Patent Publication Number: US-10758899-B2

Title: Electronic dosing drive

Description:
Cross-Reference to Related Applications 
     This application claims priority to European Patent Application Number 17 169 764.2 filed May 5, 2017, the entire contents of which being incorporated by reference herein. 
     The invention relates to an electronic dosing drive comprising a spindle drive and an electronic drive motor for driving a plunger in a cylinder. 
     BACKGROUND OF THE INVENTION 
     Electronic dosing devices are utilized in particular in scientific and industrial laboratories with medical, molecular biological and pharmaceutical areas of application for dosing liquids. Electronic dosing devices have an electronic dosing drive for driving a plunger in a cylinder. In direct displacement systems, the dosing device is coupled with an exchangeable syringe. The electronic dosing drive drives a syringe plunger in a syringe cylinder of the syringe, through which the receiving of liquid into the syringe and the discharge of liquid from the syringe is controlled. In doing this, the syringe plunger comes into contact with the liquid. The discharge occurs preferably in multiple steps. The syringe is exchangeable in order to prevent carryovers when different liquids are dosed with the same dosing device. 
     In the case of air cushion systems, the electronic dosing device comprises, besides the dosing drive, a cylinder and a plunger that can be displaced therein and is coupled with the dosing drive. Furthermore, the dosing device has a seal seat for firmly clamping and sealing a pipette tip. A hole in the seal seat is connected to the cylinder via a channel. The pipette tip is a tube with a lower opening on the lower end and an upper opening on the upper end. By moving the plunger in the cylinder, air can be displaced through the upper opening in order to suck liquid into and expel liquid out of the pipette tip through the lower opening. In doing this, the plunger and cylinder do not come into contact with the liquid. The pipette tip can be exchanged after use. 
     The syringe and pipette tip are typically made of plastic. 
     Electronic manual dosing devices can be carried and operated by the user with only one hand. Direct displacement systems are also termed electronic dispensers or repeating pipettes. Air cushion systems are also termed pipettes. They are hereby semi-automated, since they must be positioned and operated by hand, wherein the (syringe) plunger is driven by an electric drive motor. Compared to dosing devices with manual drives, the high reproducibility and the precision, the user-friendliness and ergonomics as well as the multi-functionality are advantageous and enable dispensing, reverse pipetting, diluting, mixing and titrating. 
     Furthermore, electronic dosing devices are integrated into automated dosing systems (LHS=liquid handling stations) and automated laboratory systems (WS=work stations). These have a dosing tool and a robot arm for positioning the dosing tool. The robot arm is, for example, an XYZ transfer system. They enable quick and reproducible fully automated dosing via pipetting, dispensing or other dosing methods. 
     The electronic dispensers Multipette® E3/E3x comprise a housing with a first receiver for a syringe flange of a syringe cylinder of the syringe and a receiving body with a second receiver for a plunger rod end of the syringe plunger. Furthermore, the housing comprises an electronic dosing drive that comprises a spindle drive with a threaded spindle and a spindle nut, and an electric drive motor. The receiving body is firmly attached to one end of the threaded spindle and is guided in the longitudinal direction of the threaded spindle in the housing. The electric drive motor firmly arranged in the housing is coupled with the spindle nut. An electric control apparatus is connected to the electric drive motor, and an electrical power supply is connected to the electric drive motor and the electric control apparatus. The threaded spindle and spindle nut are made of metal. 
     The electronic pipettes Xplorer®/Xplorer® plus from Eppendorf AG have in the housing at least one cylinder with a plunger movable therein. Each cylinder is connected via a channel to a hole in an attachment for clamping on a pipette tip. These pipettes exist as single-channel pipettes with only one cylinder, one plunger movable therein and one attachment connected to the cylinder. They also exist as multi-channel pipettes with multiple cylinders, plungers movable therein and attachments connected to the cylinders. A threaded spindle is connected to the at least one plunger and is guided in the longitudinal direction in the housing. Otherwise, the electronic dosing drive of these electronic pipettes corresponds to that of the electronic dispensers. 
     A disadvantage is the complex manufacturing of the threaded spindle by means of highly precise lathes and finishing, for example by deburring. Furthermore, a hitting of the threaded spindle can occur if it protrudes farther out of the spindle nut with the non-guided end. The spindle drive is susceptible to corrosion. Corrosion increases the friction and therefore the wear as well as decreasing the dosing accuracy. The spindle drive requires lubricant, which binds dust, through which the wear is increased and the dosing accuracy is lowered. Overload can lead to plastic deformation which also lowers the precision of the spindle drive. 
