Abstract:
The pump unit according to the invention is formed by assembling a pump module ( 9 ) comprising a body having a cavity ( 10 ) forming a working chamber, a translationally mobile piston ( 15 ) engaging leaktightly in the cavity ( 10 ) via a seal ( 14 ), at least one channel ( 12, 13 ) formed in the body to connect the working chamber to a use circuit, a linear actuating module comprising an actuating member ( 3 ) that is translationally mobile coaxially with the piston ( 15 ), and a connecting and guiding module ( 18 ) for establishing a mechanical connection between the pump module ( 9 ) and the linear actuating module ( 2 ) and for precise guidance of the piston ( 15 ) coaxially with the seal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a long-life pump unit, which can be used for a number of types of withdrawals with a view to analyses. It is more particularly, but not exclusively, applicable to pipetting, dilution, rinsing and/or distribution of samples of liquid substances. 
     In general, one knows that a number of devices have already been proposed making it possible to perform pipetting and rinsing cycles, in particular within an analysis device. 
     2. Description of the Prior Art 
     These devices typically involve the use of a pumping module comprising a body provided with a working chamber, for example cylindrical, and a piston which can be in the form of a plunger which engages leaktightly in the working chamber. Actuation the piston is then done by a linear actuator comprising a rotating electric motor, for example of the step-by-step type, and a member converting the rectilinear movement into a rectilinear translational movement. 
     It has been seen that the pumping devices of this type currently produced have a certain number of drawbacks: 
     First of all, the conversion system which is used significantly increases the complexity of the device assembly as well as its cost. 
     Moreover, one encounters alignment problems between the linear movement actuation member and the piston: the alignment defects at this level lead to creating, on the seal which procures the leaktightness between the piston and the body of the pumping module, transverse stresses and, as a result, areas where abnormally high friction is produced which leads to premature wear of the seal. This is a relatively important drawback which increases maintenance costs and which, very often, reduces the life of the pumps. 
     Moreover, one drawback of the existing pump devices resides in the absence of modular nature and, in particular, of the possibility of quick interchangeability of the pumping module and the actuator. 
     OBJECT OF THE INVENTION 
     The invention therefore more particularly aims to eliminate all of these drawbacks. 
     SUMMARY OF THE INVENTION 
     To this end, it proposes a pump unit realized in three modules able to be easily assembled or disassembled, namely: 
     a pump module of the aforementioned type comprising a body provided with a cavity constituting a working chamber, a translationally mobile piston engaging leaktightly in the cavity via a seal arranged between said body and said piston, at least one channel formed in the body to connect the working chamber to a use circuit, said body comprising an assembly surface centered perpendicular to the axis of movement of the piston, 
     a linear actuating module comprising an actuating member that is translationally mobile coaxially with the piston, and 
     a connecting and guiding module for establishing a mechanical connection between the pump module and the linear actuating module and for precise guidance of the piston coaxially with the seal, this guidance being independent of the guide means used by the actuating module. 
     Advantageously, the coupling between the actuating member and the piston is ensured by the assembly, on one hand, of a cylindrical-spherical seal involving the use of a spherical head centered on the axis of the actuating member and connected thereto by an under-head portion with a section smaller than the diameter of the sphere and, on the other hand, a cylindrical groove formed in the end of the piston opposite the pump member, perpendicular to the axis of said piston, this cylindrical groove opening axially to the outside via a slot having a width smaller than the diameter of the groove and slightly larger than said under-head portion. The spherical head which is integral with the actuating member engages in the spherical groove and is held there axially in both directions. However, it can swivel in the groove while also being able to move in the axis of the groove. 
     Thus, thanks to these arrangements, an alignment flaw between the actuating member and the piston will not create any stress of a nature to cause premature wear of the dealing device, or even a sealing defect. 
     Moreover, the aforementioned channel may be formed so as to be able to receive all or part of a single- or multi-path valve or a hollow needle serving for pipetting. 
     In the latter case, the pump unit may comprise means allowing its fixing on a mobile element of an automatic or semi-automatic pipetting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the invention will be described below, as a non-limiting example, with reference to the appended drawings in which: 
         FIG. 1  is a side view of a pump unit according to the invention; 
         FIG. 2  is an axial cross-section along A/A of  FIG. 1 ; 
         FIG. 3  is a side view of a variation of embodiment of the pump unit; 
         FIG. 4  is an axial cross-section along B/B of  FIG. 3 ; 
         FIG. 5  is a partial diagrammatic cross-section showing a pump module on which a multi-path solenoid valve or a pipetting needle can be connected. 
