Air cushion pipette

Description

[0001] The invention relates to an air cushion pipette with at least one pipette tip.

[0002] Air-cushion pipettes are used primarily in laboratories for dispensing liquids. For this purpose, a pipette tip with an upper opening is clamped onto a seat on the pipette. The seat is usually a conical and / or cylindrical projection at the lower end of a pipette housing, onto which a pipette tip can be clamped with an upper opening in its tubular body. The pipette tip can aspirate and dispense liquid through a lower opening in its downwardly tapered body. Air-cushion pipettes have a displacement device for air, which communicates with the pipette tip through an opening in the seat. The displacement device displaces an air cushion to suck liquid into the pipette tip and expel it from it. For this purpose, the displacement device has a displacement chamber with a displaceable displacement element.The displacement device is usually a cylinder with a movable piston inside it.

[0003] After use, the pipette tip is removed from its seat and replaced with a fresh one. This prevents contamination from liquid transfer during subsequent dispensing. Pipettes usually have an ejector mechanism that allows the tip to be ejected by pressing a button without touching the tip. Single-use pipette tips are usually made of plastic.

[0004] The displacement element is coupled to a drive device that serves to displace the displacement element in the displacement chamber. In known manually operated pipettes, the drive device has a lifting rod that can be moved between an upper and a lower stop using a stop element. Before air is displaced from the cylinder, the stop element rests against the upper stop. By moving the lifting rod downwards until the stop element rests against the lower stop, air is displaced from the cylinder. When the lifting rod is moved upwards until the stop element rests against the upper stop, air is sucked into the cylinder and sample liquid is drawn into the pipette tip. By moving the lifting rod downwards again, the liquid is dispensed from the pipette tip. The amount of liquid aspirated or dispensed depends on the stroke of the lifting rod between the lower and upper stops.

[0005] In fixed-volume pipettes, the distance between the upper and lower stops is constant. In pipettes with adjustable dispensing volumes, the position of the upper stop is adjustable. Common pipettes with adjustable dispensing volumes have an upper stop on the underside of a threaded spindle, which can be adjusted using a spindle nut fixed in the housing. Adjustment devices are provided for adjusting the threaded spindle. These are coupled to display devices that indicate the set dispensing volume in the form of a counter.

[0006] Air-cushion pipettes have an overtravel feature to dispense residual liquid from the pipette tip. To achieve this overtravel, the lower stop can be moved with increased force. In conventional pipettes, the lower stop is formed by a stop body, which is supported in the housing by an overtravel spring, allowing it to be moved by a certain amount with increased force.

[0007] Furthermore, electronic pipettes are known in which the drive device comprises an electric motor and a gear coupling the electric motor to the displacement element and which have an electronic control device which controls the electric motor so that the displacement element executes the desired strokes.

[0008] Both manual and electronic air-cushion pipettes are designed and calibrated for use with the forward pipetting technique. With forward pipetting, the stroke rod is moved from the upper stop to the lower stop by pressing the control button before aspirating liquid. After the pipette tip is immersed in the liquid and the control button is released, the stroke rod returns to the upper stop, and the desired volume of liquid is aspirated. To dispense liquid, the control button is pressed until the stop element reaches the lower stop and the overstroke is complete. There is then no liquid left in the pipette tip.

[0009] However, a second pipetting technique can also be used by the user, known as "reverse pipetting." Starting from the resting position, in which the lifting rod rests against the upper stop, the operating button is pressed down until the overstroke is completed. After the pipette tip is immersed in the liquid, the operating button is released to aspirate the liquid, so that the lifting rod slides back to the upper stop. To dispense the liquid, the operating button is pressed down until the lifting rod reaches the lower stop. Afterward, there is still residual liquid in the pipette tip, as the overstroke is not performed during dispensing. This residual liquid is not part of the dispensing volume and is discarded or returned to the original container. Reverse pipetting is particularly advantageous for viscous solutions, solutions with high vapor pressure, and highly wetting solvents. There are also laboratories, e.g.in the USA, which uses this technology generally, ie also for aqueous liquids.

[0010] Gravimetric tests (EN ISO 8655-6) have shown that the reverse pipetting technique results in a larger systematic error (EN ISO 8655-1) than the forward pipetting technique. Furthermore, the use of the reverse pipetting technique is associated with increased reagent consumption, as the residual liquid (overflow) may be discarded with the tip ejection. Finally, the overflow during liquid aspiration leads to increased sample aspiration, which can potentially be drawn into the pipette or the filter of a filter pipette tip.

[0011] The documents WO 97 / 32666 A1, US 2009 / 000350 A1 and US11084030 B2 disclose air cushion pipettes.

[0012] Based on this, the invention is based on the object of creating an air-cushion pipette that, in addition to forward pipetting, enables reverse pipetting with reduced measurement error, saves reagents, and prevents the aspiration of liquid into the pipette or the filter of a filter pipette tip. This object is achieved by an air-cushion pipette according to claim 1 and by an air-cushion pipette according to claim 10. Advantageous embodiments of the air-cushion pipettes are specified in the subclaims and in the following description.