     DE 10 53 883 A describes a threaded spindle made of sheet metal that is composed of two U-profile strips that are welded to each other on their longitudinal edges. The distance between the welding beads on both sides of the threaded spindle is smaller than the diameter of the thread core. This threaded spindle is suitable for simple jacks taken along by the driver, for work-holding devices on workbenches and joiner&#39;s benches, for example in joiner&#39;s and glazier&#39;s workshops, for screw clamps and other apparatuses for which the requirements on the spindle regarding the running characteristics are not too high. 
     GENERAL DESCRIPTION OF THE INVENTION 
     Starting from this, it is the object of the invention to create an electronic dosing device for actuating a syringe with improved dosing accuracy. 
     According to the invention, the object is achieved by an electronic dosing device having the features of claim  1 . Advantageous embodiments of the dosing device are specified in the dependent claims. 
     The electronic dosing drive according to the invention comprises:
         a support structure,   a threaded spindle with an external thread for driving a plunger in a cylinder,   at least one first guide element firmly connected to the threaded spindle that is guided parallel to the threaded spindle on a second guide element firmly connected to the support structure,   a spindle nut with an internal thread that is in engagement with the external thread of the threaded spindle,   an electric drive motor attached to the support structure that has a motor shaft coupled with the spindle nut,   an electric control apparatus connected to the electric drive motor,   an electrical power supply connected to the electric drive motor and the electric control apparatus,
 
characterized in that
   the external thread of the threaded spindle has multiple threaded areas that are separated from each other by first flattenings on their circumference extending in the longitudinal direction, and   the first flattenings have guide areas that abut the core diameter of the internal thread of the spindle nut.       

     According to the invention, the spindle drive has a threaded spindle that is subdivided into multiple threaded areas and multiple guide areas. In the circumferential direction, a threaded area is arranged on both sides of each guide area and a guide area is arranged on both sides of each threaded area. The threaded areas engage with the internal thread of the spindle nut, whereby the displacement of the threaded spindle while turning is ensured. The guide areas abut the core diameter of the internal thread of the spindle nut so that they are guided in the spindle nut. As a result, the spindle nut is simultaneously a guide bushing for the threaded spindle. Additional components for guiding the threaded spindle can be omitted and space for accommodating additional components is spared. Therefore, an improved guiding of the threaded spindle is possible even with limited space. The spindle drive is particularly precise because the threaded spindle is guided two-fold, namely by the first guide element on the second guide element and at a distance from the first guide element by the guide areas on the spindle nut. This increases the dosing accuracy. 
     According to one embodiment of the invention, the threaded spindle is an injection molded part. In this embodiment, the threaded spindle is produced by means of injection molding from one or more plastics or from at least one other injection-moldable material. The subdivision of the threaded spindle into threaded areas and guide areas is advantageous for the production of the threaded spindle by injection molding since the subdivision of the external thread enables an injection-molded production by means of an injection molding tool with multiple mold parts. The parting plane of the injection molding tool can be placed so that it falls in the guide areas. Undercuts in the threaded areas which hinder the demolding of the threaded spindle from the injection molding tool and impair the precision can hereby be avoided or greatly reduced. The costs for the production of the threaded spindle can be reduced and finishing is spared. 
     According to another embodiment, the threaded spindle is made of a first plastic. The plastic threaded spindle has improved anti-friction properties. The wear is hereby reduced and the loss of dosing accuracy is diminished. The corrosion resistance and chemical durability of the plastic threaded spindle also diminishes the wear and the associated loss of precision. Moreover, plastics with improved anti-friction properties are available so that lubricant, which binds dust and causes wear as well as loss of dosing accuracy, can be omitted. It is, however, also possible to improve the anti-friction properties even more by applying small amounts of lubricant. The reduced friction between the threaded spindle and spindle nut lowers the power consumption of the motor and increases the battery life. Finally, the plastic threaded spindle reduces the weight of the dosing device and improves the ease of operation. Plastics with high mechanical resilience are available. Since these plastics have only a low or no plastic deformation but rather break when overloaded, an overloading does not lead to a deterioration of the dosing accuracy but rather to breakage so that the necessity of a repair is easily discernible. According to a preferred embodiment, the plastic threaded spindle is an injection molded part. According to another embodiment, the plastic threaded spindle is a sintered part, i.e., the threaded spindle is produced by means of sintering plastic particles. According to another embodiment, the plastic threaded spindle is produced by means of cutting, rolling and/or milling. According to another embodiment, the plastic threaded spindle is produced by means of 3D printing. 
     According to another embodiment, the threaded spindle is made of metal. According to another embodiment, the metal threaded spindle is produced by means of cutting, rolling and/or milling. According to another embodiment, the metal threaded spindle is produced by means of sintering metal powder. 
     According to another embodiment, the threaded spindle is produced by means of MIM (metal injection molding). For this, a metal powder is mixed with a plastic matrix and injection molded. The result is a threaded spindle that is made completely or substantially of metal because the plastic is removed during the production process. 
