Abstract:
An apparatus for analyzing liquid samples packed in tubes ( 6 ) closed with a top ( 7 ) capable of being perforated, includes a support ( 4 ) for the tubes and a unit ( 8 ) for sampling an aliquot from each tube and delivering it into a receptacle for treatment and/or analysis, the unit ( 8 ) including a hollow needle ( 45 ) connected to a suction/delivery device and vertically mobile; the support ( 4 ) has a circular tray provided with several tube-holders ( 5 ) on its periphery and capable of rotating about a vertical axis to bring a position successively and selectively the tubes ( 6 ) borne by the tube-holders ( 5 ) in line with the unit ( 8 ); each tube-holder ( 5 ) is connected to the tray ( 4 ) through a linkage ( 31 ) with two degrees of freedom.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus for the analysis of liquid samples in sample tubes closed by a pierceable stopper. 
     Such apparatus is used at present particularly in the fields of chemistry, biochemistry and biology to analyze various liquids by different analysis techniques, as for example liquid chromatography. For example, this apparatus is used by medical analysis laboratories to analyze blood and other liquids of human or animal origin. 
     DESCRIPTION OF THE RELATED ART 
     International patent application WO90/03834 discloses an automatic apparatus for the treatment and analysis of blood serum comprising a first support in the form of a rack adapted to receive test tubes closed by a pierceable stopper and containing samples of blood and a separator gel, a centrifugation unit capable of receiving several test tubes to subject their contents to centrifugation, an optical detection unit adapted to receive individually the test tubes which have been subjected to centrifugation, and to generate output signals indicating whether the centrifugation has been correctly carried out and indicating the position of the separator gel layer between the serum and the red blood cells, and a computer which analyzes the output signals from the optical detection unit. The apparatus described in this document moreover comprises a unit for removing and distributing, comprising a hollow needle which can be moved vertically downwardly to perforate the stopper of a test tube placed in an optical detection unit, so as to remove a serum sample in this test tube. The apparatus moreover comprises a second support in the form of a rack, which supports empty bowls adapted to receive samples of serum removed from the test tubes individually brought to the optical detection unit, a third support in the form of a rack, adapted to receive the centrifuged test tubes which the optical detection unit has detected as being defective, a fourth support in the form of a rack, adapted to receive the test tubes and the bowls containing the serum samples removed respectively from the test tubes, each bowl surmounting the associated test tube, and a robot arm adapted to take the samples one by one from the first support, to transfer them into the centrifugation unit and from there, one by one, into the optical detection unit. If this latter reveals an unsatisfactory result of centrifugation, the robot arm removes the defective test tube and will place it in the third rack, them it will get a new sample from the centrifugation unit to place it in the optical detection unit. On the contrary, if the optical detection unit reveals that the test tube which is located therein has undergone a correct centrifugation, the needle of the removal and distribution unit is lowered to perforate the stopper of the test tube and its lower end is immersed in the serum to a level located above the layer of separator gel, as a function of the position of this layer detected by the optical detection unit. The removal and distribution unit then removes a sample of serum from the test tube, then the hollow needle is withdrawn from this latter. The robot will then get from the second support an empty bowl and bring it below the hollow needle. The removal and distribution unit will then deliver the sample of the serum removed from the empty bowl, then the robot places the filled bowl and the serum sample on the stopper of the test tube which is located at this moment in the optical detection unit. Finally, the test tube and the associated bowl are transferred by the robot from the optical detection unit to the fourth support. The operations described above are repeated successively for each of the test tubes contained in the centrifugation unit. 
     The known apparatus briefly described above is relatively complicated and voluminous, and its capacity per unit time of treatment is relatively limited, given the large number of transfer operations the robot must carry out to transfer each test tube and/or the associated bowl between the different units and the different supports in the form of racks provided in the apparatus. 
     U.S. Pat. No. 4,713,974 discloses an analyzer robot comprising a carousel which can turn about a vertical axis and on which several racks are fixed removably. Each rack comprises three series of cylindrical cells, with vertical axes, adapted to receive containers of the samples to be analyzed and each closed by a pierceable stopper. When the racks, provided with containers, are fixed on the plate of the carousel, the containers are disposed in three concentric circles centered on the axis of rotation of the plate of the carousel, and the containers are aligned radially in groups of three containers. Thus, by turning the carousel stepwise, it is possible to bring each time a group of three containers to a fixed working station located near the periphery of the plate of the carousel. In this workstation is located a unit for removal and distribution comprising a hollow needle extending vertically, which is connected to a suction/delivery means and which is mounted on a spring such that its lower end is located at a level slightly higher than that of the stoppers of the containers. In addition to its movement of rotation, the carousel plate can be given a horizontal translatory movement in a radial direction relative to the axis of rotation of the plate, toward and spaced from the workstation, such that any container selected from among three radially aligned containers and present at a given time at the workstation can be brought below the needle of the removal and distribution unit, into vertical alignment with said needle. The plate of the carousel comprises several holes which are aligned respectively with the holes formed in the bottom of the cells of the racks fixed on the plate. The removal and distribution unit moreover comprises an elevator, in the form of a vertical rod, which is aligned axially with the needle and which can be moved vertically upwardly through a hole in the plate of the carousel to raise the selected container which has been brought into vertical alignment with the needle. Because of the raising of the selected container, the stopper of this latter impales itself on the needle and the raising of the container is continued until the lower end of the needle abuts against the bottom of the container. 
