EP2626134A2 - Pipette - Google Patents

Abstract

The pipette (1) has a decoupling device (44) for decoupling a drive element (34) i.e. sleeve, from a cylindrical lifting rod (6) during contact of a circular collar (38) at an overlifting spring bearing (32) and continued displacement of an actuating element (4) in an actuating direction. A lower stop body (27) is coupled with the rod, and strikes an actuating end of a dropping extension (74) during decoupling of the drive element from the rod for downwardly displacing the extension and a dropping slider (72) during displacement of the drive element in the actuating direction.

Description

The invention relates to a pipette with a discharge device for pipette tips.

Pipettes are used especially in the laboratory for dosing liquids. For this purpose, a pipette tip is clamped with an upper opening on a neck of the pipette. Through a lower opening, the pipette tip can absorb and dispense liquid. Bubble pipettes include a positive displacement device for air communicating with the pipette tip through the hub. By means of the displacement device, an air cushion is displaced, so that liquid is sucked into the pipette tip and ejected therefrom. The displacement device is usually a cylinder with a piston displaceable therein.

The pipette tips are released from the batch after use and replaced with a fresh pipette tip. As a result, contamination can be avoided at subsequent dosages. Single-use pipette tips are available inexpensively from plastic.

The approach for releasably holding pipette tips is a conical or cylindrical projection with respect to a housing of the pipette, on which a pipette tip with a matching upper opening is clamped. This can be done without touching the pipette tip by pressing the pipette with the approach in the upper opening of the pipette tip standing in a holder.

To avoid contamination, known pipettes have a discharge device with a drive device. By actuating a ejector button, a discharge slide is displaced via a discharge rod, that he loosens the pipette tip from the approach without the user having to touch it. These pipettes have a dosing button for operating the displacement device and the separate ejector button for actuating the ejection device, so that two buttons must be operated.

From the DE 25 49 477 C3 is a hand-held pipette with one-button operation known. This has a housing from which protrudes above a depressible against spring action actuator, which is connected via a lifting rod with a piston movable in a cylinder. Upon actuation of the actuator, the piston performs an adjustable power stroke. To blow out remaining liquid from the pipette tip, the piston can perform an overstroke. For this purpose, a separable magnet arrangement is present between the actuating element and the piston-cylinder unit, which indicates to the user the end of the working stroke by means of a resistance, after which the overstroke is carried out. In addition, a discharge stroke is provided for ejecting the pipette tip. For this purpose, the piston rod has a stop element, which can move a discharge sleeve at an actuating end, so that it pushes the pipette tip at its upper edge from the approach with a discharge end. The beginning of the discharge stroke is indicated to the user by the resistance of a spring acting on the discharge sleeve. During the discharge stroke, the piston is moved, so that a clearance in the cylinder is needed. The free space forms a dead volume, which affects the dosing accuracy.

The DE 197 08 151 A1 describes another pipette with one-button operation, which has a lower dead volume. The pipette has a moving means, a piston for moving air movable therefrom in a cylinder, a mounting boss having a connection with the cylinder-having opening for fixing a pipette tip, and a movement of the piston when moving air to the opening of the attachment approach limiting stop. The stop is an end face of the cylinder, which the piston encounters when moving air to the opening of the attachment approach. Furthermore, the pipette has a discharge device, which has a discharge section for separating a pipette tip from the attachment approach during a dropping movement of the discharge device and an actuation section for effecting the discharge movement. In addition, a decoupling device is present, which decouples the piston when reaching the stop of the movement device. The decoupling device is formed by a magnet arrangement with a magnet and a magnetizable counterpart, which come loose after overcoming a holding force. A driver coupled to the movement device acts on the actuation section when the piston is decoupled, wherein movement of the carrier by the movement device forces the ejection movement of the ejection device. In this pipette, the movement of the piston is limited by the stroke after the power stroke and possibly a Ausblashub to blow out residual fluid. Then the decoupling device decouples the piston from the moving means. Upon further actuation of the movement means in the same sense, the piston is not moved further, however, a coupled with the moving means driver moves, which acts on the actuating portion of the ejection device and forces the ejection movement. The ejection movement without further movement of the piston reduces the dead volume and improves the dosing accuracy.

In the known pipette, the piston is loaded when hitting the end face of the cylinder, so that it must be carried out sufficiently stable. For small sizes for low dosing volumes, this is expensive. During assembly, the upper part of the housing, which includes the decoupling device and the piston, must be with a housing base are screwed together, which includes the cylinder. In the production of pipettes with different sizes for different Dosierbereiche the housing tops must be equipped with different decoupling devices and cylinders and then assembled with the respective housing lower parts.

The DE 10 2004 003 434 B4 describes a pipette with a displacement device and a drive device releasably connected thereto. The displacement device has a displacement chamber with a displaceable restriction, a connection for connection to a pipette tip and a connection channel between the displacement chamber and the free end of the attachment. The drive device for driving the displaceable boundary of the displacement device has a drive element which has a detachable operative connection with the displaceable boundary. Between the drive device and the displacement device, a bayonet connection is present, which can be produced while establishing the operative connection between the drive element and displaceable boundary and releasing the active connection between the drive element and displaceable boundary. The pipette has a separate ejection device for releasing a pipette tip from the projection, which has a release drive arranged separately on the drive device, an ejector arranged on the displacement device and a detachable axial clamping connection directed between the discharge drive and ejector in the direction of the longitudinal axis of the bayonet connection.

Based on this, the object of the invention is to provide a pipette which reduces the effort for the provision of different sizes and is easier to handle.

The object is achieved by a pipette having the features of claim 1. Advantageous embodiments of the pipette are specified in subclaims.

