Abstract:
A pipette for use with pipette tips in which a set metering volume is secured in that the locking body is arranged on the circumference of the annular cylindrical locking element when it is in the locking position. Through this, the transmission part which the locking element comprises on the outer circumference is held fast. The annular cylindrical locking element can be formed separately from a toothed ring for driving a counter mechanism. Thus, it is possible to perform the locking in arbitrary positions or in more selectable rotational positions than in the conventional locking equipment, where a locking element engages into the toothed ring for driving the counter mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to a pipette for replaceable pipette tips. 
         [0004]    Pipettes are used in the laboratory in particular for metering liquids. For this purpose, a pipette tip is clamped fast on a seat of the pipette with an upper opening. The seat is mostly a conical or cylindrical projection with respect to a casing of the pipette, onto which a pipette tip can be clamped with the upper opening thereof. The pipette tip can pick up and give out liquid through a lower opening. Air cushion pipettes comprise a displacement equipment for air, which is communicatingly connected to the pipette tip through a hole in the seat. An air cushion is relocated by means of the displacement equipment, so that liquid is sucked into the pipette tip and ejected out from there. For this purpose, the displacement equipment has a displacement chamber with a relocatable limit. The displacement equipment is mostly a cylinder with a piston that can be relocated therein. 
         [0005]    After use, the pipette tips are released from the seat and replaced by a fresh pipette tip. Contaminations in subsequent meterings can be avoided through this. Pipette tips have usually an ejection device for ejecting the pipette tips, which permit ejection by actuation of a button without having to touch the pipette tips. Single use pipette tips made of plastics are available at low cost. 
         [0006]    The relocatable limit is coupled to a drive equipment, which serves for shifting the piston in the cylinder. The drive equipment has a lifting rod, which can be shifted between an upper and a lower stop with a stop element. In the beginning of the aspiration of air into the displacement chamber, the stop element is situated at the lower stop. In the beginning of the displacement of air out of the cylinder, the stop element rests on the upper stop. The amount of liquid that is picked up or delivered, respectively, depends on the stroke of the relocatable limit, and thus on the stroke of the lifting rod. The stroke volume of the relocatable limit does not correspond exactly to the amount of liquid that is picked up or delivered. As the air column expands somewhat under the weight of the liquid, the stroke volume exceeds the volume of the liquid. The deviation between the stroke volume and the liquid&#39;s volume depends in particular on the density and viscosity of the liquid, the temperature, the air pressure and on wetting effects. For instance from the document WO 03/0331515 or U.S. Pat. No. 3,827,305, it is known to calibrate pipettes to a certain metering volume by adjusting the position of an upper stop body. 
         [0007]    In fixed volume pipettes, the distance between upper and lower stop is constant. A fixed volume pipette with an upper stop body in the form of a threaded sleeve that is adjustable by a calibration tool is known from the document U.S. Pat. No. 4,020,698. 
         [0008]    In pipettes with adjustable metering volume, the position of the upper stop is variable. Known pipettes have an upper stop body in the form of a threaded spindle, which is adjustable in a spindle nut which is fixedly disposed in the casing. In order to adjust the threaded spindle, there are adjustment equipments, which are coupled to indicating equipments in the form of a counter for indicating the set metering volume. 
         [0009]    The documents DE 43 35 863 C1 and U.S. Pat. No. 5,531,131 describe a pipette where a cylindrical actuating element projects out of the casing at the top, and is connected to an upper end of a lifting rod that is connected to the piston at its lower end. The lifting rod is guided through the upper passage channel of a threaded spindle and the lower passage channel of a lower stop body. It comprises a stop element in the form of an outward projecting bead, which limits the movement of the lifting rod between the threaded spindle and the lower stop body. By pressing in the actuating element against the force of a pull back spring, the piston is moved deeper into the cylinder, until the stop element bears against the lower stop body. After releasing the actuating element, the piston reverts into its starting position due to the action of the pull back spring, in which the stop element bears against the threaded spindle. Adjustment equipments for adjusting the threaded spindle comprise an adjusting sleeve, which projects out of the casing at the top and in which the actuation button can be relocated axially. The adjusting sleeve is rotatably mounted in the casing and connected to the upper end of the threaded spindle via catch dogs so as to rotate together with it. By rotating the adjusting sleeve, the threaded spindle can be relocated together with the spindle nut, wherein the catch dogs are axially relocatable in axial grooves of the adjusting sleeve. 
         [0010]    Moreover, pipettes are known in which a cylindrical actuating element serves as an adjusting element for adjusting the threaded spindle at the same time. For this purpose, the actuating element is connected to the upper end of the threaded spindle so as to rotate with it and to be axially relocatable. A driving tenon in the form of a polygon on the upper end of the threaded spindle immerses into a complementary axial accommodation of the actuating element. The actuating element is relocatably arranged in a break-through of a sleeve-shaped transmission part, which is rotatably mounted in the casing. The actuating element is connected to the transmission part so as to be rotationally blocked via catch dogs in the form of ribs that project outward engaging into axial grooves of the transmission part. The transmission part has a toothed ring with axially projecting teeth on its circumference at the outside, into which a toothed wheel of a counter mechanism engages which serves for indicating the set metering volume. 
         [0011]    The known pipettes have a locking equipment which prevents that a set metering volume is changed without intention in the metering. For this purpose, an axially directed tooth on a lever arm of a two-arm lever, which is pivotal around a horizontal axis, engages between two neighbouring axially directed teeth of a toothed ring on the circumference of the transmission part. The lever is pressed into this locking position via a spring. In order to unlock, there is a push button which partly projects out of the casing and acts within the casing on the other lever arm of the lever via a chamfered surface. By pressing the push button deeper into the casing, the lever is swung so that the tooth is released from the toothed ring. In this position, the actuating element can be rotated in order to adjust the metering volume. Such a locking of the rotational position of the actuating element is described in the document EP 0 527 170 B1. 