[0013] According to claim 1, an air cushion pipette according to the invention comprises at least one seat for releasably holding a pipette tip, a displacement device comprising a displacement chamber with a displacement element displaceable therein, which delimits a displacement volume within the displacement chamber, a connecting channel connecting the displacement volume to an opening in the seat, a drive device coupled to the displacement element for displacing the displacement element in the displacement chamber, an upper stop, a lower stop, and a stop element connected to the drive device for limiting the displacement of the displacement element in the displacement chamber, an overtravel device having the lower stop, which is designed and configured such that the stop element displaces the lower stop downwards when the stop element presses against the lower stop with a certain minimum force,wherein the downward displacement of the lower stop is limited to a first overstroke, a displaceable overstroke limiter which, in a release position, allows the downward displacement of the lower stop by the first overstroke and, in a blocking position, limits it to a second overstroke which is shorter than the first overstroke, and a switching device connected to the overstroke limiter in order to selectively displace the overstroke limiter into the release position for forward pipetting or into the blocking position for reverse pipetting.

[0014] According to claim 10, an alternative air cushion pipette according to the invention comprises at least one seat for releasably holding a pipette tip, a displacement device comprising a displacement chamber with a displacement element which can be displaced therein and which delimits a displacement volume within the displacement chamber, a connecting channel connecting the displacement volume to an opening in the seat, a drive device coupled to the displacement element for displacing the displacement element in the displacement chamber, wherein the drive device comprises an electric motor and a gear coupling the electric motor to the displacement element, an electronic control device is connected to the electric motor which controls the electric motor such that in an operating mode for forward pipetting, the displacement element moves from an upper end position to a lower end position,from the lower end position to the upper end position and from the upper end position to a first overstroke position arranged lower than the lower end position by a first overstroke, and in an operating mode for reverse pipetting, the displacement element is moved from the upper end position to a second overstroke position arranged lower than the lower end position by a second overstroke that is smaller than the first overstroke, from the second overstroke position to the upper end position and from the upper end position to the lower end position, and a switching device connected to the electronic control device in order to set the electronic control device selectively to the operating mode for forward pipetting or to the operating mode for reverse pipetting.

[0015] With the air-cushion pipette according to the invention (hereinafter also "pipette"), the systematic measurement error during reverse pipetting is significantly reduced by reducing the over-stroke volume during reverse pipetting compared to the over-stroke volume during forward pipetting, and is adjusted to the systematic measurement error during forward pipetting. According to the findings underlying the invention, the systematic error for one and the same air-cushion pipette with a certain over-stroke during forward pipetting and during reverse pipetting differs significantly. By switching from a first over-stroke during forward pipetting to a comparatively smaller second over-stroke during reverse pipetting, the systematic measurement errors for these two pipetting techniques can be brought closer together. Test results from different users who prefer different pipetting techniques thus become more comparable.

[0016] The switching device allows for easy switching between the first overstroke for forward pipetting and the second overstroke for reverse pipetting without having to recalibrate the air-cushion pipette. This gives the user maximum freedom to alternate between using their air-cushion pipette for forward pipetting of aqueous liquids and reverse pipetting of non-aqueous or special liquids.

[0017] With reverse pipetting, the reduced over-stroke saves reagents compared to reverse pipetting with the same over-stroke as with forward pipetting, since with reverse pipetting the sample volume aspirated with the over-stroke is usually discarded.

[0018] Due to the reduced over-stroke during reverse pipetting, conventional pipette tips, in particular filter tips, can also be used with the nominal volume for reverse pipetting. On the other hand, reverse pipetting of the nominal volume of the pipette tip with the same over-stroke as with forward pipetting can lead to sample liquid being sucked into the working cone of the pipette, which may become contaminated, or to the sample liquid getting into the filter of the pipette tip, where it is contaminated by the filter material, or is dispensed incompletely (i.e., inaccurately). Overall, the invention improves pipetting accuracy, makes switching between forward pipetting and reverse pipetting easier, saves reagents during reverse pipetting, and expands the range of applications for pipette tips for reverse pipetting.

[0019] The first overstroke and the second overstroke each represent a displacement path of the displacement element with a specific, fixed length. In one embodiment, the first overstroke for forward pipetting is 4 mm, and the second overstroke for reverse pipetting is 1 mm, with a distance from the upper stop to the lower stop (dosing stroke) of 16 mm.

[0020] The invention relates to both manually driven and electronic pipettes. Claim 1 is directed to a manually driven pipette, and claim 10 to an electronic pipette.

[0021] According to one embodiment of the manually driven pipette, the drive device is connected to a control knob with which the displacement of the displacement element can be controlled. The control knob is preferably a push button that protrudes upward from the upper end of a rod-shaped housing. By pressing the control knob downward, the drive device can be actuated to displace the displacement element within the displacement chamber.

[0022] According to a further embodiment, the drive device comprises a lifting rod coupled to the displacement element at its lower end, longitudinally displaceable, and having the stop element on its outer circumference, and an operating knob connected to the upper end of the lifting rod for displacing the displacement element in the displacement chamber. According to a further embodiment, the coupling between the lifting rod and the displacement element is designed such that the lower end of the lifting rod presses against the upper side of a plate connected to the upper end of a piston displaceable in a cylinder, which forms the displacement element. According to a further embodiment, the plate is loaded toward the lifting rod by a spring device.This is advantageous for a design in which the pipette has an upper part containing the drive mechanism and a lower part containing the displacement mechanism, whereby the coupling of the lifting rod and the displacement element is established when the upper and lower parts are assembled. Alternatively, the lifting rod is permanently connected to the displacement element.

[0023] Another design features a return spring that loads the drive mechanism in the direction the stop element rests against the upper stop. This ensures that, when the control knob is released, the drive mechanism automatically assumes a rest position in which the stop element rests against the upper stop.