• eine Verdrängungseinheit umfassend ein stangenförmiges Gehäuseunterteil mit einer darin angeordneten Verdrängungskammer mit einer verlagerbaren Begrenzung, einem mit der verlagerbaren Begrenzung verbundenen Kontaktelement an einer oberen Gehäuseöffnung oben im Gehäuseunterteil, einem Ansatz zum Verbinden mit einer Pipettenspitze unten am Gehäuseunterteil und einem Verbindungskanal zwischen der Verdrängungskammer und dem freien Ende des Ansatzes,
• eine Antriebseinheit zum Antreiben der verlagerbaren Begrenzung der Verdrängungseinheit mit einem stangenförmigen Gehäuseoberteil, einer darin angeordneten Antriebseinrichtung, einem mit der Antriebseinrichtung zusammenwirkenden Betätigungselement am Gehäuseoberteil und einem mit der Antriebseinrichtung zusammenwirkenden Antriebselement an einer unteren Gehäuseöffnung unten am Gehäuseoberteil, das durch Betätigen des Betätigungselement in Betätigungsrichtung nach unten verlagerbar ist, um einen Dosierhub der verlagerbaren Begrenzung auszuführen,
• Mittel zum lösbaren Verbinden, die das Gehäuseoberteil und das Gehäuseunterteil in einer Anordnung, in der das Antriebselement an dem Kontaktelement anliegt, zu einem stangenförmigen Gehäuse lösbar miteinander verbinden,

eine Abwurfeinrichtung, die einen am Gehäuseunterteil verlagerbar angeordneten Abwurfschieber aufweist, der unten ein Abwurfende

• zum Lösen einer Pipettenspitze vom Ansatz hat und die Abwurfeinrichtung ferner eine verlagerbar am Gehäuseoberteil angeordnete Abwurfverlängerung aufweist, die unten mit dem oberen Ende des Abwurfschiebers verbunden ist,
• einen im Gehäuseoberteil angeordneten, fest mit dem Gehäuseoberteil verbundenen Endanschlag und ein fest mit dem Antriebselement verbundenes Endanschlagelement zum Begrenzen der Bewegung des Antriebselements nach unten,
• eine Entkopplungseinrichtung zwischen Antriebseinrichtung und Antriebselement, die bei Anlage des Endanschlagelements am Endanschlag und fortgesetzter Verlagerung des Betätigungselements in Betätigungsrichtung das Antriebselement von der Antriebseinrichtung entkoppelt, und
• einen mit der Antriebseinrichtung koppelbaren unteren Anschlagkörper, der bei Entkopplung des Antriebselements von der Antriebseinrichtung durch die Entkopplungseinrichtung auf ein Betätigungsende der Abwurfverlängerung trifft, um bei weiterem Verlagern des Betätigungselements in Betätigungsrichtung die Abwurfverlängerung und den Abwurfschieber nach unten zu verlagern.

The pipette according to the invention has

• a displacement unit comprising a rod-shaped housing lower part with a displacement chamber arranged therein with a displaceable boundary, a contact element connected to the displaceable boundary at an upper housing opening at the top of the housing base, a lug for connection to a pipette tip at the bottom of the housing base and a connection channel between the displacement chamber and the free one End of the approach,
• a drive unit for driving the displaceable boundary of the displacement unit with a rod-shaped housing upper part, a drive device arranged therein, an actuator cooperating with the drive device on the housing upper part and a drive element interacting with the drive device on a lower housing opening at the bottom of the housing upper part, which actuates the actuating element in the actuation direction is displaceable down to perform a Dosierhub the movable limit,
• Means for releasably connecting, the housing upper part and the lower housing part in an arrangement in which the drive element is applied to the contact element, releasably connect to a rod-shaped housing,

a discharge device having a displaceable arranged on the lower housing part discharge slide, the bottom of a discharge end

• for releasing a pipette tip from the approach and the discharge device further comprises a displaceable on the upper housing part disposed Abwurfverlängerung, which is connected at the bottom to the upper end of the discharge slide,
• a stopper disposed in the housing top, integral with the housing top, and an end stopper fixedly connected to the driver for limiting movement of the driver downward;
• a decoupling device between the drive device and the drive element which decouples the drive element from the drive device when the end stop element bears against the end stop and continued displacement of the actuating element in the direction of actuation, and
• a lower stop body which can be coupled to the drive device and, when the drive element is decoupled from the drive device by the decoupling device, strikes an actuating end of the discharge extension in order to displace the discharge extension and the discharge slide downwards upon further displacement of the actuating element in the direction of actuation.

The pipette according to the invention has a displacement unit and a drive unit, which are detachably connected to each other by means of a detachable connection. The detachable connection can be configured as a bayonet connection, as in the DE 10 2004 003 434 B4 described. In this regard, reference is made to the DE 10 2004 003 434 B4 and US 2005/155438 A1 , the content of which is hereby incorporated into this application. The displacement unit is arranged in a housing lower part. It includes the displacement chamber and the movable boundary. This is preferably
a cylinder with a piston displaceably arranged therein. When assembling the displacement unit and drive unit so the piston or another movable limit must not be installed in the displacement unit. When the upper housing part is connected to the lower housing part is, the drive element is applied to the contact element. The coupling of the drive device of the drive unit with the displaceable boundary is effected in that the drive element of the drive unit contacts the contact element of the displacement unit. The contact can be easily made by assembling and making the detachable connection between the displacement unit and the drive unit. Further, the pipette has an end stop on which an end stop element connected to the drive element strikes, in order to limit the displacement of the drive element downwards. Unlike the DE 197 08 151 A1 the end stop is not the bottom face of the cylinder. Rather, the end stop is arranged in the upper housing part and fixedly connected to the upper housing part and the drive element has the end stop element. As a result, the piston is not subjected to stress by hitting the end stop. In particular, in a drive unit that is to be used unchanged for a pipette series with pipettes of different sizes, the end stop and end stop element can be designed so that they withstand the largest forces expected. It is also possible to use displacement units that are not designed so that the piston hits the end face of the cylinder at the end of the displacement downwards. Upon reaching the end stop, the piston is preferably just before or just on the lower end face of the cylinder in order to keep the dead volume and associated dosing errors as low as possible. Furthermore, the drive unit has a decoupling device between the drive element and drive member. The decoupling decoupled at system of the end stop element at the end stop the drive element of the drive device when the actuating element is further displaced in the direction of actuation. Consequently the drive device is moved on in the same sense as before. The drive device is coupled to a lower stop body, which strikes the operating end of the discharge extension when the drive element is decoupled from the drive device. As a result, the ejection extension is shifted by further displacement of the actuating element in the direction of actuation and with this the discharge slide downwards. As a result, a pipette tip is deported from the approach. The pipette according to the invention thus enables the control of the dosage and the ejection of pipette tips by operating only a single actuator. When the pipette tip is dropped, the displacement chamber and displaceable boundary are not adversely affected. Larger dead volumes and associated metering errors are avoided. The basic structure of the pipette of displacement unit and drive unit facilitates assembly and disassembly. In addition, the displacement unit and drive unit can be used to assemble different types of pipettes. In particular, displacement units, which are not originally designed to perform the control of dosing operations and discharge operations by means of only one actuator, may be used with the drive unit to form one-touch operation pipettes. Furthermore, the same drive unit can be assembled with different displacement units to form pipettes with different dosing ranges.