     The advantageous effects of the production of the threaded spindle by injection molding apply to a plastic threaded spindle produced by means of injection molding as well as to the threaded spindle produced by means of MIM. 
     According to a preferred embodiment of the invention, there is a clearance fit between the guide areas and the core diameter of the internal thread. The nominal core diameter of the internal thread is hereby the same as the nominal diameter of the threaded spindle on the guide areas. The nominal diameter on the guide areas is the diameter of the smallest circle touching the guide areas and fully enveloping them. The tolerances of the two diameters are chosen so that there is a clearance fit. For example, in the case of a nominal diameter of 3.25 mm a tolerance H11 is chosen for the core diameter, which allows a deviation of 0 to +75 μm from the nominal diameter. Furthermore, a tolerance d9 is chosen for the external diameter of the guide areas, which allows a deviation from the nominal diameter of −30 μm to −60 μm. The clearance between the internal thread and the guide ribs is minimally 30 μm and maximally 135 μm. 
     The clearance of the clearance fit is, according to a preferred embodiment, maximally 150 μm and minimally 0 μm, further preferably maximally 135 μm and minimally 30 μm. 
     According to another embodiment, the flattenings bear guide ribs that have the guide areas on the outer ends. A particularly low-friction guiding of the threaded spindle in the spindle nut is hereby achieved. Moreover, guide ribs are advantageous for the production of the threaded spindle by means of injection molding because the parting plane of the injection molding tool can be placed in the plane of the guide ribs. 
     According to a preferred embodiment, the threaded spindle has only two first flattenings diametrically opposite each other in which the parting plane of two tool halves of an injection molding tool can be placed. According to another embodiment, there are only two guide ribs diametrically opposite each other. This enables a comparatively simple injection molding tool with easy demolding and high dimensional stability. 
     According to another embodiment, the guide ribs have a second flattening on each end and, bordering the two side edges of the second flattening, guide areas at a distance from the central axis of the threaded spindle corresponding to half of the core diameter of the spindle nut. In this embodiment, the guide ribs are each guided on the guide areas on both sides of the second flattenings. This has the advantage that the demolding burrs generated on the second flattenings during injection molding of the threaded spindle do not come into contact with the spindle nut and prevent a precise guiding of the threaded spindle in the spindle nut. In principle, however, it is also possible to guide the threaded spindle on the outer ends of the guide ribs where the parting plane of the injection molding tool is located during production. Demolding burrs can be avoided by precise production of the injection molding tool or respectively removed by finishing. 
     According to another embodiment, the first flattenings are planar surfaces and/or the second flattenings are planar surfaces. According to a preferred embodiment, guide ribs project to the outside from first flattenings formed by planar surfaces. The areas of a first flattening in the form of planar surfaces that are arranged on various sides of the same guide rib can be aligned parallel or at an angle to each other. 
     According to an alternative embodiment, the first flattenings are curved to the outside and/or the second flattenings are curved to the outside. The curvature radii of the first flattenings are larger than half of the core diameter of the internal thread of the spindle nut or are the same, and/or the curvature radii of the second flattenings are larger than half of the core diameter of the internal thread of the spindle nut. 
     According to an alternative embodiment, the guide areas are simultaneously the first flattenings that are curved to the outside or sections thereof. In this embodiment, the first flattening do not bear guide ribs. The first flattenings can additionally be provided with second flattenings, wherein the curvature radius of the second flattenings is larger than half of the core diameter of the spindle nut. Demolding burrs generated during injection molding in the second flattenings do not come into contact with the spindle nut. Alternatively, demolding burrs are avoided by precise production of the injection molding tool or removed by finishing. 
     According to another embodiment, the external thread and the internal thread is a trapezoidal thread or a V-thread or a round thread or a buttress thread. 
     According to another embodiment, the threaded areas of the external thread taper between the first flattenings in the radial direction to the outside. This is advantageous for the demolding of the threaded spindle from an injection molding tool. 
     According to another embodiment, the outer longitudinal edges of the guide ribs and/or the transitions from the guide ribs to the first flattenings are rounded. This is advantageous for the demolding from the injection molding tool. The rounded-off longitudinal edges of the guide ribs reduce the friction of the threaded spindle in the spindle nut. 
     According to another embodiment, the side edges of the thread profiles delimited by the flattenings are rounded off. This promotes the low-friction sliding of the threaded spindle in the spindle nut and reduces the wearing. This is also advantageous for the demolding from the injection molding tool. 
     According to another embodiment, the transitions of the flanks of the thread profiles to the core of the threaded spindle and/or the outer edges of the thread profiles in the radial direction are rounded off. This promotes the low-friction sliding of the threaded spindle in the spindle nut and reduces the wearing. This is also advantageous for the demolding from the injection molding tool. 
