Abstract:
A pipetting system including a syringe ( 2 ), a working piston ( 5 ) connectable with the syringe piston ( 24 ) and extending into a working chamber ( 3 ), an actuating piston ( 7 ) extending into the working chamber, and a storage chamber ( 4 ) connected with the working chamber ( 3 ) by a valve ( 12 ) that provides for flow of the hydraulic liquid, which fills both chambers, from the working chamber ( 3 ) into the storage chamber when the working piston ( 5 ) is displaced into the working chamber ( 3 ), for flow of the hydraulic fluid from the storage chamber ( 4 ) into the working chamber ( 3 ) when the actuating piston is displaced out of the working chamber, and that separates the storage and working chambers ( 3, 4 ) when the actuating piston ( 7 ) is advanced into the working chamber.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a pipetting system using a step-and-repeat pipette and a syringe releasably connected thereto. 
     2. Description of the Prior Art 
     Pipetting systems of the above-mentioned type serve for proportioning certain liquid volumes (e.g. reagents) and are especially employed at a laboratory. The step-and-repeat pipette is used to hold and actuate the syringe in order to draw liquid into it and dispense the liquid therefrom. The syringe may be replaced with a clean syringe after use and may be disposed of. Suction into the syringe is effected, as a rule, by a single step whereas delivery of certain proportioning volumes may be done by several steps. Pipetting systems using adjustable proportioning volumes have been known before. 
     Thus, DE 29 26 691 C2 discloses a step-and-repeat pipette which has a rack-actuated pawl means for a step-by-step forward motion of a piston by means of a reciprocating driving lever. The rack further has provided on it an adjustably slidable cover to limit the effective pawl engagement to advance the piston. The cover is adapted to be displaced by a regulating member disposed in the pipette casing, which may be designed with a rotary knob. In this: pipetting system, the proportioning volume can only be adjusted by steps the fineness of which is limited by the pitch of the rack. 
     Pipetting systems having hydraulic actuators in the widest sense are known from the following publications: DE 40 11 548 A1, DE 42 14 430 A1, DE 25 58 672 A1, U.S. Pat. No. 5,456,885, JP 63-169 565 A, JP 4-161 856 A, Measurement Techniques, Vol. 1987, issue 1, pp. 51-53. 
     Therefore, it is the object of the invention to create a pipetting system of the aforementioned type which makes it possible to continuously change the proportioning volume. 
     SUMMARY OF THE INVENTION 
     The inventive pipetting system has a step-and-repeat pipette and a syringe releaseably connected thereto. The step-and-repeat pipette retains the syringe and has means that provides for disfigurement of the syringe piston back away from the syringe aperture and for pushing the syringe piston forward towards the syringe aperture dependent on the liquid volumes to be ejected from the syringe. The providing means includes a working piston connected to the syringe piston and an actuating piston. The working and actuating pistons are sealingly introduced in a working chamber, with the actuating piston having an actuating end which can be actuated from outside. The working piston may be connected directly or indirectly to the syringe piston and the actuating end may be actuated directly or indirectly from outside. A storage chamber is arranged adjacent to the working chamber and has a variable stock volume. The volume may be variable because of an equalizing piston which is sealingly and slidably; introduced in the storage chamber, and/or because of a flexible wall of the storage chamber. In addition, the connection between the working chamber and storage chamber has a valve means which, while the working piston is pushed into the working chamber, especially while the syringe piston is pushed back, allows a hydraulic fluid to pass from the working chamber to the storage chamber. As a result, the liquid volume which is displaced by the working piston while it is pushed it is pushed in is caught by the variable stock . volume of the storage chamber. This makes it possible to charge the syringe with liquid and/or to adjust the working piston in an initial position for the delivery of liquid. In addition, the valve means separates the working chamber from the storage chamber while the actuating piston is pushed into the former in order that the hydraulic liquid may force the working piston out of the working chamber by one step with a view to pushing the syringe piston forward. Separation of the working chamber from the storage chamber will prevent the liquid volume displaced by the actuating piston from being received by the variable stock volume without forcing out the working piston. However, while the actuating piston is pushed back from the working chamber the valve means allows hydraulic liquid to pass from the storage chamber over to the working chamber for refilling. This will replace a volume of hydraulic fluid, which corresponds to the motion of the working piston out of the working chamber so that the working piston is forced out by another step while the actuating piston is actuated next time. 
