Abstract:
The present invention relates to a recording apparatus comprising a conveyance roller; a driven roller rotating as driven from the conveyance roller; pushing means for pushing the driven roller to the conveyance roller;a bearing for supporting the conveyance roller; driving means for rotating the conveyance roller; and drive transmitting means. The bearing includes two contact portions with the circumference of a spindle for supporting the conveyance roller and the bearing supports the conveyance roller as to locate a perpendicular direction of a line coupling the two contact portions within a varying range of a vector direction of exertion force exerted to the bearing at a time of stop and operation of the conveyance roller.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a recording apparatus for formimg images on a recording medium.  
           [0003]    2. Description of Related Art  
           [0004]    Quality of output images produced by a recording apparatus, particularly an inkjet recording apparatus, is improved significantly, and a higher accuracy is needed to realize this. As a means for improving image quality of a recording apparatus, it is exemplified that an ink discharging amount is reduced to lower particulate feeling of dots of discharged ink as images and that the dot size on the recording medium tends to be smaller. Where the dot becomes smaller, a region where otherwise the dots are overlapped with one another enters in a state not overlapping each other if the dot arrival position is changed even a little (or conversely, a region not to be overlapped becomes overlapped), so that the density and color tone of the region may be shifted. Such shifts in density and color tone render inferior the image quality as of white or black stripe in images or unevenness in color. The positional shifts among the dots here are of a level from several microns to ten and several microns, and means for ensuring this accuracy has been used.  
           [0005]    With respect to conveyance mechanisms for a recording medium as one of important mechanisms for image formation, drive structures or the like have been proposed and used for keeping an assembly accuracy as a structure canceling stop errors of a motor or eccentric accuracy components of gears by rendering the level of the parts highly accurate, e.g., improving eccentricity, cylindrical degrees, and diameter allowable deviations of conveyance rollers and classes of the gears and by rendering the conveyance amount coinciding to rotation integer components of the motor and the gears. A method, in addition to the accuracy consideration of an ideal rotary amount (conveyance surface moving amount) of the conveyance roller, is also used in which micro protrusions are formed on an outer peripheral surface of bearings to stabilize the position of the bearings for supporting the conveyance roller for the purpose of prevention of positional shifts of the conveyance roller itself and in which any deviation between the bearing of the conveyance roller and the chassis otherwise generated on an allowance is eliminated by inserting the bearing as grinding those protrusions when the bearing is attached to the chassis.  
           [0006]    With such a conventional means, however, though the accuracy in the ideal rotary amount (conveyance surface moving amount) of the conveyance roller is adequately considered, a solution regarding the position of the conveyance roller is inadequate. FIG. 10 shows a bearing structure for a general conveyance roller. In FIG. 10, numeral  1001  denotes a conveyance roller; numeral  1002  denotes a bearing; numeral  1003  denotes a chassis supporting the bearing; numeral  1004  denotes a pinch roller. The pinch roller  1004  is pushed to the conveyance roller  1001  with force Fp from a spring, not shown, to produce conveyance force of recording media.  
           [0007]    The conveyance roller  1001  is structured as to move easily in Y, Y′ directions on an inner circumference of the bearing  1002  because the cross section of the conveyance roller  1001 , the bearing  1003 , the chassis  1003 , as well are in a circular shape, respectively, even where positional deviations between the conveyance roller  1001  and the bearing  1002  and between the bearing  1002  and the chassis  1003  are accumulated together in a lower direction in FIG. 10 by pushing force Fp from the pinch roller  1004 , and the bearing  1002  is also structured as to easily move in the Y, Y′ directions where the relation between the chassis  1003  and the bearing  1002  is the same as the above, so that the conveyance roller  1001  easily moves upon exertion of external force from external disturbances and so that the position of the conveyance roller  1001  is statically unstable with respect to the chassis  1003 .  
           [0008]    In the above described method, as a conventional art, in which micro protrusions are formed on the outer peripheral surface of the bearing and in which the bearing  1002  is inserted as these protrusions are ground when the bearing  1002  is attached to the chassis, though positional deviations are eliminated when the bearing  102  is inserted, the protrusions have to be easily ground, namely to be weak protrusions, because the protrusions are necessarily of a degree not to deform the inner diameter of the bearing during insertion of the bearing, so that the protrusions may be deformed due to fallings during transportations or vibrations, thereby creating positional deviations. In general, there are differences in thermal expansion property among the bearing made of a resin such as POM or the like, and the chassis and the conveyance roller shaft, which are made of a metal, so that problems are raised such that the size may vary from changes in temperature and thereby positional deviations may occur.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the invention to provide a recording apparatus preventing a recording medium from moving caused from movement of a conveyance roller by stabilizing the position of the conveyance roller and a bearing without any cost increase as well as improving accuracy of arrival positions of ink droplets.  
