Abstract:
Disclosed is a cannula that can decrease the rate of increase in resistance that is generated when penetrating an incision formed in tissue. The cylindrical cannula ( 1 ) configures a trocar (B) used during surgery; an incision member (C) can be inserted and removed therewithin; one side of the end portion of the cylinder forms a protruding slanted cut end ( 2 ); and a tapered surface ( 3 ) having an uneven width and a width that is wider on the protruding side (the side of point  2   a ) of the slanted cut end than the non-protruding side (the side of point  2   b ) is formed on the outer periphery of the slanted cut end ( 2 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a cannula, which constitutes a trocar inserted through tissue in surgery and forming a passage through which surgical instruments and tubes for injecting chemicals reach an affected area, and a method of manufacturing the cannula. 
       BACKGROUND ART 
       [0002]    A trocar is adapted to have a tubular cannula. A portion of body surface tissue is cut out to make the cannula penetrate and, thus, to arrange the cannula, so that the trocar forms a passage for passing surgical instruments and light fixture required for surgery for the affected area or tubes for injecting chemicals. 
         [0003]    In an ophthalmic vitreous surgery, for example, there are used a plurality of trocars including a trocar for inserting a tube for injecting saline for keeping eye pressure, a trocar for inserting surgical instruments typified by forceps and scissors for incising and removing the affected area, and a trocar for inserting a probe for irradiating laser beam to the affected area. Those trocars are penetrated through a hole formed by incising a conjunctiva and a sclera to insert an end of a cannula into a vitreous body, necessary instruments and tubes are inserted in this state, and intended surgery is performed. 
         [0004]    As described above, although it is essential to incise a conjunctiva and a sclera in vitreous surgery, the diameter of a cannula is extremely small, and therefore, a cutting instrument is previously inserted through inside the cannula, a conjunctiva and a sclera are incised by the cutting instrument, and then the cannula is inserted into a vitreous body. After the cannula is inserted into the vitreous body, only the cutting instrument is drawn out to leave the cannula. 
         [0005]    In eye surgery, in order to reduce a period required for curing, an incised portion can be closed without suturing. Thus, the invention described in Patent Document 1 is proposed. In this technique, a conjunctiva and/or a sclera can be saved so that an opening (incisional wound) formed within the eye for the execution of intraocular surgical procedures can be closed by the tissue of the opening after the surgical procedures. With the technique, a small opening is realized by using a surgical instrument whose operable end has such an extremely small diameter as 20 to 27 gauges, so that the tissue of the opening can be closed. 
         [0006]    In the above trocars, the end of the cannula through which the cutting instrument is inserted is formed in a state of being cut at right angles with respect to an axis line. Namely, the thickness of the cannula as a flat surface is exposed at the end of the cannula. Thus, the end of the cannula is screwed into and penetrates through a conjunctiva and a sclera incised by the cutting instrument. Accordingly, the tissues around the incisional wound may be dissected. If the tissues are dissected, a problem that it takes time to cure completely may occur. 
         [0007]    In order to solve the problems, the invention described in Patent Document 2 is proposed. In this technique, an oblique cut surface is formed at the end of the cannula constituting the trocar, and the oblique cut surface is formed into a tapered shape. In the technique, the oblique cut surface formed at the end of the cannula has an inclined surface corresponding to the taper from the inner peripheral surface side of the cannula toward the outer peripheral surface side. 
         [0008]    Thus, in order to have the cannula penetrate through an incisional wound formed in tissue by a cutting instrument mounted to the cannula, the cutting instrument and the tapered portion formed at a pointed portion of the oblique cut surface are first passed through the incisional wound. After that, a thick portion of the taper is passed through the incisional wound while following the inclination of the oblique cut surface. Namely, since the cannula penetrates through the incisional wound so that the incisional wound is pushed and opened by the oblique cut surface and the taper, there is no possibility that the tissue is dissected. 
       PRIOR ART DOCUMENTS 
     Patent Documents 
       [0000]    
       
         Patent Document 1: Japanese Patent Application National Publication (Laid-Open) No. 2003-526461 
         Patent Document 2: Japanese Patent Application Laid-Open No. 2008-142533 
       
     
       DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0011]    In the cannula constituting the trocar described in the Patent Document 2, when the cannula penetrates through an incisional wound formed in tissue, there is no possibility that the tissue is dissected. However, even this technique is not complete yet, and there are some problems to be improved. 