[0024] According to a further embodiment, the lifting rod passes through a central bore of a threaded spindle, which is screwably held in a spindle nut and has the upper stop for the stop element on the lower end. By adjusting the threaded spindle, the stroke can be adjusted that the lifting rod performs when moving the stop element from the upper stop to the lower stop and vice versa. This makes it possible to adjust the dispensing volume that is taken up or dispensed during pipetting. According to a further embodiment, the threaded spindle is coupled to an adjustment knob in order to adjust the threaded spindle in the spindle nut. According to a further embodiment, the adjustment knob is designed separately from the operating knob. According to a further embodiment, the adjustment knob is sleeve-like and encloses the operating knob, which protrudes upwards relative to the adjustment knob.According to another design, the adjustment knob is also the control knob.

[0025] According to another embodiment, the stop element is at least one projection on the circumference of the lifting rod. According to another embodiment, the stop element is a single circumferential projection or bead on the circumference of the lifting rod.

[0026] According to a further embodiment, the movable overtravel limiter is a slide which is guided in a guide in the operating knob and which can be moved in the guide from a release position in which it does not protrude outwards from the operating knob, into a locked position above a frame arranged next to the operating knob, partially protruding outwards with respect to the operating knob. In the release position, the slide does not limit the displacement of the operating knob, so that the operating knob can be actuated in such a way that the first overtravel is executed. In the locked position, the slide limits the downward displacement of the operating knob by resting on the frame, so that it can only control the execution of the second overtravel. According to a further embodiment, the frame is an adjustment knob.

[0027] According to another embodiment, the movable overstroke limiter is a slide that is guided in a fixed guide and can be moved in the guide from a release position, in which it does not protrude outwards from the guide, to a locked position, in which it partially protrudes outwards from the guide, within the travel path of the operating button, the lifting rod, or the overstroke device. In the release position, the slide does not limit the movement of the operating button, the lifting rod, or the overstroke device, so that the first overstroke can be carried out. In the locked position, the slide limits the movement of the operating button, the lifting rod, or the overstroke device, so that only the second overstroke can be carried out.

[0028] According to another embodiment, the switching device is an operating element or tool engagement formed on the slide. The slide can be moved by manually actuating the operating element (e.g., a protruding hook or knurling) or by applying a tool to the tool engagement (e.g., a slot for attaching a screwdriver blade).

[0029] According to one embodiment of the electronic pipette, the electronic control device is connected to a switch (e.g., a button), touchscreen, microphone, and / or another input device to operate the pipette. By means of one or more input devices, in particular, the displacement of the displacement element can be controlled, pipetting parameters (e.g., the dispensing volume, the piston speed) can be set, and the electronic pipette can be switched to the operating mode for forward pipetting or for reverse pipetting. According to another embodiment, the input device is a button, wherein successive actuations of the button control different displacements of the displacement element. According to another embodiment, switching between the different operating modes is carried out by an additional button or other switch (e.g.,toggle switch or slide switch) or another input device.

[0030] A touchscreen can be used, in particular, for entering dosing parameters and / or switching between different operating modes. A microphone can be used for voice-activated operation of the pipette.

[0031] According to a further embodiment, the electronic control device controls the electric motor in reverse pipetting mode such that, after moving the displacement element from the upper end position to the lower end position, the displacement element is displaced downward by the first overstroke or the second overstroke in a further step. This allows residual sample liquid to be dispensed from the pipette tip.

[0032] The following statements apply to both manually driven and electronic pipettes.

[0033] According to one embodiment, during forward pipetting after liquid aspiration, the displacement element is moved from the upper end position to the lower end position for dispensing the dosing volume. The displacement element then remains in the lower end position for at least a short pause so that any liquid can continue to flow along the inner wall of the pipette tip. According to a preferred embodiment, the displacement element is then moved from the lower end position by the first overstroke, and any residual liquid is blown out of the pipette tip, preferably into a waste container or, if necessary, back into the original container (" blow out "). From the first overstroke position, the displacement element is moved back to the upper end position, which forms the starting position for a new liquid aspiration. The overstroke step is good laboratory practice for forward pipetting. However, it can also be omitted and the displacement element can be moved directly from the lower end position back to the upper end position. The manually driven pipette according to the present invention can be operated in accordance with the above, and the electronic pipette according to the present invention can be controlled by means of the electronic control device and the switching device in accordance with the above.

[0034] According to a further embodiment, there are two options for reverse pipetting after liquid dispensing by moving the displacement element from the upper end position to the lower end position: According to a first option, the pipette tip can be immersed in the liquid again for further liquid aspiration and then the displacement element can be moved from the lower end position to the upper end position. According to a second option, the residual liquid in the pipette tip can be emptied, for example, into a waste container or, if necessary, back into a starting container; i.e., the displacement element is moved downwards from the lower end position by the second overstroke. The pipette tip can then be ejected.The manually driven pipette according to the present invention can be operated according to the above, and the electronic pipette of the present invention can be controlled by means of the electronic control device and the switching device according to the above.

[0035] According to another embodiment, the displacement device comprises a cylinder and a piston movable within the cylinder. By moving the piston within the cylinder, the displacement volume in the displacement chamber can be varied. Air-cushion pipettes with a displacement device comprising a cylinder and a piston movable within it are widely used.

[0036] Alternatively, the displacement device is a flexible membrane that is fixed in the displacement chamber to provide a seal at the edges.