     The analysis robot described in U.S. Pat. No. 4,713,974 is substantially more compact than the apparatus described in the international patent application WO90/03834, and it permits avoiding numerous transfers and manipulations which must be carried out for each test tube in the apparatus described in the mentioned international patent application. However, the analysis robot of U.S. Pat. No. 4,713,974 does not permit subjecting the content of the containers to centrifugation. In the case in which the liquid samples must be centrifuged before being analyzed, centrifugation must therefore be carried out in a conventional centrifuge. 
     U.S. Pat. No. 4,478,095 discloses an analysis robot similar to that which is described in U.S. Pat. No. 4,713,974. It differs essentially by the fact that the carousel comprises a principal plate which can be given only a rotatable movement and which carries four planetary auxiliary plates that can be turned relative to the principal plate, each auxiliary plate comprising several cells disposed in a single circle and its periphery to receive containers of liquid samples to be analyzed. A drive device comprising an electric motor and a transmission system with belts and pulleys, as well as an electromagnetic brake and an electromagnetic clutch permit selectively turning either the principal plate with the auxiliary plates without the latter being able to turn relative to the principal plate, or the auxiliary plates without the principal plate being able to turn, according to whether the electromagnetic brake or the electromagnetic clutch is excited. Thus, by turning first of all the principal plate, then the auxiliary plates, it is possible to bring any selected container to the workstation where the removal and distribution unit is located. Here again, the carousel of the analysis robot of U.S. Pat. No. 4,478,095 does not permit centrifuging the liquid samples contained in the containers carried by the auxiliary plates of the carousel, such that if the liquid products to be analyzed must be centrifuged before analysis, the centrifugation must be carried out in a conventional centrifuge before placing the containers in the cells of the planetary auxiliary plates of the carousel of the analysis robot. 
     SUMMARY OF THE INVENTION 
     The present invention thus has for its object to provide an analysis robot which permits, as needed, centrifuging the liquid samples to be analyzed, whilst being more compact and capable of processing per hour a larger number of liquid samples than the apparatus described in international patent application WO90/03834. 
     To this end, the invention has for its object an apparatus for the analysis of liquid samples in test tubes closed by a pierceable stopper, comprising a support adapted to support in vertical position the sample tubes, a removal and distribution unit to remove from each sample tube carried by the support a portion of the liquid sample contained in the sample tube and to distribute at least a fraction of the removed portion of liquid sample into at least one receptacle for processing and analysis of said distributed fraction, said removal and distribution unit comprising a hollow needle which is connected to a suction/distribution means and fixed in vertical position to a vertically movable needle carrier, and drive means to move vertically the needle carrier between a first position in which the lower end of the needle is located at a level higher than that of the cork of said sample tube carried by the support, and a second position in which the lower end of the needle is within the liquid contained in said sample tube carried by the support, characterized in that said support is constituted by a circular plate provided with several tube carriers which are disposed at intervals about its periphery and which each comprise a recess with a vertical axis to receive and support a sample tube, said circular plate being adapted to turn about a vertical axis to bring and position successively and selectively the tube carriers to a workstation where the removal and distribution unit is located, such that this latter can act on the sample tube supported by the tube carrier brought to and positioned in the workstation, in that each tube carrier is connected to the circular plate by a connection with two degrees of freedom, namely freedom of vertical movement of translation and freedom of movement of rotation about a horizontal axis oriented tangentially relative to the circular plate, and in that at the workstation is disposed a bearing means adapted to support from below the tube carrier brought to and positioned in the workstation. 
     Thus, with the apparatus according to the invention, if the liquid samples must be centrifuged so as to separate them into at least two phases for analysis of at least one of the two phases of each sample, it suffices to turn the rotatable plate at a suitable speed of rotation for centrifugation. Thanks to the fact that each tube carrier is connected to the turning plate by a connection with two degrees of freedom permitting rotational movement of each tube carrier about a horizontal axis tangential to the turning plate, each sample tube can, under the action of centrifugal force, take a horizontal or substantially horizontal position which is particularly favorable to the separation of the phases of the sample liquids by said centrifugal force. When the speed of rotation of the plate is then reduced so as selectively and step by step to bring the tube carrier to the workstation, the sample tubes automatically return, by gravity, to a vertical position. 