         [0012]    For example, since the taper formed on the oblique cut surface formed at the end of the cannula is formed on the basis of the central axis of the oblique cut surface, there is increased the angle of the tapered surface at the end of the cannula relative to an axial center of a cylindrical body constituting the cannula. Therefore, there is increased the rate of the increase in diameter with respect to the length that the oblique cut surface passes through the incisional wound when the cannula is penetrated through the incisional wound. Accordingly, the rate of the increase in resistance generated in impaling (impalement resistance) is increased. 
         [0013]    In eye surgery requiring a delicate operation, an incisional wound is formed in a conjunctiva and a sclera by a cutting member, and when a cannula is then penetrated through the incisional wound, it is not preferable that the power required for the operation significantly varies. Namely, if the power required for the operation is largely varied, the cannula may be penetrated to an excessive depth. 
         [0014]    An object of the present invention is to provide a cannula which can reduce the rate of the increase in resistance generated when the cannula is penetrated through an incisional wound formed in tissue. 
       Solutions to the Problems 
       [0015]    A cannula according to the present invention for solving the above problem is a cylindrical cannula constituting a trocar used in a surgery and inserting thereinto a cutting member in a detachably attachable manner. In the cannula, an inclined cut surface in which one side of a cylinder protrudes is formed at the end of the cannula. A tapered surface with uneven width, where the protruding side of the inclined cut surface has a larger width than the nonprotruding side, is formed on an outer peripheral surface of the inclined cut surface. 
         [0016]    Further, a cannula manufacturing method according to the present invention is for manufacturing the above cannula. In the cannula manufacturing method, an inclined cut surface in which one side of a cylinder protrudes is formed at an end of a cylindrical material. When the outer peripheral surface of the inclined cut surface is ground or polished, the angle of the axial center of the cylinder relative to a ground surface or a polished surface is changed corresponding to the progression of grinding or polishing. Therefore, a tapered surface with uneven width, where the protruding side of the inclined cut surface has a larger width than the nonprotruding side, is formed on the outer peripheral surface of the inclined cut surface. 
       Effects of the Invention 
       [0017]    In the cannula according to the present invention, an inclined cut surface in which one side of a cylindrical material more protrudes along the cylinder than the other side is formed at an end of the cylindrical material. A tapered surface with uneven width, where the protruding side of the cylindrical material has a larger width than the nonprotruding side, is formed on the outer peripheral surface of the inclined cut surface. Namely, since the width of the tapered surface on the protruding side (the width in a direction along the axis of the cylinder) is larger than the width of the tapered surface on the nonprotruding side, the angle of the tapered surface on the protruding side relative to the axial center of the cylindrical material can be made smaller than the angle of the tapered surface on the nonprotruding side relative to the axial center of the cylindrical material. 
         [0018]    Thus, when the cutting member is inserted through the inside of the cannula, the angle formed by the outer peripheral surface of the cutting member and the tapered surface on the protruding side of the cylindrical member becomes small. Accordingly, when the cannula passes through an incisional wound formed in tissue by the cutting member, the impalement resistance at the time when the protruding side of the inclined cut surface passes can be made small. After the protruding side of the inclined cut surface passes through the incisional wound, as the passage length of the inclined cut surface increases, from the protruding side to the nonprotruding side passes sequentially. At that time, there is reduced the rate of the increase in the outer diameter size of the inclined cut surface corresponding to the length that the inclined cut surface passes. 
         [0019]    Accordingly, the rate of the increase in the impalement resistance accompanying the passage of the inclined cut surface can be reduced, and when the incisional wound is formed in tissue and, the operation of passing the cannula through the incisional wound is performed, the variation of the power required for the operation can be reduced. 
         [0020]    In the cannula manufacturing method according to the present invention, an inclined cut surface in which one side of a cylinder protrudes along the cylinder is formed at an end of a cylindrical material constituting a cannula. When the outer peripheral surface of the inclined cut surface is ground or polished, the angle of the axial center of the cylindrical material relative to a ground surface or a polished surface is changed corresponding to the progression of the grinding or polishing. Accordingly, a tapered surface with uneven width, where the protruding side of the inclined cut surface has a larger width than the nonprotruding side, can be formed on the outer periphery surface of the inclined cut surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a view for describing a configuration of a cannula. 
           [0022]      FIG. 2  is a perspective view for describing a configuration of a trocar. 
           [0023]      FIG. 3  is a view for describing a relationship between a cutting member and the cannula constituting the trocar. 
           [0024]      FIG. 4  is an explanatory view of an enlarged relevant part of  FIG. 3 . 