The actuating element interacts with the drive device by being mechanically or directly connected therewith. The drive element cooperates with the drive device, in which it is directly or indirectly mechanically connected thereto. The actuating direction of the actuating element preferably runs in a straight line. It preferably runs in the longitudinal direction of the rod-shaped housing. Alternatively, it runs in one Angle (for example, 45 ° or 90 °) to. According to another alternative, the actuating direction runs along a curved curve, for example on a circular path. In a rectilinear actuator, the actuator is preferably a push button and in a curved actuator a pivoting lever.

The displacement unit is according to a preferred embodiment, a cylinder with a piston displaceable therein. Alternatively, the displacement unit is a displacement chamber with a flexible wall or membrane displaceable therein.

The drive device is according to a preferred embodiment, a lifting rod. According to a further embodiment, the lifting rod is a cylindrical lifting rod. According to a further embodiment, the lifting rod is made of metal or plastic.

The contact element is according to a preferred embodiment, a piston plate at the upper end of the piston or a piston rod connected to the upper end of the piston. The piston plate is preferably aligned horizontally. According to an alternative embodiment, the contact element is the upper end of the piston or the upper end of a piston rod connected to the piston.

The lower stopper body is according to a preferred embodiment, against the action of an overstroke spring downwardly displaceable stop body on which a stop element of the drive means impinges at the end of a Dosierhubes. In a further displacement of the drive element down an overstroke is performed and displaced the stopper body against the action of the over-travel spring down. In this shift down the lower stop body meets the Abwurfverlängerung and pushes them in the direction of actuation down. According to one embodiment, the pipette is a hand-held pipette, ie a pipette, which the user can hold and operate during pipetting with just one hand.

According to a further embodiment, the drive device has a stop element and an upper stop body and the lower stop body, between which the stop element is displaceable to perform a Dosierhub, wherein the lower stop body is supported by a Überhubfeder in the upper housing part to after execution of the Dosierhubes by another Relocating the actuating element in the direction of actuation against the spring force of the overstroke spring to reach the end stop by the end stop an overstroke. During Dosierhub the stopper member is moved between the upper and lower stopper body, being displaced from the upper stopper body to the lower stopper body for sucking liquid in a pipette tip attached to the approach from the lower stopper body to the upper stopper body and to eject air or liquid from the pipette tip. The impact of the stop element feels the user, since the lower stop body is supported by a Überhubfeder in the upper housing part. As a result, it is ensured when taking in liquid that exactly the intended metering stroke is performed. When dispensing liquid, the user can also perform an overstroke to blow out residual liquid from the pipette tip. By applying an increased force on the actuator, the user can overcome the spring force of the overstroke spring and cause an overstroke until the drive element is stopped by the end stop. After the overstroke, the user can control the ejection of the pipette tip in the manner described by decoupling the decoupling device by applying a corresponding force to the actuator.

The lower stop body sits with its outer edge at the end of the overstroke or at the beginning of the further displacement of the actuating element in the direction of actuation on the operating end of the ejection extension to move as a driver, the ejection extension down. As a result, the lower stopper body satisfies the functions to limit the metering stroke, to allow the overtravel and to control the ejection of the pipette tip in an advantageous manner that reduces the structural complexity. In addition, this embodiment makes it possible for the discharge extension to be guided laterally past the overstrokes, the drive element and the decoupling device. In addition, space for an ejection spring for resetting the ejection device is thereby created below the overstroke to a starting position in which a pipette tip is attachable to the approach.

According to a further embodiment, the upper stop body in the upper housing part is displaceable and has the upper housing part coupled to the upper stop body adjusting device for adjusting the position of the upper stop body and set the Dosierhubes on. By means of the adjusting device, the amount of liquid to be metered is adjustable. The upper stop body is according to another embodiment, a threaded spindle having an upper passageway through which a lifting rod of the drive means is passed. The threaded spindle is arranged by means of the adjusting in a housing upper part and fixedly connected to this spindle nut rotatable and thereby axially displaceable. The lower end face of the threaded spindle serves as a stop for the stop element. The position of the lower end face is decisive for the metering stroke.

According to one embodiment, the stop element is a collar on the circumference of the lifting rod and the lifting rod is hindurcherstreckt through an upper passageway of the upper stop body and through a lower passage channel of the lower stop body and the collar between the upper stop body and the lower stop body is arranged.

According to a further embodiment, the decoupling device comprises two decoupling elements, of which one decoupling element is connected to the drive device and the other decoupling element to the drive element, wherein the decoupling elements are releasably held together in a specific connection position and after removing a certain holding force from each other and removable the holding position are displaced back. The decoupling device can be easily integrated between the drive device and the drive element. The decoupling device decouples only when the force acting on the decoupling device by actuation of the actuating element exceeds the holding force. The user thus senses a resistance at the end of dispensing liquid from a pipette tip. This makes it easier for the user to first aim the pipette at a vessel for dosing and then direct the pipette to a pipette tip waste bin to eject the pipette tip with increased actuation force. The holding force is preferably a maximum of 25N, more preferably a maximum of 22N. The holding force is preferably at least 10N, furthermore preferably at least 16N. It is preferably 19N.

According to one embodiment, the decoupling elements comprise two magnets or a magnet and a ferromagnetic counterpart and / or a pawl device and / or a spring device which the Releasably hold the decoupling elements in the connection position. The decoupling elements preferably have a magnet arrangement with two magnets or a magnet and a ferromagnetic counterpart. The magnet is preferably a permanent magnet.

The decoupling device can in particular be designed as in the DE 197 08 151 A described. In this regard, reference is made to the DE 197 08 151A , the content of which is hereby incorporated into this application.

According to a further embodiment, the drive element is a sleeve whose lower end is seated on the contact element, the decoupling device comprises an upper decoupling element with an upper through hole, which is arranged in the sleeve and fixedly connected thereto, and a lower decoupling element which is displaceable in the Sleeve is arranged and fixed to the lower end of a lifting rod, which is from the top into the sleeve and through the upper through hole extends therethrough, and the sleeve through a further through hole of the end stop extends and has a radially outwardly projecting further collar, the the movement of the drive element is limited downwards by seating on top of the end stop. In this embodiment, the decoupling device is integrated to save space in the drive element. The decoupling device can be mounted with the drive element on the lifting rod of the drive device. The end stop element is simply realized by a further collar of the sleeve.

According to a further embodiment, a decoupling spring is arranged in the sleeve below the lower decoupling element, via which the decoupling element is supported in the sleeve. The decoupling spring presses to relieve the Actuator the lower decoupling element to the upper decoupling element back to bring the decoupling element in the connecting position.

