Abstract:
A tube for supplying a fluid therethrough having a base wall and an enlarged wall is provided. The base wall is outside a first closed line segment which defines an inside of the inner surface of the tube and is inside a second closed line segment which is similar to the first closed line segment and encloses the first closed line segment with a gravity center of the second closed line segment coincident with a gravity center of the first closed line segment. And the enlarged wall is outside the second closed line segment and is inside a third closed line segment which encloses the second closed line segment, wherein either the third closed line segment is dissimilar to the second closed line segment or a gravity center of the third closed line segment is different from that of the second closed line segment.

Description:
CROSS-REFERENCE OF RELATED APPLICATION  
       [0001]     This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2005-328727 in Japan on Nov. 14, 2005, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND  
       [0002]     The present invention relates to a tube and a method of using the same for supplying a fluid.  
         [0003]     A tube (An ink tube) for supplying an ink has commonly a circular form in the cross section of which both the inner and outer surfaces are concentric, as disclosed in Japanese Patent Application Laid-Open No. 10-278289 (See  FIG. 1 ).  
       BRIEF SUMMARY  
       [0004]     When a wall of an ink tube is gas permeable, water in the ink may often be evaporated and escaped from the ink tube. As the result, the ink will be increased in viscosity. Alternatively, air which intrudes into the ink tube from the outside dissolves in the ink, so that the ink declines in quality.  
         [0005]     For attenuating the gas permeability of the ink tube, it is a good idea to increase the thickness of the wall of the ink tube. In order to realize a ink tube which is less gas permeability that the ink tube having the cross section shown in  FIG. 3A , the thickness of the wall may increase while its inner and outer surfaces remaining concentric as shown in  FIG. 3B .  
         [0006]     However, when its thickness is only increased as shown in  FIG. 3B , the ink tube can be bent in all the directions in the same way with difficulty and not applied while remaining bent such as ink tubes  100   a  to  100   d  shown in  FIG. 1 . Further, since the ink tube having been increased in thickness becomes greater in resistance to tensile stress or compression stress when being bent, in the case of remaining a bent form for a long time, the ink tube may deteriorate in quality.  
         [0007]     It is an object to provide an ink tube being suitable for use in a bent form and lower in both deterioration in the case of remaining the bent form for a long time and in the gas permeability.  
         [0008]     An ink tube according to one aspect is a tube for supplying a fluid therethrough, comprising: a base wall, from the viewpoint of the cross section vertical to a longitudinal direction of the tube, being outside a first closed line segment which defines an inside of the inner surface of the tube and being inside a second closed line segment which is similar to the first closed line segment and encloses the first closed line segment with a gravity center of the second closed line segment coincident with a gravity center of the first closed line segment; and an enlarged wall, from the viewpoint of the cross section vertical to the longitudinal direction of the tube, being outside the second closed line segment and being inside a third closed line segment which encloses the second closed line segment, wherein either the third closed line segment is dissimilar to the second closed line segment and a gravity center of the third closed line segment is coincident the gravity center of the second closed line segment or the third closed line segment is similar to the second closed line segment and a gravity center of the third closed line segment is different from the gravity center of the second closed line segment.  
         [0009]     The aspect has the following advantages. In the case where either the third closed line segment is not similar to the second closed line segment and the gravity center of the third closed line segment is coincident that of the second closed line segment or the third closed line segment is similar to the second closed line segment and the gravity center of the third dosed line segment is different from that of the second closed line segment, the enlarged wall at the cross section is biased in either of the two opposite directions. Therefore, when the ink tube is bent in one of the two opposite directions, the maximum of the compression stress or the tensile stress received at the outer surface becomes smaller than when it is bent in the other direction. Accordingly, the ink tube can selectively be bent in such a direction that the compression stress or the tensile stress to be received is minimized. Further, since the ink tube having the enlarged wall is greater in the size of the cross section than any ink tubes having only a base wall, it can be improved in vapor barrier property and gas barrier property between the inside and the outside of the ink tube.  