         [0012]    The known locking equipment has the disadvantage that it may be destroyed in the locking position by rotating the actuating element with increased force. Moreover, it is tedious to push the unlocking push button and to adjust the metering volume at the same time. Moreover, actuating the wedge gear system formed by the push button and the lever requires a relatively high expenditure of force. Further, the engagement of the tooth into the toothed ring of the transmission part limits the fineness of the setting of the metering volume. Moreover, the assembly of the many single parts is sumptuous. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    Starting from this, the present invention is based on the task to provide a pipette with a releasable locking of the rotational position of the actuating element which has favourable utilization properties. 
         [0014]    The pipette of the present invention has
       a rod-shaped casing,   a seat for detachably holding a pipette tip on the lower end of the casing,   a displacement equipment, comprising a displacement chamber with a limit that is relocatable therein,   a connection channel, connecting the displacement chamber with an opening in the seat,   a drive equipment, coupled to the relocatable limit, for relocating the relocatable limit of the displacement chamber,   adjustable means for limiting the relocation of the relocatable limit by the drive equipment,   an actuating element, connected to the drive equipment and projecting out from the upper end of the casing, for controlling a relocation of the relocatable limit by relocation along an axis, and for adjusting the adjustable means for limiting by rotating the actuating element,   a cylindrical transmission part, which is rotatable in the casing and bearing mounted at a certain position in the axial direction, wherein the actuating element is relocatable in an axially extending accommodation of the transmission part and is connected to the transmission part, so as to rotate together with it, via means for rotation-blocked connection,   first means for transmitting a rotational movement of the actuating element to a movement for adjusting the adjustable means for limiting the relocation, coupled to the actuating element and the adjustable means for limiting the relocation,   adjustable means for indicating a metering volume with a display that is visible from the outside,   second means for transmitting a rotational movement of the transmission part to a movement for adjusting the adjustable means for indicating, coupled to the transmission part and the adjustable means for indicating,   an annular cylindrical locking element on the outer circumference of the transmission part,   a locking body with a partly cylindrical acting surface, which bears against the circumference of the locking element in the locking position,   means for relocating the locking body into the locking position,   at least one unlocking element, projecting from the casing and being movably mounted with respect to the casing,   third means for transmitting a movement of the unlocking element with respect to the casing to a movement, away from the locking element, of the locking body from out the locking position, the means being coupled to the locking body and the unlocking element.       
 
         [0031]    In the pipette of the present invention, a set metering volume is secured in that the locking body is arranged on the circumference of the annular cylindrical locking element when it is in the locking position. Through this, the transmission part which the locking element comprises on the outer circumference is held fast. The annular cylindrical locking element can be formed separately from the toothed ring for driving a counter mechanism. Thus, it is possible to perform the locking in arbitrary positions or in more selectable rotational positions than in the conventional locking equipment, where a locking element engages into the toothed ring for driving the counter mechanism. Errors in the setting of the metering volume are reduced through this. Further, finding a locking point is facilitated. The partial cylindrical acting surface of the locking body can be made greater than the one tooth of the locking lever in the state of the art. Thus, the locking can be overcome or destroyed less easily, and the safety of the locking is improved. Further, it is advantageous that the locking body, the unlocking element and the third means for transmitting a movement can be housed in a space-saving way above a toothed ring for driving a counter mechanism. In this, the third means for transmitting do not necessitate a wedge slide gear, which is impaired by friction and increases the force of operation. 
         [0032]    According to one embodiment, the pipette has unlocking elements, projecting from the casing on side walls of the casing facing away from each other, each of them being coupled to the locking body via third means for transmitting, in order to relocate the locking body away from the locking element by actuating the one or the other unlocking element at option. This embodiment is particularly advantageous with respect to the utilization of the pipette by left handed and right handed persons, an easily reachable unlocking element being provided for both of them. 
         [0033]    According to one embodiment, the locking element is a toothed ring on the circumference of the transmission part with radially outward directed teeth, and the locking body has a toothed ring with radially inward directed teeth on the partly cylindrical acting surface, which engage into the teeth of the locking element in the locking position. In another embodiment, the locking element is ferromagnetic and the locking body is a magnetic body. According to another embodiment, the locking element is a brake cylinder and the locking body is a brake shoe. The two first and the two last variants can also be used in combination. 
         [0034]    The locking body has preferably at least 5 and/or at most 35 teeth, further preferably at least 15 and/or at most 25 teeth. 
         [0035]    According to a further embodiment, the third means for transmitting comprise a two-arm lever with a first lever arm acting on the locking body and a second lever arm, which either acts on the unlocking element or is itself the unlocking element. This embodiment can be implemented in a space-saving way and permits force-saving unlocking. It favours designs wherein the locking body is brought into the locking position with exceptionally high force, so that the locking is particularly safe. 
         [0036]    According to a further embodiment, the lever arms of the two-arm lever are inclined towards each other in an obtuse angle, and/or extend in an arc around the actuating element. This embodiment is also advantageous for space-saving accommodation around the transmission part. 
         [0037]    According to a further embodiment, the unlocking element has a further lever, pivotally mounted in the casing, with a lever arm acting on the third means for transmitting and an actuating portion protruding from the casing. This embodiment permits a force conversion via a gear system composed of several lever arms, which facilitates unlocking. It favours designs wherein the locking body is brought into the locking position with exceptionally high force, so that the locking is particularly safe. 
         [0038]    According to a further embodiment, means for arresting the further lever in an unlocking position exist between the further lever and the casing. This embodiment favours the adjustment of the metering volume by only one single hand, because the user can disengage the further lever in the unlocking position, and then easily turn the actuating element with thumb and forefinger. 
         [0039]    According to a further embodiment, the means for relocating the locking body into the locking position comprise a spring element which loads the locking body in the locking position and is supported in a spring support that is fixedly connected to the casing. The spring element keeps the locking body in the locking position when the unlocking element is unloaded. Upon actuation of the unlocking element, the locking body is moved away from the locking position against the action of the spring element. After unloading the unlocking element, the spring element moves the locking body back into the locking position. Preferably, the spring element moves the third means for transmitting and the unlocking element also back into a starting position, from out which the unlocking can take place by actuating the unlocking element. According to a preferred embodiment, the spring element is a helical spring or a conical wire spring. 