     Each time the turning plate is stopped to immobilize a sample tube in the workstation, the needle of the removal and distribution unit can be lowered to pierce the stopper of the sample tube immobilized in the workstation and to remove from this tube a sample of desired quantity (aliquot) of the liquid sample or of the desired phase of this liquid sample. Thanks to the fact that each tube carrier has freedom of movement vertically in translation and thanks to the support means which permit supporting from below the tube carrier brought to and positioned in the workstation, the vertical forces, which are applied to the stopper of the sample tube at the moment it is pierced by the needle of the removal and distribution unit and which can sometimes amount to several dozens of Newtons, is not transmitted by the tube carrier to the turning circular plate. As a result, this latter is not in danger of being deflected by the vertical forces mentioned above. Stated otherwise, if the plate were deflected, vibration forces would be produced each time the plate is driven at high speed, during the centrifugation steps. These vibrations would lead to rapid wear of the roller bearings of the plate and would have an undesirable influence on the separation of the liquid samples into several phases. 
     Because the circular turning plate is freed from the above-mentioned vertical forces, it does not need to have high rigidity and it can be relatively light, and hence have a low inertia. This permits using an electric motor of low power and consuming less electrical energy for driving the plate in rotation. Moreover, thanks to its light weight, the turning plate can be stopped more easily and with greater precision for the positioning of the sample tubes below the needle of the removal and distribution unit. 
     The apparatus according to the invention can moreover have one or several of the following characteristics:
         each tube carrier is constituted by a cylindrical sleeve which is open at its upper end and closed at its lower end, and which comprises, adjacent its upper end, two aligned pivots which define the horizontal axis of the connection with two degrees of freedom;   the upper end of each cylindrical sleeve is disposed between two legs of a mounting member in the form of a fork, which is secured to the circular plate and whose two legs extend radially outwardly of said circular plate, the two pivots of the cylindrical sleeve being supported respectively by the legs of the mounting piece by means of the connection with two degrees of freedom;   each leg of the mounting piece comprises a vertical notch, in which is engaged one of the two pivots of the cylindrical sleeve;   in a first embodiment of the invention, each of the two pivots is supported resiliently in the corresponding vertical notch by a flexible spring;   each vertical notch is formed in the upper surface of the corresponding leg of the mounting member and the flexible spring is disposed in the vertical notch between the bottom of the latter and the pivot;   in this case, the mounting member carries removable retaining means which, in service, retain the two pivots in the corresponding vertical notches;   in a modified embodiment, each vertical notch is formed in the lower surface of the corresponding leg of the mounting member and the flexible spring is constituted by a flexible blade, of which one end is fixed to the lower surface of said corresponding leg and of which the other end resiliently supports and retains the pivot in the corresponding vertical notch;   in one or the other case, the support means can be constituted by fixed stop disposed below the lower end of the cylindrical tube-carrying sleeve brought to and positioned in the workstation, at a vertical distance from said lower end which is smaller than a maximum path of vertical movement which is permitted the cylindrical tube-carrying sleeve by said connection with two degrees of freedom and by the flexible spring when the needle of the removal and distribution unit exerts a vertical penetration force, directed downwardly, against the stopper of the sample tube in said cylindrical tube-carrying sleeve;   in another embodiment, each vertical notch is formed in the upper surface of the corresponding leg of the mounting member and each pivot rests on the bottom of the corresponding vertical notch;   in this case, the support means can be constituted by a wedge, which can be moved by an actuator between a first position in which said wedge does not interfere with the cylindrical tube-carrying sleeves when the circular plate is rotated, and a second position in which said wedge is in contact with the end of the cylindrical tube-carrying sleeve brought to and positioned in the workstation and supports said cylindrical sleeve in a vertical position such that its two pivots no longer rest on the bottom of the corresponding vertical notches in the legs of the mounting member;   said wedge is constituted by a piece in the form of a wedge which can slide, under the control of the actuator, over a fixed horizontal support and guide surface;   each mounting member comprises an abutment means adapted to prevent the cylindrical tube-carrying sleeve from pivoting about the horizontal axis defined by the two pivots and to hold said cylindrical sleeve in a vertical position when the wedge is moved from its first to its second position by the actuator and comes in the course of movement into contact with the lower end of said cylindrical sleeve;   in all embodiments, the circular plate is preferably connected to drive means adapted to turn said circular plate selectively at a first relatively rapid speed to subject to centrifugation the liquid samples contained the sample tubes carried by the circular plate, and at a second speed, substantially slower than the first speed, to bring and position successively and selectively said sample tubes to the workstation;   in all embodiments, the tube-carrying cylindrical sleeves can be made of a transparent material or each sleeve can comprise a wide window in its cylindrical wall, so as to permit reading an individual identification code carried by a label fixed to each sample tube, by a code reader installed at a fixed station in a predefined angular position relative to the vertical axis of rotation of the circular plate.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will become apparent from the following description given by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view of an analysis robot according to the present invention; 
         FIG. 2  is a partial perspective view showing a removal and distribution unit of the analysis robot of  FIG. 1 ; 
         FIG. 3  is a view partially in elevation and partially in cross-section on the broken line III—III of  FIG. 1 ; 
         FIG. 4A  is a perspective view, on a larger scale, showing one of the tube carriers used in the analysis robot of  FIGS. 1  to  3 ; 
         FIG. 4B  shows a modified embodiment of the tube carrier of  FIG. 4A ; 
         FIG. 5  is a view partially in elevation and partially in cross-section on the line V—V of  FIG. 1 , the needle of the removal and distribution unit being shown in the upper position; 
         FIG. 6  is a view similar to  FIG. 5 , the needle of the removal and distribution unit being shown in a lower position; 
         FIG. 7  is a view similar to  FIG. 3 , showing a modified embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The analysis robot shown in  FIGS. 1  to  3  comprises a housing  1 , whose upper plate  2  has a large circular opening  3 , which exposes a rotatable circular plate  4  located below the opening  3 . Several tube carriers  5 , adapted each to support a sample tube  6  closed by a stopper  7 , are mounted at the periphery of the plate  4  in a manner that will be described in greater detail later. 