         [0010]     The above and further objects and features will more fully be apparent from the following detailed description with accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0011]      FIG. 1  shows a top view of the interior of a printer in which ink tubes according to an embodiment are used;  
         [0012]      FIG. 2  shows a top view of the ink tube shown in  FIG. 1  in actual use;  
         [0013]      FIGS. 3A  to  3 E show cross sectional views of ink tubes showing prior arts and three embodiments;  
         [0014]      FIGS. 4A and 41  show top views of one in actual use of the ink tubes of the embodiments shown in  FIGS. 3A  to  3 E; and  
         [0015]      FIGS. 5A  to  5 K show cross sectional views of ink tubes showing the other embodiments. 
     
    
     DETAILED DESCRIPTION  
       [0016]     Some embodiments will be described below. First, an ink jet printer equipped with ink tubes will be described. Next, ink tubes according to a preferred embodiment will be described in more detail.  
         [0000]     (Concept of Printer)  
         [0017]      FIG. 1  illustrates an ink jet printer  1  (printer) equipped with ink tubes.  FIG. 1  is a top view showing the interior of the printer  1 .  
         [0018]     The printer  1  includes two guide shafts  6  and  7  therein. A head unit  8  is mounted on the guide shafts  6  and  7  as a carriage for traveling forward and backward along a primary scanning direction. The head unit  8  has a head holder  9  made of a synthetic resin material. The head holder  9  holds an ink jet head  30  for delivering a jet of ink onto a sheet of printing paper P which is conveyed beneath the head unit  8 .  
         [0019]     The printer  1  includes a carriage motor  12 . An endless belt  11  is mounted on the driving shaft of the carriage motor  12  and can thus rotate by driving of the carriage motor  12 . The head holder  9  is linked to the endless belt  11  and can be moved forward and backward along the primary scanning direction by rotating of the endless belt  11 .  
         [0020]     The printer  1  includes a set of ink cartridges  5   a,    5   b,    5   c,  and  6   d.  The ink cartridges  5   a,    5   b,    5   c,  and  5   d  contain yellow ink, magenta ink, cyan ink, and black ink respectively. The ink cartridges  5   a,    5   b,    5   c,  and  5   d  are joined at one end to ink tubes  100   a,    100   b,    100   c,  and  100   d  respectively. The other ends of the ink tubes  100   a  to  100   d  are joined to a tube joint  20  mounted on the head unit  8 . The inks in the ink cartridges  5   a  to  5   d  are supplied via the corresponding ink tubes  100   a  to  100   d  to the ink head  8 . The inks received by the ink head  8  are transferred along an ink passages provided in the head unit  8  to the ink jet head  30  and delivered from their respective nozzles, not shown, of the ink jet head  30  onto the printing paper P. In the present embodiment, the ink tubes are made of a particular material such as natural rubber which is higher in the resistance to compression stress than to tensile stress (that is, having resistance properties).  
         [0000]     (Use of Ink Tubes)  
         [0021]      FIG. 2  illustrates an action of using the ink tubes in the printer  1 . One  100   b  of the four ink tubes  100   a  to  100   d  is shown in  FIG. 2  while the other tubes are identical in the arrangement.  
         [0022]     As described, the head unit  8  travels forward and backward along the primary scanning direction. The ink tube  100   b  is arranged to a generous length for inhibiting from being bent at acute angles or entangled with the others regardless of the location of the head unit  8 . As shown in  FIG. 2 , the ink tube  100   b  is joined between the head unit  8  and the ink cartridge  5   b  so that it can be curved in one direction in relation to the primary scanning direction when the head unit  8  travels forward and backward.  
         [0023]     In this way, the ink tubes  100   a  to  100   d  are set up in the printer  1  while remaining in arcuate forms along uniform directions for a long time.  
         [0024]     When water in the ink is evaporated, the viscosity of the ink will increase. If worse, the ink to be delivered as a jet may choke the nozzle. Alternatively, when the delivery of the ink is varied in the speed or the amount, its printing image will be declined in quality. Moreover, air may be dissolved into the ink, and thus the ink is declined in quality. As the result, the amount of the ink to be delivered will be changed and thus repeatability of its printing image is declined. When the ink tube is higher in the gas permeability through its wall, water in the ink may be evaporated to easily immigrate from the ink tube to the outside. The air may sneak into the ink tube from the outside and be easily dissolved into the ink in the ink tube.  