         FIG. 6  is an axial cross-section of another variation of embodiment of the pump unit. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the example illustrated in  FIGS. 1 and 2 , the pumping unit  1  involves the use of an actuating module  2  of the jack screw type comprising: 
     A step-by-step electric motor whereof the rotor comprises a tapped coaxial central bore in which a rod  3  having a threaded portion cooperating with the tapping is engaged. This rod  3 , which forms the actuating member, has, moreover, a ribbed portion which engages in a sliding bearing having a complementary smaller section, integral with the stator part of the motor. One of the two ends of the rod is extended by a tip  4  comprising a spherical head  5  connected to a cylindrical socket  6  via an underhead portion  7  having a diameter smaller than that of the head  5  and the cylindrical socket  6 . The cylindrical socket  6  is provided with a tapping which screws on a threading provided at the end of the rod  3 . 
     The stator part of the motor comprises a coupling sleeve  8  whereof the outer shape is that of a cylinder, stepped. It has a coaxial central passage in which the rod  3  slides. 
     The pump unit  1  comprises a pump module  9  including a single-piece body, for example cylindrical or parallelepiped rectangle, precisely formed in a machinable and/or moldable material and having a very low coefficient of expansion. 
     This body comprises a coaxial cylindrical cavity  10  opening via an orifice located at the center of one of these surfaces  11  which constitute an assembly surface. 
     This cavity  10 , which constitutes the working chamber of the pump, is connected with the outside via two channels  12 ,  13  enabling a connection to respective use circuits. 
     One of these channels  12  is arranged coaxially to the cavity  10 , opposite the orifice. It opens at the top of a coaxial conical surface constituting the bottom of the cavity. 
     The other channel  13  extends perpendicular to the axis of the cavity  10 , near the surface  11 . 
     The cavity  10  comprises, near its orifice, a bore stepping in which a seal  14  is engaged, through which the piston  15  of the pumping module  9  slides leaktightly. 
     This piston  15 , which consists of a plunger having a cylindrical shape, has on one side, a conical end  16 , with a shape substantially complementary to that of the bottom of the cavity  10  and, on the other side, a flat terminal surface in which opens a diametric cylindrical groove  16 ′, centered perpendicular to the axis of the piston  15 . 
     In this example, the connecting and guiding module  18  consists here of a metallic block  17  (for example in aluminum alloy) with a parallelepiped shape whereof two opposite surfaces F 1 , F 2  serve as assembly surface for the pump module  9  and for the actuating module  2 , respectively, and a lateral surface  19  which serves as a fixing surface of the pump unit on a support (for example in an analysis machine). 
     The block  17  comprises a coaxial central bore  20  opening into the surfaces F 1 , F 2 . 
     This bore  20  comprises, on the side of the surface F 1 , a bore stepping extending over approximately ¼ of its length in which a tubular section  21  in a material with a small friction coefficient (such as, for example, a fluorocarbon, PTFE, FEP) is arranged. This tubular section  21  serves as sliding bearing for the piston  15 . 
     The bore  20  comprises, on the side of the surface F 2 , steps in which the steps of the coupling sleeve  8  of the actuating module  2  engage tightly. 
     Thus, in the assembled position of the three modules, with coupling of the rod  3  and the piston  15 , all of the elements animated by the translational movements are supposed to be coaxial. 
     However, if there is an alignment flaw between the rod  3  and the piston  15  (for example due to the dimensional tolerance of the steppings of the actuating module, for example in the case where the actuating module is purchased such as in business), this alignment defect cannot have consequences for the sealing device due to the precision of the guidance of the piston  15  and the type of piston  15 /rod  3  coupling which is used. 
     This structure also has the advantage of being able to be assembled or disassembled very simply (for example by screwing/unscrewing of screws arranged parallel to the axis of the rod  3 /piston  15  assembly). 
     This structure allows interchangeability of the modules, for example to adapt the pump unit  9  to the application of which it is the object. 
     The fixing of the pump unit  9  on a support can be done using two screws centered parallel to the axis of the piston. Channels  22 ,  23  realized in the module  18  perpendicular to the assembly surface  19  serve to fix the pump. 