           [0025]      FIG. 5  is a view for describing a method of manufacturing the cannula. 
       
    
    
     DESCRIPTION OF REFERENCE SIGNS 
       [0000]    
       
         A Cannula member 
         B Trocar 
         C Cutting member 
         D Handle 
           1  Cannula 
           1   a  Axial center 
           2  Inclined cut surface 
           2   a ,  2   b  Point 
           3  Tapered portion 
           4  Cut-out line 
           10  Socket 
           20  Main body 
           20   a  Tale portion 
           21  Cutting blade 
           25  Material 
           30  Grinding belt 
           31  Supply portion 
           32  Winding portion 
           33  Transfer portion 
       
     
       DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0045]    Hereinafter, a configuration of a cannula according to the present invention and a method of manufacturing the cannula will be described. The cannula according to the present invention constitutes a trocar which forms an incisional wound in tissue by means of a cutting member mounted in a detachably attachable manner and impales the incisional wound to form a passage through which surgical instruments and tubes for injecting chemicals reach an affected area. 
         [0046]    The cannula of the present invention has been made based on the following finding. Namely, when the outer diameter and the inner diameter of the cannula have the same value (the thicknesses are equal to each other), the maximum values of impalement resistance generated when the cannula passes through tissue are the same regardless of the shape of an end of the cannula. However, the rate of the increase in resistance value accompanying increase in a passage length at the time when the end of the cannula passes through tissue is changed according to the shape of the end of the cannula. When a doctor performs a surgery, the doctor can perform a more stable operation if the rate of change in the resistance value is small. 
         [0047]    In the cannula of the present invention, when the cannula is arranged to penetrate through tissue, the cannula is required to have a strength that can keep the shape against the force from the tissue. In this case, both of the cannula having enough strength to avoid deformation of the cannula when a cutting member is pulled out and the cannula having enough strength to allow the deformation of the cannula can be used. Materials that can exhibit such strength include metal typified by stainless steel and a synthetic resin, and a pipe formed of these materials can be preferably used. Especially when a tool inserted into the cannula is moved in use, a deformable cannula is preferably used. 
         [0048]    Before describing the configuration of the cannula  1  according to the present embodiment, a configuration of a trocar B provided with a cannula member A having the cannula  1  will be described using  FIG. 2 . The trocar B illustrated in  FIG. 2  is adapted to be used in eye surgery and incises a conjunctiva and a sclera to insert the cannula member A through the incisional wound, and, thus, to leave the cannula member A. Using the cannula member A, surgical instruments and a tube can be inserted and passed through. 
         [0049]    The trocar B is configured so that the cannula member A mounted with a cutting member C in a detachably attachable manner is further mounted to a handle D in a detachably attachable manner. A doctor grips and operates the handle D to incise a target portion of a living organism and, thus, to form an incisional wound. Then, accompanying further operation, the cannula member A is moved with the cutting member C and inserted through the incisional wound. After that, the handle D is released from the cannula member A and, in addition, the cutting member C is released from the cannula member A, therefore a hole penetrating through the incisional wound can be formed by the cannula member A. 
         [0050]    According to the above constitution, as illustrated in  FIG. 2A , the handle D has a length and thickness large enough to be gripped and operated by a doctor and is formed into a shape that is easily gripped. Further, as illustrated in  FIG. 2B , an end of the handle D can be mounted by engaging with a cut-out portion and a groove of a socket  10  of the cannula member A. The handle D can be released by releasing the engagement. 
         [0051]    Next, the configuration of the cannula  1  according to the present embodiment will be described using  FIGS. 1 ,  3 , and  4 . The cannula member A illustrated in the drawings is adapted to have the cannula  1  formed into a cylindrical shape and mounted with the cutting member C inside in a detachably attachable manner, and the socket  10  having the cannula  1  attached. The cannula  1  includes a metal pipe or a synthetic resin pipe having a rigidity, has an inclined cut surface  2  formed at the end, and is fixed to the socket  10  in such a state that the end on the other side is fitted and inserted into the socket  10 . 
         [0052]    The cannula  1  penetrates through an incisional wound in tissue formed by the cutting member C in a surgery for the affected area, and forms a passage through which surgical instruments and tubes are inserted while maintaining the penetration state. Thus, the cannula  1  includes a cylindrical member having a suitable rigidity. 