         [0000]     (Details of Ink Tube)  
         [0025]      FIGS. 3A  to  3 E show cross sectional views vertical to the longitudinal direction of the ink tubes in various ink tubes, for example, taken along the line III-III of  FIG. 2  vertically and lengthwisely. The ink tube shown in  FIG. 3A  has an inner surface  108   a  and an outer surface  109   a  which have a concentric circle. The ink tube shown in  FIG. 3B  has an inner surface  108   b  having same size and form as the inner surface  108   a  and an outer surface  109   b  having a same concentric as the inner surface  108   b.  The outer surface  109   b  is greater in size than the outer surface  109   a.  Accordingly, the thickness  104   b  of the wall of the ink tube shown in  FIG. 3B  is greater than the thickness  104   a  of the wall of the ink tube shown in  FIG. 3A . Therefore, the ink tube shown in  FIG. 3B  is lower in the gas permeability than the ink tube shown in  FIG. 3A . Since the thickness of its wall is increased while the inner surface and the outer surface remain concentric, the ink tube can be minimized in the gas permeability.  
         [0026]     However, since the ink tube shown in  FIG. 3B  is less flexible in each direction than the ink tube shown in  FIG. 3A , its application to a bent form such as shown in  FIG. 2  will be unfavorable. When the ink tube shown in  FIG. 3B  is bent, its greater thickness will increase the resistance to compression stress or tensile stress to a higher level than that of the ink tube shown in  FIG. 3A . For example, when the ink tube shown in  FIG. 3B  is bent to be convex towards a direction vertical to the line  101   b,  its receiving stress at the point  110   b  on the outer surface is greater than that at the point  110   a  on the outer surface of the ink tube shown in  FIG. 3A  which is bent to be convex towards a direction vertical to the line  101   a.  As the ink tube is remained for a long time with such a greater stress remaining urged, its quality will be possibly deteriorated.  
         [0027]      FIGS. 3C, 3D , and  3 E illustrate modifications of the ink tube which are lower in the gas permeability the ink tube shown in  FIG. 3A  and suited for use in bent forms. The constructions of the ink tubes of the embodiment will be explained below. Their base wall parts  105   c,    105   d,  and  105   e  are similar to the wall of the ink tube shown in  FIG. 3A . That is, the base walls  105   c,    105   d,  and  105   e  have the cross section composed of regions between the inner surface (a first closed line segment)  108   c  and its corresponding concentric circle (a second closed line segment)  107   c,  between the inner surface  108   d  and its corresponding concentric circle  107   d,  and between the inner surface  108   e  and its corresponding concentric circle  107   e,  respectively.  
         [0028]     The ink tubes have enlarged wall parts  106   c,    106   d,  and  106   e  thereof, respectively, which are enlarged in the thickness. Among them, the enlarged walls  106   c  and  106   d  have the cross section composed of regions between the concentric circle  107   c  and the outer surface  109   c  (a third closed line segment) which is not similar to the circle  107   c  and between the concentric circuit  107   d  and the outer surface  109   d  which is not identical in the size and form to the circle  107   c.  The enlarged wall  106   e  has the cross section composed of a region between the concentric circle  107   e  and the outer surface  109   e  (a third closed line segment) which is similar but not equal in the center to the circle  107   e.  In  FIG. 3C , the outer surface  109   c  is equal in the gravity center to the circle  107   c.  In  FIG. 3D , the outer surface  109   d  is not equal in the gravity center to the circle  107   d.    
         [0029]     Since the ink tubes are arranged in the construction as shown in  FIGS. 3C  to  3 E, their enlarged walls are biased in at least one direction from the gravity center of the base wall at the cross section, More specifically, the enlarged walls  106   c  of the ink tube shown in  FIG. 3C  are biased in two opposite directions which extend in parallel with the line  102   c.  The enlarged walls  106   d  of the ink tube shown in  FIG. 3D  are biased from the gravity center of the base wall in two directions which extend across two divisions out of the four divisions divided by the two lines  102   d  and  103   d.  The enlarged wall  106   e  of the ink tube shown in  FIG. 3E  is biased in a direction which extends in parallel with the line  103   e.  The ink tubes shown in  FIGS. 3C, 3D , and  3 E are thickened in the wall as compared with the base wall of the ink tube, thus being low in the gas permeability.  