     Of course, the invention is not limited to the embodiment previously described. 
     Thus, for example, the pump module  9  could comprise at least one solenoid valve controlling the passage of fluid in one of the channels  12 ,  13 . Advantageously, this solenoid valve could be integrated into the block constituting the pump module  9 . 
     In the example illustrated in  FIGS. 3 and 4 , the pump module comprises a single-piece body  30  similar to that described in the preceding example. 
     Similarly, it comprises a coaxial cylindrical cavity  31  opening at the assembly surface  32 . This cavity  31 , which constitutes the working chamber of the pump, is connected with the outside via two channels, namely: 
     a channel  33  arranged coaxially to the cavity  31  and opening at the top of a coaxial conical surface  34  constituting the bottom of the cavity  31 , 
     a channel  35  which extends perpendicular to the axis of the cavity  31 , near the assembly surface  32 . 
     In this example, each of the channels  33 ,  35  successively comprises, starting from the cylindrical cavity  31 , a cylindrical section of small diameter connected to a cylindrical section  36 ,  36 ′ with a larger diameter via a conical portion  37 ,  37 ′ serving as sealing face. The cylindrical section of larger diameter  36 ,  36 ′ is extended by a tapped portion  38 ,  38 ′ leading to the outside. 
     In the tapped portions  38 ,  38 ′ are leaktightly screwed the bodies  39 ,  39 ′ of a solenoid valve closing device  40 ,  40 ′ comprising a closure which is in the form of a needle  41 ,  41 ′ whereof the conical end has the same conicity as the conical portion  37 ,  37 ′. 
     This needle  41 ,  41 ′ is actuated by a coil (not illustrated) located inside the solenoid valve  40 ,  40 ′. 
     The cylindrical section  36 ,  36 ′ defines a closure chamber which is connected to the outside via a channel  42 ,  43  opening into a cylindrical cavity  44 ,  45  provided with a tapping serving to connect a flexible tube, preferably in transparent plastic material. 
     In this example, the channel  43  which opens into the cylindrical section  36  extends perpendicular to the axis of the cylindrical cavity  31  such that the cavity  45  is formed in a lateral surface of the block. 
     The channel  42  which opens into the cylindrical section  36 ′ extends parallel to the axis of the cylindrical cavity  31  such that the cavity  44  is formed in the (upper) surface of the body  30  located opposite the motorization. 
     The interest of the solution previously described consists in that insofar as the body  30  is formed in transparent material, the entire journey of the liquid through the pump is visible. Moreover, the connections of the tubes are done in a plane parallel to the front surface of the body (plane of  FIG. 4 ) such that one can also observe the circulation of the liquid inside these tubes. 
     Moreover, thanks to the integration of solenoid valves  40 ,  40 ′ in the body  30 , one obtains a compact and not very voluminous assembly which can easily be housed in an apparatus, possibly on a mobile part. 
     In the example illustrated in  FIG. 5 , the cylindrical cavity  50  of the body  51  is only connected to the outside via a single channel  52  arranged coaxially to the cavity  50 , in a position similar to that of the channel  38 . 
     This channel  52  is extended by a coaxial cylindrical cavity  53  in which can be assembled, leaktightly: 
     either a pipetting needle  54  provided with a connection tip, for example by screwing, 
     or a multi-path closure, for example a three- or four-path solenoid valve  55  having suction and/or discharge outlets on which flexible conduits  56 ,  57  can be connected. 
     In the variation of embodiment illustrated in  FIG. 6 , inside the cavity  60  of the body  61 , a piston  62  provided with a sealing gasket  63  slides leaktightly. 
     This piston  62  is itself driven by an actuating module  64  of the type described with regard to  FIGS. 1 and 2 . 
     Here also, the cylindrical cavity  60  is only connected to the outside via a single channel  64  arranged coaxially to the cavity  60 . 
     This channel  64  is extended by a coaxial cylindrical cavity  65  which opens on the upper surface  66  of the body  61 . 
     It also opens at the outside by a channel/cavity  68  assembly centered perpendicular to the axis of the cylindrical cavity  60 . The cavity  68  opens at a lateral surface of the body  61 . 
     The cavities  65  and  68  are designed so as to be able to receive solenoid valves and/or flexible conduits. One of these cavities could possibly be blocked by a closure, the other cavity then being able to receive, for example, a pipetting needle or a stylet.