     The upper plate  2  of the housing  1  supports at least one and preferably two removal and distribution units  8  and  9  which will described in detail later. 
     The plate  4  is disposed in a bowl  11  (FIG.  3 ), for example a bowl with a circular edge, whose diameter is substantially greater than that of the plate  4 . At the middle of the bowl  11  is located a cylindrical well  12  which projects upwardly from the bottom  11 a of the bowl  11 . The circular plate  4  is fixed at the upper end of a vertical hollow shaft  13  which extends downwardly within the well  12  and is mounted rotatably in the latter by means of roller bearings  14  and  15 . The plate  4  and the shaft  13  can be made in a single piece, preferably of a light material, for example a plastic material or a light metal such as aluminum or aluminum alloy. The bowl  11  is supported by a horizontal plate  16 , which forms a part of the housing  1 , by means of several small column crosspieces  17 , so as to provide a space  18  between the plate  16  and the bottom  11 a of the bowl  11 . The lower end of the hollow shaft  13  projects into the space  18 . The hollow shaft  13  and thus the plate  4  can be driven in rotation by an electric motor  19 , preferably a stepping motor, which is fixed to the plate  16  below the latter, the output shaft of the motor  19  passes through the plate  16  and carries, at its upper end, in the space  18 , a toothed pulley  21 , which is connected kinematically by a toothed belt  22  to another toothed pulley  23  which is fixed at the lower end of the hollow shaft  13 . 
     As shown in  FIG. 4A , each tube carrier is preferably constituted by a cylindrical sleeve  24 , which is open at its upper end and closed at its lower end. Each sleeve  24  comprises, adjacent its upper end, two pivots  25  whose axes are aligned and perpendicular to the longitudinal axis of the tube  24 . The upper end of each sleeve  24  is disposed between the two legs  26  and  27  of a mounting member  28  in the form of a fork, which is fixed to the circular plate  4 , at the periphery of this latter. For example, the mounting member  28  comprises, on the side opposite the two legs  26  and  27 , a groove  29  whose width corresponds to the thickness of the edge of the circular plate  4 . The mounting member  28  is fitted around, by its groove  29 , the edge of the circular plate  4  and it is fixed to the latter by gluing, by welding, by screws or by any other suitable securement means. Once the mounting member  28  is fixed to the plate  4 , the legs  26  and  27  extend radially outwardly of the plate. 
     The two pivots  25  of the sleeve  24  are supported by the legs  26  and  27  of the mounting member  8  by means of a connection  31  with two degrees of freedom, which gives to the sleeve  24  the possibility of having a vertical translatory movement and a movement of rotation about a horizontal axis which is oriented tangentially to the circular plate  4  and which is defined by the two pivots  25 . More precisely, as shown in  FIG. 4A , each of the two legs  26  and  27  of the mounting member  28  comprises, in its upper surface, a deep vertical notch  32  in which is engaged one of the two pivots  25  of the sleeve  24 . A flexible spring  33 , for example a helicoidal spring, is disposed in each of the two notches  32 , between the bottom of the latter and the pivot  25 . A plate  34 , cut out in the form of a U, is fixed detachably by at least one screw  35  to the upper surface of the mounting member  28  such that, in service, the plate  34  covers the notches  32  thereby to retain the pivots  25 . 