         [0053]    The inclined cut surface  2 , in which one side of a cylinder protrudes, is formed at the end of the cannula  1  and a tapered portion  3  is formed on an outer peripheral surface of the inclined cut surface  2 . In the inclined cut surface  2 , a circumferential point  2   a  at an end of the cylindrical member constituting the cannula  1  is the top, and a point  2   b  on the opposite side of the point  2   a  is the bottom. Namely, a portion corresponding to the point  2   a  is the protruding side, and a portion corresponding to the point  2   b  is the nonprotruding side. 
         [0054]    In the present invention, although an angle θ relative to an axial center  1   a  of the cannula  1  of the inclined cut surface  2  is not limited, the angle of about 60 degrees is formed in the present embodiment (see,  FIG. 4 ). 
         [0055]    In the present embodiment, although the inclined cut surface  2  is formed linearly, it is not limited to this constitution. Any shape may be used as far as the point  2   a  at the end of the cylindrical member constituting the cannula  1  more protrudes than the other circumferential portion. Namely, in the lateral view having the point  2   a  of the cannula  1  at the right side, the shape of the inclined cut surface  2  may be linear as illustrated in  FIG. 4 . The shape in lateral view of the inclined cut surface  2  may be curved or may be a shape in which straight lines and curved lines are combined. 
         [0056]    The tapered portion  3  is formed on the outer peripheral surface of the inclined cut surface  2 . The tapered portion  3  is formed so that the center coincides with the axial center  1   a  of the cannula  1  as much as possible. Further, the tapered portion  3  is formed so that a cut-out line  4 , which is a border between the tapered portion  3  and the outer peripheral surface of the cannula  1 , is substantially at right angle to the axial center  1   a.    
         [0057]    The tapered portion  3  is not formed to have a uniform taper angle over the entire circumference of the outer peripheral surface of the inclined cut surface  2 , but formed to have different tapered angles and different tapered surfaces over the entire circumferences. Namely, the length from the point  2   a  to the cut-out line  4  that is the width on the protruding side constituting the inclined cut surface  2  is larger than the length from the point  2   b  to the cut-out line  4  that is the width on the nonprotruding side. Thus, the size from the circumference of the inclined cut surface  2  to the cut-out line  4  that is the width of the tapered portion  3  is not uniform over the entire circumference. 
         [0058]    In the tapered portion  3 , the taper angle (formed by the axial center  1   a  and the tapered surface) relative to the axial center  1   a  of the cannula  1  is not uniform but is different over the entire circumference. Namely, the angle formed by the tapered surface on the point  2   a  side that is the protruding side in the tapered portion  3  and the axial center  1   a  is smaller than the angle formed by the tapered surface on the point  2   b  side that is the nonprotruding side and the axial center  1   a.    
         [0059]    The shape of the tapered surface formed on the entire outer peripheral surface of the tapered portion  3  is not a straight line in the lateral view but is a curved line. Specifically, the curved line is not a simple curved line with a prescribed curvature but a complex curved line whose curvature is changed corresponding to a direction along the axial center  1   a . Such a tapered surface can be formed by using a manufacturing method to be described later. 
         [0060]    The tapered portion  3  is configured as described above, accordingly the inclination angle of the tapered portion  3  relative to the axial center  1   a  of the cannula  1  become small, and a reduced rate of the increase in the outer diameter with respect to the axial center  1   a , from the point  2   a  constituting the inclined cut surface  2  to the cut-out line  4  through the point  2   b , can be achieved. Thus, when the cannula  1  is penetrated through an incisional wound formed in tissue, the rate of the increase in the resistance generated when the point  2   a  of the inclined cut surface  2  passes through the incisional wound, the inclined cut surface  2  passes through the incisional wound sequentially from the point  2   a  toward the point  2   b , and the cut-out line  4  further passes through the incisional wound is reduced corresponding to the rate of the increase in the outer diameter. 
         [0061]    Accordingly, after forming the incisional wound in tissue by the cutting member C operated by a doctor, when the cannula  1  is penetrated through the incisional wound with the subsequent operation, the resistance increases as the inclined cut surface  2  starts to pass through the incisional wound. However, since the angle of the tapered portion  3  corresponding to the point  2   a  that is the protruding side of the inclined cut surface  2  is small, the increase in the resistance is small. Then, although the resistance increases with the passage of the tapered portion  3 , the rate of increase is small, and variation of the force required for operation can be reduced. The resistance reaches the maximum value at the time of the penetration of the cannula  1  with the passage of the cut-out line  4 , and the maximum value is the same regardless of the shape of the end of the cannula  1  if the inner diameter and the outer diameter of the cannula  1  are the same. 
