Patent Publication Number: US-10328438-B2

Title: Tube rack of a centrifugal separator having bottom rubber members

Description:
TECHNICAL FIELD 
     The present invention relates to a tube rack of a centrifugal separator for holding tubes each containing a sample to carry out a centrifugal treatment. 
     BACKGROUND ART 
     Conventionally, there are mainly provided an angle rotor and a swinging rotor as rotors used for a centrifugal separator. In the angle rotor, a constant value of an angle is used for the angle of a tube hole for holding each tube containing a sample to carry out a centrifugal treatment. The swinging rotor is formed by a rotor yoke and a bucket. The bucket is used to accommodate tubes each containing a sample, and detachably and swingably attached to the rotor yoke. The tubes are accommodated in the bucket while they are held in a tube rack. The bucket is swung up by the centrifugal force up to an angle of 0 to 90° along with the rotation of the rotor yoke. 
     The tubes used for the swinging rotor are generally, mainly made of glass or plastic. 
     In a conventional tube rack, one or a plurality of individual tube holes is formed to hold a tube. A tube containing a sample is inserted into the tube hole, and held. 
     There are mainly two reasons why the tube is inserted into the individual tube hole. The first reason is to prevent, if one of the tubes is damaged during the centrifugal treatment, any effect of the damage from spreading to other adjacent tubes. 
     The second reason is to keep the sample contained in the damaged tube within the tube rack so as to prevent toxic substance and toxic bacteria from adhering to the bucket and the like. 
     Each tube hole of the tube rack is often formed as a non-through hole conforming to the outer shape and bottom shape of the tube, that is, a blind hole shape. The reason for this is to prevent the tube from being deformed or damaged by the centrifugal force. 
     In general, tube racks are made of plastic, and some are cut out by machining and some are formed by resin molding. Some of the tube racks formed by resin molding include tube holes each divided into an upper portion, middle portion, and bottom surface, and some others include tube holes each including no middle portion and supporting a tube by only an upper portion and bottom surface. 
     There is provided a conventional tube rack in which a bottom rubber portion (elastic body) is inserted into the bottom surface of a tube hole. This tube rack is used when the strength of the tube bottom surface is low and the bottom shape varies for each tube. 
     When the bottom shape of a tube hole contacting a tube in the tube rack is considerably different from the bottom shape of the tube, an excessive force is applied to a portion of the tube bottom surface, and the tube bottom portion is unwantedly deformed or damaged. As for the tube rack in which a bottom rubber portion is inserted into the bottom surface of the tube hole, the bottom rubber portion can be deformed in accordance with the shape of the tube bottom surface, and it is thus possible to prevent an excessive force from being applied to the portion of the tube bottom surface. 
     As a conventional tube rack including a bottom rubber portion, there is provided, for example, a tube rack described in patent literature 1. The bottom rubber portion disclosed in patent literature 1 includes a film-like projection or fin-shaped projection around a cushion portion contacting the bottom portion of the tube. An arrangement in which the film-like projection or fin-shaped projection is pressed against the hole wall of the tube hole is adopted. By forming the film-like projection or fin-shaped projection in the bottom rubber portion, it is possible to prevent, when the tube is removed from the tube hole, the bottom rubber portion from being separated from the tube hole together with the tube. 
     RELATED ART LITERATURE 
     Patent Literature 
     Patent Literature 1: Japanese Utility Model Registration No. 2509308 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     The tube rack including the bottom rubber portion described in patent literature 1 has three following problems. 
     The first problem is that the assembly operation of the tube rack will be complicated. In the conventional tube rack, a bottom rubber portion is individually inserted into the opening of each individual tube hole. Therefore, an operation of inserting a bottom rubber portion into a tube hole needs to be performed the number of times corresponding to the number of tube holes, thereby causing greater burden in carrying out the insertion operation. Especially, as described in patent literature 1, if the film-like projection or fin-shaped projection is formed in the bottom rubber portion, a frictional force is generated by a contact with the hole wall surface of the tube hole, and thus a tool is required in order to insert the bottom rubber portion into the tube hole. 