     The liquid volume dispensed from the syringe will be dependent upon the distance by which the actuating piston is pushed into the working chamber. Thus, the proportioning volume is infinitely variable. Preferably, the actuating piston is adapted to be moved between a first stop limiting the push-back motion and a second stop limiting the pushing-in motion, which creates reference points for the proportioning volume. When the actuating piston is moved from one stop to the other the proportioning volume is precisely defined. Also preferably, the spacing between the first and second stops may be adjusted by means of an adjustment means. This also helps adjust the volume to be proportioned, which is achieved by moving the actuating piston from one stop to the other. The adjustment means may have a micrometer means and may be coupled to an indicator means for the proportioning volume. Preferably, the actuating piston is biased by a spring in the push-back direction so that it will independently reset itself, after undergoing actuation, to an initial position. for another proportioning step. 
     The valve means may have a check valve, which opens in the direction of flow from the storage chamber to the working chamber and closes in a reverse direction. The check valve automatically causes a separation of the storage chamber and working chamber while the actuating piston is pushed into the working chamber and automatically eliminates such separation while the actuating piston is drawn out. Moreover, the check valve may be adapted to be actuated from outside for the passage of hydraulic liquid while the working piston is pushed in. In lieu of an active check valve, there may be an extra valve adapted to be actuated from outside between the working chamber and storage chamber. 
     A springback of the syringe piston sealing lip following a proportioning step may result in the syringe sucking back a small liquid volume. To avoid faulty proportioning, a first working chamber and a second working chamber may exist, the working piston being associated with the first working chamber and being connected to the storage chamber via a valve of the valve means, which may be opened while the working piston is pushed into the first working chamber. Further, the second working chamber may have associated with it the actuating piston and may be connected to the storage chamber via a valve of the valve means, which separates it from the second working chamber while the actuating piston is pushed in and connects it to the second working chamber while the actuating piston is pushed back. The further valve may be a check valve. The working chambers are interconnected by a further valve means which closes upon completion of the forward motion of the actuating piston. The further valve means may be a further check valve which opens in the direction of flow from the second working chamber to the first working chamber and closes in a reverse direction. When the actuating piston is then relieved and withdrawn the working piston will not be relieved, however, but will be kept under a tension by the closing procedure of the second valve means in the first working chamber, as will the syringe piston. On the other hand, the second working chamber will fill while the actuating piston is withdrawn with the hydraulic liquid volume required. This volume is forced into the first working chamber during the next actuation by the further valve means so that the syringe will at any time dispense the proper proportioning volume. 
     In addition, there may be a means for avoiding a residual lift, which prevents another proportioning step when the residual liquid volume existing in the syringe is smaller than the adjusted proportioning volume. To this end, the means for avoiding a residual lift may have a means for sensing the position of the working piston while the actuating piston is pushed back, and a means for comparing the residual lift determined to the volume to be proportioned as well as a means for preventing the working piston from further being pushed out when the residual lift is insufficient. Sensing the position of the working piston only during each backward motion of the actuating piston will achieve that the last proportioning procedure possible may still be effected completely. Blocking the further motion of the working piston will achieve that the succeeding proportioning action can no more be started. Preferably, in addition, the blockage of a further motion of the working piston is coupled by the means for avoiding a residual lift to the setting procedure of the adjustment means so that the respective proportioning volume will then be taken into account. Also preferably, the actuating piston will not be blocked when the operation to avoid a residual lift becomes effective, but its actuation is possible with no displacement of the working piston. 
