Patent Publication Number: US-2020282390-A9

Title: Pipetting device with an easily replaceable magnet piston

Description:
The present invention relates to a pipetting apparatus for aspirating and dispensing metered liquids, encompassing:
         at least one guidance tube extending along a cylinder axis, the cylinder axis defining: an axial direction proceeding along its direction of extent; a radial direction proceeding orthogonally thereto; and a circumferential direction extending therearound;   a piston received in the guidance tube axially movably relative thereto;   a coupling configuration embodied for temporary or permanent coupling of a pipetting tip; and   a drive apparatus for driving the piston to move axially relative to the guidance tube,       

     the guidance tube comprising a coupling-side longitudinal end that is located closer to the coupling configuration; and comprising a servicing-side longitudinal end that is located oppositely from the coupling-side longitudinal end and is located farther from the coupling configuration; the piston encompassing at least one permanent magnet; and the drive apparatus comprising an energizable coil arrangement at least partly surrounding the guidance tube in a circumferential direction. 
     A pipetting apparatus of the species is known from WO 2011/083125 A1. This pipetting apparatus is disadvantageous in that any type of seal with which the pipetting piston is sealed with respect to its guidance tube wears very quickly. This is due to the large accelerations and decelerations that are achievable with the magnetic piston, i.e. a pipetting piston having at least one permanent magnet, and with the coil arrangement surrounding the guidance tube. The magnetic piston and the coil arrangement constitute a linear drive system. 
     The object of the present invention is therefore to refine the pipetting apparatus of the species in such a way that it withstands the seal wear that is elevated as compared with conventional pipetting apparatuses not having a linear-motor drive system. 
     This object is achieved according to the present invention by a pipetting apparatus of the kind recited previously in which the servicing-side longitudinal end of the guidance tube is open or is openably closed off with an intentionally detachably arranged cover, so that a withdrawal longitudinal end of the piston, located closer to the servicing-side longitudinal end of the guidance tube, is movable by an external magnetic field axially out of the guidance tube. 
     This conformation, which can be realized only with the linear-motor piston drive system discussed here, thus permits the magnetic piston to be easily extended out of the guidance tube along the cylinder axis. The piston needs to be moved out of the guidance tube only sufficiently far that it can be completely pulled out of the guidance tube by being grasped with a hand or tool. There is therefore no need for complex installation operations such as those necessary when replacing a pipetting piston coupled to conventional mechanical drive systems, for example having a piston driven by a worm-gear or spindle drive, in which at least one piston rod that connects the piston to the drive apparatus is usually provided between the piston and the servicing-side longitudinal end of the guidance tube. 
     It may merely be necessary to take off a cover that is intentionally detachably arranged on the servicing-side longitudinal end of the guidance tube, if the servicing-side longitudinal end is closed off in intentionally detachable fashion with the cover in order to prevent the ingress of dirt. 
     In principle, the magnetic piston (pipetting piston) comprising at least one permanent magnet can be moved out of its guidance tube with a sufficiently strong magnetic field of any magnetic field source. But because the drive apparatus already comprises a coil arrangement constituting a magnetic field source for displacing the piston along the cylinder axis of the guidance tube during operation, the coil arrangement is preferably a source of the external magnetic field for extending the withdrawal longitudinal end of the piston. The number of components required for manufacturing the pipetting apparatus can thereby be minimized. 
     In order to allow the piston to move in positionally accurate fashion along the longitudinal axis with the finest possible axial positional resolution, the coil arrangement preferably comprises at least three separate coil strands, each coil strand being connected to a different phase of a multi-phase, in particular three-phase, power supply. Windings of different coil strands preferably alternate in an axial sequence along the cylinder axis. 