     The second problem is that the bottom rubber portion may be separated or lost. The bottom rubber portion described in patent literature 1 includes, as a separation preventive measure, the film-like projection or fin-shaped projection to prevent the bottom rubber portion from being separated from the tube hole. However, since the separation preventive measure relies on friction between the hole wall of the tube hole and the film-like projection or fin-shaped projection, the bottom rubber portion may be separated when fraction resistance decreases caused by an aging degradation of the bottom rubber portion. When a centrifugal treatment of another tube is performed in a state in which the bottom rubber portion is being separated, the tube can be damaged at high probability. When the bottom rubber portion is lost, the rotation of the rotor becomes unbalanced, and a vibration occurs during the rotation of the rotor. When a vibration occurs in the rotor, the life of a motor decreases, and noise is generated. 
     The third problem is the difficulties in replacing the bottom rubber portion. The bottom rubber portion may deteriorate or be damaged with use by the user. The bottom rubber portion described in patent literature 1 is inserted into the bottom of the tube hole formed from a blind hole, and locked by the film-like projection or fin-shaped projection. Therefore, it is difficult to detach the bottom rubber portion for replacement. 
     The present invention has been made to solve these problems, and has as its object to provide a tube rack of a centrifugal separator, in which a bottom rubber portion can be readily mounted, and readily replaced, and yet such a bottom rubber portion cannot be easily separated. 
     Means of Solution to the Problem 
     In order to achieve the above object, according to the present invention, there is provided a tube rack of a centrifugal separator, comprising a holder including a plurality of tube holes each configured to accommodate a tube that is used for a sample, and the plurality of tube holes each includes an opening at one end portion of the holder serving as a tube insertion side and an opening at a bottom portion of the holder that is at the other end, a bottom rubber main body including a plurality of bottom rubber members each fits in an opening of the bottom portion of each of the plurality of tube holes, and including connecting portions each configured to connect the plurality of bottom rubber members that are adjacent to each other, and a base formed in a cylindrical shape that has a bottom configured to accommodate and detachably hold the holder and the bottom rubber main body, and to be inserted into a bucket of the centrifugal separator. 
     Effect of the Invention 
     According to the present invention, when the connecting portions of the bottom rubber main body abut against the hole walls of the tube holes, the bottom rubber members are regulated so that the bottom rubber members do not come off the tube holes. Unlike the conventional technique, the separation preventive measure does not rely on friction between the bottom rubber portion and the hole wall surfaces of the tube holes. Thus, even if the bottom rubber members deteriorate over time, they will not be separated. Therefore, it is possible to prevent the rotation of the rotor from becoming unbalanced caused by the loss of the bottom rubber members. As a result, it is possible to suppress a decrease in life of the motor for driving the rotor. 
     According to the present invention, since the plurality of bottom rubber members are connected by the connecting portions to form one bottom rubber main body, it is unnecessary to insert each bottom rubber member into each tube hole when incorporating the bottom rubber members in the holder. Therefore, even though the plurality of bottom rubber members is provided, it is possible to provide the tube rack of the centrifugal separator, that has high assemblability. 
     An operation of replacing the deteriorated bottom rubber members can be readily performed because by detaching the holder from the base, the bottom rubber main body can be exposed. 