           [0010]    To accomplish the above object, a representative structure according to the invention includes, in a recording apparatus: a conveyance roller; a driven roller rotating as driven from the conveyance roller; pushing means for pushing the driven roller to the conveyance roller; a bearing for supporting the conveyance roller; driving means for rotating the conveyance roller; and drive transmitting means, wherein the bearing includes two contact portions for supporting the circumference of the conveyance roller, and wherein the bearing supports the conveyance roller as to locate a perpendicular direction of a line segment coupling the two contact portions within a varying range of a vector direction of exertion force exerted to the bearing at a time of stop and operation of the conveyance roller.  
           [0011]    As described above, in this invention, because a recording apparatus includes: a conveyance roller; a driven roller rotating as driven from the conveyance roller; pushing means for pushing the driven roller to the conveyance roller; a bearing for supporting the conveyance roller; driving means for rotating the conveyance roller; and drive transmitting means, wherein the bearing includes two contact portions for supporting the circumference of the conveyance roller, and wherein the bearing supports the conveyance roller as to locate a perpendicular direction of a line segment coupling the two contact portions within a varying range of a vector direction of exertion force exerted to the bearing at a time of stop and operation of the conveyance roller, can prevent a recording medium from moving caused from movement of a conveyance roller by stabilizing the position of the conveyance roller and a bearing without any cost increase as well as can improve accuracy of arrival positions of ink droplets. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view showing an inkjet printer according to the first embodiment of the invention;  
         [0013]    [0013]FIG. 2 is a structural diagram showing a conveyance roller and a bearing according to the first embodiment of the invention;  
         [0014]    [0014]FIG. 3 is an illustration showing force exerting to the conveyance roller and the bearing according to the first embodiment of the invention;  
         [0015]    [0015]FIG. 4 is an illustration showing the conveyance roller&#39;s force exerting to the bearing at respective states during driving according to the first embodiment of the invention;  
         [0016]    [0016]FIG. 5 is a relation diagram between the contact portion of the bearing and bearing exerting force according to the first embodiment of the invention;  
         [0017]    [0017]FIG. 6 is a schematic view showing a shape of the bearing according to the first embodiment of the invention;  
         [0018]    [0018]FIG. 7 is a structural diagram showing a conveyance roller and a vicinity of a bearing according to the second embodiment of the invention as well as an illustration showing exerting force;  
         [0019]    [0019]FIG. 8 is a schematic view showing a shape of a chassis according to the second embodiment of the invention;  
         [0020]    [0020]FIG. 9 is a structural diagram showing a conveyance roller and a vicinity of a bearing according to the third embodiment of the invention; and  
         [0021]    [0021]FIG. 10 is a structural diagram showing a conveyance roller and a vicinity of a bearing of a prior art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    [First Embodiment] 
         [0023]    Now, the first embodiment is described. In this embodiment, exemplified is a serial type inkjet printer on which a recording head as a recording means with a detachable ink tank is mounted. FIG. 1 is a whole diagram showing the serial type inkjet printer. In FIG. 1, numeral  101  is a recording head having an ink tank; numeral  102  is a carriage mounting the recording head thereon. A guide shaft  103  is inserted at a bearing portion of the carriage  102  in a state capable of sliding in a main scanning direction perpendicular to the conveyance direction of a recording medium  301 , and each end of the shaft is secured to a chassis  116 . Drive force of a drive motor  105  serving as a carriage driving means is transmitted to the carriage  102  via a belt  104  serving as carriage drive transmitting means engaged thereto, and thereby the carriage  102  is movable in the main scanning direction (X direction).  