     According to another embodiment, the spindle nut is produced from a second plastic and/or from a metal. The production of the spindle nut from at least one plastic or from at least one other injection-moldable material can occur by means of injection molding. The injection molding tool can hereby have a corresponding tool core for generating the internal thread of the spindle nut. Furthermore, the production of the spindle nut from plastic can occur by means of sintering, cutting, rolling and/or milling or 3D printing. The production of the spindle nut from metal can occur by means of thread cutting, tapping or thread milling, by means of MIM or by means of sintering metal powder. 
     According to another embodiment, the first plastic is a high-performance plastic or an engineering plastic. 
     According to another embodiment, the first plastic is selected from at least one of the following high-performance plastics: PEEK, PPS, LCP, PPA, PEI, PES, PPSU, PSU, PC-HT. According to another embodiment, the first plastic is selected from at least one of the following engineering plastics: PA, ABS. The threaded spindle can be produced exclusively from one of the aforementioned plastics or with the multi-component injection molding method from a combination of multiple of the aforementioned plastics. 
     According to another embodiment, the second plastic is a high-performance plastic or an engineering plastic. 
     According to another embodiment, the second plastic is selected from at least one of the following high-performance plastics: PEEK, PPS, LCP, PPA, PEI, PES, PPSU, PSU, PC-HT. According to another embodiment, the second plastic is selected from at least one of the following engineering plastics: PA, ABS. The spindle nut can be produced with the single-component injection molding method from only one of the aforementioned plastics or with the multi-component injection molding method from multiple of the aforementioned plastics. 
     According to a preferred embodiment, the first plastic and the second plastic are high-performance plastics. 
     According to another embodiment, the threaded spindle and the spindle nut are produced from the same plastic material. According to another embodiment, the threaded spindle and spindle nut are produced from the same plastic material, wherein, however, various variations of the plastic types are used. According to another embodiment, the threaded spindle and spindle nut are produced from the same plastic material that, for example, differ regarding the addition of fillers or additives. 
     Furthermore, the invention relates to an electronic dosing device comprising an electronic dosing drive according to the invention, a first receiver for a syringe flange of a syringe cylinder of a syringe firmly arranged on the support structure, and a receiving body with a second receiver for a plunger rod end of a syringe plunger of a syringe, wherein the receiving body is firmly connected to a lower end of the threaded spindle. 
     This electronic dosing device according to the invention is a direct displacement system. 
     The dosing drive is designed according to one of claims  1  to  13 . 
     According to another embodiment, the electronic dosing device comprises first means for releaseably holding the syringe flange in the first receiver and second means for releaseably holding the plunger rod end in the second receiver. The first receiver and the second receiver as well as the first means for releaseably holding and the second means for releaseably holding are preferably designed as described in EP 0 656 229 B1 and U.S. Pat. No. 5,620,660 A, the contents of which are hereby introduced into the present application. 
     Furthermore, the invention relates to an electronic dosing device comprising an electronic dosing drive according to the invention, at least one cylinder in which a plunger is movably arranged which is coupled with the lower end of the threaded spindle, at least one seal seat for firmly clamping and sealing a pipette tip, and at least one connecting channel that connects a hole in the seal seat to the cylinder. 
     This electronic dosing device is an air cushion system. The dosing drive is designed according to one of claims  1  to  13 . 
     According to one embodiment, the seal seat is the lateral surface of a conical and/or cylindrical attachment and there is the hole in the end surface of the attachment. 
     According to another embodiment, the electronic dosing device has only one cylinder with a plunger that is movable therein. This is hereby a single-channel dosing device. According to another embodiment, the electronic dosing device has multiple parallel cylinders with a moveable plunger therein as well as multiple seal seats that are each connected to a cylinder via a connecting channel. This is hereby a multi-channel dosing device. 
     The support structure can be any structure that is suitable for attaching the second guide element and the drive motor in defined positions in relation to each other. According to another embodiment, the support structure is made of one or of multiple components. 
     According to another embodiment, the electronic dosing device is an electronic manual dosing device. According to another embodiment, the electronic manual dosing device is an electronic manual dispenser or an electronic manual pipette. According to another embodiment, the support structure of the electronic manual dosing device is a housing and/or a frame (chassis) and/or a support of the electronic manual dosing device. 
     According to another embodiment, the electronic dosing device is an automated dosing system or a work station. According to another embodiment, the spindle drive is arranged in an exchangeable dosing tool that is connected to the robot arm on which the drive motor is attached. The dosing tool is connected to the robot arm so that it is held on the arm and the drive motor is connected to the spindle nut. The connection of dosing tool and robot arm is designed so that it can be intentionally released. The dosing tool and its connection to a tool holder of a robot arm is, for example, designed as described in EP 1 449 586 B1 and U.S. Pat. No. 7,402,440 B2, the contents of which are hereby introduced into the present application. 