     Because aspiration in laboratories occurs as a rule from and into containers arranged in grid fashion, from example from microtitration plates having “wells” embodied in grid fashion therein, in order to enhance its operating efficiency the pipetting apparatus of the present invention preferably comprises a plurality of parallel guidance tubes arranged in grid fashion, in each of which an axially movable piston comprising at least one permanent magnet is received, and the servicing-side longitudinal ends of which are each open or are openably closed off with an intentionally detachably arranged cover, and each of which is partly surrounded in a circumferential direction by an energizable coil arrangement constituting part of the drive apparatus. It is not to be excluded, however, that the pipetting apparatus comprises only a single guidance tube and thus only one pipetting channel. 
     In accordance with a further aspect of the present invention, the object recited previously is also achieved by a method for replacing a linear-motor-driven piston of a pipetting apparatus as described above, the method encompassing the following step:
         energizing the coil arrangement in such a way that a withdrawal longitudinal end of the piston, located closer to the servicing-side longitudinal end of the guidance tube, is moved by an external magnetic field axially out of the guidance tube at the servicing-side longitudinal end.       

     Regarding the advantages of the method according to the present invention, reference may be made to the explanations above of the advantages of the apparatus according to the present invention. 
     If the guidance tube happens to be closed off at its servicing-side longitudinal end by an intentionally detachably arranged cover in order to prevent the ingress of dirt, the method preferably encompasses the step of removing an intentionally detachably arranged cover from the servicing-side longitudinal end of the guidance tube. 
     For replacement of the linear-motor-driven piston, the method preferably furthermore encompasses extraction of the piston from the guidance tube and/or insertion of a further piston into the guidance tube. It is thus possible, as has already been explained above, for the magnetic piston to be moved in linear-motor fashion at least part of the way out of the guidance tube, so that an end region of the piston which comprises the withdrawal longitudinal end is no longer surrounded by the guidance tube and can therefore be grasped. Starting at that point in time, the piston can very easily be pulled out, serviced, or replaced with a new or already serviced piston, and the piston provided for further operation of the pipetting apparatus can be inserted into the guidance tube. 
     In order to bring the pipetting apparatus into an operationally ready state as quickly as possible after a piston replacement, the method according to the present invention furthermore preferably encompasses the step of moving the piston into a reference position, in particular into a reference position defined by a mechanical stop. 
     The present invention will be explained in more detail below with reference to the appended Figures, in which: 
       FIG. 1  is a schematic longitudinal section view through an embodiment of a magnetic piston of the present invention; and 
       FIGS. 2 a  to 2 c    depict an embodiment according to the present invention of a schematically depicted pipetting apparatus having the magnetic piston of  FIG. 1 , received movably in the guidance tube, in different relative positions relative to the guidance tube; and depict the coil arrangement that surrounds the guidance tube and constitutes a drive apparatus. 
    
    
     In  FIG. 1  an embodiment according to the present invention of a magnetic piston, hereinafter also referred to as a “piston subassembly,” of the pipetting apparatus of the present invention is labeled generally with the number  10 . 
     Piston subassembly  10  extends along a piston axis K and encompasses a sheath tube  12  that is concentric with piston axis K and forms a kind of exoskeleton of piston arrangement  10 . For strength reasons, sheath tube  12  can be constituted from a nonmagnetic and non-magnetizable metal, for example a high alloy stainless steel. Given weight considerations, however, the sheath tube can also be made of plastic, in particular (for strength reasons) of filled, especially fiber-reinforced plastic. 
     A sheath-tube axis H thus coincides with piston axis K. 
     Several permanent-magnet arrangements  14   a , . . . ,  14   i  to  14   m  are preferably arranged in sheath tube  12  successively along piston axis K, a preferably ferromagnetic separating body  16  being arranged between each two directly axially successive permanent-magnet arrangements  14   i ,  14   j.    
     In the present case, all separating bodies  16  are embodied identically and have a substantially shorter axial length than permanent-magnet arrangements  14   i ,  14   j  adjoining them on either side. 