According to a further embodiment, the sleeve has a lower sleeve portion and an upper sleeve portion, wherein the lower sleeve portion has a smaller diameter than the upper sleeve portion is hineinerstreckt through the upper housing opening of the housing base and seated with the lower end on the contact element and the upper sleeve portion the decoupling elements are arranged. As a result, sufficient space for the accommodation of the decoupling elements is provided and allows insertion of the sleeve in an upper housing opening with a small diameter of a displacement device.

According to a further embodiment, the overstroke spring is supported on an annular Überhubfederlager in the upper housing part, the sleeve passed through the through hole of the overstroke spring bearing and is the overstroke spring bearing of the end stop for the collar of the sleeve. Hereby, the function of the overstroke spring bearing and the end stop is merged and the structural complexity is reduced.

In accordance with a further embodiment, the discharge extension is supported in the upper housing part by a discharge spring arranged below the overhub spring bearing in the upper housing part.

According to a further embodiment, the discharge spring is at the top of a arranged below the Überhubfederlagers upper Abwurffederlager to the Shedding extension and supported at the bottom of a housing fixed lower Abwurffederlager.

According to a further embodiment, the discharge slide is a discharge sleeve, which is guided on its inner circumference on the housing lower part. The discharge sleeve has the shape of a sleeve. According to a further embodiment, the Abwurfverlängerung a plurality of parallel rods, which are connected to each other at a distance from the discharge slide by an annular upper Abwurffederlager. The execution of the discharge slide as a sleeve allows easy installation on the displacement unit. Optionally, the discharge slide for cleaning, maintenance or repair is easy to disassemble and assemble. The design of the ejection extension with several parallel rods favors a space-saving guidance in the housing upper part. Due to the annular ejection spring bearings, the rods are stabilized in the upper region and prevented from accidentally pulling out of the upper housing part.

According to a further embodiment, the discharge slide and the discharge extension are connected to each other by at least one snap connection. A snap connection facilitates the mounting and, if necessary, dismantling of discharge slide and discharge extension.

According to a further embodiment, the discharge extension is connected by a first snap connection with a Abwurfring and the Abwurfring is connected by a second snap connection with the discharge slide. This favors the captive installation of the ejection extension from above and the Abwurfringes from the bottom of the upper housing part, the separate mounting of the discharge slide on the lower housing part and the connection of the upper housing part and lower housing part and simultaneous connection of the Abwurfringes with the discharge slide.

According to a further embodiment, the overstroke spring and / or the decoupling spring and / or the piston spring and / or the ejection spring is / are a helical spring and / or a conical spring. Coil springs or conical springs can be advantageously accommodated in the rod-shaped housing and can be provided with a suitable spring hardness.

Fig. 1

eine erfindungsgemäße Pipette in einem Längsschnitt;

Fig. 2

dieselbe Pipette in einem vergrößerten Längsschnitt durch einen oberen Teil;

Fig. 3

ein vergrößerter Schnitt entlang der Linie III - III von Fig. 2;

Fig. 4

vergrößertes Detail IV von Fig. 2;

Fig. 5

dieselbe Pipette in einem vergrößerten Längsschnitt durch einen unteren Teil;

Fig. 6.

dieselbe Pipette ohne Hubkörper in einem vergrößertem Längschnitt durch einen unteren Teil;

Fig. 7a bis d

dieselbe Pipette vor dem Betätigen des Betätigungselement (Fig. 7a), nach dem vollständigen Ausführen des Dosierhubes und vor Ausführung des Überhubes (Fig. 7b). nach dem Ausführen des Überhubes vor dem Abwerfen der Pipettenspitze (Fig. 7c) und nach dem Abwerfen einer Pipettenspitze (Fig. 7d) jeweils in einem teilweisen Längsschnitt;

Fig. 8

Kraft-Wegdiagramm bei Dosierhub, Überhub und Abwurfhub, einer erfindungsgemäßen Pipette (in strichlierten Linien) und einer herkömmlichen Pipette (in ausgezogenen Linien).

The invention will be explained in more detail with reference to the accompanying drawings of an embodiment. In the drawings show:

Fig. 1

a pipette according to the invention in a longitudinal section;

Fig. 2

the same pipette in an enlarged longitudinal section through an upper part;

Fig. 3

an enlarged section along the line III - III of Fig. 2 ;

Fig. 4

enlarged detail IV of Fig. 2 ;

Fig. 5

the same pipette in an enlarged longitudinal section through a lower part;

Fig. 6.

the same pipette without lifting in an enlarged longitudinal section through a lower part;

Fig. 7a to d

the same pipette before operating the actuator ( Fig. 7a ), after complete execution of the metering stroke and before execution of the overstroke ( Fig. 7b ). after running the Overlifting before dropping the pipette tip ( Fig. 7c ) and after dropping a pipette tip ( Fig. 7d ) each in a partial longitudinal section;

Fig. 8

Force-travel diagram during metering, overstroke and discharge stroke, a pipette according to the invention (in dashed lines) and a conventional pipette (in solid lines).

In the present application, the terms "up" and "down", "above" and "below" and "horizontally" and "vertically" refer to an orientation of the pipette in which the housing is aligned with the approach vertically downwards. In this orientation, an attached on the approach pipette tip can be directed to an underlying vessel to absorb liquid or give.

According to Fig. 1 and 2 the pipette 1 has a rod-shaped, molded as a handle housing with an upper housing part 2 and a lower housing part 3. The upper housing part 2 with all the parts included forms a drive unit and the lower housing part 3 with all parts contained a displacement unit. From the upper housing part 2 is above an actuator 4 in the form of a cylindrical push button out. The actuating element 4 is mounted axially displaceably and rotatably in the upper housing part 2.

The actuating element 4 is screwed with a thread in a cover 5 on a cylindrical lifting rod 6. The lifting rod 6 is passed in the upper housing part 2 through an upper passage channel 7 of a threaded spindle 8. The threaded spindle 8 is screwed into an internal thread of a housing upper part 2 held in a defined position spindle nut 9.

The spindle nut 9 is fixedly connected to a lifting body 10 which is fixed in the upper housing part 2. The lifting body 10 is substantially cylindrical and is a support for the spindle nut 9, the threaded spindle 8 screwed therein and the lifting rod 6 guided therein. During assembly of the pipette, these and other components are preassembled on the lifting body 10 and the lifting body 10 equipped with the components is mounted in the upper housing part 2, so that it is firmly held in the upper housing part 2. For this purpose, the lifting body 10 is locked to the upper housing part 2. In principle, it is also possible to mount the components preassembled on the lifting body 10 directly in the upper housing part 2. For this purpose, the upper housing part 2 can be equipped inside corresponding to the lifting body 10.