         [0062]    As described above, in the cannula  1  of the present embodiment, the cannula  1  is not required to be rotated when the cannula  1  is penetrated through the incisional wound formed by the cutting member C, and therefore, tissue is not dissected. Thus, a cure period after a surgery does not become longer. 
         [0063]    The socket  10  is mounted to the handle D in a detachably attachable manner, and as described above, the cannula  1  inserting therethrough the cutting member C is mounted to the handle D through the socket  10 . A doctor operates the handle D, so that an incisional wound is formed in tissue by the cutting member C, and the cannula  1  can be penetrated through the tissue with further insertion of the cutting member C into the tissue. 
         [0064]    After that, the socket  10  is released from the handle D, and, in addition, the cutting member C is pulled out from the cannula  1 , so that the cannula member A (the cannula  1 ) is left in the incisional wound to thereby form a passage reaching an affected area. Through the formed passage, the surgery for the affected area using surgical instruments can be performed, and chemicals can be supplied through tubes. 
         [0065]    As illustrated in  FIG. 3 , the cutting member C is inserted through the cannula  1  of the cannula member A in a detachably attachable manner. The cutting member C is adapted to have a main body  20 , which is formed of a round bar-shaped solid material and is satisfactorily longer than the cannula member A, and a cutting blade  21  provided at an end of the main body  20 . 
         [0066]    The outer diameter of the main body  20  has a size slightly smaller than the inner diameter of the cannula  1  constituting the cannula member A, and is formed into a substantially straight needle shape. Namely, a doctor grips a tail portion  20   a  on the opposite side of the end provided with the cutting blade  21  and performs pulling-out operation, so that the cutting member C can be easily eliminated from the cannula  1 . 
         [0067]    However, when a dimensional difference of the outer diameter of the main body  20  with respect to the inner diameter of the cannula  1  is too large, the cannula  1  is easily released, and thus it is not preferable. When a difference between the outer diameter and the inner diameter is too small, the operation at the time of inserting the cutting member C through the cannula  1  or the operation of pulling out the cutting member C from the cannula  1  is not easy, and thus it is not preferable. Accordingly, the outer diameter of the main body  20  can be slightly smaller than the inner diameter of the cannula  1 . The tail portion  20   a  side that does not enter into the cannula  1  may have a straight needle shape continuing from the end side or a different shape such as a tapered shape, and the outer diameter is not limited. 
         [0068]    When the cannula  1  has flexibility and deformability, the outer diameter of the main body  20  can be made larger than the inner diameter of the cannula  1 . 
         [0069]    In the cutting member C, both a solid needle and a hollow needle can be used, and needles having various needlepoint shapes, such as a suture needle and an injection needle, can be used. When the needlepoint shape of the suture needle is used, the cutting blade  21  can have a straight-line shape as viewed from the end side. However, the cutting blade  21  is not necessarily formed to coincide with the straight line passing through the center of the main body  20 . The shape of the cutting blade  21  may be a straight line passing through a position displaced from the center or a smooth curved line passing through a position displaced from the center, or may be a combination of straight lines or a combination of a straight line and a smooth curved line. 
         [0070]    A material constituting the cutting member C is not particularly limited, and a piano wire, a steel wire, a stainless steel wire rod, and so on can be selectively used. However, when a risk of rust in distribution process is considered, the stainless steel wire rod with a high level of rust resistance is preferably used. Especially, there can be used a wire rod formed of austenitic stainless steel having high reliability with respect to biocompatibility. Furthermore, when an austenitic stainless steel wire rod having a predetermined diameter is subjected to cold drawing process with a reduction in area previously set, the structure of the wire rod is elongated in a fiber shape. The resultant wire rod has suitable elasticity and flexibility and a high toughness, and therefore, it is preferable. 
         [0071]    The present inventor attempted a comparative experiment using a trocar having the cannula  1  according to the present invention and the cannula described in the Patent Document 2. In the experiment, the inner diameter and the outer diameter of the cannula are the same in the both cannulas, cutting members having the same specifications are inserted through the cannulas, and the size of projection of the cutting member from the cannula end is the same in the both cannulas. Further, resistance (load N) at the time when test materials having the same coating are impaled was measured. 
         [0072]    As a result, in the trocar described in the Patent Document 2 (the trocar of the comparative example), after the start of impalement of the cannula through the test material, the load was increased by 0.797 N while the cannula passes by 0.5 mm. Meanwhile, in the present invention, the load increased during the passage of the cannula by 0.5 mm was 0.363 N. The maximum load at the time of penetration of the test material was 3.5 N in both of the cases. 
