formed on its surface. The spiral tooth lead on the surface of the helical gear  52   f  and that on the surface of the helical gear  52   c  are formed in different directions.  
         [0056]     The helical roller  52   f  is not provided with a shaft member, and hence not pivotally supported by the housing  52   b.  However, an inner wall portion of the housing  52   b  is located along and close to the surface of the helical roller  52   f.  Accordingly, a gap between the inner wall portion of the housing  52   b  and the surface of the helical roller  52   f  is small. Such a configuration allows the helical roller  52   f  to rotate guided by the inner wall portion of the housing  52   b,  and thereby allows the helical gear  52   c  and the helical roller  52   f  to be mutually engaged. Consequently, when the helical gear  52   c  is rotated by the driving unit  30  in a direction of the arrow B, the helical roller  52   f  can be allowed to rotate in a direction of the arrow C, accompanied by the rotation of the helical gear  52   c.    
         [0057]     Adopting the helical roller  52   f  thus designed allows omitting the shaft member, resulting in reducing the manufacturing cost of the wet type printer  100 . The helical roller  52   f  may be made of an elastic material. Employing an elastic material as the helical roller  52   f  causes an elastic deformation thereof, which achieves a closer contact between the helical roller  52   f  and the helical gear  52   c.  The closer contact of the helical roller  52   f  and the helical gear  52   c  enables kneading the developing solution DS with greater force.  
       Third Embodiment  
       [0058]      FIG. 5  is a schematic perspective view showing a helical gear  52   g  and a helical roller  52   f  incorporated in a wet type printer  100  according to a further embodiment (third embodiment). The helical gear  52   g  includes, for example, three pieces of helical gears  52   h  joined along a rotating shaft  521   c.  Each of the helical gears  52   h  has the same cross-sectional shape along a plane orthogonal to the rotating shaft  521   c  as that of the helical gear  52   c  according to the first embodiment, and an axial length corresponding to one third of the axial length of the helical gear  52   c.  In other words, the helical gear  52   g  including the three helical gears  52   h  has substantially the same outer shape as that of the helical gear  52   c  according to the first embodiment. Here, it is desirable to connect the helical gears  52   h  such that the tooth leads on the respective pieces are continuously aligned with one another.  
         [0059]     Adopting the helical gear  52   g  thus designed allows utilizing a smaller mold, in the case of fabricating the helical gear  52   h  by resin molding, thereby reducing the fabricating and developing cost of the molding die.  
         [0060]     The present disclosure relates to the subject matter contained in Japanese Patent Application No. P2004-334226, filed on Nov. 18, 2004, which is expressly incorporated herein by reference in its entirely.