         [0030]     When the ink tubes shown in  FIGS. 3C  to  3 E are bent to be convex in two different directions A and B, their receiving stresses are different between the two directions A and B. For example, when the ink tube shown in  FIG. 3D  is bent to be convex in the direction B, its receiving stress becomes maximum at two points  111   d  and  112   d  on the outer surface  109   d.  More particularly, the tensile stress is received at the point  111   d  while the compression stress is received at the point  112   d.    
         [0031]     Alternatively, when the ink tube shown in  FIG. 3D  is bent to be convex in the direction A, it receives a maximum of the compression stress at a point  113   d  on the outer surface  109   d  and a maximum of the tensile stress at a point  114   d.  Since the distance between the point  114   d  and the line  102   d  or the neutral axis is shorter than the distance between the point  113   d  and the line  102   d,  the stress received at the point  114   d  is smaller than that at the point  113   d.    
         [0032]     As described, the stress is different between the two directions A and B in which the ink tube is bent to be convex. Further, smaller one of two levels of the stress received at the two points, one (the point  113   d  in the above description) where a maximum of the compression stress is received and the other (the point  114   d  in the description) where a maximum of the tensile stress is received, when the ink tube has been bent to be convex in the direction A is smaller than smaller one of the two levels of the stress received at the two points ( 111   d  and  112   d  in the description, where the two points  111   d  and  112   d  are equal in the distance from the neutral axis or the line  113   d  and thus equal in the receiving stress and the smaller stress may be received at either of the two points), one where a maximum of the compression stress is received and the other where a maximum of the tensile stress is received, when the ink tube has been bent to be convex in the direction B.  
         [0033]     Consequently, the ink tube shown in  FIG. 3D  receives a smaller level of the stress at the outer surface when it is bent to be convex in the direction A than when it is bent to be convex in the direction B during the service in its bent form. Further, when the ink tube shown in  FIG. 3D  is bent to be convex in the direction A, its receiving stress is smaller at the point  114   d  than at the point  113   d.  It is hence preferable that the ink tube made of a particular material which is higher in the resistance to compression stress than to tensile stress is arranged to be bent so that it can receive the tensile stress at the point  114   d  on its outer surface. When the ink tube is made of a particular material which is higher in the resistance to tensile stress than to compression stress, it is then arranged to be bent (to be convex in the direction opposite to the direction A) so that it can receive the compression stress at the point  114   d  on its outer surface. This allows the ink tube to ease the stress with the action of its material for a long time in its bent form, hence minimizing the deterioration of the equality.  
         [0034]     Similarly, the ink tube shown in  FIG. 3E  receives a stress smaller at the point  114   e  (of which the distance from the line  102   e  at the neutral axis is shorter than that of the point  113   e ) where the maximum of either the compression stress or the tensile stress becomes smaller when it has been bent to be convex in the direction A than at the point  111   e  (where the stress received is equal to that received at the point  112   e  and the smaller stress may be received at either of the two points  111   e  and  112   e ) where the maximum of either the compression stress or the tensile stress becomes smaller when it has been bent to be convex in the direction B. This is explained by the fact that the distance between the point  114   e  and the line  102   e  at the neutral axis is shorter than the distance between the point  111   e  and the line  103   e  at the neutral axis. Accordingly, when the ink tube shown in  FIG. 3E , like the ink tube shown in  FIG. 3D , is used in its bent form so that it projects in the direction A while adjusting depending on its material whether the stress received at the point  114   e  is the tensile stress or the compression stress, it can be minimized in the deterioration of the quality.  
         [0035]     The ink tube shown in  FIG. 3C  is similar. The ink tube receives a stress smaller at the point  113   c  (where the stress received is equal to that received at the point  114   c  and the smaller stress may be received at either of the two points  113   c  and  114   c ) where the maximum of either the compression stress or the tensile stress becomes smaller when it has been bent to be convex in the direction A than at the point  111   c  (where the stress received is equal to that received at the point  112   c  and the smaller stress may be received at either of the two points  111   c  and  112   c ) where the maximum of either the compression stress or the tensile stress becomes smaller when it has been bent to be convex in the direction B. This is explained by the fact that the distance between the point  113   c  and the line  102   c  at the neutral axis is shorter than the distance between the point  111   c  and the line  103   c  at the neutral axis. Accordingly, when the ink tube shown in  FIG. 3C , like the ink tube shown in  FIG. 3D , is uses in its bent form so that it projects in the direction A during a long time, it can be minimized in the deterioration of the quality. Since the stress received at the point  113   c  is equal to that received at the point  114   c,  the ink tube shown in  FIG. 3C  may be used while remaining beat to be convex in the direction opposite to the direction A.  