     Therefore, according to the present invention, it is possible to provide the tube rack of the centrifugal separator, in which the bottom rubber portion can be readily mounted and readily replaced, and yet the bottom rubber portion cannot be easily separated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a swinging rotor on which tube racks are mounted according to the present invention; 
         FIG. 2  is a perspective view showing a state in which a bucket is mounted on a rotor yoke; 
         FIG. 3  is a perspective view showing a state in which the tube rack into which tubes are inserted is mounted on the bucket; 
         FIG. 4  is an exploded perspective view showing a state in which the tube rack and tubes are removed from the bucket; 
         FIG. 5  is an exploded perspective view showing the tube rack when viewed from obliquely above; 
         FIG. 6  is an exploded perspective view showing the tube rack when viewed from obliquely below; 
         FIG. 7A  is a plan view showing a holder; 
         FIG. 7B  is a sectional view taken along a line  7 B- 7 B in  FIG. 7A ; 
         FIG. 7C  is a bottom view showing the holder; 
         FIG. 8A  is a plan view showing a bottom rubber portion; 
         FIG. 8B  is a sectional view taken along a line  8 B- 8 B in  FIG. 8A ; 
         FIG. 8C  is a bottom view showing the bottom rubber portion; 
         FIG. 9  is a plan view showing the tube rack; 
         FIG. 10  is a sectional view taken along a line X-X in  FIG. 9 ; 
         FIG. 11  is a sectional view taken along a line XI-XI in  FIG. 9 ; 
         FIG. 12  is a plan view showing the tube rack into which the tubes are inserted; 
         FIG. 13  is a sectional view taken along a line XIII-XIII in  FIG. 12 ; 
         FIG. 14  is an enlarged sectional view showing a portion of the tube rack, where no groove is formed; 
         FIG. 15  is an enlarged sectional view showing a portion of the tube rack, where a groove is formed; and 
         FIG. 16  is an enlarged sectional view showing a portion of the tube rack, where the bottom rubber portion is not inserted into the tube holes. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of a tube rack of a centrifugal separator according to the present invention will be described in detail below with reference to  FIGS. 1 to 16 . 
     Tube racks  1  shown in  FIG. 1  are mounted on a swinging rotor  2  for the centrifugal separator. The swinging rotor  2  is formed by a rotor yoke  3  and a plurality of buckets  4 . The rotor yoke  3  is driven by a motor (not shown), and rotates about an axis indicated by a one-dot dashed line C in  FIG. 1 . The rotor yoke  3  includes a plurality of arms  5 , as shown in  FIG. 2 . Each of the distal end portions of the arms  5  is provided with trunnion pins  6 . 
     Each bucket  4  is formed in a cylindrical shape having a bottom, and opening upward. In the bucket  4 , trunnion pin grooves  7  in which the trunnion pins  6  of the rotor yoke  3  are engaged are formed. The bucket  4  is held by the rotor yoke  3  to be swingable about the trunnion pins  6 . 
     The swinging rotor  2  is mounted on the motor shaft of the centrifugal separator (not shown), and rotates integrally with the motor shaft. When the swinging rotor  2  rotates, each bucket  4  is swung up about the trunnion pins  6  in a direction in which the bucket bottom surface moves away from the rotation center. 
     When a centrifugal treatment is performed, a plurality of tubes  11  are accommodated in the bucket  4  via the tube rack  1 , as shown in  FIG. 3 . Each tube  11  contains a sample to carry out the centrifugal treatment, and is formed in a pipe shape having a closed end and an open end, as shown in  FIG. 4 . The outer surface of a bottom portion  11   a  serving as the closed end of the tube  11  is formed in a hemispherical shape that is convex toward the opposite side of the open end. As the tube  11 , a tube made of glass or plastic is mainly used. 
     The tubes  11  are respectively inserted into tube holes  12  of the tube rack  1  from above, and held by the tube rack  1 . The tube rack  1  holding the plurality of tubes  11  is inserted into an opening  4   a  of the bucket  4  from above, and held by the bucket  4 . 
     As shown in  FIGS. 5 and 6 , the tube rack  1  is formed by combining three parts. The three parts are a base  13  located lowermost in  FIGS. 5 and 6 , a holder  14  located uppermost, and a bottom rubber portion  15  located between the base  13  and the holder  14 . In this embodiment, the bottom rubber portion  15  corresponds to the “bottom rubber main body” of the present invention. Although details will be described later, the bottom rubber portion  15  is mounted on the holder  14  from below. Furthermore, the holder  14  is mounted on the base  13  from above while the bottom rubber portion  15  is mounted on the holder  14 . 