The threaded spindle 8 has a rotatably connected thereto Spindelmitnehmer 11 above. The Spindelmitnehmer 11 has on the circumference a hexagon 12 with a central hole 13. The hexagon 12 engages in a Innsensechskant 14 of the actuating element 4 a.

The actuator 4 is provided at the bottom with two diametrically opposed, radial projections 15, 16 which project outwardly. Preferably, four radial projections 15, 16 are present. The radial projections 15, 16 engage in axially extending grooves 17, 18 on the inside of a hollow cylindrical transmission part 19, which is rotatably mounted in the upper housing part 2. The transmission member 19 has at the top of the outer circumference a sprocket 20 which meshes with a gear of a counter gear 21 which drives a plurality of juxtaposed on a horizontal axis counter wheels 22 of a counter 23. The counter 23 is attached to the upper housing part. The Zählwerksräder 22 each have digits from 0 to 9. Das - based on Fig. 1 - The last counter gear 22 is driven by the counter gear 21. The next one arranged counting wheels 22 are further rotated in each case by one digit when the behind arranged Zählwerksrad passes from 9 to 0.

Above the counter 23, the upper housing part 2 has a housing cover 24 with a window through which the digits of the counter wheels 22 can be read.

Below the threaded spindle 8, a beaded collar 25 is arranged as a stop element on the lifting rod 6. The displacement of the lifting rod 6 upwards is limited by contact of the collar 25 at the lower end face 26 of the threaded spindle 8, which forms an upper stop body for the collar 25.

Below the spindle nut 9, a substantially disc-shaped lower stop body 27 is arranged in the lifting body 10. The lower stop body 27 has a cup-shaped depression, in which a central passageway 28 is arranged centrally. Further, the lower stopper body 27 has three radially outwardly projecting projections 29 which are distributed uniformly around its circumference.

The lower stop member 27 is guided on the projections 29 in axially extending guide slots 30 of the lifting body 10. This is also in Fig. 3 shown. Upwards he is 30 until the projection of the projections 29 at the upper end of the guide slots 30 displaced.

Below the lower stop body 27, a lifting spring 31 designed as a helical spring is arranged in the lifting body 10. At the top, the overstroke spring bears against the lower side of the lower stop body 27. Bottom supports the overtravel spring 31 abuts against an overhub spring bearing 32 which is arranged and thus firmly connected.

The over-stroke spring bearing 32 is formed by a ring with L-section, wherein the horizontal leg of the L-profile surrounds a central through hole 33 of the overstroke spring bearing 32. The overstroke spring 31 is supported on the horizontal leg of the L-profile and is laterally bordered by the vertical leg. The overstroke spring 31 presses the lower stopper body 27 with the protrusions 29 under bias against the upper ends of the guide slots 30.

Below the lower stopper body 27, a drive element 34 in the form of a coaxial with the lifting rod 6 aligned sleeve is present in the lifting body 10. The drive member 34 has an upper sleeve portion 35 and a lower sleeve portion 36, wherein the upper sleeve portion 35 has larger inner and outer diameter than the lower sleeve portion 36. The lower sleeve portion 36 has a frusto-conical tip 37 at the bottom.

At the upper edge of the upper sleeve portion 35, a radially outwardly projecting, further circumferential collar 38 is present. The outer diameter of the upper sleeve portion 35 is smaller than the inner diameter of the through hole 33 of the overstroke spring bearing 32, so that the lower and the upper sleeve portion 35, 36 are insertable into the through hole 33. The outer diameter of the further collar 38 exceeds the inner diameter of the through-hole 33, so that the drive element 34 can not completely pass through the through-hole 33. The over-stroke spring bearing 32 forms an end stop and the further collar 38 an end stop element, which limit the displacement of the drive element 34 down.

In the upper sleeve portion 35, a hollow cylindrical armature 39 is arranged from a ferromagnetic material above. Below this, a hollow cylindrical magnet 40 is arranged in the upper sleeve section 35. Below this is a pot 41 which receives the magnet 40. The armature 39 has an interference fit in the upper sleeve portion 35. The lifting rod 6 extends slidably through the central hole of the armature 39 therethrough. Below the armature, the lifting rod 6 has a needle-shaped portion 42 of reduced diameter. The magnet 40 and the pot 41 are seated on the needle-shaped portion 42. Preferably, the magnet 40 and cup 41 are fixed on the needle-shaped portion 44, e.g. by having a press fit there. In addition, the magnet 40 is supported at the top on a shoulder of the lifting rod from which the needle-shaped portion 44 extends.

Below the annular disc 41 is formed on the needle-shaped portion 42 designed as a helical spring decoupling spring 43, which is supported at the bottom 43 of the lower sleeve portion 36 below. Armature 39, magnet 40 and decoupling spring 43 are components of a decoupling device 44.

According to FIG. 1 . 2 . 5 and 6 has the upper housing part 2 is provided below next to a lower housing opening 45 on the inner circumference with unspecified means for releasably connecting 46 with further means for releasably connecting the housing lower part 3.

The lower housing part 3 has a hollow cylindrical section 47 at the top, followed by a short upper hollow cone section 48 with a large cone angle, followed in turn by a long lower hollow cone section 49 with a small cone angle, with its lower end a conical projection 50 for clamping a pipette tip 51 forms. A clamped pipette tip 51 is also substantially conical with an upper opening 52 for attachment to the lug 50 and a lower opening 53 for the passage of liquid. The upper opening 52 is substantially larger than the lower opening 53 and from the upper to the lower opening, the pipette tip 51 tapers.

The hollow cylindrical portion 47 of the lower housing part 3 is provided at the top of the outer circumference with other means for releasable connection 54, which are not described in more detail, which are adapted to the means for releasably connecting 46 of the upper housing part 2 to releasably connect the lower housing part 3 with the upper housing part 2. Suitable means for releasably connecting 46, 54 of the upper housing part 2 and lower housing part 3 are in the DE 10 2004 003 434 B4 described. In this regard, reference is made to the DE 10 2004 003 434 B4 and US2005 / 155438 A1 , the content of which is hereby incorporated into this application.

The lower hollow cone section 49 has at the top a projection 55 projecting beyond the upper hollow cone section 48 in the lower housing part 3.