         [0036]     Meanwhile, the gas barrier property of the ink tube indicating whether or not gas is highly permeable depends on the wall size at the cross section of the enlarged walls of the ink tube. Assuming that the gas barrier property or the wall size at the cross section is equal, the ink tube shown in  FIG. 3D  among the three ink tubes shown in  FIGS. 3C  to  3 E is capable of being bent so that the maximum of either the compression stress or the tensile stress is the smallest. More particularly, the distance between the point  114   d  and the line  102   d  at the neutral axis is shorter than both the distance between the point  113   c  and the line  102   c  and the distance between the point  114   e  and the line  102   e.    
         [0037]     The ink tube shown in  FIG. 3C  is capable of being bent so that the maximum of either the compression stress or the tensile stress is the second smallest. The distance between the point  113   c  and the line  102   c  is shorter than the distance between the point  114   e  and the line  102   e.  However, the distance between the point  113   e  and the line  102   c  may be longer than the distance between the point  114   e  and the line  102   e  when the ink tubes shown in  FIGS. 3C and 3E  are in the wall thickness of the enlarged walls. The distance between the point  113   c  and the line  102   c  is equal to the distance between the point  110   a  and the line  101   a  in the ink tube shown in  FIG. 3A . In other words, the ink tube shown in  FIG. 3C  can selectively be bent so that it receives the maximum of the stress equal to that in the ink tube shown in  FIG. 3A .  
         [0038]     In the ink tube shown in  FIG. 3C , the gravity center of the inner surface  108   c  coincident the gravity center of the outer surface  109   c.  As the result, the ink tube shown in  FIG. 3C  is balanced in the form and can thus be installed in a stable manner.  
         [0039]     Each of the ink tubes shown in  FIGS. 3C and 3D  is symmetric about the symmetry axis. More specifically, the ink tube shown in  FIG. 3C  is symmetric about both the line  102   c  and the line  103   c  while the ink tube shown in  FIG. 3D  is symmetric about the line  103   d.  This allows the ink tubes to be manufactured with much ease.  
         [0040]     The ink tubes shown in  FIGS. 3C  to  3 E have their boundary circles  107   c  to  107   e  between the base wall and the enlarged wall arranged to overlap partially with the outer surfaces  109   c  to  109   e,  respectively. It is therefore clear that the enlarged walls are biased. This allows the ink tube to be bent to be convex in a desired direction A, for example, so that the line  102   d  at the neutral axis becomes closer to the enlarged walls. Accordingly, the distance between the neutral axis and the point ( 114   d ) where either the tensile stress or the compression stress is received at the maximum can be minimized, thus declining the intensity of the stress.  
         [0041]     In the ink tubes shown in  FIGS. 3C and 3D , the outer surfaces include locally linear lines. Accordingly, the ink tubes can easily be bent to be convex in a specific direction (the direction A in this embodiment) vertical to the linear lines which are parts of the outer surfaces.  
         [0042]     The ink tube shown in  FIG. 3E  is different from the ink tube shown in  FIG. 3B  by the fact that the gravity center of the inner surface is biased in one direction. Accordingly, the ink tube shown in  FIG. 3E  can simply be manufactured by shifting the location of the molding center while the ink tube shown in  FIG. 3B  is manufactured by molding a cylindrical material in molds. In other words, the ink tubes shown in  FIG. 3E  can be manufactured using a simple process.  
         [0043]     The gas barrier property of the ink tube depends on the wall size of the cross section. When the ink tubes are identical in the wall size at the cross section, they are uniform in the gas permeability. It is sufficient for the ink tubes shown in  FIGS. 3C  and  3 D being equal in the gas barrier property to the ink tube shown in  FIG. 3B  is equal in the wall area to the sum at the cross section of the base wall and the enlarged walls. Accordingly, the ink tubes like the ink tube shown in  FIG. 3B  can be used in the bent form while remaining high in the gas barrier property.  