     Non-defined proportioning volumes may be dispensed when the actuating piston is relieved in the meantime. Therefore, another aspect of the invention provides that there is a means ensuring that the working piston is pushed out of the working chamber, which prevents the actuating piston from moving back and/or the valve means from opening before the completion of the proportioning step. Here, the means ensuring that the actuating piston reaches the second stop is adapted to effect sensing, which is an indication that the proportioning step is fully completed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The pipetting system will be explained in detail below with reference to the accompanying drawings, wherein: 
     FIG. 1 is a basic type of the pipetting system in a roughly schematic representation; 
     FIG. 2 is an aspect of detail II of FIG. 1 in an enlarged, roughly schematic representation; 
     FIG. 3 is a pipetting system using error suppression because of syringe elasticity, residual lift blockage, and full-lift ensurance in a roughly schematic representation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the discussion below of various embodiments of the inventive pipetting system, similar elements are designated by the same reference numerals. 
     The pipetting system of FIG. 1 has a step-and-repeat pipette  1  and a syringe  2 . 
     Step-and-repeat pipette  1  has a working chamber  3  and a storage chamber  4  which are completely filled with a hydraulic medium such as hydraulic oil or water. 
     A working piston  5  which is sealingly passed through a sealing  6  in a front wall of the working chamber partially extends into working chamber  3 . On the opposite side, an actuating piston  7  which also is sealingly passed through a sealing  8  in the wall of the working chamber partially extends into it from outside. 
     An equalizing piston  9 , which is sealingly passed through a sealing  10  in the wall of storage chamber  4  partially extends into the storage chamber from outside. 
     Working chamber  3  and storage chamber  4  have a valve means  12  in their common partition wall  11 . It is designed as a ball-check valve using a ball  13  and a helical spring  14 . Check valve  12  opens in the direction of flow from storage chamber  4  to working chamber  3  and closes in the reverse direction. Moreover, it may be opened from outside by means of a pin  15 . 
     The end of actuating piston  7  which projects from working chamber  3  is designed as an actuating button  16 . In addition, actuating piston  7  is slidable between a first stop  17 , which is firmly joined to step-and-repeat pipette  1 , and a second stop  18 , against which it strikes by a lug  19 . The position of stop  18  in the direction of displacement of actuating piston  7  is adjustable by means of a micrometer screw  20  with which an indicator  21  is associated. 
     Working piston  5  is provided with a return motion lever  22  on the part projecting from working chamber  3 . 
     Furthermore, the projecting part of working piston  5  is connected to a syringe piston  24  of syringe  2  via a disconnectable coupling  23 . Syringe piston  24  of syringe  2  is releasably inserted into a seat (not shown) of pipette  1  by means of a mounting flange  26 . At the other end, the syringe cylinder  25  has a dispensing syringe  27  in which a syringe opening  28  is formed. 
     The pipetting system operates as follows: 
     Initially, step-and-repeat pipette  1  is connected to syringe  2  with working piston  5  being coupled to syringe piston  24  at  23 . Subsequently, syringe piston  24  is pulled out to draw liquid into syringe  2  by pushing working piston  5  into working chamber  3  by an actuation of return motion lever  22 . At this point, valve means  12  has been opened by an actuation of pin  15  to cause the liquid displaced by working piston  5  to flow over to storage chamber  4  and force out equalizing piston  9  accordingly. After syringe  2  is filled pin  15  is relieved and valve means  12  closes working chamber  3  with respect to storage chamber  4 . When a completely filled syringe  2  is connected working piston  5  may be pushed in before. 
     In addition, the proportioning volume to be dispensed is adjusted by means of micrometer screw  20  and indicator means  21 . The pipetting system makes it possible to set any proportioning volumes within the limits given by the removability of stops  17 ,  18 . For the delivery of the volume set, actuating piston  7  is moved from its initial position at the first stop  17  to the second stop  18 . The liquid displaced by actuating piston  7  forces working piston  5  out of working chamber  3  accordingly because valve means  12  is closed. The distance passed through by working piston  5  here corresponds to the spacing between stops  17 ,  18  multiplied by the ratio of diameters of actuating piston  7  and working piston  5 . Accordingly, liquid is forced out of syringe aperture  28  by syringe piston  24 . 