         [0073]    Accordingly, the rate of the increase in resistance of the cannula of the comparative example is about 2.2 times that of the cannula of the present invention. The position where the resistance with the passage of the cannula through the test material changes to increase is the same in the both cannulas. However, with regard to the position where the maximum load occurs, the position in the cannula of the present invention is more rearward than the position in the cannula of the comparative example, and a difference of about 0.8 mm is found between the two positions. 
         [0074]    The above result is due to that while the cannula of the comparative example forms a taper based on the central axis of an oblique cut surface formed at the end of the cannula, the cannula of the present invention forms a taper with uneven width, where the width on the protruding side of the inclined cut surface formed at the end of the cannula is larger than the width on the nonprotruding side. 
         [0075]    As described above, in the cannula of the present invention, the rate of the increase in resistance is small when the cannula is operated by a doctor to make it penetrated through an incisional wound in tissue. Accordingly, since an excessive force is not required to be applied, the cannula can be operated in a stable state. 
         [0076]    Next, a method of manufacturing the cannula having the above constitution will be described using  FIGS. 4 and 5 . The present invention provides a method of forming a tapered surface, having uneven width where the width of the tapered surface on the protruding side of the inclined cut surface is larger than the width of the tapered surface on the nonprotruding side, on the outer peripheral surface of the inclined cut surface formed at the end of the cylindrical material so as to manufacture the cannula  1  illustrated in  FIG. 4 . 
         [0077]    When the cannula  1  is manufactured, there is provided a material  25  in which a cylindrical material coinciding with the material of the intended cannula  1  and the inner and outer diameters is previously cut into a length corresponding to the length of the intended cannula  1 . One end of the material  25  is cut at a previously set angle, and the inclined cut surface  2  is formed. 
         [0078]    The outer peripheral surface of the inclined cut surface  2  of the cylindrical material  25  prepared as described above is ground or polished so as to form the tapered portion  3  on the outer peripheral surface. When the tapered portion  3  is formed on the outer peripheral surface of the cylindrical material  25 , whether the cylindrical material  25  is ground or polished is not limited. Whether the cylindrical material  25  is ground or polished can be suitably determined depending on the conditions such as the material of the cylindrical material  25  and the outer diameter size. In the present embodiment, the cylindrical material  25  is polished to thereby form the tapered portion  3 . 
         [0079]      FIG. 5  is a view schematically illustrating a grinding device for manufacturing the cannula  1 . As illustrated in  FIG. 5 , the grinding device is adapted to have a flexible grinding belt  30 , a supply portion  31  for extending the grinding belt  30 , a winding portion  32  for winding the grinding belt  30 , and a transfer portion  33  for transferring the grinding belt  30  at a substantially constant speed. 
         [0080]    The grinding belt  30  may be adapted so that the belt can be continuously transferred at a constant speed in a constant direction, and may be adapted so that the belt can move in a certain direction while reciprocally moving at a constant speed within a given length range. 
         [0081]    Specifically, in the grinding device, a member for supporting the grinding belt  30  is not provided at a portion where the material  25  is brought into press contact with the grinding belt  30 . Accordingly, when the material  25  is brought into press contact with the grinding belt  30 , deflection corresponding to a pressure contact force is generated in the grinding belt  30 . Then, grinding corresponding to the deflection is performed. 
         [0082]    In the grinding belt  30 , a grinding material is secured to one side surface of a continuous flexible belt. The grinding belt  30  is wound around the supply portion  31  in an unused state. The material of the flexible belt constituting the grinding belt  30  and the specifications, such as the material and grain size of the grinding material secured to the belt, are not limited. The material of the flexible belt constituting the grinding belt  30  and the specifications can be suitably set depending on the conditions such as the material and outer diameter of the cylindrical material  25 . 
         [0083]    The supply portion  31  is adapted to have a reel which winds therearound the grinding belt  30  in an unused state and a driving member which drives the reel in the arrow direction. The supply portion  31  is adapted to allow to extend and supply the grinding belt  30  with the progression of the grinding of the cylindrical material  25  by means of the grinding belt  30 . 
         [0084]    The winding portion  32  is adapted to have a reel which reels the used grinding belt  30  and a driving member which drives the reel. The winding portion  32  is adapted to allow to reel the used grinding belt  30  transferred with the progression of the grinding of the cylindrical material  25  by means of the grinding belt  30 . 