         [0040]    According to a further embodiment, there is a further spring element, which loads the unlocking element in the unlocking position and is supported in a spring support that is fixedly connected to the casing. The unlocking element can be actuated against the action of the further spring element, and is moved back into the unlocking position by the same after unloading. 
         [0041]    In an alternative embodiment, the unlocking element can be actuated in two different directions, and the locking body is coupled to the unlocking element via the third means for transmitting, such that by actuating the unlocking element in the one direction, the locking body can be moved away from the locking position, and thus be unlocked, and that by actuating the unlocking element in the other direction, the locking body can be moved back into the locking position. 
         [0042]    According to a further embodiment, the second means for transmitting comprise a toothed ring with axially directed teeth on the outer circumference of the transmission part, into which engages a toothed wheel of the means for indicating. Thus, this embodiment corresponds to the conventional pipette, but in difference to the conventional pipette, the annular cylindrical locking element is designed so as to be separate from the toothed ring with axially directed teeth. In the design of the annular cylindrical locking element as a toothed ring, it has preferably more teeth than the toothed ring with axially directed teeth. The number of teeth of the annular cylindrical locking element is preferably at least two times, further preferably three times as big as the number of teeth of the toothed ring with the axially directed teeth. 
         [0043]    According to a further embodiment, the drive equipment comprises an axially relocatable lifting rod for relocating the relocatable limit of the displacement equipment, the adjustable means for limiting comprise an upper stop body, relocatable in the axial direction of the lifting rod, a lower stop body and a stop element, disposed on the circumference of the lifting rod between the upper and the lower stop body, for limiting the stroke of the lifting rod, and the actuating element is connected to the lifting rod. According to a preferred embodiment, there is a pull-back spring, which is supported in a spring support that is fixedly connected to the casing and which loads the drive mechanism in a starting position in which the stop element bears against the upper stop body. 
         [0044]    The relocatable limit can be relocated into the displacement chamber by actuating the actuating element against the action of the pull-back spring, in order to eject fluid from the pipette tip. After unloading the actuating element, the pull-back spring moves the drive mechanism, and with it the relocatable limit, back into the starting position, in order to aspirate liquid into the pipette tip. 
         [0045]    According to a further embodiment, the upper stop body is a threaded spindle which has an upper passage channel through which the lifting rod is guided through and which is screwed into a spindle nut that is fixedly connected to the casing, and the lower stop body has a lower passage channel through which the lifting rod extends, and the lifting rod with the stop element can be relocated between the upper stop body and the lower stop body. Alternatively, there is a toothed rack instead of a threaded spindle, which can be adjusted by way of a toothed wheel gear system and has the upper stop body at its lower end. 
         [0046]    These embodiments of the drive equipment and of the adjustable means for limiting the relocation are constructionally simple and permit to set the metering volume accurately. 
         [0047]    According to a further embodiment, the first means for transmitting are further means for connecting the actuating element to the threaded spindle so as to rotate together with it, which permit axial relocation of the actuating element with respect to the threaded spindle. Through this embodiment of the first means for transmitting, it is ensured that a rotational movement of the actuating element is transmitted to the threaded spindle, and the actuating element can be axially relocated with respect to the threaded spindle. 
         [0048]    According to a further embodiment, the further means for connecting the actuating element to the threaded spindle so as to rotate together with it comprise a polygon which engages into a complementary, axially extending accommodation of the actuating element. 
         [0049]    According to a further embodiment, one or several of the following component parts are entirely or partially mounted on a base board which is fixed in the casing: counter mechanism, counter gear system, locking body, lever, further lever, spring element and further spring element. The component parts can be pre-assembled on the base board, and the pipette can be equipped with the pre-assembled base board. An assembly gasket is achieved through this. 
         [0050]    The pipette of the present invention is preferably a hand-held pipette. In this, it is dealt with a pipette which can be held and operated by the user with only one hand in the pipetting. The pipette is preferably a mechanically driven pipette. But in principle it is also possible to realise the pipette with an electric drive or with a mechanical drive having force assistance by an electric drive (servo drive). 
         [0051]    The invention will be explained in more detail below by way of the attached drawings of an example of its realisation. In the drawings show: 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0052]      FIG. 1  a pipette of the present invention in a longitudinal section; 
           [0053]      FIG. 2  the same pipette in a magnified longitudinal section through an upper portion; 
           [0054]      FIG. 3  an enlarged section along the line III-III of  FIG. 2 ; 
           [0055]      FIG. 4  a magnified detail IV of  FIG. 2 ; 
           [0056]      FIG. 5  the same pipette in a magnified longitudinal section through a lower portion; 
           [0057]      FIG. 6  the same pipette without lifting body in a magnified longitudinal section through a lower portion; 
           [0058]      FIG. 7  transmission part with counter mechanism and locking equipment in the casing of the pipette with casing cover taken off, in a perspective view skew from the top and from the side; 
           [0059]      FIG. 8  the same arrangement from another perspective; 
           [0060]      FIG. 9  transmission part with counter mechanism and parts of the locking equipment in the casing of the pipette, in a perspective view skew from the top and from the side; 
           [0061]      FIG. 10  transmission part with parts of the counter mechanism and locking equipment, in a perspective view skew from the top and from the side; 
           [0062]      FIG. 11  transmission part with locking equipment in a magnified partial view from the top; 
           [0063]      FIG. 12  counter mechanism with locking equipment in a magnified partial view skew from the bottom; 
           [0064]      FIG. 13  transmission part with counter mechanism and parts of the locking equipment in the unlocked condition, in a perspective partial view skew from the top and from the side; 
           [0065]      FIG. 14  transmission part with locking equipment in the unlocked condition, in a magnified partial view from the top; 
           [0066]      FIG. 15  transmission part with parts of the counter mechanism and parts of a variant of the locking equipment, in a perspective view skew from the top and from the side; 
           [0067]      FIG. 16  the component parts of  FIG. 15  without the control button, in a perspective view skew from the bottom and from the side; 
           [0068]      FIG. 17  the component parts of  FIG. 15  in the unlocked condition in the casing of the pipette with casing cover taken off, in a perspective view skew from the top and from the side; 
           [0069]      FIG. 18  transmission part with parts of the counter mechanism and parts of a further variant of the locking equipment in the casing of the pipette with casing cover taken off, in a perspective view skew from the top and from the side; 
           [0070]      FIG. 19  the same arrangement with unlocked locking equipment in the same perspective view; 
           [0071]      FIG. 20   a  to  d  the same pipette before the actuation of the actuating element ( FIG. 20   a ), after the complete execution of the metering stroke and before the execution of the overstroke ( FIG. 20   b ), after the execution of the overstroke before the ejection of the pipette tip ( FIG. 20   c ) and after the ejection of a pipette tip ( FIG. 20   d ), always in a partial longitudinal section. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0072]    While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated. 