     For another actuating step, actuating piston  7  requires to be withdrawn against the first stop  17 , which may be effected automatically by a spring (not shown). During withdrawal, check valve  12  will open automatically and hydraulic liquid will again flow into working chamber  3  from storage chamber  4  in order to substitute for the volume released by actuating piston  7 . Irrespective of this embodiment, valve means  12  is allowed to admit liquid slippage only to an extent such that the limits for the precision and correctness of the proportioning system are adhered to. When actuating piston  7  arrives at the first stop  17  the pipetting system will be prepared for another dispensing operation. 
     The sequence may be repeated several times until syringe piston  24  is completely forced in or until a residual lift blocking device engaging working piston  5  prevents a residual volume falling below the adjusted proportioning volume from being dispensed. 
     The pipetting system of FIG. 3 has a first working chamber  3 ′ and a second working chamber  3 ″. Working piston  5  is introduced in first working chamber ″ through sealing  6 . Actuating piston  7  is introduced in second working chamber  3 ″ through sealing  8 . Next to the first and second working chambers  3 ′, 3 ″ there is storage chamber  4  the storage chamber wall of which is formed as a corrugated bellows  30 ″. Disposed in partition wall  11 ″ which is common with second working chamber  3 ″ is ball-check valve  13 ,  14  which forms part of a valve means  12  and opens in the direction of flow from storage chamber  4  to second working chamber  3 ″ and closes in the reverse directions. 
     Disposed in the common partition wall  11 ′ of storage chamber  4  and working chamber  3 ′ is a valve  31  adapted to be actuated from outside, which also forms part of valve means  12  and is designed to allow liquid to pass in either direction. Arranged between second working chamber  3 ″ and first working chamber  3 ′ is a further valve means  32  in the form of a ball-check valve, which opens in the direction of flow from the second working chamber to the first working chamber and closes in the inverse direction. 
     Actuating piston  7  strikes its end projecting from second working chamber  3 ″ against a first stop  17 ′ which is defined by the underside of a plate  33  which is adjustable by means of a micrometer screw  20  in the axial direction of the actuating piston. Another plate  34  which protrudes at its two ends is fixed to the projecting end of actuating piston  7 . The path of actuation of actuating piston  7  is defined by the stroke of further plate  34  against the adjoining front-end wall of working chamber  3 ″ which forms a fixed stop  18 ′. 
     An actuating button  35  having a pin  36  acts on the short protruding leg of further plate  34 . A helical spring  37  supported in step-and-repeat pipette  1  acts on the other leg in the opposite direction. Syringe  2  is retained in step-and-repeat pipette  1  by a syringe flange  26  of its syringe cylinder  25  and is connected, by means of its syringe piston  24 , to working piston  5  via a coupling  23  so that it may be disconnected after use. 
     Step-and-repeat pipette further has a linkage  38 . This includes a first articulated bar  39  which is pivotally supported in a fixed bearing  40  in step-and-repeat pipette  1  and extends transversely, while passing by syringe piston  24 , in such a way that coupling  23  (or a particular flange) urges against the upper surface of articulated bar  39  towards the end of the displacement motion of syringe piston  24 . This one, however, is biased by means of a helical spring  41  towards the working piston  5 . The articulated bar  39  senses the position of the working piston ( 5 ) when the actuating piston ( 7 ) is pushed back. 
     At the side of syringe piston  24  opposed to bearing  40 , articulated bar  39  is linked via a joint to a transfer bar  42  which is guided by a guide  43  in step-and-repeat pipette  1  and has a member  44  angled towards micrometer screw  20 . Linkage  38  with its angled member  44  is pressed by spring  41  against a stationary stop  45  in step-and-repeat pipette  1 . 
     Angled member  44  has an electric contact  46  at the side which is directed in a direction opposed to the action of spring  41 . An electric contact  47  of plate  33  is associated with this contact. Both the contacts,  46 ,  47  touch each other when articulated bar  39  is pivoted against the action of spring  41 , and transfer bar  42  is pulled downwards accordingly. The downward position of the articulated bar  39  indicates that a residual liquid volume in the syringe ( 2 ) is less than the adjusted proportioned volume. 