       FIG. 4B  shows a modified embodiment of the connection  31  with two degrees of freedom. In  FIG. 4B , the elements which are identical or which play the same role as those in  FIG. 4A  are designated by the same reference numerals. In the modified embodiment of  FIG. 4B , each vertical notch  32  is formed in the lower surface of the corresponding leg  26  or  27  of the mounting member  28  and each flexible spring  33  is constituted by a flexible blade, of which one end is fixed to the lower surface of the leg  26  or  27  by a nut and bolt assembly or by a screw  36 . The other end of each spring blade  33  resiliently supports and retains the pivot  25  in the corresponding vertical notch  32 . This latter can have for example a semicircular profile, of which the diameter corresponds to the external diameter of the pivot  25 . In this case, each spring blade  33  comprises rounded portion  33   a , which also has a semicircular profile matching the external cylindrical surface of the pivot  25 . Preferably, each spring blade  33  moreover comprises, at its free end, a portion  33   b  which is elbowed at a right angle upwardly and engaged in an opening  37  formed in the corresponding leg  26  or  27  of the mounting member  28 . The two elbowed portions  33   b  permit preventing the pivots  25  from radially outwardly escaping beyond the free ends of the spring blades  33  when these latter are bent downwardly under the action of a vertical force applied to the stopper  7  of the sample tube  6  supported by the sleeve  24 . 
     Each sample tube  6  is provided, in a known manner, with a self-sticking label  38  carrying an identification code  39 , for example in the form of a barcode, which can be read by a code reader  41  installed at a fixed station in a predefined angular relation to the vertical axis of rotation of the circular plate  4 . For example, as shown in  FIGS. 5 and 6 , the code reader  41  can be disposed outside the bowl  11 , below an upper plate  2  of the casing  1 , in line with the removal and distribution unit  8 . To permit reading of the identification code  39  carried by the label  38  of each sample tube  6 , each tube-carrying sleeve  24  comprises, in its cylindrical wall, a wide window  42 . By way of modification, each sleeve  24  could be made of a transparent material, for example a transparent plastic material. Similarly, the bowl  11  is made of transparent plastic material or a portion of its peripheral wall located facing the code reader  41  comprises a window. 
     Thus, each time a sample tube  6  is brought in position by the turning circular plate  4  into an angular position corresponding to the position of the removal and distribution unit  8 , the code  39  carried by the label  38  of the sample tube  6  can be read by the code reader  41 . It should be noted that the code reader  41  is not necessarily located in a position corresponding to that of the removal and distribution unit  8 . In fact, the code reader  41  could be installed in anywhere along the periphery of the bowl  11 . Thus, an angular coder  43  (FIG.  3 ), associated for example with the electric motor  19  (it could as a modification be associated with the turning circular plate  4 ), permits knowing at any time the angular position of the plate  4 . As a result, if the code reader  41  is installed in a different angular position from that of the removal and distribution unit  8 , to bring any one of the sample tubes  6  of which the identification code  39  has been read by the code reader  41 , it suffices to turn the circular plate  4  through an angle corresponding to the angular spacing between the angular positions in which are located respectively the code reader  41  and the removal and distribution unit  8  at the periphery of the bowl  11 . 
     Referring now to  FIGS. 3 ,  5  and  6 , there can be seen a stop  44 , for example of hard rubber, which is fixed on the bottom  11   a  of the bowl  11  at a position such that the stop  44  will be vertically aligned with the tube-carrying sleeve  24  which, at a given time, is positioned in correspondence with the removal and distribution unit  8 . The upper surface of the stop  44  is located at a vertical distance d from the lower end of the tube-carrying sleeve  24 , which is smaller than the maximum path of vertical movement which is permitted the sleeve  24  by the above-mentioned connection  31  with two degrees of freedom, in combination with the spring  33 . As will be seen later, the stop  44  serves as a bearing means for the sleeve  24  when the removal and distribution unit  8  removes a liquid sample (aliquot) from the sample tube  6  supported by said sleeve. 
     The removal and distribution unit  8  comprises, in a manner known per se, a hollow needle  45 , which is connected by a flexible tube  46  to a suction/delivery means  47  which can for example be constituted by a syringe whose piston can be moved by an actuator, and which is shown only schematically in  FIG. 2  as such a syringe and the manner in which it is connected to the hollow needle  45  are well known, for example from the two U.S. Pat. Nos. 4,478,095 and 4,713,974 mentioned above. 
     Differently from the analysis robots described in these two American patents, the hollow needle  45  of the removal and distribution unit  8  of the analysis robot according to the invention is fixed in vertical position to a needle carrier  48  which can be moved vertically between one position ( FIG. 5 ) in which the lower end of the needle  45  is located at a level higher than that of the stopper  7  of the sample tube  6  which has been brought at a given time into correspondence with the removal and distribution unit  8 , and a second position ( FIG. 6 ) in which the lower end of the needle, after having pierced the stopper  7 , is located within the liquid contained in said sample tube. 