         [0073]    In the present application, the designations “up” and “down”, “above” and “below” and “horizontal” and “vertical” refer to an orientation of the pipette in which the casing is oriented vertically downward with the seat. In this orientation, a pipette tip fastened on the seat can be directed towards a vessel situated there under, in order to aspirate or to deliver a liquid. 
         [0074]    According to  FIGS. 1 and 2 , the pipette  1  has a rod-shaped casing  1 . 1 , formed as a handle, with an upper part  2  of the casing and a lower part  3  of the casing. The upper part  2  of the casing forms a drive unit with all the components contained therein, and the lower part  3  of the casing a displacer unit with all the components contained therein. An actuating element  4  in the form of a cylindrical push-button projects upward from the upper part  2  of the casing at the topside thereof. The actuating element  4  is mounted in the upper part  2  of the casing so as to be axially movable and rotatable. 
         [0075]    The actuating element  4  is screwed fast on a cylindrical lifting rod  6  by a thread in a cover  5 . In the upper part  2  of the casing, the lifting rod  6  is guided through an upper passage channel  7  of a threaded spindle  8 . The threaded spindle  8  is screwed into an internal thread of a spindle nut  9  which is held in a defined position in the upper part  2  of the casing. 
         [0076]    The spindle nut  9  is fixedly connected to a lifting body  10 , which is fastened in the upper part  2  of the casing. The lifting body  10  is essentially cylindrical and is a carrier for the spindle nut  9 , the threaded spindle  8  screwed in therein and the lifting rod  6  guided therein. When the pipette is being assembled, these and other component parts are pre-assembled on the lifting body  10 , and the lifting body  10  equipped with the component parts is mounted in the upper part  2  of the casing, so that it is fixedly held in the upper part  2  of the casing. For this purpose, the lifting body  10  is latched with the upper part  2  of the casing. But in principle it is also possible to mount the component parts that are pre-assembled on the lifting body  10  directly in the upper part  2  of the casing. For this purpose, the upper part  2  of the casing can be configured at the inside corresponding to the lifting body  10 . 
         [0077]    At the topside, the threaded spindle  8  has a spindle driving tenon  11 , connected to it so as to rotate together with it. On the circumference, the spindle driving tenon  11  has a hexagon  12  with central hole  13 . The hexagon  12  engages into a hexagon socket  14  of the actuating element  4 . 
         [0078]    At the bottom, the actuating element  4  is provided with two diametrically opposite radial projections  15 ,  16 , which project outwardly. There are preferably four radial projections  15 ,  16 . The radial projections  15 ,  16  engage into axially running grooves  17 ,  18  at the inner side of a hollow cylindrical transmission part  19 , which is rotatably mounted in the upper part  2  of the casing. At the top, the transmission part  19  has a toothed ring  20  on the circumference, which is engaged with a toothed wheel of a counter gear system  21 , which drives several counter wheels  22 , disposed side by side on a horizontal axis, of a counter mechanism  23 . The counter mechanism  23  is fastened on the upper part of the casing. Each of the counter wheels  22  has numerals from 0 to 9. The rearmost counter wheel  22  with respect to  FIG. 1  is driven by the counter gear system  21 . The counter wheels  22  disposed aside are each turned further for one numeral when the counter wheel disposed behind them changes over from 9 to 0. 
         [0079]    Above the counter mechanism  23 , the upper part  2  of the casing has a casing cover  24  with a window, through which the numerals of the counter wheels  22  can be read out. 
         [0080]    A bead-like collar  25  is disposed on the lifting rod  8  as a stop element below the threaded spindle  8 . The relocation of the lifting rod  6  towards the upside is limited by bearing of the collar  25  against the lower front side  26  of the threaded spindle  8 , which forms an upper stop body for the collar  25 . 
         [0081]    An essentially disc-shaped lower stop body  27  is disposed in the lifting body  10  below the spindle nut  9 . The lower stop body  27  has a cup-shaped deepening, in which a lower passage channel  28  is centrally disposed. Further, the lower stop body  27  has several (for instance three or four) projections  29 , radially projecting outwardly, which are uniformly distributed about its circumference. 
         [0082]    The lower stop body  27  is guided on the projections  29  in axially running guide slots  30  of the lifting body  10 . This is also shown in  FIG. 3 . It can be relocated upwardly up to the abutment position of the projections  29  at the upper end of the guide slots  30 . 
         [0083]    An overstroke spring  31  realised as a helical spring is arranged in the lifting body  10  below the lower stop body  27 . At the topside, the overstroke spring sits close on the bottom side of the lower stop body  27 . At the downside, the overstroke spring  31  is supported on an overstroke spring support  32  which is disposed in the upper part  2  of the casing and fixedly connected to it. 
         [0084]    The overstroke spring support  32  is formed by a ring with L-cross section, wherein the horizontal leg of the L-profile borders a central guide-through hole  33  of the overstroke spring support  32 . The overstroke spring  31  is supported by the horizontal leg of the L-profile and is laterally enclosed by the vertical leg. The overstroke spring  31  pushes the lower stop body  27  against the upper ends of the guide slots  30  under bias with the projections  29 . 
         [0085]    Below the lower stop body  27 , a drive element  34  in the form of a sleeve, aligned coaxially to the lifting rod  6 , exists in the lifting body  10 . The drive element  34  has an upper sleeve portion  35  and a lower sleeve portion  36 , wherein the upper sleeve portion  35  has greater inner and outer diameters than the lower sleeve portion  36 . The lower sleeve portion  36  has a tip  37  in the form of a truncated cone at the downside. 