     According to another embodiment, the support structure is a housing and/or frame (chassis) and/or a support of the dosing tool and/or of the robot arm of the automated dosing system or automated laboratory system. 
     According to another embodiment that is designed as a direct displacement system, the dosing tool comprises the first receiver and the second receiver as well as the first means for releaseably holding and the second means for releaseably holding. According to another embodiment that is designed as an air cushion system, the dosing tool comprises at least one cylinder with a plunger that is movable therein, at least one seal seat for firmly clamping and sealing a pipette tip, and at least one connecting channel for connecting a hole in the seal seat to the cylinder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further explained in the following with reference to the accompanying drawings of exemplary embodiments. In the drawings: 
         FIG. 1  shows an electronic manual dosing device in a perspective view from the side; 
         FIG. 2  shows the lower part of the same dosing device without the front half of the housing in the same perspective view; 
         FIG. 3  shows the spindle drive and electric drive motor of the same dosing device in a perspective view from the side; 
         FIG. 4  shows the spindle drive of the same dosing device in an enlarged, partially exploded perspective view from the side; 
         FIG. 5  shows the threaded spindle of the same dosing device in an enlarged, perspective partial view; 
         FIG. 6  shows the spindle drive in a cross-section through the spindle nut; 
         FIG. 7  shows enlarged detail VII from  FIG. 6 ; 
         FIG. 8  shows another electronic manual dosing device in a perspective view from the side; 
         FIG. 9  shows a vertical section of the same manual dosing device; 
         FIG. 10  shows the lower part of the same manual dosing device with dosing drive in a perspective view transversely from the side; 
         FIG. 11  shows a vertical section of the lower part of the same manual dosing device with dosing drive; 
         FIG. 12  shows the same dosing drive in a perspective view from the side; 
         FIG. 13  shows the same dosing drive in a rear view; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the present application, “up” and “down” as well as indicators derived therefrom refer to a vertical orientation of the threaded spindle and arrangement of the drive motor above the threaded spindle. 
     Features of various exemplary embodiments that are addressed with the same terms are provided with the same reference signs in the following. 
     The electronic manual dosing device  1  according to  FIGS. 1 and 2  is an electronic manual dispenser. It has a rod-shaped housing  2  that is divided in the longitudinal direction into a front housing hull  3  and a rear housing hull  4 . 
     On the front side of the housing  2 , a selection wheel  5  for selecting the respective operating mode is located on the upper end. By means of the selection wheel  5 , the dosing functions pipetting, dispensing and titrating, for example, can be set. 
     Under that, a display  6  is recessed into the front side of the housing  2 . 
     Beneath the display  6 , two rocker switches  7 ,  8  that serve to call up various menu functions and to set parameters project from the front side of the housing  2 . 
     At the height of the rocker switches  7 ,  8 , electrical contacts  9 ,  10  for charging a battery of an electrical power supply  11  are located on the left and the right side of the housing. The battery is accommodated in the upper part of the housing  2 . 
     Between the two rocker switches  7 ,  8 , a reset button  12  is located in the front of the housing. 
     In the middle underneath the reset button  12 , a trigger button  14  is located above on a curvature  13  on the front side of the housing  2  for triggering sucking and dispensing steps as well as for saving parameter settings. In front of the trigger button  14 , an ejector button  15  is located that engages with the curvature  13  that fits snugly downward against the flat front side of the housing  2 . 
     A hook-shaped finger rest  16  projects to the back from the back side of the housing  2 . 
     On the lower end, the housing  2  has a first opening  17  through which a first receiver  18  in the housing  2  for a syringe flange of a syringe cylinder of a syringe is accessible from the outside. According to  FIG. 2 , above the first receiver  18  a bell-shaped receiving body  19  is located in which a second receiver  20  is arranged that is accessible through a second opening  21  on the underside of the receiving body  19  for inserting a plunger rod end of a syringe plunger of the syringe. 
     In the first receiver  18 , first means for releaseably holding the syringe flange are located on a stop  22  in the housing  2  that are designed as a syringe gripping lever  23 . 
     The receiving body  19  has second means for releaseably holding in the form of plunger gripping levers  24  that serve to releaseably hold the syringe plunger in the second receiver  20 . 
     The attachment of the syringe flange and syringe plunger in the first and second receivers  18 ,  20  by means of the first and second means for releaseably holding can be loosened by actuating the ejector button  15  that works via a gear  25  on the syringe gripping lever  23  and plunger gripping lever  24 . 
     When a syringe is held in the dosing device, the syringe plunger is displaceable by means of a dosing drive  26 . 
     According to  FIGS. 3 and 4 , the dosing drive  26  comprises a spindle drive  27  that has a threaded spindle  28  and a spindle nut  29 . 