         [0024]    In FIG. 1, numeral  106  is a feeding base for stacking the recording media; numeral  107  is a conveyance motor as a drive source for conveyance of the recording media; numeral  108  is a conveyance roller for conveying the recording media (in this embodiment, the conveyance surface of the conveyance roller for the recording media and the bearing supporting portion are considered to have the same diameter, and hereinafter, the conveyance roller and the conveyance roller shaft as spindle (supporting axis) of a conveyance roller are dealt as the same meaning.); numeral  109  is a bearing for supporting a shaft of the conveyance roller  108  at the opposite ends of the conveyance roller  108  and is attached to the chassis  116 ; numeral  110  is a conveyance roller gear for transmitting the drive force of the conveyance motor  107  and is attached to the conveyance roller  108 ; numeral  111  is a pinch roller for pressing the recording media to the conveyance roller  108 ; numeral  112  is a pinch roller spring serving as pressing means for pressing the pinch roller.  
         [0025]    The recording media during waiting time for printing are stacked on the feeding base  106 , and the recording media are fed at the beginning of the printing operation by a feeding roller, not shown. The recording media thus fed are conveyed by a proper feeding amount in a conveyance direction of Y upon rotation of the conveyance roller  108  from the drive of the conveyance motor  107  for the recording media. Images are thus formed by discharging ink or inks to the recording media from the recording head  101  during scanning operation of the carriage  102 . The media are delivered by the delivering means after images are formed, and recording operation is completed.  
         [0026]    In this embodiment, as an ink discharging structure, it is structured to energize an electro-thermal converter in response to a recording signal to make recording by discharging the inks from orifices upon growth and contraction of bubbles generated in the inks in utilizing film boiling generated in the inks from the thermal energy thereof. As a representative structure and the principle, it is preferable to used a fundamental principle disclosed in U.S. Pat. Nos. 4,723,129, and 4,740,796. This method is applicable to any of, so-called, on-demand type and continuous type, but particularly, upon applying at least one drive signal providing rapid temperature increase exceeding nucleus boiling and corresponding to the recording information to the electro-thermal converter disposed as to correspond to a sheet to which a fluid (ink) is held or to a fluid route, and thereby generating thermal energy at the electro-thermal converter to generate a film boiling at a thermal operative surface of the recording head, the on-demand type is effective because bubbles can be consequently formed in a fluid corresponding, one to one basis, to the drive signal. With growth and contraction of the bubbles, the fluid is discharged out of discharging openings, and at least one droplet is formed. If the drive signal is formed as a pulse shape, the growth and contraction of the bubbles can be done instantly, so that the fluid can be discharged excellently, and therefore it is preferable.  
         [0027]    [0027]FIG. 2 shows a structure of the conveyance roller  108  and the bearing  109 . Pushing force of the pinch roller  111  is here exerted to the conveyance roller  108  by elastic force of the pinch roller spring  112 . On the other hand, the bearing  109  has two surfaces supporting the conveyance roller  108 , and therefore, tangents (contact points when seen in the cross section)  109   a,    109   b  exist between the two surfaces and the conveyance roller  108 . With this structure, the conveyance roller  108  is supported only to the two portions defined geometrically of the bearing  109 , and because the conveyance roller  108  is positionally set by the tangents  109   a,    109   b  in the conveyance direction (Y, Y′ direction in FIG. 2), the conveyance roller  108  does not move positionally in the conveyance direction (Y, Y′ direction in FIG. 2) as far as the conveyance roller  108  does not float from the bearing  109 . The bearing  109  is fastened to the chassis  116  with a rotary limiting portion, not show, and does not move pivotally with respect to the chassis  116 . It is to be noted that assembling property can be improved by proving an opening capable of inserting in a radial direction the conveyance roller  108  with respect to the bearing  109  or the bearing  109  with respect to the chassis  116 . The two surfaces supporting the conveyance roller  108  can be any shape, but a plane is preferable.  