[0037] According to a further embodiment, the pipette has a housing, a frame, a chassis or another support structure. The support structure serves to hold the components of the pipette. Components of the pipette that do not change their relative position during operation can be attached to the support structure. These include, for example, a fixed working cone or another seat for releasably holding a pipette tip, the displacement chamber, parts of the drive device (e.g., the spindle nut or the electric motor), parts of the overtravel device, a fixed guide for the overtravel limiter, the electronic control device, the switching device and / or another input device. Other components of the pipette are displaceably mounted on the support structure. These include, for example, the displacement element, parts of the drive device (e.g.,the lifting rod), the upper stop, the lower stop, the threaded spindle and the movable overstroke limiter.

[0038] According to another embodiment, the pipette is a hand pipette, an automated pipetting device, or a pipetting device integrated into a laboratory machine. A hand pipette is a pipette that can be held and operated with only one hand. The hand pipette can be a manually operated pipette or an electronic pipette. An automated pipette or a pipetting device integrated into a laboratory machine is preferably an electronic pipette.

[0039] According to another embodiment, the pipette is a mechanically driven pipette, an electrically driven pipette, or a combined mechanically and electrically driven pipette. A combined mechanically and electrically driven pipette can have a mechanical drive with electrical assistance (servo drive).

[0040] According to another embodiment, the pipette is a single-channel pipette or a multi-channel pipette. A single-channel pipette has only a single seat for releasably holding a pipette tip and a single displacement device. A multi-channel pipette has multiple seats for releasably holding pipette tips, which are connected to a single displacement device or to multiple displacement devices.

[0041] The invention is explained in more detail below with reference to the accompanying drawings of exemplary embodiments. In the drawings: Fig. 1 a pipette in a longitudinal section from the left side; Fig. 2 the same pipette in a longitudinal section from the right side; Fig. 3.1 to 3.4 an adjustment mechanism of the same pipette enlarged in a side view from the right side ( Fig. 3.1 ), in a front view ( Fig. 3.2 ), in a side view from the left side ( Fig. 3.3 ) and in a rear view ( Fig. 3.4 ); Fig. 4.1 to 4.4 the same adjustment mechanism switched in a different switching stage, enlarged in a side view from the right side ( Fig. 4.1 ), in a front view ( Fig. 4.2 ), in a side view from the left side ( Fig. 4.3 ) and in a rear view ( Fig. 4.4 ); Fig. 5.1 to 5.3 the pipette during forward pipetting in a perspective view obliquely from above; Fig. 6.1 to 6.3 the pipette during reverse pipetting in a perspective view obliquely from above; Fig. 7.1, 7.2 a movable overstroke limiter with a rod-shaped slider guided in the control knob in the release position ( Fig. 7.1 ) and in locked position ( Fig. 7.2 ), each in a perspective view diagonally from above; Fig. 8.1, 8.2 a movable overstroke limiter with an L-shaped slider guided in the control knob in the release position ( Fig. 8.1 ) and in locked position ( Fig. 8.2 ), each in a perspective view diagonally from above; Fig. 9.1, 9.2 a movable overtravel limiter with a cover guided in the housing in the release position ( Fig. 9.1 ) and in locked position ( Fig. 9.2 ), each in a perspective view obliquely from above, Fig. 10 a displaceable overstroke limitation with a slide guided in a guide in the adjustment ring in a longitudinal section through the upper area of ​​a pipette.

[0042] In this application, the terms "top" and "bottom," "above" and "below," and derivatives such as "bottom" and "top," and "horizontal" and "vertical" refer to an orientation of the pipette in which the seat is located at the bottom of the pipette and oriented vertically downward. In this orientation, a pipette tip mounted on the seat can be directed toward a vessel below to aspirate liquid into the pipette tip and dispense it from the pipette tip.

[0043] Based on the Fig. 1 bis 6 Basic features of a manually driven air cushion pipette are explained, which are also present or can be present in the air cushion pipette designed according to the invention. A movable overstroke limiter of the pipette according to the invention is provided in the pipette of Fig. 1 bis 6 not available. Examples of the different designs of a movable overtravel limiter are shown in the Fig. 1 bis 10 These versions of a movable over-stroke limiter can be used with a pipette according to Fig. 1 bis 6 be developed with appropriate adaptation and additions to the design. Fig. 1 bis 6 Although they do not show all the features of an air cushion pipette according to the invention, they do make it easier to understand.

[0044] According to Fig. 1 und 2 a pipette 1 has a rod-shaped housing 2 with a lower housing part 3 and a housing upper part 4. The lower housing part 3 has a tubular base body 5 with a conical bottom at the top, from which a slender tubular, slightly conical extension 6 projects downwards, which has a seat 7 at the lower end for attaching a pipette tip 8. In the extension 6, a displacement chamber 9 in the form of a cylinder is formed, which is connected via a connecting channel 10 to an opening 11 in the underside of the seat 7.

[0045] The lower housing part 3 comprises a displacement element 12 in the form of a piston of the displacement device, which is guided into the cylinder 11 via a sealing system 13 on the upper side of the base. The displacement element 12 has a plate 14 at its upper end, which has a dome-shaped recess centrally on the upper side. A first spring device 15 in the form of a helical spring is arranged between the plate 14 and the upper side of the base. The first spring device 15 presses the plate 14 from below against a closure cap 16, which is connected to the base body 5 and has a passage in the center through which the plate 14 is accessible from above.