     To this end, the needle carrier  48  is slidably mounted on two guide columns  49  whose upper and lower ends are fixed rigidly respectively to an upper horizontal plate  51  and to a lower horizontal plate  52 . An endless screw  53  is disposed vertically between the two columns  49  and is in engagement with a nut  54 , for example a ball nut, fixed to the needle carrier  48 . The screw  51  is mounted rotatably in bearings  55  and  56 , for example roller bearings, carried respectively by the plates  51  and  52 . The screw  53  can be driven in rotation by an electric motor  57 , for example a stepping motor, which is fixed to the plate  52 , and by a transmission constituted for example by two toothed pulleys  58  and  59  which are fixed respectively to the output shaft of the motor  57  and to the lower end of the screw  53 , and by a toothed belt  61 . 
     An angular coder  62  carried by the plate  51  and associated with the screw  53  permits at any time knowing the number of turns or fractions of turns made by the screw  53 , and hence the position height-wise of the needle carrier  48  and the needle  45 . Thus, by giving the stepping motor  57  a suitable number of impulses, it is possible to bring the needle carrier  48  into any desired vertical position under the control of the angular coder  62 . In particular, the lower end of the needle  45  can be brought to the desired depth within the liquid sample contained in the sample tube  6  which at a given time has been brought to and positioned in correspondence with the removal and distribution unit  8 . 
     When the needle carrier  48  is lowered to remove an aliquot from the sample tube  6 , the needle  45  first perforates the stopper  7  of the tube  6 . This done, the needle  45  applies to the stopper  7  a force whose intensity can vary according to the nature and/or the thickness of the stopper  7 . If this force, which can reach several tens of Newtons, were applied to the circular plate  4 , it could be prejudicial to the good operation of this plate. It is thus important that this force not be transmitted to the plate  4 . This problem is solved in combination with the above-mentioned connection  31  with two degrees of freedom, which connects each tube carrier  5  (sleeve  24 ) to a corresponding mounting member  28  fixed to the plate  4 , and by the support means constituted by the stop  44 . Thus, under the action of the force exerted by the needle  45  on the cork  7 , the pivots  25  of the sleeve  24  are displaced downwardly, against the opposite force of the flexible springs  33 , in the vertical notches  32  of the mounting member  28 , until the lower end of the sleeve  24  comes into contact with the upper surface of the stop  44 , which thus absorbs entirely the vertical force exerted by the needle  45  on the stopper  7 . It is to be noted that the springs  33  must have a high flexibility so as to transmit only a very small vertical force to the mounting member  28 , hence to the circular plate  4 . 
     With the needle carrier  48  can be associated a pusher  63  in the form of a foot which surrounds the lower end of the needle  45  and which is fixed to the lower end of a rod  64  mounted slidably in a vertical hole  65  in the needle carrier  48  ( FIGS. 2 ,  5  and  6 ). A helicoidal spring  66  is attached by its lower end to the needle carrier  48  and by its upper end to a securement tongue  67  which is itself fixed to the rod  64  above the needle carrier  48 . The rod  64  can be blocked by blocking means  68  fixed to the plate  51 . The blocking means  68  can for example be constituted by an electromagnet whose core has an end formed like a wedge that can be engaged between the teeth of a rack  69  formed on the upper portion of the rod  64 . 
     When the core of the electromagnet  68  is spaced from the rack  69 , and the needle carrier  48  is lowered by means of the screw  53 , the rod  64  and the foot  63  are also lowered until the foot comes into contact with the stopper  7 , whilst the lower end of the sleeve  24  is in contact with the stop  44 . At this time, the descending movement of the rod  64  stops and the spring  66  is stressed while the needle carrier  48  continues its descent until the lower end of the needle  45  reaches the desired depth within the sample tube  6 . Under the influence of the tension of spring  66 , the foot  63  holds the sleeve  24  in contact with the stop  44 . While the needle  45  removes a liquid sample from the tube  6 , the electromagnet  68  can be actuated such that its core engages between two teeth of the rack  69  to block the rod  64 . After the desired quantity of liquid sample (aliquot) has been removed from the sample tube  6 , the needle carrier  48  is raised to its upper position by means of the endless screw  53 , the raising being helped by the spring  66  which is tensioned. During the rising of the needle carrier  48 , the electromagnet  68  continues to block momentarily the rod  64  so as to hold the foot  63  in engagement against the stopper  7  of the sample tube  6  and thereby to prevent the stopper  7  and the tube  6  from being raised by friction exerted between the needle  45  and the stopper  7 . After the needle carrier  48  has been raised an amount such that the needle  45  has been completely withdrawn from the tube  6  and the stopper  7 , the electromagnet  68  is actuated so as to free the rod  64 . Then, when the needle carrier  48  continues its rising movement, it encounters the securement tongue  67 , thereby causing the raising of the rod  64  and the foot  63 . 
     In the case in which liquid samples (aliquots) removed from the sample tubes  6  are subjected to chromatographic analysis, the liquid sample removed at a given moment can be brought into an analysis loop (not shown) interposed in known manner between the needle  45  and the syringe  47 . Chromatographic analysis can also be carried out after distribution of the liquid sample into one of the receptacles  74  of the plate  73  described later. 