         [0028]    [0028]FIG. 3 shows an illustration showing forces exerting to the conveyance roller  108  and the bearing  109 . The meanings of signs in FIG. 3 are as follows:  
         [0029]    Fp: pushing force of the pinch roller  
         [0030]    Fb: conveyance resistance force  
         [0031]    Ff: conveyance roller drive force  
         [0032]    Fg: gravity force of the conveyance roller  
         [0033]    N1, N2: opposing force of the bearing (vertical opposing force)  
         [0034]    μN1, μN2: frictional force between the conveyance roller shaft and the bearing  
         [0035]    θf: positional angle of the drive gear  
         [0036]    θ1, θ2: contact positional angle with respect to the conveyance roller and the bearing  
         [0037]    α: pressure angle of the drive gear  
         [0038]    R: radius of the conveyance roller gear  
         [0039]    r: radius of the conveyance roller  
         [0040]    T: acceleration torque of a rotary body in relation to the conveyance roller  
         [0041]    In FIG. 3, numeral  107   a  is an output gear (conveyance motor gear) for conveyance motor and engages with a conveyance roller gear  110  at a position shifted with angle θf with respect to a perpendicularly lower direction of the conveyance roller gear  110 . The gear  107   a  is a drive transmitting means for driving the conveyance roller  108 , and transmits force Ff rotating the conveyance roller gear  110 . Generally, in a case of gear transmission, drive force Ff exerts in a direction shifted by pressure angle α from the common tangent direction of the conveyance motor gear  107   a  and the conveyance roller gear  110 . Pushing force Fp of the pinch roller  111  from the elastic force of the pinch roller spring  112  is exerted to the conveyance roller  108  in a perpendicularly lower direction.  
         [0042]    The recording medium  301  to be conveyed is sandwiched between the conveyance roller  108  and the pinch roller  111 . Conveyance resistance such as rigidity of the recording medium is exerted to the recording medium  301  to be conveyed. in a direction of conveyance upstream or downstream, and conveyance resistance force Fb dealt as a resultant force with a rolling friction of the pinch roller  111  is exerted to the conveyance roller  108  in a direction opposite to the conveyance direction (right direction in FIG. 3). This conveyance resistance force Fb is frictional resistance occurring when the conveyance roller  108  is moving or when force to move is exerted. The outer peripheral surface of the conveyance roller  108  (the conveyance roller shaft) is supported to contact at the two contact portions  109   a,    109   b  at the bearing, and opposing forces N1, N2 of the force supporting the conveyance roller  108  are exerted in a center direction of the conveyance roller  108  at the contact portions  109   a,    109   b.    
         [0043]    The contact portions  109   a,    109   b  are respectively in contact with the conveyance roller  108  at positions of angles θ1, θ2 from the perpendicularly lower direction. At the contact portions  109   a,    109   b,  frictional resistances in a tangent direction opposed to the rotation direction of the conveyance roller  108  are exerted with forces μN  1 , μN  2  (providing that frictional resistance μ between the conveyance roller  108  and the bearing  109 ). When the conveyance roller  108  is accelerated or decelerated, the acceleration torque T=Idω/dt (I denotes inertia of the rotary body (moment of inertia); ω denotes an angular velocity of the rotary body) of the rotary body in association with the conveyance roller  108  is exerted.  
         [0044]    Herein, where: 
           A= sin θ1+μ cos θ1, 
           B=− sin θ2+μ cos θ2, 
           C= cos θ1−μ sin θ1, 
           D= cos θ2+μ sin θ2, 
           E=Fb+Ff  cos( θf−α ) 
           F=Fg+Fp+Ff  sin( θf−α ), 
         [0045]    vertical opposing forces that the bearing  109  receives are denoted as: 
           N   1 =( DE−BF )/( AD−BC ), 
           N   2 =( AF−CE )/( AD−BC ) 
         [0046]    Furthermore, where: 
           G= (sin θ1+μ cos θ1) N   1 −(sin θ2−μ cos θ2) N 2, 
           H= (cos θ1−μ sin θ1) N 1+(cos θ2+μ sin θ2) N 2, 
         [0047]    force Fv (scalar) that the conveyance roller  108  exerts to the bearing  109  is: 
           Fv (scalar)={square root}( G   2   +H   2 ), 
         [0048]    and the exertion angle θv is: 
           θv= tan −1 ( G/H ), 
         [0049]    at that time, acceleration torque T is denoted as: 
           T=RFf  cos  α−rFb−rμ ( N   1 + N   2 ) 
         [0050]    Hereinafter, referring to FIG. 4, force Fv (vector) that the conveyance roller  108  exerts to the bearing  109  while the conveyance roller  108  is in a state of stopping (without drive force), starting up, accelerating, moving at a constant rate, decelerating, immediately before stopping, is described.  
         [0051]    Where: Fv during stopping is Fv 0 ; T is T 0 ; drive force Ff is Ff 0 , it is set as Ff 0 =0, Fb=0, μN1=0, μN2=0, T 0 =0, and Fv 0  becomes a vector directing perpendicularly downward (θv=0).  