     The threaded spindle  28  has two first flattenings  30 . 1 ,  30 . 2  on both sides that extend in the longitudinal direction and two threaded areas  31 . 1 ,  31 . 2  of an external thread  31  between them. According to  FIGS. 4 and 5 , the threaded areas  31 . 1 ,  31 . 2  taper in the cross-section in the radial direction to the outside. 
     Guide ribs  32 . 1 ,  32 . 2  project to the outside from the first flattenings  30 . 1 ,  30 . 2 . According to  FIGS. 4 and 5 , the guide ribs  32 . 1 ,  32 . 2  have two flattenings  33 . 1 ,  33 . 2  on the outer end. Next to these, they have guide areas  34 . 1 ,  34 . 2 ,  34 . 3 ,  34 . 4 , the distance of which from the central axis of the threaded spindle  28  corresponds to half of the core diameter of an internal thread  35  of the spindle nut  29 . 
     According to  FIG. 5 , the external thread  31  has trapezoid-shaped thread profiles  36 . 1 ,  36 . 2 . The outer edges of the thread profiles  36 . 1 ,  36 . 2  in the radial direction are rounded. Furthermore, the transitions of the flanks  37 . 1 ,  37 . 2  of the thread profiles  36 . 1 ,  36 . 2  are rounded on both sides to the core of the threaded spindle  28 . Finally, the side edges of the thread profiles  36 . 1 ,  36 . 2  that are delimited by the first flattenings  30 . 1 ,  30 . 2  are rounded. 
     The outer edges of the guide ribs  32 . 1 ,  32 . 2  and the transitions of the guide ribs  32 . 1 ,  32 . 2  to the first flattenings  30 . 1 ,  30 . 2  are also rounded. 
     The threaded spindle  28  is injection molded so that the parting plane of the two halves of the injection molding tool falls in the second flattenings  33 . 1 ,  33 . 2 . The roundings of the guide ribs  32 . 1 ,  32 . 2  and of the thread profiles  36 . 1 ,  36 . 2  are advantageous for the filling of the injection molding mold and the demolding of the molded part from the injection molding tool. The roundings of the profiles  36 . 1 ,  36 . 2  and of the guide areas  34 . 1 ,  34 . 2 ,  34 . 3 ,  34 . 4  are moreover advantageous for the low-friction and low-wear shifting of the threaded spindle  28  in the spindle nut  29 . 
     According to  FIG. 4 , the spindle nut  29  has a central hollow shaft  38 , on the inner circumference of which the internal thread  35  is designed. The internal thread  35  extends continually over a first section of the sleeve. The thread profile of the internal thread  35  is also trapezoid-shaped, wherein the radially inner ends of the profile are rounded and the transitions between the flanks of the profile as well. 
     A circular collar  39  that is designed as a toothed belt wheel  40  with teeth  41  on the circumference sits on the hollow shaft  38 . The hollow shaft  38  projects from the circular collar  39  to both sides. 
     The external thread  31  of the threaded spindle  28  and the internal thread  35  of the spindle nut  29  are coordinated with each other so that the threaded spindle  28  can be screwed into the spindle nut  29 . 
     According to  FIGS. 6 and 7 , the guide areas  34 . 1  to  34 . 4  internally abut each turn of the internal thread  35  of the spindle nut  29 . 
     A clearance fit occurs between them. 
     The dosing drive  26  further comprises, according to  FIG. 3 , an electric drive motor  42  that supports a further toothed belt wheel  44  on a motor shaft  43 . The spindle nut  29  is rotatably mounted on the hollow shaft  38  in two bearing bushings  45  and is held in two parallel holding plates  46  of a holder  47  at a defined distance from each other and from the drive motor  42 . The holder  47  has bearing eyes  48  for fixing in the housing  2 . 
     A toothed belt  49  is placed around the tooth belt wheels  40 ,  44  in order to transfer the rotation of the motor shaft  43  to the spindle nut  29 . 
     Furthermore, the dosing drive  26  comprises peg-shaped first guide elements  50 . 1 ,  50 . 2  that project from the receiving body  19  to the outside in opposite directions. According to  FIG. 2 , the first guide elements  50 . 1 ,  50 . 2  work together with guideways between bar-shaped second guide elements  51 . 1 ,  51 . 2  on the inner sides of the housing hulls  3 ,  4 . The threaded spindle  28  is hereby hindered from a rotation in the housing  2  and the receiving body  19  is guided in the axial direction of the threaded spindle  28 . 
     Furthermore, an electric control apparatus  52  arranged in the upper area of the housing belongs to the dosing drive  26 . The control apparatus  52 , the electric drive motor  42  and the remaining electronic components of the dosing device are fed from the electrical power supply  11 . 