     The base  13  is formed in a box shape having a pair of handle portions  16 . More specifically, the base  13  is formed in a cylindrical shape having a bottom that has a base bottom plate  13   a  as a bottom and is open upward. The base  13  is formed in a shape that can be fitted in the bucket  4  from above, and has a function of accommodating and detachably holding the holder  14  and the bottom rubber portion  15  (to be described later). 
     The handle portions  16  project upward from two facing side walls  13   b  and  13   c  of the base  13 . In each handle portion  16 , a hole  18  that is engaged with a hook portion  17  of the holder  14  (to be described later) is formed. This hole  18  is formed at a height almost equal to that of a base opening  13   d.    
     As shown in  FIGS. 5 to 7 , the holder  14  includes an upper plate  21  forming a holder upper surface  14   a , and a holder main body  22  extending downward from the upper plate  21 . The upper plate  21  and the holder main body  22  are integrally formed by integral molding using a plastic material. As shown in  FIG. 4 , the upper plate  21  closes the base opening  13   d  while the holder  14  is mounted on the base  13 . On each of two side portions of the upper plate  21 , the above-described hook portion  17  is formed in a shape projecting laterally. The hook portions  17  are engaged in the holes  18  of the base  13  while the holder  14  is inserted into the base  13 . When the hook portions  17  are engaged in the holes  18  of the base  13 , the holder  14  is regulated so that the holder  14  will not be detached from the base  13 . 
     As shown in  FIGS. 10 and 11 , the holder main body  22  is formed in a shape that is fitted in the base  13 . The holder main body  22  is detachably inserted into the base  13 . 
     The plurality of tube holes  12  are formed in the upper plate  21  and the holder main body  22 . The tube holes  12  are formed by through holes that are open to the holder upper surface  14   a  located on the tube insertion side and a holder bottom surface  14   b  (see  FIG. 6 ) on the opposite side, and are arranged in a direction (horizontal direction) along the holder upper surface  14   a . Note that the “holder upper surface” and the “horizontal direction” correspond to those in a state in which the tube rack  1  is mounted on the bucket  4  and stays still. The inner diameter of the tube hole  12  is slightly larger than the outer diameter of the tube  11 . 
     The holder bottom surface  14   b  is formed in a shape in which the bottom rubber portion  15  (to be described later) is fitted. As shown in  FIG. 6 , a groove  23  connecting the adjacent tube holes  12  is formed in a portion serving as a hole wall  12   a  of the tube hole  12  in the bottom portion of the holder  14 . The groove  23  is formed to accommodate a connecting piece  24  of the bottom rubber portion  15  (to be described later). In this embodiment, the groove  23  forms a “notch” of the invention described in claim  2 . 
     As shown in  FIGS. 5, 6, and 8 , the bottom rubber portion  15  is formed by a plurality of bottom rubber members  25  and the connecting pieces  24  connecting the bottom rubber members  25 . In this embodiment, the connecting pieces  24  form “connecting portions” of the present invention. 
     Each bottom rubber member  25  is formed in a columnar shape that is fitted in the tube hole  12  of the holder  14 . More specifically, each bottom rubber member  25  is formed in a columnar shape in which an upper surface  25   a  (distal end surface) oriented to the opening of the tube hole  12  on the tube insertion side is located at one end in the axial direction. 
     The outer diameter of the bottom rubber member  25  is slightly smaller than the inner diameter of the tube hole  12 . “Slightly smaller” indicates that the outer diameter is small to the extent such that a clearance which allows insertion and removal is formed with respect to the hole wall surface of the tube hole  12 . 
     As shown in  FIGS. 8B, 10, and 11 , the central portion of the upper surface  25   a  of each bottom rubber member  25  is formed in a shape having a concave surface. As shown in  FIG. 13 , this concave surface is formed in a shape conforming to the outer surface of the bottom portion  11   a  of the tube  11 . 