         [0052]    Where: force Fv exerting to the bearing  109  during starting up is Fv 1 ; acceleration torque T is T 1 ; drive force Ff is Ff 1 , it is set as μ=static frictional coefficient and Fb is the maximum static frictional force, and Fv 1  becomes a vector extending in a direction inclined by angle θv 1  from the perpendicularly downward direction in association with the drive force Ff 1  at which T 1 =0.  
         [0053]    Where the force Fv exerting to the bearing  109  during acceleration is Fv 2 ; acceleration torque T is T 2 ; drive force Ff is Ff 2 , it is set as μ=dynamic frictional coefficient and Fb is the dynamic frictional force, and Fv 2  becomes a vector extending in a direction inclined by angle θv 2  from the perpendicularly downward direction in association with the drive force Ff 2  at which T 2 &gt;0. The magnitude and direction of this vector is changeable according to the drive force Ff 2  (or according to T 2 ).  
         [0054]    Where the force Fv exerting to the bearing  109  during moving at a fixed rate is Fv 3 ; acceleration torque T is T 3 ; drive force Ff is Ff 3 , it is set as μ=dynamic frictional coefficient and Fb is the dynamic frictional force, and Fv 3  becomes a vector extending in a direction inclined by angle θv 3  from the perpendicularly downward direction in association with the drive force Ff 2  at which T 3 =0.  
         [0055]    Where the force Fv exerting to the bearing  109  during deceleration is Fv 4 ; acceleration torque T is T 4 ; drive force Ff is Ff 4 , it is set as μ=dynamic frictional coefficient and Fb is the dynamic frictional force, and Fv 4  becomes a vector extending in a direction inclined by angle θv 4  from the perpendicularly downward direction in association with the drive force Ff 4  at which T 4 &lt;0. The magnitude and direction of this vector is changeable according to the drive force Ff 4  (or according to T 4 ).  
         [0056]    Where the force Fv exerting to the bearing  109  at a time immediately before stopping is Fv 5 ; acceleration torque T is T 5 ; drive force Ff is Ff 5 , it is set as μ=dynamic frictional coefficient and Fb is the dynamic frictional force, and Fv 5  becomes a vector extending in a direction inclined by angle θv 5  from the perpendicularly downward direction in association with the drive force Ff 5  at which T 5 &lt;0.  
         [0057]    To reduce impacts at stop, the acceleration torque T 5  is generally set to be a value close to zero at the time immediately before stopping (T 5 &gt;T 4 ). To prevent gears from backlashing from a viewpoint to gear transmission accuracy, it is preferable that the drive gear reduces its rate always as pushing the conveyance gear during deceleration, and generally the drive forces of Ff 4 &gt;0, Ff 5 &gt;0 are set.  
         [0058]    Therefore, a relationship of θv 5 &gt;θv 4 &gt;θv 3 &gt;θv 2 &gt;θv 1 &gt;θv 0  is satisfied in a setting of acceleration during general acceleration and deceleration period, from relations of static frictional coefficient&gt;dynamic frictional coefficient, T 2 &gt;T 1 =T 3 &gt;T 5 &gt;T 4 , Ff 4 &gt;0, and Ff 5 &gt;0. According to this relation, the starting up vector Fv 1  and the stopping vector Fv 0 , existing at both most extremes, are preferably stabilized to render the conveyance roller  108  get settled at a stable position during operation inclusive the stopping state.  
         [0059]    As shown in FIG. 5, where the combined vector of vectors Fv 1  and Fv 0  is set as Ft, Ft becomes a vector extending in a direction inclined by angle θt from the perpendicularly downward direction. The contact portions  109   a,    109   b  for the conveyance roller  108  and the bearing  109  are formed at positions in symmetry with respect to a direction of angle θt of the vector Ft (namely, the contact positional angles θ1, θ2 are determined so that the angle θt direction of the vector Ft and the vertical direction of the line segmentcoupling between the two contact positions  109   a,    109   b  coincides to each other.). Because Ft and θ1, Ft and θ2 are in a depending relation to each other, the conveyance roller  108  can be made stable at a fixed position during operation including the stopping state where θ1 and θ2 are decided as to satisfy the above contents.  