The lower hollow cone portion 49 has a connecting channel 56 which connects the upper end face of the extension 55 with the lower end face of the projection 50.

In the lower housing part 3, an arrangement of a cylinder 57 is arranged with a displaceable piston 58 therein. The cylinder 57 is inserted with a lower portion in the connecting channel 56 and fixed therein by press-fitting or gluing. At the bottom, the cylinder 57 is sealed off from the connecting channel 56 by means of an O-ring 59.

The piston 58 has on the circumference a piston seal 60, which seals on the inside of the cylinder 57. Below the piston seal 60, the piston 58 has a needle-shaped Extension 61, which is insertable into a through hole 62 in the bottom of the cylinder 57 and in the connecting channel 56 in order to reduce the dead volume. Cylinder 57 and piston 58 are vertically aligned. At the top, the piston 58 carries a horizontally oriented piston plate 63, which has at the center a vertically oriented, conical recess 64 for receiving the tip 37 of the drive member 34.

The lower housing part 3 has at the top a pot-shaped closure cap 65 with a cylindrical or conical jacket. The bottom of the cap 65 is disposed above the piston plate 63 and has a central upper housing opening 67, through which the piston plate 63 is accessible from above. At the edge of your shell, the cap 65 has outwardly projecting protrusions 68 which are snapped into corresponding recesses 69 of the hollow cylindrical portion 47 of the housing base 3.

The bottom of the cap 65 limits the displacement of the piston 58 upwards. A trained as a spiral spring piston spring 70 which is supported at the bottom of the extension 55 and the top of the underside of the piston plate 63, biases the piston 58 against the underside of the cap 65 before.

Furthermore, the pipette 1 has a discharge device 71. The discharge device 71 comprises a discharge slide 72, which is arranged on the housing lower part 3. The discharge slide 72 has a contour adapted to the contours of the hollow cylindrical section 47, the upper hollow cone section 48 and the lower hollow taper section 48. Below it has an annular discharge end 73. The discharge end 73 is in the position of the discharge slide 72 of Fig. 1 pushed as far as possible up to the lower housing part 3, so that the conical projection 50 is free for attaching a pipette tip 51.

Above the discharge slide 72 is connected to a discharge extension 74. This includes three vertical discharge bars 75, which are connected to the upper edge of the discharge slide 72. The discharge bars 75 are evenly distributed over the upper edge of the discharge slide 72. The discharge bars 75 are connected at the bottom via a first snap connection with a discharge ring 76, which is connected via a second snap connection with the upper edge of the discharge slide 72. At a distance from the Abwurfring 76, the discharge rods 75 are connected at the top at its inner periphery by an annular upper Abwurffederlager 77 with each other. The upper Abwurffederlager 77 has an L-shaped cross section, wherein the horizontal leg of the cross section, the through hole 33 adjacent to the Überhubfederlagers 32. The vertical, circumferential leg of the upper Abwurffederlagers 77 is directed downward.

The discharge bars 75 have actuation ends 78 at the top.

The discharge extension 74 and the discharge bars 75 are hineinerstreckt through the lower housing opening 45 in the upper housing part 2. The displacement of the Abwurfverlängerung 74 upwards is limited by conditioning the upper Abwurffederlagers 77 on the underside of the Überhubfederlagers 32.

Below the upper Abwurffederlagers 77 are from the inside of the upper housing part 2 before three webs 79, which are arranged distributed uniformly over the inner circumference and pass through recesses of the lifting body 10. This is especially in FIG. 4 shown. The webs 79 form a lower Abwurffederlager 80. A designed as a helical spring ejection spring 81 is under bias between the upper Abwurffederlager 77 and the lower Abwurffederlager 80th arranged and pushes the discharge device 71 upwards, so that the upper Abwurffederlager 77 rests on the Überwurffederlager 32.

The lower housing part 3 is guided with an upper region of the hollow cylindrical section 47 into the lower housing opening 45 of the housing upper part 2. The means for releasably connecting 46, 54 of the lower housing part 3 and upper housing part 2 are detachably connected to each other. The drive member 34 engages with the syringe 37 in the upper housing opening 67 and is located in the recess 64 on the piston plate 63 at. The piston plate 63 pushes the drive member 34 upwards and via the decoupling device 44, the lifting rod 6 is pressed against the threaded spindle 8 with the collar.

• Sie wird am Gehäuseoberteil 2 gegriffen. Ein Dosierhub wird eingestellt, indem das Betätigungselement 4 gedreht wird, bis die Zählwerksräder 22 das gewünschte Dosiervolumen anzeigen. Beim Drehen des Betätigungselements 4 wird über den Spindelmitnehmer 10 die Gewindespindel 8 gedreht und aufgrund ihrer Gewindeverbindung mit der im Gehäuseoberteil 2 feststehenden Spindelmutter 9 axial verlagert. Dabei gleitet der Spindelmitnehmer 10 in den Innensechskant des Betätigungselements 4. Gleichzeitig wird über die weiteren Radialvorsprünge 15, 16 das Übertragungsteil 19 gedreht und das Zählwerk 23 verstellt. Infolgedessen ist die eingestellte axiale Position der Gewindespindel 8 im Gehäuseoberteil 2 und damit das Dosiervolumen am Zählwerk 23 ablesbar.

The pipette 1 can be used as follows:

• It is gripped on the upper housing part 2. A metering stroke is adjusted by rotating the actuator 4 until the meter wheels 22 indicate the desired metering volume. When turning the actuating element 4, the threaded spindle 8 is rotated about the Spindelmitnehmer 10 and axially displaced due to its threaded connection with the fixed housing upper part 2 in the spindle nut 9. At the same time, the transmission part 19 is turned over the further radial projections 15, 16 and the counter 23 is adjusted. As a result, the set axial position of the threaded spindle 8 in the upper housing part 2 and thus the metering volume at the counter 23 is read.

Further, a pipette tip 51 is clamped on the lug 50, preferably by being pressed into a pipette tip 51, which is held in a holder.

Before sucking liquid, air is expelled from the cylinder 57 by pushing the piston 58 downward by means of the operating member 4 until the further collar 38 strikes the lower stopper body 27. Here, the lifting rod 6 moves via the decoupling device 44, the drive element 34 down and the piston 58 is pushed deeper into the cylinder 57. Due to the force between the magnet 40 and the armature 39, the decoupling device 44 does not decouple.