     Each connecting piece  24  projects outward in the radial direction from the outer surface of the bottom rubber member  25  to connect the adjacent bottom rubber members  25 . More specifically, each connecting piece  24  is part of the outer surface of the bottom rubber member  25 , and projects outward in the radial direction from a part that is located in the vicinity of a bottom surface  25   b  (see  FIG. 6 ) on the opposite side of the upper surface  25   a  (distal end surface) in the axial direction of the bottom rubber member  25 . Each bottom rubber member  25  according to this embodiment is connected to at least two adjacent bottom rubber members  25  by at least two connecting pieces  24 . 
     As shown in  FIGS. 8A and 8C , a width d of each connecting piece  24  according to this embodiment is smaller than the width (outer diameter) of the bottom rubber member  25 . As shown in  FIG. 8B , a height h of the connecting piece  24  is equal to or smaller than half the length of the bottom rubber member  25  in the axial direction. That is, each connecting piece  24  is formed in a shape that has a width smaller than that of the bottom rubber member  2  and connects portions of a pair of adjacent bottom rubber members  25  up to about the middle positions in the axial direction from the bottom surfaces  25   b . Each groove  23  of the holder  14  is formed at a position corresponding to the connecting piece  24 . The depth of the groove  23  is a depth to accommodate the entire connecting piece  24 . 
     To assemble the thus formed tube rack  1 , the bottom rubber portion  15  is mounted on the bottom portion of the holder  14 . The bottom rubber portion  15  is held by the holder  14  in a state in which the bottom rubber members  25  are fitted in the tube holes  12  and the connecting pieces  24  are accommodated in the grooves  23 . Next, the holder  14  and the bottom rubber portion  15  are inserted into the base opening  13   d  from above. The hook portions  17  of the holder  14  are engaged in the holes  18  of the base  13 . When the holder  14  is mounted in the base  13  in this way, the holder  14  is fixed to the base  13  in a state in which the base opening  13   d  is closed by the upper plate  21  of the holder  14  and the holder main body  22  abuts against the base bottom plate  13   a , as shown in  FIGS. 9 to 11 . 
     In this assembly state, as shown in  FIGS. 10 and 11 , the connecting pieces  24  of the bottom rubber portion  15  are sandwiched between the grooves  23  of the holder  14  and the base bottom plate  13   a , and thus the bottom rubber portion  15  is never removed upward. 
     The thus assembled tube rack  1  is inserted into the bucket  4  in a state in which the tubes  11  are inserted into the tube holes  12 , as shown in  FIGS. 12 and 13 . The tubes  11  are supported by the bottom rubber members  25  in a state in which the bottom portions  11   a  contact the upper surfaces  25   a  of the bottom rubber members  25  and the hole walls  12   a  of the tube holes  12  regulate movement in the horizontal direction. 
     When the tube rack  1  is mounted on the bucket  4  and the swinging rotor  2  is rotated, the centrifugal force is applied to the bottom rubber portion  15  in a direction (the axial direction of the bottom rubber members  25 ) vertical to the tube rack  1 . At this time, since the bottom rubber members  25  are inserted into the tube holes  12 , deformation of the bottom rubber portion  15  caused by application of the centrifugal force to the bottom rubber portion  15  can be suppressed by the hole walls  12   a  of the tube holes  12 . Furthermore, since the bottom rubber members  25  are inserted into the tube holes  12 , the bottom rubber portion  15  never moves in the radial direction of the tube holes  12  with respect to the holder  14 . 
     The reason why deformation and movement of the bottom rubber portion  15  are restricted will be described in more detail with reference to  FIGS. 14 to 16 . 