         [0086]    On the upper edge of the upper sleeve portion  35 , there is a further circulating collar  38  which projects radially towards the outside. The outer diameter of the upper sleeve portion  35  is smaller than the inner diameter of the guide-through hole  33  of the overstroke spring support,  32 , so that the lower and the upper sleeve portion  35 ,  36  can be introduced into the guide-through hole  33 . The outer diameter of the further collar  38  exceeds the inner diameter of the guide-through hole  33 , so that the drive element  34  cannot pass completely through the guide-through hole  33 . The overstroke spring support  32  forms an end stop and the further collar  38  an end stop element, which limit the relocation of the drive element  34  towards the downside. 
         [0087]    A hollow cylindrical anchor  39  made of a ferromagnetic material is disposed at the top of the upper sleeve portion  35 . A hollow cylindrical magnet  40  is disposed there under in the upper sleeve portion  35 . Below of it there is a pot  41 , which accommodates the magnet  40 . The anchor  39  has a press fit in the upper sleeve portion  35 . The lifting rod  6  extends movably through the central hole of the anchor  39 . Underneath of the anchor, the lifting rod  6  has a needle-shaped portion  42  with reduced diameter. The magnet  40  and the pot  41  sit on the needle shaped portion  42 . Magnet  40  and pot  41  are preferably fixed on the needle-shaped portion  42 , for instance by having a press fit there. Moreover, the magnet  40  is supported at its topside on a shoulder of the lifting rod, from which the needle shaped portion  42  emerges. 
         [0088]    Below the ring disc  41 , an uncoupling spring  43  realised as a helical spring is guided on the needle-shaped portion  42  and is supported on the bottom  43  of the lower sleeve portion  36 . Anchor  39 , magnet  40  and uncoupling spring  43  are component parts of an uncoupling device  44 . 
         [0089]    According to  FIGS. 1 ,  2 ,  5  and  6 , at the inner circumference next to a lower casing opening  45 , the upper part  2  of the casing is provided with means  46  for detachable connection to further means for detachable connection to the lower part  3  of the casing, the means  46  not being explained in more detail. 
         [0090]    The lower part  3  of the casing has a hollow cylindrical portion  47  at its topside, which is followed by a short upper hollow cone portion  48  with great cone angle at the downside, which is in turn followed by a long lower hollow cone portion  49  with small cone angle, which forms a conical neck  50  for clamping up a pipette tip  51  with its lower end. A clamped-up pipette tip  51  is also essentially conical with an upper opening  52  for plugging up onto the neck  50  and with a lower opening  53  for the passage of liquid. The upper opening  52  is significantly greater than the lower opening  53 , and the pipette tip  51  tapers from the upper to the lower opening. 
         [0091]    At the upper side on the outer circumference, the hollow cylindrical portion  47  of the lower part  3  of the casing is provided with further means for detachable connection  54  not explained in more detail, which are matched to the means  46  for detachable connection of the upper part  2  of the casing, in order to detachably connect the lower part  3  of the casing with the upper part  2  of the casing. Suitable means for detachable connection  64 ,  54  of the lower part  3  of the casing and the upper part  2  of the casing are described in the document DE 10 2004 003 434 B4. In this respect, it is made reference to DE 10 2004 003 434 B4 and US2005/155438 A1, whose content is incorporated into the present application by reference. 
         [0092]    At the top, the lower hollow cone portion  49  has a prolongation  55  in the lower part of the casing  3  which projects beyond the upper hollow cone portion  48 . 
         [0093]    The lower hollow cone portion  49  has a connection channel  56 , which connects the upper front surface of the prolongation  55  with the lower front surface of the neck  50 . 
         [0094]    An arrangement of a cylinder  57  with a piston  58  relocatable therein is disposed in the lower part  3  of the casing. The cylinder  57  is set into the connection channel  56  with a lower area thereof, and fixed therein by pressing or gluing. At the bottom, the cylinder  57  is sealed with respect to the connection channel  56  by means of an O-ring  59 . 
         [0095]    The piston  58  has a piston seal  60  on its circumference, which seals on the cylinder  57  at the inside. Below the piston seal  60 , the piston  58  has a needle-shaped extension  61  which can be introduced into a passage opening  62  in the bottom of the cylinder  57  and into the connection channel  56  in order to reduce the stagnant volume. Cylinder  57  and piston  58  are aligned vertically. At the top, the piston  58  has a horizontally directed piston disc  63 , which has a vertically directed conical indentation  64  for receiving the tip  37  of the drive element  34  at its centre. 
         [0096]    At its top, the lower part  3  of the casing has a pot-shaped closing cap  65  with a cylindrical or conical shell. The bottom of the closing cap  65  is disposed above the piston disc  63  and has a central upper casing opening  67 , through which the piston disc  63  is accessible from the topside. On the edge of its shell, the closing cap  65  has outwardly projecting projections  68  which are snapped into corresponding indentations  69  of the hollow cylindrical portion  47  of the lower part  3  of the casing. 
         [0097]    The bottom of the closing cap  65  limits the relocation of the piston  58  towards the upside. A piston spring  70 , configured as a helical spring and being supported on the prolongation  55  at the bottom and on the bottom side of the piston disc  63  at the top, pre-loads the piston  58  against the bottom side of the closing cap  65 . 
         [0098]    The pipette  1  has further an ejection device  71 . The ejection device  71  comprises an ejection slide  72 , which is disposed on the lower part  3  of the casing. The ejection slide  72  has a contour that is adapted to the contours of the hollow cylindrical portion  47 , the upper hollow cone portion  48  and the lower hollow cone portion  49 . At the bottom, it has an annular ejection end  73 . In the position of the ejection slide  72  of  FIG. 1 , the ejection end  73  is pushed up towards the upside onto the lower part  3  of the casing as far as possible, so that the conical neck  50  is free for plugging up a pipette tip  51 . 