         [0060]    According to this structure, the conveyance roller  108  is pushed to the stable positions of the contact portions (supporting surfaces)  109   a,    109   b  for the bearing to eliminate a loosened space, so that the position of the conveyance roller  108  is merely changed not more than a negligible amount even where temperature changes cause the size changes of the conveyance roller  108  and the bearing  109 , and so that the positional accuracy of the conveyance roller  108  is ensured not depending on the circumstances because no loosened situation occurs. Furthermore, addition of parts may be unnecessary, and it can be realized without further costs.  
         [0061]    To determine the contact positional angles θ1, θ2, the vertical opposition forces N1, N2 produced at the bearing  109 , other than above, are necessarily of positive values (because the conveyance roller may float from the bearing if they are of negative values), and such positive values having some margins are surely selected from a viewpoint to ensure the stability against external disturbances. On the other hand, in consideration of friction and an angle (180-θ1-θ2) between the contract positions  109   a,    109   b  of the bearing  109 , the contact positional angles are designed (if the angle becomes smaller, the stability is increased but it is disadvantageous for friction.).  
         [0062]    Herein, the contact positions  109   a,    109   b  of the bearing  109  are determined based on merely a resultant vector direction (θt direction) of the vectors Fv 1 , Fv 0  as a symmetric axis. In conveyance operation, however, since stopping accuracy is the most important factor, the weight to Fv 0  may be made larger with respect to Fv 1  to improve the stability in a stopping state, thereby producing a resultant vector Ft having a direction closer to the Fv 0  side, and thereby determining the contact positional angles θ1, θ2.  
         [0063]    In a case where the angle difference between the angles θv 1 , θv 0  is too large to satisfy the condition for determining the contact positional angles θ1, θ2 as described above, in respecting most importantly the stability on a phenomenon (operation) close to stoppage, the contact positions  109   a,    109   b  of the bearing  109  are determined based on a resultant vector direction (θt direction) of, at least, the. vector Fv 5  exerting to the bearing  109  at a time immediately before stopping and the exerting vector Fv 0  in a stopping state, as a symmetric axis. If the condition is permissive, Fv 5  and the Fv 1  direction is made closer to Fv 4  and the determined target vector, respectively, thereby preferably improving the stability of the conveyance roller  108  during the operation. The contact positions  109   a,    109   b  of the bearing  109  can also be determined closer to the exerting vector direction in the stopping state in those cases.  
         [0064]    In this embodiment, the vector Fv 0  during stopping with respect to the vector Fv 1  exerting to the bearing  109  at a time of the maximum acceleration is the vector most deviated in a positive direction of Y in FIG. 4. In a case where the vector Fv 4  and the vector Fv 2  are the vector most deviated in a direction toward the negative direction of Y with respect to the vector Fv 1  and toward the positive direction of Y with respect to the vector Fv 0  respectively where the acceleration is large during the accelerating and decelerating periods from the reason for improvements in through-put or the like, however, the contact positions  109   a,    109   b  of the bearing  109  are easily introduced by replacing the vectors Fv 1 , Fv 0  used for determining the contact positional angles θ1, θ2 for the bearing, as described above, with the vector Fv 4  and the vector Fv 2 , respectively. With a conventional bearing having an annular cross section, since the conveyance roller  108  moves greatly, and since the acceleration is large during the accelerating and decelerating periods, introduction of the contact positions  109   a,    109   b  of the bearing  109  as described above can improve the stability of the conveyance roller  108 .  
         [0065]    Although in this embodiment the bearing  109  has the two surfaces supporting the conveyance roller  108  as shown in FIG. 2 and is formed in a shape covering the peripheral surface of the conveyance roller  108 , the bearing  109  is not limited to such a shape. For example, because the portion functioning as a bearing is only two conveyance roller supporting portions  109   a,    109   b,  it is allowable if the rigidity and the shape of the two conveyance roller supporting portions  109   a,    109   b  are maintained, and as shown in FIG. 6, the bearing  109  can be formed as not to cover the top of the conveyance roller  108 . With such a bearing shape, assembling can be done by placing the conveyance roller  108  on the bearing  109 , so that the apparatus can enjoy merits on reduction of assembling costs and improvement on maintenance property.  
         [0066]    Although in this embodiment the pushing direction of the pinch roller  111  coincides to the gravity direction, it is not necessary to render these coincide to one another. This invention is easily applicable only by changing the direction of the exerting force vector caused from the pushing direction of the pinch roller  111  even where the pushing direction is inclined for the purpose for pushing the recording medium to a platen serving as a printing facing portion located on a conveyance downstream side, and this does not fall out of the scope of this invention.  