[0046] The upper housing section 4 contains a lifting rod 17, which rests against the upper side of the plate 14. The lower end of the lifting rod 17 engages in the recess of the plate 14.

[0047] At the top of the lifting rod 17, an operating button 18 is fixed, which protrudes outwards from the upper end of the housing 2.

[0048] The lifting rod 17 passes through a central spindle bore 19 of a threaded spindle 20 located in the upper housing section 4. The threaded spindle 20 has an external thread 21 that can be screwed into an internal thread 22 of a lifting body 23, which is held at the bottom on a first support 24 in the upper housing section 4. The lifting body 23 forms a spindle nut.

[0049] The lower end face of the threaded spindle 20 is an upper stop 25 for a stop element 26 in the form of an annular bead on the outer circumference of the lifting rod 17.

[0050] The threaded spindle 20 is connected at its upper end in a rotationally fixed manner to a driver 27, which engages in axial grooves 29 of a driver sleeve 30 by means of radially outwardly projecting ribs 28. The driver sleeve 30 is arranged concentrically to the threaded spindle 20 and is rotatably mounted on the outer circumference of the lifting body 23. The driver sleeve 30 has a circumferential first toothing 31 on the lower edge of the outer circumference (cf. Fig. 3 , 4 ).

[0051] An adjusting sleeve 32 is slid onto the drive sleeve 30. The adjusting sleeve 32 is rotatably mounted on the outer circumference of the drive sleeve 30 and is guided axially displaceably between two limits on the drive sleeve 30. The upper end of the adjusting sleeve 32 protrudes outward from the upper end of the housing 2. There, the adjusting sleeve 32 has an adjusting ring 33 on its outer circumference, which has a knurling on the outer circumference.

[0052] The adjusting sleeve 32 has a second toothing 34 running around the outer circumference at the lower edge and a third toothing 35 running around the outer circumference slightly further up. The first toothing 31 and the second toothing 34 have the same diameter and the same number of teeth. The third toothing 35 has a larger diameter and a greater number of teeth than the second toothing 34.

[0053] The second toothing 34 is on the top side, and the third toothing 35 is closed on the bottom side by an intermediate disc 36. The bottom side of the disc 36 forms a lower limit 37, and the top side of the disc 36 forms an upper limit 38 for the displacement of the adjusting sleeve 32.

[0054] In addition to the drive sleeve 30 and the adjusting sleeve 32, a transmission shaft 39 is rotatably mounted on the first carrier 24. The transmission shaft 39 is provided with a fourth toothing 40 at the bottom, a fifth toothing 41 above it, and a sixth toothing 42 above it. The fourth toothing 40 and the fifth toothing 41 have the same diameter and the same number of teeth and are combined into a single toothing 43. The sixth toothing 42 is arranged at a distance from the fifth toothing 41. It has a smaller diameter and a lower number of teeth than the fifth toothing 41.

[0055] The transmitter shaft 39 is rotatably mounted at the top in a second carrier 44 which is fixed in the upper housing part 4.

[0056] A counter 45 in the form of a roller counter is held between the first carrier 24 and the second carrier 44. A counting roller axle 46 of the roller counter is mounted at the bottom in the first carrier 24 and at the top in the second carrier 44. The second carrier 44 is supported at the top on a projection in the housing. A drive gear 47 is rotatably mounted on an axle on the first carrier 24. This drive gear comprises two spur gears 48, 49 of different diameters that are connected to one another in a rotationally fixed manner. The spur gear 48 with the smaller diameter meshes with the first toothing 31 of the driver sleeve 30, and the spur gear 49 with the larger diameter meshes with a drive pinion 50 on a starting roller of the roller counter.

[0057] The number rollers 51 of the counter 45 are visible from the outside of the housing 2 through a window 52 in the upper housing part 4, which has a transparent cover 53 (cf. Fig. 2 ).

[0058] A cup-shaped holder 54 is arranged in the upper housing section 4 below the lifting body 23. The holder 54 has an external thread 55, which is screwed into an internal thread 56 of a third support 57 fastened in the housing 2.

[0059] The holder 54 includes a cap-shaped lower stop 58, which is held under a downwardly curved upper edge 59 of the holder 54. An overtravel spring 60 in the form of a helical spring, which is supported on the bottom 61 of the holder 54, presses the lower stop 58 against the upper edge 59. The lifting rod 17 is guided through central passages of the lower stop 58, through the overtravel spring 60, and through a central passage in the bottom 61 of the holder 54.

[0060] The adjusting sleeve 32 is a drive shaft, the driving sleeve 30 is an output shaft and the transmission shaft 39 is a countershaft of a gearbox 63 designed as a spur gear 62. Switching between the different gear stages is carried out by axially displacing the adjusting sleeve 32 in a Fig. 3 shown lower switching position (fine adjustment position) and into a Fig. 4 shown upper switching position (quick adjustment position). In the fine adjustment position of Fig. 3 The adjusting sleeve 32 is displaced downwards until the lower limit 37 rests on the upper side of the fifth toothing 41, and in the quick-adjustment position, the adjusting sleeve 32 is displaced upwards until the upper limit 38 rests on the underside of the sixth toothing 42. Thus, the adjusting sleeve 32 is simultaneously a switching device 64 of the manual transmission, with the adjusting ring 33 being a switching element 65 of the switching device 64.