         [0000]     (Optimum Use of Ink Tubes)  
         [0044]      FIGS. 4A and 4B  illustrate an optimum action of using any of the ink tubes shown in  FIGS. 3C  to  3 E in the printer  1 . In the printer  1 , the ink tubes are used in a bent sate in the same direction as shown in  FIG. 2 . When the ink tube  100  has such a cross section as shown in  FIG. 3D , it can be bent so that the neutral axis  102   d  extends vertical to of the drawing sheet and across a one-dot chain line An as being closer to the direction D 2  which extends outwardly of the bent. Particularly, in a cross section along a dashed line in  FIG. 4A , the ink tube  100  is arranged flexible so that the direction A shown in  FIG. 3D  coincident the direction outwardly of the bent.  
         [0045]     As the ink tube  100  is arranged in such a manner, the maximum of its receiving stress becomes smaller than when the ink tube is bent to be convex in the direction B. Accordingly, the bent side of the ink tube  100  has the point  114   d  designated at the outer surface and the point  113   d  designated at the inner surface. In the action of the ink tube  100 , the maximum of the tensile stress at the point  114   d  is smaller than the maximum of the compression stress at the point  113   d.  When installed in the printer  1 , the ink tube  100  which is higher in the resistance to compression stress than in the resistance to tensile stress can easily be bent and minimized in the deterioration of the quality.  
         [0046]      FIG. 4B  illustrates the ink tube  100  remaining bent at the region A 1  as shown in  FIG. 4A . As shown in  FIG. 4B , the ink tube  100  can be installed so that its bent region A 1  bent in such a direction as shown in  FIG. 4A  becomes wider along the longitudinal direction than the region A 2  bent in the opposite direction. The bent region of the ink tube  100  curved in such a direction that the maximum of the tensile stress is smaller than the maximum of the compression stress becomes greater in the size than the other region curved in such a direction that the maximum of the tensile stress is larger than the maximum of the compression stress. More specifically, since its region highly resistive to the deterioration is wider than the region less resistive to the same, the ink tube  100  can be minimized in the deterioration of the quality.  
         [0000]     (Other Modifications)  
         [0047]      FIGS. 5A  to  5 K are cross sectional views showing other modifications of the ink tube. More particularly,  FIGS. 5A, 5E , and  5 I illustrate the ink tubes with no enlarged walls while  FIGS. 5B  to  5 D,  5 F to  5 H,  5 J, and  5 K illustrate the ink tubes with enlarged walls. The ink tubes include the base walls  205   b  to  205   d,    205   f  to  205   h,    205   j,  and  205   k  respectively. Further, the ink tubes include the enlarged walls  206   b  to  206   d,    206   f  to  206   h,    206   j,  and  206   k  respectively.  
         [0048]     The ink tubes may be arranged of polygonal forms at both the inner surface and the outer surface. As shown in  FIGS. 5B  to  5 D, the base walls  205   b  to  205   d  are defined at the cross section between the inner surfaces  208   b  to  208   d  of a square form and the outer surfaces  207   b  to  207   d  of a square form of which the gravity center is equal to that of the square form of the inner surfaces  208   b  to  208   d.  As shown in  FIGS. 5F  to  5 H, the base walls  205   f  to  205   h  are defined at the cross section between the inner surfaces  208   f  to  208   h  of a regular hexagonal form and the outer surfaces  207   f  to  207   h  of a regular hexagonal form of which the gravity center is equal to that of the regular hexagonal form of the inner surfaces  208   f  to  208   h.    
         [0049]     In  FIGS. 5B and 5F , the enlarged walls  206   b  and  206   f  are defined as a form between the outer surfaces  209   b  and  209   f  of the base walls  205   b  and  205   f  and the outer surfaces  209   b  an  209   f  and are equal in the gravity center to the base walls  205   b  and  205   f,  respectively.  
         [0050]     In  FIGS. 5C and 5G , the enlarged walls  206   c  and  206   g  are defined as a form between the outer surfaces  209   c  and  209   g  of the base walls  205   c  and  205   g  and the outer surfaces  209   c  an  209   g  and are not equal in the gravity center to the base walls  205   c  and  205   g,  respectively.  