     In the case in which the liquid samples removed from the sample tubes  6  must be treated by one or several reagents, the analysis robot according to the invention can moreover comprise a reagent carrying plate  71  ( FIG. 1 ) of circular shape, at the periphery of which are fixed several cups or containers  72  each containing a reagent, as well as another plate  73  ( FIGS. 1 and 5 ) also of circular shape, at the periphery of which are disposed several receptacles  74  adapted to receive liquid samples removed from the sample tubes  6  by the removal and distribution unit  8  and one or several reagents removed by the removal and distribution unit  9 . 
     As shown in  FIGS. 1 and 3 , the reagent carrying plate  71  has a diameter slightly smaller than that of the plate  4  and it is preferably disposed coaxially above this latter plate. The plate  71  is fixed at the upper end of a shaft  75  which is rotatably mounted in bearings  76  and  77 , for example roller bearings, installed in a vertical support tube  78  which extends coaxially to within the hollow shaft  13  of the plate  4  and whose lower end is rigidly fixed to the plate  16  of the housing. The shaft  75  passes through a hole in the plate  16  and it can be driven in rotation by means of an electric motor  79 , preferably a stepping motor, and by means of a transmission comprising for example two toothed pulleys  81  and  82  fixed respectively to the output shaft of the motor  79  and to the shaft  75 , and a toothed belt  83 . The motor  79  is mounted on a suitable support (not shown) which is fixed to the plate  16  of the housing. An angular coder  84  associated with the shaft  75  permits knowing at any moment the angular position of the reagent carrying plate  71 . 
     As shown in  FIGS. 5 and 6 , the plate  73  is located just below the upper plate  2  of the housing and it is preferably disposed in a chamber  85 , shown schematically in broken lines, which can be maintained at a desired temperature by suitable thermal conditioning means (not shown). The cover  86  ( FIG. 1 ) hinged on the upper plate  2  of the casing by a hinge, gives access to a temporary storage region in the chamber  85 . When the cover  86  is raised, it is also possible to have access to a portion of the periphery of the plate  73 . The receptacles  74  are preferably organized by groups each comprising for example 16 receptacles, each group being carried by a rack  87  having, seen from above, the shape of the segment of a circle. As a modification, the receptacle  74  can be constituted by cells formed directly in the racks  87 . As shown in  FIGS. 5 and 6 , each rack  87  is provided with a securement tongue  88  by means of which it can be hooked or fixed in any other suitable manner to the periphery of the plate  73 . 
     The plate  73  can be driven in rotation by an electric motor (not shown), for example a stepping motor, and by a suitable transmission (also not shown). This electric motor and this transmission can be similar to those which were described above with respect to the drive of the reagent carrying plate  71  or with respect to the drive of the plate  4 , an angular coder being again provided to give at any moment the angular position of the plate  73 . 
     To as to permit the removal and distribution unit  8  to deliver to the receptacle  74  the samples removed from the sample tubes  6 , the two plates  51  and  52  are rotatably mounted, respectively on bearings  89  and  91 , for example roller bearings, about a fixed vertical axle  92 , whose lower end is fixed to a base plate  93 , itself fixed by screws  94  to the upper plate  2  of the chassis as shown in FIG.  5 . 
     The removal and distribution unit  8  can be turned about the axle  92  by means of an electric motor  95 , for example a stepping motor, which is vertically aligned above the electric motor  57  and which is fixed to the lower surface of the plate  51 . The output shaft of the motor  95  passes through the plate  51  and carries, at its upper end, a toothed pulley  96  in engagement with the toothed belt  97  which passes about another toothed pulley  98  fixed rigidly to the upper end of the axle  92  ( FIGS. 2 ,  5  and  6 ). As the toothed pulley  98  is fixed, a rotation of the toothed pulley  96  has the effect of turning all of the removal and distribution unit  8  about the axle  92 . 
     An angular coder (not shown) associated with the motor  95 , permits knowing at any instant the angular position of the removal and distribution unit  8  relative to the axle  92 . 
     Thus, by activating the motor  95 , the needle  45  of the removal and distribution unit  8  can be moved along a path in the arc of a circle  99  ( FIGS. 1 and 2 ) between an angular position  101  in which the needle  45  is located above a sample tube  6  at the periphery of the plate  4 , and an angular position  102  in which the needle  45  is located above one of the receptacles  74  at the periphery of the plate  73 . In the angular position  102 , the needle  45  can be lowered into the receptacle  74  through an opening  103  provided in the upper plate  2  of the housing. A washing well  104 , into which the needle  45  can be lowered to be washed and rinsed therein, is provided on the path  99  in an angular position  105  located between the angular positions  101  and  102 . 