[0061] When the adjusting sleeve 32 is rotated, the drive sleeve 30 rotates according to the currently set switching stage. The drive sleeve 30 screws the threaded spindle 20 into the internal thread 22 fixed to the housing, and the upper stop 25 moves up or down depending on the direction of rotation. This adjusts the distance between the upper stop 25 and the lower stop 58, which determines the dosing volume. The currently set dosing volume can be read off the counter 45, which is driven by the drive sleeve 30 via the drive gear 47.

[0062] At the upper edge of the upper housing part 4, next to the adjusting sleeve 32, there is an ejector button 66 on an ejector rod 67. The ejector rod 67 runs parallel to the lifting rod 17 through the upper housing part 4. Its lower end is connected to a lateral fastening projection 68 of an ejector sleeve 69, which is slidably arranged on the projection 6.

[0063] An ejector spring 70, designed as a helical spring, is arranged in the upper housing part 4. It is supported on the one hand in the housing 2 and, on the other hand, engages the ejector rod 67. The ejector spring 70 presses the ejector rod 67 upwards, so that the ejector sleeve 67 rests against the projection 6.

[0064] The lower housing part 3 and the upper housing part 4 are connected to each other by a snap connection 71.

[0065] Before pipetting, the user can set the desired dosing volume. To do this, turn the setting ring 33 until the desired dosing volume is displayed on the counter 45. To set the fast switching stage, the user pulls the setting sleeve 32 on the setting ring 33 from the fine adjustment position of Fig. 3 slightly further out of the housing 2 into the quick adjustment position.

[0066] In the quick adjustment position of Figur 4 the first toothing 31 of the driving sleeve 30 meshes with the fourth toothing 40 of the transmitter shaft 39 and the third toothing 35 of the adjusting sleeve 32 meshes with the sixth toothing 42 of the transmitter shaft 39. As a result, the rotational speed of the adjusting sleeve 32 is translated into a higher rotational speed of the driving sleeve 30, so that the user can quickly adjust the dosing volume close to the dosing volume to be set.

[0067] To set the slow shift stage, the user presses the adjusting sleeve 32 on the adjusting ring 33 deeper into the housing 2 until it reaches the fine adjustment position. In this position, the first toothing 31 meshes with the fourth toothing 40, and the second toothing 34 meshes with the fifth toothing 41. This results in rotation of the adjusting sleeve 32 at a certain rotational speed causing the driver sleeve 30 to rotate at a lower speed than in the fast shift stage. In the example, the rotational speed of the adjusting sleeve 32 is equal to the rotational speed of the driver sleeve 30, since the first toothing 31 and the second toothing 34, as well as the fourth toothing 40 and the fifth toothing 41, each have the same number of teeth and diameter.

[0068] The user can clamp a pipette tip 8 onto the pipette 1 by pressing the pipette 1 with the seat 7 into the upper opening 72 of the pipette tip 8. To pipette forward, the user first presses the operating button 18 downwards, so that the stop element 26 is moved from the upper stop 25 against the lower stop 58. The lifting rod 17 presses the displacement element 12 downwards, and the first spring device 15 is preloaded. The user then immerses the pipette tip 8 with its lower opening 73 into the sample liquid and releases the operating button 18. As a result, the first spring device 15 presses the displacement element 12 and the lifting rod 17 upwards until the stop element 26 rests against the upper stop 25. A quantity of liquid corresponding to the set dispensing volume is sucked into the pipette tip 8.

[0069] To dispense the amount of liquid, the user holds the pipette tip 8 with the lower opening 73 over another container and presses the operating button 18 downwards again. After reaching the lower stop 58, the user can press the operating button 18 even deeper, overcoming the resistance of the over-stroke spring 60, to expel residual liquid from the pipette tip 8 through an over-stroke.

[0070] A further amount of liquid can then be pipetted in the same manner, or, to change the sample liquid, the pipette tip 8 can be ejected downward by pressing the ejector button 66. The ejector sleeve 69 then strips the pipette tip 8 from the seat 7. After the ejector button 66 is released, the ejector spring 70 returns the ejector rod 67 to the starting position shown.

[0071] According to Fig. 5 During the previously described forward pipetting for liquid aspiration, the operating button 18 is pressed down so that the stop element 26 is displaced from the upper stop 25 to the lower stop 58 and air is forced out of the displacement chamber 9 ( Fig. 5.1 ). The operating knob 18 is then released and slides back until the stop element rests against the upper stop 25 ( Fig. 5.2 ). Sample liquid is sucked into a pipette tip 8 clamped onto the seat 7.

[0072] To dispense the liquid, the control button 18 is then pressed down again until the stop element 26 hits the lower stop. With increased force, the control button is pressed further down and the overstroke is executed ( Fig. 5.3 The overtravel is reached when the overtravel spring 60 is compressed to its maximum. After this time, no more sample fluid is present in the pipette tip 8.

[0073] According to Fig. 6 During reverse pipetting for liquid aspiration, the operating button 18 is pressed down so that the stop element 26 is moved from the upper stop 25 to the lower stop 58 and the lower stop 58 executes the overstroke ( Fig. 6.1 ). Air is forced out of the displacement chamber 9. After the pressure is released, the control button 18 slides back until the stop element 26 rests against the upper stop 25, whereby liquid is sucked into the pipette tip 8 ( Fig. 6.2 ).

[0074] To dispense the liquid, the control button 18 is pressed down again so that the stop element 26 is moved from the upper stop 25 to the lower stop 58. The selected dosing volume is dispensed ( Fig. 6.3 ). There will then still be residual liquid in the pipette tip 8. This can be discarded by pressing the control button 18 with increased force so that the overstroke is carried out.