         [0051]     In  FIGS. 5D and 5H , the enlarged walls  206   d  and  206   h  are defined as a form between the outer surfaces  209   d  and  209   h  of the base walls  205   d  and  205   h  and the outer surfaces  209   d  an  209   h  and are not equal in the gravity center to the base walls  205   d  and  205   h  respectively. The outer surfaces  209   d  and  209   h  are identical in the form at the cross section to the inner surfaces  208   d  and  208   h,  respectively.  
         [0052]     Moreover, the inner surfaces and the outer surfaces of the ink tubes are not limited to the circle, the regular polygonal form, or the symmetric form described above. For example, the ink tubes may be arranged of arbitrary forms with no symmetric axis or point as shown in  FIGS. 5I  to  5 K. The ink tubes shown in  FIGS. 5J and 5K  have base walls  305   j  and  305   k  which are defined between the inner surfaces  308   j  and  308   k  arranged of non-symmetric forms and the closed line segments  309   j  and  309   k  respectively of which the forms are equal in the gravity center to the forms of the inner surfaces  308   j  and  308   k.  The base wall  305   j  of the ink tube shown in  FIG. 5J  is accompanied with enlarged walls  306   j  which are defined between the outer surface  309   j  of the base wall  305   j  and the outer surface  309   j  and are equal in the gravity center to the base wall  305   j.  The base wall  305   k  of the ink tube shown in  FIG. 5K  is accompanied with enlarged walls  306   k  which are defined between the outer surface  309   k  of the base wall  305   k  and the outer surface  309   k  and are not equal in the gravity center to the base wall  305   k.  The outer surface  309   k  is identical in the form at the cross section to the inner surface  308   k.    
         [0053]     In the ink tubes shown in  FIGS. 5B  to  5 D and  5 F to  5 H, smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tubes are bent to be convex in the direction A is smaller than smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tubes are bent to be convex in the direction B. The lines  202   b  to  202   d  and  202   f  to  202   h  in the drawings are the neutral axes along which the ink tubes are bent to be convex in the direction A. Further, the lines  203   b  to  203   d  and  203   f  to  203   h  are the neutral axes along which the ink tubes are bent to be convex in the direction B.  
         [0054]     In the ink tubes shown in  FIGS. 5J and 5K , smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tubes are bent to be convex in a direction A′ is smaller than smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tubes are bent to be convex in a direction B′. The lines  303   j  and  303   k  in the drawings are the neutral axes along which the ink tubes are bent to be convex in the direction A′. Further, the lines  302   j  and  302   k  are the neutral axes along which the ink tubes are bent to be convex in the direction B′.  
         [0055]     The ink tube may further be in which the first closed line segment forms preferably a circle. Since its inner surface at the cross section is circular, the ink tube can permit the ink to flow easily. Further, the ink tube is equal in the form of the cross section to any conventional ink tube and can thus be manufactured by a known manner.  
         [0056]     The ink tube may further be in which the first closed line segment forms a polygon. Since its inner surface at the cross section is polygonal, the ink tube can be increased in the strength against bending to be convex in a direction along the cross section.  
         [0057]     In one aspect, the ink tube may be modified in which the third closed line segment and the second closed line segment are similar to each other. Since the cross section of its outer surface is similar to that of the inner surface, the ink tube can be simpler in the overall form. Accordingly, the ink tube can thus be manufactured by a simple manner.  
         [0058]     The ink tube may further be in which the gravity center of the second closed line segment is equal to the gravity center of the third closed line segment. Since its outer and inner surfaces at the cross section are equal to each other in the gravity center, the ink tube becomes stable in the form and easy for installation.  
         [0059]     The ink tube may further be in which the third closed line segment is arranged symmetric about a line extending across the gravity center of the first closed line segment. Since its outer surface at the cross section is symmetric, the ink tube can be manufactured with much ease.  
         [0060]     The ink tube may further be in which the second closed line segment and the third closed line segment are arranged overlapping partially with each other. Since its wall is certainly separated between the base part and the enlarged wall, the ink tube can increase a difference between the maximum of the tensile stress and the maximum of the compression stress when being bent to be convex in a desired direction along the cross section.  
         [0061]     The ink tube may further be in which the third closed line segment is preferably composed of arcuate parts and linear parts. Since its outer surface at the cross section includes linear parts, the ink tube can be bent with much ease.  