         [0099]    At the topside, the ejection slide  72  is connected to an ejection lengthening  74 . The latter comprises three vertical ejection rods  75 , which are connected to the upper edge of the ejection slide  72 . The ejection rods  75  are uniformly distributed over the upper edge of the ejection slide  72 . At the bottom, the ejections rods  75  are connected via a first snap connection to an ejection ring  76 , which is connected to the upper edge of the ejection slide  72  via a second snap connection. In a distance from the ejection ring  76 , the ejection rods  75  are connected to each other by an annular upper ejection spring support  77  on their inner circumference at the top. The upper ejection spring support  77  has an L-shaped cross section, wherein the horizontal leg of the cross section is adjacent to the guide-through hole  33  below the overstroke spring support. The vertical, circulating leg of the upper ejection spring support  77  is directed downward. 
         [0100]    The ejection rods  75  have actuating ends  78  at the top. 
         [0101]    The ejection lengthening  74  or the ejection rods  75 , respectively, extend into the upper part  2  of the casing through the lower casing opening  45 . The relocation of the ejection lengthening  74  towards the upside is limited by the close sitting of the upper ejection spring support  77  on the bottom of the overstroke spring support  32 . 
         [0102]    Below the upper ejection spring support  77 , three bridges  79  project from the inner side of the upper part  2  of the casing, which are uniformly distributed over the inner circumference and grasp through recesses of the lifting bodies  10 . This is shown in  FIG. 4  in particular. The bridges  79  form a lower ejection spring support  80 . An ejection spring  81 , formed as a helical spring, is disposed under bias between the upper ejection spring support  77  and the lower ejection spring support  80  and presses the ejection device  71  upward, so that the upper ejection spring support  77  sits close on the overstroke spring support  32 . 
         [0103]    The lower part  3  of the casing is guided into the lower casing opening  45  of the upper part  2  of the casing with an upper region of the hollow cylindrical portion  47 . The means  46 ,  54  for detachable connection of the lower part  3  of the casing and the upper part  2  of the casing are detachably connected to each other. The drive element  34  engages with the tip  37  into the upper casing opening  67  and sits close to the piston disc  63  in the indentation  63 . The piston disc  63  pushes the drive element  34  upward, and via the uncoupling device  44 , the lifting rod  6  is pressed against the threaded spindle  8  with the collar. 
         [0104]    According to  FIGS. 7 to 14 , the transmission part  19  has an annular locking element  82  on its outer circumference above the toothed ring with axially directed teeth. The locking element  82  comprises a toothed ring  83  with radially outward directed teeth. The toothed ring  83  has a finer spacing than the toothed ring  20 . For instance, the toothed ring  20  is provided with 60 teeth, and the toothed ring  83  with 180 teeth. 
         [0105]    A locking body  85  is arranged next to the toothed ring  83  in a radially directed guiding  84 . The locking body  85  is in general cube-shaped and has a limb-cylindrical acting surface  86  on the side facing the toothed ring  83 . The limb-cylindrical acting surface  86  is provided with a toothed ring  87  with radially inward directed teeth. In the example, the toothed ring  87  has a number of 18 teeth. 
         [0106]    A spring support  88 , fixedly connected to the casing  1 . 1 , is arranged at the end of the radial guiding  84 . A spring element  89  in the form of a conical wire spring is arranged between spring support  88  and the outer side of the locking body  85 . The spring element  89  pushes the locking body  85  under bias against the locking element  82  into a locking position in which the toothed ring  87  engages the toothed ring  83 . 
         [0107]    Further, two-arm levers  92 ,  93  are mounted in drag bearings  90 ,  91  that are fixedly connected to the casing, each of them acting on the locking body  85  with a first lever arm  94 ,  95 . For this purpose, the locking body  85  has a groove-shaped recess  96  on the top, into which engage cams  97 ,  98  that project from the bottom side of the first lever arms  94 ,  95 . The levers  92 ,  93  each comprise a second lever arm  99 ,  100  which extends towards opposing side walls  101 ,  102  of a casing head  103 . On the level of the toothed rings  20 ,  83 , the casing head  103  projects laterally with respect to the rod-shaped casing, and seen from the top it has an essentially oval shape. 
         [0108]    The toothed wheel of the counter gear system engaged to the toothed ring  20  is arranged below the two-arm lever. 
         [0109]    Further, unlocking elements  106 ,  107  in the form of further levers are mounted in further drag bearings  104 ,  105  that are fixedly connected to the casing  1 . 1 . The further levers  106 ,  107  are configured as one-arm levers in this realisation example. They engage laterally into breakthroughs of the casing head  103  and project laterally from the casing head  103  with an actuating portion  110 ,  111 . The further drag bearings  104 ,  105  of the further levers  106 ,  107  are bearing lugs into which engage portions of shafts  112 ,  113 , projecting from the bottom side of the further levers  106 ,  107 . Further, the further drag bearings  104 ,  105  comprise not shown further bearing lugs in the casing cover, into which engage portions of shafts  112 ,  113 , projecting from the upper side of the further levers. 
         [0110]    Furthermore, further spring elements  116 ,  117  in the form of leaf springs are arranged between further spring supports  114 ,  115 , fixedly connected to the casing, and the further levers  106 ,  107 . The further spring elements  116 ,  117  are fixed on the inner surfaces of the further levers  106 ,  107 . The further spring elements push the further levers  106 ,  107  with the actuating portions  110 ,  111  out of the breakthroughs in the casing head  103 , until the further levers  106 ,  107  bear against the limiting wall of the casing head with a stop element  118 ,  119  that projects from the bottom side. 
         [0111]    The two-arm levers  92 ,  93  bear against the inner side of the further levers  106 ,  107  with the outer edges of their further lever arms  99 ,  100 . 
         [0112]    A base board  120  is arranged in the casing head  103 . The counter mechanism  23  and the counter gear system  21  are mounted thereon. The radial guiding  84  as well as the drag bearings  90 ,  91  and the bearing lugs of the further drag bearings  104 ,  105  are formed in the base board  120 . 
         [0113]    The base board  120  is fixed in holes of the casing  1 . 1  via mandrels  121 ,  122 . 
         [0114]    Further, the base board is connected to complementary recesses in the casing via snap hooks  123 ,  124 . 