     The removal and distribution unit  9 , which is designed to take a reagent in a cup  72  selected from cups supported by the reagent carrying plate  71 , and to deliver the removed reagent into one of the receptacles  74  carried by the plate  73 , can have a structure similar to that described with respect to the removal and distribution unit  8 . However, in the removal and distribution unit  9 , the foot  63 , the rod  64 , the spring  66  and the electromagnet  68  are absent, and the needle  45  is replaced by a pipette. The removal and distribution unit  9  can turn as a unit about an axis  106  ( FIG. 1 ) such that the pipette describes a trajectory in the arc of a circle  107  between an angular position  108  in which the pipette is disposed above one of the cups  72  of the reagent carrying plate  71 , and another angular position  109  in which the pipette is located above one of the receptacles  74  at the periphery of the plate  73 . In the angular position  109 , the pipette can be lowered into the receptacle  74  through an opening  111  provide in the upper plate  2  of the housing. The pipette of the removal and distribution unit  9  can also be lowered into any one of the three washing wells  112  located on the path in an arc of a circle  107 . 
       FIG. 7  shows another embodiment in which the elements which are identical or which play the same role as those shown in  FIGS. 3 and 4A , are designated by the same reference numerals, and will not be again described in detail. In the embodiment shown in  FIG. 7 , the connection  31  with two degrees of freedom comprises no spring  33  and the two pivots  25  of each tube carrying sleeve  24  rest on the bottom of the two notches  32  of the mounting member  28 . Preferably, each notch  32  has, in the region of the bottom of the notch, an enlargement directed radially outwardly relative to the axis of rotation of the plate  4 . 
     In  FIG. 7 , the support means  44  is not constituted by a fixed stop, but by a wedge which can be moved by an actuator  113 , for example an electromagnet, between a first position shown in full lines in  FIG. 7 and a  second position shown in broken lines. In the first position, the wedge  44  does not interfere with the tube carrying sleeves  24  when the plate  4  is rotated. 
     When a selected sample tube  6  has been brought into correspondence with the removal and distribution unit  8 , before the needle  45  of this latter having been lowered, the electromagnet  113  is actuated so as to bring the wedge  44  into its second position, in which it is in contact with the lower end of the tube carrying sleeve  24  and supports the latter in a vertical position such that its two pivots  25  no longer rest on the bottom of the notches  32 . Under these conditions, when the needle  45  is lowered and applies to the stopper  7  of the sample tube  6  a vertical force directed downwardly, this force is not transmitted to the circular plate  4 , but it is absorbed by the wedge  44 . 
     As shown in  FIG. 7 , the wedge  44  is preferably constituted by a wedge-shaped piece which can slide, under the control of the electromagnet  113 , over a fixed horizontal support and guide surface, for example the bottom lla of the bowl  11 . The direction of movement of the wedge  44  from its first position to its second position is radial relative to the axis of rotation of the plate  4 , and perpendicular to the pivotal axis of the tube carrier  5  defined by the two pivots  25 . As a result, when the wedge  44  is moved from its first to its second position, it could result that it causes the tube carrier  5  and the sample tube  6  which it contains, to pivot through a certain angle about the axis of the pivots  25  and that, as a result, the sample tube  6  will no longer be vertical at the time the needle  45  of the removal and distribution unit  8  is lowered. To avoid this, each mounting member  28  can be provided with an abutment  114  as shown in FIG.  7 . 
     In the two embodiments, the various active members of the analysis robot, such as for example the electric motors  19 ,  57 ,  79  and  95 , the syringe  47 , the angular coders  43 ,  62  and  84 , the electromagnets  68  and  113 , and the code reader  41 , are connected respectively by lines  115 ,  116 ,  117 ,  118 ,  119 ,  120 ,  121 ,  122 ,  123 ,  124  and  125  to a control unit  126  ( FIGS. 3 and 7 ) including a computer which manages the operation of the analysis robot. In particular, when the content of the sample tubes  6  must be subjected to centrifugation before being analyzed, the control unit  126  can be programmed to control the electric motor  19  so that it turns at a high speed of rotation during the time necessary to carry out centrifugation, and then that it turns at a slower speed to bring and position successively and selectively the sample tubes  6  into correspondence with the removal and distribution unit  8 . 
     Of course, the electric motors and the angular coders (not shown) associated with the removal and distribution unit  9  and with plate  73  are also connected to the control unit  126 . This latter is programmed or programmable to control the rotation of the plates  71  and  73  and the operation of the removal and distribution unit  9  so as to remove, each time this is necessary, at least one reagent from the selected cup  72  of the plate  71  and to deliver the removed reagent into a selected receptacle  74  of the plate  73 . 
     It follows that the embodiments which have been described above have been given purely by way of indicative example and in no way limiting, and that numerous modifications can be supplied by those skilled in the art without thereby departing from the scope of the invention. It is thus that the mounting members could be an integral portion of the plate  4 .