     In a state in which the swinging rotor  2  rotates at high speed, the bottom rubber members  25  are pressed in the above-described vertical direction by the tubes  11  applied with the centrifugal force. In this case, as shown in, for example,  FIGS. 14 to 16 , the deformation state of the bottom rubber portion  15  changes in accordance with the presence/absence of the walls surrounding the bottom rubber members  25 .  FIG. 14  is a sectional view showing a portion of the tube rack  1 , where there is no groove  23 .  FIG. 15  is a sectional view showing a portion of the tube rack  1 , where there is the groove  23 .  FIG. 16  is a sectional view when a bottom rubber portion  31  that is not inserted into the tube holes  12  is used. 
     As shown in  FIG. 14 , if the centrifugal force in the vertical direction (axial direction) is applied to the bottom rubber member  25 , the bottom rubber member  25  is surrounded by the hole wall  12   a  of the tube hole  12  and the bottom portion  11   a  of the tube  11 , and thus has no room to deform. In this case, the concave shape of the upper surface  25   a  of the bottom rubber member  25  is maintained, and no excessive force is applied to part of the bottom surface of the tube  11 , thereby preventing the tube  11  from being damaged. 
     As shown in  FIG. 15 , if the height of the connecting piece  24  of the bottom rubber portion  15  is set to about half the height of the bottom rubber member  25 , and the depth of the groove  23  of the holder  14  is set to a depth that can accommodate the connecting piece  24 , the upper surface of the bottom rubber member  25  contacts the hole wall  12   a  of the tube hole  12  over the whole region in the circumferential direction. Therefore, in this case as well, the same effect as that obtained in the case shown in  FIG. 14  can be obtained. 
     On the other hand, as shown in  FIG. 16 , in a case in which the bottom rubber portion  31  that is not inserted into the tube holes  12  is used, when the centrifugal force in the vertical direction is applied to the bottom rubber portion  31 , the bottom rubber portion  31  has room to deform in the lateral direction since there is no wall (no hole wall  12   a  of the tube hole  12 ) in the lateral direction of the bottom rubber portion  31 . In this case, the bottom rubber portion  31  has room to move in the lateral direction when an operation of tilting the tube rack  1  or the like is performed. As a result, the shapes and positions of the bottom portion  11   a  of the tube  11  and a concave surface  31   a  of the bottom rubber portion  31  do not coincide, and an excessive force is applied to part of the bottom portion  11   a  of the tube  11 , thereby damaging the tube  11 . 
     In the tube rack  1  according to this embodiment, the bottom rubber portion  15  having a structure in which the plurality of bottom rubber members  25  are connected by the connecting pieces  24  and being integrated is used. Therefore, as will be described later, it is possible to prevent the bottom rubber portion  15  from being separated, and readily perform an attachment operation or replacement operation of the bottom rubber portion  15 . 
     [Bottom Rubber Portion Removal Prevention] 
     In this embodiment, the bottom rubber members  25  are inserted into the tube holes  12  from the side of the holder bottom surface  14   b . Therefore, when the connecting pieces  24  abut against the hole walls  12   a  of the tube holes  12 , it is possible to regulate the bottom rubber members  25  so that the bottom rubber members  25  do not come off from the tube holes  12 . The structure for removal prevention does not rely on friction between the bottom rubber portion and the hole walls of the tube holes, unlike the conventional technique. Thus, even if the bottom rubber members  25  deteriorate over time, the bottom rubber members  25  will not come off. Therefore, it is possible to prevent the rotation of the swinging rotor  2  from becoming unbalanced caused by the loss of the bottom rubber members  25 . As a result, it is possible to suppress a decrease in life of the motor for driving the swinging rotor  2 . 
     [Ease of Attachment/Replacement of Bottom Rubber Portion (Improvement of Assemblability)] 
     In this embodiment, since the plurality of bottom rubber members  25  are connected by the connecting pieces  24  to form the one bottom rubber portion  15 , it is unnecessary to insert each bottom rubber member  25  into each tube hole  12  when incorporating the bottom rubber members  25  in the holder  14 . Therefore, even though the plurality of bottom rubber members  25  is provided, it is possible to provide the tube rack of the centrifugal separator, that has high assemblability. 