         [0115]    The construction example of  FIG. 15-17  differs from that one described above in that the further levers  106 ,  107  are also formed as two-arm levers, which contact the outer edge of the levers with a further first lever arm  125 ,  126 . They are pushed into this position by way of a further spring element  116 ,  117 , which is arranged between a bearing, fixedly connected to the casing, and a further second lever arm  127 ,  128  of the further levers  106 ,  107 . 
         [0116]    Further, spring loaded balls  129 ,  130  are integrated into the casing  1 . 1 , which partly project upward. Corresponding holes  131 ,  132  on the bottom sides of the two further levers  106 ,  107  are associated to the spring loaded balls  129 ,  130 , they receive the spring loaded balls  129 ,  130  in an unlocking position. 
         [0117]    The construction example of  FIG. 18-19  differs from that one described above in that the locking element  82  is formed as a ferromagnetic metal ring on the transmission part  19 , and the locking body  85  as a magnet with annular cylindrical acting surface  86 . 
         [0118]    In all the construction forms, the locking body  85  prevents or hinders a twisting of the transmission part  19  in the locking position of  FIGS. 7 to 11 ,  FIGS. 15  and  FIG. 18 . By pressing against the actuating portion  110 ,  111  of an unlocking element or of a further lever  106 ,  107 , the levers  92 ,  93  are swung and the locking body  85  is moved in the radial direction, out of the locking position into the unlocking position in which the locking body  85  does not block the locking element  82 . This is shown in  FIGS. 13 ,  14 ,  16  and  19 . 
         [0119]    In the construction example of  FIG. 7-14 , the further lever  106 ,  109  must be kept in the unlocking position, so that the locking body  85  is not moved back into the locking position by the spring element  89 . In the construction examples of  FIG. 15-19 , the catch by means of the ball  129 ,  130  retains the further lever  106 ,  107  in the unlocking position, so that it can also be unloaded. Thereafter, a new locking takes place in the construction example of  FIG. 7-14 , by unloading the further lever  106 ,  107 , and in the construction examples of  FIG. 15-19  by pressing on the further lever arm  127 ,  128  of the further lever  106 ,  107 , so that the catch in the unlocking position is released. The construction form of  FIGS. 18 and 19  can be realised without spring element  89 , because the locking body  85  is relocated into the locking position by the magnetic forces. 
         [0120]    In all the construction examples, the unlocking may take place by actuating one of the two levers. Thus, right handed and left handed persons have the possibility to choose that lever which permits the easiest operation. 
         [0121]    The pipette  1  can be used as follows: 
         [0122]    It is grasped on the upper part  2  of the casing. 
         [0123]    At first, the locking is released by actuating one of the unlocking elements  106 ,  107 . Thereafter, the transmission element  9  and thus the actuating element  4 , connected so as to rotate with it, can now be rotated. 
         [0124]    A metering stroke is set by rotating the actuating element  4  until the counter wheels  22  indicate the desired metering volume. When the actuating element  4  is being rotated, the threaded spindle  8  is rotated via the spindle driving tenon  11 , and is axially relocated due to its thread connection to the spindle nut  9  which is stationary in the upper part  2  of the casing. In this, the spindle driving tenon  11  slips into the hexagon socket of the actuating element  4 . At the same time, the transmission part  19  is rotated via the further radial projections  15 ,  16 , and the counter mechanism  23  is adjusted. As a consequence, the set axial position of the threaded spindle  8  in the upper part  2  of the casing, and thus also the metering volume, can be read on the counter mechanism  23 . 
         [0125]    After setting the metering volume, the locking of the locking body  85  to the transmission part  19  is restored, in the construction example of  FIG. 7-14  by unloading the unlocking element  106 ,  107 , and in the construction examples of  FIG. 15-19  by actuating the further second lever arm  127 ,  128  of the further lever  106 ,  107 . Through this, the transmission part  19 , and with it the actuating element  4 , are prevented from unintended twisting, or the unintended twisting is made difficult. 
         [0126]    Further, a pipette tip  51  is clamped onto the neck  50 , preferably by pushing the latter into the pipette tip  51  which is held ready in a holder. 
         [0127]    Before sucking up liquid, air is ejected out of the cylinder  57  by pushing the piston  58  downward by means of the actuating element  4 , until the further collar  38  hits the lower stop body  27 . In this, the lifting rod  6  moves the drive element  34  downward via the uncoupling device  44 , and the piston  58  is pressed deeper into the cylinder  57 . Due to the force between magnet  40  and anchor  39 , the uncoupling device  44  does not uncouple in this. 
         [0128]    Thereafter, the lower end of the pipette tip  51  is dipped into the liquid by means of the pipette  1 , and the desired amount is sucked into the pipette tip  51  by releasing the actuating element  4 . In this, the piston spring  70  pushes the piston  58 , and with it the drive element  34  as well as the lifting rod  6 , back into the initial position in which the collar  25  bears against the threaded spindle  8 . 
         [0129]    The pipette  1  is shown in  FIGS. 1 ,  2 ,  5 ,  6  and  20   a  in this situation. 
         [0130]    Thereafter, the pipette tip  51  can be directed to another vessel with its lower end by means of the pipette  1 . By pushing the actuating element  4  downward, the lifting rod  6  is moved downward and the drive element  34  is relocated downward via the uncoupling device  44 , so that the piston  58  is moved downward in the cylinder  57  anew. In this, the set metering amount is essentially delivered. This situation is shown in  FIG. 20   b.    
         [0131]    Residuals that have remained in the pipette tip  51  can be blown out by pushing the actuating element  4  further downward under increased expense of force. In this, the lower stop body  27  is relocated downward in the guide slots  30  against the action of the overstroke spring  31 , and via the uncoupling device  44 , the drive element  34  is relocated further downward and pushes the piston  58  still deeper into the cylinder  57 . In the overstroke, a further positive pressure is generated, which pushes out residual liquid which is adhered on the inner wall pipette tip  51 . 
         [0132]    The overstroke is ended when the drive element  34  hits with the further collar  38  the overstroke spring support  32  which forms the end stop. At the same time, the projections  29  reach the actuating end  78  of the ejection lengthening  74  or are situated above it in a very small distance. This situation is shown in  FIG. 20   c.    