     Finally, there is yet another electric contact  48  at the side of plate  34  which is directed in the sense opposed to the action of spring  37 . An electric contact  49  which is stationary in step-and-repeat pipette  1  is associated with this contact. 
     The pipetting system operates as follows: 
     Initially, step-and-repeat pipette  1  and syringe  2  are connected to each other. Subsequently, working piston  5  is pushed into first working chamber  3 ′ with valve  31  being opened to allow hydraulic liquid to flow from first working chamber  3 ′ over to storage chamber  4  where the increase in volume is compensated by the corrugated bellows  30 ′. 
     Micrometer screw  20  is used to infinitely vary the liquid volume to be proportioned. This one displaces first stop  17 ′, which fixes the beginning of the path of motion of actuating piston  7  the end of which is determined by fixed stop  18 ′. This displacement is linked with a displacement of hydraulic liquid from second working chamber  3 ″, via a further valve means  32 , into first working chamber  3 ′, which may be equalized by opening valve  31  if working piston  5  is not to be advanced unintentionally. Of course, the volume may also be adjusted with valve  31  not being opened before working piston  5  is pushed back. When actuating button  35  is depressed actuating piston  7  is pushed into second working chamber  3 ″ according to the volume adjusted and a respective liquid volume passes into first working chamber  3 ′ via further valve means  32  and, in turn, advances working piston  5  there, which ejects the desired liquid volume via syringe piston  24 . Upon completion of the actuating lift, further valve means  32  closes and actuating piston  7  and actuating button  35  return to their initial positions under the action of spring  37 . At this point, the volume made vacant by actuating piston  7  is substituted for from storage chamber  4  by check valve  13 ,  14 . What is important is that further valve means  32  closes upon completion of the forward motion of actuating piston  7  so that working piston  5  as well as syringe piston  24  will then not be relieved while actuating piston  7  moves back so that elastic recovery effects will not occur in the syringe. 
     Once actuating piston  7  has reached first stop  17 ′ another liquid volume may be dispensed. 
     When the coupling  23  ultimately advances the articulated bar  39  downward during a proportioning step, the contacts  46 ,  47  will touch each other. The downward position of the bar  39  indicates that the residual liquid volume, which is still in syringe  2 , no longer corresponds to the proportioned volume adjusted, and the engagement of the contacts  46 - 47  prevents the following proportioning step from taking place. The proportioned volume adjusted is taken into account here by the setting of contact  47  with the micrometer screw  20 . 
     However, the fact that the residual liquid volume is found to be insufficient to accomplish another proportioning step must not result in a cease of a proportioning step under way. Therefore, a termination of proportioning steps is established by means of contacts  48 ,  49 . More proportioning operations are suppressed following a touch between contacts  46  and  47  only when contacts  48 ,  49  also have touched each other. This will avoid faulty pipettings when contacts  46 ,  47  are switched during the last pipetting procedure. Evaluation is electrical and causes valve  31  (which, for example, is electrically controlled) to open. After this, while actuating button  35  may still be actuated, the hydraulic liquid thereby displaced will be discharged into storage chamber  4  without causing working piston  5  to advance, whereby the further proportioning step is interrupted. 
     The same function can also be achieved by means of a purely mechanical construction. 
     Finally, this pipetting device has a safety device preventing non-defined volumes from being pipetted by an intermediate relief of actuating piston  34  during the pipetting procedure. For this purpose, actuating piston  7  may have a purely mechanical hold-back which will not be released until second stop  18 ′ is reached. In another solution, check valve  13 ,  14  may be blocked from outside for a time until second stop  18 ′ is reached. For example, this can be done electrically by fixing the touch between contacts  48 ,  49  and blocking check valve  13 ,  14  until the touch. This blockage prevents fresh hydraulic liquid from being drawn from storage chamber  4  to second working chamber  3 ″ in an attempt to pull out actuating piston  7  and from faultily increasing the volume dispensed up to second stop  18 ′ during the succeeding actuation.