     By applying current to the drive motor  42 , the motor shaft  43  and therefore the spindle nut  29  are set in rotation and the threaded spindle  28  is axially displaced. The threaded spindle  28  is hereby guided on the guide areas  34 . 1  to  34 . 4  in the internal thread  35 . Due to the symmetrical arrangement of the guide areas  34 . 1  to  34 . 4 , a very even running of the threaded spindle  28  is achieved. 
     The threaded spindle  28  and the spindle nut  29  are produced from plastics and/or metal. Preferably, high-performance plastics and/or engineering plastics are used for this. For example, the threaded spindle  28  and the spindle nut  29  are each made of PEEK. 
     The electronic manual dosing device  1  according to  FIGS. 8 and 9  is an electronic manual pipette. It has an upper housing part  53  in the form of a hand grip and a substantially cylindrical lower housing part  54 . The upper housing part  53  contains a drive unit and the lower housing part  54  contains a displacement unit composed of a cylinder  55  and a plunger  56  that is movable therein that can be displaced by means of the drive unit. 
     The upper housing part  53  has a substantially cylindrical trunk section  57  and a box-shaped head section  58  that with the trunk section  57  encloses an obtuse angle. The head section has a selection wheel  5  on the front side on the upper end for selecting the respective operating mode, for example pipetting, dispensing, pipetting and mixing, reverse pipetting, multiple receiving, sequential dispensing. 
     Under the selection wheel  5 , a display  6  is recessed into the front side of the head section  58 . 
     Underneath the display  6 , there is a rocker button  59  in the middle for controlling the receiving and discharge of liquid and setting parameters. To both sides of the rocker button  59 , there are further buttons  60  for selecting various menu functions and setting parameters. 
     Underneath the rocker button  59 , an ejector button  15  for controlling the ejection of pipette tips  61  is located on the front side in the transition area between the head section  58  and truck section  57 . The ejector button  15  is connected to an ejector rod that extends in the trunk section  57  to the lower end of same. 
     A hook-shaped finger rest  16  projects to the back from the back side of the head section  58 . 
     At the height of the display  6 , electrical contacts  9 ,  10  for charging a battery of an electrical power supply  11  accommodated in the head section  58  are located on the left and the right side of the head section  58 . The battery is connected to an electric control apparatus  52  accommodated in the head section  58 . The electric control apparatus  52  is connected to the rocker button  59  and the further buttons  60 , a sensor for detecting the rotational position of the selection wheel  5 , and a drive motor  42  of a dosing drive  26 . 
     The trunk section  57  has a hollow space  62  in which the dosing drive  26  is arranged at the top which will be explained in greater detail below. The trunk section  57  has a lower housing opening  63  on the lower end, through which the lower housing part  54  is inserted with its upper end into the hollow space  62  of the trunk section  57 . In the inserted position, the lower housing part  54  is releaseably connected to the upper housing part  53  by means for releaseably connecting the lower housing part  54  and the upper housing part  53 . According to  FIG. 10 , the means for releaseably connecting comprise a locking connection with spring-loaded locking hooks  64  of the lower housing part  54  that are lockable in the hollow space  62  behind locking edges of the upper housing part  53 . The locking can be intentionally reversed by moving an unlocking sleeve  65  guided on the outside of the lower housing part  54 . 
     According to  FIG. 11 , the lower housing part  54  has the cylinder  55  at the top with the plunger  56  that can be displaced within it in the longitudinal direction and is guided in a sealing manner. The cylinder  55  is designed as a bushing (liner) that is held in a cylinder section  66  of the lower housing part  54 . The cylinder section is connected at the bottom via a conical connecting section  67  to a tube  68  that has a seal seat  69  on the lower end onto which the pipette tip  61  is clamped. The tube  68  surrounds a connecting channel  70  that connects a first hole  71  on the lower end of the cylinder  55  to a second hole  72  in the seal seat  69  on the lower end of the tube  68 . 
     On the cylinder section  66 , the connecting section  67  and the tube  68 , an ejector sleeve  73  adapted to the outer shape of same is slid on for forcing off the pipette tip  61  from the seal seat  69 . The ejector sleeve  73  is connected at the top to the ejector rod via releaseable coupling means of the ejector sleeve  73  and ejector rod. The releaseable coupling means consist in a simple case in a clamping seat of the lower end of the ejector rod in a borehole in a side projection on the upper edge of the ejector sleeve  73 . 
     The lower housing part  54  supports at the top a closing cap  74 , the cap casing  75  of which is connected to the cylinder section  66  and which has a central upper housing opening  77  in a cap bottom  76 . 
     The plunger  56  is connected to a plunger rod  78  that supports a disk  79  at the top. Between the disk  79  and the upper edge of the cylinder  55 , a helical spring  80  is arranged that pushes the disk  79  into a starting position on the underside of the cap bottom  76 . 