Thereafter, by means of the pipette 1, the lower end of the pipette tip 51 is immersed in the liquid and the desired amount is sucked into the pipette tip 51 by releasing the actuating element 4. Here, the piston spring 70 pushes the piston 58 and thus the drive element 34 and the lifting rod 6 back to the starting position, in which the collar 25 rests against the threaded spindle 8.

In this situation, the pipette is 1 in Fig. 1 . 2 . 5 . 6 and 7a shown.

Thereafter, the pipette tip 51 can be aligned with the lower end to another vessel by means of the pipette 1. By pressing the actuator 4 down the lifting rod 6 is moved down and the decoupling device 44, the drive element 34 is displaced downwards, so that the piston 58 is again moved in the cylinder 57 down. In this case, the set metering is essentially delivered. This situation is in Fig. 7b shown.

Remains remaining in the pipette tip 51 can be blown out by pressing the actuating element 4 further down under increased force becomes. Here, the lower stopper body 27 is displaced against the action of the overstroke spring 31 in the guide slots 30 down and on the decoupling device 44, the drive element 34 further displaced downwards, which pushes the piston 58 even deeper into the cylinder 57. During the overstroke, a further overpressure is generated which pushes out residual liquid adhering to the inner wall of the pipette tip 51.

The overstroke is completed when the drive element 34 with the other collar 38 strikes the overstroke spring bearing 32, which forms the end stop. At the same time, the projections 29 reach the actuating end 78 of the discharge extension 74 or are located at a very small distance above it. This situation is in Fig. 7c shown.

Thereafter, the pipette tip 51 can be dropped. For this purpose, the actuator 4 is pressed with increased force further down. The over-stroke spring bearing 32 prevents the drive member 34 from moving further down. Due to the increased force, the magnet 40 releases from the armature 39 and the lifting rod 6 moves further down and takes the lower stopper body 27 with. The lower stopper body 27 presses with the projections 29, the discharge extension 74 to the operating ends 78 down. The Abwurfverlängerung 74 takes the discharge slide 72 with downward, which pushes the pipette tip 51 from the approach 50 with the discharge end 73.

During the discharge stroke, the piston 58 is not further moved in the cylinder 57 down. As a result, no dead volume is needed at the bottom of the cylinder 57, and the piston 58 does not hit the bottom of the cylinder 57. If the magnet 40 is released from the armature 39, the force required for the further displacement of the actuating element 4 down again is reduced. The discharge stroke is finished, when the Abwurfverlängerung 74 hits a discharge stop, not shown in the housing. This situation is in Fig. 7d shown.

After releasing the actuator 4, the pipette 1 automatically returns to the initial situation of Fig. 1 . 2 . 5 . 6 and 7a back. Here, the ejection spring 81 pushes the discharge extension 74 and thus the discharge slide 72 upwards. Further, the decoupling spring 43 pushes the lifting rod 6 with the magnet 40 upwards until the magnet 40 is held by the magnetic forces on the armature 39. Further, the overstroke spring 31 pushes the lower stopper body 27 upward until the projections 29 have arrived at the upper ends of the guide slots 30. Further, the piston spring pushes the piston 58, the drive element 34 and the decoupling device 44, the lifting rod 6 upwards until the collar 25 rests against the threaded spindle 8.

The upper housing part 2 can be easily connected to another lower housing part 3, in which the cylinder 57 and the piston 58 have a different cross-section. Accordingly, the same upper housing part 2 can be used for the production of pipettes 1 with different dosing volumes. Furthermore, it is possible, in the event of a defect, to easily exchange the lower housing part 3 or upper housing part 2 or, if required, to fit the upper housing part 2 with another lower housing part 3. In addition, the housing lower part 3 can be easily removed from the upper housing part 2 for maintenance, repair and cleaning purposes.

According to Fig. 8 In the case of the pipette 1 according to the invention, the actuation force to be applied increases only slightly when the metering stroke is carried out. The Dosierhub is finished after about 14mm actuation.

For a subsequent overstroke, the force to be exerted on the actuating element 4 must first be greatly increased, from about 3 Newton to about 10.5 Newton. Thereafter, an increasing operating force is applied for the overstroke, which increases slightly more than the actuation force for carrying out a Dosierhubes. The overtravel is completed after about 17mm actuation.

For a subsequent discharge stroke, a unique demolition force of about 19 Newton must be applied. Thereafter, the force to be applied for the ejection increases approximately in continuation of the straight line for the overstroke.

In a conventional pipette according to DE 25 49 477 C3 For the metering stroke, apply a force at an elevated level. During the transition from the metering stroke to the overstroke, a unique force peak occurs. Likewise, for the demolition of the magnet a transition to the discharge stroke a sudden increase in force is required. When dropping the applied actuating force increases to a higher level and steeper than in the pipette according to the invention.

List of reference numbers used

1

pipette

2

Housing top

3

Housing bottom

4

actuator

5

Cover of the actuator

6

cylindrical lifting rod

7

Upper passageway

8th

screw

9

spindle nut

10

lifting body

11

Spindelmitnehmer

12

hexagon

13

hole

14

Allen

15, 16

radial projections

17, 18

groove

19

transmission part

20

sprocket

21

Zählwerksgetriebe

22

Zählwerksräder

23

counter

24

housing cover

25

beaded waistband

26

lower front side

27

lower stop body

28

lower passageway

29

Protrusions30 guide slots

31

travel spring

32

Überhubfederlager

33

Through-hole

34

driving element

35

upper sleeve section

36

lower sleeve section

37

frustoconical tip

38

another bunch

39

hollow cylindrical anchor

40

hollow cylindrical magnet

41

pot

42

needle-shaped section

43

decoupling spring

44

decoupling device

45

lower housing opening

46

Means for detachable connection

47

hollow cylindrical section

48

upper hollow cone section

49

lower hollow cone section

50

conical approach

51

pipette tip

52

upper opening

53

lower opening

54

further means for detachable connection

56

connecting channel

57

cylinder

58

piston

59

O-ring

60

piston seal

61

needle-shaped extension

62

Through opening

63

piston plate

64

conical depression

65

cylindrical cap

67

upper housing opening

68

projections

69

deepening

70

piston spring

71

discarding equipment

72

ejection slide

73

discharge end

74

shedding extension

75

Abwurfstange

76

shedding ring

77

Upper ejection spring bearing

78

actuating end

79

web

80

Lower ejection spring bearing

81

ejection spring

Claims (15)