     Permanent-magnet arrangements  14   a  to  14   m  are arranged in such a way that like poles face toward one another at two permanent-magnet arrangements  14   i ,  14   j  located axially closest to one another, and adjoin the separating bodies located between those permanent-magnet arrangements. For example, in  FIG. 1  the north pole of permanent-magnet arrangement  14   a  can adjoin separating body  16 . The north pole of permanent-magnet arrangement  14   b  can likewise adjoin separating body  16  located between permanent-magnet arrangements  14   a  and  14   b . Permanent-magnet arrangements  14   a  to  14   m  are thus arranged with alternating polarizations along piston axis K in order to generate in the region of separating bodies  16  a magnetic field gradient that is axially as pronounced as possible. 
     The magnetic field resulting from the arrangement of permanent-magnet arrangements  14   a  to  14   m  with alternating polarization serves both to provide a maximally effective coupling of the piston magnetic field to the magnetic field of coil arrangement  32  that surrounds guidance tube  30  (see  FIGS. 2 a  to 2 c   ), in order to furnish an effective linear-motor drive system having maximum positional accuracy, and also to achieve the highest possible resolution for positional sensing of the piston position, for example by way of Hall sensors outside guidance tube  30  along the piston axis (not depicted). 
     In the present case each permanent-magnet arrangement  14   a  to  14   m  is constituted by exactly one permanent magnet. Constituting a permanent-magnet arrangement having a north pole and a south pole from several permanent magnets, or from a combination of permanent magnets and magnetizable components, is not to be excluded, however, if such might be useful in terms of production engineering. 
     Permanent-magnet arrangements  14   a  to  14   m  and separating bodies  16  arranged between them can be adhesively bonded to the inner wall of sheath tube  12  by way of an adhesive film, and thereby secured in position. Sheath tube  12  can be coated with adhesive on its inner wall for that purpose, before the permanent-magnet arrangements and separating bodies  16  are introduced. Additionally or alternatively, the permanent-magnet arrangements and separating bodies can be coated with adhesive on their outer enveloping surfaces. 
     An adhesive application between permanent-magnet arrangements  14   a  to  14   m  and their respectively adjacent separating bodies  16 , for example on the end surfaces that respectively touch one another, is possible in principle but not necessary, so that the packing made up of permanent-magnet arrangements  14   a  and  14   m  and separating bodies  16  arranged therebetween can be constructed as axially tightly as possible. 
     Sheath tube  12  in the present case is preferably circularly cylindrical. In the present case, permanent-magnet arrangements  14   a  are preferably solidly circularly cylindrical, as are the soft-magnetic, preferably ferromagnetic, separating bodies  16 . 
     Sheath tube  12  comprises at one end a sealing longitudinal end  18 , and comprises a further longitudinal end  20  located oppositely from sealing longitudinal end  18 . 
     A sealing arrangement  22  in the form of a sealing component is preferably provided at sealing longitudinal end  18 . A sealing component  22 , or centering component  24  depicted in  FIG. 1 , can likewise be provided at the oppositely located longitudinal end  20 . 
     Sealing component  22  comprises a connecting portion  26  that projects axially into sheath tube  12  at its sealing longitudinal end  18  and can likewise be adhesively bonded to the inner wall of sheath tube  12  by means of an adhesive. 
     Sealing component  22  furthermore comprises a sealing portion  28  that protrudes in an axial direction away from sheath tube  12 . This sealing portion  28  preferably comprises a sleeve configuration  34  that, for example, can be embodied in a bell shape widening axially away from sheath tube  12 . A portion of sleeve configuration  34  protrudes radially beyond sheath tube  12  so that it can come into abutment against guidance tube  30  without interference from sheath tube  12 , and can thereby perform its sealing function. 
     The sealing arrangement or sealing component  22  can comprise a central recess  36  into which a tool or a threaded rod can be threaded so that, for example, sealing component  22  can be pulled out of sheath tube  12  or so that it can be pressed radially against the inner wall of sheath tube  12  and thereby anchored more strongly on sheath tube  12 . 
     That region of sleeve portion  34  which projects radially beyond sheath tube  12  forms a sealing lip  38  proceeding around piston axis K. 