     According to  FIG. 9 to 12 , the threaded spindle  28  of the dosing drive  26  engages, with its lower end through the upper housing opening  77 , with the closing cap  74  and abuts the upper side of the disk  79 . 
     According to  FIGS. 12 and 13 , the dosing drive  26  largely corresponds to the dosing drive  26  from  FIG. 3  so that the embodiments in  FIG. 3  correspondingly apply for the features provided with the same reference numbers from  FIGS. 12 and 13 . In the case of the dosing drive  26  from  FIGS. 12 and 13 , the lower end of the threaded spindle  28  contacts the disk  79  and is not connected to a bell-shaped receiving body  19 . Accordingly, in  FIGS. 12 and 13  a guiding of the lower end of the threaded spindle  28  by guide elements  50 . 1 ,  50 . 2  on the receiving body  19  is omitted. Rather, the threaded spindle  28  is guided on the upper end in a guide cylinder  81  that projects from the upper side of the holder  47  for the bearing bushings  45  of the spindle nut  29 . 
     The guide cylinder  81  has two guide grooves  82  on the inner circumference that extend in the longitudinal direction of the guide cylinder  81 . The two guide grooves  82  are diametrically opposite each other. 
     According to  FIGS. 10 and 13 , the threaded spindle  28  supports a sleeve-shaped guide element  83  on the upper end that has two guide noses  84  projecting to the outside that engage with the guide grooves  82 . The guide element  83  is firmly connected to the threaded spindle  28 . The guide element  83  linearly guides, for one, into the threaded spindle  28  in the guide cylinder  81  and hinders, for another, a twisting. As a result, the threaded spindle  28  is displaceable by rotating the spindle nut  29  in the longitudinal direction. 
     By applying current to the drive motor  42 , the motor shaft  43  is rotated, the spindle nut  29  is set in rotation via the toothed belt  49 , and the threaded spindle  28  is axially displaced. With the downward displacement of the threaded spindle  28  the plunger  56  is pushed farther into the cylinder  55 , and with the upward displacement of the threaded spindle  28  it is displaced, since the disk  79  is held by the pretensioned helical spring  80  in abutment on the lower end of the threaded spindle  28 . An air column is hereby displaced in the tube  68  that sucks liquid into or expels liquid from the pipette tip  61 . 
     REFERENCE SIGN LIST 
     
         
           1  Electronic manual dosing device 
           2  Housing 
           3  Front housing hull 
           4  Rear housing hull 
           5  Selection wheel 
           6  Display 
           7 ,  8  Rocker switch 
           9 ,  10  Electrical contact 
           11  Power supply 
           12  Reset button 
           13  Curvature 
           14  Trigger button 
           15  Ejector button 
           16  Finger rest 
           17  First opening 
           18  First receiver 
           19  Receiving body 
           20  Second receiver 
           21  Second opening 
           22  Stop 
           23  Syringe gripping lever 
           24  Plunger gripping lever 
           25  Gear 
           26  Dosing drive 
           27  Spindle drive 
           28  Threaded spindle 
           29  Spindle nut 
           30 . 1 ,  30 . 2  First flattening 
           31  External thread 
           31 . 1 ,  31 . 2  Threaded area 
           32 . 1 ,  32 . 2  Guide rib 
           33 . 1 ,  33 . 2  Second flattening 
           34 . 1 ,  34 . 2 ,  34 . 3 ,  34 . 4  Guide area 
           35  Internal thread 
           36 . 1 ,  36 . 2  Thread profiles 
           37 . 1 ,  37 . 2  Flanks 
           38  Hollow shaft 
           39  Circular collar 
           40  Toothed belt wheel 
           41  Teeth 
           42  Drive motor 
           43  Motor shaft 
           44  Toothed belt wheel 
           45  Bearing bushing 
           46  Holding plate 
           47  Holder 
           48  Bearing eye 
           49  Toothed belt 
           50 . 1 ,  50 . 2  First guide element 
           51 . 1 ,  51 . 2  Second guide element 
           52  Control apparatus 
           53  Upper housing part 
           54  Lower housing part 
           55  Cylinder 
           56  Plunger 
           57  Truck section 
           58  Head section 
           59  Rocker button 
           60  Button 
           61  Pipette tip 
           62  Hollow space 
           63  Lower housing opening 
           64  Locking hook 
           65  Unlocking sleeve 
           66  Cylinder section 
           67  Hindering section 
           68  Tube 
           69  Seal seat 
           70  Connecting channel 
           71  Hole 
           72  Hole 
           73  Ejector sleeve 
           74  Closing cap 
           75  Cap casing 
           76  Cap bottom 
           77  Housing opening 
           78  Plunger rod 
           79  Disk 
           80  Helical spring 
           81  Guide cylinder 
           82  Guide groove 
           83  Guide element 
           84  Guide nose