         [0133]    Thereafter, the pipette tip  51  can be ejected. For this purpose, the actuating element  4  is pushed further downward with increased expense of force. The overstroke spring  32  prevents the drive element  34  from continuing the downward motion. By the increased force, the magnet  40  is detached from the anchor  39  and the lifting rod  6  moves further downward and takes the lower stop body  27  along. With the projections  29 , the lower stop body  27  pushes the ejection lengthening  74  downward on the actuating ends  78 . The ejection lengthening  74  takes the ejection slide  72  along towards the downside, which pushes the pipette tip  51  off from the neck  50  with its ejection end  73 . 
         [0134]    During the ejection stroke, the piston  58  is not moved downward any further in the cylinder  57 . As a result, no clearance volume is needed in the cylinder  57  at the downside, and the piston  58  does not hit the bottom of the cylinder  57 . When the magnet  40  is released from the anchor  39 , the force for relocating the actuating element  4  further downward is reduced again. The ejection is ended when the ejection lengthening  74  hits a not depicted ejection stop in the casing. This situation is shown in  FIG. 20   d.    
         [0135]    After releasing the actuating element  4 , the pipette  1  reverts automatically into the starting position of  FIGS. 1 ,  2 ,  5 ,  6  and  20   a . In this, an ejection spring pushes the ejection lengthening  74  upward, and with it the ejection slide  72 . Further, the uncoupling spring  43  pushes the lifting rod  6  with the magnet  40  upward, until the magnet  40  is retained on the anchor  39  by the magnetic forces. Further, the overstroke spring  31  pushes the lower stop body  27  upward until the projections  29  have reached the upper ends of the guide slots  30 . Further, the piston spring pushes upward the piston  58 , the drive element  34  and via the uncoupling device  44  the lifting rod  6 , until the collar  25  bears against the threaded spindle  8 . 
         [0136]    In a further variant, the uncoupling device  44 ,  43  can be omitted in order to perform stroke, overstroke and ejection stroke. The lifting rod  6  acts directly on the conical indentation  64  of the piston  58 . 
         [0137]    The upper part  2  of the casing can be connected quite simply with another, lower part  3  of the casing, so as to form a casing wherein the cylinder  57  and the piston  58  have another cross section. Correspondingly, the same upper part  2  of the casing can be used for making pipettes  1  having different metering volumes. Further, it is possible to replace the lower part  3  of the casing or the upper part  2  of the casing easily in case of a trouble, or to equip the upper part  2  of the casing with another lower part  3  of the casing if needed. In addition, the lower part  3  of the casing can be removed easily from the upper part  2  of the casing for purposes of maintenance, repair and cleaning. 
         [0138]    This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto. 
       LIST OF THE USED REFERENCE SIGNS 
       [0000]    
       
           1  pipette 
           1 . 1  casing 
           2  upper part of the casing 
           3  lower part of the casing 
           4  actuating element 
           5  cover of the actuating element 
           6  cylindrical lifting rods 
           7  upper passage channel 
           8  threaded spindle 
           9  spindle nut 
           10  lifting body 
           11  spindle driving tenon 
           12  hexagon 
           13  hole 
           14  hexagon socket 
           15 ,  16  radial projections 
           17 ,  18  grooves 
           19  transmission part 
           20  toothed ring 
           21  counter gear system 
           22  counter wheels 
           23  counter mechanism 
           24  casing cover 
           25  bead-like collar 
           26  lower front side 
           27  lower stop body 
           28  lower passage channel 
           29  projections 
           30  guide slots 
           31  overstroke spring 
           32  overstroke spring support 
           33  guide-through hole 
           34  drive element 
           35  upper sleeve portion 
           36  lower sleeve portion 
           37  tip in the shape of a truncated cone 
           38  further collar 
           39  hollow cylindrical anchor 
           40  hollow cylindrical magnet 
           41  pot 
           42  needle-shaped portion 
           43  uncoupling spring 
           44  uncoupling device 
           45  lower casing opening 
           46  means for detachable connection 
           47  hollow cylindrical portion 
           48  upper hollow cone portion 
           49  lower hollow cone portion 
           50  conical neck 
           51  pipette tip 
           52  upper opening 
           53  lower opening 
           54  further means for detachable connection 
           55  extension 
           56  connection channel 
           57  cylinder 
           58  piston 
           59  O-ring 
           60  piston seal 
           61  needle-shaped extension 
           62  passage opening 
           63  piston disc 
           64  conical indentation 
           65  cylindrical closing cap 
           67  upper casing opening 
           68  projections 
           69  indentation 
           70  piston spring 
           71  ejection device 
           72  ejection slide 
           73  ejection end 
           74  ejection lengthening 
           75  ejection rod 
           76  ejection ring 
           77  upper ejection spring support 
           78  actuating end 
           79  bridge 
           80  lower ejection spring support 
           81  ejection spring 
           82  locking element 
           83  toothed ring with radially outward directed teeth 
           84  radial guiding 
           85  locking body 
           86  acting surface 
           87  toothed ring with radially inward directed teeth 
           88  spring support 
           89  spring element 
           90  drag bearing 
           91  drag bearing 
           92  two-arm lever 
           93  two-arm lever 
           94  first lever arm 
           95  first lever arm 
           96  recess 
           97  cams 
           98  cams 
           99  second lever arm 
           100  second lever arm 
           101  side wall 
           102  side wall 
           103  casing head 
           104  further drag bearing 
           105  further drag bearing 
           106  unlocking element (further lever) 
           107  unlocking element (further lever) 
           110  actuating portion 
           111  actuating portion 
           112  shaft 
           113  shaft 
           114  further spring support 
           115  further spring support 
           116  further spring element 
           117  further spring element 
           118  stop element 
           119  stop element 
           120  base board 
           121  mandrel 
           122  mandrel 
           123  snap hook 
           124  snap hook 
           125  further first lever arm 
           126  further first lever arm 
           127  further second lever arm 
           128  further second lever arm 
           129  spring loaded ball 
           130  spring loaded ball 
           131  hole 
           132  hole