         [0067]    With respect to drive transmission, although in this embodiment the conveyance roller gear  110  receives only drive from the conveyance motor gear  107   a,  this invention is easily applicable merely where the conveyance roller gear  110  also serves as a transmitting means for transmitting drive to the delivery roller as well as the feeding means and merely where a load force vector (torque) exerts additionally even where a gear transmitting means is coupled as a load. With respect to drive transmission method, although the method is the gear transmission in this invention, but this invention is not limited to this, and is applicable to a belt transmission or friction transmission. In such a case, this invention is applicable easily onto a formula where the pressure angle α is changed corresponding to the transmission method or tension force of the belt is added. Although in this embodiment, the conveyance mechanism made of the conveyance roller  108  and the pinch roller  111  is described, this invention is easily applicable to a bearing structure for a conveyance mechanism made of the conveyance roller  108  (delivery roller) and spurs where the spurs are used in lieu of the pinch roller  111 . It is to be noted that the spur is a rotary body having small contact areas to the recording medium and not messing an ink image even where contacting to a surface side on which an ink image is recorded by ink discharge. In this embodiment, it is to be noted that the conveyance surface of the conveyance roller for the recording media and the bearing supporting portion are considered to have the same diameter, but a thinner (having smaller diameter) conveyance roller shaft than the conveyance roller  108  can be used.  
         [0068]    [Second Embodiment] 
         [0069]    [0069]FIG. 7 is a structural diagram of a conveyance roller shaft and a vicinity of a bearing showing features in the second embodiment of the invention as well as an illustration showing exerting force. The reference numbers and the signs as in the first embodiment indicate substantially the same meanings. In FIG. 7, in substantially the same manner, the conveyance roller  108  is supported at the shaft thereof to the two faces of the contact portions  109   a,    109   b  of the bearing  109 . In addition, in this embodiment, the relation between the bearing  109  and the chassis  1116  is, in substantially the same manner as above such that the bearing  109  is supported at the shaft thereof to the two faces of contact portions  116   a,    116   b  of the chassis  116 , thereby eliminating loosened states between the bearing  109  and the chassis  116 , and supporting the bearing  109  stably at a constant position with respect to the chassis  116 .  
         [0070]    The signs in FIG. 7 have the meanings as follows:  
         [0071]    Ft: force that the conveyance roller  108  exerts to the bearing  109  (Ft is an exerting vector sought from the vectors Fv 0  to Fv 1  exerting to the bearing  109  during each operation during the drive of the conveyance roller sought in the first embodiment);  
         [0072]    Fg 2 : weight of the bearing  109  (perpendicularly downward);  
         [0073]    Nc 1 , Nc 2 : opposing force of the chassis  116 ;  
         [0074]    Fct: for that the bearing  109  exerts to the chassis  116  (a resultant force of the force that the bearing  109  exerts to the chassis  116  and the gravity of the bearing  109 );  
         [0075]    θct: vector direction angle;  
         [0076]    θc 1 , θc 2 : contact positional angles between the conveyance roller  108  and the chassis  116 .  
         [0077]    The combined force of Nc 1  and Nc 2  is balanced with Fct as the combined vector of Ft and Fg 2 . Anglesθc 1 , θc 2  are determined from this vector Fct with the vector direction (θct) as a symmetric axis. More specifically, the contact positional angles θc 1 , θc 2  are determined so as to render the angle θct direction of the vector Fct coincide to a direction of vertically equally dividing line of the line segment coupling the two contact positions  116   a,    116   b.  No restriction exists about the angle of the contact positions  116   a,    116   b  of the chassis  116  in consideration of friction because the bearing  109  does not move rotationally at a space to the chassis  116 , but the angle is set largely to an extent not to render the bearing  109  bite the chassis  116  due to external force or not to render positional shafts or deformation of the bearing  109  occur.  