         [0085]    The transfer portion  33  transfers the grinding belt  30  at a substantially constant speed and has a function of applying a constant torque to the grinding belt  30  and applying a constant tension to the grinding belt  30 . Any transfer portion may be used as long as it has such a function. An example of the transfer portion having the function is a mechanism in which a roller pair including a pair of rollers holding the grinding belt  30  therebetween is offset by a previously set distance, and the roller pair can be driven based on a constant rotation number. Another example is a transfer portion configured so that a pair of load cells is arranged and offset by a previously set distance, and the supply portion  31  and/or the winding portion  32  can be driven corresponding to the output of the load cell. Furthermore, the transfer portion may be adapted to use a torque motor as a driving motor which drives the roller pair. 
         [0086]    Since the grinding belt  30  is transferred at a substantially constant speed by the transfer portion  33 , the cylindrical material  25  can be always ground by a new grinding material. Therefore, the reliable and stable grinding can be realized. 
         [0087]    A robot mechanism (not illustrated) is arranged at a position facing the grinding belt  30 . The robot mechanism has a chuck which grips the end side of the cylindrical material  25  on the opposite side of the end formed with the inclined cut surface  2 . The chuck is adapted to be rotatable and be able to change the posture with respect to the grinding belt  30 . Namely, the chuck is adapted to enable to change the inclination angle relative to the grinding belt  30  of the material  25  gripped by the chuck (the angle of the axial center of the cylinder relative to a ground surface or a polished surface) and to enable to change a position in a height direction and a coming and going direction relative to the grinding belt  30 . 
         [0088]    There will be described a procedure of grinding the cylindrical material  25  in which the inclined cut surface  2  is formed at the end by the grinding device configured as above and forming the tapered portion  3  on the outer peripheral surface of the inclined cut surface  2 . 
         [0089]    First, the winding portion  32  is driven and the transfer portion  33  is operated to transfer the grinding belt  30 . At the same time, the cylindrical material  25  is gripped by a chuck (not illustrated). In this state, as illustrated in  FIG. 5A , the material  25  is held vertically to the transfer direction of the grinding belt  30 . At the same time, as illustrated in  FIG. 5B , the material  25  is held in such a posture that the material  25  is inclined at an angle α 1  (for example, 45 degrees) with respect to the width direction of the grinding belt  30 . 
         [0090]    Thereafter, the chuck is rotated to rotate the cylindrical material  25  around the axial center, and meanwhile, the cylindrical material  25  is lowered to bring the point  2   a  of the inclined cut surface  2  into press contact with the grinding belt  30 . By virtue of the press contact, deflection illustrated in  FIG. 5  is generated in the grinding belt  30 . Then, when the end of the material  25  is in press contact with the grinding belt  30 , and the grinding belt  30  is rotated by a previously set number of times, the outer peripheral surface near the point  2   a  including the point  2   a  is ground into a curved surface shape, so that a portion of the tapered portion  3  can be formed. 
         [0091]    When the chuck completes a predetermined number of rotations, the chuck is raised to offset the material  25  from the grinding belt  30 . After the chuck is raised to offset the cylindrical material  25  from the grinding belt  30 , the inclination angle of the chuck is changed to a second angle (for example, 40 degrees) smaller than the angle α 1 , and the position of the chuck in the width direction of the grinding belt  30  is changed, so that the point  2   a  constituting the inclined cut surface  2  of the material  25  is located closer to the width direction center side of the grinding belt  30 . 
         [0092]    Thereafter, the chuck is rotated to rotate the cylindrical material  25  around the axial center, and meanwhile, the cylindrical material  25  is lowered, so that the outer peripheral surface of the inclined cut surface  2  already formed with a portion of the tapered portion  3  is in press contact with the grinding belt  30 . The deflection is generated in the grinding belt  30  by the press contact. When the end of the material  25  is in press contact with the grinding belt  30  and the grinding belt  30  has been rotated by a previously set number of times, the outer peripheral surface of the inclined cut surface  2  can be ground into a curved surface shape, including a portion of the already formed tapered portion  3 . Namely, the tapered portion  3 , in which a portion of the tapered portion  3  formed in a posture at the angle α 1  is elongated continuously, can be formed. 