     Centering component  24 , shown by way of example at the other longitudinal end  20  of sheath tube  12 , also comprises a fastening portion  40  that, analogously to connecting portion  26 , is introduced axially into sheath tube  12  from longitudinal end  20 . Fastening portion  40  can also be connected adhesively, by way of an adhesive, to the inner wall of sheath tube  12 . Centering component  24  furthermore comprises a centering portion  42  that protrudes axially out of sheath tube  12  and beyond it, an effective portion  44  of centering portion  42  having a radially larger dimension than sheath tube  12  and projecting radially beyond the latter either along the entire circumference or locally in distributed fashion around the circumference. The radial projection of effective portion  44  is preferably less than the radial projection of sleeve portion  34  of centering component  22  in order to avoid unnecessary frictional resistance at centering component  24 . Centering component  24  serves, together with sealing component  22 , to avoid contact between sheath tube  12  and the guidance tube that surrounds it in an operational context. 
     Centering component  24  as well can comprise a recess  46 , accessible from its free longitudinal end, into which a tool is introducible and fastenable for easier removal of centering component  24  from sheath tube  12 . Contrary to what is depicted in  FIG. 1 , recess  46  can extend axially into the region of sheath tube  12  and can serve to press centering component  24  radially against the inner wall of sheath tube  12 . Centering component  24  and sealing component  22 , which preferably are constituted in one piece, are preferably embodied from plastic, specifically from a filled thermoplastic, the plastic matrix preferably being polytetrafluoroethylene or a polyolefin, and solid particles of mica or graphite being embedded therein. Particularly low-friction and low-wear contact with guidance tube  30  that surrounds piston subassembly  10  in an operational context is thereby enabled. 
       FIGS. 2 a  to 2 c    show piston subassembly  10  of  FIG. 1  in various relative positions. 
     By corresponding energization of coil arrangement  32 , permanent-magnet piston subassembly  10  can be moved quickly and highly accurately along cylinder axis Z, which coincides with piston axis K during operation, of guidance tube  30 . 
     Guidance tube  30  comprises a coupling longitudinal end  48  located closer to a coupling configuration (not depicted in  FIG. 2 ) and, oppositely from it, a servicing-side longitudinal end or servicing longitudinal end  50 . 
     Axially adjacent to coupling longitudinal end  48  is a region of the pipetting apparatus (not depicted in  FIGS. 2 a  to 2 c   ) to which guidance tube  30  belongs, a coupling configuration being provided thereon in a manner known per se for detachable temporary coupling of a pipetting tip. 
     In the example depicted, servicing-side longitudinal end  50  of guidance tube  30  is open. It can also be closed off by a cover  52  that is intentionally detachably arranged at servicing-side longitudinal end  50  and that constitutes an end stop of piston subassembly  10  in order to limit its axial motion path toward servicing-side longitudinal end  50 . 
     After any removal of detachable cover  52 , piston subassembly  10  can be moved in simple fashion axially out of guidance tube  30  at least far enough that its removal longitudinal end  54 , constituted by centering component  24 , is no longer surrounded by guidance tube  30  and can thus be grasped manually or with a tool. It is thereby possible to pull piston subassembly  10  axially completely out of guidance tube  30  and remove it completely from the guidance tube. 
     A serviced or new piston subassembly  10  can then be slid axially, starting with a piston-sealing longitudinal end  56  having sealing component  22 , far enough into guidance tube  30  (see  FIG. 2 c   ) that a magnetic field generatable by coil arrangement  32  is thereby couplable to the magnetic field of permanent-magnet arrangements  14   a  to  14   m  sufficiently that piston subassembly  10  can be pulled by the magnetic field of coil arrangement  32  completely into guidance tube  30 . Cover  52  can then be mounted again, if necessary, on servicing-side longitudinal end  50  of guidance tube  30 . 
     In order to set up the pipetting apparatus to be ready for operation again after a replacement of piston subassembly  10 , coil arrangement  32  can move the pulled-in piston subassembly  10  into a defined reference position, determined e.g. by a mechanical stop, in which its sensor system becomes referenced to the known position. The pipetting arrangement is then once again ready for operation with high dynamics and high accuracy.