[0075] The pipette from Fig. 1 bis 6 can be designed according to the invention in the following way: The overstroke system of the pipette formed by the holder 54 with the lower stop 58 and the overstroke spring 60 of Fig. 1 bis 6 can be designed such that the first overstroke is achieved by maximum compression of the overstroke spring 60. In addition, an adjustable stop can be provided, which can be displaced via a slide or a thread to limit the downward travel of the cap-shaped lower stop 58, so that the stop 58 can only execute the second overstroke, which is smaller than the first overstroke.

[0076] In the embodiment of Fig. 7 The control knob 18 has a horizontal guide 74. A rod-shaped slide 75 is inserted into the guide 74, which can be pushed completely into the guide 74 so that in a release position it does not protrude beyond the adjusting ring 33 at the ends of the guide 74. This allows the control knob 18 to be pressed deep into the adjusting ring 33 so that the complete first overstroke (e.g. 4 mm) is carried out. This is Fig. 7.1 shown. This setting of slider 75 is selected for forward pipetting.

[0077] The slide 75 can be displaced in the guide 74 by pressing against a front side 76 so that it protrudes laterally partially beyond the guide 74 in a locked position. The laterally protruding part of the slide 75 strikes the upper edge of the setting ring 33 when the control button 18 is pressed down. This limits the downward displacement of the control button 18 so that only a reduced second overstroke (e.g. 1 mm) can be carried out. This is Fig. 7.2 This setting of slider 75 is selected for reverse pipetting, as it reduces the systematic measurement error.

[0078] The embodiment of Fig. 8 differs from the previously described embodiment in that an L-shaped slider 77 with a horizontal leg 78 is inserted into a horizontal guide 74 of the control knob 18. A vertical leg 79 of the slider is accessible from above through a vertical channel 80 in the control knob 18 in order to displace the slider 77 laterally.

[0079] In Fig. 8.1 The slider 77 is shown in a release position in which it does not protrude laterally from the control knob 18. As a result, the control knob 18 can be pushed down completely during forward pipetting and the first overstroke can be performed. Fig. 8.2 the slide 77 is moved into the locking position in which its horizontal leg 78 partially protrudes laterally from the operating button 18, so that the protruding part of the leg 78 strikes the setting ring 33 when the operating button 18 is pressed down, so that only the reduced second overstroke is possible during reverse pipetting.

[0080] The embodiment of Fig. 9 has a shutter-shaped slide 81 behind the ejector button 66, which is guided in a fixed vertical guide 82 in the housing 2. The slide 81 can be displaced downwards within the vertical guide 82 for forward pipetting, so that it does not restrict the downward displacement of the control button 18, as in Fig. 9.1 shown. In this release position of the slide 81, the first overstroke can be performed by pressing the control button 18.

[0081] According to Fig. 9.2 For reverse pipetting, the slide 81 can be moved upwards in the vertical guide 82 into a locked position and secured therein by means of suitable locking means (e.g., with a toothing). In the locked position of the slide 81, when the control button 18 is pressed down, a circumferential flange 83 on its upper edge strikes the upper edge of the slide 81, preventing further pressing of the control button 18 and allowing only the second overstroke to be performed.

[0082] According to Fig. 10 An L-shaped slide 77 is inserted into a horizontal guide 84 in the adjustment ring 33, the end region of which can be pushed under a shoulder 85 of its horizontal leg 78 of the operating knob 18. To move the slide 77, it has an operating element in the form of an upwardly projecting vertical leg 79. In the release position, the slide 77 does not engage under the shoulder 85 of the operating knob 18, so that the latter can be pressed down completely and the first overstroke can be executed. In the locked position, the end region of the slide 77 engages under the shoulder 85, so that the operating knob 18 can only be pressed down to a reduced extent and only the reduced second overstroke can be executed.

[0083] In the examples of Fig. 7 bis 10By moving the slider from the release position to the lock position, the systematic error during reverse pipetting is reduced and adjusted to the systematic error during forward pipetting. For forward pipetting, the slider is moved to the release position. List of reference symbols

[0084] 1 Pipette 2 Housing 3 Housing base 4 Housing top 5 Base body 6 Attachment 7 Seat 8 Pipette tip 9 Displacement chamber 10 Connecting channel 11 Opening 12 Displacement element 13 Sealing system 14 Plate 15 Spring device 16 Closure cap 17 Lifting rod 18 Operating knob 19 Spindle bore 20 Threaded spindle 21 External thread 22 Internal thread 23 Lifting body 24 First carrier 25 Upper stop 26 Stop element 27 Driver 28 Ribs 29 Grooves 30 Driver sleeve 31 Toothing 32 Adjusting sleeve 33 Adjusting ring 34 Second toothing 35 Third toothing 36 Disc 37 Lower limit 38 Upper limit 39 Transmitter shaft 40 Fourth toothing 41fifth toothing 42sixth toothing 43toothing 44second carrier 45counter 46counter roller axle 47drive gear 48,49 Spur gear 50 Drive pinion 51 Number wheel 52 Window 53 Cover 54 Holder 55 External thread 56 Internal thread 57 Third carrier 58 Lower stop 59 Upper wheel 60 Overtravel spring 61 Base 62 Spur gear 63 Switching gear 64 Switching device 65 Switching element 66 Ejector button 67 Ejector rod 68 Mounting lug 69 Ejector sleeve 70 Ejector spring 71 Snap connection 72 Upper opening 73 Lower opening 74 Horizontal guide 75 Rod-shaped slide 76 End face 77 L-shaped slide 78 Horizontal leg 79 Vertical leg 80 Channel 81 Aperture-shaped slide 82 Fixed vertical guide 83 Flange 84horizontal guidance 85paragraph,