     An operation of replacing the deteriorated bottom rubber members  25  can be readily performed because by detaching the holder  14  from the base  13 , the bottom rubber portion  15  can be exposed. 
     Therefore, according to this embodiment, it is possible to provide the tube rack of the centrifugal separator, in which the bottom rubber portion  15  can be readily mounted and readily replaced, and yet the bottom rubber portion  15  cannot be easily separated. 
     [Bottom Rubber Portion Displacement Prevention/Deformation Suppression] 
     Each bottom rubber member  25  according to this embodiment is formed in a columnar shape in which the upper surface  25   a  oriented to the opening of the tube hole  12  on the tube insertion side is located at one end in the axial direction. Each connecting piece  24  of the bottom rubber portion  15  is part of the outer surface of the bottom rubber member  25 , and projects outward in the radial direction from a part that is located in the vicinity to the bottom surface  25   b  on the opposite side of the upper surface  25   a , in the axial direction of the bottom rubber member  25 . The grooves  23  that accommodate the connecting pieces  24  are formed in portions serving as the hole walls  12   a  of the tube holes  12  in the bottom portion of the holder  14 . 
     Since the bottom rubber members  25  inserted into the tube holes  12  are held by the hole walls  12   a  of the tube holes  12  and the base bottom plate  13   a , it is possible to prevent the bottom rubber portion  15  from being displaced. 
     Each connecting piece  24  is provided on the side of the bottom surface  25   b  on the outer surface of the bottom rubber member  25 . Therefore, the distal end surface (upper surface  25   a ) of the bottom rubber member  25  contacts the hole wall  12   a  of the tube hole  12  over the whole region in the circumferential direction. As a result, when the tube  11  is pressed against the bottom rubber member  25  by the centrifugal force, the hole wall  12   a  of the tube hole  12  regulates deformation of the bottom rubber member  25  outward in the radial direction. Therefore, it is possible that the shape of the upper surface  25   a  of the bottom rubber member  25  supporting the bottom portion  11   a  of the tube  11  can be prevented from changing along with deformation of the bottom rubber member  25 . As a result, it is possible to prevent an excessive force from being applied to part of the bottom portion  11   a  of the tube  11 , thereby reliably preventing the tube  11  from being damaged. 
     [Suppression of Decrease in Strength of Holder} 
     In this embodiment, since each entire connecting piece  24  is accommodated in the groove  23  of the holder  14 , a portion except for the grooves  23  in the bottom portion (holder bottom surface  14   b ) of the holder  14  readily contacts the base  13 . This indicates that the area of the contact portion between the holder  14  and the base  13  increases, and the centrifugal force acting on the holder  14  at the time of rotation of the swinging rotor  2  can be received by a wide area of the base  13 . Therefore, a decrease in strength of the holder  14  is suppressed, and it is possible to reliably prevent the holder  14  from being damaged by the centrifugal force. 
     [Effects on Adjacent Tubes and Sample Scattering Prevention] 
     The holder  14  includes the plurality of individual tube holes  12 . Therefore, even if the tube  11  is damaged, this never has any effects on the adjacent tubes  11 . Furthermore, the holder  14  and the bottom rubber portion  15  are covered with the base  13  from below and the side. Thus, even when the tube  11  is damaged, the sample is kept within the base  13 , thereby preventing the sample from contacting the bucket  4  and the like. As a result, it is possible to prevent toxic substance and bacteria and the like from scattering. 
     EXPLANATION OF THE REFERENCE NUMERALS AND SIGNS 
     
         
         
           
               1  . . . tube rack,  4  . . . bucket,  11  . . . tube,  12  . . . tube hole,  12   a  . . . hole wall,  13  . . . base,  14  . . . holder,  15  . . . bottom rubber portion (bottom rubber main body),  23  . . . groove (notch),  24  . . . connecting piece (connecting portion),  25  . . . bottom rubber member