         [0062]     The ink tube may further be modified, in another point of view, in which the form at the cross section is arranged vertical to the longitudinal direction of the ink tube to define two different directions A and B which satisfy (a) the requirement that the two directions extend along the cross section arranged vertical to the longitudinal direction of the ink tube and (b) the requirement that smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tube is bent to be convex in the direction A is smaller than smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tube is bent to be convex in the direction B. The maximum of either the tensile stress or the compression stress received at the outer surface of the ink tube becomes smaller when the ink tube is bent to be convex in the direction A along the cross section than when the same is bent to be convex in the direction B. Accordingly, the ink tube can selectively be bent so that the maximum of either the tensile stress or the compression stress is minimized.  
         [0063]     The ink tube may further be in which the form at the cross section is arranged vertical to the longitudinal direction of the ink tube to define two different directions A and B which satisfy (a) the requirement that the two directions extend along the cross section arranged vertical to the longitudinal direction of the ink tube and (b) the requirement that smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tube is bent to be convex in the direction A is smaller than smaller one of the maximum of the tensile stress and the maximum of the compression stress received at the outer surface when the ink tube is bent to be convex in the direction B, provided that the maximum of the compression stress received at the outer surface when the ink tube is bent to be convex in the direction A is different from the maximum of the tensile stress received at the outer surface.  
         [0064]     Accordingly, the maximum of either the tensile stress or the compression stress received at the outer surface of the ink tube becomes smaller when the ink tube is bent to be convex in the direction A along the cross section than when the same is bent to be convex in the directions B. Accordingly, the ink tube can selectively be bent so that the maximum of either the tensile stress or the compression stress is minimized. Moreover, the ink tube can selectively be bent to be convex in either the direction A or the direction opposite to the direction A, depending on the material of the ink tube which is highly resistant to the tensile stress or the compression stress. This allows the ink tube to be bent selectively depending on its material and held at its bent form with a minimum of deterioration.  
         [0065]     A method of using the ink tube described above is also provided involving, when the ink tube is made of a material which is highly resistant to compression stress rather than tensile stress, bending the ink tube to be convex in either the direction A or the direction opposite to the direction A so that a region at the cross section of the ink tube satisfying the requirement that the maximum of the tensile stress received at the outer surface of the ink tube is smaller than the maximum of the compression stress received at the outer surface becomes greater in the area along the longitudinal direction of the ink tube than the other region failing to satisfy the requirement. Accordingly, when the ink tube is made of a material highly resistant to the compression stress, it can be used while receiving a smaller level of the tensile stress than that of the compression stress. This allows the ink tube to be deteriorated to minimum.  
         [0066]     Another method of using the ink tube described above is provided involving, when the ink tube is made of a material which is highly resistant to tensile stress rather than compression stress, bending the ink tube to be convex in either the direction A or the direction opposite to the direction A so that a region at the cross section of the ink tube satisfying the requirement that the maximum of the compression stress received at the outer surface of the ink tube is smaller than the maximum of the tensile stress received at the outer surface becomes greater in the area along the longitudinal direction of the ink tube than the other region failing to satisfy the requirement. Accordingly, when the ink tube is made of a material highly resistant to the tensile stress, it can be used while receiving a smaller level of the compression stress than that of the tensile stress. This allows the ink tube to be deteriorated to minimum.  
         [0000]     (Other Embodiments)  
         [0067]     The preferred embodiments are described above. However, it is not limited to the preferred embodiments above and various changes may be made without departing from claims.  
         [0068]     For example, the ink tube is applied to an ink jet printer of which the print head is moved along the primary scanning direction in relation to a sheet of printing paper. The ink tube is also applicable to another type of ink jet printer where the print head is fixed along the primary scanning direction in relation to a sheet of printing paper. The delivery of ink from the ink jet printer head may be conducted by any known technique.  
         [0069]     The ink tube is not limited to the above described forms and may be arranged of any possible form at the cross section forms such as an oval form or an irregular polygonal form.  
         [0070]     As this description may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope is defined by the appended claims rather than by description preceding them, and all changes that fall within metes and bounds of the claims or equivalence of such metes and abounds thereof are therefore intended to be embraced by the claims.