         [0093]    When the chuck completes a predetermined number of rotations, the chuck is raised to offset the material  25  from the grinding belt  30 . After that, the inclination angle of the chuck is changed to an angle α m  (for example, 35 degrees) smaller than the second angle, and the position of the chuck in the width direction of the grinding belt  30  is changed, so that the point  2   a  constituting the inclined cut surface  2  of the material  25  is located closer to the width direction center side of the grinding belt  30 . After that, as described above, the chuck is rotated to rotate the cylindrical material  25  around the axial center, and meanwhile, the cylindrical material  25  is lowered. The outer peripheral surface of the inclined cut surface  2  on which a portion of the tapered portion  3  is already formed is brought into press contact with the grinding belt  30 , and the grinding belt  30  is rotated by a previously set number of times. Accordingly, the outer peripheral surface of the inclined cut surface  2  can be ground into a curved surface shape, including a portion of the already formed tapered portion  3 , and the tapered portion  3 , in which a portion of the tapered portion  3  formed in a posture at the second angle is further elongated, can be formed. 
         [0094]    While the inclination angle α of the chuck is changed to become smaller in order, from the angle α 1  to the angle α m , the position in the width direction of the grinding belt  30  is changed. The chuck is then lowered while being rotated to bring the outer peripheral surface of the inclined cut surface  2  formed at the cylindrical material  25  into press contact with the grinding belt  30  to grind the outer peripheral surface of the inclined cut surface  2 . Repeating the series of operation enables the tapered portion  3  formed on the outer peripheral surface of the inclined cut surface  2  to be elongated. When the inclination angle α of the chuck is changed to become smaller in order, from the angle α 1  to the angle α m , the angle may be changed in a stepwise manner or in a continuous manner. 
         [0095]    Specifically, as the inclination angle of the chuck becomes smaller, the point  2   a  constituting the inclined cut surface  2  and the vicinity including the points  2   a  are offset from the grinding belt  30 , and grinding is not progressed. When the inclination of the chuck is set to the smallest angle α n  (for example, 25 degrees) to bring the cylindrical material  25  into press contact with the grinding belt  30 , the ground portion of the material  25  ground by the grinding belt  30  is located offset from the inclined cut surface  2 . By virtue of the grinding at that time, the tapered portion  3  and the outer peripheral surface of the cylinder portion of the material  25  are smoothly continued through the cut-out line  4 . 
         [0096]    Accordingly, although the cut-out line  4  is described as a clear line in  FIGS. 1 to 4 , in the actual cannula  1 , the cut-out line  4  does not appear as a clear discontinuous portion. 
         [0097]    As described above, by virtue of the use of the flexible grinding belt  30 , when the end of the cylindrical material  25  to be ground is in press contact with the grinding belt  30 , deflection is generated in the grinding belt  30 . The material  25  can be ground so that the press contact portion of the material  25  is encompassed by the deflected grinding belt  30 . Namely, the end of the material  25  to be ground is not ground linearly but can be ground in a curved surface manner. 
         [0098]    Accordingly, the outer peripheral surface of the inclined cut surface  2  formed at the material  25  is ground so that the inclination angle α of the material  25  relative to the grinding belt  30  is changed to become smaller in sequence, so that the outer peripheral surface of the inclined cut surface  2  is formed into a curved surface shape having a large curvature at the point  2   a  and in the vicinity including the point  2   a , into a curved surface shape having a smaller curvature at the point  2   b  and in the vicinity including the point  2   b , and into a curved surface shape having an even smaller curvature at a portion offset in the longitudinal direction of the material  25  relative to the point  2   b.    
         [0099]    As described above, because the grinding belt  30  has flexibility, the curved surfaces having different curvatures smoothly continue to each other to constitute the tapered portion  3 . Especially, the inclination angle of the material  25  at the time of grinding at the final stage is made extremely small, so that the cut-out line  4 , that is a border between the tapered portion  3  and the outer peripheral surface of the cylinder portion of the material  25 , can be formed at a substantially right angle to the axial center of the material  25  (the axial center  1   a  of the cannula  1 ). 
         [0100]    Accordingly, the tapered portion  3  with an uneven tapered width, where the dimension from the point  2   a  to the cut-out line  4  (width on the protruding side) is larger than the dimension from the point  2   b  to the cut-out line  4  (width on the nonprotruding side), can be provided. 
         [0101]    By going through the above processes, the cannula  1  can be manufactured from the cylindrical material  25 . 
       INDUSTRIAL APPLICABILITY 
       [0102]    In the present embodiment, although the cannula used in an eye surgery and the method of manufacturing the cannula have been described, the cannula can be utilized in endoscopic surgery as the cannula penetrated through an incisional wound formed in surface tissue, and the method can be utilized when such a cannula is manufactured.