Claims

1. An air cushion pipette comprising • at least one seat (7) for releasably holding a pipette tip (8), • a displacement apparatus comprising a displacement chamber (9) having a displacement element (12) that can be displaced therein and that delimits a displacement volume inside the displacement chamber, • a connecting channel (10) that connects the displacement volume to an opening (11) in the seat (7), • a drive apparatus coupled to the displacement element (12) for displacing the displacement element (12) in the displacement chamber (9), • an upper stop (25), a lower stop (58), and a stop element (26) connected to the drive apparatus for limiting the displacement of the displacement element (12) in the displacement chamber (9), • an overstroke apparatus comprising the lower stop (58) that is designed and configured such that the stop element (26) displaces the lower stop (58) downwards when the stop element presses with a certain minimum force against the lower stop, wherein the downward displacement of the lower stop is limited to a first overstroke, characterised in that the air cushion pipette further comprises: • a displaceable overstroke limiting means (75, 77) which permits the displacement of the lower stop (58) downwards by the first overstroke in a release position and limits said displacement to a second overstroke that is shorter than the first overstroke in a blocking position, and • a switching apparatus (76, 79) connected to the overstroke limiting means (75, 77) in order to either displace the overstroke limiting means into the release position for forward pipetting or into the blocking position for reverse pipetting.

2. The air cushion pipette according to claim 1, wherein the drive apparatus comprises an operating button (18) for actuating the drive apparatus.

3. The air cushion pipette according to claim 1 or 2, wherein the drive apparatus comprises a stroke rod (17) that is coupled to the displacement element (12) at the lower end, that can be displaced in the longitudinal direction, and that comprises the stop element (26) on the outer periphery, and an operating button (18) that is connected to the upper end of the stroke rod (17) for displacing the displacement element (12) in the displacement chamber (9).

4. The air cushion pipette according to any one of claims 1 to 3, which comprises a return spring (15) which loads the drive apparatus in the direction of contact of the stop element (26) on the upper stop (25).

5. The air cushion pipette according to any one of claims 1 to 4, wherein the stroke rod (17) is guided through a central spindle bore (19) of a threaded spindle (20) that is screwably held in a spindle nut and comprises the upper stop (25) for the stop element (26) on the lower end face.

6. The air cushion pipette according to any one of claims 1 to 5, wherein the stop element (26) is at least one projection on the periphery of the stroke rod (17).

7. The air cushion pipette according to any one of claims 2 to 6, wherein the displaceable overstroke limiting means is a slider (75, 77) that is guided in a guide (74) in the operating button (18) and can be displaced in the guide (74) from a release position, in which it does not protrude outwards from the operating button (18), into a blocking position that protrudes outwards at least in part from the operating button (18), above an edging of the operating button (18) that is stationary in the axial direction.

8. The air cushion pipette according to any one of claims 2 to 6, wherein the displaceable overstroke limiting means is a slider (77, 81) that is guided in a stationary guide (82, 84) and can be displaced in the guide from a release position, in which it does not project outwards from the guide, into a blocking position that projects outwards at least in part from the guide, in the displacement path of the operating button (18), stroke rod (17), or overstroke apparatus.

9. The air cushion pipette according to claim 7 or 8, wherein the switching apparatus is an operating element (76, 79) or tool engagement portion formed on the slider.

10. An air cushion pipette comprising • at least one seat for releasably holding a pipette tip, • a displacement apparatus comprising a displacement chamber having a displacement element that can be displaced therein and that delimits a displacement volume inside the displacement chamber, • a connecting channel that connects the displacement volume to an opening in the seat, • a drive apparatus coupled to the displacement element for displacing the displacement element in the displacement chamber, • wherein the drive apparatus comprises an electric motor and a transmission coupling the electric motor to the displacement element, • an electronic control apparatus is connected to the electric motor and controls the electric motor such that, in a mode of operation for forward pipetting, the displacement element is displaced from an upper end position into a lower end position, from the lower end position into the upper end position, and from the upper end position into a first overstroke position arranged deeper than the lower end position by a first overstroke and, in a mode of operation for reversing pipetting, the displacement element is displaced from the upper end position into a second overstroke position that is arranged deeper than the lower end position by a second overstroke that is shorter than the first overstroke, from the second overstroke position into the upper end position, and from the upper end position into the lower end position, and • a switching apparatus that is connected to the electronic control apparatus in order to set either the mode of operation for forward pipetting or the mode of operation for reverse pipetting.

11. The air cushion pipette according to claim 10, wherein the switching apparatus comprises an electrical switch, pushbutton, or another input apparatus for setting the mode of operation.

12. The air cushion pipette according to any one of claims 1 to 11, which comprises a housing, a frame, a chassis, or another support structure.

13. The air cushion pipette according to any one of claims 1 to 12, which is a handheld pipette, an automatic pipetting machine, or a pipetting device integrated in an automatic laboratory machine.

14. The air cushion according to claim 13, which is a mechanically driven handheld pipette, an electrically driven handheld pipette, or a hybrid mechanically and electrically driven handheld pipette.

15. The air cushion pipette according to any one of claims 1 to 14, which is a single-channel pipette or a multichannel pipette.