With pipette - a displacement unit comprising a rod-shaped housing lower part (3) with a displacement chamber (57) arranged therein with a displaceable boundary (58), a contact element (63) connected to the displaceable boundary (58) at an upper housing opening (67) at the top of the housing lower part ( 3), a lug (50) for connection to a pipette tip (1) at the bottom of the housing lower part (3) and a connecting channel (56) between the displacement chamber (57) and the free end of the lug (50), - A drive unit for driving the displaceable boundary (58) of the displacement unit in a rod-shaped housing upper part (2), a therein drive means (6), cooperating with the drive means (6) actuating element (4) on the housing upper part (2) and one with the Drive device (6) cooperating drive element (34) at a lower housing opening (45) at the bottom of the housing upper part (2) which is displaceable by actuating the actuating element (4) in the actuation direction down to perform a Dosierhub the displaceable boundary (58), - means for releasably connecting (46, 54) releasably connecting the upper housing part (2) and the lower housing part (3) in an arrangement in which the drive element (34) on the contact element (63) to a rod-shaped housing, - A discharge device (71) having a lower part on the housing (3) displaceably arranged discharge slide (72), the bottom a discharge end (73) for releasing a pipette tip (1) from the projection (50), and the discharge device (71) further comprising a displaceable on the upper housing part (2) arranged Abwurfverlängerung (74) which at the bottom with the upper end of the discharge slide (72 ) and has an actuating end (78) at the top, - One in the upper housing part (2) arranged fixedly connected to the upper housing part (2) fixedly connected end stop (32) and one with the drive element (34) connected to the end stop element (38) for limiting the displacement of the drive element (34) down a decoupling device (44) between the drive device (6) and the drive element (34), which upon actuation of the end stop element (38) on the end stop (32) and continued displacement of the actuating element (4) in the actuating direction, the drive element (34) of the drive means (6 ) decoupled, and - A lower stop body (27) which can be coupled to the drive device (6) and which strikes the actuating end (78) of the discharge extension (74) when the drive element (6) is decoupled from the drive device (6) by the decoupling device (44) further displacement of the actuating element (34) in the direction of actuation the discharge extension (74) to shift the discharge slide (72) downwards. A pipette according to claim 1, wherein the drive device (6) has a stop element (25) on a lifting rod of the drive device, an upper stop body (8) and the lower stop body (27), between which the stop element (25) is displaceable Performing metering, wherein the lower stopper body (27) via an overstroke spring (31) in the upper housing part (2) is supported to after execution of a Dosierhubes by further displacement of the actuating element (4) in the actuating direction against the spring force of the overstroke spring (31) until reaching the end stop (32) by the end stop element (38) an overstroke and move the discharge extension (74) downwards. A pipette according to claim 2, wherein the upper stopper body (8) is displaceable in the upper housing part (2), and the upper housing part (2) has an adjusting means (4, 9, 10) coupled to the upper stopper body (8) for adjusting the position of the upper one Having stop body (8) in the upper housing part (2) and setting the Dosierhubes. Pipette according to claim 2 or 3, wherein the stop element (25) is a collar on the circumference of the lifting rod (6), the lifting rod (6) through an upper passage (7) of the upper stop body (8) and a passageway (28) of the bottom stop body (27) is extended therethrough and the collar (25) between the upper stop body (8) and the lower stop body (27) is arranged. Pipette according to one of Claims 1 to 4, in which the decoupling device (44) has two decoupling elements (39, 40), of which one decoupling element (40) with the drive device (6) and the other decoupling element (39) with the drive element (39). 34) is connected, wherein the decoupling elements (39, 40) are held together releasably in a certain connection position and are removable after overcoming a certain holding force from each other and in the connection position are displaced back. A pipette according to claim 5, wherein the decoupling elements comprise two magnets or a magnet and a ferromagnetic counterpart and / or a pawl device and / or a spring device which releasably hold the decoupling elements in the connecting position. A pipette according to any one of claims 1 to 6, wherein the drive member (34) is a sleeve, the lower end of which is seated on the contact element (63), and one of the decoupling elements (39, 40) of the decoupling means (44) is disposed in the sleeve and is firmly connected to this and is designed as an upper decoupling element (39) with an upper through hole, and the other decoupling element (40) of the decoupling device (44) arranged displaceably in the sleeve and designed as a decoupling element (40), which at the lower end a lifting rod (6) is fixed, which extends from above into the sleeve and through the upper through hole, and the sleeve through a through hole (33) of the end stop (32) extends therethrough and a radially outwardly projecting further collar (38 ), which limits the movement of the drive element (34) downwards by seating on the top of the end stop (32). A pipette according to claim 7, wherein below the lower decoupling element (40), a decoupling spring (43) is disposed in the sleeve via which the lower decoupling element (40) is supported in the sleeve. A pipette according to claim 5 or 6, wherein the sleeve has a lower sleeve portion (36) and an upper sleeve portion (35), the lower sleeve portion (36) having a smaller diameter than the upper sleeve portion (35) through the upper housing aperture (35). 67) of the Housing bottom part (3) is hindurcherstreckt and with the lower end on the contact element (63) is seated and in the upper sleeve portion (35), the decoupling elements (39, 40) are arranged. The pipette according to one of claims 1 to 9, wherein the overstroke spring (31) is supported on an annular disc-shaped overstroke spring bearing (32) in the upper housing part, the sleeve is passed through the through-hole (33) of the overstroke spring bearing (32) and the overstroke spring bearing (32) of End stop for the collar (38) of the sleeve is. Pipette according to one of claims 1 to 10, wherein the lower stop body (27) with an outer laterally projecting edge at the end of the overstroke or at the beginning of the further displacement of the actuating element (4) in the actuation direction on the actuating end (78) of the Abwurfverlängerung (74 ) is seated, as a driver to shift the discharge extension (74) down. Pipette according to one of Claims 1 to 11, in which the ejection extension (74) is supported in the upper housing part (2) by a discharge spring (81) arranged below the overstroke spring bearing (32) in the upper housing part (2). A pipette according to claim 12, wherein the ejection spring (81) at the top of a Überhubfederlagers (32) arranged upper Abwurffederlager (77) on the Abwurfverlängerung (74) and at the bottom of a housing upper part (2) arranged and fixedly connected to the upper housing part lower Abwurffederlager (80) is supported. Pipette according to one of claims 1 to 13, wherein the discharge slide (72) is a discharge sleeve, which is externally guided on the lower housing part (3) and / or the Abwurfverlängerung (74) a plurality of parallel discharge bars (75) which at a distance of the discharge slide (72) by an annular upper Abwurffederlager (77) are interconnected. A pipette according to any one of claims 1 to 14, wherein the ejector slide (72) and the ejection extension (74) are interconnected by at least one snap connection.

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