         [0078]    With this structure, during the stop and drive period of the conveyance roller  108 , loosened states not only between the conveyance roller  108  and the bearing  109  but also between the bearing  109  and the chassis  116 , can be eliminated, thereby ensuring the positional accuracy of the conveyance roller  108  with respect to the chassis  116 , and thereby improving further the conveyance accuracy. It is to be noted that in respect to the positional accuracy between the chassis  116  and the bearing  109  in this embodiment, in substantially the same manner as the first embodiment, it is effective to use determining methods giving the priority to the stopping state, applying Ft, Fct with weights, and shifting toward the exerting force vector at the stop state.  
         [0079]    Although in substantially the same manner as in the first embodiment the chassis  116  in this embodiment has the two surfaces supporting the bearing  109  as shown in FIG. 7 and has a shape in a letter of C orienting upward whose top is opened, a portion covering the top of the bearing  109  is not necessary because the portion functioning as a position setter for the bearing  109  is only the two supporting surfaces for bearing. For example, where the chassis  116  is made in a chassis shape as shown in FIG. 8, the apparatus can enjoy some merits such as reduction of assembling costs and improvement on maintenance property because assembling can be made only by placing the bearing  109  on the chassis  116 .  
         [0080]    [Third Embodiment] 
         [0081]    In regarding the third embodiment of the invention, FIG. 9 shows a structural diagram showing a conveyance roller shaft and the vicinity of a bearing. The reference numbers and the signs as in the first, second embodiments indicate substantially the same meanings. In the third embodiment, the contact positional angles θc 1 , θc 2  between the bearing  109  and the chassis  116  are set as equal to the contact positional angles θ1, θ2 between the conveyance roller  108  and the bearing  109  sought in the first embodiment. That is, the contact portions  109   a,    109   b  for bearing and the contact portions  106   a,    106   b  for the chassis  116  are set as located on the same line passing the center of the conveyance roller  118 . Actually, because in general the mass of the bearing  109  is adequately small in comparison with the mass of the conveyance roller  108 , the influence of the gravity Fg 2  of the bearing  109  is negligible.  
         [0082]    Because with this structure the exerting force that the bearing  108  receives from the conveyance roller  108  operates to the chassis  116  with the same angle, contraction load only exerts to the bearing  109 . Therefore, in a case that the bearing  109  is easily subject to load deformation or creep deformation, there are merits that deformation hardly occurs because of exertion of only the contraction load, and the apparatus can prevent the positions of the bearing  109  and the contact positions between the bearing  109  and the conveyance roller  108  due to deformation of the bearing  109  from changing. This structure therefore ensure the positional accuracy of the conveyance roller  108  with respect to external force and the chassis  116  during preservation, thereby improving further the conveyance accuracy.  
         [0083]    [Other Embodiments] 
         [0084]    In the above described embodiments, though a recording means of a serial type is used for description, such as a recording head secured to a carriage, a replaceable recording head of a chip type, upon an attachment to the carriage, in which ink can be supplied from an apparatus body and in which electrical connection can be made with the apparatus body, and a recording head of a cartridge type in which an ink tank is formed in a united body with the recording head, can be used.  
         [0085]    In addition, although in the above embodiment, the ink is described as a fluid, but can be an ink solidified at the room temperature or below as well as softened or fluidified at the room temperature, and be an ink fluidified at a time of application of recording signals in use because in the inkjet recording method it is general to control the temperature so that the ink&#39;s viscosity is set in a stably discharging range upon temperature adjustment of the ink itself in a range no less than 30° C. and no more than 70° C. Furthermore, this invention is applicable in a case that an ink is used having property that fluidified first by thermal energy such that fluid ink is discharged where ink is fluidified upon application of thermal energy in response to recording signals, where increased temperature by thermal energy is positively prevented by use of energy for phase change from the solid state to the fluid state in the ink, or where an ink solidified in a released state is used for the purpose of prevention of ink evaporation, or in any event, and that beginning to solidify already at a time reaching the recording sheet.  
         [0086]    As a feature of the inkjet recording apparatus as described above, apparatuses used as image output terminal apparatuses of information processing apparatuses such as computers or the like, photocopiers in combination of a reader or the like, facsimile machines having transmitting and receiving functions, can be used.  
         [0087]    It is to be noted that although described is an example using the inkjet recording method as a recording means as above, this invention&#39;s recording method is not limited to the inkjet recording method, and this invention is applicable to recording methods such as thermal transfer recording method, thermal sensing recording method, impact recording methods such as wire-dot recording methods, and any other recording methods. This invention is not necessarily limited to the serial recording method, and a so-called line recording method can be used for the invention.